Fluid control system having float control

Details Fluid control system having float control Fluid control system having float control

1999-05-07

2001-01-16

Lopez, F. Daniel (Department: 3745)

Motors: expansible chamber type

With motive fluid valve

Independent control of bypass between opposed working chambers

C091S447000

Reexamination Certificate

active

06173639

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to a fluid system having a fluid control circuit for a lift actuator of a bucket of a loader or the like, and more articularly, to a fluid control circuit having a float function.
BACKGROUND ART
Fluid control systems including a float function, that is, the ability for fluid to move between opposite ends of actuator under equalized pressure conditions to provide a ground following capability, are well known. Typically however, the known systems do not provide load check valves between the directional control valve and the actuator. When load check valves are disposed therein it is necessary to provide an arrangement that not only provides the float function but also unseats the load check valves. Additionally, it is desirable to provide a circuit that provides zero leak or at least substantially zero leak from the actuator. In order to help ensure at least low leakage, a closed center directional control valve is normally used as opposed to an open center directional control valve.
Accordingly, 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 present invention, a fluid control circuit is provided for use in a fluid control system to permit an actuator to float. The fluid control circuit includes a source of pressurized fluid connected to a reservoir, a source of pressurized pilot fluid, and a fluid actuator having first and second fluid actuating chambers. The fluid control circuit includes a pilot operated directional control valve disposed between the source of pressurized fluid and the first and second fluid actuating chambers of the fluid actuator and being operative to control the flow of fluid to and from the actuator. The directional control valve is movable from a centered, neutral position towards first and second operative positions and a float position. A pilot control arrangement is included and has an input control arrangement. The pilot control arrangement is connected to the pilot operated directional control valve and operative to move the directional control valve from its neutral position towards the first and second operative positions and the float position in response to receiving a signal from the input control arrangement. A first pilot controlled load check valve is disposed between the directional control valve and the first fluid actuating chamber of the fluid actuator and a second pilot controlled load check valve disposed between the directional control valve and the second fluid actuating chamber of the fluid actuator. Each of the first and second pilot controlled load check valves is respectively opened in response to the directional control valve being moved towards the first and second operative positions. Both of the first and second pilot controlled load check valves are simultaneously opened in response to the directional control valve being moved to its float position.


REFERENCES:
patent: 3381587 (1968-05-01), Parquet
patent: 3965587 (1976-06-01), Johns
patent: 5331882 (1994-07-01), Miller

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