GB1314230A - Automatic adjusting devices for internal shoe drum brakes - Google Patents

Abstract

1314230 Internal shoe drum brakes; wear adjustment AUTOMOTIVE PRODUCTS CO Ltd 27 Oct 1971 [5 Nov 1970] 52721/70 Heading F2E An internal shoe drum brake has brake shoes 12, 13 operable alternatively by a double-acting hydraulic cylinder 19 and by a mechanical linkage including a lever 23 extending with a lost motion clearance through a slot 24 in the web 16 of shoe 13; the brake incorporates an automatic adjusting device including a strut 21 extending between the two shoes 12, 13 and a wedge member 29 interposed between the strut 21 and an abutment member 25 on the brake shoe 12 and slidable under the action of a tension spring 32 to push the strut 21 toward the shoe 13 to compensate for brake wear if the aforesaid clearance is taken up without full brake application. As shown, the abutment member 25 is pivotally mounted on the web 16 of shoe 12, although it may be fixed thereto, and the wedge member 29 projects between edge surface 26 of the abutment member 25 and a notch 31 in the strut 21: the wedge member 29 is guided for sliding by a stepped tubular member 39 engaged in a slot 41 in the wedge member 29 and is retained against the shoe 12 by a spring loaded washer 43 carried by a steady pin 44. The lever 23 is urged clockwise by a tension spring 34 against an abutment 35 fixed to the strut 21 and a torsion spring 36 acting between the strut 21 and the shoe 13 tends to urge the outer side of the slot 24 against the outer side of that part of the lever 23 which passes through the slot 24. The lever 23 has a cranked arm 46 connected to a mechanical brake applying linkage which is actuable to pivot the lever 23 relative to the strut 21 to move the strut 21 and the shoe 13 in opposite directions to apply both shoes 12, 13 to the drum 11. During hydraulic actuation by cylinder 19, the strut 21 and lever 23 move initially with the shoe 12, the lever 23 remaining in contact with the abutment 35 and moving towards the inner end of the slot 24. If before full brake application the clearanc between the lever 23 and the inner end of the slot 24 is taken up further relative outward movement of the shoes 12, 13 pulls the strut 21 away from the shoe 12 so that the wedge member 29 is free to move under the action of spring 32 to take up the resulting clearance. Upon brake release the tension spring 36 pulls the brake shoe 13 inwardly to an extent determined by the clearance. The wedge member 29 is shaped as to only allow adjustment to the maximum safe extent when an edge of the member 29 engages abutment member 25; members 25 and 29 are roughened to provide good grip.