JP2008298236A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance fixing strength of a shaft part of a shaft member and a flange part at low costs. <P>SOLUTION: A shaft member 2 has: a shaft part 21 having a radial bearing face A; and a flange part 23 extending toward an outside diameter at one end of the shaft part 21. The flange part 23 is fixed to a bottom end of the shaft part 21 by friction press-fitting. An end face of the flange part 23 is coated with a coating layer 24 having thrust bearing faces B, C. <P>COPYRIGHT: (C)2009,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 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, magnetic disk devices such as HDDs, optical disk devices such as CD-ROM, CD-R / RW, DVD-ROM / RAM, spindle motors such as magneto-optical disk devices such as MD and MO, laser beams, etc. It is preferably used as a motor bearing device such as a polygon scanner motor of a printer (LBP), a color wheel motor of a projector, and a fan motor.

  For example, a hydrodynamic bearing device for a spindle motor includes a bearing sleeve and a shaft member that is inserted into the inner periphery of the bearing sleeve and rotates relative to the bearing sleeve. As the shaft member, a member having a shaft portion having a radial bearing surface and a flange portion projecting to one end outer diameter side of the shaft portion is often used. As the shaft member with flange, there are an integral type in which the shaft portion and the flange portion are integrally formed by cutting, forging, and the like, and a separate type in which the shaft portion and the flange portion manufactured individually are integrated by appropriate means. .

The integral-type flanged shaft member can secure a high fastening strength between the shaft portion and the flange portion, but on the other hand, a dedicated processing facility is required for the production thereof, and the cost is extremely high. Therefore, recently, the flanged shaft member may be a separate type. Various types of shaft members with flanges have been proposed. For example, (1) the flange portion is a shaft that has a fixing strength sufficient to satisfy the impact resistance required for the shaft member. Screwed and fixed to one end of the part (see, for example, Patent Document 1), (2) One end of the shaft part is fitted to the inner periphery of the annular flange part, and laser is irradiated to one end of the fitting part to produce the shaft part (See Patent Document 2), (3) Protrusion is provided on at least one end surface of the mutually opposing shaft portion and flange portion, and the protrusion is attached to the other end. Known is one that is resistance-welded to the end face (see, for example, Patent Document 3).
JP 2004-84864 A JP 2000-324753 A JP 2004-340368 A

  By the way, in recent years when the price of information equipment has been remarkably progressing, it is required to further reduce the cost of the hydrodynamic bearing device. Therefore, the cost of the shaft member, which is a constituent member of the hydrodynamic bearing device, is further reduced. There is a need to do that. However, with the means (1), an increase in processing cost due to the provision of screw grooves in the shaft portion and an increase in component cost due to an increase in the number of components are inevitable. With the means (2), the flange portion can be firmly fixed to one end of the shaft portion without increasing the number of parts, but it is difficult to use for mass production because a high investment is required. Further, in the method (3), the flange portion can be firmly fixed to one end of the shaft portion as in (2), but the shaft portion or the flange portion is often formed of a difficult-to-work material such as stainless steel. It is not easy to form the projections on the end face of the metal plate with high accuracy and at low cost.

  An object of the present invention is to increase the fixing strength of the flange portion with respect to the shaft portion at a low cost, thereby making it possible to provide a fluid bearing device having high rotational accuracy and high reliability at a low cost.

  In order to solve the above-described problems, the present invention includes a bearing sleeve and a shaft member that is inserted into the inner periphery of the bearing sleeve and rotates relative to the bearing sleeve, and the shaft member has a shaft portion having a radial bearing surface; A hydrodynamic bearing device having a flange portion projecting to one end outer diameter side of the shaft portion, wherein the shaft portion of the shaft member and the flange portion are friction-welded. The radial bearing surface here is intended to form a radial bearing gap with the inner peripheral surface of the bearing sleeve, and a dynamic pressure generating portion such as a dynamic pressure groove is formed on this surface. It does not matter whether or not.

