JP2005098486A - Shaft member for hydrodynamic bearing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To furthermore reduce the cost of a shaft member for a hydrodynamic bearing apparatus. <P>SOLUTION: The outside peripheral surface of the journal portion 2a of the shaft member 2 is arranged so as to face to the inside peripheral surface of a bearing sleeve across a radial bearing clearance. In addition, both end faces 2b1, 2b2 of a flange portion 2b face to one end face of the bearing sleeve and the bottom surface of a housing across thrust bearing clearances respectively. The shaft member 2 is supported, in a non-contact state, by the hydrodynamic pressure produced in the respective bearing clearances. The core portion of the journal portion 2a and the flange portion 2b of the shaft member 2 are made of a resinoid material 21. The outside periphery of the shaft member 2 is made of a metallic material 22. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a shaft member used in a hydrodynamic bearing device. The hydrodynamic bearing device here is an information device, for example, a magnetic disk device such as HDD or FDD, an optical disk device such as CD-ROM, CD-R / RW, or DVD-ROM / RAM, or a magneto-optical disk such as MD or MO. It is suitable as a bearing device for a spindle motor such as a device, a polygon scanner motor of a laser beam printer (LBP), a color wheel of a projector, or a small motor such as an electric device such as an axial fan.

  A dynamic pressure bearing is a bearing that supports a shaft member in a non-contact state by a fluid dynamic pressure generated in a bearing gap. A bearing device (dynamic pressure bearing device) using this dynamic pressure bearing includes a contact type in which a radial bearing portion is constituted by a dynamic pressure bearing and a thrust bearing portion is constituted by a pivot bearing, and a radial bearing portion and a thrust bearing portion. They are broadly classified into non-contact types in which both are constituted by dynamic pressure bearings, and are properly used according to individual applications.

Among these, as an example of a non-contact type hydrodynamic bearing device, one disclosed in Japanese Patent Application Laid-Open No. 2000-291648 proposed by the present applicant is known. In this configuration, the shaft portion and the flange portion constituting the shaft member are integrally configured from the viewpoint of cost reduction and high accuracy.
JP 2000-291648 A

  However, demands for cost reduction in recent years tend to be more severe, and in order to meet this demand, further cost reduction is required for each component of the hydrodynamic bearing device.

  In view of such circumstances, the present invention mainly aims to further reduce the cost of a shaft member in a non-contact type hydrodynamic bearing device.

  As a means for achieving this object, the present invention provides a shaft member for a hydrodynamic bearing device having a shaft portion and a flange portion projecting to the outer diameter side of the shaft portion. And the core part and the flange part of the shaft part are made of a resin material. In the hydrodynamic bearing device, the shaft member of the present invention is supported in a non-contact manner in the radial direction by the hydrodynamic action of the fluid generated in the radial bearing gap of the radial bearing portion, and the fluid dynamics generated in the thrust bearing gap of the thrust bearing portion. Non-contact support in the thrust direction by pressure action.

  By forming the outer periphery of the shaft portion with a metal material, the strength and rigidity required for the shaft member can be secured, and the wear resistance of the shaft portion with respect to a metal bearing sleeve made of sintered metal or the like can be secured. On the other hand, since many portions of the shaft member (core portion and flange portion of the shaft portion) are formed of a resin material, the weight of the shaft member can be reduced, thereby reducing the inertia of the shaft member. The impact load when the shaft member collides with other bearing constituent members (bearing sleeve, housing bottom, etc.) can be reduced, and the occurrence of damage and damage due to the collision can be avoided. Further, since the flange portion is made of resin and the sliding friction is small, the friction coefficient can be reduced between the flange portion and the other bearing constituent member.

  In general, in a non-contact type dynamic pressure bearing, the viscosity of a fluid (oil or the like) decreases at a high temperature, so that a decrease in bearing rigidity particularly in the thrust direction becomes a problem. In this case, as described above, if the flange portion is formed of a resin material, the surface of the mating member (the end surface of the bearing sleeve, the inner bottom surface of the housing, etc.) facing the end surface of the flange portion is usually made of metal. As a result, the axial bearing thermal expansion of the resin flange portion with a larger linear expansion coefficient than that of the metal (particularly the axial linear expansion coefficient) reduces the thrust bearing gap, resulting in a thrust bearing stiffness in the thrust direction at high temperatures. Can be suppressed. On the other hand, at low temperatures, the motor torque increases due to an increase in the viscosity of the fluid. However, if the flange part is made of a resin material, the axial bearing differential increases the thrust bearing gap, so the motor torque increases at low temperatures. Can be suppressed.

