GB2093947A

GB2093947A - Cylinder liner manifold for hydraulic jack

Info

Publication number: GB2093947A
Application number: GB8204129A
Authority: GB
Original assignee: JACOTTET PAUL ETS
Current assignee: JACOTTET PAUL ETS
Priority date: 1981-03-04
Filing date: 1982-02-12
Publication date: 1982-09-08
Also published as: DE3204303A1; FR2501306B1; ES263652Y; DE3204303C2; FR2501306A1; GB2093947B; ES263652U

Abstract

The invention relates to a double- acting hydraulic jack. The jack body (11) contains a cylindrical liner (20) having a cylindrical bore (21) in which a piston (14) is guided. The outer surface of the liner has channels or passages for working fluid. They are in communication with orifices (18) for admitting fluid into the jack body and for returning it therefrom. The invention is particularly applicable to hydraulic jacks for use in vibrating devices in machine tools. <IMAGE>

Description

SPECIFICATION Hydraulic jack The invention relates to a hydraulic jack, and more particularly to a jack suitable for use in vibration testing at low frequency (i.e. less than 10 Hz, for example), or as a positioning unit in machine tools, etc. Such a jack is servo-controlled and generally includes a servo-valve mounted on the body of the jack and connected thereto by a plate which constitutes a manifold for distributing pressure fluid to the chambers of the jack.

Such a plate is expensive, and its relatively complex structure leads to head losses in the pressure fluid flowing therethrough.

Preferred embodiments of the invention avoid these drawbacks by omitting the manifold plate.

The present invention provides a hydraulic jack comprising a body provided with pressure fluid inlet and return orifices and with a piston movable inside the body, wherein the body includes an add-on inside liner, delimiting a cylindrical bore in which the piston is sealed and guided, and whose axial or longitudinal ends communicate with the fluid inlet and return orifices in the body via passages or channels in said liner.

Thus, in accordance with the invention, it is the add-on liner inside the body which performs the function of a manifold for distributing pressure fluid to the chambers of the jack on either side of the piston. The pressure fluid inlet and return orifices formed in the body of the jack may thus be directly connected to the servo-valve (optionally via a pressure limiter), with the manifold plate that used to be provided between the servo-valve and the jack body being omitted.

It follows that the invention makes it possible to simplify manufacture of the jack body, since the bore therein which receives the liner can now be made in a single operation. This leads to a cheap and compact jack.

Further, it becomes possible to offer a range of different jacks, all having the same jack body and differing from one another in the dimensions of the liner received inside the body of the jack, and in the dimensions of the pistons and piston rods.

In the following description, given by way of example, reference is made to the accompanying drawings, in which: Figure 1 is a diagrammatic axial longitudinal section through a hydraulic jack in accordance with the invention; Figure 2. is an axial longitudinal section on a larger size through a liner in the jack of Figure 1; Figure 3 is an end view of the liner in Figure 2; Figure 4 is a partial outside view of the liner in Figures 2 and 3; and Figures 5, 6 and 7 correspond to Figures 2, 3 and 4 respectively, but show another embodiment of a liner.

Reference is made initially to Figure 1, which is a diagrammatic axial section through a jack in accordance with the invention.

The jack 10 in Figure 1 comprises a hollow body 11, e.g. substantially in the shape of a cylindrical tube, with open ends that are closed by caps 12 through which there pass axially the rods 1 3 of a piston 14 movable with rectilinear alternating motion inside the body. The cross sections of the two piston rods 1 3 are substantially identical, and one of the rods has its end 1 5 connected to a member that is to be moved in a rectilinear alternating motion, while the other rod is associated in known manner with a motion detector 16, e.g. of the coil and moving core type.

The caps 12 closing the ends of the body 11 of the jack, constitute guide bearings for the rods 13 and are fitted with sealing means 17.

The jack body 11 has two fluid-passing orifices 18, disposed, for example, symmetrically about the middle cross section plane 1 9 through the body 11. The orifices 18 may be radial or transverse drillings through the jack body.

In the embodiment shown in the drawings, the inside surface of the jack body is a cylinder of circular section and receives a liner 20 which is in the shape of a substantially cylindrical tube and which is held fast inside the body 11 by its ends pressing against the caps 1 2.

The liner 20 can be seen more clearly in Figures 2, 3, and 4. It has an axial bore 21 opening out at each end of the liner 20 in a facing 22 via a bevel 23 for guiding the piston 14 of the jack into the bore 21. The outer cylindrical surface of the piston is provided with an annular sealing ring 24 that is intended to press against the cylindrical surface of the bore 21. Advantageously the outside diameter of the piston 14 is slightly less than the diameter of the bore 21 so that the piston and the bore only come into contact with each other via the sealing ring 24, thereby avoiding metal on metal friction.

