Fluid handling – Self-proportioning or correlating systems – Self-controlled branched flow systems
Patent
1996-06-11
1998-04-07
Michalsky, Gerald A.
Fluid handling
Self-proportioning or correlating systems
Self-controlled branched flow systems
91451, 13759613, F15B 1308
Patent
active
057353050
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an unloading system to be employed in a hydraulic circuit for supplying a discharged pressurized fluid of a hydraulic pump to an actuator by a direction control valve.
BACKGROUND ART
In a hydraulic circuit employing a closed center type direction control valve which is designed for closing an inlet port at a neutral position, flow of a discharged pressurized fluid of the hydraulic pump is shut off in the direction control valve to elevate the discharge pressure. As a result, power loss of a driving power source for driving the hydraulic pump becomes large.
Therefore, as a system for reducing the power loss, an unloading system shown in Japanese Examined Patent Publication (Kokoku) No. Heisei 2-53641 has been known, for example.
Namely, it has been known that an unloading system which comprises an unload valve including a pressure receiving portion and a valve portion varying an opening area depending upon variation of the pressure at the pressure receiving portion, and a switching valve, is provided. The switching valve is opened while the direction control valve is held in the neutral position, for establishing fluid communication between a discharge passage of the hydraulic pump and a tank. The switching valve is closed upon switching of the valve position of the direction control valve from the neutral position to the supply position. In conjunction therewith, the opening area of the valve portion is varied by a load pressure acting on the pressure receiving portion of the unload valve to branch a part of the discharged pressurized fluid of the hydraulic pump to the tank to make a pressure difference at the upstream and downstream of the direction control valve constant.
Such unload system encounters a problem in complicated construction since the unload valve constituted of the pressure receiving portion and the valve portion and the switching valve are separated.
The present invention is to overcome such defect in the prior art. Therefore, it is an object of the present invention to provide an unload system for a hydraulic circuit which can significantly simplify the construction.
DISCLOSURE OF THE INVENTION
In order to accomplish the above-mentioned object, according to one aspect of the invention, there is provided an unloading system which is characterized in that an unload valve draining a part of supplied pressurized fluid to a tank and a switching valve for draining a pressurized fluid for biasing the unload valve in a direction for reducing a flow rate for draining to the tank, are arranged in series in an axial direction in a valve main body.
With the construction set forth above, since the unload valve and the switching valve are arranged in axial direction of the valve main body, the construction can be significantly simplified.
It should be noted that, in the construction set forth above, it is desirable that the unload valve is constructed by forming a valve bore having an inlet port, a tank port and an outlet port in the main valve body, fitting a valve body for communicating the inlet port, the tank port and the outlet port, and for increasing and decreasing open area between the inlet port and the tank port, in one side of the valve bore, and forming a first pressure receiving chamber communicated with the inlet port, in which a pressure biases the valve body in a direction for reducing the open area, in the valve bore, and the switching valve is constructed by engaging a spool at the other side of the valve bore for defining a second pressure receiving chamber to be supplied a load pressure between the spool and the valve body, and providing a spring for biasing the spool in a direction for communicating the first pressure receiving chamber to the tank against the load pressure of the second pressure receiving chamber.
Furthermore, it is preferred that the first pressure receiving chamber is defined between the valve body, a valve main body and the plug and the second pressure receiving chamber is defined between the valve
REFERENCES:
patent: 2781049 (1957-02-01), Binford et al.
patent: 3722543 (1973-03-01), Tennis
patent: 4040438 (1977-08-01), Wilke
patent: 4139021 (1979-02-01), Ailshie et al.
patent: 4216797 (1980-08-01), Budzich
Ikei Kazunori
Taka Keisuke
Komatsu Ltd.
Michalsky Gerald A.
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