  The shaft member can be formed by resin molding using a metal material as an insert part. If the shaft member is insert-molded in this way (including outsert molding: the same applies hereinafter), the mold accuracy can be improved and the metal material as the insert part can be positioned accurately within the mold. Can be mass-produced at low cost. In particular, in non-contact type hydrodynamic bearing devices, high dimensional accuracy is required for shaft members, including the perpendicularity of the shaft and flange, but this type of request must be fully met with insert molding. Can do.

  Of the shaft member, it is desirable to provide a plurality of dynamic pressure grooves on at least one end face of the flange portion. In this case, the dynamic pressure groove can be formed by forming a groove mold corresponding to the dynamic pressure groove shape in the mold, filling the mold with a molten resin and curing it, and then transferring the groove mold shape. Thus, a precise dynamic pressure groove can be formed at low cost. At this time, the dynamic pressure groove can be formed simultaneously with the molding of the flange portion. Therefore, when the molding of the flange portion and the shaping of the dynamic pressure groove are performed in separate processes, for example, after forging the metal flange, Compared with the case where dynamic pressure grooves are press-formed on both end faces, the number of steps can be reduced and the cost can be reduced.

  By forming a screw part for screw fastening with other members at the end of the shaft member described above on the side opposite to the flange, the end on the side opposite to the flange provided at one end of the shaft member is formed. It becomes possible to fix other members (for example, a cap for pressing the disc, etc.) accurately and reliably. In this case, if the screw portion is formed on the inner periphery of the end portion of the metal material, the other member can be screw-fastened with the metal material, and the fastening strength is increased.

  According to the present invention, since a lightweight shaft member is provided, the impact caused by the collision between the shaft member and another member during transportation or the like can be mitigated, and the occurrence of scratches due to the impact load can be prevented. Further, it is possible to secure the bearing rigidity in the thrust direction at high temperatures and to suppress an increase in motor torque at low temperatures.

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

  FIG. 3 shows a configuration example of a spindle motor for information equipment in which the hydrodynamic bearing device 1 according to this embodiment is incorporated. This spindle motor is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 mounted on the shaft member 2, and a radial direction. A motor stator 4 and a motor rotor 5 are provided to face each other through a gap. The stator 4 is attached to the outer periphery of the casing 6, and the rotor 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is fixed to the inner periphery of the casing 6 by adhesion or press fitting. The disk hub 3 holds one or more disks D such as magnetic disks. When the stator 4 is energized, the rotor 5 is rotated by the exciting force between the stator 4 and the rotor 5, whereby the disk hub 3 and the shaft member 2 are rotated together.

  FIG. 4 shows an embodiment of the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a bottomed cylindrical housing 7 having an opening 7a at one end and a bottom 7c at the other end, a cylindrical bearing sleeve 8 fixed to the inner peripheral surface of the housing 7, and a shaft portion. The shaft member 2 composed of 2a and the flange portion 2b and the seal member 10 fixed to the opening 7a of the housing 7 are configured as main members. In the following description, for convenience of explanation, the description will proceed with the opening 7a side of the housing 7 as the upward direction and the bottom 7c side of the housing 7 as the downward direction.

  The housing 7 is formed of a soft metal material such as brass, for example, and includes a cylindrical side portion 7b and a disc-shaped bottom portion 7c as separate structures. At the lower end of the inner peripheral surface 7d of the housing 7, a large-diameter portion 7e having a larger diameter than other places is formed. It is fixed by means such as. In addition, the side part 7b and the bottom part 7c of the housing 7 can also be made into an integral structure.

  The bearing sleeve 8 is formed of a sintered metal, more specifically, an oil-containing sintered metal impregnated with oil. On the inner peripheral surface 8a of the bearing sleeve 8, two upper and lower dynamic pressure groove regions serving as radial bearing surfaces for generating dynamic pressure are provided in the axial direction.

