A motor includes a stator with an annular stator yoke, a stator core having a plurality of inner and outer teeth projecting from the stator yoke toward inside and outside respectively, a plurality of coils wound on the stator core, and an inner rotor and an outer rotor confronting the inner and outer teeth respectively via an air-gap, and having an permanent magnet respectively. The number of slots “S” and the number of poles “P” establish a relation of S:P=3:2N−1, where N is an integer equal to 1 or more, and a case when 2N−1 becomes a multiple of 3 is excluded.
1. A motor comprising:
a stator including:
a stator core having:
an annular stator yoke;
a plurality of inner teeth projecting from the stator yoke toward inside along a radial direction;
a plurality of outer teeth, in equal quantity to the inner teeth, projecting from the stator yoke toward outside along the radial direction;
inner slots formed between each one of the inner teeth; and
outer slots formed between each one of the outer teeth;
a plurality of coils wound on the stator yoke between the inner slots and the outer slots, and coupled together in one of a three-phase star-shaped wire connection manner and a three-phase delta-shaped wire connection manner,
an inner rotor confronting the inner teeth with an air-gap in between, and including an inner rotor yoke and an inner permanent magnet; and
an outer rotor confronting the outer teeth with an air-gap in between, and including an outer rotor yoke and an outer permanent magnet,
wherein the inner rotor is coupled to a rotary shaft to which the outer rotor is coupled,
wherein the inner slots and the outer slots are in equal number “S”, and the inner permanent magnet and the outer permanent magnet have poles in equal number “P”,
wherein the number of slots “S” and the number of poles “P” establish a relation of S:P=3:2N−1, where N is an integer equal to 3 or more, and where a case when 2N−1 becomes a multiple of 3 is excluded.
2. The motor of claim 1 , wherein the number of slots “S” and the number of poles “P” establish a relation of S:P=3:5.
3. The motor of claim 1 , wherein at least one of the inner permanent magnet and the outer permanent magnet is disposed on a surface of the inner rotor yoke and a surface of the outer rotor yoke.
4. The motor of claim 1 , wherein at least one of the inner permanent magnet and the outer permanent magnet is embedded in the inner rotor yoke and inside the outer rotor yoke.
5. The motor of claim 1 , wherein the rotary shaft rotates at a speed including as low as 10 rpm-100 rpm.
6. The motor of claim 1 , wherein driving torque produced by the inner rotor and that produced by the outer rotor are added up, and cogging torque produced by the inner rotor and that produced by the outer rotor are cancelled out.