Spindle motor and disk drive device equipped therewith

Abstract

This spindle motor comprises a shaft, a base part, a stator core, a rotor, and a bearing part. The shaft extends along a center axis extending in the vertical direction. The shaft has a screw hole extending axially downward from the upper end thereof. The screw hole has a screw section screwed to a screw. The bearing part comprises an upper annular member, a lower annular member, and a sleeve. The upper annular member and the lower annular member protrude radially outward from an outer peripheral surface of the shaft and are disposed to be spaced apart from each other in the axial direction. The sleeve has an insertion hole into which the shaft is inserted. The sleeve covers the outer peripheral surface of the shaft, axially extends, and is formed in a cylindrical shape. The upper end of the upper annular member is disposed further axially downward than the lower end of the screw section.

Description

【Technical Field】 【0001】 The present invention relates to a spindle motor and a disk drive device including the same. 【Background Art】 【0002】 A conventional spindle motor includes a shaft portion extending along a central axis extending in the vertical direction, a bracket main body (base portion), a hub member (rotor), and bearing means (bearing portion). The shaft portion is fixed to the bracket main body. The bearing means rotatably supports the hub member with the shaft portion as the central axis. The shaft portion extends downward in the axial direction from the upper end and has a clamp hole (screw hole) into which a mounting screw is screwed (see, for example, Patent Document 1). 【Prior Art Documents】 b 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Laid-Open No. 4-112645 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 However, when a mounting screw is screwed into the clamp hole of the spindle motor disclosed in the above patent document, the vicinity of the clamp hole of the shaft portion may be deformed, the axis center may be displaced, and shaft runout may occur. 【0005】 An object of the present invention is to provide a spindle motor capable of reducing the occurrence of shaft runout. 【Means for Solving the Problems】 【0006】 An exemplary spindle motor of the present invention comprises a shaft, a base, a stator core, a rotor, and a bearing. The shaft extends along a central axis that extends vertically. The base has a through hole to which the lower end of the shaft is fixed. The stator core is positioned on the upper surface of the base and surrounds the shaft. The rotor rotates around the central axis. The bearing supports the rotor so that it can rotate around the shaft as the central axis. The shaft has a threaded hole extending axially downward from its upper end. The threaded hole has a threaded portion that engages with a screw. The bearing comprises an upper annular member and a lower annular member and a sleeve. The upper annular member and the lower annular member project radially outward from the outer circumferential surface of the shaft and are positioned axially apart. The sleeve has an insertion hole into which the shaft is inserted. The sleeve extends axially, covering the outer circumferential surface of the shaft, and is formed in a cylindrical shape. The upper end of the upper annular member is positioned axially lower than the lower end of the threaded portion. [Effects of the Invention] 【0007】 According to an exemplary example of the present invention, a spindle motor capable of reducing the occurrence of axial runout can be provided. [Brief explanation of the drawing] 【0008】 [Figure 1] Figure 1 is a longitudinal cross-sectional view of a disk drive device according to an embodiment of the present invention. [Figure 2] Figure 2 is a longitudinal cross-sectional view of a motor according to an embodiment of the present invention. [Figure 3] Figure 3 is a longitudinal cross-sectional view of a motor according to an embodiment of the present invention. [Figure 4] Figure 4 is a longitudinal cross-sectional view showing an enlarged portion of the base of a motor according to an embodiment of the present invention. [Figure 5] Figure 5 is a graph showing the evaluation results of the excitation response of a motor according to an embodiment of the present invention. [Figure 6] Figure 6 is a graph showing the evaluation results of the excitation response of a motor according to an embodiment of the present invention. [Modes for carrying out the invention] 【0009】 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In this application, the direction parallel to the central axis C is referred to as the "axial direction," the direction perpendicular to the central axis C is referred to as the "radial direction," and the direction along the arc centered on the central axis C is referred to as the "circumferential direction." Furthermore, in this application, the axial direction is defined as the vertical direction, and the cover side is considered the upper side relative to the base, and the shapes and positional relationships of each part will be described accordingly. However, this definition of the vertical direction is not intended to limit the orientation in which the motor and disk drive device 1 according to the present invention may be used. 