Study On Steering Drive Control Strategy Of Four-wheel Drive Electric Vehicle

With the development of the automobile industry and the country's strict requirements for automobile exhaust and environmental pollution,the new energy vehicle have been vigorously promoted and gradually entered into the public view because of their zero emission,low noise and low energy consumption.Four-wheel motor-driven electric vehicle as a prominent representative of the new energy vehicle,with four wheel motor independent controllable characteristics,however,if there is an improper control,it will lead to traffic accidents.Therefore,the steering stability analysis of four-wheel motor-driven electric vehicle is necessary.First of all,a seven-degree-of-freedom dynamic model on a certain type of electric vehicle was studied.Some subsystem model of four-wheel motor-driven electric vehicle was established using simulation software CARSIM,including the frame,brake system,steering system,suspension,tire,driver and road.The power transmission system is established in SIMULINK according to the speed-torque characteristics of motor.Then input the power transmission system into the CARSIM model by the software interface to obtain a four-wheel motor-driven electric vehicle simulation model.Verify the accuracy of the vehicle simulation model,which provides a good simulation platform for the subsequent design and control system.Secondly,the causes of instability of the vehicle body were analyzed and two significantly affected parameters were obtained,which is yaw rate and side-slip angle.The vehicle instability judgment model is established in SIMULINK.A yaw moment fuzzy controller is designed to adjust the yaw moment when the vehicle has too much steer or less steer,which has two input of yaw rate deviation and side-slip angle deviation and one output of yaw moment.The slip-rate fuzzy controller is designed to avoid tires having slip on the low attached road.The dynamic distribution coefficient is calculated for the dynamic change of the vertical load of the wheel when the vehicle is turning,and the total moment is reasonably distributed to the four wheels,so that the right and left wheel moment can be adjusted reasonably when the vehicle is steering,which improved the steering stability of the vehicle.Finally,four-wheel motor-driven electric vehicle with control module and without control module are made test simulation and comparison on different steering angle,different speed and different road conditions.Simulation results find that the control module can make timely judgment and produce adjustment moment,so that the vehicle can follow the given speed and the established trajectory regardless less steering or too much steering.Therefore,the control strategy and scheme studied have improved the steering stability of the four-wheel motor-driven electric vehicle by adjusting the distribution of the motor's torque.