JP2000125506A - Spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spindle motor, where the shock resistance required in a notebook type personal computer or the like and the reliability can be raised, by optimizing the structure of the screw hole or its periphery for stopping a clamper to the top end face of a rotary shaft. SOLUTION: In a spindle motor 1 corresponding to a 2.5-inch disk, as ball bearings 5 and 6, the largest ones which are tolerable when viewed from the outside dimension D2 of a disk guide 76 are used, so they are of high shock resistance by that amount. Moreover, when it is defined that the thickness of the rotary shaft at the section where a screw hole 75 to stop a clamper 100 is made is t and that the minor diameter of a screw hole 75 is D at the top end part of the rotary shaft 71, it is arranged so that the ball bearing 6 may not be transformed by the stress at the time of having fixed the screw 101, arranging it such that t and Do/satisfy the formula [t>=Do/2].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor used as a rotary drive for a hard disk or the like. More specifically, the present invention relates to a technique for improving the reliability of a spindle motor.

[0002]

2. Description of the Related Art Spindle motors used as rotary drive devices for recording disks such as hard disks include:
A fixed shaft in which a recording disc mounting hub is rotatably supported via a ball bearing on a fixed shaft that stands upright from the motor frame, and a rotating shaft is mounted on a ball bearing supported by the motor frame, There is a shaft rotation type in which a hub for mounting a recording disk is connected to the rotation shaft.

[0003] Of these spindle motors, for example, of the rotary shaft type, as shown in FIG. 1, a hub 7 holding a hard disk 200 and an outer diameter extending downward from the center of the hub 7 to 4 mm are provided. Of the rotary shaft 71 via the first and second ball bearings 5 and 6.
And a frame 21 having a bearing holding hole 211 rotatably supporting the frame 21. The frame 21 is fitted and fixed to the base plate 2 which is a mounting portion to the information recording / reproducing apparatus main body. Here, the cylindrical portion 217 constituting the bearing holding hole 211 stands up from the bottom 218 of the frame 21.

The hub 7 has a cup shape with the opening facing downward, and a rotating shaft 71 extends downward from the center of the top plate 78. The hub 7 is formed with a cylindrical disk guide portion 76 into which the center hole of the hard disk 200 is fitted, and a portion extending from the lower end of the disk guide portion 76 is used as a disk mounting surface 77. Here, the outer diameter dimension D2 of the disk guide portion 76 is 20 mm corresponding to a 2.5-inch hard disk. A screw hole 75 is formed in the upper end surface of the rotating shaft 71 for fixing the clamper 100 holding the hard disk 200 mounted on the disk mounting surface 77 with a spring property by the screw 101.

[0005] In the spindle motor 1 thus constructed, conventionally, the ball bearings 5 and 6 have an outer diameter of 9 mm, an inner diameter of 4 mm, and bearing balls 50 and 60.
Having a diameter of 1.4 mm is used. Also, 3.
In the case of a 5-inch hard disk, the outer diameter D2 of the disk guide portion 76 is 25 mm, and the outer diameter of the ball bearings 5 and 6 is 13 mm and the inner diameter is 5 m.
m and the diameter of the bearing balls 50 and 60 are 2.0 mm.

[0006]

However, in the conventional spindle motor, since the ball bearings 5 and 6 have low impact resistance, the impact resistance of a notebook computer or the like in which such a spindle motor 1 is mounted for driving a disk is used. There is a problem that cannot be cleared. That is,
Notebook computers are required to have high impact resistance because they are frequently carried and may be dropped. However, in the conventional spindle motor, since the ball bearings 5 and 6 have low shock resistance, when the impact is transmitted to the ball bearings 5 and 6 via the base plate 2 and the frame 21 when the notebook personal computer is dropped, the ball bearings 5 and 6 are moved. There is a problem that the bearings 5 and 6 are deformed and noise and rotation runout are generated when the disk rotates, and furthermore, the disk cannot rotate.