  As described above, if the shaft portion and the flange portion of the shaft member are friction-welded, it is not necessary to use other media such as a screw, a laser, or an electric current when providing the flange portion at one end of the shaft portion. In addition, there is no need to provide a thread groove at one end of the shaft portion, and no protrusion on the end surface of the shaft portion or the flange portion facing each other, simplifying the end surface shape of the shaft portion and the flange-shaped material facing each other. Therefore, the cost of the shaft member can be reduced. On the other hand, since the shaft part and the whole end surface of a flange part which mutually oppose can be joined, the fixation strength of the flange part with respect to a shaft part can be raised through expansion of a joining area.

  In particular, in resistance welding, the forming material of the two members to be joined is limited to conductive metal. However, if friction welding is used, it is not necessary to consider the strength or non-existence of conductivity. It can be firmly joined. Therefore, it is possible to widen the choice of the material for forming the shaft and flange, that is, it is possible to select and use the optimum material according to the required quality. From this point also, the cost of the shaft member can be reduced. It becomes.

  By the way, it is usual that the end face of the flange portion is provided with a thrust bearing surface that forms a thrust bearing gap with an end face of an opposing member (for example, a bearing sleeve or a lid member). When the shaft portion and the flange portion are friction-welded as described above, a bulge of meat called “return” is formed particularly at one end of the flange portion on the shaft portion side. The above thrust bearing surface can be formed by removing the “return” by cutting when it is excessive. However, a cleaning process is provided, and the cleaning process is performed in the cleaning process. The accompanying cutting powder must be carefully removed. This is because the cutting powder is mixed with a fluid (for example, lubricating oil) that fills the bearing gap and becomes contaminated to prevent deterioration of the bearing performance. In addition, when the shaft portion and the flange portion are friction-welded, the flange portion may be deformed by the pressure applied during the pressure-welding, and it may be necessary to further provide a correction process. However, this complicates the processing steps and inevitably increases the manufacturing cost.

  Therefore, the present invention provides a configuration in which the end face of the flange portion is covered with a molded coating layer, and a thrust bearing surface is formed on the surface of the coating layer. By adopting such a configuration, even when the “return” formed with friction welding is excessive, or when the flange portion is deformed with friction welding, only one step of providing a coating layer is performed. Thus, the thrust bearing surface can be formed, and the problem of an increase in manufacturing cost can be effectively solved. In this case, various precisions required for the thrust bearing surface (for example, the perpendicularity of the shaft portion with respect to the radial bearing surface) can be ensured by the coating layer, so that the processing conditions during friction welding are relaxed. Can do.

  The coating layer can be injection-molded by inserting the shaft portion and the flange portion after the flange portion is friction-welded to one end of the shaft portion. With such a configuration, it is desirable that the perpendicularity of the thrust bearing surface with respect to the radial bearing surface of the shaft portion can be easily increased in accuracy simply by improving the mold accuracy.

  A thrust dynamic pressure generating portion that generates fluid dynamic pressure in the thrust bearing gap can be provided on the thrust bearing surface of the coating layer. The thrust dynamic pressure generating portion can be molded at the same time as the injection molding of the coating layer, and it is possible to save the labor of providing this type of dynamic pressure generating portion separately and to suppress the manufacturing cost.

  The coating layer can be formed in an arbitrary shape. For example, a sealing space can be formed between the outer peripheral surface of the coating layer and another member facing the coating layer. In addition, the other member referred to here includes, for example, a housing that houses a bearing sleeve on the inner periphery.

  The above-mentioned coating layer can be molded with resin or metal, and it can be arbitrarily selected depending on the required characteristics whether resin or metal is used.

  As described above, according to the present invention, the fixing strength of the flange portion with respect to the shaft portion of the shaft member can be increased at low cost. A hydrodynamic bearing device with high rotational accuracy and high reliability can be obtained at low cost.

  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. This spindle motor is used for a disk drive device such as an HDD, and has a hydrodynamic bearing device 1 that rotatably supports a shaft member 2, a disk hub 3 mounted on the shaft member 2, and a radial gap, for example. And a stator coil 4a and a rotor magnet 4b that are opposed to each other. The stator coil 4 a is attached to the outer periphery of the bracket 5, and the rotor magnet 4 b is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is attached to the inner periphery of the bracket 5. The disk hub 3 holds one or a plurality of disks 6 such as magnetic disks. When the stator coil 4a is energized, the rotor magnet 4b is rotated by the electromagnetic force between the stator coil 4a and the rotor magnet 4b, whereby the disk hub 3 and the shaft member 2 are rotated together.

