Patent GB-1499518-A (GB)
Title: Automatic slack adjusters for vehicle brake linkages
IPC: F16D65/60
Filed: 1975-03-25
Abstract: 1499518 Automatic slack adjusters for vehicle brake linkages GIRLING Ltd 19 Feb 1976 [22 Feb 1975] 7543/75 Heading F2E An automatic slack adjuster for a vehicle brake linkage comprises a housing 1 which constitutes a lever in the linkage and is mounted for rocking movement about an axis of a shaft which is adapted to be rotated for applying or releasing a brake, force being transmitted between the housing 1 and the shaft by means of a worm 6 mounted with end float in a blind bore 5 in the housing 1 and meshing with a worm-wheel 2 splined to the shaft, the arrangement being such that adjustment of slack in the linkage is effected by rotation by automatic worm-driving means 9 of the worm 6 to alter the angular position of the worm-wheel 2 with respect to the housing 1. The automatic worm driving means 9 comprising a one-way clutch 17 coupling relatively movable parts 10, 15 which clutch 17 is disengaged during each brake applying movement. In the illustrated embodiment the worm 6 is provided on a spindle 4 rotatably mounted in a blind bore 5 in housing 1, and the spindle 4 also comprises a skew gear 7. A cam plate 8 rigidly connected to a stationary member acts on the spindle 4 through the worm driving means 9 which comprise a piston 10 slidable in a bore 11 in the housing 1 the cam plate 8 engaging the piston 10 through a coupled spindle part 12. The piston 10 is keyed to a stem 14 on which is slidably and rotatably mounted a pinion 15 meshing with the skew. gear 7. Stem 14 carries a head 16 slidable in bore 11 and the clutch 17 which is adapted to couple piston 10 and pinion 15 comprises an inclined clutch face 18 between head 16 and stem 14 and a complementary inclined clutch face 19 on pinion 15 for engagement with face 18. When the clutch is engaged abutment faces 20, 21 on piston 10 and pinion 15 are spaced by a distance corresponding to the desired braking clearances.  In operation, angular movement of the housing 1 in an anti-clockwise direction rotates the shaft to cause a cam expander thereon to apply shoes to a drum-spindle 4 initially slides in bore 5 to take the end float until the spindle 4 engages with the closed end of the bore 5 to lock the spindle 4 against rotation and axial movement with respect to the housing 1. Thereafter angular movement of housing 1 is transmitted to worm-wheel 2 and the shaft through the worm 6. In turn movement of housing 1 causes the piston 10 to slide in bore 11 to disengage clutch 17. If the distance between abutment faces 20, 21 is taken up then pinion 15 is raised by piston 10, and with clutch 17 disengaged, the pinion 15 is caused to rotate as it passes over the teeth on gear 7. When the housing 1 moves angularly in the opposite direction, initially the pinion 15 is held against rotation by engagement with the skew gear 7 until the clutch 17 re-engages to lock the pinion 15 to the piston 10. Thereafter additional movement of the piston 10 urges pinion 15 axially and causes worm 6 to rotate by the engagement of the pinion 15 with skew gear 7- this in turn rotates worm-wheel 2 to advance the shoes towards the drum.