Back-drivable steer-by-wire system with positive scrub radius

A back-drivable steer-by-wire steering system, comprising:

• a road wheel actuator assembly coupled to a vehicle wheel for effecting turning movement of the wheel wherein the road wheel actuator assembly defines a steering axis and wherein the steering axis is off-set from a longitudinal axis of the wheel by a positive scrub radius;
• wherein in a normal mode of operation, movement of the road wheel actuator assembly is effectuated by the steer-by-wire system;
• wherein in a failure mode of operation, the road wheel actuator assembly is back-drivable by a brake force applied to the wheel and acting through the positive scrub radius;
• and
• further wherein the road wheel actuator assembly includes an electric motor and wherein windings of the motor are shorted to damp a movement of the road wheel actuator assembly via back electro-motive forces.

A method to steer a vehicle after failure of a road wheel actuator assembly in a back-drivable steer-by-wire steering system, the road wheel actuator assembly coupled to a vehicle wheel for effecting turning movement of the wheel and the road wheel actuator assembly defining a steering axis, the steering axis off-set from a longitudinal axis of the wheel by a positive scrub radius, comprising the acts of:

• applying a braking force to the wheel;
• generating a torque on the road wheel actuator assembly by the applied braking force, the applied braking force acting on the road wheel actuator assembly through a moment arm defined by the positive scrub radius;
• moving the road wheel actuator assembly in response to the torque;
• turning the vehicle wheel in response to moving the road wheel actuator assembly;
• and
• damping a movement of the road wheel actuator assembly.

A method to steer a vehicle after failure of a road wheel actuator assembly in a back-drivable steer-by-wire steering system, the road wheel actuator assembly coupled to a vehicle wheel for effecting turning movement of the wheel and the road wheel actuator assembly defining a steering axis, the steering axis off-set from a longitudinal axis of the wheel by a positive scrub radius, comprising the acts of:

• applying a braking force to the wheel;
• turning the wheel a first degree in a direction in response to the applied braking force;
• generating a torque on the road wheel actuator assembly by the applied braking force, the applied braking force acting on the road wheel actuator assembly through a moment arm defined by the positive scrub radius;
• moving the road wheel actuator assembly in response to the torque;
• and
• turning the wheel a second degree in the direction in response to moving the road wheel actuator assembly, the second degree greater than the first degree.

A vehicle, comprising:

• a vehicle body including a wheel;
• and
• a back-drivable steer-by-wire system including a road wheel actuator assembly coupled to the wheel wherein the road wheel actuator assembly defines a steering axis and wherein the steering axis is off-set from a longitudinal axis of the wheel by a positive scrub radius;
• wherein the road wheel actuator assembly includes a damping assembly.