JP2011021649A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device which can be manufactured at low cost and can stably maintain high bearing performance. <P>SOLUTION: The fluid bearing device 1 is equipped with a bearing member 7 containing radial bearing surfaces A1, A2 and a shaft member 2 inserted into an inner periphery of the bearing member 7. A radial bearing clearance filled with a lubricating oil is formed between the radial bearing surfaces A1, A2 of the bearing member 7 and an outer peripheral surface 2a1 of the shaft member 2. An upper end of the radial bearing clearance is connected to a lower end of a seal clearance S for holding an oil surface of lubricating oil in an upper end opening of the bearing member 7. The bearing member 7 is formed of a sintered-metal porous body having a seal surface 7b1 facing the seal clearance S. Hole sealing parts 9 for sealing surface opening holes on these surfaces are provided in at least the seal surface 7b1 and a surface exposed outside in the bearing member 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device.

  The hydrodynamic bearing device supports a shaft member rotatably with an oil film of lubricating oil formed in a bearing gap. This hydrodynamic bearing device has characteristics such as high-speed rotation, high rotation accuracy, and low noise. In recent years, the hydrodynamic bearing device has been utilized as a motor bearing device for motors mounted on various electrical devices including information devices. More specifically, spindle motors for magnetic disk devices such as HDD, optical disk devices such as CD-ROM, CD-R / RW, DVD-ROM / RAM, etc., polygon scanner motors for laser beam printers (LBP), PCs It is suitably used as a motor bearing device such as a fan motor.

  For example, Patent Literature 1 includes a bearing member having at least one axial end opening and a shaft member inserted into the inner periphery of the bearing member as main components, and a radial bearing surface of the bearing member and an outer periphery of the shaft member. There has been disclosed a hydrodynamic bearing device in which a shaft member is supported in a radial direction by an oil film of lubricating oil formed in a radial bearing gap with a surface. As disclosed in Patent Document 1, the bearing member is often composed of a sintered metal bearing sleeve having a radial bearing surface and a non-porous housing in which the bearing sleeve is housed in the inner periphery. . This is because the oil film in the radial bearing gap can be prevented and the lubricating oil leakage to the outside of the bearing can be prevented. In addition, a seal member is formed in the opening of the bearing member (housing) so as to form a seal gap with one end leading to the radial bearing gap with the outer peripheral surface of the shaft member. The seal gap has a so-called buffer function, and always keeps the oil level of the lubricating oil within the axial range within the operating temperature range of the hydrodynamic bearing device. Thereby, the lubricating oil leakage from the bearing opening is prevented.

JP 2003-336636 A

  By the way, in recent years when the price of the disk device has been rapidly reduced, it is necessary to reduce the cost of the hydrodynamic bearing device. However, in the hydrodynamic bearing device described in Patent Document 1 including a number of members such as a housing, a bearing sleeve, and a seal member in addition to the shaft member, the manufacturing cost and management cost of the member, and the assembly cost between the members are also included. Is bulky. In addition, in order to stably maintain the desired bearing performance in such a configuration, it is necessary to increase the manufacturing accuracy of individual members and the assembly accuracy between the members, so that the cost reduction can be achieved. It becomes even more difficult.

  As one means for reducing the cost of the hydrodynamic bearing device, it is conceivable that the bearing sleeve is used as an insert part, and the housing and the seal member are injection molded with resin. However, in this case, due to molding shrinkage of the part injection-molded with resin and dimensional fluctuation due to temperature change, the fixing accuracy to the motor bracket, the oil retaining ability of the seal gap, and the width accuracy of the radial bearing gap are adversely affected. There is a risk. For this reason, it is difficult to stably exhibit and maintain the desired bearing performance.

  An object of the present invention is to provide a fluid dynamic bearing device that can be manufactured at low cost and can stably maintain high bearing performance.

  In order to solve the above problems, in the present invention, a bearing member having a radial bearing surface on the inner periphery and having at least one axial end opened, a shaft member inserted in the inner periphery of the bearing member, and a radial of the bearing member A radial bearing gap formed between the bearing surface and the outer peripheral surface of the shaft member, filled with lubricating oil, and one end in the axial direction lead to the radial bearing gap, and the oil surface of the lubricating oil is passed through one end opening of the bearing member. In a hydrodynamic bearing device having a seal gap to be held, the bearing member is made of a sintered metal porous body having a seal surface facing the seal gap, and at least the surface opening of the seal surface and the surface exposed to the outside The hydrodynamic bearing device is characterized by having a sealing portion for sealing. Here, the radial bearing surface is intended to be a surface on one side forming a radial bearing gap, and it does not matter whether a radial dynamic pressure generating portion such as a dynamic pressure groove is formed on this surface. .

  According to the configuration of the present invention, various functions that are satisfied by the three members of the housing, the bearing sleeve, and the seal member in Patent Document 1 can be satisfied by a single bearing member. Therefore, the number of members and the number of assembly steps between members can be reduced, and the cost of the hydrodynamic bearing device can be reduced. Also, in order to obtain this bearing member, it is not necessary to assemble the members, and the bearing member made of sintered metal has almost no shape (dimension) fluctuation due to temperature change, so high bearing performance is stable. Can be maintained. In addition to the externally exposed surface, the sealing surface is also provided with a sealing part, preventing the seepage of lubricating oil from the surface opening of the sealing surface and maintaining the desired sealing performance stably. can do.

