GB1591735A - Disc brakes - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO DISC BRAKES (71) We, ABEX PAGID EQUIPE MENT S.A., a French Body Corporate, of 9 Rue Klock, 92112 Clichy, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a disc brake having a warning system which is actuated in response to brake pad wear.

Disc brakes in motor vehicles are often fitted with a system permitting a warning to be given to the driver that the friction linings of the brake pads are reaching the end of their wear and that it is therefore necessary to replace them. The warning device may comprise, on the vehicle dashboard, a luminous warning signal which includes a lamp which lights up as soon as the friction lining has worn to a predetermined thickness.

According to the present invention, there is provided a disc brake comprising brake pads on opposite sides of a brake disc, each said brake pad comprising a support plate carrying a friction lining, and two electrical contacts each carried by a respective one of the two support plates and projecting towards the other plate, with the two contacts being in axial alignment one with the other, the contacts being located outside of the friction lining, at least one of said contacts being electrically insulated from earth, and both contacts forming part of an electrical warning circuit including a warning device, said circuit being closed to actuate the warning device upon inwards movements of said contacts over a predetermined distance as a result of a predetermined amount of pad wear.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a radial section, taken on line II of Figure 2, or a disc brake incorporating one embodiment of a pad wear warning system; Figure 2 is an axial section taken on line II-II Figure 1; Figure 3 is a fragmentary plan view of the brake of Figures 1 and 2; and Figure 4 is a section similar to Figure 1, but showing a second embodiment of a pad wear warning system.

In Figures 1, 2 and 3 there is shown a disc brake comprising a brake disc 1 which is disposed in known manner between two friction linings 2, 2a, fixed on metal support plates 3, 3a which are subject to the action of the control members of a hydraulic or pneumatic braking circuit.

Between the plates 3, 3a there is disposed a cross-shaped spring 4 which comprises a resilient arm which is bent downwardly at each end and resiliently biases the plates 3, 3a apart with a view to obviating friction between the linings 2, 2a and the disc when no pressure is applied to the control members of the braking circuit. The cross-shaped spring 4 is of metal and is earthed.

The resilient arm 4a is fixed on an arm 4b whose longitudinal axis is situated along the plane of symmetry of the brake disc 1, the opposed ends of the arm 4b being mounted on two parallel pins 5, Sa on which the support plates 3, 3a slide. This arm remains in a predetermined position between the opposed pads because it is centered in the brake caliper.

On the plates 3 and 3a there are fixed by means of insulating sleeve 7 contact members 6 each of which has an internal bore into which there is engaged a terminal pin 8 fixed at one of the ends of an insulated conductor wire 9 connected to one of the terminals 10 of an incandescent bulb 11, the other terminal 12 of which is connected to that of a source of electric current 13 whose other terminal is connected to earth 14. The contact members are in axial alignment one with the other.

Facing the contact members 6 is the arm 4b of the spring 4, which is earthed.

The distances x provided between the insulated contact members 6 and the adjacent edges of the arm 4b of the cross-shaped spring 4 correspond to a predetermined thickness of wear of the friction linings beyond which the linings should be replaced. When the friction linings are worn and their thickness has reduced by a distance x, the contact members 6 comes in contact with the arm 4b of the cross-shaped spring 4, this closing the electric circuit by earthing the contact members 6 to earth 14, which causes the supplying by the current source 13 of the pilot lamp 11 and its lighting which warns the user that it is necessary to replace the friction linings 2, 2a.

In the embodiment shown in Figure 4, the cross-shaped spring is omitted and contact members 6 and 15 are disposed on the metal plates 3, 3a in such a manner as to project by a greater distance than in the previous embodiment, particularly using extended portions 6a and 15a. In this case the distance x2 provided between the opposed faces of the contact members 6 and 15, which contact members are in axial alignment one with the other, corresponds to the total of the thickness of the two friction linings 2, 2a for a specific wear. The contact member 15 is connected to earth.

When the wear of the two linings 2, 2a corresponds to the distance xj2, the contact members 6 and 15 come into contact causing, as in the foregoing embodiment, the lighting of the pilot lamp 11, by earthing the contact member 6 due to its contact with the contact member 15.

In the embodiments particularly described, the contacts are located outside of the zone of the friction linings which avoids difficulties in manufacture which would arise if the contacts were to be mounted in holes drilled in the linings or if the contacts were to be moulded within the linings so as to engage the brake disc and thereby close the warning circuit, after a predetermined amount of wear.

