GB549914A - A new or improved automatic adjusting mechanism for brakes - Google Patents

Abstract

549,914. Adjusting brakes. BENDIX, Ltd., and IRVING, J. S. Oct. 22, 1941, Nos. 13589/41 and 45/42. [Class 103 (i)] An automatic adjusting device for brakes of the kind in which the shoes move circumferentially to a limited extent when applied comprises a cone or wedge which is advanced by a ratchet wheel and pawl to separate a pair of adjacent shoes abutments during release movement of the shoes if the application movement is sufficient to cause the pawl to slip a tooth of the wheel. Adjustment may be automatically prevented when the brake is hot. The brake shown is of the kind described in Specification 499,598 in which a floating shoe or each of a pair of shoes is applied by an actuating means acting on a bell-crank pivoted on the shoe end and connected to a similar lever pivoted on the other end of the shoe and adapted to engage an abutment, the shoe anchoring at one end or the other according to the direction of rotation of the drum. As shown a bell-crank 12 pivoted on one end of one 11 of a pair of shoes 10, 11 is connected by a link 13 to a bell-crank pivoted on the other end of the shoe 11. The abutment for the shoe end and for the bellcrank is one of a pair of tappets 14 slidable in a housing 15 fixed to the back plate 16 and which can be separated by advancing a cone 17 by the rotation of a ratchet wheel 21 having a spindle 20 that screws into the cone. When the brake is applied a plunger 27 held in contact with the shoe 11 by a spring 29, follows up the shoe movement and if this is excessive a pawl 25 carried by the plunger slips a tooth of the wheel 21 and turns this wheel during the release movement of the shoe. The pawl is prevented from slipping more than one tooth by engagement of the plunger with a stop 31 on the tappet 14. To avoid overadjustment consequent upon heating of the brake, movement of the plunger 27 may be prevented when the brake is hot by the insertion into a slot 32 in the plunger of a stop 33 by a bimetallic strip 36. The strip 36 may instead be arranged to disengage the pawl. Rotation of the cone 17 during automatic adjustment may be prevented by the engagement of the tappets 14 with grooves 38 in the cone but the cone can also be turned by the head 19 to effect an adjustment.