Study On Handling Dynamics And Control Strategy Of Four-wheel Steering Vehicle In MATLAB Software Environment

The appearance of a four-wheel steering vehicle has solved the inherent defects of the front wheel ones to the automobile to a large extent,which response is slow and a type of turning radius is large in low speeds;the stability and the safety performancing is poor in high speeds.In addition,the appearance of the four-wheel steering technology greatly improves the stability of the vehicles.In recent decades,the modern control theory has been developed rapidly,and there are many research methods to control a four-wheel steering system,such as robust control,fuzzy control and neural network control.But each of these approaches has its pluses and minuses.This paper adopted different control methods for four-wheel steering vehicles in the MATLAB environment.Through MATLAB/Simulink,the response curves of the four-wheel steering stability evaluation index are obtained,and those curves are analyzed and compared to find a most suitable control method.The dynamic analysis of four-wheel steering vehicles is conducted in the standard coordinate system of the national automobile engineers association(SAE coordinate system).The paper established three different degrees of freedom dynamic model of the four-wheel steering vehicle,transformed the dynamic model into the kinematics one in mathematics and physics knowledges,and transformed the kinematics one into a mathematical model according to the knowledge of modern control theory,the mathematical model includes the transfer function model and the state equation model,which provides the theoretical basis for the research on the control strategy of the four-wheel steering vehicle.A four-wheel steering system control strategy is designed based on the model of the two-freedom four-wheel steering vehicle with its tire model,and the two problems of vehicle stability control research are analyzed.The basic operation of MATLAB and Simulink is briefly introduced.On the basis of the two-degree-of-freedom vehicle model,the relationship between the angular velocity and stability of the vehicle and the relationship between the lateral angle and the stability of the vehicle are analyzed.In addition,the two degrees of freedom four-wheel steering system for horizontal pendulum angular velocity feedback control,separately in the speed of 30 km/h and 90 km/h in simulation,and compared with other control methods are simulated,which results are qualitatively analyzed.The optimal simulation module is established for four-wheel steering system in the MATLAB/Simulink environment.First of all,the motion differential trasforms into state equation model with modern control theory knowledge.By analyzing the controllability matrix is full rank matrix and considerable sex to determine the controllability of the system and can view,are able to view and controllability,on the basis of model simulation module in MATLAB,get the steering stability evaluation index response curve,the model simulation results are analyzed.The PID controller,the construction of PID subsystem and the design of parameters are designed.On the basis of predecessors' researching,the mathematical model of fractional PID control is established with using application knowledges,and the module model of fractional PID control of four-wheel steering system is established in MATLAB/Simulink,and the response curves of the evaluation index are obtained.