GB2147368A - Hydraulic apparatus - Google Patents

Abstract

An hydraulic ram (10) includes at least one end of its cylinder one or more control valves (14a, 15a) which are engaged by the piston (11) at the end of its stroke and arranged to control the supply of hydraulic fluid to the cylinder. In a preferred embodiment of the invention as applied to a double- acting hydraulic ram, control valves (14a, 15a; 14b, 15b) are provided at opposite ends of the cylinder and control the operation of a main changeover valve (16) through an intermediate changeover valve (22). As shown, piston (11) is at the left-hand limit of its travel, depressing valves (14a and 15a) so allowing fluid to flow from source (P) through lines (20 29a and 27) to drive changeover valve (22) to the right. This connects line (25) to the supply (P) and drives the spool of valve (16) also to the right. Consequently compartment A is pressurised through lines (17, 13a) and piston (11) moves to the right, releasing valves (14a, 15a) and eventually depressing valves (14b, 15b), reversing the process. This may be part of a hydraulic intensifier. <IMAGE>

Description

SPECIFICATION Hydraulic apparatus This invention reiates to hydraulic apparatus, more particularly in the form of double-acting piston and cylinder units, herein for convenience called hydraulic rams.

The invention concerns the control of such hydraulic rams, particularly but not exclusively of the double-acting type, by means of an hydraulic circuit which includes valves for directing hydraulic fluid under pressure to alternate ends of the cylinder, for example, when such a ram is used on a double-acting hydraulic intensifier.

In a conventional intensifier, the valves which control admission of the hydraulic fluid to the cylinder are operated by some form of striker mechanism coupled to the piston rod, and for this purpose part of the rod at at least one end, and often at both ends, of the ram must be accessible to such striker mechanism.

As a result, the overall length of the intensifier is increased by approximately the length of the working stroke, or even twice that length.

Alternatively electrical solenoid valves are operated by micro-switches but are unsuitable for hazardous environments.

In accordance with one specific aspect of the present invention, we provide a doubleacting hydraulic ram wherein the admission of hydraulic fluid under pressure alternately to opposite ends of the cylinder is controlled by means of an hydraulic circuit having fluid control valves, at least one such valve being provided at each end of the working stroke of the piston in the cylinder so as to be operable by engagement with the piston.

Thus, the cylinder may comprise a barrel with respective end blocks, said valves being housed in said end blocks and each having a respective valve member which is movable between a retracted position in which it is disposed substantially within the respective block, and a projected position in which it extends substantially into the interior of the cylinder space for engagement with the piston or a member carried thereby. The control valves may be resiliently biased into their projected positions and incorporate a plunger portion to engage the piston.

The respective control valves at each end of the barrel may in some cases directly control a main changeover valve which directs the supply of hydraulic fluid under pressure to one end of the cylinder and exhausts fluid from the other end. However, for high speed operation or where it is imperative that the correct main valve position is held at all times, it is desirable to utilise an intermediate changeover valve which itself operates the main changeover valve.

Preferably, two control valves are provided at each end of the cylinder, one connecting a source of fluid under pressure to a control line for one side of the intermediate valve, and the other connecting said control line to a return line. Nevertheless, if desired the two functions could be performed by a single control valve.

The double-acting hydraulic ram in accordance with this aspect of the invention may be incorporated into a double-acting hydraulic intensifier, the opposite ends of the piston rod operating in respective intensifier cylinders which may each include a barrel connected directly to the respective end blocks of the hydraulic cylinder.

However, the invention is not limited in its application to double-acting hydraulic rams for use in double-acting intensifiers. Indeed, the invention is not limited to double-acting rams, but can be applied to single acting rams, especially if such rams require to be reciprocated rapidly. Thus, more broadly, the invention resides in an hydraulic ram having at at least one end of the stroke of the piston one or more control valves connected in an hydraulic circuit for control of the ram and arranged so as to be operable by engagement with the piston.

