Spindle motor and hard disk drive

Abstract

To provide a technique for strongly joining a member that closes an opening to a bearing sleeve of a spindle motor.SOLUTION: A spindle motor 3 comprises: a columnar shaft 60 extending in an axial direction; an annular thrust plate 43 attached to one end of the shaft 60; a cylindrical bearing sleeve 40 for rotatably supporting the shaft 60 and having a circumferential direction and a radial direction orthogonal to the circumferential direction, the bearing sleeve 40 having a lower end part 40E in the axial direction, and an external peripheral recess 42 extending in the circumferential direction and having a depth in the axial direction formed on the radially outer side of the lower end part 40E; and a counter plate 44 having a lid part 44S for covering the lower end part 40E, and a protrusion 44P protruding toward the external peripheral recess 42 from the lid part 44S and joined to the lower end part 40E. The bearing sleeve 40 and the counter plate 44 are joined to each other with an adhesive.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a spindle motor and a hard disk drive device.

Background Art

[0002] A type of spindle motor that supports a shaft with a bearing sleeve needs to close an opening at one end of the bearing sleeve so that the shaft is held inside the bearing sleeve. Since an axial force is applied to the shaft, the member that closes the opening needs to be firmly joined to the bearing sleeve.

[0003] For example, Patent Document 1 discloses a technique of joining a cup-shaped member to a bearing sleeve with an adhesive.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for firmly joining a member that closes an opening to a bearing sleeve of a spindle motor.

Means for Solving the Problems

[0006] To solve the above problems, the spindle motor comprises a columnar shaft extending in the axial direction, an annular thrust plate attached to one end of the shaft, a cylindrical bearing sleeve that rotatably supports the shaft and has a circumferential direction and a radial direction perpendicular to the circumferential direction, having an end in the axial direction, and a recess extending along the circumferential direction and having depth in the axial direction formed radially outward of the end, a cover portion that covers the end, and a projection that protrudes from the cover portion into the recess and joins with the end, and the bearing sleeve and the counter plate are joined by adhesive. [Effects of the Invention]

[0007] According to the present invention, a member that closes the opening can be firmly joined to the bearing sleeve. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view of the hard disk drive unit 1. [Figure 2] This is a cross-sectional view of the spindle motor 3. [Figure 3] This is an enlarged view of part III in Figure 2. [Figure 4] This is an enlarged cross-sectional view of the spindle motor 3 in which a gap 145 is formed. [Figure 5] This is an enlarged cross-sectional view of the spindle motor 3 in which the gap 147 is formed. [Figure 6] This is an enlarged cross-sectional view of the spindle motor 3 in which the gap 247 is formed. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below are subject to various technically preferred limitations for carrying out the present invention, but the scope of the present invention is not limited to the following embodiments and illustrated examples.

[0010] <Hard disk drive> Figure 1 is a perspective view showing the configuration of the hard disk drive unit 1. The hard disk drive unit 1 comprises a case 2, a spindle motor 3, a recording disk 4, a bearing device 5, and a cover 6.

[0011] Case 2 has a bottomed box shape with one side open, forming a roughly rectangular parallelepiped. Inside Case 2 are a spindle motor 3, recording disks 4, and a bearing device 5. The spindle motor 3 rotatably supports multiple recording disks 4. The multiple recording disks 4 are supported by the spindle motor 3 so that their respective disk surfaces face each other. A gap is formed between each recording disk 4. The bearing device 5 swingably supports multiple swing arms 7, which are positioned in the gap between each recording disk 4. A magnetic head 8 is provided at the tip of each swing arm 7. The magnetic head 8 is a component that applies magnetism to the recording disks 4 or reads magnetism from the recording disks 4. Cover 6 is a plate-shaped component that closes the open side of Case 2. Cover 6 is sealed together with Case 2 by a sealing means to form a housing 9. Inside the housing 9, an internal space S is formed. The internal space S is filled with air, or helium gas, which has a lower density than air. In addition to air and helium gas, the internal space S may also be filled with, for example, nitrogen gas or a mixture of helium and nitrogen.

[0012] When the spindle motor 3 rotates, the recording disk 4 also rotates. In this state, when the swing arm 7 swings, the magnetic head 8 moves over the rotating recording disk 4. The magnetic head 8 then applies magnetism to the recording disk 4 or reads magnetism from the recording disk 4. In this way, the hard disk drive 1 can record information on the recording disk 4 and read information recorded on the recording disk 4.

