GB2258902A - Bearer springs - Google Patents

Abstract

A bearer spring comprises a body of elastomer 20 bonded to a rigid support surface 21 and having a concavely curved peripheral surface portion 28 adjacent the support surface. The body of elastomer increases in cross-section as it extends away from the support surface so that, upon compression of the elastomer, outlying portions 29 thereof are deformed towards the support surface. A support ring 32 is provided which encircles the body of elastomer 20 adjacent the support surface 21 and engages the peripheral surface of the elastomer so as to support it and inhibit the tendency of the concavely curved surface portion 28 to collapse as the elastomer is compressed. The support ring may be other than circular in cross-section and may be spaced outwardly from the peripheral surface portion 28. <IMAGE>

Description

"Improvements in bearer springs" The invention relates to bearer springs and particularly, but not exclusively, to bearer springs of a kind sometimes used as part of the suspension arrangement for a rail vehicle bogie truck.

One form of bearer spring of the kind to which the present invention relates is commonly refer-red to as an "hourglass" spring. Springs of this type may be located at each side of a bogie frame to connect the bogie frame to the underframe of the rail vehicle.

Each spring comprises a lower support plate for mounting on the bogie frame, an upper support plate for mounting on the underframe of the rail vehicle, and two bodies of elastomer sandwiched between the support plates and separated by an intermediate plate structure to which the bodies of elastomer are also bonded. Each elastomer is in the form of a body of revolution, and the two bodies together have an overall configuration reminiscent of an hourglass.

Where each body of elastomer is bonded to its associated support plate, it is formed with a concavely curved peripheral surface portion immediately adj acent the support plate, and then increases in cross-section as it extends away from the support surface. When the bearer spring is compressed the outlying portions of each body of elastomer are deformed towards and into contact with their associated support plate.

Existing bearer springs of this type suffer from the disadvantage that, after a prolonged period of service, each body of elastomer may begin to separate from its support plate.

Tests under laboratory conditions have shown that this tendency may result, at least partly, from the fact that the concavely curved peripheral surface portion of the elastomer, adjacent each supportplate, tends to collapse into an irregular fold each time the outlying portions of the elastomer are compressed into contact with the support plate. It is believed that this repeated collapsing and opening of the concavely curved periphery, combined with shear stress in the elastomer, weakens the elastomer around the periphery adjacent the support plate and initiates failure of the integrity of the elastomer in this region, leading to a separation which is eventually propagated across the whole area of the elastomer adjacent the bond.

The present invention sets out to alleviate this failure problem by providing means for inhibiting the tendency of the concavely curved peripheral surface portion of the body of elastomer to collapse when the spring is subjected to compression.

According to the invention there is provided a bearer spring comprising a body of elastomer bonded to a rigid support surface and having a concavely curved peripheral surface portion adjacent said support surface, the body of elastomer increasing in crosssection as it extends away from said surface whereby, upon application of a sufficient compressive force to the elastomer towards the support surface, outlying portions of the elastomer are deformed towards and into contact with the support surface outwardly of said concavely curved peripheral surface portion, support means being provided which engage the peripheral surface of the elastomer adjacent the support surface in a manner to support said surface and inhibit the tendency of the aforesaid concavely curved surface portion to collapse as said outlying portions of the elastomer are deformed towards the support surface.

Said support means may comprise an annular support member which encircles the body of elastomer adjacent the support surface and is disposed at least partly in contact with said concavely curved peripheral surface portion thereof. For example, the support member may be substantially circular in transverse cross-section, the radius of curvature of the transverse cross-section being similar to the radius of curvature of at least a major part of said concavely curved surface portion of the elastomer.

Alternatively, the annular support member may provide, as seen in cross-section, a substantially flat surface which engages the support surface, a convexly curved inwardly facing surface engageable with said concavely curved peripheral surface portion of the elastomer, and an inclined surface tapering outwardly away from said convex inwardly facing surface towards said flat surface.

Alternatively the annular support member may comprise a ring which encircles the body of elastomer, is spaced outwardly of the peripheral surface thereof, and engages the support surface so as to hold said outlying portions of the elastomer away from the support surface and thereby inhibit collapsing of said concavely curved peripheral surface portion of the elastomer. For example the support member may be in the form of a flat annular ring.

In any of the above arrangements in which the support means engages the support surface, said means may be secured to the support surface, for example by welding. Alternatively the support means might be integral with the support surface.

Instead of being a continuous annular support member, the support means may comprise a plurality of separate support members, of any of the cross-sectional configurations referred to above, spaced apart around the periphery of the elastomer and secured to the support surface.

The bearer spring may, in the manner of the particular embodiment described earlier, comprise two similar bodies of elastomer bonded to respective facing support surfaces and coaxial with one another, the adjacent faces of the two bodies of elastomer being bonded to a common central structure. The common central structure may comprise two flat plates secured together face-to-face, the bodies of elastomer being bonded to the flat plates respectively.