【0010】 (1. Configuration of the disk drive unit) An exemplary embodiment of the present invention, a disk drive device 1, will now be described. Figure 1 is a longitudinal cross-sectional view of a disk drive device 1 according to an embodiment of the present invention. 【0011】 The disk drive unit 1 is a hard disk drive. The disk drive unit 1 comprises a spindle motor 10, a disk 50, an access unit 60, and a housing 70. 【0012】 The housing 70 houses the spindle motor 10, the disk 50, and the access section 60. The inside of the housing 70 is filled with a gas with a lower density than air. Specifically, helium gas is used. Alternatively, hydrogen gas or other gases may be used instead of helium gas. 【0013】 The housing 70 has a base portion 71 and a cover portion 72. The base portion 71 is formed by casting a die-cast metal member made of an aluminum alloy. Note that a metal other than aluminum alloy may be used for the die-cast member. The cover portion 72 is formed from metal formed by press working. 【0014】 Inside the housing 70, the disk 50, spindle motor 10, and access section 60 are arranged on the base section 71. The base section 71 has side walls surrounding its sides and an open top. The opening at the top of the base section 71 is closed by the cover section 72. 【0015】 The disk 50 is a disk-shaped information recording medium having a hole in the central portion. Each disk 50 is mounted on the spindle motor 10 and is arranged axially parallel to and at equal intervals from each other via the spacer 80. 【0016】 The access unit 60 performs at least one of reading and writing information with respect to the disk 50. Specifically, the access unit 60 includes a head 61, an arm 62, and a head movement mechanism 63. The head 61 magnetically reads or writes information with respect to the disk 50. The arm 62 supports the head 61. The head movement mechanism 63 relatively moves the head 61 with respect to the disk 50 by moving the arm 62. 【0017】 (2. Configuration of Spindle Motor) FIG. 2 is a longitudinal sectional view of the spindle motor 10. The spindle motor 10 rotates the disk 50 about the central axis C while supporting the disk 50. The spindle motor 10 includes a shaft 11, a stator 20, a rotor 30, a bearing portion 40, and a base portion 71. 【0018】 The base portion 71 is a part of the housing 70 and also a part of the spindle motor 10. The base portion 71 has a through hole 720 penetrating axially and a cylindrical annular protrusion 721 protruding axially upward from the upper surface and surrounding the shaft 11. The through hole 720 is disposed on the central axis C. 【0019】 The shaft 11 is a columnar member extending along the central axis C extending in the vertical direction. The lower end portion of the shaft 11 is press-fitted and fixed into the through hole 720. Thereby, the shaft 11 and the base portion 71 are fixed. The shaft 11 has a screw hole 11a extending axially downward from the upper end. The screw hole 11a has a screw portion 110a that engages with the screw 90. Note that the screw portion 110a may be formed by, for example, cutting and may be formed into either a female screw shape or a male screw shape depending on the shape of the engaging screw. 【0020】 The screw hole 11a and the cover screw hole 72a provided in the cover portion 72 overlap in the axial direction and are screwed together via a screw 90 (see FIG. 1). Thereby, the shaft 11 and the cover portion 72 are fixed. Note that the cover screw hole 72a may be a through hole that is not threaded. 【0021】 Further, the shaft 11 has a hollow hole 11b that extends axially upward from the lower end. Thereby, the second moment of area at the lower end portion of the shaft 11 is reduced. Therefore, the load required for press-fitting the shaft 11 into the through hole 720 is reduced, and the press-fitting workability is improved. Also, the upper end of the hollow hole 11b is disposed axially above the upper end of the through hole 720. Thereby, the press-fitting workability is further improved when the shaft 11 is press-fitted into the through hole 720. 