JP3602317B2 - Dynamic pressure type porous oil-impregnated bearing unit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrodynamic porous oil-impregnated bearing unit in which a hydrodynamic porous oil-impregnated bearing is fixed to a housing to form a unit. The bearing unit is an information storage device such as a magnetic disk device (HDD, FDD, etc.), an optical disk device (CD-ROM, DVD-ROM / RAM, etc.), a magneto-optical disk device (MD, MO, etc.), and an information processing device. It is suitable as a supporting device for equipment requiring high rotational accuracy, such as a spindle motor of a laser beam printer or the like.
[0002]
[Prior art]
The spindle motors of the various information devices are required to have high rotational accuracy, high speed, low cost, low noise, and the like. One of the components that determine these required performances is a bearing that supports the spindle of the motor. Conventionally, a ball bearing or a sintered oil-impregnated bearing is used as the bearing.
[0003]
[Problems to be solved by the invention]
However, when a ball bearing is used, there are the following problems.
[0004]
{Circle around (1)} This kind of spindle motor is often used at a high speed of about 8000 to 10000 rpm, particularly, tens of thousands of rpm in a laser beam printer. Ball bearings have a unique race sound (sound of the ball rolling on the raceway) and noise generated by the self-excited vibration of the cage. When used at high speed, the noise level is large, and noise reduction has reached its limit.
[0005]
{Circle around (2)} Since the ball bearing is composed of many components such as an outer ring, an inner ring, a ball, a retainer, a seal, and grease, there is a limit in reducing the cost.
[0006]
On the other hand, a sintered oil-impregnated bearing is superior to a ball bearing in terms of low noise in terms of performance, small number of parts and easy management, but has the following disadvantages.
[0007]
(1) In a spindle motor such as a CD-ROM and a DVD-ROM, a whirling load is applied to a bearing due to an unbalanced load of a disk. When the rotation speed is high and the whirling is large, the load area moves in the circumferential direction with the rotation, so that the oil film cannot follow this. In the case of a sintered oil-impregnated bearing, air is also entrained with the rotation. However, under high-speed rotation, the entrained amount increases, impeding the formation of an oil film. If the oil film formation is insufficient, metal contact occurs and abrasion proceeds, and the abrasion increases due to the abrasion, resulting in a vicious cycle in which the formation of an oil film becomes more difficult. Therefore, there is a problem in durability.
[0008]
{Circle around (2)} As in the case of a spindle motor such as an HDD or an LBP, when the unbalance load is small and the spindle attitude of the spindle is often used on the vertical axis, the eccentricity of the axis is reduced. Since a sintered oil-impregnated bearing is a kind of a perfect circular bearing, unstable vibration such as whirl tends to occur under such conditions, and high rotational accuracy cannot be achieved.
[0009]
Then, this invention aims at solving the said problem which a ball bearing and a sintered oil-impregnated bearing have.
[0010]
[Means for Solving the Problems]
As a solution to the above problems, a hydrodynamic porous oil-impregnated bearing unit according to the present invention has a bearing surface facing an outer diameter surface of a rotating shaft and a bearing gap,Made of copper or iron, or a sintered metal mainly composed of bothBearing body, a porous oil-impregnated bearing impregnated with lubricating oil or lubricating grease is fixed to the inner diameter surface of the housing,Provide a plurality of bearing surfaces spaced apart in the axial direction,Bearing bodyeachA dynamic pressure groove is provided on the bearing surface at an angle to the axial direction,By compressing and molding each bearing surface, the apertures on the bearing surface are evenly distributed, the density of the surface layer is made larger than that inside, and the density of the surface layer of the bearing body including the bearing surface is reduced. Larger than the density of the surface layer of the portion including the area between the bearing surfaces,A dynamic pressure oil film is formed in the bearing gap by the dynamic pressure groove to support the rotating shaft in a non-contact manner, and to circulate the oil between the inside of the bearing body and the bearing gap through the opening in the bearing surface. WestThe oil collected by the force of pushing the oil of the dynamic pressure groove toward the center in the axial direction is returned to the inside of the bearing body from the bearing gap.With something likeis there.
