IMPROVEMENTS IN FRICTION PAD ASSEMBLIES FOR VEHICLE DISC BRAKES AND IN VEHICLE DISC BRAKES

Abstract: A friction pad assembly 6 for a vehicle disc brake com­ prises a pad 11 of friction material, and a backing plate 12 which carries the pad 11. The backing plate 12 is of composite construction and comprises a metal plate which is provided in opposed parallel end edges with pairs of relatively shallow recesses 13, 14 in which inserts 15, 16 of synthetic plastics material are fixedly secured. The outer edges of the inserts 15, 16 comprise guide surfaces for sliding engagement with complementary surfaces in a brake part.

Description: IMPROVEMENTS IN FRICTION PAD ASSEMBLIES FOR VEHICLE DISC BRAKES AND IN VEHICLE DISC BRAKES This invention relates to improvements in friction pad assemblies for vehicle disc brakes, the friction pad assemblies being of the kind comprising pads of friction material for engagement with rotatable discs, and rigid backing plates carrying the pads. In known vehicle disc brakes friction pad assemblies of the kind set forth are adapted to be applied to opposite faces of a rotatable disc, and at least one of the friction pad assemblies, known as the directly actuated friction pad assembly, is guided for axial sliding movement towards and away from the disc between spaced metal abutment guide surfaces in a stationary member, for example a caliper or a drag-taking member, and with which opposite end edges of the backing plate which is of metal engage slidably, the other friction pad assembly, known as the indirectly actuated friction pad assembly, being carried by a support, for example a limb of the caliper or a yoke separate from the dragtaking member, and which is movable axially with respect to the disc simultaneously with, and. in the opposite direction to, movement of the directly actuated friction pad assembly. In such known vehicle disc brakes difficulty is experienced in preventing corrosion between the abutment guide surfaces and the directly actuated friction pad assembly, and corrosion between support surfaces on the support, which is of metal and which support the indirectly actuated pad, and the backing plate of the indirectly actuated pad assembly itself, which is also of metal. Corrosion in both places hinders replacement of the friction pad assemblies, and corrosion between the guide abutment surfaces and the directly actuated pad assembly may lead to seizure of the pad assembly with consequent failure of the brake. It has been proposed in GB 2001719A and GB 2003088A to construct the backing plates of friction pad assemblies of the kind set forth entirely from a plastics material or porcelain. Although the nature of these materials assists in reducing corrosion, friction pad assemblies incorporating backing plates of that kind may lack the necessary strength to transmit drag forces, which may often be substantial, particularly when the pad assemblies are supported in a brake over relatively small contact areas, such as occurs when the brake incorporates a yoke in the form of a relatively thin plate. In fact, since the nature of the forces to which the pad assemblies are subjected are different, it would be appropriate to provide pairs of pad assemblies of different constructions commensurate with the nature of the forces to which the pad assemblies are subjected in service. This is obviously not desirable in practice. It is the aim of the present invention to provide a friction pad assembly which will meet the requirements of both indirectly actuated and directly actuated friction pad assemblies so that a pair of similar pad assemblies can be used in a brake. According to our invention in a friction pad assembly of the kind set forth the backing plate is of composite construction comprising a metal plate having end edges provided with recesses, and inserts of plastics material which are fixedly secured in the recesses and have outer edges defining guide surfaces. The recesses and the inserts are so positioned and arranged that when the friction pad assembly acts as a directly actuated friction pad assembly, the outer edges of the inserts are slidably engageable with complementary abutment guide surfaces in a stationary member and when the friction pad assembly acts as an indirectly actuated friction pad assembly portions of the end edges of the metal plate itself engage with support surfaces on a support. Thus friction pad assemblies of identical construction can be used as directly and indirectly actuated friction pad assemblies. The inserts provide the pad assembly with the necessary means of reducing corrosion between the pad assembly and the abutment guide surfaces, without reducing substantially the effective strength of the backing plate, and by arranging the inserts such that the said portions of the metal plate itself can engage with the support surfaces on the support, the maximum strength of the metal plate is utilised for withstanding the forces to which the pad assembly will be subjected when it acts as an indirectly actuated friction pad assembly. When each abutment guide surface in a stationary member comprises a pair of aligned faces which are relatively spaced in a radial direction, two inserts are provided in spaced recesses in each end of the metal plate and the metal regions between the pairs of inserts define the said portions for engagement with the support surfaces. One embodiment of our invention is illustrated in the accompanying drawings in which: Figure 1 is a plan of a disc brake of the sliding yoke reaction type for a vehicle; Figure 2 is a section on the line 2-2 of Figure 1; Figure 3 is a section on the line 3-3 of Figure 1; and Figure 4 is a section on the line 4-4 of Figure 3. The disc brake illustrated in the drawings comprises a stationary drag-taking member 1 in the form of a metal casting or forging which is mounted on a stationary part adjacent to one face of an axially fixed rotatable disc 2. The member 1 is provided with an open-ended longitudinally extending cylinder bore in which work inner and outer opposed pistons of which only the free end of the inner piston 3 is shown. The member 1 includes a pair of circumferentially spaced arms 4 which project towards the disc 2 from the inner end of the cylinder bore. Friction pad assemblies 5 and 6 are provided for engagement with opposite faces of the disc 2. The pad assembly 5, known as the directly actuated friction pad assembly, is guided for axial movement towards and away from the disc between abutment guide surfaces 7 constituted by parallel radial inner surfaces of the arms 4 and is applied to the disc 2 directly by the inner piston 3. The pad assembly 6, known as the indirectly actuated pad assembly, is carried by a yoke 8 comprising an outer plate in the form of a closed loop and which extends over the peripheral edge of the disc 2. The yoke 8 is guided for axial sliding movement on guiding surfaces 9 in the outer faces of the arms 4. The outer piston acts on the yoke 8 and moves it axially when the space in the bore between the two pistons is pressurised so that the pad assembly 6 is applied to the disc 2 simultaneously with the application to the disc 2 of the pad assembly 5. Both pad assemblies 5 and 6 are located in the brake against movement in a radial direction by a retaining pin assembly 10. When the brake is applied the drag on the pad assembly 5 is taken directly by the arms 4, and the drag on the pad assembly 6 is transmitted to the arms 4 through the yoke 8. Each friction pad assembly 5, 6 comprises a pad 11 of friction material and a rigid braking plate 12 which carries the pad 11. The backing plate 12 is of greater area than the pad 11 so that the edge of the backing plate 12 projects outwardly from the edges of the pad 11 Each backing plate 12 is of composite construction and comprises a metal plate which is provided in opposed parallel end edges with pairs of relatively shallow recesses 13, 14 in which inserts 15, 16 of synthetic plastics material are fixedly secured. The location of, and the spacing between, each pair of inserts 15, 16 is chosen to coincide with the radial spacing between radially spaced faces 17, 18 in the abutment guide surfaces 7 so that òur the pad assembly 5 the outer edges of the inserts 15, 16, which are aligned with the edges of the plate 12, engage slidably with the faces 17, 18. A plastics material/metal engagement is therefore provided to reduce corrosion between the slidable faces in service. Also, for the pad assembly 6, the yoke 8 engages with the metal regions 19 of the plate 12 which are disposed between adjacent ends of the inserts 15, 16 of each pair. A metal/metal engagement is therefore provided so that the maximum strength of the backing plate 12 is utilised for support and drag-taking purposes.

