vii TABLES OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABREVIATIONS LIST OF SYMBOLS LIST OF APPENDICES ii iii iv v vi vii xi xiii xviii xix xxi 1 INTRODUCTION 1 1.1 Introduction 1 1.2 Research Background 2 1.3 Problem Statements 5 1.4 Objectives and Scope of the Research 6 1.5 Research Contributions 7 1.6 Organization of the Thesis 8 2 LITERATURE REVIEW 11 2.1 Introduction 11 2.2 Classification of Vehicle Suspension Systems 12 2.2.1 Passive Suspension 12 2.2.2 Semi-Active Suspension 13 2.2.3 Active Suspension 15 2.3 Performance Index 16 2.4 Pneumatic Active Suspension Control Strategies 18 2.5 Active Force Control 19 2.6 Summary 23
viii 3 METHODOLOGY 25 3.1 Introduction 25 3.2 Modelling and Simulation 25 3.3 Experimental Study 31 3.4 Summary 33 4 SKYHOOK ADAPTIVE NEURO ACTIVE FORCE CONTROL 34 4.1 Introduction 34 4.2 The SAFAFC Scheme 35 4.2.1 Adaptive Fuzzy System 35 4.2.2 Pneumatic Actuator System 39 4.2.2.1 Load Dynamics 40 4.2.2.2 Cylinder Chambers Dynamics 41 4.2.2.3 Valve Model Dynamics 42 4.2.3 Controller Design 43 4.2.3.1 Innermost Control Loop (PI Control) 43 4.2.3.2 Outermost Control Loop (PID Control) 45 4.2.3.3 Intermediate Control Loops (Skyhook and AFC) 47 4.3 Stability Analysis 54 4.4 Simulation 56 4.4.1 Road Profiles as Disturbances 59 4.5 Results and Discussions 60 4.5.1 Sinusoidal Wave Road Profile (Frequency 1.5 Hz, Amplitude 3.5 cm) 61 4.5.2 Other Results for Different Road Profiles 65 4.5.3 Effect of Load Variation 68 4.6 Summary 71 5 SKYHOOK ADAPTIVE FUZZY ACTIVE FORCE CONTROL 72 5.1 Introduction 72
ix 5.2 The SANAFC scheme 72 5.3 Neural Network Model 73 5.4 Controller Design 77 5.4.1 Adaptive Neural Network and Its Application in the AFC Loop 77 5.5 Simulation 82 5.6 Results and Discussion 83 5.6.1 Simulation Results in Time Domain 84 5.6.2 Simulation Results in Frequency Domain 96 5.7 Summary 104 6 EXPERIMENTAL IMPLEMENTATION OF THE SANAFC SCHEME 106 6.1 Introduction 106 6.2 Quarter Car Suspension Test Rig 106 6.2.1 Passive Suspension 108 6.2.2 Data Acquisition System 109 6.2.3 Sensors 110 6.2.3.1 Accelerometer 111 6.2.3.2 Displacement Sensor 112 6.2.3.3 Pressure Sensor 113 6.2.4 Pneumatic Actuator System 114 6.3 Controller Development 115 6.3.1 Force Tracking Controller 115 6.3.2 Outermost Loop Controller 116 6.3.3 Intermediate Loop Controller 117 6.3.3.1 Skyhook 118 6.3.3.2 AFC scheme 118 6.5 Results and Discussions 122 6.5.1 Time Domain Response 123 6.5.2 Frequency Domain Response 131 6.6 Summary 134
x 7 DISCUSSION ON SIMULATION AND EXPERIMENTAL DIFFERENCES 135 7.1 Introduction 135 7.2 General Findings of the Study 136 7.3 Main Simulation and Experimental Differences 140 7.3.1 Values of the Car Model Parameters 141 7.3.1.1 Sprung Mass 141 7.3.1.2 Unsprung Mass 141 7.3.2 Force Tracking Control of the Pneumatic Actuator 142 7.3.4 Relative Measurement Performance of the Various Control Schemes Compared to the Passive Suspension 143 7.4 Summary 143 8 CONCLUSION AND RECOMMENDATIONS 144 8.1 Conclusion 144 8.2 Recommendations for Future Works 146 REFERENCES 147 Appendices A-C 154-168
