GB2075441A - Leaf spring suspension devices - Google Patents

Abstract

In a vehicle suspension device at least one parabolic spring-leaf L is in contact at its central portion with a clamping plate B which is itself integral with one part of the vehicle, wherein the contact between the said central portion of the spring-leaf and the said clamping plate is made via two plane-surfaces 6, 7, forming a dihedron, and inclined in such a way that the leaf is subjected to compression stresses due to contacts with the clamping plate, the said clamping plate being made up of a single element or clamp. <IMAGE>

Description

SPECIFICATION Suspension devices comprising at least one parabolic spring leaf and at least one spring clamp compressing the central part of the said leaf The present invention relates to suspension devices with at least one parabolic spring leaf.

Heavy duty road and railway vehicles are generally suspended by springs composed of a cluster of superimposed spring leaves, interconnected through their middle part by a spring clamp integral with the axle. The leaves are held in position inside the clamp by means of a bolt which goes through a hole provided in the middle of each leaf.

The vehicle load is applied to the ends of the upper plate of the cluster of plates and determines in each leaf a bending moment which is maximum in its centre, there precisely where the hole is provided to receive the bolt. The said hole can be the start of breakings. But this can be avoided, in the case of thin leaves, by stamping in its place a dish-shaped element which projects out on the other face in the form of a knob. Each knob fits into the dish-shaped element of the next leaf and the knob of the last leaf fits into a dish-shaped element stamped into the clamp. The same result can be obtained with undulations formed in the middle of each leaf and in the clamp.

Long and thick clamps reduce the value of the maximum bending moment and thus contribute to avoid breakings. On the other hand, they reduce the flexibility of the spring and make the latter heavy, especially when said clamps are constituted, in known manner, by two portions of clamps, bolted together.

The aim is, on the contrary, to make springs lighter in order to reduce the load to be transported. The tendency to this effect is to replace the cluster of flat leaves with one or more very thick leaves joined up in their middle by a clamp: said leaves are flat only inside that clamp and, according to a parabolic law, their thickness decreases towards the ends so as to form a solid of equal strength.

At their ends, the leaves are shaped so as to be applied one against the the other are thus to share the vehicle load.

In their middle part, they are too thick to be knobbed in or undulated; therefore they are perforated or notched and centered in the clamp by positioning bolts, lugs or keys. Their thickness is carefully increased to avoid the holes or notches causing breakings, which of course reduces their flexibility.

The present invention relates therefore to a vehicle suspension device comprising at least one parabolic spring-leaf, the centre of the convex face of which is in contact with a clamping plate which is itself integral with one part of the vehicle in which suspension the contact between the said central portion of the parabolic spring-leaf and the said clamping plate is made via two plane surfaces, forming a dihedron, and inclined in such a way that the leaf is subjected to compression stresses due to contacts with the clamping plate and to the fact that said clamping plate is made up of single element or clamp.

It is thus characteristic according to the invention: -on the one hand, for the contact surfaces between the clamping plate and the spring leaf to be constituted of two plane surfaces intersecting along a straight line perpendicular to the plane of the spring-leaf.

-on the other hand, for these two surfaces, forming a dihedron, to be directionally adjusted so that the spring-leaf is subjected to compression forces, -and finally, for the known clamping plate, which has already been described in the prior art, and which can be made up of two elements assembled by bolting, to be constituted by a single element or clamp.

According to one embodiment of the invention, the centre of the convex face of the parabolic leaf is shaped as a plane dihedron, upper face of the clamp is identically shaped and the contact between the said leaf and the said clamp takes place between two surfaces situated on either side and at a certain distance of the edge (which may in some cases not be materialized) of the said dihedron. What is meant by a certain distance is an adequate distance for the forces transmitted by the contacting surfaces to have a component "in compression", whatever the deformation of the leaf.

In one other particularly interesting embodiment of the invention, the convex and concave faces of the central part of the leaf are provided with two surfaces forming a dihedron. In this way, the whole central part of the leaf can be compressed between, on the one hand, the clamp resting against the convex part of the leaf and, on the other hand, a backing-clamp present tightly on the clamp and acting in compression on the dihedron borne by the concave face of the leaf.

Thereagain, care should be taken that the forces, to which the faces of the said dihedrons are subjected, are always forces with a compression component.

The invention makes it possible to eliminate one of the causes for the leaves breaking.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings in which: -Figure 1 is an elevation view of a spring according to the invention; -Figure 2 is a variant of the spring shown in Figure 1; -Figure 3 is another variant relating to a spring with a plurality of leaves; -Figure 4 is a cross-sectional view of the spring shown in Figure 3; -Figure 5 is a variant of Figure 3.

