JP2009057990A - Fluid bearing device, spindle motor, informational device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device having such a bearing structure that a lubricating fluid will not flow out of a bearing opening of a fluid bearing even when the fluid bearing having a communication hole is subjected to a large impact, and a spindle motor mounted with the fluid bearing. <P>SOLUTION: The fluid bearing device 2 has a shaft 14, and a sleeve 13 that rotatably supports the shaft 14. A thrust bearing flange 16 is formed at one end of the shaft 14, is equipped with a protrusion 28 that is opposed to the stepped part 24 of the sleeve 13 in the axial direction, and is configured so that the thrust flange 16 does not block the communication hole 27 when the impact is applied, which suppresses the generation of the cavity near the thrust flange 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device having a lubricating fluid leakage prevention structure, a spindle motor using the same, and an information device equipped with the spindle motor.

  In recent years, a spindle motor used in an information device such as a hard disk drive (hereinafter referred to as an HDD) has been mainly used as a fluid bearing that is excellent in silence and runout accuracy. Since the usage of HDDs has expanded from stationary personal computers to small and thin products such as mobile phones and mobile players, fluid bearing devices mounted on HDDs have been required to be smaller and thinner. ing. It has become difficult to secure a sufficient design space for a 2.5-inch or less HDD mounted on a small and thin product such as a mobile phone or a mobile player.

  In the limited design space, it is the most important item to perform a design that reliably holds the lubricating fluid required for the hydrodynamic bearing device inside the bearing. Due to the lack of the lubricating fluid, the rotating body rubs against the fixed body and seizes and stops rotating. As a result, there arises a problem that data cannot be read or written from the magnetic recording disk. In other words, it is the most important item for the hydrodynamic bearing device and the important item for the HDD to reliably hold the lubricating fluid necessary for the hydrodynamic bearing device inside the bearing.

In order to prevent the lubricating fluid from flowing out and to securely hold the lubricating fluid required for the hydrodynamic bearing device inside the bearing, various studies such as studies on the capillary seal structure and dynamic pressure generating grooves have been conducted. It has been broken. Among the various studies, in order to make the pressure difference inside the bearing (inside the bag structure) uniform, there are many applications of a structure in which communication holes are formed in the bearing member (sleeve) constituting the hydrodynamic bearing device. (For example, see Patent Document 1).
JP 2005-143227 A

  In the configuration of the conventional spindle motor 801 and the hydrodynamic bearing device 802 shown in FIG. 7, the sleeve 813 is positioned on the axially opposed portion of the flange 816 as a retaining member attached to the shaft 814. A second opening 827 b of the communication hole 827 is provided. A first opening 827 a is provided on the other end side of the sleeve 813 as another opening of the communication hole 827. In this configuration, it is possible to reduce the size in the radial direction by providing the communication hole 827 in the sleeve 813, but there is a problem that the lubricating fluid 819 leaks to the outside due to an impact or the like. This will be described below.

  A flange 816 is arranged to face the step 824 of the sleeve 813 in which the second opening 827b of the communication hole 827 is formed. The flange 816, the shaft 814, and the hub 812, which are rotating bodies, are floated by the dynamic pressure generated by the dynamic pressure generating grooves (not shown) of the thrust bearing portion 818 and the radial bearing portion 817. When an impact or the like is not applied, the second opening 827 b on the flange side of the communication hole 827 is in contact with the flange 816 because of the balance between the flying force and the attractive force between the magnet 809 and the magnetic body 829 facing in the axial direction. It is supposed not to.

  Further, lubrication is performed by balancing the surface tension of the lubricating fluid 819 and the air pressure of the outside air in the capillary seal portion 821 formed between the inner peripheral surface 812b of the protruding portion 812a of the hub 812 and the outer peripheral surface 813a of the sleeve 813. It is designed to prevent the fluid 819 from flowing out.

