The present invention relates to a steering angle control system for a four-wheel-steerable vehicle, and more specifically to a fail-safe steering angle control system designed to minimize the change in vehicle steering characteristic when an abnormal condition occurs in either the front or rear wheel steering systems.
In a vehicle steering angle control system having a front wheel auxiliary steering system and a rear wheel steering system, as disclosed in U.S. Pat. No. 4,705,131, a fail-safe system detects an abnormal condition in the front and rear steering systems, and makes the front wheel auxiliary steering angle or the rear wheel steer angle equal to zero by stopping the operation of only the abnormal system, i.e., either the front or rear steering system.
However, this conventional fail-safe system, markedly changes the handling characteristic of the vehicle by reducing the controlled steering angle of the abnormal steering system to zero, so that it becomes difficult for the driver to control the vehicle.