Patent GB-683673-A (GB)
Title: Improvements relating to slack adjusting mechanism for vehicle brakes
IPC: B61H15/00
Filed: 1951-04-23
Abstract: 683,673. Brake slack adjusting devices. SVENSKA AKTIEBOLAGET BROMSREGULATOR April 23, 1951 [April 22, 1950; Feb. 27, 1951], No. 9406/51. Class 103 (i). An automatic brake slack adjuster is provided with means to prevent an unintended displacement of the parts of the brake rod relatively to one another in a direction to increase the shoe clearance before the two parts of the adjuster are properly coupled together as a result of an abnormally high resistance to movement of the brake gear occurring on starting to brake, caused for example by an accumulation of snow or ice between the brakeblocks and wheels of the vehicle. For the construction of the invention as applied to a double-acting adjuster as shown in Figs. 1, 2 and 3 in the brakes released condition, the adjusting nut 23 is locked in normal rest position at a distance " d " from the coupling nut 17, both nuts 17 and 23 being rotatable on the reversible pitch threaded spindle 1 connected at 3 to the brake shoe actuating levers. During a normal brake application, the eye 4 connected to brake lever 53 is moved to the right, whereby initially the entire slack adjuster makes a parallel movement. If the brake shoe clearances are correct, the actual braking stress occurs at the moment the ring 48, which moves with the brake-rod 51, bears against end wall 38 of tube 37. This braking stress is transmitted through the tube 2, flange 9, Belleville discs 13, locking-ring 6, sleeves 7 and 8 and coupling nut 17 to the spindle 1. Under the action of the braking stress, the discs 13 are flattened, whereby the locking engagement between the members 6, 40 is released. This action through the intermediary of springs 41, 42 and outer casing parts 38, 37, 26 unlocks the adjusting nut 23 to allow it to rotate on spindle 1. Such rotation takes place on any further movement to the right of spindle 1 as a result of elastic deflection of the brake gear, the friction surface 25 no longer engaging the sleeve 26. On release, the spindle 1 is moved to the left and by pressure of adjusting- nut 23 on the sleeve 26 brings about a reduction of pressure between the end wall 38 and stopring 48 and a torque between spindle 1 and nut 23 so that the casing 37 is not carried with it, but rotates on ball-bearing 43. This movement is continued until the brake stress falls to such a value that the Belleville discs 13 expand so that the friction edge 39 on sleeve 6 locks on the member 40 at which time, if the brake clearance were correct, the bearing 22 has reached the sleeve 32 so that the nut 17 is also arrested and the slack adjuster moves in one piece. If the brake block clearances had been too large, in braking, the end wall 38 contacts the ring 48 before the shoes meet the wheel and during a further movement of the spindle 1 to the right the adjusting nut 23 rotates thereon so that the distance between the members 23 and 17 is increased, this distance being restored to its normal value d on the return movement so that the brake-block clearance is correctly re-set. With the above construction, if, for example, due to snow on the blocks, the resistance to movement during an application becomes so great that springs 41, 42 and discs 13 are compressed and the locking mechanism 6, 40 prematurely released so that the distance between the nuts 17 and 23 falls below the value d. Thereafter the end wall 38 bears against the stop-ring 48, the nut 17 nevertheless moves to the right and increases the distance. The adjustment of the distance between the locking- nuts 17, 23 is only dependent upon at what stroke of the brake the braking stress ceases. This is an important advantage as compared with automatic double-acting slack adjusters hitherto constructed, according to which the amount of adjustment in a direction to increase the slack was determined by forces arising in the brake gear already during the initial brake application movement, such forces often being incalculable.