JP2004132402A - Fluid bearing device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device having a small number of components, low in cost and high in reliability and capable of surely preventing the mixture of foreign matters into a bearing gap. <P>SOLUTION: A housing 7 is formed by resin molding using a bearing sleeve 8 as an insert component. The bearing sleeve 8 is formed of a sintered alloy with a herringbone dynamic pressure groove in the inner periphery. Burrs formed at a P point following the molding are deposited on the upper end face 7d of the housing 7 at the glass transition point or higher and the melting point or lower of a resin. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrodynamic bearing device that supports a rotating member in a non-contact manner by an oil film of lubricating oil generated in a radial bearing gap. This bearing device is a spindle for information equipment, for example, a magnetic disk device such as an HDD or FDD, an optical disk device such as a CD-ROM, a CD-R / RW, a DVD-ROM / RAM, or a magneto-optical disk device such as an MD or MO. It is suitable for a motor, a polygon scanner motor of a laser beam printer (LBP), or a small motor such as an electric device such as an axial fan.
[0002]
[Prior art]
The above various motors are required to have high speed, low cost, low noise, etc. in addition to high rotational accuracy. One of the components that determine the required performance is a bearing that supports the spindle of the motor.In recent years, the use of a fluid bearing having characteristics excellent in the required performance has been studied or actually used. .
[0003]
Fluid bearings of this type include a so-called dynamic pressure bearing having a dynamic pressure generating means for generating dynamic pressure in lubricating oil in a bearing gap, and a so-called circular bearing without a dynamic pressure generating means (the bearing surface is a perfect circle). Bearings).
[0004]
For example, in a fluid bearing device incorporated in a spindle motor of a disk device such as an HDD or a polygon scanner motor of a laser beam printer (LBP), a radial bearing portion that rotatably supports a shaft member in a radial direction in a non-contact manner, and a shaft member A thrust bearing portion rotatably supported in the thrust direction is provided, and a dynamic pressure generating groove (dynamic pressure groove) is provided as a radial bearing portion on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member. Bearings are used. As the thrust bearing portion, for example, a bearing (a so-called pivot bearing) having a structure in which one end surface of a shaft member is supported in contact with a thrust plate is used. Normally, the bearing sleeve is fixed at a predetermined position on the inner circumference of the housing, and a seal member may be provided at the opening of the housing to prevent the lubricating oil injected into the internal space of the housing from leaking outside. Many (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-11-191945 [0006]
[Problems to be solved by the invention]
The hydrodynamic bearing device having the above configuration is composed of many parts such as a housing, a bearing sleeve, a shaft member, a thrust plate, and a seal member, and secures a high bearing performance required as information devices become more and more sophisticated. Efforts have been made to increase the processing accuracy and assembly accuracy of each part. On the other hand, with the trend toward lower price and smaller size of information equipment, demands for cost reduction of this type of hydrodynamic bearing device are becoming more and more severe.
[0007]
In addition, in this type of hydrodynamic bearing device, it is necessary to strictly control the accuracy of the bearing gap in order to ensure the bearing performance, and it is necessary to minimize the entry of foreign matter into the bearing gap.
[0008]
Therefore, an object of the present invention is to provide a hydrodynamic bearing device which has a small number of parts, is low in cost, has high reliability, and can reliably prevent foreign substances from being mixed into a bearing gap.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a fluid bearing device according to the present invention includes a resin housing, a bearing sleeve provided inside the housing, a shaft member inserted into an inner peripheral surface of the bearing sleeve, and a bearing sleeve. A radial bearing portion that is provided between the inner peripheral surface and the outer peripheral surface of the shaft member and that non-contactly supports the shaft member in a radial direction with an oil film of lubricating oil generated in a bearing gap; and It is formed by molding a resin as an insert part, and burrs formed along with the molding are welded to the surface of the housing.
[0010]
By forming the housing by resin molding (insert molding) with the bearing sleeve as an insert part, the manufacturing cost of the housing can be reduced as compared with the case where the housing is formed of a metal material. When the fluid bearing device is provided with a thrust bearing portion for supporting the shaft member in the thrust direction, the thrust bearing portion may have a structure in which one end surface of the shaft member is directly supported by the bottom of the housing. Therefore, the thrust plate conventionally provided in this type of hydrodynamic bearing device becomes unnecessary, and the number of parts can be reduced. Further, since the operation of assembling the bearing sleeve to the housing is unnecessary, the assembly cost is reduced.
