GB2140130A - Improvements in or relating to a hydraulic valve - Google Patents

Abstract

A hydraulic loading valve 10 comprises a housing having an axial bore therethrough. A spring loaded valve member 16 is axially aligned within said bore and a check valve means 24 is located within the bore cooperating with the valve member such that flow from an outlet port 22 through the bore to an inlet port 20 is prevented when the spring loaded valve member is in a first position and permitted when the spring loaded valve member is in a second position. A relief valve means 46 is in communication with an internal bore of the spring loaded valve means. A pilot means 38 is in connection with the end of the central bore for moving the spring loaded valve member against the spring 50 and into the second position to permit fluid flow from the outlet port to the inlet port to release a load. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a hydraulic valve THIS INVENTION relates to a hydraulic valve and more specifically to a hydraulic valve which allows a hydraulic cylinder to hold a load in a given position.

In the past hydraulic load locking or load holding valves that comprise a check valve, and a pilot assisted style differential area relief valve have been used but have been found to provide inadequate relief when a load holding hydraulic cylinder associated with the valve is put under a severe shock load. In a typical application of this type of valve a load is lifted by a hydraulic cylinder on a machine (which may be of a vehicular type such as a front end loader or a continuous mining machine) and is held in position while the vehicle moves from one place to another, the load locking valve serving to retain the hydraulic fluid in the hydraulic cylinder.

Occasionally as the vehicle is being moved the load being held by the hydraulic cylinder is inadvertently rammed into some fixed object. This puts a severe shock load on the fluid pressure within the hydraulic cylinder holding the load in position. Consequently hydraulic fluid must be relieved fast enough to prevent damage to the cylinder and other hydraulic components.

The prior art hydraulic load holding or load locking valves have had a relief facility which has not been adequate to relieve the pressure within the cylinder fast enough to prevent damage thereto. Typically the prior valves have included a single relief valve means.

According to this invention there is provided a hydraulic load holding valve comprising: a housing having an axial bore therethrough, said housing having inlet port and an outlet port spaced axially on said bore: means for closing each end of said axial bore in said housing: a spring biassed valve member axially aligned within said bore: means located within said bore and cooperating with said valve member such that flow between said outlet port through said bore and said inlet port is prevented when said spring biassed valve member is in a first position and is permitted when said spring biassed valve member is in a second position: and spring biassed pressure relief valve means in sealing engagement with an internal passageway formed in said valve member, said passageway being in communication with said outlet port, the arrangement being such that a build up of pressure in said outlet port first moves said spring biassed valve member against said spring into said second position thereby allowing flow from said outlet to said inlet and such that a further increase in pressure in said outlet port beyond a predetermined limit causes said relief valve means to move against the associated spring and out of sealing engagement with said passageway thereby permitting further flow from said outlet through said passageway around said relief valve means and through a vent means.

Preferably the valve further comprises pilot means in connection with the end of said central bore opposite said vent means for moving said spring biassed valve member against said spring and into said second position to permit fluid flow from said outlet port to said inlet port to release said load.

Said relief valve means may consist of a spherical ball or a conical member forced against the end of said passageway in said spring biassed valve member by the same spring that biasses the valve member.

Preferably said means which cooperate with the valve member comprises a spring biassed hollow cylinder forming a check valve, the outer surface of which is slidingly sealingly engaged with the inner surface of said bore, the spring biassing said cylindrical member into said first position in which part of the member is brought into contact with said spring biassed valve member for sealing off the flow path between said inlet and outlet ports there being means for limiting the travel of said cylindrical member along said central bore to permit said spring biassed valve means to move to said second position in which the cylinder is spaced from the valve member thereby creating a flow path from said inlet to said outlet.

The preferred embodiment of the present invention incorporates a direct acting relief valve in the same cartridge as the prior art valve (see Fig. 3) which had only one relief system. The direct acting relief valve will allow pressures in excess of normal relieving capabilities of the system to relieve to the fluid reservoir or to the atmosphere. As described in more detail herein the direct acting relief valve is adjusted by the same adjusting means as is used by the differential area relief valves so that any change in adjustment or setting will automatically change both relief valve systems by the same ratio.

Besides relieving peak surges which results in a better component life the opening sequence of the relief valve is always the same regardless of the adjusted pressure setting.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a sectional view of a load holding valve in accordance with the present invention; Figure 2 illustrates a hydraulic circuit including the load holding valve shown in Fig.

1; and Figure 3 shows a sectional view of a prior art load holding valve.

