Ricardo Study_with Cover

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Impact of Vehicle Weight Reduction on Fuel Economy

for Various Vehicle Architectures

Research ReportConducted by Ricardo Inc.

for The Aluminum Association

2008-04


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Ricardo Inc 2007FB769 - RD.07/71602.2

Impact of Vehicle Weight Reduction on FuelEconomy for Various Vehicle Architectures

Prepared for: The Aluminum Association, Inc.

By: Anrico Casadei and Richard Broda

Project FB769

RD.07/71602.2

Technical Approval: __Reviewed by [Frederic Jacquelin]______________

Date: _________________ (20-Dec-2007)


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Content

Ricardo vehicle model development for high-level representation of existingvehicles

Baseline vehicle selection

Model inputs and assumptions

Model validation

Simulation Methodology

Results

Gasoline vehicles

Diesel vehicles

Conclusions


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Vehicle Modeling Using MSC.EASY5TM

A full forward-looking, physics-based model was developed for each baselinevehicle using commercially available MSC.EASY5TM simulation software with

Ricardo proprietary data as well as published information. The model simulates what happens to the vehicle when the driver applies the

accelerator and/or brake pedal in order to achieve a certain vehicle speed ata certain time.

The simulation runs on a millisecond-by-millisecond basis and predicts thefuel usage and actual speed with time as the model driver follows a certainvehicle speed trace (drive cycle).

The model physics includes torques and inertias as well as detailed sub-models for the influence of factors such as turbocharger lag and engineaccessories.


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Example of Model Developed Using MSC.EASY5TM Software

Fuel EconomyPost-processing

Tools

Driver Model

PowertrainModel

Vehicle Model


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Vehicle Model and Sub-Model Components

Engine

Torque curves for full load and closed throttle motoring correlated to

published power ratings Fuel consumption rates covering entire speed and load range

Idle and redline speeds

Rotational inertia

Turbo-lag model for turbocharged diesel engines Alternator parasitic load (constant throughout drive cycle)

Power steering parasitic load as a function of engine speed

Cooling fan parasitic load

Electric (Small Car, Mid-Size Car, Small SUV) fan loads specific to dutycycle

Belt-driven (Large SUV, Truck) fan loads as a function of engine speed


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Transmission

Torque converter characteristic curves for torque ratio and capacity factor

Gear ratios Shift and lock-up clutch strategy maps for all engine throttle positions and

vehicle speeds

Efficiency and pumping losses for each gear

Rotational inertias


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Final drive differential

Gear ratio

Efficiency Rotational inertia

The spin losses of the 4-wheel drive vehicles front axle were also included inthe model to simulate the fuel economy and performance of the 4-wheel drivepowertrain operating in 2-wheel drive mode (similar to EPA procedure foremissions and fuel economy certification testing).


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Vehicle Configuration (FWD, RWD or AWD)

Weight (front / rear distribution)

Center of gravity

Wheelbase

Frontal area

Coefficient of drag (Cd)

Wheels / Tires Rolling resistance coefficients

Rotational inertia

Rolling radius (tire size)

Maximum friction coefficient Slip at peak tire force

Driver

Drive cycle (time vs. velocity trace)


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Vehicle Selection

Five vehicle classes were chosen to represent a variety of vehicle weights andengine sizes in the U.S passenger and light-duty truck vehicle fleet.

A specific comparator vehicle for each class was chosen to verify that eachvehicle model was representative of the class.

Vehicle Class / Comparator Vehicle:

Small Car / Mini Cooper Mid-Size Car / Ford Fusion

Small SUV / Saturn Vue

Large SUV / Ford Explorer

Truck / Toyota Tundra


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Model Input Vehicle Parameters


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Model Input Baseline Gasoline Engine and Transmission


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Diesel Engine Selection

Diesel engines were selected to provide improved fuel economy andacceptable (not equivalent) vehicle performance.

