Improvements in disc assemblies for vehicle disc brakes

Abstract: A disc assembly for a vehicle disc brake has a rotor (1) with a pair of opposite faces (5,6) from which are mounted annular braking discs (7,8). Each disc is mounted for limited radial movement on a carrier means (9) by fasteners (20) located outside the braking area of the disc; and the disc and the carrier means have complementary radial abutment faces (10,11), the carrier means being mounted on the rotor (1) by connectors (22). The brake torque is transmitted from the discs (7,8) to the carrier means (9) by the abutment faces (10,11) and then to the rotor (1) by the connectors (22). This provides a simple construction which reduces stress on the discs (7,8) and permits and guides radial expansion of the discs during braking.

Description: This invention relates to disc assemblies for vehicle disc brakes of the kind comprising a rotor with a pair of opposite faces, from at least one of which is mounted an annular brake disc having a braking area. In an assembly of the kind set forth the discs are normally secured to the rotor by bolts passing through clearance openings in the braking areas of the discs. This allows thermal expansion of the discs relative to the rotor, and ensures a frictional engagement so that the braking torque is transmitted from the discs to the rotor. Particular problems arise where such assemblies are used for heavy duty applications, such as high speed trains, because a large amount of heat is generated during braking, causing differential expansion of the discs. This results in large internal stresses around the openings in the discs, which causes surface cracking. Furthermore, if the openings are not located accurately, the discs may not be able to expand freely in a radial direction, and will then run out of balance. As a result, both the braking efficiency and the life of the discs are reduced, which is undesirable. One attempt at solving these problems is shown in EP-A-0 215 597, where the discs are mounted by roll pins on the rotor, or a support member attached to the rotor, the roll pins being located in complementary recesses in the rotor or support member, and the inner periphery of the discs. Gripping members provided at the outer periphery allow radial movement of the discs while maintaining their frictional engagement with the rotor. The tendency to surface cracking is reduced as there are no openings in the braking area of the discs, and radial expansion is accommodated by flexing of the roll pins. However, the assembly is relatively complex, and costly to manufacture, because of the extra components - the support and gripping members - and the necessity to machine the recesses. In EP-A-0170438 a disc assembly for a vehicle disc brake is disclosed. The disc assembly comprises a rotor having a pair of oppositely directed faces and an annular braking disc mounted on one side of a wheel. The outer periphery of the braking disc has a number of circumferentially spaced apart radially outwardly extending projections by means of which the braking disc is mounted on the wheel. Each projection has a radial slot in which a bush is located, a bolt passing therethrough and being theadedly engaged in a complementarily threaded bore in the wheel. A holder which grips the radial projection holds the bush and bolt in position whilst the braking disc is located in piston on the wheel, and also serves as a spring washer for the bolt as it is tightened to the wheel. Thus the braking disc has a limited amount of available radial movement, the bush being radially movable in the slot, and the braking force is conveyed to the wheel by the sides of the slot engaging against the bush. According to the present invention, there is provided a disc assembly for a vehicle disc brake comprising a rotor, a pair of oppositely directed faces defined on said rotor, and an annular braking disc mounted on at least one of said faces, the or each said braking disc having a braking area and circumferentially spaced apart lugs which extend radially outwardly from the perimeter of the braking disc radially beyond the braking area, carrier means comprising a carrier plate, being secured both to the braking disc for limited radial movement relative thereto, and to the rotor, the carrier plate having a number of lugs which extend radially outwardly with respect to the brake disc, characterised in that interengaging radially extending abutment faces are provided on the carrier plate and on the brake disc, with at least one of the lugs of the carrier plate being secured to the rotor and a further lug of the carrier plate being secured to a superimposed lug of the brake disc only so as to allow for limited relative radial movement therebetween. As the fastening means are outside the braking area, there need be no openings in this area, so that stresses and surface cracking are reduced. Expansion of the disc is permitted by the fastening means, and it is guided on the radial abutment surfaces to ensure that it remains in balance. Furthermore, a relatively simple construction is provided. The carrier means has at least two abutment faces, by means of which the braked torque is transmitted from the disc to the carrier means. The torque is then transmitted to the rotor by any suitable means. Conveniently, the torque is transmitted by the connecting means. The carrier means preferably comprises one or more plates. Conveniently four plates of segmental outline are provided. The disc may be secured to each plate by at least one fastener. Each fastener preferably comprises a bolt passing through an opening in the plate and a clearance opening