Patent ID: 8796897

Claim:
A motor comprising: an annular rotor member made of a soft magnetic material and rotatably provided in the motor, the rotor member comprising: a plurality of first magnetic poles arranged in a circumferential direction of the rotor member at spaces therebetween, each of the plurality of first magnetic poles being formed by an outer peripheral portion of the rotor member and a permanent magnet, the plurality of first magnetic poles having a same first magnetic polarity; and a plurality of second magnetic poles radially extending from the rotor member and respectively arranged between the plurality of first magnetic poles, the plurality of second magnetic poles being consequently magnetized as a plurality of consequent poles by the plurality of first magnetic poles, the plurality of second magnetic poles having a same second magnetic polarity that is opposite to the first magnetic polarity; and an armature provided to be opposite to the rotor member for generating a rotating magnetic field, the armature comprising: plural sets of teeth arranged in a direction of rotation of the rotor member such that each set of teeth in the plural sets of teeth is within one electrical angular cycle of the rotating magnetic field, the one electrical angular cycle corresponding to one pole-pair pitch of the annular rotor member, a number of teeth in the plural sets of teeth within the one pole-pair pitch being set to 2k (k is a natural number), a number of teeth facing each of the first magnetic poles in the plurality of teeth being set to be equal to or greater than the sum of k and 1.