GB2221269A - Wear indicator for friction lining - Google Patents

Abstract

An indicator which signals wear of a friction lining, e.g. for a brake or clutch, has a dead-ended tube 14 embedded beneath the surface of the friction material. When a wall of the tube is breached by wear, gas escapes, triggering a signal that it is time to replace the lining. The tube may be coiled within the friction lining. <IMAGE>

Description

Friction Pad ear Indicator The invention relates to an indicator or alarm which gies a physically sensible signal when a component subject to wear has been sworn past an acceptable limit. ore specifically, the indicator is described with reference to a wear indicator for a friction pad in a brake or clutch.

The friction material used as the lining of a brake or clutch will necessarily wear during use and will eentually require replacement. Failure to replace a orn lining can result in damage to machinery and even to dangerous brake or clutch failure.

Various prior art arrangements to indicate that friction lining has become worn so as to require replacement have employed electrical or electronic sensing means, such as electrical contacts embedded in the friction material.

These systems have the major drawback that thep can cause sparking, for example, when the come into contact with a brae disc surface, which can be hazardous. Spavin in an atmosphere of fine particles, or flammable vapour, can result in fire or explosion.

It would be desirable to provide a wear indicator or alarm which avoids the drawbacks of prior art systems.

The friction lining wear indicator of the present invention advantageously empios means for sensing the pressure of air or some other gas such as carbon dioxide fed under pressure to the interior of the friction lining to indicate when the lining is read for replacement.

Gas under pressure is fed to a passage within the bod of the friction material, the passage is closed within the material so that during normal operation the gas pressure remains constant. When the friction lining has worn down to a predetermined thickness, a wall of the gas passage is breached, allowing the escape of gas and a consequent reduction in gas pressure which is sensed b a suitable pressure sensor, triggering an alarm signal. The friction lining is then replaced.

Since any electrical components can coneniently be located remotely from the brake or clutch there is no danger of fire or explosion resulting from the triggering of the alarm.

Fig. 1 shows a friction lining wear indicator according to the invention as employed in conjunction with a friction pad of a disc brake.

Fig. 2 is a view in perspective of the wear indicator of Fig. with parts broken away to show internal structure.

Fig. 3 is a cross sectional view of the friction pad of Figs. 1 and 2.

Fig. s shows the same view as that of Fig. 2 after the friction pad has worn down to the point at which replacement is called for.

Fig. 5 is a view in cross section similar to that of Fig. 3 but with the friction material worn down to the point at which the wear indicator is activated.

Fig. 6 shows an embodiment of the friction lining wear indicator applied to a friction pad which may be subjected to uneven wear.

Fig. f is a side view of the friction paid of Fig. 6 with dotted lines showing the location of the gas passage.

The friction lining wear indicator of the invention has applications to a great variety of devices in which parts are subject to wear and need replacement after a period of service. In Fig. 1 of the drawing the wear indicator is illustrated as employed in connection with a generally discshaped pad 10 held in position for frictional engagement with the disc 11 of a brake or clutch by means of screws 12. This application is merely illustrative and numerous other uses of the invention will suggest themselves to those acquainted with the art.

Embedded within the pad 10, as illustrated in Figs. 1is is tube 13 impermeable to the gas under pressure contained therein which is closed off at a tube end 14 within the pad a 10. The tube 13 can be suitably made of plastics material which is resistant to the temperaturesnenerated in the pad 10 as a result of frictional engagement with the disc 11 when urged into contact with the disc 11 b means illustrated generally at 15.

During operation of a friction coupling mechanism such as the braking device illustrated in the drawings, the tube 13 is supplied with air or das under constant pressure. As shown in Fig. 1 the tube 13 extends beyond the friction pad 10 to a Cas supply tube 16 to which the tube 13 is connected by a releasable connector 17.

The gas supply tube 16 is in turn connected to a source of gas through a pressure sensing deice (not illustrated in detail) housed in an alarm module 18, which is generally shown in Fig. 1. The alarm module includes means responsive to the sensing of a pressure drop in line 16 for activating a signal such as an audible or visible alarm.

