JP2005331033A - Dynamic pressure bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing device for improving abrasion resistance of a thrust bearing part. <P>SOLUTION: A flange part 2b of a shaft member 2 is formed of resin, and pressure is generated by the dynamic pressure action of fluid in thrust bearing clearance between its end surface 2b1 and a housing inner bottom surface 7c1, and the shaft member 2 is supported in a noncontact state in the thrust direction by this pressure. An inclined face 24 approaching the inner bottom surface 7c1 toward the outer diameter side, is formed in a part facing the thrust bearing clearance C of the end surface 2b1 of the flange part 2b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrodynamic bearing device. This bearing device is a spindle motor, laser beam printer (LBP) such as information equipment, magnetic disk devices such as HDD and FDD, optical disk devices such as CD-ROM and DVD-ROM, magneto-optical disk devices such as MD and MO, etc. This is suitable for a polygon scanner motor 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 these required performances is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing device having characteristics excellent in the required performance has been studied as this type of bearing. Or actually used.

  As an example of the hydrodynamic bearing device, Japanese Patent Laid-Open No. 2002-61641 (Patent Document 1) discloses a bottomed cylindrical housing, a bearing member fixed to the inner periphery of the housing, and an inner peripheral surface of the bearing member. A shaft member inserted into the shaft, 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 effect generated when the shaft member and the bearing sleeve rotate relative to each other are disclosed.

Of the radial bearing portion and the thrust bearing portion, the thrust bearing portion is pressurized by the dynamic pressure action of oil in the thrust bearing gap between the flange member both end faces and the housing bottom face and the end face of the bearing sleeve facing each other. Is generated to support the shaft member 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. There is a case where the wear of the sliding surface due to is sometimes a problem, and further improvement of wear resistance is desired. In particular, when the flange portion is formed of a resin, wear tends to proceed more easily than when the metals are slid, and the bearing performance may be deteriorated in a short period of time due to the influence of wear powder.

  Accordingly, an object of the present invention is to provide a dynamic pressure bearing device capable of suppressing wear of a thrust bearing portion.

  In order to achieve the above object, a hydrodynamic bearing device according to the present invention provides a fluid dynamic pressure in a thrust bearing gap between a shaft member having a shaft portion and a flange portion, and an end surface of the flange portion and a surface facing the shaft member. In the hydrodynamic bearing device comprising a thrust bearing portion that generates pressure by the action and supports the shaft member in the thrust direction without contact with this pressure, the flange portion end surface facing the thrust bearing gap is made of resin, and the end surface At least a portion facing the thrust bearing gap is an inclined surface whose outer diameter side approaches the opposing surface.

  Thereby, the outermost diameter part of the part which faces a thrust bearing clearance among the end surfaces of a flange part becomes the minimum width of a thrust bearing clearance. This portion is also the portion with the fastest peripheral speed in the thrust bearing gap. In this case, since the pumping function by the dynamic pressure generating means such as the dynamic pressure groove is enhanced at the minimum width portion, the contact time between the thrust bearing surface and the thrust receiving surface at the time of starting / stopping the motor can be shortened. It is possible to suppress wear at the thrust bearing portion. The inclined surface may be a curved surface as well as a flat tapered surface.

  The inclined surface of the end surface of the flange portion can also be formed by utilizing a difference in sink marks that occurs when the resin portion of the shaft member is cured. For example, the inner diameter side of the flange end face that faces the thrust bearing gap is made of a thick resin, and the outer diameter side is made of a thinner resin (thickness / thinness is distinguished by the axial thickness). When formed, since the amount of sink in the axial direction is larger on the inner diameter side than on the outer diameter side when the resin is cured, an inclined surface can be provided on the end surface of the flange portion due to the difference in the sink amount.

  The shaft member is provided with an outer shaft portion that forms an outer peripheral surface of the shaft portion and an inner shaft portion that is disposed on the inner periphery of the outer shaft portion, and the outer shaft portion is formed of metal, and the inner shaft portion and the flange portion Are integrally formed of resin, the inner diameter side of the flange portion is formed of a thicker resin than the outer diameter side because the inner shaft portion exists. Therefore, a difference in sink amount is produced between the inner diameter side and the outer diameter side of the flange portion, and thereby an inclined surface can be formed on the end surface of the flange portion.

  The inclination angle θ of the inclined surface is set to θ ≦ 0.6 °, preferably θ ≦ 0.3 °. This is because, as a result of verification by the present inventors, it has been found that, at an inclination angle exceeding this upper limit value, the contact rotational speed becomes excessive, leading to a decrease in the dynamic pressure effect.

