Patent GB-337268-A (GB)
Title: Improvements in and relating to vehicle brake mechanism
IPC: F16D65/09
Filed: 1929-12-18
Abstract: 337,268. Clark, D'A. M., (Bendix Brake Co.). Dec. 18, 1929. Blocks and shoes acting on drums; compensating for wear.-In brakes of the kind comprising a pair of shoes of which the first applies the second when the drum is rotating in one direction and the second applies the first when the drum rotates in the opposite direction, the shoes are positioned with equal clearance from the drum when released by means of friction stops which, at least when the shoes are worn, are shifted slightly each time the brake is applied and are returned to their original positions when the brake is released. The shoes may be connected by means whereby the clearance may be adjusted to compensate for wear. Means for restraining lateral movement of the shoes are described. The brake shown comprises a pair of shoes 28, 30 having a floating pivotal connection at 50 and applied by a floating cam device 66. The shoes are of T-section and on either side of the end of the web of each shoe is mounted a roller 58 engaged by a pair of parallel cams 66 in the form of flat stampings. An operating shaft 68 is mounted in fixed bearings in a pair of parallel plates 60, 62 secured by posts 64 to the fixed back plate of the brake. This shaft passes with ample clearance through openings in the cams 66 and has secured to it an arm 72 which is coupled by a pin 74 to corresponding extensions of the cams. The pivots 56 of the rollers 58 serve to anchor the ends of the shoes by engaging notches formed in the fixed plates 60. When the brake is applied one or other of the pivots 56 takes the torque of both shoes according to the rotational direction of the drum. The shoes are connected together by a pair of rods 40 each having a screw thread engaging teeth in the edges of a slot in the web of each shoe and held by upper and lower plates 46 secured to the shoes. The rods have non-circular heads 42 recessed to receive a spherical thrust member 44 and embraced by a sleeve 50 perforated to receive a tool by which the rods can be turned to adjust the clearance of the shoes from the drum. A spring 82 urges the shoes away from the drum and also holds the rods 40 to the thrust member 44. Other release springs 78, 80 are connected to the shoes and to the posts 64. The device for ensuring equal clearance of the shoes from the drum comprises a plate 86 pivoted with frictional resistance by a bolt 88, Fig. 4, to the web of each shoe and formed with a slot at its other end through which and a hole in the web of the shoe passes a fixed pin. 94. Washers 102 on each side of the plate 86 and shoe each positioned by a nut and a shoulder on the pin 94 serve to prevent lateral movement of the shoe without however offering resistance to angular movement of the shoe. The slot in the plate 86 is sufficiently wider in the direction of the radius of the drum, than the pin 94 that, with a new brake shoe, when the brake is applied the plates are not shifted but when the lining becomes worn the plates are slightly shifted by the pin about the bolts 88 each time the brake is applied and on release the springs 28, 80, 82 are strong enough to return the plates to the original position giving equal clearance to the shoes. Fig. 14 shows a device which may be arranged adjacent the pivotal end of each shoe for preventing lateral movement thereof and comprising a pair of washers 124, 126 on either side of the web of the shoe, positioned on a fixed pin 120 by a cotter pin 128 and a spring 130. The spring 130 may be replaced by a shoulder on the pin.