Single Seat Holding Valve

Abstract

A holding valve for regulating the exhaust flow of fluid from a hydraulic actuator including a cartridge defining a first port adapted to be connected to a directional control valve, a second port adapted to be connected to one side of the hydraulic actuator and a third port adapted to be connected to the other side of the hydraulic actuator, there being provided a pilot operated poppet valve that closes in opposition to fluid pressure in the actuator through the second port to control exhaust flow from the actuator and also to prevent exhaust flow when the directional valve is in neutral, there also being provided a check valve surrounding the poppet valve for the purpose of permitting the free flow of line pressure from the first port to the second port and the hydraulic actuator, with this check valve being annular in configuration, surrounding the poppet valve and having a shoulder defining the seat for the poppet valve to improve the characteristics of the holding valve and also to permit the simple replacement of the main poppet valve seat when necessary.

Description

BACKGROUND OF THE PRESENT INVENTION

Pilot operated holding valves have been provided in the past for regulating the exhaust flow from a hydraulic actuator. The primary purpose of these holding valves is to control the lowering of a load connected to the hydraulic actuator. With the pilot piston that operates the poppet valve connected to one side of the actuator the poppet valve controls exhaust flow from the other side of the actuator, so that if the load tends to overrun, the pressure in the load lowering side of the actuator will drop, reducing pilot pressure which in turn tends to close the main poppet valve and restrict the exhaust flow from the actuator and reduce the speed of load lowering to a controlled condition.

It is also known in the art to provide a bypass check valve that permits the free flow of fluid from a directional control valve to the load raising side of the actuator for the purpose of bypassing the poppet holding valve.

There have been several problems associated with these prior art pilot operated holding valves. The first results from the fact that the seat for the main poppet valve is formed in prior art constructions either in the holding valve housing, or cartridge. If deterioration of the seat occurs, which it oftentimes does, it is necessary to replace the holding valve housing or remachine the seat which is a difficult and expensive machining operation.

Other disadvantages in prior art holding valves are that it is difficult to control the effective area of the poppet upon which cylinder pressure acts and also difficult to control the area of the poppet valve upon which pilot pressure acts. These parameters control the responsiveness of the valve and also control the change of the size of the poppet valve orifice with changes in travel or movement of the poppet valve.

SUMMARY OF THE PRESENT INVENTION

In accordance with the present invention an improved holding valve is provided in which the main valve seat may be easily replaced and in which the various areas that control the valve characteristics may be easily changed to control the performance of the valve in a simpler manner than prior art constructions.

Toward this end a counter-balance holding valve is provided that has a cartridge sleeve defining a first port communicating with a directional control valve, a second port connected to one side of the hydraulic actuator and a third port connected to the other side of the hydraulic actuator. Disposed within this sleeve is a pilot operated main poppet valve that controls and regulates flow from the second port to the first port to control the lowering of the load connected to the hydraulic actuator. This main poppet valve also serves to hold the load in position by preventing flow from the second port to the first port when the directional control valve is in neutral.

To provide for forward flow from the control valve to the actuator, and hence from the first port to the second port in the sleeve, a check valve is provided that is annular in configuration, slidable in the cartridge sleeve, and surrounding the main poppet valve. This check valve has the novel characteristic that its internal bore defines a seat for the main poppet valve. In this manner when deterioration of the poppet valve seat occurs it is merely necessary to replace the inexpensive check valve, since it also defines the seat for the main poppet valve.

The term "percentage characteristic" refers to the sensitivity of the poppet valve in response to variations in pilot pressure acting on the poppet valve and is equal to the area of the poppet valve against which cylinder pressure acts divided by the area of the poppet valve against which pilot pressure acts. A higher pilot piston area relative to the cylinder pressure area referred to means that a lower pilot pressure is required to open the main poppet valve and hence the valve has an increased sensitivity.

This percentage characteristic can be easily varied in the present holding valve since the area of the poppet valve against which cylinder pressure acts may be made either positive, balanced or even negative if desired, and the pilot piston area may also be easily varied as desired.

