Rotor and motor

1. A motor comprising:

a rotor having an axial direction, the rotor comprising:

at least a pair of rotor cores arranged in the axial direction; and

a field magnet arranged between the rotor cores and magnetized in the axial direction, wherein

each of the rotor cores includes a plurality of claw poles extending in the axial direction, and

each of the rotor cores are configured to appropriately cause a magnetic flux to flow to the claw poles, and

a stator around which a coil is wound, the stator having an annular stator core located outside of the rotor in its radial direction,

wherein

an axial length of the rotor core of the rotor is greater than an axial length of the stator core,

auxiliary magnets are located on the back surfaces of the claw poles,

the claw poles of a first rotor core of each pair of the rotor cores extend in the axial direction to an axial outer end surface of a second rotor core of the pair,

the claw poles of the second rotor cores extend to axial outer end surfaces of the first rotor cores in the axial direction, and

the axial outer end surface of each of the auxiliary magnets protrudes from a corresponding axial outer end surface of the stator core in the axial direction.

2. The motor according to claim 1 , wherein

each of the rotor cores further includes a disk-shaped core base,

the claw poles extend in a radial direction of the rotor from an outer periphery of the core base and extend in the axial direction,

each of the claw poles is formed into a rectangular shape as viewed in the radial direction,

at least the pair of rotor cores are arranged such that the claw poles of each of the rotor cores extend in directions opposite from each other in the axial direction and the claw poles of the rotor cores are arranged alternately in a circumferential direction of the rotor, and

each of the rotor cores includes magnetic flux restricting portions, which are formed on distal ends of the claw poles and open outward in the radial direction.

3. The motor according to claim 2 , wherein each of the magnetic flux restricting portions is an auxiliary groove, which extends from a distal end toward a proximal end of the claw pole, and extends from an outer peripheral surface to an inner peripheral surface of the claw pole.

4. The motor according to claim 2 , wherein two or more of the magnetic flux restricting portions are formed on a distal end of each of the claw poles in the circumferential direction.

5. The motor according to claim 1 , wherein

each of the rotor cores further includes a disk-shaped core base,

the claw poles extend in a radial direction of the rotor from an outer periphery of the core base and extend in the axial direction,

at least the pair of rotor cores are arranged such that the claw poles of each of the rotor cores extend in directions opposite from each other in the axial direction and the claw poles of the rotor cores are arranged alternately in a circumferential direction of the rotor,

the rotor further includes a plurality of interpole magnets each arranged between a circumferentially adjacent pair of the claw poles,

the interpole magnets are magnetized such that each of surfaces thereof that faces a claw pole in the circumferential direction has the same polarity as that of the faced claw pole, and

each of the rotor cores includes a magnetic flux guiding portion, which is formed on a distal end of the claw pole and guides magnetic flux of the interpole magnet to an outer peripheral surface of the claw pole.

6. The motor according to claim 5 , wherein

each of the magnetic flux guiding portions includes a radially inner end surface and a radially outer end surface,

the radially inner end surface includes circumferential ends and a circumferential central portion, and

a distance between the circumferential central portion and the radially outer end surface in the radial direction is smaller than a distance between the circumferential ends and the radially outer end surface in the radial direction.

7. The motor according to claim 6 , wherein

at least two pairs of rotor cores are arranged in the axial direction, and

circumferential widths of proximal ends of claw poles possessed by the rotor cores arranged on axial ends are narrower than circumferential widths of proximal ends of the claw poles possessed by the other rotor cores.

8. The motor according to claim 5 , wherein a circumferential central portion of the magnetic flux guiding portion projects inward in the radial direction.

9. The rotor according to claim 1 , wherein

at least two pairs of rotor cores are arranged in the axial direction,

the rotor cores are arranged such that the rotor cores having the same polarities are adjacent to each other, and

a cross-sectional area in the circumferential direction of the proximal end of the claw poles possessed by the rotor cores arranged on axial ends is narrower than a cross-sectional area in the circumferential direction of the proximal end of the claw poles possessed by the other rotor cores.

10. The motor according to claim 9 , further comprising an auxiliary magnet arranged between the claw pole of first one of each of the pairs of rotor cores and the core base of second one of the pair of rotor cores, wherein

the auxiliary magnet is magnetized such that a portion of the auxiliary magnet close to the claw pole has the same polarity as that of the claw pole and that a portion of the auxiliary magnet close to the core base has the same polarity as that of the core base.

11. The motor according to claim 9 , further comprising a plurality of interpole magnets each arranged between a circumferentially adjacent pair of the claw poles, wherein each of the interpole magnets is magnetized such that a surface of the interpole magnet that faces the claw pole in the circumferential direction has the same polarity as that of the faced claw pole.

12. The motor according to claim 11 , wherein each of the interpole magnets extends from an axial outer end surface of the rotor core located on a first end in the axial direction to an axial outer end surface of the rotor core located on a second end in the axial direction.

13. The motor according to claim 1 , wherein

at least two pairs of rotor cores are arranged in the axial direction,

the rotor cores are arranged such that the rotor cores having the same polarities are adjacent to each other,

the rotor further includes interpole magnets, each arranged between a circumferentially adjacent pair of the claw poles,

each of the interpole magnets is magnetized such that a surface thereof facing the claw pole in the circumferential direction has the same polarity as that of the faced claw pole, and

the claw pole of each of the rotor core is formed such that circumferential center lines of the two interpole magnets located on both sides in the circumferential direction have an angle with respect to a radial direction of the rotor.

14. The motor according to claim 1 , wherein

at least two pairs of rotor cores are arranged in the axial direction,

the rotor cores are arranged such that the rotor cores having the same polarities are adjacent to each other, and

a cross-sectional area in the circumferential direction of the proximal end of the claw poles possessed by the rotor cores located on axial ends is wider than a cross-sectional area in the circumferential direction of the proximal end of the claw poles possessed by the other rotor cores.

15. The motor according to claim 14 , wherein all of radially outer end surfaces of the claw poles have the same shapes.

16. The motor according to claim 14 , further comprising a plurality of interpole magnets each arranged between a circumferentially adjacent pair of the claw poles, wherein each of the interpole magnets is magnetized such that a surface of the interpole magnet that faces a claw pole in the circumferential direction has the same polarity as that of the faced claw pole.

17. The motor according to claim 16 , wherein each of the interpole magnets extends from an axial outer end surface of the rotor core located on a first end in the axial direction to an axial outer end surface of the rotor core located on a second end in the axial direction.

18. The motor according to claim 1 , wherein

at least two pairs of rotor cores are arranged in the axial direction, and

axial thicknesses of the rotor cores located on axial ends are thicker than axial thicknesses of the other rotor cores.