[0013] <Spindle Motor> Next, the detailed configuration of the spindle motor 3 will be described. FIG. 2 is a cross-sectional view showing the configuration of the spindle motor 3. The spindle motor 3 includes a stationary part 10 and a rotating part 20 that rotates with respect to the stationary part 10 via a bearing mechanism.

[0014] Here, as shown in FIG. 2 and the like, the direction parallel to the central axis of the shaft 60 described later is the axial direction, the direction around the central axis of the shaft 60 is the circumferential direction, and the direction perpendicular to the axial direction is the radial direction. Also, for the sake of explanation, the axial direction is the vertical direction, the rotating part 20 side with respect to the stationary part 10 is the upper side, and the stationary part 10 side is the lower side.

[0015] [[ID=*]] <Stationary part> The stationary part 10 has a base plate 30, a bearing sleeve 40, and a stator core 50.

[0016] The base plate 30 is a member made of metal. As shown in FIG. 2, a through hole 31, a circumferential groove portion 32, and a circumferential wall portion 33 are formed in the base plate 30. The through hole 31 is a hole for fixing the bearing sleeve 40 and is provided so as to penetrate the base plate 30 in the axial direction. Also, the through hole 31 is cylindrical, and the inner diameter of the cylinder is substantially the same as or larger than the outer diameter of the bearing sleeve 40. The circumferential groove portion 32 is formed on the radially outer side of the through hole 31. The circumferential groove portion 32 is an annular groove provided so as to be coaxial with the central axis of the through hole 31 in the axial view. The circumferential wall portion 33 is formed as an annular wall surface portion that protrudes upward in the axial direction along the through hole 31 from the bottom surface of the circumferential groove portion 32 in the axial view. The circumferential wall portion 33 partitions the through hole 31 and the circumferential groove portion 32.

[0017] The bearing sleeve 40 is a cylindrical member made of a copper alloy such as brass that rotatably supports the shaft 60. The bearing sleeve 40 is inserted into the through hole 31 (see FIG. 2). In the state shown in FIG. 2, the outer peripheral surface 40B of the bearing sleeve 40 faces the inner peripheral surface 31A of the through hole 31. The bearing sleeve 40 is fixed to the through hole 31 by an adhesive applied between the outer peripheral surface 40B of the bearing sleeve 40 and the inner peripheral surface 31A of the through hole 31.

[0018] Inside the bearing sleeve 40, a shaft 60 is disposed. The inner peripheral surface 40A of the bearing sleeve 40 surrounds the outer peripheral surface 60B of the shaft 60, and the inner peripheral surface 40A and the outer peripheral surface 60B face each other with a minute gap therebetween. This minute gap is filled with lubricating oil (not shown). At least one of the inner peripheral surface 40A or the outer peripheral surface 60B is provided with a radial dynamic pressure generating groove 61. In the embodiment shown in FIG. 2, the radial dynamic pressure generating groove 61 is formed in a row continuous in the circumferential direction on the inner peripheral surface 40A, and two rows are formed at intervals in the axial direction.

[0019] The bearing sleeve 40 has a lower end portion 40E (an example of an end portion) in the vertical direction. As shown in FIGS. 2 and 3, the bearing sleeve 40 is formed with an inner concave portion 41 that opens downward and is recessed upward inward in the radial direction of the lower end portion 40E. Further, the bearing sleeve 40 is formed with an outer concave portion 42 (an example of a concave portion) that extends along the circumferential direction outward in the radial direction of the lower end portion 40E and is recessed upward. In the present embodiment, the outer concave portion 42 is formed along the outer periphery of the bearing sleeve 40, but it may be formed radially inward of the outer periphery.

[0020] The lower end portion 40E is formed with a tapered cross section in which the radial thickness becomes thinner toward the upper and lower end surfaces 40S of the lower end portion 40E. Since the outer diameter of the lower end portion 40E decreases downward, a gap 45 (an example of a first gap) is formed between the lower end portion 40E and a counter plate 44 described later.