The characteristic turbocharged diesel power curve (high torque at low speed)has more torque in the typical cruising and light acceleration engine operatingrange (1100 3000 RPM). At 50 to 70 MPH in 6th gear the diesel providesmore reserve torque so that light pedal tip-in acceleration demands aresuperior to the gasoline engine. Full pedal (WOT) accelerations at these

speeds will be slower due to the lower maximum engine speed of the diesel(4000 RPM) and resultant lower horsepower vs. the high speed gasolineengine (5600 6500 RPM).


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Diesel Engine Power Curve

2.7L V6 Diesel vs. 3.6L V6 Gasoline Engines

0

50

100

150

200

250

300

350

0 1000 2000 3000 4000 5000 6000 7000Engine RPM

Eng

ine

Torque

/HP

2.7L Diesel Torque

3.6L Gas Torque

2.7L Diesel HP

3.6L Gas HP


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Model Input Baseline Diesel Engine and Transmission


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Model Input Downsized Gasoline Engines(Displacement reduced to provide equivalent performance to baseline vehicles)


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Model Input Downsized Diesel Engines(Displacement reduced to provide equivalent performance to baseline vehicles)


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Model Validation

Each vehicle model was run and the simulation output for total vehicle roadloadtractive effort from 0 to 60 MPH and EPA City and Highway fuel economy wascompared to published data for the comparator vehicle.

No attempt was made to calibrate the model to achieve a given output result.

SimulationRoadload Force

Simulated Fuel Economy vs. Comparator (% diff)

VEHICLE MaximumVariation vs.

Comparator

EPA City EPA Highway Combined

Small Car 0.2% 2.5% -0.6% 1.3%

Mid-Size Car 2.5% 0.2% -1.4% -0.4%

Small SUV 1.1% 1.8% -4.4% -0.4%

Large SUV 1.7% 5.9% -1.1% 3.5%

Truck -1.3% 2.2% -1.9% 0.7%


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Vehicle Simulations

Vehicle fuel economy (MPG) is simulated over the following drive cycles at EPAEquivalent Test Weight (ETW):

EPA FTP75 (city)

EPA HWFET (highway)

ECE (European)

Steady State 30, 45, 60 and 75 MPH

All simulations are performed with an engine at normal operating temperature.The EPA FTP (city) cycle result is obtained by using a bag #1 correction factor

of 0.8 (bag #1 fuel economy = 80% of bag #3 fuel economy) Vehicle acceleration performance (sec.) is simulated over the following drive

cycles at loaded vehicle weight conditions (GCVW for truck):

0 10 MPH

0 60 MPH 30 50 MPH

50 70 MPH

Each vehicle is weight reduced by 5%, 10% and 20% and the enginedownsized to match the baseline vehicle acceleration performance. Fueleconomy benefits are recorded.


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Simulation Drive Cycles

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400 1600 1800

Time (sec)

Ve

hicleVel

oc

ity

(MPH)

Euro ECE

EPA City

EPA Highway


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Vehicle Performance Matching

The Wide Open Throttle (WOT) performance of each vehicle is simulated at aloaded weight condition to approximate what a customer would expect from agiven class of vehicle (number of passengers, luggage or trailer towing). All

fuel economy simulations are performed at ETW.

Additional Performance Weight:

Small Car 300 lb. (2 passengers)

Mid-Size Car 450 lb. (3 passengers)

Small SUV 550 lb. (3 passengers + 100 lb. Luggage)

Large SUV 750 lb. (5 passengers)

Truck 9800 lb. (Trailer + load to rated combined weight of 15,800 lb.)

Engines were downsized in displacement to give the weight reduced vehiclesequivalent performance to the baseline vehicle with a priority given to passingmaneuvers (30-50 and 50-70 MPH).


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Fuel Economy Labeling of Vehicles

The EPA requires that all new light-duty motor vehicles have a fuel economy label thatgives the consumer an estimate of the city and highway fuel economy. This estimate isused to compare to the fuel economy of other vehicles that they may be considering forpurchase.

