Friction Potential Estimation for Autonomous Driving

Produktbeschreibung

Autonomous vehicles need information about the environment for trajectory planning. This information is usually stored in a high-definition map. This map is made available to the vehicle. This thesis deals with the friction potential, which is important for planning. The unitless value determines the maximum forces that can be transmitted between tyre and road. The friction potential is a function of many influencing factors. In this work, possibilities are evaluated to capture the most important of these influencing factors, the road surface and the intermediate layer, via external data sources. To determine the influence of the road surface, friction measurement methods established in road construction are compared with vehicle measurements. To determine the intermediate layer, data from weather stations, rain radar and a test vehicle are evaluated.

Contents
Abbreviations VIII
Symbols X
Abstract XVI
Kurzfassung XVIII
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2.1 Friction Potential Measurement Methods . . . . . . . . . . . . . 11
1.2.2 Friction Potential Estimation Methods . . . . . . . . . . . . . . . 23
1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.4 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2 Fundamentals of Tyre Friction and its Effect in Tyre Models 36
2.1 Important Influencing Factors . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1.1 Road Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.1.2 Tyre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.1.3 Intermediate Layer . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.1.4 Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.2 Tyre Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3 Development of a Friction Potential Measurement Method 55
3.1 Test Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.2 Measurement Method – Single Wheel Braking . . . . . . . . . . . . . . 57
3.2.1 Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . 58
3.2.2 Measurement Data Processing . . . . . . . . . . . . . . . . . . . 61
3.2.3 Comparison with Full Braking Measurements . . . . . . . . . . 67
3.3 Measurements on Public Roads . . . . . . . . . . . . . . . . . . . . . . . 70
3.3.1 Variation of Measured Friction Potential Values . . . . . . . . . 71
3.3.2 Influence of the Road Surface . . . . . . . . . . . . . . . . . . . . 74
3.3.3 Influence of the Road Condition . . . . . . . . . . . . . . . . . . 75
3.3.4 Influence of the Surface Temperature . . . . . . . . . . . . . . . 77
3.3.5 Influence of the Velocity . . . . . . . . . . . . . . . . . . . . . . . 78
4 Grip Map 81
4.1 SKM Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.1.1 Test Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.1.2 Public Road . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.1.3 Comparison with Single Wheel Braking . . . . . . . . . . . . . . 90
4.2 RoadSTAR Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.2.1 Test Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.2.2 Public Road . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.2.3 Comparison with Single Wheel Braking . . . . . . . . . . . . . . 101
5 Intermediate Layer Classification 104
5.1 Input Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.1.1 Road Weather Information System . . . . . . . . . . . . . . . . . 105
5.1.2 Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.1.3 Vehicle Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2 Ground Truth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5.3 Classification methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.3.1 Established Intermediate Layer Classification Methods . . . . . 111
5.3.2 Application of Classification Methods . . . . . . . . . . . . . . . 117
5.4 Comparison of Classification Results . . . . . . . . . . . . . . . . . . . . 125
6 Remaining Risk of Overestimating the Friction Potential 127
6.1 Friction Requirements for Normal Driving . . . . . . . . . . . . . . . . 127
6.2 Risk Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
7 Conclusions 136
Appendix 139
A Vehicle Model 139
B Vehicle Measurements 142
B.1 Friction Measurements on FAT track . . . . . . . . . . . . . . . . . . . . 142
B.2 Hydroplaning Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
B.3 Measurements on Snow/Ice . . . . . . . . . . . . . . . . . . . . . . . . . 145
C Continuous Friction Potential Measurements 147
Bibliography 155

Keywords: Reifen, Reibwert, Autonomes Fahren, Trajektorienplanung, Straßenbau, Straßenwetter, Klassifizierungsverfahren, Tyre, Friction, Autonomous Driving, Trajectory Planning, Road Maintenance, Classification Methods