GB736778A - Improvements in shoe drum brakes - Google Patents

Abstract

736,778. Shoe-drum brakes. BRISSON, L. C. June 22, 1951 [June 30, 1950], No. 14946/51. Class 103 (1). A shoe-drum brake comprises an actuating cylinder 2 containing a double ended piston assembly 3, 4, pivoted shoes 7, 11, 18, a bell-crank lever 20-21 pivoted at 22, and a bell-crank lever 34 fixed to a pin 32 on the lever end 21 and operating a cam 37. The lever 20-21 has clevis ends, the part 20 of which carries slide blocks 26, 27 which engage a slot 30 in a lug 31 on the shoe 18, and the part 21 being embraced by a forked end-piece 5 pivoted to the pin 32 and arranged to abut against the cylinder 2 while being free to move away from it. In operation, movement of the lever 34 by means of a hand brake cable 36 moves either the lever 21 to lower the pin 32 by the action of the cam 37 against the piston 4, or displaces the piston 4 which pushes back the end 3, Wrapping action of the shoes against the drum in the direction of movement f1 applies the part 5 against the cylinder 2 with a greater force than that applied by the cam 37 which will in consequence be displaced. In reverse movement the ratio of forces is reversed and the part 5 moves away from the cylinder 2. For hydraulic operation the expander member through the action of the head 4 would itself act directly upon the cam 37 and the lever 21. In the direction f the instantaneous centre of revolution and the pivotal point of the shoe 18 are thrown off to infinity, while the instantaneous centres of revolution of the two adjacent shoes and their pivotal connection are aligned in a straight line. Specification 681,657 is referred to.