WO2013041884A1

WO2013041884A1 - A valve with integrated pressure compensator

Info

Publication number: WO2013041884A1
Application number: PCT/GB2012/052351
Authority: WO
Inventors: Jason LEGG; Alexis DEL RIO
Original assignee: Parker Hannifin Manufacturing Limited
Priority date: 2011-09-23
Filing date: 2012-09-21
Publication date: 2013-03-28
Also published as: GB201116435D0; GB2494902A; GB2494902B

Abstract

A three position four way compensating valve comprises an outer body member (6) having a valve inlet port (28)(30) and a valve outlet port (26)(32). A fluid pathway is defined between the inlet port (28)(30) and the outer port (26)(32). A valve member (38) is arranged to selectively open and close the fluid pathway. A pressure compensator (84)(86) is received within the outer body member (6) which is configured to variably restrict the fluid pathway in response to a variation in the pressure differential between the inlet (28)(30) and outlet (26)(32) ports. This variable restriction of the fluid pathway acts to maintain a constant flowrate through the fluid pathway when the fluid pathway is open.

Description

A VALVE WITH INTEGRATED PRESSURE COMPENSATOR

The present invention relates to a valve including a pressure compensator, and in particular to a pilot valve including an integrated pressure compensator.

Hydraulic actuators receive their power from pressurised fluid such as oil, which is provided under pressure by a hydraulic pump. The pressurised fluid is provided to a hydraulic cylinder barrel, in which a piston connected to a piston rod moves back and forth under the action of the fluid. In two way cylinders, a fluid port is provided at either end of the cylinder barrel and the direction of movement of the piston is determined by the flow direction. A valve controls the application and direction of flow.

The velocity of the hydraulic actuator is controlled by controlling the flow of fluid to the cylinder. The flow is determined by the area of the flow, with a larger flow area permitting a higher flow, and the pressure drop across the flow control, with an increase in pressure drop resulting in an increase in flow.

It is desirable in many applications for the flow velocity to be kept constant, to avoid erratic or jerky movement of the actuator. Therefore, in addition to a valve for controlling the activation and direction of flow, a means of maintaining a constant flow is required. It is know to provide a pressure compensator within a flow system, which selectively constricts the flow area in response to a variation in pressure drop to maintain a constant flow. However, such pressure compensators add additional complexity to a fluid control system, requiring additional space and independent installation, and increasing the cost of a system.

It is therefore desirable to provide an improved flow control means comprising valve and means for compensating for variations in pressure drop to maintain a constant flow, which addresses the above described problems and/or which provides improvements generally.

According to the present invention there is provided a valve comprising an outer body member having a valve inlet port and a valve outlet port; a fluid pathway defined between the inlet port and outlet port; a valve member arranged to selectively open and close the fluid pathway; and a pressure compensator received within the outer body member. The pressure compensator is configured to variably restrict the fluid pathway in response to a variation in the pressure differential between the inlet and outlet ports to maintain a constant flowrate through the fluid pathway when the fluid pathway is open.

Preferably the outer body member comprises an axial bore, and the valve member comprises a spool received within the axial bore and arranged to slide therewithin to open and close the fluid pathway, the valve member includes an axial bore which forms part of the fluid pathway when the fluid pathway is opened by the valve member.

The pressure compensator may be received within the axial bore of the cartridge and preferably within the axial bore of the spool. Preferably the valve inlet port may comprise at least one first aperture extending through the outer body member to its axial bore and the valve outlet port comprises at least one second aperture longitudinally spaced from the inlet port along the length of the outer body member and extending through the outer body member to its axial bore; the spool includes at least one third aperture extending through the inner valve member to its axial bore to define an intermediate inlet port and at least one forth aperture longitudinally spaced from the third inlet port along the length of the inner valve member, the at least one forth aperture extending through the inner valve member to its axial bore to define an intermediate outlet port, the intermediate inlet port and intermediate outlet port being in fluid communication through the axial bore of the inner valve member; the valve member is longitudinally movable within the axial bore of the outer body member between a first position in which it closes the valve inlet port, and a second position in which the intermediate inlet port is in fluid communication with the valve inlet port and the intermediate outlet port is in fluid communication with the valve outlet port such that a fluid pathway is defined between the valve inlet port and the valve outlet port through the intermediate ports and the bore of the inner valve member; the pressure compensator comprises a closure member slideably disposed within the axial bore of the spool and is arranged to automatically move within the axial bore to vary the size of one of the intermediate inlet or intermediate outlet in response to variations in the pressure differential between the valve inlet and valve outlet.

Preferably the closure member varies the size of the intermediate inlet and the closure member is movable between a first position in which the intermediate inlet is closed and a second position in which it is open, the valve further comprising a biasing member configured to bias the closure member to the second position, the closure member being configured such that an increase in the pressure differential between the valve inlet and valve outlet urges the closure member towards the first position against the action of the biasing member, the position of the closure member being determined by the resultant force of the fluid pressure and the biasing force acting on the closure member.