  As shown in FIG. 5, the upper radial bearing surface includes a plurality of herringbone-shaped dynamic pressure grooves 8a1 and 8a2. In this radial bearing surface, the axial length of the dynamic pressure groove 8a1 on the upper side of the drawing is larger than the dynamic pressure groove 8a2 on the lower side of the drawing inclined in the opposite direction, and has an axially asymmetric shape. Similarly, the lower radial bearing surface also includes a plurality of herringbone-shaped dynamic pressure grooves 8a3 and 8a4, a plurality of dynamic pressure grooves 8a3 inclined in one of the axial directions, and a plurality of dynamic pressures inclined in the other of the axial directions. A groove 8a4 is formed apart in the axial direction. However, in this embodiment, unlike the dynamic pressure grooves 8a1 and 8a2 on the upper radial bearing surface, the axial lengths of both dynamic pressure grooves 8a3 and 8a4 are equal and have an axially symmetrical shape. The axial length of the upper radial bearing surface (the distance between the upper end of the dynamic pressure groove 8a1 and the lower end of the dynamic pressure groove 8a2) is the axial length of the lower radial bearing surface (the upper end of the dynamic pressure groove 8a3 and the dynamic pressure groove). 8a4 lower end distance).

  Radial bearing gaps 9a and 9b are formed between the upper and lower radial bearing surfaces on the inner periphery of the bearing sleeve 8 and the outer peripheral surface of the shaft portion 2a facing the upper and lower radial bearing surfaces. Each of the radial bearing gaps 9a and 9b has an upper side opened to the outside air through the seal member 10, and a lower side blocked from the outside air.

  In general, in a dynamic pressure groove having a shape inclined with respect to the axial direction, such as a herringbone shape, an oil drawing action in the axial direction occurs during operation of the bearing. Therefore, also in this embodiment, the dynamic pressure grooves 8a1 to 8a4 serve as oil drawing portions, and the oil drawn into the radial bearing gaps 9a and 9b by the drawing portions 8a1 to 8a4 is between the dynamic pressure grooves 8a1 and 8a2. An oil film is formed around the smooth portions n1 and n2 between the dynamic pressure grooves 8a3 and 8a4 and is continuous in the circumferential direction.

  At this time, due to the asymmetry of the upper radial bearing surface and the difference in the axial length of the upper and lower radial bearing surfaces, the gap between the outer peripheral surface of the shaft portion 2a and the inner peripheral surface 8a of the bearing sleeve 8 is filled. The oil is pushed downward as a whole. In order to return the oil pushed downward to the upper side, circulation grooves (not shown) are formed in the outer peripheral surface 8d of the bearing sleeve 8 so as to open at both end surfaces 8b and 8c. This circulation groove can also be formed in the inner peripheral surface 7d of the housing.

  In addition, the dynamic pressure groove shape in each dynamic pressure groove region is sufficient if each of the dynamic pressure grooves 8a1 to 8a4 is inclined with respect to the axial direction. As the dynamic pressure groove shape corresponding to this, in addition to a herringbone shape as shown in the figure, a spiral shape may be considered.

  As shown in FIG. 4, the sealing member 10 as a sealing means is annular, and is fixed to the inner peripheral surface of the opening 7 a of the housing 7 by means such as press fitting and adhesion. In this embodiment, the inner peripheral surface of the seal member 10 is formed in a cylindrical shape, and the lower end surface 10 b of the seal member 10 is in contact with the upper end surface 8 b of the bearing sleeve 8.

  A tapered surface is formed on the outer peripheral surface of the shaft portion 2 a facing the inner peripheral surface of the seal member 10. The taper surface and the inner peripheral surface of the seal member 10 are directed upward of the housing 7. A taper-shaped seal space S that gradually expands is formed. Lubricating oil is injected into the internal space of the housing 7 sealed by the seal member 10, and each clearance in the housing, that is, a clearance between the outer peripheral surface of the shaft portion 2 a and the inner peripheral surface 8 a of the bearing sleeve 8. (Including radial bearing gaps 9a and 9b), a gap between the lower end surface 8c of the bearing sleeve 8 and the upper end surface 2b1 of the flange portion 2b, a lower end surface 2b2 of the flange portion and the inner bottom surface 7c1 of the housing 7 (housing bottom surface) ) Is filled with lubricating oil. The oil level of the lubricating oil is in the seal space S.

  The shaft portion 2 a of the shaft member 2 is inserted into the inner peripheral surface 8 a of the bearing sleeve 8, and the flange portion 2 b is accommodated in a space portion between the lower end surface 8 c of the bearing sleeve 8 and the inner bottom surface 7 c 1 of the housing 7. Two radial bearing surfaces on the upper and lower sides of the inner circumferential surface 8a of the bearing sleeve 8 are opposed to the outer circumferential surface of the shaft portion 2a via radial bearing gaps 9a and 9b, respectively, and the first radial bearing portion R1 and the second radial bearing portion. R2 is configured.

