JP3984091B2 - Hydrodynamic bearing device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic bearing device that supports a rotating member with an oil film formed in a bearing gap. This bearing device is a motor for information equipment, for example, a magnetic disk device such as HDD / FDD, an optical disk device such as CD-ROM / DVD-ROM, a spindle motor such as a magneto-optical disk device such as MD / MO, and a laser beam printer. It is suitable for (LBP) polygon scanner motors or small motors such as electrical equipment such as axial fans.
[0002]
[Prior art]
In addition to high rotation accuracy, the various motors are required to have high speed, low cost, and low noise. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, as this type of bearing, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied, or It is actually used.
[0003]
For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk device such as an HDD, a radial bearing portion that rotatably supports a shaft member in a radial direction, and a thrust bearing portion that rotatably supports the shaft member in a thrust direction; A dynamic pressure bearing having a dynamic pressure generating groove (dynamic pressure groove) on the bearing surface is used at least in the radial bearing portion. The dynamic pressure groove of the radial bearing portion is formed on either the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member.
[0004]
Normally, the bearing sleeve is fixed to the inner periphery of the housing by means such as press-fitting or bonding, and a seal member is provided at the opening of the housing in order to prevent the lubricating oil injected into the inner space of the housing from leaking to the outside. Often fixed.
[0005]
[Problems to be solved by the invention]
The bearing device configured as described above is composed of parts such as a housing, a bearing sleeve, a shaft member, and a seal member. In order to ensure high bearing performance required as information devices become more and more sophisticated, It is necessary to further improve the processing accuracy and assembly accuracy of parts. In addition, along with the trend toward lower prices of information equipment, the demand for cost reduction for this type of bearing device has become increasingly severe.
[0006]
In order to meet these demands, the adoption of a resin insert molding method using a sintered metal bearing sleeve as an insert part and a housing made of resin is being studied. Adequate bearings due to the fact that the adhesion to the metal bearing sleeve is likely to be insufficient, the resin may be peeled off from the bearing sleeve surface, and the positioning accuracy of the bearing sleeve during injection molding is difficult to achieve. There is a problem that it is difficult to ensure accuracy.
[0007]
Therefore, an object of the present invention is to provide a fluid dynamic bearing capable of ensuring high bearing accuracy even when an insert-molded resin housing is used, and a manufacturing method thereof.
[0008]
[Means for Solving the Problems]
To achieve the above object, the present invention provides a bearing sleeve made of sintered metal that forms a radial bearing gap with the outer periphery of a shaft member to be supported, and a housing molded with resin using the bearing sleeve as an insert part. A hydrodynamic bearing device that holds the shaft member and the bearing sleeve in a non-contact manner by a fluid film formed in a radial bearing gap when the shaft member and the bearing sleeve rotate relative to each other. The seal portion that extends from the inner diameter side to form a seal space and the bottom portion that closes the other end of the side portion are integrally provided, and is molded from a resin injected from the gate facing the bottom end surface. has a portion which is not covered with resin facing space, said portion of the bearing sleeve, and the type and engageable reference surface for molding the inner circumferential surface of the seal portion of the housing, the bearing Three The pores in the vicinity of the surface of the is characterized in that intruded resin.
[0009]
The sintered metal used as the material of the bearing sleeve is a porous metal, and is obtained by mixing, molding and sintering metal powder. Such a sintered metal has a large number of pores (pores as an internal structure) inside and a large number of apertures formed so as to communicate with the outer surface. As the metal powder, for example, one or more powders selected from copper, iron, and aluminum are used as raw materials, and powders such as tin, zinc, lead, graphite, molybdenum disulfide, or the like, if necessary An alloy powder added may be considered.
[0010]
Since the resin enters the pores (including those opened on the surface) near the surface of the sintered metal bearing sleeve in this way, the resin that has entered the pores exerts an anchor effect, so the housing and the bearing sleeve Can be firmly fused to reliably prevent the resin from peeling from the sintered metal.
[0012]
In addition to the sintered metal described above, the metal bearing sleeve is a normal metal material (a metal material having no systematic pores, or a metal material having a small porosity even though it has systematic pores). Can be formed. As this metal material, for example, a soft metal such as stainless steel, a copper alloy, or brass can be used.
[0013]
Since the portion of the bearing sleeve that is not covered with the resin is used as a reference surface that can be engaged with the mold for molding the inner peripheral surface of the seal portion of the housing , the bearing sleeve is accurately positioned in the mold. The inner peripheral surface of the bearing sleeve and the outer peripheral surface of the housing are finished with high accuracy, and thereby the accuracy of the bearing device itself can be improved.