The pressure compensator may be located within the axial bore of the outer body member between the outer body member and the spool.

The biasing member is preferably located within a first chamber defined within the axial bore of the spool at a first end of the closure member and a second chamber is defined with the spool at the axially opposing end of the closure member; the valve inlet comprises at least one first valve inlet aperture and at least one second valve inlet aperture

longitudinally offset from the at least one first aperture; the spool comprises a fifth aperture extending from its outer surface to the second chamber which is configured such that when the fifth aperture is aligned with the first valve inlet aperture fluid is permitted to fluid flow into the second chamber from the first valve inlet aperture; the closure member comprises a closure portion which is configured to align with and close the intermediate inlet and includes a fluid channel extending between and fluidly connecting the closure portion and the first end of the closure member such that when the closure portion is aligned with the intermediate inlet a fluid pathway is defined between the intermediate inlet and the second chamber; and the spool is configured such that when the fifth aperture is aligned with the first valve inlet aperture the intermediate inlet aperture aligns with the second valve inlet aperture such that fluid from the first valve inlet aperture flows to the second chamber while fluid from the second valve inlet aperture simultaneously flows to the intermediate inlet and when the closure portion is aligned therewith flows onwardly to the first chamber via the channel in the closure member.

The closure member may comprise a recess portion which defines a fluid channel between the intermediate inlet and intermediate outlet when the closure member is in the open position.

The valve preferably comprises a second valve outlet port and a second fluid pathway defined between the valve inlet and the second valve outlet and the spool is movable between a neutral position in which both fluid pathways are closed, a first open position in which the first fluid pathway is open and the second fluid pathway is closed, and a second open position in which the first fluid pathway is closed and the second fluid pathway is open. The closure member preferably operates to variably restrict the first fluid pathway when the spool is in the first open position in response to a variation in the pressure differential between the valve inlet and the first valve outlet, and the pressure compensator includes a second closure member arranged to variably restrict the second fluid pathway in response to a variation in the pressure differential between the valve inlet and the second valve outlet.

The second closure member may be arranged within the spool on an opposing side of the second chamber to the first closure member with the opposing end faces of the first and second closure members defining the end walls of the second chamber, and the spool includes a third chamber at the other end of the second closure member to the second chamber which includes a biasing member for biasing the second closure member to the closed position in which it closes a second intermediate inlet of the spool in an opposite biasing direction to the first closure member. Preferably the second closure member comprises a closure portion which is configured to align with and close the second intermediate inlet and includes a fluid channel extending between and fluidly connecting the closure portion and the end of the closure member contiguous with the third chamber such that when the closure portion is aligned with the second intermediate inlet a fluid pathway is defined between the second intermediate inlet and the third chamber; and the spool is configured such that when the fifth aperture is aligned with the second valve inlet aperture the second intermediate inlet aligns with the first valve inlet aperture such that fluid from the second valve inlet aperture flows to the second chamber while fluid from the first valve inlet aperture simultaneously flows to the second intermediate inlet and when the closure portion of the second closure member is aligned therewith flows onwardly to the third chamber via the channel in the second closure member.

The valve may include means for supplying pressurised fluid to either end of the spool, independently of the fluid supply to the valve inlet, to selectively cause the spool to move between the neutral and first and second open positions. Preferably the at least one first valve inlet aperture comprises a plurality of apertures in the outer body member arranged circumferentially in a row at a common axial position and the at least one second valve inlet aperture comprises a plurality of apertures in the outer body member arranged circumferentially in a row at a common axial position which is offset from the axial position of the row of first valve inlet apertures.

In another aspect of the invention there is provided a valve comprising closure means for selectively opening and closing a fluid channel; and pressure compensating means integrated within the valve configured to variably restrict the fluid channel automatically in response to a variation in the pressure differential across the valve to maintain a constant flow rate through the fluid channel.

The valve is preferably a pilot valve, and may be a three-position four- way pilot valve.

The present invention will now be described by way of example only with reference to the following illustrative figures in which: Figure 1 is a diagrammatic cross sectional view of a valve according to the present invention in the neutral position;

Figure 2 shows the valve of Figure 1 in the primed unopened

position;

Figure 3 shows the valve of Figure 1 with the spool in the first

open position; Figure 4 shows the valve of Figure 1 in the open position with the closure member having returned towards the distal end to

compensate for pressure variation; and

Figure 5 shows the valve of claim 1 in the second open position.

