Patent ID: 8207648

Claim:
A dual-rotor motor comprising: a stator in which a winding is wound around a stator core; an inner rotor disposed on a radially inner side of the stator; and an outer rotor disposed a radially outer side of the stator, wherein the inner rotor and the outer rotor are held in a position to face the stator so as to rotate in a circumferential direction around a rotary shaft, the stator core includes a ring-like yoke, a plurality of inner teeth protruding radially inwardly from the yoke, and a plurality of outer teeth protruding radially outwardly from the yoke, the inner teeth including an inner leg extending radially inwardly from the yoke and an inner head extending circumferentially in both ways from a tip of the inner leg, wherein there is formed between a respective pair of adjacent inner teeth an inner slot open having an inner slot open width between opposing circumferential ends of the inner heads of the respective pair of adjacent inner teeth, the outer teeth including an outer leg extending radially outwardly from the yoke and an outer head extending circumferentially in both ways from a tip of the outer leg, wherein there is formed between a respective pair of adjacent outer teeth an outer slot open having an outer slot open width between opposing circumferential ends of the outer heads of the respective pair of adjacent outer teeth, the inner head has an inner surface opposite to the inner rotor, the inner surface comprising a circumferentially extending inner center portion and an inner slope portion extending continuously at an inner spread angle from a respective circumferential end of the inner center portion such that the inner slope portion goes apart progressively from the inner rotor towards its end, and the outer head has an outer surface opposite to the outer rotor, the outer surface comprising a circumferentially extending outer center portion and an outer slope portion extending continuously at an outer spread angle from a respective circumferential end of the outer center portion such that the outer slope portion goes apart progressively from the outer rotor towards its end, and the inner and outer spread angles are respectively set so as to reduce a combination of an inner cogging torque caused by rotation of the inner rotor and an outer cogging torque caused by rotation of the outer rotor.