【0022】 Also, since the load required for press-fitting the shaft 11 into the through hole 720 is reduced, deformation of the shaft 11 and the through hole 720 due to the press-fitting load can be prevented. The outer diameter of the shaft 11 is preferably 5.5 mm or more and 7.0 mm or less. Thereby, while ensuring the rigidity of the shaft 11, it is possible to suppress the shaft 11 from tilting with respect to the base portion 71. 【0023】 The stator 20 surrounds the lower portion of the shaft 11 and is fixed to the base portion 71. The stator 20 has an annular stator core 21 and a plurality of coils 22. The stator core 21 is an annular laminated structure in which a plurality of magnetic bodies are laminated. The stator core 21 is disposed on the upper surface of the base portion 71 and surrounds the shaft 11. Specifically, the inner peripheral surface of the stator core 21 is press-fitted into the outer peripheral surface of the annular protrusion 721. 【0024】 Note that the upper end of the hollow hole 11b is disposed at a position that overlaps the annular protrusion 721 and the stator core 21 in the radial direction. Thereby, it is possible to reduce deformation of the annular protrusion 721 disposed around the through hole 720 during press-fitting. Therefore, it is possible to reduce the occurrence of axial displacement of the stator core 21 supported by the annular protrusion 721. 【0025】 The stator core 21 has a plurality of teeth 21a that protrude radially outward. The plurality of coils 22 are composed of conductors 22a wound around the teeth 21a. 【0026】 The rotor 30 includes a hub member 31, a magnet 32, and a yoke 33. The hub member 31 is formed in a cylindrical shape, and a sleeve 42 is fixed inside it. 【0027】 The yoke 33 is formed in an annular shape and fixed to the lower inner circumferential surface of the hub member 31. The magnet 32 ​​is attached to the inner circumferential surface of the yoke 33. As a result, the magnet 32 ​​is held to the hub member 31 via the yoke 33. The inner circumferential surface of the magnet 32 ​​is the magnetic pole surface and faces radially with the outer circumferential surfaces of the multiple teeth 21a. Note that if the hub member 31 is made of a magnetic material (for example, SUS), the magnet 32 ​​may be directly fixed to the inner circumferential surface of the hub member 31 and the yoke 33 may be omitted. 【0028】 The bearing section 40 is a conical type fluid dynamic bearing that supports the rotor 30 so that it can rotate around a central axis C. That is, the bearing section 40 supports the rotor 30 so that it can rotate around the shaft 11 as its central axis, and the rotor 30 rotates around the central axis C. The bearing section 40 comprises an upper annular member 41a, a lower annular member 41b, and a sleeve 42. 【0029】 The upper annular member 41a and the lower annular member 41b are fixed to the outer circumferential surface of the shaft 11 by press-fitting or the like, and protrude radially outward from the outer circumferential surface. The upper annular member 41a and the lower annular member 41b are fixed vertically to the outer circumferential surface of the shaft 11 with an axial gap between them. That is, the upper annular member 41a and the lower annular member 41b protrude radially outward from the outer circumferential surface of the shaft 11 and are arranged axially apart. 【0030】 The outer circumferential surfaces of the upper annular member 41a and the lower annular member 41b that are radially opposite to the sleeve 42 are substantially conical in shape. The lower part of the upper annular member 41a is formed to gradually decrease in diameter towards the bottom, and the upper part of the lower annular member 41b is formed to gradually decrease in diameter towards the top. 【0031】 The upper end of the upper annular member 41a is positioned axially lower than the lower end of the threaded portion 110a. By positioning the upper annular member 41a axially lower than the threaded portion 110a, deformation of the bearing portion 40 due to tightening the screw into the threaded hole 11a can be reduced. This prevents axial runout. Therefore, when the spindle motor 10 is driven, the generation of vibration and noise due to axial runout can be suppressed. 【0032】 Furthermore, by positioning the upper annular member 41a axially below the lower end of the threaded portion 110a, the center of gravity of the rotor 30 can be positioned closer to the center of the disk drive unit 1 in the axial direction. This improves the rotational stability of the spindle motor 10 and suppresses a decrease in the vibration performance of the disk drive unit 1. 【0033】 Furthermore, when viewed from the axial direction, the radially inner end of the annular projection 721 overlaps with at least a portion of the upper annular member 41a and the lower annular member 41b. In this embodiment, the radially inner end of the annular projection 721 is located radially inward from the radially outer ends of the upper annular member 41a and the lower annular member 41b. This allows the stator core 21 to be made radially larger and placed on the base portion 71. Consequently, the torque of the spindle motor 10 can be improved. 