  As shown in FIG. 1, the shaft member 2 has a composite structure of a resin material 21 and a metal material 22, of which the core portion of the shaft portion 2 a and the entire flange portion 2 b are integrally formed with the resin material 21. The outer periphery of the portion 2a is covered with a hollow cylindrical metal material (for example, stainless steel) 22 over its entire length. As the resin material 21, 66 nylon, LCP, PES or the like can be used, and a filler such as glass fiber is blended with these resins as necessary. Moreover, as the metal material 22, for example, stainless steel having excellent wear resistance can be used.

  In order to prevent separation of the resin material 21 and the metal material 22, at the lower end (left side of the drawing) of the shaft portion 2a of the shaft member 2, the end portion of the metal material 22 is embedded in the flange portion 2b. And the resin material 21 are in the engaged state in the axial direction via the engaging portion. In the example of illustration, the case where it is mutually engaged by the taper surface 22b which expanded the upper side as this engaging part is illustrated. In order to prevent the metal material 22 from rotating, an uneven engagement portion that can be engaged with the flange portion 2b in the circumferential direction by knurling or the like is provided on the outer periphery or the edge of the metal material 22 embedded in the flange portion 2b. desirable.

The shaft member 2 is manufactured by resin injection molding (by insert molding) using, for example, a metal material 22 as an insert part. The shaft member 2 is required to have high dimensional accuracy including the perpendicularity of the shaft portion 2a and the flange portion 2b and the parallelism of both end surfaces 2b1 and 2b2 of the flange portion due to the function of the non-contact type bearing device. If it is shaping | molding, it will become possible to mass-produce at low cost, ensuring the required precision by raising the precision of a mold | die and positioning the metal material 22 as an insert goods accurately in a mold. In addition, since the assembly of the shaft portion 2a and the flange portion 2b is completed simultaneously with these moldings, the shaft portion and the flange portion are made of separate parts made of metal, and compared to the case where these are integrated by press-fitting etc. in a subsequent process. The cost can be further reduced by reducing the number.

  On both end faces 2b1 and 2b2 of the flange portion 2b, dynamic pressure groove regions serving as thrust bearing surfaces for generating dynamic pressure are formed. As shown in FIGS. 2 (a) and 2 (b), a plurality of dynamic pressure grooves 23 and 24 having a spiral shape and the like are formed on the thrust bearing surface. The dynamic pressure groove area is formed by injection molding of the flange portion 2b. Molded at the same time. The thrust bearing surface formed on the upper end surface 2b1 of the flange portion 2b is opposed to the lower end surface 8c of the bearing sleeve 8 via a thrust bearing gap, thereby forming the first thrust bearing portion T1. Further, the thrust bearing surface formed on the lower end surface 2b2 of the flange portion 2b faces the inner bottom surface 7c1 of the housing bottom portion 7c via a thrust bearing gap, thereby forming the second thrust bearing portion T2.

  From the above configuration, when the shaft member 2 and the bearing sleeve 8 are rotated relative to each other, in this embodiment, when the shaft member 2 is rotated, the radial bearing portions R1 and R2 are operated by the action of the dynamic pressure grooves 8a1 to 8a4 as described above. The dynamic pressure of the lubricating oil is generated in the radial bearing gaps 9a and 9b, and the shaft portion 2a of the shaft member 2 is supported in a non-contact manner in the radial direction by the lubricating oil film formed in each radial bearing gap. At the same time, the dynamic pressure of the lubricating oil is generated in the thrust bearing gaps of the thrust bearing portions T1, T2 by the action of the dynamic pressure grooves 23, 24, and the flange portion 2b of the shaft member 2 is lubricated to be formed in the thrust bearing gaps. The oil film is supported in a non-contact manner so as to be rotatable in both thrust directions.

  In the present invention, as described above, the shaft member 2 is formed of the metal material 22 only on the outer periphery of the shaft portion 2a, while the other portion is formed of the resin material 21, which is lighter than conventional metal products. ing. Accordingly, the impact at the time of collision between the shaft member 2 and the bearing sleeve 8 or the housing bottom 7c is reduced, and it becomes possible to suppress the occurrence of scratches at the collision part. Further, since the flange portion 2b is made of resin, the slidability with respect to the lower end surface 8c of the metal bearing sleeve 8 and the housing bottom portion 7c is good, and the torque can be reduced.

