Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1980-05-16
1982-08-10
Cohen, Irwin C.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
91446, 13759613, F04B 4908, F15B 1304
Patent
active
043431526
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to means for sensing the fluid pressure in an actuator and more particularly to a porting arrangement employed with a control valve for selectively communicating a fluid control signal to a servo-system of a hydraulic pump, a pressure compensated flow control valve, or the like.
BACKGROUND ART
Various systems have been proposed for sensing the fluid pressure in a fluid actuator, such as a double-acting hydraulic cylinder, and communicating such fluid pressure in the form of a control signal to a device for controlling operation of a servo-system of a hydraulic pump, a pressure-compensated flow control valve, and/or the like. In systems wherein a spool-type control valve is employed to effect such fluid signal, the spool must normally move a substantial linear distance which poses packaging as well as leakage problems.
The leakage problem is aggravated in high pressure systems wherein two or more ports are uncovered simultaneously. In addition, such ports generally do not circumvent the valve spool whereby fluid forces are not equally distributed therearound, thus necessitating the use of means to restrain rotation of the spool to effect the desired sensing function. Other systems of this type employed resolver or check valves which tend to complicate the system and also require close calibration.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF INVENTION
In one aspect of the present invention, a fluid circuit comprises a pump, a fluid actuator, a control valve having an inlet and first and second outlets, and a reciprocal spool. An improved load sensing means is employed with the control valve for sensing fluid pressure in the first or second outlet and comprises an annular land defined on the spool and an annulus disposed axially between the first and second outlets and further disposed in circumventing relationship relative to the land when the spool is maintained in its neutral position of operation.
The improved load sensing means of this invention is adapted to be activated with a minimal amount of valve spool travel and minimizes high pressure leakage paths. In addition, equal distribution of pressure forces about the spool by the annulus of the load sensing means eliminates the need for any device to restrain rotation of the spool which could adversely affect proper sensing of the fluid signal.
BRIEF DESCRIPTION OF THE DRAWING
Other objects and advantages of this invention will become apparent from the following description and accompanying drawing which illustrates a fluid circuit, including a cross-sectional view of a control valve having an improved load sensing means embodiment of the present invention associated therewith.
BEST MODE OF CARRYING OUT THE INVENTION
The drawing illustrates a fluid circuit 10 comprising a pump 11 for communicating pressurized fluid from a tank 12 to a pressure-compensated flow control valve 13, via an inlet port 14. The displacement of pump 11 may be controlled by a standard servo-system 15 operatively connected therewith to be controlled by a fluid signal in a line 16 in a conventional manner. Pressurized fluid communicated to valve 13 from inlet port 14 will pass through a plurality of ports 17, defined in a piston 18 thereof, to urge the piston rightwardly against the opposing force of a compression coil spring 19. As explained more fully hereinafter, a chamber 20 containing spring 19 is adapted to have a fluid signal communicated thereto to control the position of piston 18 and the quantity of fluid flow passing through valve 13 and a check valve 21.
Fluid flow through check valve 21 will pass into an inlet 22 of a directional control valve 23 with inlet 22 branching out into first and second inlets 24 and 25, respectively. Control valve 23 further includes a spool 26 reciprocally mounted in a bore 27, defined in a housing 28, for sequential movement between first (R), second (N), and third (E) positions. Spool 26 is normally maintained in i
REFERENCES:
patent: 2941547 (1960-06-01), Rood
patent: 3401521 (1968-09-01), Plate
patent: 3592216 (1971-07-01), McMillen
patent: 3602243 (1971-08-01), Holt et al.
patent: 3707988 (1973-01-01), Hodgson
patent: 3858393 (1975-01-01), Budzich
patent: 4030522 (1977-06-01), Heiser
patent: 4129987 (1978-12-01), Blume
Caterpillar Tractor Co.
Cohen Irwin C.
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