[0007] The hard disk 200 on the disk mounting surface 77 is held by the clamper 100 which is screwed using the screw hole 75.
When 0 is reduced to 3.5 inches or 2.5 inches, the ball bearings 5 and 6 also have small diameters, so that the rotating shaft 71 becomes thinner accordingly. As a result, the thickness t of the rotary shaft 71 in the portion where the screw hole 75 is formed becomes thinner. Therefore, when the screw 101 is fixed to the screw hole 75, the stress is transmitted through this portion of the rotary shaft 71. The inner ring 61 of the ball bearing 6 may be deformed by being transmitted to the ball bearing 6. Such a deformation
It is not preferable because it causes noise and lowers reliability.

Accordingly, an object of the present invention is to improve the impact resistance and reliability required for a notebook computer or the like by optimizing the structure around a screw hole for fixing a clamper on the upper end surface of a rotating shaft. An object of the present invention is to provide a spindle motor capable of achieving the following.

[0009]

According to the present invention, there is provided a rotary shaft extending downward from a hub for mounting a recording disk and rotatably supporting the rotary shaft via a ball bearing. A frame, an armature mounted on the frame, and an annular rotor magnet mounted on the hub so as to face the armature. A screw hole for stopping a clamper that presses and fixes the recording disc mounted on the hub to the hub is formed,
The thickness of the portion of the rotary shaft where the screw hole is formed is t
When the root diameter of the screw hole is D0, t and D0 are characterized by satisfying the following expression: t ≧ D0 / 2.

Here, t and D0 may be set to substantially equal dimensions.

In the present invention, a ball bearing having a large center-to-center distance of the bearing ball is used up to an allowable maximum in view of the outer diameter of the disk guide portion defined by the size of the recording disk. . For this reason, the ball bearing has high impact resistance, such as being not deformed even when an impact is applied to the ball bearing. Therefore,
In a notebook personal computer equipped with a spindle motor for driving a disk to which the present invention is applied, a shock resistance of 300 G or more required for 2.5 inches and a shock resistance of 500 G or more required for 3.5 inches. Sex can be cleared. When the diameter of the ball bearing is as large as possible, the rotating shaft can be made thicker. Therefore, when the thickness of the rotary shaft in the portion where the screw hole is formed is t, and the root diameter of the screw hole is D0, the relationship t satisfies the following equation: t ≧ D0 / 2 That is, a sufficient thickness t can be secured.
Therefore, when the screw is fixed to the screw hole, the stress is not transmitted to the ball bearing through this portion of the rotating shaft, and the inner ring of the ball bearing is not deformed. Therefore, it is possible to reliably prevent the occurrence of noise and a decrease in reliability.

According to the present invention, in the hub, the outer diameter of the disk guide portion into which the center hole of the recording disk fits is 25 m.
It is effective when applied to a spindle motor of m or less. That is, when the size of the hard disk is reduced to 3.5 inches (the center hole of the disk is 25 mm), a ball bearing having a considerably small diameter is used. As a result, the thickness of the rotary shaft in the portion where the screw hole is formed is reduced, but in the present invention, the thickness is set to be appropriate for the thickness of the rotary shaft in the portion where the screw hole is formed. Therefore, even if the rotating shaft becomes thin, high reliability can be secured in the rotating performance of the disk.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

[First Embodiment] FIG. 1 is a sectional view showing a spindle motor for driving a disk according to a first embodiment of the present invention. The basic structure of the spindle motor according to the present embodiment is the same as that of the conventional spindle motor, and therefore the description will be given with reference to FIG. In FIG. 1, since the scale and the like are arbitrarily set depending on parts, in the description of the related art and the description of the present invention, the dimensional relationship and the like will be clearly described in the specification.

In FIG. 1, a spindle motor 1 is
A rotation drive device for driving a 2.5-inch hard disk 200, a hub 7 for holding the hard disk 200 (not shown), and a rotation having an outer diameter of 5 mm extending downward from the center of the hub 7 The frame 21 includes a shaft 71 and a bearing holding hole 211 that rotatably supports the rotating shaft 71 via the first and second ball bearings 5 and 6. The frame 21 is fitted and fixed to the base plate 2 which is a mounting portion of the notebook personal computer with the information recording / reproducing apparatus main body. Here, the cylindrical portion 217 forming the bearing holding hole 211
Stands from the bottom 218 of the frame 21.

The rotary shaft 71 has a straight through hole 70 formed at the center thereof so as to penetrate in the axial direction. The through hole 70 is closed by a shielding plate 701.