Referring first to Figure 1 , the spring according to the invention comprises a parabolic leaf L and a clamp B. The parabolic leaf L is composed of two arms 1 and 2 of parabolic shape joined up by a central portion 3 clamped by the clamp B. Each one of the two arms 1,2 ends buy a slide 4,5 which applies on the supports At, A2 integral with the vehicle.

The central part of the leaf L comprises two inclined planes 6 and 7 in contact with the inclined planes of identical gradient of the clamp B; the inclined planes 6' and 7' of the clamp B end on the outside into rounded portions 8, 9 and are joined up by a clearance 10; the inclined planes 6 and 7 of the leaf L extend a little to the outside of the clamp B.

The force F which corresponds to the load of the vehicle on the axle is appled to the clamp B where it is resolved into two forces Fi, and F2, perpendicular to the force F and two forces F1,, and F2,, parallel to the force F.

The forces F1, and F2, directed one towards the other compress the parabolic leaf in its clamped central portion 3. As a result, not only do they ensure a reliable positioning of the leaf L with respect to the clamp B, but they also increase its strength with forces which oppose a breaking.

This effect can be accentuated by two clamps B1 and B2 pressing on either side of the leaf L1, as shown in Figure 2.

The leaf L1 comprises on one face, two inclined planes 11 and 12 and on the other face, two other inclined planes 13 and 14.

The inclined planes 11 and 12 are applied against corresponding planes of the clamp B1 and the inclined planes 13 and 14 are likewise applied against two inclined planes of the backing clamp B2.

The clamps B1 and B2 are tightly pressed against the leaf L1 by a plurality of bolts 1 5, 1 6 etc., situated on either side of the said leaf.

Any forces exerted by the bolts add up to the force F1 applied to the clamp B1 and increase the compression forces exerted on the central part 17 of the leaf.

The length of the compressed central part 1 7 is not defined, the inclined planes 11 and 13, on the one hand, and 12 and 14, on the other, being joined up by a flat part 18 and 19.

The invention also applies to springs composed of more than one leaf, such as shown in Figures 3 and 4, where the spring comprises two parabolic leaves 20,21 joined up by a single clamp in several elements : a cage 22 inside which blocks 23, 24 are welded after assembly and two wedges 25, 26 force-fitted between the leaves 20 and 21, and then welded in 27, 28 on the cage 22.

Said blocks 23, 24 are always necessary. For space reasons, it is possible to only use the wedges 25 and 26 which cooperate with the cage 22 to ensure the positioning and reinforcement of the leaves 20 and 21. The spring leaves are not necessarily all parabolic; the invention can also apply to the case, such as shown in Figure 5, where the spring is composed of three flat leaves 29, 30, 31 and one parabolic leaf 32, joined up in a clamp made up of a cage 33 and a block 34.

Said cage 33 is shrunk-on over the assembly constituted by the leaves and the block 34, and then welded on said block. At cooling time, the shrinking-on exerts on the parabolic 32 the desired compression stresses.

The blades 29,30 and 31 which are thin, each comprise a dish-shaped element 41, 35, 36 and the corresponding knob 37, 38, 39.

The said knob 37 in engaged in the dish-shaped element 35, the knob 38 in the dish-shaped element 36, the knob 39 in a dish-shape 40 provided in the clamp. All the flat leaves are thus held in position together and with respect to the clamp.

The accompanying drawings have given examples of embodiment of parabolic springs according to the invention, but the latter in effect applies to all springs with one or more leaves of varying thickness and one clamp which bears on the spring via two inclined planes of reverse gradient. Said springs find an application in railway vehicles with a clamp which is normally shrunk-on or held tightly by wedges, as well as in road vehicles with one or more clamps held tightly on the leaves by threaded members.

Claims (7)

1. Vehicle suspension device comprising at least one parabolic spring-leaf the centre of the convex face of which is in contact with a clamping plate which is itself integral with one part of the vehicle, wherein the contact between the said central portion of the parabolic spring-leaf and the said clamping plate is made via two planesurfaces, forming a dihedron, and inclined in such a way that the leaf is subjected to compression stresses due to contacts with the clamping plate and to the fact that said clamping plate is made up of a single element or clamp.

2. Device according to claim I, whernin the two faces of the leaf are provided with means, which, owing to clamps constituting a cage, allow them to be subjected to compression forces.

3. Device according to claim 2, wherein a stack of parabolic blades are used and wherein, between the leaves, the compression forces are obtained by forcing in wedges suitably held in position.

4. Device according to claim 1, wherein the leaf is compressed by bolts placed on both sides thereof.

5. Device according to one of the preceding claims, wherein the clamp is constituted by blocks presenting inclined planes which are applied against the faces of the dihedron of the leaf, and secured to the cage by welding.

6. Device according to one of the preceding claims, wherein the cage comprises wedges applied on the faces of the dihedron of the leaf, and secured to the cage by welding.

7. Device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings,