JPH06121483A - Spindle motor - Google Patents

Abstract

PURPOSE:To prevent the contraction of life by leakage of lubricant or the pollution of space outside a motor by suppressing the radial and axial displacement during the relative rotation between a shaft and a sleeve enough low by a dynamic-pressure bearing. CONSTITUTION:A radial dynamic-pressure bearing R1 is composed of the inside periphery 38a1 of a sleeve 38a and the outside periphery 14c of a fixed pole 14. The inside periphery 38a1 is provided with a herringbone groove 46 for generating high pressure in a lubricant 44. Axial dynamic-pressure bearings A1 and A2 are composed of the upper and lower circular faces 26a and 26b of a thrust plate 26 and the upper and lower circular plates 42a and 42b of a circular recess 42. The upper and lower circular faces 26a and 26b are provided with spiral grooves 48 and 50, which generate the dynamic pressure by which a lubricant flow radially, and circular recesses 52 and 54. Treatment by which the contact angles with the lubricant 44 becomes obtuse, is applied to the inner surface of the recesses 52 and 54.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle motor in which a sleeve body is externally fitted to a shaft body so as to freely rotate relative to the shaft body through a lubricant.

[0002]

2. Description of the Related Art Due to further miniaturization and higher capacity of devices such as personal computers,
Further miniaturization and higher precision are also required for spindle motors for driving recording media (for example, hard disks) incorporated therein. Along with this, further miniaturization and higher precision are required for the bearings of the spindle motor.

Conventionally, ball bearings have been widely used as bearings used in spindle motors. However, as miniaturization of spindle motors, especially smaller outer diameters progresses, ball bearings with smaller outer diameters that match the smaller spindle motors may be used, which may cause deformation of the inner and outer rings during motor assembly. It tends to be practically difficult to achieve. Also, noise and vibration problems are likely to occur.

In the case of a spindle motor for driving a recording medium, high speed rotation is required as the outer diameter becomes smaller, so these problems are further aggravated. Furthermore, regardless of the size of the outer diameter, there is a limit to the accuracy of the ball bearing, and it may be possible that the required specifications are not satisfied.

Therefore, as a small-sized spindle motor, a rotary sleeve portion is provided on the inner peripheral side of the base portion of the rotor hub portion, and the rotary sleeve portion is externally fitted to the fixed column portion and rotatably supported to move. A spindle motor having a pressure radial bearing has been proposed.

However, in the case of a spindle motor for reading / writing by flying a magnetic head or the like on the surface of a recording medium that is rotationally driven in the order of microns or submicrons, the axial displacement of the rotor also occurs. It must be kept sufficiently small, and the lubricant of the bearing must be effectively prevented from scattering and contaminating the surface of the recording medium.

The present invention has been made in view of the above-mentioned problems existing in the prior art, and its object is to provide a radial displacement and an axial line during relative rotation of the shaft body and the sleeve body. The directional displacement can be kept sufficiently small by the dynamic pressure bearings, and the leakage of lubricant from the dynamic pressure bearings reduces lubrication and shortens its life, and contaminates the space outside the motor. It is an object of the present invention to provide a spindle motor that is prevented from running.

[0008]

In order to achieve the above object, the spindle motor of the present invention has a substantially cylindrical surface-shaped outer peripheral portion and a radially outward projecting portion, and both annular surfaces in the axial direction have the substantially cylindrical surface. A shaft body having an annular protrusion that is perpendicular to the outer periphery of the shape, a substantially cylindrical inner peripheral portion that is externally fitted to the outer peripheral portion of the substantially cylindrical surface, and an annular protrusion that fits in the axial direction. A sleeve body having both annular surfaces, each annular surface of the annular protrusion being parallel to the annular recess of the radially inward opening, wherein the sleeve body is free to the shaft body via a lubricant. In a spindle motor fitted so as to be able to rotate relative to each other, a radial dynamic pressure bearing portion is constituted by a radial receiving portion having a substantially cylindrical surface-shaped outer peripheral portion and a radial sliding portion having a substantially cylindrical surface-shaped inner peripheral portion. And the axial receiving portion and the ring respectively provided on both annular surfaces of the annular protrusion. An axial dynamic pressure bearing portion is configured by the axial slide portions that are respectively provided on both annular surfaces of the recessed portion, and the axial receiving portion or the axial slide portion of each axial dynamic pressure bearing portion is lubricated by relative rotation of the shaft body and the sleeve body. Grooves are provided so as to generate a dynamic pressure that causes the agent to flow radially outward, and on both sides in the axial direction,
An annular recess with an obtuse contact angle with the lubricant on the inner surface is provided on the part of the annular surface of the annular protrusion or annular recess that is radially inward of the groove. I am trying.