  However, as shown in FIG. 8A, when a large impact force is applied to the motor (fluid bearing) when dropped, the shaft 814, the hub 812, and the magnet 809, which are rotating bodies, are axially moved. (The broken line in the figure indicates the state before the movement). As a result, the balance due to the floating force and the attractive force between the magnet 809 and the magnetic body 829 facing in the axial direction is lost, and the flange 816 moves until it comes into surface contact with the step portion 824. Since the flange-side second opening 827b is closed by the flange 816, the abrupt axial movement of the flange 816 prevents the lubricating fluid from flowing around the lower side of the flange 816, and the shaft 814 and the flange 816 in the axial direction. A negative pressure portion 850 (bubble or cavity) is generated in the space facing the plate 823. Then, under normal atmospheric pressure, the gas component in the air that is absorbed in the lubricating fluid 819 cannot be dissolved due to the negative pressure state, and appears as bubbles in a short time.

  When the impact load is lost in the state where the negative pressure portion 850 is generated, as shown in FIG. 8B, the shaft 814 and the flange 816, which are rotating bodies, are opposed to the magnet 809 in the axial direction. It will return to the original state by the suction force between. However, since the gas component constituting the negative pressure portion 850 cannot be dissolved again in the lubricating fluid in a short time, the negative pressure portion 850 is not eliminated and the shaft 814, the flange 816, and the plate 823 It will remain in the space formed by. As a result, the lubricating fluid 819 having a volume substantially equal to that of the negative pressure portion 850 is pushed out to the bearing opening. As a result, there is a problem that the balance between the surface tension of the lubricating fluid 819 of the capillary seal portion 821 and the air pressure of the outside air is lost, and the lubricating fluid 819 flows out to the outside.

  The present invention solves the above-described conventional problems, and a fluid bearing device having a bearing configuration in which a lubricating fluid does not flow out from a bearing opening of a fluid bearing even when a large impact is applied to a fluid bearing having a communication hole, and the fluid It is an object of the present invention to provide a spindle motor equipped with a bearing device.

  In order to solve the above-described conventional problems, a hydrodynamic bearing device according to the present invention includes a sleeve having a bearing hole that is open on one side and closed on the other side, and a shaft that is inserted into the bearing hole so as to be rotatable relative to the sleeve. And an annular flange that is housed on the closed side of the sleeve and is formed at the end of the shaft, and has a diameter larger than the outer diameter of the shaft, and a first opening that is formed on the opening side of the sleeve A communication hole having a second opening formed on the sleeve and facing the flange in the axial direction and covering the opening side end surface of the sleeve and between the opening side end surface of the sleeve An annular cover member arranged so as to form a space, a lubricating fluid filled in a clearance and a communication hole between the shaft and the sleeve, and a surface of the flange facing the sleeve, than the second opening. In the radial direction Are formed on, it is obtained by; and a protrusion protruding toward the opening side of the sleeve.

  The present invention also includes a sleeve having a bearing hole that is open on one side and closed on the other side, a shaft that is inserted into the bearing hole so as to be rotatable relative to the sleeve, and a shaft that is housed on the closed side of the sleeve. An annular flange formed at the end of the shaft, which is larger than the outer diameter of the shaft, and a hub that is fastened to the shaft and covers the opening side of the sleeve, and a gap between the shaft, the sleeve, and the hub is filled A communication fluid having a lubricating fluid, a first opening formed on the opening side of the sleeve, and a second opening formed on a flange-facing surface on the sleeve and facing the flange in the axial direction; On the surface of the flange facing the sleeve, there is a convex portion that is formed radially inward of the second opening and protrudes toward the opening of the sleeve. .

  In this hydrodynamic bearing device, when a large axial external impact is applied to the hydrodynamic bearing, it is between the convex portion formed on the flange and the surface on which the second opening of the sleeve is formed. By contact, the surface where the second opening of the sleeve is formed and the flange surface other than the convex portion do not contact each other, and the lubricating fluid flows from the communication hole to the space formed by the shaft, flange and sleeve. Therefore, a negative pressure portion does not occur, and the lubricating fluid does not flow out from the bearing opening.

  Further, the spindle motor of the present invention is equipped with the above-described hydrodynamic bearing device, and the lubricating fluid that affects the life of the hydrodynamic bearing device can be reliably held inside the hydrodynamic bearing.

  According to the fluid dynamic bearing device and the spindle motor of the present invention, even when a sudden impact is applied, the lubricating fluid of the fluid dynamic bearing device can be reliably held, and an external impact is easily applied to a mobile phone or mobile player. Thus, it is possible to provide a hydrodynamic bearing device and a spindle motor suitable for use in a small and thin HDD.

