model-based analysis of wheel speed vibrations for road friction classification … ·...

MODEL-BASED ANALYSIS OF

WHEEL SPEED VIBRATIONS FOR

ROAD FRICTION CLASSIFICATION

USING MF-SWIFTAntoine Schmeitz, Mohsen Alirezaei

CONTENTS

Introduction

Road friction classification from wheel speed vibrations

Tyre modelling

Simulation environment

Evaluation of the estimation method

Concluding remarks

21 April 2015MODEL-BASED ANALYSIS OF WHEEL SPEED VIBRATIONS FOR ROAD FRICTION CLASSIFICATION USING MF-SWIFT

INTRODUCTION

Consider an Autonomous Emergency Braking (AEB) test:


INTRODUCTION

Now imagine that it is winter

and the road is icy?

What would happen with the cyclist

if the controller does not know the

friction coefficient between

tyre and road?

Probably this:


INTRODUCTION

Basic problem: identifying friction potential during normal driving conditions

Solution becomes more important with higher levels of vehicle automation

when task are taken over from the human driver

Interesting possible solutions was presented by Toyota (Umeno):

Wheel speed vibrations are used for friction estimation

T. Umeno: Estimation of Tire-Road Friction by Tire Rotational Vibration Model,

Review of Toyota CRDL, vol. 37 No. 3, 2002.


http://www.tytlabs.com/english/review/rev373epdf/e373_053umeno.pdf

INTRODUCTION

In 2006 this method was evaluated by Pavković et al. together with the slip-

slope method (SAE paper 2006-01-0556)

Able to distinguish different road friction conditions from both methods

Identified slip stiffnesses from both methods did however not agree

Contribution of this paper:

Review method and tyre modelling

Developing a simulation environment to study the estimation method in

terms of accuracy and robustness

Simulation environment to develop Integrated Friction Estimator using

multiple methods


ROAD FRICTION CLASSIFICATION

FROM WHEEL SPEED VIBRATIONS

Estimation method:

identify parameters of a second order linear time-invariant (LTI) system

use discrete time autoregressive (AR) model in combination with

instrumental variable (IV) method21 April 2015MODEL-BASED ANALYSIS OF WHEEL SPEED VIBRATIONS FOR ROAD FRICTION CLASSIFICATION USING MF-SWIFT

ABS wheel speed sensor

Signal conditioning

Bandpass filter

Estimation method

Tyre model• Slip stiffness• Friction

TYRE MODELLING

Basic idea:

Slip stiffness is measure

for friction

Slip stiffness drops at

low friction surfaces

Magic Formula model:

Slip stiffness is changed

by scaling factor LKX


TYRE MODELLING

Simple tyre model of Umeno

2nd order model for describing the 1st tyre in-plane resonance

Natural frequency affected by sidewall stiffness (e.g. inflation pressure)

Damping ratio increases with decreasing slip stiffness (i.e. friction)


( )22

1

2

1

RC

JJ

J

C

J

Cf

F

ba

a

an

κ

θ

θ

ζ

π

+=

=

TYRE MODELLING

MF-Swift

rigid ring

Magic Formula slip model

contact patch model

enveloping model

Well-validated

Accurately represents

primary tyre modes

(rigid ring modes)


SIMULATION ENVIRONMENT

Quarter vehicle model

rigid car body, wheel carrier and rim bodies

suspension stiffness and damping

linear elements, uncoupled in X, Z

TNO’s MF-Swift tyre model

Measured road profiles



Power spectral densities of wheel speed for different slip stiffness (i.e. friction)

Tyre resonance ‘disappears’ for low friction surfaces (i.e. small LKX)



Natural frequencies and damping ratios from eigenvalue analysis

Conclusions:

Damping increases with decreasing slip stiffness (i.e. friction)

(similar conclusion as Umeno et al.)

However: natural and peak frequencies (fn, fp) also decrease21 April 2015MODEL-BASED ANALYSIS OF WHEEL SPEED VIBRATIONS FOR ROAD FRICTION CLASSIFICATION USING MF-SWIFT

EVALUATION OF ESTIMATION METHOD


Algorithms have

been implemented

Results can be

compared

LKX = 0.5

Model Estimation

fp [Hz] 32 34

ζζζζ [-] 0.24 0.20


similar trends as found by others

generally resonance frequency is

rather accurately estimated

LKX = 0.2 (~ice): no excitation

inaccurate results

increased damping is still good

measure for low friction

Inaccurate simple tyre model:21 April 2015MODEL-BASED ANALYSIS OF WHEEL SPEED VIBRATIONS FOR ROAD FRICTION CLASSIFICATION USING MF-SWIFT

LKX = 1 LKX = 0.5 LKX = 0.2

Model Estimation Model Estimation Model Estimation

fp [Hz] 35 35 32 34 23 30

ζζζζ [-] 0.17 0.14 0.24 0.20 0.44 0.32

ζζζζref / ζζζζ [-] 1 1 0.71 0.70 0.39 0.44

( ) ( )( ) 22* LKX2

1

2

1,

2

1

RC

JJ

J

C

RC

JJ

J

C

J

Cf

F

ba

aF

ba

aan

κ

θ

κ

θθ ζπ ⋅

+=

+==


Influence of road roughness

as expected influence of road

roughness

deviations are relatively small

estimation method is quite

robust


Model Estimation

Smooth road Rough road 1 Rough road 2 Rough road 3

fp [Hz] 35 35 39 37 37

ζζζζ [-] 0.17 0.14 0.15 0.13 0.15

ζζζζref / ζζζζ [-] 1 0.93 1.1 0.93

CONCLUDING REMARKS

First tyre resonance as indicator for monitoring tyre-road friction is studied

Simulation environment to study this application has been developed:

results qualitatively agree well with results found in literature

reference for algorithm design and testing, i.e.: ‘real’ values are known

frequencies and damping ratios can be estimated with reasonable accuracy

trends observed with changing road friction are consistent

Review of method:

Simple tyre model (Umeno) is insufficiently accurate to identify slip stiffness

MF-Swift model can be used to translate identified frequencies and damping

ratios to correct slip stiffness values21 April 2015MODEL-BASED ANALYSIS OF WHEEL SPEED VIBRATIONS FOR ROAD FRICTION CLASSIFICATION USING MF-SWIFT

CONCLUDING REMARKS

Next steps:

Test the method using real car data

identify operating range, accuracy and limitations

Implement method in an Integrated Friction Estimator

sensor / estimator fusion

basic idea: several algorithms should give the same tyre characteristic

values (i.e. comparing apples with apples)

one source (tyre model) to relate tyre characteristic values to friction

estimate


THANK YOU FOR YOUR ATTENTION

model-based analysis of wheel speed vibrations for road friction classification … ·...

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