[0014]
As described above, when the bearing sleeve is molded with resin, particularly when the outer periphery and both end surfaces of the bearing sleeve are molded with resin, how to secure the reference surface of the bearing sleeve becomes a problem. In this case, if the chamfered portion formed on the inner periphery of the bearing sleeve is used as a reference surface, the reference surface can be used as it is without being removed in a separate process after the product is manufactured, so that the manufacturing process can be simplified. it can. Since this chamfered portion is usually tapered or curved, if the engagement portion of the mold is brought into surface contact with this, the bearing sleeve is reliably positioned both in the axial direction and in the radial direction of the bearing sleeve. be able to.
[0015]
In this hydrodynamic bearing device, the reference surface formed on the inner periphery of the bearing sleeve is engaged with the mold inserted in the inner periphery of the bearing sleeve at the time of mold forming to position the bearing sleeve, and the resin is injected at the time of molding. It can be manufactured by pressing the bearing sleeve with pressure in the direction of engagement between the reference surface and the mold .
[0016]
Thereby, positioning of a bearing sleeve can be performed reliably until resin hardens | cures, and the precision of a bearing apparatus can be raised more.
[0017]
If the gate for injecting the resin at the time of mold molding is provided at only one place, more preferably, if it is provided on the center line of the cavity (the center line of the side portion 7b formed after the injection molding), the air caught at the time of resin injection And gas can be reliably discharged out of the mold without stopping in the cavity, so that the formation of nests after curing of the resin can be avoided reliably, and the high adhesion between the bearing sleeve and the housing Can be secured.
[0018]
If the bearing sleeve is heated above the mold temperature during molding, the molten resin can easily enter the pores of the bearing sleeve, so that the resin can be deeply impregnated from the surface of the bearing sleeve, and the housing and the bearing sleeve are in close contact with each other. The degree can be further increased.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS.
[0020]
As an example of a hydrodynamic bearing device, FIG. 1 supports a shaft member by generating dynamic pressure of fluid (oil in this embodiment) such as oil or air in a bearing gap by a dynamic pressure generating groove (dynamic pressure groove). 1 shows a hydrodynamic bearing device 1 that performs the following.
[0021]
The hydrodynamic bearing device 1 includes a bottomed cylindrical housing 7 having one end opened and the other end closed, a cylindrical bearing sleeve 8, and a shaft member 2 as main components. This hydrodynamic bearing device is used in a disk drive device such as an HDD, and in this case, the housing 7 is fixed to a stationary member such as a casing, and one end (upper end in the illustrated example) of the shaft member 2 is one or Fixed to a disk hub that holds multiple disks. In the following description, the description will proceed with the opening side (seal side) of the housing 7 as the upper side and the closed side of the housing 7 as the lower side.
[0022]
The shaft member 2 is formed of a metal material such as stainless steel. The shaft end portion (lower end in the illustrated example) of the shaft member 2 is formed in a spherical shape, and a pivot type thrust bearing portion T is configured by contacting and supporting the shaft end portion 2a with the bottom portion 7c of the housing.
[0023]
The bearing sleeve 8 is disposed at a predetermined position on the inner peripheral surface of the housing 7, more specifically, on the inner peripheral surface 7c1 of the side portion 7b. The bearing sleeve 8 is formed of, for example, a porous body made of sintered metal, particularly a sintered metal porous body mainly composed of copper, and in particular, impregnated with lubricating oil or lubricating grease to hold the oil in the pores. It is made of a porous body (oil-containing sintered metal). Between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface of the shaft member 2, the first radial bearing portion R1 and the second radial bearing portion R2 are provided apart in the axial direction.
[0024]
On the inner peripheral surface 8a of the bearing sleeve 8 formed of this sintered metal, two regions serving as radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2 are provided apart in the axial direction. In these two regions, for example, herringbone-shaped dynamic pressure grooves are formed. In addition, you may employ | adopt spiral shape, an axial direction groove shape, etc. as a shape of a dynamic pressure groove. On the upper end surface 8b of the bearing sleeve 8, a groove 8e for identifying the direction of the bearing sleeve 8 is formed in an annular shape.
