RIDE QUALITY ANALYSIS OF ACTIVE BY F ARIED BIN …

IN -· LIB;MRY , · -TERNATIONAL ISLAMIC UNIVERSITY ~1ALAYS1.

RIDE QUALITY ANALYSIS OF ACTIVE SUSPENSION SYSTEMS FOR OFF-ROAD VEHICLE

BY

F ARIED BIN HASBULLAH

A dissertation submitted in fulfilment of the requirement for the degree of Master of Science in Mechatronics

Engineering

Kulliyyah of Engineering International Islamic University

Malaysia

AUGUST 2012 -

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ABSTRACT

In designing passive suspensions, a compromise has to b~ made between ride comfort and car handling. For an off-road vehicle that requires both good ride comfort and good handling capability, a passive suspension alone is not enough. Therefore, there is a need to introduce active elements to further improve vehicle suspensions, which could offer both better ride comfort and car handling to this type of vehicle. This work deals with dynamics and control methods analysis of active suspension systems for off-road vehicles. Comprehensive comparison on three different configurations; 2-axle, 3-axle and 4-axle half-vehicle models were conducted to analyze the effect of using active control methods. The application of two control methods, namely LQR and fuzzy logic controls have been analyzed and compared with passive systems. Sprung mass vertical and pitch acceleration responses were analyzed for measurements of ride quality and road handling. Suspension deflection and tire deflection responses were observed to identify any compromise in the other aspects of vehicle dynamics. Results show that the LQR and FLC successfully controlled the active suspension, improving ride quality and handling of the vehicles without compromising the rattle-space requirement and road holding performance of the vehicles. Comparison of all models also shows that in general, improving ride quality performance will also improve vehicle handling. Moreover, it is observed that FLC control requires less amount of actuator force compared to LQR control to achieve the desired performances.

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APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion, it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science in Mechatronics Engineering.

~eed Fekry Faris

Supervisor ~ ~

~ani Abdul Muthalif Co-Supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science in Mechatronics Engineering.

Mahbubur Rashid Examiner (Internal)

Hishamuddin Jamaluddin Examiner (External)

This dissertation was submitted to the Department of Mechatronics Engineering and is accepted as a fulfillment of the degree of Mast Science in Mechatronics Engineering.

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Md. Raisuddin Khan Head, Department of Mechatronics Engineering

Dean, Kulliyyah of Engineering

DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Faried Bin Hasbullah

Signature: ... Date: ... :t/~/+RI ?:- ..•..••

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INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

Copyright© 2012 by International Islamic University Malaysia. All rights reserved.

RIDE QUALITY ANALYSIS OF ACTIVE SUSPENSION SYSTEMS FOR

OFF-ROAD VEHICLE

I hereby affirm that The International Islamic University Malaysia (IIUM) holds all

rights in the copyright of this Work and henceforth any reproduction or use in any

form or by means whatsoever is prohibited without the written consent of IIUM. No

part of this unpublished research may be reproduced, stored in a retrieval system, or

transmitted, in any form or by any means, electronic, mechanical, photocopying,

recording or otherwise without prior written permission of the copyright holder.

Affirmed by Faried Bin Hasbullah

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...... JL $. /.':<?. '. ?: ... Date

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ACKNOWLEDGEMENTS

First and foremost, gratitude and appreciation are for Allah, the Most Merciful and Most Compassionate for granting me a precious opportunity to complete this work and granted me health and strength.

I would like to gratefully thank my supervisor, Prof. Dr. Waleed Fekry Faris for this scholarly guidance and effort in assisting me in this work. Truly this work shall not be completed without his continuous encouragement and support.

I would like to thank my co-supervisor, Dr, Asan Gani Abdul Muthalif for his motivation and guidance in keeping me going with the work and always making himself available for any assistance.

Not to forget my colleagues at the Vehicle Dynamics Lab of the Kulliyyah of Engineering, HUM. Also, to all academic and non-academic staff for their assistance during the period of my study.

This work would not be possible without the scholarship provided by the Government of Malaysia and International Islamic University Malaysia throughout the study period.

Last but not least, I owe the greatest debt of gratitude to my beloved parents and family. It would surely be impossible for me to complete this work without their love, support and prayers.