Referring to figure 1 , a three-position four-way valve assembly 1 is show in cross section, in a neutral position. The valve 1 is elongate and substantially cylindrical in shape, configured to be received within a corresponding cavity (not shown) such as a cylindrical bore of a valve manifold, having corresponding flow passageways, to provide a cartridge valve arrangement. The valve 1 includes a distal end 2 which extends farthest within the bore, and an opposing proximal end 4 which is accessibly located at the open end of the bore. The valve 1 includes a substantially cylindrical, tubular outer body section 6, having a wall with an inner surface defining an axial bore 20. The outer body 6 includes a stepped diametrically enlarged end section 8 located at the proximal end 4 for seated engagement with a corresponding outer surface section of the manifold within which the valve assembly 1 is mounted. An O-ring 10 ensures sealed engagement between the stepped formation 8 of the valve 1 and the manifold.

A cap 11 closes the proximal end 4 of the outer body member 8. The cap 11 includes a hollow body section 12 which extends into the inner bore 20 of the outer body member 8. The outer body 6 includes a plurality of radial projections 14a-f spaced belong its length and projecting outwardly from its outer surface, Each radial projection 14a-f includes at least one corresponding O-ring seal 16 for sealing against the inner bore of the manifold. Additionall o-rings and/or back up seals may be provided. A series of cavities 18a-e are defined between the radial projections 14a-f. The axial bore 20 extends through the centre of the outer body 6. A series of ports 26, 28, 30, 32 and 34 extend through the wall of the outer body 6, connecting the exterior of the outer body 6 with the bore 20. The ports 26, 28, 30, 32 and 34 are arranged at longitudinally spaced locations along the length of the outer body 6. Each port is positioned within one of the cavities 18a-e.

The tank line port 26 is located within cavity 18a closest to the proximal end 4 of the valve 1. The tank line port 26 comprises a plurality of apertures arranged circumferentially around the outer body member at a common longitudinal position, within the cavity 18a. The O-ring seals 16 of projections 14a and 14b which are located on longitudinally opposed sides of the cavity 18a, seal the cavity 18a against the bore of the manifold to prevent liquid from passing directly from the cavity 18a to adjacent cavity 18b, or vice versa.

The cavity 18a is longitudinally positioned to align with a corresponding fluid pathway within the manifold, which is in fluid connection with the hydraulic fluid reservoir tank of the hydraulic system in which the valve is located. As such, when the valve 1 is located with the manifold, the tank line port 26 fluidly connects with the hydraulic fluid tank line through the manifold pathway to return fluid to the reservoir. The supply port 28 is located within cavity 18b and comprises a plurality of apertures arranged circumferentially around the outer body member at a common longitudinal position, within the cavity 18b. The O-ring seals 16 of projections 14b and 14c which are located on longitudinally opposed sides of the cavity 18b, seal the cavity 18b against the bore of the manifold to prevent liquid from passing directly from the cavity 18b to adjacent cavities 18a or 18c. The cavity 18b is longitudinally positioned to align with a corresponding fluid pathway within the manifold, which is in fluid connection with one side of the hydraulic actuator of the hydraulic system in which the valve is located. As such, when the valve 1 is located within the manifold, the supply port 34 fluidly connects with the hydraulic actuator through the manifold pathway, for supplying hydraulic fluid to the hydraulic actuator from the pump, or for returning fluid from the actuator to reservoir via the tank line. There is no fluid pathway defined between the supply port 34 and the tank line port 26 such that the to ports are fluidly isolated. The supply port 30 is located within cavity 18d and comprises a plurality of apertures arranged circumferentially around the outer body member at a common longitudinal position, within the cavity 18d. The O-ring seals 16 of projections 14d and 14e which are located on longitudinally opposed sides of the cavity 18d, seal the cavity 18d against the bore of the manifold to prevent liquid from passing directly from the cavity 18d to adjacent cavities 18c or 18e.

The tank line port 32 is located within cavity 18e closest to the distal end 2 of the valve 1. The tank line port 32 comprises a plurality of apertures arranged circumferentially around the outer body member at a common longitudinal position, within the cavity 18e. The O- ring seals 16 of projections 14e and 14f which are located on longitudinally opposed sides of the cavity 18e, seal the cavity 18e against the bore of the manifold to prevent liquid from passing directly from the cavity 18e to adjacent cavity 18d.

The cavity 18d is longitudinally positioned to align with a corresponding fluid pathway within the manifold, which is in fluid connection with the opposing side of the hydraulic actuator to the supply port 28. As such, when the valve 1 is located with the manifold, the supply port 34 fluidly connects with the hydraulic actuator through the manifold pathway, for supplying hydraulic fluid to the hydraulic actuator from the pump to move the actuator, or for returning fluid from the actuator to reservoir via the tank line when the actuator is being moved in an opposing direction by fluid from supply port 28. The cavity 18e is longitudinally positioned to align with a corresponding fluid pathway within the manifold, which is in fluid connection with the hydraulic fluid reservoir tank of the hydraulic system in which the valve is located. As such, when the valve 1 is located with the manifold, the tank line port 32 fluidly connects with the hydraulic fluid tank line through the manifold pathway to return fluid to the reservoir.