In the frame 21, the bearing holding hole 2
The outer peripheral surface of the cylindrical portion 217 constituting the core holding portion 2
The stator core 10 is attached using a step formed on the outer peripheral surface of the core holding portion 210. This stator core 10 has a coil 9
Are wound to form an armature 12.

The hub 7 has a cup shape with the opening facing downward, and a rotating shaft 71 extends downward from the center of the top plate 78. The hub 7 is formed with a cylindrical disk guide portion 76 into which a 2.5-inch hard disk 200 is fitted. A portion extending from the lower end of the disk guide portion 76 serves as a disk mounting surface 77. Here, the outer diameter dimension D2 of the disk guide portion 76 is 20 mm corresponding to the 2.5-inch hard disk 200.

A screw hole 75 is provided at the upper end surface of the rotating shaft 71 for fixing the clamper 100 holding the hard disk 200 mounted on the disk mounting surface 77 with a spring property with the screw 101. It is formed.

On the inner peripheral surface of the hub 7, the annular rotor magnet 14 extends from the disk guide portion 76 to the lower end portion.
Is fixed, and the rotor magnet 14 is in a state of facing the armature 12. Therefore, by supplying current to the coil 9, the hub 7 can be rotated, and the hard disk 200 attached to the hub 7 can be rotated. Here, since the hub 7 is made of iron (magnetic material), the hub 7 itself can be used as a yoke for the rotor magnet 14. Therefore, in this embodiment, the rotor magnet 14 is directly fixed to the hub 7 and the yoke is omitted. Therefore,
Compared with a hub having the same external dimensions, the spindle motor 1 of the present embodiment has a wider space inside the hub 7 (space where the armature 12 is arranged).

Out of the pair of ball bearings 5, 6, the first ball bearing 5 located on the side of the shaft end 72 of the rotating shaft 71 has an outer end surface 512 corresponding to the lower end surface of the inner ring 51.
Are located on substantially the same plane as the shaft end surface 73 of the rotating shaft 71, and in this state, the inner peripheral surface 513 of the inner race 51 is
Adhesively fixed. On the other hand, in the second ball bearing 6 located on the base end side of the rotating shaft 71, the outer end surface 611 of the inner ring 61 is in contact with the inner surface 781 of the top plate 78 of the hub 7, and in this state, the inner peripheral surface of the inner ring 61 613 is adhesively fixed to the outer peripheral surface 74 of the rotating shaft 71.

An annular step 220 protruding toward the rotating shaft 71 is formed on the inner peripheral surface 212 of the bearing holding hole 211 formed in the frame 21. The outer ring 62 of the second ball bearing 6 is mounted on the upper annular end face of the step 220. The outer ring 52 of the first ball bearing 5 is in contact with the lower annular end surface of the step 220. In this state, the outer ring 52 of the first ball bearing 5 and the outer ring 62 of the second ball bearing 6 are pressurized by the step 220 in a direction away from each other in the direction of the axis L. Outer ring 52
The outer peripheral surface 523 of the inner peripheral surface 21 of the bearing holding hole 211
2. The outer end surface of the outer ring 52 of the first hole bearing 5 is connected to the shaft end surface 73 of the rotating shaft 71.
It is located below. On the other hand, the second hole bearing 6 is in a state in which an outer end surface corresponding to the upper end surface of the outer ring 62 projects toward the base end side of the rotating shaft 71 from the outer end surface of the inner ring 61, and in this state, the outer periphery of the outer ring 62 The surface 623 is adhesively fixed to the inner peripheral surface 212 of the bearing holding hole 211. In addition, the outer peripheral side of the top plate 78 of the hub 7 that is in contact with the inner ring 61 is slightly concave in an annular shape so that the outer end surface of the outer ring 62 of the second ball bearing 6 does not contact.

Here, the spindle motor 1 is configured as follows in order to prevent grease and rust preventive oil added to the ball bearings 5 and 6 from scattering outside. First, in each of the first and second ball bearings 5 and 6, the outer races 52 and 62 have
Shielding plates 501 and 601 are attached so as to close the opening. The lower end on the outer peripheral side of the hub 7 is opposed to the annular rising portion 219 of the frame 21 via a small gap, and a labyrinth structure is formed at the opposed portion. Further, since the bearing holding hole 211 formed in the frame 21 is opened on the side of the shaft end 72 of the rotating shaft 71, the opening 214 is formed so that the rust-preventive oil of the ball bearing 5 does not scatter from the opening 214. The seat 8 is closed.