  The sealing portion can be obtained, for example, by crushing each surface, impregnating the surface layer portion of each surface with a sealing material, or forming a film on each surface. The sealing part may be obtained using any of these methods, but when the sealing part is constituted by a film formed on each of the above surfaces, it is desirable to use this film as a conductive film. In particular, in a hydrodynamic bearing device for a spindle motor incorporated in a disc device, static electricity that charges the disc or the like due to friction with air during operation is grounded (generally, a motor bracket that holds the hydrodynamic bearing device on the inner periphery). This is because it is necessary to provide a conductive path for discharging. That is, even when the sealing portion is formed of a film, the conductive path can be prevented from being blocked by providing the film with conductivity. The conductive film can be obtained, for example, by forming a film with a resin material containing a conductive filler, or by forming a film by plating.

  By the way, in order to improve the bearing performance, it is effective to expand the bearing span of the radial bearing portion and increase the load capacity (moment rigidity) against the moment load. However, in the configuration of the present invention in which the bearing member is made of sintered metal, it is necessary to increase the volume of the seal gap as much as the lubricating oil can be retained even in the internal holes of the bearing member. Accordingly, in a hydrodynamic bearing device having a structure in which one end in the axial direction of the seal gap is connected to the radial bearing gap, that is, the seal gap and the radial bearing gap are stacked in the axial direction, the radial bearing portion is not taken without any measures. If the bearing span is increased, the axial dimension of the hydrodynamic bearing device becomes longer.

  Such a problem can be solved, for example, by increasing the density of the bearing member and reducing the porosity of the bearing member. This is because the total amount of lubricating oil retained in the internal holes of the bearing member can be reduced, and the volume (for example, axial dimension) of the seal gap can be shortened by this oil amount reduction. Here, the “porosity” is the ratio of the total volume of the internal pores per unit volume of the bearing member. However, if the porosity of the bearing member is reduced as a whole, the amount of the lubricating oil that oozes out into the radial bearing gap becomes insufficient, and the oil film may be cut off. For this reason, when the porosity of the bearing member is partially different, it is desirable to provide a radial bearing surface in a region having the highest porosity.

  In addition, as means for obtaining a bearing member having partially different porosities, for example, partial impregnation with a sealing material, or integration of a plurality of green compacts having mutually different porosities can be considered. .

  The bearing member can be formed in a cup shape in which only one end in the axial direction is opened, or can be formed in a cylindrical shape in which the other end in the axial direction is also opened. When the bearing member is formed in a cylindrical shape, by fixing the lid member to the other end of the bearing member, the lid member closes the other end opening of the bearing member and supports the shaft member in one thrust direction. A first thrust bearing portion can be formed.

  When the lid member closes the other end opening of the bearing member, it is necessary to ensure a sufficient fixing strength between the bearing member and the lid member. When the lid member is fixed to the inner peripheral surface of the bearing member as described in Patent Document 1, it is necessary to increase the thickness of the lid member in order to ensure a sufficient fixing strength between them. However, increasing the thickness of the lid member may lead to an undesirable situation such as an increase in the axial dimension of the hydrodynamic bearing device or a reduction in the bearing span of the radial bearing portion. It cannot be made.

  On the other hand, if the lid member is fixed to the outer peripheral surface of the bearing member, the fixed area can be increased by the difference in diameter between the inner peripheral surface and the outer peripheral surface, compared to the case where the lid member is fixed to the inner peripheral surface of the bearing member. Therefore, it is possible to increase the fixing strength of the lid member with respect to the bearing member (resistance to drop resistance of the lid member). In this case, the lid member requires a disk-shaped portion that closes the opening and a cylindrical portion that is fixed to the outer peripheral surface. It is sufficient to increase the length in the axial direction, and it is not necessary to thicken the disk-shaped portion. Moreover, even if the cylindrical portion is elongated in the axial direction, the axial dimension of the entire bearing device is not affected. Therefore, in order to ensure a sufficient resistance to coming off, it is desirable to fix the lid member to the outer peripheral surface of the bearing member.

  If the lid member fixed to the outer peripheral surface of the bearing member is a press-molded product, a cup-shaped lid member integrally having a disk-shaped portion and a cylindrical portion can be manufactured at low cost.

  The hydrodynamic bearing device may further include a second thrust bearing portion that supports the shaft member in the thrust other direction. In this case, the bearing member can be provided with a thrust bearing surface facing the thrust bearing gap of the second thrust bearing portion. Even in this case, it is desirable to provide the thrust bearing surface in the region with the highest porosity in order to prevent the amount of lubricating oil from seeping into the thrust bearing gap and the oil film from being cut out in the thrust bearing gap. .

  In the above configuration, if the axial dimension of the seal gap is 17% or less of the axial dimension of the hydrodynamic bearing device, the bearing span, particularly the rotational accuracy in the radial direction, is increased by expanding the bearing span of the radial bearing portion. Can be increased. In addition, the axial direction dimension of the hydrodynamic bearing device said here means the axial direction dimension except the axial direction dimension of the part which protruded from the opening part of the bearing member among axial members. Specifically, in the hydrodynamic bearing device 1 shown in FIGS. 2 and 7, the axial dimension of the bearing member 7. In the hydrodynamic bearing device 1 shown in FIG. 6, the outer bottom surface of the lid member 8 from the upper end of the bearing member 7. This is the axial dimension that leads to

  Further, it is desirable that the cylindricity of the outer peripheral surface of the bearing member (see JISB0621) is 10 μm or less, and the cylindricity of the radial bearing surface of the bearing member is 0.7 μm or less. As a result, the width accuracy of the radial bearing gap can be increased to increase the rotational accuracy in the radial direction, and the fixing accuracy of the bearing member (fluid bearing device) to the motor bracket can be increased to ensure high motor performance.

  As described above, according to the present invention, it is possible to provide a fluid dynamic bearing device that can be manufactured at low cost and can stably maintain high bearing performance.