  FIG. 2 shows the hydrodynamic bearing device 1 according to the first embodiment of the present invention. The hydrodynamic bearing device 1 shown in FIG. 1 seals a bearing sleeve 8, a shaft member 2 inserted into the inner periphery of the bearing sleeve 8, a housing 7 housing the bearing sleeve 8 in the inner periphery, and one end opening of the housing 7. A lid member 9 for stopping and a seal member 10 for sealing the other end opening of the housing 7 are provided. For convenience of explanation, the following explanation will be given with the side of the seal member 10 as the upper side and the opposite side to the axial direction as the lower side.

  The housing 7 is formed in a cylindrical shape with a metal material such as brass or a resin material. A bearing sleeve 8 is fixed to the inner peripheral surface 7a of the housing 7 by appropriate means such as adhesion, press-fitting, and welding. A lid member fixing surface 7b having a larger diameter than the inner peripheral surface 7a is formed on the lower end side of the inner peripheral surface 7a.

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body of sintered metal whose main component is copper, for example. Besides the sintered metal, the bearing sleeve 8 can be formed of a soft metal material such as brass or another porous body (for example, a porous resin) that is not a sintered metal.

  As shown in FIG. 3, a region in which a plurality of dynamic pressure grooves 8a1 and 8a2 are arranged in a herringbone shape is formed on the inner peripheral surface 8a of the bearing sleeve 8 as shown in FIG. Is done. In the present embodiment, the upper dynamic pressure groove 8a1 is formed 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 8a2 is formed symmetrically in the axial direction, and the axial dimensions of the upper and lower regions thereof are respectively equal to the axial dimension X2. By forming the dynamic pressure groove in the above-described manner, a fluid (for example, lubricating oil) that fills the gap between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 21a of the shaft portion 21 is positive during the bearing operation. Flows downward. The dynamic pressure groove may be formed on a radial bearing surface A of the shaft portion 21 described later, and the shape thereof may be other known shapes such as a spiral shape.

  On the outer peripheral surface 8c of the bearing sleeve 8, one or a plurality of axial grooves 8c1 opened at both end surfaces are formed. The axial groove 8c1 is provided to flow and circulate the lubricating oil filled in the bearing, and is formed by the axial groove 8c1 and the inner peripheral surface 7a of the housing 7 during the bearing operation. Lubricating oil flows and circulates inside the bearing through the fluid passage. As a result, the pressure imbalance state inside the bearing is resolved, and problems such as the occurrence of lubricating oil leakage and vibration can be effectively avoided.

  The lid member 9 is formed, for example, in a disk shape from a metal material or a resin material, and is fixed to the lid member fixing surface 7b of the housing 7 by an appropriate means such as adhesion or press fitting.

  The seal member 10 is formed in a ring shape from, for example, a soft metal material such as brass, another metal material, or a resin material, and is fixed to the upper end portion of the inner peripheral surface 7a of the housing 7 by an appropriate means such as adhesion or press fitting. Is done. A predetermined seal space S is formed between the inner peripheral surface 10 a of the seal member 10 and the outer peripheral surface 21 a of the shaft portion 21. The seal space S has a buffer function that absorbs the volume change accompanying the temperature change of the lubricating oil filled in the hydrodynamic bearing device 1, and the oil level of the lubricating oil is always sealed within the assumed temperature change range. It is within the space S.

  The shaft member 2 includes a shaft portion 21 and a thrust member 22 protruding from the lower end of the shaft portion 21 to the outer diameter side, and has a hybrid structure of metal and resin as a whole. More specifically, the shaft portion 21 is formed of a metal material, while the thrust member 22 covers the flange portion 23 and a metal flange portion 23 whose upper end surface 23 a is friction-welded to the lower end of the shaft portion 21. And a resin-made coating layer 24. The method for manufacturing the shaft member 2 will be described in detail later.

