Patent GB-549245-A (GB)
Title: Improvements in brakes
IPC: F16D65/22
Filed: 1941-05-17
Abstract: 549,245. Internal-expanding brakes. PRATT, J. H., MANLEY, G. E., and GIRLING, A. H. G. May 17, 1941. Nos. 6380 and 10864. [Class 103 (i)] In an internal-expanding brake the friction member or members are displaceable along a diameter relatively to a torque reactive member or carrying means which in turn is displaceable relatively to a fixed part along a diameter at right angles to that first mentioned whereby the friction member or shoes are self-centering and equalised radial pressures are applied thereto. A self-energising action may be obtained by the transfer through the torque reactive member of force from one shoe to another. In Fig. 1, the friction band 21 is free to move by projections and slots 21a along a diameter, relatively to a torque frame 22 which can move relatively to the fixed back plate 23 by means of projections and slots 23a, along a diameter at right angles to that of the projections 21a. The band 21 is applied by a fluid-pressure cylinder 24 carriedby the band. In Figs. 12, 15 the application cylinder 24 and adjuster 58 of two pairs of articulated shoes 34 are mounted on a plate 53 which is mounted upon the fixed plate 23 by a pair of links 54 so that it is free to move along a horizontal diameter relatively to the plate. The connections between the cylinder and adjuster and the shoes comprise struts 57 having spherical ends. The shoes can thus move along a vertical diameter relating to the plate 53. When the brake is applied with the drum rotating clockwise the lefthand upper shoe anchors through associated the piston on the cylinder 24 and the right-hand lower shoe on the adjuster 58, the drag on the right-hand shoes being transferred through the plate 23 to the left-hand shoes. The drag on one shoe of each pair is also transmitted to the other shoe of the pair. Each link 54 is pivoted at 54b to a member 55 which is secured to the plate 23 by bolts 55b passing through slots in the plate whereby adjustment of the pivot of the links is obtained and which also serves as an abutment for a return spring 56 for the link. In another construction, Figs. 7, 9, a pair of plates 35 each having pivoted thereto at 36, a pair of shoes 34 bear at one end at 35a on a wedge adjuster 39 and at the other end on an expander comprising rollers interposed between a wedge 45 and correspondingly inclined surfaces of members 43 upon which the ends of the plates have a pivoted bearing. Guide plates 46a, 46b are secured at 47 respectively to the members 43. Return springs 37 are attached to the shoe pivots 36. The adjuster 39 is operated by a screw 40 and is mounted in a housing 41 a projection 41a on which is slidable vertically in a slot in an annular torque reaction member 42 of channel section. A projection 52 on the member 42 forms a stop for the plates 35. The plates with the shoes can thus move vertically relatively to the member 42 which is attached to the fixed plate 23 by bolts 48 passing through slots 23c so that the member 42 can move along a horizontal diameter with respect to the plate 23. Nuts 49a on the bolts 48 hold the plates 35 against lateral movement. When the brake is applied with the drum rotating clockwise, the upper end of the left-hand plate 35 anchors on the stop 52 and the lower end of the righthand plate on the wedge 39 the drag on the right-hand shoes being transmitted through the wedge to the left-hand shoes and to the member 42 the forces acting on this member at the stop 52 and housing 41 being balanced since it is free to move horizontally. Fig. 5 shows a friction band 21 mounted upon an inner band comprising a series of links 26, an adjusting screw 29a being interposed between the lower pair of links and a fluid-pressure cylinder and piston 24, 25 by which the band is expanded, between the upper pair. The band 21 is anchored to the band 26 by a lug 21c. The bands are mounted between a pair of parallel annular plates 27 attached to the fixed back plate by pins and slots 23a so as to be movable with respect to the back plate. One arm of each of a pair of bell-crank levers 30, 32, projects respectively between the upper pair of links 26 and the toothed operating discs 29c of the adjuster 29a. When the brake is applied by the cylinder 24 the bands 21, 26 anchor by one or other of the upper links upon a projection 27b on the plates 27 and the drag on the bands causes a self-energising force to be transmitted to the upper link through the levers. The levers and stop 27b permit movement of the bands along a vertical diameter, relatively to the plates 27. According to the Provisional Specification the drum may be rendered self-centering relatively to a brake shoe by a mounting operating on the principle of the Oldham coupling. Specification 548,986 is referred to.