JP2008002650A - Dynamic-pressure bearing unit, its manufacturing method, and spindle motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability and impact resistance of a spindle motor by further stably and surely obtaining prescribed fixing strength while maintaining bearing accuracy by a simple configuration and manufacturing method. <P>SOLUTION: A dynamic-pressure bearing unit 1 is provided with a housing 2, a bearing 3, which is fixed in the housing and has each dynamic-pressure generation groove on the shaft-hole inner periphery 30 and the bearing end face 32, a rotary shaft 4 inserted into a shaft hole of the bearing 3, and lubricating oil sealed in the housing. The dynamic-pressure bearing unit supports the rotary shaft 4 in the radial direction and in the thrust direction in a non-contact state by a dynamic-pressure action occurring in the dynamic-pressure generation grooves during rotation of the rotary shaft 4. The bearing 3 is joined to the inner periphery of the housing 2 by press-fitting imparted with a tightening margin. The dynamic-pressure bearing unit has a gap 25 located between the inner periphery of the housing 2 and the outer periphery of the bearing 3 and formed in the circumferential direction on the side of either of upper/lower end parts. The housing and the bearing are bonded with each other by an adhesive P arranged in the gap. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing unit excellent in high rotational accuracy and high-speed stability required for a disk drive motor of a magnetic disk device or an optical disk device, a manufacturing method thereof, and a spindle motor, for example.

  A spindle motor used for a heart disk drive of a magnetic disk device is required to have high rotational accuracy particularly in terms of high recording density and high-speed information processing. For this reason, as disclosed in Patent Documents 1 and 2, recent spindle motors generate oil film pressure on the sliding surface using the rotation of the shaft body (rotating shaft), and the shaft body is moved in the thrust direction and Dynamic pressure type bearing units that can be supported in a non-contact state in the radial direction have come to be used. By the way, in this dynamic pressure bearing unit, for example, when applied to an information device such as a laptop computer, the housing has durability and impact resistance in order to maintain the bearing accuracy even if it receives an excessive impact. The fixing strength of the bearing against the must be improved. Against this background, in the past, the bearing was fixed to the inner periphery of the housing by press-fitting or shrink-fitting in order to ensure sufficient fixing strength of the bearing, that is, the removal force. If is increased, the inner diameter of the shaft hole is shrunk or deformed more than necessary, and high rotational accuracy and high-speed stability are impaired. Thus, Patent Documents 1 and 2 propose a device for increasing the bonding strength using an adhesive.

JP 2006-17299 A JP 2005-163903 A

  That is, in the hydrodynamic bearing unit of Patent Document 1, an adhesive groove is provided over the entire circumference of the bearing, and an injection hole facing the groove is formed around the housing. In this structure, in the pre-bonding process, after the bearing is fitted with a clearance fit or light pressure (tightening margin of 2 to 3 μm) in order to ensure the positioning of the bearing with respect to the housing, the anaerobic adhesive is applied to the hole. Then, it is poured into the concave groove and the capillary is used to allow the adhesive to penetrate into the fitting surface. In this structure, there is no problem in positioning the bearing and the housing, but when the adhesive is infiltrated into the mating surface using capillary action, the adhesive cannot be expected to spread uniformly over the entire mating surface. Variation in adhesive strength is inevitable. Further, when the bearing and the housing are fitted with a clearance fit, the lubricating oil to be sealed permeates the fitting surface of the bearing and the housing, which may cause a shortage of lubricating oil on the bearing surface.

  On the other hand, in the dynamic pressure bearing unit of Patent Document 2, a method of fitting the bearing and the housing by light press fitting is used, and a plurality of adhesive reservoirs are provided in the circumferential direction or axial direction of the inner peripheral surface of the housing. The adhesive is applied in advance to the inner periphery of the housing, and then the bearing is press-fitted into the housing. The surplus adhesive scraped out during the press-fitting of the bearing is captured by the adhesive reservoir, and another means is provided on the bearing end surface to capture the part at this portion. In this structure, since the adhesive is applied to the inner periphery of the housing, the workability is poor, and when a sintered bearing is used for the bearing, the adhesive is absorbed by the bearing, so the adhesive force is reduced and the enclosed lubricating oil In the same manner as in Patent Document 1, there is a possibility that the bearing surface lacks lubricating oil.

