GB2231120A

GB2231120A - Resilient bush

Info

Publication number: GB2231120A
Application number: GB8927145A
Authority: GB
Inventors: Marc Richard Murray
Original assignee: BTR PLC
Current assignee: BTR PLC
Priority date: 1989-04-15
Filing date: 1989-11-30
Publication date: 1990-11-07
Anticipated expiration: 2009-11-30
Also published as: GB2231120B; GB8927145D0; JPH02275127A

Abstract

In a resilient bush of the kind having an elastomeric interlayer (13) positioned between inner and outer rigid members (11, 12) the interlayer is reinforced by a tubular sleeve (14) of substantially non-rigid form. The sleeve (14) preferably is semi-rigid and preferably is formed from a material having a flexural strength in the range 600 to 2,500 Kgf/ cm<2>, such that the sleeve (14) deforms in response to compressive forces arising in a radially inner or outer tubular portion of the interlayer (13). <IMAGE>

Description

RESILIENT BUSH This invention relates to a resilient bush of the kind comprising an inner rigid member, an outer rigid member which extends around and is spaced from the inner rigid member, and an interlayer of resilient elastomeric material which extends between and interconnects the inner and outer rigid members.

The invention is directed in particular to a resilient bush of the aforedescribed type and in which the interlayer of resilient elastomeric material is provided with an embedded reinforcement for the purpose inter alia of increasing the radial stiffness of the bush as compared with the radial stiffness which it would exhibit if the interlayer were not reinforced.

The invention relates also, but not exclusively, to a resilient bush having an embedded reinforcement as described above and in which the elastomeric material is radially pre-compressed. In one established form of resilient bush of this type the embedded reinforcement is provided by a tubular steel insert.

This is arranged to divide the resilient elastomeric interlayer into radially inner and radially outer tubular portions and conventionally these are each secured to the insert by bonding. Radial pre-compression of the interlayer is achieved by swaging the outer rigid member to precompress the radially outer tubular portion of the interlayer, and the radially inner tubular portion of the inter layer is then subject to pre-compression by expansion of the inner rigid member which therefore also must be of a tubular cross-sectional shape.

Whilst the form of bush described in the preceding paragraph exhibits good performance and fatigue life when used in many applications, it suffers the disadvantage of being slow and expensive to manufacture because of the need to effect two operations, namely a swaging operation and an expansion operation, in order to provide pre-compression of both the radially inner and outer portions of the interlayer of reinforced resilient elastomeric material. Furthermore, the bush necessarily must have an inner rigid member of tubular rather than solid form. Also, for some applications it is found that the fatigue life of the resilient bush is not as good as desired.

To avoid the need to perform both swaging and expansion operations and also to permit the use of solid section inner rigid members it has been proposed to make use of an interlayer reinforcement comprising a pair of semi-cylindrical steel shells which, as in the case of a tubular steel reinforcement, are bonded to radially inner and outer portions of the interlayer. During initial assembly the respective neighbouring longitudinal edges of the shells are arranged to be slightly spaced apart in a circumferential direction. Upon swaging of the outer rigid member the radially outer portion of the interlayer becomes compressed and urges the neighbouring edges of the shells to move towards one another thereby also to result in compression of the radially inner portion of the interlayer without the need for expansion of the inner rigid member.

The use of a reinforcement of a pair of semicylindrical shells therefore improves the ease of manufacture and also permits the use of an inner rigid member of a solid cross-sectional form. Unfortunately these advantages are often outweighed, in many product applications, by a reduction in fatigue life. Notably, undesirable stresses can arise at and are concentrated in the regions of the neighbouring longitudinal edges of the shells and this leads to premature fatigue failure of the bush. Also difficulties can arise in properly locating the shells in the moulding tool.

The present invention in its broadest aspect seeks to provide an improved resilient bush of the kind having a reinforced interlayer. In another of its aspects the invention seeks to provide an improved radially pre-compressed resilient bush which has the ease of manufacture of bushes of the kind which have semi-cylindrical shell reinforcements, does not necessitate the use of an inner rigid member of a hollow cross-sectional form, and may be designed to have a good fatigue life.

