Patent GB-1447359-A (GB)
Title: Automatic adjusters for vehicle brakes
IPC: F16D65/56
Filed: 1972-11-09
Abstract: 1447359 Actuators and anchor members with slack adjusters for drum brakes GIRLING Ltd 10 Oct 1973 [9 Nov 1972] 51851/72 Heading F2E An automatic adjuster for a vehicle brake comprises housing 8, Fig. 2, screwthreaded strut assembly 13, 23, 29, 14 movable relative thereto between an inoperative retracted position and an operative advanced position to transmit a brake-applying force to a friction member (not shown) from a brake-applying means, e.g. wedge 15, abutment means 34 disposed in one datum position to define the retracted position, a first part of the adjuster, e.g. right side of groove 35, engaging means 34 in this position of the strut assembly, a second part of the adjuster, e.g. left side of groove 35, moving abutment means 34 to a second datum position when the strut assembly moves from the retracted position to the operative advanced position through a distance exceeding the spacing 36 between the "second part" and the abutment means 34, which spacing defines a desired braking clearance, and adjuster means, e.g. springs and flanges for increasing automatically the effective length of the strut assembly to compensate for wear of the friction member after the abutment means 34 has moved to the second datum position. Fig. 2 shows the adjuster applied to a wedge actuator of an internal shoe drum brake. The right-hand roller 21 acts upon the inclined face 20 of a single thrust member 14 which has a coarse fast-thread connection 25 with a clutch ring 29, which is urged by spring 30 against sleeve 23, the sleeve having a threaded connection with piston 13 forming part of a tappet 12. Parts 14, 29, 23, 13 form the strut assembly; thrust member 14 and piston 13 are prevented from rotating. A friction ring 34 is an interference fit in the bore 10 of a housing 8, and is accommodated in a groove 35 which is axially longer than ring 34 by an amount 36 equal to the normal brake clearance. In operation, when the brake clearance exceeds the normal, the applying force is sufficient to push the ring 34 outwards, but on brake release the ordinary return springs (not shown) are not able to push the ring back again, so the piston 13 comes to rest further out. This permits a spring 31 to push thrust member 14 back to its normal position, but in so doing it frees ring 29 from sleeve face 27 and the ring is forced to rotate by spring 30 until the ring again contacts sleeve 23. The head of thrust member 14 is now spaced from the end of sleeve 23. At the next brake application, ring 29 is held fast against sleeve face 27, and the force exerted on thrust member 14 causes ring 29 and sleeve 23 to rotate together and therefore relative to piston 13, in a direction to increase the overall length of the thrust assembly. As applied to a relay unit between the lower ends of the primary and the secondary shoe in a duo-servotype brake, the adjuster includes an extension 58, Fig. 4, of the thrust member 14, separated from a thrust-transmitting assembly 46 by a block of resilient material 59. The ring 34 is now accommodated in a groove 35 in the housing, and piston 13 is an interference fit in the ring. In the modified actuator of Fig. 3, sleeve 23 is a sliding fit in piston 13, thrust member 14 has screw-threaded engagement with sleeve 23, and a stem 39 having a clutch-surface head 41 has a fast-thread connection 40 with clutch ring 29, which here is secured to sleeve 23. Stem 39 is freely slidable in member 14. The strut assembly here comprises the thrust assembly (member 14 and stem 39 with head 41), sleeve 23 and attached ring 29. Leftward movement of ring 34 (after rightward movement for slack adjustment) is further prevented by tapering the right-hand wall of groove 35.