A further port 34 is located centrally between ports 26, 28, 30 and 32, and defines the pressure inlet port for the valve 1. The pressure inlet port 34 comprises a plurality of inlet apertures 34a and 34b extending into the inner bore 20. The first set of inlet apertures 34a extend in a row circumferentially around the outer body 6 at a common longitudinal position along the length of the outer body 6, and are located longitudinally within the cavity section 18c towards the distal end 2. The second set of inlet apertures 34b are arranged circumferentially at a common longitudinal position along the length of the outer body 6, within the cavity 18c. The first row of inlet apertures 34a is longitudinally spaced from the second row of inlet apertures 34b, with the first inlet apertures 34a being arranged towards the distal end 2 and the second inlet apertures 34b arranged towards the proximal end 4. The first row of inlet apertures 34a and second row of inlet apertures 34b are arranged such that they are parallel and angularly offset in a staggered arrangement, with both rows being located longitudinally within the cavity section 18c.

A spool 38 is slideably disposed within the axial bore 20 of the outer body 6. The spool 38 is elongate and substantially cylindrical in shape. The spool 38 has a wall having an inner surface defining an axial central bore 40. A cap 42 is provided at the distal end of the spool 38, to close the axial bore 40. The cap 42 is sealed against the inner bore 40 of the spool 38 by O-ring 44. The main body section of the cap 42 extends axially into the bore 40 and includes a reduced diameter spindle section 46 at its innermost end.

A second cap 50 is provided at the proximal end of the spool 38 to close the axial bore 40 at that end. An O-ring 52 seal is provided between the inner bore 40 and the cap 50. A spindle section 54 of reduced diameter extends axially into the bore 40 at the inner end of the cap 50. An additional end cap 56 is provided at the proximal end 4 of the outer body 6 to close the inner bore 20 at that end and to close the chamber 22. The end cap 56 comprises a hollow body section extending into the bore 20. A cylindrical guide member 60 is located within the open body section of the cap 56 and is slidable therein. The distal end of the guide member 74 has a diameter corresponding to the inner diameter of the end cap 56, and a main body section of reduced diameter. The guide member has an axial bore 62 therethrough. The bore 62 includes a proximal end chamber and a reduced diameter portion 67 defining a step 65. A guide shaft 58 is partially received in the bore 62 and extends between the guide member 60 and the cap 50. The distal end of the guide shaft 58 is secured to the cap 50 by a threaded connection, such that the two components are longitudinally fixed to each other. A ball 59 of a known fixed diameter is located at the base of the bore within the cap 50 to act as a stop for the guide shaft 50 to ensure that the guide shaft 58 is threaded within cap 50 to a predetermined depth. The guide shaft 58 is slideably received within the bore 62 of the guide member 60, and includes an annular radial projection 64 at its proximal end which is accommodated within the proximal end chamber 63 of the bore 60. Longitudinal axial movement of the guide shaft 58 in the direction of the distal end 2 is limited by the engagement of the annular projection 64 with the stepped seat 65 defined by the reduced section of the bore 62 relative to the bore 60.

A stop member 66 is located within the bore 20 between the cap 50 and the guide member 60. The stop member 66 has a central guide aperture through which the guide shaft 58 extends and is slidably received. The stop member 66 is longitudinally slidable within the bore 20 along the guide shaft 58. A step 70 in the bore 20 limits movement of the stop member 66 in the direction of the distal end 2. A spring 72 is provided about the shaft 58 and cap 60 on the proximal side of the stop member 66. At its proximal end the spring 72 engages the outwardly stepped section 74 of the cap 60, and at the distal end the spring engages the stop member 66. The spring 72 is a compression spring and biases the guide member 60 and stop member 66 in opposing directions. In the neutral position shown in figure 1, the stop member 66 is urged against the step 70, and the guide member 60 is urged against the inner surface of the end cap 56. The spool 38 includes a series of recesses 76a-d arranged along its length. Each recess 76 is defined by a section of reduced wall thickness extending circumferentially about the outer surface of the spool 38 and having radially projecting portions spaced either side thereof. The spool 38 further includes a series of radial bores 78a-d extending entirely through the wall of the spool 38 from its outer surface to its inner bore 40. the radial bores 78a-d are arranged in sets, and each set comprises a plurality of apertures arranged circumferentially at a fixed longitudinal position along the length of the spool 38. The sets of radial bores 78a-d correspond to and are located within the recess sections 76a-d respectively, with each defining a fluid pathway between the axial bore 20 of the outer body member and the axial bore 40 of the spool 38.