A hydraulic load holding valve in accordance with the present invention is shown in Fig. 1 and is generally denoted at 10.

The preferred valve 10 consists of a valve cartridge or body 1 2 which has an inner bore 14. A valve means or spool 1 6 is slidably engaged within the bore 14. The valve means 1 6 has a seal 18 which seals a first end 1 9 of the spool 1 6 within bore 14.

The valve body 1 2 has inlet and outlet ports therein generally denoted as 20 and 22 respectively which communicate with the bore 14. A check valve 24 is sealingly and slidingly engaged within the bore 14 between the inlet and outlet ports 20 and 22. In the preferred embodiment the check valve is provided with a peripheral seal located between the inlet and outlet port constituted by a 0ring 26 which sealingly engages the exterior of the spool 1 6 and the interior of the bore 14.

A first end cap 28 is sealingly engaged within a first end of the bore 14 within the body 1 2 to close off that first end. In the preferred embodiment the end cap 28 is sealed within the bore 14 by an O-ring 30. A ring clamp or circlip 32 is utilised to retain the end cap 28 within the bore 14.

A second end 34 of the spool 16 is sealingly engaged within an axial bore 36 that is formed in the end cap 28. An O-ring seal is provided between the end 34 of the spool, and the bore 36. An axial pilot bore 38, of lesser diameter than bore 36 is cut right through said end cap 28 into communication with the bore 36.

A spring 40 engages the check valve means and the end closure cap 28 to force the check valve 24 axially away from the end closure cap 28 within said bore 14 and towards port 22.

The end 1 9 of the spool 16 has a bore 44 therethrough. The bore 44 at one end, in the area of the check valve 24, is bifurcated to terminate at two permanently open ports, but terminates at the opposite end at a port that may be closed by a member 46.

The member 46 forms part of the direct acting pressure relief valve system generally denoted as 48. The system includes spring 50 and vent 52. In the preferred embodiment the member 46 is a steel ball with a diameter sized to seal off the port of the bore 44. The spring 50 is retained within the bore 14 of body 1 2 by an retaining cap 54. In the preferred embodiment the retaining cap 54 is threaded into threads which are formed in the inside of bore 14 of body 12. A locking nut 56 is utilised to prevent the retaining cap from unscrewing. In the preferred embodiment the vent means 52 are holes through the retaining cap 54. The compressive force developed by the spring 50 is adjusted by screwing the retaining cap 54 into or out of the bore 14, thus adjusting the permitted length of the spring 50.As can be seen as the compressive forces on the spring 50 increase the force of the fluid required to lift closure member 46 off bore 44 increases. In addition the force of the fluid entering through the pilot bore 38 or the inlet port 20 which is required to move the spool 1 6 axially a given predetermined distance within bore 14 would also have to increase.

Fig. 2 discloses a hydraulic circuit typical of that in which the load holding valve 10 is employed. A hydraulic cylinder 60 is used to move a load designated as 62. The cylinder has lines 64 and 66 to carry hydraulic fluid to and from the hydraulic cylinder. A control valve 68 is utilised to control the movement of the piston 70 within the cylinder 60. If movement in one direction is desired the control valve allows fluid to flow in the cylinder via line 64 at a high pressure which moves the piston within the cylinder 60 and forcing out low pressure hydraulic fluid at line 66. In order for the fluid to flow through the load hold valve 10 the spool 16 must be moved axially against spring 50 to provide a flow path between inlet port 20 and outlet port 22.In order to effectuate this movement of spool 1 6 the control valve directs high pressure fluid through a pilot line 72 and through the pilot bore 38 in the cap 28 thereby forcing end 34 of spool 16 axially against spring 50.

In the preferred embodiment the spool 16 moves a sufficient distance to allow the check valve 24 to seat on a ledge 74 of the valve 12. The spring 40 forces the check valve 24 into hard contact with the ledge 74 as spool 1 6 moves against spring 50. After ledge 74 stops the movement of valve 24 as the spool 16 continues to move a flow path is created between the portion 76 of the spool 16 and check valve 24, thus permitting the flow of fluid through the load holding valve. The fluid flows from the outlet 22 of the load holding valve via line 80 through the control valve 68 to reservoir 82. In the preferred embodiment a pump 84 takes hydraulic fluid from the reservoir 82, increases the pressure thereof, and directes it through the control valve for use in to actuate the hydraulic cylinder 60.

