The Development of an Experimental Four-Wheel-Steering Vehicle

This paper describes the development of a vehicle with four-wheel steering in which the rear wheels can be controlled electronically in addition to the conventional front-wheel steering system. In the method for steering the rear wheels, the side-slip angle at the vehicle's center of gravity is maintained at zero, which improves the basic dynamic properties of the vehicle. This approach allows greater maneuverability at low speed by means of counter-phase rear steering and improved stability at high speed through same-phase rear steering. However, the use of counter-phase rear steering to improve maneuverability gives rise to problems in regard to practicality. In addition, continuously controlled four-wheel steering, using counter-phase at low speed and same-phase at high speed, leads to many other problems regarding practicality because of the strong apparent understeer characteristics. Therefore a selection must be made between two approaches if a vehicle with four-wheel steering is to become a practical reality. That is, either sepatate systems must be adopted for low and high speed use, or a four-wheel steering system must be designed that would apply active steering to the front wheels as well. This paper further describes an optimum control system based on active steering at both front and rear wheels, which brings out the maximum effects of four-wheel steering.