[0011]
Meanwhile, burrs are formed on the surface of the molded product after the insert molding by solidifying the molten resin that has entered the gap between the dies. If the burrs are left unattended, if the burrs fall off for some reason, they may enter the inner peripheral surface of the bearing sleeve and seriously affect bearing performance. Therefore, it is necessary to prevent such burrs from being prevented from being generated, or to remove the burrs by some method after demolding.
[0012]
However, it is difficult to completely prevent generation of burrs in insert molding. Therefore, the latter method must be taken as the above-described countermeasure against burrs. Specifically, a method of removing burrs by, for example, mechanical processing can be considered. However, in the case of shaving, there is a concern that a debris may enter the inner peripheral surface of the bearing sleeve, or a dimensional accuracy around the burr generating portion may be lost due to a pressing force at the time of working.
[0013]
Therefore, in the present invention, burrs formed during the molding are welded to the housing surface. Instead of removing burrs in this way, by welding to the surface of the housing, it is possible to reliably prevent the burrs from falling off.On the other hand, debris is not generated when processing burrs like machining. Therefore, it is possible to reliably prevent the bearing sleeve from entering the inner periphery. Also, at the time of heat welding, a high pressing force does not act on the burr generating portion unlike machining, and even if it is deformed, it is also possible to correct the dimension of the deformed portion with a jig for heat welding. Therefore, this part can be molded with high precision. As described above, it is possible to reliably prevent a decrease in bearing performance due to the occurrence of burrs, and to ensure high bearing performance.
[0014]
The above-mentioned welding is desirably performed at a temperature equal to or higher than the glass transition point of the resin and equal to or lower than the melting point temperature.
[0015]
The housing may have, at one end, a seal portion that forms a seal space with the outer peripheral surface of the shaft member. This seal portion can be formed integrally with the housing by insert molding.
[0016]
FIG. 2 shows an example of an injection molding apparatus for insert-molding the housing 7 having the seal portion 7a. As shown in the drawing, the apparatus includes a movable mold 10 and a fixed mold 20. One mold, for example, the movable mold 10 is configured by a cylindrical shaft portion 11 and an outer peripheral portion 16 fitted on the outer periphery thereof. You. The molten resin is injected from the gate portion 31 into the cavity 30 around the bearing sleeve 8 to fill the cavity 30, and when the resin is cured, first, the shaft portion 11 of the movable mold 10 is pulled out from the inner periphery of the bearing sleeve 8, Further, when the outer peripheral portion 16 is separated from the fixed mold 20 and opened, the housing 7 with the seal portion 7a in which the bearing sleeve 8 is molded with resin is obtained.
[0017]
In this injection molding apparatus, the inner peripheral surface 7a2 of the seal portion 7a can be molded on the outer peripheral surface of the shaft portion 11 (specifically, the seal molding portion 13) inserted into the inner periphery of the seal portion 7a. Since the burrs are formed mainly at the sliding portions of the dies, the burrs slide on each other when the dies are opened, and the inner peripheral surface of the outer peripheral surface of the shaft portion 11 and the outer peripheral portion 16 fitted in the outer periphery thereof (in the illustrated example, the outer peripheral portion 16). Is formed in the axial direction of the sliding portion A, that is, the inner peripheral surface 7a2 of the seal portion 7a. In this case, as shown in FIG. 3, the welding jig 40 is inserted into the inner periphery of the seal portion 7a and pressed against the end surface 7d of the housing 7, so that the burr 41 is softened and bent to be integrated with the end surface 7d of the housing 7. (Welding) (see FIGS. 4A and 4B), and the protruding portion of the burr 41 disappears. Therefore, it is possible to surely prevent the above-mentioned problems caused by the occurrence of burrs.
[0018]
When insert-molding a housing integrally having a seal portion as described above, it is preferable that the burr is formed on the outer diameter side of the inner peripheral surface of the seal portion. Thereby, it is possible to prevent a situation in which the dimensional accuracy of the seal portion is degraded due to deformation due to welding, and it is possible to avoid a risk that burrs fall off during welding and enter the inner peripheral surface of the bearing sleeve.
[0019]
Depending on the application of the fluid dynamic bearing device, the radial bearing portion may be constituted by a dynamic pressure bearing that generates pressure by dynamic pressure action of lubricating oil in a bearing gap.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0021]
FIG. 1 shows a hydrodynamic bearing device (fluid dynamic bearing device) 1 according to this embodiment. The hydrodynamic bearing device 1 is incorporated in, for example, a spindle motor of a disk device such as an HDD or a polygon scanner motor of a laser beam printer (LBP), and includes a housing 7, a bearing sleeve 8, and a shaft member 2. It is composed.