In the spindle motor 1 thus configured, the ball bearings 5 and 6 have an outer diameter of 11
mm, the inner diameter is 5 mm, and the diameter of the bearing balls 50 and 60 is 1.6 mm. In such ball bearings 5 and 6, a pair of bearing balls 50 located at positions facing each other with the rotation center axis (axis L) interposed therebetween.
The center-to-center distance D1 of 60 is 8.7 mm.

That is, the distance between the centers of a pair of bearing balls 50, 60 located at positions opposing each other across the rotation center axis (axis L) in the ball bearings 5, 6 is represented by D
1. Assuming that the outer diameter of the disk guide portion 76 in which the center hole of the hard disk 200 fits in the hub 7 is D2, D1 and D2 are represented by the following equation: 2.0 ≦ (D2 / D1) = 2.30 ≦ 2 .5. Moreover, in the present embodiment, since D1 and D2 are 10.6 mm and 20 mm, respectively, D1 and D2 are in a relationship that also satisfies the following expression: 2.2 ≦ (D2 / D1) = 2.30 ≦ 2.4 is there.

As described above, the spindle motor 1 of this embodiment
In the above, the ball bearings 5, 6 having a large center-to-center distance D1 between the bearing balls 50, 60 are used up to an allowable maximum when viewed from the outer diameter dimension D2 of the disk guide portion 76, and accordingly, the bearing balls 50, 60 are correspondingly large. . Therefore, the ball bearings 5 and 6 have high impact resistance. Therefore, for example, a notebook personal computer in which the spindle motor 1 of the present embodiment is mounted for driving a disk can meet the shock resistance requirement of 300 G or more required for 2.5 inches.

In the present embodiment, the ball bearings 5,
Since a large-diameter one is used as 6, the rotating shaft 71 can be stably supported. Further, since the ball bearings 5 and 6 have large diameters, the rotating shaft 71 can be thickened up to 5 mm, so that the rigidity is high. Therefore, ball bearing 5,
6 can be reduced to 3.2 mm, which is shorter than the center distance D1 between the bearing balls 50 and 60, and is suitable for flattening the spindle motor 1.

Further, in the present embodiment, since the ball bearings 5 and 6 have large diameters, the rotating shaft 71 is thicker than the conventional one and the outer diameter is 5 mm. Therefore, at the upper end of the rotating shaft 71, the diameter D0 of the female thread valley is 1.70 mm and the inner diameter D10 of the screw 101 and the screw hole 75.
Is 1.32mm (JIS standard M1.7) and the screw length is 4
A thick screw 101 which is set to 0 mm and corresponds to M1.7 in the JIS standard is used. For this reason, the clamper 100 has a large clamping force on the hard disk 2.
00, the hard disk 200 rotates stably. Nevertheless, since the thickness t of the rotating shaft 71 at the portion where the screw hole 75 is formed is 1.65 mm, the rotation shaft 71 has an inner diameter D10 (1.32 mm) to a valley diameter D0 (1.7 mm). In range. When the thickness of the rotation shaft 71 at the portion where the screw hole 75 is formed is t, and the root diameter of the screw hole 75 is D0, t and D
0 has a relationship satisfying the following expression: t ≧ D0 / 2. Moreover, the thickness t is set to be thicker as it is substantially equal to the diameter D0 of the valley. Therefore, clamper 1
Even if the screw 101 for stopping the screw 00 is fixed to the screw hole 75, the stress does not deform this portion of the rotating shaft 71 and the ball bearings 5 and 6. Therefore, noise can be reduced, resonance with the main body can be prevented, and reliability can be improved.

