Hybrid Car Transmission

7/29/2019 Hybrid Car Transmission

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A Simple Mechanical Transmission

System For Hybrid Vehicles

Incorporating A Flywheel

Ulises Diego-Ayala, Pablo Martinez-Gonzalez, Keith Pullen

Monday, 08 December 2008

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Speaker: Pablo Martinez-Gonzalez


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Outline

1. Introduction

1. Transport Emissions

2. The ever-expanding global vehicle fleet2. Flywheel Technology

1. Comparison of Energy Storage Technologies

2. Flywheels in Hybrid Vehicles

3. The Mechanical Hybrid Transmission

1. The Mechanical Hybrid Transmission

2. The CVT-brake Hybrid Transmission

3. Operating Modes of the Mechanical Hybrid Powertrain

4. Simulations

1. Control Strategy

2. Vehicle and Hybrid System Specification

3. Driving Schedules4. Results

5. Summary

5. Future Work

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Transport Emissions

There is consensus among the scientific community that observed increases in global average

temperatures over the past decades were caused mostly by greenhouse emissions from human

related-activities.

Significant reductions in GHG emissions are required to mitigate the effects of climate change.

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Power & heat

39%

Industry

16%

12% Services, etc

7%

Road

84.1%

Air

13.6%

Inland

Navigation

1.5%Rail

0.7%

Transport

26%

Total emissions, 2004Transport emissions, 2004

Households12%

Industry16%

Power &Heat 39%

Services,etc 7%

Households12%

Road83%

Rail1%

Inlandnavigation

2%

Air14%

Share of EU25 emissions by sector for year 2006

Prepared with data from the European Directorate-General for Energy and Transport

The European Parliament has promised to introduce binding legislation to limit CO2emissions for the average new car fleet to 120 g CO2/km by 2012.

These limits are deemed unfeasible by European automobile manufacturers with

current technology.


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The ever-expanding global vehicle fleet

The global vehicle fleet will continue to expand, fuelled primarily by

increased accessibility in developing countries.

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Global sales forecast for ultra-low cost vehicles

Source: A.T.Kearney

Hybrid vehicles have shown some of

the most promising advances on fuel

economy and emissions mitigation.They deliver higher fuel economy and

lower emissions than conventional

vehicles by employing regenerative

braking, by a more efficient use of the

Internal Combustion Engine (ICE),

and by shutting off the ICE when it isnot required (i.e. vehicle at rest).


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Comparison of Energy Storage Technologies

Comparison of specific energies and power of various energy storage technologies

From: O. Briat et al, Principle, design and experimental validation of a flywheel-battery

hybrid source for heavy-duty electric vehicles 5

The power density of flywheels is considerably higher than for batteries, being only

constrained by torque limitations of the transmission system.

High power density means that a much higher fraction of braking energy can be regenerated,

and that high rates of acceleration are possible.

Power density is independent of state

of charge and ambient conditions and

does not deteriorate with time.

Energy density is comparable to that ofbatteries for short-term storage, but it

is time-dependant.

Flywheels must be kept spinning in a

vacuum in order to minimise

aerodynamic losses.

Flywheels are constructed with inert

materials of easy after-life disposal.

103

102

101

100

10-1

10-2

101 102 103 104 105 106 107

Specific power, W/kg

Specificenergy,

Wh/kg


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Flywheels in Hybrid Vehicles

Hybrid Electric Vehicles (HEVs), store energy in an on-board bank of

batteries and must undergo the energy transformation: kinetic(car)-

electric(generator)-chemical(battery)-electrical(motor)-kinetic(car), with the

associated efficiency penalties.

In a hybrid powertrain with a flywheel and a mechanical transmission, the

energy transfer is solely mechanical and there is thus no energy conversionpenalties.

The power and energy capabilities of flywheels makes them better suited to

deal with the power surges of regenerative braking and acceleration rather

than as primary energy storage devices.

