An Energy Saving Technique in an Electro-Hydraulic Power Steering (EHPS) System

This paper deals with an energy-saving electro-hydraulic power steering (EHPS) system using a center-closed servo valve without an accumulator. During non-steering operation, the pump and motor in this EHPS system operate at an extremely low speed with a low voltage. At neutral position in non-steering condition, the pump delivery flow leaks through the clearances in the hydraulic components, raising the pump pressure because the center-closed servo valve does not pass oil-flow. With a lower delivery flow rate, the pump pressure rises slightly and the motor current is also low, resulting in low electric energy consumption. When the steering wheel is turned, the pump and motor operate at a high speed and supply as much oil as needed to produce sufficient assist force.

This EHPS system was tested on a conventional engine-driven vehicle with a front weight of 720kg and its effectiveness was revealed.