In accordance with the subject invention it is provided that the interlayer of resilient elastomeric material in a resilient bush is reinforced by a tubular reinforcement layer of a material which is able to deform in response to compressive forces arising in a radially inner or outer tubular portion of the interlayer. Preferably the tubular reinforcement layer is able to respond to any such compressive forces which arise in consequence of radial expansion or radial contraction of a respective inner or outer rigid member thereby to cause a radial compression of the other of said radially inner and outer tubular portions of the interlayer.

For the avoidance of doubt it is stated that in this specification "deform" is used to mean a change of shape, which may be a localised change of shape, and also a change of dimension which may not necessarily involve a change of shape.

The invention provides that the tubular reinforcement layer shall be of a non-metallic material in contrast to the conventionally used steel material.

Accordingly the invention envisages that use should be made of a reinforcement of a tubular, one piece, type as opposed to a multi-piece assembly of shells and that the reinforcement should be formed from a material which, in contrast to the high rigidity of the conventionally used steel material, is substantially semi-rigid.

The semi-rigid reinforcement material should be a material having a Young's modulus of elasticity in the range 5,000 to 70,000 Kgf/cm2 and more preferably in the range 16,000 to 30,000 Kgf/cm2. Thus if a swaging operation is performed on the outer rigid member it will cause radial compression of the radially outer portion of the resilient elastomeric inter layer and also create compressive hoop stresses in the tubular reinforcement to result, having regard to the Young's modulus of the material of the reinforcement, in a consequential radial compression of the radially inner portion of the resilient elastomeric material interlayer.Conversely if an expansion operation is performed on the inner rigid member, when that is of a tubular form, it can be utilised to radially compress the radially inner portion of the interlayer, to result in consequential tensile hoop stresses in the tubular reinforcement and thus effect radial expansion of the tubular reinforcement sufficient to cause a required radial compression of the outer portion of the resilient elastomeric interlayer.

In general it is envisaged that radial compression of the outer rigid member will be more convenient to perform and have the advantage that compression of the radially inner portion of the inter layer will be achieved more easily than compression of the radially outer portion would be achieved by expansion of the inner rigid member.

In accordance with a further aspect of the subject invention it is provided that the inter layer of resilient elastomeric material is reinforced by a tubular reinforcement layer of a material having a flexural strength in the range 600 to 2,500 Kgf/cm2, and more preferably a flexural strength in the range 900 to 1,000 Kgf/cm2.

It is believed that by providing a tubular reinforcement layer of a material having a flexural strength in the broad range recited in the preceding paragraph the reinforcement is able to deform appropriately when the bush is subject to relative radial movement, or conical movement, between the inner and outer rigid members and thereby avoid or reduce the occurrence of undesirably high levels of stress concentration which normally would adversely affect the fatigue life of the bush.

In general materials having a flexural strength lying in the broad range recited above, and more preferably in the restricted range, appropriately lend themselves to the provision of a tubular reinforcement layer of a thickness which is adequate to provide the required reinforcing effect to stiffen the bush particularly to withstand relative radial movement of the inner and outer rigid members but also which is adequately circumferentially compressible or expansible to result, if desired, in the transmission of radial compression from a radially inner or outer portion of the interlayer to the other portion of the interlayer.

In accordance with the present invention it is further preferred that the tubular reinforcement layer is deformable, in use of the bush, only within its elastic limit. Thus, it will tend inherently to revert to its original shape and configuration when the bush is released from externally applied loads.

Particularly suitable non-metallic materials for forming the tubular reinforcement layer include plastics materials such as polyamides, nylon 6 and nylon 66, acetal, Hytrel and Delrin. The reinforcement layer may be of a fabric type construction but in general this will not have a sufficiently high flexural strength and thus it is envisaged that normally the tubular reinforcement layer will be formed from a tubular layer of non-textile material. However, the reinforcement layer may comprise an embedded reinforcement. Thus, for example, the tubular reinforcement may comprise a tubular sleeve of nylon 6 containing an embedded reinforcement of staple glass fibres, beads or spheres, or of woven material.