Further, the spindle motor of the present invention may have one or more through holes penetrating the annular projection in the axial direction inward of the annular projection in the radial direction from the annular groove. preferable.

[0010]

According to the first aspect of the invention, the radial dynamic pressure bearing is constituted by the radial receiving portion provided on the outer peripheral portion of the substantially cylindrical surface of the shaft body and the radial sliding portion provided on the inner peripheral portion of the substantially cylindrical surface of the sleeve body. The radial displacement of the shaft body and the sleeve body during the relative rotation of the shaft body is regulated by the portion, and the axial receiving portion provided on both annular surfaces of the annular projection of the shaft body and the axial sliding portion provided on both annular surfaces of the annular recess of the sleeve body. Both axial dynamic pressure bearing portions configured by and regulate axial displacement of the shaft body and the sleeve body during relative rotation.

The dynamic pressure generated in the lubricant by the grooves of both axial dynamic pressure bearing portions due to the relative rotation of the shaft body and the sleeve body is such that the lubricant flows radially outward, and therefore, the dynamic pressures of the two Are balanced on the outer circumference of the annular projection. Therefore, normally, the lubricant is held substantially on both axial dynamic pressure bearing portions and their radial outwards.

On the other hand, during rotation, the balance of the dynamic pressure between the axial dynamic pressure bearing portions is disturbed for some reason, or during the rotation or non-rotation, the thermal expansion of the lubricant or the radial dynamic pressure bearing portion. The lubricant may try to flow inward in the radial direction due to thermal expansion of the gas in the gas pool that is likely to occur between the bearing and the axial dynamic pressure bearing portion. When the lubricant flows inward in the radial direction, the lubricant flows into the annular recess provided in the annular surface of the annular projection or the annular recess. The contact angle of the inner surface of the recess with the lubricant is obtuse and the inner surface of the recess is not wet by the lubricant, so that the lubricant is prevented from oozing out from the recess and effectively retained in the recess. It

According to the second aspect of the present invention, the portion of the annular projection that is radially inward of the annular recess penetrates through the through hole in the substantially axial direction, so that the radial dynamic pressure bearing portion and the axial dynamic bearing are formed. Even if the gas in the gas pool that is likely to form between the pressure bearing and the thermal expansion expands due to the temperature rise, the pressure on the radial inner side of the annular recess on both axial sides of the annular protrusion is equalized by the through hole. Be converted. Therefore, it is possible to prevent the lubricant from flowing out inward in the radial direction of the axial dynamic pressure bearing portion on the side opposite to the radial dynamic pressure bearing portion.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a spindle motor of a fixed shaft type as one embodiment of the present invention, and FIG. 2 is a schematic enlarged view of a main part thereof.

The fixed column 14 is vertically installed with respect to the bracket 10 in a state where the lower end of the columnar fixed column 14 is fitted and fixed in the fitting hole 12 provided in the central portion of the bracket 10. . An annular protrusion 16 protruding upward is provided on the outer peripheral portion of the fitting hole 12 in the bracket 10, and the stator coil 1 is provided on the outer peripheral portion of the annular protrusion 16.
The stator core 19 around which 8 is wound is fixed. The lead wire 20 of the stator coil 18 is led out below the bracket 10 through a lead hole 22 provided in the bracket 10. Annular projection 1 in bracket 10
An annular groove 24 is provided on the upper surface of 6 at the outer side in the radial direction.

An annular plate-shaped thrust plate 26 is externally fitted and fixed to the upper end reduced diameter portion 14a of the fixed column 14. Furthermore,
The thrust plate 26 is sandwiched between the fixed strut 14 and the annular end surface 14b of the fixed strut 14, and a recess 30a formed in the center of the lower end of a substantially cylindrical fixed bush 30 having a screw hole 28 penetrating in the center thereof is compressed at the upper end of the fixed strut 14. It is fitted and fixed to the diameter part. The upper and lower annular surfaces 26a and 26b of the thrust plate 26, which project outward in the radial direction, are perpendicular to the cylindrical outer peripheral surface 14c of the fixed column 14. In this embodiment, these fixed columns 14, thrust plates 26 and fixed bushes 3 are provided.
0 constitutes the shaft body.

