Analysis And Control Research Of Vehicle Operational Stability Based On Four-Wheel Steering Technology

As the demand for car is increasing,active safety of automobile is gotten more and more attention.The automobile steering system belong to a branch of active safety directly affects the operation stability.Traditional Front Two-Wheel Steering System(2WS)always has big steering radius lead to poor mobility and flexibility at low speed.At high speed,tracking ability is not very ideal.By contrast,Four-Wheel Steering System(4WS)perform better than AFS,which make a car have a smaller steering radius at low speed and great tracking ability at high speed.Four-wheel steering system is a vital component of the active chassis controller,which has become an important development direction of cars.The thesis mainly studies control methods of 4WS and analyzes simulation results,the principal content is as follows:First of all,the development of 4WS at home and abroad has been made a detailed summarize.After the mathematical model of 2WS has carried on according to two degree of freedom and been detailed analyzed,deducing mathematical model of 4WS is easy.Second,with the mathematical model of 4WS under two degree of freedom as an example,the proportional control of front and rear wheel angle,the yaw velocity feedback control,the joint control between a proportional control and the yaw velocity feedback control were compared and analyzed separately.By comparison with the results,we have obtained the pros and cons of various control methods and a conclusion that joint control is better than the first two control methods.However,these three control methods can't achieve ideal yaw velocity value,so the PID control method is proposed,which the simulation results show that this method can make the yaw velocity to achieve an ideal value.Because of the simple PID control method can't adjust parameters by itself,we have introduced intelligent control method-fuzzy control with current practical significance.The simulation results prove the effectiveness of the proposed method.Finally,because 4WS model is derived under many assumptions,this thesis uses the Carsim to establish multi-body model more close to the real vehicle.By combining with Matlab/Simulink simulation,we powerful verify the feasibility of the fuzzy PID control method that can make the car get good operation stability.The method also can provide some reliable simulation data,which has some reference value.