Upload
ngotruc
View
224
Download
0
Embed Size (px)
Citation preview
Hybrid Electric Powertrain Comparative Study
Friday, June 29, 2012
Rémy Laporte
KTH Royal Institute of Technology
‐i‐
Abstract
New trends for environmentally‐friendly mobility are rising and expectations derived from customers are significant. Urban areas such as London or even Stockholm are starting to build urban tolls by charging conventional vehicles while full‐electric powered vehicles are exempted. Carbon taxes will be certainly introduced at the EU scale in the next decade, which will strengthen those expectations of transportation changes especially regarding private vehicles. High electrification degree of conventional vehicles has to be performed to answer to those expectations. To avoid range restriction mainly related to the energy content limitations in battery electric vehicles (BEV), fuel tank has to be kept in conjunction with internal combustion engine. Thereby, according to this statement, the design of either a plug‐in hybrid electric vehicle (PHEV) or a range extender (REX) in a second extent with an extensive full‐electric range is relevant in the next decade.
Figure 1: Peugeot 208 (side view)
The conventional vehicle here considered as reference is the Peugeot 208 manufactured by PSA Peugeot Citroën since April 2012 and depicted in Figure 1. This vehicle will be transformed in a PHEV according to four hybrid electric powertrains considered as relevant: Parallel hybrid topology, Series hybrid topology, Power‐Split hybrid topology, and Series/Parallel hybrid topology. Energy consumptions i.e. electric or fuel consumptions, performances such as top speed capabilities and acceleration capabilities, and even manufacturing cost assessment are discussed in this material. Advantages and drawback of the four hybrid drivetrains are highlighted regarding those specifications. The Series hybrid topology is definitely more suitable for urban areas, whilst the Parallel hybrid topology is more dedicated for road and highway driving conditions both regarding energy conversion efficiency. The Power‐Split and the Series/Parallel hybrid topologies are more multipurpose regarding energy consumptions. Basically carbon dioxide emissions are significantly reduced for all the hybrid topologies in the same magnitude due to the similar extensive range capability in full‐electric mode derived from the large battery pack implemented (PHEV/REX design). Performances of the hybrid drivetrains are either enhanced especially regarding acceleration capabilities mainly owing to power addition capabilities or degraded especially regarding top speed capabilities mainly due to the vehicle gross mass increase. Manufacturing costs are significantly increased since electrical machines, wirings, power electronics, battery pack and so on are added. The most affordable PHEV/REX regarding exclusively manufacturing costs is the Parallel hybrid topology for which the electrical machine is mounted on the front wheel.
‐ii‐
Keywords
Hybrid electric vehicle, Range extender, Plug‐in hybrid, Parallel hybrid electric topology, Parallel hybrid electric topology, Series hybrid electric topology, Power‐split hybrid electric topology, Peugeot 208, Emission reduction, Fuel consumption, Performances, Powertrain, Three‐cylinder engine, Electrical Machine, Electrochemical battery, Planetary gear set, Atkinson, Matlab, Simulink.
Thanks
My 6‐month Master Thesis was carried out at PSA Peugeot Citroën Company in the Vélizy facilities in southwestern Paris suburb. First of all I wish to thank a lot my company supervisor M. Ardeshir GOLGOLAB to bring me supports and advice throughout my internship. In addition, I thank also a lot all the staff members of the DPVE department at PSA which have pleasantly hosted me. Besides, I thank M. Mats LEKSELL, teacher at the KTH Electrical Engineering department, who will recognize in this material a relevant continuation of his course “Hybrid Vehicle Drives” [1]. Finally, I thank a lot my academic supervisor, Ms. Annika STENSSON TRIGELL, teacher at the KTH Vehicle Engineering department, for her support despite the distance.
‐iii‐
Content
Abstract .................................................................................................................................................... i
Keywords .................................................................................................................................................. ii
Thanks ...................................................................................................................................................... ii
Content .................................................................................................................................................... iii
1 Background ...................................................................................................................................... 1
1.1 Context .................................................................................................................................... 1
1.2 Aims & Purposes ...................................................................................................................... 1
1.3 Scopes ...................................................................................................................................... 1
2 Basics of Electrical Hybridization ..................................................................................................... 3
2.1 Electrical Hybridization Topology ............................................................................................ 3
2.2 Electrical Hybridization Degree ............................................................................................... 5
2.3 Summary.................................................................................................................................. 7
3 Presentation of Vehicle Components .............................................................................................. 8
3.1 Internal Combustion Engines .................................................................................................. 8
3.2 Electrical Machine & Power Electronics ................................................................................ 11
3.3 Battery Pack ........................................................................................................................... 13
3.4 Transmissions ........................................................................................................................ 18
4 Design & Modeling ........................................................................................................................ 22
4.1 Vehicle Specifications ............................................................................................................ 22
4.2 Reference Vehicles ................................................................................................................ 23
4.3 Power Preliminary Design of Hybrid Electric Powertrains .................................................... 30
4.4 Parallel Topology ................................................................................................................... 31
4.5 Series Topology ..................................................................................................................... 39
4.6 Power‐Split Topology ............................................................................................................ 45
4.7 Active Strategy Control .......................................................................................................... 50
4.8 Series/Parallel Topology ........................................................................................................ 53
5 General Comparisons .................................................................................................................... 58
5.1 Gross Mass Comparisons....................................................................................................... 58
5.2 Energy Consumptions ............................................................................................................ 58
5.3 Performances ........................................................................................................................ 62
5.4 Powertrain Manufacturing Cost Assessment ........................................................................ 63
6 Conclusion & Discussion ................................................................................................................ 64
‐iv‐
Appendix 1: Driving Cycles .................................................................................................................... 66
Appendix 2: Optimum Operating Line .................................................................................................. 69
Appendix 3: Energy Consumptions: Case Studies ................................................................................. 71
Appendix 4: Atkinson Cycle for Spark‐Ignition Internal Combustion Engine ........................................ 75
References ............................................................................................................................................. 78
Tables & Illustrations ............................................................................................................................. 79
Nomenclature ........................................................................................................................................ 83
‐1‐
1 Background
1.1 Context Transportation is fundamental for societal and economic growth. However, nowadays, transportation is mainly based on fossil fuels such as oil and coal which are used through combustion process which is both not so efficient and generator of greenhouse gases such as carbon dioxide. In addition, those fuels are considered as non‐renewable energy that mankind is depleting faster than the necessary time to aggregate the energy in them. Therefore, the exclusive use of those fuels will lead to a quick overall depletion and major emission of greenhouse gases, which will induce both a global warming hastiness and significant societal risks of instability. Accordingly, changes to a more sustainable society less dependent on fossil fuels have to be operated, and consist of both pollutant emission reduction and use of more environmentally‐friendly fuels for transportation purposes.
Here only the issues related to pollutant emission reduction are going to be discussed. The first statement related to emission reduction can be achieved by improving energy conversion efficiency of the various types of engine used today. One way to do that is to use energy buffering devices to support the internal combustion engine during peak power requirements by making it operate at higher efficiency without load amplitude requirements. Hybrid Electric Vehicles (HEVs) are induced by this statement where the most known and simplest energy buffering system is implemented, the so‐called electric battery.
1.2 Aims & Purposes HEVs are characterized by their on‐board battery energy content and power capability, their electrical machine power, and their powertrain layout. The first two features are more related to vehicle performances such as acceleration capability, whilst the last feature is more related to the core of the hybrid electric system. The aims and purposes of this material are to draw up a comparative investigation between the main hybrid electric powertrains and the equivalent conventional vehicle regarding energy conversion efficiency, performances, and costs.
1.3 Scopes The comparative study drawn up in this material is focused on the Peugeot 208 (cf. Figure 2). Two vehicles based on this car model powered either by the 1.0‐litre 3‐cylinder in‐line gasoline EB0 engine or by the 1.2‐litre 3‐cylinder in‐line gasoline EB2DT turbocharged engine are going to be discussed and will be considered as reference vehicles in this study. The Peugeot 208 is considered as a car from the B segment as the Volkswagen Polo for instance.
Figure 2: Peugeot 208 (rear view)
‐2‐
In addition, the comparative study regarding energy efficiency is going to be drawn up exclusively through the WLTP (World harmonized Light‐duty Test Procedure) driving cycle, even though some specific model validations and power designs are going to be made through other driving cycles: NEDC (New European Driving Cycle) and INRETS UL1 cycle. Those three driving cycles are presented with their respective details in Appendix 1.
Furthermore, only four hybrid electric powertrain families were considered to be relevant according to HEV market today, technical feasibility, and development maturity. They are going to be investigated in this material. In addition to those hybrid electric powertrains, only an application plug‐in hybrid (PHEV) or range extender (REX) in a larger extent related to the electric hybridization degree of the Peugeot 208 is going to be studied.
Finally, acceleration performance assessment is going to be carried out only according to the two major performance tests: standing start testing up to 100 km/h, and acceleration testing from 80 up to 120 km/h.
Handling and vehicle dynamics will not be discussed in this material.
2 BaAs preseefficiencthe implpropulsi
Electric powertrto under
2Hybridizelectric already three sp
‐ ‐ ‐
Note thaoperate the road
The firstfeaturesThe powdevice (power dthe dedi
Figure
The secofeaturesparallel
asics of Elented previocy by supportlementation on mode and
Hybridizatioain and its drstand that b
.1 Electration topolopowertrain. purchasableecific feature
ICE speed adICE torque aPower addit
at engine spat specific o
d power requ
t hybrid elects are ICE torqwer‐split topoassumed to evices, and acated part.
e 3: Power‐Split
ond hybrid s are ICE tohybrid pow
lectrical ously, the aiting engine dof electricad regenerati
on is defineegree regardboth fields ar
rical Hybrogy is the firsPlenty of v today. Howes which are
djustment cadjustment caion capabilit
peed and toroperating pouirements.
tric family inque & speedology is depibe a planeta battery pac
t Hybrid Electri
electric famorque adjustwertrain cons
Hybridizm of vehicleduring peak l machines bve braking.
ed both by ding its relatre clearly ind
ridizationst feature revarious electwever, all of te the followin
apability apability ty (engine &
rque adjustmoints with hi
n term of veh adjustmenticted in Figutary gear seck. More det
ic Powertrain
mily in term tment capabsists of an e
‐3‐
zation e electric hyload, and thbrings new c
its topologive electricadependent.
n Topologlated to HEVtric hybrid dthem can beng:
EM power a
ment capabilgh efficienci
hicles sold tot capability inre 3. It conset as implemtails, especia
of vehiclesbility in conelectrical ma
ybridization ien reduce emcapabilities t
gy related tl machine po
gy Vs. Any HEV idrivetrains are gathered in
ddition)
lities are reqies for a giv
oday is the pn conjunctioists of two e
mented in thally regarding
Figure 4: P
sold today junction witachine, an a
is to improvmissions suco the vehicle
to its dedicower for inst
is first charare either unn four main
quired to eaen required
power‐split tn with poweelectrical mahe Toyota Prg related for
Parallel Hybrid
is the parath power aautomated g
ve energy coch as CO2. In e such as fu
ated hybridtance. The re
cterized by inder developfamilies acco
sily make thpower deriv
topology wher addition cachines, a porius), two elmula, will be
Electric Powert
llel topologyddition capagearbox or
onversion addition, ll‐electric
d electric eader has
its hybrid pment or ording to
he engine ved from
ose main apability. ower‐split ectronics e given in
train
y, whose ability. A a CVT, a
‐4‐
reduction gear set if required, a power electronics device, and a battery pack. Two layouts for the EM implementation are today established:
‐ EM mounted between the engine shaft and the gearbox (or the CVT) after the gearbox clutch ‐ EM mounted somewhere between the gearbox (or the CVT) and the transaxle gear set
The first layout allows the vehicle to recharge its battery at standstill in neutral position of the gearbox or the CVT. In addition, the EM mounted after the gearbox clutch allows the vehicle to be propelled in full‐electric mode without engine friction. Note that the reduction gear set is potentially not required for this layout since the shaft is rotating at high speed (engine speed). The second layout does not allow the vehicle to recharge its battery at standstill, but nonetheless allows smoothing breaking torque during gear change if a gearbox is implemented. In addition, mechanical transmission efficiency is closely similar with this derived from the first layout in full‐electric mode since the gears of the gearbox have to rotate partially. Finally the second layout with a 5‐speed automated gearbox was selected as the reference parallel topology as pictured in Figure 4 for similar concept development purposes with the hybrid system already developed by PSA Peugeot Citroën under the name of “HYbrid4” [2] and the slightly better mechanical transmission efficiency in full‐electric mode. Here the EM is mounted on the front transaxle gear set, whilst this is mounted on the rear transaxle in the HYbrid4 system to get four wheel drive capability. Both are basically similar to the second layout though the EM is not mounted on the shaft between the transaxle and the gearbox (or the CVT). More details, especially regarding related formula, will be given in the dedicated part.
In addition, the series topology defined as an electric generator for propulsion purposes, is the third hybrid electric family in term of vehicles sold today (currently only sold by Fisker). The series topology is depicted in Figure 5. Here only ICE torque & speed adjustment capability related to the hybridization topology is achievable. The series hybrid electric powertrain consists of two EMs, one defined as generator and another defined as traction machine, a reduction gear set for EM speed adaptation purposes for the traction machine since the generator speed is assumed to fit with engine speed, two power electronics devices, and a battery pack. More details will be given in the dedicated part.
Figure 5: Series Hybrid Electric Powertrain
Figure 6: Series/Parallel Hybrid Electric Powertrain
Finally, ttorque &additionPower‐Spicturedthe equion the trregardin
Thereforspecific fis the onare arranbe kept
2Hybridizregardinfollowing
‐ ‐ S‐ ‐ ‐
the last hyb& speed adju capability. Split topologd in Figure 6.ivalent seconransaxle geang related for
re, hybrid elefeatures sucnly one whicnged by featafterwards.
.2 Electration degreng various eleg:
Power ratio Stop & Start RegenerativePower assistFull‐electric
rid electric fustment capaThose featu
gy since the. It consist ond, fourth anar set, two pormula, will b
ectric powerch as power ch can both atures in Figur
Figure 7:
rical Hybre is the secectrification
between ICEcapability e braking catance to the propulsion c
family is theability or ICEures are notey cannot bof two EMs, nd fifth gearower electroe given in th
rtrain topoloaddition capadjust enginre 7. Note th
Principle Diagr
ridizationcond featuredegrees, the
E power and
pability (limiICE (limited capability (lim
‐5‐
e Series/ParaE torque adjut exactly sime performedan automater ratios, a redonics deviceshe dedicated
gies were intpability for ine operating hat the color
ram of Electric
n Degree e related toe HEV is def
EM power
ted or expanor permanenmited or exp
allel topologustment capmilar to themd at the saed gearbox wduction gears, and a battepart.
troduced annstance in Fipoints and ar code for ea
Hybridization T
o HEVs. Accofined differen
nded) nt) anded)
y, whose feaability in conm presentedame time. Twith only thr set for the ery pack. Mo
d are gathergure 7. The allow power ch hybrid ele
Topologies
ording to rently. Those s
atures are enjunction witd in the casThe Series/Phree speed rorange EM ore details, e
red accordingPower‐Split addition. Toectric power
elevant specspecification
either ICE th power se of the Parallel is elated to mounted especially
g to their topology opologies rtrain will
ifications s are the
‐6‐
Those specifications are closely dependent on the electrification degree of the vehicle since this latter has to be increased through higher EM power design or/and larger battery pack for instance to achieve them. Five main hybridization degrees can be highlighted according to both their specifications and their respective electrification degree and are depicted in Figure 8. Each hybridization degree is discussed below in details:
‐ Micro Hybrid related to Stop & Start capability through the implementation of an ISG (Integrated Starter Generator), and limited or optional regenerative braking capability
‐ Mild Hybrid related to Stop & Start capability, limited regenerative braking capability, and limited power assistance to ICE
‐ Full Hybrid related to Stop & Start capability, expanded regenerative braking capability, power assistance to ICE, and limited full‐electric propulsion capability
‐ Plug‐in Hybrid and Range Extender related to Stop & Start capability, expanded regenerative braking capability, power assistance to ICE, and expanded full‐electric propulsion capability
Figure 8: Hybridization Degree
The list above is indexed from the lighter electrification degree to the more advanced electrification degree as shown in Figure 8. Indeed, the micro hybrid is the first step of electric hybridization of a vehicle, whilst the plug‐in hybrid is the final one since the next step of electrification leads to remove the engine and therefore to design a BEV. A range extender in this classification is basically similar to a plug‐in hybrid about both electrification degree and specifications but is derived from a BEV whom the need of a longer autonomy was resolved by adding a combustion engine. In addition, the relative power curves related to both ICE & EM given in Figure 8 have to be considered as indicative. Nonetheless, the slope changes for both curves pictured in Figure 8 are representative of the design requirements of such‐and‐such HEV in conjunction with their respective electrical hybridization degree.
Conventional Vehicle Mild HybridMicro
HybridFull Hybrid Plug‐in Hybrid Battery
Electric Vehicle
ICE power
EM power
Absolute Power Electrification Degree0% 100%
Range Extender
Stop&Startcapability (ISG introduction) Regenerative
braking capability (optional & limited)
Stop&Start capability
Regenerative braking capability (limited) Power
assistance to ICE (limited)
Stop&Start capability
Regenerative braking capability Power
assistance to ICE
ZEV capability (limited)
Stop&Start capability
Regenerative braking capability Power
assistance to ICE
ZEV capability (expanded)
‐7‐
2.3 Summary To design a hybrid electric vehicle (HEV), two fields have to be taken into consideration independently: the electrical hybridization topology and the electrical hybridization degree. On the one hand, the electrical hybridization topology deals with powertrain layout, which induces specific capabilities such as power addition capability for instance. On the other hand, the electrical hybridization degree deals with electrification degree related to both electric power capability through the EMs and energy storage capability through the battery. This electrification degree allows the vehicle to get specifications such as stop & start capability, more or less extensive full‐electric driving mode, and so on.
Through this introduction of Electrical Hybridization, the reader could accordingly get a better understanding of both the aims and the scopes of this comparative study of hybrid electric powertrains. Thereby, a significant battery content capacity in conjunction with high relative EM power has to be considered since the main scope of this study is to design either a plug‐in hybrid or a range extender in a larger extent. In addition, the four main hybrid electric families derived from the Chapter 2.1 and their respective powertrain layout were introduced. Those four hybrid electric powertrain families presented as another scope of this comparative study will be discussed later on with more details regarding their respective energy efficiency, performances and costs.
‐8‐
3 Presentation of Vehicle Components The main vehicle components and their related efficiencies are going to be discussed in details in this section. First of all, the internal combustion engines used in this study are going to be introduced, and then the electrical machine in conjunction with its related power electronics is going to be presented. Finally, battery pack and mechanical transmission devices are going to be discussed.
3.1 Internal Combustion Engines Internal combustion engines and related specifications are going to be discussed here. In the context of electrical hybridization, the internal combustion engine is considered as the primary energy converter. As specified in Chapter 1.3, the engines used in this study are the so‐called EB0 and EB2DT engines manufactured by PSA Peugeot Citroën since the first quarter of 2012.
3.1.1 EB0 Engine The EB0 engine is a 1.0‐litre 3‐cylinder in‐line spark‐ignition engine which delivers 50 kW peak power (about 65 hp). This peak power provided by the engine allows the Peugeot 208 to reach a top speed of about 170 km/h over a road gradient of 0%.
Figure 9: Efficiency Map, Full‐Load Line (left) & Maximum Power Diagram (right) of the EB0 Engine
The efficiency map and the full‐load line of this engine are presented on the left side in Figure 9, whilst the engine power diagram is presented on the right side. The engine idle speed is of 1000rpm, whilst the idle fuel consumption is of 0.28l/h. The red line corresponds to the engine full‐load line, which corresponds to highest delivering engine torques for a given engine speed. The maximum torque delivered by this engine is equal to 95Nm. The engine peak power of 50kW is reached for the engine top speed of 5500rpm as depicted in Figure 9. In addition, the highest energy conversion efficiency achieved by the EB0 engine is about 35%.
For both hybridization and gear shifting strategy purposes, the OOL (Optimum Operating Line) related to this engine has to be drawn up. The OOL gathers the most efficient operating points of this
0 2000 40000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1 0.1
0.15
0.15
0.150.15
0.2
0.2
0.20
0.22
0.22 0.22
0.25
0.25
0.25
0.27
0.27
0.27
0.3
0.3
0.3
0.3
0.32
0.32
0.32
0.32
0.35
0.35
Speed [rpm]
Torq
ue [N
m]
0 2000 40000
10
20
30
40
50
Speed [rpm]
Pow
er [k
W]
‐9‐
engine for a specific load requirement. The blue line in Figure 10 shows the OOL related to the EB0 engine. More information about the OOL and its purposes are depicted in Appendix 2.
Figure 10: Efficiency Map, Full‐Load Line & OOL of the EB0 Engine
3.1.2 EB2DT Engine The EB2DT engine is a 1.2‐litre turbocharged 3‐cylinder in‐line spark‐ignition engine which delivers 75kW peak power (about 100 hp). This engine is implemented in the sportive version of the Peugeot 208. The peak power provided by the engine allows the Peugeot 208 to reach a top speed of about 195km/h over a road gradient of 0%
Figure 11: Efficiency Map, Full‐Load Line (left) & Maximum Power Diagram (right) of the EB2DT Engine
The efficiency map and the full‐load line of this engine are presented on the right side in Figure 11, whilst the delivering engine power is on the left side. According to its related engine efficiency map, the best energy conversion efficiency achieved by the EB2DT engine is equal to 37% i.e. 2% higher
0 1000 2000 3000 4000 50000
10
20
30
40
50
60
70
80
90
0.1
0.10.1
0.1 0.1
0.15
0.15
0.15 0.150.15
0.2
0.2
0.2 0.20
0.22
0.22
0.22 0.220.
0.25
0.25
0.250.25
0
0.27
0.27
0.270.27
0.30.3
0.3
0.3
0.3
0.32
0.32
0.32
0.320.
32
0.35
0.35
Speed [rpm]
Torq
ue [N
m]
0 2000 40000
20
40
60
80
100
120
140
160
180
0.10.1
0.10.15
0.15
0.15
0.20.2
0.2
0.220.22
0.22
0.25
0.25
0.25
0.27
0.27
0.27
0.3
0.3 0 3
0
0.32
0.32
0 3
0.3
0.35
0.35
0.35
0.35
0.36
0.36
0.360. 37
0.37
Speed [rpm]
Torq
ue [N
m]
0 2000 40000
10
20
30
40
50
60
70
80
Speed [rpm]
Pow
er [k
W]
‐10‐
than the EB0 highest efficiency owing to the turbocharged feature. The engine peak power equal to 75kW and is achieved at top engine speed i.e. 5500rpm. In addition, the maximum torque delivered by this engine is of 187Nm as depicted by the full‐load line. Finally, the idle engine speed is equal to 1000rpm, whilst the idle fuel consumption is of 0.47 liters per hour.
