Power assistance steering systems for vehicles

摘要

A power assistance steering system 10 for a vehicle comprises steering gear 12 having an internal hydraulic ram supplied with hydraulic fluid by a pump 14 from a reservoir 16 via a solenoid valve 18 controlled by a micro-processor 20 which also controls an electric motor 22 for driving pump 14. Steering input torque is sensed by a torque sensor 36 and steering direction is sensed by a direction switch 34. Output signals from these devices are fed to micro-processor 20 which controls solenoid valve 18 and pump motor 22 accordingly, varying the motor speed in accordance with the pressure requirements of the steering ram as sensed by the torque sensor. In a further embodiment the pump is driven at a constant speed and a proportional control valve 74 is controlled by a micro-processor 78 to vary the fluid pressure supply.