The present invention relates to a bush and in particular to a bush capable of absorbing radial and axial forces exerted upon the bush.

Figure 1 illustrates a known type of bush 1 comprising a tubular bearing 2 and a sleeve 3 arranged coaxially such that the bearing 2 and sleeve 3 are free to rotate relative to one another about their longitudinal axis. The bearing 2 and sleeve 3 are prevented from separating along the longitudinal axis by a radially-extending flange 6 and a washer 7 provided at opposite ends of the bearing 2.

The sleeve 3 consists of an elastomer 4 sandwiched between two layers 5 of a rigid material. The elastomer 4 serves to absorb radial displacement of the bearing 2 relative to the sleeve 3. As a result, the bush 1 is able to dampen vibrations as well as compensate for minor misalignments between the objects to be mounted.

As the bearing 2 and sleeve 3 are free to rotate relative to one another, the bush of Figure 1 has a significant advantage over conventional damping bushes, in which the bearing and sleeve are secured to one another by an interposing elastomer. Consider, for example, a stationary object mounted onto a rotating axle using a conventional damping bush. Friction between the rotating axle and the bearing creates shearing forces between the bearing and sleeve, causing the elastomer to degrade and eventually shear. With the bush 1 of Figure 1 , however, rotation of the bearing 2 and sleeve 3 is decoupled and consequently rotational shearing forces acting on the elastomer 4 are greatly reduced.

A problem with the bush of Figure 1 is that the flange 6 and washer 7 provided at opposite ends of the bearing 2, which are required to prevent the bearing 2 and sleeve 3 from separating, complicate the manufacture and assembly of the bush 1. In particular, the washer 7 must be secured to the bearing 2 by press fitting or welding after the sleeve 3 has been fitted. Additionally, although the flange 6 and washer 7 resist displacement of the bearing 2 relative to the sleeve 3 along the longitudinal axis, the resulting axial displacement exerts shearing forces upon the elastomer 4. As a result, the elastomer 4 is susceptible to longitudinal shearing with repeated and/or excessive axial displacement.

It is therefore an object of the present invention to provide a bush that overcomes one or more of the aforementioned disadvantages of the prior art. In particular, it is an object of the present invention to provide a bush that is more effective at absorbing axial forces.

Accordingly, in a first aspect, the present invention provides a bush comprising a tubular bearing, a sleeve surrounding the bearing, and a resilient member disposed between the bearing and the sleeve, wherein a surface of the resilient member is concave or convex and a surface of at least one of the bearing and sleeve is conversely convex or concave and co-operates with the surface of the resilient member such that the resilient member is compressed upon displacing the bearing relative to the sleeve in a longitudinal direction.

By compressing the resilient member whenever the bearing and sleeve are displaced longitudinally, the bush is able to effectively absorb and dampen axial forces exerted upon the bush. Additionally, the co-operating surfaces of the resilient member and the bearing and/or sleeve prevent the bearing and sleeve from separating along the longitudinal axis. Consequently, the bush does not require the provision of flanges or washers at the ends of the bush and therefore the manufacture and assembly of the bush may be simplified.

Compression of the resilient member preferably occurs in at least a direction normal to the longitudinal direction. Additionally, the surfaces of the resilient member, bearing and/or sleeve preferably co¬ operate such that compression of the resilient member increases as the bearing is further displaced relative to the sleeve. As a result, the bush is well-equipped at absorbing excessive axial forces.

The surfaces of the resilient member, bearing and/or sleeve preferably co-operate such that the bearing is able to rotate relative to the sleeve about the longitudinal axis. Consequently, the bush is able to accommodate not only axial and radial forces but also rotational forces acting upon the bush.

The surface of only one of the bearing and sleeve may be convex or concave, with the resilient member secured to the other so as to prevent the bearing and sleeve from separating. Alternatively, the surfaces of both the bearing and sleeve may be convex or concave. In this case, the surfaces of the resilient member adjacent the bearing and the sleeve are concave or convex.

In a particularly preferred embodiment, the surfaces of the resilient member, the bearing and/or sleeve have non-spherical radii of curvature, i.e. the bearing is not a spherical bearing. The resilient member preferably includes a layer of elastomeric material, such as rubber. A layer of harder material may be provided over one or more surfaces of the elastomeric material, which protect the elastomeric material from frictional wear as the resilient member moves relative to the bearing and/or sleeve, e.g. due to axial or rotational movement of the bearing relative to the sleeve. A lubricant or self-lubricating liner may additionally be provided between the resilient member and the bearing and/or sleeve to reduce friction.