[0022]
A first radial bearing portion R1 and a second radial bearing portion R2 are provided between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a of the shaft member 2 so as to be separated in the axial direction. A thrust bearing portion T is provided between the lower end surface 2b of the shaft member 2 and the inner bottom surface 7c1 of the bottom 7c of the housing 7. For convenience of description, the description will be made with the side of the thrust bearing portion T being the lower side and the side opposite to the thrust T being the upper side.
[0023]
The shaft member 2 is formed of, for example, a metal material such as stainless steel, and its lower end surface 2b is formed in a convex spherical shape.
[0024]
The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of a sintered metal. As the sintered metal, for example, one or more metal powders selected from copper, iron, and aluminum, or metal powder or alloy powder that has been subjected to a coating treatment such as copper-coated iron powder as a main raw material, According to the above, a powder obtained by mixing, molding, and sintering a powder of tin, zinc, lead, graphite, molybdenum disulfide or the like, or an alloy powder thereof can be used. Such a sintered metal has a large number of pores (pores as an internal structure) inside, and also has a large number of openings formed through these pores to the outer surface. This sintered metal is used as an oil-impregnated sintered metal impregnated with lubricating oil or lubricating grease. The bearing sleeve 8 can be formed of not only a sintered metal but also another metal material such as a soft metal.
[0025]
On the inner peripheral surface 8a of the bearing sleeve 8, two upper and lower regions serving as radial bearing surfaces of a first radial bearing portion R1 and a second radial bearing portion R2 are provided axially separated from each other. As the dynamic pressure generating means, for example, a herringbone-shaped dynamic pressure groove is formed. As the dynamic pressure generating means, a spiral shape or an axial groove may be formed, or a three-arc bearing may be used. Further, a chamfered portion 8d is formed on the inner peripheral upper end portion of the bearing sleeve 8, and a chamfered portion 8f is formed on the inner peripheral lower end portion.
[0026]
The housing 7 is formed by injection molding (insert molding) a resin such as nylon 66 using the bearing sleeve 8 as an insert part, as described later. The housing 7 has a bottomed cylindrical shape having one end opened and the other end closed, a cylindrical side portion 7b, and an annular seal portion 7a integrally extending from the upper end of the side portion 7b to the inner diameter side. It has a bottom part 7c which is continuous with the lower end of the side part 7b. The inner peripheral surface 7a2 of the seal portion 7a faces the outer peripheral surface 2a of the shaft member 2 via a predetermined seal space S. In this embodiment, the outer peripheral surface 2a of the shaft member 2, which faces the inner peripheral surface 7a2 of the seal portion 7a and forms the seal space S, is tapered so as to gradually reduce its diameter upward (outward of the housing 7). It is formed in a shape. When the shaft member 2 rotates, the tapered outer peripheral surface 2a also functions as a so-called centrifugal seal. The seal space S may be formed in a cylindrical shape having the same diameter in the axial direction, in addition to the tapered space.
[0027]
FIG. 2 conceptually shows an injection molding apparatus for insert-molding the housing 7. This injection molding apparatus has a movable mold 10 and a fixed mold 20.
[0028]
Either the movable mold 10 or the fixed mold 20, for example, the movable mold 10 has a shaft portion 11 having a circular cross section and an outer peripheral portion 16 fitted around the shaft portion 11. The shaft portion 11 has a fitting portion 12 fitted to the inner peripheral surface 8a of the bearing sleeve 8, and a seal molding portion 13 for molding the inner peripheral surface 7a2 of the seal portion 7a of the housing 7. The outer diameter of 13 is larger than the outer dimension of the fitting portion 12. A tapered contact portion 14 is formed at the boundary between the fitting portion 12 and the seal forming portion 13. The contact portion 14 comes into contact with a chamfered portion 8 d formed on the inner peripheral upper end portion of the bearing sleeve 8, thereby positioning the bearing sleeve 8 in the cavity 30.
[0029]
The fixed mold 20 has a hollow cylindrical molded part 21, and by maintaining its coaxial state with the movable mold 10, the abutment surface 22 abuts against the abutment surface 15 of the movable mold 10, A cavity 30 is formed around the bearing sleeve 8. A molten resin is injected into the cavity 30 from the gate 31 to fill the cavity 30, and then, when the resin is cured, the mold is opened to obtain the housing 7 in which the bearing sleeve 8 is molded with the resin. The mold opening is performed, for example, by first removing the shaft portion 11 of the movable mold 10 from the inner periphery of the bearing sleeve 8 and then separating the outer peripheral portion 16 of the movable mold 10 from the fixed mold 20.
