Bearing apparatus, spindle motor, and disk drive apparatus

This bearing apparatus includes a shaft portion, a sleeve portion, and a fluid arranged between the shaft portion and the sleeve portion. A thrust dynamic pressure portion is filled with the fluid, and a surface of the fluid is defined in a seal portion. The thrust dynamic pressure portion includes a dynamic pressure generation portion including thrust dynamic pressure grooves, an intermediate portion arranged outside of the dynamic pressure generation portion and including an annular groove in the shape of a circular ring, and a discharge portion arranged outside of the annular groove and including discharge grooves. The annular groove is arranged to have a depth smaller than a minimum radial width of the seal portion. This makes it easier for any air bubble in the thrust dynamic pressure portion to travel into the seal portion in accordance with a flow of the fluid caused in the discharge portion to be discharged outward. This reduces the likelihood that any air bubble will stay in the vicinity of the dynamic pressure generation portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2015-218040 filed Nov. 6, 2015. The entire contents of this application is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bearing apparatus, a spindle motor, and a disk drive apparatus.

2. Description of the Related Art

Spindle motors arranged to rotate disks are typically installed in hard disk apparatuses and optical disk apparatuses. Such a spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to generate a torque centered on a central axis through magnetic flux generated between the stationary portion and the rotating portion, so that the rotating portion is caused to rotate with respect to the stationary portion.

A fluid dynamic bearing apparatus, for example, is used as a bearing apparatus to support the rotating portion such that the rotating portion is rotatable with respect to the stationary portion. A known spindle motor including a fluid dynamic bearing apparatus is described in, for example, JP-A 2004-270820.

The fluid dynamic bearing apparatus includes a dynamic pressure generation portion in which a dynamic pressure groove is defined in a member of a stationary portion or a member of a rotating portion. Accordingly, once the rotating portion starts rotating, a dynamic pressure is generated in a fluid arranged between the member of the stationary portion and the member of the rotating portion. This produces a supporting force that supports the rotating portion with respect to the stationary portion. In the fluid dynamic bearing apparatus as described above, an air bubble may be introduced into the fluid, or an air bubble may be generated in the fluid due to a change in pressure on the fluid, while the rotating portion is rotating. If any air bubble stays in the vicinity of the dynamic pressure generation portion, the dynamic pressure generated in the dynamic pressure generation portion may become unstable.

SUMMARY OF THE INVENTION

A bearing apparatus according to a preferred embodiment of the present invention includes a shaft portion, a sleeve portion, and a fluid arranged between the shaft portion and the sleeve portion, wherein the shaft portion includes a columnar portion arranged to extend along a central axis, an annular portion arranged to extend radially outward from the columnar portion, and a tubular portion arranged to extend from the annular portion to one axial side. The sleeve portion is arranged on the one axial side of the annular portion, radially outside of the columnar portion, and radially inside of the tubular portion. A radial dynamic pressure portion, a thrust dynamic pressure portion, and a seal portion are defined between the shaft portion and the sleeve portion. The radial dynamic pressure portion is defined in a gap between an outer circumferential surface of the columnar portion and an inner circumferential surface of the sleeve portion. The thrust dynamic pressure portion is defined in a gap between a first thrust surface and a second thrust surface, the first thrust surface being an end surface of the annular portion on the one axial side, the second thrust surface being an end surface of the sleeve portion on another axial side. The seal portion is defined in a gap between an inner circumferential surface of the tubular portion and an outer circumferential surface of the sleeve portion. Each of the radial dynamic pressure portion and the thrust dynamic pressure portion is filled with the fluid. The seal portion has a surface of the fluid defined therein. The thrust dynamic pressure portion includes a dynamic pressure generation portion, an intermediate portion, and a discharge portion. The dynamic pressure generation portion includes a plurality of thrust dynamic pressure grooves defined in one of the first and second thrust surfaces, each thrust dynamic pressure groove extending from a radially inner side to a radially outer side. The intermediate portion is arranged radially outside of the dynamic pressure generation portion, and includes an annular groove in a shape of a circular ring with the central axis as a center defined in one of the first and second thrust surfaces. The discharge portion is arranged radially outside of the annular groove, and includes a plurality of discharge grooves defined in one of the first and second thrust surfaces, each discharge groove extending from the radially inner side to the radially outer side. The annular groove is arranged to have a depth smaller than a minimum radial width of the seal portion.

