Slide 1

Estimation of Road Load Parameters via On-roadgVehicle Testing
Dr. Rahul Ahlawata, Dr. Jürgen Bredenbeckb & Mr. Tatsuo Ichigeca A&D Technology,Michigan, USA

b A&D Europe GmbH, Griesheim, Germanyc A&D Company, Tokyo, Japan

Tire Technology Expo 2013
February 5-7,
5-7 Cologne,
Cologne Germany
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Slide 2

Energygy Loss in Vehicles
Standby
17%(4%)

Accessories
2%(2%)
Aerodynamic Drag
3%(11%)

Fuel Tank
100%(100%)()

Rolling Resistance
4%(7%)Braking
6%(2%)Engine Loss
62%(69%)

Drivetrain Loss
6%(5%)

Losses of fuel energy in a vehicle in city usage (highway usage)[U.S. National Academy of Science, 2006]

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Slide 3

Energygy Loss in Vehicles
Standby
17%(4%)

Accessories
2%(2%)
Aerodynamic Drag
3%(11%)

Fuel Tank
100%(100%)()

Rolling Resistance
4%(7%)Braking
6%(2%)Engine Loss
Drivetrain Loss
VehicleRoad
Load
62%(69%)6%(5%)

Road GradeRoad load is define as the “…force…force or torque which opposes the movement ofa vehicle…”
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[ISO 10521‐1, 2006]

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Slide 4

Significance of Road Load Determination
Vehicle platooning [1,2]Roll‐over prevention [3]EEnergymanagement [4,5][SARTRE project test, Sweden]

Offline modeling &control development [6][Toyota]Engine certification [7][Mathworks]

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Slide 5

Objectivej
Estimate the road load parameters of a vehicle
 Focus on rolling resistance & aerodynamic drag Use on‐road testing of a production vehicle
 Use a novel force measurement method & comparepresultswith traditional method(s)Proprietary and Confidential, A&D Technology, Inc.

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Slide 6

Outline1. Introduction
2. Road load fundamentals

3. Instrumentation &sample data
4. Coast down method
5. Force measurement
method
6. Summary
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Slide 7

Rolling Resistance
For a free rolling tire under no slip:
Mg: Vertical load on the tire due to sprung & unsprung mass
vx: Tire longitudinal velocity
ω: Tire angular speed
Rz: Ground reaction force
Rx: Rolling resistance forceMrr: Rolling resistance moment
r: Loaded tire radius

vx

Mg

vx

ωMg

vx

ωMg

ωMrrRxTire normal force
distribution is asymmetric.
The resultant normal force
acts towards the leading
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edge.

Rx
a
Rz

Rz

a∙Rz = Mrr= r∙ Rx Rolling resistancewww.aanddtech.com

forceSlide 8

AerodynamicyDragg[BMW]

Density of air
Frontal area of the vehicle
Coefficient of aerodynamic dragRelativel i velocity
l i off theh vehicle
hi l wrt theh windi d
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Slide 9

Total Road Load
The most commonly used form of road load equation is:

IIncludesl d influence
i flPredominantly
Pd itlIncludesl dof road grade
includes theaerodynamic drageffect of rolling
resistance Includes dependenceof rolling resistance on
velocity & drivetrain
losses• ‘b’ term is not always included• A number of other formulations exist [8], including• Influence of rotational inertias• Correction factors• Additional dependencies

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Slide 10

Road Load Measurement Methods
1. Individual component measurements[Terrametrix][Nissan][Volvo]Rolling resistance: Tiretesting

Aerodynamic drag:Wind tunnel testing[M t k][Maptek]

Grade: Road profiling

Pros: High repeatability, aids in parametric evaluation
Highercost, Inc.
may not represent real
driving conditions
Cons:
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Slide 11

Road Load Measurement Methods
2. Coast‐down method [8,10]

3. Torque measurement [9][VTI Sweden][Timken][9]Pros: Less instrumentation
Cons: Time consuming tests,tests include
drivetrain losses
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Pros: Drivetrain losses are excluded
Cons: Difficult to install on
production vehicle
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Slide 12

Road Load Measurement Methods
4. Complete vehicle measurement system
[A&D]

