DEGREE PROJECT IN VEHICLE ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2019 Robust post impact vehicle motion control using torque vectoring NIKHIL JAIN KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF ENGINEERING SCIENCES Robust post impact vehicle motion control using torque vectoring Nikhil Jain © Nikhil Jain, 2017 Supervised by: Jenny Jerrelind, Department of Aeronautical and Vehicle Engineering Lars Drugge, Department of Aeronautical and Vehicle Engineering Mustafa Ali Arat, Motion control and software, NEVS Eduardo Simoes˜ da Silva, Motion control and software, NEVS Master thesis 2017 Department of Aeronautical and Vehicle Engineering KTH Royal Institute of Technology SE-100 44, Stockholm, Sweden Telephone: + 46 8 790 60 00 i Abstract Several statistical studies have suggested that the risk of injury is significantly higher in multiple event accidents (MEAs) than in single event crashes. Improper driving in such sce- narios leads to hazardous vehicle heading angles and excessive lateral deviations from the vehicle path, resulting in severe secondary crashes. In these situations, the vehicle becomes highly prone to side impacts and such impacts are more harmful to the occupants since the sides of the vehicle have less crash energy absorbing structures than the front and rear ends. Significant advancements have been made in the area of automotive safety to ensure pas- senger safety. Active safety systems, in particular, are becoming more advanced by the day with vehicles becoming over actuated with electric propulsion and x-by-wire systems. Keep- ing that in mind, in this master thesis a post impact vehicle motion control strategy for an electric vehicle is suggested based on a hierarchical control structure which regulates the lat- eral deviation of the affected vehicle while maintaining safe heading angles after an impact. Sliding Mode Control (SMC) has been utilized in the higher controller which generates a virtual output used as an input for a lower controller performing torque allocation. The allocation methods were based on optimization, aimed to minimize tire utilization, and a normal force based approach. The performance of the controller was first evaluated with single track and two track model of the vehicle because of their simplicity making them easy to debug and also since they allowed for quick simulations. This was followed with eval- uation with a high fidelity vehicle model in IPG CarMaker for fine tuning the controller. It was observed that the use of SMC strategy to generate virtual yaw moment to be used in torque vectoring for controlling vehicle trajectory post impact proved to be a robust strategy managing to control the vehicle even in cases of actuator failure. So it can be concluded that the hierarchical control structure with the higher Sliding mode controller, generating a vir- tual yaw moment, and a lower controller doing torque allocation using a normal force based strategy and an optimization approach worked as intended. ii Sammanfattning Flera statistiska studier har foreslagit¨ att risken for¨ skador ar¨ signifikant hogre¨ vid flerfoljd-¨ skollisioner an¨ vid enskilda kollisioner. Felaktig korning¨ i sadana˚ scenarier leder till farliga fordonspositioner och stora avvikelser fran˚ fordonets ursprungliga fardriktning,¨ vilket resul- terar i svara˚ sekundara¨ kollisioner. I dessa situationer blir fordonet ofta utsatt for¨ sidokol- lisioner vilka ar¨ mer skadliga for¨ passagerarna, eftersom sidorna pa˚ fordonet har mindre energiabsorberande strukturer vid deformation an¨ framre¨ och bakre delarna pa˚ fordonet. Betydande framsteg har gjorts inom omradet˚ bilsakerhet¨ for¨ att sakerst¨ alla¨ passagerarsaker-¨ heten. Aktiva sakerhetssystem,¨ i synnerhet, blir alltmer avancerade i och med att fordon blir overaktuerade¨ med bland annat elektrisk framdrivning och x-by-wire system. Med tanke pa˚ detta foresl¨ as˚ i detta examensarbete en strategisk styrning av fordonets rorelse¨ for¨ ett elfor- don baserat pa˚ en hierarkisk reglerstruktur som reglerar laterala avdriften hos det drabbade fordonet samtidigt som det uppratth¨ aller˚ saker¨ fordonsriktning efter en kollision. Sliding Mode Control (SMC) har anvants¨ i den hogre¨ kontrollenheten som genererar ett virtuell utvarde¨ som anvands¨ som invarde¨ for¨ en lagre¨ styrenhet som utfor¨ momentalloker- ing. Allokeringsmetoderna baserades pa˚ optimering, som syftade till att minimera dackut-¨ nyttjandet och ett normalkraftsbaserat tillvagag¨ angss˚ att.¨ Styrenhetens prestanda utvarder-¨ ades forst¨ med en ”singel track model” och en ”two track model” av fordonet pa˚ grund av deras enkelhet som gor¨ dem enkla att felsoka¨ och mojligg¨ or¨ snabba simuleringar. Darefter¨ gjordes en utvardering¨ med en mer detaljerad och komplex fordonsmodell i IPG CarMaker for¨ finjustering av regulatorn. Det observerades att anvandningen¨ av SMC-strategin for¨ att generera ett virtuellt girmoment for¨ att anvandas¨ i momentvektoriseringen for¨ reglering av fordonsriktningen efter kollision visade sig vara en robust strategi som klarar av att styra fordonet aven¨ i handelse¨ av aktuatorfel. Slutsatsen ar¨ att den hierarkiska reglerstrukturen med en hogre¨ ”sliding mode controller”, som genererar ett virtuellt girmoment och en lagre¨ styrenhet som utfor¨ momentallokeringen med en normalkraftbaserad strategi samt optimer- ing fungerade som det var tankt.