The tubular reinforcement layer may be formed with at least one aperture in the wall thereof. This facilitates a flow of material radially inwards or outwards through the reinforcement layer during a moulding operation to form the radially inner and outer portions of the resilient elastomeric interlayer.

It also results in continuity and a mechanical interlock between moulded material of said radially inner and outer portions of the interlayer. Preferably the reinforcement layer is provided with at least one circumferentially extending series of apertures.

It is envisaged that the radial thickness of the tubular reinforcement layer typically shall lie in the range 15% to 25% of the radial space of the confronting surfaces of the inner and outer rigid members. This contrasts, on an average basis, with the hitherto used tubular or semi-cylindrical reinforcements of steel and which typically have a thickness in the range 10% to 20% of the radial spacing of the confronting surfaces of the inner and outer rigid members.

To further facilitate reduction or elimination of stress concentrations one or preferably each axial end portion of the tubular reinforcement layer is of a reduced wall thickness as compared with a central portion of the layer. Inner and outer surfaces of the reinforcement layer may be shaped so as to provide the layer with end regions of a tapered form.

One embodiment of the subject invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a longitudinal sectional view of a resilient bush in accordance with the present invention; Figure 2 is an end view of the resilient bush of Figure 1; Figure 3 is a longitudinal sectional view of an alternative sleeve for use in the resilient bush of Figures 1 and 2, and Figure 4 is an end view of the sleeve of Figure 3.

A resilient bush 10 of circular cross-sectional shape, as shown in Figures 1 and 2, comprises tubular inner and outer rigid members 11,12 each formed from steel, and a two portion resilient elastomeric interlayer 13 of natural rubber which extends between and is bonded to confronting surfaces of the rigid members 10,11.

The rubber interlayer 13 is reinforced by a tubular sleeve 14 of nylon 66, which divides the interlayer into radially inner and radially outer portions 16,15 each of which are bonded to the sleeve 14. The sleeve 14 is formed of nylon 66 and, over the main part of its length, it has a thickness of 1.5 mm which is 23% of the 6.5 mm distance by which confronting outer and inner surfaces of the inner and outer rigid members are radially spaced. Axial end portions of the wall of sleeve 14 are of tapered cross-section; this is achieved by providing chamfers at the inner and outer surfaces of the sleeve 14 at each of its axial ends.

The nylon 66 material has a flexural strength of 880 Kgf/cm2 and a Young's modulus of 18,000 Kgf/cm2.

The sleeve 14 has in this case a thickness of 1.5 mm, an axial length of 3 mm and mean diameter of 24.5 mm.

The axial length of the outer rigid member is less than that of the inner rigid member, and the axial length of the sleeve is between that of the inner and outer rigid members. The sleeve 14 is disposed radially substantially mid-way between the inner and outer rigid members, but is slightly closer to the inner rigid members whereby the inner and outer portions 16,15 of the resilient interlayer are of substantially equal volume.

The inner rigid member is of a relatively thick wall section and is provided between end regions 17 with a circumferential recess 18 of an axial length corresponding to the axial length of the sleeve 14.

Following assembly of the resilient bush as described above and bonding together of the confronting surfaces of the rigid members and sleeve with respective portions of the elastomeric interlayer 13, the radially outer portion 15 of the interlayer is put in pre-compression by radial contraction of the outer rigid member 12. In consequence the sleeve 14 is subject to compressive hoop stresses and reduces in diameter thereby to effect compression of the inner portion 16 of the elastomeric interlayer against the outer surface of the inner rigid member.

In a resilient bush in accordance with a further aspect of the present invention use is made of an alternative type of tubular reinforcing sleeve 20 as shown in Figures 3 and 4. The sleeve 20 is formed of nylon 66 and is provided between its ends with two axially spaced series 21 of apertures 22 of circular shape. Each series 21 comprises four of said apertures which are uniformly spaced in the circumferential direction. Axial end portions of the sleeve 20 may be of a U-shape in cross-section, as illustrated in figure 3, or may, for example be chamfered in the manner described for the sleeve 14 of figure 1.The provision of an apertured type of sleeve facilitates formation of the inner and outer portions 16,15 of the rubber inter layer 13 by an in situ moulding operation in which the mouldable material may flow through the wall of the sleeve and in which a mechanical interlock can be achieved between said inner and outer portions 16,15.