Claims: CLAIMS 1. A friction pad assembly (5 or 6) for a vehicle disc brake comprising a pad (11) of friction material for engagement with a rotatable disc (2), and a rigid backing plate (12) carrying the pad (11), characterised in that the backing plate (12) is of composite construction comprising a metal plate having end edges provided with recesses (13, 14), and inserts (15, 16) of plastics material which are fixedly secured in the recesses (13, 14) and have outer edges defining guide surfaces. 2. A friction pad assembly according to claim 1, characterised in that the recesses (13, 14) and the inserts (15, 16) are so positioned and arranged that, when the friction pad assembly acts as a directly actuated friction pad assembly (5) the outer edges of the inserts (15, 16) are slidably engageable with complementary abutment guide surfaces (7) in a stationary member (1), and when the friction pad assembly acts as an indirectly actuated pad assembly (6) portions (19) of the end edges of the metal plate itself engage with support surfaces on a support (8). 3. A friction pad assembly according to claim 1 or claim 2, characterised in that two spaced recesses (13, 14) are provided in each end of the metal plate, and an insert (15, 16) of plastics material is fixedly secured in each recess (13, 14). 4; A vehicle disc brake comprising friction pad assemblies (5, 6) adapted to be applied to opposite faces of a rotatable disc (2), and at least one of the friction pad assemblies known as the directly actuated friction pad assembly (5), is guided for axial sliding movement towards and away from the disc (2) between spaced metal abutment guide surfaces (7) in a stationary member (1), the other friction pad assembly known as the indirectly actuated friction pad assembly (6), being carried by a support (8) which is movable axially with respect to the disc (2), simultaneously with, and in the opposite direction to, movement of the directly actuated friction pad assembly (5), in which each friction pad assembly (5, 6) comprises a pad (11) of friction material for engagement with the disc (2), and a rigid backing plate (12) carrying the pad (11), characterised in that the rigid backing plate (12) is of composite construction comprising a metal plate having end edges provided with recesses (13, 14), and inserts (15, 16) of plastics material fixedly secured in the recesses (13, 14), the recesses (13, 14) and the inserts (15, 16) being so positioned that in the directly, actuated friction pad assembly (5) outer edges of the inserts (15, 16) define guide surfaces which slidably engage directly with the surfaces (7) in the stationary member (1), and in the indirectly actuated friction pad assembly (6) the end edges (19) of the metal plate itself engage with support surfaces on the support (8). 5. A disc brake according to claim 4, characterised in that both friction pad assemblies (5, 6) are identical in construction. 6. A disc brake according to claim 4 or claim 5, characterised in that each abutment guide surface (7) in the stationary member (1) comprises a pair of aligned faces (17, 18) which are relatively spaced in a radial direction and two inserts provided in each end of the metal plate of the directly actuated friction pad assembly (5) are slidably engageable with the aligned faces (17, 18), metal regions between the pairs of inserts (15, 16) of the indirectly actuated friction pad assembly (6) define portions which engage with the support surfaces.

Inventors: MATHIAS, CHRISTOPHER NEIL
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1980
Main classification: F16D65
IPC codes: F16D65