| 摘要 |
1,088,444. Control of D.C. motors. SEVCON ENGINEERING Ltd. Aug. 5, 1966 [July 13, 1965], No. 29595/65. Heading H2J. [Also in Division G3] A series or compound motor M driving, e.g. an hydraulic pump in a fork-lift truck, is energized from a battery in pulses, the mark/ space ratio of which is controlled by an evaluation of load current so as to produce substantially constant torque at variable speed. A thyristor SCR1 is triggered on for constant time periods by a transistor relaxation oscillator circuit; the interval between pulses is determined by the charging of a capacitor Cl by a Zener voltage ZX1 and is increased when a transistor Tr2 is conducting, due to current through a freewheeling diode D8 shunting the motor. Thus, when the motor is pumping to move a ram its speed is high and the current through the diode decays rapidly, causing frequent pulses, but when the pump is merely maintaining a static pressure motor speed is low and the pulses are greatly spaced apart. It is mentioned that the load signal may alternatively be derived from an oil pressure transducer. |