A further advantage in the present invention is that fluid flow passing through the valve in either direction does not pass through the coils of either the poppet valve spring or the spring urging the check valve closed.

Further advantages are that a thermal relief valve may be easily provided and the main counterbalance spring may be adjusted as desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the cartridge holding valve according to the present invention;

FIG. 2 is an enlarged longitudinal section of the holding valve shown in FIG. 1 taken generally along line 2--2 thereof illustrated in conjunction with a typical fluid actuator circuit shown schematically; and

FIG. 3 is a longitudinal section of a somewhat modified form of the holding valve illustrated in FIG. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and particularly FIGS. 1 and 2 a cartridge type holding valve 10 is illustrated in circuit with a 4-way directional control valve 12 and a reciprocating piston hydraulic actuator 14 shown schematically in FIG. 2.

The 4-way control valve 12 selectively ports fluid from a supply line 16 to line 18 to the right side 20 of actuator 14 which drives piston 21 in what may be assumed to be a load lowering direction, or to line 23 through holding valve 10 to line 24 connected to the left side 26 of actuator 14 to drive the piston 21 in what may be assumed to be a load raising direction.

The primary purpose of the holding valve 10 is to control the speed of piston 21 when moving in a load lowering direction to control the smooth lowering of the load connected to the piston 21. Holding valve 10 also serves to lock the piston 21 in position when the directional control valve 12 is in its neutral position.

The holding valve 10 includes a stepped cylindrical cartridge sleeve 30 seated within a stepped counterbore 31 in valve housing 32 and threaded therein as seen at 34. Sleeve 30 has a hexagonal head portion 35 projecting from the housing 32 and sealed thereto with a sealing ring 36.

The sleeve 30 has lands 39 and 40 that define recesses for seal assemblies 42 and 43 in turn defining annular recesses 46, 47 and 48 around the periphery of the sleeve 30 within the housing 32.

The sleeve 30 has a first annular array of ports 50 communicating across recess 46 with housing port 48 connected to fluid supply and return line 23.

The sleeve 30 has a second annular array of ports 50' communicating across recess 37 with housing port 52 connected to receive and deliver fluid relative to line 24 connected to actuator 14. The sleeve 30 has a reduced annular end portion 55 that is spaced from the end of counterbore 31 defining a flow passage 56 which communicates across recess 48 with a port 58 in the housing 32 that communicates with a pilot pressure line 60 having a restrictor 61 therein. Line 60 communicates with line 18 that delivers fluid to the right side 20 of cylinder 14.

The sleeve 30 has threaded therein a hollow sleeve cap 62 having a hexagonal head portion 63 for the purpose of threading the sleeve 62 within the sleeve 30 as indicated at 65.

The cartridge sleeve 30 has a first counterbore portion 67 communicating with port 50, and a somewhat reduced counterbore 68 communicating with a further reduced counterbore 70 in turn communicating with port 50'. A still further smaller bore portion 73 in turn communicates with a somewhat larger bore 75 opening to the right end of the sleeve 30 and communicating with passage 56 defined in the housing bore 31.

Slidable within the stepped bore cartridge sleeve 30 is a poppet valve assembly 77 having a semi-spherical valving surface 78 at the left end thereof defining with stub shaft 79 a seat for the right end of a heavy duty counter balance spring 82 that urges the poppet valve 77 closed in opposition to fluid pressure in actuator chamber 26 as sensed through ports 52 and 50'.

The spring 82 is adjustable through spring seat 85 and threaded member 87 threadedly engaged in sleeve cap 63 and held in position by a locking nut 89.

The purpose of poppet valve 77 is to control flow between port 52 and port 48, or more specifically between ports 50' and 50 in the sleeve 30 to regulate flow from the actuator chamber 26.

Toward this end the valve 77 has a reduced stem portion 91 connected to a somewhat enlarged head 92 having a seal 93 slidable in cartridge bore 73, in turn connected to an enlarged pilot piston 95 having a sealing ring 96.