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TABLE OF CONTENTS

Abstract .......................................................................................................................... ii Abstract in Arabic ........................................................................................................ .iii Approval Page ............................................................................................................... iv Declaration ..................................................................................................................... v Acknowledgement ........................................................................................................ vii List of Tables .................................................................................................................. x List of Figures ............................................................................................................... xi List of Abbreviations ................................................................................................... xiv List of Symbols ............................................................................................................ xv

CHAPTER 1: INTRODUCTION ............................................................................... 1 1.1 Background ...................................................................................................... 1 1.2 Problem statement and its significance ........................................................... 3 1.3 Research objectives ......................................................................................... 3 1.4 Research Methodology .................................................................................... 4 1.5 Scope of Research ........................................................................................... 5 1.6 Dissertation Outline ......................................................................................... 6

CHAPTER 2: LITERATURE REVIEW .................................................................. 8 2.1 Introduction ..................................................................................................... 8 2.2 Vehicle Response to Excitations ..................................................................... 8 2.3 Control Methods ............................................................................................ 10 2.4 Multiple Axle Vehicle Models ...................................................................... 30 2.5 Summary ........................................................................................................ 33

CHAPTER 3: MODELING AND PERFORMANCE CRITERIA ....................... 35 3.1 Introduction ................................................................................................... 35 3.2 Vehicle Ride Models ..................................................................................... 35 3.3 Two-axle half car model ................................................................................ 36 3.4 Three-axle half car model .............................................................................. 39 3.5 Four-axle half car model. ............................................................................... 41 3.6 Disturbance Model ........................................................................................ 44 3.7 Performance Criteria ...................................................................................... 50 3.8 Summary ........................................................................................................ 52

CHAPTER 4: ACTIVE CONTROLLER DESIGN ................................................ 54 4.1 Introduction ................................................................................................... 54 4.2 LQR Controller .............................................................................................. 54 4.3 Fuzzy Logic Controller .................................................................................. 56 4.4 Optimization of Controller's Parameters ....................................................... 59

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4.5 Validation ...................................................................................................... 63 4.6 Summary ........................................................................................................ 64

CHAPTER 5: RESPONSE TO POTHOLE INPUT ............................................... 65 5 .1 Introduction ................................................................................................... 65 5.2 Optimized Parameters .................................................................................... 65 5.3 Response for Two-Axle Vehicle ................................................................... 66 5.4 Response for Three-Axle Vehicle ................................................................. 69 5.5 Response for Four-Axle Vehicle ................................................................... 73 5.6 All Model Comparison .................................................................................. 76 5.7 Summary ........................................................................................................ 79

CHAPTER 6: RESPONSE TO RANDOM INPUT ................................................ 80 6.1 Introduction ................................................................................................... 80 6.2 Optimized Parameters .................................................................................... 80 6.3 Response for Two-Axle Vehicle ................................................................... 81 6.4 Response for Three-Axle Vehicle ................................................................. 84 6.5 Response for Four-Axle Vehicle ................................................................... 87 6.6 All Model Comparison .................................................................................. 89 6.7 Summary ........................................................................................................ 91

CHAPTER 7: CONCLUSION AND RECOMMENDATION ............................... 92 7 .1 Conclusion ..................................................................................................... 92 7 .2 Main contribution .......................................................................................... 93 7.3 Recommmendation for Future Work ............................................................. 94

BIB LI OG RAP HY ...................................................................................................... 95

APPENDIX A: STATE-SPACE REPRESENTATION ....................................... 100 APPENDIX B: SAMPLE MATLAB CODE ......................................................... 103 APPENDIX C: SAMPLE SIMULINK BLOCK ................................................... 107

List of Publications ................................................................................................... 110

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LIST OF TABLES

Table No. Page No.

2.1 Summary of works done by other researches 33

3.1 Example of sensors for measuring the states of a two-axle 39 vehicle

3.2 Model parameters for the two, three, and four-axle 43 vehicles

3.3 State variables and inputs description for the two, three, 44 and four-axles vehicles

3.4 Value of N and Csp for two unprepared terrains (Wong, 47 2008)

3.5 Classification of road roughness by ISO 48

5.1 LQR controller's parameters for 2, 3, and 4-axle vehicles 65 for pothole input

5.2 Gains of the FLC for two, three, and four axle vehicles for 66 pothole input

5.3 PTP response to pothole input for two, three, and four- 77 axle vehicles

5.4 Settling time for two, three, and four-axle vehicles (in 78 second, s)

6.1 Gains of the FLC for two, three, and four axle vehicles for 80 random input

6.2 Parameters of the LQR controller for 2, 3, and 4-axle 81 vehicles for random input

6.3 Comparison of all responses bound with 90% probability 90 for passive, active LQR, and active FLC systems

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LIST OF FIGURES

Figure No. Page No.

