GB2059005A - Improvement to shock absorbers for automatic coupling devices for railway vehicles - Google Patents

Abstract

A shock absorber, in particular for automatic coupling devices for railway vehicles, comprises an hydraulic piston and cylinder damping unit and an assembly of superposed deformable elements 18 between which annular metal spacer elements 19 are disposed, each of which is provided with a pair of plane surfaces coupled with corresponding surfaces of two contiguous deformable elements 18, each of the said plane surfaces of each spacer element having axial reliefs formed by balls 23 projecting therefrom which engage corresponding cavities 24 formed in the said surfaces of the contiguous deformable element. Each deformable element has, in cross section, a substantially rectangular external contour and a circular internal contour (hole). The balls 23 are located in holes 22a, b, c formed in each spacer element and so disposed as to be equidistant from the internal and external contours of the deformable elements. <IMAGE>

Description

SPECIFICATION Improvement to shock absorbers for automatic coupling devices for railway vehicles The present invention relates to shock absorbers of the type of those used to absorb and dissipate, partially, the shock energy transmitted through the devices for the automatic coupling of railway vehicles.

As is known, such shock absorbers normally comprise a first hydraulically operated stage apt to give rise to a certain dampering action by having fluid passing through holes of preestablished dimensions, and a second stage with viscoelastic behaviour apt to exert the dampering action through dissipation by hysteresis of potential elastic energy stored as a result of the deformation of an assembly of superposed annular deformable elements.

The improvement according to the present invention relates to this second stage.

The assemblies of deformable elements, of the type suitable for forming the said second stage, also comprise metal spacer elements, each of which is desposed between two contiguous deformable elements.

In order to control, in the desired manner, the transversal deformations of each of said deformable elements when an axial compression load acts onto the assembly it has been proposed (our Italian Patent Application No.

68324-A/79 filed 21 July 1979) to form each plane surface of each spacer element with reliefs projecting from the said surface, each relief being arranged to engage a corresponding cavity of the adjacent deformable element. With this structural arrangement each relief is capable of limiting the transversal deformation of the deformable element located near the relief itself, without, however, limiting the longitudinal deformability of the element. In this way, by suitably arranging the said reliefs it is possible to suitably limit the transversal deformability of the deformable elements.

The shock absorbers of the type described hereinabove have some disadvantages. Firstly, the elastic characteristic, i.e. the behaviour of the camber as a function of the axial applied onto the shock absorber, is not or only in a first portion linear; such behaviour is unfavourable, because the regulations fixed by the users of such devices require straigth lines as reference elastic characteristics for accepting the said evices.

Furthermore, the deformability of such shock generally is too high, though the deformable elements being made of materials (elastomers or rubbers) having rather high stiffness and hardness, so that excessively high deformations both axially and transvesally are obtained.

The object of the present invention is to provide a shock absorber of the type described, which will be free from the disadvantages mentioned hereinabove.

According to the present invention there is provided a shock absorber, in particular for automatic coupling devices for railway vehicles, of the type comprising a first hydraulically operated stage apt to exert a certain dampering action by having fluid passing through holes of pre-established dimensions, and a second stage with viscoelastic behaviour apt to exert a dampering action through dissipation by hysteresis of potential elastic energy stored as a result of the deformation of an assembly of superposed annular deformable elements between which annular metal spacer elements are disposed, each of which is provided with a pair of plane surfaces coupled with corresponding surfaces of two contiguous deformable elements, each of the said plane surfaces of each spacer element having axial reliefs projecting therefrom which are apt to engage corresponding cavities formed on the said surfaces of the contiguous deformable element, characterized in that the cross-section of each of the said deformable elements in a direction perpendicular to the longitudinal axis of the shock absorber is defined externally by a substantially rectangular contour and internally by a circular contour, each of the said cavities formed on each surface of each spacer element being disposed substantially at the same distance from the said rectangular contour and from the said circular contour.