  Therefore, the present invention aims to obtain a predetermined fixing strength more stably and reliably while maintaining the bearing accuracy by a simple structure and manufacturing method, thereby improving the durability and impact resistance of the spindle motor. Yes.

  In order to achieve the above object, the invention of claim 1 is characterized in that a housing, a bearing having a dynamic pressure generating groove on an inner periphery of the shaft hole and a bearing end face, and a shaft fixed to the housing are inserted into the shaft hole of the bearing. A rotating shaft and lubricating oil sealed in the housing, and the rotating shaft is brought into a non-contact state in a radial direction and a thrust direction by a dynamic pressure action generated in the dynamic pressure generating groove when the rotating shaft rotates. In the supportable hydrodynamic bearing unit, the bearing is coupled to the inner circumference of the housing by press-fitting with a tightening margin, and is located between the inner circumference of the housing and the outer circumference of the bearing, and either the upper or lower end. It has a gap formed in the side circumferential direction, and the housing and the bearing are bonded by an adhesive disposed in the gap.

The above hydrodynamic bearing unit is more preferably embodied as follows.
(A) The bearing is a sintered bearing in which pores are sealed with a resin, and the tightening allowance of the sintered bearing is formed from 1 μm to 10 μm, and the gap exceeds 0 and is formed to 20 μm. (Claim 2).
(A) The gap has a tapered shape that expands toward the end side (Claim 3).
(C) An adhesive supply section having a one-step larger diameter is provided on the outer side of the end of the gap (side where the adhesive is supplied) (Claim 4).
(D) A plurality of grooves extending in the axial direction are provided on the outer peripheral surface of the bearing, and the inner peripheral surface of the housing communicates with the groove on the bearing side and has a circumferential direction deeper than the groove. A groove is provided (Claim 5).

  According to a sixth aspect of the present invention, the above hydrodynamic bearing unit is specified from a manufacturing method, and after the bearing is coupled into the housing by press-fitting, the adhesive is introduced from the corresponding end side into the gap. And is spread over almost the entire region of the gap by capillary action. On the other hand, the invention of claim 7 is specified from the application, and is a spindle motor provided with the above hydrodynamic bearing unit.

In the hydrodynamic bearing unit according to the first aspect of the present invention, since the press-fitting is performed with a tightening allowance, the positioning of the bearing can be surely performed. In addition, the press-fitting strength according to the tightening allowance and the adhesive strength according to the gap can be used to connect the housing and the bearing. The variation in the fixing strength is suppressed, and the fixing strength can be increased while maintaining the bearing accuracy. In this structure, the manufacturing method of claim 6, that is, after the bearing is coupled into the housing by press fitting, the adhesive is spread over the entire gap by capillarity.
In other words, the inventions of claims 1 and 6 can provide the required removal strength as compared with the prior art in which a tightening margin is given and only coupled by press-fitting while maintaining accuracy with the press-fitting strength and adhesive strength. Compared with the conventional structure (such as Patent Document 1) in which the adhesive is fixed exclusively by the adhesive force, it is possible to suppress variations in adhesive strength because it is a local adhesive on the end side, and the bearing is press-fitted into the housing from a state where the adhesive has been applied in advance. Compared to conventional structures (such as Patent Document 2), the pressure input and the adhesive force are clearly separated, so that the desired fixing strength can be reliably imparted while suppressing variations.