[0021] A thrust plate 43 is positioned in the inner recess 41. The thrust plate 43 is an annular flange member that expands radially in an axial view, fixed to the lower end of the shaft 60. The thrust plate 43 is fixed to the shaft 60 by press-fitting it onto the shaft 60 or by bonding it with an adhesive. By positioning the thrust plate 43 between the lower surface 40C of the bearing sleeve 40 formed in the inner recess 41 and the counter plate 44 (described later), axial movement of the thrust plate 43 and the shaft 60 is prevented. The outer diameter of the thrust plate 43 is smaller than the inner diameter of the inner recess 41. Also, the axial thickness of the thrust plate 43 is thinner than the axial depth of the inner recess 41.

[0022] A counter plate 44 is attached to the outer recess 42. The counter plate 44 is a cover that closes the inner recess 41 of the bearing sleeve 40. The counter plate 44 is made of a metal such as iron or a copper alloy, and in this embodiment it is made of iron such as stainless steel. The counter plate 44 prevents the thrust plate 43, which is positioned in the inner recess 41, from moving downward and coming out of the bearing sleeve 40. The counter plate 44 has a cover portion 44S, which is a disc-shaped member in an axial view, and a projection 44P that extends along the outer circumference of the cover portion 44S and protrudes upward from the cover portion 44S. In the state shown in Figure 2, the cover portion 44S is in contact with the end face 40S. The diameter of the cover portion 44S is smaller than the outermost diameter of the bearing sleeve 40. The height of the projection 44P from the cover portion 44S is approximately equal to the axial depth of the outer recess 42. The inner diameter of the projection 44P is smaller than the outer diameter of the lower end portion 40E. The radial thickness t1 of the projection 44P is thinner than the radial thickness t2 of the lower end portion 40E (i.e., the thickness t2 of the lower end portion 40E is thicker than the thickness t1 of the projection 44P).

[0023] The counter plate 44 is press-fitted below the bearing sleeve 40 with adhesive applied to the outer circumferential surface of its lower end portion 40E. At this time, the projection 44P is fitted into the outer recess 42, and the projection 44P and the lower end portion 40E are joined together. Also, because the inner diameter of the projection 44P is smaller than the outer diameter of the lower end portion 40E, some of the adhesive applied to the lower end portion 40E comes into contact with the inner circumferential surface of the projection 44P and is pushed out toward the end face 40S. Some of the pushed-out adhesive accumulates in the gap 45, forming an adhesive reservoir. In other words, the adhesive is held in the gap 45. Note that the counter plate 44 may also be press-fitted below the bearing sleeve 40 with adhesive applied to the upper surface or the inner circumferential surface of the projection 44P, in addition to the outer circumferential surface of the lower end portion 40E.

[0024] In the state shown in Figure 3, the upper surface of the thrust plate 43 and the lower surface 40C of the bearing sleeve 40 face each other with a small gap between them. Also, the lower surface of the thrust plate 43 and the upper surface of the cover portion 44S of the counter plate 44 face each other with a small gap between them. These small gaps are filled with lubricating oil (not shown).

[0025] A thrust dynamic pressure generating groove is provided on at least one of the upper surface of the thrust plate 43 or the lower surface 40C of the bearing sleeve 40 (in this embodiment, the upper surface of the thrust plate 43). In addition, a thrust dynamic pressure generating groove is provided on the upper surface of the cover portion 44S in the portion facing the thrust plate 43. A thrust dynamic pressure generating groove may also be provided on the lower surface of the thrust plate 43 facing the upper surface of the cover portion 44S.

[0026] The stator core 50 is a component formed by stacking multiple annular electromagnetic steel sheets in the axial direction when viewed axially. The stator core 50 is placed inside the circumferential groove 32 and fixed to the outer surface of the circumferential wall 33 by adhesive or other means. The stator core 50 also has pole teeth (salient poles) that extend radially outward and are arranged in multiple locations along the circumferential direction. Coils 51 are wound around the pole teeth. When current flows through the coils 51, the stator core 50 generates magnetic flux.

[0027] <Rotating part> The rotating part 20 includes a shaft 60, a rotor hub 70, and a rotor magnet 80.

[0028] The shaft 60 is a columnar iron component, such as stainless steel, that serves as the rotation axis of the spindle motor 3, and is positioned inside the bearing sleeve 40. The upper end of the shaft 60 protrudes from the bearing sleeve 40. The radial dynamic pressure generating groove 61 may be provided not on the inner circumferential surface 40A of the bearing sleeve 40, but on the outer circumferential surface 60B of the shaft 60, in a portion facing the inner circumferential surface 40A.

