calvin bradley & arnaud delaval presented at the 2011 meeting of the tire society

On-Road Fuel Consumption Testing to Determine the Sensitivity Coefficient Relating Changes in Fuel Consumption to Changes in

Tire Rolling Resistance

Calvin Bradley & Arnaud Delaval

Presented at the 2011 meeting of the Tire Society

Page : 2 / 192011 Tire Society Conference

Agenda

Environmental and regulatory context

Rolling resistance basics

Previous results

Derivation of sensitivity coefficient

On-road testing General procedure Methods to monitor fuel consumption Data Analysis

Results

Conclusions


Rolling resistance role in production of greenhouse gases

Rolling resistance contribution to over the road transport Passenger vehicles: 20% of forces opposing motion Heavy duty trucks: 30% of forces opposing motion

United States transportation Transportation accounts for 29% of CO2 production The majority comes from over the road vehicles

– Passenger Vehicle: 59%– Heavy Truck: 19%

In the U.S. alone 337 million metric tons (MMT) of CO2 are produced to overcome rolling resistance

1 MMT of CO2 is 200,000 Hot air balloons by volume 1 MMT of CO2 requires almost 800,000 acres of Pine forest to offset


Tire Efficiency Labeling Around the World

Final Label TBD


Tire Deformations

As a tire is deformed to carry the load three types of deformations are occurring

Bending Compression Shearing


Definition of Tire’s Rolling Resistance

Tire’s rolling resistance is characterized by a rolling resistance coefficient :

Tire’s rolling resistance is defined as the energy dissipated by a tire per unit of distance traveled

Ztire

tire

tireRRRR Z

FC ,

7-12 kg/t 4-8 kg/t

001.01 tkg

Driving with 10kg/t tires is as if the vehicle was climbing a permanent 1% slope


J. Barrand and J. Bokar established a first order estimate for predicting differences in fuel consumption

The sensitivity coefficient α was further demonstrated to be relatively independent to drive cycle

Empirical prediction Simulations Closed circuit stabilized

speed testing

Previous results

MgCFC RR


α

aerodynamic drag

internal frictioninertia

accessories

Example of accessories : air conditioning, power steering, on-board entertainment…

V

P

V

PgM

dt

dVMVACgMCF AccInt

eqDRRRM )sin(2

1 2

gravity

rolling resistance

A vehicle requires energy to move forward and improve the driving comfort

Resistance to Movement characterizes the effort to be overcome

Rolling Resistance is one of the force acting on the vehicle

Rolling Resistance & Resistance to Movement


Fuel consumption for at a given moment can be described by;

From previous discussion we know

Engine efficiency is a function of required torque

So efficiency η is also a function of CRR

E

RMFFC

Force Resisting Motion

Energy Density of Fuel

Engine Efficiency

Fuel Consumption (volume per distance)

V

P

V

PgMMVACgMCF Acc

dtdv

dRRRM int221 )sin(

Derivation of Sensitivity Coefficient

0

50

100

150

200

250

300

500 1500 2500 3500 4500 5500 6500engine speed [1/min]

Engin

e t

orq

ue [

Nm

]

Iso engine efficiency

32%

30%31%

13%

21%

29%

27%


Derivation of Sensitivity Coefficient

Taking the derivative of fuel consumption with respect to CRR

and simplifying we obtain

Relating this to previous publications then we see

If the change in efficiency with respect to CRR is very small

However, this approximation proves to be insufficient and the second term for α cannot be neglected

MgdCdFC RRE

1

MgCFC RR

MgdCdC

d

Mg

FdFC RR

RRE

RM

E

2

1

RRE

RM

E dC

d

Mg

F

2

1

E

1

Fuel Consumption Testing


Test Overview

All tires were machine tested to determine their coefficient of rolling resistance

The impact of these tires on fuel consumption is measured Real world conditions Drive cycle with both urban and city portions Typical E10 gasoline

3 different vehicle segments tested Compact: Toyota Corolla Midsize: Chevrolet Impala Light Truck: Chevrolet Silverado

Wide range of tires evaluated 30 tire sets 10 different brands Approximate range rolling resistance: 7 to 13 kg/t


Test Overview

Significant variation can occur during testing

Sources of variation are controlled for consistency as much as possible

Fueling procedures Vehicle factors such as alignment, AC, windows, lights, weight

Other sources of variation are permutated through all tire sets Convoy position Driver Vehicle

Fuel consumption is measured by multiple independent methods

Test length must be sufficient to provide enough data for significant differences between tire sets

Duration of each test ranged from 12,500 km to 23,500 km Results come from approximately 587,000 vehicle kilometers of testing


Methods to monitor fuel consumption Fuel pump records

Defines what the consumer actually pays for Measures volume of fuel at ground temperature Data cannot be taken as frequently as other methods Requires a precise fueling procedure

Fuel injector information Measures fuel by injector pulse frequency and duration Vehicle on board fuel economy displays

– Injector data is calibrated by vehicle manufacturer– Can include error from tire diameter variations

Scan Gauge II OBD tool– Injector data must be calibrated for each vehicle – Independent of tire diameter

Inline volumetric flow meters Significant cost Requires cutting of fuel lines for install Measures volume of fuel at fuel line temperatures

Fuel tank

Filter

Runbackfrom engine

Feedlineto engine

Fuel consumption indicator

2000

pu

lses

pe

rlit

er

FeedlineFrom tank

~180 l/h

Fuel tank

Filter

Runbackfrom engine

Feedlineto engine

Fuel consumption indicator

2000

pu

lses

pe

rlit

er

FeedlineFrom tank

~180 l/h


Methods Summary Injector Data (Vehicle display & Scan Gauge)

Cost: Low Complexity: Low or Medium Precision: High Accuracy: Low

Fuel Meter (fuel line volumetric meter) Cost: High Complexity: High Precision: High Accuracy: High

Fuel Pump (Service Station Records) Cost: Low Complexity: Medium Precision: Low Accuracy: Highest


Results ANOVA analysis was used to correct for driver and vehicle effects

All methods were normalized to fuel pump levels

Results demonstrate agreement between methods


Results

ANOVA revealed within a test, fuel consumption changes greater than 1.2% were critically different at 95% confidence

Repeats of testing on each vehicle show similar relationship to CRR


Results Testing did not reveal significant differences between

sensitivity coefficients for each vehicle

Thus a single value for α was determined sufficient for all tested vehicles

Value of α confirms that is not small enough to be completely neglected

MgCFC RR

∆FC with lowest RR tire set as reference Measured FC for all testing

km

kgfL

100

*082.0RRdC

d


Conclusion

Tire rolling resistance has a significant impact on vehicle fuel consumption

Changes in fuel consumption can bepredicted by the linear empirical model

The sensitivity coefficient α primarily depends on fuel energy density and effective engine efficiency

The sensitivity coefficient α is not strongly a function of vehicle (outside of vehicle weight) or drive cycle

For typical American usage with E10 gasoline fuel savings can be predicted with:

α = 0.082 with ∆FC in L/100km, CRR in kg/t, and Mg in metric tons

α = 1.58E-5 with ∆FC in gal/100miles, CRR in kg/t, and Mg in lbs

MgCFC RR

calvin bradley & arnaud delaval presented at the 2011 meeting of the tire society

Documents

tire society conferencej

tire societypage

resistance tires

rolling resistance coefficient

resistance contribution

driving comfort resistance

derivative of fuel consumption

road fuel consumption