A backup system for automotive steer-by-wire, actuated by selective braking

In this paper we propose an alternate approach to improve steer-by-wire (SbW) reliability in which we utilize brake-actuated steering (BAS) as an independent secondary backup steering system. In SbW systems, component and module redundancy is the common approach used to maintain the steering function when a failure occurs. Unfortunately this adds a significant amount of complexity and cost and, what is more important, it is not possible to overcome unanticipated and common mode failures of the SbW system. BAS utilizes the torque generated by selective wheel braking and/or acceleration to actuate the steering mechanism. With this approach, if the primary steering system (SbW) fails uncovered or there is a common mode failure, the steering rack is decoupled from the primary steering actuator and the wheels are instead steered by the torque generated by application of asymmetric braking (or acceleration). BAS, as well as SbW, will be a heavy user of power electronics, electrical actuators, sensors and sophisticated control systems, many of which are already available from electronic stability systems (e.g., ESP), which are becoming more common in passenger cars. In this paper we detail the characteristics of the BAS system and provide the models necessary for designing appropriate power electronics and control systems.