Flywheels can be integrated into conventional or electrical vehicles.

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The Mechanical Hybrid Transmission

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Bolt-in system. The hybrid system can be

integrated in parallel to a conventional

powertrain.

Power flow is directed through a planetary

gear set (PGS), which acts as a

continuously variable transmission (CVT),

providing a wide range of speed ratios.

Control of energy flow (whether the

flywheel is being charged or delivering

power) is accomplished by applying a

torque at the ring of the PGS.

Using a brake to control the torque at the

ring gear wastes energy though, and itsoperation is limited to reducing the speed

of the ring gear. The systems has thus a

limited operability.

The brake-only mechanical-flywheel transmission

Power flow at the PGS during Regenerative Braking

Flywheel

Planetarygearset

Frictionalbrake


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The CVT-brake Hybrid Transmission

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The CVT Mechanical-Flywheel Hybrid Transmission

Adding a CVT between the carrier and ring

branches of the PGS provides an additional

control system.

The CVT transmits power to and from the

ring of the PGS, and it is able to brake or

accelerate the ring gear.

The CVT is used when possible todecelerate the ring gear, greatly reducing

the use of the frictional brake and the losses

at the ring gear.

FlywFlywFlywheel

Planetarygearset

Frictionalbrake

CVT

Clutch

The operation of the hybrid system is also extended as the CVT is also capable of

accelerating the ring gear.

However under certain conditions the CVT must be disconnected to avoid recirculation

of power.


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Vehicles speed

Flywheels speed

a) Neutral with vehicle stationary9

t

FlywheelFlywheel


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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

b) Flywheel Assisted Acceleration with clutch slipping

Clutch slipping

CVT at

minimumratio

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

c) Flywheel Assisted Acceleration with CVT

CVT

increasingratio

Clutch engaged

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

d) Flywheel Assisted Acceleration with brake at ring

Ring gear deceleratedby brake

CVT at

maximumratio

Clutch disengaged

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

e) Neutral with vehicle being accelerated by engine or braked byconventional brakes

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

f) Regenerative Braking with brake at ring

Ring gear deceleratedby brake

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

g) Regenerative Braking with clutch slipping

Clutch Slipping

CVT at

maximumratio

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Vehicles speed

Flywheels speed

t

FlywheelFlywheel

h) Regenerative Braking with CVT

CVT

decreasingratio

Clutch engaged

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Simulations

A computational model of the mechanical energy storage system was developed inMatlab/Simulink and validated using experimental data. This model was then integrated

into ADVISOR.

This program was validated experimentally (see article below for details1)

To assess the performance of the mechanical energy storage system, simulations were

carried out on a conventional and a mechanical hybrid vehicle.

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1. Diego-Ayala, U, P Martinez-Gonzalez, N McGlashan, and K R Pullen. The mechanical hybrid vehicle: an investigation of aflywheel-based vehicular regenerative energy capture system. Proceedings of the Institution of Mechanical Engineers, PartD: Journal of Automobile Engineering 222, no. 11 (November 1, 2008


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Control Strategy

All the braking is provided by the regenerative system, which transfers the available

energy into the flywheel.

When the vehicle requires power, it is first provided by the flywheel reservoir.

The ICE is turned off when not in use (at rest, when braking and when the vehicle is

propelled by the energy reservoir).

The flywheel is only allowed to charge up to a maximum safety speed, and can only

assist in acceleration between a minimum and an operating speed.