  The outer peripheral surface 21a of the shaft portion 21 has a smooth cylindrical surface shape, and radial bearing surfaces A and A that are opposed to the formation regions of the dynamic pressure grooves 8a1 and 8a2 provided on the inner peripheral surface 8a of the bearing sleeve 8 in the radial direction. Two locations are formed apart in the axial direction. Between both the radial bearing surfaces A and A, a sumi portion 21b having a smaller diameter than the radial bearing surface A is formed.

  The upper end surface 22a of the thrust member 22 is provided with a region serving as a thrust bearing surface B that forms a thrust bearing gap with the lower end surface 8b of the bearing sleeve 8. The thrust bearing surface B includes, for example, FIG. As shown in FIG. 5, a plurality of dynamic pressure grooves 22a1 are arranged in a spiral shape as the thrust dynamic pressure generating portion. Further, the lower end surface 22b of the thrust member 22 is provided with a region serving as a thrust bearing surface C that forms a thrust bearing gap with the upper end surface 9a of the lid member 9, and the thrust bearing surface C is illustrated in the figure. Although omitted, a plurality of dynamic pressure grooves are arranged in a spiral shape as the thrust dynamic pressure generating portion. The dynamic pressure grooves provided on the thrust bearing surfaces B and C can be arranged in other known shapes such as a herringbone shape. The thrust bearing surfaces B and C may be formed on a smooth plane, and dynamic pressure grooves may be formed on the lower end surface 8 b of the bearing sleeve 8 and the upper end surface 9 a of the lid member 9.

  The hydrodynamic bearing device 1 is mainly composed of the above components, and the internal space of the housing 7 sealed with the seal member 10 is filled with lubricating oil including the internal pores of the bearing sleeve 8.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the dynamic pressure grooves 8a1 and 8a2 formation regions of the bearing sleeve 8 are provided at radial bearing surfaces A which are provided separately at two upper and lower portions of the shaft portion 21. , A and the radial bearing gaps. As the shaft member 2 rotates, the oil film formed in the radial bearing gap is enhanced in its rigidity by the dynamic pressure action of the dynamic pressure grooves 8a1 and 8a2, and the shaft member 2 rotates in the radial direction by this pressure. It is supported non-contact freely. As a result, radial bearing portions R1 and R2 that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are spaced apart at two locations in the axial direction.

  When the shaft member 2 rotates, the thrust bearing surfaces B and C of the thrust member 22 face the lower end surface 8b of the bearing sleeve 8 and the upper end surface 9a of the lid member 9 through a thrust bearing gap. As the shaft member 2 rotates, the oil film formed in the thrust bearing gaps has its oil film rigidity increased by the dynamic pressure action of the dynamic pressure grooves, and the shaft member 2 can rotate in both thrust directions by this pressure. Is supported in a non-contact manner. Thereby, the 1st thrust bearing part T1 and the 2nd thrust bearing part T2 which non-contact-support the shaft member 2 rotatably in both thrust directions are formed.

  Next, the structure and manufacturing method of the shaft member 2 used in the hydrodynamic bearing device 1 will be described in detail with reference to the drawings. The shaft member 2 is manufactured through (A) a friction welding process and (B) an injection molding process.

(A) Friction Welding Step FIG. 5 is a diagram conceptually showing a step of fixing (joining) the flange portion 23 to the lower end of the shaft portion 21 by friction welding. The manufacturing apparatus (friction welding apparatus) shown in the figure includes a first jig 30 and a second jig 33 arranged coaxially so as to be relatively movable in the axial direction as main components. The first jig 30 includes a bearing 31 that rotationally drives the shaft portion 21 and a chuck 32 that is provided so as to be able to advance and retreat in the radial direction of the shaft portion 21 and restrains the outer peripheral surface 21 a of the shaft portion 21. Is done. The second jig 33 restrains the outer peripheral surface 23 c and the lower end surface 23 b of the flange portion 23. In the present embodiment, the first jig 30 is the fixed side, and the second jig 33 is the moving side. Of course, the first jig 30 can be the moving side and the second jig 33 can be the fixed side.