The spool 38 includes a further set of radial channels 80 located longitudinally at the centre of the spool 38. The central channels 80 extend though the wall of the spool 38 to the inner bore 40. Each radial channel 80 comprises a circular mouth section at the outer surface of the spool 38, and a reduced diameter bore section extending inwardly therefrom. A circlip 82 within the bore 40 and is longitudinally coincident with the channels 80 in an annular channel formed within the bore 40. The circlip 82 is longitudinally aligned with the set of radial channels 80. The circlip 82 has a width narrower than the width of the bore section of each channel 80, such that where the circlip 82 coincides with the internal opening of each channel 80 into the central bore 40, the bore opening extends

longitudinally either side of the circlip 82 maintaining a fluid channel between the channel 80 and the central bore 40 passing either side of the circlip 82. A first compensating piston 84 and second compensating piston 86 are disposed within the bore 40 of the spool 38. The first compensating piston 84 includes a piston block 88 and a spring 90. Similarly, the second compensating piston 86 includes a piston block 92 and a compensating spring 94. The first 84 and second 86 piston blocks are configured to slide within the bore 40. Each piston block 84 and 86 includes a reduced diameter section 96 and 98 respectively along its length defining a fluid cavity between the piston block 84 and 86 and the bore 40, and a radially protruding portion at each end having a diameter equivalent to the inner diameter of the bore 40. The spring 90 of the first compensating piston 84 extends around the spindle 54 of the cap 50 and engages the cap 50 at its proximal end and the piston block 88 at its distal end. The spring 90 is a compression spring and biases the cap 50 and the piston block 88 apart such that when the cap 50 is longitudinally fixed, the piston block 88 is biased towards the circlip 82. The second piston block 92 is similarly biased away from the cap 42 by the spring 94.

In the arrangement shown in figure 1 , the valve 1 is in the neutral position, with no pressure applied from the pump of the hydraulic system. The stop member 66 is urged into engagement with the step 70 the spring 72, and the guide member 60 is similarly urged against the end cap 56, such that the proximal end 74 of the guide member 60 and the stop member 60 are at their maximum separation. In this position the proximal end section 64 of the guide rod 58 is in engagement with the step 65. Both the first 88 and second 92 piston blocks are urged towards each other against the circlip 82 by their respective springs 90 and 94. The outer openings of the radial bores 80 are partially aligned with and overlap with the first set of bores 34a of the inlet port 34. With the pump deactivated, there is no fluid flow into the valve 1 through the inlet port 34. Activation of the pump (not shown) causes fluid to begin to flow into the valve 1 through the ports 34a of the inlet port 34, with the pressure at the inlet ports 34a being equal to the pump supply pressure. The secondary ports 34b, which are longitudinally offset from the inlet ports 34a, are initially covered by the central annular radially projecting section 77 of the spool 38, with part of the secondary ports 34b also being in connection with the radial ports 80 of the spool 38. Hydraulic fluid flows through the ports 34a into the radial set of ports 80 of the spool 38 and into the central chamber 102, passing either side of circlip 82. The pressure in the central chamber 102 As fluid continues to be pumped into the central chamber 102, the pressure rises to the supply pressure. This pressure acts on the end faces 100 and 103 of the piston blocks 88 and 92 respectively, forcing the piston blocks 88 and 92 to move slidingly away from the circlip 82 in opposing longitudinal directions. The first piston block 88 moves towards the proximal end 4 and the second piston block 92 moves towards the distal end 2, as shown in figure 2. As each of the piston blocks 88 and 92 move in an axial direction away from the partition plate 82, they do so against the action of the respective corresponding springs 90 and 94, which are compressed against the corresponding end caps 50 and 44. Eventually, the supply pressure acting on each piston member 88 and 92 is balanced by the returning force of the springs 90 and 94, until there is no further fluid ingress into the central chamber 102. Before the valve 1 is activated no further fluid flow through the valve 1 occurs as there is no further fluid channel defined from the radial bores 80 and central chamber 102 to any other part of the valve when the valve is in the neutral position.

To operate the valve 1 to supply fluid to the hydraulic actuator, a separate hydraulic pilot circuit is used to apply fluid under pressure to either the proximal end or the distal end of the spool 38, to cause axial movement within the bore 20 of the outer body 6. To cause movement of the valve 1 to a first operational state in which hydraulic fluid under pressure can be transferred to the first outlet port 28, pressurised fluid is provided at the proximal end of the spool 38 through port 24. The fluid passes into the cavity 22 defined within the proximal end of the outer body member 6. This pressurised fluid flows around the stop member 70 and acts on the proximal end of the spool 38 defined by the proximal end surface of the cap 50. The pressure force acting on the end of the cap 50 causes the spool 38 to begin to move axially in the direction of the distal end 2 of the valve 1. As the spool 38 moves axially towards the distal end 2, it pulls with it the guide rod 58. The guide rod 58 in turn pulls the cap 60 away from the end cap 56 against the action of the spring 72, which generates a return force for returning the spool 38 to the neutral position when the pressure at port 24 is removed.

