A front Steer-by-Wire (SBW) vehicle does not have conventional mechanical linkage; an actuator such as a brushless motor exclusively powers the front steering gear, and the steering wheel is an interface between the driver and the vehicle controller. The SBW vehicles have good prospects of innovative driveability. The performance depends on the vehicle controller that commands the front steer angle according to driver's input. By the use of D* controller that the authors have developed, for instance, the center of gravity (CG) of SBW vehicle promptly follows a trajectory intended by the driver. The SBW system requires an interface that corresponds to the steering wheel for conventional steering vehicle. Challenging problems will be found concerning the structure and the function of such interfaces. A variety of driver models have been proposed so far for the conventional steering vehicles for numerical simulation and theoretical analysis. These models cannot be applied to the SBW because the driver operates the vehicle indirectly via the interface. This paper newly introduces a curvature output driver model, which is applicable to various vehicles including the one with conventional mechanical linkage. Theoretical insights are obtained from steady state constant radius turn characteristics, rather than a straight line driving often investigated for the conventional driver models. A SBW vehicle is simulated for various cases including constant radius turns, lane changes, and crosswind responses.
Abstract