GB2127918A

GB2127918A - Disc brakes

Info

Publication number: GB2127918A
Application number: GB08228157A
Authority: GB
Inventors: Ronald Wadsworth; Bernard Rowbottom
Original assignee: Ferodo Ltd
Current assignee: Federal Mogul Friction Products Ltd
Priority date: 1982-10-01
Filing date: 1982-10-01
Publication date: 1984-04-18
Also published as: DE3335571A1; GB2127918B; JPS6057026A

Abstract

A shim for a disc brake pad which includes a shim pad 4 of heat resistant composite material and a metal clip 3 to hold the shim pad on the back-plate of the disc brake pad. The metal clip preferably protects the shim pad from direct contract with the brake piston, and also is provided with a means, e.g. a retaining lip 5, for holding the shim pad in the correct position. <IMAGE>

Description

SPECIFICATION Improvements relating to disc brake pads This invention relates to disc brake pads, and more particularly to disc brake pads using shims behind their back-plate.

In a disc brake for a vehicle such as a car, braking effort is applied to the vehicles by forcing disc brake pads, consisting of friction material attached to a steel backing plate, against a brake disc. The force is applied to the disc brake pads by means of a hydraulic piston in a brake caliper, and it is usual in a brake caliper for a piston to bear against the back-plate of at least one disc brake pad. In some cases a caliper contains more than one piston, in others the caliper uses only one piston and one pad is forced directly against the disc, an opposed pad being dragged onto the disc by reaction forces.

Shims of various kinds are in common use on the back of disc brake pads mainly to reduce noise by damping effects, or in some cases to vary the centre of pressure of the piston.

Several methods are in use for applying the shims to the pads. In the case of a metal shim this may be made to clip onto the back-plate of the pad, gripping the back-plate at its edges. Alternatively the shim may be adhered to the back-plate either by means of pressuresensitive adhesive or by means of a heat curable adhesive. In a further alternative a form of shim may be moulded onto the packplate by heat and pressure during moulding of the disc-brake pad.

Various disadvantages and problems have risen in the use of shims mentioned above.

For example, where the shim has been applied by means of pressure sensitive adhesive problems have been encountered with the shims moving out of position under the influence of radial forces in certain brake caliper designs.

The use of a heat-curable adhesive is expensive and inconvenient in disc brake pad production and it is difficult to achieve a bond which will withstand the cyclic high temperatures to which the bond is subject during service.

Metal shims have the disadvantage that in general they are not as efficient in damping out noise as non-metallic or metal/rubber sandwich varieties.

We have now found a means of applying and using shims which obviates many of the above disadvantages.

The present invention provides a shim for a disc brake pad which comprises a shim pad of heat resistant composite material and, to locate said shim pad in position on the back of said disc brake pad and attach it to said disc brake pad a metal clip which overlies the shim pad, locates it in position and clips on to said disc brake pad.

The shim pad is a composite material which when protected by the steel clip, will stand up to the pressures applied by a brake piston over a wide range of temperatures ie. from below 0 C to over 400"C. It may, for example be a polymer bonded compressed asbestos fibre material, or a resin bonded glass fibre reinforced material. It is preferably a material with a relatively low thermal conductivity. This is to reduce heat flow from the disc-brake pad to the hydraulic piston and hence the brake fluid which can be a problem particularly when using non-asbestos disc brake pads which often have a much higher thermal conductivity than asbestos ones.

If desired the shim pad may be confined to the area of the back plate in which the piston bears, especially if it is thermally insulating.

This is to minimize the effect on heat dissipation from the disc-brake pad which must be allowed to continue to prevent damage to the disc-brake pad through interior overheating. It will be appreciated that in use the face of a disc brake pad is being rapidly heated by friction against the brake disc. If the back surface of the pad were covered with thermally insulating material the only surfaces left for heat dissipation would be the edges of the pad, which may be inadequate.

The metal clip is preferably so arranged that it prevents direct contact between the piston and the shim pad, thus preventing the piston, which is usually annular, from cutting into the shim pad. Preferably also the metal clip does not bridge over the shim pad, and all the pressure from the piston is transmitted through the shim pad and the maximum damping effect is thus obtained.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which Figure 1 is to a rear view of a disc brake pad with a shim in accordance with the invention.