The above preferred embodiment of the present invention is able to achieve a reduction in the likelihood that any air bubble will stay in the vicinity of the dynamic pressure generation portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It is assumed herein that a direction parallel to a central axis of a spindle motor is referred to by the term “axial direction”, “axial”, or “axially”, that directions perpendicular to the central axis of the spindle motor are each referred to by the term “radial direction”, “radial”, or “radially”, and that a direction along a circular arc centered on the central axis of the spindle motor is referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”. It is also assumed herein that an axial direction is a vertical direction, and that a side on which an armature is arranged with respect to a base portion is an upper side, and the shape of each member or portion and relative positions of different members or portions will be described based on the above assumptions. It should be noted, however, that the above definitions of the vertical direction and the upper and lower sides are not meant to restrict in any way the orientation of a spindle motor or a disk drive apparatus according to any preferred embodiment of the present invention when in use.

Also note that the wording “parallel direction” as used herein includes both parallel and substantially parallel directions. Also note that the wording “perpendicular direction” as used herein includes both perpendicular and substantially perpendicular directions.

FIG. 1is a vertical sectional view of a disk drive apparatus1according to a first preferred embodiment of the present invention. The disk drive apparatus1is, for example, an apparatus arranged to perform reading and writing of information from or to a magnetic disk12while rotating the magnetic disk12. Referring toFIG. 1, the disk drive apparatus1includes a spindle motor11, the magnetic disk12, an access portion13, and a housing10.

The spindle motor11is arranged to rotate the magnetic disk12about a central axis9while supporting the magnetic disk12. The spindle motor11includes a base portion21arranged to extend perpendicularly or substantially perpendicularly to the central axis9.

The access portion13is arranged to move heads131along recording surfaces of the magnetic disk12to perform the reading and the writing of information from or to the magnetic disk12.

The housing10includes a housing body14defined integrally with the base portion21, and a cover15arranged to cover an upper side of the housing body14. The housing body14includes a bottom portion141arranged to extend perpendicularly or substantially perpendicularly to the central axis9below a rotating portion3of the spindle motor11, the magnetic disk12, and the access portion13, and a wall portion142arranged to extend upward from an outer circumference of the bottom portion141. The rotating portion3of the spindle motor11, the magnetic disk12, and the access portion13are accommodated in the housing10.

Note that the disk drive apparatus1may alternatively be arranged to include two or more magnetic disks12. Also note that the access portion13may alternatively be arranged to perform only one of the reading and the writing of information from or to the magnetic disk12.

Next, the structure of the spindle motor11will now be described below.FIG. 2is a vertical sectional view of the spindle motor11.FIG. 3is a partial vertical sectional view of the spindle motor11.

Referring toFIG. 1, the spindle motor11includes a stationary portion2and the rotating portion3. The stationary portion2is arranged to be stationary relative to the housing10. The rotating portion3is supported to be rotatable with respect to the stationary portion2.

Referring toFIG. 2, the stationary portion2according to the present preferred embodiment includes the base portion21, an armature22, a stationary bearing unit23, and a circuit board24.

The base portion21is arranged to extend perpendicularly or substantially perpendicularly to the central axis9below the rotating portion3. Referring toFIG. 1, the base portion21defines a portion of the bottom portion141of the housing body14. The housing body14is defined by, for example, subjecting a metal plate material to press working. Note, however, that the housing body14may alternatively be defined by another process, such as, for example, a casting process or a cutting process.

Referring toFIG. 2, the base portion21includes a cylindrical portion211and a bottom plate portion212. The cylindrical portion211is a substantially cylindrical portion arranged to extend in the vertical direction with the central axis9as a center. A sleeve231of the stationary bearing unit23, which will be described below, is fixed to an inner circumferential surface of the cylindrical portion211. The bottom plate portion212is a plate-shaped portion arranged to extend radially outward from a lower end portion of the cylindrical portion211. The armature22and a portion of the rotating portion3are arranged above the bottom plate portion212.

The armature22includes a stator core41and a plurality of coils42. The stator core41is defined, for example, by laminated steel sheets, that is, electromagnetic steel sheets, such as silicon steel sheets, placed one upon another in the axial direction. The stator core41is fixed to an outer circumferential surface of the cylindrical portion211. In addition, the stator core41includes a plurality of teeth411arranged to project radially outward. The teeth411are preferably arranged at substantially regular intervals in the circumferential direction. Each coil42is defined by a conducting wire wound around a separate one of the teeth411.

