Patent GB-327770-A (GB)
Title: Improvements in brakes for motor vehicles
IPC: F16D51/66
Filed: 1929-01-18
Abstract: 327,770. Lindsay, A. Jan. 18, 1929. Blocks and shoes acting on drums.-A selfenergizing or servo-brake of the two-shoe internal expanding type is characterized by the employment of one composite shoe composed of a rocker or liner portion 2 which alone is directly affected by the actuating-cam 5, and a movable friction member 3 slidably surmounting said lever portion 2, opposed pairs of co-acting thrust members being provided between the member 3 and the plain secondary shoe 13 by means of which the tangential force developed between the drum 1 and the member 3 is transmitted to the secondary shoe in forward and reverse braking. In one construction, Figs. 1 and 2, the friction member 3 is of channel section and embraces the lever portion 2, rollers 8 being interposed between the two. The channel sides of the part 3 are extended downwardly to form thrust members 14, 15 which co-operate with similar parts 17, 18 of the shoe 13 which pivots at 16 during forward running and at 4 during reverse. Alternatively shoe 13 may be formed to pivot on cam 5. The thrust members 14, 15 are connected by an integral yoke 21 which provides abutments for springs 10 secured to either side of a radial lug 9 formed on the lever 2; these springs serve to return part 3 to its normal position when the brake is released. Springs 23 fixed to yoke 21 prevent radial movement between parts 2, 3. The flange of shoe 13 is formed with an upwardly extending finger 20 which provides a positive means of release in forward braking. To prevent chatter a curved rod 28 sliding in bracket 29, 30 on the flange of shoe 13 is kept up to cam 5 by a spring 31. Figs. 4, 7 and 9 show alternative friction reducing means, that in Fig. 4 comprising a curved plate 32 having studs 33 on its outer surface and greaseretaining grooves on its inner. In a modification the lug 9 is replaced by two angle brackets, one on either side of the web of the lever 2. Two pairs of springs are carried upon wires threaded through the angle brackets and secured at each end in blocks fixed to the inner faces of the members 3. The thrust members 14, 17 may be replaced by prolonging the flange of part 3 to form an arm situated between the pivot 4 and the drum 1, and by a co-acting shoulder on the side of the bearing 44 of shoe 13, respectively. Alternatively the lever 2 may have a ringed middle web which fits into a recess in the bearing 44, the sides of which are extended upwardly to form thrust members. Fig. 15 illustrates a modification suited to front wheel braking; in this form shoe 13 pivots during forward running on the end of lever 2 which has a recess 55 accommodating a projection 55<A> on shoe 13, and during reverse running on a pivot 56 embraced by the forked end of the shoe 13. The pairs of co-acting thrust members are formed respectively by the abutting portions 52, 53 of the flanges of parts 3 and 13, and by curved links 49, 50, Figs. 16. Alternatively shoe 13 may pivot during forward rotation on cam 5 and the thrust members be arranged between the cam and the drums. Fig. 19 shows a modified arrangement of thrust members; these are constituted by curved links 63, 64 secured to the channel sides of part 3 by pins 65, 67 passing through slots 69, 70 in the web of lever 2 at their lower ends these links have pins 66, 68 which engage in slots 71, 72 in the web of part 13, the arrangement being such that rotary movement of part 3 in either direction causes one of the pins 66, 68 to bear on the end of its slot and thus apply to shoe whilst the other pin slides freely in the second slot.