[0025]
As will be described later, the housing 7 is formed by injection molding of resin using a bearing sleeve 8 made of sintered metal as an insert part. The housing 7 is integrally provided with a cylindrical side portion 7b, a seal portion 7a extending from the upper end of the side portion 7b to the inner diameter side, and a bottom portion 7c closing the lower end of the side portion 7b. The inner peripheral surface 7a1 of the seal portion 7a and the inner peripheral surface 7b1 of the side portion 7b extend straight in the axial direction, and the inner peripheral surface 7a1 of the seal portion 7a is formed with a tapered outer peripheral surface formed on the shaft member 2. It faces through a tapered seal space S having a predetermined width. In the housing 7, the inner surface 7 a 1 of the seal portion 7 a and the upper end surface 8 b of the bearing sleeve 8, the inner peripheral surface 7 b 1 of the side portion 7 b and the outer peripheral surface of the bearing sleeve 8, the inner surface 7 c 1 of the bottom 7 c and the lower end surface of the bearing sleeve 8. 8c is in close contact with each other. The chamfered portion 8d formed on the inner peripheral surface 8a of the bearing sleeve 8 and the inner periphery of the upper end surface 8b is not covered with resin.
[0026]
The shaft member 2 is inserted into the inner peripheral surface 8a of the bearing sleeve 8, and the spherical surface portion 2a is brought into contact with the inner end surface 7c1 of the bottom portion 7c of the housing. Lubricating oil is supplied to the internal space of the housing 7 sealed by the seal portion 5a, and the radial bearing gaps R1, R2 are filled with the lubricating oil.
[0027]
When the shaft member 2 and the bearing sleeve 8 rotate relative to each other (in this embodiment, when the shaft member 2 rotates), the regions (two upper and lower regions) serving as the radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 are respectively It faces the outer peripheral surface of the shaft member 2 via a radial bearing gap. Along with the rotation of the shaft member, an oil film of lubricating oil is formed in the radial bearing gap, and the shaft member 2 is instructed to contact non-contact freely in the radial direction by the dynamic pressure. Thereby, the 1st radial bearing part R1 and 2nd radial bearing part R2 which non-contact-support the shaft member 2 rotatably in the radial direction are comprised. On the other hand, the shaft member 2 is rotatably supported by a pivot-type thrust bearing portion T in the thrust direction. In the illustrated example, the shaft end 2a of the shaft member 2 is in direct contact with the inner side surface 7c1 of the housing bottom 7c. However, a thrust plate made of an appropriate material (such as a low friction material) is disposed on the housing bottom 7c. The shaft end portion 2a can be slidably contacted with this.
[0028]
FIG. 2 shows an injection molding apparatus for insert molding the housing 7. This injection molding apparatus has an inner mold 10 and an outer mold 20, and one of them is a movable mold (for example, the inner mold 10), and the other is a fixed mold.
[0029]
The inner mold 10 has a cylindrical shaft portion 11. The shaft portion 11 has a fitting portion 12 fitted to the inner periphery of the bearing sleeve 8 and a seal molding portion 13 for molding the inner peripheral surface 7a1 of the seal portion 7a. The outer diameter of the seal molding portion 13 is as follows. It is larger than the outer dimension of the fitting part 12. A tapered engagement portion 14 is formed between the fitting portion 12 and the seal molding portion 13. The engaging portion 14 can engage with a chamfered portion 8d formed on the inner periphery of the upper end portion of the bearing sleeve 8, and can be engaged with each other, and the bearing sleeve 8 is positioned in the mold by the engagement of both.
[0030]
The outer mold 20 has a cylindrical hollow-shaped molding portion 21 and maintains a coaxial state with the inner mold 10 while abutting the abutting surface 22 with the abutting surface 15 of the inner mold, thereby providing a bearing. A cavity 30 is formed around the sleeve 8. The molten resin is injected into the cavity 30 from the gate 31 and filled into the cavity 30. After that, when the resin is cured, the inner mold 10 and the outer mold 20 are separated by the abutting surfaces 15 and 22, and the mold is opened. A housing 7 in which the sleeve 8 is molded with resin is obtained. This molded product is a composite part composed of a bearing sleeve 8 and a housing 7, and both members 8 and 7 are fixed to each other without going through a separate fixing step.
[0031]
As the molten resin, thermoplastic resins such as polypropylene, polyacetal, and polyphenylene sulfide can be used. This molten resin is preferably blended with a solid lubricant such as PTFE, graphite, molybdenum disulfide or the like in order to improve lubricity and wear resistance in the thrust bearing portion T. Further, in order to ensure the strength of the housing 7 and ensure good housing accuracy, it is desirable to add a reinforcing material such as glass fiber.
