GB1419254A - Textensible strut assemblies - Google Patents

Abstract

1419254 Internal shoe drum brakes; slackadjusting GIRLING Ltd 26 Nov 1973 [7 Dec 1972 23 Jan 1973 8 June 1973] 56474/72 3304/71 and 27351/73 Heading F2E In an automatic adjuster for vehicle brakes of the kind comprising a two-part strut assembly of which the parts have a non-reversible screwthreaded connection, one part, which is provided with a helically-inclined surface with which engages a complementary helical surface on adjusting means, being rotatable relative to the other part to increase the effective length of the strut assembly to maintain the braking clearance constant, the helical surfaces comprise meshing helical gears provided with a predetermined degree of backlash corresponding to a desired braking clearance which is taken up to cause rotation of the adjusting means from one datum position to another only when movement of the strut assembly in a brake-applying direction has exceeded the predetermined degree, whereafter movement of the strut assembly in the opposite direction first takes up the backlash and then the gears engage to cause the "one part" to rotate with respect to the adjusting means, which is held fast, and with respect to the other part, thereby increasing the effective length of the strut assembly. As shown, the strut assembly forms part of a tappet 12 and comprises a non-rotatable piston 15 and a rotatable thrust member 16 whose stem 17 has a non-reversible screw threaded connection with piston 15 and whose enlarged head 18 has a helical gear 42, Fig. 3. The adjusting means 14, Fig. 3, comprises a helical gear assembly 35 provided with a heilcal gear 41 meshing with gear 42. A degree of backlash is provided between gears 41 and 42 sufficient to permit normal brake-applying movement between a friction lining of the brake and the drum. In operation, when movement of tappet 12 in brake-applying direction exceeds the backdash, the teeth of gears 41 and 42 engage; this initial engagement causes gear assembly 35 to rise against spring 38, thereby disengaging a clutch face 37 on assembly 35 from a clutch face 34 on housing 6. Further movement causes thrust member 16 to rotate gear assembly 35 (without thrust member 16 itself rotating). When the brake is released, return springs (not shown) acting through the shoes urge tappets 11 and 12 inwardly. Initial movement of tappet 12 causes gear 42 to disengage from gear 41: this permits clutch faces 37 and 34 to re-engage. Upon further movement of tappet 12, the backlash between gears 41 and 42 is taken up and after they have re-engaged and while piston 15 is moving further, thrust member 16 is rotated relative to piston 15 to increase the effective length of the strut, since gear assembly 35 is prevented from rotating by the engaged clutch faces 37, 34. For re-setting, a re-wind member 50 is pressed down to engage the gear assembly 35 and is rotated in a direction so as to screw thrust member 16 back into piston 15: in this operation both gear assembly 35 and thrust member 16 rotate. In two modifications, the two-part construction of gear assembly 35 is arranged differently and in one of these modifications the re-wind apparatus is arranged on the lower side of housing 6 (and therefore of the brake back-plate 4), so the drum need not have an access opening or be removed prior to re-setting.