  By the way, in this type of shaft member with flange, for example, the perpendicularity of the thrust bearing surface with respect to the radial bearing surface affects the rotational performance of the shaft member. In the present embodiment, the squareness is ensured in an injection molding process described later, but if the fixing accuracy of the flange portion 23 with respect to the shaft portion 21 is too bad, the shaft member 2 may be swung around. Therefore, it is desirable that the perpendicularity of the inner bottom surface of the second jig 33 with respect to the inner peripheral surface of the first jig 30 is sufficiently increased.

  The shaft portion 21 is made of a highly rigid metal material such as stainless steel, and at this stage, the shaft portion 21 is finished in a predetermined shape except for the overall length. Specifically, the axial dimension of the joint portion 21c (the lower end portion of the shaft portion 21 including the lower radial bearing surface A) of the shaft portion 21 that is joined to the flange portion 23 is increased by the amount shortened by the friction welding. Is set to On the other hand, the flange portion 23 is formed of a stainless steel similar to the shaft portion 21 and is formed in a disc shape without irregularities.

  In the above configuration, the second jig 33 is brought close to the first jig 30 in a state where the shaft portion 21 and the flange portion 23 are held by the first and second jigs 30 and 33, respectively. The upper end surface 23a of 23 is brought into contact with the lower end surface 21c1 of the shaft portion 21 (joining portion 21c). Next, as shown in FIG. 6A, the bearing 31 is driven to rotate the shaft portion 21 to generate frictional heat at the contact portions on both sides. In the contact portion, when the forming material of the shaft portion 21 and the flange portion 23 is heated to near the melting point, the second jig 33 is further brought closer to the first jig 30, and the upper end surface 23 a of the flange portion 23. Is pressed against the joint lower end surface 21c1 of the shaft portion 21.

  As a result, as shown in FIG. 6B, the joint portion M in which the shaft portion 21 and the flange portion 23 are joined to each other by friction welding, and the rise (return) N of the meat formed on the outer periphery of the joint portion M. A pressure contact fixing portion 25 is formed. Then, after releasing the restrained state of the flange portion 23 and the shaft portion 21, when the shaft portion 21 is extracted from the bearing 31, an assembly 26 in which the flange portion 23 is joined to the lower end of the shaft portion 21 is obtained.

(B) Injection molding process The assembly 26 obtained as described above is transferred to the injection molding process. In this step, the assembly 26 is used as an insert part, and the coating layer 24 constituting the thrust member 22 is injection-molded with a molten material (here, a molten resin) using the radial bearing surface A of the shaft portion 21 as a reference. FIG. 7A conceptually shows an example of an injection molding process. The mold shown in FIG. 7 is composed of a movable upper mold 34 and a fixed side coaxially arranged so as to be relatively movable in the axial direction. A main part is constituted by the lower die 35, and a cavity 37 corresponding to the shape of the coating layer 24 (thrust member 22) is formed by both the die 34 and 35.

  The upper die 34 is provided with a gate 34 a for injecting and filling the molten material P into the cavity 37. Among the end surfaces of the upper die 34, the lower end surface 34 b that faces the lower end surface 23 b of the flange portion 23 and the cavity 37 in the axial direction corresponds to the dynamic pressure groove shape to be provided on the thrust bearing surface C of the thrust member 22. A mold part 39 is provided.

  The lower die 35 is provided with a housing portion 35a, and the assembly 26 is positioned and disposed by inserting the shaft portion 21 into the inner periphery of the housing portion 35a. A dynamic pressure groove to be provided on the thrust bearing surface B of the upper end surface 22a of the thrust member 22 in a portion of the upper end surface 35b of the lower mold 35 that faces the upper end surface 23a of the flange portion 23 in the axial direction via the cavity 37. A mold portion 38 corresponding to the shape of 22a1 is provided. A knockout pin 36 that can move in the axial direction relative to the lower die 35 is provided on the inner circumference of the lower die 35, and the upper end surface 36 a of the knockout pin 36 supports the upper end surface of the shaft portion 21. FIG. 7A shows a state in which the knockout pin 36 is at the origin position. In this state, the axial separation distance between the upper end surface 35b of the lower mold 35 and the upper end surface 36a of the knockout pin 36 is as follows. It is set shorter by a predetermined amount than the axial dimension of the shaft portion 21. Accordingly, the pressure contact fixing portion 25 is not in contact with the upper end surface 35a of the lower die 35 in a state where the shaft portion 21 is inserted into the housing portion 35a.