The OOL of the EB2DT engine was also drawn up for both hybridization and gear shifting strategy purposes. The blue line in Figure 12 corresponds to the OOL related to the EB2DT engine, whilst both engine efficiency map and engine full‐load line are also depicted. More information regarding the OOL and its purposes are located in Appendix 2.
Figure 12: Efficiency Map, Full‐Load Line (blue line) & OOL (red line) of the EB2DT Engine
3.1.3 Dynamic Operation of Internal Combustion Engines The engine operating points vary as quickly as the power requirement is varying. All the engine efficiency maps presented previously are related to combustion performances in stationary operation. Thereby, the same maps are not clearly similar in transient transition when changing from one stationary operating point to another. Indeed there are several phenomena related to change of operating point which impact combustion performances such as [3]:
‐ Air and exhaust gas flow changes i.e. “plug” effect of these gases ‐ Injection of more or less fuel leads to wall‐wetting phenomenon i.e. partial condensation of
injected fuel to the inlet manifold, which reduces fuel that reached combustion chamber
The engine control system associated with a rate of change of operating point via the means of a first order time constant allows the operation of the ICE to avoid dynamic effects. Thereby, if an internal combustion engine is used with limited dynamics owing to e.g. a 1‐second time constant, then the stationary maps presented above are more accurate to describe engine combustion performances. The motivation beyond better accuracy is that the intended use in a hybrid electric powertrain in a natural way allows limitation of engine dynamics. Note that this dynamic limitation is not possible with conventional powertrains since the engine has to supply power at any time according to the very variable road power requirements. Thereby, those engine efficiency maps will be assumed to be enough correct for simulation purposes even for the two reference vehicles powered by a conventional powertrain and presented later on.
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
20
40
60
80
100
120
140
160
180
0.1
0.10.1 0.1
0.150 .15
0.15 0.15
0.20.2
0.2 0.2
0.22
0.220.22 0.22
0.25
0.250.25
0.25
0.27
0. 270.27
0.270.3
0.30.3
0.32
0.32
0.32
0.320.
35
0.35
0.35
0.35
0.350.3
6
0.36
0.36
0.37
0.37
0.37
Speed [rpm]
Torq
ue [N
m]
‐11‐
3.2 Electrical Machine & Power Electronics
3.2.1 Electrical Machine The electrical machine (EM) used in this material is the so‐called EHA machine manufactured by the BMW/PSA Joint Venture (BPCE). This machine is a radial three‐phase permanent magnet synchronous machine whose rotor consists of an alloy of neodymium, iron and bore. In addition, the EM full‐load line is depicted as a red line in Figure 13. In addition to the full‐load line, the efficiency map pictured in corresponds to the EM efficiency by including power electronics efficiency as well. Thereby, copper losses, iron losses (hysteresis losses and eddy current losses), friction and windage losses of the machine [4] coupled with conduction and switching losses of the power electronics [5] are depicted in this efficiency map. Note that beyond the full‐load line the efficiency map was expanded in order to avoid computing failures. The maximum torque delivered by the machine is equal to 170Nm and is achievable up to the base speed. The base speed of this machine is equal to 200rad/s.
Field weakening operation is included in the full‐load line depicted in Figure 13. However, the field weakening used with the EHA machine is not equivalent to an ideal field weakening since the machine mechanical power is not constant beyond its base speed. Figure 14 depicts this difference caused by EM design limitations and EM control strategies between ideal field weakening operation and real operation through both a ωT diagram on the left side and a ωP diagram on the right side. Therefore, the peak power delivered by the EHA machine is equal to 43kW and is only reachable for a speed of about 400rad/s. The mechanical power released at EM top speed is equal to 32.5kW i.e. almost one quarter less than its peak power. In addition, a maximum energy conversion efficiency of 93% is achievable by the EHA machine.
Figure 13: Efficiency Map & Full‐Load Curve (red line) of the EHA Electrical Machine
Both the efficiency map and the full‐load curve of the EHA machine were considered as reference for either upsizing or downsizing purposes through machine torque and speed distortions according to power design of various hybrid electric powertrains. Note that the value of 35kW was considered as the EM reference power for upsizing/downsizing purposes. This reference power value is closer to the top speed power than the peak power since the designed vehicles in this material have to be
0.4
0.4
0.4
0.4 0.4 0.4
0.5
0.5
0.5
0.5 0.5 0.5
0.6
0.6
0.6
0.6 0.6 0.6
0.7
0.7
0.7
0.7 0.7 0.7
0.8
0.8
0.8
0.8 0.8 0.8
0.85
0.85
0.85 0.85 0.85
0.9
0.9
0.90.9
0.9 0.90.9
0.9
0.9
0.9
0.9
0.9
0 .9
0.9
0.9
0.9
0.9
0.90.9
0.9
0.9
0 .90.9
0.9
0.9
0.920.92
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
0 200 400 600 800 1000 1200 14000
20
40
60
80
100
120
140
160
‐12‐
designed for relatively high top speed in full‐electric driving mode as discussed later on in the Chapter 4.1.
Figure 14: Ideal & Real Field Weakening Operations related to the EHA Electrical Machine
3.2.2 Power Electronics Power electronics used in conjunction with the EM are four‐quadrant AC‐DC converters since the battery pack used in this material supplies a DC current, whilst reverse and braking capabilities have to be carried out by the EM through an AC current. The AC‐DC three‐phase converter consists of a three parallel‐connected full‐bridge converters, as depicted in Figure 15. Power electronics efficiency is already included in the EM efficiency map presented previously.
Figure 15: Three‐phase ac‐dc Converter [5]
In addition, pulse width modulation (PWM) is the method used for controlling the output voltages in this three‐phase AC‐DC converter through the three power transistor devices. Power MOSFETs (Metal‐Oxide‐Semiconductor field‐Effect Transistor) are usually the best candidates as transistor devices in applications below 400V as assumed here. Indeed, in this voltage range, power MOSFETs have lower on‐state voltage drop, faster‐switching speeds and are easier to control in comparison with IGBTs (Insulated‐Gate Bipolar Transistors). Figure 16 depicts the circuit symbol of both a power MOSFET and an IGBT.
0.4
0.4
0 4 0.4
0.5
0.5
0.5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.90.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
0 500 1000
0
20
40
60
80
100
120
140
160
Efficiency Mapideal ωT diagramreal ωT diagram
0 500 10000
5
10
15
20
25
30
35
40
45
Speed [rad/s]
Pow
er [k
W]
ideal ωP diagramreal ωP diagram
‐13‐
Figure 16: Circuit Symbols of Power MOSFET (left) & IGBT (right) [5]
In addition to the AC‐DC converter whose efficiency is included in the EM efficiency map depicted previously, a DC‐DC converter has to be implemented between the battery pack circuit and the DC circuit dedicated for the auxiliaries. This converter has a given conversion efficiency between 95 and 98% and was assumed to be negligible in this study. Thereby, the DC‐DC converter efficiency implemented in all the hybrid electric powertrains was assumed to be equal to 100%, and therefore was not taken into consideration for modeling.
3.2.3 Regenerative Braking Capability One of the main advantages of the design of EMs implemented in vehicles is the capability to recover energy during braking, the so‐called regenerative braking. Here full capability to recover braking energy was assumed in all this material since four‐quadrant power electronics were assumed to be implemented in conjunction with suitable motor control system and braking management system such as the so‐called EHB system (Electronic Hydraulic Brake). Note that this full capability is however limited by the design regarding torque, speed, and power of the reference EM depicted previously by assuming that both the full‐load line and the efficiency map are similar between the quadrants.
3.3 Battery Pack Plug‐in hybrid electric vehicles and related issues are going to be discussed in this material. As depicted in the part “Context”, one way to improve efficiency of the ICE‐powered vehicles is to implement a buffering energy system in order to handle energy consumption variations such as absorbing braking energy or supporting the primary energy converter (internal combustion engine). Here in the electrification context, the secondary energy storage i.e. the battery pack is in most cases electrochemical.
First of all, a short overview of the electrochemical storage systems related to the battery pack technologies are going to be introduced. The aim of this first part is to warrant the finally selected battery technology. In addition, the battery simulation model is going to be discussed. And finally, the three battery strategy managements considered as relevant are going to be depicted in details.
3.3.1 Electrochemical Storage An overview of the technologies of electrochemical storage related to the electrical battery pack is going to be introduced in this part.
Numerous battery types have been developed, but only a small number of them can be taken into consideration for traction purposes. Four main features are related to the battery technology. The energy density (Wh/kg) gives a relation between battery weight and battery energy content. This parameter allows usually assessing vehicle range. The power density (W/kg) is a measure of the peak power capability related to the maximum available electrical current that the battery can deliver as a function of its weight. This parameter is directly connected to both the vehicle acceleration capability
‐14‐
and its achievable top speed. In addition to those two features, the cycle life is the number of discharge/charge cycles a battery can sustain. The cycle life capability is closely related to many factors such as power level at which the battery operates, the temperature, the depth of discharge, and so on. The cycle life feature is given in number of cycles i.e. a charge followed by a discharge according to specific charging and discharging degrees. Here the life cycle is considered as terminated when the battery capacity falls under 70% of its nominal energy capacity. Finally, the last battery feature is its cost given per kWh. Table 1 gathers all the main electrochemical battery technologies used today and their respective features. The energy content values given in Table 1 have to be compared with those from both the gasoline and the diesel which are both equal to about 12kWh/kg.
Battery Technology
Energy Content [Wh/kg] (cell level)
Power Density [W/kg] (cell level)
Cycle Life Cost Assessment
Lead‐Acid 35 110 600‐1000 € Nickel‐Cadmium 50 175 1500‐2000 €€€ Nickel‐Metal Hydride (NI‐MH)
70 200 1500 €€
Sodium‐Sulphur 107 100 600 €€ Sodium‐Nickel Chloride (ZEBRA)
90 110 1000 €€
Zinc‐Bromine 70 100 1000 €€ Zinc‐Air 180 125 400 € Lithium 100‐200 1000 1500 €€‐€€€
Table 1: Energy Content, Power Density, Cycle Life & Cost Assessment of Main Battery Technologies [3]
High power density is required for power assistance to the engine and high energy recovering capability during braking in battery charge sustaining mode. In addition to this specification, high energy content is also required since one of the scopes of this study is to design a PHEV with an extensive full‐electric mode i.e. an extensive battery charge depleting mode capability. Finally, the battery cycle life has to be as high as possible since the full‐electric driving mode will be regular. Therefore, according to those requirements, only the nickel‐metal hydride and the lithium technologies are likely to be used as secondary energy storage system in a PHEV. The main advantage of the NiM‐H technology is its cost in comparison with this related to the Lithium technology. However, its high energy content capability in conjunction with its higher power density makes the lithium technology as electrochemical energy storage the best candidate for the design of a PHEV.
According to the Vehicle Specifications, by assuming in a first extent an electric consumption of about 120Wh/km, a requirement of about 9kWh lithium‐ion battery pack whose 85% is considered as useful is implemented in each hybrid electric powertrain with an energy content of 80Wh/kg (battery packaging mass included).
3.3.2 Battery Model The battery model depicts the battery losses that are dissipated through heat. A battery model can be made very complex, since many factors have to be taken into consideration such as the SOC (State‐Of‐Charge), the temperature, the electrical current, the SOH (State‐Of‐Health), and so on. In
‐15‐
this comparative study, a simple battery model was implemented which is characterized by both a constant internal resistance and a constant battery voltage. This battery model is one of the simplest one, but is well suitable for comparison purposes, and allows also the simulation computing times to be shorter. This battery model is depicted in Figure 17.
Figure 17: Schematic Model of the Battery used in this material
Here a battery voltage of 300V was assumed coupled with a battery loss at nominal power (PtermMAX=50kW) equal to 10%. This value of 50kW is derived from the electrical machine power requirement according to the Vehicle Specifications discussed later on. By taking into consideration those two assumptions, a battery resistance can be computed by taking into consideration Equations ( 1 ), ( 2 ) and ( 3 ). Here the battery resistance is thereby equal to 0.22Ω. Note that all parameters are described in the
Nomenclature.
. . ( 1 )
0.90 ( 2 ) 0.10
( 3 )
In addition to those two main assumptions, the battery efficiency can be computed owing to Equations ( 4 ) and ( 5 ) . Finally, the battery efficiency as a function of the battery terminal power is depicted in Figure 18. Negative power corresponds to battery discharging, whilst positive power corresponds to battery charging. Moreover, the battery efficiency values in the battery discharging area have to be understood by comparing them with two, which leads to get a battery efficiency of about 60% as battery discharging level of 50kW.
2. 2.
( 4 )
.
( 5 )
Note finally that the assumption of a constant battery terminal voltage is not so aberrant since the related power electronics converter is usually used to adapt the battery to a fixed voltage in order to
Rbatt
ebatt
ibatt
Ploss
Pterm
Pcharge
‐16‐
ensure right operation of the traction system components. The most aberrant assumption in this battery model is the constant resistance. Indeed, this latter parameter is significantly dependent on the battery SOC, its temperature, and the battery terminal power level. However, the value of 0.22Ω for the battery resistance taken into consideration in this material is not so aberrant. Indeed, this value is close to the overall resistance value of the 192‐cell lithium‐ion battery whose 96 cells are in series studied currently at PSA Peugeot Citroën. This specific battery delivers an overall voltage of almost 345V for a nominal voltage of 3.6V per cell while its overall capacity is of 15kWh. The nominal cell resistance is about equal to 2.5mΩ at 20°C and equal to 3.5mΩ at 10°C. Thereby, the overall cell resistance of this battery is included between 0.12Ω and 0.17Ω respectively. Even though this specific battery pack is slightly different to this implemented in this study especially regarding its capacity, the magnitude is similar since windings and connectors were not taken into consideration previously. Windings and connectors have to be taken into consideration. That is why a slightly higher overall resistance of 0.22Ω was finally chosen afterwards.
Figure 18: Battery Efficiency as a function of Battery Terminal Power
3.3.3 Battery Strategy Managements Two basic battery charge modes are implemented for the design of a PHEV. Those two basic modes are depicted in Figure 19. The main purpose of a PHEV is to get the capability to recharge the battery directly from the grid and therefore consume first cheap electricity. This capabilty is depicted through the charge depleting mode from a maximum SOC value (100%) up to a specific reference SOC value considered as 5% in this material. When the battery SOC reaches the reference SOC value, the SOC value has to be maintained around the reference SOC value. The battery is never emptied completely. Here the second battery charge mode, the so‐called charge sustaining mode, is implemented as depicted in Figure 19.
-4 -3 -2 -1 0 1 2 3 4
x 104
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2Battery Charge Efficiency
Battery Power [W]
Effi
cien
cy
‐17‐
Figure 19: Principle Chart of the Battery Charge Modes for a PHEV
As discussed, the battery charge sustaining mode is dedicated to maintain the SOC value around the reference SOC value. In this material, two charge sustaining strategies were implemented in order to assess more accurately and without bias the energy conversion efficiency capabilities related to each hybrid electric powertrain investigated in this material.
The first sustaining mode, the so‐called “sustaining I”, corresponds to a basic controller whose reference value is equal to the reference SOC value. In all the Simulink models related to each powertrain topology, a basic proportional controller was introduced in order to adjust power requirement derived from the battery. Thereby, a continuous power balance over the battery has to be performed and the main adjustment variable is to change the power delivered by the engine by taling into consideration the road power requirements as well. This specific sustaining mode is depicted in Figure 20.
Figure 20: Principle Charts of “Sustaining I” mode (left) and “Sustaining II” mode (right)
In addition to the “sustaining I” charge sustaining mode, a second sustaining mode, the so‐called “sustaining II”, was introduced and corresponds to an alternation of short charge depleting mode followed by short recharging mode. The main idea of this charge sustaining mode is to make the engine operate at its highest efficiency when this latter is turned on. The power related to this best efficient operating point is called PiceOPTIMAL and is derived from ωiceOPTIMAL and TiceOPTIMAL. Obviously when the power delivered by the engine at its highest efficient operating point is not enough to keep
SOCsustRef
Distance
Distance
ICE on @ highest efficient operating point
ICE offICE on @ highest power
SOCsustMin
SOCsustMax
SOCsafety
Distance
SOC sustMax
SOC Max
SOC sustRef
SOC
sustMin
Charge Sustaining mode
Charge Depleting mode
‐18‐
the SOC value around the reference SOC value, the engine has to operate at its maximum power. Thereby, three parameters related to respective SOC values were introduced in this charge sustaining mode under the names of SOC max, SOC min, and safety SOC. A basic algorithm was implemented through Simulink in order to make this mode operate properly as depicted previously (cf. Equation ( 6 ) where P*iceDEPLETION is the reference engine power requirement when ICE turned on). The basic principle of this algorithm is presented in Figure 20. This particular charge sustaining mode is more dedicated for specific hybrid electric powertrains such as Series hybrid powertrain which have the capability to make the engine to operate along its OOL. Note however that basically this strategy is based also on a power balance over the vehicle, only the SOC target is changed regularly and this induces high power requirements to charge and then discharge the battery. Thereby the engine will not operate all the time at its highest efficiency especially when the SOC value is close to the SOC max value since the engine power requirements might be lower than PiceOPTIMAL. However experiments have shown that most of the time the engine is operated at its highest efficient operating point owing to the battery charge controller design especially.
0. ( 6 )
The reader has to understand that CO2 emissions related to fuel consumption is closely dependent on the battery strategy implemented in charge sustaining mode. Thereby, specific driving conditions such as urban conditions are more beneficial for such‐and‐such battery strategy management, whilst highway conditions would be rather more beneficial for the other one. Switch between the two battery strategies in charge sustaining mode was taken into consideration in this material and was called “Active Strategy Control”. This active battery management will be discussed more in details later on.
3.4 Transmissions
3.4.1 Reduction Gear Set In each hybrid powertrain topologies, one reduction gear set at least was implemented in order to adjust the EM top speed with the vehicle top speed. Thereby, reduction gear ratio issues are going to be discussed later on according to the power design for each hybrid electric powertrain layout. This reduction gear ratio corresponds also to the final gear ratio derived from the transaxle gear set in the conventional vehicles as the reference EB0‐powered Peugeot 208 for instance.
A reduction gear set is characterized by a fixed‐gear ratio (gr). Torque and speed relations over a reduction gear set are depicted in Equations ( 7 ) and ( 8 ). Those two formulas are based on the principle sketch presented below in Figure 21. In this material, a constant transmission efficiency of 98% was assumed for a reduction gear set.
( 7 ) ( 8 )
‐19‐
Figure 21: Principle Sketch of a Reduction Gear Set
3.4.2 Gearbox Both gear ratios and gear shifting strategy are going to be discussed in this section. Two gearboxes are going to be considered in this study. A first one dedicated for the EB0‐powered Peugeot 208, and another one dedicated for the EB2DT‐powered Peugeot 208. Those gearboxes introduced in this material have to be considered as automated gearboxes i.e. with automatic gear selection according to a specific gear shifting strategy. The mechanical efficiency of this transmission is assumed to be equal to 96% with transaxle gear set efficiency included.
3.4.2.1 Gear Ratios The term “gearbox” here gathers the automated 5‐speed gearbox coupled with a transaxle gear set. Table 2 shows the gear ratios and the final gear ratio derived from the transaxle gear set for the EB0‐powered Peugeot 208. In addition, gear ratios and final gear ratio for the EB2DT‐powered Peugeot 208 are depicted in Table 3. All those ratios were given in vehicle speed according to an engine reference speed of 1000 rpm. Note that the gear ratios are similar, which implies that the two gearboxes are basically similar. Only the final gear ratios are different, and reflect the higher available engine torque delivered by the EB2DT engine in comparison with the less powerful EB0 engine.
Gear Ratio 1st 3.42 2nd 1.81 3rd 1.28 4th 0.98 5th 0.77
Final gear set 4.92 Table 2: Gear Ratios of the Gearbox & Final Gear Ratio
for the EB0‐powered Peugeot 208
Gear Ratio 1st 3.42 2nd 1.81 3rd 1.28 4th 0.98 5th 0.77
Final gear set 4.52 Table 3: Gear Ratios of the Gearbox & Final Gear Ratio
for the EB2DT‐powered Peugeot 208
3.4.2.2 Gear Shifting Strategy The main issue related to a gearbox is to know when to change speed. The aim of this gearbox has to be an eco‐gearbox related to emission reduction in the context of this study. Therefore, the main purpose of the gear shifting strategy is to maximize engine efficiency in order to reduce fuel consumption, and then restrict CO2 emissions. Thus, the engine OOL is going to be used in order to find the most appropriate gear ratio to maximize energy conversion efficiency through the engine.
The gear selection strategy related to the gear shifting strategy is depicted in Figure 22 and was used in each powertrain equipped with a gearbox. First of all, the given road power requirement (velocity and wheel torque are given respectively by the driver model) allows getting access to engine speed and torque related to the engine OOL. Then, the ideal gear ratio is computed and corresponds to the
gr Tinput ωinput
Toutput ωoutput
‐20‐
speed ratio between the wheel speed and the engine speed derived from its OOL. Later on, gear selection is carried out through a Look‐up Index block by selecting the closest gear ratio to the ideal ratio. Therefore, the real engine speed can be computed and the real engine torque is then derived from a power balance over the gearbox. Finally, the real engine operating point is thereby known.
Figure 22: Gear Shifting Strategy related to Gearbox
Note that when a need of acceleration is required, gear position is likely to be reduced. Indeed, the vehicle speed is relatively low at the beginning, whilst the engine speed has to be high according to its OOL in order to get enough power to propell the vehicle.
3.4.3 Planetary Gear Set A planetary gear set is used in general as a power‐split device in the power‐split hybrid electric powertrain. Thereby, this mechanical transmission device is going to be discussed in this part and is highly related to the power design of the power‐split hybrid electric powertrain discussed more in details later on.
In this material, the power‐split powertrain layout corresponds to one introduced by Toyota with its Prius i.e. the ICE connected to the carrier wheel, and the two electrical machines EM1 and EM2 connected respectively to the solar wheel and the ring wheel [6]. In addition, the ring wheel is connected to the vehicle wheels through the transaxle gear set. This specific layout is depicted in Figure 23. The way how this transmission device is working in the case of the power‐split topology is going to be discussed later on.
0 200 4000
10
20
30
40
50
60
70
80
90 0.1
0.1
0.1
0.15
0.15
0.15
0.2
0.2
0.2
0.22
0. 22
0.22
0.25
0.2 5
0.250.