The control valves may each include a sliding member which is biased by spring means into a position in which a plunger portion projects into the interior of the cylinder and into the path of the piston at the end of its stroke so that when engaged by the piston, the sliding member is momentarily displaced to a retracted position. Alternatively, instead of biasing the sliding member resiliently,. the control valve may be re-set by means of a fluid pressure signal applied thereto, derived for example from the line applying driving pressure to the end of the cylinder at which the valve is provided, or from the fluid pressure established in that end of the cylinder, or in any other suitable manner to return the sliding member to its projected position.

These and other aspects of the invention will now be described by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a hydraulic diagram illustrating the invention as applied to the control of a double-acting hydraulic ram; and Figure 2 is a partial transverse section through one end of the ram showing a pair of control valves in accordance with the invention.

The ram, as illustrated, comprises a main cylinder 10 having a piston 11 slidable therein carried by a rod 1 2 which extends beyond both ends of the cylinder. The cylinder is divided by the piston into two chambers A and B, and in the accompanying drawings the piston 11 is shown at the left-hand end of the cylinder 10 at the beginning of a stroke directed to the right.

Control valves 14a and 15a are, in this position, engaged by the piston and retracted against reslient bias whereby similar control valves 14b and 1 sub at the opposite end of the cylinder are maintained in a projected position whilst not engaged by the piston.

Referring now specifically to Fig. 1, hydraulic lines 1 3a and 1 3b connect the respective chambers A and B to a main changeover valve 16, itself connected by lines 1 7 and 1 8 to a main pressure line 20 connected to a source P of hydraulic fluid under pressure and a main return line 21 connected to a sump or tank T. The main valve 1 6 is itself controlled by an intermediate valve 22 which is connected as shown between pressure and return lines 23 and 24 and control lines 25 and 26 for the main valve 1 6. The intermediate valve 22 is operated by control lines 27 and 28 which divide respectively into branch lines 29a, 30a and branch lines 29b, 30b, which respectively lead to the control valves 14a, 15a, 14b and 15b.Control valves 14a and 1 4b are both connected to the main pressure line 20 and control valves 15a, 15b are both connected to a separate return line 1 9 direct to tank.

By utilising a separate tank line 1 9 the invention may be operated in both open and closed loop hydraulic circuits, that is to say return line 21 may be taken direct to tank (open loop arrangement) or connected to the inlet port (closed loop arrangement) of the pressure source without back pressure affecting the change over of valves 1 6 and 22 via control lines 25,27,30a and 26,28,30b.

In operation, when the piston is as shown at the left-hand end of the cylinder, hydraulic fluid from the main pressure line 20 is fed by control valve 1 4a in its retracted position to branch line 29a and control line 27 to the left-hand side of intermediate valve 22, and the associated branch line 30a is closed by control valve 15a. At the same time, control line 28 from the right-hand side of intermediate valve 22 is connected by way of branch line 30b and control valve 15b to tank line 1 9. Thus, the spool of the intermediate valve 22 moves to the right and connects supply line 23 to the control line 25 to the left-hand side of the main changeover valve 16, and also connects control line 26 from the righthand side of the main valve to the return line 24.Thus, the spool of the main changeover valve 1 6 moves to the right and in this position connects supply line 1 7 to line 1 3a and thereby establishes a supply of pressurised fluid from the main pressure line 20 to chamber A to drive the piston 11 to the right.

Fluid thereby displaced from chamber B flows along line 13b, through the main changeover valve 1 6 and return line 1 8 to the main return line 21.

As soon as the piston 11 moves away from the left-hand of the cylinder 10, the control valves 1 4a and 15a are released, so that valve 1 4a closes to isolate control line 27 from the main pressure line 20, and control valve 1 5a opens to connect control line 27 to tank line 19, so that the spool of the intermediate valve 22 is free to move to the left when required. However, this spool does not m-ve until pressure is applied to the control line 28, as it is held by a mechanical latch or detent and therefore pressure is maintained in contra line 25, keeping the main changeover valve in the position shown in Fig. 1.

