Patent GB-993686-A (GB)
Title: Improvements in automatic slack adjusters for vehicle brake linkages
Inventor: LARSSON KARL BERTIL
IPC: B61H15/00
Filed: 1963-12-20
Abstract: 993,686. Automatic brake adjustment. SVENSKA AKTIEBOLAGET BROMSREGULAR. Dec. 20, 1963, No. 50315/63. Heading F2E. A two-way slack-adjuster for a vehicle brake-linkage, as in Fig, 1, comprises a leader nut 15 and an adjuster nut 16 on non-selflocking screw threads on a rod 5 which extends into a tube 17, a traction-sleeve 23, 24 which, in its normal released-brake condition, is pressed by a main locking spring 21 against a stop-ring secured to the tube 17, and limits the axial movement of the adjuster nut 16, a first endplate 30 secured to an outer barrel 29 and engaging the leader nut 15 in its normal releasedbrake position, and a compression barrel-spring 27 bearing at one end against a second barrelend-plate 28 and at the other end against a support ring 26 mounted loose on the tube 17, the barrel-spring 27 thereby providing forces whereby the leader nut 15 is engaged at e-e by the first plate 30. A slack adjuster of the kind just described is characterized in that the spring support 27 bears against the traction sleeve 23, 24 which is provided with clutch surfaces b-b for engaging it with a flange 18 fixed on the tube 17 when the said sleeve 23, 24 is moved axially relative to the tube against the locking spring 21 and by an abutment 19 on the tube which limits axial movement of the spring support 26 so that after some of such movement of the sleeve the support 26 bears against the abutment 19 instead of against a shoulder at d-d on the sleeve 23, 24, and the latter is relieved from the force of the spring. Fig. 1 shows brake shoes 8 on a dead brake-lever 7 and a live brake-lever 6 connected through the slack adjuster and a crosshead 4 to a lever 3 operated by a brake cylinder 1. A link 11 connects the live lever 3 to a dead lever 10 pivoted on the cylinder and carrying a rod 13, supported as shown in Fig. 2. The tube 17 and rod 5 cannot rotate and for purposes of the following explanation the rod 13 is regarded as stationary. When the brake is applied the crosshead 4 moves to the right carrying with it the barrel 29 and the rod 5. A stop 39 is mounted at 14 on the rod 13 at a distance A from the end-plate 28 which it normally Contacts to stop rotation at the same time as the brake blocks 8 contact the wheel 9. If the brakes are worn the stop 39 will contact the plate 28 to close clutch h-h earlier than the blocks contact the wheel 9 and further movement of the tube 17 will not then be possible until the force on the crosshead has risen above the force of the spring 27. When further movement of the tube 17 does occur a clutch g-g will engage and the braking force will be transmitted from the tube 17 through flange 18, ballbearing 20, locking spring 21, flange 22, traction nut 16 to the rod 5. At the same time the barrel 29 and end-plate 30 will remain stationary due to the stop 39. Clutch e-e is released and shortly after the stop-ring 31 will engage the ballbearing 34 to prevent the leader nut from moving further to the right. The rod 5 will therefore be drawn through the nut 15. The clutch f-f will be released and the axial distance between its mating surfaces f-f will be increased to a value which corresponds to the amount of superfluous slack. Owing to elastic deformation of the brake linkage some further axial movement of the tube 17 is possible after the block 8 has engaged the wheel 9. The spring 21 will be compressed and the clutch c-c released, but as the clutches d-d, g-g and h-h still establish a rigid connection with the stop 39 by way of the sleeve 23, 24, ring 26, barrel spring 27 and end-plate 28 rotation of the adjuster nut does not at first take place. After a further increase in braking force clutch d-d is disengaged and clutch b-b is closed so that the braking force is transmitted from the tube 17 to the flange 18, clutch b-b, ring 25, sleeve part 24, clutch g-g and nut 16 to the rod 5 causing the nut 15 to rotate further. On release of the brakes any extra rotation of the nut 15 which has occurred due to excessive elastic strain on the brake linkage is reversed by further appropriate sequential applications of the clutches which inter alia permit the barrel 29 to rotate with the nut. The distance f-f is thereby restored to agree with the superfluous slack and the subsequent sequence of operations which take place on releasing the brake ensure that it is held until the next application of the brakes. In the instance of the slack being too small, due to new brake shoes &c., a braking force greater than the force of the spring 21 may arise before the clutch h-h has engaged as described above. The force is then transmitted from the flange 18 through a ballbearing 20, spring 21, flange 22, sleeves 23, 24, clutch g-g and adjuster nut 16 to the rod 5. But as soon as the spring is compressed, the coupling c-c is disengaged and all the adjuster parts inside the barrel 29 rotate on the ballbearing 20. Rod 5 will therefore be drawn out of the nuts 15 and 16 until the clutch h-h is engaged. The adjuster has now increased its length corresponding to the desired increase in slack. Further application of the braking force will cause the nut 15 to rotate relative to the nut 16 but this rotation will be reversed by sequential operation of the clutches whilst the brake is being released so that the assembly is restored to its adjusted length with the clutch f-f in engagement and the brake is fully off.