The sleeve member 38 has a small-diameter sleeve portion 38a having an inner peripheral surface 38a1 having a substantially cylindrical surface shape, an annular portion 38b projecting radially outward at the upper end of the sleeve portion 38a, and an outer periphery of the annular portion 38b. It comprises a large diameter portion 38c extending upward from the portion. The sleeve portion 38a is the fixed column 1.
4, the annular rotary bush 4 is fitted to the large diameter portion 38c with the thrust plate 26 interposed between the large diameter portion 38c and the annular portion 38b with a slight radial gap between the thrust bush 26 and the fixed bush 30.
0 is fixed internally. Therefore, the sleeve member 38 and the rotating bush 40 allow the annular recess 4 to be opened radially inward.
2 is formed, and the thrust plate 26 is fitted in the annular recess 42. In this embodiment, the sleeve body composed of the sleeve member 38 and the rotating bush 40 can freely rotate with respect to the shaft body through the lubricant 44.

A radial dynamic pressure bearing portion R1 is formed by an inner peripheral surface 38a1 (radial sliding portion) of the sleeve portion 38a and a portion (radial receiving portion) of the outer peripheral surface 14c of the fixed strut 14 facing the inner peripheral surface 38a1. Has been done. Sleeve part 3
Along the entire circumference of the upper end portion and the lower end portion of the inner peripheral surface 38a1 of 8a, the forward rotation of the sleeve member 38 causes a high pressure in the lubricant present between the sleeve portion 38a and the outer peripheral surface 14c of the fixed support column 14. There is a herringbone groove 46 for generating In addition, such a herringbone groove may be provided on the outer peripheral surface 14 c of the fixed column 14. It is also possible to adopt a groove other than the herringbone groove.

The upper and lower annular surfaces 26a, 26 of the thrust plate 26
b (axial receiving portion) and upper and lower annular surfaces 42 of the annular recess 42
The axial dynamic pressure bearings A1 and A2 are respectively configured by a and 42b (axial sliding portions). The upper and lower annular surfaces 26a and 26b of the thrust plate 26 and the upper and lower annular surfaces 42a and 42b of the annular recess 42 face each other in parallel,
Each of them is separated by a slight axial gap of, for example, about 12 μm. The thrust plate 26 is interposed between the upper and lower annular surfaces 42a and 42b of the annular recess 42 by the forward rotation of the sleeve member 38 and the rotating bush 40 over the entire circumference on the outer peripheral side of the upper and lower annular surfaces 26a and 26b. Spiral grooves 48 and 50 (groove portions) are provided so that a dynamic pressure in which the lubricant 44 flows radially outward is generated. Note that such spiral grooves may be provided on the upper and lower annular surfaces 42a and 42b of the annular recess 42. It is also possible to adopt a groove other than the spiral groove.

The upper and lower annular surfaces 26a, 26 of the thrust plate 26
Annular recesses 52 and 54 are provided radially inward of the spiral grooves 48 and 50 in b. The inner surfaces of these annular recesses 52 and 54 are treated so that the contact angle with the lubricant 44 is obtuse.

The thrust plate 26 has an annular recess 52.5.
A plurality of through-holes 55 penetrating in a substantially axial direction are provided at constant center angles on a constant circumference radially inward of 4.

The rotor hub 56 has a tubular shape as a whole, and has a base portion 56a located at the upper end portion, a peripheral wall portion 56b whose diameter is expanded downward from the lower end portion of the base portion 56a, and a lower end portion of the peripheral wall portion 56b. And an outer overhanging portion 56c for extending. The rotor hub 56 is externally fitted and fixed to the large diameter portion 38c of the sleeve member 38 at the base portion 56a.
Of course, the rotor hub 56 and the sleeve member 38 may be integrally formed. A cylindrical rotor yoke 60 in which a cylindrical rotor magnet 58 is fitted and held is internally fitted and fixed to the inner peripheral portion of the peripheral wall portion 56b, and faces the stator core 19 with a radial gap. Base 56
A clamper (not shown) for holding a recording medium such as a hard disk, which is fitted on the peripheral wall portion 56b, between the outer peripheral portion of a and the outward protruding portion by screwing is fixed. A male screw portion 62 is formed. The lower portion of the outward projecting portion 56c is located in the annular groove 24.