  Embodiments of a hydrodynamic bearing device and a spindle motor according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
Embodiment 1 of the present invention will be described with reference to FIG. 1 and FIG.

  FIG. 1 shows a cross-sectional view of a hydrodynamic bearing device 2 and a spindle motor 1 on which it is mounted in Embodiment 1 of the present invention. FIG. 2 is a sectional view of the hydrodynamic bearing device 2.

  In the description of the present embodiment, for the sake of convenience, the upward direction and the downward direction in FIGS. 1 and 2 are referred to as “axis upward direction” and “axis downward direction”, but the direction in which the spindle motor 1 is used is limited. is not.

  The spindle motor 1 mainly includes a rotor unit 3, a hydrodynamic bearing device 2 for rotatably supporting the rotor unit 3, and a stator unit 4. The stator unit 4 includes a stator 8 including a stator core 6 fixed to a base 5 and a coil 7 wound thereon. Further, the rotor portion 3 has a magnet 9 positioned on the stator 8 via a radial gap. The stator 8 and the magnet 9 can generate a rotating magnetic field in cooperation with each other, and these serve as a magnetic circuit unit for applying a rotational force to the rotor unit 3. A base hole 10 opened in the axial direction is formed in a substantially central portion of the base 5. At the edge of the base hole 10, a cylindrical portion 11 extending in the axial upper direction is formed.

  The rotor unit 3 is a member that is rotatably supported by the base 5 via the hydrodynamic bearing device 2. The rotor unit 3 includes a hub 12 on which a recording disk (not shown) is placed on the outer periphery, and a shaft 14 that is positioned on the inner periphery side of the hub 12 and is pivotally supported by the sleeve 13 via the hydrodynamic bearing device 2. Is mainly formed from.

  The hub 12 is a cup-shaped member disposed so as to cover the sleeve 13 from the upper side in the axial direction. The hub 12 mainly has a disk-shaped part 12a and an outer peripheral side cylindrical part 12b extending in the axial lower direction at the outer peripheral edge thereof. The shaft 14 is fitted in the center hole 12c of the disk-shaped part 12a. A magnet 9 is fixed to the outer peripheral surface of the outer cylindrical portion 12b by an adhesive means or the like.

  The magnet 9 is opposed to the stator 8 via a gap in the radial direction. When the coil 7 of the stator 8 is energized, an electromagnetic interaction between the stator 8 and the magnet 9 occurs. As a result, rotational torque is generated in the rotor unit 3.

  The axially upper end of the shaft 14 is fitted in the center hole 12 c of the hub 12. A thrust flange 16 is fixed to the lower end of the shaft body 14a in the axial direction. That is, the shaft 14 includes a cylindrical shaft body 14 a and a thrust flange 16.

  The hydrodynamic bearing device 2 is a bearing portion for rotatably supporting the rotor portion 3 with respect to the stator portion 4. More specifically, the hydrodynamic bearing device 2 mainly includes a shaft 14 fixed to the rotor unit 3 and a sleeve 13 fixed to the base 5 and rotatably supporting the shaft 14.

  The hydrodynamic bearing device 2 includes a radial bearing portion 17 and a thrust bearing portion 18 as dynamic pressure generating portions. Further, the lubricating fluid 19 in each bearing portion is between the outer peripheral surface 14b of the shaft main body 14a and the inner peripheral surface 20a of the cover member 20 arranged so as to cover the sleeve 13 at the end portion on the axially upper side of the sleeve 13. It is sealed by a capillary seal portion 21 formed in the above. Further, the gaps constituting the bearing portions 17 and 18 are completely filled with the lubricating fluid 19, and an interface is formed at the capillary seal portion 21 so as to communicate with the outside air.

  The sleeve 13 includes a substantially hollow cylindrical sleeve main body 13a and a disk-shaped thrust plate 23 that closes a lower portion of the sleeve main body 13a. The sleeve body 13a has a through hole extending in the axial direction at the center thereof, and an inner peripheral surface 13b is formed there. The thrust plate 23 is a circular plate-like member, and closes the lower end opening of the through hole by being fixed to the lower end of the sleeve main body 13a.

