Patent GB-353897-A (GB)
IPC: B61H15/00
Filed: 1930-04-22
Abstract: 353,897. Compensating for wear in brakes. SVENSKA AKTIEBOLAGET BROMSREGULATOR, 5, Adelgatan, Malmo, Sweden. April 22, 1930, No. 12380. Convention date, July 10, 1929. [Class 103 (i).] Relates to automatic slack adjusters for brakes on railway cars &c. of the type adapted both to reduce and to increase slack between the brake shoes and the wheels and wherein the increase of slack is effected by the braking forces, such increase being limited by means controlled in accordance with a predetermined length of idle stroke of the operating member. According to the invention the adjuster is operated in a direction for reducing slack by means of the braking forces. In the construction shown in Fig. 1, eyes 1, 2 form the ends of piston-rods the pistons 6, 5 of which are mounted in connected fluid cylinders 4, 3, one side of the cylinder 4 being in communication with a reservoir 7. A pipe 9 with one-way valves 12, 10 allows fluid to flow from the cylinder 4 to cylinder 3 whenever cock 11 is open. Flow in the reverse direction is permitted by the one-way valve 14 when the brakes are released. When the brakes are applied, the slack adjuster is subjected to tension and the piston 6 moves to the left until the cock 11 closes and prevents flow along the pipe 9. The cock 11 is connected to the operating member (not shown) and is thereby closed when the operating member has moved a predetermined distance idly. At the commencement of this operation the piston 5 is drawn outwardly against a spring 8 and sucks a definite amount of fluid from the reservoir into the cylinder 3 through the pipe 16. When the brakes are finally released fluid is returned by the action of the spring 8 through the pipe 15 to the cylinder 4 and reduces slack. If the slack is normal the amount of fluid forced through pipe 9 by piston 6 before the brakes are applied equals the amount returned through the pipe 15 by the spring 8 and piston 5 when the brakes are released. Any departure from normal slack results in these two amounts of fluid differing and altering the adjustment of the apparatus so as to restore the slack to normal. In a modification, slack is reduced initially by the piston 5 instead of when the brake is released. The construction shown in Fig. 3 forms a mechanical analogy to that shown in Fig. 1, the adjuster comprising a screw connection 18, 20 having a quick pitched thread causing relative rotation of the parts under an axial pull. The nut 20 is part of a rotatable housing 19 mounted on a pivot pin 21 integral with the eye 2. A pressure spring 24 acts between a flange 22 on the pin 21 and an abutment 23 in the housing 19. Freely rotatably mounted on the pin 21 is a ring 28 connected with a lever 30 which can be oscillated by the brake piston in a manner corresponding to the actuation of the cock 11 in Fig. 1. Another ring 31 is mounted on the pin 21 being axially displaceable but non-rotatably connected relatively to the ring 28 and the ring 31 is provided with cam surfaces 33 coacting with similar surfaces on the end of the pin 21. A toothed ring 35 axially slidable on the pin 21 is urged by a spring 38 towards a toothed flange 34 in the housing 19 but is kept from it by the cam surfaces 33. Another clutch arrangement comprises a toothed ring 37 adapted to engage the toothed end 42 of a screw-threaded sleeve 41 freely rotatable on the pin 21 and engaging a projecting part 40 of the housing 19 to form a quick-thread screw connection similar to 18, 20. The clutches 34, 35 and 37, 42 act in one direction of rotation only and in opposition to each other. When braking the initial tension of the adjuster compresses the spring 24 and relieves the contact pressure between the flanges 23, 26 so that the housing 19, when the tension increases, rotates to lengthen the distance between the eyes 1, 2. At the same time the lever 30 is rotated and turns the ring 31 until the cam surfaces 33 engage and force the ring 31 to the left, so that the clutch 34, 35 is engaged and relative rotation of the parts 18, 20 is prevented. Increase of tension now forces the sleeve 41 to rotate until the flange 26 engages the abutment 27 when all movement ceases. At this point the clutch 34, 42 will be engaged and the sleeve 41 positioned for a reduction of slack corresponding, it is stated, with the initial charging of the cylinder 3 in Fig. 1. On release of the brake the spring 24 tends to push the pin 21 to the left. The sleeve 41 cannot rotate as the clutch 34, 42 is engaged and so the housing 19 rotates to reduce slack, the teeth of the clutch 34, 35 sliding backwardly on each other until the cam surfaces 33 separate them. The ring 37 is disengaged from the ring 42 by the abutment 39 before the flanges 23, 26 contact. When slack is normal the lever 30 engages the clutch 34, 35 at the moment when the screw connection 18, 20 has lengthened the adjuster by an amount equal to the shortening of the adjuster by the sleeve 41 on release of the brake. When slack is insufficient the adjuster will be placed under tension before the lever 30 commences to rotate and consequently the screw connection 18, 20 lengthens the adjuster by a greater amount than the final shortening by the sleeve 41. If slack is excessive the tension increases after the lever 30 is actuated and may not arise until the clutch 34, 35 has been engaged in which case the reduction will be entirely due to the return action of the sleeve 41. In a modification the pitch of the screw 41 is opposite and greater than that of the connection 18, 20.