GB1578750A

GB1578750A - Springs

Info

Publication number: GB1578750A
Application number: GB35898/76A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1976-08-28
Filing date: 1976-08-28
Publication date: 1980-11-12
Also published as: JPS5329470A; DE2738168A1; PL200494A1; IN148753B; CA1070721A; RO76133A; CH612253A5; JPS6131331B2; PL119454B1; FR2363032A1; HU173176B; FR2363032B1; SE7709528L

Description

(54) IMPROVEMENTS IN OR RELATING TO SPRINGS (71) We, DUNLOP LIMITED, a British Company of Dunlop House, Ryder Street, St. James's, London S.W.1. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to springs, and in particular to sandwich type springs comprising a stack of layers of rubber or like elastomeric material bonded to interleaving metal plates.

Sandwich type springs of this type are often used, amongst other applications, as part of a railway vehicle bogie suspension and in such an application the springs are usually mounted with their rubber layers and metal plates substantially horizontal so that the vehicle weight acts to cause substantially only compression loading of the rubber layers whilst relative lateral movements between parts of the vehicle suspension causes shear deflection of the rubber layers.

Especially under relatively large shear displacements there is a significant reduction in the effective cross-sectional area of the spring directly to support compression loads as upper layers of the spring move laterally relative to lower layers and only a relatively small part of an upper layer lies above and is directly supported by lower layers. It is found in this situation that the resulting combination of shear and compression loadings results in the rubber layers being subjected to bending moment stresses, and fatigue failures commonly occur at the outermost layers of the spring where the bending moment stresses are greatest.

It is an object of the present invention to provide a sandwich type spring having an improved fatigue life under the action of shear loadings.

According to the present invention a spring comprises a plurality of layers of rubber or like elastomeric material bonded to and interlocking with a plurality of metal plates wherein the length of the layers of rubber or like elastomeric material as considered in at least one cross-sectional plane extending substantially perpendicular to the plane of said layers and metal plates decreases from each outermost- layer in a direction towards the centre layer or layers and the thickness of the centre layer or layers of rubber or like elastomeric material is less than the thickness of the outermost layers.

Preferably the length of the layers in said cross-sectional plane decreases uniformly from each outermost layer in a direction towards the centre layer or layers of the spring, and successive layers preferably are positioned centrally relative to each other such that, in an unloaded condition.

the spring has a symmetrical profile when viewed in said plane.

In operation of the spring when subjected to shear forces acting in a direction lying in said plane the effective area of the spring for supporting compression loads remains substantially unaltered, at that of the central or smallest area layer of rubber or like elastomeric material, and there is no significant reduction of area as in the case of a conventional sandwich spring where all layers are of equal- size.

Furthermore, it is found in comparison with a conventional sandwich spring that each rubber layer and metal plate is more able to move angularly relative to end faces of the spring under the action of shear loads; the bending resistance of any one layer is more nearly proportional to the bending moment applied by the combination of external compression and shear forces and this results in an improvement of fatigue life compared with a conventional spring.

In addition to the variation in length of successive rubber layers in said cross-sectional plane, the length of the rubber layers may be varied similarly in one or more other planes substantially perpendicular to the plane of the rubber layers and metal plates so as to improve the fatigue resistance of the spring to shear loads acting in more than one direction.

The outer profiles of the rubber layers as considered in planes parallel to the metal plates may be rectangular, square, circular, or elliptical, though other shapes, such as polygonal shapes, may be employed. Considered also in said planes, the rubber layers may be formed with apertures so as to be essentially -ring-shaped, and the metal plates may also be formed with apertures such that the spring has- - a hollow cavity therein, though to obtain good fatigue life it is generally preferred that neither rubber layers nor plates are formed with apertures. The spring may be provided with a passage communicating between the hollow cavity and outside of the spring. The cavity may be air-tight, a suitable valve or seal being provided to maintain the cavity air-tight where the spring is formed with a passage.

In a preferred constructon the thickness of the layers of rubber or like elastomeric material increases progressively from the centre layer or layers towards each outermost layer.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which: Figure 1 is a side - view of a spring in accordance with the present invention in an unloaded condition; Figure 2 is a similar view to that of Figure 1 showing the spring loaded in compression, and Figure 3 is a similar view to that of Figure 1 showing the spring loaded in compression and shear.

A sandwich type suspension spring 10 for use in a railway vehicle bogie suspension comprises a plurality of rubber layers 11 bonded to and interleaved with a plurality of metal plates 12 and metal end plates 13.

The thickness of the rubber layers 11 increases progressively from the central layers 1 lea to the outermost layers, and the length of the rubber layers and interleaving plates as viewed in the direction of Figure 1 also increase progressively from the central layers and plates to the outermost layers and plates.

All rubber layers are of equal depth in a direction perpendicular to the plane of Figure 1 along the entire length of each layer as viewed in Figure 1 and the plates are like wise-shaped. The central rubber layers and metal plate are of a square outer profile and accordingly the relatively outer rubber layers and plates are of rectangular outer profile.