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The simple control strategy employed for the hybrid powertrain works on the following

premises:


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Vehicle and Hybrid System Specification

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The vehicle chosen for the simulations

was a Ford Focus Estate with a 1.8 turbo

diesel engine with specifications:

Hybrid System Specification

Parameter Value

Additional weight due to hybrid system (kg) 100

Flywheel inertia (kgm2) 0.11

Value of constantA for double PGS (-) 0.978

Maximum CVT ratio (-) 2.5

Minimum CVT ratio(-) 0.4

Flywheel min. speed (rad/s) 900

Flywheel operating speed (rad/s) 1100

Flywheel max. speed (rad/s) 2500

Vehicle Specification

Parameter Value

Total vehicle weight (kg) 1511

Frontal area (m2) 2.06

Radius of wheels (cm) 28.2

Rolling friction coefficient (--) 0.009

Aerodynamic drag coefficient (--) 0.312

Maximum Engine power (kW) 65 @ 4400rpm

The main specification for

the hybrid system are:


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Driving Schedules

The driving schedules used are all city cycles.

They present ample opportunities for the hybrid system to

store braking energy and to reuse it to propel the vehicle.

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Time [s]Urban Artemis Driving Schedule

0 200 400 600 800 1000

70

60

50

40

30

20

10

0

Vel[kph]

100

80

60

40

20

0

0 500 1000 1500Time [s]

Urban Dynamometer Drive Schedule

Vel[k

ph]

18

15

12

9

6

3

00 1000 2000 3000

Time [s]Indian Urban Drive Cycle

Vel[kph]


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Results

Results suggest that an important amount of the fuel economy gains derives

from tuning off the engine when the hybrid system is in operation.

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Performance of the CVT-brake hybrid vehicles following the Artemis-urban cycle. The

continuous thin black line at the top, illustrates engine operation (Engine on or off); while the

dashed thin black lines refer to flywheel maximum [upper], minimum operating and minimum

[lower] speeds of the flywheel

75

60

45

30

15

0

3000

2500

2000

1500

1000

500

00 200 400 600 800 1000

Time [s]

Flywheelspeed[rad/s]V

ehiclespeed[

km/h]


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Results

Despite carrying more weight, the use of the hybrid system resulted in improvements in

fuel economy and reductions in emissions for all the drive cycles.

The results suggest that an important amount of the fuel economy gains stem from tuning

off the engine when the hybrid system is in operation.

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UDDS ARTEMIS INDIAN

Conv MHV Conv MHV Conv MHV

Distance travelled (km) 12 12 4.9 4.9 17.6 17.6

Total Time (s) 1368 1368 993 993 2668 2668

Energy to accelerate vehicle (MJ/km) 0.43 0.46 0.6 0.66 0.39 0.42

Energy to decelerate vehicle (MJ/km) 0.19 0.2 0.39 0.4 0.19 0.2

Energy from fuel (MJ/km) 2.27 2.05 3.66 2.91 2.29 1.98

Overall efficiency vehicle (--) 0.19 0.22 0.16 0.23 0.17 0.21

Fuel economy (mpg) 44.9 49.9 28 35.2 44.7 51.6

Improvement in Fuel economy - 11% - 26% - 15%

Emissions CO2 (gr/km)1 166 149 266 212 166 144

Reductions in CO2 emissions - -10% - -20% - -13%

Time Engine on 100% 73% 100% 60% 100% 67%


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Summary

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A mechanical transmission system for hybrid vehicles incorporating a

flywheel has been proposed.

A computational model of a hybrid vehicle was developed in advisor and

validated experimentally.

Results show that under city driving savings of up to 20% can be obtained for

the system presented.

There is ample opportunity for further improvements in transmission efficiency

and operability of the system by using different powertrain configurations and

control strategies.


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Future Work

An improved version of the experimental test bed is being built a City University in

collaboration with Imperial College researchers.

This rig will be used to test different configurations of the mechanical hybrid powertrain

under various driving cycles and conditions, including the effect of road gradients.

EVT in Barcelona, Spain is currently developing a novel

type of CVT.

This transmission is based on planetary systems,

transmitting 92% of total power via mechanical means. This improves transmission efficiency while having a CVT

performance.

A transmission based on this novel CVT can also be used

for hybrid vehicles.

The rig will also be used to test a

powertrain with a hydraulic control

system intended to be used in trains.


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Questions

Thank you!

Documents

Hybrid Car Transmission