1.1 Flow diagram of research methodology 5

2.1 FPID scheme proposed by Yang et al. (2004) 19

2.2 FPID scheme proposed by Bei et al. (2008) 21

2.3 Structure of FPID controller by Xinjie and Shengjin (2009) 21

2.4 Multi-wheeled tracked vehicle (Srinivasa et al., 2003) 31

2.5 3D view of a light armoured vehicle for a class of mobile gun 32 system (Hudha et al., 2008)

3.1 Block diagram for active suspension system 36

3.2 Two-axle 4-DOF half-car model 38

3.3 Three-axle 5-DOF half-car model 39

3.4 Four-axle 6-DOF half-car model 41

3.5 Pothole track at the Gerotek test facilities 45

3.6 Pothole input for 2-axle vehicle model 45

3.7 Simulink block to generate road profile 46

3.8 PSD as a function of spatial frequency for two types of 48

unprepared terrain

3.9 PSD of ISO road classes and unprepared terrains vs spatial 49 frequency

3.10 Generated random surface profile 49

4.1 Block diagram for the LQR controller 56

4.2 Membership function for FLC's inputs and output 58

4.3 Block diagram for Fuzzy Logic Controller 58

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4.4 Rule base for the fuzzy logic controller 59

4.5 Flowchart for genetic algorithm 60

4.6 Sprung mass displacement response by Kumar and Vijayarangan 63

(2006b) (top) and reproduced result (bottom)

4.7 Suspension travel response by Kumar and Vijayarangan (2006b) 64 (top) and reproduced result (bottom)

5.1 ms vertical acceleration response for 2-axle vehicle - pothole 67 input

5.2 ms vertical acceleration ts and PTP values for 2-axle vehicle 67

5.3 ms pitch angular acceleration ts and PTP values for 2-axle vehicle 68

5.4 Suspension deflection ts and PTP values for 2-axle vehicle 69

5.5 Tire deflection ts and PTP values for 2-axle vehicle 69

5.6 Sprung mass vertical acceleration response for 3-axle vehicle - 70 pothole input





5.11 ms vertical acceleration response for 4-axle vehicle - pothole 73 input





6.1 ms vertical acceleration response for 2-axle vehicle - random 82

input

6.2 Comparison of ms responses bound with 90% probability (2-axle) 82

6.3 Comparison of suspension deflection responses bound with 90% 83

probability (2-axle)

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6.4 Comparison of tire deflection responses bound with 90% 83



input

6.6 Comparison of ms responses bound with 90% probability (3-axle) 85






input

6.10 Comparison ofms responses bound with 90% probability (4-axle) 88


probability ( 4-axle)


probability ( 4-axle)

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DOF

FIS

FLC

FPID

GA

HTGC

ISO

LMI

LQG

LQR

MF

MR

NF

OFA

PID

PISMC

PSD

PTP

RMS

SF

LIST OF ABBREVIATIONS

Degree-of-freedom

Fuzzy inference system

Fuzzy logic controller

Fuzzy-PIO

Genetic algorithm

Hybrid Taguchi-genetic algorithm

International Organization for Standardization

Linear matrix inequalities

Linear quadratic gaussian

Linear quadratic regulator

Membership function

Magneto-rheological

N euro-Fuzzy

Orthogonal functions approach

Proportional-integral-derivative

Proportional integral sliding mode control

Power spectral density

Peak-to-peak

Root-mean-square

Scaling factor

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r

sprung mass

unsprung mass

vehicle velocity

LIST OF SYMBOLS

time delay between two consecutive axle

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1.1 BACKGROUND

CHAPTER ONE

INTRODUCTION

An off-road vehicle is referred to any type of vehicle that is capable of driving on and

off paved or gravel surface. In general, it is characterized by having large tires with

deep, open treads and a flexible suspension, or even caterpillar tracks. Other types of

vehicles that do not travel on public streets or highways are generally referred to as

off-highway vehicles, which would include cranes, tractors, bulldozers, backhoes and

forklifts (Faris et al., 2009).

Unlike a road vehicle, an off-road vehicle is subjected to ride vibrations of low

frequency and large amplitude, which cause bodily discomfort to the operator, and

limit the mobility and performance of the vehicle. Generally, the speed of off-road

vehicles over rough terrain is determined by the ride quality not by the engine power.

Forthis reason, researches are currently being undertaken to improve the ride

dynamics of these vehicles using an advanced suspension system (BenLahcene et al.,

2009; Srinivasa et al., 2003).

Suspension system is the main tool to achieve ride comfort and vehicle control.

