GB2107013A

GB2107013A - A brake pad assembly including a feeler of a wear indicator means

Info

Publication number: GB2107013A
Application number: GB08227711A
Authority: GB
Inventors: Heinz Baum; Hans Madzgalla
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1981-09-30
Filing date: 1982-09-29
Publication date: 1983-04-20
Also published as: FR2513716A1; DE8128633U1; IT1152659B; IT8223466A0; GB2107013B

Abstract

in a motor vehicle disc brake the feeler 32 of a wear indicator is fixed to the backing plate 12 by a pin 40, 40' projecting from the feeler 32 into a hollow rivet 22 which is riveted to the backing plate (12). A split ring spring (46) secures the pin 40 or alternatively spring arms 56 on the pin 40' engage shoulders within the hollow rivet. In this manner the feeler is fixed safely to the brake pad and yet can be released, if required. <IMAGE>

Description

SPECIFICATION A brake pad assembly including a feeler of a wear indicator means The present invention relates to a friction pad assembly for use in a motor vehicle disc brake.

More particularly, the present invention relates to a brake pad assembly of the type comprising a backing plate to which a pad of friction lining material is secured, a feeler of a wear indicator means being fixed to the backing plate in an area thereof which is free of friction lining, the feeler comprising a support body of insulating material and a pin projecting away from the same and received in a hollow rivet which is riveted to the backing plate.

It is the task of wear indicator means of the type of interest to give an alarm signal when the wear of the friction lining of a brake pad assembly has reached a certain degree. For this purpose a feeler disposed at the brake pad is connected by an electrical line to a power source and a signal transmitter, such as a warning lamp located on the instrument panel of a motor vehicle. When the brake is actuated after the friction lining has reached a predetermined, still admissible degree of wear, the feeler is pressed against the corresponding brake disc or drum and due to the abrasion thus caused the cable originally embedded in insulating manner in the feeler becomes exposed whereby the circuit of the signal transmitter is closed through the brake disc or drum.

In motor vehicles the brake pads usually are not replaced only when a signal is given by such a wear indicator means. Instead, they are exchanged when it is foreseeable, on the occasion of a regular service inspection, that the friction iinings will not last until the next service inspection, which may not be envisaged before another 10,000 kilometers of travel. Under these circumstances the feeler has not yet made contact with the brake disc or drum and, therefore, is undamaged. For this reason it is desirable not to have to exchange the feeler together with the brake pad assembly but instead to continue to use it together with the next set of brake pads. This requires that the fixing of the feeler to the corresponding brake pad assembly be releasable.

Published German patent application DE-OS 28 13 244, discloses an arrangement of brake pad and feeler of the kind described initially, with which an internally cylindrical, smooth hollow rivet is riveted to the backing plate and the pin of the feeler is made of a plastics material and is integral with the support body thereof, the pin being retained only by friction lock in the hollow rivet.

The support body has an extension which extends substantially parallel to the backing plate and into a bore of the friction lining. A wire is embedded in the extension and in the support body itself and is secured to a contact pin which projects axially away from the pin within the hollow rivet. The contact pin is received in a plug-in socket attached to the end of a connecting cable and pushed into the hollow rivet from the rear of the backing plate.

Upon replacing the brake pad it is possible to remove the plug-in socket together with the connecting cable and use the same again together with a new brake pad, whereas the feeler and the worn brake pad are discarded. In case of premature exchange of the brake pad, however, in other words before wear has reached the feeler, any renewed use of the feeler is hardly possible because its pin certainly cannot be pulled out of the hollow rivet without suffering damage, the pin being so dimensioned as to be a firm, rattle-proof force fit with the hollow rivet under any operating conditions. Among the operating conditions to be considered in this context also are the great thermal stress by convection and above all radiation.In modern disc brakes prolonged vigorous braking may heat the brake disc to 7000 and higher and, when that occurs, the feeler located in the direct vicinity of the brake disc may attain a temperature of similar order. After such thermal strain the feeler of the known arrangement no longer can be separated undamaged from the brake pad assembly.

The same applies to another arrangement of brake pad and feeler known from German utility model DE-GM 70 47 480, with which the feeler also comprises a support body of insulating material and a pin formed integrally with the same, the pin being pushed from the back of the backing plate through a hole formed in the same and being secured by a collar within an area left free of the friction lining. Here too, it is necessary to exchange the feeler together with the brake pad even though the feeler may not yet have been touched by the brake disc so that actually it would still be useful.

It is, therefore, an object of the present invention to design an arrangement of brake pad and feeler of the kind described initially such that, on the one hand, the feeler is fixed firmly and against vibration, to the brake pad, not only during the severest thermal strain occurring in operation but also afterwards, and on the other hand can be removed from the brake pad and reused together with a new one, provided the old brake pad is exchanged when in a state of wear at which the feeler has not yet made contact with the brake disc or drum.

