Brake monitoring system

Claim 1

A brake monitoring system particularly suited for use in monitoring brake shoe adjustment, brake lining wear and brake temperature for the brake shoes of an expansible brake shoe subassembly circumscribed by a metallic wear plate of an annular brake drum subassembly for one wheel of a wheeled vehicle comprising: A. at least two groups of normally open electrical switches, each group consisting of a pair of brake adjustment switches and a wear detection switch, each switch of each group being characterized by a resiliently supported shorting bar and an axially movable stem formed of Mylar and connected with the switch for displacing the shorting bar in a circuit closing direction; B. means for separately mounting the switches of each group in angular spaced relation on a given brake shoe of a radially expansible brake shoe subassembly having a non-metallic lining, the thickness of which is reducible by wear, with the stem of each switch being projected axially into an aperture extended radially through the lining, the stem of each brake adjustment switch being characterized by a length such that the stem extends through the lining for engaging the circumscribing wear plate of a brake drum subassembly as the brake shoe subassembly is expanded, whereby axial motion is imparted to the stem, while the stem of the wear detection switch is characterized by a length such that the stem extends through the lining for engaging the wear plate, as the brake shoe subassembly is expanded, only after the thickness of the lining has been reduced by wear, whereby axial motion is imparted to the stem, subsequent to a reduction in the thickness of the lining; C. a pair of circuits, each of which includes a pair of pin-receiving sleeves supported in a fixed relationship adjacent to the brake shoe subassembly and singly connected to one brake adjustment switch, and a testing circuit having an alarm signal generator connected with a pair of terminal pins adapted to be received by said pin-receiving sleeves; D. an alarm circuit connected with the wear detection switch of each group including a remotely related alarm signal generator for generating an alarm signal in response to axial motion imparted to the stem of the wear detection switch; and E. a pair of temperature responsive switches, each being separately mounted on one brake shoe of said pair of brake shoes and connected in a circuit including an alarm signal generator for completing the electrical circuit in response to changes of determinable magnitude in the temperature of the brake shoe on which the switch is mounted.