GB1341549A - - Google Patents

Abstract

1341549 Service and mechanical shoe-drum brakes; slack adjusters GIRLING Ltd 19 April 1971 [30 Jan 1970] 3374/71 Divided out of 1341548 Addition to 1199191 Heading F2E An internal shoe-drum brake comprises a mounting such as backing plate 12, Fig. 1, a pair of opposed arcuate friction elements 11 carried from the backing plate, e.g. by holddown spring assemblies 13, Fig. 3, pull-off springs 14 biasing the friction elements towards each other, a torque-absorbing means 15, Fig. 1, between one pair of element ends, an actuator 16 between the other pair of element ends, a strut 20 to establish a controlled spacing between the elements and comprising screwengaged parts 24, 26, part 26 having ratchet wheel rotating means on its exterior arranged for elongation of the strut, a rocker arm 30, Fig. 1, having the lower end pivotal but longitudinally located relative to the strut and the other end pivotal (at 101, 29) with one of the friction elements but located for movement with it, and an arm 34 movable by the rocker arm (and integral with or attached to it) and carrying a pawl 36, Figs. 2 and 3, for engagement with the ratchet wheel to cause rotation of the ratchet wheel when the actuator is operated and the distance between the friction elements is excessive. As shown, a lever 28 for actuation by a brake cable, for example, is pivoted at 29 to the righthand shoe 11 and the rocker arm 30 is pivoted at 100 to this lever but also has a slot 101 which fits over pivot 29. The strut part 24 with exterior thread is slidable in a tubular part 25 against which abuts the ratchet-wheel part 26, which is threaded on part 24. The lower end of rocker arm 30 is held in contact with the end of part 25 by a spring 32. Slotted end 22 of part 26 engages lever 28 only, Fig. 3. On operation of actuator 16, pivot 29 and the upper end of lever 28 move to the right, Fig. 1, while spring 32 holds the lower end of the rocker arm against the strut, and maintains the strut in contact with the left-hand shoe. Thus rocker arm 30 pivots about pivot 100, carrying with it the pawl-carrying arm 34. When the separation between the shoes is excessive, arm 34 will cause the strut to extend by rotating the ratchet wheel 26, this action occurring whilst the brake is being applied. When the strut 20 has an axial compressive load imposed on it, either by the pull-off springs 14 during brake-release, or by the lever 28 during actuation by it, the friction between parts 24, 26, prevents any rotation of part 26. Preferably the left-hand shoe is the leading shoe. In the modification of Fig. 5, the strut has two exteriorly-threaded parts 52, the left one of which is pivoted to the leading shoe at 56, and the right one of which has a hole in it which engages a spherical projection 54 of rocker arm 30. The threads are opposite-handed and are engaged by a ratchet wheel part 26B. The pawl-carrying arm 34A is a resilient member movable by the rocker arm. Spring 32 is rendered unnecessary by connection 54. In the modification of Fig. 4 (not shown, similar to Figs. 1 to 3), the lower end of the rocker arm is pivoted to the strut and the upper end abuts against the web of the right-hand shoe for sliding pivotal movement. The pawlcarrying arm is biased by a torsion spring in place of spring 32.