The radial dynamic pressure bearing portion R1 can sufficiently suppress the radial displacement of the sleeve member 38 with respect to the fixed column 14 during rotation, and the axial dynamic pressure bearing portions A1 and A2 can prevent the sleeve member 38 from rotating. The axial displacement with respect to the fixed column 14 can be suppressed sufficiently small.

The dynamic pressure generated in the lubricant 44 by the spiral grooves 48 and 50 of the upper and lower axial dynamic pressure bearing portions A1 and A2 is that the dynamic pressure of the lubricant 44 flows outward in the radial direction. The outer peripheral portion of the thrust plate 26 is balanced. Therefore, normally, the lubricant 44 is held on both the axial dynamic pressure bearing portions A1 and A2 and radially outward thereof.

On the other hand, during rotation, the balance of the dynamic pressures in the upper and lower axial dynamic pressure bearings A1 and A2 is lost for some reason, or during rotation or during non-rotation, the lubricant 44 or the radial movement is caused by the temperature rise. The lubricant 44 may try to flow inward in the radial direction due to thermal expansion of the gas or the like in the gas reservoir 64 that is likely to occur between the pressure bearing portion R1 and the axial dynamic pressure bearing portions A1 and A2. When the lubricant 44 flows radially inward, the annular surface 26a.2 of the thrust plate 26
The lubricant 44 flows into the annular recesses 52 and 54 provided in 6b. Since the contact angle of the inner surface of the annular recesses 52 and 54 with the lubricant 44 is an obtuse angle, the lubricant 44 is prevented from oozing out from the annular recesses 52 and 54, and the recess 5
It is effectively retained within 2.54.

Further, a gas pool 64 which may be formed between the radial dynamic pressure bearing portion R1 and the axial dynamic pressure bearing portions A1 and A2.
Even if the gas in the table expands due to the temperature rise, the thrust plate 26
Since the through holes 55 equalize the pressure in the portion radially inward of the annular recesses 52 and 54 on both sides in the axial direction, the lubricant 44 is applied radially inward of the upper axial dynamic bearing portion A1. Is prevented from flowing out.

FIG. 3 is a half sectional view of a shaft rotation type spindle motor as another embodiment of the present invention, and FIG. 4 is a schematic enlarged view of the main part thereof.

The bracket 70 is composed of an inner peripheral wall portion 74 which forms an annular groove 72, a bottom plate portion 76 and an outer peripheral wall portion 78, and an annular protruding portion 80 which extends outward from the upper end portion of the outer peripheral wall portion 78. The stator coil 8 is provided on the outer peripheral portion of the inner peripheral wall portion 74.
The stator core 84 around which 2 is wound is fixed. A cylindrical sleeve member 86 is fitted and fixed to the inner peripheral portion of the inner peripheral wall portion 74. Of course, the bracket 70 and the sleeve member 86 may be integrally formed.

The sleeve member 86 includes a cylindrical rotating shaft 8
8 is fitted inside. A screw 90 is screwed into the lower end opening of the rotating shaft 88, and an annular plate-shaped thrust plate 92 is fixed between the annular lower end surface of the rotating shaft 88 and the head of the screw 90. The upper and lower annular surfaces 92a and 92b of the thrust plate 92, which project outward in the radial direction, are perpendicular to the cylindrical outer peripheral surface 88a of the rotary shaft 88. In this embodiment, the rotary shaft 88, the thrust plate 92, and the screw 90 form a shaft body.

At the lower end of the inner peripheral wall portion 74 of the bracket 70, a deep dish-shaped fixing bush 94 is fitted and fixed.
The fixed bush 94 has a circular concave portion 94a that covers the lower portion and the outer peripheral portion of the screw 90 with a gap at the center bottom portion,
The upper end surface of the outer peripheral wall portion 94b is in close contact with the outer peripheral portion of the lower end surface of the sleeve member 86. Further, the thrust plate 92 is sandwiched between the annular middle surface 94c of the fixed bush 94 on the outer peripheral side of the circular recess 94a and the lower end surface inner peripheral portion 86a of the sleeve member 86. Therefore, the sleeve member 86 and the fixed bush 94 form an annular recess 96 having an opening in the radial direction, and the thrust plate 92 is fitted in the annular recess 96. In this embodiment, the sleeve body composed of the sleeve member 86 and the fixed bush 94 can freely rotate with respect to the shaft body through the lubricant 98.

