Patent GB-1494221-A (GB)
Title: Brake adjusters
IPC: F16D65/56
Filed: 1974-02-16
Abstract: 1494221 Slack-adjusters; spot-type disc brakes GIRLING Ltd 29 Jan 1975 [16 Feb 1974] 7157/74 Addition to 1343111 Heading F2E  A slack adjuster for a vehicle brake system includes first and second members 23, 25, respectively, Fig. 1, having a reversible screwthread connection 28 (as defined in the Specification) therebetween so that in one direction of axial load between the first and second members (as shown, when the first member moves to the right), relative rotation is effected therebetween, and a third member 15, the second and third members 25 and 15 having interengageable wedging surfaces 30, 29, respectively, thereon effective, upon axial loading in a direction opposite to the first-mentioned direction (first member 23 now moving to the left), to tend to cause relative radial displacement between the first and second members 23 and 25 to hold them in frictional engagement with each other at the reversible screw-thread connection 28 to prevent reverse relative rotation between them, the first and second members 23 and 25 being spring-biased against each other at the reversible screw-thread connection in a substantially radial direction to inhibit undesired rotation there. As shown, the spring-biasing is achieved by providing the second member 25, which is a nut, with three longitudinal slits 31, Fig. 2, which divide at least the screw-threaded portion into three springy fingers 25a, 25b, 25c, and by ensuring that the free-state dimensions of the slit nut are such that the springy fingers press radially inwards against the first member or strut 23. During hydraulic operation, pistons 15, 16 are urged apart, and the hydraulic pressure acts on the left-hand end of strut 23 to urge it to the right relative to piston 15 and thereby holds this strut in abutment with the dolly 22, the cam 20 being held in the position shown by a stop (not shown). The clearance 37 between a wheel 36 attached to piston 15 and base 32 of nut 25 is sufficient to permit relative axial movement between pistons 15, 16 without affecting screw-thread connection 28 during normal piston travel. With excessive travel, clearance 37 is taken up and nut 25 is prevented by wheel 36 from moving further to the right, so nut 25 is caused to turn on strut 23 by the reversible screw-thread connection 28 in the direction to increase the at-rest distance between the pistons. When the handbrake is applied, cam 20 is turned counterclockwise, thereby urging piston 15 to the left relative to piston 16. But in this case the brake-applying force is transmitted through the automatic adjuster, i.e. between strut 23 and nut 25, and it is in this situation that the wedging surfaces 30, 29 are forcefully interengaged, thereby causing the springy fingers 25a, &c., to clamp strut 23 between them, preventing relative axial movement and consequent relative rotation; nut 25 also cannot rotate. For application to a disc brake, a yoke 19 associated with piston 16 is slidably supported on a body member 18, by means not shown, for reaction operation of the remote friction pad (not shown); piston 15 applies the directlyoperated pad (not shown); body member 18  provides bore 17 for the pistons. In Fig. 5 (not shown), which resembles Fig. 1, provision is made for rendering the automatic adjuster non-responsive to brake deflection caused by heavy brake-application. In Figs. 3, 4 (not shown), the first member is a nut having a reversible screw-thread connection with the second member which is a screw split at the left-hand end into three fingers, and the third member is the strut, and the wedging surfaces are provided between the strut end and the split part of the screw. A split spring ring around the strut acts radially outwardly against the screw fingers.