Research On The Control Strategy Of The Vehicle's Active Steer By Wire

In this paper,the steer by wire system is taken as the research object,theoretical research,modern intelligent control theory and software simulation test are used to study the modeling of the steer-by-wire system,variable angle transmission ratio control,active front wheel steering control and the design of the observer for the sideslip angle of the vehicle.(1)Simulink is used to build the simulation model of the steer by wire system,which replaces the mechanical steering system in Car Sim,completes the construction of the joint simulation platform of the steer by wire vehicle and verifies the accuracy of the model,and provides a simulation test platform for the subsequent control strategy research.(2)Based on the joint simulation platform of the steer-by-wire vehicle,the simulation tests under different conditions are carried out.Based on the analysis of the steering characteristics of the vehicle with fixed steering ratio,the concept of ideal variable transmission ratio is introduced to reduce the impact of the driver's repeatedly correcting the steering wheel angle to compensate for the change of vehicle characteristics through variable transmission ratio control,and make the vehicle have a better performance in the low-speed driving stage Sensitivity and high-speed driving stage have good stability.The method based on the constant yaw rate gain is selected to design the variable transmission ratio,and the variable transmission ratio is modified in the low speed stage and the middle and high stage.Aiming at the problem that this method is not suitable for designing variable transmission in high-speed stage,the variable transmission ratio in high-speed stage is designed by fuzzy control method.Finally,the design of variable transmission ratio control in the whole speed section of the steer by wire vehicle is completed,and the typical test conditions are selected for the Car Sim/Simulink joint simulation test.The results show that the variable transmission ratio control can achieve the expected control effect.(3)In view of the problem that it is difficult to obtain the sideslip angle of the vehicle center of mass in the practical application process,the second-order sliding mode observer theory based on super-twisting algorithm is adopted,and the design method that the design parameters in the observer model adjust with the vehicle speedis proposed,and a side slip angle observer with variable design parameters is designed.The simulation results show that the designed observer has better observation accuracy.(4)Considering that automobiles are often under non-steady-state conditions,based on the variable transmission ratio control,the active front wheel steering control strategy is designed based on the dynamic comprehensive feedback of yaw rate and sideslip angle.By adopting sliding mode variable structure control theory,on the basis of introducing virtual intermediate variables to construct a single sliding mode surface method,the weight coefficient configuration method of deviation in virtual intermediate variables is improved,and a sliding mode surface with integral form is constructed;The sliding mode control law of equivalent control plus switching control is designed to realize the sliding mode decoupling control of the integrated feedback of yaw rate and side slip angle,and to complete the design of the wire controlled active front wheel steering controller.Finally,different typical test conditions are selected for the Car Sim/Simulink joint simulation test.The simulation results show that the designed control strategy has better control effect,improves the control stability and active safety of the vehicle under extreme conditions,and improves the following ability of the ideal value.