JP2006194383A - Dynamic pressure bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the wear of a thrust bearing portion of this kind of dynamic pressure bearing device. <P>SOLUTION: Pressure is generated in a thrust bearing gap C between a thrust bearing face 8b1 having a dynamic pressure groove and a thrust receiving face 2c opposed thereto by the dynamic pressure operation of lubricating oil, to support a shaft member 2 in no contact in the thrusting direction. The thrust receiving face 2c is a flat face, while the thrust bearing face 8b1 has an inclined face 11 and a reduced portion 10 whose axial width is gradually getting smaller as going to the outer diameter side, in the thrust bearing gap C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrodynamic bearing device that supports a rotating member in a non-contact manner by a hydrodynamic action of a fluid (lubricating fluid) generated in a bearing gap. This bearing device is a spindle of information equipment such as magnetic disk devices such as HDD and FDD, optical disk devices such as CD-ROM, CD-R / RW and DVD-ROM / RAM, and magneto-optical disk devices such as MD and MO. It is suitable for a motor, a polygon scanner motor of a laser beam printer (LBP), or an electric device such as a small motor such as an axial fan.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied or actually used. Yes.

  As an example of this hydrodynamic bearing device, Japanese Patent Laid-Open No. 2002-61641 (Patent Document 1) discloses a bottomed cylindrical housing, a bearing member fixed inside the housing, and an inner peripheral surface of the bearing member. A shaft member that includes an inserted shaft member, and a radial bearing portion and a thrust bearing portion that rotatably support the shaft member in a non-contact manner by a dynamic pressure generated when the shaft member and the bearing member rotate relative to each other is disclosed.

Of the radial bearing portion and the thrust bearing portion, the thrust bearing portion generates, for example, pressure in the thrust bearing gap between the flange portion end surface of the shaft member and the end surface of the bearing member facing the shaft member by the dynamic pressure action of oil. The shaft member is supported in a non-contact manner in the thrust direction.
JP 2002-61641 A

  By the way, in this type of hydrodynamic bearing device, it is inevitable that the rotation-side member and the stationary-side member slide at high speed when starting and stopping. For this reason, in dynamic pressure bearing devices used for information devices that frequently start and stop motors, for example, consumer devices such as HDD-DVD recorders and storage devices for mobile phones, repeated start and stop depending on usage conditions, etc. Wear of the sliding surface due to may be a problem.

  The subject of this invention is suppressing the abrasion of the thrust bearing part in this kind of hydrodynamic bearing apparatus.

  In order to solve the above problems, a hydrodynamic bearing device according to the present invention includes a housing having one end opened, a bearing sleeve fixed inside the housing, and a flange portion projecting to the outer diameter side. A shaft member that rotates relative to the sleeve, a radial bearing portion that supports the shaft member in a non-contact manner in the radial direction by a dynamic pressure action of a fluid generated in a radial bearing gap between the bearing sleeve and the shaft member, and a thrust bearing gap A thrust bearing portion that non-contact-supports the shaft member in the thrust direction by the dynamic pressure action of the generated fluid, and includes an end surface on the housing opening side of the bearing sleeve and an end surface of the flange portion of the shaft member facing the shaft sleeve , One of which is a thrust bearing surface including a dynamic pressure groove region in which a plurality of dynamic pressure grooves are arranged, and the other is a thrust receiving surface which is opposed to the thrust bearing surface in the axial direction, Thrust bearing gap is formed between the strike bearing surface and the thrust receiving surface, the thrust bearing gap, and having a reduced portion having a reduced its axial width as the outer diameter side.

  As a result, the portion with the large peripheral speed of the outermost diameter portion of the reduced portion has the minimum width, so the pumping function by the dynamic pressure groove is enhanced, and the contact time between the thrust bearing surface and the thrust receiving surface at the start / stop of the motor Can be shortened.

