US Patent 7500537 Steering apparatus for vehicle

A steering apparatus for a vehicle is set to a steer-by-wire mode with an electromagnetic clutch being in a disconnected state. In response to steering operation applied to a steering wheel, first and second electric motors turn left and right front wheels. When a failure arises in one of first and second turning control systems including the first and second motors, the turning characteristic of the left and right front wheels is gradually changed from a turning characteristic for steer-by-wire to that for steer-by-mechanical connection. When a failure arises in the first and second turning control systems or after the turning characteristic is changed, the electromagnetic clutch is brought into a connected state, whereby the steering apparatus is switched to a steer-by-mechanical connection mode. Even when the steer-by-wire mode is switched to the steer-by-mechanical connection mode, a driver is not given an unnatural sensation, and excellent steering stability is maintained.