GB2086501A

GB2086501A - Wear indicator

Info

Publication number: GB2086501A
Application number: GB8130849A
Authority: GB
Original assignee: PA Management Consultants Ltd
Current assignee: PA Management Consultants Ltd
Priority date: 1980-10-22
Filing date: 1981-10-13
Publication date: 1982-05-12

Abstract

A device for indicating wear of a consumable material, such as a drum brake lining or clutch plate comprises a support member (12) having a head (18) located within the depth of the consumable material. An insulated conductor (30) is associated with the support member (12) and extends across the head (18) thereof, the insulating material being no more resistant to wear than the consumable material. In use, as wear of the consumable material occurs, the insulating material is exposed to an abrading surface (e.g. of brake drum) causing the wear of the consumable material so that the insulating material is itself worn away so as eventually to expose the conductor. When the conductor is exposed, an alarm signal is generated. Preferably a further alarm is generated when the conductor is completely worn through. Support member (12) is secured in position by circlip, barb fixing washer or, as shown, has a screw threaded portion (16) engaged by nut (48) to retain member (12) on a brake shoe. Conductor (30) is retained in position by a washer (34) (see also Figures 4, 5) or a washer (52) (Figures 6-8). <IMAGE>

Description

SPECIFICATION Wear indicator Field of invention This invention concerns devices for indicating wear, particularly the wear of brake linings and brake pads in motor vehicle braking systems.

Background to the invention There are many pieces of apparatus and equipment which rely on the fitness of a consumable material to achieve braking or drive transmission as in clutches where the consumable material is normally well hidden and considerable dismantling of the apparatus or motor vehicle has to be undertaken in order to determine whether or not sufficient wear has occurred to warrant replacement or repair.

This is particularly the case in vehicle brake drums where the brake linings are wholly contained within the brake drum and are not normally visible. The first warning that a vehicle driver gets that the brakes are worn and require replacement is when squeaking and screaming occur on brake application and by this stage scoring and marking of the internal surfaces of the drums has often occurred.

To a lesser extent the same problem exists with disc brakes although the pads can be more easily seen and inspected during routine servicing and worn pads replaced in anticipation of failure.

The same problem exists in clutches where plates of brake lining type material are clamped together in which wear occurs between the mating surfaces finally resulting in a loss of proper transmission through the clutch.

In all such applications it would be advantageous to be able to determine in advance whether or not the consumable materials forming the linings and clutch plates had worn to an amount sufficient to warrant replacement.

It is, therefore, an object of the present invention to provide a device which can be fitted into brakes and clutches and the like to indicate when wear of the material has occurred to such an extent as to warrant replacement.

The invention According to the present invention a device for indicating wear of a consumable material comprises a support member having a head at one end adapted to be located within the depth of the consumable material, an insulated conductor associated with the support and extending across the head thereof, the insulating material being no more resistant to wear than the consumable material within which the head is to be located so that, in use, as wear of the consumable material occurs, the insulating material is exposed to an abrading surface causing the wear of the consumable material so that the insulating material is itself worn away so as to expose the conductor.

By dimensioning the head so that the insulating material becomes subject to abrasion at a depth within the consumable material corresponding to a small remaining thickness of the consumable material sufficient to give a warning of a replacement requirement, and by arranging that the contact between the abrading surface and the exposed conductor completes an electrical circuit, so an alarm can be made to operate so as to attract the attention of the user of the apparatus or driver of the vehicle to the fact that the consumable material concerned needs urgent attention and/or replacement. In preferred arrangements a further alarm is generated when the conductor is completely worn through.

In the case of a brake lining, the brake drum is itself normally of metal and is normally reliably electrically earthed through the motor vehicle chassis so that an electrical circuit can be established from the motor vehicle chassis to the electrical conductor and by arranging that this inner circuit containing a battery and a lamp and/or audible alarm, so the latter will be activated when the brake lining material wears down to an extent sufficient to expose the conductor to the inside of the brake drum.

The support member preferably comprises an elongate cylindrical memberwiththe head being constituted by an enlarged region at one end thereof. This configuration permits the device to be readily fitted in a position of use, eg in a brake shoe, by being located with the shank of the member passing through a hole in the relevant component or components, eg the brake lining and brake shoe, with the head engaging against a suitable shoulder region, eg in a recess in the brake lining, to locate the insulated conductor in the correct position.

The support member may be secured in such a position by any convenient means, eg by use of a circlip or barb fixing washer. In one preferred arrangement, however, the shank includes a screw threaded region for receiving a securing nut or nuts.

