Simulation Research On Active Steering Of Four Wheel Steering Based On Road Identification

With the increasing complexity of road traffic conditions,more and more traffic accidents are shocking.Therefore,the research on automobile safety performance has become an important driving point of the global automobile industry.Among them,applying the accurate information of road adhesion coefficient to each control system of the vehicle can effectively improve the control system’s accuracy,to improve the handling stability and safety of the vehicle.In this paper,the real-time road adhesion information is taken into account and deeply studied in the research of four-wheel steering(4WS)vehicle control systems.The specific contents are as follows:Firstly,to meet the needs of 4WS vehicle controller design,simulation,and control effect verification,this paper establishes 4WS vehicle linear 2-degree-of-freedom(DOF)dynamic model,4WS vehicle kinematics model,ideal vehicle model and brush tire model,and uses Car Sim to establish active rear-wheel steering(ARS)vehicle model and four-wheel active steering(4WAS)vehicle model respectively,the joint simulation platform of Car Sim and Simulink is established to make preliminary preparations for the subsequent research on road adhesion coefficient estimation and ARS and 4WAS vehicle controller.Secondly,aiming at the problem that most existing road adhesion coefficient estimation methods only consider the single excitation of pure lateral deviation and pure slip,a road adhesion coefficient estimation method considering longitudinal and lateral excitation is proposed: firstly,a road adhesion coefficient estimate based on lateral force is established by using Luenberger observer;secondly,an estimate of road adhesion coefficient based on longitudinal force is established by using high-order sliding mode observer;finally,based on the fuzzy controller,the results obtained by the longitudinal and lateral estimators are fused and optimized,and the joint fuzzy controller of longitudinal and lateral road adhesion coefficient is established.The simulation demonstrates that the longitudinal and lateral joint estimator has a lower error and stronger robustness than the single longitudinal and lateral estimator.Then,aiming at the problem that the existing ARS controller fails to fully consider the road adhesion conditions,the influence of sideslip angle on vehicle stability is analyzed by using the phase plane method,and a variable weight coefficient ARS controller based on optimal control is designed: firstly,the ARS controller is established based on LQR optimal control;secondly,genetic algorithm is used to obtain the optimal weight coefficients under high and low adhesion coefficients and vehicle speed,which is used as the domain division standard of variable weight coefficient controller;then a reasonable fuzzy rule is established and a variable weight coefficient regulator based on fuzzy control is designed.The weight coefficient of the optimal controller is adjusted in real-time according to the real-time road adhesion coefficient information and vehicle speed;finally,the simulation analysis of the variable weight coefficient ARS controller based on optimal control is carried out.The results show that the variable weight coefficient ARS controller improves the stability and safety of vehicles under different speed and adhesion coefficient road conditions compared with the fixed-parameter controller.Finally,for the problem that the existing 4WAS vehicle controller fails to fully consider the road adhesion conditions,two 4WAS vehicle controllers are established by using the methods of sliding mode control and optimal control respectively;then through the simulation analysis of the steady-state side slip angle of the two controllers under different vehicle speeds and road adhesion coefficients,it is found that the two controllers have different performances under different vehicle speeds and road adhesion coefficients;Finally,based on the analysis results of the two controllers,a 4WAS vehicle switching controller is established.The simulation results show that the switching controller can maintain the lowest sideslip angle under various attachment conditions and vehicle speed,and maintain the stability of the vehicle to the greatest extent.