Integrated Vehicle Control Of Four Wheel Steering And Direct Yaw Moment Control

Integrated Vehicle Dynamics Control (IVDC) can improve vehicle handling performance by coordinating and integrating the steering system, brake/traction system, active suspension and so on. Due to the rapid development of vehicle electronic control technology, a number of automotive manufacturers have put great efforts into the IVDC research and therefore, more and more products related to this area are now on the global market. Hence, IVDC has recently become a hot topic in the research field of vehicle chassis technology.Based on the theoretical derivation and simulation analysis, this dissertation mainly focuses on the research of integrated control of four-wheel-steering and direct yaw moment control. Also, a vehicle state observer is proposed aiming to estimate the vehicle lateral velocity.An 8-DOF vehicle dynamics model is proposed, which includes vehicle motion within horizontal plane and body roll motion. On tire modeling, a static tire model based on Burckhardt approach is established. In order to make the tire model more precise and pratical for the state observer and stability controller, several virtual tire tests based on CarSim have been carried out and the obtained tire statistical data are used for fitting in the modeling.Generally, vehicle lateral velocity is difficult to be measured directly by sensors mainly due to the high sensing cost. Therefore, an indirect approach—a state observer for lateral velocity can be used in practice. Based on vehicle kinematics and dynamics, an observer is designed by using Extended Kalman Filter (EKF) which can accurately estimate the lateral velocity and thus can be used for the stability controller design.Aiming at improving vehicle handling performance, a main-loop/servo-loop structured vehicle stability controller is designed. In the main-loop, sliding mode control theory is used to calculate the desired stabilizing forces/moments for the vehicle. Meanwhile, the tire nonlinearity can be directly taken into consideration within the servo-loop.The controller proposed in this dissertation is tested in the MATLAB/Simulink and CarSim co-simulation environment. The results show that the stability controller can greatly improve yaw rate tracking and suppress vehicle side slip motion, and thus be able to greatly improve the vehicle handling and stability performance.