Rightward movement of the valve member 77 is limited by a snap ring 98 seated within counterbore 75 in the cartridge sleeve 30.

When the 4-way directional valve 12 is shifted to a position porting fluid to line 18 and draining fluid from line 23 to tank, actuator side 20 is pressurized, tending to drive piston 21 to the left, and also the pilot passage 56 is pressurized across restrictor 61 and port 58 in housing 32. Upon sufficient pressurization of the pilot piston 95 valve member 77 will shift to the left against the force of spring 82, opening valve surface 78 permitting the exhaust flow of fluid from actuator side 26 through line 24, port 52, recess 47, port 50', bore 70, across the valve orifice, through ports 99 in sleeve 62, ports 50 in sleeve 30, and port 48 to line 23 and across the directional control valve 12 to tank.

If the load on the piston 21 tends to overrun the flow of fluid to actuator chamber 20, the pressure in chamber 20 will drop somewhat as will the pressure acting on the pilot piston 98, which in turn causes a shifting of the valve 77 to the right tending to close the valve and restrict the return flow of fluid from actuator chamber 26 and thus return load lowering to the desired speed. The counterbalance valve 77 has a modulating action to control the exhausting of fluid from the return side 26 of the actuator to provide smooth load lowering movement.

Provision is made for permitting the free flow of fluid from the control valve 12 through line 23, port 48 and port 50 across the poppet valve seat to the port 50', port 52 to line 24 to the left side 26 of actuator 14 for the purpose of driving piston 21 to the right. Toward this end a sleeve check valve 101 is provided having a counterbore that receives a biasing spring 102 that biases the check valve 101 into engagement with the valve surface 78 of the main poppet valve 77. A reduced interior shoulder 105 on the check valve defines a floating seat for the main poppet valve 77. The advantage in this is that when the valve seat 105 deteriorates, it is easily replaced merely by replacing the check valve 101. Upon sufficient line pressure in line 23, check valve 101 will shift to the right with poppet valve stopped by ring 98, permitting the forward flow of fluid to the left side of actuator 14.

During the opening movement of the poppet valve 77 the check valve 101 will move slightly to the left therewith holding the main poppet valve orifice closed until the check valve hits shoulder 107 on the sleeve 62 stopping the check valve. Thereafter the poppet valve 77 continues its movement to the left under the influence of pilot pressure on piston 95 opening the poppet valve when the right side of the actuator 14 is pressurized.

The poppet valve 77 has an aperture 110 extending centrally therethrough that permits the left side 112 of the pilot piston to drain into the cavity defined by bore 67 within the cartridge sleeve.

Diameter D.sub.s equaling the diameter of the main poppet seat is made as small as possible so that the area of the orifice does not change significantly as the poppet valve opens.

It is possible to easily vary the pressure area diameters to vary the characteristics of the valve. Firstly, the diameter D.sub.s is easily varied.

Moreover the diameter D1 may also be easily varied which in conjunction with D.sub.2 determines the effective area of the poppet valve 77 upon which pressure in actuator chamber 26 acts. By making diameter D.sub.s slightly greater than diameter D.sub.1 the net pressure acting on the valve member 77 from cylinder pressure is in a positive direction or to the left. However, the pressure in the actuator acting on valve 77 may be equal merely by making the area D.sub.s equal to the area D.sub.1 And moreover the net cylinder force acting on the valve member 77 can be negative by making the area defined by diameter D.sub.1 greater than the area defined by diameter D.sub.s so that cylinder pressure tends to close the poppet valve 77.

Further advantage in the present invention is that the pilot area defined by pilot diameter D.sub.p may be selected as desired.

The "percentage characteristic" is defined as the effective area upon which cylinder pressure acts on the poppet valve divided by the area of the poppet valve upon which pilot pressure acts. A higher "percentage characteristic" means that a higher pilot pressure will be required to fully open the valve than with a low percentage characteristic. Thus the capability of varying the areas D.sub.p, D.sub.1 and D.sub.s will vary the valve opening characteristics of poppet valve 77 as desired for the particular load application.

