GB1179235A - Improvements in Brake Adjusters. - Google Patents

Abstract

1,179,235. Brake wear-adjusters. GIRLING Ltd. 15 March, 1967 [18 March, 1966; 7 May, 1966], Nos. 11915/66 and 20309/66. Heading F2E. An automatic brake wear-adjuster mechanism, which is operable between, a piston of an hydraulic actuating cylinder of e.g. a disc brake and a rotatable cam journalled in a reaction member and forming part of an alternative manual brake applying mechanism, comprises a first non-rotatable member, a second member, and an intermediate rotatable member which is in screw-threaded engagement with the first member and in axial engagement with the second member through at least one helically inclined surface, the arrangement being such that after a predetermined travel of the piston has occurred the intermediate member is rotated by the effect of axial forces on the helically inclined surface to increase the overall length of the assembly to compensate for wear of the friction means of the brake. In the embodiment of Fig. 1, the first non-rotatable member is the brake pad applying piston 12, the intermediate member being in the form of a rod 13 having a first threaded portion 16 engaging a threaded portion 18 of a bore 17 in the piston, a coarser second threaded portion 20 engaging a nut 19 to provide the helically inclined surfaces, and a plain end portion abutting rotatable cam 30 of a manual brake applying mechanism. A flange 21 of the nut 19 normally engages a ball race 22 and after limited movement in the brake applying direction engages a ring 23 loaded by a spring 25, the arrangement being such that application of the brake either hydraulically or manually causes rod 13 to be rotated to take up wear through the action of the reversible screw thread 20 and nut 19 whenever piston travel exceeds the clearance between the flange 21 and the ring 23. Since hydraulic pressure is able to act upon the end of rod 14 located within the piston, friction between the threaded portions 16 and 18 increases with increase of hydraulic pressure and by suitably choosing the compression of the spring 25 the ring 23 is able to give at high pressures, or alternatively the friction between the flange 21 and ring 23 is overcome, so that adjustment occurs only at fairly low brake pressures. On brake release the flange 21 engages the ball race 22 so that the nut 19 is rotated freely and does not disturb the adjustment. The piston and cylinder assembly is adapted to form part of a floating caliper assembly. Figs. 2-5 (not shown) disclose alternative constructions which are functionally equivalent to that of Fig. 1, Figs. 4 and 5 showing assemblies which comprise two pistons in a fixed cylinder. In the embodiment of Fig. 6, the ball race is dispensed with, the nut 279 being formed with radial and conical engagement faces 282, 283 respectively to provide the differing resistances to rotation of the nut desired for adjustment to be effected on brake application and undisturbed on brake release. In the constructions of Figs. 2-6, the brake applying force when applied manually via the cam is transmitted via the non-reversible screw-threaded adjustment assembly, so that adjustment only takes place during hydraulic operation. In the embodiment of Fig. 7, the reversible helical thread is replaced by an assembly of three balls (Fig. 8, not shown) engaged between inclined recesses 321, 322 in members 316, 317 which are rotatable in one direction only on a rod 313 having threaded engagement with a nut member 312 engageable with cam 330 carried by one piston 309 which acts on a floating caliper (350, Fig. 9, not shown), a second piston 308 containing the assembly comprising members 316, 317 and the balls and acting directly on a brake pad. Further modifications are also disclosed (Figs. 10-20, not shown). Adjustment may be arranged to take place on brake release (Figs. 19 and 20) instead of on brake application.