The stationary bearing unit23includes the sleeve231and a cap232. The sleeve231is arranged to extend in the axial direction to assume a substantially cylindrical shape around a shaft31, which will be described below. A lower portion of the sleeve231is arranged radial inside of the cylindrical portion211of the base portion21, and is fixed to the cylindrical portion211through, for example, an adhesive. An inner circumferential surface of the sleeve231is arranged radially opposite to an outer circumferential surface of the shaft31. The cap232is arranged to close a lower opening of the sleeve231. Note that the sleeve231may be defined by a plurality of members.

The circuit board24is arranged on a lower surface of the bottom plate portion212of the base portion21. A flexible printed circuit board, which has flexibility, is used as the circuit board24according to the present preferred embodiment. The circuit board24is electrically connected to the conducting wires defining the coils42. An electric drive current is supplied to each coil42through the circuit board24.

The rotating portion3is supported to be rotatable about the central axis9, which extends in the vertical direction. The rotating portion3according to the present preferred embodiment includes the shaft31, a hub32, an annular member33, and a magnet34.

The shaft31is a substantially columnar member arranged to extend in the axial direction radially inside of the sleeve231. A metal, such as, for example, a ferromagnetic or nonmagnetic stainless steel, is used as a material of the shaft31. An upper end portion of the shaft31is arranged to project above an upper surface of the sleeve231.

The hub32includes a hub body portion321, an annular projection322, and a magnet fixing portion323. The hub body portion321is arranged to extend radially outward from a peripheral portion of the upper end portion of the shaft31. The annular projection322is arranged to project downward from a lower surface of the hub body portion321radially outside of the sleeve231. The annular projection322is arranged to extend in the vertical direction to assume a substantially cylindrical shape with the central axis9as a center. The annular member33is fixed to an inner circumferential surface of the annular projection322. An inner circumferential surface of the annular member33is arranged radially opposite to an outer circumferential surface of the sleeve231.

The magnet fixing portion323is arranged to project downward from the lower surface of the hub body portion321, and is arranged radially outside of the armature22. An inner circumferential surface of the magnet fixing portion323defines a substantially cylindrical surface extending in the vertical direction with the central axis9as a center. The magnet34is fixed to the inner circumferential surface of the magnet fixing portion323.

In addition, the hub body portion321includes a first holding surface324, which is substantially cylindrical, and a second holding surface325arranged to extend radially outward from a lower end portion of the first holding surface324. An inner circumferential portion of the magnetic disk12is arranged to be in contact with at least a portion of the first holding surface324. In addition, a lower surface of the magnetic disk12is arranged to be in contact with at least a portion of the second holding surface325. The magnetic disk12is thus held.

A lubricating fluid50is arranged between the stationary bearing unit23and a combination of the shaft31, the hub32, and the annular member33. The combination of the shaft31, the hub32, and the annular member33is supported to be rotatable with respect to the stationary bearing unit23through the lubricating fluid50. That is, in the present preferred embodiment, a bearing mechanism5is defined by the sleeve231and the cap232, which are components of the stationary portion2, the shaft31, the hub32, and the annular member33, which are components of the rotating portion3, and the lubricating fluid50arranged therebetween. The structure of the bearing mechanism5will be described in detail below.

The magnet34is arranged radially outside of the armature22, and is fixed to the magnet fixing portion323of the hub32. The magnet34according to the present preferred embodiment is in the shape of a circular ring. An inner circumferential surface of the magnet34is arranged radially opposite to a radially outer end surface of each of the teeth411. In addition, the inner circumferential surface of the magnet34includes north and south poles arranged to alternate with each other in the circumferential direction.

Note that, in place of the annular magnet34, a plurality of magnets may be used. In the case where the plurality of magnets are used, the magnets are arranged in the circumferential direction such that north and south poles alternate with each other.

Once, in the spindle motor11described above, the electric drive currents are supplied to the coils42through the circuit board24, magnetic flux is generated around each of the teeth411. Then, interaction between the magnetic flux of the teeth411and magnetic flux of the magnet34produces a circumferential torque, so that the rotating portion3is caused to rotate about the central axis9with respect to the stationary portion2. The magnetic disk12supported by the hub32is caused to rotate about the central axis9together with the rotating portion3.