WHAT WE CLAIM IS: 1. A disc brake comprising brake pads on opposite sides of a brake disc, each said brake pad comprising a support plate carrying a friction lining, and two electrical contacts each carried by a respective one of the two support plates and projecting towards the other plate, with the two contacts being in axial alignement one with the other, the contacts being located outside of the friction lining, at least one of said contacts being electrically insulated from earth, and both contacts forming part of an electrical warning circuit including a warning device, said circuit being closed to actuate the warning device upon inwards movements of said contacts over a predetermined distance as a result of a predetermined amount of pad wear.

2. A disc brake according to claim 1, wherein both of said contacts are electrically.

insulated from earth, a spring of cruciform shape is disposed between the support' plates, said spring having a resilient arm extending between the plates and applying a resilient bias acting in a sense to move the plates apart, and an arm extending in the plane of symmetry of the disc, this latter arm supporting the resilient arm, and being earthed whereby the circuit is closed by at least one of the contacts engaging the earthed arm in response to inwards movement of the brake pads as a result of pad wear.

3. A disc brake according to claim 1, wherein the plates are slidable on two parallel pins, and the opposed ends of the earthed arm are mounted on the pins.

4. A disc brake according to claim 1, wherein the other of said contacts is connected to earth, and the said circuit is closed by direct engagement between the two contacts in response to inwards movement of the brake pads as a result of pad wear.

5. A disc brake substantially as hereinbefore described with reference to Figures 1 to 3, or Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. contact members are in axial alignment one with the other. Facing the contact members 6 is the arm 4b of the spring 4, which is earthed. The distances x provided between the insulated contact members 6 and the adjacent edges of the arm 4b of the cross-shaped spring 4 correspond to a predetermined thickness of wear of the friction linings beyond which the linings should be replaced. When the friction linings are worn and their thickness has reduced by a distance x, the contact members 6 comes in contact with the arm 4b of the cross-shaped spring 4, this closing the electric circuit by earthing the contact members 6 to earth 14, which causes the supplying by the current source 13 of the pilot lamp 11 and its lighting which warns the user that it is necessary to replace the friction linings 2, 2a. In the embodiment shown in Figure 4, the cross-shaped spring is omitted and contact members 6 and 15 are disposed on the metal plates 3, 3a in such a manner as to project by a greater distance than in the previous embodiment, particularly using extended portions 6a and 15a. In this case the distance x2 provided between the opposed faces of the contact members 6 and 15, which contact members are in axial alignment one with the other, corresponds to the total of the thickness of the two friction linings 2, 2a for a specific wear. The contact member 15 is connected to earth. When the wear of the two linings 2, 2a corresponds to the distance xj2, the contact members 6 and 15 come into contact causing, as in the foregoing embodiment, the lighting of the pilot lamp 11, by earthing the contact member 6 due to its contact with the contact member 15. In the embodiments particularly described, the contacts are located outside of the zone of the friction linings which avoids difficulties in manufacture which would arise if the contacts were to be mounted in holes drilled in the linings or if the contacts were to be moulded within the linings so as to engage the brake disc and thereby close the warning circuit, after a predetermined amount of wear. WHAT WE CLAIM IS:

1. A disc brake comprising brake pads on opposite sides of a brake disc, each said brake pad comprising a support plate carrying a friction lining, and two electrical contacts each carried by a respective one of the two support plates and projecting towards the other plate, with the two contacts being in axial alignement one with the other, the contacts being located outside of the friction lining, at least one of said contacts being electrically insulated from earth, and both contacts forming part of an electrical warning circuit including a warning device, said circuit being closed to actuate the warning device upon inwards movements of said contacts over a predetermined distance as a result of a predetermined amount of pad wear.

2. A disc brake according to claim 1, wherein both of said contacts are electrically.

insulated from earth, a spring of cruciform shape is disposed between the support' plates, said spring having a resilient arm extending between the plates and applying a resilient bias acting in a sense to move the plates apart, and an arm extending in the plane of symmetry of the disc, this latter arm supporting the resilient arm, and being earthed whereby the circuit is closed by at least one of the contacts engaging the earthed arm in response to inwards movement of the brake pads as a result of pad wear.

3. A disc brake according to claim 1, wherein the plates are slidable on two parallel pins, and the opposed ends of the earthed arm are mounted on the pins.

4. A disc brake according to claim 1, wherein the other of said contacts is connected to earth, and the said circuit is closed by direct engagement between the two contacts in response to inwards movement of the brake pads as a result of pad wear.

5. A disc brake substantially as hereinbefore described with reference to Figures 1 to 3, or Figure 4 of the accompanying drawings.