Dynamic Control Of Four-wheel Drive Electric Vehicles Under Low Adhesion Conditions

With the general downturn of the domestic economy in the second half of 2018,the domestic passenger car market sales have experienced the first decline in 28 years,but the sales of new energy passenger cars have achieved a contrarian rise.Coupled with the government's subsidy policy for pure electric vehicles,the automakers have accelerated the development of pure electric vehicles.In this paper,a four-wheeled wheel drive pure electric vehicle is taken as the research object,and a four-wheeled wheel drive modified vehicle platform is built to study the longitudinal force torque vector control(TVC)under low adhesion conditions.The specific research contents of this paper are as follows.First of all,this paper analyzes the characteristics and advantages of the hub motor.Introduced the modified examples of the wheel hub motor car of the OEM,such as Ford,Mercedes-Benz.Then the current research status of the dynamic control of the hub motor is summarized.Then,this paper modifies and debugs a compact car,and realized the normal driving of the car after modification.Secondly,the dynamic mechanism of vehicles on low-attachment vehicles is studied.In view of the low adhesion road condition,this paper divides the driving anti-skid system into four control modes according to the different wheel slip conditions of the vehicle,and establishes the driving anti-skid strategy of the four-wheel hub driven pure electric vehicle controlled by the logic threshold control.Then,the response process of the vehicle yaw rate is obtained by the two-degree-of-freedom vehicle model,and the yaw rate transient response is regarded as the second-order system.The ideal yaw rate is designed by adjusting the natural frequency and damping ratio of the second-order system.Then use the ideal yaw rate and the actual yaw rate error for PI control to determine the vehicle yaw moment.Thirdly,the optimal distribution of the longitudinal torque of the pure electric vehicle of the four-wheel drive hub motor is studied.The minimum of the four-wheel wheel adhesion coefficient consumption rate is the optimization target.After derivation,the quadratic programming method suitable for the longitudinal force distribution of the wheel motor pure electric vehicle is obtained,and the longitudinal moment of the wheel is obtained.Then,the vector control of the longitudinal moment of the vehicle is realized by driving the anti-skid sub-module,the direct yaw moment sub-module and the quadratic programming optimization module.Then,offline simulation of the control strategy and hardware-in-the-loop testing are performed.The simulation results show that TVC can significantly improve the vehicle's power.At the same time,the TVC improves the under-steering characteristics of the vehicle during the DLC simulation process,and reduces the vehicle's centroid side yaw angle and the lateral displacement of the vehicle,so that the vehicle can better bend.At the same time,the load rate of the four tires is significantly reduced,and the vehicle stability is better.Finally,hardware-in-the-loop testing and real-world testing are conducted.Based on Labview-RT,the vehicle controller(VCU)is tested in the loop,and the VCU software and hardware functions are tested.The actual vehicle test results show that TVC can significantly improve the power of the vehicle.At the same time,after the TVC is turned on,the passing speed of the DLC and the snake line can be obviously improved,and the centroid side angle and the wheel load rate are significantly reduced.In the amplified trapezoidal test,after the TVC is turned on,the stability of the vehicle is obviously improved,and the occurrence of instability is reduced.