A rear wheel steering angle control apparatus is provided with a rear wheel steering angle determining unit and a rear wheel steering mechanism so as to determine a steering angle ratio based upon vehicle speed and perform a rear wheel steering angle control. An alerting unit alerts that the output of the rear wheel steering mechanism is beyond a predetermined allowable range when an observing unit detects a control condition being abnormal and releases the alert when the output of the rear wheel steering mechanism is within the predetermined allowable range.
This application is based on and claims priority under 35 U.S.C. .sctn.119 with respect to Japanese Application No. 2001-093468 filed on Mar. 28, 2001, the entire content of which is incorporated herein by reference.
A four wheel drive system for bilaterally symmetric vehicles is characterized by separate drive systems for the front and rear wheels. Each drive system is operable to independently drive each wheel. The rear wheels of the vehicle are steering wheels which are connected with the vehicle frame for independent rotation about a vertical axis. Steering and driving of the wheels is controlled by a controller. The combination of independent steering for the rear wheels and independent powering of all four wheels provides the vehicle with a zero turning radius for improved mobility as well as improved traction on unstable surfaces.
