GB2033536A - Piston-and-cylinder device - Google Patents

Abstract

A piston-and-cylinder device 1 comprises a cylinder 2 which includes a main cylindrical portion 3 having an end wall 4, 5 at each end thereof and having a cylindrical liner 6 disposed therein. The material of the liner has greater wear-resistance and a different co-efficient of expansion from the material of the main portion 3. Metallic spring means 7 is so disposed and compressed between the end wall 4 and the adjacent end portion of the liner 6 as to maintain the liner in positive engagement at its other end portion with the other end wall 5. <IMAGE>

Description

SPECIFICATION Piston-and-cylinder device This invention relates to a piston-and-cylinder device.

Where, in order to provide a relatively light-weight piston-and-cylinder device, at least the cylinder thereof is formed of a relatively light-weight material, for example, aluminium, it has been found desirable to provide the interior surface of the cylinder either with a wear-resisting coating, for example of chrome, or eith a cylindrical wearresisting liner, for example, of steel.

If however in service damage to such a coating in a cylinder occurs, it is an expensive procedure to remove the damaged coating and to apply a new coating, whereas in the case of a liner it is a relatively straight-forward matter to replace a damaged liner with a new one.

Where a piston-and-cylinder device having such a liner is required to operate under high fluid pressures, it is essential that no reciprocatory movement of the liner with respect to the main portion of the cylinder under fluid pressure differentials acting upon it is permitted to occur, as this could result in wear in the interior surface of the main portion of the cylinder, possibly setting up undesirable fluid leakage paths.

If a piston-and-cylinder device having a linerwhich is firmly held against such movement is likely to be operable over a wide temperature range, we have found that the means for holding the liner firmly in place must be capable of accommodating differential expansion which will occur between the lightweight material of the main portion of the cylinder and the material of the liner, otherwise some distortion of the cylinder can be expected to take place particularly at extremes of operating temperature giving rise to unsatisfactory operation of the device.

The invention as claimed is intended to provide a remedy. It solves the problem of accommodating such differential expansion where a liner is so held in place in the main portion of a cylinder.

According to this invention there is provided a piston-and-cylinder device, the cylinder of which includes a main cylindrical portion having an end wall at each end thereof and having a cylindrical liner disposed therein, the material of said liner having greater wear-resistance and a different coefficient of expansion from the material of said main portion, wherein metallic spring means is so disposed and compressed between one of said end walls and the adjacent end portion of said liner, as to maintain said liner in positive engagement at its other end portion with the other of said end walls.

The advantages offered by the invention are mainly that the characteristics of said metallic spring means can be predetermined to ensure such loading of the liner into engagement with said other of said end walls that the liner is maintained in such engagement irrespective of pressure differentials to which it is subjected in use and irrespective of the temperatures, within a predetermined range, to which the piston-and-cylinder device is subjected.

One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which: Figure 1 is a cross-sectional side elevation of a piston-and-cylinder device in accordance with the invention and, Figure 2 is an end view of metallic spring means forming part of the construction shown in Figure 1.

The figures show a piston-and-cylinder device 1, suitable for operating an aircraft aileron (not shown).

The cylinder 2 of the device includes a main cylindrical portion 3 having an end wall 4,5 at each end thereof and having a cylindrical liner 6 disposed therein. The material of the liner 6 has greater wear-resistance and a different co-efficient of expansion from the material of the main portion 3.

In accordance with the invention metallic spring means 7 is so disposed and compressed between the end wall 4 and the adjacent end portion of the liner 6 as to maintain the liner in positive engagement at its other end portion with the end wall 5.

The metallic spring means 7 comprises a disc spring which, in its free state, is of frusto-conical form. This spring is provided with a plurality of apertures 8 which are circumferentially equi-spaced around the spring and which are each of circuiar shape. The disc spring is of spring steel.

The end walls 4 and 5 are both of annular shape and each includes a bush 9, 10 for slidably supporting a piston rod 11. The piston rod carries a piston 12 which is reciprocable in the liner 6. As shown the piston rod extends through both said end walls 4 and 5 to the exterior of the cylinder.

