A
steering system selectively operable in one of six
modes: steer-by-wire with rear steering, steer-by-wire without rear steering, electronic power assist steering (EPAS) with rear steering,
electronic power steering (EPAS) without rear steering, mechanical
backup manual steering with rear steering, and mechanical
backup manual steering without rear steering. The steer-by-wire
system includes a driver interface
system (DIS), a front road wheel
actuator system (FRWAS), a rear road wheel
actuator system (RRWAS), and a controller for monitoring and implementing the preferred control strategy. The
steering system operates normally in a steer-by-wire mode. In each of the EPAS mode and manual mode, the controller causes a
clutch mechanism to engage, thus creating a mechanical linkage between the steerable member and the
rack and pinion system while maintaining rear wheel assisted steering. In the EPAS mode, one of the front road wheel
actuator or the reaction torque generator is available to assist in the steering operation along with rear wheel steering. Alternatively, in the manual mode, both the DIS and the FRWAS are deactivated and the vehicle is steerable through mechanical device along with the rear wheel assisted steering.