A radial dynamic pressure bearing is formed by an inner peripheral surface 86a (radial sliding portion) of the sleeve member 86 and a portion (radial receiving portion) of the outer peripheral surface 88a of the rotary shaft 88 facing the inner peripheral surface 86a of the sleeve member 86. The part R2 is configured. A lubricant which is interposed between the sleeve member 86 and the outer peripheral surface 88a of the rotary shaft 88 by the forward rotation of the rotary shaft 88 over the entire circumference of the upper end portion and the lower end portion of the inner peripheral surface 86a of the sleeve member 86. A herringbone groove 100 for generating a high pressure is provided at 98. Note that such a herringbone groove may be provided on the outer peripheral surface 88 a of the rotating shaft 88.
It is also possible to adopt a groove other than the herringbone groove.

The upper and lower annular surfaces 26a, 26 of the thrust plate 92
b (axial receiving portion) and the upper and lower annular surfaces 42 of the annular recess 96.
The axial dynamic pressure bearings A3 and A4 are formed by a and 42b (axial sliding portions), respectively. The upper and lower annular surfaces 26a and 26b of the thrust plate 92 and the upper and lower annular surfaces 42a and 42b of the annular recess 96 face each other in parallel,
Each of them is separated by a slight axial gap of, for example, about 12 μm. The lubricant 98 interposed between the upper and lower annular surfaces 86a and 94c of the annular recess 96 by the forward rotation of the thrust plate 92 over the entire circumference on the outer peripheral side of the upper and lower annular surfaces 92a and 92b of the thrust plate 92.
The spiral grooves 102 and 104 are provided so that a dynamic pressure that flows radially outward is generated. The spiral grooves 102 and 104 may be provided on the upper and lower annular surfaces 86a and 94c of the annular recess 96. It is also possible to adopt a groove other than the spiral grooves 102 and 104.

Upper and lower annular surfaces 92a, 92 of the thrust plate 92
Annular recesses 106 and 108 are provided radially inward of the spiral grooves 102 and 104 in b. The inner surfaces of these annular recesses 106 and 108 are coated with the lubricant 9
The treatment is performed so that the contact angle with 8 is an obtuse angle.

The thrust plate 92 has an annular recess 10
A plurality of through-holes 110 penetrating in a substantially axial direction at constant center angles on a constant circumference radially inward of 6 · 108.
Is provided.

A substantially disk-shaped rotor hub 112 to which a recording medium such as a hard disk is fitted and fixed is fitted and fixed to the upper end of the rotary shaft 88. An upper end of a cylindrical rotor yoke 116 in which a cylindrical rotor magnet 114 is fitted and held is fixed to the outer peripheral portion of the rotor hub 112, and the rotor magnet 114 faces the stator core 84 with a radial gap.

Even if the gas in the gas reservoir 118, which is likely to be generated between the radial dynamic pressure bearing portion R2 and the axial dynamic pressure bearing portions A3 and A4, thermally expands due to a temperature rise, an annular shape is formed on both axial sides of the thrust plate 92. Since the pressure in the portion radially inward of the recesses 106 and 108 is equalized by the through hole 110, the lubricant 98 may flow out radially inward of the lower axial dynamic pressure bearing portions A3 and A4. It is prevented.

Further, the thrust plate 92 is fixed to the rotary shaft 88 by screw 90 in a screw hole opened at the lower end of the rotary shaft 88.
Alternatively, an annular plate-shaped thrust plate 9 is provided between the annular lower end surface of the rotary shaft 88 and the head of the screw 90 by screwing a bolt or the like.
This can be easily performed by fixing the inner peripheral portion of 2 by clamping.

Other functions and effects of this embodiment are substantially the same as those of the above embodiment. The vertical position relationship in the description of each of the above examples is
It is merely for convenience of description based on the drawings, and does not limit the actual use state or the like.