It is sectional drawing which shows notionally the spindle motor for disk apparatuses. It is sectional drawing which shows the hydrodynamic bearing apparatus which concerns on 1st Embodiment of this invention. FIG. 4A is a sectional view of a bearing member, and FIG. 4B is a view showing a lower end surface of the bearing member. It is a figure which shows the upper end surface of a cover member. It is a principal part expanded sectional view of FIG. It is sectional drawing which shows the hydrodynamic bearing apparatus which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows the hydrodynamic bearing apparatus which concerns on 3rd Embodiment of this invention. It is a figure which shows typically the manufacturing process of the bearing member shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 conceptually shows one configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device. The 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, a disk hub 3 provided at one end of the shaft member 2, and a radial direction, for example. A stator coil 4 and a rotor magnet 5 which are opposed to each other through a gap, and a motor bracket 6 are provided. The stator coil 4 is attached to the outer periphery of the motor bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The bearing member 7 of the hydrodynamic bearing device 1 is fixed to the inner periphery of the motor bracket 6. One or a plurality (two in the illustrated example) of disks D such as magnetic disks are placed on the disk hub 3, and the disks D are fixed by a clamp mechanism (not shown). In the above configuration, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the disk hub 3 and the disk D held by the disk hub 3 are rotated. It rotates integrally with the shaft member 2.

  FIG. 2 shows the hydrodynamic bearing device 1 according to the first embodiment of the present invention. The hydrodynamic bearing device 1 includes a bearing member 7 having both ends opened in the axial direction, a shaft member 2 inserted into the inner periphery of the bearing member 7, and a lid member 8 that closes one end opening of the bearing member 7. The internal space is filled with lubricating oil. In the following description, for the sake of convenience, the description will proceed with the side on which the lid member 8 is provided as the lower side and the opposite side in the axial direction as the upper side.

  The shaft member 2 has a shaft portion 2a and a flange portion 2b. The shaft portion 2a and the flange portion 2b are made of a metal material having high rigidity and high wear resistance, such as stainless steel. A small-diameter portion 2a2 is formed at the lower end of the shaft portion 2a, and the shaft member 2 is formed by fitting and fixing the small-diameter portion 2a2 to the inner periphery of the perforated disk-like flange portion 2b. A method for fixing the shaft portion and the flange portion is arbitrary, and press-fitting, adhesion, welding (particularly laser welding) and the like can be employed. As the shaft member 2, a shaft member 2a and a flange portion 2b integrally formed by forging or the like can be used.

  The bearing member 7 has a substantially cylindrical shape with both axial ends open, and includes a sleeve portion 7a, a seal portion 7b disposed above the sleeve portion 7a, and a fixed portion 7c disposed below the sleeve portion 7a. And integrally.

  As shown in FIG. 3A, cylindrical radial bearing surfaces A1 and A2 forming radial bearing gaps between the inner peripheral surface 7a1 of the sleeve portion 7a and the outer peripheral surface 2a1 of the opposed shaft portion 2a are provided. They are provided separately at two axial positions. From the viewpoint of improving the width accuracy of the radial bearing gap, that is, the bearing performance of the radial bearing portions R1 and R2, the cylindricity of the radial bearing surfaces A1 and A2 is respectively set to 0.7 μm or less. Radial dynamic pressure generating portions formed by arranging a plurality of dynamic pressure grooves Aa1 and Aa2 in a herringbone shape are formed on the radial bearing surfaces A1 and A2, respectively. In the present embodiment, the upper dynamic pressure groove Aa1 is formed to be axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions), and the axis in the upper region from the axial center m. The direction dimension X1 is larger than the axial direction dimension X2 of the lower region. On the other hand, the lower dynamic pressure groove Aa2 is formed symmetrically in the axial direction, and the axial dimensions of the upper and lower regions thereof are equal to the axial dimension X2. With this configuration, when the shaft member 2 rotates, the lubricating oil interposed between the inner peripheral surface 7a1 of the sleeve portion 7a and the outer peripheral surface 2a1 of the shaft portion 2a is pushed downward (unbalanced pumping ability). In addition, you may form a radial dynamic pressure generation | occurrence | production part in the outer peripheral surface 2a1 of the axial part 2a which opposes.

  The lower end surface 7a2 of the sleeve portion 7a is provided with an annular thrust bearing surface B that forms a thrust bearing gap of the second thrust bearing portion T2 between the upper end surface 2b1 of the opposing flange portion 2b, and the thrust bearing. A thrust dynamic pressure generating portion is formed on the surface B. As shown in FIG. 3 (b), the thrust dynamic pressure generating portion alternately includes a plurality of dynamic pressure grooves Ba arranged in a spiral shape and hill portions shown by cross-hatching in the drawing to divide the grooves in the circumferential direction. Arranged. The thrust dynamic pressure generating portion may be formed on the upper end surface 2b1 of the opposing flange portion 2b.

  A seal surface 7b1 is provided on the inner peripheral surface of the seal portion 7b. Between the seal surface 7b1 and the outer peripheral surface 2a1 of the shaft portion 2a facing the seal surface 7b1, the upper end opens to the atmosphere and the lower end communicates with the radial bearing gap. A seal gap S is formed. The outer peripheral surface 2a1 of the shaft portion 2a is formed in a cylindrical surface shape having a constant diameter, while the seal surface 7b1 is formed in a tapered surface shape whose diameter is gradually reduced downward. Accordingly, the seal gap S has a tapered shape in which the gap width is gradually reduced downward.

