Fault tolerant control using disturbance observer by mutual compensation of steer-by-wire and in-wheel motors

In this paper, a fault tolerant control method is proposed for vehicles with steer-by-wire and in-wheel motors. In such vehicles, the lateral motion of the vehicle can be controlled by two means, the steering angle and driving force difference between the left and right wheels. Therefore, even if one of the steering or driving systems fail, the influence of the failure on the lateral motion of the vehicle can be compensated by the other system. The objective of this study is to achieve this function without detecting which system is faulty. This is realized by the disturbance observer following the yaw rate to the target value calculated from the target steering angle. The convergence to the target yaw rate is analyzed considering three cases: (i) both the steering and driving systems are normal, (ii) the steering system is faulty but the driving system is normal, and (iii) the steering system is normal but the driving system is faulty. The performance and effectiveness of the control is demonstrated through simulation.