Patent GB-643059-A (GB)
Title: Improvements in or relating to fluid pressure control devices
IPC: B60T13/68
Filed: 1948-02-24
Abstract: 643,059. Fluid pressure brakes. BENDIX-WESTINGHOUSE AUTOMOTIVE AIR BRAKE CO. Feb. 24, 1948, No. 5510. Convention date, Oct. 31, 1944. [Class 103 (i)] . [Also in Group XXXVII] A fluid pressure control system, .particularly for the brakes of vehicles and their trailers, of the type in which a more rapid application and release of the brakes is obtained for a given movement of the operator's control member by means of switches near to the control member operating electromagnetic relay valves located in the fluid pressure system near to the brakes or member to be operated, is characterised mainly by an improved form of fluid pressure operated switch mechanism. As shown in Fig. 1, the system includes the usual master cylinder control unit 16, main reservoir 6, auxiliary reservoir 14, triple valve 10, and brake cylinder 8. Interposed in the pipe 18 from the master cylinder unit 16 to the triple valve 10 which pipe may be of considerable length, is a fluid pressure operated switch unit 32. The. unit 32, shown in detail in Fig. 2, comprises a casing within which slides a piston 40 dividing two chambers 42 and 43 connected respectively by connections 35 and 36 to the triple valve 10 and master cylinder unit 16. Movement of the piston 40 in either direction away from its central position is resisted by springs 45 and 50, such movement operating one or other of two snap-action switches 55 and 56 which when operated close the circuits between terminals 60, 61 and 68, 69, respectively. These terminals form part of circuits energized by battery 71 and switch 72 connected to electromagnetic relay valves 21 and 22 which may be of the type described in Specification 543,989 located adjacent to the brakes or other units to be operated. In operation, if the control lever 20 is depressed to operate the brakes, the resulting fluid flow in pipe 18 moves the piston 40 to the right to operate switch 56, closing the circuit between terminals 68 and 69. This results in the energization of the magnet of relay valve 22 which allows air to flow from the auxiliary reservoir 14 by pipes 24, 25, 18 and 11 to the triple valve 10 so that the brakes are rapidly applied at a corresponding pressure. If now the lever 20 is allowed to rise so as to release the brakes by exhausting fluid to atmosphere by outlet 19, the pressure in pipe 18 to the right of piston 40 moves it to the left thus operating switch 55, connecting terminals 60 and 61 and energizing the magnet of relay valve 23. The valve 23 by pipes 11, 18, 26 and 27 exhausts fluid to atmosphere from the triple valve 10, thus correspondingly reducing the pressure in the brake cylinder 8 in accordance with the operation of the lever 20. The fluid pressure operated control member 33 is so constructed that if the electrical system should be defective for any reason, the piston 40 by movement away from its central position near to the annular ridge 41. provides a substantial area of flow between the chambers 42 and 43 so that the brakes may be applied by direct fluid pressure control of the triple valve 10 in the usual way. In Fig. 1a, the system is shown extended to a trailer in which relay valves 101 corresponding to valves 21 and 22 on the tractor are also controlled by the switches 55 and 56. A special reservoir 114, restriction 117 and one-way valve 116 is provided in the fluid supply piping 89 to prevent the drop of pressure caused by the exhausting of the unit 101 being sufficient to actuate the emergency unit 98 of the triple valve 94.