  The motor having the hydrodynamic bearing device, the rotor magnet, and the stator coil described above has high durability while having high rotational accuracy, and is suitable as a motor for information equipment.

  According to the present invention, since wear in the thrust bearing portion can be suppressed, the bearing performance of the hydrodynamic bearing device can be stably maintained for a long period of time.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 2 shows a spindle motor used in a disk drive device such as an HDD as an example of an information equipment spindle motor incorporating the fluid dynamic bearing device 1. This motor includes a dynamic pressure bearing device 1, a rotating member 3 (disk hub) attached to a shaft member 2 of the dynamic pressure bearing device 1, a stator coil 4 and a rotor magnet that are opposed to each other with a radial gap, for example. 5 and a bracket 6. The stator coil 4 is attached to the outer periphery of the bracket 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 disks D such as magnetic disks on the outer periphery thereof. A housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the bracket 6. When the stator coil 4 is energized, the rotor magnet 5 is rotated by an exciting force generated between the stator coil 4 and the rotor magnet 5, and the disk hub 3 and the shaft member 2 are rotated accordingly.

  FIG. 3 shows an example of the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes radial bearing portions R1 and R2 that support the shaft member 2 in the radial direction, and thrust bearing portions T1 and T2 that support the shaft member 2 in the thrust direction. Both R1 and R2 and the thrust bearing portions T and T2 are configured by dynamic pressure bearings. The dynamic pressure bearing forms a bearing surface having a dynamic pressure groove on one of the rotation side member and the fixed side member, and forms a smooth receiving surface opposite to the bearing surface on the other side to rotate the rotation side member. Occasionally, pressure is generated in the bearing gap between the bearing surface and the receiving surface by the hydrodynamic action of the fluid, and the rotating side member is rotatably supported in a non-contact state.

  Hereinafter, a specific configuration of the fluid dynamic bearing device 1 will be described.

  As shown in FIG. 3, the hydrodynamic bearing device 1 according to the present embodiment includes a bottomed cylindrical housing 7 having an opening 7 a at one end, and a cylindrical bearing sleeve fixed to the inner peripheral surface of the housing 7. 8, the shaft member 2, and a seal member 10 fixed to the opening 7 a of the housing 7 are included as main bearing constituent members. In the following description, for convenience of explanation, the description will proceed with the opening side of the housing 7 as the upper side and the opposite side in the axial direction as the lower side.

  The housing 7 is formed in a bottomed cylindrical shape including a cylindrical side portion 7b and a bottom portion 7c. In this embodiment, the bottom 7c is formed of a thin disk-shaped thrust plate that is a separate member from the side 7b. The thrust plate 7c is attached to the lower opening of the side portion 7b by adhesion, press-fitting, or a combination thereof, so that the housing 7 with one end sealed is formed. The bottom 7c of the housing 7 may be integrated with the side 7b. The side portion 7b and the bottom portion 7c of the housing 7 can be formed of either a metal material or a resin material.

  As will be described later, the shaft member 2 is a composite product of resin and metal, and includes a shaft portion 2a and a flange portion 2b projecting to the outer diameter side at the lower end of the shaft portion 2a. The lower end surface 2b1 of the flange portion 2b is opposed to the upper end surface 7c1 of the thrust plate 7c, and the upper end surface 2b2 of the flange portion 2b is opposed to the lower end surface 8c of the bearing sleeve 8.

  In the present embodiment, the portion of the upper end surface 7c1 of the thrust plate 7c that faces the lower end surface 2b1 of the flange portion 2b becomes the thrust bearing surface of the lower thrust bearing portion T1. As shown in FIG. 4, in a partial region of this thrust bearing surface, for example, near the central portion in the radial direction, a plurality of dynamic pressure grooves P1 and a back portion P2 forming a hill between the dynamic pressure grooves P1 are spirally formed. An annular dynamic pressure groove region P arranged in the above is formed. The dynamic pressure groove shape of the dynamic pressure groove region P is arbitrary as long as it generates dynamic pressure, and may be a herringbone shape, for example.

