GB2172676A

GB2172676A - Improvements relating to discs for disc brakes

Info

Publication number: GB2172676A
Application number: GB08602776A
Authority: GB
Inventors: John Adamson; Colin John Frederick Tickle
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1985-02-06
Filing date: 1986-02-05
Publication date: 1986-09-24
Also published as: GB8502952D0; FR2576991A1; DE3603547A1; GB8602776D0

Abstract

A disc for use in a disc brake, especially a disc brake for railway vehicles, comprises two annular members 1, 3 which are coaxially aligned with each other and which are joined to opposite sides of a central web 5 by radially extending vanes 7, the central web being formed by a number of spaced apart segments, each of which is attached to a finger shaped portion 15 of the central hub. Preferably the segments are cast onto the central hub. This segmented construction of the central web allows for local expansion without large internal stresses being produced due to thermal expansion. Thus the likelihood of premature heat damage is reduced. <IMAGE>

Description

SPECIFICATION Improvements relating to discs for disc brakes The present invention relates to a disc for use in a disc brake.

In particular the present invention relates to a disc of the type comprising two annular members which are coaxially aligned with each other and which are joined to opposite sides of a central annular web by generally radially extending vanes. The web is attached to a central hub by means of which the disc can be mounted on a rotatable shaft. The annular members have annular surfaces which face in opposite directions, and these surfaces are, in use, engaged by friction pads to provide the required braking action.

As will be appreciated, a considerable amount of heat is generated in the annular members under braking and this is dissipated to a degree, by the air which is pumped between the generally radially extending vanes.

However it has been found that the difference in temperature between the annular members and the central web, and the internal stresses produced by the resultant differential expansion, can under extreme conditions of use, cause undesirable stresses to arise at the junction between the annular members and the vanes or other spacing features, and within the annular members, to the extent that premature failure by cracking may be experienced.

As will be appreciated, radial expansion of the disc can and does also induce internal stresses in the control hub. To alleviate such internal stresses it has been proposed in Brit ish Patent Specification No. 1 ,133,110 to to pro- vide axially and radially extending slots in the control hub, the slots being open-ended to thus form fingers on the central hub. In British Patent Specification No. 1,133,110 the fingers are bolted to an annular member of the disc so that thermal expansion of the disc, due for example, to braking, can be absorbed by flexure of the separate fingers, thereby reducing the resultant stress in the central hub and in the said annular member.

The aim of the present invention is to provide a disc wherein the stress and consequent damage resulting from the heat produced under braking, is at least reduced, as compared to known disc constructions of the above type.

According to the present invention there is provided a disc for use in a disc brake, the disc comprising two annular members which are coaxially aligned with each other and which are joined to opposite sides of a central web by generally radially extending vanes, the web being formed by a number of spaced apart segments, each of which is attached to a central hub.

In a preferred embodiment of the present invention the segments are cast onto the central hub to permit optimisation of material properties in the annular friction and hub portions of the disc. Alternativeiy the disc assembly may be cast or otherwise found in a homogeneous piece.

The hub is generally bell-shaped and preferably has slots formed therein, in accord with British Patent Specification No. 1,133,110, to thus define fingers which are re-entrant shaped, each finger being cast into one of said segments during manufacture. This finger construction reduces internal stresses which are produced in the central hub as a result of thermal expansion of the annular members and said central web. The slots between the segments extend generally radially with respect to the hub and the side edges of adjacent segments, which define each slot, are preferably parallel to each other.

By virtue of the slotted or segmented construction of the central web, expansion can occur locally without large internal stresses being created due to differential expansion.

Thus the present invention reduces the likelihood of premature heat damage.

In the preferred embodiment of the present invention, the hub is made of steel and the segments of the central web are cast onto the re-entrant fingers of the hub.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partially cutaway cross-sectional view of a preferred embodiment of the present invention; and Figure 2 is a cross sectional view of Fig. 1, taken along line l-l.

The disc illustrated in the accompanying drawings comprises two annular members (1, 3) which are coaxially aligned with each other and which are joined to a central web (5), by generally radially extending vanes (7) and pillars (9). The central web (5) is attached to a bell-shaped hub (11) by means of which the disc can be mounted on a rotatable shaft.

As best seen in Fig. 2 of the accompanying drawings, the central web (5) is formed by a number of generally wedge-shaped, generally planar segments (13) which are each cast onto a finger-shaped portion (15) of the hub (11). The bell-shaped hub (11) has a number of equi-spaced apart, generally radially extending slots (17) in its periphery, which slots define said finger-shaped portions (15). Each finger shaped portion (15) has a re-entrant shaped end region (19) which is cast onto a segment (13) during manufacture, and which improves the attachment of the segments (13) to the hub (11).

The slots (21) defined by adjacent edges (23) of adjacent segments (13), extend generally radially with respect to the hub (11), the adjacent edges (23) being parallel to each other. However alternative arrangements are possible within the present invention.

Thus by virtue of the slots (21) thermal expansion is allowed for, and the previous internal stresses encountered between the annular members and the central web, in prior art discs of this type, are reduced, thereby extending the life of the disc by the reduction in premature cracking.

The present invention thus provides a simple disc construction wherein previous problems which reduced the life of a disc, are obviated.

Claims

1. A disc for use in a disc brake, the disc comprising two annular members which are coaxially aligned with each other and which are jointed to opposite sides of a central web by generally radially extending vanes, the web being formed by a number of circumferentially spaced apart segments, each of which is attached to a central hub.

2. A disc as claimed in claim 1, in which the segments of said central web are cast onto the central hub.

3. A disc as claimed in claim 1, in which the segments of said central web and said central hub, are formed as one-piece.

4. A disc as claimed in any one of claims 1 to 3, in which said central hub is formed with circumferentially spaced apart fingers which are each connected to a segment of the central web.

5. A disc as claimed in claim 4 when dependent upon claim 2, in which said fingers are re-entrant shaped with each finger having been cast into a said segment during manufacture.

6. A disc as claimed in any one of claims 1 to 5, in which the slots formed between adjacent segments extend generally radially with respect to the central hub and the side edges of adjacent segments which define said slots, are parallel to each other.

7. A disc as claimed in claim 2, in which the hub is made of steel and the segments of the central web are cast onto the hub.

8. A disc for a disc brake constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.