Brushless motor with low cogging torque
View Patent ↗A brushless DC motor provided with nine slots and eight poles includes a stator including a stator core having pole teeth on the outer circumference thereof and a coil wound around each pole tooth; a rotor disposed at an outside position of the outer circumference of the stator via a gap and having a multiply magnetized permanent magnet with plural magnetic poles; a pole tooth surface formed at a portion of the pole tooth and facing an inner circumference of the rotor; a recessed portion formed on the pole tooth surface; and a slot formed between the adjacent pole teeth and extending a first angular range around a rotational center of the rotor; in which the recessed portion extends in a second angular range around the rotational center of the rotor, the second angular range is 1.2 to 3.0 times the first angular range, the recessed portion has a radial depth which is 0.5% or more of an inner diameter of the permanent magnet, the pole tooth extends in a third angular range around a rotational center of the rotor, and the third angular range is 0.58 to 0.8 times a value which is obtained by dividing 360 degrees by the number of magnetic poles of the permanent magnet.
1. 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.
2. 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 flat portion at a portion facing the rotor,
wherein a ratio of (i) an angle of the flat 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, 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.
3. A brushless motor according to claim 1 , wherein the recessed portion has a bottom surface portion which is curved along an arc, and a center of a radius of curvature of the bottom surface portion of the recessed portion is equal to a center of a radius of curvature of the pole tooth surface portion.
4. A brushless motor according to claim 1 , wherein the rotor is disposed outside the stator in a radial direction.
5. A brushless motor according to claim 1 , wherein the rotor is disposed inside the stator in a radial direction.
6. A brush less motor according to claim 2 , wherein the rotor is disposed outside the stator in a radial direction.
7. A brushless motor according to claim 2 , wherein the rotor is disposed inside the stator in a radial direction.