  The bearing sleeve 8 is formed in a cylindrical shape with an oil-containing sintered metal obtained by impregnating a porous material, in particular, a sintered metal mainly containing copper with a lubricating oil (or lubricating grease). On the inner peripheral surface 8a of the bearing sleeve 8, the radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2 are provided apart from each other in the axial direction. A dynamic pressure groove is formed. In addition, as the shape of the dynamic pressure groove, a spiral shape, an axial groove shape, or the like may be adopted, and the radial bearing surface having the dynamic pressure groove may be formed on the outer peripheral surface of the shaft portion 2a of the shaft member 2. Good. Further, the bearing sleeve 8 can be formed of a soft metal such as brass or copper alloy in addition to the porous material. An annular dynamic pressure groove region (not shown) in which a plurality of dynamic pressure grooves are arranged in a spiral shape is formed on the lower end surface 8 c of the bearing member 8. In this dynamic pressure groove region, the shape of the dynamic pressure groove is arbitrary, and a herringbone shape may be adopted.

  As shown in FIG. 3, the seal member 10 is annular, and is fixed to the inner peripheral surface of the opening 7 a of the housing 7 by means such as press-fitting and bonding. In this embodiment, the inner peripheral surface 10 a of the seal member 10 is formed in a cylindrical shape, and the lower end surface of the seal member 10 is in contact with the upper end surface 8 b of the bearing member 8.

  The shaft portion 2a of the shaft member 2 is inserted into the inner peripheral surface 8a of the bearing sleeve 8, and the flange portion 2b is accommodated in a space portion between the lower end surface 8c of the bearing member 8 and the upper end surface 7c1 of the thrust plate 7c. The tapered surface 2a1 of the shaft portion 2a is opposed to the inner peripheral surface 10a of the seal member 10 via a predetermined gap, thereby gradually moving toward the outside direction of the housing 7 (upward in the same figure) therebetween. An expanding tapered seal space S is formed. When the shaft member 2 rotates, the tapered surface 2a1 of the shaft portion 2a also functions as a so-called centrifugal force seal. The interior space of the housing 7 (including the pores inside the bearing sleeve 8) sealed with the seal member 10 is filled with lubricating oil, and the oil level is in the seal space S. The seal space S can be a cylindrical space having the same diameter in the axial direction in addition to such a tapered space.

  In the above embodiment, when the shaft member 2 is rotated by the rotation of the motor, in the radial bearing portions R1 and R2, the radial bearing surface of the inner periphery of the bearing sleeve 8 and the outer peripheral surface of the shaft portion 2a (radial receiving surface) opposed thereto. Pressure is generated in the radial bearing gap between the shaft member 2 and the shaft portion 2a of the shaft member 2 so that the shaft portion 2a of the shaft member 2 is rotatably supported in the radial direction. Further, in the lower thrust bearing portion T1, a dynamic pressure groove region P formed on the upper end surface 7c1 (thrust bearing surface) of the thrust plate 7c, and a lower end surface 2b1 (thrust receiving surface) of the flange portion 2b facing the same. Pressure is generated by the dynamic pressure action of the lubricating oil in the thrust bearing gap between them, and at the same time, in the upper thrust bearing portion T2, a dynamic pressure groove region (not shown) formed in the bearing sleeve end surface 8c (thrust bearing surface); Since pressure is generated by the dynamic pressure action of the lubricating oil in the thrust bearing gap between the upper end surface 2b2 (thrust receiving surface) of the flange portion 2b facing the flange portion 2b, the flange portion 2b of the shaft member 2 is rotatable in the thrust direction. Is supported in a non-contact manner.

  As described above, the dynamic pressure groove region P is formed on the upper end surface 7c1 of the thrust plate 7c and the lower end surface 8c of the bearing sleeve 8, and on either one or both of the both end surfaces 2b1, 2b2 of the flange portion 2b. It can also be formed. In this case, the upper end surface 7c1 of the thrust plate 7c or the lower end surface 8c of the bearing sleeve 8 functions as a thrust receiving surface without a dynamic pressure groove.

  As shown in FIG. 1, the shaft member 2 has a composite structure of resin and metal. The resin portion has a configuration in which an inner shaft portion 22 extending in the axial direction and a flange portion 2b projecting to the outer diameter side of the inner shaft portion 22 are integrally formed. The outer shaft portion 22 that covers the outer periphery of the inner shaft portion 22 is formed of a hollow cylindrical metal material, for example, stainless steel having excellent wear resistance. As the resin material, PEEK, PPS, LCP, 9T nylon or the like can be used, and a filler such as glass fiber, carbon fiber, or conductive agent is blended with the base resin as necessary. In particular, when carbon fiber is used, a PAN-based carbon fiber having an average fiber diameter of 1 to 12 μm and an average fiber length of 100 to 500 μm is used as a base resin in a proportion of 5 to 30 vol%. It is preferable to mix and use.

