GB1117329A - Brushless direct-current motor - Google Patents

Abstract

1,117,329. Electric motors. HITACHI SEISAKUSHO K.K. 20 Aug., 1965 [21 Aug., 1964], No. 35903/65. Heading H2A. [Also in Division H3] A brushless motor has a stator wound with a concentrated full-pitch winding whose conductors are energized with direct current in a sequence determined by rotor position in such a way that the current does not flow when the instantaneous value of the magnetic field influencing the conductor is less than its maximum value. As shown, the conductors D1, D2 ... , are each connected to respective semiconductor switching devices 1a, 2a, ... , and current flows in the conductors when gates G1, G2 ... , are energized by the rotor position detector. The detector is designed so that the triggering signal is present for less than 180 degrees and thereby cuts off the current at an instant when the magnetic field linking the respective conductor is still near maximum, and in this way motor efficiency is improved. In a two pole machine either two stator windings can be used each controlled by a single semiconductor switch, or if a single winding is used pairs of opposite conductivity type switches are used to provide current flow in both directions in the winding. The detector may use photosensitive devices which are actuated by light passing through a slot in a plate mounted on the rotor shaft, where the length of the slot corresponds to the angle of required current flow. Alternatively a Hall generator system can be used and the operating angle determined either by the construction of the influencing magnet or by including a pulse shaping circuit in the output of the Hall generator. The pulse shaping circuit may employ diodes or Zener diodes or include a differential amplifier and bi-stable circuit using transistors or SCR's. In a further construction a magneto-resistive element may be used in the detector circuit. The motor rotor is a permanent magnet.