Control of Brake- and Steer-by-Wire Systems During Brake Actuator Failure

In this paper a method of mitigating the consequences of potential brake actuator failure in vehicles with brake-by-wire (BBW) and possibly with steer-by-wire (SBW) systems is described. The proposed control algorithm is based on rules derived from general principles of vehicle dynamics. When a failure of one actuator is detected, the algorithm redistributes the braking forces among the remaining actuators in such a way that the desired deceleration of vehicle is followed as closely as possible, while the magnitude and the rate of change of the yaw moment caused by asymmetric braking are properly managed. When vehicle is equipped with BBW system only, or when the desired deceleration can be obtained by redistributing of braking forces, without generating an undesired yaw moment, no steering correction is used. Otherwise, a combination of brake force redistribution and steering correction (to counter the yaw moment generated by non-symmetric braking) is applied.

The proposed algorithm is tested using a high fidelity vehicle model, in which the traditional brake and steering systems are replaced by their by-wire counterparts. Results of simulations demonstrate that during brake failure, the vehicle with the proposed algorithm enabled follows the desired deceleration more closely, helping to reduce the stopping distance. More importantly, dramatic reductions in the lateral path deviation and undesired yaw rate of vehicle are achieved.