The bush 9 of said end wall 4 is provided with a spigot portion 13 which extends inwardly of the cylinder 2 and which supports the disc spring 7. The bush 10 is also provided with a spigot portion 14 which extends inwardly of the cylinder 2 and which carries a plate 15, apertured at 16, forming part of the end wall 5.

In this embodiment the main cylindrical portion 3 is of aluminium, the liner 6 of steel and the bushes 9 and 10 of bronze.

The main portion of the end wall 4 is secured to the main portion 3 by means of bolts and nuts as at 17 and 18, and the main portion of the end wall 5 is secured to the main portion 3 by means of bolts and nuts as at 19 and 20.

The main portions of the end walls 4 and 5 are of aluminium and are each provided with a port 21, 22 by way of which liquid can be supplied under pressure to, or alternatively allowed to exhaust from, the respective chamber 23, 24 of the device 1.

The flow of liquid into and out of the chamber 23 is by way of said apertures 8, and the flow of liquid into and out of the chamber 24 is by way of aperture 16.

Axial clearance 25 is provided between the disc spring 7 and the end wall 4 and radial clearance 26 is provided between the circular outer edge of the disc spring and the interior surface of the cylinder 2.

These clearances are needed to permit deformation of the disc spring 7 to take place upon axial compression thereof. Such compression occurs during assembly of the device and as a result the disc spring is deformed from the frusto-conical shape in its free state to the flattened shape as shown in the drawing which it adopts upon reaching the compressed condition necessary to maintain the liner in positive engagement with the end wall 5.

Sealing rings 27 and 28 are provided in suitable grooves in the positions shown in the interior surface of the main portion 3 for fluid-sealing between that surface and the outer surface of the liner 6.

Other sealing rings are respectively provided at 29 and 30 in the main portion of the end wall 4 and in the bush 9, and at 31 and 32 in the main portion of the end wall 5 and in the bush 10. Energised sealing ring assemblies 33 and 34 are respectively provided in the bushes 9 and 10 for sealing with respect to the piston rod 11.

The piston 12, which with the piston rod is of hard chrome on steel, is provided with a seal assembly 35.

The lengths of the liner 6 and of the bush 9 are such that upon assembly of the components of the device 1 and upon suitable tightening of the bolts 17, 19 and nuts 18,20, a predetermined pre-load is applied through the intermediary of the disc spring 7 to the liner 6.

During operation of the device 1 liquid is supplied under high pressure either to the chamber 23 by way of the port 21 or to the chamber 24 by way of the port 22. Since that chamber not so pressurised is open by way of its port to tank, a relatively high pressure differential exists across the piston 12 and the liner 6 is subjectable to this pressure differential. However, the pre-loading effect by way of the disc spring 7 upon the liner 6 is sufficiently great that the pressure differential is inadequate to have any displacing effect upon the liner and thus the liner is maintained in the position shown in the drawing, that is, in positive engagement with the end wall 5.Since, therefore, the liner is not permitted to move axially bodily in either direction with respect to the main portion 3 under the fluid pressure differentials upon it or under the effect of piston movement, no wear of the aluminium of the main portion 3 by the steel of the liner can take place. Since there can be no such wear, sealing rings 27 and 28 can maintain their sealing effect and no leakage paths are likely to be set up from the chamber 23 to the chamber 24, or vice versa, past these sealing rings.

During such operation relatively high temperatures are likely to be experienced in the piston-andcylinder device. Since the aluminium of the main portion 3 has a greater co-efficient of expansion than the steel of the liner 6 there will be resultant differential expansion between the main portion and the liner. This, however, is accommodated by the disc spring 7 which is maintained at all times in engagement with the left-hand end in Figue 1 of the liner due to the pre-load applied and the characteristics of the disc spring.Had the end wall 4 simply directly engaged the liner without the interposition of a disc spring, then upon such differential expansion an axial clearance would have been established between the main portion of the end wall 4 and the liner, whereupon alternating pressure differentials upon the liner could have caused a degree of reciprocation of the liner with respect to the main portion 3 with attendant undesirable wear of the aluminium of the main portion 3. Also liquid capacity problems within the chambers 23 and 24 might have arisen.