Prior to the 2008 model year, the City fuel economy prediction for the vehicle windowsticker was calculated as 90% of the EPA Federal Test Procedure (FTP) result and theHighway fuel economy was 78% of the EPA Highway Fuel Economy Test (HWFET)result.

Starting with the 2008 model year, new test methods that include high speeds,

aggressive accelerations, cold temperatures and the use of air conditioning have beenintroduced to more accurately reflect real world fuel economy.

As a transition to the increased testing requirements, a manufacturer has the option ofusing a derived 5-cycle approach for fuel economy labels for the 2008-2010 modelyears that uses only the FTP and HWFET tests based on regression formulae derivedfrom the fuel economy test results of more than 600 vehicles in the EPA database(subject to revision as more data becomes available).

City MPG = 1 / (0.003259 + (1.1805 / FTP MPG))

Highway MPG = 1 / (0.001376 + (1.3466 / HWFET MPG))


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Results

Vehicles with Gasoline Engines


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Small Car 1.6L-4V gas engine with variable intake and exhaust camtiming and lift

Fuel Economy Simulation Results

EPA fuel economy label projections are based on the derived 5-cycle regression equation for the 2008 model year.


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Small Car 1.6L-4V gas engine with variable intake and exhaust camtiming and lift

Vehicle Performance Simulation Results at Wide Open Throttle (WOT)


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Mid-Size Car 3.0L-4V gas engine with variable intake cam timing




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Mid-Size Car 3.0L-4V gas engine with variable intake cam timing



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Mid-Size Car Additional Engine Downsizing Study

Fuel economy simulation results with gasoline engine downsized to vehicle performance level at ETW(Degraded vehicle acceleration performance vs. baseline at loaded weight)

Engine displacement is further reduced by 0.1% per 1% of weight reduction with a resultantimprovement in fuel economy of 0.1%


Mid Size Car Additional Engine Downsizing Study


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Mid-Size Car Additional Engine Downsizing Study

Vehicle performance simulation results with gasoline engine downsized to vehicle performance levelat ETW (Degraded vehicle acceleration performance vs. baseline at loaded weight)


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Small SUV 3.6L-4V gas engine with variable intake cam timing



S ll SUV 3 6L V i i h i bl i k i i


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Small SUV 3.6L-4V gas engine with variable intake cam timing


L SUV 4 6L 3V i


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Large SUV 4.6L-3V gas engine



L SUV 4 6L 3V i


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Large SUV 4.6L-3V gas engine


Truck 5 7L-4V gas engine with variable intake and exhaust cam


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Truck 5.7L 4V gas engine with variable intake and exhaust camtiming



Truck 5 7L 4V gas engine with variable intake and exhaust cam


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Truck 5.7L-4V gas engine with variable intake and exhaust camtiming


Fuel Economy Improvement (%) per 100 lb Weight Reduction -


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Fuel Economy Improvement (%) per 100 lb. Weight Reduction -Gasoline Engines

Drive Cycle Fuel Economy Improvement (%) per 100 lb. Weight Reduction -


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y y p ( ) p gGasoline Engines

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Fuel

Economy

Increase

per 100 lb.

Weight

Reduction

(%)

FTP75

Hwy

Combined

ECE

Truck

Large SUVSmall SUV

Mid-Size Car

Small Car

Engine Downsizedto Baseline Performance

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Fuel

EconomyIncrease

per 100 lb.

Weight

Reduction

(%)

FTP75

Hwy

C

om

bine

dECE

Truck

Large SUV

Small SUV

Mid-Size Car

Small Car

Baseline Engine

Steady State Fuel Economy Improvement (%) per 100 lb. Weight Reduction -


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Gasoline Engines

0.0

0.5

1.0

1.5

2.0

2.5

Fuel

Economy

Increase

per 100 lb.

Weight

Reduction

(%)

30

MPH

45

MPH

60

MPH

75

MPH

Truck

Large SUV

Small SUV

Mid-Size Car

Small Car

Engine Downsizedto Baseline Performance

0.0

0.5

1.0

1.5

2.0

2.5

Fuel

Economy

Increase

per 100 lb.