  In this embodiment, various accuracies required for the shaft member 2, for example, the perpendicularity of the thrust bearing surface B of the thrust member 22 with respect to the radial bearing surface A of the shaft portion 21 and the parallelism between the thrust bearing surfaces B and C are obtained. The specifications are ensured when the coating layer 24 is injection molded. Therefore, the perpendicularity of the upper end surface 35b of the lower mold 35 with respect to the inner wall surface of the accommodating portion 35a and the parallelism of the lower end surface 34b of the upper mold 34 with respect to the upper end surface 35b of the lower mold 35 in the abutting state of the upper and lower molds 34, 35 are In addition, it is finished to an accuracy that can satisfy the required accuracy. If the thickness of the covering layer 24 is partially different, the thrust member 22 having a desired shape may not be obtained due to a difference in molding shrinkage. For this reason, it is desirable that the dimensions of the cavity 37 be set to be substantially uniform throughout.

  In the mold configured as described above, after the shaft portion 21 is inserted into the housing portion 35a of the lower die 35 and the radial bearing surfaces A and A of the shaft portion 21 are constrained, the upper die 34 is brought close to the lower die 35 and clamped. To do. After completing the mold clamping, the molten material P (molten resin) is injected and filled into the cavity 37 through the gate 34a, and the coating layer 24 is molded. When the mold opening is performed after the solidification of the molten resin is completed and the knockout pin 36 is pushed up, as shown in FIG. 7B, the flange portion 23 and the pressure contact fixing portion 25 that are friction-welded to the lower end of the shaft portion 21 are included. A thrust member 22 comprising a coating layer 24 covering the entire surface of the flange portion 23 is formed, whereby the shaft member 2 shown in FIG. 2 is obtained. Further, thrust bearing surfaces B and C (dynamic pressure grooves) are formed on the upper and lower end surfaces 22 a and 22 b (surface of the coating layer 24) of the thrust member 22 simultaneously with the molding of the coating layer 24.

  The molten resin as the molten material P can be used regardless of whether it is an amorphous resin or a crystalline resin as long as it can be injected. Examples of the amorphous resin that can be used include polysulfone (PSU), polyethersulfone (PES), polyphenylsulfone (PPSU), and polyetherimide (PEI). Examples of the resin include liquid crystal polymer (LCP), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), and the like. These base resins can be used alone or in combination of two or more. Moreover, various fillers for imparting various properties to the above base resin can be blended at an arbitrary ratio.

  As the molten material P, it is also possible to use a metal material, for example, a low melting point metal such as a magnesium alloy, in addition to the above resin. In this case, the covering layer 24 is made of metal, and the wear resistance of the thrust member 22 can be improved as compared with the case where the covering layer 24 is made of resin as described above. The metal coating layer 24 can be formed by so-called MIM molding in which a mixture of a metal powder and a binder is injection molded, and then degreased and sintered, in addition to injection molding with a low melting point metal.

  As described above, in the hydrodynamic bearing device 1 according to the present invention, since the shaft portion 21 and the flange portion 23 of the shaft member 2 are joined by friction welding, other media such as screws and lasers are used for joining them. Need not be used. In addition, it is not necessary to provide a screw groove at the lower end of the shaft portion 21 or to provide a protrusion on the lower end surface 21c1 of the shaft portion 21 or the upper end surface 23a of the flange portion 23 that face each other. The shape of the end face can be simplified. Moreover, the whole lower end surface 21c1 of the axial part 21 and the upper end surface 23a of the flange part 23 which mutually oppose can be joined, and the fixation strength between both can be raised through expansion of a joining area. As described above, the fixing strength of the flange portion 23 with respect to the shaft portion 21 can be increased at low cost. The shaft member 2 has a fixing strength equivalent to that when the shaft portion 21 and the flange portion 23 are integrally formed.