  This thrust bearing gap can be obtained by setting at least one of the thrust bearing surface and the thrust receiving surface of the reduced portion as an inclined surface. In this case, in order to avoid a decrease in the dynamic pressure effect, it is desirable that the radial width of the inclined surface is r, the height of the inclined surface is h, and h / r ≦ 0.01.

  The said structure WHEREIN: A radial bearing part can be comprised with the multi-arc bearing which has a several wedge-shaped clearance gap in a radial bearing clearance.

  The hydrodynamic bearing device described above can be suitably used by being incorporated in a spindle motor of a disk device such as an HDD.

  According to the present invention, since wear in the thrust bearing portion can be suppressed, durability of this type of hydrodynamic bearing device can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 conceptually shows a configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device 1 according to an embodiment of the present invention. This spindle motor is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 mounted on the shaft member 2, and a radial direction, for example. The stator coil 4 and the rotor magnet 5 are opposed to each other with a gap therebetween. The stator coil 4 is attached to the outer periphery of the casing 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The disk hub 3 holds one or more disk-shaped information recording media (hereinafter simply referred to as disks) D such as magnetic disks on the outer periphery thereof. In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force generated between the stator coil 4 and the rotor magnet 5. The disk D held by the hub 3 rotates integrally with the shaft member 2.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a shaft member 2, a housing 7, a bearing sleeve 8 fixed to the housing 7, and a seal member 9 as main components. For convenience of explanation, the following description will be made with the side of the opening 7a of the housing 7 as the upper side and the side opposite to the opening 7a as the lower side.

  The shaft member 2 is formed of a metal material such as stainless steel, for example, and includes a shaft portion 2a and a disk-shaped flange portion 2b. The flange portion 2b is provided above the lower end of the shaft portion 2a, and is integral with or separate from the shaft portion 2a. The core portion of the shaft portion 2a and / or the flange portion 2b can be formed of a resin material.

  The housing 7 has an opening 7a at one end and is formed in a bottomed cylindrical shape with the other end closed, and includes a cylindrical side portion 7b and a bottom portion 7c integrally connected to the other end side of the side portion 7b. I have. The housing 7 is formed, for example, by injection molding a resin composition having a base resin of liquid crystal polymer (LCP), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), or the like. The housing 7 can be molded (insert molding) using the bearing sleeve 8 as an insert part. Alternatively, the side part 7b and the bottom part 7c can be formed separately, and both can be bonded to each other by means of adhesion and welding (such as ultrasonic welding). Note that the housing 7 does not necessarily need to be formed of resin, and can be formed by, for example, pressing a metal material. Only the side portion 7b or only the bottom portion 7c may be formed of a metal material.

Examples of the resin composition include fibrous fillers such as glass fibers, whisker-like fillers such as potassium titanate, scaly fillers such as mica, carbon fibers, carbon black, graphite, carbon nanomaterials, An appropriate amount of a fibrous or powdery conductive filler such as various metal powders can be blended depending on the purpose.

  The bearing sleeve 8 is made of, for example, a soft metal material such as copper or aluminum (including an alloy) or a sintered metal material. In this embodiment, the bearing sleeve 8 is formed in a cylindrical shape with a porous body made of a sintered metal, for example, a porous body of a sintered metal mainly containing copper. The bearing sleeve 8 has its lower end surface 8c abutted against the bottom portion 7c of the housing 7 to determine the axial position of the bearing sleeve 8 with respect to the housing 7, and then the inside of the housing 7 is fixed by fixing means such as adhesion or welding. Fixed around the circumference.

  As shown in FIG. 3, a plurality of arcuate surfaces 8a1 serving as the radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2 are respectively provided in regions spaced apart from each other on the inner peripheral surface 8a of the bearing sleeve 8. It is formed. Each arcuate surface 8a1 is an eccentric arcuate surface centered at a point offset from the rotational axis O by an equal distance, and is formed at equal intervals in the circumferential direction. An axial separation groove 8a2 is formed between each eccentric arc surface 8a1.