At the end of the stroke to the right, the piston 11 contacts the plungers of control valves 1 4b and 1 sub thus operating these valves. Control valve 1 sub closes before control valve 1 4b opens. Thus, pressure from the main pressure line 20 is suppiied through control valve 14b, branch line 29b(branch line 30b being closed by control valve 1 5b) and control line 28 to the right-hand side of intermediate valve 22. This changes over since the left-hand side control line 27 is now connected to tank line 1 9 through control valve 1 spa. Changeover of the intermediate valve 22 connects control line 26 to the pressure line 23 and control line 25 to the return line 24. Thus, the main valve 1 6 changes over.

Changeover of the main valve 1 6 connects pressure line 17 to line 13b and line 13a to return line 18. Thus, the flow of hydraulic fluid is directed to chamber B and the piston movement is reversed, and fluid is displaced from chamber A through line 1 3a, changeover valve 1 6 and return line 1 8 to the main return line 21.

Instead of operating the main valve 1 6 by way of the intermediate valve 22, the latter could in some applications be omitted. In such a case, control lines 27 and 28 would be connected directly to the main valve 1 6.

Instead of having two control valves at each end of the ram cylinder 10, it would be possible to provide all the required functions on a single valve at each end. Further, whilst the hyraulic circuit shown controls only one double-acting ram, it would be possible to connect a plurality of such rams in a single control circuit in such a manner that the rams operate in a predetermined sequential relation by arranging for the changeover valve associated with one such ram to be controlled at least for one direction of movement by a control valve associated with another such ram.

Alternatively, a number of additional rams could be connected in parallel with the ram having the control valves 1 4a, 1 4b, 1 Sa, 15b, so that such valves co-ordinate the operation of all such rams without it being necessary for every ram to have individual control valves.

Fig. 2 is a partial section through the lefthand end of the cylinder 10 with the piston 11 on rod 1 2 at the left-hand end of its stroke. The cylinder 10 in this embodiment comprises a barrel 31 received in an end block 32 which houses the control valves 14a, 15a. The block 32 includes a pair of hydraulic seals 33 and 34 and a water seal 35. One end of a further, high pressure, barrel 37 is also received in the block 32, and this defines a high pressure chamber 38 of an hydraulic intensifier. Water is admitted to the chamber 38 at low pressure and expelled at high pressure under the control of further valves (not shown) in a further end block 36.

The control valve 1 4a includes a plunger 41 slidable in a sleeve 42 having a counterbored inner end portion 43 receiving a headed inner end portion 44 of the plunger.

A bore 45 extends axially through the plunger whereby the pressure within the main cylinder compartment A is communicated to the inner end of the sleeve 42. The plunger has a counterbore 46 at its inner end in which a compression spring 47 is located to bias the plunger outwardly so that the outer end portion 48 normally projects into the chamber A.

A central part of the plunger is formed with an annular recess 49 which registers with an inlet port 50 in the sleeve when the plunger is in its retracted position as shown. This allows fluid from the port 50 to flow into the counterbored portion 43 of the sleeve and thence through an outlet port (not shown). When the plunger is in its projected position, the inlet port 50 is closed by the plunger 42. Inlet port 50 is connected to the main pressure line 20 of Fig. 1.

Control valve 15a is of similar construction, except that the recess 51 in its plunger is positioned nearer to the inner end of the plunger and is axially shorter than the recess 49 of control valve 14a. The arrangement is such that an inlet port (not shown) opens into the inner end portion of the sleeve, and an outlet port (not shown) is so positioned as to register with the recess 51 only when the plunger is in its projected position. In this way, valve 15a is open when projected whereas valve 1 4a is closed when projected.