  A lid member 8 formed of a metal material in a disc shape is fixed to the inner peripheral surface 7c1 of the fixing portion 7c by appropriate means such as press-fitting, bonding, and press-fitting adhesion (here, press-fitting adhesion). The upper end surface 8a1 of the lid member 8 is provided with an annular thrust bearing surface C that forms a thrust bearing gap of the first thrust bearing portion T1 between the opposed lower end surface 2b2 of the flange portion 2b, and the thrust bearing. A thrust dynamic pressure generating portion is formed on the surface C. In the present embodiment, the thrust dynamic pressure generating portion has a herringbone shape as shown in FIG. 4, and has a plurality of dynamic pressure grooves Ca bent in a V shape and a convex shape shown by cross hatching in the drawing to partition the dynamic pressure grooves Ca. The hills are arranged alternately in the circumferential direction. The thrust dynamic pressure generating portion may be formed on the lower end surface 2b2 of the opposing flange portion 2b.

  The bearing member 7 having the above configuration is formed of a sintered metal porous body, particularly a sintered metal porous body mainly composed of copper. Of the bearing member 7, a seal surface 7b1 and a surface exposed to the outside (here, an upper end surface and an outer peripheral surface of the seal portion 7b, an outer peripheral surface of the sleeve portion 7a, an outer peripheral surface and a lower end surface of the fixing portion 7c, and an inner peripheral chamfer) ) Is formed with a sealing portion 9 for sealing the surface openings of these surfaces. On the other hand, the sealing portion 9 is not formed on the inner peripheral surface 7a1 of the sleeve portion 7a provided with the radial bearing surfaces A1 and A2 or the lower end surface 7a2 of the sleeve portion 7a provided with the thrust bearing surface B. The lubricating oil can ooze out from the surface openings of the radial bearing surfaces A1 and A2 and the thrust bearing surface B, and the oil film formed in the radial bearing gap and the second thrust bearing gap is prevented from breaking (so-called oil film breakage). Because.

  As will be described later, in the present embodiment, the sealing portion 9 is constituted by the resin film formed on each of the above surfaces. In the present embodiment in which the sealing member 9 is formed on the inner peripheral surface 7c1 of the fixing portion 7c, the lid member 8 is bonded (press-fit) to the inner peripheral surface 7c1 of the fixing portion 7c. There is a possibility that sufficient adhesive force cannot be secured between the two. From this viewpoint, the sealing portion 9 is not formed on the inner peripheral surface 7c1 of the fixing portion 7c. However, for example, when the sealing portion 9 is formed by performing a plating process or a crushing process, a sufficient adhesive strength can be ensured between the lid member 8 and the bearing member 7. The sealing portion 9 may be formed on the inner peripheral surface 7c1.

  In the present embodiment, the sealing portion 9 is formed in a film shape that covers the sealing surface 7b1 and the surface exposed to the outside. The film-shaped sealing portion 9 is a resin material in which a thermosetting resin such as an epoxy resin, a phenol resin, or a melamine resin is used as a base resin on each of the surfaces, and an appropriate amount of a conductive filler is blended therein. Is applied by an appropriate means and then cured. The conductive filler to be blended with the base resin is not particularly limited, but for example, fibrous or powdery materials such as carbon fiber, carbon black, graphite, carbon nanomaterial, and metal powder can be used. Thus, the sealing part 9 has electroconductivity by forming the film-form sealing part 9 with the resin material containing a conductive filler.

Furthermore, the porosity of the bearing member 7 is partially different. Here, among the bearing members 7, the porosity of the inner diameter side region of the sleeve portion 7a provided with the radial bearing surfaces A1 and A2 and the thrust bearing surface B is relatively increased, while the porosity of the other regions is relatively set. It is made small. The porosity is the ratio of the total volume of the internal holes per unit volume of the bearing member 7 and is calculated by the following mathematical formula.
Porosity [%] = 100−Density ratio [%] = {1− (ρ1 / ρ0)} × 100
ρ1: density of the bearing member 7 ρ0: true density of the material having the same composition as the bearing member 7

  In the present embodiment, the above-described configuration is obtained by impregnating the inner hole in the outer diameter side region of the bearing member 7 with the sealing material and solidifying it. The sealing material is not particularly limited as long as it does not melt within the operating temperature range of the hydrodynamic bearing device 1 (maintains a solid state). For example, a low melting point metal such as a tin alloy or a zinc alloy, Melting glass and resin material can be used.

  The bearing member 7 having the above configuration is manufactured, for example, as follows.

  First, a raw powder mainly composed of copper powder is compacted to obtain a green compact, and then the green compact is sintered to obtain a sintered body. Next, the sintered body is sized so that the surface accuracy of each surface of the sintered body and the dimensional accuracy of each part are corrected to a predetermined accuracy, and the radial bearing surfaces A1 and A2 and the thrust bearing surface among the sintered bodies A dynamic pressure generating portion is molded in each of the portions to be B to obtain a bearing member 7 having a finished product shape. Next, a sealing material is impregnated into the internal holes of the outer diameter side region of the bearing member 7, and the impregnated sealing material is solidified. As a result, the bearing member 7 having a partially different porosity, specifically, a relatively high porosity in the inner diameter side region of the sleeve portion 7a and a relatively low porosity in the other regions is obtained. Then, the sealing member 7 shown in FIG. 2 and FIG. 3 is completed by forming the sealing part 9 in the sealing surface 7b1 and the surface exposed to the outside of the bearing member 7. However, the part which comprises the outer peripheral surface of the bearing member 7 among the sealing parts 9 is finished so that the cylindricity of the outer peripheral surface of the bearing member 7 may be 10 micrometers or less. This is to secure the fixing accuracy with respect to the motor bracket 6.

