Patent GB-218538-A (GB)
Title: Slack adjuster for brakes
IPC: B61H15/00
Filed: 1923-10-19
Abstract: 218,538. Djurson, A. R. K. Oct. 19, 1923. Compensating for wear.-An automatic slack-adjusting device comprises a screwed rod arranged to be turned by a friction clutch co-operating with a one-way detent so controlled that the amounts of rotation imparted to the rod during the application and release movements of the mechanism are unequal if the slack is greater or less than a predetermined amount. In another form a one-way driving mechanism co-operating with the friction clutch becomes operative during the application movement if the slack is excessive. The brake mechanism comprises the usual levers 11, 12 pivoted at 16, 14 respectively to the piston rod 17 and to the cylinder 10 and connected by a tie-rod comprising a rod 33 screwing into one end part 32 and rotatably connected with the other end part 31. The rod 33 is adapted to be turned by a clutch device comprising friction discs 38, 40, the alternate members of which are keyed respectively to a sleeve 37 and to the rod 33, the discs being pressed into engagement by a spring 43 abutting against a nut 42 on the rod 33. The sleeve 37 is journaled upon the rod 33 by means of a head 44 and also upon a hub 45 fast on the rod and formed in one with a ratchet disc 46. The sleeve has a crank-arm and pin 30, 29 for the attachment of connections 21 - - 27 bv which it is actuated by the piston rod 17. A pawl 47 pivoted upon a casing 48 secured to the rod 31 adapted to engage the ratchet disc 46 is controlled by a cam surface 50 on the sleeve 37 which engages an arm 49 on the, pawl so as normally to hold the pawl in the disengaged position. During the application movement of the mechanism the sleeve 37 turns the rod 33 in the direction of the arrow, Fig. 4, until this rod becomes locked by the friction between it and the rod 32 due to the development of tension in these rods when the blocks are applied to the wheels. Further movement of the sleeve is taken up by slipping of the friction discs 38, 40. If the slack is normal the cam 50 permits engagement of the pawl with the disc 46 only when the rod 33 has become looked, and during the return movement of the parts the rod is reversely rotated to the same extent as it was turned during the application movement. Should there be excessive slack, however, the pawl becomes engaged before the rod 33 has been locked, and during the return movement holds it for a time during the reverse movement of the sleeve 37, with the result that the reverse movement of the rod is less than its forward movement and slack is taken up. The mechanism also operates to increase the slack if this should be insulficient, as may happen for instance by the unloading of a vehicle. In this case the rod 33 becomes locked by friction before the pawl 47 becomes engaged with the ratchet diso 46 and on account of the lost motion in the adjuster connections 21 - - 27 the return travel of the sleeve 37 after the friction lock on the rod 33 has been released is greater than its travel during the braking action before the rod is locked, and the rod is thus given a permanent turn such as to increase the slack. Manual adjustment of the slack may be effected by the member 34 secured to the rod 35. In a modification, Figs. 5 and 6, a pawl 62 carried by a crank arm 53 connected to the piston rod and freely mounted upon the rod 33 is adapted to engage a ratchet disc 56 which is also freely mounted on the rod and disposed between a pair of friction discs 55, 57 keyed on the rod and pressed together by a spring 58. The pawl is controlled by an arm 63 actuated by a fixed cam 64. When the brakes are applied the arm 53 moves from the position shown in broken lines, and if the slack in the mechanism is normal the pawl engages the ratchet 56 only when the rod 33 has become frictionally locked, the ratchet turning idly between the discs 55, 57 during the completion of the movement of the arm 53 by the piston. But if there is excessive slack the pawl engages the ratchet before the locking of the rod, which is then turned by the discs 55, 57 acting as a friction clutch. Friction detents or pawls in the form of pivoted cams may be substituted for the ratchet and pawl mechanisms 46, 47 and 56, 62.