Abstract
A new steering system which has variable gear ratio according to vehicle speed and steering wheel angle has been developed with the aim of ideal steering. As the steering gear ratio in existing vehicles is almost constant, the yaw rate gain increases with increasing vehicle speed. Moreover, for under-steer vehicle, the yaw rate gain tends to decrease with increasing lateral acceleration. With a view to making driver-vehicle response improvement, a steering system which the equivalent steering gear ratio increases with increasing vehicle speed and decreases with steering wheel angle has been created with simple mechanism. This paper presents the procedure for selecting variable gear ratio characteristic from hypothesis of ideal gear ratio which was derived from observation of driver's steering behavior to the compensation of the gear ratio for vehicle speed and steering wheel angle, and the estimation of the effects of the gear ratio by simulation. And this also introduces the construction in order to realize the selected gear ratio, the effects that were confirmed by vehicle test, and the results that were confirmed if the vehicle with VGS was easy to drive for many ordinary drivers.