[0032]
By the way, when the chamfered portion 8d of the bearing sleeve 8 is engaged with the engaging portion 14 of the inner mold 10 as described above, it is necessary to maintain the engaged state until the resin is completely cured. There is. For this purpose, it is desirable to provide the gate 31 only at a portion facing the lower end surface 8 c of the housing 7, particularly at one place on the central axis of the cavity 30. As a result, the pressure of the resin injected from the gate 31 acts on the lower end surface 8c of the bearing sleeve 8 and pushes the bearing sleeve 8 upward (housing opening side). Therefore, the chamfered portion 8d of the bearing sleeve 8 The engagement state of the inner mold 10 with the engagement portion 14 can be reliably maintained, and the positioning accuracy of the bearing sleeve 8 can be increased.
[0033]
If a sufficient pressing force is applied to the bearing sleeve 8 in the direction of engagement with the engagement portion 14, the gate 31 may be eccentric from the central axis of the cavity 30, or the resin injection direction may be set to the cavity. It can also be tilted with respect to the central axis.
[0034]
When gates 31 are provided at a plurality of locations as in general injection molding, for example, when gates are provided at two locations near the outer periphery of the cavity 30 in addition to the gates 31 on the axis of the cavity 30 (three-point gate) ), Air and gas (hereinafter referred to as air) entrained during injection interfere with the flow of resin injected from other gates and remain in the cavity, causing the formation of nests after curing. There is a case. On the other hand, as shown in the figure, when the gate 31 is disposed only at one place, particularly when it is disposed on the central axis of the cavity 30, the entrained air or the like rides on the flow of the resin and the bottom 30 a of the cavity 30. Is moved to the outer diameter side, the inside of the cavity side portion 30b is pushed out to the housing opening side, and further discharged through the abutting surfaces 15 and 22 between the molds to the outside of the cavity 30. Can be avoided. In order to smoothly discharge air or the like at this time, it is desirable to form an exhaust passage 32 on the abutting surfaces 15 and 22 between the molds.
[0035]
The mold holding pressure during mold clamping is set to 1.2 to 2.5 times the injection pressure. If the holding pressure is less than 1.2 times, sufficient adhesion between the resin and the sintered metal cannot be obtained, and the resin is peeled off from the sintered metal and the fixing state of the resin sleeve becomes unstable. Further, if the holding pressure exceeds 2.5 times, it becomes difficult to remove the housing 7 after injection molding. On the other hand, if it is the range of 1.2 to 2.5 times, these moldability and demoldability can be made compatible.
[0036]
By the way, when a solid lubricant or a reinforcing material is blended in the molten resin as described above, the viscosity of the molten resin increases and the fluidity decreases. In this case, it is necessary to increase the injection pressure of the resin in order to increase the filling efficiency of the resin. With such a high injection pressure, the cavity side portion 30b on the outer peripheral side of the bearing sleeve 8 is formed as thin as possible in the cavity. There is a need to. This is because if this portion is thick, a higher injection pressure is required, and the bearing sleeve 8 may be deformed by the injection pressure and the accuracy of the dynamic pressure groove may be reduced. On the other hand, the cavity bottom 30c is preferably formed as thick as possible to ensure wear resistance against sliding with the shaft member 2 and strength when the shaft member 2 is inserted into the inner periphery of the bearing sleeve 8. On the other hand, if the cavity bottom 30c is too thick, the problem of resin peeling due to the formation of nests and sink marks occurs.
[0037]
As a result of intensive studies by the inventors, if the ratio L1 / L2 of the thickness L1 of the side portion 7b of the housing 7 to the thickness L2 of the bottom portion 7c is set between 0.15 and 1.2, the flow of the resin It has been found that the resin is peeled off due to the occurrence of defects, nests and shrinkage, and that the deformation of the bearing sleeve 8 due to the injection pressure can be reliably prevented. Here, the thickness L2 of the housing bottom 7c refers to the distance between the housing lower end surface 8c of the bearing sleeve 8 and the outer surface 7c2 of the housing bottom 7c.
At the time of injection molding, it is desirable to heat the bearing sleeve 8 at a temperature higher than the mold temperature (about 100 ° C.) (for example, 150 ° C. or higher), more preferably above the melting point of the molten resin. When the bearing sleeve 8 is preheated during the injection molding as described above, the molten resin 7d enters the inside through pores 8f (surface opening) opened on the surface of the bearing sleeve 8 as shown in FIG. Since the pores in the vicinity are filled, the adhesive strength of the housing 7 and the bearing sleeve 8 is increased by the anchor effect of the cured resin 7d, and the bearing sleeve 8 and the housing 7 can be more firmly fused without causing resin separation. .
