GB1507550A - Internal shoe drum brakes - Google Patents

Abstract

1507550 Adjusting drum brakes for wear GIRLING Ltd 21 Sept 1976 [13 Oct 1975 10 Nov 1975] 41879/75 and 46422/75 Heading F2E In an automatically adjustable drum brake, thermally responsive means are interposed between one shoe and a shoe movement sensing element and is operative to increase the shoe movement required to effect adjustment as the brake heats up. As shown in Figs. 1 and 2, shoe movement is sensed by a bell-crank lever 15 whose teeth 16 are urged into engagement with pinion 7A by spring 10. An arm 17 of the lever projects with clearance into a slot in shoe 1 and a wedge 31 on the end of a bimetallic strip 30 projects into the slot to a greater or lesser extent depending on brake temperature so that the shoe movement necessary to take up the clearance, and hence effect adjustment, is greater at higher temperatures. The wedge may be stepped so as to have incremental rather than progressive effect and the strip may be pivotable under the action of thermally responsive washers to remove the wedge completely from the opening at a predetermined temperature; this may be effected with a snap action (Figs. 10-14, not shown). In Fig. 4, the bimetallic element 32 constitutes a spring acting on arm 17 in opposition to spring 10. In normal operation the strip 32 is deflected in the initial stages of shoe movement until it is sufficiently stressed to overcome spring 10 and rotate the lever. As the brake heats spring 32 moves away from arm 17 increasing the shoe movement required for adjustment. In Fig. 6, the strip is replaced by an arched plate 33 of invar metal anchored at each end 34 to the shoe and with initial clearance between it and arm 17. This clearance increases due to differential expansion of shoe and plate. The arrangement is also load-sensitive in that the plate tends to straighten due to brake actuator force straining the shoe. Alternatively (Figs. 8 and 9, not shown) an invar strut may determine the angular position of a lever which is pivoted to the shoe and has its end adjacent the arm 17. Specifications 1,405,094 and 1,410,514 are referred to.