RECIPROCATING DRIVE APPARATUS

Abstract: In a hydraulic pressure intensifier, a high pressure hydraulic pump (16, 17) is driven by hydraulic reciprocating drive apparatus (10) in which a reciprocable low pressure driving piston (15) carries control valve means (29, 30) operable to direct fluid from a source of fluid under pressure alternately to the opposite sides of the low pressure piston. The control valve means (29, 30) comprises mutually separate valves of which one (29) is adapted to be operable by pressure fluid and is arranged for reversing the action of the piston (15). The other valve (30) is a pilot valve arranged for controlling the action of the reversing valve (29). The action of the reversing valve (29) is bi-stable and occurs over a relatively short period of time whereas the action of the pilot valve (30) occurs at the speed of the movement of the low pressure piston (15). A feature of the low pressure drive apparatus (10) is an absence of dynamic seals in the reversing valve (29) and the pilot valve.

Description: RECIPROCATING DRIVE APPARATUS This invention relates to reciprocating drive apparatus. The invention is concerned especially, but not exclusively, with hydraulic reciprocating drive apparatus in combination with a hydraulic pump. Hereinafter, the expression "pressure intensifier" is used for the combination of a hydraulic reciprocating drive operable by means of hydraulic fluid from a relatively low pressure source with a hydraulic pump dimensioned and arranged to deliver relatively high pressure hydraulic fluid. Hydraulic reciprocating drives have been proposed, comprising a piston-and-cylinder assembly for double-acting operation, and control valve means operable to direct hydraulic fluid from a source of fluid under pressure alternately to the opposite sides of the piston of the said assembly thereby to obtain a reciprocating drive. Usually, the control valve means includes piston end-of-stroke detecting means deployed to effect automatic regular operation of the control valve means. Such drives hitherto have the disadvantages that they involve relatively numerous components and complex assembly, costly to manufacture and maintain. An object of the present invention is to provide a hydraulic reciprocating drive apparatus of improved design whereby the aforementioned disadvantages are obviated or mitigated. According to the present invention, there is provided a a reciprocating drive apparatus comprising a piston-and-cylinder assembly for double-acting operation, and control valve means mounted in the body of the piston and operable to direct fluid from a source of fluid under pressure alternately to the opposite sides of the piston of said assembly; characterised in that the said valve means comprises mutually separate valves of which one is adapted to be operable by pressure fluid and is arranged for reversing the action of the piston and the other is a pilot valve arranged for controlling the action of the reversing valve. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:- Fig. 1 is a sectional elevation on two different planes showing a hydraulic reciprocating drive apparatus in accordance with the present invention, combined with a double-acting high pressure piston-and-cylinder assembly; Fig. 2 is a sectional end elevation on the line II-II in Fig. 1; Fig. 3 is a sectional end elevation on the line III-III in Fig. 1; and Fig. 4 is a cross-sectional partial plan view on the line IV-IV in Fig. 2. In the drawings, a pressure intensifier consists of a relatively low pressure piston-and-cylinder assembly (drive apparatus) which is indicated generally by reference numeral 10 surrounding a relatively high pressure piston-and-cylinder assembly which is indicated generally by reference numeral 11. The low pressure assembly 10 has a cylinder 12 with end caps 13 and 14, and a low pressure piston 15 reciprocable within the cylinder 12 between the end caps 13, 14. The high pressure assembly 11 has a cylinder 16 and a high pressure piston 17 which is directly connected with the low pressure piston 15 by means of a piston rod 18 which extends through sets of seals 19 which serve to keep the low pressure and high pressure systems mutually separate. The swept volume on the right hand side of the high pressure piston 17 is approximately twice that on the left hand side of that piston for the reason explained hereinafter. The low pressure cylinder 12 is provided with an inlet port 20 and an associated hydraulic coupling socket 21 for connection to a source of hydraulic drive fluid at relatively low pressure. The cylinder 12 is provided also with an exhaust port 22 and an associated hydraulic coupling socket 23 for connection with a return fluid reservoir (not shown) . The low pressure piston 15 has three axially spaced lands 24, 25 and 26 each provided with an annular seal or piston ring. Between these lands 24, 25 and 26, the piston 15 outer wall surface defines two galleries 27 and 28, the arrangement being such that for all positions