The following is a more detailed description of embodiments of the invention, reference being made to the accompanying drawings in which: Figure 1 is a plan view of a bogie truck incorporating bearer springs of the general type to which the present invention relates; Figure 2 is a side elevation of the bogie truck shown in Figure 1; Figure 3 is an end elevation of the bogie truck; Figure 4 is a diagrammatic side elevation, partly in section and on a larger scale, of a bearer spring of the kind to which the invention relates; Figure 5 is an enlarged view of a portion of the bearer spring; Figure 6 is a similar view to Figure 5, showing deformation of the portion of the bearer spring when compressively loaded;; Figure 7 is a similar view to Figure 5 showing the use of support means in accordance with the invention, and Figures 8 and 9 are similar views showing alternative forms of support means.

The bogie truck shown in Figures 1 to 3 is of a generally known type, and the specific details of its construction do not form part of the present invention.

The bogie truck will therefore be described only briefly.

The bogie truck comprises an H-frame 10 including two spaced side frames 11 connected by a cross structure 12. The axles 13 of two wheelsets 14 are rotatable in bearings 15 which are resiliently mounted on the respective side frame 11 by helical compression springs 16. The wheels of the wheelsets are indicated at 17.

A central pivotal mounting 18 connects the bogie frame 10 to the underframe of the rail vehicle (not shown) and each side frame 11 is also connected to the underframe by a central "hourglass" bearer spring 19. These bearer springs are one particular form of spring of the general kind to which the present invention relates. One of the bearer springs 19 is shown in greater detail in Figure 4.

The upper part of the spring comprises a body of elastomer 20, which is a body of revolution of circular cross-section, and is bonded to a flat steel support plate 21. The surface of the body of elastomer which is bonded to the support plate 21 is formed with a central concavity 22. Studs 23 are provided to locate the support plate 21 on the vehicle underframe.

A similar body of elastomer 24 is bonded to a lower support plate 25. The adjacent flat surfaces of the two bodies 20, 24 of elastomer are bonded to respective support plates 26 and 27 which are riveted together.

During operation of the bogie truck, the bodies 20, 24 of elastomer are subjected to compression, as the support plates 21 and 25 move towards and away from one another, and are also subjected to shear as the plates 21 and 25 are displaced laterally with respect to one another as a result of pivotal movement of the bogie truck relatively to the rail vehicle. As previously mentioned, over a prolonged period it is found, with conventional bearer springs of this type, that the bodies of elastomer 20 and 24 tend to separate from their associated support plates 21 and 25.

Each body of elastomer has a concavely curved peripheral surface portion 28 adjacent its junction with the support plate and the body of elastomer is of increasing cross-section as it extends away from the support plate. Upon compression of the bearer spring the outlying portions 29 of the body of elastomer are deformed towards the support plate and eventually come into contact with that plate.

The region, indicated at 30, of the junction between the elastomer and the support plate is shown on an enlarged scale in Figure 5, which shows more clearly the concavely curved peripheral portion of the elastomer 20, the inner part of an outlying portion 29 of the elastomer and the support plate 21. The radius of curvature of the concavely curved portion may be of the order of 2mm.

Figure 6 shows diagrammatically this region when the bearer spring is under compression. It will be seen that the outlying portions 29 of the body of elastomer have been brought into contact with the surface of the support plate 21 and, as a result, the concavely curved peripheral portion 28 has collapsed into a number of irregular folds as indicated at -31. As previously mentioned, it is believed that the strain imparted to the elastomer by the repetitive folding and unfolding in this region eventually leads to breakdown of the integrity of the elastomer and the initiation of fracture which eventually propagates across the crosssection of the elastomer, leading to its eventual separation from the support plate 21.

Figure 7 shows one embodiment in accordance with the invention where a rigid metal ring 32 of circular cross-section is located around and within the concave peripheral portion 28 adjacent the surface of the support plate 21. The ring 32 serves to support the concave portion 28 as the outlying portions 29 of the elastomer are urged towards the support plate 21 and thus to prevent the collapsing and folding of the elastomer in this region. This therefore inhibits the fracture of the material of the elastomer and thus reduces or eliminates any tendency for the elastomer to separate from its support plate.

Figure 8 shows an alternative arrangement where the support ring 33 is of different cross-section.

It comprises a flat surface 34 which engages the surface of the support plate 21 and a convexly curved inner surface 35 which mates with the concave peripheral surface portion 28 of the elastomer. The ring also has an inclined surface 36 which tapers outwardly towards the surface of the support plate 21.

Figure 9 shows an alternative arrangement in which the support member 37 is in the form of a flat annular ring which engages the surface of the support plate 21 outwardly of the concave peripheral surface 28 of the elastomer 20. In this case the support member 37 does not directly engage and support the concave surface 28 but instead engages the outlying portions 29 of the body of elastomer and holds them slightly away from the surface of the support plate 21 and, in this manner, again prevents the concave surface portion 28 from collapsing.

In In the arrangement of Figure 9 the ring 37 is preferably secured to the support plate 21 and may, for example, be secured by riveting or welding. The ring 37 could, alternatively, be integral with the support plate 21 and could be formed by machining a circular recess in a thicker support plate, the elastomer being bonded to the bottom wall of the recess.

