Steering Stability Control of a Four In-Wheel Motor Drive Electric Vehicle on a Road with Varying Adhesion Coefficient

In order to improve the steering stability of a four in-wheel motor independent-drive electric vehicles (4MIDEVs) on a road with varying adhesion coefficient, such as on a joint road and a μ-split road, this paper presents a hierarchical electronic steering control (ESC) strategy. The upper level controller of the proposed ESC strategy achieves the adaptive control of the yaw rate and sideslip angle in the direct yaw-moment control based on the influence of road adhesion. The lower level controller is designed as a two-hierarchy structure, which can adaptively change the torque allocation algorithm and achieve different weight controls of each wheel torque according to road adhesion coefficient. The results of real-time simulation conducted in the RT-LAB testing platform and a real-car test indicate an improvement in the steering stability of the 4MIDEV on a road with varying adhesion coefficient. Particularly the 'double lane change' testing carried out on a joint road and a μ-split road shows a yaw rate error reduction of up to 55.1%, compared with the ordinary control strategy, with output torque and its fluctuation of each in-wheel motor significantly reduced.