The head conveniently includes two grooves or slots in diametrically opposed regions of the head sidewall for receiving the insulated conductor which extends across the end wall of the head. The grooves or slots house and protect the relevant portions of the insulated conductor.

The shank of the support member conveniently also includes diametrically opposed grooves running along its length for receiving and protecting lengths of the insulated conductor to be passed from the head region to connections located externally of the brake drum etc. In preferred embodiments, as discussed above, in which the shank includes a screw threaded region, the grooves are preferably formed to such a depth that the insulated conductor may be located therein so as to be within the root diameter of the screw thread profile. With this arrangement, a securing nut may be screwed onto the shank without damaging the insulated conductor located in the grooves.

Awasher may be provided to be fitted to the support member head for retaining the insulated conductor in position, extending across the head.

Such a washer preferably includes diametrically oposed inwardly protruding tongues for fitting into co-operating slots in the head (as discussed above).

Alternatively, the washer may include an upstanding rim which is to be bent inwardly overthe outer region of the head end face when the washer is located in position. With the latter arrangement the washer does not need to be located rotationally relative to the head for fitting, simplifying assembly.

The conductor is conveniently copper braid or similar.

The insulating sleeve around the conductor is conveniently of plastics material or braided glass fibre, but any convenient form of insulating material may be used provided it is no more wear resistance than standard brake lining material.

In order to prevent accidental shorting of the conductor to the chassis of the vehicle through the brake shoe, additional insulation may be provided in the form of a ceramic disc or the like below the insulated conductor where it extends across the head of the bolt.

The present invention also includes within its scope a vehicle when fitted with a device in accordance with the invention.

The invention will be further described, by way of example, with reference to the accompanying drawings.

In the drawings Figure 1 is a sectional view of one embodiment of a brake wear indicator in accordance with the invention; Figure2 is a section view of a support member forming part of the indicator illustrated in Figure 1; Figure 3 is an end view of the head of the support member shown in Figure 2; Figure 4 is a sectional view of a washerforming part of the indicator illustrated in Figure 1; Figure 5 is an end view of the washer shown in Figure 4; Figure 6 is a sectional view of a further embodi ment of brake wear indicator in accordance with the invention; Figure 7 is a sectional view of a washer for use in the indicator illustrated in Figure 6; and Figure 8 is an end view of the washer shown in Figure 7.

Detailed description of the drawings Figure 1 illustrates a wear indicator device 10 for brake drums, comprising a support member 12. The support member 12 is shown in Figures 2 and 3, and comprises an elongate generally cylindrical shank 14, the lower part 16 of which is screw threaded. The upper end terminates in a head 18 comprising a protruding flange portion 20 and a central circular protrusion 22 separated by a recessed region 24.

Two grooves 26 and 28 are machined on diametrical ly opposed regions of the shank 14 and are con tinued at 26' and 28' along diametrically opposed regions of the head side wall.

As shown in Figure 1,a length of insulated conductor 30 comprising a heat-resistant insulated wire is passed around the support member 12, lying within the grooves 26, 26-, 28- and 28 and being looped around the head, lying on the central protru sion 22, with this looped region being designated 32.

It is to be noted that the dimensions of the grooves are such that the conductor 30 lies totally within the root diameter of the screw thread profile in region 16.

The insulated conductor 30 conveniently comprises a braided copper wire with an insulated sleeve of plastics material or braided glass fibre.

The looped region 32 of the conductor is retained in position by use of a washer 34 of the configuration shown in Figures 4 and 5. The washer is of generally annular configuration, with its inner face 36 being inclined at an angle of approximately 5 as shown in Figure 4. The internal dimensions of the washer 34 are approximately equivalent to, and slightly larger than, the external dimensions of the support head 18. The washer includes two diametrically opposed protruding tongues 38 extending inwardly from the inner face 36, the tongues being dimensioned to fit in slots 26' and 28- in the support head 18.

The washer 34 is push-fitted over head 18 with the conductor 30 looped therearound, as illustrated in Figure 1, and acts to captivate and restrain the conductor 30.

The two strands of conductor 30 leaving the opposed end of the support are twisted together if desired to assist in retention at that end.

Figure 1 illustrates the device 10 located in a position of use in a brake drum. The brake lining material 40 on a brake shoe is recessed to provide a generally cylindrical hole 42 having an appropriate diameter to accommodate the support head 18 and associated washer 34. A concentric hole 44 is provided through which the support shank 14 is passed. The support head and washer act to restrain the device in an appropriate position in the hole 42, abutting against shoulder 46, and a hexagonal nut 48 is located on the shank threaded portion 16 and tightened to indicated position so as to retain the sensor on the brake shoe.