  By inserting the shaft portion 2a of the shaft member 2 into the inner peripheral surface 8a of the bearing sleeve 8, the eccentric arc surface 8a1 and the separation groove 8a2 of the bearing sleeve 8 and the perfect circular outer peripheral surface 2a1 of the shaft portion 2a are interposed. The radial bearing gaps of the first and second radial bearing portions R1 and R2 are respectively formed. In the radial bearing gap, a region facing the eccentric arc surface 8a1 is a wedge-shaped gap 8a3 in which the gap width is gradually reduced in the circumferential direction. The reduction direction of the wedge-shaped gap 8a3 coincides with the rotation direction of the shaft member 2.

  For example, although not shown in the drawings, a spiral dynamic pressure groove is formed on the entire upper surface 8b of the bearing sleeve 8 or a part of the annular region as a thrust dynamic pressure generating portion. In this embodiment, the thrust bearing surface 8b1 includes the entire or part of the dynamic pressure groove forming region of the upper end surface 8b, and the thrust receiving surface 2c formed on the lower end surface 2b2 of the flange portion 2b It faces the bearing surface 8b1. When the shaft member 2 rotates, a thrust bearing gap of a thrust bearing portion T, which will be described later, is formed between both surfaces 8b1 and 2c (see FIG. 2).

The seal member 9 is formed in an annular shape with, for example, a resin material or a metal material. The seal member 9 is disposed on the inner periphery of the opening 7 a of the housing 7, and ultrasonic welding or the like is performed with the flange portion 2 b accommodated between the lower end surface 9 b of the seal member 9 and the upper end surface 8 b of the bearing sleeve 8. It is fixed to the housing 7 by fixing means such as welding or adhesion. In this case, the cylindrical inner peripheral surface 9a of the seal member 9 forms a predetermined seal space S between the outer peripheral surface of the opposing shaft member 2 and, in this embodiment, the outer peripheral surface 2a1 of the shaft portion 2a. The inner space of the housing 7 sealed with the seal member 9 is filled with lubricating oil as a lubricating fluid including the inner pores of the bearing sleeve 8, and the oil level of the lubricating oil is within the range of the sealing space S. Maintained.

  The lower end surface 9b of the seal member 9 is opposed to the upper end surface 2b1 of the flange portion 2b via a gap in the axial direction. When the shaft member 2 is displaced upward, the upper end surface 2b1 of the flange portion 2b is engaged with the lower end surface 9b of the seal member 9 in the axial direction, and the shaft member 2 is locked. Thus, the sealing member 9 in this embodiment has both a sealing function and a retaining function.

  In the dynamic pressure bearing device 1 configured as described above, when the shaft member 2 is rotated, the region (two upper and lower regions) of the inner peripheral surface 8a of the bearing sleeve 8 is the same as the outer peripheral surface 2a1 of the shaft portion 2a. The bearings are opposed to each other through a bearing gap to form multi-arc bearings (also referred to as taper bearings). In the multi-arc bearing, as the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed into the reduction side of the wedge-shaped gap 8a3, and the pressure rises. The first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft portion 2a in a non-contact manner are configured by the dynamic pressure action of the lubricating oil.

  At the same time, the thrust bearing gap between the thrust bearing surface 8b1 formed on the upper end surface 8b of the bearing sleeve 8 and the thrust receiving surface 2c of the flange portion 2b facing the thrust bearing surface 8b is also lubricated by the dynamic pressure action of the dynamic pressure groove. An oil film of oil is formed, and a thrust bearing portion T that supports the flange portion 2b in a non-contact manner so as to be rotatable in the thrust direction is configured by the pressure of the oil film.