  A stepped portion 24 that is continuous from the inner peripheral surface 13b is formed in the axial lower side direction of the sleeve main body 13a. The step portion 24 is formed between the inner peripheral surface 13b of the sleeve main body 13a and the inner peripheral surface 13c larger in diameter than the inner peripheral surface 13b, and is an annular shape for accommodating a thrust flange 16 of the shaft 14 described later. The recessed space is secured. From the above, the sleeve 13 has the disk-shaped hollow portion formed by the columnar hollow portion formed by the inner peripheral surface 13b of the sleeve main body 13a, the step portion 24, the inner peripheral surface 13c, and the thrust plate 23 of the sleeve main body 13a. And will form.

  The shaft body 14 a of the shaft 14 is generally disposed in the columnar hollow portion along the through hole of the sleeve 13. The outer peripheral surface 14b of the shaft main body 14a is opposed to the inner peripheral surface 13b of the sleeve main body 13a in the radial direction with a small gap. The thrust flange 16 is a disk-shaped portion disposed in the disk-shaped hollow portion of the sleeve 13.

  A herringbone-shaped dynamic pressure generating groove 25 for generating dynamic pressure in the lubricating fluid 19 as the shaft 14 rotates is formed in the inner peripheral surface 13b of the sleeve body 13a. The dynamic pressure generating grooves 25 are a plurality of grooves arranged in the rotational direction, and each groove is a substantially “<”-shaped groove formed by connecting a pair of spiral grooves inclined in directions opposite to the rotational direction. It is. As described above, the radial bearing portion 17 is configured in the axial direction by the inner peripheral surface 13b of the sleeve main body 13a of the sleeve 13, the outer peripheral surface 14b of the shaft main body 14a, and the lubricating fluid 19 therebetween. In the radial bearing portion 17, the dynamic pressure generating groove 25 has an unbalanced shape so that the fluid dynamic pressure works from the upper side of the axis to the lower side of the axis.

  The thrust surface 16 a forming the thrust bearing portion 18 of the thrust flange 16 has a spiral or herringbone-shaped dynamic pressure generating groove for generating dynamic pressure in the lubricating fluid 19 as the shaft 14 rotates. 26 is formed. The dynamic pressure generating grooves 26 are a plurality of grooves arranged in the rotation direction, and support the rotor unit 3 in the thrust direction during rotation. Thus, the thrust bearing portion 18 is formed by the surface 16a of the thrust flange 16 forming the thrust bearing portion 18, the thrust plate 23, and the lubricating fluid 19 therebetween. Further, the dynamic pressure generating groove 26 may be formed on the surface of the thrust plate 23.

  The capillary seal portion 21 is a structure for preventing leakage of the lubricating fluid 19 from the radial bearing portion 17, and in the vicinity of the end portion of the sleeve main body 13a in the axial upper direction, the inner peripheral surface 20a of the cover member 20 and the shaft It is comprised by the outer peripheral peripheral surface 14b of the main body 14a. More specifically, the capillary seal portion 21 is configured by an inclined surface 20 b provided on the inner peripheral side surface of the cover member 20. The inclined surface 20b is formed such that a gap between the inclined surface 20b and the outer peripheral surface 14b of the shaft body 14a expands toward the upper side of the axis. From the above-described structure, the surface tension of the lubricating fluid 19 held in the hydrodynamic bearing device 2 is balanced with the air pressure of the outside air, thereby preventing the lubricating fluid 19 from moving outside the hydrodynamic bearing device 2. .

  The communication hole 27 is formed so as to communicate the stepped portion 24 and the end surface 13d facing the cover member 20 of the sleeve main body 13a in the axial direction. On the surface 16b in the axial upper direction of the thrust flange 16 that is located radially inward from the second opening 27b of the communication hole 27 formed in the stepped portion 24 of the sleeve body 13a and is opposed in the axial direction, An annular convex portion 28 is formed. A first opening 27 a is provided on the other end side of the sleeve 13 as another opening of the communication hole 27.

  In this manner, in the spindle motor 1 having the one-end-opening type hydrodynamic bearing device 2, the convex portion 28 is formed on the surface 16b of the thrust flange 16 facing the step portion 24 formed in the sleeve main body 13a in the axial direction. Therefore, it is possible to suppress the occurrence of a strong negative pressure portion that generates air bubbles in the bearing gap when a sudden external impact is applied to the rotor portion 3 that is a rotating body. Thus, it is possible to prevent the lubricating fluid 19 from leaking from the capillary seal portion 21.