[Second Embodiment] FIG. 2 is a sectional view showing a spindle motor for driving a disk according to a second embodiment of the present invention. In FIG. 2, this spindle motor 1
Is a rotary driving device for driving a 3.5-inch hard disk, a hub 7 holding a hard disk (not shown), and a rotary shaft having an outer diameter of 6 mm extending downward from the center of the hub 7. The frame 21 includes a shaft 71 and a bearing holding hole 211 that rotatably supports the rotating shaft 71 via the first and second ball bearings 5 and 6. Here, on the upper end surface of the rotating shaft 71, a hard disk mounted on a disk mounting surface 77 (see FIG. 1).
Is formed with a screw hole 75 for fixing a clamper (see FIG. 1) holding the spring with a screw (see FIG. 1).

The cylindrical portion 217 constituting the bearing holding hole 211 stands up from the bottom 218 of the frame 21.

In the frame 21, the bearing holding hole 2
The outer peripheral surface of the cylindrical portion 217 constituting the core holding portion 2
The stator core 10 is attached using a step formed on the outer peripheral surface of the core holding portion 210. This stator core 10 has a coil 9
Are wound to form an armature 12.

The hub 7 has a cup shape with the opening facing downward, and the rotating shaft 71 extends downward from the center of the top plate 78. The hub 7 is formed with a cylindrical disk guide portion 76 into which a 3.5-inch hard disk is fitted, and a portion extending from the lower end of the disk guide portion 76 serves as a disk mounting surface 77. Here, the outer diameter dimension D2 of the disk guide portion 76 is 25 mm corresponding to a 3.5-inch hard disk.

In the hub 7, a cylindrical side surface portion 78 extends downward from the outer peripheral side of the disk mounting surface 77, and the inner peripheral surface of the side surface portion 78 has an annular rotor via an annular yoke 13. The magnet 14 is fixedly bonded. Therefore, by supplying current to the coil 9, the hub 7 can be rotated, and the hard disk attached to the hub 7 can be rotated.

In the spindle motor 1 thus configured, the ball bearings 5 and 6 have an outer diameter of 15 mm.
mm, the inner diameter is 6 mm, and the diameter of the bearing balls 50 and 60 is 2.4 mm. In such ball bearings 5 and 6, a pair of bearing balls 50 located at positions facing each other with the rotation center axis (axis L) interposed therebetween.
The distance D1 between the centers of 60 is 10.6 mm.

That is, the distance between the centers of the pair of bearing balls 50, 60 at positions opposing each other across the rotation center axis (axis L) in the ball bearings 5, 6 is represented by D
1. When the outer diameter of the disk guide portion 76 in which the center hole of the hard disk fits in the hub 7 is D2,
1 and D2 are in a relationship satisfying the following expression: 2.0 ≦ (D2 / D1) = 2.36 ≦ 2.5. Moreover, in the present embodiment, D1 and D2 are 10.6 mm and 20 mm, respectively, so that D1 and D2 satisfy the following relationship: 2.2 ≦ (D2 / D1) = 2.36 ≦ 2.4 is there.

As described above, the spindle motor 1 of the present embodiment
In the above, the ball bearings 5, 6 having a large center-to-center distance D1 between the bearing balls 50, 60 are used up to an allowable maximum when viewed from the outer diameter dimension D2 of the disk guide portion 76, and accordingly, the bearing balls 50, 60 are correspondingly large. . Therefore, the ball bearings 5 and 6 have high impact resistance. Therefore, for example, in a notebook computer in which the spindle motor 1 of the present embodiment is mounted for driving a disk, the impact resistance is 3.
The requirement of 500 G to 700 G required in the case of 5 inches can be met.

In this embodiment, the ball bearings 5,
Since a large-diameter one is used as 6, the rotating shaft 71 can be stably supported. Further, since the ball bearings 5 and 6 have large diameters, the rotating shaft 71 can be thickened up to 6 mm, so that the rigidity is high. Therefore, ball bearing 5,
6 can be reduced to 8.6 mm, which is shorter than the center distance D1 between the bearing balls 50 and 60, so that the spindle motor 1 is suitable for flattening.