【0034】 The lower end of the lower annular member 41b is positioned axially above the upper end of the hollow hole 11b and the upper end of the stator core 21. By positioning the lower annular member 41b axially above the hollow hole 11b and the stator core 21, deformation of the bearing portion 40 can be reduced when the shaft 11 is press-fitted into the through hole 720. This further reduces axial runout. 【0035】 The sleeve 42 has an insertion hole 420 into which the shaft 11 is inserted and is formed in a cylindrical shape. The sleeve 42 extends axially, covering the outer circumferential surface of the shaft 11. The sleeve 42 has an upper inner circumferential surface 42a, a middle inner circumferential surface 42b, and a lower inner circumferential surface 42c, in that order from top to bottom. The upper inner circumferential surface 42a is inclined upward (upper axial direction) away from the shaft 11 and is radially opposite to the outer circumferential surface of the upper annular member 41a. The middle inner circumferential surface 42b is formed along the central axis C and is opposite to the outer circumferential surface of the shaft 11. The lower inner circumferential surface 42c is inclined downward (downward axial direction) away from the shaft 11 and is radially opposite to the outer circumferential surface of the lower annular member 41b. 【0036】 Furthermore, the sleeve 42 has a small gap S between the upper annular member 41a, the lower annular member 41b, and the shaft 11. The sleeve 42 may also be integrally molded with the hub member 31. 【0037】 The seal portion 44a is attached to the upper surface of the sleeve 42, and the seal portion 44b is attached to the lower surface of the sleeve 42. The seal portions 44a and 44b seal lubricating oil 43 in the minute gap S. Alternatively, the minute gap S may be filled with a fluid such as gas instead of lubricating oil. 【0038】 Figure 3 is a longitudinal cross-sectional view of the sleeve 42, with the shaft 11 shown by a dashed line. The upper inner circumferential surface 42a has a first dynamic pressure groove 421 and a second dynamic pressure groove 422, which are arranged adjacent to each other in the axial direction. The first dynamic pressure groove 421 and the second dynamic pressure groove 422 are inclined in different directions in the circumferential direction toward the axial upward side. In this embodiment, the first dynamic pressure groove 421 is located in the upper axial part of the upper inner circumferential surface 42a and is formed in multiple locations in the circumferential direction, inclined toward one side X1 in the circumferential direction toward the axial upward side. The second dynamic pressure groove 422 is located in the lower axial part of the first dynamic pressure groove 421 and is formed in multiple locations in the circumferential direction, inclined toward the other side X2 in the circumferential direction toward the axial upward side. 【0039】 The lower inner circumferential surface 42c has a third dynamic pressure groove 423 and a fourth dynamic pressure groove 424 that are arranged adjacent to each other in the axial direction. The third dynamic pressure groove 423 and the fourth dynamic pressure groove 424 are inclined in different directions in the circumferential direction toward the axial upward side. In this embodiment, the third dynamic pressure groove 423 is located in the lower axial part of the lower inner circumferential surface 42c and is formed in multiple locations in the circumferential direction, inclined toward the other circumferential side X2 toward the axial upward side. The fourth dynamic pressure groove 424 is located axially above the third dynamic pressure groove 423 and is formed in multiple locations in the circumferential direction, inclined toward one circumferential side X1 toward the axial upward side. 【0040】 In this embodiment, the first dynamic pressure groove 421 and the fourth dynamic pressure groove 424 are formed inclined toward one side X1 in the circumferential direction toward the axial upward direction, but they may also be formed inclined toward the other side X2 in the circumferential direction toward the axial upward direction. In this case, the second dynamic pressure groove 422 and the third dynamic pressure groove 423 are formed inclined toward one side X1 in the circumferential direction toward the axial upward direction. 【0041】 The first dynamic pressure groove 421, the second dynamic pressure groove 422, the third dynamic pressure groove 423, and the fourth dynamic pressure groove 424 induce fluid dynamic pressure in the lubricating oil 43 when the rotor 30 rotates. 