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ACEEE / ICCT Workshop on Emerging Technologies for Heavy-Duty Fuel Efficiency - Downspeeding and Downsizing
July 22, 2014
Don Keski-Hynnila
Detroit Diesel ad c.1961
Daimler Trucks North America
Major drivers in 2020 from global HD powertrain perspective differ across markets
2
Competition Legislation Cost Reduction Size/Weight
TE
Fuel
Economy
Leadership
CO2 Weight
GHG
2020
Fuel
Economy
Leadership
Weight
pJP15 FES
(2023?)
tbd
Fuel
Economy
Leadership
Fuel Economy Leadership is a, if not the, major driver in all marketplaces!
TN
Weight
TA
Modified for potential use Downspeeding and downsizing
Daimler Trucks North America
Vehicle and Drivetrain
3
Downspeeding and downsizing
Vehicle Improvements
• Aerodynamic improvements
• Tractor
• Trailer
• Tire rolling resistance
• Accessory management
• Weight
• Other
Optimization for fuel efficiency requires integrated vehicle, engine, transmission, axle
and controls development approach.
with
Daimler Trucks North America
Daimler Truck SuperTruck Program Goals
4
Evaluate technologies capable of demonstrating potential for a 50% increase in
vehicle freight efficiency:
30% increase via vehicle improvements.
20% increase via engine improvements; specifically 50% brake thermal efficiency.
Identify pathway to 55% brake thermal efficiency via modeling and analysis.
500
400 350
300
250
200
150
100 BHP
450
Baseline
Vehicle
Baseline15 L
SuperTruck 11 L
RPM
Bra
ke
To
rqu
e –
Nm
Gear and
Axle Ratio Aero,
Tires, etc
Downsize
so higher
% load
1
2
3/4
PARTNERS
Department of Energy
Oak Ridge National Laboratory
Massachusetts Institute of Technology
Atkinson LLC
Daimler Trucks North America
SuperTruck Concept: Engine Down-Speed and Down-Size
1 2
Efficient vehicle – better
aerodynamics, reduced
rolling resistance, etc.
2 3
Downspeeding
3 4
Downsize from 15L to
11L to increase road load
BMEP
500
400
350
300
250
200
150
100 BHP
450
Baseline
Vehicle
Baseline 15L
SuperTruck 11L
RPM
Bra
ke
To
rqu
e –
Nm
Gear and
Axle Ratio
Aero, Tires,
etc
Downsize
so higher
% load
1
2
3/4
SuperTruck Technical Accomplishments and Progress
Daimler Trucks North America 5
Daimler Trucks North America
Downspeeding – industry snapshot
6
Downspeeding and downsizing
Courtesy of Volvo
Volvo “XE” powertrain packages optimized to max torque @
1050 RPM engines – 200 RPM reduction
Cummins – SAE 2013-24-0094
• Push to optimized drivetrains
having lower operating speeds is
consistent across the HD Class 8
truck industry.
Daimler Trucks North America
Downspeeding – comparison to emissions test cycle
• Development towards lower operating speeds for fuel efficiency improvement
• Shifts operation to lowest speeds of existing Supplemental Emissions Test cycle (SET) test speeds
Inclusion of actual engine fuel map within drive cycle simulation tool will link actual
engine operation with evolving drivetrains and changing operation speeds.
Downspeeding and downsizing
0.0
100.0
200.0
300.0
400.0
500.0
600.0
0.0
200.0
400.0
600.0
800.0
1000.0
1200.0
1400.0
1600.0
1800.0
0.0 500.0 1000.0 1500.0 2000.0 2500.0
ft-l
brpm
NTE zone
NTE pts
TCG curve
T@30%P
30%maxT
Nlo
A B C
Typical in-use test result Supplemental emissions test points
7
Daimler Trucks North America
Downspeeding – Efficiency Improvement
8
Decreased friction and pumping losses with decreased speed
EPA Phase 1 Generic GEM fuel map
Downspeeding and downsizing
Efficiency improvements are realized as operating speeds decrease and losses due to
friction and pumping are reduced, actual fuel map in GEM is essential.
Efficiency
improvement potential:
Dependent on multiple
factors including map
characteristics, axle
ratio, transmission
ratios, tire size, vehicle
aero, weight, tire
rolling resistance,
vehicle drive cycle,
governed vehicle
speed.
