Variable ratio steering system

摘要

In a variable ratio steering system of a vehicle with a variable steering ratio mechanism varying a steering ratio R of steering wheel angle theta_S to road wheel steer angle theta_W at steered road wheels, a vehicle speed sensor, and a steering angle sensor, a steering ratio control unit controls the steering ratio according to a fixed steering ratio characteristic when the steering wheel angle theta_S is less than or equal to a predetermined angle theta₁ substantially corresponding to a neutral position of a steering wheel. Conversely when the steering wheel angle theta_S is greater than the predetermined angle theta₁ substantially corresponding to the neutral position of the steering wheel, the steering ratio control unit controls the steering ratio according to a vehicle-speed dependent steering ratio characteristic that a steering angle versus road wheel steer angle characteristic varies depending on a vehicle speed value.