【0042】 In this embodiment, the first dynamic pressure groove 421 and the second dynamic pressure groove 422 are formed on the upper inner circumferential surface 42a, but they may also be formed on the outer circumferential surface of the upper annular member 41a that is radially opposite to the upper inner circumferential surface 42a. 【0043】 Furthermore, in this embodiment, the third dynamic pressure groove 423 and the fourth dynamic pressure groove 424 are formed on the lower inner circumferential surface 42c, but they may also be formed on the outer circumferential surface of the lower annular member 41b that is radially opposite to the lower inner circumferential surface 42c. 【0044】 If the outer diameter of the shaft 11 is 5.5 mm or more and less than 6.5 mm, it is preferable that the axial distance L1 between the boundary P1 between the first dynamic pressure groove 421 and the second dynamic pressure groove 422 and the upper end of the shaft 11 be 0.60 to 0.85 times the axial distance L2 between the boundary P1 and the boundary P2 between the third dynamic pressure groove 423 and the fourth dynamic pressure groove 424. If the outer diameter of the shaft 11 is 6.5 mm or more and 7.0 mm or less, it is preferable that the distance L1 be 0.50 to 0.80 times the distance L2. In this case, it is preferable that the distance L1 be 8.5 mm or more. 【0045】 When the outer diameter of the shaft 11 is 5.5 mm or more and less than 6.5 mm, and the distance L1 is greater than 0.85 times the distance L2, or when the outer diameter of the shaft 11 is 6.5 mm or more and 7.0 mm or less, and the distance L1 is greater than 0.80 times the distance L2, the distance L1 increases, and in the disk drive device 1, the distance between the upper end of the shaft 11 fixed to the cover portion 72 and the upper annular member 41a widens. As a result, the support rigidity of the shaft 11 with respect to the rotor 30 decreases at the upper part of the shaft 11, and the generation of vibration and noise increases when the spindle motor 10 is driven (excitation response deteriorates). In addition, when the distance L1 increases and the center of gravity of the rotor 30 is located axially lower than the center of the disk drive device 1 in the axial direction, the rotational stability of the spindle motor 10 decreases and the excitation response deteriorates further. 【0046】 On the other hand, if the outer diameter of the shaft 11 is 5.5 mm or more and less than 6.5 mm, and the distance L1 is less than 0.60 times the distance L2, or if the outer diameter of the shaft 11 is 6.5 mm or more and 7.0 mm or less, and the distance L1 is less than 0.50 times the distance L2, the distance L1 becomes smaller, and the distance between the upper end of the upper annular member 41a and the lower end of the threaded portion 110a becomes narrower. As a result, when screwing the screw 90 into the threaded hole 11a, the vicinity of the threaded hole 11a deforms, the axis is displaced, and axial runout is more likely to occur. 【0047】 Furthermore, in the disk drive unit 1, the distance between the lower end of the shaft 11 fixed to the base portion 71 and the lower annular member 41b increases. As a result, the support rigidity of the shaft 11 relative to the rotor 30 decreases at the lower part of the shaft 11, and the generation of vibration and noise increases when the spindle motor 10 is driven (excitation response deteriorates). Also, when the distance L1 becomes smaller and the center of gravity of the rotor 30 is positioned axially above the center of the disk drive unit 1 in the axial direction, the rotational stability of the spindle motor 10 decreases and the excitation response deteriorates even further. 【0048】 Furthermore, by setting the distance L1 to 8.5 mm or more, the lower end of the threaded portion 110a can be positioned axially above the upper end of the upper annular member 41a, while ensuring a certain width of axial length for the threaded hole 11a and the threaded portion 110a. This allows for a more secure fastening of the shaft 11 and the cover portion 72 via the screw 90. 【0049】 When a drive current is supplied to the coil 22, magnetic flux is generated in multiple teeth 21a. Then, the interaction of the magnetic flux between the teeth 21a and the magnet 32 ​​generates a circumferential torque. As a result, the rotor 30 rotates around the central axis C relative to the stator 20. The disk 50, supported by the hub member 31, rotates together with the rotor 30 around the central axis C. 