The outside surface of the liner 20 is substantially cylindrical and of circular cross section. It has a shoulder or flange 25 about its middle with a groove 26 therein suitable for receiving a sealing ring. On either side of the middle flange 25 there are respective cylindrical bearing surfaces 27 of smaller diameter than the flange 25, with further cylindrical bearing surfaces 28 being formed by the outer surface of the liner 20 near its ends, said bearing surfaces 28 being of substantially the same diameter as the middle flange 25.

The liner 20 is provided with channels or passages for fluid under pressure which, in the present embodiment, are constituted by longitudinal grooves 29 in the bearing surfaces 28 of the liner 20. The longitudinal grooves 29 are made, for example, by milling and open out at the ends of the liner 20 into the above-mentioned facings 22. The depth of the grooves 29 is slightly less than the difference in radius between the liner's cylindrical surfaces 27 and 28.

The cylindrical surfaces 28 and the flange 25 are of very slightly smaller diameter than the inside cylindrical surface of the jack body 11, whereby the liner is a snug fit inside the body of the jack.

Inside the body of the jack, the pressure fluid inlet and return orifices 1 8 are separated by a cylindrical bearing surface 30 intended to cooperate with a sealing ring housed in the groove 26 of the liner 20. Each orifice 18 leads to an annular passage 31 of slighly greater diameter than the remainder of said inside cylindrical surface.

During assembly, the liner 20 is placed inside the jack body 11, the piston 14 is placed inside the liner 20, and then the caps 1 2 and their sealing means 1 7 are placed at the ends of the jack body 11. The piston 14 and its piston rods 13 are moved one way or the other by the pressure fluid delivered by a servo-valve 32, via an orifice 18, the grooves 29, and one of the end facings 22, to one of the chambers formed on either side of the piston 14 in the bore 21 of the liner 20.

The operation of such a jack is well known and is not described in greater detail.

Reference is now made to Figures 5, 6 and 7 which show another embodiment of a liner for the jack.

This liner 40 differs from the liner 20 of Figures 2 to 4 in that the its peripheral fluid channels or passages are not grooves or millings, but are longitudinally drilled holes 49 formed through the end cylindrical bearing surfaces 48 of the liner, opening out at the ends of the liner into the facings 43, whereby they communicate with the axial bore 41 of the liner, and opening out at their opposite ends over the cylindrical bearing surfaces 47 which are of smaller diameter than the end cylindrical surfaces 48, the cylindrical surfaces 47 being arranged on either side of a middle annular flange 45 having a groove 46 for receiving a sealing ring.

The liners 20 or 40 provide a simple means for conveying the pressure fluid to the chambers on one side or the other of the piston 14, and they do so with relatively small head loss.

The bore through the jack body may be made in a single operation, which facilitates manufacture and reduces machining costs.

Further, a varied range of jacks may be provided using the same jack body and associating it with liners of differing inside dimensions.

Claims

1. A hydraulic jack comprising a body provided with pressure fluid inlet and return orifices and with a piston movable inside the body, wherein the body includes an add-on inside liner, delimiting a cylindrical bore in which the piston is sealed and guided, and whose axial or longitudinal ends communicate with the fluid inlet and return orifices in the body via passages or channels in said liner.

2. A jack according to claim 1, wherein the outer peripheral surface of the liner has at least one annular flange provided with a sealing ring bearing against a cylindrical bearing surface of the inside surface of said body, said bearing surface being formed in between the openings of the fluid inlet and return orifices in the body.

3. A jack according to claim 1 or 2, wherein said liner includes, near its ends, annular flanges or shoulders coming substantially into contact with the inside surface of the jack body and in which the said passages or channels are formed.

4. A jack according to claim 3, wherein said passages or channels are longitudinal grooves in said annular flanges or shoulders at the ends of the liner, and communicate at the ends of the liner with the cylindrical bore thereof.

5. A jack according to claim 3, wherein the said passages or channels are longitudinal drillings through the said annular flanges or shoulders at the ends of the liner, and communicate at the ends of the liner with the cylindrical bore thereof.

6. A jack according to claim 4 or 5, wherein the ends of the liner are provided with facings in which the said passages or channels open out.

7. A jack according to any one of claims 2 to 6, wherein that the said annular flange of the liner provided with a sealing ring, is located half way along the liner.

8. A jack according to any preceding claim, wherein the inside surface of the body of the jack is a cylinder of circular cross section, and the said liner is substantially cylindrical in shape and is held in place by its ends bearing against the end walls of the jack body.

9. A jack according to any preceding claim, wherein the fluid inlet and return orifices in the body are drillings through the peripheral wall of the body and open out on the inside thereof into annular passages formed on either side of the cylindrical bearing surface that co-operates with the liner's sealing ring.

10. A hydraulic jack substantially as herein described with reference to and as illustrated in Figures 1,2,3 and 4, or 1,5,6 and 7 of the accompanying drawings.