[0030]
The housing 7 and the bearing sleeve 8 are mutually fixed by the above-mentioned insert molding without going through a separate fixing step. As shown in FIG. 1, inside 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, the outer peripheral surface 8 g of the bearing sleeve 8, and the bottom 7 c The bottom surface 7c1, the lower end surface 8c of the bearing sleeve 8, and the chamfered portion 8f of the inner peripheral lower end portion are in close contact with each other. Note that the inner peripheral surface 8a of the bearing sleeve 8 and the chamfered portion 8d on the inner peripheral upper end side are not covered with the resin.
[0031]
The dynamic pressure bearing device 1 of this embodiment can be assembled by mounting the shaft member 2 to the housing 7 and the bearing sleeve 8 fixed to each other by insert molding. That is, the shaft member 2 is inserted into the inner peripheral surface 8a of the bearing sleeve 8, and the lower end surface 2b is brought into contact with the inner bottom surface 7c1 of the housing 7. Then, for example, in a state of vacuum evacuation, lubricating oil is injected into the inside of the housing 7 sealed by the seal portion 7a, and the space inside the housing such as a bearing gap is filled with oil, and the pores of the bearing sleeve 8 are impregnated with oil. .
[0032]
When the shaft member 2 rotates, regions (two upper and lower regions) of the inner peripheral surface 8a of the bearing sleeve 8 to be radial bearing surfaces respectively oppose the outer peripheral surface 2a of the shaft member 2 via the radial bearing gap. Then, with the rotation of the shaft member 2, a dynamic pressure action of the lubricating oil is generated in the radial bearing gap, and the shaft member 2 is non-rotatably rotatable in the radial direction by an oil film of the lubricating oil formed in the radial bearing gap. Contact supported. Thus, a first radial bearing portion R1 and a second radial bearing portion R2 that rotatably support the shaft member 2 in the radial direction in a non-contact manner are configured. At the same time, the lower end surface 2b of the shaft member 2 is contacted and supported by the inner bottom surface 7c1 of the housing 7. Thus, a thrust bearing portion T that rotatably supports the shaft member 2 in the thrust direction is configured.
[0033]
As described above, in the movable mold 10, sliding occurs between the shaft portion 11 and the outer peripheral portion 16 during insert molding. The molten resin enters the sliding portion A with the filling of the resin into the cavity 30, and as shown in FIG. 4A, after solidification, this portion becomes a burr 41 projecting in the axial direction. The burr 41 is formed along the inner peripheral edge P of the upper end surface 7d of the housing 7 (the length, size, and the like of the burr 41 are exaggerated).
[0034]
The burr 41 is welded to the surface of the housing 7 (the upper end surface 7d in the present embodiment). As shown in FIG. 3, the welding is performed by inserting a welding jig 40 into the inner periphery of the upper end opening of the housing 7 (the upper and lower sides are inverted in FIG. 1 in the drawing). The welding jig 40 has a small-diameter portion 40a fitted to the inner peripheral surface 7a2 of the seal portion 7a of the housing 7, and a large-diameter portion formed with a larger diameter than the small-diameter portion 40a. Unit 40b. By heating the jig 40 and pushing it into the upper end opening of the housing 7, the burr 41 is softened and bent as shown in FIG. 7d (denoted by reference numeral 41 '), whereby the axial projection of the burr 41 disappears.
[0035]
When welding the burrs 41, no burrs are generated as in the case of machining. Therefore, it is possible to reliably prevent the burrs and their debris from entering the inner periphery of the bearing sleeve 8 (radial bearing gap). In addition, since the jig 40 for heat welding corrects the size of the vicinity of the generation portion P of the burr 41, in this embodiment, the upper end surface 7d of the housing 7 and the inner peripheral surface 7a2 of the seal portion, the accuracy of these portions can be improved. Can be. As described above, according to the present invention, it is possible to reliably prevent a decrease in bearing performance due to the occurrence of burrs, and to ensure high bearing performance.
[0036]
As described above, during the heat welding, the welding jig 40 is heated, and the welding temperature at that time is set to a temperature equal to or higher than the glass transition point of the material resin of the housing 7 and equal to or lower than the melting point. If the temperature is lower than the glass transition point temperature, the burr 41 cannot be softened. If the temperature exceeds the melting point, the resin at the contact portion with the welding jig 40 is in a molten state, and the accuracy is rather lowered. For example, when the housing 7 is molded from 66 nylon, the glass transition point is 80 ° C. and the melting point is 200 ° C., so that the welding is performed at the temperature (80 to 200 ° C.) therebetween.