【0050】 At this time, when the sleeve 42 is rotationally driven relative to the upper annular member 41a and the lower annular member 41b, the first dynamic pressure groove 421, the second dynamic pressure groove 422, the third dynamic pressure groove 423 and the fourth dynamic pressure groove 424 induce fluid dynamic pressure in the lubricating oil 43 filled in the minute gap S by a pumping action. As a result, the sleeve 42 is supported radially and axially without contact with the upper annular member 41a and the lower annular member 41b, and can rotate smoothly at high speed relative to the upper annular member 41a, the lower annular member 41b and the shaft 11. 【0051】 (3. Detailed configuration of the base section) Figure 4 is a longitudinal cross-sectional view showing an enlarged portion of the base portion 71. The through hole 720 has a hole inclination portion 722 at its upper end, in which the inner diameter decreases as it is directed downward in the axial direction. The shaft 11 also has a curved surface portion 112 and a shaft inclination portion 111. The curved surface portion 112 is formed in a curved shape at the radial outer end of the lower end of the shaft 11. The shaft inclination portion 111 is formed continuously with the upper end of the curved surface portion 112, and its outer diameter increases as it is directed upward in the axial direction. 【0052】 When the shaft 11 is press-fitted into the through hole 720, even if there is a deviation in the press-fitting angle, the curved portion 112 can correct the press-fitting angle of the shaft 11. Furthermore, after the press-fitting angle is corrected by the curved portion 112, the shaft inclined portion 111 guides the shaft 11 to the appropriate angle relative to the through hole 720 while it is press-fitted. This reduces the occurrence of axial runout of the shaft 11 and improves the workability of the press-fitting process. 【0053】 Furthermore, by forming a hole inclined portion 722 on the through-hole 720 side, the press-fitting angle of the shaft 11 can be more easily corrected as the curved portion 112 of the shaft 11 passes through the hole inclined portion 722. 【0054】 Next, the effects of the present invention will be specifically explained using examples and comparative examples. In the following experiments, the excitation response of the spindle motor 10 was simulated and evaluated by mounting it on the disk drive device 1. 【0055】 First, the vibration response of the spindle motor 10 was evaluated when the outer diameter of the shaft 11 was 6.5 mm. In the following Examples 1, 2, 3, 4 and Comparative Examples 1 and 2, the outer diameter of the shaft 11 was 6.5 mm and the distance L2 was 16.3 mm. In Example 1, the distance L1 was set to 0.50 times the distance L2. In Example 2, the distance L1 was set to 0.60 times the distance L2. In Example 3, the distance L1 was set to 0.70 times the distance L2. In Example 4, the distance L1 was set to 0.80 times the distance L2. In Examples 1, 2, 3 and 4, the upper end of the upper annular member 41a is located axially lower than the lower end of the threaded portion 110a. 【0056】 In Comparative Example 1, the distance L1 was set to 0.40 times the distance L2. In Comparative Example 2, the distance L1 was set to 0.90 times the distance L2. In Comparative Example 1, the upper end of the upper annular member 41a is located axially above the lower end of the threaded portion 110a. 【0057】 Table 1 and Figure 5 show the evaluation results of the excitation response of the spindle motor 10 in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, and Comparative Example 2. 【0058】 [Table 1] 【0059】 As shown in Table 1 and Figure 5, the excitation response of Examples 1, 2, 3, and 4 is 0.6 (um / G) or less, which is superior to the excitation response of Comparative Examples 1 and 2. Furthermore, the excitation response of Examples 2 and 3 is superior to that of Examples 1 and 4. 【0060】 This revealed that when the outer diameter of the shaft 11 is between 6.5 mm and 7.0 mm, the vibration response is superior when the distance L1 is between 0.50 and 0.80 times the distance L2. 【0061】 Next, the vibration response was evaluated when the outer diameter of the shaft 11 was 6.0 mm. In Examples 5, 6, 7, Comparative Example 3, and Comparative Example 4, the outer diameter of the shaft 11 was 6.0 mm, and the distance L2 was 15.5 mm. In Example 5, the distance L1 was set to 0.60 times the distance L2. In Example 6, the distance L1 was set to 0.70 times the distance L2. In Example 7, the distance L1 was set to 0.80 times the distance L2. In Examples 5, 6, and 7, the upper end of the upper annular member 41a is located axially lower than the lower end of the threaded portion 110a. 【0062】 In Comparative Example 3, the distance L1 was set to 0.50 times the distance L2. In Comparative Example 4, the distance L1 was set to 0.90 times the distance L2. In addition, in Comparative Example 3, the upper end of the upper annular member 41a is located axially above the lower end of the threaded portion 110a. 