Patent GB-909122-A (GB)
Title: Improvements in or relating to air brake cylinders with a built-in slack adjuster
IPC: B61H15/00
Filed: 1961-01-18
Abstract: 909,122. Fluid-pressure brakes. SVENSKA A.B. BROMSREGULATOR. Jan. 18, 1961 Jan. 27, 1960], No. 2074/61. Class 103 (1). A brake air cylinder having a built-in slack adjuster comprises a piston returned by spring means and having a tubular piston-rod, a push-rod telescoping within the pistonrod and formed as a ratchet bar or screw having first and second pawls or nuts thereon adapted in operation to move relative to the push-rod only in the slack reducing direction, one of the pawls or nuts having movement relative to the brake cylinder restricted to normal travel of the brake so that more than this amount of travel of the push-rod causes slack to be reduced by said relative movement, after which the other pawl or nut follows up the movement during return of the brake linkage, the arrangement being such that during said return of the linkage the second pawl or nut is held locked to the push-rod so that the latter is returned positively to and retained positively in its fully returned position. In one embodiment, Fig. 1, a cylinder 1 contains a piston 2 returned by a spring 5 and having a tubular piston-rod 3 in which is telescopically mounted a push-rod 8 on which are threaded nuts 10, 11. The thread on the rod 8 is sufficiently coarse to allow the nuts to be rotated by axial pressure acting on one side through respective ball races 13, 15. The nut 10 is arranged to be clamped against rotation by forces acting on the side opposite its ball-race 13 by having a conical face engageable with a corresponding conical face 9a of an abutment 9 secured within the piston-rod 3, a spring 14 urging the nut 10 towards the abutment 9. The nut 11 can be clamped against rotation by a force acting in either direction, having two conical faces respectively engageable with corresponding faces on the abutment 9 and on an abutment 12 which is held against rotation but slidable under the action of a spring 16 for a distance corresponding to normal brake travel by having a pin 17 passing through a slot 6 in the pistonrod 3 and engageable with abutments 18, 19 in a front extension 4 of the cylinder 1, the former of these abutments being adjustable. A pin 7 in the extension 4 holds the piston rod 3 against rotation by engagement in the slot 6. In operation, application of the brake causes nut 10 to be clamped by the abutment 9 so that movement of piston 2 is communicated to the push-rod 8, while abutment 12 similarly clamps nut 11 by the action of the spring 16. Should normal brake travel be exceeded, however, the pin 17 engages the abutment 18 so that nut 11 is freed and subsequently rotated by engagement of ball race 15 with a rear face of the abutment 12. When the piston 2 is returned the nut 11 is clamped in its new position between the abutments 9 and 12, the nut 10 following up the movement of nut 11 during completion of the return movement by engagement of its ball race 13 with an abutment at the front end of the piston-rod 3. In the modification of Fig. 2, the push-rod 8 has a screw of finer pitch and acts as a ratchet bar, the nuts 10, 11 being segmented and encircled by spring clips so that they act as pawls. The abutment 12 operates as in the first embodiment, but since the ball races are not required it acts directly on the forward end of the nut 11 while a portion 20 acts on the rear conical face of the nut 11. A separate member 21 acts on the rear conical face of the nut 11, being connected with the abutment 9 by pins 22. The springs 14, 16 of the first embodiment are omitted, but a light spring 23 is interposed between the members 20 and 21.