Weight

Reduction

(%)

3

0MPH

4

5MPH

6

0MPH

7

5MPH

Truck

Large SUV

Small SUV

Mid-Size Car

Small Car

Baseline Engine

EPA City (FTP75) Drive Cycle Fuel Economy Improvement (%) -


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EPA City (FTP75) Drive Cycle Fuel Economy Improvement (%) Gasoline Engines

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Fuel

Economy

Increase

(%)

Sma

llCar

Mid-S

iz

eCar

Sma

llSUV

Large

SUV

Truc

k

5%

10%

20%

We ight

R e d u c t io n

(%)

Baseline Engine

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12141618

Fuel

Economy

Increase

(%)

SmallCar

Mid-SizeCar

SmallSUV

Large

SUV

T

ruck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized

to Baseline Performance

EPA Highway (HWFET) Drive Cycle Fuel Economy Improvement (%) -


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g y ( ) y y p ( )Gasoline Engines

02468

1012141618

Fuel

Economy

Increase(%)

Sma

llCar

Mid-Size

Car

Sma

llSUV

Larg

eSUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

0246810

12141618

Fuel

Economy

Increase

(%)

SmallCar

Mid-SizeCar

SmallSUV

Large

SUV

T

ruck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


EPA Combined Drive Cycle Fuel Economy Improvement (%) -


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y y p ( )Gasoline Engines

02468

1012141618

Fuel

Economy

Increase(%)

Sm

allCar

Mid-Size

Car

Sma

llSUV

Larg

eSUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

0246810

12141618

Fuel

Economy

Increase

(%)

SmallCar

Mid-SizeCar

SmallSUV

Large

SUV

T

ruck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


European (ECE) Drive Cycle Fuel Economy Improvement (%) -


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Gasoline Engines

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Fuel

Economy

Increase(%)

Sm

allCar

Mid-Size

Car

Sma

llSUV

Larg

eSUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

02468

10

1214161820

Fuel

Economy

Increase

(%)

SmallCar

Mid-SizeCar

SmallSUV

Large

SUV

T

ruck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


Results


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Results

Vehicles with Diesel Engines

Mid-Size Car 2.2L I4 diesel engine


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Mid-Size Car 2.2L I4 diesel engine


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Vehicle Performance Simulation Results at Full Engine Load (WOT)

Small SUV 2.7L V6 diesel engine


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Small SUV 2.7L V6 diesel engine


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Large SUV 3.2L V6 diesel engine


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Large SUV 3.2L V6 diesel engine


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Truck 4.8L V8 diesel engine


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Fuel Economy Improvement (%) per 100 lb. Weight Reduction -Diesel Engines


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Diesel Engines

Drive Cycle Fuel Economy Improvement (%) per 100 lb. Weight Reduction -Diesel Engines


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0.0

0.5

1.0

1.5

2.0

2.5

3.0

Fuel

EconomyIncrease

per 100 lb.

Weight

Reduction

(%)

FTP75

Hwy

Combined

ECE

Truck

Large SUV

Small SUV

Mid-Size Car

Engine Downsized


0.0

0.5

1.0

1.5

2.0

2.5

3.0

Fuel

Economy

Increase

per 100 lb.

Weight

Reduction

(%)

FTP75

Hwy

Combined

ECE

TruckLarge SUV

Small SUV

Mid-Size Car

Baseline Engine

Steady State Fuel Economy Improvement (%) per 100 lb. Weight Reduction -Diesel Engines


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0.0

0.5

1.0

1.5

2.0

2.5

FuelEconomy

Increase

per 100 lb.

Weight

Reduction

(%)

30MPH

45MPH

60MPH

75MPH

Truck

Large SUV

Small SUV

Mid-Size Car

Engine Downsized


0.0

0.5

1.0

1.5

2.0

2.5

FuelEconomy

Increase

per 100 lb.