[0011]
In a porous oil-impregnated bearing, the lubricant (lubricating oil or lubricating grease) inside the bearing body oozes from the inner peripheral surface (including the inner diameter chamfer portion) of the bearing body as the rotating shaft rotates, and is drawn into the bearing gap. . The oil drawn into the bearing gap forms a lubricating oil film and supports the rotating shaft in a non-contact manner. At this time, if a plurality of axially inclined dynamic pressure grooves (for example, a herringbone type or a spiral type) are provided on the bearing surface, the lubricant inside the bearing body is further drawn into the bearing gap by the dynamic pressure action. At the same time, since the lubricant is continuously pushed into the bearing surface, the oil film strength is increased, and the rigidity of the bearing can be improved. Further, generation of unstable vibration such as whirl can be prevented.
[0012]
When a positive pressure is generated in the bearing gap, there is a hole in the surface of the bearing surface (opening portion: a portion in which pores of the porous body structure are opened on the outer surface), so that the lubricant returns to the inside of the bearing body. However, since new lubricants continue to be pushed in one after another, the oil film strength and the rigidity are maintained in a high state. Accordingly, high rotational accuracy is achieved, and shaft runout, NRRO (non-repetition accuracy), jitter and the like are reduced. In addition, since the shaft and the bearing body rotate in a non-contact manner, low noise and low cost are obtained. Further, even when bubbles are generated or entrained in the oil film, the oil is circulated, so that the bubbles are absorbed into the inside of the bearing body and the bearing function is not destabilized.
[0013]
Suitable porous oil-impregnated bearings are sintered oil-impregnated bearings containing copper or iron or both as the main components.I have.Such a sintered oil-impregnated bearing can be easily manufactured and supplied at low cost..
CWhen two porous oil-impregnated bearings are housed in a housing, the accuracy of the two bearings, such as coaxiality and cylindricity, becomes a problem. If the accuracy is poor, the shaft may come into line contact with the bearing, or in the worst case, the shaft may not pass through the two bearings.
[0014]
In this case, Bearing bodyIf the inner diameter of the area between the bearing surfaces is larger than the inner diameter of the bearing surfaceGood.Since this bearing has a single bearing body and is provided with dynamic pressure bearing surfaces at a plurality of locations on the inner diameter surface thereof, the above-described adverse effects such as poor accuracy caused by disposing a plurality of bearings separately are described. Can be avoided.
[0015]
If the area between the bearing surfaces is a straight surface having the same diameter as the bearing surface, torque may increase due to the viscous resistance of the oil, but if the inner diameter of the area is set to be larger than the inner diameter of the bearing surface. Thus, an increase in torque can be reliably avoided.
[0016]
It is not always necessary to form the dynamic pressure grooves on all of the plurality of bearing surfaces, and it is also possible to form the dynamic pressure grooves on at least one bearing surface depending on the use conditions and the like.
PorousThe oil-impregnated bearing can be fixed to the inside diameter of the housing by pressing the porous oil-impregnated bearing into the inside diameter of the housing.it can.In this press-fitting operation, in the case of a normal sintered oil-impregnated bearing having no dynamic pressure groove, as shown in FIG. 9, a press-fit pin (22: straightening pin) is inserted into the bearing 21 and one end face of the bearing 21 is press-fitted. It can be performed by pressing with a jig 23. That is, the inner diameter surface of the bearing that contracts with pressurization is pierced by the press-fit pin 22, and the outer diameter surface of the bearing is pressed into the inner diameter surface of the housing 24 while correcting the inner diameter surface of the bearing.
[0017]
However, when a dynamic pressure groove is provided, in this method, a part of the dynamic pressure groove may be crushed by correction at the time of press-fitting due to an influence of deviation in coaxiality (unevenness, uneven thickness) of the inner and outer diameters of the bearing. If the press-fitting is performed without using the press-fit pin 22, it is possible to avoid the problem that the dynamic pressure groove is crushed. ) And the shape of the housing 24 (such as a change in wall thickness), the cylindricity and coaxiality of the bearing surfaces may be deviated.
