An Investigation Into Electronic Differential Control System Based On Yaw Moment And Variable Slip Rate Joint Control

With the emergence of energy crisis and environmental pollution, the development of the traditional internal combustion engine vehicles face more and more resistance, and the new energy vehicle-electric vehicle (EV) has been paid more and more attention to. Because of the simple structural layout, high efficient transmission, each wheel can be controlled independently, and has large potential in improving vehicle handling and safety, the electric vehicle based on in-wheel motor draw more and more attention. However, while the electric vehicle based on in-wheel motor has more freedoms can be controlled, the problem that harmonizing the drive wheels also occurred, namely electronic differential (ED) problem.In order to solve the problem mentioned above, firstly, established an 8 DOF vehicle model which contains longitudinal, lateral, yaw, roll and wheel rotate motions, and also a non-linear tire model based on "magical formula", as the platform for electronic differential control system design and development. Secondly, design of the key state parameters of the vehicle and road identification parameters estimation module, proposed an new method for road identification parameters estimation based on quadratic function fitting and linear interpolation combined, which plays a significant role in improving the adaptability of vehicle on various roads. Thirdly, in the view of existing situation that relies solely on the driving wheel speed or torque control to realize the electronic differential is shortage, with the development trend of present active safety technology, developed the electronic differential control system based on yaw moment and variable slip rate joint control, which contains three main module:(1) Yaw motion control module, this module calculates the deviation of yaw rate between real model and ideal model, and uses the sliding mode variable structure control to output the yaw moment value that need to be acted on the vehicle, in order to improve the vehicle's handling; (2) Differential drive control module, this module distributes the driving torque according to the total driving torque and the yaw moment, considering the limitations of the driving wheel; (3) Variable slip rate control module, this module controls the total driving torque by control the driving wheels' slip rate when the road's condition can not satisfy the total driving torque output, in order to guarantee the driving wheel working in stable area, meanwhile, uses variable slip rate control method to replace the traditional fix slip rate control method, in order to ameliorate the driving wheels'lateral stability in extreme conditions and improve the vehicle's handling.In order to verify the effectiveness of the electronic differential control system, the vehicle, the tire, the estimation module and the control system simulation model were built in the Matlab/Simulink software, and the tests combined of acceleration in low adhesion road, butt road, bisectional road and high speed handling were carried out. The simulation results showed that, compared with conventional mechanical differential, the electronic differential control system was simple and effective. Through yaw moment and variable slip rate joint control, the electric vehicle can not only realize the differential function, but also improve the vehicle's handling and safety.