When the spring is subjected to a combination of shear and compression loadings, as illustrated in Figure 3, the effective area of the spring directly to support compression loads remains substantially unaltered at the cross-sectional area of the centre rubber layers I la and this assists to minimise the bending stresses on the outermost rubber layers and thus improve their fatigue life as compared with a conventional spring having rubber layers and plates all of similar dimensions. It will be further appreciated from Figure 3 that by use of central rubber layers and plates which are shorter than relatively outer layers and plates, all layers and plates are more able to move angularly relative to the end plates than in a conventional spring where all plates and layers are of similar dimensions, and accordingly there results a more uniform distribution of bending stresses between all of the rubber layers so as to assist in improving the fatigue life of the spring.

WHAT WE CLAIM IS: 1. Aspring comprising a plurality of layers of rubber or like elastomeric material bonded to and interleaved with a plurality of metal plates wherein the length of the layers of rubber or like elastomeric material as considered in at least one cross-sectional plane extending substantially perpendicular to the plane of said layers and metal plates decreases from each outermost layer in a direction towards the centre layer or layers and the thickness of the centre layer or layers of rubber or like elastomeric material is less than the thickness of the outermost layers.

2. A spring according to claim 1 wherein the length of the layers in said cross-sectional plane decreases uniformly from each outermost layer in a direction towards the centre layer or layers of the spring.

3. A spring according to claim 1 or claim 2 wherein successive layers are positioned centrally relative to one another when viewed in cross-sectional plane.

4. A spring according to any one of the preceding claims wherein the length of the layers of rubber or like elastomeric material as considered in one or more other planes substantially perpendicular to the plane of said layers and metal plates decreases from each outermost layer in a direction towards the centre layer or layers.

5. A spring according to any one of the preceding claims wherein considered in planes parallel to the layers of rubber or like elastomeric material and metal plates a layer and/or a metal plate is apertured.

6. A spring according to claim 5 having

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. successive rubber layers in said cross-sectional plane, the length of the rubber layers may be varied similarly in one or more other planes substantially perpendicular to the plane of the rubber layers and metal plates so as to improve the fatigue resistance of the spring to shear loads acting in more than one direction. The outer profiles of the rubber layers as considered in planes parallel to the metal plates may be rectangular, square, circular, or elliptical, though other shapes, such as polygonal shapes, may be employed. Considered also in said planes, the rubber layers may be formed with apertures so as to be essentially -ring-shaped, and the metal plates may also be formed with apertures such that the spring has- - a hollow cavity therein, though to obtain good fatigue life it is generally preferred that neither rubber layers nor plates are formed with apertures. The spring may be provided with a passage communicating between the hollow cavity and outside of the spring. The cavity may be air-tight, a suitable valve or seal being provided to maintain the cavity air-tight where the spring is formed with a passage. In a preferred constructon the thickness of the layers of rubber or like elastomeric material increases progressively from the centre layer or layers towards each outermost layer. One embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing in which: Figure 1 is a side - view of a spring in accordance with the present invention in an unloaded condition; Figure 2 is a similar view to that of Figure 1 showing the spring loaded in compression, and Figure 3 is a similar view to that of Figure 1 showing the spring loaded in compression and shear. A sandwich type suspension spring 10 for use in a railway vehicle bogie suspension comprises a plurality of rubber layers 11 bonded to and interleaved with a plurality of metal plates 12 and metal end plates 13. The thickness of the rubber layers 11 increases progressively from the central layers 1 lea to the outermost layers, and the length of the rubber layers and interleaving plates as viewed in the direction of Figure 1 also increase progressively from the central layers and plates to the outermost layers and plates. All rubber layers are of equal depth in a direction perpendicular to the plane of Figure 1 along the entire length of each layer as viewed in Figure 1 and the plates are like wise-shaped. The central rubber layers and metal plate are of a square outer profile and accordingly the relatively outer rubber layers and plates are of rectangular outer profile. When the spring is subjected to a combination of shear and compression loadings, as illustrated in Figure 3, the effective area of the spring directly to support compression loads remains substantially unaltered at the cross-sectional area of the centre rubber layers I la and this assists to minimise the bending stresses on the outermost rubber layers and thus improve their fatigue life as compared with a conventional spring having rubber layers and plates all of similar dimensions. It will be further appreciated from Figure 3 that by use of central rubber layers and plates which are shorter than relatively outer layers and plates, all layers and plates are more able to move angularly relative to the end plates than in a conventional spring where all plates and layers are of similar dimensions, and accordingly there results a more uniform distribution of bending stresses between all of the rubber layers so as to assist in improving the fatigue life of the spring. WHAT WE CLAIM IS:

1. Aspring comprising a plurality of layers of rubber or like elastomeric material bonded to and interleaved with a plurality of metal plates wherein the length of the layers of rubber or like elastomeric material as considered in at least one cross-sectional plane extending substantially perpendicular to the plane of said layers and metal plates decreases from each outermost layer in a direction towards the centre layer or layers and the thickness of the centre layer or layers of rubber or like elastomeric material is less than the thickness of the outermost layers.

6. A spring according to claim 5 having

formed therein a hollow cavity.

7. A spring according to claim 6 wherein a passage communicates between the hollow cavity and the outside of the spring.

8. A spring according to claim 6 or claim 7 wherein the hollow cavity is airtight.

9. A spring according to any one of the preceding claims wherein the thickness of the layers of rubber or like elastomeric material increases progressively from the centre layer or layers towards each outermost layer.

10. A spring constructed and arranged substantially as herein described with reference to the accompanying drawing.