Patent GB-1152642-A (GB)
Title: Vehicle Brake Actuator
IPC: B60T17/16
Filed: 1967-03-20
Abstract: 1,152,642. Fluid-pressure brakes. NORTH AMERICAN ROCKWELL CORP. 20 March, 1967 [26 April, 1966], No. 12911/67. Heading F2F. In a double diaphragm compressed-air brake motor which includes locking means for preventing return of one of the diaphragms when the latter is moved to apply the brakes by the admission of air to an auxiliary chamber behind this diaphragm, and wherein there is disposed in a service chamber between the two diaphragms an elastic spacer member, the spacer member is deformable when the assembly is subjected to excessive back pressure as when a contraction of the brake drum of an internal shoe drum brake operated thereby occurs while the locking means is operative, whereby jamming of the locking means is precluded. As shown, the motor 17 comprises service and auxiliary diaphragms 38, 39 between which is a spacer member 60 which is secured, together with the diaphragm 39, a clamp plate 68 and a washer 69, to a wedge rod 66, the latter, together with a pair of rollers 84, 85, which are supported by a pair of slotted plates secured to a piston 74 and which co-operate with inclined surfaces 96, 97, constituting the locking means. Air is supplied to service chamber 42 between the diaphragms from a service reservoir 15 on operation of a driver's valve 12 controlling a relay valve 13, resulting in movement of the diaphragm 38 independently of the diaphragm 39 to operate a wedge 52 of a drum brake via a rod 53 and abutment plate 48. An auxiliary reservoir 22 supplies air via a selector valve 26 to auxiliary chamber 43 when the valve 26 is operated manually by the driver, either in an emergency or for parking, to connect conduits 27, 28 to this reservoir, the two diaphragms then moving together and brake applying force being transmitted via the spacer member 60. As a result, the wedge rod 66 is also moved so that wedge portion 83 is disposed between the rollers 84, 85, whereby on subsequent venting of the chamber 43, in an intermediate position of the selector valve 26, the brake is locked by the wedging action of the rollers. Should the brake drum subsequently contract, the excess back pressure causes deformation of the spacer member owing to its relatively thin central portion 62, so that the locking force is not increased to a great extent. As a result, the lock can be released without in such event it being necessary to apply a hammer blow to the release plunger 103 which is provided solely for releasing the lock in the event of a failure of the pressure source, lock release normally being effected by moving selector valve 26 to a position in which conduits 32, 33 leading to a release chamber 80 behind the piston 74 are connected to the reservoir 22. Various alternative forms of the spacer member 60, which is preferably of non-metallic elastomeric material but may be of metal, are disclosed (Figs. 6-20, not shown), these generally comprising a relatively thin central portion and a thicker annular portion, as in Fig. 1, but modified by the provision of circumferentially spaced recesses in the annular portion, the provision of a metal backing member or by a variation in the profile of the annular portion. The plunger 103 may be screwthreaded in the end of the motor housing and adapted to be rotated to release the lock in the absence of air pressure, instead of being a sliding plunger (Fig. 5, not shown). In a modification, Fig. 21, a resilient button 305 is additionally provided within the spacer 306 and is secured both to the wedge rod 66 and to a sleeve 315 on which the spacer member and diaphragm 39 are secured by a nut 317.