The rear wheels of a vehicle are turned together with the front wheels in response to the operation of a steering wheel. Turning ratio changing means is provided so as to be able to change a turning ratio of the rear wheels to the front wheels. In altering the turning ratio, a speed of changing the turning...http://www.google.de/patents/US4730839?utm_source=gb-gplus-sharePatent US4730839 - Four-wheel steering apparatus for vehicles
