Springs

Abstract

A spring and a suspension system primarily for railway vehicles, comprising a chevron-type rubber sandwich spring in which the spring width increases towards the apex end of the spring wherein the central region of the apex-end of the spring is cored-out to provide a cavity extending into the spring. Of which the following is a specification.

Description

This invention relates to chevron type springs for use under compressive and shear loading, of the type comprising a stack of resilient blocks having parallel metal plates interleaved between and bonded to the resilient blocks, the blocks and plates each being of V-shaped cross-section, that is, taking the form of a V-shaped trough, and to vehicle suspension units and systems incorporating springs of the type described.

When a spring of the type described above is subjected to compressive and shear loading the spring is deflected to a position in which the internal stresses in the spring are in a state of equilibrium with the external forces. Under this loading the plates and blocks tend to open out imposing high bending stresses on the intermediate plates. In such springs it is essential to ensure that the range of bending stresses imposed at the apices of the metal plates during use of the spring does not exceed the fatigue limit of the metal with regard to the required spring life in cycles.

The intermediate plates also tend to cant relative to the outer plates and the associated resilient blocks become deformed to wedge shapes. This deformation gives an uneven distribution of stress in the blocks which may place an excessive stress on some parts of the spring resulting in a reduction in the life of the spring and placing a limitation on the load-carrying capacity of the spring.

Reduction of the bending moment on the intermediate metal plates of springs of the type described above by progressively increasing the width of the plates and blocks from one end of the spring to the other is already known and disclosed in British Patent specification No. 720,365.

Reduction of the tendency of the plates to cant by progressively displacing and decreasing the length of the resilient blocks and plates in a direction at right angles to their direction of stacking is also already known and disclosed in British Patent specification No. 753,995.

One object of the present invention is to provide an improved spring of the type described above.

According to one aspect of the present invention a chevron-type spring for use under compressive and shear loading comprises a stack of V-shaped cross-section resilient blocks having parallel V-shaped cross-section metal plates interleaved between and bonded to the resilient blocks, the stack terminating in end plates, the end plate, blocks and interleaves at the apex end of the spring being wider than the end plate, blocks and interleaves at the other end of the spring, the central region of the wider end of the spring being cored-out to provide a cavity extending through the associated end plate and into at least the resilient block adjacent the said associated end plate.

Successive resilient blocks of the spring described in the preceding paragraph may be progressively displaced in a common direction perpendicular to the direction of stacking of the blocks so that the spring has an echelon profile.

According to another aspect of the present invention a vehicle axle suspension device comprises two springs as described in either of the preceding paragraphs, one end of each spring being operatively associated with an axle box housing and the other end of the spring being arranged to be operatively associated with a sprung portion of the associated vehicle, the operative association of the springs with the housing being such that when mounted in an operational position on the associated vehicle the springs are arranged in spaced-apart relationship considered longitudinally relative to the vehicle.

According to a further aspect of the present invention a vehicle axle suspension system comprises an axle assembly suspended at each end from an associated vehicle body structure by two devices as described in the preceding paragraph.

Some embodiments of the invention will now be described by way of example only, in conjunction with the accompanying diagrammatic drawing in which:

FIG. 1 is a part-sectional side view of a suspension for an axlebox.

FIG. 2 is a part-sectional top view of the suspension in FIG. 1 on the line II--II of FIG. 1.

FIG. 3 is a part section on the line III--III of FIG. 2.

FIG. 4 is a part section of the spring unit of FIG. 1.

FIG. 5 is an alternative spring unit.

FIG. 6 is a section on line VI--VI of FIG. 5.

FIGS. 7 and 8 show diagrammatically springs used for explanation of the principles involved.

In FIG. 1 an axle suspension assembly for a rail vehicle comprises two chevron type spring units 1, 2. Each spring unit comprises a stack of five V-shaped cross-section rubber blocks 3 with parallel V-shaped cross-section steel plates 4 interleaved between and bonded to the rubber blocks 3, both ends of the stack terminating in steel end plates 5 and 6. Successive spring blocks 3 are progressively displaced in a common direction perpendicular to the direction of stacking of the blocks 3 so that the spring units 1, 2 have an echelon profile when viewed in a plane containing the directions of stacking and displacement of the rubber blocks 3.