The annular recesses are so positioned that control valve 15a closes its outlet port before 1 4a opens its inlet port when retracting, thus preventing the pressure line 20 being connected direct to tank line 1 9.

The inlet port of valve 15a is connected to the outlet port of valve 1 4a by the branch lines 29a and 30a of Fig. 1 which are formed as passageways (not shown) within the block 32. A further passageway (not shown) affords an outlet for connection to line 27 of Fig. 1, and the outlet port of valve 15a is connected to tank line 19 of Fig. 1.

As will be evident, the slidable members of the two valves are normally biased into their projected positions, but are displaced into their retracted positions, as shown in Fig. 2, when engaged by the piston 11 at the lefthand end of its stroke. For this purpose, the piston 11 may carry adjustable abutment elements if desired to engage the outer end portions 48 of the plungers 41.

Instead of biasing the plungers 41 by means of a spring 47, it would alternatively be possible in some circumstances to rely on the pressure of hydraulic fluid in the space between the headed end portion 44 of the plunger and the opposed end face engaged by the spring 47, by forming the head of a plunger as a piston sealingly engaging in the counterbored inner end portion 43 of the sleeve 42, and suitably proportioning the cross-sectional area of the headed end and outer end of the plunger which are both exposed to the hydraulic pressure established within the adjacent chamber A, or by otherwise applying hydraulic pressure to the inner end of the plunger.

It will be appreciated that similar control valves could be included in single acting hydraulic rams and also for the purpose of controlling other apparatus external to the ram.

Claims (11)

1. An hydraulic ram having at at least one end of the stroke of the piston one or more control valves connected in an hydraulic circuit for control of the ram and arranged so as to be operable by engagement with the piston.

2. A ram according to Claim 1 wherein the control valves each include a sliding member which is normally in a position in which a plunger portion projects into the interior of the cylinder and into the path of the piston at the end of its stroke so that when engaged by the piston, the sliding member is momentarily displaced into a retracted position.

3. A ram according to Claim 2 wherein the control valves each include spring means arranged to bias the sliding member resiliently into the normal position.

4. A ram according to Claim 3 wherein the control valves each include hydraulic means whereby the sliding member is re-set into its normal position by means of a fluid pressure signal.

5. A double-acting hydraulic ram wherein the admission of hydraulic fluid under pressure alternately to opposite ends of the cylinder is controlled by means of an hydraulic circuit having fluid control valves, at least one such valve being provided at each end of the working stroke of the piston in the cylinder so as to be operable by engagement with the piston.

6. A ram according to Claim 5 wherein the cylinder comprises a barrel with respective end blocks, said valves being housed in said end blocks and each having a respective valve member which is movable between a retracted position in which it is disposed substantially within the respective block, and a projected position in which it extends substantially into the interior of the cylinder space for engagement with the piston or a member carried thereby.

7. A ram according to Claim 6 wherein said valve members are resiliently biased into their projected positions.

8. A ram according to Claim 6 or Claim 7 wherein the valve members incorporate a plunger portion arranged to engage the piston.

9. A ram according to any one of Claims 5 to 8 wherein said hydraulic circuit includes an intermediate changeover valve which is operated by means of said control valves and itself operates a main changeover valve arranged to control the supply of fluid to opposite ends of the cylinder.

10. A ram according to Claim 9 wherein two of said control valves are provided at each end of the cylinder, one of said two valves connecting a source of fluid under pressure to a control line for one side of the intermediate valve, and the other of the two valves connecting said control line to a return line.

11. A double-acting hydraulic intensifier incorporating a double-acting hydraulic ram according to any one of Claims 5 to 10 wherein opposite ends of a piston rod on which the piston is carried operate in respective intensifier cylinders at opposite ends of said ram.

1 2. An hydraulic ram arranged to operate substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawings.

1 3. An hydraulic ram having a pair of control valves arranged at at least one end of the cylinder and substantially as hereinbefore described with reference to and as shown in Fig. 2 of the accompanying drawings.