  Hereinafter, the point that the lubricating fluid 19 is prevented from leaking when a sudden external impact is applied by forming the convex portion 28 will be described with reference to FIG.

  As shown in FIG. 3, when a sudden external impact is applied to the spindle motor, the shaft 14 constituting the rotor unit 3, which is a rotating body, moves in the axial upper direction (broken line in the figure). The part shows the state before moving). As a result, between the end surface 14e on the axial lower direction side of the shaft body 14a, the surface 16a on the axial lower direction side of the thrust flange 16, and the end surface 23a on the axial upper direction side of the thrust plate 23, A space 50 is newly formed in the bearing gap.

  On the other hand, a convex portion 28 is formed on the surface 16b on the axial upper side side of the thrust flange 16, and the convex portion 28 comes into contact with the step portion 24 of the sleeve main body 13a. However, the stepped portion 24 where the second opening 27b of the communication hole 27 is located does not contact the surface 16b. That is, the communication hole 27 and the space 50 are always connected even if the thrust flange 16 moves.

  The space 50 formed by the rapid movement of the shaft 14 tends to be in a negative pressure state. In the negative pressure state, when the lubricating fluid 19 is not filled in the rapidly formed space 50, air dissolved in the lubricating fluid 19 expands to generate bubbles. In addition, it takes a long time for the bubbles to melt into the lubricating fluid 19 again. For this reason, when bubbles are generated at one end, the volume of the air enters a state in which the lubricating fluid 19 filled in the bearing gap is pushed out.

  However, since the communication hole 27 and the space 50 are connected in the present invention, the movement of the lubricating fluid 19 of M1 → M2 → M3 shown in FIG. 3 occurs, and the lubricating fluid 19 is supplied to the space 50. , Strong negative pressure conditions that generate bubbles do not occur. Even if a negative pressure is generated, the lubricating fluid 19 is supplied from the communication hole 27, so that bubbles having a diameter smaller than the bearing gap are generated, and the lubricating fluid 19 is transferred from the capillary seal portion 21 to the outside of the bearing. Large bubbles that cause extrusion are not formed.

  As described above, the convex portion 28 is formed on the surface 16b of the thrust flange 16 so that the lubricating fluid 19 is prevented from leaking from the capillary seal portion 21 even when a sudden external impact is applied to the spindle motor. It has become.

  In the above description, the thrust flange 16 and the shaft body 14a have been described as separate parts, but the present invention is not limited to this. For example, in the hydrodynamic bearing device 302 shown in FIG. 4, the axial length of the radial bearing portion 17 is shortened and the radial direction length of the thrust bearing portion 18 is lengthened in order to realize a reduction in thickness. The bearing rigidity as a fluid bearing is ensured.

Since the outer diameter of the thrust flange 16 is large and thin, the thrust flange 16 is integrally formed with the shaft body 14a in order to ensure a perpendicularity with respect to the shaft 14.
The shaft 14 in which the shaft body 14 a and the thrust flange 16 are integrally formed constitutes a radial bearing portion 17 and a thrust bearing portion 18. The parts that make up each bearing part have a bearing clearance of about 1 μm to 5 μm for the radial bearing part and about 10 to 30 μm for the thrust bearing part. Therefore, high precision is required and polishing is performed. ing.

  As an example, the polishing of the shaft 14 is performed by first polishing the shaft outer peripheral surface 14b constituting the radial bearing gap 17. Next, the surface 16b of the axial direction of the thrust flange 16 is polished. Next, the surface 16a of the thrust flange 16 facing the thrust plate 23 is polished using the polished surface 16b as a receiving surface. Finally, the shaft outer peripheral surface 14b constituting the radial bearing gap 17 is first ground again with the surface 16a of the thrust flange 16 facing the thrust plate 23 as a reference. Note that the polishing step is not limited to this.