[A&D]

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Slide 13

On-road Vehicle Testing
Stop

Test Vehicle: FWD Mini Cooper SSStart

Test Track: Proving ground in Tochigi, Japan
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Slide 14

Instrumentation

Anemometer
Measures wind velocity & direction
6‐Component Wheel Force Transducer(Fx, Fy, Fz, Mx, My, Mz)
o Distributed force bridges with model based decomposition to get
orthogonal force componentso Very low cross sensitivity, interference & temperature sensitivity andhigh sampling rate
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o 0.1% resolution (6N or 1.8Nm) www.aanddtech.com

Slide 15

Instrumentation

Anemometer
Measures wind velocity & direction
6‐ComponentpWheel Force Transducer(Fx, Fy, Fz, Mx, My, Mz)
I flInfluence
off ddrivetrain
ii losses
liis included
i l d d iin thishi measurement
Influence of a and b terms is included in this measurement (ignoring bearing
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friction and wheel well aerodynamic losses) www.aanddtech.com

Slide 16Vehicle Instrumentation II
Laser Doppler Sensor
Measures vehicle velocity & slip
angle
GPS Sensor & In‐vehicle Network
Measures vehicle longitude,
latitude, altitude, and ECU CAN
communication
Inertial SensorMeasures vehicle roll,
pitch and yaw

Wheel Position Sensor
Measures 6 degrees of freedom of the tire
Digital Signal Processing&AAcquisition
i iti
100Hz sampling
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(max 100kHz)

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Slide 17

Sample Data

FLRL

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FRRR

Slide 18

Sample Data
Acceleration

FLRL

Coast‐down

Acceleration

FRRR

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Braking

Slide 19

Sample Data
Acceleration

Coast‐downAcceleration

Braking

Contribution of a and b terms
FLRL

FRRR

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Slide 20Outline
1. Introduction
2. Road load fundamentals
3. Instrumentation &sample data
4. Coast down method

5. Force measurement
method
6. Summary
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Slide 21

Coast-down Tests
Procedure:• Conduct tests on a flat road with low wind conditions• Accelerate the vehicle and put the transmission in N
• Begin coast down in a straight line
• Record vehicle velocity and vehicle velocity relative to wind as a function
off time
i3530

Velocity (m/s))

2520

Coast‐down

15
10
50-50

1020

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304050Time (sec)60

70

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8090

Slide 22

Coast-down Tests
Procedure:• Conduct tests on a flat road with low wind conditions• Accelerate the vehicle and put the transmission in N
• Begin coast down in a straight line
• Record vehicle velocity and vehicle velocity relative to wind as a function
off time
iFlat road assumption

6Road grade (deg)Road grade (deg)420-2-4-620 Technology,
4060
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80

100120Time (sec)

140
160
180
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200

Slide 23

Coast-down Tests
Procedure:• Conduct tests on a flat road with low wind conditions• Accelerate the vehicle and put the transmission in N
• Begin coast down in a straight line
• Record vehicle velocity and vehicle velocity relative to wind as a function
off timei••

Use linear regression to obtain coefficients a, b & c• Use minimization of• Verify by Simulated Annealing
SAE J1263,
J1263 J2263 and ISO 10521‐1
10521 1 contain more detailed procedures

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Slide 24

Coast-down Test Results
1200
Measured road load force
Regression estimates

1000• Front tires: Bridgestone
Coefficient ofdetermination, R2=0.9087 Sneaker

Force (N)800

Rear tires: Bridgestone
Sneaker• Estimated Values:a = 194.87, b = 3.87, c = 0.37
•

600
400
200
0-200
0

Data‐sets augmented
1020304050Time (sec)

60

3530

a: 184 – 20425

b: 2.7 – 5
c: 0.35 – 0.39

Velocity (mm/s)

95% Confidence
C fidbbounds
d:

70

80

90

(33m/s, 118km/hr, 73mph)

Measured velocity
Calculated velocity

20
1510

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50

(7.5m/s, 27km/hr, 16mph)1020

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30
40
50
Time (sec)

60

70

8090

Slide 25

Coast-down Test Results
1200
Measured road load force
Regression estimates

1000• Front tires: Bridgestone
Coefficient ofBlizzak
2determination, R =0.9280 • Rear tires: Bridgestone

600

Sneaker• Estimated Values:a = 191.69, b = 2.54, c = 0.41

400
2000-200
0Data‐sets augmented
1020304050
35Time (sec)

60

7080
Measured velocity
Calculated velocity

95% C
Confidence
fidbbounds
d : 30a: 183 – 200
b: 1.5 – 3.5
c: 0.39 – 0.4325
Velocity (mm/s)

Force (N)
F

800

2015
10

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501020www.aanddtech.com
30
40
Time (sec)

50

60

7080

Slide 26

Validation Procedure

During coast‐down:
Generalized equation under all conditions (including coast‐down):
Tire traction/brakingforceWheel force
sensor
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Slide 27

Validation Procedure

3530

Velocity (mm/s)

25
20
15

Parameter
identification

1050-50

Parameter Validation
1020

30

40

50

60

70

80

90

Time (sec)

Estimates are poor outside the coast‐down region
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Slide 28

Residual Analysis
yAnalyze cross‐correlation coefficient of residuals:

0.1
Norrmalized cross correlation coefficient

Normalized cross correelation coefficient

An example:0.050-0.05-0.1-1000-800-600-400-2000Time

200

400

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600

800

1000

1.2
10.806
0.6
0.4
0.2
0-0.2
-1000

-800

-600

-400-200

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0Time

200

400

600

800

1000

Slide 29

Residual Analysis
yAnalyze cross‐correlation coefficient of residuals:
0.5
0.4

0.5

Residuals & steering angle

0.3
0.2
0.1
0-0.1
0102030

4050

Norm
malized cross-correlationn coefficient(Residuals & Acc pedal position)Normmalzed cross-correlationn coefficient(Residuals & Steeringg angle)

0.660

Residuals & accelerator
pedal ppposition

0.4

0.3

0.2

01
0.1

001020Time (sec)

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30
Time (sec)www.aanddtech.com

405060Slide 30

Limitations of Coast-down Tests
Procedure:
1. A long straight flat track is needed• SAE procedures requires a minimum speed band of 70 to 15 mph
2. Results include drivetrain losses and may not be suitable for some
applications
pp
3. Results are not consistent for all driving conditions, especially outside thecoast‐down region• Residuals are correlated with accelerator pedal position, steering
angle,…
4. Predictor basis is not orthogonal giving rise to the mathematicalcomplications due to multicollinearity• Estimates of a, b, c might be biased or have high variance

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Slide 31

Outline1. Introduction
2. Road load fundamentals
3. Instrumentation &sample data
4. Coast down method
5. Force measurement
methodth d

6. Summary
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Slide 32Identification usingg Force Method

Use regression to identify cID

35c = 0.5371

ID30

Velocity (m/s)

2520
151050-550Validation
50

100150Time (sec)

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200250Slide 33

Validation Test

R2 = 0.9926
0 992695% confidence limit forc: 0.53‐ 0.55
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Slide 34

Comparison of Coast-down & Force Method• Front tires: Bridgestone Blizzak• Confidential,Rear tires:Bridgestone
Sneaker
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Slide 35

Comparison of Coast-down & Force Method

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Slide 36

Comparison of Coast-down & Force Method

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Slide 37

Cross-correlation of Residuals
Normalzed cross-correlation coeffiicientN(Residuals & Steering angle))

0.5

Normalized cross-coorrelation coefficieent(Residuals & Acc
c pedal position)

0.6
0.5
0.4

0.4

Residuals & steering angle

0.3
0.2
0.1
0-0.101-0.20Residuals & accelerator
pedald l position
iti50

New residuals
100150(sec)Coastdown Time
residuals

0.3020.20.10-0.1-0.2050

New residuals
Coastdown residuals

100

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150
Time (sec)200
250
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200250Slide 38

Traction & Braking Scenarios
Assumptions:• Small inclination and side‐slip angles• No vertical displacement of the tireMg • No slipvx

ωMrrZTXr
Fa

Let WFS measurements be represented as Fx, Fz and MyThen,
From laser Doppler sensorRz
Fa

m: Mass of tire wheel assembly
J: Polar moment of inertia of tire‐wheel
assemblyy about the center of wheel hub
T: Applied torque at wheel hub
Fa: Tire‐road friction force

