Patent GB-512279-A (GB)
Title: Improvements in or relating to internal shoe drum brakes
IPC: F16D51/30
Filed: 1938-06-17
Abstract: 512,279. Brakes. AUTOMOTIVE PRODUCTS CO., Ltd., and LAPWOOD, K. E. June 17, 1938, No. 18075. [Class 103 (i)] In an internal shoe brake of the kind in which a brake shoe has an actuating device and an anchorage device at each end enabling the shoe to act in a leading sense during drum rotation in each direction, there is interposed between an actuating element and the shoe a member which is pivotally connected with one of these parts and has a flat surface slidable on the other part, the direction of the sliding surfaces being such that they would if extended pass to that side of the drum axis remote from the shoe. Both shoes of a pair may act in a leading sense in both directions of drum rotation or only one of them. There may be alternative hydraulic and mechanical means for expanding a pair of shoes. In Figs. 1, 3, shoes 14, 15 are expanded 'by cylinders 11, 12 each containing a pair of pistons. One piston of each pair engages one shoe end by a forked rod 45 screwed into an adjusting nut 47 fitting into the piston. A member, 33 has a spherical head 32 which fits a corresponding recess in the other piston 29 of a pair and a flat surface 42 which engages a similar surface on the end of the web 35 of the shoes and of a reinforcing plate 40 thereon. A lug 34 on the member 33 is held in contact with the web 35 by a pin 36 passing through a slot in the parts 35, 40 and a spring washer 37 whereby the sliding movement of the surfaces 42 is frictionally damped. The inclination of these surfaces is such that they would, if extended, pass to the side of the drum axis remote from the shoe and is preferably arranged as described in Specification 487,252. Return springs 19, 20 for the shoes are attached to fixed pins 21, 22. To prevent access of dirt, skirts 48, 30 attached to the pistons slide on the exterior of the cylinders. When the brake is applied with the drum rotating in the direction indicated, the shoes 14, 15 anchor respectively at the lower and upper ends, flanged end of the pistons 29 abutting on the cylinders. With the drum rotating oppositely, the other ends of the shoes anchor by engagement of the nuts 47 on the cylinder ends. Both shoes thus act in the leading sense in both cases. The sliding surfaces 42 permit accommodation of the shoes to the drum and prevent grabbing action. According to the Provisional Specification these surfaces may be provided at both ends of the shoes. Alternative applying means comprise a lever 52 pivoted at 53 to shoe 15 and a link 54 pivoted to the lever and sliding between pegs 56, 57 on shoe 14 and operated by a cable 58. In Figs. 4-6, the upper shoe-ends are expanded by a pair of sectors 68, 69 pivoted at 67 on a forked member 66 and rolling on inclined surfaces on plungers 63, 64 slidable in the casing 60. The end of shoe 15 has a sliding and pivotal connection with the plunger 64 similar to that of Fig. 1, the part 86 on a shoulder of which the shoeend is slidable at 42 fitting into a slot in the plunger and bearing at 85 with its concave end on the convex bottom of the slot. The sectors 68, 69 are actuated by a rod 74 and a part 75 operated normally by a hydraulic piston 76 or alternatively by a rod 82 with a head 81 engaging the part 75. Adjustable anchorage means for the lower ends of the shoes and operating means for one of them comprises a body 91 fixed to the back plate 10 and formed with a cylinder 90 containing a piston 92, the piston rod 94 comprising adjustable screw and-nut parts and engaging shoe 15. The cylinder 90 has a casing 103 secured to the back ,plate which has holes 104 to permit the circulation of cooling air from outside around the cylinder. The lower end of shoe 14 is permitted pivotal and slidable movement similarly to the upper end of shoe 15 the slot with the convex surface 85 engaged by the concave end of the member 86 being provided in a plunger 106 which engages one of the oblique faces 112 of an adjusting member 110, the other face 113 of which engages a rod 100 slidable in the end of cylinder 90 and forming an adjustable stop for an extension 99 of piston 92. Both shoes are thus adjustable by advancing the member 110 by a screw 109 which may have a diametral ridge across its end engageable in succession with a number of grooves in member 110 to facilitate the adjustment. When pressure liquid is supplied to the cylinders 77, 90 to apply the brake with the drum rotating counter-clockwise, shoe 14 anchors at its lower end through the parts 106, 110 and shoe 15 at its upper end by engagement of plunger 64 with a shoulder in the casing 60, both shoes acting in the leading sense. With clockwise rotation, however, both shoes anchor at the lower end, the shoe 15 through parts 99, 100, 110, so that only the shoe 15 acts in the leading sense. The Provisional Specification also refers to Specification 495,834.