in the disc, together with a nut. Each plate preferably has two opposed abutment faces for transmitting torque. The connecting means preferably comprises at least one connector securing each plate to the rotor. Each connector may comprise a bolt passing through superimposed openings in the rotor and the plate. The connectors may also serve to locate the disc, while allowing it radial movement, in which case the bolt passes through clearance openings in the disc (outside the braking area) as well. The fastening means and connecting means are preferably located at the outer peripheral edge of the disc. The disc and the carrier plates may be provided with lugs accommodating the openings for the fastening and connecting means. An embodiment of the present invention is illustrated, by way of example, in the accompanying drawings, in which:- Figure 1 is a side view of part of a disc assembly for a vehicle disc brake; Figure 2 is a section along the line 2-2 of Figure 1; Figure 3 is a section along the line 3-3 of Figure 1; and Figure 4 is a section along the line 4-4 of Figure 1. The disc assembly shown in the drawings has a rotor 1 in the form of a wheel adapted to be rotatably mounted on an axle (not shown), and comprises a central hub 2 and an outer rim 3 connected by a web 4, from opposite faces 5,6 of which are mounted annular brake discs 7,8. The discs 7,8 are each mounted on the rotor 1 by carrier means in the form of four carrier plates 9 (only three of which are shown), connected to the rotor 1. The discs 7,8 are fastened to the plates 9 for limited radial movement, and the discs 7,8 and plates 9 have complementary radial abutment surfaces 10,11. Each disc 7,8 has a planar outer braking face 12, and on its inner face has strengthening ribs 13, several of which are adapted to form the radial abutment surfaces 10. Each disc 7,8 also has at its outer peripheral edge a plurality of angularly spaced radially projecting lugs 14, which are outside the braking face 12. Each lug 14 has an opening 15, and the two discs 7,8 are arranged such that the lugs 14 and openings 15 are superimposed. Each carrier plate 9 (shown in Figure 1 in chain-dotted outline) is of segmental outline and is substantially planar with its inner face in engagement with the rotor 1, and its outer face engaging the ribs 13. The radial edges of each plate 9 form the abutment surfaces 11, and the engagement of these surfaces 11 with the surfaces 10 acts both to guide the discs 7,8 as they move radially, and to transmit the braking torque from the discs 7,8 to the carrier plates 9. Each carrier plate 9 also has three angularly spaced radially projecting lugs at its outer peripheral edge corresponding to three lugs 14 on the discs. The two outer lugs 16 are co-planar with the plate 9, but the central lug 17 is cranked outwardly, to give the plate 9 some resilience. Each lug 16,17 has an opening 18, and the plates 9 are arranged on the opposite sides of the rotor 1 so that the lugs 16,17 and openings 18, and the corresponding lugs 14 and openings 15 on the discs 7,8, are superimposed. The rotor 1 also has a plurality of angularly spaced openings 19 adjacent the outer periphery of the web 4, these openings 19 corresponding to the openings 18 in the lugs 16 of the plates 9. The assembly is fastened together as follows. Each disc 7,8 is fastened to its carrier plates 9 (as shown in Figure 3) by a bolt 20 passing through the opening 18 in the central lug 17 of each plate and the opening 15 in the corresponding lug 14, a nut 21 being screwed onto the bolt 20. The openings 15 provide a clearance round the bolts 20, so that the disc 7,8 can move radially relative to the plates 9. Each plate 9 is fastened to the rotor 1 (as shown in Figure 2) by bolts 22 which fit closely in the openings 19 in the rotor 1 and the openings 18 in the outer lugs 16, and which pass with clearance through the openings 15 in the discs 7,8. A nut 23 is screwed onto each bolt 22. This arrangement allows radial movement of the discs 7,8 relative to the plates 9 and rotor 1, but provides a connection between each plate 9 and the rotor 1 which transmits braking torque during operation of the brake. Thus, in use, the braking torque is transmitted from the discs 7,8 to the carrier plates 9 through the abutment surfaces 10,11, and then to the rotor 1 through the bolts 22. In use, the radial abutment surfaces 10,11 guide the thermal expansion of the discs 7,8 in a radial direction, and it is accommodated by the movement of the discs 7,8 relative to the plates 9 and the rotor 1 allowed by the clearance openings 15 round the bolts 20,22. As the expansion is guided, the discs 7,8 will remain centred, and not run out of balance, and there will be little stress put on the openings 15 and bolts 20,22. Furthermore, as the bolts and openings are outside the braking surface, they will not be affected greatly by the differential expansion across the discs which occurs in heavy duty applications. The resilience of the plates 9, provided by the cranked lugs 17, also accommodates any axial movement of the discs 7,8 relative to the rotor 1. This disc assembly has the advantage not only of increased life in comparison with known designs, but also of increased braking efficiency, particularly as continuous discs 7,8 are used rather than segmented discs. Of course, if required, the assembly could be modified to accommodate segmented discs. Furthermore, it will be noted that the construction of the disc assembly is relatively simple, and that it is easy and cheap to manufacture. The particular arrangement of the carrier plates 9 reduces problems with tolerances between the components.