In use, wear of the brake lining material will occur normally until the brake lining is the same thickness as the height of the insulated sleeve of conductor 30 above the brake shoe whereupon wear of the sleeve will also occur with continued wear of the brake lining material. As soon as sufficient wear has occurred to expose the conductor, this makes contact with the inside surface of the brake drum, establishing an electrical circuit between the conductor and the brake drum, which is normally of electrically conductive metallic material, and the making of this circuit is used automatically to generate an alarm, eg an audible and/or visible alarm, to alert the user of the vehicle to the fact that the brake lining has worn down to a predetermined level and that maintenance is required.

If action is not taken at this stage, further use of the brakeswill result in further wear of the brake lining material and also wear of the conductor - the 4 conductor is preferably of copper or some similar soft material so that it will be worn away appropri ately under such conditions. Eventually, the conductor will be completely worn through providing an open circuit which is detected and used to generate a further alarm indicating that the brake lining is now fully worn and that continued use of the vehicle is dangerous.

Figure 6 illustrates an alternative embodiment of wear indicator device 50 in accordance with the invention. This embodiment comprises a support member 12 of the configuration previously described, as illustrated in Figures 2 and 3. A conductor 30 is looped around the support member in exactly the same manner as described previously.

In place of washer 34 an alternative washer 52 of the configuration illustrated in Figures 7 and 8 is used. This washer comprises a generally annular member the inner diameter of which is generally equivalent to, but slightly larger than, the external diameter of the support head. The inner face 54 of the washer 52 is inclined at an angle of approximately 5", as illustrated in Figure 7 and is extended to form a inner lip or upstanding rim region 56.

In use, the washer 52 is fitted over the support head and associated conductor, and the rim 56 is bent inwardly to the configuration shown in Figure 6 using a suitable bending machine. In this position, the washer acts to retain the conductor in position and performs the other functions of washer 34. It is to be noted that washer 52 does not have to located rotationally with respect to the support, because of the absence of tongues to be fitted into the slots in the head region, thus simplifying assembly.

The device 50 is used in exactly the same way as device 10 as described previously.

Claims

1. A device for indicating wear of a consumable material, comprising a support member having a head at one end adapted to be located within the depth of the consumable material, an insulated conductor associated with the support and extending across the head thereof, the insulating material being no more resistant to wear than the consumable material within which the head is to be located so that, in use, as wear of the consumable material occurs, the insulating material is exposed to an abrading surface causing wear of the consumable material so that the insulating material is itself worn away so as to expose the conductor.

2. A device according to claim 1, wherein the support member comprises an elongate cylindrical member with the head being constituted by an enlarged region at one end thereof.

3. A device according to claim 1 or 2, wherein the support member includes a shank having a screw threaded region.

4. A device according to claim 1,2 or 3, wherein the head includes two grooves or slots in diametrically opposed regions of the head side wall for receiving the insulated conductor.

5. A device according to any one of the preceding claims, wherein the support member includes a shank having diametrically opposed slots or grooves running along its length for receiving lengths of the insulated conductor.

6. A device according to claim 5, wherein the shank includes a screw threaded region and the slots or grooves in the shank are formed to such a depth that the insulated conductor may be located therein so as to lie within the root diameter of the screw threaded profile.

7. A device according to any one of the preceding claims, including a washer fitted to the support member head for retaining the insulated conductor in position.

8. A device according to claim 7, wherein the washer includes diametrically opposed inwardly protruding tongues for fitting into co-operating slots in the head.

9. A device according to claim 7, wherein the washer includes an upstanding rim which is bent inwardly over the outer region of the head end face.

10. A device for indicating wear of a consumable material, substantially as herein described with reference to, and as shown in, Figures 1 to 5 of the accompanying drawings.

11. A device for indicating wear of a consumable material, substantially as herein described with reference to, and as shown in, Figures 2,3 and 6 to 8.

12. A vehicle when fitted with one or more devices in accordance with any one of the preceding claims.

13. A vehicle according to claim 12, wherein a respective device is fitted to one or more brake drums of the vehicle.

14. A vehicle according to claim 12 or 13, wherein the device is connected so as to generate an alarm signal when the abrading surface contacts the conductor.

15. A device according to claim 14, wherein the device is connected so as to generate a further alarm when the conductor is completely worn through.