In the inventions of claims 2 to 6, since the pores of the sintered bearing are sealed with resin, it is possible to prevent a decrease in adhesive strength. In the invention of claim 2, for example, the upper limit value (10 μm) of the tightening allowance eliminates the possibility that the bearing accuracy is reduced due to shrinkage deformation, and the upper limit value (20 μm) of the gap is that the adhesive becomes thick and the adhesive force is reduced. Prevent fear. On the other hand, in the invention of claim 3, the gap is tapered so that the adhesive is efficiently spread over the entire gap by capillary action. On the other hand, in the invention of claim 4, an adhesive supply section is provided outside the gap so that the adhesive can be easily dropped, and the adhesive is reliably supplied to the gap.
On the other hand, in the invention of claim 5, the axial groove on the outer peripheral surface of the bearing is inserted into the lubricant by removing air through the groove when the lubricant is sealed by vacuum impregnation after the bearing is fixed to the housing. Make it better. The circumferential grooves on the inner peripheral surface of the housing allow the axial grooves to communicate with each other and prevent the axial grooves from being blocked by the adhesive.

  According to the seventh aspect of the present invention, the dynamic pressure bearing unit described above, that is, the bearing inner peripheral surface and the bearing end surface have the dynamic pressure generating grooves, and the dynamic pressure action of the grooves supports the rotating shaft with high accuracy. Is firmly fixed and excellent in impact resistance. For example, even if a disk device or the like incorporating a spindle motor is dropped, the rotational accuracy is not impaired, thereby improving the quality and reliability.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a hydrodynamic bearing unit (hereinafter abbreviated as a bearing unit) of an embodiment, FIG. 2 shows a cross section of the main part of the bearing unit, FIG. 3 shows a single bearing, and FIG. 4 shows a modification of the bearing unit. FIG. 5 shows a spindle motor. Note that the adhesive is omitted in FIGS. 1A, 4A, and 5, and the gaps and grooves of the main parts are shown exaggerated larger than actual. In the following description, the bearing structure, assembly, modification, and spindle motor will be referred to in this order.

(Bearing structure) The bearing unit 1 in FIG. 1 has a bottomed cylindrical housing 2, a shaft hole inner periphery 30 forming a dynamic pressure generating groove, and an upper bearing end surface 32. The bearing 3 is fixed to the circumference 20 by press-fitting and bonding, the rotary shaft 4 inserted into the shaft hole of the bearing 3, and a lubricating oil (not shown) sealed in the housing 2. In this bearing unit 1, the thrust bearing portion S (SFDB) is set between the upper bearing end surface 32 of the bearing 3 and the flange 41 provided on the rotating shaft 4, and the radial bearing portion R (RFDB) is the bearing 3. Is set between the inner periphery 30 of the shaft hole and the outer periphery of the rotating shaft 4. However, structurally, a type in which the thrust bearing portion S (SFDB) is set between the lower bearing surface of the bearing and the corresponding portion of the rotating shaft as in Patent Document 1 may be used.

  Here, the housing 2 has a cylindrical shape in which the entire bearing 3 enters the inner periphery 20, and the lower side of the inner periphery 20 is closed by a bottom plate 21. The bottom plate 21 is fixed to the housing 2 by welding or the like while maintaining confidentiality. A gap 25 is provided between the housing inner periphery 20 and the outer periphery 31 of the bearing 3 in the upper end side circumferential direction. The rotating shaft 4 includes a shaft portion 40 inserted into the shaft hole of the bearing 3, a flange 41 provided above the shaft portion 40 and facing the bearing end surface 32 on the upper side of the bearing 3, and a central portion of the flange 41. And a circumferential groove 43 provided on the outer periphery of the shaft portion 40.

  The gap 25 is a space for placing an adhesive, and has an adhesive supply portion 25a that is one step larger on the outside (upper side). The gap 25 is formed in a range of more than 0 and 20 μm or less depending on the viscosity of the adhesive P used. This value is a preferable size when the adhesive P is dripped onto the supply part 25a so as to spread over the entire area of the gap 25 by capillary action. Further, the gap 25 and the supply portion 25a are partitioned by a taper 22 provided at a corresponding portion of the housing inner periphery 20, that is, a smooth taper 22a on the back side and an acute taper 22b on the end side. However, the shape may be other than the V shape shown in this example, and a taper 30a corresponding to the taper 22a or the like may be formed on the outer periphery 30 of the bearing as illustrated in FIG. You may make it form in both the bearing outer periphery 30 and the housing inner periphery 20. FIG. When such a gap is formed, the gap becomes narrower at the tip of the taper, and the adhesive is sucked by the capillary force to improve the adhesive force.

