GB2038431A

GB2038431A - Arrangement for Indicating the Wear of a Brake Lining

Info

Publication number: GB2038431A
Application number: GB7937939A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1978-11-04
Filing date: 1979-11-01
Publication date: 1980-07-23
Also published as: FR2440493A1; IT7969145A0; IT1119565B; GB2038431B; DE2847911A1

Abstract

The arrangement has two conductor loops 39 embedded in a or a respective brake lining 57 and arranged to come into electrical contact with a or a respective brake element 6 (for example, a brake disc or drum) when the brake lining has become worn to a predetermined extent, when electrical contact occurs, an indicator e.g., lamp 24 is operated to warn of impermissible wear of the brake lining and with a view to reducing current consumption and enabling the arrangement to be easily reset each conductor loop is in series connection with resistors 2,4 and 8, 10 in a respective detector circuit, the detector circuits being in parallel with each other and each providing an input 11,12 to a comparator circuit 13 which responds to one of the loops contacting element 6 or being interrupted. A change in the comparator output is stored by a memory element 19 which can be manually reset, the output of the memory element 19 serving to operate the indicator lamp. As shown comparator circuit is a differential amplifier 13 and memory element is flip-flop 19. <IMAGE>

Description

SPECIFICATION Device for Indicating the Wear of a Brake Lining The invention relates to an arrangement for indicating the wear of a brake lining of a vehicle.

A known device of this kind comprises a closed circuit containing two conductor loops embedded in different brake linings and connected in series to a relay winding and a fuse. The conductor loops are so arranged that, when a brake lining is worn to the maximum permissible extent, the corresponding conductor loop comes into electrical contact with the brake element (brake disc, brake drum) which is earthed. When this occurs, the relay winding is short-circuited and, as a result, the fuse is overloaded so that it is destroyed. In this manner, the relay winding becomes dead and an indicator lamp, which is supplied via the make contact of the relay, is illuminated.

Although this known device has the advantage that the warning indicator lamp is permanently illuminated in response to wear in a brake lining, the current consumption of the circuit is relatively high. In addition, the replacement of a destroyed fuse is awkward and expensive. Moreover, when conventional fuses are used, it is also not possible with the known device to ensure a response in the case of very brief contact between the conductor loop and the brake element.

An object of the present invention is to provide a device which enables the disadvantages mentioned above to be avoided while requiring little circuitry and having a reliable mode of operation.

The present invention provides an arrangement for indicating the wear of a brake lining which, on braking, is urged against a brake element, the arrangement comprising two detector circuits which are connected in parallel with each other and each of which contains a conductor loop adapted for embedding in a brake lining to form an electrical contact with an associated brake element when a predetermined wear of the lining has been reached, and a warning device operable to respond to a disruption of one of the detector circuits, the warning device including a comparator circuit having two inputs each of which is connected to a respective one of the detector circuits.

By way of example, two embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows, diagrammatically, an embodiment of the invention for a brake having two brake linings and Figure 2 shows, diagrammatically, an embodiment of the invention for monitoring the two brakes of one axle of a vehicle.

The drawings show, in Figure 1 an embodiment of the invention in which a respective one of two conductor loops 3, 9 is embedded in each of the two brake linings 5, 7 of a wheel brake. The two brake linings 5 and 7 are so arranged that, for the purpose of braking, they can be urged against a brake element constructed as a brake disc 6.

The conductor loops 3 and 9 extend so far into the brake linings 5 and 7 that, when the maximum permissible wear of the lining has been reached, one or other of the conductor loops comes into contact with the brake disc 6. When this occurs the brake disc 6, being electrically earthed, thus forms, at least for a short period, an electrical connection between earth and the relevant conductor loop. The circuit shown in Fig.

1, which is described in detail below, serves to evaluate this electrical connection (which represents a signal that the maximum permissible wear of a lining has been exceeded) in such a manner that an indicating element constructed as a lamp 24 then lights up.

The circuit shown consists substantially of two closed circuits 2, 3, 4 and 8, 9, 10, together with a warning device having a comoarator circuit constructed as a differential amplifier 13, a memory element constructed as an "RS" flip-flop 19, an amplifier 22 and the said lamp 24.

The first closed circuit, which is assigned to the brake lining 5, consists of two resistors 2 and 4 which are connected in series to each other and arranged between the live terminal 1 of an operating voltage source and earth, and between which resistors the conductor loop 3 is arranged.

Correspondingly, the second closed circuit, which is assigned to the brake lining 7, consists of the resistors 8 and 10 and the conductor loop 9. The connection point between the resistor 2 and the conductor loop 3 is connected to a first input 11 of the differential amplifier 13, whereas the second input 12 of the differential amplifier 13 is connected to the connection point between the resistor 8 and the conductor loop 9. The output 14 of the differential amplifier 13 is connected to the "R" input 1 8 of the memory element (flip-flop) 19 and the arrangement, which is shown merely in principle is so constructed that the input 18 of the flip-flop is set by the output signal of the differential amplifier 13 if a predetermined voltage difference occurs between the two inputs 11 and 12 of the differential amplifier 13.

The "tri" output 20 of the flip-flop 19 is connected to the input 21 of the amplifier 22, the output 23 of which amplifier supplies the said lamp 24. The "S" input 1 7 of the flip-flop 1 9 is connected, via the series connection consisting of a button 1 5 and a protective resistor 16, to the terminal 1 of the operating voltage source, so that the "S" input 1 7 can be energised by pressing the button 1 5.