The design of passive suspension has always been focused on obtaining a good

compromise between these two goals. However, structural limitations prevent passive

suspension from achieving the best performances for both targets. For example, soft

springs facilitate good ride characteristics at the expense of increased wheel motion

and increased variations in dynamic tire loadings on rough roads. On the other hand,

good road handling characteristics and smaller wheel motion is an attribute of larger

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spring rates. Thus, spring rates should be chosen large enough to limit wheel motion

and dynamic tire variations but small enough to provide a comfortable ride (Barr &

Ray, 1996). As pointed by Barr and Ray (1996), the choice and arrangement of the

elements of passive suspension has evolved into a near optimal design through many

years of experimentation and testing.

Active suspension system has the capability to continuously adjust itself, hence

has a better design trade-offs compared to a conventional suspension system. The

desired additional force in active suspension system is usually employed by hydraulic

or pneumatic actuators which are secured in parallel with a spring and damper. The

amount of force required for the actuators are controlled by the controller based on the

motions of the vehicle which is received from various sensors located at different

points of the vehicle.

A lot has been reported on the control strategies of the active suspens10n

system for passenger car, which basically falls under the category of active vibration

isolation. These researches on active suspensions however are concentrated on a

passenger car model. Little works have been done on multiple-axle off-road vehicle.

Moreover, works on vehicle other than passenger car are mainly done for two-axle

railway vehicles as produced by Mei et al. (1998) and Selamat et al.(2009).

In recent years, a lot of studies, analyses, and optimizations have been

conducted in the area of semi-active suspension systems for multiple-axle off-road

vehicle. Among the most recently published are by Faris et al.(2009b) who performed

analysis of semi-active suspension systems for four-axles off-road vehicle using half

vehicle model and by BenLahcene et al. (2009) who did the same analysis but for two

axle, three-axle, and four-axle off-road vehicle. Therefore, to further improve the ride

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quality of the off-road vehicles, attempt is made to introduce an active element to the

systems.

This work is intended to look at the ride quality performance of active

suspension system for three configurations of an off-road vehicle, namely the two

axle, three-axle and four-axle by using a half-vehicle model.

1.2 PROBLEM STATEMENT AND ITS SIGNIFICANCE

In designing passive suspensions, a compromise has to be made between ride comfort

and car handling. For example, softer suspensions could be used to improve ride

comfort while stiffer suspensions could be used to improve car handling. For an off

road vehicle that requires both good ride comfort and good handling capability, a

passive suspension alone is not enough. Therefore, there is a need to introduce active

elements to further improve vehicle suspensions, which could offer both better ride

comfort and car handling to this type of vehicle.

1.3 RESEARCH OBJECTIVES

The objectives of this research project are:

1. To model active and passive suspension system for three configurations of

off-road vehicles, namely: two-axle, three-axle, and four-axle vehicles

using half-vehicle models.

2. To implement LQR controller for the suspension systems to improve ride

quality of the vehicle.

3. To develop fuzzy logic controller (FLC) for the suspension systems to

improve ride quality of the vehicle.

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4. To evaluate the performance of the LQR, FLC and passive systems using

two types of inputs namely pothole and random excitation.

1.4 RESEARCH METHODOLOGY

The methodology chosen to conduct this research is as the following:

1. Critical literature review.

The research begins with literature review on the related works. In general, the

related works can be divided into 3 categories - vehicle response to excitations,

control methods, and multiple axle vehicle models.

2. Derivation of mathematical model of the systems.

Mathematical model of active and passive off-road half-vehicle suspension

systems are developed. Three configurations are presented for the active

suspension analyses which are two-axle, three-axle and four-axle vehicles.

3. Design of LQR controller.

LQR controller is investigated and designed for the active suspension system.

4. Design of fuzzy logic controller.

FLC is investigated and designed for the active suspension system.

5. Validation of active suspension model.

To ensure that all MATLAB codes and SIMULINK models used in this work

is valid, they are used to reproduce and compare with work done by other

researchers in this area of research.

6. Simulation of the systems.

The simulation of the LQR, FLC and passive suspension systems were done

using MATLAB software.

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7. Analysis of result.

The responses of the systems are analyzed and compared between each active

controller and vehicle models as well as with the responses of the passive

system according to performance criteria discussed in chapter 3. Figure 1.1

shows the steps that have been employed in this research.

Figure 1.1: Flow diagram of research methodology

1.5 SCOPE OF RESEARCH

The goals of an automotive suspension usually can be categorized into two: vehicle

control and ride comfort. Control is achieved by keeping the vehicle body from

pitching and rolling excessively, as well as maintaining good contact between the tire

and the road. On the other hand, comfort is provided by isolating the vehicle's

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passengers from road (surface) disturbances. This work focuses on improving ride

comfort while maintaining vehicle control.

