Vehicle steering systems

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).