Patent GB-1303541-A (GB)
IPC: F16D55/224
Filed: 1970-10-05
Abstract: 1303541 Spot-type disc brakes; indicating friction lining wear AISIN SEIKI KK 5 Oct 1970 [4 Oct 1969 1 Nov 1969] 47172/70 Heading F2E The Specification describes various arrangements to indicate wear of the friction linings 20, 25 of a disc brake assembly to a point where replacement is necessary, wherein operation of an electrical switch actuating means 32 causes opening or closing of a contact 32<SP>1</SP> thereby causing a warning lamp 44 to be lit, the means 32 being operated other than by the brake disc 10 to avoid damage thereto. The brake assembly comprises a piston housing 16 wherein two pistons 17, 18 are slidable to act on backing- plate 19 of lining 20 directly and on backing- plate 24 of lining 25 through a reaction transfer plate 22. The backing-plates 19, 24 are supported on two parallel pins 28, 29 and one end of each pin 28 or 29 is fixed to the piston housing 16 by means of clip 30 or 31 and the other end of each pin 28 or 29 is bent outwardly and is secured to torque counteracting arms 26, 27, respectively. As shown in Figs. 1, 2, 3 the means 32 comprises a tubular insulating member 33 which is movably fitted in a stepped hole 34 of the backing-plate 24 and a switch shaft 36 biased by a spring 39 towards the disc 10 is held in the tubular member 33 by a set-screw 43. A metal plate 40 connected to an electrical terminal 41 is tightly fitted in a groove 42 of the insulating member 33. When the linings 20, 25 have worn down the head 37 of the switch shaft 36 makes contact with the backing-plate 19 and the shaft 36 and member 33 are urged to the right to break electrical connection between plate 40 and backing-plate 24 and thereby turn off the current from terminal 41 through plate 40, backing-plate 24 and pins 28, 29 to light an indicating lamp 44. The lamp 44 is included in a circuit shown in Fig. 7 which is applicable to the embodiments of Figs 1-6 and 8-10. The circuit includes a battery 46 and a transistor 48 which upon electrical contact 32<SP>1</SP> opening is caused to conduct and thereby light the lamp 44. The circuit also includes an ignition switch 48 and when an open terminal 49 and starter motor terminal 51 are connected the lamp 44 is lit; the operator can thereby inspect the condition of the circuit prior to operation. In the embodiment of Fig. 4 (not shown), a tubular insulating member (133) is mounted around the pin 28 and upon excessive wear of the linings a metal plate (140) on the member (133) is forced out of contact with the backing- plate 24 to open means 32. In the embodiment . of Fig. 5 (not shown), an insulating shaft (233) is screwed to the backing-plate 19 and the shaft (233) projects through a hole (234) in the backing-plate 24 to act on a metal plate (240) to open the means 32. In the embodiment of Fig. 6 (not shown) an insulating member (302) is fitted into a groove on the pin 28 and comes into contact with a metallic contacting piece (340) attached to backing-plate 24 to thereby open means 32. The embodiments of Figs. 9-12 show the means 32 fitted into the piston housing 16 to protect it from damage. As shown in Fig. 9 an insulating member 433 extends from a bore in the piston housing 16 and through the backing-plate 19. A contact member 440 has contact with a terminal 441 and the means 32 is opened when the linings wear sufficiently by movement of the contact member 440 from bore 405 into a larger bore 404. In the embodiment of Fig. 10 (not shown) a shoulder (508) of an insulating member (533) is moved by the backing-plate 19 to open the means 32. The embodiments of Figs. 11 and 12 utilize the circuit of Fig. 13 (not shown), wherein closure of a contact (32<SP>1</SP>) causes warning lamp (44<SP>1</SP>) to light. As seen in Fig. 11, a contactor 640 is brought into contact with a metallic cover 607 to close the means 32. In the embodiment of Fig. 12 (not shown) an electrical contacting member (740) is brought into contact with a metallic core (707) to close the means 32.