In a second aspect, the present invention provides a bush comprising a tubular bearing, a sleeve surrounding the bearing, and a resilient member disposed between the bearing and the sleeve, wherein a surface of the resilient member and a surface of at least one of the bearing and sleeve include one or more protrusions and recesses, and the protrusions and recesses of the resilient member co-operate with those of the at least one bearing and sleeve such that the resilient member is compressed upon displacing the bearing relative to the sleeve in a longitudinal direction. A method of manufacturing a bush comprising the steps of: providing a tubular bearing; surrounding the bearing with a sleeve; and providing a resilient member between the bearing and the sleeve, wherein a surface of the resilient member is concave or convex and a surface of at least one of the bearing and sleeve is conversely convex or concave and co-operates with the surface of the resilient member such that the resilient member is compressed upon displacing the bearing relative to the sleeve in a longitudinal direction.

Although the resilient member is described herein as being disposed between the bearing and sleeve, it is to be understood that the resilient member need not be immediately adjacent either the bearing or sleeve. Instead, one or more elements, such as a lubricating liner, may be disposed between the resilient member and the bearing and sleeve.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal cross-sectional view of a prior art bush;

Figure 2 is a longitudinal cross-sectional view of a bush in accordance with a first embodiment of the present invention; and

Figure 3 is a longitudinal cross-sectional view of a bush in accordance with a second embodiment of the present invention.

The bush 10 of Figure 2 comprises a tubular bearing 11 , a sleeve 12 arranged about the bearing 11 , and a resilient member 13 disposed between the bearing 11 and the sleeve 12. The innermost surface 14 of the bearing 11 defines a bore 16 through the centre of the bearing 10 for receiving a shaft, axle or the like. The bore 16 preferably has a circular cross-section of substantially uniform diameter along its length. Nevertheless, alternative designs of bore 16 may be employed. This is particularly true since, as is discussed below, the bearing 11 and sleeve 12 are preferably arranged so as to rotate freely with respect to one another. Consequently, the shaft or axle received by the bearing 11 need not necessarily rotate within the bore 16.

The resilient member 13 is secured to the sleeve 12 such that the bearing 11 is free to rotate about its longitudinal axis relative to the sleeve 12 and resilient member 13. As a result, the bush 10 is able to accommodate rotational forces acting upon bush 10. As discussed above in regard to the prior-art bush 1 of Figure 1 , this has the advantage that rotational shearing forces acting upon the resilient member 13 are substantially reduced.

A lubricant or self-lubricating liner 19 may be disposed between the bearing 11 and the resilient member 13 to reduce friction.

The resilient member 13 preferably extends completely around the bearing 11 to form a longitudinally-extending tube or collar between the bearing 11 and the sleeve 12. Alternatively, the resilient member 13 may be formed as a plurality of resilient elements (not shown), each element being secured at different points around the surface of the sleeve 12. The resilient member 13 comprises a first layer 17 of an elastomeric material, such as rubber, attached to a second layer 18 of a different material. The first layer 17 is secured to the sleeve 12 of the bush 10 such that the second layer 18 is adjacent the bearing 11. The second layer 18 is intended to prevent wear of the first layer 17 against the bearing 11 when the bearing 11 and sleeve 12 move relative to one another. Consequently, the second layer 18 is preferably of a material having a relatively high hardness and the surface of the second layer 18 adjacent the bearing 11 is preferably smooth. The second layer 18, however, is not essential and may be omitted from the resilient member 13, particularly when the bush 10 is intended to be used in applications for which relative motion of the bearing 11 and sleeve 12 is minimal.

Although the resilience of the resilient member 13 is preferably provided by a layer of elastomeric material, alternative means, such as a sealed fluid, may be used.

The outermost surface 15 of the bearing 11 is convex such that the shape of the bearing 11 resembles that of a barrel. The surface 20 of the resilient member 13 adjacent the bearing 11 mirrors that of the outermost surface 15 of the bearing 11 and is concave. As a result, the surfaces 15,20 of the bearing 11 and resilient member 13 co-operate to form a longitudinal interlock.

The interlock formed between the bearing 11 and the resilient member 13 prevents the bearing 11 and sleeve 12 from separating. Nevertheless, movement of the bearing 11 relative to the sleeve 12 along the longitudinal axis is permitted. As the bearing 11 and sleeve 12 move relative to one another along the longitudinal axis, the resilient member 13 is compressed. Additionally, as the bearing 11 and sleeve 12 are further displaced relative to one another, compression of the resilient member 13 increases making it progressively more difficult to displace the bearing 11 relative to the sleeve 12.