Figure 2 is a side elevation of the assembly shown in Fig. 1.

Figure 3 is a detail cross-section on A-A showing a portion of the shim in position.

Figure 4 is a rear view of a disc brake pad with a shim which is a further embodiment of the invention.

Figure 5 is a side elevation of the assembly shown in Fig. 4 and Figure 6 is a detail cross-section on B-B showing a portion of the shim of Fig. 4 in position.

As shown in Figs. 1 and 2 a disc-brake pad consists of a back-plate 1 in which is moulded a pad of friction material 2. A shim on the back-plate 1 consists of a zinc-plated steel clip 3 overlying a shim pad 4 of compressed asbestos fibre composite material. As shown in Fig. 3 the steel clip 3 overlies the shim pad 4, there being a retaining lip 5 around the edge of the clip 3 which acts as a locating means for the shim pad beneath it. The clip 3 is attached to the disc brake pad back plate by means of four claws 6, 7, 8 and 9 which are disposed such that the clip 3 cannot readily slide along the back-plate 1.

In the alternative embodiment shown in Figs. 4 and 5 a disc brake pad having a backplate 10 and pad of friction material 11 is provided with a shim comprising a steel clip 12 and a shim pad 13. In this case the clip 1 2 again overlies the shim pad 1 3 but location means for the shim pad is achieved by virtue of five small projections 14 on the steel clip disposed around the edges of the shim pad 1 3 to stop it sliding from under the steel clip 12. In this case three claws 15, 1 6 and 1 7 serve to attach the clip 1 2 to the back plate 10.

In both the embodiments illustrated it will be noted that the steel clips 3 and 1 2 touch the back-plates 1 and 10 only on the edges of the back plates but the steel clips each form plates, overlying the shim pad, onto which the hydraulic piston can bear.

In each case the provision of location means for the shim pad implies that the shim pad and clip could be reduced in size so that the shim pad was located only in the contact area of the piston. Indeed, an annular shim pad to match the shape of the piston could be used if desired. The physical means used to locate the shim pad, ie. the retaining lip 5 and humps 14, are preferable to the use of adhesive, which would have to stand the high temperatures encountered in service. On the other hand an adhesive could be used to fasten the shim pad onto the steel clip for easy assembly in a disc brake pad, since it would not subsequently be needed for location in service.

In some cases it may not be possible to arrange that the disposition of the claws will restrain movement of the clip in all directions.

In such cases the shape and size of the clip may be adjusted so that it will locate in the same way as the back-plate in the brake caliper in the appropriate direction and so provide the necessary constraint on movement.

Claims

1. A shim for a disc brake pad which comprises a shim pad of heat-resistant composite material and, to locate said pad in position on the back of said disc brake pad and attach it to said disc brake pad a metal clip which overlies the shim pad, locates it in position and clips on to said disc brake pad.

2. A shim according to claim 1 in which the metal clip is so positioned as to protect at least part of the shim pad from direct contact with a brake piston when in use.

3. A shim according to claim 1 or 2 in which the metal clip is provided with a retaining lip at the edges of the shim pad to serve as the means for location of the shim pad.

4. A shim according to claim 1 or 2 in which the metal clip is provided with a plurality of projections serve as a means for location of the shim pad.

5. A shim according to any preceding claim in which the shim pad is a thermally insulating material.

6. A shim according to any preceding claim in which the shim pad is dimensioned such as to occupy substantially only the area of a disc brake pad back-plate which is to be contacted by a brake piston in service, in order to avoid overheating of said disc brake pad in service.

7. A shim according to any preceding claim in which the shim pad is made from a polymer-bonded compressed asbestos fibre material.

8. A shim according to any one of claims 1 to 6 in which the shim pad is made from a resin bonded glass fibre reinforced material.

9. A shim substantially as described herein with reference to any one of the accompanying drawings.

1 0. A disc brake pad and shim assembly comprising a shim as claimed in any one of the preceding claims.