[0018]
In order to solve this, a press-fit interference is formed between an outer diameter portion of the outer diameter surface of the bearing body corresponding to a region between the bearing surfaces and an inner diameter surface of the housing facing the outer diameter portion. If an outer diameter portion corresponding to the bearing surface of the outer diameter surface and a housing allowance or clearance smaller than the press-fitting allowance are formed between the outer diameter portion corresponding to the bearing surface and the inner diameter surface of the housing opposed thereto.Good.With this configuration, the dimensions and accuracy of the bearing surface do not change before and after press-fitting, while adopting the low-cost assembly method of press-fitting, so that cost reduction and securing of bearing surface accuracy are achieved at the same time. be able to.
[0019]
The same effect can be obtained even if the porous oil-impregnated bearing is adhered and fixed to the inner surface of the housing.Can beIn the case of such bonding, there is a concern that oil containing an adhesive component may enter the inside of the bearing. However, in order to prevent such a problem, the oil is bonded to the inner diameter surface of the housing among the outer diameter surfaces of the bearing body. The surface porosity of the part is 12% or less, preferably 8% or lessWest,What is necessary is just to prevent the applied adhesive from entering the inside of the bearing. As the adhesive, it is preferable to use an anaerobic adhesive or an ultraviolet-curable adhesive, or an adhesive having both properties.Good.
[0020]
Bearing bodyThe surface porosity of the bearing surface is smaller than the surface porosity of the region between the bearing surfaces.if,The rigidity of the bearing surface can be increased, and the oil film strength can be improved. In addition, durability can be improved by increasing the oil content in the region between the bearing surfaces.
[0021]
It is desirable to provide a ventilation path between the outer diameter surface of the bearing body and the inner diameter surface of the housing, which is open at both axial ends of the bearing body.New
[0022]
Form an identification mark on one end face of the bearing body to identify the assembly directionIf you do,The direction in which the porous oil-impregnated bearing is fixed to the housing can be easily determined.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0024]
As shown in FIG. 1, the hydrodynamic porous oil-impregnated bearing unit according to the present invention is configured by fixing a porous oil-impregnated bearing 1 to an inner diameter surface 2 a of a housing 2.
[0025]
The housing 2 has a thick cylindrical shape having a small-diameter portion 2a1 and a large-diameter portion 2a2 on the inner diameter surface, and is formed by cutting a soft metal such as copper or aluminum.
[0026]
As shown in FIG. 2, the porous oil-impregnated bearing 1 has a porous bearing body 1a having a bearing surface 1b opposed to an outer diameter surface of a rotating shaft (3: see FIGS. 4 and 5) via a bearing gap 4. And lubricating oil or lubricating grease. The bearing body 1a is formed as a thick cylindrical porous body having a large number of pores by sintering, foaming, or the like of powder metallurgy, cast iron, synthetic resin, ceramics, or the like. Alternatively, it is formed of a sintered metal mainly composed of iron or both.
[0027]
As the lubricating oil or the base oil of the lubricating grease, one having a kinematic viscosity at 40 ° C. of 5 to 60 cSt is used. If the kinematic viscosity at 40 ° C. is larger than 60 cSt, high-speed driving is hindered. Conversely, if it is less than 5 cSt, the kinematic viscosity is too small and oil is liable to be scattered, causing a problem in durability. When lubricating grease is used as the lubricant, the apparent viscosity becomes significantly larger than that of the oil except for the bearing gap where the shearing force is applied, and it is difficult to flow out to the surroundings. However, if the amount of the thickener mixed and dispersed in the oil is larger than 5% by weight, the apparent viscosity is too high to impregnate the bearing body, and the work of removing excess grease adhering to the surface after impregnation is complicated. It becomes. On the other hand, when the amount of the thickener is less than 0.5 wt%, the effect of forming grease is small, and the degree of outflow is the same as when oil is used. Therefore, the lubricating grease used should have a thickener concentration of 0.5 to 5.0 wt%. The type of the lubricating oil or the lubricating grease base oil is not particularly limited, but a poly-α-olefin-based, ether-based, or ester-based synthetic oil (diester, polyol ester-based synthetic oil) is suitable. As the thickener for lubricating grease, a lithium-based thickener which is easy to handle and has excellent productivity is suitable.