  The bearing 3 is a sintered bearing preferable in terms of mass productivity and cost, and the pores of the sintered body are impregnated with resin. Further, the bearing 30 is fixed by a pressure input that gives a tightening margin to the inner periphery 20 of the housing and an adhesive force through an adhesive P disposed in the gap 25. In addition, it is preferable that the shaft portion fixed by press-fitting is set larger than the shaft portion to be bonded. This is to suppress variations in fixing strength by mainly using the pressure input and using the adhesive force as a sub. The tightening margin is set to 1 μm to 10 μm, more preferably 3 μm to 10 μm. This is because, in the case of a bearing with an inner diameter of about 3 mm, the experimental results show that the positioning of the housing 2 and the bearing 3 may not be maintained if the tightening margin is about 2 μm, and if the tightening margin exceeds 10 μm, the bearing inner diameter shrinks This is for deformation.

  In the case of a disk drive spindle motor, the impact resistance of 1000 G to 1500 G is required in the class of 2.5 inch disk diameter, and when this is converted into the bearing pull-out strength, the load is approximately 400 N. If the tightening allowance (housing and bearing press-fit allowance) is 11 μm or more, this degree of pull-out strength can be obtained. The present invention has been devised in particular from the viewpoint of how to suppress variations in adhesive strength based on such knowledge.

  As shown in FIG. 3B, the shaft hole inner periphery 30 has a substantially semicircular cross section as a dynamic pressure generating groove and extends straight in the axial direction, and the shaft hole inner periphery extends in the circumferential direction. A plurality of separation grooves 35 that are equally divided into two are provided. The depth of each separation groove 35 is preferably set to 0.05 to 0.15 mm. Between adjacent separation grooves 35, an arcuate surface 36 having a shape that is eccentric with respect to a circle having an axial center as a fulcrum in a horizontal cross section and is reduced in diameter toward the inner peripheral side in the counterclockwise direction. Is formed. Each circular arc surface 36 is formed in a wedge shape in which a minute clearance between the outer periphery of the corresponding shaft portion 40 of the rotating shaft 4 is gradually narrowed toward the rotating direction of the rotating shaft.

  The upper bearing end surface 32 has a plurality of spiral grooves 37 for generating dynamic pressure that are curved toward the inner peripheral side in the counterclockwise direction (in the drawing, these grooves are hatched for easy understanding). It is provided at equal intervals in the direction. Each spiral groove 37 has a configuration in which, for example, the inner peripheral end is not opened to the shaft hole but is closed, whereas the outer peripheral end is open to the bearing outer periphery, the inner peripheral side, Various contrivances are made such that each end on the outer peripheral side is open to the shaft hole and the outer periphery of the bearing.

  In addition, the above bearing 3 is produced through resin impregnation which is powder compaction, sintering, recompression, and sealing treatment. In the green compact, the raw material powder is compressed and formed as a green compact with a molding die. In sintering, the green compact is formed as a porous sintered body by a sintering process. In the recompression, the sintered body is formed into a designed bearing shape by plastic processing such as sizing, and the separation groove 35, the circular arc surface 36, and the spiral groove 37 are respectively formed by a mold transfer method. In the resin impregnation, the sintered body after recompression, that is, the bearing pores, is sealed with resin. In this process, if the resin is impregnated and solidified, a thin resin film remains on the surface of the bearing 3. If this is allowed to stand, even if an adhesive is applied on the resin film remaining on the bearing surface, almost no adhesive force can be obtained. For this reason, in this operation, after impregnating the resin, the bearing surface is washed with water before solidifying to completely remove the resin on the surface.