Further, in this embodiment, since the ball bearings 5 and 6 have large diameters, the rotating shaft 71 is thicker than the conventional one and the outer diameter is 6 mm. Therefore, at the upper end of the rotating shaft 71, the diameter D0 of the female thread root and the inner diameter D10 of the screw and the screw hole 75 are 1.20 mm.
57 mm (JIS standard M2) and a screw length of 60 mm are set, and a thick screw corresponding to M2 according to JIS standard is used. Therefore, the clamper holds the hard disk with a large clamping force, so that the hard disk rotates stably. Nevertheless, the thickness t of the rotating shaft 71 in the portion where the screw hole 75 is formed is 2.
00 mm, the inner diameter D10 of the screw hole 75 (1.57 m
m) to the valley diameter D0 (2.00 mm). In addition, the rotation shaft 7 at the portion where the screw hole 75 is formed
Assuming that the thickness of 1 is t and the root diameter of the screw hole 75 is D0, t and D0 are in a relationship satisfying the following expression: t ≧ D0 / 2. In addition, the thickness t is set so as to be substantially equal to the diameter D0 of the valley. Therefore, even if the screw for fixing the clamper is fixed to the screw hole 75, the stress does not deform this portion of the rotating shaft 71 and the ball bearings 5 and 6. Therefore, noise reduction,
It is possible to prevent resonance with the main body and improve reliability.

[0039]

As described above, in the spindle motor of the present invention, the distance between the centers of the bearing balls is large to the maximum allowable from the outer diameter of the disk guide portion defined by the size of the recording disk. , The size of the bearing ball is correspondingly large. For this reason, the ball bearing has high impact resistance, such as being not deformed even when an impact is applied to the ball bearing. Therefore, in a notebook computer in which the spindle motor to which the present invention is applied is mounted for driving a disk, 3 is required in the case of 2.5 inches.
The shock resistance of 00G or more and the shock resistance of 500G or more required for 3.5 inches can be satisfied.
When the diameter of the ball bearing is as large as possible, the rotating shaft can be made thicker. Therefore, according to the present invention, it is possible to make the thickness of the rotation shaft in the portion where the screw hole is formed sufficient. Therefore, when the screw is fixed to the screw hole, the stress is not transmitted to the ball bearing through this portion of the rotating shaft, and the inner ring of the ball bearing is not deformed. Therefore, it is possible to reliably prevent the occurrence of noise and a decrease in reliability.

[Brief description of the drawings]

FIG. 1 is a sectional view of a shaft rotation type spindle motor for 2.5 inches.

FIG. 2 is a sectional view of a 3.5-inch rotary shaft type spindle motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Spindle motor 5, 6 Ball bearing 7 Hub 9 Coil 10 Stator core 14 Rotor magnet 21 Motor frame 50, 60 Bearing ball 51, 61 Inner ring of ball bearing 52, 62 Outer ring of ball bearing 71 Rotary shaft 75 Screw hole 76 for holding clamper 76 Disk guide part 77 Disk mounting surface 100 Clamper 101 Screw 200 Hard disk 211 Bearing holding hole D0 Root diameter of screw hole for stopping clamper D1 Distance between centers of bearing balls D2 Outer diameter dimension of disk guide part D10 Stopper for clamper Inner diameter of screw hole L1 Bearing span t Thickness of screw hole formed part on rotating shaft

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[Procedure amendment]

[Submission date] November 11, 1998 (1998.11.
11)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D109 BB01 BB12 BB16 BB21 CA01 5H019 AA06 CC04 CC07 CC08 DD01 EE14 FF03 5H605 AA00 AA05 BB05 BB19 CC04 CC05 DD03 EB10 GG21 5H621 AA04 BB07 GA01 HH01 JK17 J19

Claims (3)

[Claims] A rotating shaft extending downward from a hub for mounting a recording disk; a frame rotatably supporting the rotating shaft via a ball bearing; an armature mounted on the frame; A spindle motor having an annular rotor magnet mounted on the hub so as to face the child, wherein a recording disk mounted on the hub is pressed and fixed to the upper end surface of the rotating shaft on the hub. When a screw hole for stopping the clamper is formed, the thickness of the rotary shaft at the portion where the screw hole is formed is t, and the root diameter of the screw hole is D0, t and D0 are: A spindle motor characterized by satisfying the following expression: t ≧ D0 / 2. 2. The spindle motor according to claim 1, wherein t and D0 are substantially equal. 3. The spindle motor according to claim 1, wherein an outer diameter of the disk guide portion in which the center hole of the recording disk is fitted in the hub is 25 mm or less.