[0028]
Two bearing surfaces 1b axially separated from each other are formed on the inner periphery of the bearing main body 1a, and a plurality of dynamic pressure grooves 1c (herrings) that are respectively inclined with respect to the axial direction are formed on both of the two bearing surfaces 1b. (Bone type) are arranged in the circumferential direction. The bearing surface 1b of this embodiment includes a first groove region m1 in which the inclined hydrodynamic grooves 1c are arranged on one side, and a hydrodynamic groove 1c axially separated from the first groove region m1 and inclined on the other side. Are provided, and an annular smooth portion n is located between the two groove regions, and the dynamic pressure groove 1c of the two groove regions m1 and m2 is partitioned by the smooth portion n. It is discontinuous. The back portion 1e between the smooth portion n and the dynamic pressure groove 1c is at the same level.
[0029]
This non-continuous type dynamic pressure groove is a continuous type, that is, the smooth portion n is omitted and the dynamic pressure groove 1c is formed in a V-shape that is continuous with each other between the two groove regions m1 and m2. This has the advantage that the oil film pressure is high due to the oil being collected and that the bearing stiffness is high because it has a smooth portion n without grooves. If there is no particular problem, a continuous dynamic pressure groove may be employed.
[0030]
Generally, in the herringbone type dynamic pressure groove, it is said that the continuous type has no portion that generates a negative pressure in the bearing, so that no bubbles are generated, and the oil sealing property is excellent, but as in the present invention, When the bearing body 1a is a porous body, the oil circulates between the bearing gap and the inside of the bearing, so that even if bubbles are generated, the oil does not stay in the bearing gap. It is considered that there is no problem that the material is extruded from the material and the sealing property is impaired.
[0031]
Assuming that the axial width of each bearing surface 1b is 1, the ratio R of the smooth portion n in the bearing width direction is in the range of R = 0.1 to 0.6, preferably, R = 0.2 to 0. It is better to set it in the range of 4. If the width is less than 0.1 with respect to the bearing surface width 1, the effects (increase in dynamic pressure and increase in bearing stiffness) provided by the smooth portion n do not appear remarkably, and are the same as in the case of continuous grooves. Further, when R is larger than 0.6 with respect to the bearing width 1, the dynamic pressure groove is reduced, the force for pushing the oil into the central portion in the axial direction is weakened, and the dynamic pressure effect is not effectively exhibited.
[0032]
There is an optimal range for the ratio between the groove depth (h: see FIG. 4) of the dynamic pressure groove 1c and the radial gap c, and the ratio between the bearing gap (radial gap: c) and the radius r of the rotating shaft 3. Outside this range, a sufficient dynamic pressure effect cannot be obtained. In order to clarify this optimum range, the shaft runout was measured using a CD-ROM actual motor and an LBP actual motor, and as a result, c / h was in the range of 0.5 to 4.0 and c / r was 0.0005. It has been found that the shaft runout can be suppressed to a practically sufficient level within the range of 0.003 to 0.003. Therefore, in order to maintain high accuracy, it is desirable to set c / h = 0.5 to 4.0 and c / r = 0.0005 to 0.003. In FIG. 4, the radial gap c and the groove depth h are exaggerated as compared with the actual case.
[0033]
The dynamic pressure groove 1c described above can be formed by, for example, compression molding. That is, a groove having an uneven shape corresponding to the shape of the dynamic pressure groove 1c is formed on the outer peripheral surface of a core rod (for example, a sizing pin), and a porous material as a material of the bearing body 1a is supplied to the outer peripheral surface of the core rod. A pressing force is applied to the material to press the inner diameter portion thereof into the groove shape of the core rod, and the dynamic pressure groove 1c corresponding to the shape of the groove shape is transferred to the inner diameter portion. At this time, the back portion 1e can be formed simultaneously with the dynamic pressure groove 1c. After the formation of the dynamic pressure grooves, the core rod is released from the inner diameter of the porous material by utilizing the springback of the porous material by removing the pressing force.