(Assembly) In the assembly operation, the bearing 3 is first positioned and fixed while being press-fitted into the housing 2. In this structure, a predetermined gap 26 is formed between the bottom plate 21 and the lower end surface of the bearing 3 in a state where the bearing 3 is positioned in the housing 2. The lubricant described later is also stored in the gap 26. The bottom plate 21 may be either a method of fixing the bearing 3 to the housing 2 before press-fitting the bearing 3 or a method of pressing the bearing 3 to the housing 2 after the bottom plate 21 is fixed to the housing 2.

  Next, the adhesive P is disposed in the gap 25. In this operation, an appropriate amount of adhesive is dropped onto the supply unit 25a. Then, the adhesive P spreads from the supply part 25a to the entire area of the gap 25 by the capillary phenomenon and spreads uniformly. For this reason, the bearing 3 is coupled to the inner periphery 20 of the housing 2 by press-fitting with a tightening margin on the lower side from the middle and the upper side is joined via a thin film of the adhesive P. In the above structure, the supply unit 25a is set to a size that accepts the amount of adhesive used, and the received adhesive can be efficiently led out from here into the gap 25 by capillarity, or excess adhesive can be contained in the housing. Do not protrude from the end face side of the bearing. As described above, after the bearing 3 is fixed in the housing 2 by pressure input and adhesive force, the rotating shaft 4 inserts the shaft portion 4a into the inner periphery 30 of the shaft hole of the bearing 3. The agent is sealed in the housing 2 from the separation groove 35 and the like, and the flange 41 is disposed to face the bearing end surface 32.

(Modification) FIG. 4 is a modification of the bearing unit 1 described above, (a) is a sectional view corresponding to FIG. 1 (a), and (b) is a sectional view taken along the line DD of (a). . In this modification, the same reference numerals are assigned to the same members and parts as those in the above-described embodiment, and a duplicate description is omitted, and only changes are described in detail. That is, in this modified example, it has the groove | channel 38 provided in the bearing outer periphery 31 and continuing in the axial direction, and the circumferential groove 23 provided in the inner periphery 20 of the housing 2. The groove 23 is on the inner peripheral surface of the housing, communicates with the groove 38, and has a circumferential groove shape deeper than the groove 38.

  The groove 38 is provided at a portion equally divided in the bearing circumferential direction, and a plurality (three in this example) each extending straight in the axial direction are provided. Each groove 38 is a deaeration groove in the housing 2, and is communicated with a circumferential groove 23 provided on the inner periphery 20 of the housing. That is, in this structure, since the gap for the lubricant constituted by the housing 2 and the bottom plate 21 and the inner peripheral surface of the bearing 3 is extremely narrow, when the lubricant is sealed in the bearing unit 1, the bearing unit in advance. 1 is evacuated, and in that state, a designed amount of lubricant is lubricated along, for example, the outer peripheral portion of the flange 41 of the rotary shaft 4 and the groove 38, and then released to atmospheric pressure, so that the lubricant is released. It is possible to draw in and enclose in the gaps between the parts in the bearing unit 1. Each groove 38 has a narrow gap 25 when the adhesive P in the previous step is disposed in the gap 25 by capillary action, so that the adhesive is sucked into the gap 25 by the capillary force and spreads in the groove 38. Absent. Even if the adhesive enters the groove 38, the circumferential groove 23 becomes an adhesive pocket, and the groove 38 is not blocked by the adhesive.

(Spindle Motor) A spindle motor 10 in FIG. 5 is a disk drive motor, and includes the above-described bearing unit (hereinafter abbreviated as a bearing unit) 1, a base 5 holding the bearing unit 1, and a disk. A hub 6, a rotor 7, a stator 8 having a coil wound around a core, and the like are provided. Here, the base 5 has a cylindrical holding portion 50, and the bearing unit 1 is mounted in the cylinder of the holding portion 50. A stator 8 connected to an external power source via a wiring board (not shown) is mounted on the outer periphery of the holding unit 50. The disk hub 6 holds a disk (not shown), and is supported by the rotating shaft 4 of the bearing unit 1 and rotated integrally. The rotor 7 is attached to the inner periphery of the disk hub 6 and faces the stator 8.