Claims: A disc assembly for a vehicle disc brake comprising a rotor (1), a pair of oppositely directed faces (5,6) defined on said rotor (1), and an annular braking disc (7,8) mounted on at least one of said faces (5,6) the or each said braking disc (7,8) having a braking area and circumferentially spaced apart lugs (14) which extend radially outwardly from the perimeter of the braking disc (7,8) radially beyond the braking area, carrier means comprising a carrier plate (9), being secured both to the braking disc (7,8) for limited radial movement relative thereto, and to the rotor (1), the carrier plate (9) having a number of lugs (16,17) which extend radially outwardly with respect to the brake disc (1), characterised in that interengaging radially extending abutment faces (10,11) are provided on the carrier plate (9) and on the brake disc (7,8), with at least one of the lugs (16) of the carrier plate (9) being secured to the rotor (1) and a further lug (17) of the carrier plate (9) being secured to a superimposed lug (14) of the brake disc (7,8) only so as to allow for limited relative radial movement therebetween. A disc assembly as claimed in claim 1, wherein a number of segmental carrier plates (9) form said carrier means, each carrier plate (9) having at least two said abutment faces (11) for transmitting brake torque from the brake disc (7,8) to the carrier means (9). A disc assembly as claimed in claim 2, wherein said brake torque is transmitted from said carrier means (9) to said rotor (1) by the said carrier plate lugs (16, 17). A disc assembly as claimed in claim 1, wherein superimposed lugs (14, 17) of the brake disc (7,8) and carrier plate (9) are secured together by a nut and bolt assembly (20,21), said bolt (20) passing through an opening (18) in the carrier plate lug (17) and a clearance opening (15) in said brake disc lug (14). A disc assembly as claimed in claim 1 wherein said at least one lug (16) of the carrier plate (9) is secured to the rotor (1) by a nut and bolt assembly (22,23), said bolt (22) passing through superimposed openings (19, 18) in said rotor (1) and said carrier plate lug (16). A disc assembly as claimed in claim 5 wherein each said bolt (20) also passes through a clearance opening (15) in a brake disc lug (14). A disc assembly as claimed in claim 1, wherein four carrier plates (9) are secured to each of the oppositely directed faces (5,6) of the rotor (1), each carrier plate (9) having two abutment faces (11) which engage against radially extending complementary abutment faces (10) on a brake disc (7,8), and three spaced apart radially outwardly projecting lugs (16,17), the outermost lugs (16) being secured to the rotor (1) by respective nut and bolt assemblies (22,23), and the central lug (17) being secured to a radially extending lug (14) provided on the brake disc (7,8) by a nut and bolt assembly (20,21), the bolt (20) of the nut and bolt assembly securing the said central lug (17) to the brake disc (7,8) passing with clearance through an opening (15) in said brake disc lug (14). A disc assembly as claimed in claim 7, wherein the central lug (17) is of cranked configuration, the central lug (17) being thus spaced from the rotor (1).

Inventors: MUNGO KEITH, RUSSELL DAVID FRASER, MUNGO, KEITH, RUSSELL, DAVID FRASER
Applicants: WABCO HOLDINGS SAB, SAB WABCO HOLDINGS B.V.
Application year: 1989
Main classification: F16D65
IPC codes: F16D65