GB2277354A

GB2277354A - Hydraulic piston and cylinder assembly

Info

Publication number: GB2277354A
Application number: GB9305275A
Authority: GB
Inventors: Brian Edward Mason
Original assignee: SCANLAN THOMAS ROBERT
Current assignee: SCANLAN THOMAS ROBERT
Priority date: 1993-03-15
Filing date: 1993-03-15
Publication date: 1994-10-26
Also published as: GB9305275D0

Abstract

A self-contained hydraulic pump and working piston and cylinder arrangement comprises a cylinder 1 with a piston rod 7 extending through an annular plug 2 at one end of the cylinder, the opposite end of the cylinder being closed by pump body 3. The cylinder 1 is divided by the working piston 6 into a pressure chamber 24 and a reservoir chamber 19 whose volumes are varied with the stroke of the piston 7. During operation of the hydraulic pump 14, fluid from the reservoir 19 is delivered by the pump under pressure to the pressure chamber 24 causing the piston 6 to retract the piston rod 7. In order to release the pressure in the pressure chamber 24 a manually actuable pressure release valve (28 Fig. 2 not shown) is opened to allow fluid to return to the reservoir chamber 19. <IMAGE>

Description

HYDRAULIC PISTON AND CYLINDER ASSEMBLY This invention concerns improvements in hydraulic piston and cylinder arrangements, and more especially to a piston and cylinder arrangement with a self-contained hydraulic pump and reservoir for actuation of the hydraulic piston.

Arrangements of the above kind are known for example for use in manually or foot operated hydraulic jacks. In the known arrangements, however, the hydraulic reservoir is separate from the space provided for displacement of the hydraulic piston, and thus the overall size of the assembly is relatively large in relation to the working displacement of the piston and cylinder.

Such known arrangements incorporate a so-called compression cylinder, wherein the power is delivered to the hydraulic piston during extension of the piston and cylinder so that the piston rod is under compression and is required to be of relatively large diameter in relation to the stroke of the piston.

In accordance with the present invention there is provided a self-contained hydraulic pump and working piston and cylinder arrangement, wherein the working piston is displaceable within a cylinder defining on both sides of the piston hydraulic chambers the volume of which is varied with the stroke of the piston, the arrangement being such that one of the said chambers forms a pressure chamber on the delivery side of the pump whilst the other chamber forms a reservoir for the pump.

In such an arrangement, during operation of the hydraulic pump fluid is transferred from one side of the piston to the other and thus the volume of the hydraulic reservoir is reduced as the volume of the pressure chamber increases, and vice versa.

Advantageously, the hydraulic piston and cylinder is a tension cylinder having a piston rod that extends through said pressure chamber.

Preferably, the output of the hydraulic pump is coupled to the said pressure chamber via a feed pipe extending parallel to the axis of the cylinder and passing through the working piston.

Conveniently, a non-return valve at the outlet of the hydraulic pump is mounted within the pump housing coaxially with the said feed pipe and incorporates a manually actuatable pressure release valve that can be opened by axial movement of the body of the non-return valve relatively to an orifice of said feed pipe.

Further preferred features and advantages of the arrangement in accordance with the invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which; Fig.l is a sectional side elevation of a hydraulic piston and cylinder arrangement in accordance with the invention, and; Fig.2 is a sectional view along the line II-II of Fig.1.

Referring to the drawings, the piston and cylinder device illustrated comprises a cylinder 1 closed at one end by means of an annular plug 2 screw threaded therein and closed at the other end by means of a generally cylindrical pump body 3 that is sealed with respect to the cylinder 1 by means of an O-ring 4 and retained within the cylinder 1 by means of a shaft (not shown) extending through a transverse bore 5 provided in the cylinder 1 and pump body 3.

A working piston 6 is secured to a piston rod 7 extending through the annular plug 2 the piston 6 being sealed with respect to the cylinder 1 by means of a ring seal 8 and the plug 2 likewise being sealed with respect to the piston rod 7 by means of a ring seal 9.

The piston rod 7 has a longitudinal axial bore 10 bleeding to atmosphere via a radial bore 11 and communicating with the cylinder 1 via a radially extending bleed tube 12. The inner axial end of the bore 10 is closed by means of a plug 13.

A pump piston 14 is axially displaceable within a bore 15, being retained therein against the pressure of a return spring 16 by means of a gland nut 17 engaging a seal 18 around the periphery of the piston 14.

The bore 15 is coupled to a hydraulic reservoir 19 by means of a passage 20 and non-return ball valve 21.

A feed pipe 22 extends from the pump body 3 parallel to the axis of the cylinder 1 and passes through a bore in the piston 1, being sealed by means of a ring seal 23. The end of the feed pipe 22 remote from the pump body 3 abuts against the surface of the plug 2 and is coupled to a pressure chamber 24 within the cylinder 1, by means of an annular groove 25 in the plug 2.