Next, the structure of the bearing mechanism5, which is included in the spindle motor11, will now be described below. Each ofFIGS. 3 and 4is a partial vertical sectional view of the spindle motor11, illustrating the bearing mechanism5and its vicinity.FIG. 5is a top view of the sleeve231. The bearing mechanism5is a fluid dynamic bearing apparatus. In each ofFIGS. 3 and 4, the position of a bottom surface of each of a thrust dynamic pressure groove and a discharge groove is represented by a broken line. In addition, inFIG. 5, groove regions, which are recessed downward from an upper end surface of the sleeve231, are represented by oblique lines.

Referring toFIGS. 2 to 4, the bearing mechanism5is defined by a shaft portion51, a sleeve portion52, and the lubricating fluid50arranged between the shaft portion51and the sleeve portion52. A polyolester oil or a diester oil, for example, is used as the lubricating fluid50.

As described above, in the spindle motor11, the lubricating fluid50is arranged between the stationary bearing unit23and the combination of the shaft31, the hub32, and the annular member33. That is, in the present preferred embodiment, the shaft portion51is defined by the shaft31, a portion of the hub32, and the annular member33. Meanwhile, the sleeve portion52is defined by the sleeve231of the stationary bearing unit23.

The shaft portion51includes a columnar portion511arranged to extend along the central axis9, an annular portion512arranged to extend radially outward from the columnar portion511, and a tubular portion513arranged to extend from the annular portion512to one axial side (downward, in the present preferred embodiment). The columnar portion511is defined by the shaft31. The annular portion512is defined by a portion of the hub body portion321of the hub32which lies radially inward of the annular projection322. The tubular portion513is defined by the annular projection322of the hub32and the annular member33.

Although the shaft portion51according to the present preferred embodiment is defined by a plurality of members, this is not essential to the present invention. The shaft portion51may alternatively be defined by a single monolithic member including the columnar portion511, the annular portion512, and the tubular portion513.

The sleeve portion52is arranged on the one axial side (i.e., a lower side) of the annular portion512, radially outside of the columnar portion511, and radially inside of the tubular portion513. A liquid surface of the lubricating fluid50is defined between the sleeve portion52and the tubular portion513.

Referring toFIGS. 3 to 5, the sleeve portion52includes a communicating hole521arranged to extend from an upper surface to a lower surface thereof. The communicating hole521includes a first opening522defined in an end surface of the sleeve portion on another axial side (i.e., an upper side), and a second opening523defined in an end surface of the sleeve portion52on the one axial side (i.e., the lower side). The communicating hole521is filled with the lubricating fluid50.

The spindle motor11according to the present preferred embodiment is a rotating-shaft motor. Accordingly, as illustrated inFIG. 2, the stationary portion2includes the sleeve portion52of the bearing mechanism5and the armature22, while the rotating portion3includes the shaft portion51of the bearing mechanism5and the magnet34. The shaft portion51is supported through the lubricating fluid50to be rotatable with respect to the sleeve portion52. The rotating portion3is thus supported to be rotatable about the central axis9with respect to the stationary portion2.

Referring toFIG. 3, a radial dynamic pressure portion61, a thrust dynamic pressure portion62, and a seal portion63are defined between the shaft portion51and the sleeve portion52.

The radial dynamic pressure portion61is defined in a gap between an outer circumferential surface of the columnar portion511and an inner circumferential surface of the sleeve portion52. The radial dynamic pressure portion61is filled with the lubricating fluid50. Upper and lower radial dynamic pressure groove arrays71, each of which is arranged in a herringbone pattern, are defined in the outer circumferential surface of the columnar portion511.

While the spindle motor11is running, the shaft portion51rotates with respect to the sleeve portion52. At this time, each radial dynamic pressure groove array71induces a dynamic pressure in a portion of the lubricating fluid50which is present between the outer circumferential surface of the columnar portion511and the inner circumferential surface of the sleeve portion52. The shaft portion51is thus radially supported with respect to the sleeve portion52. Note that the radial dynamic pressure groove array71is defined in at least one of the outer circumferential surface of the columnar portion511and the inner circumferential surface of the sleeve portion52.

The thrust dynamic pressure portion62is defined between a first thrust surface510, which is an end surface of the annular portion512on the one axial side (i.e., the lower side), and a second thrust surface520, which is the end surface of the sleeve portion52on the other axial side (i.e., the upper side). The thrust dynamic pressure portion62is filled with the lubricating fluid50.

