GB2256016A - Improvements relating to friction element assemblies for use in vehicle brakes - Google Patents

Abstract

A friction element assembly (1) for use in a motor vehicle, comprises a backing plate (3) to one face of which a pad (7) of friction material is secured, and to the other face of which an audible wear warning indicator is attached. The indicator comprises a stylus (23) which is secured to an end face (21) of a sounding box (13), the stylus (23) projecting through an aperture (25) in the backing plate (3) and into a recess (29) formed in said pad (7) of friction material. Thus, when the friction material (7) has worn away sufficiently to allow the stylus (23) to contact a braking disc, the sounding box (21) generates an audible warning each time the brakes are applied. A similar indicator can be used with a drum brake shoe. <IMAGE>

Description

DESCRIPTION IMPROVEMENTS RELATING TO FRICTION ELEMENT ASSEMBLIES FOR USE IN VEHICLE DISC BRAKES The present invention relates to a friction element assembly for use in a vehicle brake.

More particularly the present invention relates to a friction element assembly comprising a backing plate to which friction material is secured, and including an audible pad wear warning indicator which emits an audible signal when the friction material reaches a state of wear at which the manufacturer recommends replacement.

A known friction element assembly of the above construction and adapted for use in a disc brake includes an audible pad wear warning indicator in the form of a tuning fork type clip fitted to the brake pad backing plate, which on vibrating, due to contact with a brake disc, is intended to emit an audible warning signal. However, in practice there is a tendency for the signal to be in-audible. Further there is a tendency for the tuning fork clip to become fatigued and break in service. Also it can be difficult, if not impossible, to install such a tuning fork clip into existing brake designs due to the small space available.

An aim of the present invention is to provide a friction element assembly including an audible pad wear warning indicator which has improved audibility as compared to the above prior art construction.

According to the present invention there is provided a friction element assembly for use in a vehicle brake, said assembly comprising a backing plate to one face of which friction material is secured, and an audible wear warning indicator, said indicator comprising a stylus which is secured to one face of a sounding box which is located on the face of the backing plate which is opposite to the said one face, the stylus projecting through an aperture in the backing plate and into a recess formed in said pad of friction material.

A preferred embodiment of friction element assembly constructed according to the present invention takes the form of a friction pad assembly for use on a disc brake. Said assembly comprises a planar backing plate to one face of which a pad of friction material is secured, and an audible wear warning indicator. Said indicator comprises a stylus which is secured to one face of a sounding box which is located on the face of the backing plate which is opposite to the said one face, the stylus projecting through an aperture in the backing plate and into a recess formed in said pad of friction material.

In another embodiment of the present invention the friction element assembly is adapted for use in a shoe drum brake, the sounding box being attached to the shoe backing plate.

The sounding box of the present invention is preferably formed as a cylindrical box pressed out of or secured to a planar shim which is attachable to said opposite face of the backing plate by tabs which engage over the edges of the backing plate. The box is thus closed at one axial end remote from the backing plate, with the stylus secured to the centre of the closed end and projecting co-axially within the box. Preferably the closed end of the box is formed with concentric convolutions ie. smooth ridges, suitably designed and spaced holes or any other appropriate features to encourage the sound generating properties of the box when the stylus vibrates. The free end of the stylus is preferably bulbous to prevent the stylus from damaging the braking disc when the friction pad is worn and the stylus contacts the braking disc.The recess in the friction pad may be either a closed cavity or an open hole or slot extending through the friction pad.

In an alternative embodiment the stylus is formed by a radial section which is cut out of the closed end of the sounding box, and bent inwardly of the box so as to extend generally coaxially within the box.

Preferably the free end of the stylus is bent over to reduce the chance of the stylus damaging the braking disc.

A further embodiment of the present invention includes a cylindrical sounding box which is secured by bonding, welding or any other suitable means, to the backing plate, during manufacture of the friction pad assembly.

The stylus projects from the closed end of the box remote from the backing plate, through the aperture on the backing plate. As desired the stylus may be a separate item attached to said closed end, or a section cut out of said closed end and bent inwardly of the box. Preferably the sounding box has a cover which closes the other end of the box, adjacent to the backing plate, the stylus projecting through an aperture in said cover.