For a better understanding of the present invention a particular embodiment of the invention itself will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a partly sectional longitudinal view of shock absorber; Figure 2 is a longitudinal section along a plane orthogonal to the plane of the section of Fig. 1, indicated by ll-ll in Fig. 1; Figure 3 is a section along a plane Ill-Ill of Fig. 2; Figure 4 illustrates a stresses-deformations characteristic of a shock absorber according to the present invention.

Referring, first, to Figs. 1, 2 and 3, the shock absorber according to the present invention comprises a first hydraulically operated stage, indicated by reference numeral 1, and e second stage, of viscoelastic behaviour, indicated by reference numeral 2.

The first stage comprises substantially a piston 3 slidable in a casing 4 defining with the said piston a first cavity 5 filled with a suitable hydraulic fluid, for example oil; this first cavity communicates with a second cavity 6 also formed between the piston and the casing and communicating with the first cavity through a series of radial holes 7 which open into an axial channel 8 a pin 9 rigidly connected to the casing 4, during the move ment of the piston 3 to the right in Fig. 2.

The diameter of the said pin varies along its axis, so as to allow a control of the resistance against the passage of fluid through the holes 7 and the channel 8 during the displacement of the piston 3.

This latter is rigidly connected to a rod 10, guided within a tubular element 11 rigidly connected to the casing 4, and fixed on its free end is a plate 1 2 onto which the axial force to be absorbed by the shock absorber is applied; conveniently, the connection between the said end and the plate 1 2 is obtained by means of two half rings 1 3 inserted into an annular groove 1 4 of the said end and accomodated within a corresponding seating of the said plate.

The second stage 2 comprises a plurality of deformable annular elements 1 8 and a plurality of spacer elements 19, each of which is inserted between two adjacent deformable elements. The stack of elements of the two types is disposed between the plate 1 2 and the casing 4, so as to be compressed when an axial force is exerted onto the said plate.

According to the invention, the cross-section of each deformable element 1 8 is perpendicular to the axis of the shock absorber (visible in Fig. 3) is defined, externally, by a rectangular profile 20 and internally by a circular profile 21, having a diameter slightly larger than the diameter of the tubular element 11. Such elements may be made of any deformable material having viscoelastic properties, such as rubber, an elastomer or the like.

Each spacer element 19, made of a metal, has a cross-section similar to that of the deformable elements and is defined by two opposed plane surfaces; it is provided with a plurality of through holes 22a, 22b, 22c (Fig.

3), into each of which a ball 29 is inserted whose end caps are lodged within corresponding cavities 24 of the two contiguous deformable elements.

According to the present invention, each spacer element has 8 holes formed therein, arranged according to the configuration shown in Fig. 3, i.e. in which two pairs of said holes (indicated by reference numeral 22a) are disposed substantially on two diagonals of the rectangle which defines externally the rectangular cross-section of each element, whilst two (indicated by reference numeral 22b) of the other four holes are disposed on a median of the said rectangle and the other two (indicated by reference numeral 22c) are disposed on the other median. As can be clearly seen from Fig. 3, each of these holes is disposed at substantially the same distance from the rectangular profile 20 and from the circular profile 21 of the deformable element.

Conveniently the thickness of each deformable element is chosen in such a way that the ration between the thickness and the length of the diagonal of the rectangular profile 20 will be between 0,10 and 0,20.

Preferably, the number of deformable elements is 9, as can be seen in Figs. 1 and 2.

The behaviour of the shock absorber described hereinabove during the use is as follows.

When an axial force is applied onto the plate 1 2 as a consequence of the impact between two railway vehicles having the shock absorbers according to the invention mounted thereon, the said force is transmitted to the deformable elements 1 8 and to the fluid contained in cavity 5.

Under the action of the said force, the said elements deform in an axial direction and in a radial direction orthogonal to the former. No restraint exists for the first deformation, whilst the second deformation is controlled by the reliefs generated by the caps of the balls 23 inserted into the corresponding cavities 24 of the deformable elements. It has been found that if the number and arrangement of the balls are as described (visible in Fig. 3), these balls exert a correct action of limitation of the radial deformations of the deformable elements 18, not only by limiting the value of these deformations both towards the exterior and towards the interior, but also by helping in rendering them uniform.

