Tire Sensors for the Measurement of Slip Angle and FrictionCoefficient and Their Use in Stability Control Systems

Gurkan Erdogan, Sanghyun Hong, Francesco Borrelli, Karl Hedrick

Department of Mechanical EngineeringDepartment of Mechanical Engineering

University of California at Berkeley

Content � Objective

� Motivation� Integration of Tire Sensors and Vehicle Control Systems

� Background

� Estimation Algorithms

� Slip Angle

� Tire-Road Friction Coefficient

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� Tire-Road Friction Coefficient

� Accelerometer Based Tire Sensor� Lateral Acceleration

� FAE Simulations

� Surface Transition Tests

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Objective

� Understanding Tire Deformations

� Deflection Profiles

� Acceleration Profiles

� Developing Estimation Algorithms

� Slip Variables

� Friction Coefficient

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� Tire Forces

� Integration of Tire Sensors and Vehicle Control Systems

� Stability Control Systems

� Traction Control Systems

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� Estimation of slip angle, slip ratio, tire forces and tire road friction coefficient may

lead to significant improvements in vehicle control systems.

� Slip angle is directly related to skidding,

� Slip ratio is directly related to loss of traction

� Vertical forces are directly related to rollover

� Friction coefficient provides a good measure of the available tire forces.

Motivation

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MotivationIntegration of Tire Sensors and Vehicle Control Systems

Benefit of Friction Estimation

� A stability control system enhanced with tire sensors can …

� Generate slip angle and yaw rate references based on the friction information coming from the roadway.

� Follow the references smoothly.

EXAMPLE SCENARIO :

Default value of the friction

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Default value of the friction coefficient inside the controller is set to a high friction value, however the driver is executing a double lane change maneuver on a slippery road surface with a low friction coefficient.

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MotivationIntegration of Tire Sensors and Vehicle Control Systems

Benefit of Slip Angle Estimation

� Uncertainties of each sensor and observer used in the estimation of tire slip angles reduce the accuracy and reliability of slip angle estimations.

+−= −

x

fy

ffv

Lv ψδα

&1tan

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� Estimation of the tire slip angles directly from the tire sensor measurements can improve the accuracy and reliability.

xv

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Tire Deformations

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� Sidewall Deformations� Radial

� Lateral

� Tangential

� Tread Deformations� Radial

� Lateral

� Tangential

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Background

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� G. Erdogan, L. Alexander, R. Rajamani, “Estimation of Tire-Road Friction Coefficient Using a Novel Wireless Piezoelectric Tire Sensor,” IEEE Sensors, Volume 11, No. 2, pp. 267-279, February 2011.

� G. Erdogan, L. Alexander, R. Rajamani, “Measurement of Uncoupled Lateral Carcass Deflections with a Wireless Piezoelectric Sensor and Estimation of Tire Road Friction Coefficient”, Proceedings of the ASME Dynamic Systems and Control Conference, Cambridge, MA, September 2010

� G. Erdogan, L. Alexander, R. Rajamani, “A Novel Wireless Piezoelectric Tire Sensor for the Estimation of Slip Angle”, Measurement Science and Technology, Volume 21, No. 1, pp. 015201 , January 2010

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qqcp

qcp

×++=

+=

ω&&&

Estimation Algorithms – Slip Angle

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α−=∂∂

=∂∂

x

v

x

u0

cgy

cgx

Vs

v

x

vxV

Vs

u

x

uyV

∂∂

+∂∂

−−−=

∂∂

+∂∂

−=

ϕα

ϕ • Full Adhesion

• No Turn Slip

• Steady State

• Small Slip Angle

At the beginning of the contact patch, the slope of the deflection curve can be used to determine the slip angle.

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Estimation Algorithms –Lateral Force & Aligning Moment

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Lateral Deflection Profile of Carcass Inside the Contact Patch:

lat

y

b

yaw

zb

bend

y

bc

Fx

c

Mx

c

Fy +

′+= 2

2

Bend Yaw ShiftSuperposed

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Brush Model

Estimation Algorithms – Friction Coefficient

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( )( )

( )( )

( )( )

+−=

slslsl

zy FFαα

αα

αα

µ2

2

tan

tan

3

1

tan

tan1

tan

tan3

( )slz

py

F

acαµ tan

3

2 2

=

Lateral Tire Force :

Friction Coefficient :

( )( )

( )( )

( )( )

( )( )

}|tan

tan|)

tan

tan(3|

tan

tan|31{

tan

tan 32'

slslslsl

zz aFMαα

αα

αα

αα

µ −+−−=Aligning Moment :

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Accelerometer Based Tire Sensor� 3D MEMS accelerometer is located at the centerline of the inner liner.� X, Y and Z coordinates of the accelerometer are aligned with the tangential, lateral and radial directions of the tire, respectively.

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Tire FEA Model

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Coordinate Transformation

FEA results are transformed from inertial frame to accelerometer body frame in order to simulate the measured lateral acceleration profiles.

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Experimental Verification

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Slip Angle Estimations based on FAE Model

V = 40 km/hr

µµµµ = 0.9

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Friction Estimations based on FAE Model

V = 40 km/hr

αααα = 2o

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Recent Tests of Tire Sensors on a Vehicle

Lateral acceleration

profiles measured on a

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profiles measured on a

vehicle at a slip angle

close to zero.

Lateral Deflection and Acceleration Profiles

Vθδα −=

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Lateral Deflection and Acceleration Profiles

Vθδα −=

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Lateral Deflection and Acceleration Profiles - All Four Tires

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Lateral Deflection and Acceleration Profiles - All Four Tires

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Acknowledgements

� Pirelli Tyre, SpA

� Giorgio Audisio

� Riccardo Tebano

� Roberto Villa

� Marco Sbrosi

Ford Research and Innovation Center

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� Ford Research and Innovation Center

� Davor Hrovat

� Eric Tseng

� Michael Fodor

� Mitch McConnell

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Thank you for listening …

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