  The accuracy required for the shaft 14 is dimensional accuracy such as perpendicularity and flatness between the shaft outer peripheral surface 14b and the surface 16a of the thrust flange 16 facing the thrust plate 23. Since this dimensional accuracy is processed (polished) with high accuracy, the hub 12 fastened to the shaft 14 which is a rotating body can rotate with respect to the rotation center axis with high accuracy and is mounted on the hub 12. There is also an effect that it is possible to prevent contact between the magnetic recording disk placed thereon and the head for reading and writing data.

  Furthermore, the flatness and perpendicularity of the thrust flange 16 with respect to the shaft outer peripheral surface 14b can be reduced by polishing only the convex portion 28 formed on the thrust flange 16 instead of polishing the entire surface 16b of the thrust flange 16. It is easy and accurate. In addition, the convex portion 28 formed on the thrust flange 16 can be polished simultaneously with the polishing of the shaft outer peripheral surface 14b, and the entire thrust flange 16 is not polished. Even when the grinding stone (grinding stone) is worn, the fine adjustment work is simplified.

  As described above, only the convex portion 28 in the axial upper direction of the thrust flange 16 is polished, so that the capillary can be rotated with high accuracy with respect to the rotation center axis, and leakage of the lubricating fluid is formed. Since the clearance dimension of the seal part 21 is ensured with high accuracy, the leakage of the lubricating fluid can be prevented more effectively even when a sudden impact is applied.

(Embodiment 2)
Hereinafter, Embodiment 2 of the present invention will be described with reference to FIG. 5 and FIG. FIG. 5 is a sectional view of the spindle motor 201 according to the second embodiment of the present invention, and FIG. 6 is a sectional view of the hydrodynamic bearing device 202 mounted on the spindle motor according to the second embodiment.

  5 and FIG. 6, the same reference numerals are given to portions having the same effects as those of the first embodiment, and the following description is omitted.

  The hub 12 constituting the rotor unit 3 is a cup-shaped member that is disposed close to the sleeve 13 so as to cover the sleeve 13 from the upper side in the axial direction. The hub 12 mainly has a disk-shaped part 12a and an outer peripheral side cylindrical part 12b that extends downward in the axial direction at the outer peripheral edge thereof. A shaft 14 which will be described later is fixed to the center hole 12c of the disc-like portion 12a. A magnet 9 is fixed to the inner peripheral surface of the outer peripheral cylindrical portion 12b by an adhesive means or the like.

  The hydrodynamic bearing device 202 includes a radial bearing portion 17 and a thrust bearing portion 18 as dynamic pressure generating portions. Here, the hub 12 has a disk-like portion 12a on the inner peripheral portion, and an annular protruding portion 12e protruding further on the outer periphery thereof in the axial lower direction. The lubricating fluid 19 in the bearing is sealed by a capillary seal portion 21 formed between the inner peripheral surface 12f of the annular protrusion 12e and the outer peripheral surface 13e of the sleeve 13 in the axial upper direction. Further, the gaps constituting the bearing portions 17 and 18 are filled with a lubricating fluid 19, and an interface is formed at the capillary seal portion 21 so as to communicate with the outside air.

  The capillary seal portion 21 is a structure for preventing leakage of the lubricating fluid 19 from the radial bearing portion 17, and the inner peripheral surface of the annular projecting portion 12 e of the hub 12 near the end portion of the sleeve 13 in the axial upper direction. 12f and the outer peripheral surface 13e of the sleeve 13 in the axial upper direction. More specifically, the capillary seal portion 21 is configured by an inclined surface 13f provided on the outer peripheral surface 13e in the axial upper direction of the sleeve body 13a. The inclined surface 13f is formed such that the gap between the inclined surface 13f and the inner peripheral surface 12f of the annular projecting portion 12e of the hub 12 expands toward the lower side of the axis. Due to the structure described above, the surface tension of the lubricating fluid 19 held in the hydrodynamic bearing device 202 is balanced with the air pressure of the outside air, thereby preventing the lubricating fluid 19 from leaking out of the hydrodynamic bearing device 2. .

  In FIG. 6, when the shaft 14 constituting the rotor portion 3 that is a rotating body moves upward in the axial direction, the end surface 14 e of the shaft main body 14 a in the lower axial direction and the surface of the thrust flange 16 in the lower axial direction. A negative pressure tends to be generated between 16a and the surface 23a in the axial upper direction of the thrust plate 23.

