Patent GB-752988-A (GB)
Title: Improvements relating to brake control apparatus for hydraulic braking systems
IPC: B64C25/46
Filed: 1954-09-08
Abstract: 752,988. Hydraulic brakes. WESTING. HOUSE AIR BRAKE CO. Sept. 8, 1954 [Sept. 15, 1953], No. 26009/54. Class 103 (1). In a brake control apparatus for hydraulic braking systems of the type described in Specification 751,772, in which slipping of braked wheels of a vehicle is prevented, provision is made such that in the event of failure of the pneumatic supply to the piston valve device during the time that it is desired to bring the vehicle to rest, the brakes may be controlled manually. In the embodiment illustrated in Fig. 1, the brake control apparatus is similar to the arrangement described in the abovementioned Specification ; hydraulic fluid being supplied via the conduit 3 from the master brake cylinder (not shown) and the conduit 2 to the wheel brake cylinder device 1. Interposed between the conduits 2 and 3 is a displacement piston valve device 4 for controlling the communication between the master brake cylinder and the wheel brake cylinder device 1. The brake cylinder device comprises a piston 22 which is provided with a piston valve 25 having a reduced portion 27 which is adapted to register with the inlet and outlet passages 26 (as illustrated) to establish communication between conduits 2 and 3 when pneumatic pressure is supplied via conduit 6 from a reservoir 8 through an inertia controlled release valve device 9 to pressurise the chamber 23 when the vehicle wheel is not slipping. In order to compensate for the possibility of the pneumatic pressure in reservoir 8 being reduced to a point below which the pressure, when supplied to the chamber 23 of the piston valve device 4, would be insufficient to overcome the hydraulic pressure in chamber 24 to operate the piston 22 and the piston valve 25 to their normal position illustrated, a by-pass valve device 4a is provided at the base of the piston valve device 4 to permit manual control of the application and release of the brakes until the pneumatic pressure failure in the reservoir 8 has been corrected and the vehicle has been brought to rest. The by-pass valve device 4a comprises a piston valve device 37 which is normally forced to the left against the valve seat 42 by pneumatic pressure supplied to chamber 40 via by-pass conduit 7 from the reservoir 8; the apparatus thus functioning as described in the above-mentioned Specification when the pneumatic pressure is normal. If, however, the pneumatic pressure is sufficiently reduced, the piston-valve device 37 is moved to the right to abut cap 39 and to unseat the piston valve device 37 from the seat 42 to permit manual control of the operation of the brakes via passageway 43, hydraulic pressure chamber. 38, passageways 28, and 26 and conduit 2. An alternative arrangement is described whereby in the event of a sufficient reduction in the pneumatic pressure in reservoir 8, an electrical contact is made which operates an electromagnetic locking device to force a plunger into the recess 33 of the piston 22 of the piston valve device 4 to lock the piston in its illustrated position wherein the reduced portion 27 of the piston valve 25 is kept in alignment with the conduit 3, passageway 26 and conduit 2 for manual control of the operation of the hydraulic brakes. Specification 674,506 also is referred to.