27
0.27
0.27
0.3
0 .3
0.3
0.3
0.32
0 .32
0.32
0.32
0.35
0.35
Speed [rad/s]
Torq
ue [N
m]
Wheel Torque Requirement Vehicle Velocity
Traction Power Requirement
Ideal Engine Torque Ideal Engine Speed
Ideal Gear Ratio
Gear Selection (Look‐up Index)
real Engine Speed real Engine Torque
f
uk k
f
Prelookup
OOL
Energy Balance
A planetradius. Tleads to carrier w
In additias a func
By assumbetweenmaterialreflects t
tary gear setThis ratio is dbe altered o
wheel leads t
on to those ction of the p
ming that tn gears, a m. This value the limited a
F
t is charactedepicted in Eon the solar to be altered
relations, spplanetary ge
he transmismechanical tincluded be
amount of ge
igure 23: Plane
rized by its rEquation ( 9wheel accor
d on the ring
(
peed relationar ratio (kpl).
ssion losses ransmission etween thosears operate
‐21‐
etary Gear Set a
ratio betwee) and is callrding to Equwheel accor
10 )
n between p.
of a planetefficiency o
se derived frd in this mec
and Basic Layo
en the ring wed kpl. A torqation ( 10 ).rding to Equa
lanetary whe
tary gear seof 97% for trom the redchanical tran
ut
wheel radiusque applied This same toation ( 11 ).
eels is depict
et are purelthis device wuction gear nsmission de
s and the solon the carriorque applie
( 9
ted in Equat
( 12
y related towas assumeset and thevice.
lar wheel ier wheel ed on the
)
( 11 )
tion ( 12 )
2 )
o friction ed in this e gearbox
‐22‐
4 Design & Modeling This part is dedicated to the power design of each hybrid electric powertrain and the related justifications according to the vehicle specifications. In addition, modeling is going to be discussed meanwhile for each investigated powertrain.
4.1 Vehicle Specifications Vehicle specifications regarding top speed, acceleration, ranges, and so on have to be presented in order to make the power design feasible for each hybrid electric powertrain. Those specifications are depicted in and are indexed according to either ideal specifications (top edges) or admissible specifications (limit edges). In addition, three driving modes are discussed in Table 4. The “electric mode” corresponds to a full‐electric traction mode where the engine is turned off. The “hybrid mode” corresponds to a battery charge sustaining mode where both ICE and EMs are working. Finally, the “Unavailable battery mode” is related to a driving mode where the battery reaches its minimum SOC and cannot assist any more the engine. Long slope and extreme temperature conditions are the typical example of this latter driving mode.
Specifications Ideal Admissible
Car model Peugeot 208 Peugeot 208
Passengers 5 4
Usage Multipurpose MultipurposeCO
2 emission [g/km] < 25 < 49
Electric
mod
e
Range [km] based on WLTC 90 60
Vmax [km/h] (4% road gradient) 145 130
0 ‐> 100 km/h [s] 10 16
80 ‐> 120 km/h [s] 8 14
Hybrid
mod
e
Range [km] based on WLTC 700 300
Vmax [km/h] (4% road gradient) 145 130
0 ‐> 100 km/h [s] 10 16
80 ‐> 120 km/h [s] 8 14
Una
vailable
Battery
mod
e
Range [km] based on WLTC 700 300
Vmax [km/h] (4% road gradient) 145 130
0 ‐> 100 km/h [s] 12 20
80 ‐> 120 km/h [s] 8 17Table 4: Vehicle Specifications
One of the main scopes of this study is to design either a plug‐in hybrid or a range extender. Thereby, the related electrification degree has to be high, which means high EM power and high battery energy content for extensive full‐electric mode purposes. In Table 4, the specifications related to the electric mode and to the hybrid mode are similar. To reflect this, the design of a high electrified vehicle where the driver cannot feel the driving mode shift is considered. The values regarding performances are directly derived from the Nissan Leaf in the Ideal column and from the Peugeot Ion
‐23‐
in the Admissible column. In addition, most of the required top speeds are given with a road gradient of 4% in order to make the designed vehicles to get robust features regarding gradeability for instance. Note also that top speeds in “Unavailable Battery” mode are basically similar to those derived from the Hybrid mode since the speed has to be maintained and that involves no battery power assistance. Performances related to acceleration ability are also discussed through two standard acceleration tests: standing start testing up to 100km/h, and acceleration testing from 80 up to 120km/h.
4.2 Reference Vehicles In this part, the two reference vehicles, the EB0‐powered Peugeot 208 and the E2DT‐powered Peugeot 208, are going to be introduced with more details especially regarding modeling.
4.2.1 Power Design Basic technical parameters of the Peugeot 208 powered by either the EB0 engine or the EB2DT engine are depicted in Table 5. The wheel radius of those two vehicles was induced owing to Equation ( 13 ) where Rwheel and Iwheel stand respectively for the wheel radius and the wheel involute. Note that a Stop&Start system, also called Stop&Go system, is introduced in term of weight in Table 5 for energy efficiency comparison purposes.
Engine EB0 EB2DT MV (Vehicle Mass) 1001 kg 1050 kg
Stop&Start +16kg +16kg Wheel Radius 0.3014 m 0.3014 m
Cr (rolling resistance coefficient) 0.008 0.008 S.Cx (drag surface & coefficient) 0.655 m2 0.655 m2
Table 5: Technical Parameters of the EB0‐powered Peugeot 208 and the EB2DT‐powered Peugeot 208
2. ( 13 )
In addition to the wheel radius, both rolling resistance coefficient and drag resistance coefficient with related surface are also given. All those parameters allow acceding to the so‐called road resistance force. A road power requirement can be derived from this road resistance force and is depicted in Equation ( 14 ) where α is the road angle.
. . 12. . . . . ( 14 )
Power requirement for both reference vehicles with 75kg of cargo are depicted in Figures 24 and 25. Note that the power requirements for those two car models are very close due to a relative similar vehicle mass. In addition, the road power requirements were also drawn up for various road gradients from 0% up to 7%. Thereby, as a first approach the top speeds achievable are respectively 145km/h and 175km/h for the EB0‐powered Peugeot 208 (50kW) and the EB2DT‐powered Peugeot 208 (75kW) for a road gradient of 4%. Note here that the gearbox ratios are not taken into consideration and are closely related to the top speed capability. The gearbox ratios are taken into consideration in Figures 26 and 27. Thereby, the top speed of the reference vehicle powered by the
‐24‐
EB0 engine is of 140km/h for a road gradient of 4%, whilst the top speed of the second reference vehicle is decreased to 170km/h.
Figure 24: Road Power Requirement for the EB0‐powered Peugeot 208
Figure 25: Road Power Requirement for the EB2DT‐powered Peugeot 208
Figure 26: Top Speed Capability (Road Gradient of 4%) of the EB0‐powered Peugeot 208
Figure 27: Top Speed Capability (Road Gradient of 4%) of the EB2DT‐powered Peugeot 208
Figure 28: Wheel Torque Diagram for the EB0‐powered Peugeot 208
Figure 29: Wheel Torque Diagram for the EB2DT‐powered Peugeot 208
In addition to the top speed definition for both reference models, performances of the two reference vehicles have to be assessed owing to wheel torque diagrams. Note that acceleration performances
0 20 40 60 80 100 120 140 160 1800
10
20
30
40
50
60
70
80
90
100
Vehicle Speed [km/h]
Roa
d P
ower
[kW
]
0% gradient4% gradient7% gradient
0 20 40 60 80 100 120 140 160 1800
10
20
30
40
50
60
70
80
90
100
Vehicle Speed [km/h]
Roa
d P
ower
[kW
]
0% gradient4% gradient7% gradient
0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
0 50 100 150 200 2500
10
20
30
40
50
60
70
80
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
0 20 40 60 80 100 120 140 160 180 2000
200
400
600
800
1000
1200
1400
1600
1800
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
5th4th3rd2nd1stMaximum Wheel Torque
0 50 100 150 200 2500
500
1000
1500
2000
2500
3000
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
5th4th3rd2nd1stMaximum Wheel Torque
‐25‐
are assessed according to a road gradient of 0%. Maximum wheel torque is depicted in Figures 28 and 29 respectively for the EB0‐powered Peugeot 208 and the EB2DT‐powered Peugeot 208. Note that the engine top speeds were intentionally slightly reduced (blue lines) since the required ideal top speed according to the Vehicle Specifications is only of 145km/h. Since the maximum available wheel torque is known for any vehicle speeds, the acceleration performances can be computed owing to Equation ( 15 ) (force balance over the vehicle). Twheel stands for the wheel torque provided by the engine while Froad is the road resistance force (rolling and drag resistance forces). Note that inertia masses for all the topologies derived from rotating parts were neglected in this study as depicted in Equation ( 15 ) since considered as negligible compared with the vehicle gross mass.
. ( 15 )
Performances regarding numerical values related to those two reference vehicles are gathered later on in 8 in the section 4.2.3. The related acceleration performances were computed instead by the Simulink models by introducing speed echelons as reference speeds. By using models, delay times such as gear shifting times and time constant responses are here taken into consideration through the Simulink modeling.
4.2.2 Modeling
4.2.2.1 Driver Model The driver model is designed as a simple PI‐controller with anti‐windup on the integrator to prevent saturation in the actuator. The required wheel torque (Twheel) to perform the requested vehicle speed (v*) is computed owing to Equation ( 16 ). Note that the requested vehicle speed is provided by the driving cycle speed‐point diagram through a look‐up table.
.1.
. ( 16 )
The parameters of the PI controller (K and τ) are going to be discussed through a simple closed loop speed control system (cf. Figure 30). The poles of this system were placed at the limit to oscillatory poles i.e. poles equal to 0. This choice gives rather good dynamic performance without an oscillatory behavior.
Figure 30: Simple Driver Model
The basic speed control transfer function is depicted in Equation ( 17 ) where Kv is the static gain and Ti is the integration time constant.
11
( 17 )
Speed Controller 1
1+
‐
v* F
* F v
‐26‐
Thereby, the closed system transfer function and its related poles are presented respectively in Equations ( 18 ) and ( 19 ). As discussed previously, by placing the poles at the limit to oscillatory poles i.e. the equation discriminant equal to zero for dynamic purposes, the static gain of the speed controller has to be related to its integration time constant as depicted in Equation ( 20 ).
1 ( 18 )
2 4 ( 19 )
4 ( 20 )
Thus the gain is proportional to the vehicle mass. Finally, the integration time constant has to be selected as Ti = 3s in this material. This value is dedicated for a 1000kg vehicle and is then proportional to the vehicle weight. The basic relation between Ti and Mv is depicted in Equation ( 21 ) and was used for all the models designed in this material. Thereby, for a 10000kg vehicle, the integration time constant is equal to 10s instead of 3s. In addition the integration time constant corresponds also to a fraction of the acceleration time to 100km/h that can be expected.
3 7.1000
9000 ( 21 )
The driver model implemented in all the Simulink models is depicted in Figure 31. Note the anti‐windup on the integrator through the capabilities to initialize the controller integral to a desired value (initial condition equal to 0), to disable the integral function until the to‐be‐controlled process variable has entered the controllable region (closed loop applied on the wheel torque difference through the “Max Wheel Torque” saturation block), and to apply saturation limits over the integration block.
Figure 31: Simulink Model of the Driver Model
4.2.2.2 Model of ICE Operating Point Selection As described previously, the gear shifting strategy related to the gearbox is based on the engine OOL. Thereby, ideal engine torque and speed according to the engine OOL as a function of the traction power requirement derived from the Driver Model has to be computed.
Driver is modelled as a PI controllerTactive torque is computed by the control ler
1Ttot*
Max Wheel Torque
1s
Integration
Kv
1/Ti rw
F * -> T *
Close the integral action at standstil l
|u|
|u|
Abs
2v
1v*
‐27‐
This ICE operating point selection is ensured by two Look‐up Table blocks as depicted in Figure 32. In addition, Saturation blocks were also added in order to reflect engine torque and speed limitations. A Min/max block was also added in order to reflect torque limitation as a function to engine speed.
Figure 32: ICE Operating Point Selection according to its OOL
4.2.2.3 Gearbox Model The gearbox model implemented in the two reference models and also in all the powertrains requiring a gearbox with more and less gears is going to be depicted in this part. The gear shifting strategy was discussed previously and is presented in Figure 22.
The core issue of this strategy is to select the right ratio according to the methodology derived on the ideal gear ratio. This selection is carried out by a Look‐up Index Search block in conjunction with a Direct Look‐up Table block as depicted in Figure 33. One of the inputs of this Simulink model is the ideal gear ratio computed upstream. The closest gear is then selected owing to the Look‐up Index Search block which locates the input’s relative position within a specific range of number (here the gear ratios derived from the gearbox). An interval index (here the gear position) and a distance fraction (here the gear ratio distance expressed in percentage between the selected ratio and the next one) are returned by this block. In addition, gear shifting hysteresis is introduced through a Relay block applied on the distance fraction. Finally the gear position is known and the related gear ratio has to be computed owing to the Direct Look‐up Table block located upstream.
Figure 33: Gear Ratio Selection Model
Note that a so‐called “Speedy” variable was introduced in the Simulink model through a Relay block called “Downshift”. The aim of this variable is to make the gear shifting strategy be more sportive i.e. a “one gear down” strategy. As long as the new ICE speed reference is low, a one gear ratio higher i.e. a lower gear position than the ideal one is selected. This strategy is given up when the engine speed reaches 85% of the engine maximum speed, and is reengaged when the engine speed drops below 55% of the engine maximum speed.
2wice*
1Tice*
wopt_ice
Torquelimitation
Topt_icemin
MinMax
-> T
1
10s+1
Switch4
Scope
SaturationRelay
u k
f
PreLook-UpIndex Search
Downshift
1-D T[k]
Direct Look-UpTable (n-D)
em
0
0Number_of_gears
Hybrid
OOL_Follower
3SOC
2wice_new
1Ideal_ratio
‐28‐
Furthermore, a second Direct Look‐up Table block in conjunction with a Compare To Constant block was added in order to avoid the engine to operate at higher engine speed than its related maximum speed. This second loop is not depicted in Figure 33 and is located just downstream.
4.2.2.4 Road Model The road resistance force derived from Equation ( 14 ) was modeled in Simulink through the following model (cf. Figure 34). The input data of this model are the vehicle velocity (only variable input), the air density, S.Cx, Cr, the road gradient given in %, the vehicle mass, the gravitational constant, whilst the only output is the road resistance force. This output data is then used to compute the new vehicle velocity through a force balance over the vehicle, which induces vehicle acceleration calculation.
Figure 34: Road Model
4.2.2.5 Stop&Start Model The reference vehicles can be equipped with a Stop&Start system, also called Stop&Go system. This system can turn off the engine as a function of a dedicated methodology: the engine is turned off if both the wheel speed is low and the wheel torque requirement derived from the driver model is equal to zero. This system was introduced in order to make more relevant energy conversion efficiency comparisons between powertrain topologies. The Simulink modeling of the Stop&Start system is depicted in Figure 35. This Simulink model consists of a “NAND” logical operator box in conjunction with two Relay blocks.
Figure 35: Stop&Start Model
4.2.2.6 Model Validation Model validation is going to be discussed in this part in term of energy conversion efficiency expressed as C02 emission per kilometer in the case of the EB0‐powered Peugeot 208 in comparison
1Froad
atansin
100
Slope
Slope [%]
Sat +/-1
Roll resistance
sqrtu2
u2
-K-Cr
S.Cx
Mv
grav
rho_air
1/2
-1
Air resistance
|u|
Abs
1v
Turn off ICE @ low speed and low torque if StopAndGo option is on
Switch2StopAndGo
11 @ wwheel low
NAND
1 @ standstil lwith T*wheel >1
1 @ Twheel=0
2Twheel*
1wwheel
‐29‐
with the official emission value. The emission value related to this specific conventional powertrain is of 100gCO2/km over the NEDC cycle [7].
A fuel consumption of 4.37l/100km over the NEDC cycle through the EB0‐powered Peugeot 208 model was computed. Thereby, the CO2 emissions related to the Simulink model are equal to 100gCO2/km for an auxiliary load of 100W (instead of 200W). This specific choice concerning the auxiliary load allows getting results closer to the official emission certification. Therefore, a load of 100W was applied for all the powertrains depicted in this material later on.
In addition, fuel consumption reduction of 5% according to the NEDC cycle was computed through the Simulink model by implementing the Stop&Start system presented previously. This magnitude regarding fuel consumption saving related to the implementation of such system is common in the literature. For instance, fuel saving of 6% was achieved by the Valeo‐made Stop&Start system over the European cycle [8].
Thereby, the conventional Simulink model related to both the EB0‐powered Peugeot 208 and the more sportive EB2DT‐powered Peugeot 208 is validated and was used as a basis for model creation of all the hybrid electric powertrains.
4.2.3 Results: Energy Consumptions & Performances This last part dedicated to the two reference vehicles gathers the gasoline consumptions over the European cycle and the WLTP cycle. In addition to those figures, those derived from the implementation of a Stop&Start system are also depicted in this part. Gasoline consumptions given in liter per 100 kilometers for both car versions are depicted in Tables 6 and 7. Those results will be compared with those coming from hybrid electric powertrains later on.
Gasoline
Consum
ptions
[l/10
0km]
Engine EB0 EB0 (Stop&Start) NEDC 4.37 4.15 WLTC 4.68 4.62 WLTC Urban 4.38 3.99 WLTC Urban 2 3.86 3.83 WLTC Road 4.34 4.32 WLTC Highway 5.62 5.62
Table 6: Fuel Consumptions of the EB0‐powered Peugeot 208
Gasoline
Consum
ptions
[l/10
0km]
Engine EB2DT EB2DT (Stop&Start) NEDC 5,02 4,64 WLTC 5,12 4,99 WLTC Urban 5,55 4,86 WLTC Urban 2 4,36 4,29 WLTC Road 4,69 4,63 WLTC Highway 5,82 5,81
Table 7: Fuel Consumptions of the EB2DT‐powered Peugeot 208
Fuel consumptions are higher over the WLTC cycle in comparison with those derived from the European cycle. Higher severity regarding acceleration requirements related to the WLTP cycle is reflected in those results and is discussed in more details in Appendix 1. Note that the fuel saving capability owing to the implementation of a Stop&Start system is significantly reduced over the WLTC cycle. In addition, larger fuel saving capability is noticed in the case of the EB2DT engine with
‐30‐
the implementation of a Stop&Start system. This extensive fuel saving is explained by a higher idle fuel consumption for the EB2DT engine.In addition to energy consumptions, performances regarding acceleration and tops speeds of both reference vehicles are depicted in 8. Figures in Tables 6, 7 and 8 are gathered in Chapter 5 with those derived from the other investigated drivetrains to ease the comparisons.
Engine EB0 EB2DT Top Speed [km/h] (4% gradient) 139 175 Top Speed [km/h] (0% gradient) 172 197 0‐>100 [s] 12.2 7.2 80‐>120 [s] 10.4 5.9
Table 8: Performances of Reference Vehicles
4.3 Power Preliminary Design of Hybrid Electric Powertrains This part is dedicated to the preliminary design for the various hybrid electric powertrains according to the Vehicle Specifications in order to get basic assumptions related to their power requirements.
The vehicle gross mass assumed in this part for calculation purposes and its related parameters such as drag coefficient and rolling resistance coefficient are directly derived from the EB0‐powered Peugeot 208 as depicted previously in Table 5. Specific power margins were added in order to offset the gross mass differences between the EB0‐powered Peugeot 208 and the various hybrid electric powertrains. Note that the powers computed in this part have to be considered exclusively as indicative powers regarding the different driving modes and their related top speed requirements since the gross mass of each PHEV are not yet known.
Figure 36: Power Requirement in Electric & Hybrid Modes
According to the Vehicle Specifications, a top speed of at least 130km/h along a road gradient of 4% is expected in full‐electric mode, hybrid mode (battery charge sustaining mode) and unavailable battery mode. Thereby, by applying a relative power margin of 25% since vehicle gross mass increase not taken into consideration in a first extent, a power of 50kW is required (cf. Figure 36).
0 20 40 60 80 100 120 140 160 1800
10
20
30
40
50
60
70
80
Vehicle Speed [km/h]
Roa
d P
ower
[kW
]
4% gradient
‐31‐
Preliminary design of power requirements are gathered in Table 9 according to the three driving modes depicted in the Vehicle Specifications.
Preliminary Design of Power Requirements Electric Mode Hybrid Mode Unavailable Battery Mode
50kW 50kW 50kW Table 9: Preliminary Design of Power Requirements for the Various Hybrid Electric Powertrains
4.4 Parallel Topology In this part, the Peugeot 208 parallel hybrid electric topology powered by the EB0 engine is going to be discussed in details regarding power design and modeling. In addition to those two topics, basic results of this hybrid topology will be depicted such as energy consumptions and performances.
4.4.1 Operating Principle This part is dedicated to the operating principle of a parallel hybrid electric powertrain. Various parallel hybrid electric powertrains with various layouts exist. The selected parallel topology layout for similar concept development purposes is depicted upstream in this material in Figure 4.
Figure 37: Operating Principle of the Parallel Hybrid Electric Powertrain
Operating principle related to the selected parallel hybrid topology is depicted in Figure 37. The traction wheel torque (Twheel) and then the traction power (Ptraction) are computed by the Driver Model. A basic energy balance over the vehicle is depicted in the first equation where the part related to the battery power is reflected as a SOC difference. The ideal engine power requirement (PICE) is then computed. According to the engine OOL, ideal engine torque (TICE) and speed (ωICE) are computed. The Gear Shifting Strategy related to the gearbox is then applied through the gear
. 0
&
OOL
&
& .
Fuel consumption & CO
2 emission
0 200 400 600 800 1000 12000
20
40
60
80
100
120
Time [s]
Spe
ed [k
m/h
]
0.1
0.1
0.1
0.1
0.15
0.15
0 .15 0.15
0.2
0.2
0.2
0.2
0.22
0.22
0.22
0.22
0.25
0.2 5
0.25
0.25
0.27
0.27
0.27
0.27
0.3
0.3
0.3
0.3
0.32 0.32
0.32
0.3 2
0.35
0.35
Speed [rad/s]
Torq
ue [N
m]
ICE Efficiency Map
0 100 200 300 400 500 6000
10
20
30
40
50
60
70
80
90
selectionconsumpfills in wthat gr cfunctionsuch as s
This parconsiderMass aspower dthe gear
As said pdiscussedifferencdiscussepreviouselectricapower palso impin Battermass of
Table
Since grrequiremThereby least 42/that the
n (grx). The ption and COwhat the engiorresponds t of the vehshaft inertia
4.4.2rt is dedicatration both tsessment foesign is goinr ratio of the
previously, td. Mass assce between d is the engsly since theal machine wpreliminary dplemented acry Pack. Thethe EB0‐pow
10: Gross Mass
ross mass oment along to reach a t/43kW is reqtop speed o
real engineO2 emissionsine cannot dto a reductioicle top spein order to r
2 Power Dted to the the EB0 engor two parallng to be discutransaxle ge
4.4.2.1 wo basic posessments ofthose two pgine downsie vehicle growith its relatdesign in eleccording to t row “Mass wered Peuge
s of the EB0‐po
4.4.2.2 of each scena road gradtop speed of quired for boof any hybrid
e torque ans is finally dedue to dynamon gear set aed requiremreduce comp
Design power desiine as primael scenariosussed accordear.