A friction pad assembly constructed according to the present invention may be used as the outboard friction pad assembly in a reaction type disc brake wherein the inboard pad assembly is usually directly engaged by a hydraulic actuator, the brake having a caliper which straddles the braking disc, the outboard limb of the caliper having fingers which extend generally radially of the braking disc, which fingers engage the backing plate of the outboard friction pad assembly. In such an installation the fingers of the outboard limb of the caliper engage the backing plate of the outboard friction pad assembly on each side of the sounding box which is preferably centrally located on the backing plate.

In use when the friction pad wears sufficiently so that the free end of the stylus engages the brake disc and vibrates, the sounding box produces an audible signal which warns of the state of the friction pads. Due to the construction of the present invention it is unlikely that the indicator will become fatigued during service and further it takes up no additional space when located between the fingers of the outboard limb of the caliper, the fingers protecting the indicator from possible damage due to flying debris etc. Also, the audible indicator used in the present invention is readily adaptable to existing brake designs.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig.1 is a perspective view of a preferred embodiment of the present invention; Fig.2 is a cross-sectional view along line A-A in Fig.1; Fig.3a is a transverse cross-sectional view of a modified form of a sound box for use in the present invention; Fig.3b is an end view of the sound box of Fig.3a; Fig.4 is a cross-sectional view of a disc brake incorporating an alternative embodiment of the present invention; and Fig.5 is an inverted plan view of part of the brake of Fig.4.

The preferred embodiment of friction pad assembly 1 constructed according to the present invention and illustrated in Figs. 1 and 2 of the accompanying drawings, comprises a planar backing plate 3 to one face 5 of which , a pad 7 of friction material is secured, an audible pad wear warning indicator generally designated 9 being carried on the opposite face 11 of the backing plate 3.

The audible pad wear warning indicator 9 comprises a cylindrical sounding box 13 which is integral with a planar shim 15, i.e. it is welded in an aperture in the shim or pressed out of the shim, the shim 15 having peripheral tabs 17 which engage over the edges 19 of the backing plate 3 to hold the shim 15 and sounding box 13 on the backing plate 3.

The end 21 of the sounding box 13 remote from the shim 15 and backing plate 3 is closed, the closed end 21 carrying a stylus 23 which extends from the centre of the closed end 21, coaxially within the sounding box 13, through an aperture 25 in the backing plate 3 and into a recess in the form of a blind cavity 27 in the friction pad 7. Alternatively, the cavity 27 can be open or in the form of a slot in the friction pad 7.

The free end 29 of the stylus 23 is bulbous to reduce the chance of the stylus damaging the brake disc.

In use, when the friction pad 7 has worn sufficiently to open the cavity 27, expose the bulbous end 29 of the stylus 23 and the brake disc engages the stylus, the stylus vibrates causing the sounding box 13 to emit an audible warning signal. As best seen in Fig.2, the closed end 21 of the sounding box 13 is formed with concentric convolutions 31 to enhance the sound producing properties of the box 13.

Alternatively or additionally, holes of a specific design and arrangement can be provided in the walls of the sounding box 13, or other suitable features can be provided, to enhance the production of an audible signal.

Whilst the stylus 23 in the preferred embodiment of Figs.1 and 2 is secured to the inside surface of the closed end 21 of the sounding box 13 by, for example, welding, in a modified sounding box 13' shown in Figs.3a and 3b, the stylus 23' is formed by a radial section A cut out of the closed end 21' of the sounding box 13', and bent inwardly of the box. The free end 24 of the stylus 23' is bent over to prevent damage to a brake disc.

An alternative embodiment of an audible wear warning indictor constructed according to the present invention is illustrated in Figs. 4 and 5 of the accompanying drawings, and the same reference numerals as used in Figs. 1 and 2 will be used for equivalent parts. The main difference between the indicator of Fig.4 and that of Fig.1 is the fact that the indicator does not form an integral part of a shim 15. The indicator 9 in Fig.4 'comprises a cylindrical sounding box 13 which has a lateral flange 33 at its open end, the flange 33 being welded to the backing plate 3 so that the stylus 23 passes through the aperture 25 in the backing plate 3 and into an open slot 26 in the friction pad 7. Alternatively the box 13 can be secured to the backing plate by any other suitable means.Also, whilst the closed end 21 of the box 13 is illustrated as being planar, it can alternatively have concentric convolutions and/or holes etc. to enhance the production of an audible signal. As is evident from Fig.4 and Fig.5, the open end of box 13 is closed by a cover 35, the stylus 23 passing through an aperture 37 in the cover 35. Such a cover can be used, if desired, in the embodiment of Figs. 1 and 2.