  In the spindle motor 10 described above, when the stator 8 is energized, the rotor 7 is rotated together with the disk hub 6 and the rotating shaft 4 by the exciting force between the stator 8 and the rotor 7. When the rotary shaft 4 rotates, the disk hub 6 generates dynamic pressure in the radial and thrust directions by the spiral groove 37 and the separation groove 32 that are the dynamic pressure generating grooves of the bearing unit 1 described above. 3 is supported with high accuracy in a non-contact state. Further, in the spindle motor 10, since the housing 2 and the bearing 3 are firmly fixed by pressure input and adhesive force in the bearing unit 1, the spindle motor 10 is excellent in impact resistance and adopts the spindle motor 10. Even if the disk device is dropped inadvertently, the rotational accuracy is not impaired, thereby improving the reliability.

  In addition, this invention is not restrict | limited at all to the above example of embodiment, A various deformation | transformation is possible except the requirements specified by each claim.

(A) is a longitudinal cross-sectional view showing the bearing unit of the invention form, (b) is an enlarged view of part C of (a), and (c) is a modification. (A), (b) is the sectional view on the AA line and BB line of FIG. (A), (b) is the side view and top view which show the single bearing of FIG. (A) And (b) is a schematic cross section which shows a modification. It is a schematic cross section which shows the spindle motor which uses the said bearing unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Bearing unit 2 ... Housing (20 is an inner periphery, 21 is a baseplate, 23 is a circumferential groove | channel)
3 ... Bearing (30 is inner circumference of shaft hole, 31 is outer circumference, 32 is bearing end face)
4 ... Rotating shaft 10 ... Spindle motor (5 is base, 6 is hub, 7 is rotor, 8 is stator)
25 ... Gap (25a is a supply section)
35 ... separation groove 36 ... arc surface
37 ... spiral groove 38 ... axial groove
P: Adhesive S: Thrust bearing R: Radial bearing

Claims (7)

A housing, a bearing having a dynamic pressure generating groove on the inner periphery and end face of the shaft hole, fixed in the housing, a rotating shaft inserted in the shaft hole of the bearing, and a lubrication sealed in the housing A hydrodynamic bearing unit capable of supporting the rotary shaft in a non-contact state in a radial direction and a thrust direction by a dynamic pressure action generated in the dynamic pressure generating groove when the rotary shaft rotates.
The bearing is coupled to the inner periphery of the housing by press-fitting with a tightening margin, and a gap formed between the inner periphery of the housing and the outer periphery of the bearing and formed in either the upper or lower end side circumferential direction. A hydrodynamic bearing unit characterized in that the housing and the bearing are bonded by an adhesive disposed in the gap.   The bearing is a sintered bearing in which pores are sealed with resin, and a tightening margin of the sintered bearing is formed from 1 μm to 10 μm, and the gap is formed to be greater than 0 and less than 20 μm. Item 2. The hydrodynamic bearing unit according to Item 1.   The hydrodynamic bearing unit according to claim 1, wherein the gap has a tapered shape whose diameter is increased toward the end.   The hydrodynamic bearing unit according to any one of claims 1 to 3, wherein a large-diameter adhesive supply portion is formed outside an end portion of the gap.   A plurality of axially extending grooves are provided on the outer peripheral surface of the bearing, and a circumferential groove deeper than the groove is provided on the inner peripheral surface of the housing. The hydrodynamic bearing unit according to any one of claims 1 to 4.   6. The method of manufacturing a hydrodynamic bearing unit according to claim 1, wherein after the bearing is coupled into the housing by press fitting, the adhesive is supplied to the gap from a corresponding end side. A method of manufacturing a bearing unit, wherein the gap is spread over substantially the entire region by capillary action. A spindle motor comprising the hydrodynamic bearing unit according to claim 1.

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