  The bearing member 7 manufactured as described above is supplied to the assembly process, and the shaft member 2 and the lid member 8 are assembled. When the cover member 8 is assembled, first, an adhesive is applied to the inner peripheral surface 7 c 1 of the fixing portion 7 c of the bearing member 7 or the outer peripheral surface of the cover member 8 with the shaft member 2 inserted into the inner periphery of the bearing member 7. Then, the outer peripheral surface of the lid member 8 is fitted (press-fitted) into the inner peripheral surface 7c1 of the fixed portion 7c. The lid member 8 is pushed forward as it is, and the lower end surface 7a2 of the sleeve portion 7a of the bearing member 7 and the upper end surface 8a1 of the lid member 8 are brought into contact with both end surfaces 2b1, 2b2 of the flange portion 2b (that is, both thrust bearing gaps). Set the gap width to 0). Next, after the shaft member 2 is pushed down by the total amount of the clearance widths of the thrust bearing gaps to position the lid member 8 in the axial direction, the adhesive interposed between the bearing member 7 and the lid member 8 is solidified. Let Thereby, the assembly of the lid member 8 and the setting of the width of the thrust bearing gap, that is, the assembly of the hydrodynamic bearing device 1 is completed. After the assembly is completed, the hydrodynamic bearing device 1 shown in FIG. 2 is completed by filling the internal space of the hydrodynamic bearing device 1 including the internal holes of the bearing member 7 with lubricating oil as a fluid.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the radial bearing surfaces A1 and A2 provided at two positions above and below the inner peripheral surface 7a1 of the sleeve portion 7a, and the shaft portion opposed thereto A radial bearing gap is formed between the outer peripheral surface 2a1 of 2a. As the shaft member 2 rotates, the oil film pressure in the radial bearing gaps is increased by the dynamic pressure action of the dynamic pressure grooves Aa1 and Aa2, and as a result, the radial bearing portion R1, which supports the shaft member 2 in a non-contact manner in the radial direction. R2 is formed separately at two axial positions. At the same time, between the lower end surface 2b2 of the flange portion 2b and the thrust bearing surface C provided on the upper end surface 8a1 of the lid member 8, and the thrust bearing surface B and flange provided on the lower end surface 7b2 of the sleeve portion 7b. First and second thrust bearing gaps are respectively formed between the upper end surface 2b1 of the portion 2b. As the shaft member 2 rotates, the oil film pressure in the thrust bearing gaps is increased by the dynamic pressure action of the dynamic pressure grooves Ca and Ba. As a result, the shaft member 2 is contactlessly supported in one thrust direction. A thrust bearing portion T1 and a second thrust bearing portion T2 that supports the thrust in the other direction are formed.

  Further, since the seal gap S has a tapered shape in which the radial dimension is gradually reduced toward the inner side of the bearing member 7, the lubricating oil in the seal gap S is drawn into the bearing member 7 by a capillary action. It is drawn inside. Further, the seal gap S has a buffer function that absorbs the volume change accompanying the temperature change of the lubricating oil filling the internal space of the bearing member 7, and always keeps the oil level of the lubricating oil within the range of the assumed temperature change. Hold in the seal gap S. From these configurations, lubricating oil leakage from the bearing member 7 is effectively prevented.

  As shown in FIG. 5 in an enlarged manner, the shaft member 2 is provided with a communication passage 10 that opens to the upper end surface 2b1 and the lower end surface 2b2 of the flange portion 2b. By providing such a communication path 10, the lubricating oil can be circulated between the first thrust bearing gap and the second thrust bearing gap via the communication path 10 during rotation of the shaft member 2. Thereby, pressure balance (especially pressure balance at the time of motor starting) can be taken between the first thrust bearing gap and the second thrust bearing gap.

  The communication passage 10 shown in FIG. 5 has a radial portion 10a and an axial portion 10b, so that the thrust bearing surfaces B and C provided with the dynamic pressure grooves Ba and Ca are avoided and opened to the inner diameter side thereof. It has a bent shape. More specifically, the outer diameter end of the radial direction portion 10a is in a space formed by the upper end surface 2b1 of the flange portion 2b, the inner peripheral chamfer of the bearing member 7, and the Nusumi portion 2a3 provided at the lower end portion of the shaft portion 2a. An axial portion 10b that is open and connected to the inner diameter end of the radial portion 10a extends along the outer peripheral surface of the small diameter portion 2a2 of the shaft portion 2a, and is a space on the inner diameter side of the thrust dynamic pressure generating portion provided on the thrust bearing surface C. Is open. In addition, the communication path 10 can be provided at a plurality of locations in addition to being provided at one location in the circumferential direction.

  During rotation of the shaft member 2, the inner periphery of the sleeve portion 7 a of the bearing member 7 is caused by an imbalance (see FIG. 3A) of the pumping ability of the radial dynamic pressure generating portions that are provided apart in two axial directions. Lubricating oil between the surface 7a1 and the outer peripheral surface 2a1 of the shaft portion 2a is pushed downward. For this reason, the pressure tends to increase in the space on the closed side inside the bearing, particularly in the space on the inner diameter side of the thrust bearing gap of the first thrust bearing portion T1. In such a case, if the dynamic pressure groove Ca of the first thrust bearing portion T1 is made into a pump-in type spiral shape often used in the conventional product, the lubricating oil interposed in the first thrust bearing gap is pushed into the inner diameter side. The pressure increase in the space on the inner diameter side than the first thrust bearing gap is promoted. In order to avoid this, it is desirable that the dynamic pressure groove Ca for generating a dynamic pressure action in the first thrust bearing gap has a herringbone shape (see FIG. 4) as described above.

  As described above, according to the configuration of the present invention, the single bearing member 7 can satisfy various functions that were satisfied by the three members of the housing, the bearing sleeve, and the seal member in Patent Document 1. it can. Therefore, the number of parts and the number of assembly steps can be reduced, and the cost of the hydrodynamic bearing device 1 can be reduced. Further, in order to obtain this bearing member 7, it is not necessary to assemble the members, and since the bearing member 7 made of sintered metal hardly changes in shape (dimension) due to temperature change, high bearing performance is achieved. Can be stably maintained.

