Patent GB-1420742-A (GB)
Title: Wedge brakes
IPC: F16D65/22
Filed: 1971-11-24
Abstract: 1420742 Wedge actuators for internal shoe drum brakes CENTRAX Ltd and R H H BARR 26 Feb 1973 [24 Nov 1971 1 Sept 1972] 54630/71 and 40585/72 Heading F2E A wedge assembly for an internal shoe drum brake comprises a wedge element at least part of which is in the form of a wedge, a stop on each wedge surface at the narrow end of the wedge, a roller on each wedge surface, a retainer element mounted for relative movement along the wedge element, and spring means biasing the retainer element towards the stops, the retainer element and the stops being shaped to hold the rollers between them when the retainer element and the stops are separated by less than a predetermined distance or the retainer element has reached the limit of its travel in the direction of the stops. In Figs. 2 and 3 the stops 35, 36, are formed by the bight section, 33, Fig. 7, of a cheek element 29 which is folded to U-form and has its limbs 31, 32, secured to respective flat sides of the wedge element 21 by welding through holes 34. The limbs 31, 32 extend beyond the wedge element to form cheeks 27, 28, Fig. 3, for retention of rollers 17, 18; the plungers 11, 12, which are interposed between the wedge assembly and the shoes (not shown) are grooved at 13, 14 respectively. The retainer element is in the form of a washer 37 slidable relative to the wedge element 21 and provided with a flange 40; it is urged towards the rollers by a spring 38. The wedge assembly is accommodated in a bore 45 of a housing 8, Fig. 2, and the washer 37 engages a shoulder (not shown) in the bore to restrict its movement leftwards. The hemispherical outer end 26 of the wedge element 21 is engaged by the stem of a fluid-pressure actuator (45, Fig. 1, not shown). When the actuator stem is retracted for brake release, spring 38 moves wedge element 21 to the right from the operative position (not shown) until the inoperative position of Figs. 2 and 3 is reached, stops 35 and 36 ensuring the return of rollers 17, 18. Return springs (7, Fig. 1, not shown) ensure the return of plungers 11, 12. A top-hat-shaped rubber seal 42 is provided. In Fig. 8, stops 52, 53 are integral with the wedge element, and the wedge surfaces 19<SP>1</SP>, 20<SP>1</SP> are non-uniformly sloped (see portions 46, 47) to produce a large initial approach of the brake shoes followed by small movement at great mechanical advantage; plungers 11<SP>1</SP>, 12<SP>1</SP>, are complementarily shaped at 48, 49, respectively. Flat cheek elements 27<SP>1</SP>, 28<SP>1</SP> are riveted to the wedge element. In Figs. 11, 12 (not shown) the cheek elements are omitted, each roller has end flanges (60), and the surfaces of the plungers with which the rollers engage are ridges rather than grooves. In Figs. 13, 14, each roller has trunnions 75, 76, received between pairs of lugs 71, 72 and 73, 74 respectively formed in the limits of a U- shaped cage 70 which takes the place of cheek elements. The bight portion of the cage engages loosely the stem portion 25 of the wedge element and its inner surface 79 does not engage shoulder 80 formed between portions 22 and 25 of the wedge element in the rest position shown, so the location of the rollers by washer 37 and integral stops 77, 78 is not impeded.