GB1453693A - Wedge brakes - Google Patents

Abstract

1453693 Internal shoe drum brakes CENTKAX Ltd and R H H BARR 26 Nov 1973 [25 Aug 1972] 39741/72 Heading F2E An internal shoe drum brake includes an operating mechanism 6 comprising a pair of plungers 11, 12 movable by axial movement of a wedge element 21 to move respective brake shoes 2, 3 to apply the brake; the plungers 11, 12 have surfaces 15, 16 inclined to the direction of movement of the wedge element 21 which surfaces 15, 16 respectively face inclined surfaces 19, 20 on the wedge element 21 with the interposition of rollers 17, 18; the portions of the surfaces 15, 16 and 19, 20 that co-operate with the rollers 17, 18 during a first part of a brake applying movement of the wedge element 21 have greater angles of inclination than the portions of the surfaces that co-operate with the rollers 17, 18 during a second part of a brake applying movement of the wedge element 21. This ensures that at least the majority of slack between the brake shoes 2, 3 and the brake drum 1 is taken up during the first part of the movement of the wedge element 21. As shown the transverse edges 46, 47 of the wedge element 21 are rounded as are the adjacent corners 48, 49 of the surfaces 15, 16 of the plungers 11, 12. The different angles of inclination may alternatively be achieved by providing a plurality of flat surfaces of progressively smaller angles of inclination on each of the plungers 11, 12 and the wedge element 21. As shown, the plungers have grooves 13, 14 whose bottom surfaces comprise the surfaces 15, 16 and grooves are also provided for the wedge element 21 by the limbs 31, 32 of a U-shaped check element 29, which limbs 31, 32 extend beyond the wedge surfaces 19, 20 to provide the grooves. The rollers 17, 18 are guided along the wedge surfaces 19, 20 by the check element 29 a bight section 33 of which provides lugs 35, 36 for holding the rollers 17, 18: the rollers 17, 18 are also held by a washer 37 held against movement to the left as seen in Fig. 2. The check element 29 is welded to the wedge element 21 through holes 34. The wedge element 21 is movable by operation of a fluid pressure actuator 45a a compression spring 38 between a washer 39 and a lug 43 on a rubber seat 42a biasing the element 21 towards its retracted position. There may be two operating mechanisms 6 respectively between each pair of adjacent shoe ends or one pair of shoe ends may be pivoted. Where two operating mechanisms are provided a second actuating means such as a spring may be provided for one mechanism.