With the prior-art bush 1 of Figure 1 , the elastomer 4 fails to compress when the bearing 2 and sleeve 3 move relative to one another along the longitudinal axis. As a result, the bush 1 is ill- equipped at absorbing axial forces and the elastomeric member 4 is found to shear with repeated and/or excessive axial displacement of the bearing 2 and sleeve 3. With the bush 10 of the present invention, on the other hand, the resilient member 13 is compressed upon axial displacement of the bearing 11 and sleeve 12. Moreover, as the axial displacement increases, the resistance to further axial displacement by the resilient member 13 increases. Accordingly, the bush 10 is well-equipped at absorbing axial forces and to resist excessive axial forces which would otherwise shear the elastomer 4 of the prior-art bush 1.

The bush 10 of the present invention is also capable of absorbing and applying a restorative force to cardanic forces which act upon the bush 10. Any cardanic force will cause the resilient member 13 to compress in at least a direction normal to the longitudinal axis of the bush 10. Consequently, when the cardanic force is removed, the compressed resilient member 13 will act to restore the bush 10 to its former shape and position. In the embodiment described above and illustrated in Figure 2, the shape of the outermost surface 15 of the bearing 11 is convex and the shape of the adjacent surface 20 of the resilient member 13 is concave. However, it will be appreciated that the same technical effect of providing a longitudinal interlock is provided if the shapes of these surfaces are reversed, i.e. such that the outermost surface 15 of the bearing 11 is concave-shaped and the adjacent surface 20 of the resilient member 13 is convex-shaped. Moreover, the surfaces 15,20 of the bearing 11 and the resilient member 13 may include any number of protrusions and recesses so as to form a longitudinal interlock. For example, in the embodiment illustrated in Figure 3, the bearing 11 include a single protrusions in the form of a radially- projecting ring 22 formed halfway along the length of the bearing 11 , and the resilient member 13 include a corresponding groove 23 for receiving the ring 22. Any protrusions and recesses formed in the bearing 11 and resilient member 13 are preferably smoothly varying such that no sharp corners are formed in the surface 20 of the resilient member 13. As a result, forces exerted on the resilient member 13 are more evenly distributed.

With the bush 10 of Figure 2, whenever the bearing 11 and sleeve 12 are moved relative to one another along the longitudinal axis, the resilient member 13 is compressed in a direction normal to the longitudinal axis. Nevertheless, the protrusions and recesses formed in the surfaces 15,20 of the bearing 11 and resilient member 13 may be configured such that compression of the resilient member 13 occurs along a different or additional direction. For example, when the bearing 11 and sleeve 12 of Figure 3 are displaced relative to one another along the longitudinal axis, the resilient member 13 is compressed in a direction substantially parallel to the longitudinal axis.

In the embodiment illustrated in Figure 2, the convex surface 15 of the bearing 11 may be regarded as a single protrusion extending around the full radius and along the full length of the bearing 11. Similarly, the concave surface 20 of the resilient member 13 may be regarded as a single recess, extending around the full radius and along the full length of the resilient member 13. Whilst the protrusions and recesses formed on or in the surfaces 15,20 of the bearing 11 and resilient member 13 are preferably annular (i.e. extending completely around the surface), the protrusions and recesses may alternatively be formed around only part of the bearing 11 and resilient member 13. However, in order for the bearing 11 to rotate relative to the sleeve 12, at least the recess of each pair of mating protrusions and recesses must be annular. For example, the outermost surface 15 of the bearing 11 may include a single protrusion in the form of a pin. An annular groove capable of receiving the pin would then need to be formed in the surface 20 of the resilient member 13 so as to ensure that the bearing 11 and sleeve 12 can rotate relative to one another.

The degree of resistance offered by the resilient member 13 to longitudinal displacement of the bearing 11 relative to the sleeve 12 will depend upon several factors, including the thickness and material used for the layer 17 of elastomeric material, as well as the shape and dimensions of the protrusions and recesses. For example, if the resilient member 13 has a single recess, the degree of resistance to axial forces for a shallow recess will be less than that for a deeper recess.

