This paper deals with energy-savings in a hydraulic power steering systems by the reduction of the driving torque of a hydraulic pump in non-steering operation. In normal driving, steering operation is infrequent although the pump is continuously driven by the engine. Therefore, for energy-savings in power steering, it is effective to reduce the pump driving torque during non-steering operation. A reduction of the pump driving torque in non-steering operation is possible by decreasing the pump outlet flow rate regulated by a flow control valve.
The authors have investigated a prototype pump with an additional device to minimize the regulated flow rate under a non-steering condition and to restore the flow rate during steering operation. The mechanism is a kind of pressure reducing valve that changes the operation of the flow control valve in response to the pump outlet port pressure which is an indication of steering operation. As a result, the driving torque of this pump decreases to about 70% of that of the conventional pump in non-steering operation.