Research On Dynamic Coordinated Control System Of 4WS-4WD Electric Vehicle

As one of the measures to cope with energy shortages and environmental pollution,our country has become more and more powerful in the promotion of electric vehicles.In order to improve the performance of vehicle handling,stability,comfort,economy and safety,various kinds of active control systems are increasingly being applied to automobiles,and electric vehicles provide a great platform for the research of these control systems.But many control systems are designed for improving the performance of a certain aspect of vehicle,and some of them have a coupling effect.Therefore,it is necessary to coordinate the work between these control systems,which is also a hot and difficult topic at home and abroad.This paper takes a four-wheel steering and four-wheel independent in-wheel motors driving electric vehicle as the research object.The vehicle dynamics control principle of active rear steering(ARS)and direct yaw moment control(DYC)based on in-wheel motors differential driving or braking are studied and analyzed separately.On the basis of this,the coordinated control strategy of ARS and DYC is studied to improve the performance of vehicle handling and stability.Then,this paper makes a preliminary exploration of the G-vectoring control(GVC),and studies the influence of its joint control with the ARS and DYC on the vehicle handling and stability.First,this paper built a four-wheel steering(4WS)and four-wheel driving(4WD)electric vehicle dynamic model based on the CarSim and Simulink.The body model and the lateral driver model were built in CarSim.Based on the peak torque characteristics and the actual torque response curve of the Protean motor,an equivalent driving motor torque response model was built in Simulink.Also,a simplified steering motor position tracking control model and longitudinal driver model were built in Simulink.So the joint simulation of Carsim and Simulink has been realized.Second,the ARS control strategy which takes the centroid sideslip angle equal to zero as the target,and the DYC control strategy which aims to follow the ideal yaw rate were studied separately.The simulation results showed that the ARS system can effectively reduce the centroid sideslip angle,and obviously reduce the phase difference between the yaw rate and the lateral acceleration in the low frequency range,but at the same time,it changes the steady-state value of the yaw rate and the lateral acceleration,so influences the steady-state steering characteristic of the vehicle.The results of simulation and actual vehicle tests have proved that the differential driving can actively control the change of the yaw rate,so that the steering characteristics of the vehicle can be designed.Third,this paper designed a coordinated fuzzy-PID controller of ARS and DYC based on their advantages,in order to reduce the centroid sideslip angle and follow the ideal value of yaw rate at the same time.The simulation results showed that the coordinated control system of ARS and DYC can make use of their own advantages to make up for the shortcomings of the other one,so that the performance of the vehicle handling and stability can be greatly improved.Later,G-vectoring control was studied.With the GVC system,whether DYC system or the coordinated control system of ARS and DYC,the vehicle’s path tracking capability and stability in low surface have been greatly improved.Last,the coordinated control strategy of four-wheel steering and four-wheel driving was converted to automatic code,and was downloaded into the electronic control unit(ECU).The control strategy was verified by the ECU-in-loop simulation.The feasibility of the coordinated control algorithm running in the ECU environment was verified.The results of real-time simulation also showed that the coordinated controller can improve the performance of vehicle handling and stability.