【0063】 Table 2 and Figure 6 show the evaluation results of the excitation response of the spindle motor 10 in Example 5, Example 6, Example 7, Comparative Example 3, and Comparative Example 4. 【0064】 [Table 2] 【0065】 As shown in Table 2 and Figure 6, the excitation response of Examples 5, 6, and 7 is 0.6 or less, which is superior to the excitation response of Comparative Examples 3 and 4. Furthermore, as shown in Figure 6, even when the distance L1 is 0.85 times the distance L2, the excitation response is 0.6 or less, demonstrating excellent excitation response. 【0066】 This revealed that when the shaft 11 has an outer diameter of 6.0 mm or more and less than 6.5 mm, the vibration response is superior when the distance L1 is between 0.60 and 0.85 times the distance L2. 【0067】 (4. Other) The embodiments described above are merely illustrative examples of the present invention. The configuration of the embodiments may be modified as appropriate without exceeding the technical spirit of the present invention. Furthermore, the embodiments may be combined to the extent possible. [Industrial applicability] 【0068】 According to the present invention, it can be used in the enclosure of a disk drive device such as a hard disk drive. [Explanation of symbols] 【0069】 1. Disk drive unit 10 Spindle motors 11 shafts 11a Screw hole 11b Hollow hole 20 stata 21 Stator Core 21a Teeth 22 coils 22a conductor 30 rotors 31 Hub component 32 Magnets 33 York 40 Bearing section 41a Upper annular member 41b Lower annular member 42 sleeves 42a Upper inner surface 42b Middle inner circumferential surface 42c Lower inner surface 43 Lubricating oil 44a, 44b Seal section 50 discs 60 Access Section 61 heads 62 Arms 63 Head movement mechanism 70 cabinets 71 Base section 72 Cover section 72a Cover screw holes 80 Spacer 90 screws 110a Threaded part 111 Shaft Inclined Section 112 Curved part 420 Insertion holes 421 First Dynamic Pressure Groove 422 Second Dynamic Pressure Groove 423 Third Dynamic Pressure Groove 424 Fourth Dynamic Pressure Groove 720 Through hole 721 Annular projection 722 Hole slope C center axis L1 distance L2 distance P1 boundary P2 boundary S micro gap X1 One side in the circumferential direction X2 Other side in circumferential direction

Claims

[Claim 1] A shaft extending along a central axis that extends vertically, A base portion having a through hole to which the lower end of the shaft is fixed, An annular stator core is positioned on the upper surface of the base portion and surrounds the shaft, A rotor that rotates around the aforementioned central axis, The system includes a bearing portion that rotatably supports the rotor with the aforementioned shaft as its central axis, The shaft has a screw hole extending axially downward from its upper end, The screw hole has a threaded portion that engages with the screw, and it overlaps axially with the cover screw hole provided in the cover portion that covers the shaft, and is screwed in via the screw. The bearing portion is An upper annular member and a lower annular member are arranged to protrude radially outward from the outer surface of the shaft and to be spaced apart in the axial direction, The system comprises a cylindrical sleeve having an insertion hole into which the shaft is inserted, and extending axially to cover the outer circumferential surface of the shaft, The upper end of the upper annular member is positioned axially lower than the lower end of the threaded portion of the spindle motor. [Claim 2] The aforementioned sleeve is An upper inner circumferential surface that is radially opposite to the upper annular member and inclined toward the axial upward direction toward the shaft, It has a lower inner circumferential surface that is radially opposite to the lower annular member and inclined toward the axial downward direction toward the shaft, The aforementioned upper inner surface is, It has first and second dynamic pressure grooves, which are arranged adjacent to each other in the axial direction and each has multiple grooves formed in the circumferential direction, The first and second dynamic pressure grooves are inclined in different circumferential directions toward the axial upward side. The lower inner surface is, It has third and fourth dynamic pressure grooves, which are arranged adjacent to each other in the axial direction and each has multiple grooves formed in the circumferential direction, The third and fourth dynamic pressure grooves are inclined in different circumferential directions toward the axial upward side, The outer diameter of the shaft is 5.5 mm or more and less than 6.5 mm, The spindle motor according to claim 1, wherein the