Patent GB-1420724-A (GB)
Title: Brake actuator mechanism with automatic brake wear take-up
IPC: B61H15/00
Filed: 1974-04-01
Abstract: 1420724 Brake actuators; transmitting- mechanism slack-adjusters KNORR-BREMSE GmbH 1 April 1974 [4 April 1973] 14414/74 Heading F2E A brake actuator mechanism which is automatically adjustable to take up brake wear and which includes the following features: an axially-displaceable adjustment spindle 1 which is non-rotatable about its axis and which is adapted to be coupled at 2 with a brake linkage, a non-self-locking external thread 3 on the spindle 1, a coupling nut 4 which can turn on the spindle upon application of a force tending to displace the nut axially, a non-rotatable actuator sleeve 16 displaceable relative to the spindle and the nut in directions parallel to the spindle axis (e.g. in response to actuation of a piston-cylinder device 19, 20), and a non- rotatable control sleeve 11 mounted for limited movement (distance a) parallel to the spindle axis and biased (by a spring 13) towards a position of co-operation with the nut in which the control sleeve holds the nut against rotation, and in which the actuator sleeve 16 is displaceable relative to the nut 4 into a position of co-operation therewith so as to hold the nut against rotation when the actuator sleeve is displaced in a brake-apply direction, is characterized by a stop 9 provided to control the movement of the actuator sleeve in a brake-release direction from the last-mentioned position of cooperation with the nut, and biasing means 33, provided to oppose movement of the actuator sleeve 16 in the brake-apply direction. In operation, for normal clearance, when compressed air is supplied at 22, spindle 1 is initially held by sluggish movement of linkage connected at 2, so counterface 18 of flange 17 of sleeve 16 is separated from abutment face 9 of nut 4 and then coupling face 14 of annular member 15 secured to sleeve 16 engages coupling face 8 of nut 4. On further movement of sleeve 16 (integral with piston 19) nut 4, prevented from rotating by the 8, 14 coupling, entrains spindle 1; control sleeve 11 is forced by spring 13 to follow the nut 4 until, after distance a, end face 31 of radial projection 27 of control sleeve 11 meets end face 32 of a slot 26 in a fixed tubular extension 24. The brake is now just applied. (Release from this position involves a reversal of these steps.) For more forceful application, of if the clearance is excessive due to wear, compressed air displaces piston 19 further, whereupon sleeve 16 continues to entrain nut 4 and spindle 1 (by the 8, 14 coupling), sleeve 11 being held at face 32. A coupling face 7 on nut 4 thereupon separates from coupling face 10 on sleeve 11, and spring 13 is progressively compressed. On release, if the release stroke is excessive due to wear, in the first phase the distance between faces 10 and 7 represents the excessive clearance. As spring 33 pushes piston 19 and sleeve 16 back further, spindle 1 is initially held. by a spring 35 acting between an adjusting ring 19 and a flange 34 of spindle 1, so nut 4 is also held, so coupling 8, 14 opens. The nut 4 is now free to turn, and is turned, by spring 13 (reacting from control sleeve 11) through ball bearing 12. This release phase continues until face 7 of nut 4 again meets face 10 of sleeve 11, such engagement preventing further rotation of the nut. Next, faces 18, 9 re-engage, and thereafter the release procedure is effectively the brake-apply procedure for normal clearance, in reverse. In Fig. 2 (not shown), the piston-cylinder is separate from the slack-adjuster assembly; extension 24 is connected to one lever of an H- brake linkage, actuator sleeve 16 is connected to the other lever, and the piston-cylinder is connected between the other ends of the levers. Since in this case spindle 1 must move leftwards relative to extension 24 during brake application, the parts 4, 11, 15, 17 are all axially reversed.