Simulation Research On Combined Control Strategy Of Yaw Moment And Active Steering For Vehicle Dynamic Stability

The development trends of modern vehicle are "safety,energy saving and environmental protection", among them, vehicle active safety is an important aspect which influents road traffic safety. The effective way to improve vehicle active safety is to carry out the research on vehicle stability control and it is the international research focus in the field at present. Based on the analysis of vehicle driving and braking stability on large turn, the dissertation studies the technology of vehicle stability control by way of yaw moment and active steering separately. On the basis of the theories of fuzzy and Fuzzy-PID control, the corresponding control strategies and control algorithms are determined, and the mechanisms of separate and combined control by the two methods are also studied. The research fruits provide a certain train of thought to integrated control of vehicle stability.The dissertation begins with the nature of vehicle dynamics. On the basis of the existing experimental data of tyre, the multi-dimensional characteristic curved surface of neural network tyre force model is got, the influence of variations of vertical load and side slip angle of tyre on braking force is analyzed, the control strategy of finding tyre optimum slip rate according to characteristic curved surface is put forward and the simulation of vehicle braking condition on a turn is made. The simulation results show the control strategy of optimum slip rate has better braking effect than that of constant slip rate.To the condition of deviation from side path when vehicles are turning and braking, according to the deviation distance, the control strategies and control algorithms of vehicle braking stability by two control methods, yaw moment and active steering, are determined. The fuzzy controller are designed whose outputs can be adjusted online according to the variation of slip rate and dynamic proportionality factor. The simulation results prove that the method of fuzzy control which is based on the yaw meoment and front wheel active steering can improve vehicle braking stability and ability of path tracking.Based on the models of unlinear tyre and full vehicle dynamics, the characteristics of the control methods of yaw moment and front wheel active steering under the conditions of excessive vehicle and less steering are analyzed. The technology of unlinear Fuzzy-PID with robustness for vehicle stability control is selected. The Fuzzy-PID controllers are designed whose tracking objects are ideal yaw rate and side slip angle and the outputs are wheel braking force and front wheel steering angle. The simulation experiments by two methods, yaw moment stability control which is based on the optimum slip rate of tyre and active steering control that is based on front wheel nestification, are carried out. The results prove that the vehicles applied Fuzzy-PID control have good performance stability.To the coupling function of the combined control by yaw moment and active steering, coordination between two control sub-systems is required to improve the performance of the full vehicle. The control strategy of feedforward combined with feedback is applied to track the ideal model. According to the working conditions by two different control methods, the double fuzzy controller for combined control is designed and the coordination control strategy and switch logic between sub-systems are determined. The combined control performances between sub-systems are balanced by adjusting the weight coefficient of the double fuzzy controller whose inputs are yaw rate and side slip angle and outputs are wheel braking force and front wheel steering angle. The simulation of vehicle stability control under conditions of angle step input and variable lane input is made, the stabilities of control sub-systems are analyzed by way of Lyapunov and phase plane and Lyapunov discretization analyses of the control sub-systems are made. The results show from coordinating between control sub-systems, the combined control can realize complementation of the functions between sub-systems and improve vehicle performance stability to a higher level.The research in the dissertation is a front subject in the control field of vehicle dynamics. Studies of vehicle stability control can improve vehicle driving safety and performance stability, provide theoretical basis for combined control of vehicle stability and prompt the development of control technology of vehicle dynamics.