Mass Asseswer designsf those two ower designizing capabiloss masses ated mass ofctric mode. the assumptincrease” inot 208 i.e. 10
owered ParalleT
Scenario Senario are knient of 4% at least 130
oth scenariosd electric top
‐32‐
nd speed aerived frommic limitatioand its valuement. Note tputing time.
ign of the ary energy cois going to ding to the V
ssment regarding tscenarios a
n scenarios islity despite are now knof 45kg for bFinally, a 9ktion regardinn Table 10 is 001kg.
l Topology (leftTopology (right
election nown and arelated to e0km/h along s (overlappinpology is giv
are then cothe real ICEn and operae is fixed for that no inert
Parallel Peuonverter andbe first carrVehicle Speci
he primary eare depicted s equal to 14the power own in bothoth scenariokWh lithium‐ng full‐electrcomputed a
t) and Gross Mt)
are slightly each scenaria road gradi
ng curves). Then by the po
mputed (TIC operating ption only at speed adapttia was take
ugeot 208 Pd a 2/3 EB0 ied out. Theifications by
energy convin Table 10
4kg only. Notrequirementh scenarios. os was impl‐ion technoloric range speas a function
ass of the 2/3
different, tio can be drient of 4%, ahe reader haower exclusi
CEreal & ωICEr
point. Finallyhigh efficientation of theen into cons
PHEV by takengine (dowen justificatioadjusting m
erter are go0. Thereby, tte here that ts of 50kW In addition,emented toogy battery ecifications en of the vehi
EB0‐powered P
he two roarawn (cf. Figan engine poas to understvely delivere
real). Fuel y, the EM ncy. Note e EM as a ideration
king into wnsizing). on of the eanwhile
ing to be the mass the issue depicted a 50kW
o suit the pack was expressed icle gross
Parallel
d power gure 38). wer of at tand here ed by the
‐33‐
engine (primary energy converter) since only this latter is working at constant speed in battery charge sustaining mode (hybrid mode). Obviously, this top speed is purely indicative and can be overtaken with the EM boost but only during a short time since the battery charge has to be kept around a specific SOC value as discussed in Chapter 3.3.3.
Figure 38: Road Power Requirements respectively for 2/3 EB0‐powered and EB0‐powered Parallel Hybrid Electric Scenarios
Therefore, the 2/3 engine downsizing scenario is finally given up due to top speed limitation in comparison to the Vehicle Specifications, and only the EB0‐powered scenario is thereafter kept.
In addition, the 50kW EM implemented according to the power preliminary design is kept also since this power allows the vehicle to reach top speed specifications in full‐electric mode. Thereby, the EM presented in Electrical Machine was upsizing of 1.4 regarding its torque magnitude.
4.4.2.3 Transmission Adaptation The parallel hybrid electric powertrain discussed in this part consists of an EM used both for regenerative braking and for acceleration requirements (electric boost). Thereby the gearbox and the transaxle gear basically designed for the EB0‐powered Peugeot 208 (reference vehicle) have to be adapted in order to enhance energy conversion efficiency and to keep in parallel admissible performances. Here only the transaxle gear ratio i.e. the final gear ratio is going to be adapted for cost effective purposes.
The method used to solve this issue was to make a Matlab program where the value of the final gear ratio related to the transaxle gear varies between 1 up to 5 with a step of 0.5 knowing that the initial final gear ratio for the mechanical transmission of the EB0‐powered Peugeot 208 is equal to 4.92.
Here the limit case is that related to the Unavailable Battery mode for which the EM boost is not available. However both driving modes, Hybrid mode and Unavailable Battery mode, related to engine turned on operation were investigated. Fuel consumptions over the WLTP cycle and performances for both driving modes are depicted in Figures 39 and 40. Note that the fuel consumptions in Hybrid mode presented in Figure 39 are corrected with respect to the SOC reference value since this specific driving mode corresponds to a battery charge sustaining mode (“sustaining I” here). Note also that the top speed is equal to 130km/h along a 4% road gradient in
0 20 40 60 80 100 120 140 160 1800
10
20
30
40
50
60
Vehicle Speed [km/h]
Roa
d P
ower
[kW
]
Parallel Hybrid Topology powered by EB0 (4% gradient)Parallel Hybrid Topology powered by 2/3 EB0 (4% gradient)
‐34‐
Hybrid mode, whilst this is only 90km/h along a 0% road gradient in Unavailable Battery mode (admissible vehicle specifications). Owing to the EM boost capability, no transaxle adaptation limitations regarding performances are highlighted in Hybrid mode. Only limitations regarding performances for transaxle gear adaptation appear in Unavailable Battery mode. Those limitations allow determining the adequate final gear ratio. Thereby, according to the diagrams, the best final gear ratio value regarding energy conversion efficiency by keeping admissible performances will be 3 for both the Hybrid mode and the Unavailable Battery mode.
Figure 39: Corrected Fuel Consumption (left) & Performances (right) as a function of Final Gear Ratio in
Hybrid mode
Figure 40: Fuel Consumption (left) & Performances (right) as a function of Final Gear Ratio in Unavailable
Battery mode
Figure 41: Fuel Consumptions over INRETS UL1 cycle
However, beyond performance verifications, fuel consumptions over very slow driving cycles such as the INRET UL1 cycle (cf. Appendix 1) have to be computed to know if the transaxle gear elongation is not too much. Corrected fuel consumption over this specific cycle with a final gear value of 3 is slightly higher than this given by the EB0‐powered Peugeot 208 with the initial final transaxle gear equipped with a Stop&Start system. Two other final gear ratios were considered 2.5 and 3.5 as depicted in Figure 41. The final gear value of 3.5 allows the parallel PHEV to achieve lower fuel consumption than this given by the Stop&Start system. Note that the slightly over fuel consumptions of the various parallel PHEVs are mainly caused by the gross mass increase, the transaxle gear elongation and the bad efficiencies of the EM operating points (black points on the EM efficiency map) due to low‐speed conditions as depicted in Figure 42.
1 2 3 4 53.5
4
4.5
5
5.5
6
Final Gear Ratio
Fuel
Con
sum
ptio
n [l/
100k
m]
1 2 3 4 54
6
8
10
12
14
16
Final Gear Ratio
Tim
e [s
]
Vmax0->100 km/h80->120 km/h
1 2 3 4 53.5
4
4.5
5
5.5
6
Final Gear Ratio
Fuel
Con
sum
ptio
n [l/
100k
m]
1 2 3 4 510
15
20
25
30
35
40
45
50
Final Gear Ratio
Tim
e [s
]
Vmax0->100 km/h80->120 km/h
0,001,002,003,004,005,006,007,008,009,0010,00
INRETS UL1
Fuel Con
sumption [l/10
0km]
Conventional
Stop & Start
Parallel (kgear = 2.5)
Parallel (kgear = 3)
Parallel (kgear = 3.5)
‐35‐
Figure 42: EM Operating Points over the INRETS UL1 Cycle with a Transaxle Gear Ratio of 3.5
Since the fuel consumption difference is limited, the initial transaxle gear adaption from a ratio value of 4.92 to 3 could be finally kept afterwards for energy consumption purposes. However a transaxle gear ratio of 3.2 was finally preferred for performance purposes especially regarding top speed capability i.e. to reach at least 130km/h over a road gradient of 4%. Indeed a top speed of only 132km/h is reachable and considered as too close to the related admissible specification (cf. Vehicle Specifications) due to the gearbox ratios for a transaxle gear ratio of 3 as depicted in Figure 43.
Figure 43: Top Speed Capability (Road Gradient of 4%) for the EB0‐powered Parallel Topology with a Transaxle Gear Ratio of 3 instead of 4.92
4.4.3 Modeling Many models such as the Model of ICE Operating Point Selection, the Gearbox Model and the Road Model used in the models of the two reference vehicles equipped with a conventional basic powertrain are also used in the parallel PHEV model. However, here power balance has to be carried out according to the battery power requirements and the road power requirements. In addition, the selection of the EM operating points has to be made and its related model will be also presented.
4.4.3.1 Power Flow Control The Power Flow Control block depicted in Figure 44 is dedicated for the power balance calculation and consists of the Battery Charge block (green block), the ICE Operating Point Selection block (red
0 200 400 600 800 1000 1200 14000
50
100
150
200
0.4
0.4
0.4
0.4 0.4 0.4
0.5
0.5
0.5
0.5 0.5 0.5
0.6
0.6
0.6
0.6 0.6 0.6
0.7
0.7
0.7
0.7 0.70.
80.
8
0.8 0.8 0.80.
85
0.85
0.85 0.85 0.85
0.9
0.9
0.9
0.9
0.9 0.90.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.9
0.9
0.920.92
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
0 50 100 150 200 250 3000
10
20
30
40
50
60
70
80
90
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
‐36‐
block) according to its related OOL, the Gearbox block (blue block) where the specific gear shifting strategy according to the engine OOL is applied, and the EM Operating Point Selection block (yellow block).
Figure 44: Power Flow Control Block
Dynamic operations of the internal combustion engine are limited by a low‐pass filter whose time constant is the so‐called τcharge. Fuel consumption and related emissions are out of proportion when making the engine operating points to change faster in comparison with the fuel consumption and related emissions in stationary operation. Thereby, the required engine power derived from the energy balance is processed by this low‐pass filter as depicted in Figure 45. This dynamic limitation capability related to the engine is applied for all the hybrid electric powertrains. A value of 2s was selected for τcharge and was unchanged between the hybrid electric powertrain models. Thus, peak powers of less than 2s derived from both road power and battery power requirements are not taken into consideration by the engine.
Figure 45: Low‐pass Filter for Engine Dynamic Limitation
Figure 46: Battery Charge Controller
The battery charge control is ensured through a basic proportional controller whose static gain is called kSOC. This specific controller is depicted in Figure 46. The Switch block implemented in this block allows the battery strategy in charge sustaining mode to be switched. In addition, kSOC is determined owing to Equation ( 22 ) where Wbatt is the total battery energy content i.e. 9kWh
These blocks split the torque between the ICE and EM
The EM fil ls in what the ICE cannot in hybrid mode
In Charge depletion mode the ICE fi l ls in when the EM cannot.
In NON-Hybrid mode the ICE is alone
7utvx
6Tem*
5wem
4Speed
3wice*
2ICEoff
1Tice*
-K-
gr
1/rw
Vehicle speedto
Wheel speed
TractivePower
P*
wwheel
Twheel*
Tice*
wice*
ICEof f
Optimaloperating point
Tice_new*
wice_new*
Tice*
wice*
OOL Follower
No Emif conventional
No ChargeControl if
Conventional
w_wheel
Tice*
wice*
ICEof f
SOC
ICEof f
Tice_new*
wice_new*
utv x
Gear Selection Tice*
utv x
Twheel*
Tem*
EM Torque
Hybrid
0
0
-C-
SOC P charge *
Charge control
3SOC
2v
1Twheel*
1
P ice
1s
Wbatt
1/(Tau_charge)1
P ice*
1
P charge *
Switch1
Sum1
ksoc
SOC controller gain
Strategy
From
SOC_batt_ref
1SOC
‐37‐
expressed in Joules and τcharge is the time constant to limit the dynamics of the engine output power. Thereby, a battery power of about 40.5kW is required for a SOC difference of 1% with the reference SOC value. This specific kSOC value was considered for all the hybrid electric powertrain models for the basic control of the battery charge.
400. ( 22 )
0 1 ( 23 )
0 1 ( 24 )
20.9 ( 25 )
21.1 ( 26 )
The engine ignition management is ensured through two Relay blocks and a Look‐up Table block as a function of both the engine efficiency and the engine required power. The engine ignition management is depicted in Equations ( 23 ) and ( 24 ). The two implemented Relay blocks are reflected by those two equations, whilst the Look‐up Table block allows the model to know the engine efficiency according to the engine power requirements through its OOL. Here for all the hybrid electric powertrain models, ηiceOFF and ηiceON are equal respectively to 0.28 and 0.30, whilst PiceOFF and PiceON are computed respectively through Equations ( 25 ) and ( 26 ) where PiceMAX is equal to 50kW for the EB0 engine. This methodology allows the PHEV to turn on its primary energy converter only when either this latter is efficient or high engine power is required.
Low‐pass filter for engine dynamic limitation purposes, engine operating point selection through its OOL and engine ignition management models are depicted in Figure 47.
Figure 47: Engine Best Operating Point Selection & Engine Ignition Management
4.4.3.2 Simulink Battery Model The battery model on Simulink is derived from the battery model presented previously in the part “Battery Pack”. Here the modeling of this basic model is going to be discussed. A Look‐up Table block was implemented in order to assess battery efficiency and battery charging or discharging power as a function of Pterm derived from the sum between the EM power and the auxiliary load. Note that an auxiliary load of only 100W was assumed for all the powertrains discussed in this material. The basic battery efficiency model is depicted in Figure 48. The Compare To Constant block was added in conjunction with a Constant block in order to get battery efficiency values below 1 every time.
3ICEoff
2wice*
1Tice*
wopt_ice
eta_ice
Torquelimitation
Topt_ice
Switch1
Switch
Scope
NO ICE Torque @ to low efficiency
min
MinMax
OR
P ice* P ice
LP-fi lter
ICE always at high powerHybrid
-> T
1P*
‐38‐
Figure 48: Battery Efficiency Model
4.4.4 Results: Energy Consumptions & Performances Energy consumptions both in battery charge depleting mode (electric mode) and in battery charge sustaining mode (hybrid mode) according to the charge sustaining strategy called “sustaining I” are depicted in Table 11 over the WLTP cycle according to the Power Design presented previously. Note that the charge sustaining strategy called “sustaining II” was not considered for this hybrid electric powertrain since the engine operating point selection according to its OOL is not possible. Indeed this inability is due to both the limited number of gears of the gearbox and the close relation regarding speed between road and engine.
Driving Mode Electric Mode [Wh/km]
Hybrid Mode [l/100km]
WLTC 114.66 3.94 WLTC Urban 70.62 2.52 WLTC Urban 2 79.96 3.00 WLTC Road 104.60 3.64 WLTC Highway 162.98 5.35
Table 11: Energy Consumptions of the EB0‐powered Parallel Topology
Driving Mode Electric Mode Hybrid Mode Unavailable Battery Mode
Top Speed [km/h] (4% gradient) 137 134 134 Top Speed [km/h] (0% gradient) 145 161 161 0‐>100 [s] 10.8 6.2 17.2 80‐>120 [s] 10.9 5.1 13.1
Table 12: Performances of the EB0‐powered Parallel Topology
The respective available powers to the wheel according to the gearbox ratios allow inferring top speeds at various road gradients. Top speed capabilities over a road gradient of 0% and 4% are respectively depicted in Figures 49 and 50. Note that here the electric boost is not available to assess each top speed in hybrid mode since the speed has to be maintained. Thereby the top speed capabilities are similar between the Hybrid mode and the “Unavailable Battery” mode. In addition, top speed capability in electric mode over a road gradient of 4% was assessed by taking into consideration only the EM power as depicted in Figure 51. Furthermore, the Simulink model of this specific powertrain allows also getting access to acceleration performances through simulations by applying specific speed echelons as reference vehicle speeds. Another way to compute the acceleration performances could be to use maximum wheel torque diagram derived here from the combination between the torques delivered by the EM and the ICE as depicted in Figure 52. However this method does not highlight gear shifting time as this introduced over the Simulink model. Thereby the acceleration performances were computed owing to the Simulink model. Note that both methods gave very close results with lower times for the method based on the maximum wheel
2eta
1Pcharge
Switch
Subtract
Saturation
P/ n
Look-UpTable
2
Constant
<= 1
CompareTo Constant
1Pterm
‐39‐
torque diagram as expected. In addition note that acceleration performances in “Unavailable Battery” mode were computed by assuming transaxle gear elongation and not taking into consideration EM power assistance. Performances of the EB0‐powered Parallel topology are gathered in Table 12. Finally note that the values gathered in Tables 11 and 12 are suitable with the Vehicle Specifications regarding ranges and performances for the three driving modes. Figures in Tables 11 and 12 are gathered in Chapter 5 with those derived from the other investigated drivetrains to ease the comparisons.
Figure 49: Top Speed Capability (Road Gradient of 0%) of the EB0‐powered Parallel Topology in Hybrid Mode
Figure 50: Top Speed Capability (Road Gradient of 4%) of the EB0‐powered Parallel Topology in Hybrid Mode
Figure 51: Top Speed Capability (Road Gradient of 4%) for the EB0‐powered Parallel Topology in Electric Mode
Figure 52: Maximum Wheel Torque Diagram of the EB0‐powered Parallel Topology
4.5 Series Topology In this part, the Peugeot 208 series hybrid electric topology powered by the EB0 engine is going to be discussed in details regarding power design and modeling. In addition to those two topics, basic results of this hybrid topology will be depicted such as energy consumptions and performances.
4.5.1 Operating Principle This part is dedicated to the operating principle of a series hybrid electric powertrain. Few series hybrid electric powertrain layouts exist. This used in this material is certainly the most common and is depicted upstream in Figure 53.
0 50 100 150 200 250 3000
10
20
30
40
50
60
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
0 50 100 150 200 250 3000
10
20
30
40
50
60
70
80
90
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
0 50 100 1500
10
20
30
40
50
60
70
Vehicle Velocity [km/h]
Pow
er [k
W]
EM PowerRoad Power
0 50 100 150 200 250 3000
500
1000
1500
2000
2500
3000
3500
4000
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
5th4th3rd2nd1stEMMaximum Wheel Torque
‐40‐
Figure 53: Operating Principle of the Series Hybrid Electric Powertrain
Operating principle related to the selected series hybrid topology is depicted in Figure 53. The traction wheel torque and then the traction power are computed by the Driver Model. A basic energy balance over the vehicle is depicted in the first equation where the part related to the battery power is reflected as a SOC difference. The ideal engine power requirement is then computed. According to the engine OOL, ideal engine torque and speed are computed. Here the ideal engine operating point corresponds to the real operating point. Fuel consumption and CO2 emissions derived finally from the ICE operating point. The engine torque is entirely absorbed by EM1, whilst the EM1 speed is similar to this derived from the engine. The traction machine, EM2, is directly connected to the road through a reduction gear set and has to ensure traction torque. Note that gr1 and gr2 correspond each one to a reduction gear set and their values are derived from the speed adaptation of the EM as a function of either the engine top speed or the vehicle top speed requirements respectively. Note that no inertia was taken into consideration such as shaft inertia in order to reduce computing time.
4.5.2 Power Design
4.5.2.1 Scenarios & Mass Assessment As discussed in Chapter 4.3, the required power to reach the required top speed in charge depleting mode (electric mode) and in charge sustaining mode (hybrid mode) is of 50kW by taking into consideration specific arbitrary power margin.
Two scenarios have to be investigated in order to be more accurate regarding the requirements derived from the Vehicle Specifications especially in term of top speeds. Those two scenarios are the following: a first one powered with the EB0 engine, and a second one powered by a hypothetical downsizing EB0 engine with only two‐cylinders instead of 3 initially. In both cases, a 50kW traction electrical machine is considered since this power magnitude is required by the power preliminary design. Note that the required power of the generator (EM1) is closely dependent of the power
0
&
11
& 1 1. 22
& 2 2.
Fuel consumption & CO
2 emission 0 200 400 600 800 1000 1200
0
20
40
60
80
100
120
Time [s]
Spe
ed [k
m/h
]
0.1
0.1
0.1
0.1
0.15
0 .15
0.15 0.15
0.2
0.2
0.2
0.2
0.22
0.22
0.22
0.22
0.25
0 .25
0.25
0.25
0.27
0.27
0.27
0.27
0.3
0.3
0.3
0.3
0.32 0.32
0.32
0.32
0.35
0.3 5
Speed [rad/s]
Torq
ue [N
m]
ICE Efficiency Map
0 100 200 300 400 500 6000
10
20
30
40
50
60
70
80
90
OOL
deliveredin term oassessedthe genecompute
The grosrequiremtwo scen
Figure 54:
Therebyof 4%. includedfor bothassessm( 27 ) anthe 2/3
d by the engof power, whd regarding terator has toed as a funct
ss mass diffments regardnarios as dep
: Road Power R
, 42kW is neBy assumind), the directh scenarios ent purposend ( 28 ). NotEB0‐powere
gine. Therebyhich involvestheir respecto be similar ttion of the ve
Table
4.5.2.2 ference betwding the top picted in Figu
Requirements r
eeded in firstng best elect energy striin order to
es. The directe thereby thed scenario,
00
10
20
30
40
50
60
Roa
d P
ower
[kW
]
y, the 2/3 EBs a mass redtive gross mo this deliveehicle gross m
e 13: Power De
Scenario Seween the twspeed capa
ure 54 (overl
respectively for
t extent to rectrical machng i.e. by avo determinect energy strhat only a mwhilst a po
20 40 60
Series Hybrid TSeries Hybrid T
‐41‐
B0‐powered suction in a laass (cf. Tablered by the emass of the
esign Scenarios
election wo scenariosbility along apping curve
r 2/3 EB0‐powe
each a top sphine efficienvoiding passie the maximring for bothmaximum powower of at le
0 80 100Vehicle Speed [km
Topology powered byTopology powered by
scenario leadarger extente 13). Obviongine. The roEB0‐powere
s for Series Top
s is only of a road grades).
ered and EB0‐p
peed of at leancies of 93%ing through mum availabh cases is rewer of 28kWeast 43kW is
120 140 1m/h]
y EB0 (4% gradient)y 2/3 EB0 (4% gradie
ds to implemt. Those two ously for bothow “Mass ind Peugeot 2
pology
24kg. Thereient of 4% a
powered Series
ast 130km/h% (power ethe battery
ble wheel pespectively dW is availables available f
160 180
ent)
ment a downscenarios hah cases the crease” in Ta08 i.e. 1001k
eby, the roaare very clos
Hybrid Electric
h over a roadelectronics ehas to be cower for todepicted in Ee on the whefor the EB0‐
sized EM ave to be power of able 13 is kg.
ad power e for the
c Scenarios
gradient efficiency omputed op speed Equations eels in for ‐powered
‐42‐
scenario by assuming in both cases EMs and power electronics efficiencies equal to 92% (cf. efficiency map in Electrical Machine & Power Electronics). Therefore, only the EB0‐powered scenario is kept afterwards for performance purposes.
. . 43kW ( 27 )
/ . . 28kW ( 28 )
In addition, the initial assumption of a 50kW power for the traction motor for performance purposes is also validated according to Figure 54.