From the foregoing it will be appreciated that the use in a resilient bush of a reinforcing layer of the kind specified, and which is a significant departure from the long established practices in the art of resilient bush manufacture and design, facilitates ease of manufacture and a freedom to use tubular type inner rigid members without any notable disadvantages such as limitation of fatigue life.

Indeed it is believed that use of a reinforcing sleeve of the kind recited herein in accordance with the subject invention leads to a most useful improvement in fatigue life as compared with that exhibited by conventional bushes of long established design.

Although the invention has been described particularly in relation to a resilient bush in which the reinforced elastomeric interlayer can be subject to radial pre-compression by expansion of an inner rigid member or compression of an outer rigid member, in a modified form the elastomeric material is not radially pre-compressed or is radially pre-compressed by alternative means. Thus in a modified form a bush is provided in the form illustrated in Figures 1 to 4 but without radial pre-compression of the rubber interlayer 13.

Claims

CLAIMS:

1. A resilient bush comprising an inner rigid member, an outer rigid member which extends around and is spaced from the inner rigid member and an interlayer of resilient elastomeric material which extends between and interconnects the inner and outer rigid members1 said interlayer of resilient elastomeric material being reinforced by a tubular reinforcement layer of a material which is able to deform in response to compressive forces arising in a radially inner or outer tubular portion of the interlayer.

2. A resilient bush according to claim 1 wherein the tubular reinforcement layer is formed from a material which is substantially semi-rigid.

3. A resilient bush comprising an inner rigid member, an outer rigid member which extends around and is spaced from the inner rigid member and an interlayer of resilient elastomeric material which extends between and interconnects the inner and outer rigid members, said interlayer of resilient elastomeric material being reinforced by a tubular reinforcement layer of a material having a flexural strength in the range 600 to 2,500 Kgf/cm2.

4. A resilient bush according to claim 3 wherein the material of said tubular reinforcement layer has a flexural strength in the range 900 to 1;000 Kgf/cm2.

5. A resilient bush according to any one of the preceding claims wherein the tubular reinforcement layer is a layer of nonmetallic material.

6. A resilient bush according to any one of the preceding claims wherein the tubular reinforcement layer is able to deform in response to compressive forces arising in the elastomeric material in consequence of radial expansion or radial contraction of a respective inner or outer rigid member thereby to cause a radial compression of the other of said radially inner and outer tubular portions of the interlayer.

7. A resilient bush according to claim 6 wherein portions of the interlayer of resilient elastomeric material lying respectively inwards and outwards of the tubular reinforcement layer are in residual compression.

8. A resilient bush according to claim 7 the outer rigid member is a member which has been subject to compression to cause residual compression of both the inner and outer portions of the inter layer of resilient elastomeric material.

9. A resilient bush according to any one of the preceding claims wherein the tubular reinforcement layer is of a kind which under normal use of the resilient bush will tend inherently to revert to its original shape and configuration when the bush is released from externally applied loads.

10. A resilient bush according to any one of the preceding claims wherein the tubular reinforcement layer is formed from a tubular layer of non-textile material.

11. A resilient bush according to any one of the preceding claims wherein the radial thickness of the tubular reinforcement layer is in the range 15% to 25% of the radial spacing of the confronting surfaces of the inner and outer rigid members.

12. A resilient bush according to claim 11 wherein said thickness of the tubular reinforcement layer is in the range 20 to 25% of the radial space of the confronting surfaces of the inner and outer rigid members.

13. A resilient bush according to any one of the preceding claims wherein the tubular reinforcement layer is formed with at least one aperture in the wall thereof.

14. A resilient bush according to claim 13 wherein the reinforcement layer is provided with at least one circumferentially extending series of apertures.

15. A resilient bush according to any one of the preceding claims wherein at least one axial end region of the tubular reinforcement layer is reduced in thickness compared with an axially central region.

16. A resilient bush constructed and arranged substantially as hereinbefore described with reference to figures 1 and 2 or figures 3 and 4 of the accompanying drawings.