  Further, because the bearing member 7 is formed of a sintered metal porous body, when the sealing surface 7b1 of the seal portion 7b is not subjected to a sealing treatment or the like, the seal gap S from the surface opening of the seal surface 7b1. As a result, the lubricating oil may ooze out and the desired sealing performance may not be ensured. On the other hand, in the present invention, since the sealing portion 7 is also provided in the seal surface 7b1, the seepage of the lubricating oil into the seal gap S can be prevented and high sealing performance can be stably maintained.

  In addition, since the porosity of the bearing member 7 is partially varied, the total amount of lubricating oil that can be held in the internal holes of the bearing member 7 can be reduced, and the seal gap S of the seal gap S can be reduced by this oil amount reduction. The axial dimension can be shortened. Therefore, the span of the radial bearing portions R1 and R2 can be expanded without increasing the axial dimension of the hydrodynamic bearing device 1, and the bearing performance (especially moment rigidity) can be enhanced. On the other hand, since the radial bearing surfaces A1 and A2 and the thrust bearing surface B are provided in the region having the highest porosity (the region having a relatively high porosity in the present embodiment) of the bearing member 7, during the bearing operation. Can positively exude the lubricating oil into the radial bearing gap and the second thrust bearing gap. For this reason, it is possible to prevent a situation in which the oil film runs out due to insufficient amount of lubricating oil interposed in the bearing gaps, and high bearing performance can be stably maintained.

  In addition, when this inventor verified, by employ | adopting the said structure, the axial direction dimension Ls of the seal | sticker clearance gap S (seal part 7b) is the axial direction dimension (here, the axis | shaft of the bearing member 7) of the fluid bearing apparatus 1. (Direction dimension) can be 17% or less of L. For example, in the configuration of Patent Document 1, since the axial dimension Ls of the seal gap is about 20% of the axial dimension L of the bearing member, the axial dimension of the seal gap S can be increased by adopting the configuration of the present invention. It can be shortened sufficiently.

  Incidentally, as shown in FIG. 1, the hydrodynamic bearing device 1 is used by being incorporated in the inner periphery of the motor bracket 6. At this time, in the present embodiment in which the surface opening of the outer peripheral surface of the bearing member 7 is sealed with the film-shaped sealing portion 9, the film-shaped sealing portion 9 is generally formed only of a resin material that is an insulating material. The static electricity charged during the rotation of the disk D cannot be efficiently released to the ground side, which may cause a disk crash in the worst case. On the other hand, since the surface opening of the outer peripheral surface of the bearing member 7 is sealed by forming the film-shaped sealing portion 9 with a resin material containing a conductive filler, the disk D rotates. Thus, the charged static electricity can be reliably discharged to the ground side through the path of the shaft member 2 → the bearing member 7 → the motor bracket 6.

  However, when the bearing member 7 is bonded and fixed to the motor bracket 6, there is a possibility that the conductive path may be blocked by the adhesive. It is desirable to apply a suitable conductive material across the lower end inner diameter end of the motor bracket 6 and form a conductive coating.

  From the viewpoint of securing the conductive path, the sealing portion 9 can be formed into a film by plating the predetermined surface of the bearing member 7. However, the sealing part 9 does not necessarily have to be formed in a film shape. For example, the surface opening can be sealed by applying a crushing process to the predetermined surface of the bearing member 7 or impregnating a surface layer portion of the predetermined surface with a sealing material. In these cases, a conductive path can be formed between the motor bracket 6 and the bearing member 7 made of sintered metal.

  Although one embodiment of the hydrodynamic bearing device 1 according to the present invention has been described above, the present invention is not limited to this. Hereinafter, other embodiments of the present invention will be described, but only differences from the hydrodynamic bearing device 1 described above will be described in detail, and substantially the same members and the like will be denoted by common reference numerals. Therefore, duplicate explanation is omitted.

  FIG. 6 shows a hydrodynamic bearing device 1 according to a second embodiment of the present invention. The main difference of the hydrodynamic bearing device 1 shown in FIG. 2 from that shown in FIG. 2 is that the lid member 8 is fixed to the outer peripheral surface of the bearing member 7. More specifically, the lid member 8 is formed in a cup shape integrally including a disk-shaped plate portion 8a and a cylindrical tube portion 8b extending upward from the outer diameter end of the plate portion 8a. The inner peripheral surface 8 b 1 is fixed to a small diameter outer peripheral surface 7 a 3 provided on the bearing member 7. The lid member 8 is formed in a cup shape integrally including the plate portion 8a and the cylindrical portion 8b by pressing a metal plate such as stainless steel. Thereby, the lid member 8 having such a shape can be manufactured at low cost.

  Thus, if the lid member 8 is fixed to the outer peripheral surface of the bearing member 7 (here, the small-diameter outer peripheral surface 7a3), compared to the case where the lid member 8 is fixed to the inner peripheral surface of the bearing member 7 (see FIG. 2), Since the fixed area can be increased by the difference in diameter between the inner peripheral surface and the outer peripheral surface, the fixing strength of the lid member 8 with respect to the bearing member 7 (the resistance to falling off of the lid member 8) can be increased. In this case, the lid member 8 requires a plate portion 8a that closes the lower end opening of the bearing member 7 and a cylindrical portion 8b that is fixed to the small-diameter outer peripheral surface 7a3. In order to increase the fixed area, it is sufficient to lengthen the cylindrical portion 8b in the axial direction, and it is not necessary to increase the thickness of the plate portion 8a. Moreover, even if the cylindrical portion 8b is elongated in the axial direction, the axial dimension of the entire hydrodynamic bearing device 1 is not affected. Therefore, it is possible to increase the slip-proof strength of the lid member 8 without affecting the axial dimension of the hydrodynamic bearing device 1 and the bearing spans of the radial bearing portions R1 and R2.

