Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
2002-08-26
2004-08-31
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S452000, C091S445000
Reexamination Certificate
active
06782697
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a fluid control system and, more particularly, to a pressure-responsive hydraulic system including a pressure-compensating valve with load check.
BACKGROUND
It is well known that when operating two different fluid circuits in parallel with a common pump, the circuit having the lightest load will automatically take the pump's flow. Likewise, the circuit with the heaviest load will stall or slow to such an extent that the operation of that circuit is severely hampered. Thus, in a hydraulic system with a single pump supplying flow to multiple circuits in parallel, it is desirable to provide a control valve that will meter pump flow to the cylinders independent of the load on the cylinder.
In some conventional fluid control systems, a compensator may be disposed between the meter-in directional control area on a main control spool and an actuator conduit. The compensator regulates the pressure of the flow of oil coming from the meter-in flow control area as needed, such that all fluid circuits will experience the same load pressure and command the same flow as the circuit with the highest load pressure. When all the circuits have equal load pressure, the flow being supplied from the pump to the actuators is proportional to the commanded flow and independent of the load on the cylinder.
For example, U.S. Pat. No. 5,890,362 discloses a pressure-compensated hydraulic system where the valve section of each fluid circuit has a pressure-compensating valve. However, because the pump flow is being used to operate the pressure compensation mechanism and provide a control signal, pressurized fluid flow is being taken away from the actuators. Also, this directional control valve has a relatively complicated stem structure and requires additional machining to vent the bridge passage to tank when the control valve is in neutral.
The present invention is directed to overcoming one or more of the problems set forth above.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a fluid system may include a source of pressurized fluid in operable communication with a first actuator and a second actuator. First and second control valves may be operable to control fluid communication to and from the first and second actuators. A first pressure compensating valve may be in fluid communication with the first control valve and the first actuator, and a first signal conduit may be in fluid communication with fluid flow being directed by the first control valve to the first pressure compensating valve and the first actuator. A second pressure compensating valve may be in fluid communication with the second control valve and the second actuator, and a second signal conduit may be in fluid communication with fluid flow being directed by the second control valve to the second pressure compensating valve and the second actuator. A greater of a first signal pressure carried by the first signal conduit and a second signal pressure carried by the second signal conduit may be used to generate a control signal pressure, and the control signal pressure may be in fluid communication with the first pressure compensating valve and the second pressure compensating valve.
According to another aspect of the invention, a method of operating a hydraulic system having more than one actuator supplied by a single source of pressurized fluid is provided. The method may include supplying pressurized fluid to a first actuator via a first control valve and a first pressure compensating valve and supplying pressurized fluid to a second actuator via a second control valve and a second pressure compensating valve. The method may also include generating a first control signal pressure from pressurized fluid being directed by the first control valve to the first pressure compensating valve and generating a second control signal pressure from pressurized fluid being directed by the second control valve to the second pressure compensating valve. The method may still further include generating a control signal pressure from a greater of the first control signal pressure and the second control signal pressure and directing the control signal pressure to the first and second pressure compensating valves to affect fluid flow to the first and second actuators.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 5067389 (1991-11-01), St. Germain
patent: 5077972 (1992-01-01), Bianchetta et al.
patent: 5251444 (1993-10-01), Ochiai et al.
patent: 5291821 (1994-03-01), Yamashita et al.
patent: 5890362 (1999-04-01), Wilke
patent: 6082106 (2000-07-01), Hamamoto
patent: 6334308 (2002-01-01), Sato et al.
Barnes D. James
Burrows J. W.
Caterpillar Inc.
Finnegan, Henderson, Farabow, Garret & Dunner
Kershteyn Igor
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