The first piston block 88 includes an axial bore 104 extending through, but not entirely through its centre, from the end face at its proximal end. Within the distal end portion of the piston block 88 the bore 104 stops short of the distal end face and connects with a set of radially extending bores 108 which extend substantially perpendicularly to the bore 104. Each radial bore 108 includes a bore channel which expands at the radial outer surface of the piston member 88 to define a wider mouth section. The axial bore 104 and the radial bores 108 are contiguous and define a continuous fluid channel between the radial outer surface at the distal front end of the piston body 88 and its proximal end face.

In the neutral position, once the piston block 88 has moved towards the proximal end 4 under the action of the upstream supply pressure P within the central chamber 102, the mouth of each of the radial bores 108 are substantially aligned with the radial ports 78b of the spool 38. The secondary inlet ports 34b of the outer body member 6 are covered by the central portion 77 of the spool 38. As the pilot pressure is applied to the proximal end of the spool 38, the spool 38 begins to move towards the distal end 2, as shown in figure 3. The centre portion 77 of the spool 38 begins to move towards the distal end 2, uncovering the secondary inlet ports 34b. As the secondary ports 34b begin to open, fluid flows through the ports 34b into the recess 76b at the inlet pressure. The fluid then flows through the radial ports 78b of the spool 38 and into the radial ports 108 of the first piston member 88. The pressurised fluid flows through the radial bores 108 and axial bore 104 into the spring chamber 109 defined within the central bore 40 of the spool 38 between the first piston member and the cap 50. The spring chamber 109 fills with fluid and the pressure P_s in the spring chamber rises until it substantially equals the inlet pressure P at 76b.

The pressure Ps within the spring chamber 109 acts against the proximal end face of the piston block 88, and the pressure Pc in the central chamber 102 acts in the opposing direction against the distal end face. The resultant pressure force Fp acting on the piston block is therefore:

Fp = P_S.A + P_C.A where A is the surface area of both the proximal and distal ends of the piston block. When the pressure P_s within the spring chamber 109 equals the pressure Pc within the central chamber 102, the resultant pressure force F_P acting on the piston block 88 is zero. Hence the resultant force F acting on the piston block 88 is the spring force Fs in the distal direction. The piston block 88 therefore moves in the distal direction due to Fs.

As the piston block 88 axially slides within the bore 40 of the spool 38 towards the distal end 2 of the valve 1 and towards the circlip 82, the set of radial ports 78b of the spool 38 are uncovered. This creates a fluid pathway between the secondary inlet ports 34b and outlet ports 28, through the ports 78a and 78b of the spool via the cavity 96 of the piston member 88. Once a flow path between the inlet ports 34b and the outlet port 28 is established, the pressure in the cavity 96 and hence the pressure Ps in the spring chamber 109 falls to the system pressure P_SYS. As PSYS is lower than the supply pressure P, the spring chamber pressure Ps no longer cancels the pressure Pc in the central chamber 102 which remains equal to the supply pressure P. The resultant pressure force F_P, acting in the proximal direction, acts against the spring force F_s and is sufficient to begin to cause compression of the spring causing the piston block 88 to move in the proximal direction while closing radial ports 78b to stop flow from chamber 76b through to the outlet port 28 via radial ports 78a and chamber 76. As the piston block 88 moves back towards the proximal end 4 it covers slightly the ports 78b. This position represents the equilibrium position of the piston block 88 where it remains providing there is no variation in the supply pressure P or system pressure Pa.

In systems of the prior art which do not include a piston block 88 within the spool of the valve, any rise in supply pressure would cause a corresponding rise in flowrate through the valve. The increased flowrate causes acceleration of the actuator to which the fluid is being supplied, which leads to control instability. To counter this instability, a separate flow compensating valve arrangement must be introduced into the system adding additional cost and complexity to the system.

In contrast, in the present invention, in the event that supply pressure P rises, the resultant pressure force F_P acting on the piston block increases in the proximal direction due to the fall in the spring chamber pressure Ps, and acts to further compress the spring 90 and move the piston block 88 towards the proximal end 4. Movement of the piston block 88 further closes the ports 78b, thereby restricting flow through the ports. This flow restriction counters the tendency to an increased flowrate caused by the increase in supply pressure P, to maintain a constant flow rate. Any further increases in supply pressure in turn causes the piston block 88 to further close and restrict the ports 78b. Similarly, if the supply pressure reduces, the piston block 88 returns towards the distal end thereby causing an opening of the ports 78b and increasing their effective size to increase the size of the flow channel to counter the drop in supply pressure. As such, any variation in flow rate caused by a variation in system pressure P is compensated for by the piston block 88, with the piston block increasing the effective size of the ports 78b to compensate for a fall in pressure and decreasing the effective size of the ports 78b to compensate for an increase in system pressure, with the respective decreases and increases in supply pressure acting to cause the compensating movement of the piston block 88. Similarly, any variations in the system pressure, for example due to increased loading of the actuator, causes variation in the spring chamber pressure Ps and consequential compensating movement of the piston block to maintain flow rate. At the same time the opposing end of the piston is discharging, pressurised fluid from outlet port 30 discharges into tank line outlet 32. In order to return the hydraulic actuator to a neutral position, or operate the actuator in opposing directions, the valve 1 is operated in an opposing direction to permit the application of hydraulic pressure to the opposing side of the actuator through outlet ports 30, and to permit fluid flow from the first side of the actuator to the tank line via ports 28 and to 26 through ports 76a.