However, since the convex portion 28 is formed on the thrust flange 16, the space between the communication hole 27 and the surface 16 a of the thrust flange 16 in the lower axial direction and the surface 23 a of the thrust plate 23 in the upper axial direction is between. As shown in FIG. 3, the movement of the lubricating fluid 19 occurs in the same way as M1 → M2 → M3 shown in FIG. 3, and the axial lower surface 16a of the thrust flange 16 and the axis of the thrust plate 23 Since the lubricating fluid 19 is supplied to the surface 23a in the line upper direction, a strong negative pressure portion (gage pressure −−) that causes the lubricating fluid 19 to be pushed out of the bearing from the tapered capillary seal portion 21. (About 0.7 atm) is not formed.
As described above, the convex portion 28 is formed on the surface 16b of the thrust flange 16 to prevent the lubricating fluid 19 from leaking from the capillary seal portion 21 even if a sudden external impact is applied to the spindle motor. Can do.

  Furthermore, the relationship between the bearing gaps (A, B, C) shown in FIG. 6 is set to a dimension that satisfies the formula (1), so that when a sudden external impact is applied, the lubricating fluid 19 It is possible to provide a hydrodynamic bearing device that can prevent leakage and has a longer life, and a spindle motor equipped with the hydrodynamic bearing device.

(Equation 1)
C> A + B (1)
A: Axial clearance between the convex portion 28 and the stepped portion B B: Axial clearance between the thrust flange 16 and the thrust plate 23 C: Radial clearance between the thrust flange 16 and the inner peripheral surface 13c of the sleeve 13 Specifically, A + B = 0.02 mm and C = 0.1 mm. By making the above-mentioned dimensions satisfying the formula (1), when a sudden external impact is applied, a capillary force that causes the lubricating fluid 19 to move from a wide gap to a narrow gap will act, Even if a negative pressure portion is generated between the thrust flange 16 and the thrust plate 23, the lubricating fluid 19 flows through the portion where the negative pressure portion is likely to be generated, thereby suppressing the generation of bubbles, and the capillary seal portion. It is possible to prevent the liquid level fluctuation of 21.

  Further, when the motor is used for a long time (around the life end), the weight of the lubricating fluid 19 decreases due to evaporation or the like. However, by satisfying the expression (1), a capillary force that causes the lubricating fluid 19 to move from a wide gap to a narrow gap works, and the hydrodynamic bearing device 2 generates dynamic pressure until the end. Since the lubricating fluid 19 is always filled, it is possible to extend the service life of the conventional bearing device.

  When the diameter of the thrust flange 16 is 10 mm or less, the viscosity of the lubricating fluid is about 5 to 50 mm 2 / s, and the height of the convex portion 28 is 4 μm or more, the situation in which the lubricating fluid leaks has not occurred. This viscosity corresponds to a temperature range of about −10 ° C. to 60 ° C. in a normal fluid bearing for HDD.

  In the second embodiment, the thrust bearing portion is configured between the thrust flange 16 and the thrust plate 23, but the present invention is not limited to this. For example, a thrust dynamic pressure generating groove is disposed between the disc-like portion 12a of the hub 12 and the upper end surface of the sleeve 13 so that a gap is always ensured between the thrust flange 16 and the thrust plate 23. Also good. In this case, the thrust flange 16 mainly functions as a stopper.

  In the above embodiment, the shape of the convex portion is not particularly specified, but it is of course possible to use a ring shape in consideration of productivity, but it is not a ring shape using, for example, coining or etching. For example, an arc shape may be used.

  Moreover, you may form a tomorrow and a dynamic pressure groove in the convex part or the sleeve side end surface facing a convex part. This also makes it possible to reduce wear during application of an impact.

  Although the above embodiment has been described as a spindle motor for HDD, the present application is not limited to this. For example, the present invention can also be applied to an optical disk device such as a CD, DVD, and BD, an optical disk device such as an MO, a laser printer device using a polygon scanner motor, and a rotary head drum motor such as a video tape recorder and a streamer device.

