Study on fail-safe strategy of electric power steering system

Based on the six-freedom-degree model of four-wheel-drive electric vehicles, the fail-safe problem of (Electric Power Steering system) EPS is analyzed, and an EPS fail-safe strategy based on state observer is proposed in this paper. When EPS failed, by detecting the cornering angle of the steer wheel or the torsion of the steer wheel, the yaw rate command can be estimated. The vehicle´s body is forced to turn around to the desired direction by the distribution of the proper brake torque to the four wheels. In order to speed up system´s response, a yaw feed forward compensator is employed in the controller. The simulation results show that when EPS failed, by distributing brake torques, the vehicle turns to the expected direction without steering angle. Consequently, the effectiveness of EPS fail-safe control strategy is validated.