Motors: expansible chamber type – With motive fluid valve – Contracting chamber exhaust valve controlled by expanding...
Patent
1980-12-24
1983-02-08
Walton, George L.
Motors: expansible chamber type
With motive fluid valve
Contracting chamber exhaust valve controlled by expanding...
91433, 91461, 91517, 91518, 13759613, 13759614, 91516, F15B 1110
Patent
active
043721931
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention is directed to pilot operated control valve systems and particularly those having an actuator requiring a continuous force on the actuator at the same time other work is being performed.
2. Background Art
Many systems use an accumulator to maintain a constant force on an actuator and thus allow the control valve to be returned to neutral. Even though these systems provide a constant force to the actuator, they are limited by the volume of the accumulator and the available space to locate the accumulator. Other systems use a feedback from the actuator to directly oppose the shifting force of the pilot pressure acting on the main control valve. These systems require additional components in the main control valve which adds complexity to the valve and does not allow the use of conventional available valves. Still others teach the use of reducing to a fixed level the pilot pressure to one end of the first valve in a priority system to allow the valve to attain some intermediate position in response to the actuation of the second valve. These systems will allow a constant force to the first actuator, however they do not allow the first valve total priority when the second valve is actuated.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the invention, a fluid system has a fluid source, an actuator, a tank and a pilot operated control valve. The pilot operated control valve has first and second ends and is movable between an actuated position and a neutral position. At the actuated position, the source communicates with the actuator and is blocked from a downstream control valve, and at the neutral position the fluid from the source is blocked from communication with the actuator and communicates with the downstream control valve through the pilot operated control valve. A pilot control valve is connected to a source of pressurized pilot fluid and the first and second ends of the pilot operated control valve. The pilot control valve is movable between a neutral position at which the source of pressurized pilot fluid is blocked from communication with the first and second ends, and an actuated position at which pressurized pilot fluid from the source is communicated with the first end establishing a differential pressure between the first and second ends. A means modulatably reduces the pilot differential pressure between the first and second ends of the pilot operated control valve at the actuated position of the pilot operated control valve in response to the fluid pressure in the actuator reaching a predetermined level, so that the pilot operated control valve is controllably moved between the neutral and actuated positions to maintain the predetermined pressure level in the actuator and to pass fluid to the downstream control valve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of an embodiment of the present invention.
FIG. 2 is a schematic of a portion of FIG. 1 illustrating a second embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1 a fluid system is generally indicated by reference numeral 10 and includes a fluid source, such as, a pump 12 and a pilot operated control valve 14 connected to the pump 12 by a conduit 16. An actuator 18 is connected to the pilot operated control valve 14 by a pair of conduits 20, 22. A control valve 24 is connected to the pilot operated control valve 14 by a conduit 26 and positioned downstream of the pilot operated control valve 14. A tank 28 is connected to the pilot operated control valve 14 by a conduit 30.
The pilot operated control valve 14 is movable between a first or neutral position "A", a second or actuated position "B" and a third position "C". The pilot operated control valve 14 is biased by centering springs 31 to the neutral position in a conventional manner. At the neutral position "A" the fluid source or pump 12 is blocked from communication with the
REFERENCES:
patent: 2931389 (1960-04-01), Modg, Jr. et al.
patent: 3720059 (1973-03-01), Schurawski et al.
patent: 3799200 (1974-03-01), Tipton
patent: 3927603 (1975-12-01), Bernhoft
patent: 3994325 (1976-11-01), Cryder et al.
patent: 4041983 (1977-08-01), Bianchetta
patent: 4230022 (1980-10-01), Bianchetta et al.
Burrows J. W.
Caterpillar Tractor Co.
Walton George L.
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