Weight

Reduction

(%)

30MPH

45MPH

60MPH

75MPH

Truck

Large SUV

Small SUV

Mid-Size Car

Baseline Engine


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EPA Highway (HWFET) Drive Cycle Fuel Economy Improvement (%) -Diesel Engines


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0246810

12141618

Fuel

Economy

Increase

(%)

Mid-S

ize

Car

Sm

allSUV

Large

SUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

0246810

12141618

Fuel

Economy

Increase

(%)

Mid-Siz

eCar

SmallSUV

LargeSUV

Truck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


EPA Combined Drive Cycle Fuel Economy Improvement (%) -Diesel Engines


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02468

1012141618

Fuel

Economy

Increase(%)

Mid-S

ize

Car

Sm

allSUV

Large

SUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

0246810

12141618

Fuel

Economy

Increase

(%)

Mid-Siz

eCar

Sma

llSUV

LargeSUV

Truck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


European (ECE) Drive Cycle Fuel Economy Improvement (%) -Diesel Engines


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0246810

1214161820

Fuel

Economy

Increase(%)

Mid-S

ize

Car

Sm

allSUV

Large

SUV

Truc

k

5%

10%

20%

We ight

Redu c t io n

(%)

Baseline Engine

02468

101214161820

Fuel

Economy

Increase

(%)

Mid-Siz

eCar

Sma

llSUV

LargeSUV

Truck

5%

10%

20%

We ight

R e d u c t io n

(%)

Engine Downsized


Summary EPA Combined Drive Cycle -% Improvement in Fuel Economy per % Weight Reduction


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The fuel economy benefit from weight reduction is similar for gasoline and diesel powered light dutyvehicles.

Truck engines were downsized to a lesser degree than the passenger vehicle engines due to theperformance demands on trucks when loaded. Vehicles rated to tow a trailer benefit the least fromweight reduction and subsequent engine downsizing if acceleration performance while towing is

maintained.

% Improvement in Fuel Economy / % Weight Reduction

EPA Combined (Metro-Highway) Drive Cycle

Passenger Vehicle Truck

DownsizedEngine

DownsizedEngine

0.33% 0.47%

0.39% 0.46%

Base Engine Base Engine

Gasoline 0.65% 0.35%

Diesel 0.63% 0.36%

Conclusions / Observations


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Reducing vehicle weight (mass) results in less tractive effort required to accelerate the vehicle and

less rolling resistance from the tires. Drive cycles with more acceleration events (EPA city andEuropean) show greater fuel economy benefits from weight reduction than highway or steady stateconditions. Also, at higher vehicle speeds the engine is typically at higher throttle (better BSFC)operating points and provides less opportunity for improvement. Since the tire losses are a greaterpercentage of total tractive effort at lower speeds (aerodynamic losses increase by velocity squared)the potential for fuel economy gain from weight reduction is greater at lower vehicle speeds.

Fuel economy results (and improvements) at the steady 30 MPH drive condition vary because mostvehicles are not in top gear yet and are operating the engine at a higher speed / lower load point thatis less efficient.

Less tractive effort results in less engine torque demand at a given point in the drive cycle. The lowerload (throttle) demand puts the engine at a less efficient point with more pumping loss and lowerbrake specific fuel consumption (grams fuel / power produced). Reducing the engine displacement ofthe weight-reduced vehicle to equal baseline vehicle performance increases the brake mean effectivepressure (BMEP) of the engine operating points and improves efficiency. A final drive ratio changecould also partially offset the pumping loss increase but was not investigated.

The Small Car with a 1.6L engine with variable valve timing and variable lift technologies that reduce

pumping losses shows the largest % fuel economy benefit with the baseline engine since it canoperate at the reduced engine load points more effectively (0.42% fuel economy benefit / % weightreduction vs. other gas engine vehicles at 0.27-0.32% FE benefit). When the engine is downsized itproduces fuel economy gains similar to the other passenger vehicles (0.66 vs. 0.61-0.68 % FE / %weight reduction).

Documents

Ricardo Study_with Cover