GB2115893A - An alarm device for use in indicating the wear of friction linings on brake pads - Google Patents

Abstract

The device (24) comprises a plug (28) which includes a shaft (30) and a head (32). An electrical conductor (26) is located in a longitudinal groove (40) in the shaft and passes through the head and to reduce the chance of damage to the electrical conductor a protective shield (34) is provided which is formed on the head (32) so as to extend upwardly therefrom and be offset laterally with respect to the longitudinal groove (40). When the device is secured to a brake pad (10), the protective shield (34) separates the conductor (26) as it passes upwardly out of the head (32) from the parts of the brake in which heat is generated and abrasion occurs and contributes to avoiding direct contact between the conductor and parts of the brake such as anti-rattle spring (20). The groove (40) is shown as formed from two sides with the conductor passed in in-fashion around the end of the shaft. Two forms of protective shield (34) are illustrated and in Figures 4,5, extension (56) of shield (34) is extended like a hook. <IMAGE>

Description

SPECIFICATION An alarm device for use in indicating the wear of friction linings on brake pads The present invention relates to an alarm device for use in indicating the wear of friction linings on brake pads.

More particularly the present invention relates to an alarm device for use in disc brakes, comprising an electrical conductor and a plug which has a shaft formed with a longitudinal groove to receive the conductor, and a head through which the conductor is passed.

In wear indicating alarm devices of this kind the plug which serves to secure the electrical conductor in position, is located in a bore in the friction lining to be maintained, the bore extending approximately radially if the brake lining is of a kind destined for disc brakes. Also, the device is disposed closely adjacent a backing plate for the friction lining. The electrical conductor usually is inserted in the longitudinal groove of the plug in the form of a U-shaped loop and secured to the friction lining together with the plug which is inserted in the bore and retained in the same by clamping or spreading effect or by filling of the bore with a synthetic resin or the like.

The conductor, generally a strand in an insulating sheath, is connected to an electric circuit which is closed when the brake disc has exposed the plug upon advanced wear of the friction lining, thus touching the conductor. If the conductor is in the form of a loop, it may also form part of a closed circuit which is broken as the conductor is severed by the action of the brake disc upon advanced wear of the friction lining.

In a known alarm device of the kind defined initially (German utility model DE-GM 80 24 362) the longitudinal groove extends along two opposed surface lines of the shaft and around the end thereof, and the head has two bores aligned with these surface lines, the electrical conductor inserted in U-shape in the longitudinal groove being pressed through these bores. Above the head the conductor is neither protected nor guided so that the insulation can be damaged by heat radiation from the brake disc or by contact with moving parts of the brake unless the conductor has been installed with the greatest care when assembling the brake or installing a new brake pad.

It is, therefore, an aim of the present invention to develop a wear indicating alarm device of the kind specified initially such that the risk of damaging the conductor by careless assembly, is reduced.

According to the present invention there is provided an alarm device for use in indicating the wear of friction linings on brake pads, comprising a plug which has a shaft formed with a groove extending longitudinally of the shaft, and a head formed at one end of the shaft, an electrical conductor being located in said groove and passing through said head, a protective shield being formed on the head so as to extend upwardly from the head whilst being offset laterally with respect to the longitudinal groove.

When the wear indicating alarm device according to the invention is secured to a brake pad, the protective shield separates the conductor as it passes upwardly out of the head from the parts of the brake in which heat is generated and abrasion occurs. Moreover, the protective shield contributes to avoiding direct contact between the conductor and movable or sharp-edged parts of the brake, such as a pad anti-rattle spring supported on the backing plate of the brake pad.

The protective shield preferably has an upper edge which has a desk-like slope. In this manner the protective shield is adapted to the installation space which generally is defined by a roof-shaped brake caliper or yoke.

It is especially advantageous if the protective shield has an extension projecting, spaced above the head, in the direction towards the common central plane of the shaft and the longitudinal groove. This extension prevents the conductor from forming a loop which protrudes all too far upwardly in the direction of structural elements of the brake with respect to which the respective brake pad is movable.