¨ iii Thesis contributors This master thesis work was performed at the company National Electric Vehicle Sweden (NEVS) situated inTrollhattan¨ in collaboration with Mr. David Nigicser, a master thesis stu- dent from the System, Control and Robotics Masters program at KTH Royal Institute of Technology. The designing and analysis of Model Predictive Control (MPC) [36] as a higher controller for vehicle motion control post impact has been performed by Mr. Nigicser and the literature study for this work has been a joint effort. Since the problem statement was the same, few portions of this work like vehicle models used for simulation, which were provided by NEVS, are similar in the work presented by Mr. Nigicser. This thesis work focuses on using Sliding mode control strategy in the higher controller with torque allocation methods based on optimization and normal forces for the lower controller. iv Acknowledgements I would like to start by thanking my thesis supervisors at NEVS, Mustafa Ali Arat and Ed- uardo Simoes˜ Da Silva for their immense support during the course of this thesis. It were the discussions with them which helped shape the project and built it in a way such that it could be useful for the industry. I would also like to extend my thanks to the Vehicle Motion Control team at NEVS for being so supportive and taking time to contribute to this work. I am very grateful to my supervisors at KTH, Lars Drugge and Jenny Jerrelind for their support, your suggestions in the theoretical and the practical aspect of this project were of immense help. I would also like to thank my friends David, Anand and Hjortur¨ for their suggestions and sharing their knowledge. Interactions and discussions with you all were really informative and inspiring. Lastly, my master degree studies in Sweden would have been impossible without the sup- port of my family. My deepest appreciation to my parents and my sister for being there all along the way and keeping me motivated. v List of Figures 1 Accident statistics [11]. .5 2 Free body diagram of a single track model. .9 3 Global and local coordinate system. 10 4 Free body diagram of a two track model. 11 5 Slip angle. 12 6 Non-linear tire force behavior [23]. 13 7 Data on impulse magnitude and velocities [33]. 17 8 Single track model in Simulink. 18 9 Two track model in Simulink. 20 10 Yaw rate as a function of time for an impact of 2 KNs. 21 11 Controller setup in IPG CarMaker. 21 12 Vehicle states after impact. 23 13 Torque outputs on the four wheels and corresponding tire slip ratios. 24 14 Vehicle trajectory with and without controller at 8 kNs. 24 15 Vehicle trajectory with and without controller at 4 kNs. 24 16 Force outputs with rule based approach. Impact = 8 kNs. 25 17 Force outputs with optimization. Impact = 8 kNs. 25 18 Force outputs with optimization. Impact = 8 kNs, actuator 2 failed. 26 19 Vehicle trajectories with and without actuator failure, with and without con- troller action. Impact = 8 kNs, actuator 2 failed. 26 vi Contents 1 Introduction 1 1.1 Scope and assumptions . .2 1.2 Limitations . .2 1.3 Research questions . .3 1.4 State of the art . .3 1.4.1 Safe heading angles . .5 1.4.2 Fault tolerant systems . .6 1.5 Structure of the report . .7 2 Theory 8 2.1 Vehicle modelling . .8 2.1.1 Single track model . .8 2.1.2 Two track model . 10 2.1.3 Tire modelling . 12 2.2 Sliding Mode Control . 13 2.2.1 Concept . 14 3 Method 16 3.1 Scenario selection . 17 3.2 Integration with single track plant model . 18 3.3 Integration with two track plant model . 19 3.4 Integration with IPG CarMaker plant model . 20 3.5 Actuator failure - two track plant model . 21 4 Results 22 4.1 Integration with IPG CarMaker plant model . 22 4.2 Actuator failure - two track plant model . 24 5 Conclusions 26 5.1 Feasibility of the system . 27 5.2 Future work . 27 1 1 Introduction Automotive safety is of prime importance to drivers, manufacturers and the society in gen- eral. Significant technological advancements have been made in this area till date to ensure that the passenger safety is always guaranteed. Safety systems are categorized into two main classes: active and passive safety systems. Active safety systems involve systems for accident prevention and avoidance whereas passive safety systems deals with minimizing the occu- pant injury during an accident. In the European Union (EU) alone there have been approx- imately 26000 fatalities due to road accidents in 2015 [1] and this number has been steadily decreasing over the years due to new innovations introduced to the automotive industry as well as increased safety standards from the governments [3][2].