The spring units 1, 2 are connected to an associated axlebox 7. The axlebox 7 has bearings which support one end of the vehicle axle unit 8. The springs 1, 2 are mounted in spaced relationship considered longitudinally of the vehicle with the apex ends 5 of the spring units 1, 2 attached to the axlebox 7 and the other ends 6 attached to the vehicle underframe 9, the ends 6 of the spring units connected to the underframe 9 being higher and longitudinally spaced further than the ends 5 associated with the axlebox 7 so that the vehicle weight is supported by shear and compressive forces in the spring units 1, 2.

The width of each spring unit 1, 2, that is the dimension of the spring unit in a direction at right angles to the direction of stacking and displacement of the spring unit, is arranged to progressively decrease from the apex end 5 of the spring to the other end 6 of the spring unit in the manner disclosed in the specification of U.K. Pat. No. 720,365.

The wider (when viewed in plan) apex end 5 of each spring unit is cored-out to provide a cavity 10 which extends through the end plate 5 and the first two rubber blocks 3 and associated interleaving plates 4 positioned nearest the apex end 5 of the spring unit, terminating in the third block from the apex end 5 of the spring unit.

The end plate attachment to the vehicle underframe 9 comprises an adaptor block 11 which engages a vertically-extending cut-out 12 formed in the underframe 9. This arrangement provides transverse location of the spring unit. Vertical location is achieved by means of the adaptor block 11 abutting the adjacent underside of the underframe 9.

The end plate 5 of each spring unit which is arranged to be operatively associated with the axle is provided with studs 13 to engage sockets 14 formed in the associated vehicle axle box 7. The arrangement of the studs 13 and sockets 14 is such that provided the end plate 5 is biased towards the axle box housing by the associated spring vertical movement of the end plate 5 relative to the axle box 7 is prevented. If required the axle box housing and associated end plates may be permanently secured together. The studs 13 may alternatively be provided with split-pins or other similar releasable means to hold the springs in engagement with the axle box housing. This simplifies the attachment of the suspension device to the associated bogie.

The cavity 10 provided in the apex end 5 of the spring effectively removes the apex of the chevron in the central region of the spring and allows the chevron to be mounted closer to the center of the axle thus reducing the overall longitudinal dimension of the suspension unit. Also when the wider plates and blocks are mounted immediately adjacent the axle it is possible to accommodate wider blocks and plates by recessing the rear face of the adjacent wheel (see FIG. 2).

The connection between the spring end plate 5 and the axlebox 7 prevents atmospheric and fluid contaminants from entering the spring cavity 10.

In the spring constructions shown in FIGS. 1-4 of the accompanying drawings the four plates and blocks nearest the apex end of the spring are substantially equal in length and are slightly shorter than the two plates and the intermediate block nearest the other end of the spring. The increase in the length, as compared with a normal chevron spring, of the four plates and blocks nearest the apex end of the spring, achieved by using plates and blocks of equal length as opposed to plates and blocks which decrease in length, increases the stability of the spring against buckling about an axis parallel to the associated axle.

The spring construction disclosed in FIGS. 5 and 6 of the accompanying drawings employs plates in which the lengths of the plates and blocks progressively decrease towards the apex end of the spring. This is made possible as the percentage of the volume of the spring which is cored-out is smaller than in the spring arrangements shown in FIGS. 1-4 and thus the additional stability achieved by using plates and blocks of equal length, as opposed to progressively decreasing length, at the apex end of the spring is no longer required, since the spring possesses increased stability as a result of the proportionally smaller cavity.

When the suspension device is mounted in its operational position the directions of stacking and displacement of the spring blocks are arranged to lie in a vertical plane which is substantially parallel with the longitudinal axis of the bogie as shown in FIG. 1.

The plane containing the directions of stacking and displacement of the spring blocks can be inclined with respect to the longitudinal axis of the bogie if design considerations so require.

Although in the axle suspension device and system described above the apex end of the spring is operatively associated with the axle box this situation may be reversed if design considerations dictate.

An axle suspension system can be provided by supporting each end of a vehicle axle by a suspension device as described above.

The benefits derived from coring-out the wider end of the chevron will now be explained for simplicity with reference to a chevron spring in which the blocks are not progressively displaced in a direction at right angles to the direction of stacking of the blocks. It should be understood, however, that the same explanation also applies to echelon profile chevrons.

Consider the section through a constant width chevron shown in FIG. 7, taken in the plane containing the centers of pressure of the blocks. The bending moment acting on each intermediate plate, for example, plate A, about a point B on the center-line C of the spring is as follows.

Considering the half of the spring above the center-line C of FIG. 7 each half block above this line C can be considered to have its own center of pressure D. The distance X of the center of pressure of the half block E from the center-line C, measured in a direction parallel to the portions of the plates above the center-line C as shown in FIG. 7, is a fixed proportion, approximately one third, of the total dimension Y of the block in this direction. This ratio of X to Y holds for all the blocks.