xi LIST OF TABLES TABLE NO. TITLE PAGE 2.1 The summarised literature review of the active suspension control strategy 20 2.2 The summarised literature review of the AFC strategy 23 3.1 The vehicle data 33 3.2 The pneumatic data 33 4.1 The RMS error values of the inverse dynamic model response 54 4.2 Open loop characteristic of a quarter car model 59 4.3 RMS error values of the model response 63 4.4 Percentage improvement of the model compared with passive suspension 63 4.5 A summary of results RMS error values of the model response with different road profiles 67 4.6 A summary of percentage improvement results of the model compared with passive suspension with different road profiles 68 4.7 A summary of results for the SAFAFC scheme with different road profiles Error! Bookmark not defined. 5.1 RMS error values of the inverse actuator model response using adaptive NN 81 5.2 RMS error values for the parameters of interest of the SANAFC and SANAFC schemes 90 5.3 Percentage RMS error values for the parameters of interest of the SANAFC and SANAFC schemes compared with passive suspension apply different road profiles 91 5.4 A summary of results for the SANAFC scheme with different road profiles 92
xii 6.1 Responses of the SANAFC, PID and passive suspension schemes 129 6.2 Percentage responses of the SANAFC and PID compare with passive suspension schemes 130 6.3 A summary of results for the SANAFC scheme with different road profiles 131 7.1 A summary of average percentage improvement results for the SAFAFC and SANAFC schemes compared with passive suspension using different road profiles 138 7.2 A summary of results for the SANAFC scheme with different road profiles 139
xiii LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 AFC concept applied to an active suspension system 5 2.1 Passive suspension system 13 2.2 Semi-active suspension system 14 2.3 Active suspension system 16 2.4 Power spectral density of various terrains 17 2.5 Human tolerance limits for vertical vibration 18 3.1 The flowchart of the research methodology 26 4.1 The proposed SAFAFC scheme 36 4.2 The structure of a fuzzy logic controller 38 4.3 A representation of the Gaussian membership function 39 4.4 The adaptive fuzzy structure 39 4.5 The pneumatic system 41 4.6 Force tracking control pneumatic actuator 44 4.7 Force tracking control pneumatic actuator 45 4.8 Outermost loop PID controller configuration 47 4.9 Fine tuning the PID controller 48 4.10 The intermediate loops comprising the skyhook and AFC subschemes 49 4.11 Skyhook damper configuration 49 4.12 The skyhook in the intermediate loop controller scheme 50 4.13 Tuning B sky for the skyhook method 50 4.14 Inverse dynamic of the pneumatic actuator using AF 52 4.15 Membership functions for the input and output parameters of AF 53 4.16 Response of the identified inverse dynamic model of the pneumatic actuator 53 4.17 Estimated mass of the body using AF 55
xiv 4.18 The SAFAFC block diagram 55 4.19 Simplification of the SAFAFC block diagram 56 4.20 Simulink block diagram of a passive suspension 58 4.21 Bode plot of a passive suspension 59 4.22 Simulink diagram of the SAFAFC 60 4.23 Road profile inputs as disturbances 61 4.24 The time response simulation of all the control schemes 63 4.25 The frequency domain results for all the control schemes 65 4.26 Desired and actual forces of the SAFAFC scheme 66 4.27 The computed estimated mass of the body of the SAFAFC scheme 66 4.28 The time domain results of the SAFAFC strategy with load variation and sinusoidal road profile using f = 1.5 Hz and am = 3.5 cm 70 4.29 The frequency domain results of the SAFAFC strategy with load variation and sinusoidal input road profile with f = 1.5 Hz and am = 3.5 cm 71 5.1 The proposed SANAFC scheme 73 5.2 Model of an artificial neuron 74 5.3 The structure of a three-layered multilayer perceptron 75 5.4 The intermediate loop controller scheme 78 5.5 The structure of adaptive NN to identify the inverse dynamics of the pneumatic actuator 79 5.6 Response of the adaptive NN to estimate the actuator force 80 5.7 Response of the error values the actuator force 81 5.8 A Simulink diagram of the SANAFC scheme 83 5.9 The time domain response of SANAFC scheme compared to SAFAFC scheme subjected to sinusoidal road profile, f = 1.5Hz, am = 3.5 cm 85 5.10 The time domain response of SANAFC scheme compared to SAFAFC scheme subjected to sinusoidal road profile, f = 0.8 Hz, am = 1.25 cm 86 5.11 The time domain response of SANAFC scheme compared to SAFAFC scheme subjected to chirp signal road profile 87