According to the present invention there is provided a brake pad assembly for use in a motor vehicle disc brake comprising a generally planar backing plate to which a pad of friction lining material is secured, a feeler of a wear indicator being fixed to the backing plate in an area thereof which is free of friction lining material, the feeler comprising a support body of electrically insulating material, from which a pin made of heat resistant, relatively hard material, projects, the pin engaging in a bore in a hollow rivet which is riveted to the backing plate, said bore having a shoulder which faces away from the support body, and a spring located within said rivet holding said rivet and pin together.

The heat resistant pin is preferably made of a metal which cannot become bonded to the hollow rivet which, preferably, is also made of metal, not even at the highest temperatures to be expected in operation. The spring which likewise is heat resistant, is preferably also made of metal, and on the one hand, provides a form-lock connection between the pin and the hollow rivet and, on the other hand, is compressible, due to its elasticity, such that the pin can be pulled or pushed out of the hollow rivet for exchanging the pad assembly.

In accordance with a preferred embodiment of the brake pad assembly of the present invention, the pin has an outer shoulder facing the support body, and the spring is arranged between the shoulders, being supported on both of them.

Axial bias may be established in particularly simple and yet reliable manner, by the shoulder in the hollow rivet being of frustoconical shape and the shoulder formed at the pin defining an annular groove of substantially rectangular cross section to receive the spring with radial clearance. With this arrangement, the spring constantly remains connected to the pin even when the latter has been pulled out of the hollow rivet against the -initial resistance dfthe spring.

The spring preferably is a split ring of round wire.

In a preferred embodiment of the present invention, the hollow rivet is surrounded in per se known manner by at least one winding of a depression spring This at least one winding preferably is arranged in a recess in the backing plate through which the holiow rivet extends, a flange formed on the hollow rivet abutting against an area of the backing plate which is free of friction lining, and the support body abutting against the flange: and/or directly against the backing plate under axial bias produced by the spring.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side elevational view of a brake pad assembly without a-feeler; Fig. 2 is a sectional elevation ofthe brake pad assembly of Fig 1, along line Il-Il, inclúding lhe corresponding feeler in operative position; Fig. 3 is a part elevational view as seen in-the direction of arrow Ill in Fig. 2; and Fig. 4 is a sectional elevation similar to Fig; 2 of another embodiment of the present inverttion.

Fig. 1 shows a brake pad assembly 10 for use in- a spot-type disc brake of the kind which is customary in motor vehicles, as seqn in the direction of that side of the brake pad assembly which will be opposite a brake disc upon installation. The brake pad assembly includes.-a- backing plate 12 punched out of sheet-steel-and having two laterally projecting shoulders 14 for supporting the brake pad assembly in a casing or floating caliper of the disc brake. A friction lining 1 6 is secured to the-front side of the backing plate 12 facing. the brake disc and the observer of Figs.

1 and 3, leaving the lateral shoulders 14 and a rectangular area 18, located in the middle between the shoulders, free of friction lining.

A recess 20 is formed in the backing plate 12 within the area 1 8 which is free of friction lining, and is open like a slot, toward the upper edge of the backing plate. A hollow rivet 22 extends with radial clearance through the recess 20 and is fixed to the backing plate 12 by a flange 24 abutting against the front face of the backing plate 1 2 and an annular disc 26 abutting against the back face of the backing plate. Approximately 1 2 windings of a depression spring 28 consisting of round wire extend around the hollow rivet 22 within the recess 20, the depression spring having two outwardly projecting legs 30 which are almost parallel to the upper edge of the backing plate 12 and which are bent to a U-shape at their ends.

Upon installation of the brake pad assembly 10, the legs 30 rest on the casing or floating caliper of the associated disc brake.

A feeler 32 is secured to the front face of the backing plate 12 and it comprises a support body 34 of insulating material disposed partly in the area 1 8 which is free of friction lining. The support body 34 is formed with a U-shaped groove 36 to receive a portion of an electric cable 38. As shown in Fig. 2, the thickness of the support body 34 is much less than the thickness of the friction lining 1 6. Upon brake actuation, therefore, the support body 34 is not pressed against the brake disc until a considerable portion of the thickness of the friction lining 16 has been abraded. The support body34 is made of a material which wears off in the same way as the friction lining 1 6 when the brakeis actuated, without damaging the brake disc.As soon as the electric cable 38 has been exposed and makes metallic contact with the -brake- disc, due to the wear of the support body 34; a circuit is closed of which the electric cable 38:is part; -As.-shown in Fig. 2, the feeler 32 comprises a metal--pin .40 for fixing to the brake pad assembly 1 Q::tbe foot 42 of the pin 40-being embedded- in the support body 34. The foot 42 is so arranged that; aven at an advanced state-of wear of the friction lining 1 6 and the support body 34, it-does -not reåsih the brake disc without the electric cable -3-8 having been exposed much earlier and the wear indicator means consequently having given alarm signals. Long before the brake disc can become damaged by the foot 42, the user of the motor vehicle thus knows that the brake pad 10 must be exchanged.

