Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1997-07-24
1998-10-20
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
91446, F16D 3102
Patent
active
058229884
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a flow control device of a power steering apparatus suitable for use in vehicles and like. More particularly, the present invention relates to a flow control device of a power steering apparatus which is capable of energy saving by decreasing the flow rate supplied from a pump to a control valve at low load pressure.
Background of the invention
Flow control devices of power steering apparatuses have been proposed for energy saving of vehicle engine by decreasing the flow rate supplied from a pump to a control valve at low road pressure when a steering wheel is not rotated. Examples of the flow control device are shown in the Japanese Unexamined Patent Publication No. 6-8840, the U.S. Pat. No. 5,439,070 and the German Laid-open Publication Patent No. 43 19 495 A1. The above flow control device contains a load pressure responsive valve (hereinafter referred to as a responsive valve) with a variable orifice which is responsive to the road pressure. It is possible for the flow control device to reduce the energy consumption because the variable orifice releases pressure in a spring chamber of the flow control valve to low pressure side in order to reduce the flow rate supplied to a control valve when the road pressure is relatively low.
However, the flow control device for energy saving involves some drawbacks. Namely a normal pump housing can not be applied to the pump with the responsive valve for energy saving. Because the pump housing for energy saving needs a special bore receiving the responsive valve for decreasing the flow rate supplied to the control valve, besides a normal bore receiving the flow control valve for controlling operating fluid to supply to control valve. As a result, since the pump housing for energy saving is different from the normal pump housing, the cost of the flow control device for energy saving is relatively high.
Accordingly, it is an object of the present invention to provide an improved flow control device, a pump housing of which can be made up of a normal pump housing as a common housing between a normal pump without the responsive valve and a pump with it.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above mentioned problem. Briefly, the flow control device of a power steering apparatus comprises a control valve, a pump, a power cylinder, a metering orifice, a flow control valve, a valve receiving bore, a union, and a load pressure responsive valve.
The control valve has variable throttles arranged on paths connected to the pump, both fluid chambers of the power cylinder and the reservoir. The metering orifice is arranged in a supply passage leading operating fluid discharged from the pump to the control valve. The flow control valve has the metering orifice, a spring chamber connected to the supply passage downstream of the metering orifice, and a bypass spool urged by a spring in the spring chamber so as to regulate an opening of a bypass passage in accordance with the pressure difference across the metering orifice. The valve receiving bore slidably receives the bypass spool in a housing of the pump. The union, arranged in the valve receiving bore, has the metering orifice at a first end of it and an outlet port leading operating fluid passed through the metering orifice at a second end. The load pressure responsive valve, received in the union, has a variable orifice. The load pressure responsive valve brings the spring chamber into communication with the reservoir when road pressure, caused by operation of a steering wheel, is relatively low and the load pressure responsive valve shuts the communication between the spring chamber and the reservoir in response to rising of the road pressure.
With the above configuration, in the situation where the load pressure is relatively low when the steering wheel is in its neutral position, the variable orifice of the load pressure responsive valve received in the union is open, then pressure in the
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patent: 4020867 (1977-05-01), Sumiyoshi
patent: 5170626 (1992-12-01), Ohtaki et al.
patent: 5471838 (1995-12-01), Suzuki et al.
patent: 5685146 (1997-11-01), Takeuchi et al.
Lopez F. Daniel
Toyoda Koki Kabushiki Kaisha
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