4.5.3 Modeling Compared with the models derived from the Conventional topology and the Parallel topology, no new blocks were added. In addition, the Series topology model is basically simpler than the two latters since there is no speed relation between engine and road. Only the computing way due to the specific physical relations is different.
Similar controllers regarding the driver model and the battery SOC control with similar static gain values as those used in the Parallel topology model were implemented in this Series topology model. In addition, the same engine ignition management with this derived from the Parallel topology model based on high engine efficiency and high engine power was also implemented (cf. Figure 55). The overall model of the Series topology is depicted in Figure 56.
.
( 29 )
.. ( 30 )
Figure 55: Engine Operating Point Selection Block
However, a block not entirely similar to this derived from the Parallel model is the Operating Point Selection block derived from the Control of the Drivetrain block. Indeed, since the model has to be run according to the battery charge sustaining strategy called “sustaining II”, the most efficient
No ICE motorbraking allowed
2wice*
1Tice*
wopt_ice
eta_ice
Torquelimitation
Topt_ice
Scope3
Scope1
NO ICE Torque @ to low efficiency
min
MinMaxP chargemom P charge *
Low pass -fi lter fordynamic limitation
(page 18)
OR
ICE always at high power
Strategy
From
-> T
2safety SOC
1P*
‐43‐
engine operating point has to be selected. Thereby a Saturation block was added coupled with a Switch block after the Low‐pass Filter block as depicted in Figure 55. Note that if the power requirement derived from the power balance is inferior to this derived from the best efficient engine operating point (20kW), then the delivered engine power is reduced accordingly. However, to make the engine operate almost exclusively on this best efficient specific point, the required power derived from the battery through the proportional controller is at least equal to 20kW. Indeed, a SOC target range of about 0.5% above or below of the maximum SOC value and the minimum SOC value respectively were implemented through a Relay block as pictured previously in Figure 46. The value of 0.5% is derived from Equation ( 29 )where the TiceOPTIMAL and ωiceOPTIMAL corresponds to the best engine efficient operating point. The power required by the battery in “sustaining II” battery strategy is computed according to Equation ( 30 ) as a function of SOCII derived from Equation ( 29 ).
Figure 56: Series Topology Model over Simulink
4.5.4 Results: Energy Consumptions & Performances Energy consumptions in battery charge sustaining depleting mode (electric mode) and in battery charge sustaining mode (hybrid mode) according to the two charges sustaining strategies, “sustaining I” and “sustaining II”, are depicted in Table 14 over the WLTP cycle. Note that the battery strategy “sustaining II” was here implemented with a given 1% difference between SOC minimum value and SOC maximum value, whilst the safety SOC value was set 1% beneath the SOC minimum value (cf. Chapter 3.3.3 for more information). In addition, note also that the fuel consumption values are corrected as a function of the difference between the initial SOC value and the final SOC value.
Driving Mode Electric Mode [Wh/km]
Hybrid Mode [l/100km]
Sustaining I Sustaining II WLTC 115.46 4.21 4.15 WLTC Urban 71.44 2.76 1.64 WLTC Urban 2 80.72 3.25 2.62 WLTC Road 105.38 3.83 3.52 WLTC Highway 163.80 5.97 6.01
Table 14: Energy Consumptions of the EB0‐powered Series Topology
Series Hybrid Model-K-
m/s -> km/h
Tem2
Tbrake
Froad
v
Tdriv
Wroad
Wbrake
Transmission
wem2
Tem2*
Tem2
Pel_em2
Traction Motor (em2)
FuelPower
Speed
FuelConsumption
Distance [km]
Av erageSpeed [km/h]
FuelEnergy
v Froad
Road Model
-0.513
Road Energy [kWh]
Speed
Performance
0.8096
Mecanics -> electric [kWh]
Tice*
wice
FuelPowerTicePice
EtaICE
ICE Model
wem1
Tem1*
Tem1
Pel_em1
Generator (em1)
G l S
K-Gain
v *
v Ttot*
Driver Model
Twheel*
v
SOC
saf ety SOC
Tice*
wice*
wem2
Tem2*
Control ofthe drivetrain
Paux
5.151e-015
CO2 Emission [g/km]
0
Brake Energy [kWh]
Tem2*
Tem2
T_brake
Brake
0.1351
Battery Losses [kWh]P elm1
P elm2
P aux
Speed
SOC
Wloss
Pcharge
saf ety SOC
ElectricConsumption
Energy Conv erion
Battery
2.22e-016
Average Fuel Consumption [l/100km]245.9
Average Electric Consumption [Wh/km]
Driv ing cy cle
‐44‐
Figure 57: Top Speed Diagram (road gradient of 4%) for the EB0‐powered Series Topology in Electric Mode
Figure 58: Maximum Available Wheel Torque for EB0‐powered Series Topology
Figure 59: Available Wheel Torque in “Unavailable Battery” Mode versus Ideal Wheel Torque derived from the Full‐Load Line of the Traction Electrical Machine
Driving Mode Electric Mode Hybrid Mode Unavailable Battery Mode
Top Speed [km/h] (4% gradient) 137 132 132 Top Speed [km/h] (0% gradient) 145 145 145 0‐>100 [s] 11.0 11.0 13.8 80‐>120 [s] 11.2 11.2 13.4
Table 15: Performances of the EB0‐powered Series Topology
Here no mechanical transmission limitations such as gear ratios occur since the traction machine is directly engaged to the wheels. Top speed performance in hybrid mode was assessed by using the road power requirement diagram (cf. Figure 54) by taking into consideration only the direct energy string discussed previously in Equation ( 27 ). Top speeds are of course similar in “Unavailable Battery” mode. In addition, top speed capability in electric mode was assessed by taking into consideration only the traction motor power as depicted in Figure 57. Acceleration performances were assessed by using the specific tool implemented in the Simulink model where basic speed echelons are involved. Theoretical acceleration capabilities based on available wheel torques (cf. Figure 58) were also computed and lead to get really close results through a force balance over the vehicle (cf. Equation ( 15 )). Note that the acceleration performances are similar between the two
0 50 100 1500
10
20
30
40
50
60
70
Vehicle Velocity [km/h]
Pow
er [k
W]
EM PowerRoad Power
0 50 100 1500
500
1000
1500
2000
2500
3000
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
0 50 100 1500
500
1000
1500
2000
2500
3000
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
Ideal Wheel TorqueAvailable Wheel Torque
‐45‐
different driving modes since traction torque is only supplied by EM2 in this specific powertrain. Only the theoretical way was used to compute acceleration performances in “Unavailable Battery” mode for which power limitation occurs as depicted in Equation ( 27 ) and leads to restrict available wheel torque as depicted in Figure 59. Performances of the EB0‐powered Series topology are gathered in Table 15. Finally note that the values gathered in Tables 14 and 15 are suitable with the Vehicle Specifications regarding ranges and performances for the three driving modes. Figures in Tables 14 and 15 are gathered in Chapter 5 with those derived from the other investigated drivetrains to ease the comparisons.
4.6 PowerSplit Topology In this part, the Peugeot 208 power‐split hybrid electric topology powered by the EB0 engine is going to be discussed in details regarding power design and modeling. In addition to those two topics, basic results of this hybrid topology will be depicted such as energy consumptions and performances.
4.6.1 Operating Principle
Figure 60: Operating Principle of the Power‐Split Hybrid Electric Powertrain
This part is dedicated to the operating principle of a power‐split hybrid electric powertrain. The most known power‐split hybrid is this manufactured by Toyota and considered in this material. The considered topology was depicted previously in Figure 3. This powertrain also called e‐CVT is based
. 0
&
1 1
2 .1
1 . 2
2 .
OOL
Fuel consumption & CO
2 emission
0 200 400 600 800 1000 12000
20
40
60
80
100
120
Time [s]
Spe
ed [k
m/h
]
0.1
0.1
0.1
0.1
0.15
0 .15
0.15 0.15
0.2
0.2
0.2
0.2
0.22
0.22
0.22
0.22
0.25
0.25
0.25
0.25
0.27
0.27
0.27
0.27
0.3
0.3
0.3
0.3
0.32 0.32
0.32
0 .32
0.35
0.3 5
Speed [rad/s]
Torq
ue [N
m]
ICE Efficiency Map
0 100 200 300 400 500 6000
10
20
30
40
50
60
70
80
90
‐46‐
on a planetary gear set used as a power‐split device as implemented in the Toyota Prius. The operating principle of this e‐CVT is depicted upstream in Figure 60.
The engine required power is computed from the power balance over the vehicle by taking into consideration the traction required power derived from the driver model, the auxiliary load, and the required battery power through a basic proportional controller. The aim of this powertrain is to make the engine operate according to its OOL i.e. at high efficiency as the series topology since the engine speed and torque can be adjusted independently to the road for a given required power owing to the power‐split device. Indeed, EM2 mounted on the ring wheel of the planetary gear set allows adjusting engine torque, whilst EM1 mounted on the sun wheel allows adjusting engine speed as depicted in Figure 60. Note here that compared with the series topology, a part of the engine torque is given mechanically to the road. Finally, note that an energy recirculation between EM1 and EM2 is required to keep the engine operate along its OOL, which involves compulsory losses.
4.6.2 Power Design
4.6.2.1 Design of the PowerSplit Device This part is dedicated to the design of the power‐split device i.e. the planetary gear set. One of the key parameter of this device is its kpl defined previously in Planetary Gear Set. To avoid introducing another floating parameter, kpl was considered as equal to an arbitrary value of 2.6. This value is derived from the ratio between the number of ring gear teeth and the number of sun gear teeth of the planetary gear set implemented in all the Toyota hybrid transaxle [9]. In addition, according to Figure 60, this value of 2.6 leads to 72% of the engine torque is conveyed to the wheels while only 27% is conveyed to the generator (EM1).
4.6.2.2 Speed Range of the Electrical Machines Another key parameter is the speed range of the two electrical machines implemented in this specific powertrain. Indeed, the speed relation between the three machines is significant in order to adjust engine speed independently to the road requirements. According to Toyota documentation [10], the top speed of EM2 is equal to 5273rpm for the recent P410 hybrid transmission and 6000rpm for the previous P112 hybrid transmission. In this material, the top speed of EM2 was assumed afterwards to be equal to 5500rpm i.e. similar to the engine top speed.
Figure 61: Planetary Gear Nomographs in Extreme Speed Range Operations
Thereby, by assuming top speed of 5500rpm for both the engine and EM2, two extreme top speed limits related to EM1 have to be taken into consideration and are depicted in the two planetary nomographs in Figure 61. The speed range requirement on the left side is derived from the electricity
EM2 (ring gear) ICE (carrier gear) EM1 (sun gear)
EM2 (ring gear) ICE (carrier gear) EM1 (sun gear)
generatifrom the(cf. Vehitoo demelectric dof 5500rthe literwhilst th
By assumPower Pin order absorbekpl and tthrough
Two sceconsiderreduce vdownsiztorque aengine t
Those tw16. A gropower r(overlapallow thspeed camaintainto reach
on capabilitye capability ticle Specificamanding. In driving moderpm for a staature regardhe full‐electr
ming first a pPreliminary Dto keep the d by EM1 (Tthe maximumFigure 60.
enarios withred. Those twvehicle grossing capabilitand therefororque along
wo scenariososs mass diffrequirementping curves)e vehicle toapability is sned. Here thh a higher to
y at any engto reach the ations). Electaddition, the is requisiteandstill enginding the genic top speed
4.6.2.3 power requirDesign of Hybsame powe
em1) is equal m torque de
4.6.2.4 h a commowo scenarios mass and thty, the genere the requirits OOL.
Table 1
s with their rference of onts between ). Therefore, reach 130kstrictly depee reader hasp speed but
gine speed. Tvehicle top tricity generahe capabilitye. Thereby, ane was finallnerator top scapability is
Torque Ranrement of 50brid Electric r capability eto 24Nm anelivered by t
Scenarioson tractionos are mainlyhen reduce Cerator (EM1red power d
6: Power Desig
respective enly 24kg is hthem are , the 2/3 EBkm/h over a endent on ths to understaonly for a s
‐47‐
The speed raspeed in fulation capabi to reach tha speed rangly consideredspeed in thes significantly
nge of the Ele0kW in full‐ePowertrainsespecially at nd this value the EB0 eng
electrical my based on tCO2 emission) could be delivered by
gn Scenarios fo
ngine poweighlighted bonly very s
B0‐powered road gradiehe engine poand that thehort time (e
ange requirel‐electric driility at any ehe required e of 14100rpd for EM1. Ae THS II (Toyy limited sinc
ectrical Maclectric drivins, the torquetop speed. Iis strictly deine along its
machine (EMthe engine dns in a largermore or lesEM1 is clos
r Power‐Split T
r and generaetween the slightly diffescenario is fent of 4% in ower since t battery conlectric boost
ment on theving mode iengine speedvehicle top
pm related tA value of 10yota Hybrid Sce considere
chines ng mode as de range of EMIn addition, terived from as OOL (TICEma
M2) regardidownsizing cr extent. In ass downsizedely depende
Topology
ator power atwo scenarioerent as definally given hybrid modthe vehicle tent capabilt). In additio
e right side is.e. to reach d was assump speed eveo the EM2 t0000rpm is qSystem) of td as a full‐hy
depicted prevM2 can be cthe maximuma ratio depe
ax = 87Nm) a
ing its powcapability in ddition to thd since the ent on the m
are depictedos. Thereby, picted in Fup since it
de. Note thattop speed hity allows thon, the assum
s derived 145km/h
med to be n in full‐op speed quoted in the Prius, ybrid [6].
viously in omputed m torque ndent on as shown
wer were order to
he engine required
maximum
d in Table the road igure 62 does not t the top has to be e vehicle mption of
‐48‐
50kW traction motor (EM2) is validated according to the road power requirements depicted in Figure 62 since a top speed of at least 130km/h is reachable over a road gradient of 4% in full‐electric driving mode
Figure 62: Road Power Requirements over a Road Gradient of 4% for 2/3 EB0‐powered Power‐Split Topology and EB0‐powered Power‐Split Topology.
4.6.3 Modeling Compared with the models derived from the Conventional topology and the Parallel topology, no new blocks were added. In addition, the Power‐Split topology model is basically simpler than the two latters since there is no speed relation between engine and road owing to the CVT effect. Only the computing way due to the specific physical relations is different.
Similar controllers regarding the driver model and the battery SOC control with similar static gain values as those used in the Parallel topology model were implemented in this Power‐Split topology model. In addition, the same engine ignition management with this derived from the Parallel topology model based on high engine efficiency and high engine power was also implemented.
Figure 63: Power‐Split Topology Model over Simulink
0 20 40 60 80 100 120 140 160 1800
10
20
30
40
50
60
Vehicle Speed [km/h]
Roa
d P
ower
[kW
]
Power-Split Hybrid Topology powered by EB0 (4% gradient)Power-Split Hybrid Topology powered by 2/3 EB0 (4% gradient)
Power Split Hybrid Model-K-
m/s -> km/h
Tice
Tem2
Tbrake
Froad
v
Tdriv
Wroad
Wbrake
Transmission
wem2
Tem2*
Tem2
Pel_em2
Traction Motor (em2)
FuelPower
Speed
FuelConsumptionDistance [km]Av erageSpeed [km/h]FuelEnergy
v Froad
Road Model
-0.02293
Road Energy [kWh]
Speed
Performance
0.1179
Mecanics -> electric [kWh]
Tice*
wice
Fuel PowerTicePice
EtaICE
ICE Model
wem1
Tem1*
Tem1
Pel_em1
Generator (em1)
G l S
K-Gain
6.958e+005
Fuel Energy [kWh]v *v Ttot*
Driver Model
Twheel*
v
SOC
saf ety SOC
Tice*
wice*
wem1
Tem1*
wem2
Tem2*
Control ofthe drivetrain
Paux
85.2
CO2 Emission [g/km]
-0.0005665
Brake Energy [kWh]
Tice
Tem2
Twheel*
Tbrake
Brake
0.002445
Battery Losses [kWh]P elm1
P elm2
P aux
Speed
SOCWlossPcharge
saf ety SOCElectricConsumptionEnergy Conv erion
Battery
3.672
Average Fuel Consumption [l/100km]
-22.51
Average Electric Consumption [Wh/km]
Driv ing cy cle
‐49‐
Furthermore, the same methodology was used in the Power‐Split model for the implementation of the “sustaining II” strategy in battery charge sustaining mode as depicted in the modelling of the Series model. The overall model of the Power‐Split topology is depicted in Figure 63 and looks very similar to the Series topology model.
4.6.4 Results: Energy Consumptions and Performances Energy consumptions both in battery charge depleting mode (electric mode) and in battery charge sustaining mode (hybrid mode) according to the two charge sustaining strategies, “sustaining I” and “sustaining II”, are depicted in Table 17 over the WLTP cycle. Note that the battery strategy “sustaining II” was here implemented with a given 1% difference between SOC minimum value and SOC maximum value, whilst the safety SOC value was set 1% under the SOC minimum value (cf. Chapter 3.3.3 for more information). In addition, note also that the fuel consumption values are corrected as a function of the difference between the initial SOC value and the final SOC value.
Driving Mode Electric Mode [Wh/km]
Hybrid Mode [l/100km]
Sustaining I Sustaining II WLTC 116.85 3.97 4.03 WLTC Urban 72.87 2.67 1.65 WLTC Urban 2 82.06 3.14 2.61 WLTC Road 106.75 3.70 3.41 WLTC Highway 165.24 5.50 5.63
Table 17: Energy Consumption of the EB0‐powered Power‐Split Topology
Driving Mode Electric Mode Hybrid Mode Top Speed [km/h] (4% gradient) 136 142 Top Speed [km/h] (0% gradient) 145 145 0‐>100 [s] 11.2 8.4 80‐>120 [s] 11.5 6.8
Table 18: Performances of the EB0‐powered Power‐Split Topology
Top speed performance in hybrid mode was assessed by using the road power requirement diagram (cf. Figure 62) by taking only into consideration the engine power conveyed to the wheels through the planetary gear set without using the battery capability since the speed has to be maintained. Indeed here the EB0 engine delivered 50kW and this amount of power is conveyed to the wheel through the planetary gear set without mechanical transmission limitations since the transmission here runs basically as a CVT. Top speed performance in electric mode was assessed by taking into consideration only the EM power as depicted in Figure 64. In addition, acceleration performances were assessed by using the specific tool implemented in the Simulink model where basic speed echelons are involved. Theoretical acceleration capabilities based on available wheel torque diagram (cf. Figure 65) were also computed and lead to get really close results through a force balance over the vehicle (cf. Equation ( 15 )). Note that at low vehicle speed the engine cannot operate at high speed since the speed range of EM1 is limited (cf. Equation ( 12 )). However here the torque delivered by the engine to the wheels is strictly constant and corresponds to the maximum engine torque along its OOL This capability to deliver always maximum torque at any vehicle speed is possible since the engine operating point related to this maximum engine torque according to its OOL is reachable for an engine speed of only 3500rpm. Performances of the EB0‐powered Power‐Split topology are gathered in Table 18. Note that the top speed limitations especially over a road
‐50‐
gradient of 0% are caused by the reduction gear design. Finally note that the values gathered in Tables 17 and 18 are suitable with the Vehicle Specifications regarding ranges and performances for at least the two major driving modes. Figures in Tables 17 and 18 are gathered in Chapter 5 with those derived from the other investigated drivetrains to ease the comparisons. The performances in “Unavailable Battery” mode were here not investigated because of time limitations and are accordingly assumed to be included in the Vehicle Specifications.
Figure 64: Top Speed Capability (road gradient of 4%) for the EB0‐powered Power‐Split Topology in Electric
Mode
Figure 65: Maximum Available Wheel Torque for EB0‐powered Power‐Split Topology
4.7 Active Strategy Control
4.7.1 Aims and Switch Power Values The energy consumptions in battery charge sustaining mode are relatively not similar between battery managements either based on the so‐called ”sustaining I” strategy or the so‐called “sustaining II” strategy. Urban conditions are more favorable regarding energy efficiency in “sustaining II” strategy, whilst high speed conditions are more favorable in “sustaining II” strategy for a same hybrid electric powertrain.
This energy consumption difference for a same hybrid electric powertrain is mainly explainable by the lack of power provided by the EB0 engine at its highest efficiency operating point to follow properly the road power requirements (only 22kW). Thereby, at high road power requirements, the battery SOC reaches its safety value and leads to make the engine operate at its maximum power, which alters the engine efficiency from 35% to 29%. In addition to this main drawback, higher the road power requirements are, lower the battery efficiency is since basically the battery charge/discharge frequency is in parallel higher. Thereby lower energy consumptions are noticeable in favor to the “sustaining I” battery strategy due to this high charge/discharge frequency at high road power requirements in a less extent.
A choice between those two battery charge sustaining strategies has to be carried out. Otherwise, the two battery charge sustaining strategy can be kept and have to be selected as a function of key parameters. This new battery strategy based on most efficient battery strategy selection in charge sustaining mode was called the “Active Strategy Control”. This latter option was finally considered in
0 50 100 1500
10
20
30
40
50
60
70
Vehicle Velocity [km/h]
Pow
er [k
W]
EM PowerRoad Power
0 50 100 1500
500
1000
1500
2000
2500
3000
Vehicle Velocity [km/h]
Whe
el T
orqu
e [N
m]
EM2ICEMaximum Wheel Torque
‐51‐
this material. The key parameter to choose which battery sustaining charge strategy is the most beneficial regarding energy efficiency is in a first extent the traction required power derived from the driver model through a traction required torque. Only the traction required power was finally taken into consideration for simplification purposes. Other parameters could be introduced such as vehicle speed or SOC value but were finally not taken into consideration.
Therefore, a Matlab algorithm was developed as a function of the exclusive traction required power by introducing in parallel hysteresis phenomena. The issue of this algorithm creation is to find the switch values given in kW. To highlight those switch power values, constant speed experiments were carried out for the Series, the Power‐Split, and also the Series/Parallel topologies. In addition, the corrected fuel consumptions were computed and picked up through the respective Simulink models for each speed level (power level) according to the two battery charge sustaining strategies. The battery switch strategy capability was expanded for the Series/Parallel topology by a topology switch between a series topology run with the “sustaining II” battery strategy and a parallel topology run with the “sustaining I” battery strategy. Note that only those two scenarios were taken into consideration and are mainly motivated by the results regarding energy consumptions in charge sustaining mode of those two topologies as a function of the battery strategy performed. The Series topology gives better results in urban driving conditions in “sustaining II” in the absolute, whilst the Parallel topology gives better results in high speed driving conditions in “sustaining I” in the absolute. The Parallel/Series topology will be discussed more in details later on.
