GB2063397A

GB2063397A - Brake pad

Info

Publication number: GB2063397A
Application number: GB7940093A
Authority: GB
Original assignee: Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Motor Co Ltd; Ford Motor Co
Priority date: 1979-11-20
Filing date: 1979-11-20
Publication date: 1981-06-03
Also published as: FR2470298B1; ES496985A0; FR2470298A1; US4456098A; DE3035887C2; ES8204517A1; CA1176999A; DE3035887A1; GB2063397B

Description

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GB 2 063 397 A 1

SPECIFICATION Brake pad

This invention relates to brake pads.

Conventional brake pads comprise a layer of 5 friction materials having a working face which forms a front face of the pad and which, in use, engages a braking surface such as a brake disc or a brake drum. In order to provide a warning signal when the layer of friction material is about to wear 10 out, it is known to incorporate an electrical lead in ^ the pad. This lead terminates in a contact which is so positioned relative to the layer of friction material that, in use, it will contact the braking surface when the layer of friction material has 15 become abraded by a predetermined amount.

Such a contact can be used to generate a warning signal. Our British Patent Application No.

7903576 discloses a brake pad of this type.

Hitherto, the electrical leads have been formed 20 from insulated wire. The use of insulated wire requires relatively robust mountings in order to connect the wire securely to the brake pad. As a result, the cost of the brake pad is increased and its assembly is made more difficult. 25 According to the present invention there is provided a brake pad comprising a layer of friction material having a working face which forms a front face of the pad and which, in use, engages a braking surface, and an electrical lead terminating 30 in a contact, the contact being so positioned relative to the layer of friction material that, in use, it will contact the braking surface when the layer of friction material has become abraded by a predetermined amount, characterised in that the 35 electrical lead comprises a flexible strip of insulating material having deposited thereon at least one flexible strip of electrically conductive material.

By forming the lead from a flexible conductive 40 strip deposited on a flexible insulating strip, for example from flexible printed circuit material, the weight of the lead is substantially reduced, and much less robust mountings are required in order to attach the lead to the brake pad. The cost of the 45 brake pad can therefore be reduced, and its reliability increased.

In one embodiment of the invention, the contact is formed directly by the flexible strip of electrically conductive material at one end of the 50 lead, thereby reducing the cost of the brake pad even further. Alternatively the contact may be formed by a body of solid electrically conductive material, e.g. graphite, connected to the end of the lead, for example by moulding the lead into the 55 body. In either case, the contact is conveniently connected to the brake pad by mounting the contact in a recess which extends from a rear face of the pad into the layer of friction material. With this arrangement the lead will extend from the rear 60 of the brake pad and will therefore be conveniently positioned for connection into an electrical circuit. Our copending British Patent Application No. 7903576 discloses a particularly useful method of connecting the lead to the brake pad.

65 The lead may comprise a single strip of conductive material but preferably comprises two parallel strips of electrically conductive material which are in electrical communication with each other at the contact, for example through a body 70 of solid conductive material forming the contact (as disclosed in British Patent Application No. 7903576) or through a connecting strip of conductive material deposited on the strip of insulating material. The use of a lead with two 75 such strips of conductive material has the advantage that, in a motor vehicle, the leads can be connected together in series to permit testing of the warning system.

Several particular embodiments of the 80 invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:—

Figure 1 is a rear view of a brake pad in accordance with the invention;

85 Figure 2 is an "exploded" cross-sectional view of the brake pad of Figure 1;

Figures 3 and 4 are views similar to Figures 1 and 2 respectively, showing a fuller alternate brake pad in accordance with the invention; 90 Figure 5 shows, in plan and on an enlarged scale, an alternative construction of lead for use in a brake pad of the invention;

Figure 6 is a side view, in cross-section of the lead of Figure 5.

95 Referring to Figures 1 and 2, a brake pad 1 comprises a metal back plate 2 carrying a layer of friction material 3 which is keyed into a series of apertures 4 in the back plate 1.

A recess 5 formed in the friction material filling 100 one of the apertures 4 extends from the rear face 6 of the pad to a distance from the front face 7 of the pad which is marginally less than the maximum amount of wear which the friction material can undergo during its working life. The 105 interior surface of the recess 5 is coated with an insulating material (e.g. an epoxy resin).

