Four Independent Wheels Steering System Analysis

In this paper a four independent wheel-steering system and its application on the HOST prototype are presented. The prototype is a heavy duty vehicle with four wheel motors controlled by wire, so that each wheel is mechanically not-linked to the other ones and has four degrees-of-freedom. Each wheel has an electric steering actuator to move the wheels around the steering axis, which is controlled by wire. The first part of the work deals with the model determination, reducing the four degree-of-freedom system into a one degree-of-freedom system. In the second part, the relationship between the rotations of each wheel and the linear movement of the electric steering is presented. In the third part the steering ratio is calculated and a parameter to reduce the slip angle is defined. In this way a four independent wheel steering model has been developed and applied to the specific characteristics of HOST. Finally the vehicle handling has been tested through simulations of steering-pad and moose-test, in order to verify the stationary and dynamic handling behavior. Despite the model is simplified, owing to the use of the corrective parameter, good performances in terms of turning radius, slip-angle and roll-angle are achieved, increasing maneuverability and stability.