  In order to prevent separation between the outer shaft portion 21 formed of a metal material and the inner shaft portion 22 and the flange portion 2b formed of a resin material, at the lower end of the outer shaft portion 21, the end portion 21a is connected to the flange portion 2b. The upper end of the outer shaft portion 21 is embedded and is engaged with the inner shaft portion 22 in the axial direction via an engaging portion made of, for example, a tapered surface. In order to prevent the outer shaft portion 21 from rotating, for example, the outer shaft portion 21 is engaged with the inner shaft portion 22 or the flange portion 2b in the circumferential direction on the inner peripheral surface of the outer shaft portion 21 or the outer peripheral surface of the outer shaft portion 21 embedded in the flange portion 2b. It is desirable to provide unevenness that can be combined.

  In the present invention, as shown in an enlarged view in FIG. 1, a curved surface that is closer to the opposite surface (the upper end surface 7c1 of the thrust plate 7c in this embodiment) on the lower end surface 2b1 of the flange portion 2b toward the outer diameter side. A slanted surface 24 is formed. By forming the inclined surface 24 in this manner, the axial bearing width (gap width) of the thrust bearing gap C between the dynamic pressure groove region P and the inclined surface 24 is reduced toward the outer diameter side, and the outermost side thereof is reduced. The diameter portion is the minimum width portion Wmin of the thrust bearing gap C. During the rotation of the shaft member 2, in the thrust bearing gap C, the peripheral speed of the minimum width portion is the largest, so that the pumping capacity generated in the dynamic pressure groove region P increases, and therefore sufficient dynamic pressure is achieved even at a low rotational speed. An effect can be obtained. Thereby, the contact start rotation speed of the bearing device 1 can be kept low, and the wear at the thrust bearing portion T1 due to the sliding contact between the end surface 2b1 of the flange portion 2b and the upper end surface 7c1 of the thrust plate 7c can be suppressed. It becomes possible. Therefore, high durability can be ensured even in applications where the motor is frequently started and stopped.

  Here, the contact start rotation speed is a rotation at which the end surface 2b1 of the flange portion 2b and the surface 7c1 facing the flange 2b are in contact with each other at a lower speed, and the both surfaces 2b1 and 7c1 are not in contact with each other at a higher speed. Say speed. If the contact start rotation speed is lowered, the contact time between the two surfaces 2b1 and 7c1 immediately after the start of the motor or immediately before the stop is shortened, so that wear at the thrust bearing portion T1 can be suppressed.

  1 shows the case where the dynamic pressure groove region P is formed on the upper end surface 7c1 of the thrust plate 7c, but the case where the dynamic pressure groove region P is formed on the lower end surface 2b1 of the flange portion 2b is also shown. The same effect can be obtained by forming the inclined surface 24 on the lower end surface 2b1.

  The method of forming the inclined surface 24 is arbitrary. In addition to forming the inclined surface 24 by post-processing such as polishing, an inclined portion corresponding to the inclined surface shape is provided on the molding surface of the mold for molding the resin portion. Thus, the inclined surface 24 can be formed simultaneously with the injection molding of the resin portions such as the flange portion 2b and the inner shaft portion 22.

  In particular, as in the present embodiment, when resin is disposed on the shaft core portion of the shaft portion 2a and integrated with the resin of the flange portion 2b, the outer diameter of the lower end surface 2b1 of the flange portion 2b is the outer diameter. Compared to the side, the resin thickness in the axial direction is increased by the amount of resin in the inner shaft portion 22. Therefore, the axial sink when the resin hardens is larger on the inner diameter side of the lower end surface 2b1 and smaller on the outer diameter side. Therefore, the inclined surface 24 can be formed simultaneously with the curing of the resin due to the difference in the amount of sink, and in this case, the post-processing and the processing of the mold forming surface described above are not necessary, so that the cost can be further reduced. Can do. Such an effect is obtained when the resin thickness on at least the inner diameter side of the lower end surface 2b1 is larger than that on the outer diameter side. Therefore, in the case where the inner shaft portion 22 made of resin is formed over the entire length of the shaft portion 2a as in the illustrated example, the same effect is expected when the inner shaft portion 22 is formed limited to the lower side of the shaft portion 2a. it can.

  The enlarged view of FIG. 1 illustrates the case where the entire lower end surface 2b1 of the flange portion 2b is an inclined surface 24. However, the inclined surface 24 is at least a portion facing a thrust bearing gap (dynamic pressure) that generates a dynamic pressure action. It is sufficient if it is formed in a portion facing the groove region P), and other portions can be flat surfaces having no inclination, for example. In this enlarged view, the inclined surface 24 is curved, but it may be formed in a tapered surface with a straight section. The curved inclined surface 24 may be a complex curved surface having two or more curvatures in addition to being formed with a single curvature.

