Disk drive device with appropriate number of combinations of magnetic poles and salient poles to reduce thickness of the disk drive device

1. A disk drive device comprising:

a base member;

a hub on which a recording disk is to be placed;

a bearing unit arranged on the base member for rotatably supporting the hub; and

a spindle drive unit for rotationally driving the hub, wherein

the spindle drive unit includes:

a stator core having salient poles;

a three-phase coil wound around each of the salient poles; and

a magnet having a plurality of magnetic poles arranged in a circumferential direction so as to be opposed to the salient poles,

the hub includes an outer cylindrical portion formed of a magnetic material and adapted to be engaged with an inner periphery of the recording disk, and an inner cylindrical portion fixing an outer periphery of the magnet,

the bearing unit is configured to be encircled by the recording disk in a radial direction, and includes a portion for at least partially overlapping the recording disk in an axial direction,

the number of magnetic poles is an even number in a range of 10 to 16, and

the number of salient poles is a multiple of 3 in a range of 12 to 24.

2. The disk drive device according to claim 1 , wherein the number of magnetic poles is 10 and the number of salient poles is 15.

3. The disk drive device according to claim 1 , wherein the number of magnetic poles is 12 and the number of salient poles is 18.

4. The disk drive device according to claim 1 , wherein the number of magnetic poles is 14 and the number of salient poles is 21.

5. The disk drive device according to claim 1 , wherein the number of magnetic poles is 16 and the number of salient poles is 24.

6. The disk drive device according to claim 1 , wherein the number of magnetic poles is 16 and the number of salient poles is 12.

7. The disk drive device according to claim 1 , wherein a diameter of the inner cylindrical portion is larger than that of the outer cylindrical portion.

8. The disk drive device according to claim 1 , wherein a diameter of the outer cylindrical portion is 20 mm, an axial dimension between a surface of the coil opposed to the hub and a surface of the coil opposed to the base member is 3 mm or less.

9. The disk drive device according to claim 1 , wherein a surface of the hub opposed to the coil is insulated.

10. The disk drive device according to claim 1 , wherein a surface of the base member opposed to the coil is insulated.

11. The disk drive device according to claim 1 , wherein an axial dimension of a portion of the hub opposed to the coil is larger than that of a portion of the base member opposed to the coil.

12. The disk drive device according to claim 1 , wherein a gap between the salient poles and the magnet in the radial direction is 0.2 mm or more and 0.4 mm or less.

13. The disk drive device according to claim 1 , wherein a diameter of a circumcircle of the salient poles is larger than a diameter of the outer cylindrical portion.

14. The disk drive device according to claim 1 , wherein

a diameter of the outer cylindrical portion is 20 mm,

the hub has opposite first and second ends,

the base opposed to the hub has opposite third and fourth ends, the third end of the base facing toward the second end of the hub, and

an axial dimension from the first end of the hub to the fourth end of the base is 6 mm or less.

15. The disk drive device according to claim 1 , wherein an inner diameter of the recording disk is 20 mm, and a thickness of the disk drive device is 7.5 mm or less.

16. The disk drive device according to claim 1 , wherein

the coil is formed of a wire, and

the wire has a drawn-out line drawn out to an opposite side of the base member through a hole in the base member, and connected to a wiring member at a position outside an outer periphery of the magnet.

17. The disk drive device according to claim 1 , wherein the bearing unit is a fluid dynamic bearing for generating dynamic pressure in a lubricant.