When it is desired to hold the load 62 in a given position the pressure to the pilot line 72 is relieved by the control valve 68 which allows the spool 16 to be forced against surface 86 at the end of the bore 36 in the end cap 28 by spring 50. In this position check valve 24 is forced against the portion 76 of spool 1 6 by the spring 40.In this position in ordinary circumstances the check valve 24 cuts off the flow through port 20, which is connected to the line 66 of the cylinder, thus terminating the flow from outlet port 22 in valve body 1 2. However, should the load 62 be subjected to a shock (e.g. if the load is being carried on a vehicle such as a front loader and the load encounters an obstacle as the vehicle (not shown) is moving) the resultant pressure build up in the area of the cylinder and line 66 would increase the pressure at the inlet port 20 causing the differential pressure acting on the portion 76 of spool 1 6 to increase rapidly and to move the spool 1 6 against spring 50.When sufficient pressure has developed the spool 1 6 will have moved far enough to allow check valve 24 to seat on ledge 74 thereby releiving fluid through the outlet port 22 thereby reducing the pressure. If the pressure in the cylinder 60 and line 66 is sufficiently high the pressure acting within the bore 44 of the spool 1 6 will cause the element 46 to be forced against spring 50 by sufficient force to unseat and allow further fluid to flow through bore 44 and out through vent means 52. The vent 52 may either go to atmosphere or through appropriate hydraulic lines back to the reservoir.

In the preferred embodiment spring 50 force and bore 44 are sized so that spool 16 moves a sufficient distance to allow communication between port 20 and port 22 of the valve prior to allowing the direct acting relief valve 46 to unseat thereby providing a second relief path.

When it is desired to move the cylinder in the opposite direction the control valve directs the high pressure through the load valve 10.

Specifically, the high pressure fluid would flow in through port 22 and then out through port 20. Of course, the check valve 24 must move against spring 40 to allow the flow path to open as described above. However it is clear that the relief system operates only when shock loads act to compress the fluid in the cylinder thereby raising the pressure of the fluid.

Whilst a spherical member 46 has been illustrated, a conical member could equally be used.

Fig. 3 illustrates a corresponding prior proposed device. Whenever possible the reference numerals utilised identify parts that are common to the described embodiment of the present invention. However, it is to be noted that this embodiment does not have the bore 44, nor the member 46 to close such bore.

Claims (7)

1. A hydraulic load holding valve comprising: a housing having an axial bore therethrough, said housing having inlet port and an outlet port spaced axially on said bore: means for closing each end of said axial bore in said housing: a spring biassed valve member axially aligned within said bore: means located within said bore and cooperating with said valve member such that flow between said outlet port through said bore and said inlet port is prevented when said spring biassed valve member is in a first position and is permitted when said spring biassed valve member is in a second position: and spring biassed pressure reilief valve means in sealing engagement with an internal passageway formed in said valve member, said passageway being in communication with said outlet port, the arrangement being such that a build up of pressure in said outlet port first moves said spring biassed valve member against said spring into said second position thereby allowing flow from said outlet to said inlet and such that a further increase in pressure in said outlet port beyond a predetermined limit causes said relief valve means to move against the associated spring and out of seal ing engagement with said passageway thereby permitting further flow from said outlet through said passageway around said relief valve means and through a vent means.

2. A hydraulic loading valve according to claim 1 further comprising pilot means in connection with the end of said central bore opposite said vent means for moving said spring biassed valve member against said spring and into said second position to permit fluid flow from said outlet port to said inlet port to release said load.

3. A hydraulic load holding valve according to claim 1 or 2, wherein said relief valve means consists of a spherical ball forced against the end of said passageway and said spring biassed valve member by the same spring that biasses the valve member.

4. A hydraulic load holding valve according to claim 1 or 2, wherein said relief valve means is a conical member forced against the end said passageway in said spring biassed valve member and held in position by the same spring that biasses the valve member.

5. A hydraulic load holding valve as claimed in any one of the preceding claims, wherein said means which cooperate with the valve member comprises a spring biassed hollow cylinder forming a check valve, the outer surface of which is slidingly sealingly engaged with the inner surface of said bore, the spring biassing said cylindrical member into said first position in which part of the member is brought into contact with said spring biassed valve member for sealing off the flow path between said inlet and outlet ports there being mans for limiting the travel of said cylindrical member along said central bore to permit said spring valve means to move to said second position in which the cylinder is spaced from the valve member thereby creating a flow path from said inlet to said outlet.

6. A hydraulic loading valve substantially as herein described with reference to and as shown in Fig. 1 of the accompanying drawings.

7. Any novel feature or combination of features disclosed herein.