IMPROVEMENTS RELATING TO WHEEL MOUNTED DISCS

Abstract: The present specification discloses a wheel incorporating a braking disc (7). In certain wheels where high duty braking discs (7) are required, the discs (7) are mounted one on each side of the web (5) of the wheel by bolts which pass through spaced apart holes in the discs (7). These holes, besides reducing the available braking area also act as centres for surface cracking, this surface cracking occurring around the bolt holes as a result of the large internal stresses set up by differential thermal expansion. The present invention provides an annular braking disc (7) comprising at least two curved segments (9) mounted on each side of the web (5) of the wheel by means of gripping members (11) which are each secured to the web (5) or rim (3), or form an integral part of the wheel, and engage over the outer edge (27) of the segments (9). Resilient retaining connections (15) are also secured to the web (5) and engage a curved surface (17) provided at each end (19) of the segment (9).Whilst the gripping members (11) firmly hold the outer periphery (27) of the disc (7) to the web (5), the disc (7) can still, under thermal expansion, slide circumferentially under the gripping members (11). Further , the curved surfaces (17) on the end edges (19) of the segments (9) can slide over the resilient retaining connections (15) to cater for thermal expansion.

Description: The present invention relates to a wheel incorporating a braking disc. In particular the present invention relates to a wheel comprising a central hub and an outer rim, the hub and rim being interconnected by a web, with an annular braking disc secured to each side of the web. The braking disc may be a complete continuous annulus or composed of two or more curved segments. In certain wheels, especially railway vehicle wheels, high duty braking discs are required to cater for the braking of very large masses from high speeds. Certain such known braking discs are provided with a series of spaced apart holes through which bolts extend to secure the discs to the web of a wheel. However, as a result of the large amount of heat generated in the braking discs under braking, differential expansion causes large internal stresses to be set up around the bolt holes, and as a result surface cracking can and does occur. Clearly this is undesirable as it reduces the life of the braking disc. The aim of the present invention is to provide a wheel wherein the braking discs are secured without the need for holes in the braking surfaces of the discs or disc segments, whilst accommodating thermal expansion without the occurrence of internal stresses at a detrimental level. According to the present invention there is provided a wheel comprising a central hub, an outer rim and a web extending therebetween, an annular disc comprising at least two curved segments being mounted on the web, each segment being retained by one or more gripping members which are each secured to the web or rim, or form an integral part of the wheel, and which engage over the outer edge of the segment at spaced apart locations, and by resilient retaining connections which are also secured to the web and which engage a surface provided at each end of the segment. In a preferred embodiment of the present invention the annular disc comprises two like segments, each of which has two end edges, each end edge including a curved surface which engages against a resilient retaining connection secured to the web. Two gripping members are provided for each segment and are bolted to the web at circumferentially spaced apart locations, the gripping members each engaging against the rim of the wheel and engaging around the outer circumferential edge of a segment. By virtue of the gripping members engaging against the rim of the wheel, the bolts securing the gripping members are free from any shock or centrifugal loading, and serve solely to locate the gripping members in the desired position. Preferably each gripping member has an inclined gripping face which mates with an inclined portion of the outer circumferential edge of the segment, to hold the segment to the web. Due to these inclined mating faces, any centrifugal forces exerted on the segments due to rotation of the wheel, tend to force the segments closer to the web. Further, each gripping member is designed so that the reaction line normal to these mating inclined faces passes through the interface between the gripping member and the outer rim of the wheel. In this way there is no tendency for the segment to apply pressure against the part of the gripping member which engages around the segment, in a manner which could deform the gripping member and release the segment. Preferably each resilient retaining connection comprises a roll pin which extends through a hole in the web and engages curved surfaces on adjacent end edges of the segments on both sides of the wheel. Each roll pin conventionally comprises a hollow cylindrical member made of spring steel, with an axially extending slot, preferably following a wavy path, being formed along the full length of the cylindrical member. The roll pin may be a close or a clearance fit in the hole in the web and has an end cap secured to each of its respective ends by a bolt passing axially through the pin, each end cap having an enlarged portion which engages in a recess in the curved surface provided in an end edge of a segment to aid in the retention of the segment to the wheel. Each end cap is further provided with a tongue which engages in the slot in the roll pin to thus retain the roll pin in the desired rotational position i.e. so that the slot of the roll pin does not itself face a curved end edge portion of a segment. In use, as heat is generated in the braking disc under the