Variable ratio steering system

Abstract

A variable ratio steering system on a motor vehicle can vary the ratio of the angle through which the steerable road wheels are steered to the angle through which the steering wheel is turned by the driver. The variable ratio steering system includes an input shaft coupled to the steering wheel, a first ball screw mechanism including a first nut threaded through balls over the input shaft, an output shaft coupled to the steerable road wheels, a second ball screw mechanism including a second nut threaded through balls over the output shaft, and a steering angle ratio adjusting mechanism, mechanically coupled to the first and second nuts, for varying the ratio of an axial displacement of the second nut to an axial displacement of the first nut. The steering angle ratio adjusting mechanism includes a swing member swingable in a direction substantially parallel to the input and output shafts about an axis lying in a plane transverse to the input and output shafts, the first and second nuts being coupled to respective different portions of the swing member. The steering angle ratio adjusting mechanism varies the distance between the axis about which the swing member is swingable and at least one of the different portions to which the first and second nuts are coupled.