  In addition, the cylindrical portion 8 b of the lid member 8 can be used as an attachment portion for the motor bracket 6. Since both the lid member 8 and the motor bracket 6 are made of metal, high adhesive strength can be obtained between the two members. Therefore, even when the sealing portion 9 made of a resin film is formed on the outer peripheral surface of the bearing member 7, it is possible to prevent the fluid bearing device 1 from dropping from the motor bracket 6.

  Further, since the lid member 8 is formed of a metal material, the static electricity charged to the disk D or the like with the operation of the bearing device is reliably grounded through the path of the shaft member 2 → the lid member 8 → the motor bracket 6. Can be discharged to the side. When the lid member 8 and the motor bracket 6 are bonded and fixed, in order to prevent a situation in which the conductive path is blocked by an adhesive (usually an insulator), the outer side of the lower end of the lid member 8 is removed as necessary. A conductive material is applied across the diameter end and the inner diameter end of the lower end of the motor bracket 6 to form a conductive coating. If the conductive path is constituted by the lid member 8 in this way, the conductivity of the bearing member 7 becomes unnecessary. Therefore, even if the sealing portion 9 is made of a resin film, the sealing portion 9 itself has no conductivity. It becomes unnecessary. Therefore, it is not necessary to mix the conductive filler in the resin material forming the sealing portion 9, or the blending amount can be reduced. Thereby, the material cost at the time of forming the film-form sealing part 9 can be suppressed.

  In the hydrodynamic bearing device 1 shown in FIG. 6, a part or all of the radial bearing surface A <b> 2 provided on the inner peripheral surface 7 a 1 of the sleeve portion 7 a and the cylindrical portion 8 b of the lid member 8 in the bearing member 7 are axial. It overlaps. In such a case, when the cylindrical portion 8b of the metal lid member 8 is press-fitted into the outer peripheral surface 7a3 of the bearing member 7, the radial bearing surface A2 of the bearing member 7 is deformed, which adversely affects the bearing performance of the radial bearing portion R2. There is a risk. Therefore, the cylindrical portion 8b of the lid member 8 is bonded to the small-diameter outer peripheral surface 7a3 of the bearing member 7 by a gap (a radial gap between the inner peripheral surface 8b1 of the cylindrical portion 8b and the small-diameter outer peripheral surface 7a3 of the bearing member 7). And fixed with an adhesive that fills the gap in the radial direction). Thereby, the situation where the bearing performance of radial bearing part R2 falls can be avoided. If the radial bearing surface A2 is not deformed, the cylindrical portion 8b of the lid member 8 may be lightly press-fitted into the small-diameter outer peripheral surface 7a3 of the bearing member 7.

  In FIG. 6, the sealing portion 9 is formed over the entire axial length of the small-diameter outer peripheral surface 7a3 from the viewpoint of preventing the lubricating oil from seeping out from the surface opening of the small-diameter outer peripheral surface 7a3. It is not always necessary to form the sealing portion 9 in the region of the surface 7a3 where the cylindrical portion 8b of the lid member 8 is fitted. In particular, in the present embodiment in which the lid member 8 is bonded and fixed to the small-diameter outer peripheral surface 7a3, when the sealing portion 9 is formed of a resin film as in the first embodiment shown in FIG. 2, the small-diameter outer peripheral surface 7a3 Of these, it is desirable not to form the sealing portion 9 in the fitting region of the lid member 8. This is because sufficient adhesive strength is secured between the bearing member 7 and the lid member 8.

  FIG. 7 shows a hydrodynamic bearing device 1 according to a third embodiment of the present invention. The hydrodynamic bearing device 1 shown in the figure is common to the hydrodynamic bearing device 1 shown in FIG. 2 in that the lid member 8 is fixed to the inner peripheral surface of the bearing member 7, but the first regions 71 having different porosities. 2 and the second region 72 are integrated to differ from the embodiment shown in FIG. 2 in that the bearing member 7 is formed.

  Specifically, the porosity of the first region 71 is set to be higher than the porosity of the second region 72. The first region 71 has a cylindrical shape constituting a partial region on the inner diameter side of the sleeve portion 7a of the bearing member 7, and cylindrical radial bearing surfaces A1 and A2 are spaced apart at two locations in the axial direction on the inner peripheral surface. An annular thrust bearing surface B is provided on the lower end surface. For example, a radial dynamic pressure generating portion and a thrust dynamic pressure generating portion as shown in FIGS. 3A and 3B are formed on the radial bearing surfaces A1 and A2 and the thrust bearing surface B, respectively. On the other hand, the second region 72 has a small diameter cylindrical portion 72a that constitutes the seal portion 7b when integrated with the first region 71, and a large diameter that constitutes the outer diameter side partial region of the sleeve portion 7a and the fixing portion 7c. It has a substantially L-shaped cross section integrally including a cylindrical portion 72b, and the sealing portion 9 is formed on a sealing surface 7b1 formed of a small diameter cylindrical portion 72a and a surface exposed to the outside.

  The bearing member 7 having the above configuration can be manufactured, for example, as follows.