[0029] The rotor hub 70 is attached to the upper end of the shaft 60 and rotates together with the shaft 60. The rotor hub 70 has a disc portion 71, a cylindrical portion 72, and an outer edge portion 73. The disc portion 71 is a disc-shaped member positioned above the bearing sleeve 40 and is coaxial with the central axis of the shaft 60 in an axial view. A through hole 74 is provided in the center of the disc portion 71. The disc portion 71 is fixed to the shaft 60 by fixing the upper end of the shaft 60 to the through hole 74 by methods such as press-fitting or adhesive. The lower surface of the disc portion 71 and the upper surface of the bearing sleeve 40 face each other with a gap between them. The cylindrical portion 72 is a cylindrical member having a constant thickness in the radial direction and extends downward from the outer edge of the lower surface of the disc portion 71. The inner diameter of the cylindrical portion 72 is larger than the outer diameter of the bearing sleeve 40, and the inner circumferential surface and outer circumferential surface 40B of the cylindrical portion 72 face each other with a gap between them. The outer diameter of the cylindrical portion 72 is the same as the outer diameter of the disc portion 71. The outer edge portion 73 is a member that protrudes radially outward from the lower end of the cylindrical portion 72 in an axial view and extends in a flange-like manner around the entire circumference in the circumferential direction.

[0030] The rotor magnet 80 is an annular member having a magnetic pole structure in which the polarity reverses along the circumferential direction in an axial view, in the order N, S, N, S…. In the embodiment shown in Figure 2, the rotor magnet 80 is attached to the inner circumferential surface of an annular yoke 81 attached to the lower end of the outer edge portion 73. The rotor magnet 80 is located in approximately the same position as the stator core 50 in the axial direction, and in the radial direction, it is located between the stator core 50 and the inner circumferential surface of the circumferential groove portion 32. The yoke 81 suppresses leakage of magnetic flux from the rotor magnet 80. Alternatively, the cylindrical portion 72 or the outer edge portion 73 may be arranged between the stator core 50 and the inner circumferential surface of the circumferential groove portion 32, and the annular yoke 81 may be attached to the inner circumferential surface of the cylindrical portion 72 or the inner circumferential surface of the outer edge portion 73. In that case, the rotor magnet 80 is attached to the inner circumferential surface of the yoke 81 so as to face the stator core 50.

[0031] <Spindle motor operation> When current is applied to the coil 51, the magnetic attraction and repulsion forces between the magnetic poles of the rotor magnet 80 and the pole teeth of the stator core 50 switch. As a result, the rotating part 20 rotates relative to the stationary part 10 with the shaft 60 as its axis of rotation.

[0032] The shaft 60 rotates relative to the bearing sleeve 40. During this rotation, the lubricating oil is pressurized by the radial dynamic pressure generating groove 61, generating dynamic pressure. This generated dynamic pressure supports the shaft 60 radially relative to the bearing sleeve 40 in a non-contact manner.

[0033] When the shaft 60 rotates, the thrust plate 43 rotates relative to the bearing sleeve 40 and the counter plate 44. At this time, dynamic pressure is generated when the lubricating oil is pressurized by the thrust dynamic pressure generating groove provided on at least one of the upper surface of the thrust plate 43 or the lower surface 40C of the bearing sleeve 40 and the thrust dynamic pressure generating groove provided on the upper surface of the cover portion 44S of the counter plate 44. Due to the generated dynamic pressure, the thrust plate 43 is supported in a non-contact manner in the axial direction relative to the bearing sleeve 40 and the counter plate 44. Even if the thrust dynamic pressure generating groove is provided on the lower surface of the thrust plate 43, the thrust plate 43 is supported in a non-contact manner in the axial direction relative to the bearing sleeve 40 and the counter plate 44 by the above operation.

[0034] <Effects> In the above embodiment, the spindle motor 3 comprises a columnar shaft 60 extending in the axial direction, an annular thrust plate 43 attached to one end of the shaft 60, a cylindrical bearing sleeve 40 that rotatably supports the shaft 60 and has a circumferential direction and a radial direction perpendicular to the circumferential direction, having a lower end portion 40E in the axial direction, an outer recess 42 extending along the circumferential direction and having depth in the axial direction formed radially outward of the lower end portion 40E, a cover portion 44S that covers the lower end portion 40E, and a projection 44P that protrudes from the cover portion 44S into the outer recess 42 and joins with the lower end portion 40E, and the bearing sleeve 40 and the counter plate 44 are joined by adhesive.