The circuit described operates in the following manner. As long as the brake linings 5 and 7 are not excessively worn (with a corresponding evaluation of the resistance values in the parallelconnected closed circuits 2, 3, 4 and 8, 9, 10) signals of equal magnitude or approximately equal magnitude are present at the inputs 11 and 12 of the differential amplifier 13, so that no setting signal for the input 1 8 of the flip-flop 19 appears at the output 14 of the differential amplifier 13. It is assumed that the flip-flop 1 9 has previously been switched over via the input 17 by means of the button 1 5 in such a manner that a "Low" signal appears at the output 20.The amplifier 22 is so constructed that this "Low" signal at the output 20 of the flip-flop 1 9 does not cause the lamp 24 at the output 23 of the amplifier 22 to light up.

If, after the maximum permissible wear of the lining has been reached, one of the conductor loops 3 and 9 comes into contact with the brake disc 6 (and hence with earth) then a signal appears at the output 14 of the differential amplifier 13 and switches over the flip-flop 19 in such a manner that the output 20 is set and produces a "High" signal. This signal causes the amplifier 22 to make the lamp 24 light up, and the danger of impermissible wear of the lining is therefore indicated.

Corresponding behaviour, indicating a fault in one of the brake linings 5 and 7, also occurs in the described circuit when one of the conductor loops 3 or 9 is interrupted. Since, in this circumstance, there is indeed a danger regarding the reliable operation of the wheel brake 5, 6, 7, the actuation of the lamp 24 which then occurs is very advantageous.

Since the warning device having the differential amplifier 13 has relatively high input resistance even when customary commercial components are used and responds even to very small and brief difference signals at the inputs 11 and 12, it is advantageously possible so to construct the closed circuits, 2, 3, 4 and 8, 9, 10 that they are very highly resistive. In this manner, the current consumption of the described circuit can be made comparatively low.

The circuit described can easily be re-set by pressing the button 1 5 once impermissible wear of the lining or a defect in the brake lining has been indicated.

It is also possible to assign the two closed circuits 2, 3, 4 and 8, 9, 10 to respective brake linings belonging to different wheels of a vehicle axle, rather than to brake linings in a single wheel.

An arrangement of this kind is shown in Figure 2, in which the same reference numerals as in Figure 1 denote the same components having the same functions.

The conductor loop 3 in the arrangement shown in Figure 2 is embedded in a brake lining 25 which, together with a brake disc 26, forms the brake of, for example, the left wheel of a vehicle axle. The conductor loop 9 on the other hand, is embedded in a brake lining 27 which, together with a brake disc 28, forms the brake of the right wheel of the same vehicle axle. The arrangement functions in exactly the same manner as that shown in Fig. 1 and has the advantage inter alia that the brakes of two wheels are monitored simultaneously.

It is also possible to arrange the two conductor loops of the two closed circuits in a single brake lining. This is advantageous if, in one brake, only one brake lining is to be monitored or if the brake lining being monitored is to be monitored expressly at several points.

The brake elements, shown constructed as brake discs 6, 26, 28 in the drawings, can also be constructed as brake drums or the like. It is also possible to use as the memory element, instead of the flip-flop 1 9 described, any other suitably electrical or mechanical memory elements.

Accordingly, the indicating element shown in the drawings as a lamp 24 could alternatively be completely or partly mechanical.

The embodiments of the invention described above have the advantage that, without any impairment of the very rapid response, relatively high resistance closed circuits can be used, so that the current loss is very slight. After too great wear of the brake lining has been indicated it is not necessary to replace any components such as, for example, a fuse.

Claims

1. An arrangement for indicating the wear of a brake lining which, on braking, is urged against a brake element, the arrangement comprising two detector circuits which are connected in parallel with each other and each of which contains a conductor loop adapted for embedding in a brake lining to form an electrical contact with an associated brake element when a predetermined wear of the lining has been reached, and a warning device operable to respond to a disruption of one of the detector circuits, the warning device including a comparator circuit having two inputs each of which is connected to a respective one of the detector circuits.

2. An arrangement according to claim 1, in which the conductor loops are each embedded in different brake linings.

3. An arrangement according to claim 2, in which the conductor loops are embedded in the brake linings of a single wheel.

4. An arrangement according to claim 2, in which the conductor loops are embedded in brake linings arranged in different vehicle brakes of one vehicle axle.

5. An arrangement according to any one of the preceding claims, in which the comparator circuit is a differential amplifier.

6. An arrangement according to any one of the preceding claims, in which each closed circuit includes a series connection consisting of two resistors between which resistors the relevant conductor loop is arranged.

7. An arrangement according to any one of the preceding claims in which the warning device includes a memory element for storing a change in the output signal of the comparator circuit.

8. An arrangement according to claim 7, in which the memory element is a flip-flop.

9. An arrangement according to claim 7 or 8, including a manually-operable device for resetting the memory element.

10. An arrangement according to any one of claims 7 to 9, in which the warning device includes an amplifier which is connected to the output of the memory element to supply an indicating element.

11. An arrangement for indicating the wear of a brake lining, the arrangement being substantially as described herein with reference to, and as illustrated by, Fig. 1 or Fig. 2 of the accompanying drawings.