Power steering control with damping action against rapid change in vehicle speed

Claim 1

In a wheeled vehicle hydraulic power steering system including a source of pressurized working fluid and a power steering unit supplied with said working fluid to give increased power to steering operation, a control apparatus for preventing a sudden relief of thrust on a steering shaft in response to sudden acceleration or deceleration of the vehicle, comprising: means for generating an electrical signal of which the magnitude is representative of the speed of rotation of the vehicle wheels; a timing circuit having a capacitor, a charge circuit for charging the capacitor with said electrical signal, and a discharge circuit for discharging the energy stored in said capacitor when said signal falls below the voltage developed across said capacitor, the time constant values of said charge and discharge circuits being such that the voltage developed across said capacitor varies at a rate lower than the minimum rate at which the speed of said vehicle wheels varies in response to sudden acceleration and deceleration of the vehicle; an electromagnetically operated control valve for regulating the flow of said working fluid supplied to the power steering unit in response to an electric current supplied thereto; and amplifier means including a field-effect transistor having a control gate connected to said capacitor for providing amplification of said voltage developed across said capacitor and a current amplifier connected to said field-effect transistor for providing an electric current in response to said amplified voltage to operate said control valve.