  Furthermore, since the linear flange expansion coefficient in the axial direction of the resin flange portion 2b is larger than that of the metal bearing sleeve 8 and the housing bottom portion 7c, the width of the thrust bearing gap when the bearing temperature rises due to motor driving or the like. Becomes smaller. Therefore, a decrease in oil film rigidity due to a decrease in oil viscosity can be compensated, and a bearing rigidity in the thrust direction can be ensured. Also. In general, the viscosity of the oil is high at low temperatures such as immediately after start-up, which causes an increase in torque. However, in the present invention, the thrust bearing gap increases due to the difference in linear expansion coefficient, so this type of torque increase can be avoided.

  FIG. 6 is a cross-sectional view showing another embodiment of the shaft member 2. In this embodiment, another member can be screwed to the upper end of the shaft member 2. In the illustrated example, a cap 26 for pressing a disk or the like is fixed to the shaft member 2 with a screw 27 as the other member. Is illustrated. In the shaft portion 2 a, the upper end of the cylindrical metal material 22 extends in the axial direction beyond the upper end of the resin material 21, and the internally threaded screw portion 25 that engages with the screw 27 on the inner periphery of the extended portion. Is formed. There is an upper end of the resin material 21 below the screw portion 25, and the resin material 21 and the metal material 22 are engaged with each other in the axial direction via the tapered surface 22b. By forming the screw portion 25 on the inner periphery of the metal material 22 in this way, the strength and durability of the screw fastening portion can be improved as compared with the case where the screw portion is formed on the resin material 21. Since other structures, manufacturing methods, and the like are based on the shaft member 2 shown in FIGS. 1 and 2, a detailed description thereof will be omitted.

  Although the case where the metal member 22 is disposed on the outer periphery of the shaft portion 2a is illustrated as the shaft member 2 in the above description, the configuration of the shaft member 2 is not limited thereto. For example, in the illustrated example, the flange portion 2b is formed only of resin, but a metal material may be disposed on the core portion.

  In the illustrated example, the thrust bearing surfaces having the dynamic pressure grooves 23 and 24 are formed on both end surfaces of the flange portion 1b. However, either one of the thrust bearing surfaces is connected to the end surface of the flange portion 2b. It can also be formed on the end surface 8c of the bearing sleeve 8 or the inner bottom surface 7c1 of the housing 7. Further, the bearing gap of the thrust bearing portion T2 that supports the shaft member 2 from below can be formed between the upper end surface 7f of the housing 7 (see FIG. 4) and the lower end surface of the hub 3 facing the housing 7. it can.

It is the side view and sectional drawing of the shaft member concerning this invention. (A) A figure is a top view (a arrow view in FIG. 1) of a flange part, (b) A figure is a bottom view (b arrow view in FIG. 1) of a flange part. It is sectional drawing of the HDD spindle motor incorporating the dynamic pressure bearing apparatus. It is sectional drawing of a hydrodynamic bearing apparatus. It is sectional drawing of a bearing sleeve. It is sectional drawing which shows other embodiment of the shaft member concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 2a Shaft part 2b Flange part 2b1 Upper end surface 2b2 Lower end surface 3 Disc hub 4 Motor stator 5 Motor rotor 6 Casing 8a1-8a4 Dynamic pressure groove 7 Housing 7a Housing opening part 7b Side part 7c Bottom part 7c1 Inner bottom face (Housing bottom)
8 Bearing sleeve 9a Radial bearing gap 9b Radial bearing gap 10 Seal member 21 Resin material 22 Metal material 23 Dynamic pressure groove 24 Dynamic pressure groove 25 Thread part (Female thread part)
26 Screw 27 Other member (cap)

Claims (6)

In a shaft member for a hydrodynamic bearing device including a shaft portion and a flange portion projecting to the outer diameter side of the shaft portion,
A shaft member for a hydrodynamic bearing device, wherein an outer periphery of the shaft portion is formed of a hollow cylindrical metal material, and a core portion of the shaft portion and the flange portion are formed of a resin material.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein the shaft member is formed by resin molding using the metal material as an insert part.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein a plurality of hydrodynamic grooves are provided on at least one end face of the flange portion.   The shaft member for a hydrodynamic bearing device according to claim 3, wherein the dynamic pressure groove on the end surface of the flange portion is formed simultaneously with the molding of the flange portion.   The shaft member for a hydrodynamic bearing device according to any one of claims 1 to 4, wherein a screw portion for screw fastening with another member is formed at an end on the side opposite to the flange portion.   The shaft member for a hydrodynamic bearing device according to claim 5, wherein the screw portion is formed on an inner periphery of an end portion of the metal material.