As is seen from Figs. 4 and 5, a friction pad assembly 1 constructed according to the present invention can be used to advantage in a sliding caliper reaction type brake 39, the friction pad assembly being used as the outboard pad. The brake 39 has a caliper 41 which straddles the braking disc (not shown), a hydraulic actuator 43 acting directly on the inboard pad assembly 45, whilst the outboard limb 47 acts by reaction on the outboard pad assembly 1 constructed according to the present invention. As best seen in Fig.5, the outboard limb 47 has two fingers 49 which extend generally radially of the braking disc and engage the backing plate 3 of the pad assembly 1, one on each side of the sounding box 13.

Thus the sounding box 13, i.e. indicator 9, is within the profile of the existing brake design and therefore requires no extra space for the brake on the vehicle.

Also, the fingers 49 protect the sounding box 13 to a certain extent from weather and flying debris.

The present invention as described hereabove thus provides a friction pad assembly which is readily adaptable to existing brake designs, the friction pad assembly incorporating an audible pad wear warning indictor with good audibility and a simple construction with a long life.

However, whilst the invention has been described hereabove primarily in terms of a friction pad assembly for use in a disc brake, the invention could readily be used in a shoe drum brake with the sounding box attached to the shoe backing plate.

Claims (17)

1. A friction element assembly for use in a vehicle brake, said assembly comprising a backing plate to one face of which friction material is secured, and an audible wear warning indicator, said indictor comprising a stylus which is secured to one face of a sounding box which is located on the face of the backing plate which is opposite to the said one face, the stylus projecting through an aperture in the backing plate and into a recess formed in said pad of friction material.

2. An assembly as claimed in claim 1, in which the backing plate and pad of friction material are constructed as a friction pad assembly for use in a disc brake.

3. An assembly as claimed in claim 1, in which the backing plate and pad of friction material are adapted for use in a shoe drum brake.

4. An assembly as claimed in claim 2, in which the backing plate is planar and the sounding box is in the form of a cylindrical box pressed out of or secured to a planar shim which is attachable to said opposite face of the backing plate by tabs provided at the edge of the shim, which tabs engage over edges of the backing plate.

5. An assembly as claimed in claim 2, in which the backing plate is planar and the sounding box is cylindrical and attached to the said opposite face of the backing plate by any suitable means.

6. An assembly as claimed in claim 4 or 5, in which the sounding box is closed at one axial end remote from the backing plate, with the stylus secured to the centre of the closed end and projecting coaxially within the sounding box.

7. An assembly as claimed in claim 6, in which the closed end of the sounding box is formed with concentric convolutions.

8. An assembly as claimed in claim 6 or claim 7, in which the sounding box is provided with holes to encourage the sound generating properties of the sounding box when the stylus vibrates.

9. An assembly as claimed in any one of the preceding claims, in which the free end of the stylus is bulbous.

10. An assembly as claimed in claim 4 or 5, in which the sounding box is closed at one axial end remote from the backing plate, with the stylus being formed by a radial section which is cut out of the closed end of the sounding box, and bent inwardly of the box so as to extend generally coaxially within the box.

11. An assembly as claimed in claim 10, in which the free end of the stylus is bent over.

12. An assembly as claimed in any one of claims 6 to 11, in which the end of the sounding box adjacent to the backing plate, has a cover which effectively closes this other end of the sounding box, the stylus projecting through an aperture in said cover.

13. An assembly as claimed in any one of the preceding claims, in which the sounding box is centrally located on said backing plate.

14. An assembly as claimed in any one of the preceding claims, in which the recess in the pad of friction material is formed by either a closed cavity or an open hole or slot extending through the said pad.

15. An assembly as claimed in claim 2, or in any one of claims 4 to 12, when mounted as a friction pad assembly in a disc brake.

16. An assembly as claimed in claim 2, or in any one of claims 4 to 12, when mounted as an indirectly actuated friction pad assembly in a reaction type disc brake, the brake having a caliper which straddles the braking disc, the caliper having an outboard limb which has fingers which extend generally radially of the braking disc and engage the backing plate of the indirectly actuated friction pad assembly on each side of the sounding box.

17. A friction element assembly for use in a vehicle brake, constructed and arranged substantially as hereinbefore described and as illustrated in the accompanying drawings.