  Further, in the shaft member 2 according to the present embodiment, both end surfaces 23a and 23b of the flange portion 23 including the pressure contact fixing portion 25 are covered with a molded coating layer 24, and the surface of this coating layer 24 is a thrust bearing surface B. Since C is formed, it is not necessary to remove the return N formed by friction welding by machining such as cutting, and it is necessary to perform correction processing even if the flange portion 23 is deformed by friction welding. Nor. Therefore, highly accurate thrust bearing surfaces B and C can be obtained at low cost.

  Further, the perpendicularity of the thrust bearing surface B to the required radial bearing surface A and the parallelism between the thrust bearing surfaces B and C are ensured when the coating layer 24 is formed. Accordingly, the fixing accuracy of the flange portion 23 with respect to the shaft portion 21 and the shape accuracy of the flange portion 23 can be made rough within a range where the rotational accuracy of the shaft member 2 is not adversely affected, and the processing conditions during friction welding are eased. Thus, the manufacturing cost can be reduced. Moreover, since the coating layer 24 is injection-molded by using the assembly 26 (the shaft portion 21 and the flange portion 23) as an insert part, the various required accuracy can be easily increased. Furthermore, in the present embodiment, the dynamic pressure groove as the thrust dynamic pressure generating portion is molded at the same time as the coating layer 24 is formed, so that the trouble of separately providing this type of dynamic pressure groove can be saved and the manufacturing cost can be further reduced. Cost reduction is also achieved.

  In this embodiment, the shaft portion 21 and the flange portion 23 are formed of the same kind of stainless steel. However, in the case of friction welding, even between dissimilar metals where it is difficult to ensure high joint strength by laser welding or resistance welding. High bonding strength can be ensured. Therefore, as long as the strength required for the shaft member 2 can be ensured, the choice of the material for forming the shaft portion 21 and the flange portion 23 can be expanded, that is, the optimum material corresponding to the required quality can be selected and used. In this respect, the cost of the shaft member 2 can be reduced. For example, the shaft portion 21 can be formed of stainless steel, while the flange portion 23 can be formed of brass or the like.

  In this embodiment, the case where the entire surface of the flange portion 23 is covered with the coating layer 24 is described. The coating layer 24 is a surface having thrust bearing surfaces B and C, that is, both ends of the flange portion 23. It is sufficient to provide the surfaces 23a and 23b so as to cover them.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above configuration. Hereinafter, other embodiments of the hydrodynamic bearing device according to the present invention will be described with reference to the drawings. In the following description, components similar to those described above are denoted by common reference numerals, and redundant description is omitted.

  FIG. 8 shows a fluid dynamic bearing device according to a second embodiment of the present invention. The main difference between the hydrodynamic bearing device shown in FIG. 2 and that shown in FIG. 2 is that the thrust bearing surface C is not formed on the lower end surface 22b of the thrust member 22 of the shaft member 2, and the second thrust bearing portion T2 is formed. The point provided between the lower end surface 3 a 1 of the disk portion 3 a of the disk hub 3 fixed to the upper end of the shaft portion 21 and the upper end surface 7 c of the housing 7, and the seal space S are the tapered outer periphery of the housing 7. It exists in the point provided between the surface 7d and the internal peripheral surface 3b1 of the cylindrical part 3b of the disc hub 3. FIG. In the illustrated example, the entire surface of the flange portion 23 is covered with the covering layer 24. However, the covering layer 24 covers the surface having the thrust bearing surface B, that is, the upper end surface 23a of the flange portion 23. It is enough if it is provided.

  FIG. 9 shows a third embodiment of the hydrodynamic bearing device according to the present invention. In the hydrodynamic bearing device shown in the figure, the shaft member 2 further includes a second thrust member 42 fixed to a substantially central portion in the axial direction of the shaft portion 21, and the second thrust bearing portion T 2 is a second thrust member. 42 and the upper end surface 8 d of the bearing sleeve 8, and the outer peripheral surfaces 22 c and 42 c of the thrust members 22 and 42 form a seal space S between the inner peripheral surface 7 a of the housing 7. Thus, the configuration is different from that of the embodiment shown in FIGS. Thus, even when the shaft member 2 provided with the two thrust members 22 and 42 on the shaft portion 21 is used, the shaft portion 21 and the thrust member 22 (flange portion 23) provided on the lower end of the shaft portion 21 are used. The above-described configuration of the present invention can be applied to the integrated product. In particular, in the lower thrust member 22, a sealing surface is formed on the covering layer 24, so that a highly accurate sealing space S can be obtained at low cost.