  First, as shown in FIG. 8, a raw powder mainly composed of metal powder is compression-molded, and a first green compact 71 ′ corresponding to a first region 71 having a relatively high porosity (low density), A second green compact 72 ′ corresponding to the second region 72 having a relatively low porosity (high density) is individually manufactured. The green compacts 71 ′ and 72 ′ having different densities can be obtained, for example, by using raw material powders having different particle sizes, or by using the same raw material powder and different compression ratios. At this stage, the radial dynamic pressure generating portion and the thrust dynamic pressure generating portion are not formed in the first green compact 71 ′, and the sealing portion 9 is not formed in the second green compact 72 ′. The outer diameter d1 of the first green compact 71 ′ is formed to be equal to or smaller than the inner diameter d2 of the second green compact 72 ′ in order to prevent the loss of both the green compacts 71 ′ and 72 ′ at the time of fitting. The

  Next, after the first green compact 71 ′ is fitted to the inner periphery of the second green compact 72 ′, the first green compact 71 ′ and the second green compact 72 ′ are mutually heated by heating at a predetermined temperature. Opposing surfaces are sinter bonded. As a result, both the green compacts 71 'and 72' are integrated, and the porosity of the arrangement area of the first green compact 71 'is higher than that of the arrangement area of the second green compact 72'. A sintered body is obtained. Next, dimension sizing is performed on the sintered body to correct the dimensions and the like of each part. Further, groove sizing is performed to form a radial dynamic pressure generating portion and a thrust dynamic pressure generating portion, respectively. Then, the sealing member 9 shown in FIG. 7 is completed by forming the sealing portion 9 on a predetermined surface of the sintered body.

  As described above, if the bearing member 7 made of sintered metal is formed by integrating the individually manufactured first region 71 and second region 72, the porosity (density) of each region can be easily controlled. And it becomes possible to carry out with high precision. Therefore, a sufficient amount of lubricating oil can be held in the internal holes in the first region 71 where the radial bearing surfaces A1 and A2 and the thrust bearing surface B are formed, while lubrication that can be held in the internal holes in the second region. The bearing member 7 with a reduced amount of oil can be easily obtained.

  In the above description, the case where the radial bearing portions R1 and R2 are configured by the dynamic pressure bearing by providing the dynamic pressure groove as the radial dynamic pressure generating portion has been described. However, as the radial dynamic pressure generating portion, a multi-arc surface, a step surface By providing the wavy surface, the radial bearing portion can be constituted by other known dynamic pressure bearings such as so-called multi-arc bearings, step bearings, and corrugated bearings. Moreover, a radial bearing part can also be comprised with what is called a perfect-circle bearing which made both two surfaces which oppose through a radial bearing clearance | interval the cylindrical surface.

  In the above description, the case where both thrust bearing portions T1 and T2 are composed of dynamic pressure bearings by providing dynamic pressure grooves as thrust dynamic pressure generating portions has been described. However, a step surface or a wavy surface is provided on the thrust bearing surface. By providing, one or both of the thrust bearing portions T1 and T2 can be configured by other known dynamic pressure bearings such as so-called step bearings and wave bearings. The first thrust bearing portion T1 can also be configured by a so-called pivot bearing that contacts and supports the lower end of the shaft member 2. In this case, the second thrust bearing portion T2 is basically unnecessary.

  In the above description, the case where the present invention is applied to the hydrodynamic bearing device 1 in which the shaft member 2 constitutes the rotating side and the bearing member 7 constitutes the stationary side has been described. Conversely, the bearing member 7 rotates. It is also possible to apply the present invention to a so-called fixed shaft type hydrodynamic bearing device in which the shaft member 2 forms the stationary side. Although not shown in detail, in the shaft-fixed type hydrodynamic bearing device, the disk hub 3 is fixed to the bearing member, and the shaft member is fixed to the motor bracket 6.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic bearing apparatus 2 Shaft member 7 Bearing member 7b Seal part 7b1 Seal surface 8 Lid member 9 Sealing part A1, A2 Radial bearing surface B, C Thrust bearing surface S Seal clearance R1, R2 Radial bearing part T1, T2 Thrust bearing part L Axial dimension of hydrodynamic bearing device Ls Axial dimension of seal gap

Claims (10)

A bearing member having a radial bearing surface on the inner periphery and having at least one axial end opening, a shaft member inserted in the inner periphery of the bearing member, and between the radial bearing surface of the bearing member and the outer peripheral surface of the shaft member In a hydrodynamic bearing device comprising a radial bearing gap formed in a cylinder and filled with lubricating oil, and a seal gap in which one end in the axial direction leads to the radial bearing gap and holds the oil level of the lubricating oil at one end opening of the bearing member ,
The bearing member is made of a sintered metal porous body having a seal surface facing the seal gap, and has a sealing portion that seals at least the surface opening of the seal surface and the surface exposed to the outside. Fluid bearing device.   The hydrodynamic bearing device according to claim 1, wherein the sealing portion is made of a conductive film.   3. The hydrodynamic bearing device according to claim 1, wherein the bearing member has a partially different porosity, and a radial bearing surface is provided in a region having the highest porosity.   The first thrust bearing portion that supports the shaft member in one thrust direction is formed by a lid member that opens the other end in the axial direction of the bearing member and closes the opening at the other end. The hydrodynamic bearing device according to item.   The hydrodynamic bearing device according to claim 4, wherein a lid member is fixed to the outer peripheral surface of the bearing member.   The hydrodynamic bearing device according to claim 5, wherein the lid member is a press-formed product. And a second thrust bearing portion for supporting the shaft member in the thrust other direction,
The hydrodynamic bearing device according to any one of claims 4 to 6, wherein the bearing member has a thrust bearing surface facing a thrust bearing gap of the second thrust bearing portion.   The hydrodynamic bearing device according to claim 7, wherein the porosity of the bearing member is partially varied, and a thrust bearing surface is provided in a region having the highest porosity.   The hydrodynamic bearing device according to any one of claims 1 to 8, wherein an axial dimension of the seal gap is 17% or less of an axial dimension of the hydrodynamic bearing device.   The hydrodynamic bearing device according to any one of claims 1 to 9, wherein a cylindricity of the outer peripheral surface of the bearing member is 10 µm or less, and a cylindricity of the radial bearing surface of the bearing member is 0.7 µm or less.

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