To move the valve in the opposing direction the hydraulic pilot valve circuit is reversed to apply hydraulic pressure to the distal end face of the cap 42 to move the spool 38 towards the proximal end 4. The operation of the valve when moved in this direction is precisely the same as described above but in the opposite direction. The valve 1 is primed in a neutral position with the application of pressure through the inlet port 34a causing the members 88 and 92 to move in opposing directions away from the circlip 82, causing the proximal end portion 93 of the piston member 92 to cover the radial ports 78c. As the spool 38 moves towards the proximal end 4, first inlet ports 34a are closes and the ports 80 align with the second inlet ports 34b to maintain pressure within the central chamber 102.

The cavity 76c then begins to align with the inlet port 34a permitting fluid flow to the radial ports 78c. Similarly to piston member 88, the piston member 92 includes a radial bore portion 1 12 and an axial bore portion 110 which connects the radial surface of the proximal end portion 93 with the distal end face 95. Fluid flows through the bore 112, 1 10 of the piston member 92 from the ports 78c resulting in the application of pressure to the distal end face 95 causing movement of the piston member in the proximal direction towards the circlip 82 helped by the spring 92.

In a similar manner to the previously described action of the piston member 88, the proximal movement of the piston block 92 opens the radial ports 78c permitting fluid flow into the spring cavity 98, and through the radial ports 78d into the cavity 76d and out through the outlet port 30 to the hydraulic actuator. This causes the pressure in the spring chamber to fall to the system pressure PSYS and the piston block to move back towards the distal end. Subsequent variations in the supply pressure cause compensating movement of the piston block 92 to vary the effective size of the ports 78c in the same way as described above for the ports 78b and piston block 88. At the same time the port 28 is discharging from tank line outlet 26 through ports 76a.

Where above reference is made to maintaining the flowrate as constant, it will be understood that the term 'constant' is meant is a relative manner rather than as an absolute constant, and may constitute maintaining the flowrate within a predetermined flowrate tolerance either side of the desired absolute flowrate. Furthermore, it will be appreciated that as the cross sectional area of the outlets and/or the supply pipes leading away from the valve to do not vary in cross section during operation, the constant flowrate achieved by the pressure compensating valve of the present invention will ensure a constant flow velocity to the hydraulic actuator being supplied, although the flow velocity will vary locally within the valve and in particular at the points of variable constriction generated by the pressure compensating members.

Claims

1. A valve comprising:

an outer body member having a valve inlet port and a valve outlet port;

a fluid pathway defined between the inlet port and outlet port;

a valve member arranged to selectively open and close the fluid pathway; and a pressure compensator configured to variably restrict the fluid pathway in response to a variation in the pressure differential between the inlet and outlet ports to maintain a desired flowrate through the fluid pathway when the fluid pathway is open.

2. A valve according to claim 1 wherein the pressure compensator is located within the outer body member.

3. A valve according to claims 1 or 2 wherein the pressure compensator operates to maintain a substantially constant flowrate through the fluid pathway.

4. A valve according to any preceeding claim wherein the outer body member comprises an axial bore, and the valve member comprises a spool received within the axial bore and arranged to slide therewithin to open and close the fluid pathway, the valve member includes an axial bore which forms part of the fluid pathway when the fluid pathway is opened by the valve member.

5. A valve according to claim 4 wherein the pressure compensator is received within the axial bore of the spool.

6. A valve according to claim 5 wherein the valve inlet port comprises at least one first aperture extending through the outer body member to its axial bore and the valve outlet port comprises at least one second aperture longitudinally spaced from the inlet port along the length of the outer body member and extending through the outer body member to its axial bore;

the spool includes at least one third aperture extending through the inner valve member to its axial bore to define an intermediate inlet port and at least one forth aperture longitudinally spaced from the third inlet port along the length of the inner valve member, the at least one forth aperture extending through the inner valve member to its axial bore to define an intermediate outlet port, the intermediate inlet port and intermediate outlet port being in fluid communication through the axial bore of the inner valve member;

the valve member is longitudinally movable within the axial bore of the outer body member between a first position in which it closes the valve inlet port, and a second position in which the intermediate inlet port is in fluid communication with the valve inlet port and the intermediate outlet port is in fluid communication with the valve outlet port such that a fluid pathway is defined between the valve inlet port and the valve outlet port through the intermediate ports and the bore of the inner valve member;

the pressure compensator comprises a closure member slideably disposed within the axial bore of the spool and is arranged to automatically move within the axial bore to vary the size of one of the intermediate inlet or intermediate outlet in response to variations in the pressure differential between the valve inlet and valve outlet.