[0038]
In this case, if at least 50%, preferably 70% or more of the surface opening 8f of the bearing sleeve 8 is filled with the resin 7d at the contact portion with the resin, it is practically used between the housing 7 and the bearing sleeve 8. A sufficient level of adhesion strength can be secured. Note that this does not apply to the peripheral portion of the resin layer where the resin thickness is not sufficient. The ratio of the surface opening 8f filled with the resin is determined by the surface opening 8f embedded in the resin after the housing 7 is insert-molded by the above procedure and the resin housing 7 is peeled off from the bearing sleeve 8 after the resin is solidified. Can be performed by measuring the area ratio.
[0039]
The present invention can be applied to any bottomed cylindrical housing in which the bearing sleeve is an insert product and at least one end of the housing is closed with resin. The housing shape and the bearing structure are limited to those shown in the drawings. Not. For example, as long as the shape of the housing satisfies the above conditions, the thrust bearing portion T may be constituted by a dynamic pressure bearing that supports the contact with the fluid dynamic pressure generated in the thrust bearing gap.
[0040]
Moreover, in the said embodiment, although the case where the dynamic pressure bearing which has a dynamic pressure groove is used as a dynamic pressure generation means as radial bearing part R1, R2, it illustrates as radial bearing part R1, R2 besides this. The present invention can also be applied to the case where a perfect circular bearing having no dynamic pressure groove and having a perfect circular radial bearing surface is used.
[0041]
【The invention's effect】
As described above, according to the present invention, the positioning accuracy of the bearing sleeve when molding the housing can be improved, and the occurrence of nests and shrinkage at the bottom of the housing can be reliably avoided, and the deformation of the bearing sleeve during molding can be prevented. Therefore, it is possible to improve the accuracy of the hydrodynamic bearing device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a hydrodynamic bearing device according to the present invention.
FIG. 2 is a cross-sectional view showing a housing insert molding process.
FIG. 3 is an enlarged cross-sectional view of a surface portion of a bearing sleeve molded with resin.
[Explanation of symbols]
1 Hydrodynamic bearing device 2 Shaft member 2a Spherical surface portion 7 Housing 8 Bearing sleeve 8d Reference surface (chamfered portion)
8f Pore 10 Inner die 14 Engaging portion 20 Outer die 30 Cavity 31 Gate R1 Radial bearing portion R2 Radial bearing portion S Thrust bearing portion

Claims (5)

A bearing sleeve made of sintered metal that forms a radial bearing gap with the outer periphery of the shaft member to be supported, and a housing molded with resin using the bearing sleeve as an insert part, and the relative relationship between the shaft member and the bearing sleeve In a hydrodynamic bearing device that holds a shaft member and a bearing sleeve in a non-contact manner with a fluid film formed in a radial bearing gap during rotation,
The housing is integrally provided with a side portion, a seal portion that extends from one end of the side portion toward the inner diameter side to form a seal space, and a bottom portion that closes the other end of the side portion, and is injected from the gate facing the bottom end surface. The bearing sleeve has a portion that faces the seal space and is not covered with resin, and the portion of the bearing sleeve can be engaged with a mold that molds the inner peripheral surface of the seal portion of the housing. A hydrodynamic bearing device in which resin is made to enter pores near the surface of the bearing sleeve. A reference surface, the fluid bearing apparatus according to claim 1, wherein provided on the chamfered portion of the inner periphery of the bearing sleeve.   The hydrodynamic bearing device according to claim 1, wherein the gate is provided only at one location. A metal bearing sleeve that forms a radial bearing gap with the outer periphery of the shaft member to be supported, and a housing molded with resin using the bearing sleeve as an insert component, and when the shaft member and the bearing sleeve rotate relative to each other A method for manufacturing a hydrodynamic bearing device that holds a shaft member and a bearing sleeve in a non-contact manner with a fluid film formed in a radial bearing gap,
During molding, the reference surface formed on the inner circumference of the bearing sleeve is engaged with the mold inserted in the inner circumference of the bearing sleeve to position the bearing sleeve, and the bearing sleeve is moved by the resin injection pressure at the time of molding. A method of manufacturing a hydrodynamic bearing device, wherein the pressing is performed in an engagement direction between the reference surface and the mold. The method for manufacturing a hydrodynamic bearing device according to claim 4 , wherein the bearing sleeve is heated to a temperature equal to or higher than a mold temperature at the time of molding.

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