[0039]

According to the spindle motor of claim 1, the radial dynamic pressure bearing portion and the both axial dynamic pressure bearing portions enable
It is possible to sufficiently suppress the radial displacement and the axial displacement during relative rotation of the shaft body and the sleeve body. During the relative rotation of the shaft body and the sleeve body, normally, the dynamic pressure generated in the lubricant of both axial dynamic pressure bearing sections by both grooves is balanced, and the lubricant is distributed in both axial dynamic pressure bearing sections and their radial outwards. Held in. Further, the lubricant flowing inward in the radial direction due to the unbalance of the dynamic pressure during rotation and the temperature rise during rotation or non-rotation has an annular surface with an obtuse contact angle with the lubricant. Flows into the recess of
It is effectively retained in the recess. Therefore, it is possible to prevent the lubricant from leaking from both axial dynamic pressure bearings, impairing the lubrication of both axial dynamic pressure bearings, shortening the life of the bearings, and preventing the lubricant from scattering in the external space of the spindle motor. To be done.

According to another aspect of the spindle motor of the present invention, even if the gas in the gas pool, which is likely to be generated between the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portion, thermally expands, the annular protrusion is formed on both sides in the axial direction of the annular protrusion. Since the pressure in the portion radially inward of the recess is equalized by the through hole, it is possible to prevent the lubricant from flowing out radially inward of the axial dynamic bearing opposite to the radial dynamic bearing. As a result, the lubrication of both axial dynamic pressure bearing portions is impaired and their life is shortened, and the lubricant is more reliably prevented from scattering in the external space of the spindle motor.

[Brief description of drawings]

FIG. 1 is a sectional view of a spindle motor.

FIG. 2 is a schematic enlarged view.

FIG. 3 is a half sectional view of a spindle motor.

FIG. 4 is a schematic enlarged view.

[Explanation of sign]

 14 fixed column 14c outer peripheral surface 26 thrust plate 26a annular surface 26a annular surface 38a sleeve part 38a1 inner peripheral surface 42a annular surface 42b annular surface 44 lubricant 48 spiral groove 50 spiral groove 52 recess 54 recess 55 through hole 86 sleeve member 86a lower end surface Inner peripheral portion 88 Rotating shaft 88a Outer peripheral surface 90 Screw 92 Thrust plate 92a Annular surface 92b Annular surface 94c Annular middle step surface 98 Lubricant 102 Spiral groove 104 Spiral groove 106 Recessed portion 108 Recessed portion 110 Through hole A1 Axial dynamic bearing portion A2 Axial dynamic pressure Bearing A3 Axial dynamic bearing A4 Axial dynamic bearing R1 Radial dynamic bearing R2 Radial dynamic bearing

Claims (2)

[Claims] 1. A shaft body having a substantially cylindrical surface-shaped outer peripheral portion and an annular projecting portion projecting radially outward and having both axial annular surfaces perpendicular to the substantially cylindrical surface-shaped outer peripheral portion. A radial direction in which the inner peripheral part of the substantially cylindrical surface shape fitted on the outer peripheral part of the substantially cylindrical surface shape and the annular projection part are fitted, and both annular surfaces in the axial direction are parallel to both annular surfaces of the annular projection part. A spindle motor comprising: a sleeve body having an annular recess with an inward opening; and a sleeve body externally fitted to a shaft body so as to be freely rotatable relative to a shaft body, the spindle motor being substantially cylindrical. A radial dynamic pressure bearing portion is formed by the radial receiving portion provided on the outer peripheral portion of the surface shape and the radial sliding portion provided on the inner peripheral portion of the substantially cylindrical surface shape. The axial slides on both annular surfaces enable the Each of the axial dynamic pressure bearing portions is configured with a groove portion so that the relative pressure between the shaft body and the sleeve body causes the dynamic pressure of the lubricant to flow outward in the radial direction. Is provided, and at least on one side in the axial direction, an annular surface having an obtuse contact angle with the lubricant on the inner surface is formed in a portion of the annular surface of the annular projection or the annular recess radially inward of the groove portion. A spindle motor characterized in that a recess is provided in the spindle motor. 2. The spindle motor according to claim 1, wherein one or more through holes penetrating the annular protrusion in the axial direction are provided radially inward of the annular groove in the annular protrusion.