Two-level optimal torque distribution for handling stability control of a four hub-motor independent-drive electric vehicle under various adhesion conditions

In order to increase the handling stability performance of the four hub-motor independent-drive electric vehicle (4MIDEV) under various road conditions such as joint and bisectional road, this paper present an effective two-level optimal torque distribution control method. This method can calculate torque command to each hub-motor according to the desired longitudinal force and desired extra yaw moment. The first level allocation control algorithm has small calculation cost and fast response, and can achieve the maximum stability margin of vehicle under good road adhesion condition. Because the adhesion coefficients of each wheel are different, the weight coefficient of objective function is adjusted in real time in the second level allocation control strategy, so as to ensure the vehicle's handling stability under various adhesion conditions, especially when four wheels have different road adhesion coefficients. Finally, the actual torque of the hub-motor is adjusted according to the slip rate by the sliding mode controller. The proposed distribution strategy is verified in CarSim-Matlab/Simulink joint simulation platform and hardware in the loop verification platform. Through double lane shift simulation on joint and bisectional road conditions, compared to the "general control" strategy, it is verified that the proposed distribution strategy can reduce the error of yaw rate and sideslip angle up to 47.1% and 50.3% compare to the general controller, and the calculation cost is reduced so that effectively improve the handling stability and real-time performance when facing different roads.