GB1342002A - Self-adjusting brakes - Google Patents

Abstract

1342002 Self-adjusting brakes; external shoe drum brakes; brake actuators COAL INDUSTRY (PATENTS) Ltd 20 June 1972 [29 June 1971 5 Nov 1971] 30390/71 and 51591/71 Headings F2E and F2F A self-adjusting brake especially for a rail vehicle comprises two shoe assemblies mounted for movement relative to the vehicle chassis, apparatus associated with the shoe assemblies for allowing movement in the brake application direction but restricting brake release to a preselected amount and a spring-applying, fluidpressure-releasing operating mechanism (including a piston and cylinder arrangement and a connector device) interconnecting the shoe assemblies, the connector device having mutually threaded components which constitute a slackadjustment mechanism. As shown in Fig. 3, shoes 2, 4 are each pivotable about one of two spigots 9 provided in a fixed mounting plate 6. The upper end of shoe 2 is attached to the cylinder 22 of an applying and releasing arrangement 20, while the upper end of shoe 4 is attached by a peg 28 to the body 27 of a wear-adjusting assembly 26. Brake application is by a compression spring 23 which urges cylinder 22 to the right and piston 21, attached by rod 16, central bracket 15 and rod 17 to assembly 26, to the left. Brake release is by application of pressure fluid, e.g. compressed air (e.g. when a locomotive is coupled to the rail vehicle on which the brake is mounted) to port 24. Release movement of shoe 2 is limited by the thickness of a resilient outer sleeve 49 on a pin 48, which pin extends between front and back triangular plates 51 (which engage the shoe-see below) and is engaged by a downwardly-spring-loaded wedge 44. Pin 48 is guided by four horizontal guide members 50 extending from a fixed plate 42. Self-energizing action occurs on brake application when wheel 10 is rotating clockwise, as follows. The lower of two thrust pins 53, extending from shoe 2 and engaging grooves 52 in plates 51, tends to rotate plates 51 about pin 48 as fulcrum, and since pin 48 is constrained by wedge 44 the plates urge shoe 2 towards the wheel. Shoe 4 is similarly mounted, and limited release movement and self-energizing action occur with it. Analogous self-energizing action occurs with both shoes on counter-clockwise rotation of wheel 10. Wear-adjustment.-The end of rod 17 has a multi-start coarse screw thread engaging a nut 30 with coned face 32; associated with the nut are a bearing 31, a thrust washer 33 and a compression spring 34. Rod 17 is freely slidable through a cross bore 29 in peg 28. On brake application, (rod 17 moving to the left), the nut 30 is prevented from rotating by contact with body 27, but on brake release, any excess movement beyond the limited movement allowed to the shoes is accounted for by rod 17 moving nut 30 to the right and the nut, now freed from body 27, rotates on rod 17 the requisite amount. In Fig. 4 the slack-adjusting means is incorporated with the piston and cylinder device, and in this embodiment the nut 170 is moved in slack-take-up-direction (i.e. to the right), when necessary, on brake release, by the pressure of the brake-releasing air admitted at 180. Limitation of release movement of each brake shoe is effected by a pivoted cam 150, and a resilient sleeve 148 on a pin 146 at the end of a lever 144 attached to the shoe.