Patent GB-1463074-A (GB)
Title: Hydraulic brake actuator piston and slack adjuster assemblies
IPC: F16D65/56
Filed: 1973-03-20
Abstract: 1463074 Wear adjustment; disc brakes GIRLING Ltd 19 March 1974 [20 March 1973] 13204/73 Heading F2E The retracted position of a piston 10 of a disc brake hydraulic actuator is controlled by an adjuster comprising a rotatable nut 11 having an internal screw thread 15 mating with an external thread on a non-rotatable strut (not shown) to form a non-reversible screw thread connection; a drive ring 16 encircles the nut 11 and there is a reversible screw thread connection 27 between the drive ring 16 and either a ring 17 fixed in the piston 10 or (as illustrated) the nut 11; co-operating friction surfaces 28, 29 between the drive ring 16 and either the nut 11 or (as illustrated) the ring 17 are urged towards one another by a wavy washer spring 33; and the adjuster also incorporates a differential control means 34-39 which permits rotation of the nut 11 by the drive ring 16 for adjustment but restrains reverse rotation of the nut 11 under shock loading from the piston 10 when the brake is not operated. In the illustrated embodiment, the differential control means comprises a first control washer 34 prevented from rotating by three dowels 20 received in notches 35 and a second control washer 36 fixed relative to the nut 11. The washers 34, 36 have mating faces 37, 38 formed with radial serrations or corrugations and are urged together by a heavy spring 18. The washer 36 is held by the bias of spring 18 against a spring ring 39 fitted in a peripheral groove in the nut 11 and is also splined to the nut 11; in an alternative arrangement the thread 26 of the nut 11 could continue to the left-hand end of the nut 11 and the washer 36 mesh with the thread 26; in a further alternative, the control washer 36 is an integral part of the nut 11. The dowels 20 are received in longitudinal grooves 22 in the piston 10 and three shorter dowels 21 are received in grooves 23. The dowels 20, 21 are received in notches 24 in the fixed ring 17 to prevent rotation thereof, and the ring 17 is biased against a spring ring 19 by spring 18. The wavy washer spring 33 acts between the drive ring 16 and an abutment washer 31 having cranked-fingers 32 which straddle the dowels 20, 21 and bear against the fixed ring 17. Upon application of hydraulic pressure, the piston 10 is moved and takes nut 11 with it. If brake lining wear has occurred axial clearance at the non-reversible screw thread connection will be taken up and the nut 11 will be drawn rightwards by hydraulic pressure acting on the strut and is caused to rotate, the drive ring 16 being held stationary by co-operating surfaces 28, 29. When the brake is released the surfaces 28, 29 are parted and the drive ring 16 is rotated until the nut 11 takes up its at-rest position abutting an end wall 14 of the piston 10. Upon knock-back the nut 11 is momentarily separated from end wall 14 but the serrations on washers 34, 36 move the nut 11 back, should it turn slightly, to prevent mal-adjustment. The control washers 34, 36 also assist in resisting rotation of the nut 11 in that part of an adjustment cycle in which the drive ring 16 is turned. The dowels 21 serve as limit stops for the washer 34 to limit compression of spring 18 in the event of substantial travel of the nut 11. In the arrangement where the reversible screw thread connection is between the rings 16, 17 the ring 16 and nut 11 having mating conical friction surfaces forming a friction clutch. In a further alternative the surfaces 28, 29 slope the other way and the spring washer 33 acts on the right-hand side of drive ring 16, and the reversible and non-reversible screw thread connections are of the same hand unlike the illustrated embodiment. In this case, during an adjustment cycle the drive ring rotates upon brake application and the nut turns upon brake release. The strut may bear against a cam journalled in the cylinder body or in another piston which cam serves as a mechanical actuator for handbrake operation as described in Specification 1,179,235. The cam may be omitted however, and the strut then forms part of the cylinder body or a counter piston.