Steering-based fault-tolerant control for the braking failures of an independent driving electric vehicle

Abstract

This paper focuses on the safety and stability of a four-wheel independent driving electric vehicle under various braking failure conditions. The power of this four-wheel independent driving electric vehicle is generated from four in-wheel motors using by-wire technology. A dynamic coupling vehicle model with the function of four-wheel driving and four-wheel steering, which includes a flexible suspension system, is established. Subsequently, by combining the change in the non-linear tyre forces at each corner, a quantitative analysis of the transient dynamic behaviours is conducted for different braking failure cases. The control authorities for front steering and rear steering are presented for the special electric vehicle model. Based on functional redundancy of corrective yaw moment generation, three steering control strategies are proposed for fault tolerance in braking failure cases, which include control of the front steering, control of the rear steering and control of the integrated front and rear steering. The controllers of the steering system are designed on the basis of the integral sliding-mode method and a simplified reference model with four-wheel steering. Finally, the effect of the steering control strategies for different braking failure cases are compared with numerical simulations. The result suggests that braking failure could be effectively controlled by using the functional redundancy of the steering system. However, not all steering corrective techniques are available; some even cause performance deterioration for the special condition, and an appropriate control strategy is recommended for different failure cases.