GB1311089A - Internal shoe drum brakes - Google Patents

Abstract

1311089 Internal shoe-drum brakes; indicating brake-application GIRLING Ltd 22 Oct 1970 [7 Nov 1969] 54763/69 Heading F2E The invention relates to internal shoe-drum brakes of the kind in which arcuate shoes 1, 2, Fig. 1, for engagement with a drum (not shown) are mounted on a stationary back-plate 4, and adjacent shoe-ends are separated in the application of the brake by a mechanical actuator linkage including an angularly movable lever 9 pivotally connected at 10 to one shoe and coupled at the other end to applying means such as an inextensible cable 11, and a strut 13 acting between the lever 9, at an intermediate point in its length, and the other shoe 2, and in the off position of the brake the lever cooperates with a back-stop, e.g. 17, Fig. 2, which defines a retracted position determining the braking clearance between the brake shoes and the drum, means 14 for adjusting automatically the braking clearance to compensate for wear of the friction linings being incorporated in the mechanical actuator assembly; it consists in providing an electrically-operated device, e.g. 34, Fig. 2, for indicating when the linkage is in a brake-applying position in which adjacent shoe ends are at least partially separated, the device 34 being actuated by an electrical make and break effected by the engagement and disengagement of the lever with the back-stop. As shown, the lever 9 has an abutment 19, Fig. 2, and the backstop comprises a sleeve 21 of deformable synthetic plastics material which extends into the brake through an opening in the back-plate 4; at its inner end the sleeve has an integral wall 22 through which extends part 26, of the stem of a spring-loaded contact member 27, the outer end of part 26 carrying a metallic head 28. In the "off" position of the brake shown in Fig. 2, abutment 19 is in contact with contact member 27, and the other end of member 27 is in contact with an electricallyconductive plate 29 connected through a battery 33 and a lamp 34 to earth at 35. In operation, during the first movement of lever 9 inwards (to the right in Fig. 2), during application of the brake, a spring 30 maintains contact between member 27 and lever 9, but the resulting movement of member 27 breaks contact with plate 29, so the lamp 34 is extinguished, providing an indication to the driver. In a modification, described without an accompanying drawing, the end of contact member 27 remote from part 26 has a radial projection or flange freely received within an annular recess in the end plate 29, the recess having a depth greater than the axial thickness of the projection or flange, in this case, in the "off" position, the lamp is de-energized. During the first movement of brake application, spring- urged movement of member 27 causes contact between the projection or flange abovementioned and the interior of plate 29, so the circuit is made and the lamp is illuminated.