xv 5.12 The time domain response of SANAFC scheme compared to SAFAFC scheme subjected to sinusoidal wave hole test road profile 88 5.13 The time domain response of SANAFC scheme compared to SAFAFC scheme subjected to sleeper-plate test road profile 89 5.14 The time domain response of half-laden condition for the SANAFC SAFAFC schemes subject to sinusoidal road profile, f = 1.5 Hz, am = 3.5 cm 93 5.15 The time domain response of half-laden condition for the SANAFC SAFAFC schemes subject to sinusoidal road profile, f = 1.5 Hz, am = 3.5 cm as road profile 94 5.16 The actual force generated by the SANAFC and SAFAFC schemes for various road profiles 95 5.17 The computed estimated mass the body of the SANAFC and SAFAFC schemes for various road profiles 96 5.18 The frequency domain response of the SANAFC and SAFAFC schemes subject to sinusoidal road profile, f = 1.5 Hz, am = 3.5 cm 98 5.19 The frequency domain response of the SANAFC and SAFAFC schemes subject to sinusoidal road profile, f = 0.8 Hz, am = 1.25 cm 99 5.20 The frequency domain response of the SANAFC and SAFAFC schemes subject to chirp signal as road profile 100 5.21 The frequency domain response of the SANAFC and SAFAFC schemes subject to a half sinusoidal wave hole test road profile 101 5.22 The frequency domain response of the SANAFC and SAFAFC schemes subjected to sleeper-pate test road profile 102 5.23 The frequency domain results for a half-laden condition for the SANAFC SAFAFC schemes subject to sinusoidal road profile, f = 1.5 Hz, am = 3.5 cm 103 5.24 The frequency domain results for a full-laden condition for the SANAFC SAFAFC schemes subject to sinusoidal road profile, f = 1.5 Hz, am = 3.5 cm 104
xvi 6.1 A quarter car suspension test rig 107 6.2 Configuration of the hardware-in-the-loop simulation 108 6.3 Passive suspension test rig 109 6.4 Pin assignments for the analog and digital I/O connector pins 110 6.5 The DAS1602 card in the PC 110 6.6 Signal conditioning interface 110 6.7 Accelerometer attached to the sprung mass of the rig 111 6.8 Accelerometer attached to the tyre (unsprung mass) of the rig 111 6.9 Simulink and RTW block diagram of the sprung and unsprung mass accelerometers to measure the acceleration, velocity and displacement 112 6.10 Suspension deflection sensor attached to the end of actuator 113 6.11 Tyre deflection sensor attached to the base of tyre 113 6.12 Simulink and RTW block diagram of the two LVDTs used tomeasure the suspension deflection and road profile 113 6.13 The pressure sensor 114 6.14 Simulink and RTW block diagram of the pressure sensor to measure indirectly the actuated force 114 6.15 Pneumatic actuation system 115 6.16 Simulink and RTW block diagram of the pneumatic actuation system 115 6.17 Results for the force tacking controller 116 6.18 Tuning of the PID Controller 117 6.19 Intermediate loop configuration 117 6.20 Tuning skyhook parameter B sky 119 6.21 Identification of the inverse dynamic model of the pneumatic actuator 120 6.22 Inverse dynamic pneumatic actuator using adaptive NN 120 6.23 The PLC system to generate the road profiles 121 6.24 Simulink and RTW block diagram of the LVDT to measure the road profile 122 6.25 Road profiles (a) sinusoidal wave f = 1.1 Hz, am = 1.0 cm (b) chirp signal (c) a half sinusoidal wave hole test (d) sleeperplate test 123