axial distance between the boundary between the first dynamic pressure groove and the second dynamic pressure groove and the upper end of the shaft is 0.60 times or more and 0.85 times or less the axial distance between the boundary between the first dynamic pressure groove and the second dynamic pressure groove and the boundary between the third dynamic pressure groove and the fourth dynamic pressure groove. [Claim 3] The aforementioned sleeve is An upper inner circumferential surface that is radially opposite to the upper annular member and inclined toward the axial upward direction toward the shaft, It has a lower inner circumferential surface that is radially opposite to the lower annular member and inclined toward the axial downward direction toward the shaft, The aforementioned upper inner surface is, It has first and second dynamic pressure grooves, which are arranged adjacent to each other in the axial direction and each has multiple grooves formed in the circumferential direction, The first and second dynamic pressure grooves are inclined in different circumferential directions toward the axial upward side. The lower inner surface is, It has third and fourth dynamic pressure grooves, which are arranged adjacent to each other in the axial direction and each has multiple grooves formed in the circumferential direction, The third and fourth dynamic pressure grooves are inclined in different circumferential directions toward the axial upward side, The outer diameter of the shaft is 6.5 mm or more and 7.0 mm or less, The spindle motor according to claim 1, wherein the axial distance between the boundary between the first dynamic pressure groove and the second dynamic pressure groove and the upper end of the shaft is 0.50 times or more and 0.80 times or less the axial distance between the boundary between the first dynamic pressure groove and the second dynamic pressure groove and the boundary between the third dynamic pressure groove and the fourth dynamic pressure groove. [Claim 4] The spindle motor according to any one of claims 1 to 3, wherein the lower end of the lower annular member is positioned axially above the upper end of the stator core. [Claim 5] The base portion is It has an annular projection that protrudes axially upward from the upper surface and surrounds the shaft, The stator core is held on the outer circumferential surface of the annular projection, The spindle motor according to any one of claims 1 to 4, wherein, when viewed from the axial direction, the radial inner end of the annular projection overlaps with at least a portion of the upper annular member and the lower annular member. [Claim 6] The spindle motor according to any one of claims 1 to 5, wherein the shaft has a hollow hole extending axially upward from its lower end. [Claim 7] The spindle motor according to claim 6, wherein the upper end of the hollow hole is positioned axially above the upper end of the through hole. [Claim 8] The spindle motor according to claim 6 or 7, wherein the lower end of the lower annular member is positioned axially above the upper end of the hollow hole. [Claim 9] The spindle motor according to any one of claims 6 to 8, wherein the upper end of the hollow hole is positioned to overlap radially with the stator core. [Claim 10] The aforementioned shaft is At the radially outer end of the lower end, a curved surface portion is formed in a curved shape, A spindle motor according to any one of claims 1 to 9, comprising a shaft inclined portion formed continuously with the upper end of the curved portion, the outer diameter of which increases as it is directed upward in the axial direction. [Claim 11] The spindle motor according to any one of claims 1 to 10, wherein the shaft has an outer diameter of 5.5 mm or more and 7.0 mm. [Claim 12] The spindle motor according to claim 2 or claim 3, wherein the axial distance between the boundary between the first dynamic pressure groove and the second dynamic pressure groove and the upper end of the shaft is 8.5 mm or more. [Claim 13] The spindle motor according to any one of claims 1 to 12, wherein the through hole has a hole inclination portion at the upper end where the inner diameter decreases as it is directed downward in the axial direction. [Claim 14] A spindle motor according to any one of claims 1 to 13, A disk that rotates about the central axis by the spindle motor, An access unit that reads information from and writes information to the disk, A disk drive device comprising a housing that houses the spindle motor, the disk, and the access unit, and also includes the cover unit. [Claim 15] The disk drive device according to claim 14, wherein the inside of the housing is filled with a gas that is less dense than air.

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