[0034]
At this time, if the sizing pin for transferring the dynamic pressure groove 1c is finished with high accuracy, the accuracy of the bearing is also improved. It is not so difficult to finish the precision of the sizing pin to the required precision, for example, within a circularity of 1 μm or less and a cylindricity of 2 μm or less, and it can be easily achieved.
[0035]
Before performing the above-described dynamic pressure groove sizing, it is preferable to perform rotational sizing on the inner diameter portion of the porous material to make the distribution of the apertures on the inner diameter surface uniform in advance.
[0036]
The inner diameter D1 of the region 1d between the bearing surfaces 1b in the bearing body 1a is set to be larger than the inner diameter D2 of the bearing surface 1b (strictly speaking, the inner diameter of the region of the back portion 1e between the dynamic pressure grooves 1c). . In the drawing, the axial cross section of the region 1d is drawn by one circular arc that is continuous with the bearing surface 1b, and the maximum diameter portion of the circular arc is located at the axial center of the region 1d. However, the cross-sectional shape can be arbitrarily selected, and may be drawn by another curve or straight line such as an ellipse, a parabola, or a combination thereof, in addition to a circular arc. Further, the maximum diameter portion of the region 1d may be unevenly distributed on one bearing surface 1b side.
[0037]
The density of the portion including the bearing surface 1b of the bearing main body 1a may be higher than the density of the portion including the region 1d between the bearing surfaces (the "density" herein means that the depth from the bearing surface or the region between the bearing surfaces is 0%). .. Refers to the density of the surface layer up to 1 mm). The density of the porous body is related to the porosity per unit volume. As the density increases, the volume ratio of the pores in the tissue decreases, and at the same time, the surface porosity on the surface decreases. As a result, the oil film strength on the bearing surface 1b can be improved, and the bearing rigidity can be improved. At the same time, the oil content in the region 1d can be increased to improve the durability. Specifically, the surface density of the bearing surface 1b is adjusted to 6.5 to 7.2 [g / cm].³], The surface density of the region 1d is 6.0 to 6.6 [g / cm].³], And the surface porosity on the bearing surface 1b is set in the range of 2 to 30%, preferably 2 to 12%. The setting of the surface porosity can be performed by setting the density, or by performing a surface treatment (adjustment of the porosity by rotational sizing or the like), and furthermore, by setting the density and using the surface treatment in combination.
[0038]
The outer diameter surface of the bearing body 1a is such that the outer diameter surface 1b1 corresponding to the one bearing surface 1b has a small diameter, the outer diameter surface 1d1 corresponding to the region 1d between the bearing surfaces, and the outer diameter surface corresponding to the other bearing surface 1b. 1b2 is formed in a stepped cylindrical shape having a large diameter. As shown in FIG. 1, when the porous oil-impregnated bearing 1 is press-fitted into the inner periphery of the housing 2, the outer diameter portion 1d1 corresponding to the region 1d corresponds to the small diameter portion 2a1 of the housing inner diameter surface 2a, and the outer diameter portion corresponding to one bearing surface. The diameter portion 1b1 faces the small diameter portion 2a1 of the housing inner diameter surface 2a, and the outer diameter portion 1b1 corresponding to the other bearing surface faces the large diameter portion 2a2 of the housing inner diameter surface 2a. At this time, if a press-fitting allowance is formed between the outer diameter portion 1d1 corresponding to the region 1d and the small diameter portion 2a1 of the housing inner diameter surface 2a, the fixing force of the bearing 1 can be secured by the close fitting of both. Can be. The region 1d is formed to have a diameter larger than that of the bearing surface 1b, and is not directly involved in supporting the shaft. Therefore, even if a deformation corresponding to the press-fitting occurs in the region 1d, the accuracy of the bearing is not affected. On the other hand, between the outer diameter surfaces 1b1 and 1b2 corresponding to the two bearing surfaces 1b and the housing inner diameter surfaces 2a1 and 2a2 facing the outer diameter surfaces 1b1 and 1b2, a tightening allowance smaller than the press-fitting allowance (a tightening allowance that does not affect bearing accuracy). Alternatively, if a radial gap is formed (this embodiment exemplifies a case where the radial gaps 9a and 9b are provided), deformation of the bearing surface 1b due to press-in can be prevented or reduced. As a result, a decrease in bearing accuracy can be prevented.