By so providing a plurality of apertures 8 in the disc spring 7 a predetermined spring-loading effect upon the liner 6 is achieved upon assembly of the components of the piston-and-cylinder device.

However, by changing the size andlor shape and/or number of such apertures, desired variations in the loading upon the liner can be obtained.

Although in the embodiment above-described with reference to the drawings the piston rod 11 of the device 1 extends to the exterior at both ends of the cylinder, in other embodiments of the invention the piston rod may only extend through one end of the cylinder.

Also, although in the embodiment abovedescribed with reference to the drawings the material of the main cylindrical portion 3 is aluminium and that of the liner 6 is steel, in other embodiments other suitable materials may be used.

Further, although in the embodiment abovedescribed with reference to the drawings the metallic spring means comprises a disc spring 7, in other embodiments of the invention the metallic spring means may be of any other suitable form permitting the necessary pre-loading of the liner in such manner as also to accommodate differential thermal expansion between the liner and the main cylindrical portion. For example, the metallic spring means may comprise a member generally of triangular shape with a hub portion having a central aperture affording fitment to the spigot portion 13, and the three corners of the triangular portion of the member bear upon the adjacent end of the liner.Alternatively, the means may comprise a member with a hub portion having radial spring fingers which bear upon the liner, or, again, a member with a hub portion having a radial flange which bear upon the liner and which has portions so removed therefrom as to provide a shape affording a desired spring rate.

Although in the embodiment above-described with reference to the drawings the disc spring is of frusto-conical shape in its free state and reaches a flattened condition upon compression, in other embodiments the disc spring may be flat in its free state and when compressed changes to a frustoconical shape.

Also, although in the embodiment abovedescribed with reference to the drawings the port 21 is in communication with the chamber 23 by way of the apertures 8 in the disc spring, in other embodiments this port may not be in communication with that chamber through such apertures. For example, it may be in communication with the chamber through a channel suitably provided in the bush 9, the apertures then, as desired, being either retained or not retained in the disc spring.

In yet other embodiments where the piston-andcylinder device is of relatively long stroke and thus where high differential thermal expansions with change in temperature are to be expected, a metallic de-rated spring device, for example of diaphragm or capsule type, may be used instead of a disc spring.

The invention is in no way limited to the fluid used in the piston-and-cylinder device being a liquid, as in other embodiments of the invention gaseous fluids, for example compressed air, may be used.

Claims (7)

1. A piston-and-cylinder device, the cylinder of which includes a main cylindrical portion having an end wall at each end thereof and having a cylindrical liner disposed therein, the material of said liner having greater wear-resistance and a different coefficient of expansion from the material of said main portion, wherein metallic spring means is so disposed and compressed between one of said end walls and the adjacent end portion of said liner as to maintain said liner in positive engagement at its other end portion with the other of said end walls.

2. A device as claimed in Claim 1, wherein said metallic spring means comprises a disc spring which, in its free state, is of frusto-conical form.

3. A device as claimed in Claim 2, wherein said disc spring is provided with a plurality of apertures which are spaced apart circumferentially around the spring.

4. A device as claimed in either Claim 2 or Claim 3, wherein said end walls are both of annular shape and each includes a bush for slidably supporting a piston rod which carries a piston reciprocable in said liner.

5. A device as claimed in Claim 4, wherein the bush of one of said end walls is provided with a spigot portion which extends inwardly of said cylinder and which supports said disc spring.

6. A device as claimed in Claim 5, wherein axial clearance is provided between said disc spring and said one end wall, and radial clearance is provided between the circular outer edge of the disc spring and the interior surface of said cylinder.

7. A piston-and-cylinder device substantially as hereinbefore described with reference to the accompanying drawings.