Brushless DC motor arrangement for reducing torque ripple

摘要

A brushless DC motor for driving a fan or the like, wherein the brushless DC motor comprises: a stator core; motor coils wound around the stator core; a rotor core supported rotatably with respect to the stator core; a rotor magnet attached to the rotor core, which is magnetized into a multi-pole so that the waveform of a resultant counter electromotive force generated on the motor coils has a sine wave-like shape, and faces the stator core across an uneven space so that the waveform of a resultant cogging torque has a cosine wave-like shape having twice the rotation cycle with respect to the sine wave of the waveform of the counter electromotive force; a magnetic pole position detector that detects magnetic pole positions of the rotor magnet, and is disposed at a position where the resultant waveformof an output signal fromthedetectorhas a sinewave-like shape; and a drive unit that amplifies the output signal of the magnetic pole position detector so that the maximum value of an exciting torque to excite the motor coils is substantially twice of the maximum value of the cogging torque.