[0039]
Actually, when the dimensions and precision changes of the bearing surface were measured before and after press-fitting, there was almost no change in any of the inner diameter, roundness, cylindricity, and coaxiality. Specifically, before and after press-fitting, the inner diameter dimension is φ3.002, the cylindricity is 2 μm or less, and the coaxiality (meaning the amount of axial misalignment of one bearing surface with respect to the other bearing surface) is 2 μm or less, and there is no change. The roundness was 0.9 μm before press-fitting, but only changed to 1.0 μm after press-fitting.
[0040]
FIG. 5 shows a state where the above-described bearing unit is incorporated in a spindle motor (the drawing shows a spindle motor of a CD-ROM device). The shaft 3 (rotating shaft) inserted into the inner diameter of the porous oil-impregnated bearing 1 is supported in a non-contact manner by a hydrodynamic oil film formed in the bearing gap 4, and is rotated by an exciting force generated between the rotor 5 and the stator 6. Driven. The shaft 3 is supported in contact with a thrust plate 7 fitted into one opening of the housing 2.
[0041]
By the way, the shaft 3 is usually inserted into the inner diameter of the bearing 1 with the thrust plate 7 mounted on the housing 2. At the time of this insertion, air escapes from the bearing gap 4 between the bearing 1 and the shaft 3, but since the bearing gap 4 is only about a few μm, air is trapped in the space below the housing 2 and the shaft 3 is inserted. Becomes difficult. In addition, when the motor is driven, heat is generated, and the heat may cause the trapped air to expand, pushing up the shaft 3 and destabilizing the bearing performance.
[0042]
In this case, as shown in FIGS. 1 and 5, between the outer diameter surface of the bearing main body 1 a and the inner diameter surface 2 a of the housing 2, a ventilation path 8 opened at both axial ends of the bearing main body 1 a is provided. Good. The air passage 8 can be formed by providing an axial groove 1g on the outer diameter surface of the bearing body 1a, and a gap (for example, between the outer diameter surface of the bearing body 1a and the inner diameter surface 2a of the housing 2). If there is a gap 9a between the outer diameter surface 1b1 and the housing inner diameter surface 2a1 and a gap 9b) between the outer diameter surface 1b2 and the housing inner diameter surface 2a2, the air passage 8 is formed by the gaps 9a and 9b and the groove 1g. May be configured. At this time, the groove 1g is formed in at least a portion of the outer diameter surface of the bearing body 1a which is press-fitted into the housing inner diameter surface 2a (in the present embodiment, an outer diameter portion 1d1 corresponding to a region 1d between the bearing surfaces). Is enough. The groove 1g can be provided not only at one position on the outer diameter surface of the bearing body 1a but also at a plurality of positions (three positions in the drawing) in the circumferential direction, or may be provided on the inner diameter surface 2a of the housing.
[0043]
The porous oil-impregnated bearing 1 may be press-fitted into the inner diameter surface 2a of the housing 2 or fixed by bonding. FIG. 6 shows an example of a bonding apparatus used for such bonding, in which the bearing 1 is inserted into the housing 2 and positioned and held by the jig 11, and the outer diameter of the bearing body 1a is fixed by a dispenser (not shown). An adhesive is injected between the housing and the inner surface 2a. As the bearing 1 and the housing 2 in this case, those shown in FIG. 1 can be used as they are. However, the outer diameter surface of the bearing main body 1a and the inner diameter surface 2a of the housing 2 may be straight surfaces without steps. The injection of the adhesive is performed while avoiding the air passage 8. The injected adhesive penetrates and spreads on the joint surface by capillary action. The bonding is desirably performed after the oil adhering to the outer diameter surface of the bearing body is wiped off with a rag or the like or removed by a centrifuge.
[0044]
In the case of bonding in this manner, the adhesive component and the oil are mixed at the portion of the outer diameter surface of the bearing main body 1a which is bonded to the inner diameter surface 2a of the housing 2, so that the bonding force is reduced or the bonding force is reduced. Oil containing an agent component may enter the inside of the bearing from the joint, and may ooze out on the bearing surface, which may have an undesirable effect on the bearing function.