of the piston 15 the gallery 27 always communicates with the inlet port 20, and the gallery 28 always communicates with the exhaust port 22. The low pressure piston 15 carries control valve means operable to direct hydraulic fluid entering the inlet port 20 alternately to the opposite sides of the piston 15. The control valve means consists of a main directional control valve or "reversing" valve 29 and an end-of-stroke-detecting pilot valve 30. The valves 29 and 30 are in communication with the galleries 27 and 28 by way of ports 31, 32, 33 and 34 in the low pressure piston 15. The main directional control valve 29 consists of a ported sleeve 35 which is located in a bore 36 between fixed end caps 37, and a reciprocable spool 38. The bore 36 extends through the low pressure piston 15 parallel with the central axis of the piston. The spool 38 defines annular galleries A, B, C, D and E of which galleries B and D are in communication with a blind-end core 39 which opens to the left hand side only of the low pressure piston 15. The galleries A and E are in communication with the pilot valve 30 by way of passages 40 and 41 which extend through the body of the low pressure piston 15. In Fig. 1, the passages 40, 41 are represented by broken lines. In fact, the valves 29 and 30 are side by side as shown in Fig. 2, and the passages 40 and 41 are straight drillings or may be a feature of a casting mould for the low pressure piston. The spool 38 is guided and located co-axially with respect to the sleeve 35 by means of the end caps 37; and an annular clearance of the order of 0.025 mm is provided between the lands on the spool 38 and the bore of the sleeve 35 to obviate or mitigate seizure. The pilot valve 30 consists of a ported sleeve 42 which is located in a bore 43 between circlips 44, and a reciprocable spool 45 located and guided by fixed end-caps 45A. The spool 45 is provided with galleries F, G, H and I of which galleries F, G and I communicate with a central passage 46 which is closed at each end of the spool 45 by means of plunger heads 47 for contacting the end caps 13 and 14 to effect reversing action of the pilot valve 30 as explained later in this description. The bore 43 extends through the body of the low pressure piston 15 parallel with the central axis. The pilot spool 45, similarly to the main spool 38, is clear of its sleeve 42 by an annular clearance of the order of 0.025 mm to obviate or mitigate seizure. The high pressure cylinder 16 is located in the end cap 14 by a flange-and-recess configuration, and is associated with a valve block 48 which is secured to the end cap 14 by means of screws one of which is shown at 49. The body of the high pressure cylinder 16, as seen in Fig. 4, is provided with passages which communicate with passages in the valve block 48. Thus, passage 50 in the valve block 48 conveys hydraulic fluid to and from the right hand end of the high pressure cylinder; passage 51 in the body of the high pressure cylinder 16 conveys hydraulic fluid to and from the left hand side of the high pressure cylinder and connects with passage 52 in the cylinder block 48; and passage 53 in the body of the high pressure cylinder 16 provides drainage for hydraulic fluid leakage between seals 19 and connects with passage 54 in the valve block 48. Within the valve block 48, there is provided an assembly of three check valves 55, 56 and 57. The check valve 55 is arranged to pass low pressure hydraulic fluid from an inlet to the valve block 48 to the passage 50 for supplying hydraulic fluid to the right hand side of the high pressure piston 17. The check valve 56 is arranged to pass high pressure hydraulic Uiid from the passage 50 both to the passage 52 and to the intake side of the check valve 57 which passes fluid to a high pressure fluid outlet of the valve block 48. Operation of the pressure intensifier described above is as follows. The main directional control valve 29 is bistable and therefore low pressure hydraulic fluid introduced through the inlet port 20 will gain access either to gallery B or gallery C and so quickly establish a preferred initial direction of the low pressure piston 15. Fluid in gallery B gains access to the left hand side of piston 15 by way of open core 39; and hydraulic fluid in gallery C gains access to the right hand side of low pressure piston 15 by way of a port Cl and a central recessed portion 58 of the low pressure piston 15. The recessed portion 58 is clear of the high pressure piston-and-cylinder assembly 11 permitting fluid flow between the recess 58 and the right hand side of the piston 15. Once initial movement of the piston 15 is established, greater pressure on one side of the spool 38 will cause the spool to seek a stable position against one of the end caps 37. Simultaneously, the same pressure will force the pilot spool 45 in the same direction. Thus, fluid from gallery 27 entering port 32 will _.ind its way either to gallery A or gallery E in the directional control valve 29 by way of gallery