The resultant force acting on the block E has a compressive component F acting through the center of pressure of E and at right angles to the plate A. This compressive component F sets up a reaction F' acting through the center of pressure of the adjacent block G. It can be seen from the above that the bending moment on plate A about an axis through B at right angles to the sectioning plane of FIG. 7 therefore dependent on the perpendicular spacing H between the lines of action of F and F' which in turn is dependent on the relative positioning of the centers of pressure of the adjacent blocks E and G.

As stated above it is well known to reduce this bending moment by progressively increasing the width of the blocks and plates towards the apex end of the spring. Because of the set ratio of X to Y referred to above which governs the position of the center of pressure of each half block relative to the center-line C by progressively increasing the width of the plates and blocks at the apex end of the spring the centers of pressure of the half blocks are displaced further from the center-line C by varying amounts and the perpendicular spacing H of the lines of action of F and F' and their equivalents in the other blocks is reduced, thus resulting in a reduction in bending moment on the intermediate plates.

In order to take maximum advantage of the benefit resulting from increasing the width of the blocks and plates it is necessary to adopt the chevron construction shown in FIG. 8 in which the angle R is equal to the angle S.

The construction shown in FIG. 8 suffers from the serious drawback that it is too bulky for most practical applications as a result of its considerable width. This type of spring also has a tendency to instability due to limited transverse rate.

By coring-out the apex end of the spring the centers of pressure of the cored-out half blocks are displaced further from the center line C so that for a given width of cored-out spring the lines of action of F and F' and their equivalents in the other blocks are more closely aligned, and thus the bending moments imposed on the intermediate plates are lower, than in a solid spring of the same width.

The redistribution of stress in the spring which results from the alterations in the positions of the center of pressure of the spring blocks described above allows a larger proportion of the load imposed on the axle box to be taken by the portions of the axle box housing directly connected to the associated chevrons thus relieving the loading on the central bearing-carrying region of the housing (see FIGS. 1 and 2). Thus the tendency of the housing to close in on the bearing under the compressive thrust of the spring is reduced and the pressure distribution of the bearing improved.

In addition to reducing the bending moments on the intermediate plates the cavity can also be designed to regulate the spring stiffness.

Claims

Having now described my invention what I claim is:

1. A chevron-type spring for use under compressive and shear loading comprising a stack of V-shaped cross-section resilient blocks having parallel V-shaped cross-section metal plates interleaved between and bonded to the resilient blocks, the stack terminating in end plates, the end plate, blocks and interleaves at the apex end of the spring being wider than the end plate, blocks and interleaves at the other end of the spring, the central region of the wider end of the spring being cored-out to provide a cavity extending through the associated end plate and into at least the resilient block adjacent the said associated end plate whereby the bending stress on at least the first intermediate plate from the wider end of the spring is reduced.

2. A spring as in claim 1 wherein the cavity extends through the whole stack of V-shaped resilient blocks and plates.

3. A spring as in claim 1 wherein the cavity has a progressively reducing cross-sectional area in a direction into the stack from the apex end of the spring.

4. A spring as in claim 1 wherein the plates and blocks are of reducing length towards the apex end of the spring, the length being the dimension of the plate or block along the apex of the V-shape.

5. A spring as in claim 1 wherein at least the two blocks at the apex end of the spring are equal in length.

6. A spring as in claim 1 wherein successive resilient blocks are displaced in a common direction perpendicular to the direction of stacking of the blocks so that the stack has an echelon profile.

7. A vehicle axle suspension device comprising two springs according to claim 1 one end of each spring being operatively associated with an axle box housing and the other end of the spring being arranged to be operatively associated with a sprung portion of the vehicle, the operative association with the housing being such that when mounted in the operational position in the associated vehicle the springs are arranged in spaced apart relationship considered longitudinally relative to the vehicle.

8. A vehicle axle suspension device as in claim 7 wherein the apex end of the spring is operatively associated with an abutment provided on the axle box housing.

9. A vehicle axle suspension as in claim 7 wherein the apex end of the spring is operatively associated with an abutment provided on the sprung portion of the vehicle.

10. A vehicle axle suspension as in claim 7 wherein the cored-out portion of the spring is closed by the associated abutment member to prevent the ingress of contaminants.

11. A vehicle axle suspension system comprising an axle assembly suspended at each end from an associated vehicle frame by an axle suspension as in claim 7.