Patent GB-354810-A (GB)
Title: Improvements in automatic slack adjusters for brakes on railway cars and the like
IPC: B61H15/00
Filed: 1930-05-08
Abstract: 354,810. Compensating for wear in brakes. SVENSKA AKTIEBOLAGET BROMSREGULATOR, 5, Adelgatan, Malmo, Sweden. May 8, 1930, No. 14198. Convention date, June 24, 1929. [Class 103 (i).] An automatic slack adjuster for railway vehicles &c. comprises slack increasing and decreasing mechanisms, both of which, in certain conditions of the slack, may be operative during a braking action so that the resulting adjustment is the difference between the two adjustments. In Figs. 1 and 2, variation of slack is caused by rotation of a screwed rod 1 relatively to a nut part. Two pawls 7, 8 engaging a ratchet wheel 9 fixed to the rod 1 have lugs 10, 12 for coaction with fixed cam discs 11, 13, and are mounted on a housing 3. When braking, the housing 3 is rotated by a crank 2 rocked in known manner in a clockwise direction, Fig. 2, and the pawl 7 turns the wheel 9 to increase the slack until it is disengaged by the cam 11. If the slack is small the cam 13 prevents engagement of the pawl 8 with the wheel 9. If the slack is large the pawl 8 engages the wheel 9 and moves it back on release of the brake through an angle greater than that effected by the pawl 7 so that a reduction of slack is obtained corresponding to the difference in the two angles. When the slack is normal the two angular movements are equal and the slack is unaltered. In a modification the slack is reduced during braking and is increased during release of the brake by means of a recess in one of the cams. The normal amount of the slack may be varied by adjusting a sleeve 14 carrying the cam 13. Another form of adjuster is shown in Figs. 5, 6, in which the slack is varied by the longitudinal movement of a toothed rack 15 sliding in a sleeve-shaped member 16 and engaging a toothed wheel 19. A housing 17 fixed to the rod 16 carries a shaft 18 provided with threads 18a on which the wheel 19 acts as a nut. A crank 2 is carried by a rotatably-mounted sleeve 20 on the shaft 18 and having two arms supporting pawls 7, 8 which act in opposite directions on a ratchet wheel 23 fixed to the shaft 18 a guide flange 28 being provided in the housing 17 to engage a lug on each of the pawls 7, 8. A locking pawl 24 in the housing coacts with a toothed wheel 25 freely mounted on the shaft 18. When braking the crank 2 rotates the ratchet wheel 23 and therefore the shaft 18 through a small angle until the pawl 7 is disengaged by the flange 28. The screw 18a thus displaces the wheel 19 to the left in Fig. 5 and relieves the contact pressure between a flange part 27 of the wheel 19 and the wheel 25, whereupon the rod 15, due to the stress arising when brak-. ing, is pulled towards the left in Fig. 6 to increase the slack. The displacement of the rod 15 moves the wheel 19 to the right until the flange 27 again engages the locking wheel 25. This operation continues until the pawl 7 is disengaged by the flange 28 and on continuation of braking variation of slack is determined in a similar manner as described for the adjuster shown in Figs. 1, 2. Another form of adjuster operated by air pressure is shown in Fig. 7, in which a rod 34 screws into a nut on one of the levers operating the brakes. Fixed to the screw 34 is a ratchet wheel 35 enclosed in a housing 36 joining the compressed air cylinders 30, 31 connected to the brake cylinder cover and to a point between the ends of the brake cylinder corresponding to the length of stroke for normal slack, by pipes 32, 33 respectively. Pawls 38, 40 on the ends of the cylinder piston-rods coact respectively with the ratchet wheel 35 during braking and during release. When braking, the piston 37 forces the pawl 38 to rotate the wheel 35 to increase slack until the pawl is disengaged by a fixed abutment 41. The piston in the brake cylinder will arrive at the position for connecting the pipe 33 at such a moment that the rotation of the ratchet wheel by the pawl 38 will equal or be less than the backward rotation by the pawl 40 under pressure of the piston 39, according as the slack is normal or too great. If the slack is small no air is introduced into the cylinder 31.