| 摘要 |
An electronically commutated motor (10) has a permanent-magnet external rotor (58) and an inner stator (20) with claw-poles (30,32; 44,46). Preferably, the claw-poles extend axially from opposite directions along the outside of the stator (20) and are interdigited. A galvanomagnetic sensor (14) generates a rotor position signal, based upon measurement of a stray or cross-flux field ( phi 1) of the rotating permanent-magnet external rotor (58,66). Between the claw-poles of the stator (20) are a plurality of neutral field zones (52). The motor turns in a predetermined direction (72) and the galvanomagnetic sensor (14) is positioned adjacent the stator (20) at a location which is circumferentially displaced with respect to a neutral field zone (52), in order to trigger early commutation of current to windings (22,24) of the motor (10). The stator structure includes a soft ferromagnetic element (28) which is formed with a cutout (76,76') adjacent the sensor (14) in order to increase the effective flux exerted on the sensor by the field of the rotor, and to thereby improve the precision of the rotor position signal generated by the sensor (14) during operation of the motor (10). The motor includes a control circuit actuated by the sensor output signal (86) which commutates current through the motor windings (22, 24).
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