In the embodiments of the bush 10 described thus far, the resilient member 13 is secured only to the sleeve 12 such that bearing 11 is free to rotate relative to the sleeve 12 and resilient member 13. It will be appreciated, however, that the same result is achieved by alternatively securing the resilient member 13 to the bearing 11 rather than the sleeve 12. In this alternative embodiment, the protrusions and recesses are formed on the surface 21 of the resilient member 13 adjacent the sleeve 12, and on the surface of the sleeve 12 adjacent the resilient member 4; no protrusions or recesses are formed on the bearing 11.

As a further alternative, the resilient member 13 need not be secured to either the bearing 11 or the sleeve 12. In order to prevent the bearing 11 and sleeve 12 from separating along the longitudinal axis, the surfaces 20,21 of the resilient member 13 adjacent both the bearing 11 and sleeve 12 would have one or more protrusions and recesses. Additionally, the surfaces of both the bearing 11 and the sleeve 12 adjacent the resilient member 13 would include one or more corresponding protrusions and recesses. Consequently, the resilient member 13 forms an interlock with both the bearing 11 and the sleeve 12, thereby preventing the bearing 11 and sleeve 12 from separating. The protrusions and recesses in the bearing 11 , sleeve 12 and resilient member 13 may be configured such that the bearing 11 and sleeve 12 are able to rotate independently of each other and the resilient member 13. The resilient member 13, particularly in the embodiment described above in which the resilient member 13 is secured to neither the bearing 11 nor the sleeve 12, may include a further layer of hard material such that the layer of elastomeric material is sandwiched between two layers of hard material.

In the embodiments described above, the resilient member 13 is at the very most secured to only one of the bearing 11 or the sleeve 12 such that rotation of the bearing 11 is decoupled from the sleeve 12. In a further alternative embodiment, the resilient member 13 may be secured to both the bearing 11 and the sleeve 12 such that the bush 10 resembles that of a conventional damping bush. Although the bush 10 would no longer be capable of decoupling rotation of the bearing 11 and sleeve 12, the bush 10 would nevertheless offer a significant advantage over that of a conventional damping bush. Owing to the presence of the protrusions and recesses in the mating surfaces of the resilient member 13, the bearing 11 and/or sleeve 12, the resilient member 13 continues to be compressed whenever the bearing 11 and sleeve 12 are displaced relative to one another along the longitudinal axis. Accordingly, the bush 10 of the present invention is better equipped at absorbing and damping axial forces than a conventional damping bush. With a conventional damping bush, the rubber element between the bearing and sleeve is not compressed when the two are displaced relative to one another along the longitudinal axis. As a result, conventional damping bushes suffer from the same problems as that identified above for the bush 1 of Figure 1 when subjected to axial forces. With this particular embodiment of the present invention, rotation of the bearing 11 relative to the sleeve 12 is no longer possible and consequently there is no need for the protrusions and/or recesses to be annular.

A method of manufacturing the bush 10 of Figure 2 will now be described. The bush 10 is manufactured by first providing the bearing 11 , which is machined such that the outermost surface 15 of the bearing 11 is convex. The resilient member 13 is then formed by bonding a layer of an elastomeric material 17 over the outer surface of a cylindrical tube 18, the tube being deformable. The resilient member 13 is then placed around the bearing 11 and the assembly is compressed radially by swaging. The cylindrical tube 18 is deformed by the compression such that, when the compression is released, the surface 20 of the resilient member 13 adjacent the bearing 11 is concave and co-operates with the outermost surface 15 of the bearing 11. The exposed, barrel-like convex surface 21 of the layer of elastomeric material 17 is then machined to be substantially cylindrical. The sleeve 12 is then placed over and secured to the resilient member 13, e.g. by press fitting or adhesive.

When the resilient member 13 comprises only the layer of elastomeric material 17, the cylindrical tube 18 is omitted from the manufacturing process described above. The resilient member 13 may then be formed by moulding the elastomeric material 17 around the bearing 11 in-situ. Similarly, when both the bearing 11 and sleeve 12 include protrusions and/or recesses, the bush 10 may be manufactured by placing the sleeve 12 around the bearing 11 and moulding the elastomeric material between the bearing 11 and sleeve 12.

It will, of course, be appreciated that other methods conventionally employed in bush manufacture may alternatively or additionally be used in the manufacture of the present invention, and that the process described above is provided by way of example only.

With the bush of the present invention, axial forces are absorbed and dampened more effectively than is possible with known bushes. Additionally, by having co-operable protrusions and recesses in the resilient member, the bearing and/or sleeve, the bush is able to accommodate axial, radial, cardanic and rotational forces without the need for flanges and washers to be provided at the ends of the bush. Consequently, the manufacture and assembly of the bush may be simplified.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.