[0035] With this configuration, an outer recess 42 extending circumferentially and having depth in the axial direction is formed radially outward of the lower end portion 40E. The projection 44P of the counter plate 44 fits into the outer recess 42 and is joined to the lower end portion 40E, so that the axial length of the joint can be made longer than the thickness of the counter plate 44. Since the lower end portion 40E and the projection 44P are joined by adhesive, the longer the length of the joint, the stronger the bond can be. In other words, the counter plate 44 that closes the opening can be firmly joined to the bearing sleeve 40.

[0036] Furthermore, in such a spindle motor 3, the counter plate 44 is firmly bonded to the bearing sleeve 40, allowing the shaft 60 to support a larger axial load.

[0037] Furthermore, since the inner recess 41 is filled with lubricating oil, it is preferable that adhesive does not enter the inner recess 41 when joining the counter plate 44 to the bearing sleeve 40. With the above configuration, the outer circumferential surface of the lower end portion 40E, which is the joining surface, is separated from the inner recess 41. As a result, it is difficult for adhesive to enter the inner recess 41.

[0038] Conventionally, iron counter plates 44 are difficult to weld to copper alloy bearing sleeves 40, so an iron sleeve case was attached to the outer circumference of the bearing sleeve 40, and the counter plate 44 and the sleeve case were joined by welding. With the above configuration, the lower end portion 40E and the protrusion 44P are joined with adhesive, so the counter plate 44 and the bearing sleeve 40 are directly joined. As a result, the number of parts in the spindle motor 3 is reduced, and the welding process is eliminated, thus lowering the manufacturing cost of the spindle motor 3.

[0039] Furthermore, in this embodiment, the counter plate 44 of the spindle motor 3 has a thrust dynamic pressure generating groove formed in the portion of the lid 44S that faces the thrust plate 43.

[0040] With this configuration, since a thrust dynamic pressure generating groove is formed in the portion of the lid 44S facing the thrust plate 43, there is no need to provide a thrust dynamic pressure generating groove on the lower surface of the thrust plate 43. As a result, machining of the thrust dynamic pressure generating groove on the lower surface of the thrust plate 43 is unnecessary, making the manufacturing of the thrust plate 43 easier.

[0041] Furthermore, the bearing sleeve 40 of the spindle motor 3 according to this embodiment has an axial end face 40S at its lower end portion 40E, forming a tapered cross-section that becomes thinner towards the end face 40S, and the adhesive is held in the gap 45 formed between the lower end portion 40E and the counter plate 44.

[0042] With this configuration, a gap 45 is formed between the bearing sleeve 40 and the counter plate 44. When the counter plate 44 is joined to the bearing sleeve 40, some of the adhesive applied to the outer circumferential surface of the lower end portion 40E comes into contact with the inner circumferential surface of the protrusion 44P and is pushed out toward the end face 40S. The pushed-out adhesive accumulates in the gap 45, forming an adhesive reservoir. As a result, the bearing sleeve 40 and the counter plate 44 are joined more firmly.

[0043] Furthermore, the counter plate 44 of the spindle motor 3 according to this embodiment is joined to the bearing sleeve 40 by press-fitting.

[0044] With this configuration, the counter plate 44 is joined to the bearing sleeve 40 not only by adhesive bonding but also by press-fitting. As a result, the bearing sleeve 40 and the counter plate 44 are joined more strongly than if they were joined by adhesive alone.

[0045] Furthermore, in the spindle motor 3 according to this embodiment, the thickness t2 of the lower end portion 40E is greater than the thickness t1 of the protrusion 44P in the radial direction of the shaft 60.

[0046] With this configuration, the thickness t2 of the lower end portion 40E is greater than the thickness t1 of the protrusion 44P in the radial direction, so the lower end portion 40E is less likely to deform when a force is applied radially inward. As a result, when the counter plate 44 is pressed into the bearing sleeve 40, the lower end portion 40E is less likely to deform radially inward, so the spindle motor 3 can be assembled with high precision.