action of braking, the segments of the disc expand with the outer edge of each segment, moving circumferentially whilst being held by the gripping members, and the curved surfaces at the end edges of the segments moving over the resilient retaining connections whilst still being retained by the associated end caps. Thus the segments are positively held on the web whilst being allowed to expand without internal stresses being produced to a detrimental level. The point of engagement of the roll pins with the curved or angled plane surfaces of the segment ends is preferably arranged so that the deflection of the roll pins is maintained at a minimum value during disc segment expansion and contraction. The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a front view of one embodiment of a wheel constructed according to the present invention; Fig. 2 is a cross sectional view taken along line X-X in Fig. 1; Fig. 3 is a cross sectional view taken along line Y-Y in Fig. 1; and Fig. 4 is an enlarged detail of the resilient retaining connection of Fig. 3. A high duty wheel constructed according to the present invention is illustrated in the accompanying drawings. The wheel has a central hub 1 and an outer rim 3, interconnected by a central web 5. Braking discs 7 are mounted on each side of the central web 5, each braking disc being annular and comprising two like segments 9. Each segment 9 is secured to the wheel both by two circumferentially spaced apart gripping members 11, each of which is secured to the central web 5 and engages around a protruding feature on the outer circumferential edge 13 of the segment 9, and by resilient retaining connections 15 which are also secured to the central web 5 and which engage against curved surfaces 17 on the end edges 19 of the segments 9. As can be best seen in Fig. 2 of the accompanying drawings, each gripping member 11 is generally hook-shaped in transverse cross-section, and is secured to the central web 5 by one or more bolts 21. Each gripping member 11 is designed so that when bolted to the central web 5 it has a radially outer face 23 with respect to the wheel, which face engages squarely against the rim 3. Thus the bolts 21 merely locate the gripping member 11 and do not take any radial shock or centrifugal loads, these being absorbed directly by the rim 3. Further, each gripping member 11 has an inclined face 25 which engages an equivalently inclined face 27 provided on the outer circumferential edge 13 of the segment 9. Thus any radial forces exerted on the segment 9 due to rotation of the wheel, tend to push the segment towards the central web 5, with the gripping members 11 being sandwiched between the segments 9 and the rim 3. The inclination of the mating faces 25, 27 is such that the line of reaction force passing normally through this interface, also passes through the interface between the radially outer face 23 of the gripping member 11, and the wheel rim 3. In this way there is no possibility of the radial forces on the gripping members 11 deforming the hook-shaped gripping member and releasing the segment. As can be best seen in Figs. 3 and 4 of the accompanying drawings, each resilient retaining connection 15 comprises a roll pin 29 which extends through an aperture 31 in the central web 5, each roll pin 29 engaging an end edge 19 of each segment 9 on each side of the central web 5. The roll pin 29 conventionally comprises an elongate hollow cylinder made of spring steel, with an axial slot 30 with a wavy profile, extending for the full length of the pin. An end cap 33 is located on each end of the roll pin 29 and is secured thereon by a nut and bolt 35, the bolt extending through the pin. Each end cap 33 has an enlarged portion which engages in adjacent part cylindrical recesses provided in the curved surface 17 on the end edges of adjacent segments 9, to thus secure the end edge regions of the segments to the web 5. Further, each end cap 33 has a tongue 37 which engages in the slot of the roll pin 29 so that the selected rotational position of the roll pin 29 can be maintained by the friction between the end caps 33 and the part cylindrical recesses with which they engage. Preferably the rotational position of the roll pin 29 is selected so that the slot is not engaged by the curved surfaces 17 of the segments 9. Each end cap also provides a cylindrical inwardly extending portion which is a clearance fit in the internal diameter of the roll pin, providing thereby a load bearing element to transfer the radially inwardly occurring shock loads from one segment through the diametrically opposite segment to its associated gripping members without causing the roll pin to be excessively deflected. In use, outward radial forces exerted on the segments 9, are absorbed by the wheel rim 3, and when expanding due to the heat generated under braking, the outer edge 13 of the segments 9 can slide circumferentially in the hook-like gripping member 11 and the curved surfaces 17 on the end edges 19 can slide over and compress the resilient retaining connections 15. Thus the wheel disc segments 9 are positively retained at all times whilst being allowed to expand without internal stresses building to a detrimental level. Whilst two gripping members 11 are provided in the above described embodiment of the present invention, it is envisaged that one centrally located gripping member 11 may suffice in certain applications, or alternatively more than two gripping members can be provided. Further, two or more resilient retaining connections 15 may alternatively be provided to engage each end edge 19 of each segment. The present invention thus provides a simple and efficient wheel disc mounting, especially suitable for railway vehicles, obviating the necessity for holes in the braking surfaces of the disc.