Most of the work in active suspension is limited to only passenger car and

railway vehicles. Works on off-road vehicles are very limited and often focuses on

one type of vehicle. To the author's knowledge, there has been no attempt on analysis

for two, three, and four-axle off-road vehicles which are attempted in this work.

In this work, vehicle responses to specific off-road profiles are studied. Hence,

this work focuses on time-domain analysis. To reduce the complexity of the research,

a linear and full state system is assumed. The dynamics of the actuators is not taken

into consideration since the system is nonlinear if the dynamics of the actuators is

taken into consideration due to the hydraulic properties and the presence of

uncertainties in the system.

1.6 DISSERTATION OUTLINE

In chapter 2, related literature review is presented. The review is grouped into three

parts, namely vehicle response to excitations, control methods, and multiple axle

vehicle models.

In chapter 3, general vehicle ride models are presented. Then, models of two,

three, and four-axle vehicle as well as the disturbance models are presented and their

equations of motion are derived. Detail discussion on the types of analyses and

performance criteria is also presented.

In chapter 4, design of two active controllers, namely LQR and fuzzy logic

controllers are presented. Then, optimizations of controllers' parameters are discussed.

Validation of MATLAB codes and models used throughout this work is also

presented.

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In chapter 5 and 6, comparison of results between all models is presented.

Sprung mass vertical acceleration, pitch angular acceleration, suspension and tire

deflections responses are compared between all control methods. Comparisons are

made between passive system, which is considered as reference, and the various active

controllers for all vehicle models and input types.

Finally, conclusion and recommendation for future work 1s presented in

chapter 7.

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2.1 INTRODUCTION

CHAPTER TWO

LITERATURE REVIEW

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In this chapter, works done by other researchers related to work on active suspension

system are reviewed. This section is divided into three subsections: vehicle response

to excitations, control methods, and multiple axle vehicle models. Finally, the research

gaps, which lead to the work in this thesis, are summarized at the end of this chapter.

2.2 VEHICLE RESPONSE TO EXCITATIONS

Vehicle response to excitations is usually modeled in two approaches. First approach

is using discrete modeling. This approach breaks down the car into lumped systems of

masses, springs, and dampers, which is the most popular among researchers due to its

simplicity and it is argued that it gives reasonable results with minimum computation

effort (Wong, 2008). The second approach is using what is known in dynamics as

continuous modeling. In this approach, the car is taken completely including its

geometry into consideration. The main tool for this approach is Finite Element

Method. This approach is becoming popular in industries but the main disadvantages

are the computational effort and the need for an expertise in using FEM. As

mentioned earlier, discrete system approach is still the most common among

researchers.

Stone and Demetriou (2000) have described a detail derivation of a full car

vehicle model with 6-DOF using the Newtonian approach. This model is able to

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simulate the effect of suspension (ride) as well as braking and steering (handling) in

all three translational motions (vertical, forward and side), pitch, roll and yaw (heave)

directions. General assumptions in deriving the model are the vehicle mass could be

lumped into a single mass which is referred to as the sprung mass, the vehicle center

of gravity is located above the roll and pitch centers, the vehicle suspension springs

will not be allowed to top out during maneuvering; the suspension springs will always

be in compression, aerodynamic lift and drag force, and tire rolling resistance are

neglected, the vehicle remains grounded at all times, i.e. the four tires never lose

contact with the ground, and the deflections in the pitch and roll planes are small, and

may be simplified with small angle approximation.

Gillespie and Karamihas (2000) studied quarter car model under the effect of

road roughness. They found that quarter car models to be adequate for discriminating

the roughness of the road on a scale that correlates well to the public judgment of its

severity.

Soliman et al. (2001) aimed at introducing a solution of the vehicle dynamics

problem by studying the effect of various types of suspension element on the vehicle

suspension system performance. They derived mathematical models of conventional

quarter car model, quarter car model with twin spring system, quarter car fully active

system and half car conventional model and conducted experiment to verify the

theoretical analysis. They concluded that load carrying capacity of a vehicle rear

suspension can be solved using stiff suspension spring system or a twin spring

suspension · system, a fully active suspension system can improve the vehicle

performance criteria significantly but at a high cost, the tire damping has a very small

effect on the vehicle ride comfort, when the tire stiffness parameter is increased, the

systems have higher wheel resonance peaks in the dynamic tire load response, the

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