[0047] Furthermore, the bearing sleeve 40 of the spindle motor 3 according to this embodiment is made of a copper alloy.

[0048] With this configuration, since the bearing sleeve 40 is made of copper alloy, the bearing sleeve 40 has high wear resistance against the iron shaft 60. As a result, the lifespan of the spindle motor 3 is extended.

[0049] Furthermore, the hard disk drive device 1 according to this embodiment includes the spindle motor 3 described above.

[0050] With this configuration, the hard disk drive 1 is equipped with a spindle motor 3 that can support a larger axial load, thus increasing the number of recording disks 4 supported by the spindle motor 3. In other words, the recording capacity of the hard disk drive 1 can be increased.

[0051] Furthermore, the hard disk drive 1 according to this embodiment further comprises a housing 9, the spindle motor 3 is located inside the housing 9, and the inside of the housing 9 is sealed.

[0052] With this configuration, the inside of the housing 9 is sealed, and the spindle motor 3 is positioned in its internal space S, making it difficult for foreign matter such as dust to enter from the outside of the housing 9. As a result, the spindle motor 3 is less prone to failure.

[0053] Furthermore, filling the internal space S with a gas with a lower density than air, such as helium, reduces gas resistance in the internal space S, thereby reducing rotational irregularities and vibrations of the recording disk 4. As a result, the recording disk 4 can be operated with higher precision, allowing for an increase in the number of recording disks 4 installed in the hard disk drive 1. In other words, the recording capacity of the hard disk drive 1 can be increased.

[0054] <Variation> You may apply a combination of the changes described below.

[0055] (1) Variation 1 In the above embodiment, the lower end portion 40E has a tapered cross-section in which the radial thickness decreases toward the vertical end face 40S. However, instead of a tapered cross-section, an axial end recess 46 may be formed at the lower end portion 40E.

[0056] As shown in Figure 4, the shaft end recess 46 extends circumferentially and is formed at the lower end portion 40E so as to be recessed upward. In the embodiment shown in Figure 4, the shaft end recess 46 is formed at the radially outer edge of the lower end portion 40E, which is radially inward from the outer recess 42. Because the cross-section of the shaft end recess 46 is square, a square-shaped gap 145 is formed between the lower end portion 40E and the counter plate 44.

[0057] When the counter plate 44 is joined to the lower part of the bearing sleeve 40 with adhesive, the adhesive is applied to the outer circumferential surface of the lower end portion 40E. When the counter plate 44 is fitted into the bearing sleeve 40 from below, some of the applied adhesive is pushed out toward the end face 40S. Some of the pushed-out adhesive accumulates in the gap 145, forming an adhesive reservoir. In other words, the adhesive is held in the gap 145. Note that the adhesive may also be applied to the upper surface or the inner circumferential surface of the projection 44P, in addition to the outer circumferential surface of the lower end portion 40E.

[0058] With this configuration, an adhesive reservoir is formed in the gap 145, so that the bearing sleeve 40 and the counter plate 44 are joined more firmly.

[0059] Furthermore, the aforementioned tapered cross-section and shaft end recess 46 do not necessarily need to be formed at the lower end portion 40E.

[0060] (2) Modification example 2 In the above embodiment, the inner diameter of the projection 44P is smaller than the outer diameter of the lower end portion 40E, and the counter plate 44 is joined to the bearing sleeve 40 by press-fitting and adhesive bonding. However, the inner diameter of the projection 44P may be larger than the outer diameter of the lower end portion 40E, and the counter plate 44 may be joined to the bearing sleeve 40 by adhesive bonding alone.

[0061] (3) Modification example 3 In the above embodiment, the radial thickness t2 of the lower end portion 40E is greater than the radial thickness t1 of the projection 44P. However, the radial thickness t2 of the lower end portion 40E may be the same as or less than the radial thickness t1 of the projection 44P.

[0062] (4) Modification 4 In the above embodiment, the projection height of the protrusion 44P from the cover portion 44S is approximately equal to the axial depth of the outer recess 42. However, as shown in Figure 5, the protrusion 44P may be a protrusion 144P in which the projection height of the protrusion 44P from the cover portion 44S is shorter than the axial depth of the outer recess 42.