Referring toFIG. 5, a thrust dynamic pressure groove array72arranged in a spiral pattern, an annular groove73, and a discharge groove array74arranged in a spiral pattern are defined in the second thrust surface520. The thrust dynamic pressure groove array72is made up of a plurality of thrust dynamic pressure grooves721each of which is arranged to extend from a radially inner side to a radially outer side. The annular groove73is a groove in the shape of a circular ring with the central axis9as a center. The annular groove73is arranged radially outside of the thrust dynamic pressure groove array72and radially inside of the discharge groove array74. The discharge groove array74is made up of a plurality of discharge grooves741each of which is arranged to extend from the radially inner side to the radially outer side. The discharge groove array74is arranged radially outside of the thrust dynamic pressure groove array72and the annular groove73.

Thus, the thrust dynamic pressure portion62includes a dynamic pressure generation portion621, an intermediate portion622, and a discharge portion623. The dynamic pressure generation portion621is defined between the first thrust surface510and an annular portion of the second thrust surface520in which the thrust dynamic pressure groove array72is defined. The intermediate portion622is defined between the first thrust surface510and an annular portion of the second thrust surface520in which the annular groove73is defined. The discharge portion623is defined between the first thrust surface510and an annular portion of the second thrust surface520in which the discharge groove array74is defined.

While the spindle motor11is running, the thrust dynamic pressure groove array72induces a dynamic pressure in a portion of the lubricating fluid50which is present at the dynamic pressure generation portion621. The dynamic pressure generated at the dynamic pressure generation portion621causes the shaft portion51to be axially supported with respect to the sleeve portion52.

In addition, while the spindle motor11is running, the discharge groove array74induces a dynamic pressure in a portion of the lubricating fluid50which is present at the discharge portion623. The dynamic pressure generated at the discharge portion623is smaller than the dynamic pressure generated at the dynamic pressure generation portion621.

Although, in the present preferred embodiment, all of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74, which define the dynamic pressure generation portion621, the intermediate portion622, and the discharge portion623, respectively, are defined in the second thrust surface520, this is not essential to the present invention. Each of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74is defined in at least one of the first and second thrust surfaces510and520.

The seal portion63is defined between an inner circumferential surface of the tubular portion513and an outer circumferential surface of the sleeve portion52. The radial width of the seal portion63is arranged to gradually increase with decreasing height. A surface of the lubricating fluid50is defined in the seal portion63.

While the spindle motor11is running, an air bubble may be introduced into the lubricating fluid50in the vicinity of the surface of the lubricating fluid50, or an air bubble may be generated in the lubricating fluid50due to a change in pressure on the lubricating fluid50. If such an air bubble is drawn into the dynamic pressure generation portion621, the pressure of the dynamic pressure generated at the dynamic pressure generation portion621will become unstable.

In the bearing mechanism5, the intermediate portion622, which includes the annular groove73, is arranged between the dynamic pressure generation portion621and the discharge portion623. Provision of the annular groove73results in an increase in the distance between the first and second thrust surfaces510and520at the intermediate portion622. This produces a tendency of any air bubble to stay in the intermediate portion622. Accordingly, any air bubble tends to stay in the intermediate portion622rather than in the dynamic pressure generation portion621. As a result, the likelihood that any air bubble in the thrust dynamic pressure portion62will stay in the vicinity of the dynamic pressure generation portion621is reduced.

Any air bubble staying in the intermediate portion622will be discharged out of the lubricating fluid50through the seal portion63due to a flow of the lubricating fluid50caused in the discharge portion623. Referring toFIG. 4, in the bearing mechanism5, the annular groove73is arranged to have an axial depth D1smaller than a minimum radial width D2of the seal portion63. Thus, the seal portion63is arranged to have a sufficient radial width to cause any air bubble traveling in accordance with the flow of the lubricating fluid50caused in the discharge portion623to easily travel toward the surface of the lubricating fluid50in the seal portion63. This allows any air bubble in the thrust dynamic pressure portion62to be easily discharged out of the lubricating fluid50.

In the present preferred embodiment, each of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74is defined in the second thrust surface520. When all of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74are defined in the same surface, working processes for the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74can be easily carried out. This leads to an improvement in efficiency with which the spindle motor11is manufactured.