Switch power values given in constant vehicle speed are highlighted in Figures 66, 67 and 68 for those three hybrid electric powertrains. The switch power values are gathered in as a function of the hybrid electric powertrain. Note that those values are quite close to this derived from the most efficient engine operating point i.e. 22kW according to its OOL. In addition, switch hysteresis is easily achievable since two distinctive switch power values at least are highlighted in the three “Constant Speed Experiments” diagrams. The Switch power values related to the so‐called Active Strategy Control are gathered in Table 19.
Figure 66: Constant Speed Experiments for the EB0‐powered Series Topology
Figure 67: Constant Speed Experiments for the EB0‐powered Power‐Split Topology
70 80 90 100 110 120 1303
4
5
6
7
8
9
10
Speed [km/h]
Fuel
Con
sum
ptio
n [l/
100k
m]
Sustaining ISustaining II
70 80 90 100 110 120 1303
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
Speed [km/h]
Fuel
Con
sum
ptio
n [l/
100k
m]
Sustaining ISustaining II
‐52‐
Figure 68: Constant Speed Experiments for the EB0‐powered Series/Parallel Topology
Topology Switch‐down Power [kW] Switch‐up Power [kW] Series 7 (81km/h) 19 (120km/h) Power‐Split 7 (80km/h) 20 (122km/h) Series/Parallel 7 (80km/h) 16 (112km/h)
Table 19: Switch Power Values for the Active Strategy Control
4.7.2 Modeling A specific block to make the model run according to the Active Control Strategy for the Parallel, the Series and the Series/Parallel models over Simulink was developed. As depicted previously, the switch strategy capability is focused exclusively on the required traction power derived from the driver model. Thereby, the two inputs of this block are the vehicle speed and the traction torque computed by the driver model as depicted in Figure 69. The road power requirement is then smoothed by a Discrete Mean Value block by averaging power requirement over a period of 3s. This sampling time was chosen 1s higher than the τcharge value defined previously. This arbitrary value results from a compromise between a need of smoothing peak powers as much as possible and another need to be reactive (the results of the sliding average are given in form of an echelon with 3s of delay compared with the very variable traction power requirement).
Figure 69: Active Control Strategy Block
40 50 60 70 80 90 100 110 120 1302
3
4
5
6
7
8
9
10
Speed [km/h]
Fuel
Con
sum
ptio
n [l/
100k
m]
Parallel Configuration (sustaining I)Series Configuration (sustaining II)
Road PowerRequirement
1/rw
m/s -> rad/sScope
MultiportSwitch
Strategy
Goto
In Mean
Discrete Mean value
-C--C-
Strategy
Switch
<= 02
Twheel*
1v
‐53‐
A case study to ease the understanding of this switch battery strategy capability is discussed for the Power‐Split topology over the Urban 2 part of the WLTP cycle. The main Simulink scope of the Active Strategy Control block is depicted in Figure 70. The battery charge sustaining strategy is switched from the “sustaining II” mode to the “sustaining I” mode at t = 190s and the “sustaining II” mode is reactivated at t = 205s as shown in Figure 71. Here 0 means “sustaining I” mode, whilst 1 means “sustaining II” mode.
Figure 70: Main Scope of the Active Strategy Control Block over the Urban 2 part of the WLTP Cycle for the
Power‐Split Topology
Figure 71: Strategy Implemented by Active Strategy Control Block over the Urban 2 part of the WLTP Cycle
for the Power‐Split Topology
4.8 Series/Parallel Topology In this part, the Peugeot 208 series/parallel hybrid electric topology powered by the EB0 engine is going to be discussed in details regarding power design and modeling. In addition to those two topics, basic results of this hybrid topology will be depicted such as energy consumptions and performances.
4.8.1 Operating Principles & Power Design The powertrain layout of this specific topology is directly derived from the merging of the selected Parallel topology and the selected Series topology. However, here the topology is either operated as a series hybrid electric powertrain coupled with the so‐called “sustaining II” strategy or as a parallel hybrid electric powertrain coupled with the so‐called “sustaining I” strategy for both in battery charge sustaining mode. This specific topology is outlined in Figure 6 at the beginning of this material.
Note that the generator was assumed to be not in operation (turned off) when the topology is operated as a parallel hybrid electric powertrain. In addition, the switch power values related to the Active Strategy Control are basically low. Thereby only a small powerful generator was implemented as depicted in Table 20. The battery charge depleting mode related to the full‐electric capability is ensured exclusively by the EM mounted on the transaxle gear set i.e. this derived from the parallel topology.
0 50 100 150 200 250 300 350 400 450-40
-30
-20
-10
0
10
20
30
Time [s]
Pow
er [k
W]
Road Power RequirementsSwitch-up Power ValueSwitch-down Power ValueMean Values
0 50 100 150 200 250 300 350 400 4500
0.2
0.4
0.6
0.8
1
Time [s]B
atte
ry C
harg
e S
usta
inin
g S
trate
gy
Only onpossible assessmto be copowertr20kW. EControl)that the this imp
The assuspeed ctransmistop spee
Tab
e scenario rfor both paent is preseompared witain has to bEven though , the batteryengine adaplemented in
umption of aapabilities ossion limitatied magnitude
Figure
ble 20: Gross M
regarding porallel topolonted in Tablh this derivebe switched the topolog
y buffering cptation massthe two refe
a 50kW tracover a roadions allows te required b
e 72: Road Pow
00
10
20
30
40
50
60
70
80
90
Roa
d P
ower
[kW
]
Mass Assessmen
ower design gy and seriee 20 by imped from the in parallel togy switch is apabilities res was calculaerence vehic
ction EM is hd gradient othe vehicle ty the Vehicle
wer Requireme
20 40 60
0% gradient4% gradient
‐54‐
nt of the EB0‐p
was assumees topology. Tplementing oengine best opology modcarried out egarding powated for a gacles.
here validateof 4%. Indeeto be propee Specificatio
ents for the EB0
0 80 100Vehicle Speed [km
powered Series/
ed since engThis dedicateonly a 25kW efficient opde for a roathrough filtwer and eneasoline tank
ed accordinged, a powelled up to 14ons.
0‐powered Seri
120 140m/h]
/Parallel Topol
gine downsized scenario generator. Terating poind power reqtering meansergy are hereof 30 liters i
g to Figure 7r of 50kW 40km/h, wh
es/Parallel Top
160 180
logy
zing capabiliregarding grThis power vnt i.e. 20kW quirement os (cf. Active e partially usnstead of 50
72 regardingwith no meich correspo
pology
ity is not ross mass value has since the f at least Strategy
sed. Note 0 liters as
g the top echanical onds to a
‐55‐
In addition, the transaxle gear set adaptation proposed for the Parallel topology has to be checked since the vehicle gross mass was increased significantly. By assuming first the same transaxle gear ratio of 3.2 derived from the power design of the Parallel topology, top speed capability over a road gradient of 4% has to be controlled. Gearbox ratios make top speed capability be limited as depicted in Figure 73. Indeed, the transaxle gear ratio of 3.2 is too long since only a top speed of 133km/h is expected i.e. too close to the Vehicle Specifications in Hybrid mode. Thereby, the transaxle gear ratio has to be basically increased. The value of 3.5 was finally chosen and gave more suitable results regarding performances.
Figure 73: Top Speed Capability (4% road gradient) of the Series/Parallel Topology with a Transaxle Gear Ratio of 3.2
4.8.2 Modeling
Figure 74: Control of the Drivetrain over Simulink for the Series/Parallel model
The modeling of this topology is based on the merge of the Parallel model and the Series model. Most of the blocks over Simulink are common. Only specific Switch blocks were added to make the topology computing process change from parallel to series way and vice versa as depicted in Figure 74 on the left side. Those Switch blocks are directly controlled by the Active Strategy Control block (orange block).
0 50 100 150 200 250 3000
10
20
30
40
50
60
70
80
90
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
Required wheel torque * wheel speed == required wheel power
Switch Series/Parallel Hybrid configuration according to both road power requirement
7utvx
6Tem2*
5wem2
4Tem1*
3wem1*
2wice*
1Tice*1/rw
m/s -> rad/s
Wheel Power
Switch4
Switch3
Switch1
Switch
Scope1
Scope
SOC
StrategyP charge *
SOC controller acc to equation (3-9)
Related Battery Srategy
P*
saf ety SOC
Strategy
Tice*
wice*
Optimal operatingpoint for ICE(figure 11)
ICE powerref
Switch
Goto
w_wheel
Tice*
wice*
Tnew*
wice_new*
utv x
Gear Selection
gr1
Gain2
-K-
Gain1
gr2
Final gear
1/gr2
Final gear
0
0
Constant1 1
Constant
v
Twheel*Switch
-K-
1/gr2
->Tem2*
4safety SOC
3SOC
2v
1Twheel*
‐56‐
4.8.3 Results: Energy Consumptions and Performances Energy consumptions both in battery charge depleting mode (electric mode) and in battery charge sustaining mode (hybrid mode) derived from the Active Strategy Control are depicted in Table 21. Note that the SOC values used in the two different charge sustaining strategies are similar to those introduced in the other hybrid electric models.
Driving Mode Electric Mode [Wh/km]
Hybrid Mode [l/100km]
WLTC 116.65 3.87 WLTC Urban 72.66 1.68 WLTC Urban 2 81.86 2.78 WLTC Road 106.55 3.69 WLTC Highway 165.04 5.56
Table 21: Energy Consumptions for the Series/Parallel Topology
Performances were also assessed for the three driving modes and are depicted in Table 22. Best performances are derived from the parallel topology mode since power addition between engine and electrical motor is possible. Therefore, performances of the Series/Parallel topology were computed by assuming power addition capability, which means to be exclusively in parallel topology mode with the generator turned off. Top speed capability in hybrid mode was assessed by taking into consideration only engine power since the speed has to be maintained. Note here that top speeds are similar between the Hybrid mode and the “Unavailable Battery” mode. Here mechanical transmission limitations were expected due to the gearbox ratio and are depicted in Figures 75 and 76 for a road gradient of 4% and 0% respectively. In electric mode, the top speed capabilities were assessed by taking into consideration only the EM power as depicted in Figure 77. Acceleration performances were assessed by using the tool implemented directly over Simulink. Nonetheless, theoretical calculations were also carried out through a maximum available wheel torque diagram (cf. Figure 78) by taking into consideration Equation ( 15 ) to control the accuracy of the results. Those theoretical calculations lead to asymptotic results (lower regarding time) but close to those derived from the Simulink model. Finally note that the values gathered in Tables 21 and 22 are suitable with the Vehicle Specifications regarding ranges and performances for the three driving modes. Figures in Tables 21 and 22 are gathered in Chapter 5 with those derived from the other investigated drivetrains to ease the comparison
Figure 75: Top Speed Capability (road gradient of 4%) for the Series/Parallel Topology in Hybrid Mode
Figure 76: Top Speed Capability (road gradient of 0%) for the Series/Parallel Topology in Hybrid Mode
0 50 100 150 200 250 3000
10
20
30
40
50
60
70
80
90
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
0 50 100 150 200 250 3000
10
20
30
40
50
60
Vehicle Velocity [km/h]
Pow
er [k
W]
5th4th3rd2nd1stRoad Power
‐57‐
Figure 77: Top Speed Capability (road gradient of 4%) for the Series/Parallel Topology in Electric Mode
Figure 78: Maximum Available Wheel Torque of the EB0‐powered Series/Parallel Topology
Driving Mode Electric Mode Hybrid Mode Unavailable Battery Mode
Top Speed [km/h] (4% gradient) 136 141 141 Top Speed [km/h] (0% gradient) 145 165 165 0‐>100 [s] 11.4 6.3 16.6 80‐>120 [s] 11.6 5.3 13.4
Table 22: Performances of the Series/Parallel Topology
0 50 100 1500
10
20
30
40
50
60
70
Vehicle Velocity [km/h]
Pow
er [k
W]
EM PowerRoad Power
0 50 100 150 200 250 3000
500
1000
1500
2000
2500
3000
3500
4000
Vehicle Speed [km/h]
Whe
el T
orqu
e [N
m]
5th4th3rd2nd1stEMMaximum Wheel Torque
‐58‐
5 General Comparisons General comparisons regarding gross masses, energy consumptions, performances and manufacturing costs are presented here. Most of the data depicted in this section are derived from Chapters 4.2.3, 4.4.4, 4.5.4, 4.6.4, 4.8.3 concerning respectively the two reference vehicles (EB0 and EB2DT‐powered Peugeot 208), the parallel topology, the series topology, the power‐split topology, and the series/parallel topology.
5.1 Gross Mass Comparisons As discussed previously, different scenarios regarding power design and therefore vehicle gross mass were investigated in this material for each hybrid electric topology. The results regarding vehicle gross mass are depicted in Figure 79. The lightest 9‐kWh battery pack PHEV is the Parallel topology (blue), whilst the heaviest are the Power‐Split topology (yellow) and the series/Parallel topology (red/blue). Mass values were discussed previously in each respective part related to each topology.
Figure 79: Vehicle Gross Mass Assessment
Note that all the vehicle gross masses considered for simulation purposes were overestimated by adding 75kg of cargo as required by the European legislation.
5.2 Energy Consumptions
5.2.1 Electric Mode (Charge Depleting Mode) As discussed in the Battery Strategy Managements, the main advantage of a PHEV and a Range Extender is to be able to use cheap energy from the electricity grid. Thereby, the first mode of driving is called the “electric mode” or the “charge depleting mode”. Energy consumptions are here given in Wh/km or also in kilometers to reflect the full‐electric range capability. Here a useful SOC of 85% was assumed, which involves a reference SOC value for battery charge sustaining operation equal to 15%. This value of 15% corresponds to 1.35kWh, which corresponds to the magnitude with specific margin due to other battery technology differences of the current battery pack content implemented in most of the full‐hybrid vehicles. Note here that basically the full hybrid vehicles are operated in battery charge sustaining mode. Electric ranges for each hybrid electric powertrain are depicted in
900
950
1000
1050
1100
1150
1200
1250
1300
Gross M
ass [kg]
EB0‐powered Peugeot 208
EB2DT‐powered Peugeot 208
EB0‐powered Peugeot 208 (Stop&Start)EB2DT‐powered Peugeot 208 (Stop&Start)EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power‐Split
EB0‐powered Series/Parallel
‐59‐
Figure 80. Slightly differences between powertrains regarding their respective electric ranges are mainly caused by vehicle gross mass differences.
Figure 80: Electric Range in Charge Depleting Mode over the WLTP Cycle
Note that the respective range in full‐electric mode of each designed PHEV is included between the two limits derived from the Vehicle Specifications.
5.2.2 Hybrid Mode (Charge Sustaining Mode) As discussed in the Battery Strategy Managements, the battery charge has to be maintained around a specific SOC value called the reference SOC value and here equal to 15%. This battery mode is called the charge sustaining mode and is nicknamed in this material as the hybrid mode. To keep the battery charge level, the engine has to be turned on. Thereby, energy consumptions are here given in gasoline liter per 100km. Note that all the fuel consumptions given later on are all corrected as a function of the difference between the reference SOC value and the final SOC value. Fuel consumptions over the WLTP cycle according to the Active Strategy Control are depicted in Figure 81.
Figure 81: Energy Consumptions in Charge Sustaining Mode (Active Strategy Control) over WLTP Cycle
In addition, asymptotic corrected fuel consumptions are given in Figure 82 and correspond to the lowest fuel consumptions computed for each driving cycle. Note that here the fuel consumptions
0,0
20,0
40,0
60,0
80,0
100,0
120,0
WLTC WLTC Urban 1
WLTC Urban 2
WLTC Road WLTC Highway
Electric Ran
ge [km
]
EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power Split
EB0‐powered Parallel/Series
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
WLTC WLTC Urban 1
WLTC Urban 2
WLTC Road
WLTC Highway
Fuel Con
sumption [l/10
0km] EB0‐powered Poeugeot 208
EB2DT‐powered Poeugeot 208
EB0‐powered Peugeot 208 (Stop&Start)
EB2DT‐powered Peugeot 208 (Stop&Start)
EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power‐Split
EB0‐powered Series/Parallel
‐60‐
over the entire WLTP cycle were computed by taking into consideration each fuel consumption over each segment in conjunction with their respective distance.
Figure 82: Lowest Computed Energy Consumptions in Charge Sustaining Mode over the WLTP Cycle
Note that the respective range in hybrid mode (charge sustaining mode) of each designed PHEV is relatively close to a range of 500km for a 30‐liter gasoline tank i.e. included between the two edges derived from the Vehicle Specifications.
Fuel consumptions in battery charge sustaining mode are lower for the Series, the Power‐Split and the Series/Parallel (operating in Series mode) topologies over urban driving conditions since the engine can be operated at high efficiency along its OOL as depicted in Figure 83 for Series topology while mechanical‐electrical energy conversion are restricted. Operating points of the engine implemented in the Parallel topology are depicted in Figure 84 for comparison purposes. Energy conversions are basically the key parameter regarding powertrain efficiency since this latter allows the engine to be operated along its OOL. However more the road power requirements are rising, more energy conversions is required, which leads to reduce the overall efficiency performance of the drivetrain. Two case studies over two separate driving conditions are discussed more in details in Appendix 3 for explanation purposes.
Figure 83: ICE Operating Points over WLTP Urban 1 for the Series Topology
Figure 84: ICE Operating Points over WLTP Urban 1 for the Parallel Topology
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
WLTC WLTC Urban 1
WLTC Urban 2
WLTC Road
WLTC Highway
Fuel Con
sumption [l/10
0km] EB0‐powered Poeugeot 208
EB2DT‐powered Poeugeot 208
EB0‐powered Peugeot 208 (Stop&Start)
EB2DT‐powered Peugeot 208 (Stop&Start)
EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power‐Split
EB0‐powered Series/Parallel
0 100 200 300 400 5000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1 0.1 0.
0.15
0.15
0.15 0.150.1
0.2
0.2
0.2 0.2
0.22
0.22
0.22 0.22
0
0.25
0.25
0.25 0.25
0.27
0.27
0.270.27
0.3
0.3
0.3
0.3
0.3
0.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rad/s]
Torq
ue [N
m]
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1
0.1 0.1
0.15
0. 15
0.15 0.150.15
0.2
0.2
0.2 0.20
0.22
0.22
0.22 0.220.
0.25
0.25
0.250.25
0
0.27
0.27
0.270.27
0.3
0.30.3
0.3
0.3
0.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rpm]
Torq
ue [N
m]
‐61‐
5.2.3 Unavailable Battery Mode Energy consumptions in “Unavailable Battery” mode will not be discussed since they are not required for emission certification calculation and this specific mode is considered more accidental than relevant for comparison purposes. Note however that the energy consumptions related to gasoline consumptions were controlled for each hybrid electric drivetrain regarding the expected range derived from the Vehicle Specifications (except for the Power‐Split topology).
5.2.4 Emission Certifications Emission certifications based on full‐electric range and CO2 emissions in battery charge sustaining mode are going to be discussed in this part. Today the European calculation rule depicted in Equation ( 31 ) is used for emission certification of PHEVs by assuming a common range in charge sustaining mode of 25kg. Note that in Equation ( 31 ) the symbol e stands for CO2 emissions given in gCO2/km while the symbol r stands for range given in kilometers. The emission values are computed from the fuel consumption values according to Equation ( 32 ) for gasoline four‐stroke spark‐ignition engine. The value of 23.2 is derived from the combustion process in the internal combustion engine which occurs at stoichiometric mixture for gasoline four‐stroke spark‐ignition engine. This value is equal to 26.5 for diesel four‐stroke compressed‐ignition engine.
. . 25
25 ( 31 )
23.2100
( 32 )
By using over the WLTP cycle even though this method is currently only applied over the NEDC cycle, emission certifications can be computed for all the powertrains investigated in this material as depicted in Figure 85. Note that only the Active Strategy Control was considered in charge sustaining mode regarding fuel consumptions. Note here that the CO2 emissions over the WLTP cycle for each designed PHEV are even slightly better than those derived from the Vehicle Specifications.
Figure 85: Emission Certification over the WLTP Cycle
108118
106115
25 26 25 25
0
20
40
60
80
100
120
140
CO2 em
ission
s [gCO
2/km
]
EB0‐powered Poeugeot 208
EB2DT‐powered Poeugeot 208
EB0‐powered Peugeot 208 (Stop&Start)
EB2DT‐powered Peugeot 208 (Stop&Start)
EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power‐Split
EB0‐powered Series/Parallel
‐62‐
5.3 Performances Performances of all the powertrains investigated in this material are gathered in Figure 86 regarding top speed capabilities and in Figure 87 regarding acceleration performances. Performances of the “Unavailable Battery” mode are not depicted since this mode is considered as accidental and is therefore not relevant for comparison purposes. Note that those performances are dependent on the driving mode i.e. either the full‐electric driving mode (battery charge depleting mode) or the hybrid driving mode (battery charge sustaining mode). In addition, note that the performances of the PHEVs (excluding the Series topology) are closer to those derived from the EB2DT‐powered Peugeot 208 than those from the EB0‐powered Peugeot 208. However, the top speeds of all the PHEVs are closer to this derived from the EB0‐powered Peugeot 208. Those two statements were expected since top speed capabilities are assessed without taking into consideration battery capacity in charge sustaining mode and power addition between engine and electrical machine is enable for most of the PHEVs. Note that the performances related to the vehicles equipped with a Stop&Start system were not assessed and are assumed to be really close to those derived from the reference vehicles despite the light mass increase. For more details regarding values, look at dedicated parts.
Figure 86: Top Speed Performances
Figure 87: Acceleration Performances
0
20
40
60
80
100
120
140
160
180
200
Vmax (4% gradient) Vmax (0% gradient)
Veh
icle Velocity [km/h]
EB0‐powered Poeugeot 208
EB2DT‐powered Poeugeot 208
EB0‐powered Parallel (Electric Mode)
EB0‐powered Parallel (Hybrid Mode)
EB0‐powered Seriesl (Electric Mode)
EB0‐powered Series (Hybrid Mode)
EB0‐powered Power‐Split (Electric Mode)
EB0‐powered Power‐Split (Hybrid Mode)
EB0‐powered Series/Parallel (Electric Mode)
EB0‐powered Series/Parallel (Hybrid Mode)
0
2
4
6
8
10
12
14
0‐>100 80‐>120
Time [s]
EB0‐powered Poeugeot 208
EB2DT‐powered Poeugeot 208
EB0‐powered Parallel (Electric Mode)
EB0‐powered Parallel (Hybrid Mode)
EB0‐powered Seriesl (Electric Mode)
EB0‐powered Series (Hybrid Mode)
EB0‐powered Power‐Split (Electric Mode)
EB0‐powered Power‐Split (Hybrid Mode)
EB0‐powered Series/Parallel (Electric Mode)
EB0‐powered Series/Parallel (Hybrid Mode)
‐63‐
5.4 Powertrain Manufacturing Cost Assessment Powertrain Manufacturing costs were assessed for all the powertrains investigated in this material. This assessment was carried out by taking into consideration relevant manufacturing unit costs sometimes based on forecasts derived from values assessed by specialists at PSA Peugeot Citroën. The work was to aggregate those unit costs and finally to compute the overall cost of such‐and‐such powertrain. No detail especially regarding unit costs of this powertrain manufacturing cost assessment will be depicted for confidentiality purposes. In addition, only relative differences given in percentage compared with the powertrain of the EB0‐powered Peugeot 208 are depicted in Figure 88 for confidentiality purposes as well.