  In the present invention, as shown in FIG. 4, a reduced portion 10 is formed in the thrust bearing gap C of the thrust bearing portion T in which the axial width W is reduced toward the outer diameter side (thrust bearing gap C in the figure). The width W is exaggerated). FIG. 4 schematically illustrates a case where the reduced portion 10 is provided in a region excluding a partial inner diameter side region of the thrust bearing gap C. For example, as shown in the figure, the contracting portion 10 has a thrust receiving surface 2c as a flat surface in a direction orthogonal to the axial direction, and an inclined surface 11 that approaches the thrust receiving surface 2c toward the thrust bearing surface 8b1 as the outer diameter side. Can be formed. The inclined surface 11 is preferably formed with a dynamic pressure groove region of the thrust bearing surface 8b1.

  Thus, by forming the reduced portion 10 in the thrust bearing gap C, the outermost diameter portion of the reduced portion 10 becomes the minimum width portion Wmin of the thrust bearing gap C. While the shaft member 2 is rotating, the peripheral speed of the outermost diameter portion of the reduced portion 10 is high, so that the pumping action of the dynamic pressure groove is increased. Therefore, sufficient dynamic pressure action can be obtained even at a low rotational speed, and the contact start rotational speed of the hydrodynamic bearing device 1 can be kept low. This makes it possible to suppress wear at the thrust bearing portion T due to sliding contact between the thrust bearing surface 8b1 and the thrust receiving surface 2c, and is suitable for applications where the motor is frequently started and stopped. A device 1 can be provided.

  Here, the contact start rotation speed is a rotation speed at which the thrust bearing surface 8b1 and the thrust receiving surface 2c are in contact with each other at a speed lower than that, and the both surfaces 8b1 and 2c are not in contact with each other at a higher speed. If the contact start rotational speed is reduced, the contact time between the thrust bearing surface 8b1 and the thrust receiving surface 2c immediately after the start or stop of the motor is shortened, so that wear at the thrust bearing portion T can be suppressed.

  Such an effect can be obtained as long as the thrust bearing gap C has the reduced portion 10. In addition to providing the inclined surface 11 on the thrust bearing surface 8 b 1 as shown in the figure, the thrust bearing surface 8 b 1 is made flat, while the thrust receiving surface is received. An inclined surface may be formed on the surface 2c, or an inclined surface may be formed on both the thrust bearing surface 8b1 and the thrust receiving surface 2c. As shown in FIG. 4, the inclined surface 11 has a taper shape with a straight cross section. For example, although the illustration is omitted, a curved surface (an arc having two or more radii with a radius R is formed). Including a combined complex curved surface).

  In order to confirm the above effects, the contact start rotation speed was theoretically calculated for the product of the present invention and the comparative product. Here, the product of the present invention is a thrust bearing gap having a reduced portion 10 as shown in FIG. 4, and the comparative product is an enlarged portion 10 ′ in which the axial width is enlarged toward the outer diameter side as shown in FIG. (In FIG. 5, in FIG. 5, a part corresponding to the member shown in FIG. 4 is marked with “′”).

The theoretical calculation was performed with reference to the following documents.
Jiasheng Zhu and Kyosuke Ono, 1999, "A Comparison Study on the Performance of Four Types of oil Lubricated Hydrodynamic Thrust Bearings for Hard Disk Spindles", Transactions of the ASME, Vol.121, JANUARY 1999, pp.114-120.

  The calculation conditions (DF method, Sommerfeld's boundary conditions) used in this theoretical calculation are as follows.

Rotating part mass W 6.5g
Thrust bearing outer diameter Do 6.5mm
Thrust bearing inner diameter Di 2.5mm
Groove depth ho 7μm
Number of grooves k 16
Groove angle α 30deg
Hill groove ratio γ 1
Lubricating oil viscosity η 5.97 mPa · s
However, the minimum width Wmin of the thrust bearing gap was set to 0.05 μm.

  The theoretical calculation results based on the above conditions are shown in FIG. The “flatness” on the horizontal axis in the drawing represents the height h of the inclined surface 11 shown in FIGS. 4 and 5.