Note that all of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74may alternatively be defined in the first thrust surface510. Also note that at least one of the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74may alternatively be defined in the first thrust surface510, with at least one of the rest being defined in the second thrust surface520.

Referring toFIGS. 3 to 5, the first opening522, which is defined in the second thrust surface520, is arranged to axially overlap at least in part with the annular groove73. This makes it easier for any air bubble traveling into the thrust dynamic pressure portion62through the communicating hole521to head toward the intermediate portion622. This reduces the likelihood that any air bubble will be drawn into the dynamic pressure generation portion621.

Further, in the present preferred embodiment, the first opening522is arranged radially outward of the dynamic pressure generation portion621. This further reduces the likelihood that any air bubble traveling into the thrust dynamic pressure portion through the communicating hole521will be drawn into the dynamic pressure generation portion621.

Referring toFIG. 4, in the present preferred embodiment, an axial distance D3between the first and second thrust surfaces510and520at the intermediate portion622is smaller than the minimum radial width D2of the seal portion63. The greater radial width of the seal portion63makes it easier for any air bubble traveling in accordance with the flow of the lubricating fluid50caused in the discharge portion623to head toward the surface of the lubricating fluid50in the seal portion63. This in turn makes it easier for any air bubble in the thrust dynamic pressure portion62to be discharged out of the lubricating fluid50.

Notice that the “axial distance between the first and second thrust surfaces510and520” refers to the axial distance between the first and second thrust surfaces510and520while the spindle motor11is running. While the spindle motor11is running, the rotation of the rotating portion3, which includes the shaft portion51, generates a dynamic pressure in the thrust dynamic pressure portion62, lifting the shaft portion51with respect to the sleeve portion52. Therefore, the axial distance between the first and second thrust surfaces510and520while the spindle motor11is running is greater than the axial distance between the first and second thrust surfaces510and520when the spindle motor11is not running.

Further, referring toFIG. 4, the axial depth D1of the annular groove73is greater than both an axial depth D4of each thrust dynamic pressure groove721and an axial depth D5of each discharge groove741. The depth D1of the annular groove73being greater than the depth D4of the thrust dynamic pressure groove721facilitates a flow of the lubricating fluid50from the dynamic pressure generation portion621to the intermediate portion622. This makes it easier for any air bubble in the dynamic pressure generation portion621to travel to the intermediate portion622. This in turn contributes to preventing the air bubble from staying in the vicinity of the dynamic pressure generation portion621.

Meanwhile, the depth D1of the annular groove73being greater than the depth D5of the discharge groove741facilitates a flow of the lubricating fluid50between the intermediate portion622and the discharge portion623. This makes it easier for any air bubble to travel from the intermediate portion622to the discharge portion623. This in turn makes it easier for any air bubble in the thrust dynamic pressure portion62to be discharged out of the lubricating fluid50through the surface of the lubricating fluid50in the seal portion63.

In addition, referring toFIG. 4, the axial position of the first thrust surface510is arranged to be lower at the dynamic pressure generation portion621than at the intermediate portion622and the discharge portion623. That is, the first thrust surface510includes a shoulder causing a change in the axial position thereof.

As a result, an axial distance D6between the first and second thrust surfaces510and520at the dynamic pressure generation portion621is smaller than an axial distance D7between the first and second thrust surfaces510and520at the discharge portion623. The reduction in the axial distance D6between the first and second thrust surfaces510and520at the dynamic pressure generation portion621contributes to increasing the dynamic pressure generated in the dynamic pressure generation portion621.

Meanwhile, the increase in the axial distance D7between the first and second thrust surfaces510and520at the discharge portion623makes it easier for any air bubble to travel in the discharge portion623. This makes it easier for any air bubble to travel from the intermediate portion622to the seal portion63through the discharge portion623. This in turn makes it easier for any air bubble in the thrust dynamic pressure portion62to be discharged out of the lubricating fluid50through the surface of the lubricating fluid50in the seal portion63.

Referring toFIG. 5, in the present preferred embodiment, each of the discharge grooves741included in the discharge groove array74is joined to the annular groove73at a radially inner end thereof. Joining of the radially inner end of at least one of the discharge grooves741to the annular groove73makes it easier for any air bubble in the annular groove73to travel to the seal portion63through the discharge groove741. This in turn makes it easier for any air bubble in the annular groove73to be discharged out of the lubricating fluid50.