Figure 88: Powertrain Manufacturing Cost Differences between Topologies with EB0‐powered Peugeot 208 as Reference
0%
50%
100%
150%
200%
250%
300%
350%
400%
EB2DT‐powered Peugeot 208
EB0‐powered Peugeot 208 (Stop&Start)EB0‐powered Parallel
EB0‐powered Series
EB0‐powered Power‐Split
EB0‐powered Series/Parallel
‐64‐
6 Conclusion & Discussion The aim of this study was to compare energy conversion efficiencies, top speed and acceleration performances, and cost between the four main hybrid electric vehicles (parallel, series, power‐split and series/parallel topologies) according to reference vehicles regarding a plug‐in application. The following statements summarize what it was pointed out along this material.
The Parallel topology is more suitable for road and highway driving conditions regarding energy conversion efficiency (cf. Figure 81 for instance), whilst performances are enhanced significantly or at least maintained in magnitude if compared with the EB2DT‐powered Peugeot 208 (cf. Figures 86 and 87). In addition, this topology is the most affordable PHEV solution, see Figure 88.
The Series topology is more suitable for urban driving conditions regarding energy conversion efficiency (cf. Figure 81 for instance). In addition, performances are significantly reduced even in battery charge sustaining mode 208 (cf. Figures 86 and 87). This specific topology is not the most expensive but also not the most affordable, see Figure 88.
The Power‐Split topology is the most multipurpose hybrid electric drivetrain regarding energy conversion efficiency (cf. Figure 81 for instance). In addition, performances are enhanced significantly or at least maintained in magnitude if compared with the EB2DT‐powered Peugeot 208 208 (cf. Figures 86 and 87). However, this topology is also one of the least affordable, see Figure 88.
Finally, the Series/Parallel topology is also the most multipurpose hybrid electric drivetrain in term of energy conversion efficiency (cf. Figure 81 for instance). Performances are enhanced significantly or at least maintained in magnitude if compared with the EB2DT‐powered Peugeot 208 208 (cf. Figures 86 and 87). However, this PHEV solution is one of the least affordable as well, see Figure 88.
All the PHEV solutions have to be basically considered as premium vehicles since full‐electric driving mode is possible over a relative long range while acceleration performances are significantly enhanced (except for the Series topology). Thereby the most suitable reference vehicle in term of both the specifications and the customer market could be the EB2DT‐powered Peugeot 208. Overall comparison is depicted in Table 23 regarding various specifications by assuming the EB2DT‐powered Peugeot 208 as the exclusive reference vehicle.
Criteria 208 EB2DT
208 EB0
Parallel
208 EB0 Series
208 EB0 PS
208 EB0 S/P
Comments
Acceleration ☺ ☺ ☺ Power addition capability Top Speed EM power limitation (Series) & Mass
increase
Manufacturing Cost Less electronics components (Parallel)
CO2 Emission 118g ☺
25g ☺26g
☺25g
☺25g
Multipurpose ☺ ☺ ☺ Urban usage (Series) Table 23: Chart Review of Hybrid Electric Drivetrains
‐65‐
The results of this study especially regarding energy consumptions are dependent on numerous factors and parameters introduced as constant input data such as the efficiency maps for instance. Thereby the ranking over the WLTP cycle regarding energy consumptions especially in battery charge sustaining mode can be modified in a more and less extent. One way to understand this close dependence would be to implement a new engine with another efficiency map. Or even better to increase overall efficiency of the EB0 engine by making this latter operate according to an Atkinson cycle instead of an Otto cycle. Aims and purposes of those two cycles dedicated for spark‐ignition combustion engine are discussed in details in Appendix 4. The Otto‐cycle EB0 engine was replaced by the Atkinson‐cycle (Miller‐cycle) EB0 engine. New results regarding energy consumption in charge sustaining mode were basically reduced but in different magnitudes. Corrected lowest fuel consumptions per driving conditions computed by Simulink are gathered in Figure 89. Only three hybrid electric topologies are depicted here to ease understanding. Note that the fuel consumptions over the entire WLTC were computed by taking into consideration each segment with their respective distance and corrected fuel consumption. Lowest computed fuel consumptions over each driving cycle derived from the Otto‐cycle EB0 engine are also illustrated in Figure 89 for comparison purposes. Fuel consumption reduction is indeed not similar between the three topologies especially over the entire cycle. The topologies which have the capability to make the engine operate along its OOL (Series and Power‐Split topologies) are more advantageous regarding energy conversion efficiency than the Parallel topology. The 3rd generation of Toyota Prius powered by an Atkinson‐cycle gasoline engine confirms at least partially this statement.
Figure 89: Lowest Computed Fuel Consumption in Charge Sustaining Mode over the WLTP Cycle
0,00
1,00
2,00
3,00
4,00
5,00
6,00
WLTC WLTC urban 1
WLTC urban 2
WLTC road WLTC highway
Fuel Con
sumption [l/10
0km]
EB0‐powered Peugeot 208
EB0‐powered Parallel
Atkinson‐cycle EB0‐powered Parallel
EB0‐powered Series
Atkinson‐Cycle EB0‐powered Series
EB0‐powered Power‐Split
Atkinson‐Cycle EB0‐powered Power‐Split
‐66‐
Appendix 1: Driving Cycles This part is dedicated to the three diving cycles used in order to assess energy efficiency of all the relevant powertrains studied in this material. [11]
New European Driving Cycle (NEDC) The NEDC cycle is an extended urban driving cycle with a short high speed part in the end. It was devised to represent city driving conditions. It is characterized by low vehicle speed, low engine load, and low exhaust gas temperature. The cycle is 11 km long and its average speed is 33.4 km/h, whilst its total duration is 1180 s (cf. Figure 90). Table 24 summarizes the details related to this driving cycle such as average speed and accelerations related to positive accelerations only (engine load requirement). The NEDC cycle consists of two parts: ECE 15 cycle which is an urban driving cycle, whilst the second part, the so‐called EUDC cycle, has been added after the fourth ECE 15 cycle to account for more aggressive and high speed modes.
Figure 90: Speed & Acceleration Diagrams of the NEDC Cycle
World Harmonized LightDuty Test Cycle (WLTC) The WLTC cycle is derived from the WLTP (World Harmonized Light‐Duty Test Procedure) whose aims are to establish a worldwide test procedure to measure light vehicle emissions and energy consumption. The WLTC cycle presented in Figure 91 is derived from the point of view of PSA Peugeot Citroën about this future certification driving cycle since no common agreement was yet decided as this material was written. It is characterized by high speed vehicle up to 132 km/h and higher engine load. This cycle is then 22.7 km long and its average speed is 45.4 km/h, whilst its total duration is 1800 s. In addition, this cycle consists of four segments: Urban, Urban 2, Road, and Highway as shown in the order from the left to the right in Figure 91 (dotted red lines). All the details related to the WLTC cycle are gathered in Table 24.
0 200 400 600 800 1000 12000
50
100
Time [s]
Spe
ed [k
m/h
]
NEDC
0 200 400 600 800 1000 1200-2
-1
0
1
2
Time [s]
Acc
eler
atio
n [m
/s2 ]
‐67‐
Figure 91: Speed & Acceleration Diagrams of the WLTP Cycle with Segments (between dotted red lines)
INRETS UL1 Cycle In addition to the two driving cycles depicted previously, one more cycle was used in order to assess the capability and its related limits of the final gear ratio elongation in the cases of both the parallel hybrid topology and the series/parallel hybrid topology. The INRETS UL1 cycle is characterized by low‐speed driving conditions and congested traffic. This cycle is 800 m long and its average speed is 14.7 km/h, whilst its total duration is of 800 s. Speed point diagram and related accelerations are depicted in Figure 92, whilst more details related to this cycle are presented in Table 24 for comparison purposes.
Figure 92: Speed & Acceleration Diagrams of the INREST UL1 Cycle
0 200 400 600 800 1000 1200 1400 1600 18000
50
100
Time [s]
Spe
ed [k
m/h
]
WLTC
0 200 400 600 800 1000 1200 1400 1600 1800
-2
0
2
Time [s]
Acc
eler
atio
n [m
/s2 ]
0 100 200 300 400 500 600 700 8000
5
10
15
20
Time [s]
Spe
ed [k
m/h
]
INRETS UL1
0 100 200 300 400 500 600 700 800
-2
0
2
Time [s]
Acc
eler
atio
n [m
/s2 ]
‐68‐
NEDC WLTC INRETS UL1 Duration [s] 1180 1800 800 Distance [km] 22.7 11.0 0.9 Average Speed [km/h] 45.4 33.4 3.8 Top Speed [km/h] 132 120 14.7 Average Acceleration [m/s2] 0.15 0.28 0.2 Top Acceleration [m/s2] 1.06 2.11 1.9
Table 24: NEDC, WLTC & INRETS UL1 Details
‐69‐
Appendix 2: Optimum Operating Line The Optimum Operating Line (OOL) is going to be discussed in details in this part. The OOL is a significant parameter related to an internal combustion engine. In the operation of a vehicle, the power requirements vary with the time according to the road power requirements through a speed point diagram for instance. The power (P) is the product of speed (ω) and torque (T) as depicted in Equation ( 33 ).
. ( 33 )
Thereby, a large number of combinations of speed and torque can give the same engine power according to a specific related engine efficiency map. For each achievable power level, a specific speed‐torque combination allows getting the highest engine efficiency. The OOL gathers all those specific speed‐torque combinations equivalent for each one to a specific engine power. Basically, this theoretical line corresponds also to the engine operating points in the case of the implementation of an ideal continuous variable transmission with infinite gear ratios.
Figure 93: Torque (left), Speed (middle) & Efficiency (left) as a function of engine power level related to the OOL of the EB0 engine
In this material, only two gasoline engines are introduced: the EB0 three‐cylinder in‐line spark ignition gasoline engine and the EB2DT turbocharged three‐cylinder in‐line spark ignition gasoline engine. The related features of their respective OOL are depicted in Figures 93 and 94 through their respective engine torques, speeds and efficiencies. Those two diagrams were computed through a specific algorithm by browsing on the respective engine efficiency maps.
0 500
10
20
30
40
50
60
70
80
90
Engine Power [kW]
Eng
ine
Torq
ue [N
m]
0 500
1000
2000
3000
4000
5000
6000
Engine Power [kW]
Eng
ine
Spe
ed [r
pm]
0 500
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Engine Power [kW]
Eng
ine
Effi
cien
cy
‐70‐
Figure 94: Torque (left), Speed (middle) & Efficiency (left) as a function of engine power level related to the OOL of the EB2DT engine
0 50 1000
20
40
60
80
100
120
140
160
180
Engine Power [kW]
Eng
ine
Torq
ue [N
m]
0 50 1000
1000
2000
3000
4000
5000
6000
Engine Power [kW]
Eng
ine
Spe
ed [r
pm]
0 50 1000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Engine Power [kW]
Eng
ine
Effi
cien
cy
‐71‐
Appendix 3: Energy Consumptions: Case Studies Two separate driving conditions are going to be discussed in term of energy consumptions for each drivetrain studied in this material. The two driving conditions retained as the most relevant for understanding purposes are Urban 1 and Highway both derived from the WLTP cycle. Note that here only charge sustaining mode is discussed for the hybrid electric drivetrains.
Case Studies: Urban 1 High engine efficiency occurs for all the drivetrains whose their main capability is to follow the engine OOL. Those drivetrains are basically here the Series, the Power‐Split, and the Series/Parallel topologies (since operating in Series mode). In addition, mechanical‐electrical energy conversions are restricted. Energy conversions between hybrid electric drivetrains were noticed to be similar regarding their magnitude. In addition, battery efficiencies were noticed to be slightly higher for the Parallel topology since this latter is run exclusively according to a battery strategy which restricts SOC variation (“sustaining I” battery strategy). Efficiencies of each machine, losses, corrected fuel consumptions, energy conversions, and so on are gathered in Table 25. Active Strategy Control regarding battery management was only considered for the hybrid electric drivetrain. Note that here the parameter ηpowertrain is defined by Equation ( 34 ) i.e. by not taking into consideration inertia forces through acceleration requirements. Note also that EM1 and EM2 stand respectively for the generator and the traction motor. Finally measurement regarding the reference EB2DT‐powered Peugeot 208 is not depicted to ease overall understanding.
( 34 )
FC [l/100km]
Losses [kWh]
Battery Loss [kWh]
Energy Conversion [kWh]
ηpowertrain ηICE ηEM1 ηEM2 ηBattery
EB0‐powered Peugeot 208
4.38 1.16 8.98% 25.18%
EB0‐powered Peugeot 208 (stop&start)
3.99 1.06 9.96% 25.35%
EB0‐powered Parallel
2.52 0.55 0.00 0.34 17.52% 31.40% 71.61% 99.32%
EB0‐powered Series
1.64 0.39 0.01 0.59 23.43% 34.48% 90.05% 75.04% 99.04%
EB0‐powered Power‐Split
1.65 0.39 0.01 0.53 23.68% 34.47% 86.15% 75.18% 99.03%
EB0‐powered Series/Parallel
1.68 0.40 0.01 0.60 23.25% 34.49% 89.35% 75.11% 99.03%
Table 25: Measurement over WLTP Urban 1
Operating points of various machines derived from relevant drivetrains are depicted in Figures 95, 96, 97, and in 98 in order to ease understanding. In addition ICE operating points for the Series and the Parallel topologies are pictured respectively in Figures 83 and 84 upstream in this material
‐72‐
Figure 95: ICE Operating Points for the EB0‐powered Peugeot 208 over WLTP Urban 1
Figure 96: ICE Operating Points for the EB0‐powered Power‐Split over WLTP Urban 1
Figure 97: EM1 and EM2 Operating Points for the EB0‐powered Series over WLTP Urban 1
Figure 98: EM1 and EM2 Operating Points for the Power‐Split over WLTP Urban 1
Case Studies: Highway Engine efficiencies are overall similar between the hybrid electric drivetrains since at high road power requirements in conjunction with the gearbox ratios implemented the ICE operating points are located in high efficiency areas basically close to the full‐load line even for the conventional EB0‐powered vehicle. In addition, energy conversions are higher over this driving condition and lead to reduce overall powertrain efficiency. Note that here the Series/Parallel topology is operated most of the time in Parallel mode. Active Strategy Control regarding battery management was only considered for the hybrid electric drivetrain. Efficiencies of each machine, losses, corrected fuel consumptions, energy conversions, and so on are gathered in Table 26. Note that energy conversions are not rising similarly between hybrid electric vehicles. Indeed this latter is rising only a bit for the Parallel topology since the electrical machine provides only a boost, while this is rising a lot for the Series topology since all the power has to be converted. In addition, energy conversions are rising less for the Power‐Split topology since a part of the engine torque can be conveyed to the wheels. Note also that traction motor efficiencies of the Parallel and the Series/Parallel topologies are lower compared with the two other hybrid electric powertrains since this latter provides only electric boost and is therefore less used especially at high torque. Finally battery efficiencies are lower in this driving condition since the battery has to assist more the engine regarding power to allow the vehicle to be propelled properly. All those notices are presented by operating point diagrams of engine and electrical machines (cf. Figures 99, 100, 101, 102, and 103).
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1
0.1 0.1
0.15
0.15
0.15 0.150.15
0.2
0.2
0.2 0.20
0.22
0.22
0.22 0.220.
0.25
0.25
0.250.25
0
0.27
0.27
0.270.27
0.3
0.30.3
0.3
0.3
0.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rpm]
Torq
ue [N
m]
0 100 200 300 400 5000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1 0.1 0.
0.15
0.15
0.15 0.150.1
0.2
0.2
0.2 0.2
0.22
0.22
0.22 0.22
0
0.25
0.25
0.25 0.25
0.27
0.27
0.270.27
0.3
0.3
0.3
0.3
0.30.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rad/s]
Torq
ue [N
m]
0 500 10000
50
100
150
200
250
0.4
0.4
0 4 0.4
0.5
0.5
0 5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.9
0.9
0.9 0.9
0.90.9
0.9
0 .9
0.90.9
0.9
0.9
0.9
0 .9
0.9
0.9
0.9
0.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM1 Operating Points
0 500 10000
50
100
150
200
0.4
0.4
0 4 0.4
0.5
0.5
0.5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.9
0.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM2 Operating Points
0 500 10000
20
40
60
80
100
120
140
160
180
0.4
0.4
0 4 0.4
0.5
0.5
0.5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.9
0 .9
0.9
0.9
0.9
0.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM1 Operating Points
0 200 4000
100
200
300
400
500
600
0.4
0.4
0 4 0.4
0.5
0.5
0 5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.90.9
0.9
0.9
0 .9
0.9
0.9
0 .9
0.90.9
0.92
0.92
Speed [rad/s]To
rque
[Nm
]
EM2 Operating Points
‐73‐
FC [l/100km]
Losses [kWh]
Battery Loss [kWh]
Energy Conversion [kWh]
ηpowertrain ηICE ηEM1 ηEM2 ηBattery
EB0‐powered Peugeot 208
5.62 3.85 24.42% 28.66%
EB0‐powered Peugeot 208 (stop&start)
5.62 3.86 24.45% 28.70%
EB0‐powered Parallel
5.35 2.66 0.01 0.52 26.79% 32.66% 69.01% 98.35%
EB0‐powered Series
6.05 3.16 0.03 2.65 23.62% 32.63% 91.57% 86.62% 97.53%
EB0‐powered Power‐Split
5.58 2.84 0.03 1.24 25.75% 32.96% 82.21% 82.06% 97.56%
EB0‐powered Series/Parallel
5.56 2.81 0.03 0.81 25.91% 32.58% 85.03% 77.00% 97.57%
Table 26: Measurement over WLTP Highway
Figure 99: EM Operating points for the EB0‐powered Parallel over WLTP Highway
Figure 100: ICE Operating Points for the EB0‐powered Parallel over WLTP Highway
Figure 101: ICE Operating Points for the EB0‐powered Series over WLTP Highway
0 200 400 600 800 1000 1200 14000
50
100
150
200
0.4
0.4
0.4
0.4 0.4 0.4
0.5
0.5
0.5
0.5 0.5 0.5
0.6
0.6
0.6
0.6 0.6 0.6
0.7
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8 0.8
0.85
0.85
0.85 0.85 0.85
0.90.9
0.9
0.9
0.9 0.90.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.9
0.9
0.920.92
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM Operating Points
0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1
0.1 0.1
0.15
0.15
0.15 0.150.15
0.2
0.2
0.2 0.20
0.22
0.22
0.22 0.220.
0.25
0.25
0.250.25
0
0.27
0.27
0.270.27
0.3
0.30.3
0.3
0.3
0.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rpm]
Torq
ue [N
m]
0 100 200 300 400 5000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1 0.1 0.
0.15
0.15
0.15 0.150.1
0.2
0.2
0.2 0.2
0.22
0.22
0.22 0.22
0
0.25
0.25
0.25 0.25
0.27
0.27
0.270.27
0.3
0.3
0.3
0.3
0.3
0.32
0.32
0.32
0.32
0.32
0.35
0.35
ICE Operating Points
Speed [rad/s]
Torq
ue [N
m]
‐74‐
Figure 102: EM1 and EM2 Operating Points for the EB0‐powered Power‐Split over WLTP Highway
Figure 103: EM1 and EM2 Operating Points for the EB0‐powered Series over WLTP Highway
0 500 10000
20
40
60
80
100
120
140
160
180
0.4
0.4
0 4 0.4
0.5
0.5
0.5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.9
0 .9
0.9
0.9
0.9
0.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM1 Operating Points
0 200 4000
100
200
300
400
500
600
0.4
0.4
0 4 0.4
0.5
0.5
0 5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.70.
80.
8
0.8 0.80.
850.
85
0.85
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.90.9
0.9
0.9
0 .9
0.9
0.9
0 .9
0.90.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM2 Operating Points
0 500 10000
50
100
150
200
250
0.4
0.4
0 4 0.4
0.5
0.5
0 5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.850.9
0.9
0.9
0.9 0.90.9
0.9
0.9
0 .9
0.90.9
0.9
0.9
0.9
0 .9
0.9
0.9
0.9
0.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM1 Operating Points
0 500 10000
50
100
150
200
0.4
0.4
0 4 0.4
0.5
0.5
0.5 0.5
0.6
0.6
0.6 0.6
0.7
0.7
0.7 0.7
0.8
0.8
0.8 0.8
0.85
0.85
0.85 0.85
0.90.9
0.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.9
0.9
0.90.9
0.92
0.92
Speed [rad/s]
Torq
ue [N
m]
EM2 Operating Points
‐75‐
Appendix 4: Atkinson Cycle for SparkIgnition Internal Combustion Engine
Ideal combustion cycle for reciprocating‐piston engines with internal combustion (ICE) is based on the ideal thermodynamic combustion process called “constant‐volume process” depicted in Figure 104 [12]. This process consist of isentropic compression (1‐2), isochoric heat supply (2‐3), isentropic expansion (3‐4) and finally isochoric reversion of the ideal working gas to its initial condition (4‐1). Obviously, this cycle is ideal and is only possible if the following conditions are met:
‐ No heat or gas losses i.e. no residual exhaust gas ‐ Ideal gas with constant specific heats cp, cv such as K = cp/cv = 1.4 ‐ Infinitely rapid heat supply and discharge ‐ No flow losses
1 1 1 ( 35 )
The efficiency of such ideal thermodynamic cycle is depicted in Equation ( 35 ) and is called thermal efficiency where ε corresponds to the compression ratio defined as a function of the piston displacement volume Vd and the compression volume Vc. In addition to this theoretical thermal efficiency, efficiencies related to both the real high‐pressure working effects such as wall heat losses and variable specific heat for instance, the real charge effects due to the 4‐stroke operation and the mechanical losses have to be considered as well to determine the overall engine efficiency (efficiency sequence) [12].
Figure 104: Ideal Constant‐Volume Combustion Cycle as shown in the p‐V diagram (left) and the T‐S diagram (right)
The so‐called Otto cycle based on a 4‐stroke process related to the common spark‐ignition engines consists of this sequence of thermodynamic processes depicted in Figure 104 under the name of compression and combustion with one more sequence for induction and exhaust. The stoichiometric air to fuel ratio for the spark‐ignition engine is controlled by throttling the amount of air in the inlet manifold, and leads therefore to an under pressure in the intake during induction.
pressure
volume
Vc V
h
1
2
3
4
5
5'
temprature
entropy
51
2
3
45'
W
‐76‐
According to Equation ( 35 ), one way to increase the combustion efficiency is to increase the compression ratio. However, the compression ratio of spark‐ignition engines is limited to prevent the uncontrolled combustion known as knocking, which leads to damage piston and cylinder head. Another way to increase the thermal efficiency is to increase the surface cycle on the p‐V diagram i.e. increase the available work. However as the crankshaft assembly restricts expansion to finite levels, the 4‐5‐1 area in Figure 104 is not available as extra work.