[0045]
To avoid this, the surface porosity of the portion of the outer diameter surface of the bearing body 1a that is bonded to the inner diameter surface 2a of the housing 2 may be set to 12% or less, preferably 8% or less. With such a surface porosity, most of the applied adhesive remains on the joint surface and does not enter the inside of the bearing. Therefore, the adhesive strength does not decrease and there is no adverse effect on lubrication. The surface porosity can be realized by setting the sizing margin in the dynamic pressure sizing step to 0.1 mm or more.
[0046]
As the adhesive, an anaerobic adhesive, an ultraviolet curable adhesive, or an adhesive having both properties is used. These have excellent adhesive strength on the oil surface, and have good reactivity with a copper-based material often used as a material of the bearing body 1a and the housing 2. Further, since the fixing speed is high, the time for positioning and holding the bearing 1 and the housing 2 by the jig 11 can be shortened. Further, each of them is a one-liquid type, and there is no need to mix two liquids as in the case of an epoxy adhesive, for example, so that the workability is excellent. In particular, in the case of an ultraviolet curable adhesive, even if the adhesive adheres to a chamfer or the like at the outer diameter of the bearing and remains, it can be hardened there by irradiating with ultraviolet rays.
[0047]
The bearing 1 was bonded and fixed to the housing 2 using an apparatus shown in FIG. 6, and a test for measuring the removal force, shaft runout, and the like was performed. However, in this test, the sizing margin of the outer diameter surface of the bearing main body 1a was set to 0.15 mm, thereby setting the surface porosity of the outer diameter surface of the bearing main body to 6 to 10%. The gap between the bearing (φ3 × φ6 × 9) and the housing 2 (C3602) was 20 μm in diameter, and an anaerobic adhesive 603 manufactured by Loctite Japan was used as the adhesive. After injecting 1.0 mg of the adhesive, the bearing was fixed in about 30 seconds, and the bearing unit was removed from the jig 11 about 1 minute later.
[0048]
When the removal force was measured 24 hours after bonding, it was 50 kgf or more. Usually, the removal force required for a bearing having the above dimensions is 5 to 10 kgf, and it has been found that this requirement can be sufficiently satisfied. Further, the bearing unit after bonding was incorporated into an LBP motor, and a function evaluation test was performed. At 15000 rpm, the shaft runout was 2 μm or less, and the non-repeatable rotation accuracy (NRRO) was 0.03 μm or less, showing satisfactory performance as a dynamic pressure bearing. In addition, even in the continuous operation test, it was found that the performance did not deteriorate even after lapse of 3000 hours, and that it was sufficiently practical.
[0049]
When the porous oil-impregnated bearing 1 is fixed to the housing 2 by a method such as press-fitting or bonding, the bearing 1 is arranged in the housing 2 in a direction matching the rotation direction of the rotating shaft 3 in order to generate a predetermined dynamic pressure. There is a need. If the direction of the bearing 1 is visually determined, the workability at the time of fixing is difficult to see, and the workability at the time of fixing is deteriorated.
[0050]
Therefore, in this case, as shown in FIGS. 7 and 8, an identification mark 12 for identifying the assembling direction may be formed on one end face of the bearing main body 1a. Although the drawing illustrates a case where a ring groove is formed as the identification mark 12, the shape of the identification mark 12 can be arbitrarily selected. The presence or absence of the identification mark 12 can be visually determined, or can be mechanically determined using an image processing device or the like.
[0051]
For example, when the porous material is pressed with a punch from both sides in the axial direction at the time of dynamic pressure sizing, a mold corresponding to the mark shape is formed in advance on the pressing surface of one punch (for example, a lower punch). By placing it, it can be molded.
[0052]
The bearing units described above can be widely used for various motors such as the above-mentioned various spindle motors and the like, electric products such as axial fans, ventilation fans and electric fans, and electric components for automobiles.