G, passage 46 and passage 40, or by way of gallery H and passage 41. Thus initiated, the directional control valve 29 is held firmly in either one of its two definite positions. Whilst the low pressure piston 15 is moving, fluid is exhausted through port 33, gallery 28 and exhaust port 22 either by way of gallery C or by way of gallery D. An imminent end-of-stroke condition of the low pressure piston 15 is detected by the pilot valve 30 when one of the plunger heads 47 is carried into contact with one of the end caps 13, 14. Continued movement of the low pressure piston 15 relative to the pilot spool 45 effects reverse action of the pilot spool 45 thus exhausting one of the galleries A, E and pressurising the other to effect reverse action of the directional control spool 38. Although the reverse action of the pilot spool 45 occurs at the speed of the low pressure piston 15, the action of the reversing valve 29 occurs over a shorter period so reducing the time of errosive flows within the reversing valve and extending the life thereof. Thus, the low pressure piston-and-cylinder assembly 10 will continue to operate as a hydraulic reciprocating drive so long as low pressure fluid is supplied through the inlet port 20. When the high pressure piston 17 moves from right to left, hydraulic fluid is drawn in from the low pressure fluid inlet of the valve block 48 past check valve 55 and through passage 50. simultaneously, high pressure hydraulic fluid is discharged from the left hand side of high pressure piston 17 by way of passages 51, 52, check valve 57 and the high pressure fluid outlet of valve block 48. When the high pressure piston 17 moves in the opposite direction from left to right, high pressure hydraulic fluid is delivered through passage 50 past check valve 56 whereafter approximately half of the delivery is delivered to the high pressure fluid outlet from valve block 48 and the remaining half of the delivery is transferred by way of passages 52 and 51 to the left hand side of the high pressure piston 17. This explains the reason for the relationship between the swept volumes on the opposite sides of the high pressure piston 17. It is envisaged that the low pressure piston-and-cylinder assembly 10 may be used to drive other than a high pressure hydraulic pump. Also, it is envisaged that a reciprocating drive apparatus in accordance with the present invention can use compressed gas e.g. compressed air as the driving medium with appropriately reduced annular clearances in the reversing and pilot valves. Also, it is envisaged that the pilot spool plunger heads may contact stops or adjustable stops other than the end caps of the cylinder 12.

Claims: CLAIMS 1. A reciprocating drive apparatus comprising a piston-and-cylinder assembly (15, 12) for double-acting operation, and control valve means (29, 30) mounted in the body of the piston (15) and operable to direct fluid from a source of fluid under pressure alternately to the opposite sides of the piston (15) of said assembly; characterised in that the said valve means (29, 30) comprises mutually separate valves of which one (29) is adapted to be operable by pressure fluid and is arranged for reversing the action of the piston (15) and the other (30) is a pilot valve arranged for controlling the action of the reversing valve (29) . 2. Drive apparatus as claimed in claim 1; characterised in that when the apparatus is operational the action of the reversing valve (29) is bi-stable. 3. Drive apparatus as claimed in claim 1 or 2; characterised in that the pilot valve (30) has a reciprocable spool (45) operation of which is effected, when the apparatus is operational, by the opposite ends (47) of the spool (45) alternately abutting respective stops (13, 14) within the cylinder (12) of the assembly (15, 12). 4. Drive apparatus as claimed in any one of the preceding claims; characterised in that the apparatus is hydraulic reciprocating drive apparatus. 5. Drive apparatus as claimed in claim 4; characterised in that the fluid is water. 6. Drive apparatus as claimed in claim 4 or 5; characterised in that the reversing valve (29) is a spool valve comprising a spool (38) reciprocable within a sleeve (35) with a clearance of the order of 0.025 mm, and by the absence of dynamic seals between the spool (38) and the sleeve (35) . 7. Drive apparatus as claimed in claim 4 or 5; characterised in that the pilot valve spool (45) is reciprocable within a pilot sleeve (42) with a clearance of the order of 0.025 mm, and by the absence of dynamic seals between the pilot spool (45) and the pilot sleeve (42). 8. Drive apparatus as claimed in any one of the preceding claims in combination with a high pressure piston-and-cylinder assembly (16, 17) . 9. A reciprocating drive apparatus substantially as hereinbefore defined with reference to and as shown in the accompanying drawings.

Inventors: CLAYSON ANDREW, CLAYSON, ANDREW
Applicants: PACSON LTD, PACSON LTD.
Application year: 1991
Main classification: F04B9
IPC codes: F01L21, F04B9