| 摘要 |
1,179,556. Control of D.C. motors. JOSEPH LUCAS (INDUSTRIES) Ltd. 1 May, 1967 [27 May, 1966; 22 Dec., 1966], Nos. 23927/66 and 57351/66. Heading H2J. [Also in Division H3] The power to the traction motor 49 of an industrial truck is supplied through a switch 52 of the type which, once turned on, can only be turned off by reducing the current flowing through it below a threshold value (e.g. a thyristor, thyratron or four-layer diode), switch 52 being turned off by the application of a signal to a transformer winding 54 connected, in series with a diode 53, across the motor 49. As. shown, periodic turn-off pulses are derived from oscillator 33-39; capacitor 43 charges as the flux in core 34 collapses and when the flux next rises, thyristor 47 switches on to discharge capacitor 43 and provide, through transformer 46, the turn-off pulse for thyristor 52. A capacitor 58 is held discharged through diode 61 and thyristor 52 until thyristor 52 is rendered non-conductive, whereupon capacitor 58 charges through throttle-controlled variable resistor 56 until transistor 65 is rendered conductive to provide a turn-on pulse to thyristor 52 through winding 69 of transformer 64, 67, 69. Should the charging time of capacitor 58 be greater than the period of oscillator 34, 35 (a condition ensured by opening switch 59) thyristor 52 does not switch on. In a modification (Fig. 2, not shown) winding 54 forms the third winding of transformer 34, components 42-48 being omitted, and an R.C. timing circuit having a throttlecontrolled variable resistor is attached to the gate of thyristor 52 for periodically switching it on. Turn-off may be provided on either the rise or collapse of flux in core 34 and the collapse may be caused either by saturation of core 34 or of transistor 35. |