Claims: 1. A wheel comprising a central hub (1), an outer rim (3) and a web (5) extending therebetween, an annular disc (7) comprising at least two curved segments (9) being mounted on the web, characterised in that each segment (9) is retained by one or more gripping members (11) which are each secured to the web (15) or rim (3), or form an integral part of the wheel, and which engage over the outer edge (27) of the segment (9), and by resilient retaining connections (15) which are secured to the web (5) and which engage a surface (17) provided at each end of the segment (9). 2. A wheel as claimed in claim 1, wherein the annular disc (7) comprises two like segments (9) each of which has two end edges (19), each end edge (19) including a curved surface (17) which engages against a resilient retaining connection (15) secured to the web (5). 3. A wheel as claimed in claim 1 or claim 2, wherein two gripping members (11) are provided for each segment (9) and are secured to the web (5) at circumferentially spaced apart locations. 4. A wheel as claimed in any one of claims 1 to 3, wherein each gripping member (11) is secured to the web (5) so that the gripping member (11) also engages against the outer rim (3) of the wheel. 5. A wheel as claimed in any one of the preceding claims, wherein each gripping member (11) has a gripping face inclined to the plane of the disc, said gripping face (25) mating with an inclined face (27) provided on the periphery of the disc (7). 6. A wheel as claimed in claim 5, wherein said inclined face (27) is provided on a radially projecting part of the disc periphery. 7. A wheel as claimed in claim 5 or 6, when dependent upon claim 4, wherein said inclined mating faces (25,27) are designed such that the reaction line normal to these mating inclined faces passes through the interface (23) between the gripping member (11) and the outer rim (3) of the wheel. 8. A wheel as claimed in any one of the preceding claims, wherein each resilient retaining connection (15) comprises a roll pin (29) which extends through a bore (31) in the web (5) and engages curved surfaces (17) on adjacent end edges (19) of the segments (9) on both sides of the web (5). 9. A wheel as claimed in claim 8, wherein the roll pin (29) comprises a hollow cylindrical member made of spring steel with an axially extending slot (30) extending for the full length of the pin (29), completely through the wall of the pin (29). 10. A wheel as claimed in claim 8 or claim 9, wherein the roll pin (29) is a clearance fit in said bore (31). 11. A wheel as claimed in any one of claims 8, 9 and 10, wherein the roll pin (29) ( has an end cap (33) secured to each of its respective ends by a bolt (35) passing axially through the pin (29). 12. A wheel as claimed in claim 11, wherein each end cap (33) has an enlarged portion which engages in a recess in the curved surface (17) provided in an end edge (19) of a segment (9) to aid in the retention of the segment (9) to the wheel. 13. A wheel as claimed in claim 11 or 12, when dependent upon claim 8, wherein each end cap (33) has a tongue (37) which engages in the slot (30) in the roll pin (29).

Inventors: TICKLE, COLIN JOHN FREDERICK
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1986
Main classification: F16D65
IPC codes: F16D65