GB602815A - Improved electric motor control system - Google Patents

Abstract

602,815. Automatic control systems for motors. GENERAL MOTORS CORPORATION. Aug. 10, 1945, No. 20530. Convention date, Aug. 30, 1944. [Class 38 (iv)] In a D.C. motor synchronizing system resistances are automatically inserted in series with a motor tending to overspeed and power to the system is interrupted when asynchronism exceeds a predetermined limit. In the embodiment shown, the reversible D.C. motors 25, 225 rotate screw-shafts 26, 226 through speedreducing gearing 28, 228, to operate ailerons connected to nuts 30, 230. Screw-shafts 26, 226 are fitted with movable armatures 91, 291 which normally engage with brake rings 29, 229, but which, on energization of motors 25, 225 and the associated clutch windings 90, 290 engage driven discs 92, 292. The battery 500 is connected to the system on closure of the master switch 260 and the direction of rotation of motors 25, 225 is determined by the selector switch 263. To lower the ailerons the selector switch engages the "down" terminal 264, thus energizing both the holding magnet 266, which holds contact 263 closed on contact 264, and the winding 54 of the contactor 50 which connects the series fields 85, 285 of motors 25, 225 respectively to battery 500. Simultaneously, the clutch coils 90, 290 are energized and the shafts 26, 226 rotate to move the ailerons and operate make-and-break switches 75, 275 in circuit with impulsers 122, 124 which attract and release actuators 123, 125 to rotate toothed discs 108, 110 one tooth at each impulse. With motors 25, 225 rotating at equal speeds the discs 108, 110 rotate at the same speed and the associated bosses 109, 111 remain in the separate recesses 106, 107 of the cam disc 105. If one motor over-speeds, e.g. 25, the speed of make-and-break switches 75 will rise causing disc 108 to rotate faster than cam 105 and thus to move axially by the interaction of boss 109 and recess 106 against the restoring action of a coil spring. Block 140 engages contact blade 136, separates contacts 138, 139 and inserts resistor 270 in series with field 85 to reduce the speed of motor 25. If this reduction is insufficient to produce synchronism, further axial movement of boss 140 causes the abutment block 141 to engage blade 137 to separate contacts 153, 154 and 155, 156, and thus de-energizes holding magnet 266 to release the contactor arm 263 and motor operation ceases. Similarly, should motor 225 rotate faster than 25, then disc 110 will move relative to cam disc 105 and the boss 170 will act on the lower set of contacts to insert the resistor 271 in series with field 285 and with continued asynchronism, will open contacts 185, 186 and de-energize coil 266 to release contact arm 263. To move the nuts 30, 230 upwards, the contact 265 is energized by arm 263 and so held by coil 267 to energize contactor 250 which connects motor fields 86, 286 to battery 500. The synchronizing operation of the ratchet mechanism operate as before as the direction of rotation of the motors does not alter the effect of the timer switches 75, 275. Limit switches in series with the relay coils 50, 250 are operated by the nuts 30, 230.