The section 4‐5’‐1, lying above the atmospheric pressure line, is partially available when an exhaust‐gas turbine is connected downstream [12]. Thereby, the combustion efficiency is higher since basically the overall surface 1‐2‐3‐4‐5 corresponding to an available work is larger. Note that this combustion performance enhancement is shown by the EB2DT engine equipped with an exhaust‐gas turbocharger whose peak efficiencies are higher than those derived from the EB0 engine.
Another way to make this section 4‐5’‐1 reachable and therefore increase thermal efficiency is to make the expansion ratio and the compression ratio differ. The Atkinson cycle applied on 4‐stroke spark‐ignition engines differs from the Otto cycle through this specific feature. This capability is achievable either by a basic clever arrangement of the crankshaft or by specific intake valve opening/closing timing (Miller cycle) as implemented by Toyota in its hybrid vehicles [6]. The Toyota hybrid vehicles are indeed powered by high‐expansion ratio cycle engine by reducing the volume of combustion and by evacuating the chamber only after the explosion force have sufficiently fallen through the so‐called VVT‐i system operated on the intake valves (Variable Valve Timing‐intelligent) as depicted in Figure 105. This specific technical solution proposed by Toyota is to delay intake valve opening during induction, which leads to reduce compression ratio since a part of the inducted mixture is sent back to the manifold. Even though thermal efficiency is thereby enhanced, the effective mean pressure of point 2 and 3 in a larger extent are lower, which leads to a reduction of the mean working pressure and therefore to the full‐load capability. Note that this mean working pressure reduction does not occur with an exhaust‐gas turbocharger since in parallel the pressure related to the point 2 and then point 3 are higher [13].
Figure 105: Principle Diagram of the VVT‐i System [6]
The results of a study carried out by PSA Peugeot Citroën regarding the capability to make the 1.2‐litre 3‐cylinder 4‐stroke spark‐ignition EB2 engine run according to a specific cycle closer to this derived from the Atkinson cycle than this derived from the basic Otto cycle were used afterwards.
valve lift
crank angle
Exhaust Valve
Intake Valve
Angle of action
‐77‐
The aim of this investigation is to assess energy conversion efficiency enhancement by applying the results of this study regarding engine efficiency enhancement and full‐load reduction to the EB0 engine. Initial parameters of the EB0 engine are depicted in Figure 106 and have to be compared with those in Figure 107 derived from the Atkinson‐cycle adaptation. In addition, all the details of the new OOL related to the Atkinson‐cycle EB0 engine are depicted in Figure 108.
Figure 106: Initial Efficiency Map, Full‐load Line (red line), OOL (blue line) & Power (left) of the EB0 Engine
Figure 107: Efficiency Map, Full‐load Line (red line), OOL (blue line) & Power (left) of the Atkinson‐cycle EB0
Engine
Figure 108: Torque (left), Speed (middle) & Efficiency (left) as a function of Engine Power Level related to the OOL of the Atkinson‐cycle EB0 Engine
The implementation of such Atkinson‐cycle engines over the hybrid electric powertrains makes sense. Indeed, the full‐load reduction is offset by the electric boost capability, whilst the better combustion efficiencies are useful to reduce fuel consumption and then emissions.
0 2000 40000
10
20
30
40
50
60
70
80
90
0.1
0.1
0.1 0.1
0.15
0.15
0.150.15
0.2
0.2
0.20
0.22
0.22 0.22
0.25
0.25
0.25
0.27
0.27
0.27
0.3
0.3
0.3
0.3
0.32
0.32
0.32
0.32
0.35
0.35
Speed [rpm]
Torq
ue [N
m]
0 2000 40000
10
20
30
40
50
Speed [rpm]
Pow
er [k
W]
0 2000 40000
10
20
30
40
50
60
70
80 0.1
0.1
0.1 0.1
0.1
0.15
0.150.15
0.2
0.20
00.
22
0.22
0.25
0.25
0.25
0.27
0.27
0.27
0.3
0.3
0.3
0.32
0.320.32
2
0.35
0.35
0.36
0.36
Speed [rpm]To
rque
[Nm
]
0 2000 40000
5
10
15
20
25
30
35
40
45
50
Speed [rpm]
Pow
er [k
W]
0 500
10
20
30
40
50
60
70
80
90
Engine Power [kW]
Eng
ine
Torq
ue [N
m]
0 500
1000
2000
3000
4000
5000
6000
Engine Power [kW]
Eng
ine
Spe
ed [r
pm]
0 500
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Engine Power [kW]
Eng
ine
Effi
cien
cy
‐78‐
References
[1] Laboratory of Electrical Energy Conversion, Hybrid Vehicle Drives, Stockholm: KTH Electrical Engineering, 2011.
[2] Green Car Congress, "Peugeot’s Diesel 3008 Hybrid4," 2010. [Online]. Available: http://www.greencarcongress.com/2010/08/3008‐20100824.html. [Accessed 2012].
[3] M. Alaküla, Hybrid Drive Systems for Vehicles: System Design and Traction Concepts, Lund: Lund University of Technology, 2006.
[4] M. Leksell, Electrical Machines and Drives, Stockholm: KTH, 2004.
[5] R. Ottersten, Hybrid Vehicle Drives: Power Electronics, Göteborg: Chalmers University of Technology, 2004.
[6] Toyota Motor Corporation, "Toyota Hybrid System THS II," Tokyo, 2003.
[7] Peugeot, "208 hatchback: Prices, Equipment and Technical Specifications," 2012.
[8] Valeo, "Innovation: Stop‐Start System," [Online]. Available: http://www.valeo.com/innovation/en/#/fiche2. [Accessed 2012].
[9] Toyota Motor Corporation, "Toyota Technical Training: Hybrid System Operation (Section 2)," 2005.
[10] A. Takasaki, T. Mizutani, K. Kitagawa, T. Yamahana, K. Odaka, T. Kuzuya, Y. Mizuno and Y. Nishikawa, "Development of New Hybrid Transmission for 2009 Prius," EVS24 International Battery, Stavanger, 2009.
[11] DieselNet, "Emission Test Cycles," [Online]. Available: http://www.dieselnet.com/standards/cycles/. [Accessed 2012].
[12] BOSCH, Automotive Handbook, SAE, 2004.
[13] Animated Engines, "Atkinson Engine," [Online]. Available: http://www.animatedengines.com/atkinson.html. [Accessed 2012].
‐79‐
Tables & Illustrations
Table 1: Energy Content, Power Density, Cycle Life & Cost Assessment of Main Battery Technologies [3] .......................................................................................................................................................... 14 Table 2: Gear Ratios of the Gearbox & Final Gear Ratio for the EB0‐powered Peugeot 208 ............... 19 Table 3: Gear Ratios of the Gearbox & Final Gear Ratio for the EB2DT‐powered Peugeot 208 ........... 19 Table 4: Vehicle Specifications .............................................................................................................. 22 Table 5: Technical Parameters of the EB0‐powered Peugeot 208 and the EB2DT‐powered Peugeot 208 ......................................................................................................................................................... 23 Table 6: Fuel Consumptions of the EB0‐powered Peugeot 208 ............................................................ 29 Table 7: Fuel Consumptions of the EB2DT‐powered Peugeot 208 ....................................................... 29 Table 8: Performances of Reference Vehicles ....................................................................................... 30 Table 9: Preliminary Design of Power Requirements for the Various Hybrid Electric Powertrains ...... 31 Table 10: Gross Mass of the EB0‐powered Parallel Topology (left) and Gross Mass of the 2/3 EB0‐powered Parallel Topology (right) ......................................................................................................... 32 Table 11: Energy Consumptions of the EB0‐powered Parallel Topology .............................................. 38 Table 12: Performances of the EB0‐powered Parallel Topology ........................................................... 38 Table 13: Power Design Scenarios for Series Topology ......................................................................... 41 Table 14: Energy Consumptions of the EB0‐powered Series Topology ................................................ 43 Table 15: Performances of the EB0‐powered Series Topology ............................................................. 44 Table 16: Power Design Scenarios for Power‐Split Topology................................................................ 47 Table 17: Energy Consumption of the EB0‐powered Power‐Split Topology ......................................... 49 Table 18: Performances of the EB0‐powered Power‐Split Topology .................................................... 49 Table 19: Switch Power Values for the Active Strategy Control ........................................................... 52 Table 20: Gross Mass Assessment of the EB0‐powered Series/Parallel Topology ............................... 54 Table 21: Energy Consumptions for the Series/Parallel Topology ........................................................ 56 Table 22: Performances of the Series/Parallel Topology ...................................................................... 57 Table 23: Chart Review of Hybrid Electric Drivetrains .......................................................................... 64 Table 24: NEDC, WLTC & INRETS UL1 Details ........................................................................................ 68 Table 25: Measurement over WLTP Urban 1 ........................................................................................ 71 Table 26: Measurement over WLTP Highway ....................................................................................... 73
Figure 1: Peugeot 208 (side view) ............................................................................................................ i Figure 2: Peugeot 208 (rear view) ........................................................................................................... 1 Figure 3: Power‐Split Hybrid Electric Powertrain .................................................................................... 3 Figure 4: Parallel Hybrid Electric Powertrain........................................................................................... 3 Figure 5: Series Hybrid Electric Powertrain ............................................................................................. 4 Figure 6: Series/Parallel Hybrid Electric Powertrain ............................................................................... 4 Figure 7: Principle Diagram of Electric Hybridization Topologies ........................................................... 5 Figure 8: Hybridization Degree ................................................................................................................ 6 Figure 9: Efficiency Map, Full‐Load Line (left) & Maximum Power Diagram (right) of the EB0 Engine .. 8 Figure 10: Efficiency Map, Full‐Load Line & OOL of the EB0 Engine ....................................................... 9
‐80‐
Figure 11: Efficiency Map, Full‐Load Line (left) & Maximum Power Diagram (right) of the EB2DT Engine ...................................................................................................................................................... 9 Figure 12: Efficiency Map, Full‐Load Line (blue line) & OOL (red line) of the EB2DT Engine ................ 10 Figure 13: Efficiency Map & Full‐Load Curve (red line) of the EHA Electrical Machine ........................ 11 Figure 14: Ideal & Real Field Weakening Operations related to the EHA Electrical Machine .............. 12 Figure 15: Three‐phase ac‐dc Converter [5] .......................................................................................... 12 Figure 16: Circuit Symbols of Power MOSFET (left) & IGBT (right) [5] .................................................. 13 Figure 17: Schematic Model of the Battery used in this material ......................................................... 15 Figure 18: Battery Efficiency as a function of Battery Terminal Power ................................................ 16 Figure 19: Principle Chart of the Battery Charge Modes for a PHEV .................................................... 17 Figure 20: Principle Charts of “Sustaining I” mode (left) and “Sustaining II” mode (right) .................. 17 Figure 21: Principle Sketch of a Reduction Gear Set ............................................................................. 19 Figure 22: Gear Shifting Strategy related to Gearbox ........................................................................... 20 Figure 23: Planetary Gear Set and Basic Layout .................................................................................... 21 Figure 24: Road Power Requirement for the EB0‐powered Peugeot 208 ............................................ 24 Figure 25: Road Power Requirement for the EB2DT‐powered Peugeot 208 ........................................ 24 Figure 26: Top Speed Capability (Road Gradient of 4%) of the EB0‐powered Peugeot 208 ................. 24 Figure 27: Top Speed Capability (Road Gradient of 4%) of the EB2DT‐powered Peugeot 208 ............ 24 Figure 28: Wheel Torque Diagram for the EB0‐powered Peugeot 208 ................................................ 24 Figure 29: Wheel Torque Diagram for the EB2DT‐powered Peugeot 208 ............................................ 24 Figure 30: Simple Driver Model ............................................................................................................. 25 Figure 31: Simulink Model of the Driver Model .................................................................................... 26 Figure 32: ICE Operating Point Selection according to its OOL ............................................................. 27 Figure 33: Gear Ratio Selection Model .................................................................................................. 27 Figure 34: Road Model .......................................................................................................................... 28 Figure 35: Stop&Start Model ................................................................................................................. 28 Figure 36: Power Requirement in Electric & Hybrid Modes ................................................................. 30 Figure 37: Operating Principle of the Parallel Hybrid Electric Powertrain ............................................ 31 Figure 38: Road Power Requirements respectively for 2/3 EB0‐powered and EB0‐powered Parallel Hybrid Electric Scenarios ....................................................................................................................... 33 Figure 39: Corrected Fuel Consumption (left) & Performances (right) as a function of Final Gear Ratio in Hybrid mode ...................................................................................................................................... 34 Figure 40: Fuel Consumption (left) & Performances (right) as a function of Final Gear Ratio in Unavailable Battery mode ..................................................................................................................... 34 Figure 41: Fuel Consumptions over INRETS UL1 cycle .......................................................................... 34 Figure 42: EM Operating Points over the INRETS UL1 Cycle with a Transaxle Gear Ratio of 3.5 .......... 35 Figure 43: Top Speed Capability (Road Gradient of 4%) for the EB0‐powered Parallel Topology with a Transaxle Gear Ratio of 3 instead of 4.92 ............................................................................................. 35 Figure 44: Power Flow Control Block .................................................................................................... 36 Figure 45: Low‐pass Filter for Engine Dynamic Limitation .................................................................... 36 Figure 46: Battery Charge Controller .................................................................................................... 36 Figure 47: Engine Best Operating Point Selection & Engine Ignition Management ............................. 37 Figure 48: Battery Efficiency Model ...................................................................................................... 38 Figure 49: Top Speed Capability (Road Gradient of 0%) of the EB0‐powered Parallel Topology in Hybrid Mode .......................................................................................................................................... 39
‐81‐
Figure 50: Top Speed Capability (Road Gradient of 4%) of the EB0‐powered Parallel Topology in Hybrid Mode .......................................................................................................................................... 39 Figure 51: Top Speed Capability (Road Gradient of 4%) for the EB0‐powered Parallel Topology in Electric Mode......................................................................................................................................... 39 Figure 52: Maximum Wheel Torque Diagram of the EB0‐powered Parallel Topology ......................... 39 Figure 53: Operating Principle of the Series Hybrid Electric Powertrain .............................................. 40 Figure 54: Road Power Requirements respectively for 2/3 EB0‐powered and EB0‐powered Series Hybrid Electric Scenarios ....................................................................................................................... 41 Figure 55: Engine Operating Point Selection Block ............................................................................... 42 Figure 56: Series Topology Model over Simulink .................................................................................. 43 Figure 57: Top Speed Diagram (road gradient of 4%) for the EB0‐powered Series Topology in Electric Mode ..................................................................................................................................................... 44 Figure 58: Maximum Available Wheel Torque for EB0‐powered Series Topology ............................... 44 Figure 59: Available Wheel Torque in “Unavailable Battery” Mode versus Ideal Wheel Torque derived from the Full‐Load Line of the Traction Electrical Machine .................................................................. 44 Figure 60: Operating Principle of the Power‐Split Hybrid Electric Powertrain ..................................... 45 Figure 61: Planetary Gear Nomographs in Extreme Speed Range Operations ..................................... 46 Figure 62: Road Power Requirements over a Road Gradient of 4% for 2/3 EB0‐powered Power‐Split Topology and EB0‐powered Power‐Split Topology. .............................................................................. 48 Figure 63: Power‐Split Topology Model over Simulink ......................................................................... 48 Figure 64: Top Speed Capability (road gradient of 4%) for the EB0‐powered Power‐Split Topology in Electric Mode......................................................................................................................................... 50 Figure 65: Maximum Available Wheel Torque for EB0‐powered Power‐Split Topology ...................... 50 Figure 66: Constant Speed Experiments for the EB0‐powered Series Topology .................................. 51 Figure 67: Constant Speed Experiments for the EB0‐powered Power‐Split Topology ......................... 51 Figure 68: Constant Speed Experiments for the EB0‐powered Series/Parallel Topology ..................... 52 Figure 69: Active Control Strategy Block ............................................................................................... 52 Figure 70: Main Scope of the Active Strategy Control Block over the Urban 2 part of the WLTP Cycle for the Power‐Split Topology ................................................................................................................ 53 Figure 71: Strategy Implemented by Active Strategy Control Block over the Urban 2 part of the WLTP Cycle for the Power‐Split Topology ....................................................................................................... 53 Figure 72: Road Power Requirements for the EB0‐powered Series/Parallel Topology ........................ 54 Figure 73: Top Speed Capability (4% road gradient) of the Series/Parallel Topology with a Transaxle Gear Ratio of 3.2 .................................................................................................................................... 55 Figure 74: Control of the Drivetrain over Simulink for the Series/Parallel model ................................ 55 Figure 75: Top Speed Capability (road gradient of 4%) for the Series/Parallel Topology in Hybrid Mode ............................................................................................................................................................... 56 Figure 76: Top Speed Capability (road gradient of 0%) for the Series/Parallel Topology in Hybrid Mode ............................................................................................................................................................... 56 Figure 77: Top Speed Capability (road gradient of 4%) for the Series/Parallel Topology in Electric Mode ..................................................................................................................................................... 57 Figure 78: Maximum Available Wheel Torque of the EB0‐powered Series/Parallel Topology ............. 57 Figure 79: Vehicle Gross Mass Assessment ........................................................................................... 58 Figure 80: Electric Range in Charge Depleting Mode over the WLTP Cycle .......................................... 59
‐82‐
Figure 81: Energy Consumptions in Charge Sustaining Mode (Active Strategy Control) over WLTP Cycle ...................................................................................................................................................... 59 Figure 82: Lowest Computed Energy Consumptions in Charge Sustaining Mode over the WLTP Cycle ............................................................................................................................................................... 60 Figure 83: ICE Operating Points over WLTP Urban 1 for the Series Topology ...................................... 60 Figure 84: ICE Operating Points over WLTP Urban 1 for the Parallel Topology .................................... 60 Figure 85: Emission Certification over the WLTP Cycle ......................................................................... 61 Figure 86: Top Speed Performances ..................................................................................................... 62 Figure 87: Acceleration Performances .................................................................................................. 62 Figure 88: Powertrain Manufacturing Cost Differences between Topologies with EB0‐powered Peugeot 208 as Reference ..................................................................................................................... 63 Figure 89: Lowest Computed Fuel Consumption in Charge Sustaining Mode over the WLTP Cycle .... 65 Figure 90: Speed & Acceleration Diagrams of the NEDC Cycle ............................................................. 66 Figure 91: Speed & Acceleration Diagrams of the WLTP Cycle with Segments (between dotted red lines) ...................................................................................................................................................... 67 Figure 92: Speed & Acceleration Diagrams of the INREST UL1 Cycle.................................................... 67 Figure 93: Torque (left), Speed (middle) & Efficiency (left) as a function of engine power level related to the OOL of the EB0 engine ................................................................................................................ 69 Figure 94: Torque (left), Speed (middle) & Efficiency (left) as a function of engine power level related to the OOL of the EB2DT engine ........................................................................................................... 70 Figure 95: ICE Operating Points for the EB0‐powered Peugeot 208 over WLTP Urban 1 ..................... 72 Figure 96: ICE Operating Points for the EB0‐powered Power‐Split over WLTP Urban 1 ...................... 72 Figure 97: EM1 and EM2 Operating Points for the EB0‐powered Series over WLTP Urban 1 .............. 72 Figure 98: EM1 and EM2 Operating Points for the Power‐Split over WLTP Urban 1 ........................... 72 Figure 99: EM Operating points for the EB0‐powered Parallel over WLTP Highway ............................ 73 Figure 100: ICE Operating Points for the EB0‐powered Parallel over WLTP Highway .......................... 73 Figure 101: ICE Operating Points for the EB0‐powered Series over WLTP Highway ............................ 73 Figure 102: EM1 and EM2 Operating Points for the EB0‐powered Power‐Split over WLTP Highway .. 74 Figure 103: EM1 and EM2 Operating Points for the EB0‐powered Series over WLTP Highway ........... 74 Figure 104: Ideal Constant‐Volume Combustion Cycle as shown in the p‐V diagram (left) and the T‐S diagram (right) ....................................................................................................................................... 75 Figure 105: Principle Diagram of the VVT‐i System [6] ......................................................................... 76 Figure 106: Initial Efficiency Map, Full‐load Line (red line), OOL (blue line) & Power (left) of the EB0 Engine .................................................................................................................................................... 77 Figure 107: Efficiency Map, Full‐load Line (red line), OOL (blue line) & Power (left) of the Atkinson‐cycle EB0 Engine .................................................................................................................................... 77 Figure 108: Torque (left), Speed (middle) & Efficiency (left) as a function of Engine Power Level related to the OOL of the Atkinson‐cycle EB0 Engine ........................................................................... 77
‐83‐
Nomenclature
BEV
CVT
EHB
EM
EM1
EM2
EUDC
HEV
ICE
ISG
HY
NEDC
OOL
PWM
SOC
WLTC
WLTP
ZEV
Battery Electric vehicle
Continuous Variable Transmission
Electronic Hydraulic Brake
Electrical Machine
Generator
Traction Motor
Extra Urban Driving Cycle
Hybrid Electric Vehicle
Internal Combustion Engine
Integrated Starter Generator
Hybrid mode (battery charge sustaining mode)
New European Driving Cycle
Optimum Operating Line
Pulse Width Modulation
State‐Of‐Charge
World harmonized Light‐duty Test Cycle
World harmonized Light‐duty Test Procedure
Zero Emission Vehicle
Rwheel Wheel radius
Iwheel Wheel involute
g Gravitational constant (9.81 m.s2)
MV Gross vehicle mass
α Road gradient
Cr Rolling resistance coefficient
‐84‐
S.Cx Drag surface (m2) & coefficient
v Vehicle velocity (m/s)
ω Rotational speed (rad/s)
ρair Air density (1.29 kg/m3)
hp Horsepower (1 horsepower (metric) = 735.9 W)
T Torque (Nm)
F Force (N)
P Power (W)
η Efficiency
W Work (J or Wh)
Q Heat (J or Wh)
cp Specific heat capacity at constant pressure (J/(kg.K))
cv Specific heat capacity at constant volume (J/(kg.K))
Vd Displacement volume (m3)
Vc Compression volume (m3)
kpl Planetary gear set ratio
gr Gear ratio
i Electric current (A)
R Electric resistance (Ω)
e Electric voltage (V) or CO2 emissions (gCO2/km)
Kv Static gain of the driver model
Ti Integration time constant of the driver model
ksoc Static gain of the battery charge controller