Patent GB-507612-A (GB)
Title: Improvements relating to automatic slack adjusting devices for braking apparatus
IPC: B61H15/00
Filed: 1937-12-18
Abstract: 507,612. Compensating for wear in brakes. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd., KERSHAW, A. G., and LEECH, K. H. Dec. 18, 1937, No. 35099. [Class 103 (i)] One element of the screw-and-nut device of an automatic slack adjuster is adapted to be turned by a tool for resetting the adjuster and the tool receiving part is normally shielded by a member which when the tool is applied is moved against spring action to disengage the uni-directional clutch by which the screw-andnut device is normally operated. The link by which the clutch is operated is resiliently extensible and contractible to prevent damage to the adjuster such as may occur if the adjuster is not reset after the maximum automatic adjustment has been effected. As shown in Fig. 1, the adjuster 1 forms a link between a brake operating lever arm 32 and an arm 3 on the cam-shaft 4 of a drum brake. It comprises a tubular part 1 connected at 2 to the arm 3 and into the end 5 of which screws a rod 7 rotatable in a casing 6 which is connected to the arm 32 at 27. Longitudinal movement of the rod 7 in the casing 6 is prevented by a collar 8 on the rod. Rotation of the rod to effect the automatic adjustment is effected by a rotatable sleeve 24 carrying one member 23 of a ratchet clutch having radial teeth on one of its end faces which engage corresponding teeth on a sleeve 14 slidable on a squared part 12 of an extension 11 of the rod 7. Reverse rotation of the rod is prevented by a sleeve 20 having ratchet teeth which also engage the teeth on the member 14 and urged into engagement by a spring 18, rotation of the sleeve 20 being prevented by projections 21 thereon engaging slots in the casing 6. A link 30 is connected to the sleeve 24 at 25 and to a fixed point 28 and thus movement of the adjuster to the right in Fig. 1 when the lever 32 is operated to apply the brake effects rotation of the sleeve 24 and if, due to wear of the brake linking, the rotation is excessive, the clutch member 23 slips a tooth and during the return movement, the rod 7 is turned to reduce the slack. For resetting the adjuster, as when the maximum permissible adjustment has been effected, the end 16 of the rod 7, 11 is squared to receive a tool and normally this end is covered by a sleeve 17 under the action of the spring 20. When the tool is applied the sleeve 17 is moved to the left and moves the clutch member 14 to disengage it from the members 23, 20 to enable the rod 7 to be turned. To prevent damage to the adjuster if the sleeve 24 should become locked due to failure to reset the device, the link 30 comprises two telescopic parts so that it may be extended or contracted under excessive stress against the action of an interior interposed spring. In the arrangement shown, the adjuster is interposed between the arm 3 on the brake cam shaft 4 and one arm 32 of an operating lever which has two other arms 33, 34 which serve for connection to two independent operating means, for example, a thrust rod 35 from a fluid-pressure cylinder and a pull-rod 40 to a hand-lever. The rods 35, 40 have lost-motion connections to the arms 33, 34 comprising intermediate levers 36, 41 pivoted on the arms and arranged to bear on stops 39, 44 on the arms.