Daimler Trucks North America
Downspeeding – Drivability
9
Decreased friction and pumping losses with decreased speed
EPA Phase 1 Generic GEM fuel map
Downspeeding and downsizing
Downsped operation requires development of higher torque capacity at lower engine
speeds. Actual torque curve in simulation tools is needed.
Drivability:
Shrinkage of
operating range
with usable torque
creates new
demands
• Extension of max
torque to lower
engine speeds
• Rapid shifting
automated
transmissions
Constant power:
Driveline optimization
for reduced operating
speed necessitates
higher operating
torque to meet road
load requirements.
Daimler Trucks North America
Downspeeding – Areas of Development
• To maintain required road load horsepower at reduced engine speeds, higher drivetrain
torque capacity is required since HP = [(Engine speed) * (Torque) / Constant]
• Driveline robustness to handle higher operating torques
• Size and weight tradeoff
• Engine redesign for higher torque output at lower engine speeds
• Limited by thermodynamics and
• Mechanical limits of core engine
• As engine speed at highway cruise conditions decreases, the usable engine speed range
diminishes (since minimum engine speeds are unchanged)
• Automated manual transmissions for faster shift capability
• Possible need for dual clutch technology
10
Downspeeding and downsizing
Daimler Trucks North America
Downsizing Limitations for Commercial Trucking
2014 LDV 2014 Cascadia
Engine 2.0L l-4 12.8L DD13
Horsepower 160hp @ 6500rpm 350hp @ 1800rpm
Torque 146lb-ft @ 4450rpm 1350lb-ft @ 1100 rpm
Curb Weight/GVW (lbs) 2,948 60,000
Speed (mph) 62 62
Grade Resistance (hp) 15 298
Grade Power % of Total Power 9% 85%
+15 hp due to 3% Grade
+298 hp due to 3% Grade
Downspeeding and downsizing
11
Daimler Trucks North America
Engine Downsizing - Concept
12
Constant power
EPA Phase 1 Generic GEM fuel map
Downspeeding and downsizing
Vehicles improvements reduce road load power
requirements – largest impact under relatively
level conditions
Reducing displacement (and
related friction losses)
theoretically has potential to
move efficiency islands to
lower torque region.
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Engine Downsizing – Example Concept
13
Downspeeding and downsizing
Benefits of downsizing for improved efficiency are not recognized by the RMC, but will
be in simulations using the actual torque curve and map.
1100
Equal
power
Base engine Downsized engine
Base and downsized engines have same brake specific fuel
consumption characteristics as measured on the RMC test
cycle, however, the downsized engine theoretically
produces lower CO2 under level road load conditions.
Daimler Trucks North America
Engine Downsizing – tradeoffs
• Improved efficiencies at lower displacement have not been demonstrated
• Increased thermal losses due to less favorable surface/volume ratio, exacerbated at lower operating speeds
• Torque capacity diminishes as displacement decreases, especially at low engine
speeds, due to brake mean effective pressure constraints.
• Compromises drivability
• Increased operation at higher BMEP generally sacrifices B50 Life to wearout
• Residual value – The secondary market places a higher value on lager displacement
engines which factors into the customer’s TCO equation at the end of the trade
cycle.
14
Daimler Trucks North America
Engine downsizing trade-offs
15
Downspeeding and downsizing
Factor Larger
Displacement
Smaller
Displacement
Weight - +
Gradability + -
Friction - +
Life Expectancy + -
Packaging - +
Heat Rejection + -
ATS Performance - +
NVH + -
Backpressure
sensitivity
+ -
“+” = advantage
“-” = disadvantage
Daimler Trucks North America
Summary
• Truck and engine manufacturers are focused, and can be expected to continue to focus,
on powertrain optimization at lower operating speeds for efficiency improvement.
• Trends show increasing customer adoption of downsped powertrains
• Development of drivetrain components (transmissions, prop shafts, joints, differentials, axles, etc.) with increased robustness goes hand in hand with downspeeding.
• Engine operating speed range, torque capacity, and associated tradeoffs must be considered.
• Engine downsizing must consider numerous trade-offs
• No “one size fits all” solution.
• A range of displacements is necessary to meet power and torque requirements across a broad range of applications.
16
Downspeeding and downsizing
Daimler Trucks North America
Thank you for your time! Questions?
17
Downspeeding and downsizing