Patent GB-1302928-A (GB)
IPC: B60T17/22
Filed: 1970-09-21
Abstract: 1302928 Indicating; shoe drum brakes; actuators; slack adjusters BENDIX WESTINGHOUSE Ltd 11 Aug 1971 [21 Sept 1970 27 Nov 1970] 44870/70 and 56418/70 Headings F2E and F2F A two-part electric circuit for indicating whether the brakes of a vehicle are being operated and also whether there is excessive wear in any of these brakes has in its first part a normally open switch 3 which is closed when the brakes are operated by a main controlling means to illuminate a bulb 7 and has in its second part a series of normally closed switches 9 respectively associated with the brakes which switches 9 will open if the respective brake suffers excessive wear to cause de-energization of a winding 11 of as solenoid 12, previously energized by closure of switch 3, and consequent movement of an armature 14 and an associated two part shutter 15 from a position in which a part 17 of one colour (e.g. green) is aligned with the bulb 7 to a position in which a second part 16 of another colour (e.g. red) is aligned with the bulb 7. Hence illumination of the bulb 7 indicates that the brakes are operated and the colour of the light emitted by the bulb 7 indicates whether there is excessive wear in any of the brakes. Fig. 4 illustrates a practical arrangement for the juxtaposition of the bulb 7 and the shutter 15, wherein they are mounted in a box 60 with a window at the front 62. The shutter 15 is carried on an arm 63 pivoted at 64 which is urged into the position shown by a spring 65 which is overcome by energization of solenoid 12. Fig. 1 shows a second normally open switch 20 in parallel with switch 3 which switch 20 may be used to test the circuit. Fig. 5 (not shown) illustrates a circuit suitable for a tractor-trailer vehicle wherein an additional circuit part (70) for the trailer incorporating normally closed switches (71) for the brakes of the trailer is added to the arrangement of Fig. 1 on the tractor a connection (72) normally out of circuit is brought into the tractor circuit when the tractor and trailer are uncoupled. The switch 3 may be a stop-light micro-switch closed by actuation of the foot pedal (30) of a master cylinder (31), Fig. 2, not shown. As seen in Fig. 3 a switch 9 is associated with a pneumatic actuator having a brake operating rod 46 operated by a diaphragm follower 41 engaging a diaphragm. The rod 46 is encircled by the normally closed switch 9 and excessive wear of the brake causes a roller 50 on the rod 46 to engage the rearward face of the switch 9 and open it. A spring 49 protects the switch 9 against damage by ultra-excessive movement of the rod 46. In the embodiment of Fig. 6 the switch 9 is mounted on a member 75 mounted on the vehicle chassis and has a rod 74 passing therethrough connected to a pneumatic actuator. The rod 14 is operable to move a lever 73 and thence a cam 71 which operates the shoes of a shoe drum brake. On the rod 74 collars 77, 78 trap between them abutments 79, 80 and the face 81 and of abutments 79 will cause opening of switch 9 upon excessive wear of the brake. In the embodiment of Fig. 7 a manual or automatic slack adjuster 90 is connected to a pneumatic actuator 91 and the lower part of the adjuster 91 is splined onto a splined shaft 94 by operation of which brake shoes are engaged with a drum 95. An arm 92 carried by the shaft 94 has a face 93 which opens the switch 9 on excessive wear of the brake shoes: with a manual adjuster opening of the switch 9 indicates the need for adjustment and with an automatic adjuster opening of the switch 9 indicates the limit or near-limit of the adjustment facility. The switches 9 of Figs. 6, 7 may be additional to the switches 9 of Figs. 1 and 5 to provide indication of failure of the connection between the actuator and the brake. A switch 9 may be arranged within a brake drum and operated by excessive movement of the shoes; a switch 9 could also be operated by excessive movement of the calipers of a disc brake. The switch 9 can also be a rotary switch attached to a lever 73 (Fig. 6) or slack adjuster (Fig. 7). The switches 9 can also be operated by rod, wire or fluid operated means which interconnect the brake with the switch