Patent ID: 7686124

Claim:
A vehicle steer by wire system comprising: a steering wheel ( 40 ) for setting a desired turn angle of a vehicle wheel ( 13 ); a steering wheel turn sensor ( 42 ) for sensing the desired turn angle; a hydraulic steering actuator ( 12 ) for turning the wheel; a wheel turn sensor ( 43 ) for sensing the current wheel turn angle; a control unit ( 23 ) for receiving the desired turn angle and current wheel turn angle signals; an electronically controlled steering actuator control valve means ( 14 ) for supply pressurized fluid to the steering actuator ( 12 ) via a steering circuit in response to signals from the control unit ( 23 ) to turn the wheel to the desired turn angle; a hydraulic motor ( 18 ) connected with the steering wheel ( 40 ) to provide steering feedback to the steering wheel via a feedback circuit ( 17 ); and an electrically controlled hydraulic feedback control valve means ( 21 , 24 ) which directs fluid to and from the hydraulic motor ( 18 ) in response to the signals from the control unit to generate the steering feedback; the steering system being arranged to have a fail-safe mode in which fluid pressure from the hydraulic motor ( 18 ) provides steering of the wheel ( 13 ) in the event of a failure to electronically actuate the steering actuator control valve means ( 14 ).