  As shown in the figure, the product A of the present invention has a lower contact start rotational speed than the comparative product B, and therefore shortens the contact time between the thrust bearing surface 8b1 and the thrust receiving surface 2c immediately after starting or stopping the motor. It turned out to be effective. Further, from the result of FIG. 6, when the flatness of the thrust bearing surface 8b1 (height h of the inclined surface 11) is too large, the contact start rotation speed increases, and on the contrary, the dynamic pressure effect is reduced. Is considered to have an upper limit. From this point of view, the inventors have verified that when the ratio of the height h of the inclined surface 11 to the radial width r (h / r) exceeds 0.01, the contact start rotational speed is remarkably increased. did. Therefore, the value of h / r is 0.01 or less, preferably 0.004 or less.

  Although the comparative product shown in FIG. 5 is inferior to the product of the present invention in terms of contact start rotational speed, it has the advantage that the contact surface pressure at the time of contact between the thrust bearing surface 8b1 and the thrust receiving surface 2c is low. For example, a business information device (server HDD, business LBP, etc.) having a low start / stop frequency may obtain good results.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

  In the above embodiment, the case where the seal space S is formed between the cylindrical inner peripheral surface 9a of the seal member 9 and the outer peripheral surface 2a1 of the shaft portion 2a opposed thereto is exemplified. It is also possible to take a form. For example, FIG. 7 illustrates a case where a tapered seal space S ′ is formed by gradually increasing the radial gap width toward the outside of the housing 7 (upper side in FIG. 7).

  FIG. 8 shows an inner peripheral surface 9a of the seal member 9 and an outer peripheral surface 2b3 of the flange portion 2b in order to reduce the axial dimension of the housing 7 and to reduce the size of the dynamic pressure bearing device 1. An example is shown in which a tapered seal space S ′ is formed between the opposing surfaces.

  Furthermore, as an example considering the retaining of the shaft member 2, for example, a configuration as shown in FIG. The seal space S ′ in the figure includes an upper outer peripheral surface 2b3 and an inner peripheral surface 9a of the seal member 9 facing the upper outer peripheral surface 2b3 among the outer peripheral surfaces defined by the axial step provided in the flange portion 2b. Formed between. In addition, the end surface 2 b 4 on the outer diameter side of the upper end surface 2 b 1 defined by the steps is opposed to the lower end surface 9 b of the seal member 9.

  With such a configuration, the sealing space S ′ has a sealing action due to centrifugal force and intercapillary force, and leakage of lubricating oil to the outside is prevented. Further, when the shaft member 2 is relatively displaced upward, the outer diameter side end surface 2b4 of the flange portion 2b is engaged with the lower end surface 9b of the seal member 9 in the axial direction, whereby the shaft member 2 is prevented from being detached.

  In the illustrated example, the seal member 9 has a form in which a portion of the lower end surface 9b that does not face the outer diameter side end surface 2b4 is protruded downward. Therefore, when the downward projecting portion 9 c of the seal member 9 is brought into contact with the upper end surface 8 b of the bearing sleeve 8, the seal member 9 can be easily positioned in the axial direction.

  FIG. 10 shows another embodiment of the multi-arc bearing constituting the first and second radial bearing portions R1, R2. In this embodiment, in the configuration shown in FIG. 3, the predetermined region θ on the minimum gap side of each eccentric arc surface 8a1 is configured by a concentric arc centered on the rotation axis O. Therefore, in each predetermined area θ, the radial bearing gap (minimum gap) is constant. The multi-arc bearing having such a configuration may be referred to as a tapered flat bearing.

  In FIG. 11, a region that is a radial bearing surface of the inner peripheral surface 8 a of the bearing sleeve 8 is formed by three arc surfaces 8 a 1, and the centers of the three arc surfaces 8 a 1 are offset from the rotation axis O by the same distance. Yes. In each region defined by the three eccentric arc surfaces 8a1, the radial bearing gap has a shape that is gradually reduced with respect to both circumferential directions.

