Patent GB-619161-A (GB)
Title: Improvements in automatic slack adjusters for brakes
IPC: B61H15/00
Filed: 1946-11-22
Abstract: 619,161. Automatic slack adjuster for vehicle brakes. SVENSKA AKTIEBOLAGET BROMSREGULATOR. Nov. 22, 1946, No. 34748. Convention date, Dec. 4, 1945. [Class 103 (i)] An automatic slack adjuster of the type described in Specifications 530,658 and 563,130 comprises a two-part brake push-rod, one part being in the form of a non-rotatable and non-self-locking screw spindle 1, having its outer end pivoted by a bolt 101 to the lower end of deadbrake lever 102 suspended from the vehicle bolster 93 by bracket 108 and link 106, the other part being in the form of a non-rotatable tubular rod 2 having at its outer end jaws 53 pivoted by a bolt 100 to the lower end of live brake lever 97, the top end of which is coupled to the brakepull rod 94. When the brake is in the released condition, spindle 1 is fixed longitudinally with respect to the rod 2 by the contact of edge 57 of coupling nut 3 against the locking ring 38 rigid with the rod 2, the friction of this contact being sufficient to prevent the rotation of the coupling nut 3. Leftward movement of the brake pull rod 94 pivots the live brake lever 97 and an actuating lever 115 about pins 98 and 116 respectively, a fixed distance apart on the brake beam 99, the lower end of the actuating lever 115 being pivoted to a rod 75 extending parallel to the two-part pushrod, so that the combined effect of the movements of levers 97 and 115 is a longitudinal displacement of the rod 75 to the left with respect to the two-part push-rod. Rod 75 has at each end adjustable collars 76 and 84 and is guided between forks 12 on an arm 11 secured to an operating member 4 movable internally of the tubular rod 2. Secured to rod 75, between the collar 76 and the forked arm 11 is an arm 80, linked to a pair of levers 68 pivoted to the body of the two-part pushrod by a pin 67 and having at their inner ends cup-shaped seats 69 and 70 engaging the ends of push pins 71 and 72, the other ends of which terminate just short of the outer face of a collar 34 forming an end cap for springs 35 and 36. Thus, the initial effect of a brake application and therefore a leftward movement of the rod 75 with respect to the push-rod body is that the push pins 71 and 72 by compressing springs 35 and 36, force also rings 31 and 29, anti-friction thrust ball bearings 24, ring 19, collar 17 integral with the adjusting nut 5, anti-friction thrust bearing 23 and coupling nut 3, comprising inner and outer parts 55 and 56 respectively screwed together, to the right against the force of springs 28 and 62, so that the edge 57 of coupling nut 3 is moved away from the locking ring 38 and therefore both coupling nut 3 and adjusting nut 5 are free to rotate on the spindle 1. If therefore the brake clearance was initially too small and the brake shoes come into contact with the wheels before the desired movement of the operating rod 94 to the left has taken place, the two-part pushrod will receive a compressive force which will shorten it by moving the spindle 1 to the left with respect to the rod 2, the nuts 3 and 5 being rotated during this movement. If, however, the clearance was initially too great, the collar 84 on rod 75 will meet the arm 11 before the brake shoes are in contact with the wheels, and force it together with operating member 4 and its screwed end sleeves 7 and 8 to the left. As the sleeve 8 is moved to the left, it compresses springs 35 and 36 by means of plate 31 and carries with it the locking ring 16, rings 29 and 19, ball bearing 24 and the end ring 27. As the end ring 27 moves to the left it compresses spring 28 and presses rings 18 and 25 and ball bearing 23 against the collar 17 of the adjusting nut 5 which is rigid on the spindle 1 since it cannot at first rotate owing to the friction between the conical surfaces of locking ring 16 and ring 19. When, however, the ring 19 has moved so far to the left that the projections 22 thereon no longer engage the projections 21 on the ring 18, which latter projections also engage with slots cut in the collar 17, the adjusting nut 35 will then be free to rotate on the spindle 1 and will move to the left in co-operation with the operating member 4 under the force of the spring 28 until the brake-operating member 94 has completed its desired leftward movement. On release of the brake, the operating member 4 begins moving to the right and the projections on the ring 19 re-engage with the projections on the ring 18 and the adjusting nut 5 is once more prevented from rotating. During the rest of the return movement of the operating member 4 to the right, which movement corresponds to the amount by which the brake shoe clearances exceeded their normal value at the application of the brake, the adjustable nut 5, now prevented from rotating, moves the spindle 1 to the right so that the edge 57 of coupling nut 3 is moved out of contact with the locking ring 38, thereby enabling the nut 3 to rotate freely and thus permitting the required extension of the two-part push-rod to take place. When the adjustable collar 84 on the rod 75 moves away from the arm 11, the operating member 4 has completed its return movement and during any continued release operation the two-part brake rod 1, 2 is fixed at its new length by reason of the contacting edge 57 of the coupling nut 3 again bearing against the locking ring 38.