  The hydrodynamic bearing device and spindle motor according to the present invention are used for small and thin products such as mobile phones and mobile players, and can reliably hold the lubricating fluid of the hydrodynamic bearing device even when a sudden impact is applied. Therefore, it is possible to design a hydrodynamic bearing device suitable for a small size and a thin shape, which is useful as a spindle motor for a magnetic recording disk device or the like.

  The hydrodynamic bearing device and spindle motor according to the present invention can also be applied to various spindle motor applications such as a magneto-optical disk drive device that needs to reliably hold the lubricating fluid of the hydrodynamic bearing device.

Sectional drawing of the spindle motor in Embodiment 1 of this invention Sectional drawing of the hydrodynamic bearing apparatus in Embodiment 1 of this invention FIG. 2 is a half sectional view showing a state inside the hydrodynamic bearing device when an external impact is applied to the hydrodynamic bearing device in Embodiment 1 of the present invention. Sectional drawing of the modification of the hydrodynamic bearing apparatus in Embodiment 1 of this invention Sectional drawing of the spindle motor in Embodiment 2 of this invention Sectional drawing of the hydrodynamic bearing apparatus in Embodiment 2 of this invention. Cross section of a conventional spindle motor (A) State diagram when negative pressure portion is generated in conventional hydrodynamic bearing device, (b) State diagram of lubricating fluid leakage due to negative pressure portion in conventional hydrodynamic bearing device

Explanation of symbols

1, 201, 801 Spindle motor 2, 202, 302, 802 Fluid dynamic bearing device 3 Rotor part 4 Stator part 5 Base 6 Stator core 7 Coil 8 Stator 9, 809 Magnet 10 Base hole 11 Cylindrical part 12, 812 Hub 13, 813 Sleeve 14,814 Shaft 16,816 Flange 17,817 Radial bearing portion 18,818 Thrust bearing portion 19,819 Lubricating fluid 20 Cover member 21,821 Capillary seal portion 23 Thrust plate 24,824 Step portion 26 Dynamic pressure generating groove 27, 827 Communication hole 27a, 827a First opening 27b, 827b Second opening 28 Convex 29, 829 Magnetic body 50, 850 Space 823 Plate

Claims (7)

A sleeve having a bearing hole that is open on one side and closed on the other side;
A shaft inserted into the bearing hole so as to be rotatable relative to the sleeve;
An annular flange that is housed on the closed side of the sleeve and is formed at the end of the shaft, the diameter of which is larger than the outer diameter of the shaft;
A communication hole having a first opening formed on the opening side of the sleeve, and a second opening formed on a flange-facing surface on the sleeve and facing the flange in the axial direction;
An annular cover member arranged to cover the opening-side end surface of the sleeve and to form a space with the opening-side end surface of the sleeve;
A lubricating fluid filled in a gap between the shaft and the sleeve and the communication hole;
On the surface of the flange facing the sleeve, a convex portion that is formed radially inward from the second opening and protrudes toward the opening of the sleeve;
A hydrodynamic bearing device. A cup-shaped hub that is fastened to the shaft and covers the opening side of the sleeve;
The hydrodynamic bearing device according to claim 1, wherein the cover member is located between the hub and the sleeve.   3. The hydrodynamic bearing device according to claim 1, wherein at least a surface of the convex portion facing the surface on which the second opening of the sleeve is formed is polished. 4. . A sleeve having a bearing hole that is open on one side and closed on the other;
A shaft inserted into the bearing hole so as to be rotatable relative to the sleeve;
An annular flange that is housed on the closed side of the sleeve and is formed at the end of the shaft, the diameter of which is larger than the outer diameter of the shaft;
A hub fastened to the shaft and covering the opening side of the sleeve;
A lubricating fluid filled in a gap between the shaft, the sleeve, and the hub;
A communication hole having a first opening formed on the opening side of the sleeve, and a second opening formed on a flange-facing surface on the sleeve and facing the flange in the axial direction;
On the surface of the flange facing the sleeve, a convex portion that is formed radially inward from the second opening and protrudes toward the opening of the sleeve;
A hydrodynamic bearing device.   5. The hydrodynamic bearing device according to claim 4, wherein at least a surface of the convex portion facing the surface on which the second opening of the sleeve is formed is polished.   A spindle motor comprising the hydrodynamic bearing device according to any one of claims 1 to 5. An information device comprising the spindle motor according to claim 6.

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