[0037]
By the way, in order to prevent intrusion of foreign matter into the inner periphery of the bearing sleeve 8 and deterioration of the size of the seal portion 7a during welding of the burr, the generation portion P of the burr 41 should be as far as possible outside the seal portion inner peripheral surface 7a2. Preferably it is present. FIG. 5 shows an example of a means for achieving this, in which the shaft portion 11 'of the movable die 10 and the sliding portion A' of the outer peripheral die 16 'are located outside the inner peripheral surface 7a2 of the seal portion of the housing 7. The mold structure is changed so as to be located on the radial side. Specifically, a large-diameter portion 18 having a larger diameter than the seal forming portion 13 of the shaft portion 11 'is formed, and the end surface 18a of the large-diameter portion 18 is brought into contact with the housing upper end surface 7d. The outer periphery 16 ′ of the inner mold 10 is fitted to the outer periphery of the diameter portion 18. In this case, a portion between the outer peripheral surface of the large-diameter portion 18 and the inner peripheral surface of the outer peripheral portion 16 serves as a sliding portion A ′, and a burr generation portion P ′ is formed on an upper end surface 7 d of the housing on an extension thereof.
[0038]
In the above description, as the thrust bearing portion T, a pivot bearing that contacts and supports the end of the shaft member 2 is exemplified. However, as this bearing portion T, as in the case of the radial bearing portions R1 and R2, a dynamic pressure groove is used. It is also possible to use a dynamic pressure bearing that generates the pressure by the dynamic pressure effect of the lubricating oil generated in the bearing gap by a dynamic pressure generating means such as the above and supports the shaft member 2 in a non-contact manner in the thrust direction.
[0039]
In addition, the present invention can be similarly applied to a fluid bearing device in which one or both of the radial bearing portions R1 and R2 are configured as so-called perfect bearings.
[0040]
【The invention's effect】
According to the present invention, it is possible to provide a highly reliable hydrodynamic bearing device that is compact, has a small number of parts, is even lower in cost.
[0041]
In addition, since burrs formed during insert molding of the housing are welded to the surface of the housing, debris of the burrs may enter the inner peripheral surface of the bearing sleeve, or the dimensional accuracy of the burrs may be reduced. Can be avoided.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a hydrodynamic bearing device according to the present invention.
FIG. 2 is a sectional view conceptually showing an injection molding apparatus for injection molding a housing.
FIG. 3 is a cross-sectional view showing a step of welding burrs.
FIG. 4 (a) is an enlarged sectional view conceptually showing a burr before welding, and FIG. 4 (b) is an enlarged sectional view conceptually showing a state after welding.
FIG. 5 is a sectional view showing another embodiment of the injection molding apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fluid bearing device 2 Shaft member 7 Housing 7a Seal part 7a2 Inner peripheral surface 7b Side part 7c Bottom part 8 Bearing sleeve 8a Inner peripheral surface 40 Heat welding jig 41 Burrs P, P 'Burrs generating part A, A' Sliding part R1 First radial bearing portion R2 Second radial bearing portion S Seal space T Thrust bearing portion

Claims (6)

A housing made of resin, a bearing sleeve provided inside the housing, a shaft member inserted into the inner peripheral surface of the bearing sleeve, and provided between the inner peripheral surface of the bearing sleeve and the outer peripheral surface of the shaft member, A radial bearing portion for supporting the shaft member in a radial direction in a non-contact manner with an oil film of lubricating oil generated in the bearing gap,
The housing is formed by resin molding using a bearing sleeve as an insert part,
And a burr formed by the molding is welded to a surface of the housing. The hydrodynamic bearing device according to claim 1, wherein the resin is welded at a temperature equal to or higher than the glass transition point of the resin and equal to or lower than the melting point temperature. 3. The hydrodynamic bearing device according to claim 1, wherein the housing has at one end a seal portion that forms a seal space with an outer peripheral surface of the shaft member. 4. The hydrodynamic bearing device according to claim 3, wherein the resin burr is formed on an outer diameter side of the inner peripheral surface of the seal portion. The fluid bearing device according to any one of claims 1 to 4, wherein the radial bearing portion is a dynamic pressure bearing that generates pressure by a dynamic pressure action of lubricating oil in a bearing gap. A housing made of resin, a bearing sleeve provided inside the housing, a shaft member inserted into the inner peripheral surface of the bearing sleeve, and provided between the inner peripheral surface of the bearing sleeve and the outer peripheral surface of the shaft member, A method for manufacturing a fluid bearing device including at least a radial bearing portion that supports a shaft member in a radial direction in a non-contact manner with an oil film of lubricating oil generated in a bearing gap,
A method for manufacturing a hydrodynamic bearing device, wherein a housing is formed by molding a resin having a bearing sleeve as an insert part, and burrs formed during the molding are welded to a surface of the housing.

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