[0063] Because the projection height of the protrusion 144P from the cover portion 44S is shorter than the axial depth of the outer recess 42, a gap 147 (an example of a second gap) is formed between the upper surface of the protrusion 144P and the lower surface of the outer recess 42.

[0064] When the counter plate 44 is joined to the lower part of the bearing sleeve 40 with adhesive, the adhesive is applied to the outer circumferential surface of the lower end portion 40E. When the counter plate 44 is fitted into the bearing sleeve 40 from below, the upper surface of the projection 144P and the lower surface of the outer recess 42 do not come into contact, forming a gap 147. Some of the applied adhesive accumulates in the gap 147, forming an adhesive reservoir. In other words, the adhesive is held in the gap 147. Note that the adhesive may also be applied to the upper surface of the projection 44P or the inner surface of the projection 44P, in addition to the outer circumferential surface of the lower end portion 40E. Furthermore, the adhesive may be sealed into the gap 147 after the counter plate 44 has been fitted into the bearing sleeve 40.

[0065] With this configuration, the adhesive is held in the gap 147, so that the bearing sleeve 40 and the counter plate 44 are more firmly joined.

[0066] Furthermore, as shown in Figure 6, the projection 144P may also be a projection 244P in which the upper surface of the projection 144P is inclined radially, and the height of the projection from the lid 44S increases radially inward.

[0067] The projection height of the protrusion 244P from the cover portion 44S is shorter than the axial depth of the outer recess 42, and the upper surface of the protrusion 244P is inclined radially and rises radially inward, so a gap 247 is formed between the upper surface of the protrusion 244P and the lower surface of the outer recess 42. The axial height of the gap 247 decreases radially inward.

[0068] The gap 247, like the gap 147, holds the adhesive accumulated on the upper surface of the projection 244P, or the adhesive that is sealed into the gap 247 after the counter plate 44 is fitted into the bearing sleeve 40. Here, since the axial height of the gap 247 decreases toward the radially inward direction, a capillary force acts radially inward on the adhesive held in the gap 247. As a result, the adhesive is more easily held in the gap 247, and the bearing sleeve 40 and the counter plate 44 are joined more firmly. [Explanation of Symbols]

[0069] 1...Hard disk drive, 3...Spindle motor, 9...Housing, 40...Bearing sleeve, 40E...Lower end (end), 40S...End face, 42...Outer recess (recess), 43...Thrust plate, 44...Counter plate, 44P, 144P, 244P...Protrusion, 44S...Lid, 45...Gap (first gap), 60...Shaft, 147, 247...Gap (second gap) t1...Thickness of protrusion 44P, t2...Thickness of lower end 40E

Claims

1. A columnar shaft extending in the axial direction, An annular thrust plate attached to one end of the shaft, A cylindrical bearing sleeve that rotatably supports the shaft and has a circumferential direction and a radial direction perpendicular to the circumferential direction, having an end in the axial direction, and having a recess extending along the circumferential direction and having depth in the axial direction formed radially outward of the end, A counter plate having a cover portion that covers the end portion, and a projection that protrudes from the cover portion into the recess and joins with the end portion, Equipped with, The bearing sleeve and the counter plate are joined together via an adhesive. The adhesive is held in the second gap formed between the recess and the protrusion. The aforementioned projection is a spindle motor in which the upper surface of the projection is inclined in the radial direction, and the height of the projection from the cover increases towards the radially inward direction.

2. The spindle motor according to claim 1, wherein a dynamic pressure groove is formed in the portion of the lid facing the thrust plate.

3. The spindle motor according to claim 1 or 2, wherein the end portion has an end face in the axial direction and forms a tapered cross-section that becomes thinner toward the end face, and the adhesive is held in a first gap formed between the end portion and the counter plate.

4. The spindle motor according to any one of claims 1 to 3, wherein the counter plate is joined to the bearing sleeve by press-fitting.

5. The spindle motor according to claim 4, wherein the thickness of the end of the shaft is greater than the thickness of the projection in the radial direction.

6. The spindle motor according to any one of claims 1 to 5, wherein the bearing sleeve is made of a copper alloy.

7. A hard disk drive comprising a spindle motor according to any one of claims 1 to 6.

8. The aforementioned hard disk drive further comprises a housing, The hard disk drive device according to claim 7, wherein the spindle motor is located inside the housing and the inside of the housing is sealed.

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