The latter feature may be modified such that the extension projects beyond the said central plane and is extended like a hook in downward direction. This modification dictates how the conductor must be laid properly and, furthermore, it prevents the conductor from making unintentional movements during assembly and in operation of the brake.

In the alarm device according to the invention it is convenient if the longitudinal groove extends in per se known manner, along two opposed surface lines of the shaft and around the end of the same and if the conductor is passed in a U-fashion around the end of the shaft. In this event a preferred further development of the invention resides in the fact that the head has slots at either side, in continuation of the longitudinal groove, for embedding the conductor in the same. This makes it a lot easier to mount the conductor on the plug because it need not be threaded through the holes in the head, as required with the known alarm device.The conductor strands passed upwardly through the slots in the head simply may be twisted together above the head in the area which is protected by the protective shield, or an unintentional separation of the same from the plug may be prevented by passing the conductor strands underneath the extension of the protective shield.

It is also advantageous if the longitudinal groove is deepened toward the end of the shaft. This measure also contributes to protecting the conductor during its installation as it reduces the risk of damaging the conductor when the plug is introduced with its shaft into the bore of the friction lining.

The risk of making an error during the assembly and thus damaging the conductor also may be reduced by forming the protective shield with an outer surface facing away from the said central plane of the shaft, which outer surface is located at a greater distance from that central plane than the opposite outer surface of the head. The positioning of these two outer surfaces at different spacings from the central plane is adapted to the design of the corresponding brake disc such that laterally inverse mounting of the plug is excluded, whereby it is guaranteed that the protective shield will fulfill its task of protection.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. is a side elevational view of a brake pad of a disc brake, including an alarm device according to the present invention, as seen from the corresponding brake disc, with parts being shown in section parallel to the brake disc; Fig. 2 is a view of the alarm device, as seen in the direction of arrow II in Fig. 1 and on a greatly enlarged scale; Fig. 3 is a longitudinal section along line Ill-Ill in Fig.2; Fig. 4 is a partial view corresponding to Fig. 2 of a modified embodiment of the alarm device of Figs. 1 to 3; and Fig. 5 is a partial view corresponding to Fig. 3, of the modified embodiment.

The brake pad assembly 10 shown in Fig. 1 is of the type which is used customarily in spot-type disc brakes and comprises a backing plate 12 formed with a pair of lateral shoulders 14 to guide the brake pad assembly on a brake carrier or caliper, and with a projection or tab 16 which protrudes upwardly from the centre of the upper edge of the backing plate 12. A pad anti-rattle spring 20 is supported pivotably on tab 16 by means of a hollow rivet 18, and a friction lining 22 is fixed, for instance by cementing, on the front side of the backing plate 12, which side is partly visible in Fig. 1. A wear indicating alarm device 24to be described in greater detail below is fixed to the friction lining 22. The alarm device 24 comprises an electrical conductor 26 in the form of an insulated wire strand, and a plug 28 made of a plastics material.The plug 28 has a substantially cylindrical shaft 30 and a head 32 in the form of a parallelepiped shape, a protective shield 34 extending upwardly from the head 32. The shaft 30 is, in use, fitted in a hole 36 formed along the front end side of backing plate 12 and approximately radially from outside into the friction lining 22. The shaft 30 is clamped in the hole 36 by three annular ribs 38 formed on the shaft 30. A longitudinal groove 40 is formed in the shaft 30 from two opposed sides.

The groove 40 is symmetrical with respect to the central plane 42 of the shaft 30 and extends around the lower end 44 of the shaft. The depth of the longitudinal groove 40 increases at both sides towards the end 44 of the shaft.

The head 32 has two slots 46, formed from two opposed sides of the head and aligned with the longitudinal groove 40. The conductor 26 is bent in a U-shape with the shaft 30 in the central plane 42 thereof, the conductor 26 being laid in the longitudinal groove 40 of the shaft and in the slots 46 of the head 32.