7. A valve according to claim 6 wherein movement of the closure member varies the size of the intermediate inlet and the closure member is movable between a first position in which the intermediate inlet is closed and a second position in which it is open, the valve further comprising a biasing member configured to bias the closure member to the second position, the closure member being configured such that an increase in the pressure differential between the valve inlet and valve outlet urges the closure member towards the first position against the action of the biasing member, the position of the closure member being determined by the resultant force of the fluid pressure and the biasing force acting on the closure member.

8. A valve according to claim 7 wherein:

the biasing member is located within a first chamber defined within the axial bore of the spool at a first end of the closure member and a second chamber is defined with the spool at the axially opposing end of the closure member;

the valve inlet comprises at least one first valve inlet aperture and at least one second valve inlet aperture longitudinally offset from the at least one first aperture; the spool comprises a fifth aperture extending from its outer surface to the second chamber which is configured such that when the fifth aperture is aligned with the first valve inlet aperture fluid is permitted to fluid flow into the second chamber from the first valve inlet aperture;

the closure member comprises a closure portion which is configured to align with and close the intermediate inlet and includes a fluid channel extending between and fluidly connecting the closure portion and the first end of the closure member such that when the closure portion is aligned with the intermediate inlet a fluid pathway is defined between the intermediate inlet and the second chamber; and

the spool is configured such that when the fifth aperture is aligned with the first valve inlet aperture the intermediate inlet aperture aligns with the second valve inlet aperture such that fluid from the first valve inlet aperture flows to the second chamber while fluid from the second valve inlet aperture simultaneously flows to the intermediate inlet and when the closure portion is aligned therewith flows onwardly to the first chamber via the channel in the closure member.

9. A valve according to claim 8 wherein the closure member comprises a recess portion which defines a fluid channel between the intermediate inlet and intermediate outlet when the closure member is in the open position.

10. A valve according to claim 9 wherein the valve comprises a second valve outlet port and a second fluid pathway defined between the valve inlet and the second valve outlet and the spool is movable between a neutral position in which both fluid pathways are closed, a first open position in which the first fluid pathway is open and the second fluid pathway is closed, and a second open position in which the first fluid pathway is closed and the second fluid pathway is open.

11. A valve according to claim 10 wherein the closure member operates to variably restrict the first fluid pathway when the spool is in the first open position in response to a variation in the pressure differential between the valve inlet and the first valve outlet, and the pressure compensator includes a second closure member arranged to variably restrict the second fluid pathway in response to a variation in the pressure differential between the valve inlet and the second valve outlet.

12. A valve according to claim 1 1 wherein the second closure member is arranged within the spool on an opposing side of the second chamber to the first closure member with the opposing end faces of the first and second closure members defining the end walls of the second chamber, and the spool includes a third chamber at the other end of the second closure member to the second chamber which includes a biasing member for biasing the second closure member to the closed position in which it closes a second intermediate inlet of the spool in an opposite biasing direction to the first closure member.

13. A valve according to claim 12 wherein

the second closure member comprises a closure portion which is configured to align with and close the second intermediate inlet and includes a fluid channel extending between and fluidly connecting the closure portion and the end of the closure member contiguous with the third chamber such that when the closure portion is aligned with the second intermediate inlet a fluid pathway is defined between the second intermediate inlet and the third chamber; and

the spool is configured such that when the fifth aperture is aligned with the second valve inlet aperture the second intermediate inlet aligns with the first valve inlet aperture such that fluid from the second valve inlet aperture flows to the second chamber while fluid from the first valve inlet aperture simultaneously flows to the second intermediate inlet and when the closure portion of the second closure member is aligned therewith flows onwardly to the third chamber via the channel in the second closure member.

14. A valve according to claim 13 wherein the valve includes means for supplying pressurised fluid to either end of the spool, independently of the fluid supply to the valve inlet, to selectively cause the spool to move between the neutral and first and second open positions.

15. A valve according to claim 13 wherein the at least one first valve inlet aperture comprises a plurality of apertures in the outer body member arranged circumferentially in a row at a common axial position and the at least one second valve inlet aperture comprises a plurality of apertures in the outer body member arranged circumferentially in a row at a common axial position which is offset from the axial position of the row of first valve inlet apertures.

16. A valve comprising:

closure means for selectively opening and closing a fluid channel; and pressure compensating means integrated within the valve configured to variably restrict the fluid channel automatically in response to a variation in the pressure differential across the valve to maintain a constant flow rate through the fluid channel.

17. A valve according to any preceding claim wherein the valve comprises means fr moving the spool.

18. A valve substantially as hereinbefore described with reference to, and/or as shown in figures 1 to 5.