A lead 8 connected to the pad 1 comprises a strip 9 of flexible printed circuit material of conventional construction comprising a base layer 110 of flexible plastics material (e.g. polyethylene) having deposited thereon a flexible layer 10 of electrically conductive material (e.g. copper). A top layer of flexible plastics material is deposited over the base layer and the layer of electrically 115 conductive material so that the latter is electrically insulated. The top layer is removed at one end portion 11 of the strip 8 to expose the conductive material 10. This enf portion 11 is bent over and is received in the recess 5 with the conductive 120 material facing inwardly. The end portion 11 is then retained in the recess 5 by means of a body 12 of electrically conductive material, e.g. graphite, which connects electrically with the conductive material on the end portion 11 of the 125 strip 8, thereby forming a contact for the lead 9. The body 12 is a friction fit in the recess and is additionally secured therein by an adhesive, e.g. an epoxy resin.

The other end of the lead 8 may be provided

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GB 2 063 397 A 2

with an electrical connector (not shown) for coupling the lead into an electrical circuit on a vehicle. In use, the front face 7 of the layer of friction material 3 eventually becomes abraded to 5 such an extent that the body 12 of conductive material will contact the braking surface when the brakes are applied, thereby connecting the lead 8 to earth and generating a warning signal on an instrument panel in conventional manner. 10 In an alternative construction (not shown) the body 12 could be composed of insulating material so that the layer of conductive material in the end portion of the strip 9 acts as the contact for the lead 8.

15 Referring now to Figure 3 and 4, an alternative construction is illustrated in which the lead 8 is formed of similar printed circuit material to that described above with reference to Figures 1 and 2 except that it includes two parallel strips 10a, 10b 20 of conductive material which are electrically connected to each other in the end portion 11 of the strip by a transversely extending strip of conductive material.

As best seen in Figure 4, the end portion 11 of 25 the strip 9 is bent to conform to the internal surface of the recess 5 and is retained therein by a body 12 of insulating material in a manner similar to that described with reference to Figures 1 or 2. The conductive material at the end portion of the 30 strip 9 therefore acts as a contact for the lead 8.

The use of a loop of wire in the lead 9 has the advantage that the lead 9 can be connected in series with similar leads in other brake pads in a vehicle so that the integrity of the brake warning 35 circuit can be tested. A warning signal will be generated when the circuit is broken either as a result of abrasion of the contact of the lead by the braking circuit, or as a result of physical damage to the system.

40 Figures 5 and 6 illustrate a still further alternative construction for the lead 8. In this construction the contact for the lead 8 is formed by a body of electrically conductive material 12, e.g. graphite which is bifurcated, to form two legs 45 12a, b which are separated from each other by a sheet of insulating material 13, e.g. a ceramic chip.

The strip 9 is similar in construction to that described with reference to Figures 3 and 4, 50 except that one of the strips 10a, b of conductive material is severed. The insulating material is removed from the severed ends of the severed strip 10b and the ends are bent downwardly, as seen in Figure 6 into a respective one of the legs 55 12a, b of the body 12 to make electrical contact therewith. The crown 12c of the body 12 effects electrical communication between the two legs

12a, b. Thus, since the lead includes a loop of conductive material, it is capable of being tested for circuit integrity in the manner described with reference to the brake pad of Figures 3 and 4. In addition, as the layer of friction material wears, the crown 12c will eventually make contact with the braking surface, thereby earthing the electrical circuit when the brakes are applied. This resulting change in electrical potential in the circuit can be used to generate a first warning signal indicating that the brake pad is approaching the end of its life.

Further abrasion of the pad will eventually wear away this crown 12c completely, thus producing a permanent break in the circuit and indicating that the brake pad is worn dangerously low.

Claims

1. A brake pad comprising a layer of friction material having a working face which forms a front face of the pad and which, in use, engages a braking surface, and an electrical lead terminating in a contact, the contact being so positioned relative to the layer of friction material that, in use, it will contact the braking surface when the layer of friction material has become abraded by a predetermined amount, characterised in that the electrical lead comprises a flexible strip of insulating material having deposited thereon at least one flexible strip of electrically conductive material.

2. A brake pad according to Claim 1 wherein the contact is formed by the flexible strip of electrically conductive material at one end of the lead.

3. A brake pad according to Claim 1, wherein the contact is formed by a body of solid electrically conductive material connected to the end of the lead.

4. A brake pad according to Claim 2 and Claim 3 wherein the contact is received in a recess which extends from a rear face of the pad into the layer of friction material.

5. A brake pad according to any one of Claims 1 to 4 wherein the electrical lead comprises a flexible strip of insulating material having deposited thereon two parallel flexible strips of electrically conductive material which are in electrical communication with each other at the contact.

6. A brake pad according to any one of Claims 1 to 5 wherein the electrical lead is composed of printed circuit material.

7. A brake pad substantially as hereinbefore described and as illustrated in Figures 1 to 6 of the accompanying drawings.

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printed for Her Majesty's Stationery Office by the Courier Press. Leamington Spa, 1981. Published by the Patent Office, •25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.