The protective shield 34 is offset with respect to the longitudinal groove 40 and has an outer surface 48 which extends parallel to the central plane 42, at a noticeably greater distance from said central plane 42 than the distance of the axis of the hole 36 in the friction lining 22 from the plane of the front side of the projection 16 of the backing plate 12, which distance is referred to hereinafter as "the spacing of the hole". At its side remote from the outer surface 48, the head 32 shaped like a parallelepiped also has an outer surface 50 which likewise is parallel to the central plane 42 but which is spaced from the central plane 42 by a distance a little less than "the spacing of the hole".At right angles to the outer surfaces 48 and 50 the head 32 further has two outer surfaces 52 and 54 located at a greater distance than "the spacing of the hole", from said central plane 42.

The bore 36 is offet slightly with respect to the central plane of the brake pad 10 so that the head 32 of the plug 28 is positioned by the side of the head of the hollow rivet 18 but still in overlapping relation with the projection 16. By virtue of this arrangement and the relationship of the spacings as described hereabove, the plug 28 cannot be inserted with its shaft into the hole 36 unless the outer surface 50 of the head 32 faces the projection 16. Thus the space into which the conductor 26 issuing from the slots 46, extends upwardly, is protected under any circumstances between the projection 16 and the protective shield 34.

As shown in Figs. 2 and 3 the protective shield 34 is formed above the head 32 with an extension 56 which protrudes in the direction toward the central plane 42 and partly defines the space between the projection 16 and the protective shield 34 in an upward direction. The two strands of the conductor 26 are passed along the inside of the protective shield 34 below the extension 56 and then through the hollow rivet 18 behind which they are connected to the corresponding circuit in the usual manner (not shown) buy a plug connector.Together with its extension 56 the protective shield 34 has an upper edge 58 which is sloped like a desk, being inclined outwardly from the centre of the brake pad 10 and adapted to the space requirement of the anti-rattle spring 20, the legs of which are actually inclined a little more to the outside upon installation of the brake pad than illustrated in Fig. 1.

With the alternative embodiment shown in Figs. 4 and 5 the extension 56 projects beyond the central plane 42 and is extended like a hook in a downward direction. This configuration of the extension 56 provides even better assurance that the two strands of the conductor 26 passing in the upward direction do notform a loop which might establish unintentional contact with a structural member of the brake which is movable with respect to the brake pad assembly 10, such as the anti-rattle spring 20 as this contact, in the course of time, might damage the loop.

Claims (8)

1. An alarm device for use in indicating the wear of friction linings on brake pads, comprising a plug which has a shaft formed with a groove extending longitudinally of the shaft, and a head formed at one end of the shaft, an electrical conductor being located in said groove and passing through said head, a protective shield being formed on the head so as to extend upwardly from the head whilst being offset laterally with respect to the longitudinal groove.

2. An alarm device as claimed in claim 1, in which which the protective shield has an upper edge which has a desk-like slope.

3. An alarm device as claimed in claim 1 or 2, in which the protective shield has an extension projecting, spaced above the head, in the direction toward the common central plane of the shaft and the longitudinal groove.

4. An alarm device as claimed in claim 3, in which the extension projects beyond the'.

central plane and is extended like a hook in a downward direction.

5. An alarm device as claimed in any one of claims 1 to 4, in which the longitudinal groove extends along two opposed surface lines of the shaft and around the end of the same and the conductor is passed in a U-fashion around the end of the shaft, the head having slots on either side which constitute extensions of the longitudinal groove and into which the conductor is laid.

6. An alarm device as claimed in claim 5, in which the longitudinal groove is deepened toward the said end of the shaft.

7. An alarm device as claimed in any one of claims 1 to 6, in which the protective shield has an outer surface which faces away from the central plane common to the shaft and groove, and is located at a greater distance from said central plane than the opposite outer surface of the head.

8. An~alarm device for use in indicating the wear of friction linings of brake pads, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 3, or Figs. 4 and 5 of the accompanying drawings.