  Further, FIG. 1 shows a case where the inclined surface 24 is provided on the lower end surface 2b1 of the flange portion 2b. However, the shaft of the thrust bearing gap is disposed on the upper end surface 2b2 constituting the upper thrust bearing portion T2 toward the outer diameter side. A similar inclined surface whose direction width is reduced may be formed. An inclined surface can be formed on both the lower end surface 2b1 and the upper end surface 2b2 of the flange portion 2b.

  In order to confirm the above effect, the theoretical calculation of the contact start rotation speed was performed on the product of the present invention.

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 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 30 °
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.

  As a result of theoretical calculation based on the above conditions, as the inclination angle of the inclined surface 24 (inclination angle with respect to the plane orthogonal to the axial direction) θ decreases, the contact start rotational speed decreases and θ exceeds 0.6 °. It was found that the contact start rotation speed was excessively increased. Therefore, the inclination angle θ of the inclined surface 24 is set to 0.6 ° or less, preferably 0.3 ° or less.

  The present invention is not limited to the hydrodynamic bearing device 1 having the thrust bearing portion T1 between the lower end surface 2b1 of the flange portion 2b and the bottom portion 7c of the housing 7, and the thrust bearing portion is a hydrodynamic bearing. The constructed hydrodynamic bearing device can be widely applied in general. For example, the present invention is similarly applied to a hydrodynamic bearing device (not shown) in which the thrust bearing gap of the thrust bearing portion is formed on the opening-side end surface of the housing 7 and the end surface of the rotating member (for example, the disk hub 3) opposed thereto. can do.

  Moreover, although the case where the dynamic pressure bearing which has a dynamic pressure groove was used as radial bearing part R1, R2 was demonstrated, as radial bearing part R1, R2, it is a shaft member 2 with the oil film of the lubricating oil formed in the radial bearing clearance. Can be used as long as the bearing is supported in the radial direction in a non-contact manner. For example, a bearing (arc bearing) in which a region serving as a radial bearing surface is configured by a plurality of arcs, a step bearing, and a region serving as a radial bearing surface are provided. Also, a bearing having a perfect circular cross section without a dynamic pressure groove (a perfect circular bearing) can be used.

It is sectional drawing of the shaft member used for the hydrodynamic bearing apparatus concerning this invention, and its principal part enlarged view. It is sectional drawing of the spindle motor which uses a dynamic-pressure bearing apparatus. It is sectional drawing of a hydrodynamic bearing apparatus. It is a top view of the inner bottom face of a thrust plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 2a Shaft part 2b Flange part 2b1 Lower end surface 2b2 Upper end surface 3 Disc hub 4 Stator coil 5 Rotor magnet 7 Housing 7c Bottom part (thrust plate)
7c1 Top surface (opposite surface)
8 Bearing sleeve 8a Inner peripheral surface 8c End surface 10 Seal member 10a Inner peripheral surface 21 Inner shaft portion 22 Outer shaft portion 24 Inclined surface C Thrust bearing gap P Dynamic pressure groove region R1 First radial bearing portion R2 Second radial bearing portion T1 First One thrust bearing part T2 Second thrust bearing part θ Inclination angle

Claims (5)

Pressure is generated by a fluid dynamic pressure action in a thrust bearing gap between a shaft member having a shaft portion and a flange portion, and an end surface of the flange portion and a surface facing the flange portion. In a hydrodynamic bearing device comprising a thrust bearing portion for contact support,
The dynamic pressure is characterized in that the end face of the flange portion facing the thrust bearing gap is made of resin, and at least the portion of the end face facing the thrust bearing gap is an inclined surface with the outer diameter side approaching the opposing face Bearing device. 2. The hydrodynamic bearing device according to claim 1, wherein an inner diameter side of the end face of the flange portion facing the thrust bearing gap is formed of a thick resin, and an outer diameter side thereof is formed of a thinner resin. The shaft member includes an outer shaft portion that forms an outer peripheral surface of the shaft portion, and an inner shaft portion that is disposed on the inner periphery of the outer shaft portion. The outer shaft portion is made of metal, and the inner shaft portion and the flange portion. The hydrodynamic bearing device according to claim 1, wherein is integrally formed of resin. 2. The hydrodynamic bearing device according to claim 1, wherein an inclination angle θ of the inclined surface formed on the end surface of the flange portion is θ ≦ 0.6 °. A motor comprising the fluid dynamic bearing device according to claim 1, a rotor magnet, and a stator coil.