  The multi-arc bearings of the first and second radial bearing portions R1 and R2 described above are all so-called three-arc bearings, but are not limited thereto, so-called four-arc bearings, five-arc bearings, and more than six arcs. A multi-arc bearing having a number of arc surfaces may be adopted. In addition to the configuration in which the two radial bearing portions are separated from each other in the axial direction as in the radial bearing portions R1 and R2, one radial bearing portion is provided over the upper and lower regions of the inner peripheral surface of the bearing sleeve 8. It is good also as a provided structure.

  Moreover, although the case where a multi-arc bearing is employ | adopted as radial bearing part R1, R2 is illustrated in the above embodiment, it can also be comprised with bearings other than this. As a bearing that can constitute the radial bearing portions R1 and R2, for example, although not shown, a plurality of shafts are provided in a region facing the radial bearing gap (region serving as a radial bearing surface) on the inner peripheral surface 8a of the bearing sleeve 8. An example is a step bearing in which a directional groove-shaped dynamic pressure groove is formed. Alternatively, instead of the axial groove, a herringbone-shaped or spiral-shaped inclined groove may be formed, and the dynamic pressure action of the lubricating fluid may be generated by the inclined dynamic pressure groove.

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and causes the hydrodynamic action in the radial bearing gap or the thrust bearing gap. It is also possible to use a fluid that can cause a dynamic pressure action, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or a lubricating grease.

1 is a cross-sectional view of a spindle motor for information equipment incorporating a fluid dynamic bearing device according to an embodiment of the present invention. It is a longitudinal cross-sectional view of a fluid dynamic bearing device. It is sectional drawing of a radial bearing part. It is an expanded sectional view which illustrates a thrust bearing clearance schematically. It is an expanded sectional view which illustrates schematically the thrust bearing gap of a comparative product. It is a figure which shows the theoretical calculation result of a contact start rotation speed. It is an expanded sectional view showing other examples of composition of seal space. It is an expanded sectional view showing other examples of composition of seal space. It is an expanded sectional view showing other examples of composition of seal space. It is sectional drawing which shows the other structural example of a radial bearing part. It is sectional drawing which shows the other structural example of a radial bearing part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 2a Shaft part 2b Flange part 2c Thrust receiving surface 3 Disc hub 4 Stator coil 5 Rotor magnet 7 Housing 8 Bearing sleeve 8b1 Thrust bearing surface 9 Sealing member 10 Reduction | restoration part 11 Inclined surface C Thrust bearing clearance S , S 'Seal space R1, R2 Radial bearing part T Thrust bearing part

Claims (5)

A housing having one end open, a bearing sleeve fixed inside the housing, a flange member projecting to the outer diameter side, a shaft member that rotates relative to the housing and the bearing sleeve, and the bearing sleeve A radial bearing portion that supports the shaft member in a radial direction by a dynamic pressure action of a fluid generated in a radial bearing gap between the shaft member and the shaft member, and a dynamic pressure action of a fluid generated in a thrust bearing gap A hydrodynamic bearing device comprising a thrust bearing portion that supports non-contact in the thrust direction,
One of the end surface of the bearing sleeve on the housing opening side and the end surface of the flange portion of the shaft member facing the bearing sleeve is a thrust bearing surface including a dynamic pressure groove region in which a plurality of dynamic pressure grooves are arranged, and the other is A thrust receiving surface that is axially opposed to the thrust bearing surface,
The thrust bearing gap is formed between the thrust bearing surface and the thrust receiving surface,
The dynamic bearing device according to claim 1, wherein the thrust bearing gap has a reduced portion having a smaller axial width toward the outer diameter side.   2. The hydrodynamic bearing device according to claim 1, wherein at least one of the thrust bearing surface and the thrust receiving surface of the reduced portion is an inclined surface.   3. The hydrodynamic bearing device according to claim 2, wherein r is a radial width of the inclined surface, h is a height of the inclined surface, and h / r ≦ 0.01.   The hydrodynamic bearing device according to claim 1, wherein the radial bearing portion is a multi-arc bearing.   A spindle motor of a disk device having the hydrodynamic bearing device according to any one of claims 1 to 4.

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