In the present preferred embodiment, the outside diameter (diameter) L1of the dynamic pressure generation portion621is 4.7 millimeters. The radial width of the intermediate portion622, i.e., the radial width L2of the annular groove73, is 0.2 millimeters. In the case where the outside diameter L1of the dynamic pressure generation portion621is in the range of about 4.0 millimeters to about 5.5 millimeters, the radial width L2of the annular groove73is preferably arranged to be in the range of about 0.1 millimeters to about 0.5 millimeters.

In addition, the depth D1of the annular groove73is preferably arranged to be in the range of about 30 micrometers to about 65 micrometers. The depth D4of each thrust dynamic pressure groove721is preferably arranged to be in the range of about 10 micrometers to about 20 micrometers. The depth D5of each discharge groove741is preferably arranged to be in the range of about 15 micrometers to about 40 micrometers.

While preferred embodiments of the present invention have been described above, it will be understood that the present invention is not limited to the above-described preferred embodiments.

FIG. 6is a partial vertical sectional view of a spindle motor11A according to a modification of the first preferred embodiment. In the modification illustrated inFIG. 6, the axial position of a second thrust surface520A is arranged to be higher at a dynamic pressure generation portion621A than at a discharge portion623A. That is, the second thrust surface520A includes a shoulder causing a change in the axial position thereof. As a result, an axial distance D6A between a first thrust surface510A and the second thrust surface520A at the dynamic pressure generation portion621A is smaller than an axial distance D7A between the first and second thrust surfaces510A and520A at the discharge portion623A.

In the above-described preferred embodiment, the shoulder is defined in the first thrust surface510, and the thrust dynamic pressure groove array72, the annular groove73, and the discharge groove array74are defined in the second thrust surface520. However, as in the modification illustrated inFIG. 6, a thrust dynamic pressure groove array72A, an annular groove73A, a discharge groove array74A, and the shoulder may be defined in the second thrust surface520A.

FIG. 7is a partial sectional view of a spindle motor11B according to another modification of the first preferred embodiment. In the modification illustrated inFIG. 7, a thrust dynamic pressure groove array72B, an annular groove73B, and a discharge groove array74B are defined in a first thrust surface510B. In addition, the axial position of a second thrust surface520B is arranged to be higher at a dynamic pressure generation portion621B than at an intermediate portion622B and a discharge portion623B. That is, the second thrust surface520B includes a shoulder causing a change in the axial position thereof.

As in the modification illustrated inFIG. 7, the thrust dynamic pressure groove array72B, the annular groove73B, and the discharge groove array74B may be defined in the first thrust surface510B, with the shoulder being defined in the second thrust surface520B.

FIG. 8is a partial sectional view of a spindle motor11C according to yet another modification of the first preferred embodiment. In the modification illustrated inFIG. 8, a thrust dynamic pressure groove array72C, an annular groove73C, and a discharge groove array74C are defined in a first thrust surface510C. In addition, the axial position of the first thrust surface510C is arranged to be lower at a dynamic pressure generation portion621C than at a discharge portion623C. That is, the first thrust surface510C includes a shoulder causing a change in the axial position thereof.

As in the modification illustrated inFIG. 8, the thrust dynamic pressure groove array72C, the annular groove73C, the discharge groove array74C, and the shoulder may be defined in the first thrust surface510C.

Although, in each of the above-described preferred embodiments and the modifications thereof, all of the thrust dynamic pressure groove array, the annular groove, and the discharge groove array are defined in the same one of the first and second thrust surfaces, this is not essential to the present invention. At least one of the thrust dynamic pressure groove array, the annular groove, and the discharge groove array may be defined in the first thrust surface, with the rest being defined in the second thrust surface.

Although each of the above-described preferred embodiments and the modifications thereof is applied to a spindle motor of a rotating-shaft type, this is not essential to the present invention. A bearing mechanism according to a preferred embodiment of the present invention may be applied to a spindle motor of a fixed-shaft type. In the spindle motor of the fixed-shaft type, a stationary portion includes a shaft portion and an armature, and a rotating portion includes a sleeve portion and a magnet. In addition, the sleeve portion is supported through a lubricating fluid to be rotatable with respect to the shaft portion.

Note that the detailed shape of any member may be different from the shape thereof as illustrated in the accompanying drawings of the present application. Also note that features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.

Preferred embodiments of the present invention are applicable to bearing apparatuses, spindle motors, and disk drive apparatuses.