A somewhat modified form of the present invention is illustrated in FIG. 3 wherein a holding valve 110 is seen to include a housing 112 having a threaded cartridge sleeve 113 defining a stepped bore 114 receiving a poppet valve 116 having a valve surface portion 117 at its left end and pilot piston 118 at its right end. Ports 120, 121, and flow passage 122 are adapted to be connected to the directional control valve, one side of the hydraulic actuator, and the other side of the hydraulic actuator, respectively, as in the embodiment shown in FIGS. 1 and 2. In the embodiment of FIG. 3 a movable check valve 130 defines a movable seat 132 for the main poppet valve 116 as in FIGS. 1 and 2 embodiment.

In the FIG. 3 embodiment, however, pilot piston 118 also defines one of the diameters for determining the effective area of the poppet valve 116 upon which cylinder pressure acts through ports 121. Moreover plunger 136 limits the opening movement of the poppet valve 116, while shoulder 138 within the cartridge limits the movement of the poppet valve 116 to the right towards its closed position.

The valve shown in FIG. 3 operates in substantially the same manner as the valve shown in FIGS. 1 and 2 so that detailed description thereof is not believed necessary.

Claims

We claim:

1. A holding valve assembly for controlling flow between a flow control valve and a fluid actuator, comprising; first port means adapted to be connected to receive and deliver fluid relative to the flow control valve, second port means adapted to be connected to receive and deliver fluid relative to one side of the actuator, third port means adapted to be connected to the other side of the fluid actuator, a check valve for permitting flow from the first port means to the second port means and preventing flow from the second port means to the first port means, and a poppet valve member actuated by fluid pressure in said third port means for permitting flow from said second port means to said first port means, said check valve defining a valve seat for said poppet valve.

2. A holding valve assembly as defined in claim 1, including a cartridge sleeve surrounding the valves.

3. A holding valve assembly as defined in claim 1, wherein said check valve has a cylindrical outer surface, and an internal shoulder defining the valve seat for the movable poppet valve member whereby the seat for the poppet valve member is movable.

4. A holding valve assembly as defined in claim 1, including a stop for limiting movement of said check valve in the direction of opening movement of the poppet valve member.

5. A holding valve assembly as defined in claim 1, wherein said poppet valve member has a pilot piston on the end thereof between said second and third port means.

6. A holding valve assembly as defined in claim 1, including a heavy spring urging said poppet valve to a closed position against the force of fluid in the second port means.

7. A holding valve assembly as defined in claim 1, including a stop for limiting movement of the poppet valve member in a closing direction.

8. A holding valve assembly for controlling flow between a flow control valve and a fluid actuator, comprising; a valve bore, first port means communicating with said valve bore and adapted to be connected to the flow control valve, second port means communicating with said bore and adapted to be connected to one side of the actuator, third port means communicating with said bore and adapted to be connected with the other side of the actuator, a sleeve shaped check valve slidable in said bore for preventing flow from said second port means to said first port means and permitting flow from said first port means to said second port means, said sleeve shaped check valve having an inside shoulder defining a movable valve seat, a stop within said bore for limiting movement of sleeve shaped check valve, a spring in said bore biasing said check valve toward said stop, a poppet valve in said bore actuated by fluid pressure in said third port means for selectively preventing fluid flow from said second port means to said first port means or permitting fluid flow from said second port means to said first port means, said poppet valve being seated on the seat defined by sleeve shaped check valve, a stop for said poppet valve holding said poppet valve in a position preventing flow from the second port means to said first port means, and a second spring stronger than said first spring for urging the poppet valve toward said stop against the fluid pressure in said second port means, said check valve and poppet valve opening in opposite directions.

9. A holding valve assembly, as defined in claim 8, wherein said bore is defined by a cartridge sleeve.

10. A holding valve assembly, as defined in claim 8, including a pilot piston at the end of the poppet valve slidable in an enlarged counterbore in said valve bore.