The bore 15 in the pump body 3 is coupled to the feed pipe 22 via a delivery passage 26 and a spring-loaded non-return ball valve 27. The ball valve 27 is mounted within a body 28 that is screw-threaded in the pump body 3 and has a conical valve surface 29 engaging with an orifice at the end of the feed pipe 22. The delivery passage 26 communicates with the non-return valve 27 via a recess 30 in the pump body 3 and a transverse bore 31 in the valve body 28, the resulting fluid passage being sealed by means of O-rings 32 in the valve body 28. An annular space 33 at the end of the feed pipe 22 is coupled with the hydraulic reservoir 19 via an exhaust passage 34, and thus when the valve body 28 is unscrewed relatively to the feed pipe 22, hydraulic fluid can return from the pressure chamber 24 to the reservoir 19.

The delivery passage 26 is also coupled directly to the reservoir 19 via an over pressure release valve 35 that is arranged to open when the pressure in the hydraulic pump reaches the limit of the working pressure of the pressure chamber 24.

In the normal operation of the arrangement described, when the hydraulic piston 6 is fully extended to abut against the plug 2, the hydraulic reservoir 19 is filled with a volume of hydraulic fluid slightly greater than the maximum working volume of the pressure chamber 24.

Upon actuation of the pump piston 14, fluid is delivered under pressure to the pressure chamber 24 via the feed pipe 22, causing the piston 6 to retract the piston rod 7. Since the volume of the hydraulic reservoir 19 will reduce at a greater rate than the volume of the pressure chamber 24 will increase, owing to the presence of the piston rod 7 in the pressure chamber, the hydraulic reservoir 19 is vented to atmosphere via the bleed tube 12 and the bores lo and 11 so that air can escape therefrom. It will be appreciated that this limits the effective working position of the hydraulic cylinder to one in which the level of hydraulic fluid is always below the orifice of the bleed tube 12. This is not a disadvantage in the context of the intended use of the cylinder, but the limitation could be overcome, for example, by partitioning the reservoir 19 with a diaphragm.

In order to release the pressure in the pressure chamber 24 and allow the piston and cylinder to collapse, the valve body 28 is unscrewed as already described above.

It will thus be seen from the above description that the arrangement in accordance with the invention provides a novel and compact hydraulic cylinder and pump assembly that has a relatively long working stroke in relation to its size, and which can accommodate relatively high loads as a result of the fact that the piston rod acts in tension rather than in compression.

Various alterations and modifications can be made to the arrangement illustrated without departing from the scope of the invention. For example although the hydraulic pump as described is a single speed pump a spring loaded piston assembly could be inserted in passage 26 to form a two speed pump so that the fluid displaced by piston 14 can be increased to provide rapid withdrawal of the piston rod 7 under light load.

Claims

1. A self-contained hydraulic pump and working piston and cylinder arrangement, wherein the working piston is displaceable within a cylinder defining on both sides of the piston hydraulic chambers the volume of which are varied with the stroke of the piston, the arrangement being such that one of the said chambers forms a pressure chamber on the delivery side of the pump whilst the other chamber forms a reservoir for the pump and that during operation of the hydraulic pump, fluid is transferrable between each side of the piston.

2. An arrangement as claimed in Claim 1, wherein the hydraulic piston and cylinder is a tension cylinder having a piston rod that extends through said pressure chamber.

3. An arrangement as claimed in any preceding Claim, wherein the delivery side outlet of the pump is coupled to the said pressure chamber via a feed pipe extending parallel to the axis of the cylinder and passing through the working piston.

4. An arrangement as claimed in Claim 3, wherein the pressure chamber end of the feed pipe abuts against a cylinder end surface in said chamber and communicates therewith by an annular groove in said surface.

5. An arrangement as claimed in Claim 3 or Claim 4, wherein a non-return valve at the said outlet of the pump is mounted within the pump coaxially with the said feed pipe and incorporates a manually actuatable pressure release valve that can be opened by axial movement of the body of the said valve relatively to an orifice of said feed pipe.

6. An arrangement as claimed in Claim 5, wherein said reservoir chamber communicates via an exhaust passage with an annular space at said orifice end of said feed pipe to provide a return path for fluid when said pressure relief valve is open.

7. An arrangement as claimed in any preceding Claim, wherein the piston rod has a longitudinal axial bore coupling said reservoir chamber of said cylinder to atmosphere.

8. An arrangement as claimed in Claim 7, wherein said reservoir chamber incorporates a diaphragm separating said pump input from said bore.

9. An arrangement as claimed in any preceding Claim wherein the hydraulic pump is coupled to the reservoir chamber via a nonreturn valve.

10. An arrangement as claimed in any preceding Claim, wherein the pump includes an over pressure relief valve.

11. An arrangement as claimed in any preceding Claim, wherein the pump has a plurality of speeds.

12 A self-contained hydraulic pump and working piston and cylinder arrangement substantially as hereinbefore described with reference to the accompanying drawings.