The alarm module is illustrated as electrically powdered through cord 19. The alarm module can be located as far from the friction pad 10 as desired or required for safe and convenient operation.

Figs 2-5 show the operation of the wear indictor of the invention in a brake. In Figs. 2 and 3 a new pad 10 is shown in position. The tube or passage 13 is centrally located at the middle of the pad 10. halfway between the rear face of the pad 10 and the friction surface S of the pad. Of course, the location of the passage within the pad would in practice be located so as to indicate wear of the pad 10 to the minimum acceptable thickness at which pad replacement is in order.

Figs. 4 and 5 show the condition in which the thickness of the pad 10 has been reduced by frictional wear.

The friction surface S1 of the worn pad in Figs. 4 and 5 has exposed the passage 13 to the friction disc 11 and gas escapes from within the tube passage as illustrated in Fig.

5. This escape of gas triggers the pressure sensor because of a drop in gas pressure from the constant pressure ordinarily maintained in line 16 and the alarm goes off. It is time to replace the pad 10.

ost modern friction lining materials are molded into the desired shape and it will be understood that a pad or other lining element can be- molded within the tube 13 embedded in the lining material and extending outwardly therefrom to be connected as by the connector 17 of Fig. 1 to a source of gas the pressure of which is sensed during operation. Suitable manufacturing techniques for molding or otherwise forming a pad or other friction lining element with a tube embedded therein are known.

Fig. 6 illustrates a friction pad 20 similar in shape to the pad 10 but proided with a tube 23 which follows a sort of spiral path within the pad 23 to dead end at 24 near the centre of the pad 20. This embodiment of the invention allows for uneven wear on the friction lining to trigger the alarm when the tube 23 is breached anywhere along its passage through the pad 23. The term spiral is used broadly to indicate a tube path which turns inwardly within the body of the friction lining to underlie a larger portion of the friction surface than the straight tube section shown in Figs. 1, 2 and 4. As in the previously described embodiment, the tube 23 extends beyond the pad 20 to a connector 17 and a supply line 16 for gas under pressure.

The alarm unit 28 is shown as haing a speaker grill 29 for an audible alarm and lights 30, 31 for indicating need for friction liner replacement. Any other suitable alarm indicating means could, of course, be employed.

Fig. 7 simply illustrates the tube 23 in dotted lines in a side iew of the pad 20.

Those acquainted with the art to which the invention applies will realise various applications, modifications, choices of materials, etc. which hae not been set forth in the foregoing description of a presently preferred embodiment of the invention.

Claims (13)

CLAIMS:

1. lining for a brake or clutch formed of friction material which is subject to wear during use and which has an internal passage provided with gas under pressure and means for sensing the escape of said gas and for triggering a signal when the escape of gas from said passage is sensed.

2. The lining of claim 1 wherein said passage is formed b a tube embedded within the friction material.

3. The lining of claim 2 wherein said tube has a closed end within the friction material and another end outside the friction material connected to a source of gas under pressure and to said means for sensing the escape of gas.

4. The lining of claim 1 wherein the means for sensing the escape of gas includes a pressure sensor.

An at arrangement for indicating wear on a part subject to wear comprising a tube embedded within and terminating within said part and extending outwardly to a source of gas under pressure so that wear of the part will open the tube and permit the escape of gas therefrom.

6. The arrangement of claim 5 wherein said tube is also coupled to gas pressure sensing means for triggering a signal upon opening of the tube.

I. The arrangement of claim 6 wherein the signal is audible.

8. The arrangement of claim 6 wherein the signal is visible.

9. A pad of friction material haing a tube embedded beneath a face of the pad which is subject to wear, which tube is supplied with gas under pressure.

10. The pad of claim 9 wherein said tube is formed of a plastics material that is resistant to high temperatures to which the pad is subjected during use.

11. The pad of claim 9 wherein the tube follows a spiral path within the friction material.

12. X lining for a brake or clutch, substantially as hereinbefore described and with reference to the accompanying drawings.

13. .A pad of frictional material, substantially as hereinbefore described and with reference to the accompanying drawings.