xvii 6.26 The time domain response of the passive suspension subject to sinusoidal wave road profile, f = 1.1 Hz, am = 1.0 cm 124 6.27 The time domain response of the PID and SANAFC active suspensions subject to sinusoidal wave road profile, f = 1.1 Hz, am = 1.0 cm 124 6.28 The time domain response of the SANAFC scheme with 40 kg load variation subject to sinusoidal wave road profile, f = 1.1 Hz, am = 1.0 cm 125 6.29 The time domain response of the SANAFC scheme with 75 kg load variation subject to sinusoidal wave road profile, f = 1.1 Hz, am = 1.0 cm 126 6.30 The actual force required by the PID and SANAFC schemes for various road profiles 127 6.31 The computed estimated mass for various road profiles 128 6.32 The frequency domain response of the vehicle suspension subject to sinusoidal wave road profile, f = 1.1 Hz, am = 1.0 cm 132 6.33 The frequency domain response of the SANAFC scheme with 40 kg as load variation 133 6.34 The frequency domain response of the SANAFC scheme with 75 kg as load variation 133 7.1 Time delay problem in the experiment 140 7.2 Configuration of the front unsprung mass configuration 142
xviii LIST OF ABBREVIATIONS A/D AFC AF BP DOF D/A EC FFT FLC HILS LQR LQG LM MF MRAC NN PI PID RTW RMS SANAFC SAFAFC : Analogue to Digital converter : Active Force Control : Adaptive Fuzzy : Back Propagation : Degree of Freedom : Digital to Analogue converter : Evolutionary Computation : Fast Fourier Transform : Fuzzy Logic Controller : Hardware-in-the-loop Simulation : Linear Quadratic Regulator : Linear Quadratic Gaussian : Levenberg-Marquardt : Membership Functions : Model Reference Adaptive Control : Neural Network : Proportional Integral : Proportional Integral Derivative : Real Time Workshop : Root Mean Square : Skyhook Adaptive Neuro Active Force Control : Skyhook Adaptive Fuzzy Active Force Control
xix LIST OF SYMBOLS A a - Piston effective areas a A b - Piston effective areas b am - Amplitude b - Bias b s - Damping coefficient B sky - Constant value of skyhook f - Frequency f s - Semi-active damper force f a - Active damper force g - Gravitational acceleration I - Identity matrix J - Jacobian Matrix K p - Proportional gain K i - Integral gain K d - Derivative gain k s - Spring stiffness coefficient k t - Tyre stiffness coefficient M - Mass of the air in the cylinder m s - Sprung mass m u - Unsprung mass P - Pressure of the air in the cylinder P a - Absolute pressures in actuator s chambers a P b - Absolute pressures in actuator s chambers b Q - Disturbance R - Ideal gas constant T - Temperature V - Volume of the air in the cylinder w - Weight
xx l x - Centre of Gaussian antecedent MF at rule l and input i i l y - Centre of l of consequence fuzzy set z s - Sprung mass displacement z u - Unsprung mass displacement z r - Road profile z s z u - Suspension deflection z u z r - Tyre deflection z& - Sprung mass velocity s & z& s - Sprung mass acceleration z& - Unsprung mass velocity u ψ - Cost function l σ - Width of Gaussian antecedent MF at rule l and input i i μ - LM learning rate
xxi LIST OF APPENDICES APPENDIX TITLE PAGE A List of Publications 154 B Results for the SAFAFC Scheme Subjected to Various 156 Road Disturbances C Results for the Practical Implementation of the 168 SANAFC Scheme