Research On Differential Power Steering Control Of Wheel Hub Motor Driven Vehicle

With the intensification of energy problems,the development of electric vehicles has attracted much attention.The in-wheel motor-driven car in electric vehicles has many advantages such as higher efficiency,flexible control,and larger space than traditional cars.Based on the independently controllable characteristics of the four drive wheels of the in-wheel motor driven car,the differential power steering control is achieved through the output torque of the left and right steering wheels of the car.It replaces the power-assisted components in the traditional power-assisted system,reduces manufacturing costs,and has a broad development space.In addition,the in-wheel motor-driven car has obvious advantages in the stability control of the car because of the independent controllability of each motor.When the differential power steering system works,due to the different driving torques of the left and right steering wheels,an additional yaw moment will be introduced to the vehicle,which will affect the stability of the vehicle.Therefore,the following researches are performed on the differential power steering control and yaw stability control of an in-wheel motor-driven vehicle.Firstly,based on the mechanical structure and the front wheel positioning parameters of the vehicle steering system,the mechanism that the front wheel differential torque can provide steering assistance is analyzed,and the feasibility of differential steering is verified by simulation.With reference to the method of determining the assist characteristics of the electric power steering system,the assist characteristics of the differential power steering system were determined,and a differential power steering controller was established to track the ideal steering wheel hand torque.The difference between the actual steering wheel hand torque and the ideal steering wheel hand torque is used as the input for PID controller,and the resulting differential assist torque is distributed to the left and right steering wheels of the car.The differential power steering system can be used to achieve a good boost effect through simulation analysis.Then,based on the extension control theory,a yaw stability controller was established.The difference between the ideal yaw rate and the actual yaw rate and the sideslip angle were selected as the characteristic quantities to determine the boundaries of the classical domain,the extension domain,and the non-domain,and the control area.According to the state information of the car,the yaw rate PID controller and the sideslip angle PID controller are switched to obtain a differential torque that controls the yaw stability and is distributed to the rear wheels.And through simulation,it is verified that the yaw stability coordination controller has better control effect than the single yaw rate controller and the single sideslip angle controller.Finally,the influence of the differential power steering system on the yaw stability of the vehicle is analyzed,and a coordinated controller for differential power steering and yaw stability is established to control the differential assist torque and yaw torque.The controller is divided into two layers.The upper controller is based on the extension theory,which divides the classic domain,the extension domain and the non-domain corresponding to the driving state of the vehicle,and reflects the change in the stability of the car through the correlation function.Weight of differential torque and yaw moment are determined in the lower layer.The driving torque of the four wheels of the car was redistributed,and the vehicle model and steering system model built by Simulink were simulated to verify that the method can reduce the driver's steering wheel hand force and improve vehicle driving stability.According to the analysis,the differential power steering and yaw stability coordination controller can fully exert the power-assisting effect of the differential power steering.It takes into account the steering lightness and steering road feel,and expands the differential power steering system.It extends the working range of the differential power steering system and proves the stability of the car.It has promoted the theoretical research and industrial application of the differential power steering system.