Patent GB-446887-A (GB)
Title: Improvements in or relating to electric switching devices particularly adapted for use in electric motor control systems
IPC: B60L15/34
Filed: 1936-01-15
Abstract: 446,887. Actuating controllers. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.- (Assignees of Austin, B. 0. ; 348, Avenue A, Forest Hills, Pittsburg, and Willby, N. H. ; R.F.D. No. 1, Irwin, both in Pennsylvania, U.S.A.) Jan. 15, 1936, No. 1282. Convention date, Jan. 19, 1935. [Classes 38 (iii) and 38 (v)] Pneumatic actuation.-A switching device for cutting out sections of resistance 21 in a motor circuit comprises a plurality of movable contact members 10, a plurality of flexible diaphragms 25 for actuating the contact members in sequence, and means for applying fluid pressure to the diaphragms to operate them. In the arrangement shown, the movable contacts 10 are carried by springs 12 arranged in staggered relation in two rows above and below a manifold plate 26, the co-operating fixed contacts 11 being connected to the junction points between successive sections of resistance 21. Each diaphragm 25 is provided with a central raised portion 31 engaging the corresponding spring 12, and is clamped to the manifold plate by a plate 33 having a circular opening for the passage of the raised portion. Each diaphragm is also formed with a circular groove 37 adjacent the manifold plate. In order to start the motor 51, a controller 61 is moved to the position a, which energizes a line contactor 54 and connects the motor to the line through the whole of the resistances 21. On moving the controller to the position b an electromagnetic valve 39 is operated to connect a reservoir 41 of compressed air to the manifold through a pipe 38 which opens into the groove below the first diaphragm 25 and causes the latter to rise and short-circuit the first section of resistance. At the same time a port 43 is opened to admit the compressed air to a chamber 44 which extends the entire length of the manifold plate but is closed at both ends. Small ports 45 extend through the manifold plate and connect the grooves 37 in each of the top diaphragms with the corresponding grooves 37 in the lower diaphragms. Thus, as soon as the compressed air is admitted into the groove in the first diaphragm it flows slowly through the port 45 into the groove in the second diaphragm, and the latter is slowly lifted to uncover its port 43. As soon as this happens, a large supply of compressed air is admitted from the chamber 44 to effect the closing of the contacts and provide full pressure for forcing fluid through the small port 45 to the next diaphragm. In this manner the fluid pressure is progressively transferred from one diaphragm to another. In order to prevent any diaphragm from being raised by the fluid pressure until the preceding diaphragm has closed its contact members, bleeder valves 46 are provided to release the pressure from each of the grooves 37 with the exception of that in the first diaphragm. Each of the valves 46 is operated by a lever 47 which is pivoted at 48 and engages the central raised portion 31 of the preceding diaphragm, so that when the latter rises the bleeder valve is closed. The pressure in the central chamber 44 of the manifold can be released by opening a valve 42. This valve is closed when the controller 61 is moved to position b and can be opened by a limit relay 55 controlled by a series coil 56 and two shunt coils 57, 58 connected in opposi. tion to the coil 56. In the position b the winding 58 only is energized, but the rate of acceleration of the motor can be increased by moving the controller 61 to the position c in which both coils 57, 58 are energized, thereby increasing the current which can flow in the coil 56 before the relay is operated.