Optimal torque distribution for four-wheel-motored electric vehicle stability enhancement

According to the characteristic that each wheel torque of 4WD electric vehicle is independent controllable, the control allocation method with a hierarchical structure is adopted to improve the handling stability of the vehicle by optimizing the distribution of motor torque. The controller is composed of an upper controller and a lower controller. Taking the vehicle sideslip angle and yaw rate as the state variables, the upper controller can calculate the desired generalized force of longitudinal force and yaw moment for vehicle stability by using the 2-DOF reference model. Through the weighted least square algorithm, the lower controller is used to determine the torque properly allocated to each wheel according to the desired yaw moment. Several actuator constraints are considered in the control strategy. In addition, a nonlinear tire model is utilized to improve the accuracy of tire lateral force estimation. The vehicle model and control system models are established and a simulation test is carried out. The simulation results show that the control system proposed can effectively improve the handling stability of the vehicle.