Patent GB-1473082-A (GB)
IPC: F16D65/08
Filed: 1974-05-14
Abstract: 1473082 Internal shoe-drum brakes; hydraulic braking systems AUTOMOTIVE PRODUCTS Ltd 14 May 1974 [1 June 1973] 26294/73 Headings F2E and F2F An internal shoe-drum brake has a single ended wheel cylinder 31 mounted between one pair of shoe ends 33, 34 and the piston 39 thereof acts to transmit brake applying thrust to a shoe 27 via a lever 38, arranged to pivot about a fulcrum, e.g. protuberance 43, afforded by the shoe 27 and to co-operate with a strut 46 which extends between the lever 38 and the other shoe 28 so that the brake applying thrust is also transmitted to the other shoe 28. The brakes described are for use on the front wheels 17 of a dual-circuit vehicle braking system and another single ended wheel cylinder 51 is mounted between the other pair of adjacent shoe ends 44, 54 and the piston 56 acts directly on shoe end 54-the cylinder 31 is connected to a respective branch 15 or 16 of one circuit and the cylinder 51 is connected to a respective branch 20 or 21 of the other circuit which other circuit also connects via a pressure reducing valve 26 and branches 23, 24 with brakes on rear wheels 25. In the embodiment of Fig. 2 the lever 38 is of channel-section and the web 36 of shoe 27 projects into the space between the side-arms 37. A protuberance 43 on web 36 is in contact with a dimple 45 on the lever 38 and serves as a fulcrum therefor. The strut 76 is pinned by one end 47 to the end 48 of the lever 38 and by its other end 49 to the web 50 of the brake shoe 28. In this embodiment the cross-sectional area of cylinder space 57 of cylinder 31 is greater than the cross-sectional area of cylinder space 58 of cylinder 51. In operation, fluid pressure within cylinder space 57 acts on piston 39 to apply thrust to shoe 27 via lever 38 and via lever 38 and strut 46 to shoe 28; pressure within space 58 moves piston 56 which is applied directly to shoe 28, and the arrangement is such that the brake force applied by both shoes 27, 28 to the drum is the same. The brake is provided with the usual release springs and may have manual or automatic wear adjusting devices. In the embodiment of Figs. 3, 4, the brake shoe 61 has two spaced webs 64, (65) and the lever 62 is an arcuate plate which projects into the space between the webs 64, (65) and is pinned to shoe 61 by a pin 66 anchored in webs 64, (65). The strut 68 has forked ends engaged in recesses 67, 69 in lever 62 and web 50 of shoe 28. A friction-type adjuster 71 for shoe 61 comprises a pin 72 carried by lever 62 and engaged in a slot 73 in web 64. The pin 72 carries spring loaded washers (not shown) which engage the web 64 frictionally. The frictional force is sufficient to limit release movement of the brake shoe 61 whilst being overcome by the brake applying force. A similar friction type adjuster 75 is carried by the web 50 of brake shoe 28 and is engaged in a slot 76 in a strut 77, the other end of the strut 77 being pinned to the brake shoe 61. In the embodiment of Figs. 5, 6 (not shown) a channel section lever (81) may comprise two parts (82, 83) welded together. The brake shoe web (36) receives a pin (84) anchored at its ends in the two parts (82, 83) and providing the fulcrum of the lever (81). A friction type adjuster (86) is provided similar to the adjuster 71.