GB612360A - Improvements in or relating to adjusting means for brake shoes - Google Patents

Abstract

612,360. Compensating for wear in shoe brakes. JENKINS, S., and CARDIFF JUNCTION DRY-DOCK & ENGINEERING CO., Ltd. May 21, 1946, Nos. 15342 and 27711. [Class 103 (i)] In automatic adjusting devices for shoe brakes of the type in which an adjuster acting on the anchored ends of the shoes is coupled to the shoe actuating means through mechanism including a lost-motion device and a one-way clutch so as to be operated during the application of the brake if the shoe-drum clearance exceeds a predetermined amount, a resilient device is included in the coupling between the shoe actuating means and the adjuster which allows continued movement of the shoe actuating means if the adjuster resists operation due to the reaction caused by the application of the shoes to the drum. This avoids over- .straining of the mechanism and prevents overadjustment of the shoes if the drum expands due to heating caused by a prolonged brake application. In one form, Figs. 3, 4 and 5, one tappet 3 of the shoe actuating means 2 engages a pin 19 on a disc crank 18 rotatable on the back-plate against the action of a spiral spring 35, a second pin 20 on the crank passing through a clearance hole 21 in a sleeve 22 slidable on a rod 23 against the action of a spring 25. The rod is adjustable in length and its end is connected by a ball joint to a split ring 32 clamped to the driving member 15, Fig. 4, of a one-way ball or roller clutch, the driven member 13 of which is integral with one of a pair of plungers 7 on which the ends of the shoes anchor. The plungers, Fig. 3, are formed respectively with left and right hand threads engaging corresponding threads in a housing 6 secured to the back-plate, and one plunger is formed with a driving tongue 11 slidable in a slot 12 in the other plunger. The clearance between the pin 20 and hole 21 corresponds to the desired shoe-drum clearance, and, if this is exceeded due to wear, the movement of the sleeve 22 is transmitted by the spring 25 to effect rotation of the plungers. If rotation of the plungers is resisted by the reaction of the shoes, the spring yields to allow further movement of the tappets 3 without corresponding rotation of the plungers. Manual adjustment of the shoes is effected by slackening the ring 32 and rotating the plungers by means of a tommy-bar inserted in holes 34. In a second form, Fig. 7, the rod 23 is coupled to an arm 38 driving the outer member 15 of a one-way ball or roller clutch, the inner member 13 of which is integral with a spindle 41 coupled by a pin 44 to a hollow shaft 42 integral with a crown-wheel 43 meshing with teeth 46 formed on angularly-disposed plungers 47. By withdrawing the pin 44, the crown-wheel can be slid back out of engagement with the teeth on the plungers to enable manual adjustment of the shoes to be effected. The crown-wheel may operate a cam or cone actuating slidableplungers. According to the first Provisional Specification, the adjuster is operated by the shoe actuating means through links and bellcrank levers or a Bowden cable, a resilient device and a unidirectional device having a predetermined amount of backlash corresponding to the desired shoe-drum clearance, this backlash being taken up by a spring when the shoes are retracted. According to the second Provisional Specification, the adjustment may be effected during the release movement of the shoes. Specification 565,088 is referred to in the second Provisional Specification.