In the arrangements of Figures 7 and 8 the supports rings 32 and 33 could be secured to the support plate 21 but preferably their shape and dimensions are such that they are held in position by their engagement with the peripheral surface of the elastomer.

In any of the above arrangements the support member is preferably in the form of a continuous annular ring. However, the invention includes within its scope arrangements in which the support member, for example of any of the cross-sectional shapes illustrated, comprises a plurality of separate elements spaced apart around the periphery of the elastomer. It will be appreciated that, in this case, the separate elements must be secured in position, and they are preferably therefore secured to the support plate.

The cross-sectional shapes of the support members shown above are by way of example only, and it will be appreciated that other cross-sectional shapes may be devised which achieve the same effect of supporting the concave peripheral surface portion of the elastomer to prevent it collapsing under compression.

Although the concave surface portion is shown as being generally part-circular in cross-section, other cross-sectional curved shapes are possible. In embodiments of the kind shown in Figures 7 and 8 the cross-sectional shape of the support member preferably matches closely the unstressed curved configuration of the surface of the elastomer, but it will be appreciated that such close matching is not essential and any shape which provides some support for the elastomer will be advantageous.

The invention is also not limited to the specific form of bearer spring shown in Figure 4 and may be applied to any form of bearer spring of the basic type having a concavely curved peripheral surface portion at the junction where the elastomer is bonded to its support surface.

Claims (17)

1. A bearer spring comprising a body of elastomer bonded to a rigid support surface and having a concavely curved peripheral surface portion adjacent said support surface, the body of elastomer increasing in crosssection as it extends away from said surface whereby, upon application of a sufficient compressive force to the elastomer towards the support surface, outlying portions of the elastomer are deformed towards and into contact with the support surface outwardly of said concavely curved peripheral surface portion, support means being provided which engage the peripheral surface of the elastomer adjacent the support surface in a manner to support said surface and inhibit the tendency of the aforesaid concavely curved surface portion to collapse as said outlying portions of the elastomer are deformed towards the support surface.

2. A bearer spring according to Claim 1, wherein said support means comprise an annular support member which encircles the body of elastomer adjacent the support surface and is disposed at least partly in contact with said concavely curved peripheral surface portion thereof.

3. A bearer spring according to Claim 2, wherein the support member is substantially circular in transverse cross-section, the radius of curvature of the transverse cross-section being similar to the radius of curvature of at least a major part of said concavely curved surface portion of the elastomer.

4. A bearer spring according to Claim 2, wherein the annular support member provides, as seen in crosssection, a substantially flat surface which engages the support surface, a convexly curved inwardly facing surface engageable with said concavely curved peripheral surface portion of the elastomer, and an inclined surface tapering outwardly away from said convex inwardly facing surface towards said flat surface.

5. A bearer spring according to Claim 2, wherein the annular support member comprises a ring which encircles the body of elastomer, is spaced outwardly of the peripheral surface thereof, and engages the support surface so as to hold said outlying portions of the elastomer away from the support surface and thereby inhibit collapsing of said concavely curved peripheral surface portion of the elastomer.

6. A bearer spring according to Claim 5, wherein the support member is in the form of a flat annular ring.

7. A bearer spring according to Claim 1, wherein the support means comprise a plurality of separate support members spaced apart around the periphery of the elastomer.

8. A bearer spring according to Claim 7, wherein the support members are disposed at least partly in contact with said concavely curved peripheral surface portion of the body of elastomer.

9. A bearer spring according to Claim 8, wherein each support member is substantially circular in transverse cross-section, the radius of curvature of the transverse cross-section being similar to the radius of curvature of at least a major part of said concavely curved surface portion of the elastomer.

10. A bearer spring according to Claim 8, wherein each support member provides, as seen in crosssection, a substantially flat surface which engages the support surface, a convexly curved inwardly facing surface engageable with said concavely curved peripheral surface portion of the elastomer, and an inclined surface tapering outwardly away from said convex inwardly facing surface towards said flat surface.

11. A bearer spring according to Claim 8, wherein each support member is spaced outwardly of the peripheral surface of the body of elastomer, and engages the support surface so as to hold said outlying portions of the elastomer away from the support surface and thereby inhibit collapsing of said concavely curved peripheral surface portion of the elastomer.

12. A bearer spring according to any of Claims 1 to 11, wherein the support means is separately formed from the support surface and is secured thereto.

13. A bearer spring according to Claim 12, wherein the support means is secured to the support surface by welding.

14. A bearer spring according to any of Claims 1 to 11, wherein the support means is integral with the support surface.

15. A bearer spring according to any of Claims 1 to 14, wherein there are provided two similar bodies of elastomer bonded to respective facing support surfaces and coaxial with one another, the adjacent faces of the two bodies of elastomer being bonded to a common central structure, and support means being provided for each body of elastomer.

16. A bearer spring according to Claim 15, wherein the common central structure comprises two flat plates secured together face-to-face, the bodies of elastomer being bonded to the flat plates respectively.

17. A bearer spring substantially as hereinbefore described with reference to Figure 4 and any of Figures 7 to 9 of the accompanying drawings.