The pin 40 projects to-the rear out of the support body 34 and is-received with minor radial.

clearance in the hollow rivet 22. Unintentional pullingof the pin 40-out of the hollow rivet 22 is prevented by the fact that an annular groove 44 is formed in the pin and a spring 46 embodied by a -split-ring of round wire is received in the same .with considerable radial clearance. The spring 46, ondthe one hand, rests on an outer shoulder 48 of thè-pin 40, defining the annular groove 44 in a radial plane and, on the other hand, on an inner 'shoulder 50 of frustoconical shape formed in the hollow rivet 22.

The inner shoulder 50 formed in the hollow rivet 22 has an angle of cone of 600 with a tolerance range of +30 and is so arranged that it tends to urge the spring 46 into the annular groove 44. This tendency is opposed by the spring 46 by virtue of return forces which are directed radially outwardly and converted into axial forces as a consequence of the conical shape of the inner shoulder 50. As these forces are transmitted through the foot 42 of the pin 40 to the support body 34, the latter abuts against the flange of the hollow rivet 22 under axial bias.

As shown in Figs. 2 and 3, the support body 34 further comprises a circular recess 52 in which the flange 24 of the hollow rivet 22 is received with little radial clearance. By virtue of this disposition the pin 40 is at least largely free of the radial forces of acceleration acting on the feeler 32 when the driving is over rough road surfaces.

Consequently, the pin 40 is not subjected to any bending moments worth mentioning in operation and, therefore, does not have any tendency to separate from the hollow rivet 22. On the whole, thus the fixing of the feeler 32 to the brake pad 10 is safe under all operating conditions.

It is however, possible to remove the feeler 32 from the brake pad 10 for renewed use when the friction lining 1 6 of the brake pad has worn considerably and the support body 34 has not yet suffered wear, at least not to any noticeable degree. To disassemble the feeler, the support body-34 is pulled in axial direction away from the backing plate 1 2 and/or a tool is used to press from the other side against the free front end face of the pin 40. The conically shaped inner shoulder 5Q-ofthe hollow rivet 22 then urges the spring 46 radially into the annular groove 44 so that the pin 40 can be pulled or pushed oust of the hollow rivet.

Subsequently, the pin 40 is slid into the hollow rivet -22 of a new brake pad 0. This again requires the spring 46 to be urged radially into the annular groove 44, and for this purpose the front end of the hollow rivet 22- is countersunk at 54 in frustoconical fashion. Once it has reached the shoulder 50, upon continued pushing of the pin 40 into the hollow rivet 22, the spring 46 expands again, retaining the pin in the hollow rivet 22.

In the embodiment shown in Fig. 4, the hollow rivet 22 and the support body 34 are essentially of the same design as shown in Figs. 2 and 3.

Instead of pin 40 a pin 40' is fixed to the support body 34 by having its foot -42' riveted to the same.

The pin 40' is made of metal and carries a metal spring 46'. The spring 46' is designed like a spider having four cranked legs 56 and is fixed by means of a rivet 58 formed integral with the pin 40' such that the four legs 56 surround the pin 40' with radial clearance at uniform angular spacings, pressing against the annular shoulder 50 of the hollow rivet with their feet 60.

Claims

1. A brake pad assembly for use in a motor vehicle disc brake comprising a generally planar backing plate to which a pad of friction lining material is secured, a feeler of a wear indicator being fixed to the backing plate in an area thereof which is free of friction lining material, the feeler comprising a support body of electrically insulating material, from which a pin made of heat resistant relatively hard material, projects, the pin engaging in a bore in a hollow rivet which is riveted to the backing plate, said bore having a shoulder which faces away from the support body, and a spring located within said rivet holding said rivet and pin together.

2. A brake pad assembly as claimed in claim 1, in which the pin has an outer shoulder facing the support body, and the spring is disposed between the said shoulders and supported on both of them.

3. A brake pad assembly as claimed in claim 2, in which the shoulder in the hollow rivet is frustoconical in shape and the shoulder formed in the pin defines an annular groove of substantially rectangular cross section in which the spring is received with radial clearance.

4. A brake pad assembly as claimed in claim 3, in which the spring is a split ring of round wire.

5. A brake pad assembly as claimed in any one of claims 1 to 4, the hollow rivet of which is surrounded by at least one winding of a depression spring, the winding of the depression spring being arranged in a recess in the backing plate through which the hollow rivet extends, the hollow rivet being formed with a flange which abuts against the area of the backing plate which is free of friction lining material and the support body abutting against the flange and/or directly against the backing plate under axial bias produced by the spring.

6. A brake pad assembly for use in a motor vehicle disc brake, constructed substantially as hereinbefore described with reference to the accompanying drawings.