  In the illustrated example, as in the embodiment described above, the entire surface of the flange portion 23 is covered with the coating layer 24. However, the coating layer 24 is a surface having a thrust bearing surface B and a seal surface, that is, It is only necessary to provide the upper end surface 23a and the outer peripheral surface 23c of the flange portion 23 so as to cover them.

  Each of the fluid dynamic bearing devices described above has the housing 7 and the bearing sleeve 8 as separate components. However, the present invention is also preferably applied to a fluid dynamic bearing device in which both are integrated. Can do. In particular, in the hydrodynamic bearing device shown in FIG. 2, the lid member 9 or the seal member 10 can be further integrated with the housing 7.

  In the above description, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are exemplified by the configuration in which the dynamic pressure action of the lubricating oil is generated by the dynamic pressure grooves having a herringbone shape or a spiral shape. So-called step bearings, multi-arc bearings, or non-circular bearings may be used as the portions R1 and R2, and so-called step bearings and corrugated bearings may be employed as the thrust bearing portions T1 and T2. Moreover, although the structure which provided the radial bearing part in the axial direction two places was illustrated above, a radial bearing part can also be provided in the axial direction one place or three places or more.

  Moreover, although the case where both radial bearing part R1, R2 was comprised with the dynamic pressure bearing was demonstrated above, one or both of radial bearing part R1, R2 can also be comprised with a bearing other than this. For example, although not shown in the drawings, the radial bearing surface A of the shaft member 2 is formed in a perfect circle shape, and the inner peripheral surface 8a of the bearing sleeve 8 that is opposed is a perfect circular inner peripheral surface. Can also be configured.

It is sectional drawing which shows notionally an example of the spindle motor for information devices. It is sectional drawing which shows 1st Embodiment of the hydrodynamic bearing apparatus which concerns on this invention. It is sectional drawing of a bearing sleeve. It is a figure which shows the upper end surface of a flange part. It is sectional drawing which shows a friction welding process notionally. (A) is an initial stage of friction welding, and (B) is a sectional view conceptually showing a completed state of friction welding. FIG. 4A is a sectional view conceptually showing a process of injection molding a coating layer, and FIG. 4B is an enlarged sectional view of a main part of the shaft member after the coating layer is injection molded. It is sectional drawing which shows 2nd Embodiment of the hydrodynamic bearing apparatus which concerns on this invention. It is sectional drawing which shows 3rd Embodiment of the hydrodynamic bearing apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid dynamic bearing apparatus 2 Shaft member 8 Bearing sleeve 21 Shaft part 22 Thrust member 23 Flange part 24 Covering layer 25 Pressure contact fixing part 26 Assembly A Radial bearing surface B, C Thrust bearing surface M Joint part N Return R1, R2 Radial bearing part T1 , T2 Thrust bearing

Claims (6)

A bearing sleeve and a shaft member that is inserted into the inner periphery of the bearing sleeve and rotates relative to the bearing sleeve. The shaft member has a shaft portion having a radial bearing surface, and projects to one end outer diameter side of the shaft portion. In a hydrodynamic bearing device having a flange portion,
A hydrodynamic bearing device characterized in that a shaft portion of a shaft member and a flange portion are friction-welded.   The hydrodynamic bearing device according to claim 1, wherein an end surface of the flange portion is covered with a coating layer formed by molding, and a thrust bearing surface is formed on the surface of the coating layer.   3. The hydrodynamic bearing device according to claim 2, wherein after the flange portion is friction-welded to one end of the shaft portion, the shaft portion and the flange portion are inserted and the coating layer is injection molded.   The hydrodynamic bearing device according to claim 2, wherein a sealing space is formed between the outer peripheral surface of the coating layer and another member facing the outer peripheral surface.   The hydrodynamic bearing device according to claim 2, wherein the coating layer is molded with resin.   The hydrodynamic bearing device according to claim 2, wherein the coating layer is formed of a metal.

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