From encoder

Rz

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Determined before
the experiment

Slide 39

Calculation of ‘a’ from Force Method
6 constant speed tests for each speed, 18 tests total
RL TireAssumingg that wheel well aerodynamic
ylosses are negligible
g gat lowspeeds, calculate

a = 271
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Slide 40

Calculation of ‘b’ from Force Method

Mean RRF=85.4381 N
σRRF= 1.7629 N

Mean RRF=84.5861 N
σRRF= 1.9318
1 9318 N

Mean RRF=84.8949 N
σRRF= 2.2992 N

Very slight reduction in rolling resistance as speed increasesb≈0Proprietary and Confidential, A&D Technology, Inc.

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Slide 41

Summaryy
Coast‐down Method

Force Method

a = 191.69,
191 69 b = 2.54,
2 54 c = 0.41
0 41
• R2 = 0.9280

a = 271,271 b = 00, c = 0.5371
0 5371• R2 = 0.9926• Estimate variance is higherg• Estimation only over coast‐down;road load is under‐estimated fornon coast down conditions
non‐coast‐down• Residuals are correlated withdriver inputs• Changing the tire changes ‘c’substantially• Influence of drivetrain losses isincluded• Less instrumentation is needed• Less distortion of vehicle
aerodynamic• Estimation based on p
physics;y ;variance is very low• Estimation can be carried out
d i allll conditions
duringditi• Correlation is significantly
reduced• Changing the tires preserves ‘c’very closely• Influence of drivetrain losses isNOT included• More instrumentation required• Vehicle aerodynamics aremodified
to a greater extent
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Slide 42

Acknowledgementsg•••On-roadO
dddatat acquisition
i iti team:t– Takayasu Sasaki– Yuuki Sakurai– Masaaki Banno– Hiroki YamaguchiKenji Sato
Sato, A&D Technology,
Technology Ann Arbor
Dr. Michael Smith, A&D Technology, Ann Arbor

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Slide 43

References
1.
2.
3.
4.
5.
6.
7.

8.
9
9.
10.

11.

D.Yanakiev & I.Kanellakopoulos, “Speed Tracking and Vehicle Follower Control Design for
Heavy-Duty Vehicles”, Vehicle System Dynamics, Vol. 25, No. 4, 1996
D.Yanakiev & I.Kanellakopoulos, “Nonlinear
Nonlinear spacing policies for automated heavy-duty
heavy dutyvehicles”, IEEE Transactions on Vehicular Technology, Vol. 47, No. 4Bae, Ryu & Gerdes, “Road grade vehicle parameter estimation for longitudinal control usingGPS”, 2001 IEEE Intelligent Transportation Systems
C. Musardo, G. Rizzoni & B.P. Staccia, “A-ECMS: An Adaptive Algorithm for Hybrid Electric
Vehicle Energy Management” 2005 European Control Conference
Hong Yang & Joel Maguire, “Predictive Energy Management Control Scheme for a Hybrid
Powertrain System”
System , US Patent 2011/0066308 A1
www.Carsim.com
J Fredriksson, E Gelso, M Åsbogard, M Hygrell, O Sponton, NG Vagstedt, “On emission
certification of heavy-duty hybrid electric vehicles using hardware-in-the-loop simulation”,
Chalmers University of Technology, 2011
Karlsson, Hammarström, Sörensen & Eriksson, “Road surface influence on rolling resistance- Coastdown measurements for a car and an HGV”, VTI, 2011
JŻ bJ.Żebrowski,
ki “Traction“T ti efficiency
ffi i
off a wheeledh l d tractort t ini construction
t ti operations”,
ti” Automation
A ttiin Construction, Vol. 19, No. 2, 2010
Sandburg & Ejsmont, “Noise emission, friction and rolling resistance of car tires – Summary
pstudy”,
y , National conference on noise control engineering,gg, Dec 3-5,, 2000,,of an experimental
Newport beach, California
S.K. Clark, “A handbook for the rolling resistance of pneumatic tires”, 1979

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Slide 44

More Information
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