Patent ID: 8519593

Claim:
A brushless motor comprising: a stator comprising a stator core having nine pole tooth portions arranged in a circular array separated from each other by slots located between the pole tooth portions and coils wound around the pole tooth portions, respectively, wherein each of the pole tooth portions has a circumferentially extended pole tooth surface portion at a tip portion thereof, wherein the pole tooth surface portion is curved along an arc; and a rotor comprising a permanent magnet having eight magnetic poles disposed alternately in a circumferential direction and facing the pole tooth surface portion via an air gap, wherein each pole tooth surface portion has a recessed portion at a portion facing the rotor, wherein a ratio of (i) an angle of the recessed portion with respect to a rotational center of the rotor and (ii) an angle of the slot located between the pole tooth portions with respect to the rotational center of the rotor is set in a range of 1.2 to 3.0, wherein the recessed portion has a radial depth which is 0.5% or more of an inner diameter of the permanent magnet, and wherein a ratio of (i) an angle of the pole tooth surface portion with respect to the rotational center of the rotor and (ii) an angle of the magnetic pole of the permanent magnet with respect to the rotational center of the rotor is set in a range of 0.58 to 0.8.