ROTATING ELECTRIC MOTOR WITH REDUCED COGGING TORQUE

摘要

In a brushless DC motor a cylindrical permanent magnet (23) rotating with the magnetic rotor (22) on its shaft (21) has four poles alternately north- and south-seeking at 90 deg. intervals. The shaft is supported by an armature core (24) which has six times as many teeth (26) formed between adjacent winding slots (25) and facing the poles of the permanent magnet (23). The teeth are grouped in three sets of eight between dummy slot portions of the core which constitute 'long teeth' having a greater than average effective pitch. Three-phase overlapping windings are wound in the slots which have different phases w.r.t. the dummy slot portions, so that fourier series harmonics of the shape of the core show small variation.