It follows that both towerds the interior and towerds the exterior the rectangular profiles 20 and the circular profile 21 of the deformable elements, when subjected to a load, vary only little and substantially to the same extent along themselves.

This result, joined to the selection, within the range indicated above, of the thickness of each deformable element 18 and the number of said deformable elements, leads to the obtainment of a stresses-deformations characteristic of the shock absorber which is substantially linear in its first portion, and to a very high load capacity, with modest axial deformations. An example of such characteristic is shown in Fig. 4 relating to tests carried out on a shock absorber in which the first stage comprised deformable elements made of an elastomer with a hardness Shore of 97, having the characteristics indicated hereinabove, thickness and length of the diagonal of the rectangular profile 20 equal to 47 mm and 334 mm respectively.

As can be seen from such characteristic, the run A-B, corresponding to the compression deformation phase, is substantially linear in the first portion and remains always above the straight line D-E which represents the curve which defines the limit deformability of the shock absorber, still acceptable according to the international regulations for the devices of this type. The run B-C of the said curve corresponds to the phase of recovery of the original dimensions, in consequence of the annulment of the axial force, and the area defined by the broken line A-B-C represents the energy dissipated by the shock absorber during a cycle of deformation.

Thus, with the structural arrangement described hereinabove the following favourable properties are obtained: a stresses-deformations characteristic substantially linear in the first portion of the deformation (first portion of the curve A-B), a high load capacity (limited deformations even for high loads, as proved by the run A-B being always above the straight line D-E) and a high dampering capacity (proportional to the inner area of the broken line A-B-C).

During the deformation of the first stage just described, in the second stage a passage of the fluid contained in the cavity 5 towards the cavity 6 through the holes 7 takes place; the resistance against the said passage is controlled by the pin 9 which, entering channel 8, chokes its passage, according to a law wich depends on the variation of its diameter along the axis.

It is clear that modifications and variations both in the shaped and the arrangement of the various parts, may be made to the embodiment of the invention described and illustrated herein, without departing from the scope of the present invention.

Claims (6)

1. A shock absorber, in particular for automatic coupling devices for railway vehicles, of the type comprising a first hydraulically operated stage apt to exert a certain dampering action by having fluid passing through holes of pre-established dimensions, and a second stage with viscoelastic behaviour apt to exert a dampering action through dissipation by hysteresis of potential elastic energy stored as a result of the deformation of an assembly of superposed annular deformable elements between which annular metal spacer elements are disposed, each of which is provided with a pair of plane surfaces coupled with corresponding surfaces of two contiguous deformable elements, each of the said plane surfaces of each spacer element having axial reliefs projecting therefrom which are apt to engage corresponding cavities formed in the said surfaces of the contiguous deformable element, characterized in that the cross-section of each of the said deformable elements in a direction perpendicular to the longitudinal axis of the shock absorber is defined externally by a substantially rectangular contour and internally by a circular contour, each of the said cavities formed on each surface of each spacer element being disposed substantially at the same distance from the said rectangular contour and from the said circular contour.

2. A shock absorber as claimed in Claim 1, characterized in that formed on each of the said surfaces of the spacer element are four pairs of cavities, the two cavities of each of the said two pairs being disposed substantially on a diagonal of the said rectangular contour and the two cavities of each of the other two pairs being disposed on a median line of the said rectangular contour.

3. A shock absorber as claimed in Claims 1 or 2, characterized in that each of the said reliefs projecting from each of the said spacer elements is formed by the spherical cap of a ball inserted into a through hole of the spacer element.

4. A shock absorber as claimed in any of the preceding Claims, characterized in that each of the said spacer elements has a thick nessequal to the thickness of the other spacer elements and that the ratio between the said thickness and the length of the said diagonal of the rectangular contour is comprised between 0,10 and 0,20.

5. A shock absorber as claimed in any of the preceding Claims, characterized in that the material of the said deformable elements is an elastomer having a hardness Shore of more than 95.

6. A shock absorber, substantially as described hereinabove with reference to the annexed drawings.