Patent GB-1344062-A (GB)
Title: Lining wear indicators
IPC: F16D66/02
Filed: 1971-06-21
Abstract: 1344062 Indicating brake-lining wear GIRLING Ltd 21 June 1971 [26 June 1970 25 Sept 1970 16 Jan 1971] 31004/70 45697/70 and 2210/71 Heading F2E [Also in Division H1] In a vehicle brake lining wear-indicator where relative movement, greater than a predetermined amount, of two brake parts demonstrates the need for adjustment or replacement, a pair of separable electric contacts are resiliently biased together, and apparatus associated with the contacts extends therefrom for co-operation with the parts when the indicator is fitted in a brake, so that the apparatus applies a force tending to separate the contacts against the bias when the movement is greater than the predetermined amount. The indicator of Figs. 2, 3 is intended to be located with one end (loop 23 or hole 21) connected to one shoe of a drum brake and the other end connected to either the other shoe or the backing plate. A contact 27 is fixed in an insulator at one end of a rod 23, the rod being looped at 23 and then extending through a hole 25 in each of two cranked portions 24 of a plate 20 having the hole 21. A contact 28 is similarly fixed to one end of a shorter, straight, rod 31 which extends through the other two holes 25 in the cranked portions 24. Terminals 36 are secured to the respective contacts and connected in an external circuit. The contacts are normally urged together by a spring clip 29. An adjustable stop 35, which when compressed is freely slidable on rod 31 and which when allowed to expand grips the rod, is located between the cranked portions 24 and acts as a lost-motion device in co-operation with the left-hand cranked portion 24, defining the maximum permissible wear. When such wear is exceeded the contacts are separated, the circuit is thereby altered, and a warning indication is given. In Fig. 5 two contacts 52, 53 are normally bridged by a contact 54 located by ball 56 in aperture 57 in a resilient insulator 55 urged leftwards by an elastomeric compression spring 60. A rod 61 connected to insulator 55 is provided with apertured plate 62 and lost-motion stop as before. In Figs. 8 and 10 a limit switch 94 is secured to a cover-plate 89 mounted on a spot-type disc brake. Two contacts 98 are located in an insulating housing 97 with an insulating member 99 between them. A U-shaped conductive strip 100 has each arm in contact with one of the contacts 98 and the arms are bent back to accommodate feelers 102 the outer ends of which are insulated from strip 100. The spacing between the feelers 102 in Fig. 8 is equal to the thickness of disc 85 plus twice the minimum permissible thickness of linings 82 on brake pads 81. When either feeler is deflected inwards, the corresponding limb of strip 100 is urged away from the adjacent contact 98 and the circuit is altered as before. In a simple circuit, (Fig. 6, not shown), four sets of normally-closed contacts (as previously described)-one for each brake-are arranged in series with a fuse link and the heater coil of a thermal relay between an earth connection and one terminal of the motor battery, the other terminal being earthed. In parallel with the first component assembly are located, in series, the relay contacts and an indicator lamp. When all the wear indicator contacts are closed and the ignition switch is closed, the lamp initially lights, but goes out when the heater coil causes the relay contacts to separate. When excessive brake wear occurs or the fuse blows, the heater is de-energized, permitting the relay contacts to relight the lamp. Brake wear is indicated discontinuously (at each actuation). If an indicator is associated with a wear-adjuster, the occurrence of maximum adjustment is indicated by a continuous signal. More-sophisticated circuits incorporating transistors are described (Figs. 11, 12, not shown).