Study On Chassis Integrated Control System To Improve Vehicle Handling Performance And Stability

Vehicle chassis integrated control is a research focus on vehicle dynamics in recent years. Its contents are continuously enriched with the development of vehicle dynamics, modern control theory, computer simulation technology, microelectronic technology and so on, and settle a basis for establishing X-by-Wire control vehicle. Therefore, it is worthwhile to investigate the potential performance benefits of chassis integrated control system from theoretical aspects, as well as the limitations of individual subsystem control. Based on the vehicle dynamical nature, the dissertation studies the control integration of four-wheel-steering (4WS) and direct yaw moment control (DYC) to improve vehicle handling performance and stability.In the normal condition, all vehicle dynamics control problems can be summarized to the control process of tire longitudinal force, lateral force and yaw moment. Therefore, the dissertation analyzes the steady-state and transient tire characteristics, establishes an eight-degree-of-freedom (8-DOF) vehicle model, and proposes a two-layer hierarchical chassis control system that integrates four-wheel-steering (FWS) and direct yaw moment control (DYC). The first layer is a robust model matching controller (R-MMC) based on linear matrix inequalities (LMI), which optimizes the four wheel steering angles and a desired yaw control moment, and calculates reference wheel slip for the target wheel according to the desired yaw moment. The second layer is a moving sliding mode controller that can track the reference wheel slip in a predetermined time by commanding proper braking torque on the target wheel to achieve the desired yaw moment. The moving sliding model controller traps system states on the sliding surface all the time, and improves system performance in terms of eliminating the chatting phenomenon, a decrease in the reaching time and system robustness to parameter variations. In the case of a production vehicle, measuring sideslip angle would represent a disproportional cost. Therefore, a sliding mode observer is also presented. The performance and robustness of the sliding mode observer and the integrated control system are conformed through extensive critical maneuver simulations. The simulation results showed that the sliding mode observer can track the actual sideslip angle satisfactorily in magnitude and phase, and the integrated control vehicle exhibits superior handling performance, stability and system robustness.To shorten developing time and avoid real vehicle test risk, the dissertation also proposes a comprehensive closed-loop driver-vehicle interaction system based on the chassis integrated control system and convergence field vector driver model. The driver-vehicle system has an external control loop for lane keeping assistance and an internal control loop for handling performance improvement. The controller of external control loop is the driver model that decides reference vehicle states for the chassis integrated controller. The internal control loop is the chassis integrated control system, which cooperates the chassis 4WS, DYC and TCS to control vehicle longitudinal, lateral and yaw rate dynamics. The S shape road simulation indicates the driver-vehicle system based on chassis integrated control system can not only achieve preferable vehicle handling performance and active safety, but also improve vehicle lane keeping ability, and alleviate the driver's working load.In this dissertation, a vehicle chassis electronic power steering (EPS) experimental platform is also been established. It realizes the assist steering torque output from motor. The EPS hardware includes MCU circuit and driver circuit, and its software includes bottom driver module, application module and algorithm module. Establishment of the EPS experimental platform builds a good foundation of vehicle chassis integrated hardware-in-loop simulation system, which includes both chassis steering system and breaking system.The significance of chassis integrated control can be verified and analyzed through open and closed-loop critical maneuver simulations, from which the following conclusion can be drawn: although the subsystem individual control can also improve vehicle handling performance, but exhibits evident tracking errors which usually exceeds the upper bound of uncertainties. Therefore, the subsystem individual control can not obtain satisfactory vehicle handling performance. While for the integrated control vehicle, system tracking error is limited in a satisfactory level, and shows a good robust stability and handling performance even under critical maneuvers. Therefore, the study on vehicle chassis integrated control system, development of vehicle hardware-in-loop simulation platform will improve vehicle handling performance and stability, speed up the development of control system, accelerate vehicle X-by-Wire technology, and improve vehicle active safety and comfort.