[0053]
【The invention's effect】
As described above, according to the present invention,
{Circle around (1)} Noise and cost can be reduced compared to a bearing unit using a ball bearing.
[0054]
{Circle over (2)} The bearing pressure can be increased by the dynamic pressure action of the dynamic pressure groove, and the rotational accuracy can be improved to reduce shaft runout, NRRO and jitter. Since a good oil film is always formed on the bearing surface, the durability life can be greatly improved.
[Brief description of the drawings]
FIG. 1 is an axial sectional view of a bearing unit according to the present invention.
FIG. 2 is an axial sectional view of a porous oil-impregnated bearing used in the bearing unit.
FIG. 3 is a view as viewed in the direction of the arrow A in FIG. 2;
FIG. 4 is a radial sectional view of the porous oil-impregnated bearing.
FIG. 5 is an axial sectional view of a spindle motor of the CD-ROM device.
FIG. 6 is an axial sectional view showing an example of a bonding device.
FIG. 7 is an axial sectional view of a hydrodynamic porous oil-impregnated bearing unit having an identification mark provided on a bearing.
FIG. 8 is an enlarged view of a portion B in FIG. 7;
FIG. 9 is an axial sectional view showing a method of press-fitting a bearing.
[Explanation of symbols]
1 Porous oil-impregnated bearing
1a Bearing body
1b Bearing surface
1c Dynamic pressure groove
1d Bearing surface area
2 Housing
2a Housing inner diameter
3 rotating shaft
4 Bearing clearance
8 Ventilation path
9a gap
9b gap
12 Identification mark

Claims (10)

Porous body in which a bearing body made of copper or iron, or a sintered metal mainly composed of both, has a bearing surface facing the outer diameter surface of the rotating shaft via a bearing gap, and is impregnated with lubricating oil or lubricating grease. An oil-impregnated bearing fixed to the inner diameter surface of the housing,
A plurality of bearing surfaces are provided apart from each other in the axial direction, dynamic pressure grooves are provided on each bearing surface of the bearing body at an angle to the axial direction, and each bearing surface is compression-molded to form a hole in the surface of the bearing surface. Parts are distributed uniformly, the density of the surface layer is made larger than that of the inside, and the density of the surface layer of the portion including the bearing surface of the bearing body is made higher than the density of the surface layer of the portion including the region between the bearing surfaces. Increase the size, form a dynamic pressure oil film in the bearing gap with the dynamic pressure groove to support the rotating shaft in a non-contact manner, and transfer the oil between the inside of the bearing body and the bearing gap through the opening in the bearing surface. A hydrodynamic porous oil-impregnated bearing unit that circulates and returns oil collected by the force of pushing the oil of the dynamic pressure groove toward the center in the axial direction into the bearing body from the bearing gap . Hydrodynamic type porous oil-impregnated bearing unit inner diameter dimension of the region between the bearing surfaces of the bearing body according to claim 1, wherein the larger than the inner diameter of the bearing surface. 3. The hydrodynamic porous oil-impregnated bearing unit according to claim 1, wherein the porous oil-impregnated bearing is press-fitted and fixed to an inner diameter surface of the housing. A press fit is formed between an outer diameter portion of the outer diameter surface of the bearing body corresponding to a region between the bearing surfaces and an inner diameter surface of the housing facing the outer diameter portion. 4. The hydrodynamic porous oil-impregnated bearing unit according to claim 3 , wherein a tightening margin or a gap smaller than the press-fitting margin is formed between the outer diameter portion corresponding to the surface and the housing inner diameter surface facing the outer diameter portion. 3. The hydrodynamic porous oil-impregnated bearing unit according to claim 1, wherein the porous oil-impregnated bearing is adhered and fixed to the inner diameter surface of the housing. 6. The hydrodynamic porous oil-impregnated bearing unit according to claim 5, wherein a surface porosity of a portion of the outer diameter surface of the bearing body that is bonded to the inner diameter surface of the housing is 12% or less. Anaerobic adhesive or ultraviolet curing adhesive, or hydrodynamic type porous oil-impregnated bearing unit according to claim 5 or 6, wherein the porous oil-impregnated bearing with an adhesive adhered to the inner surface of the housing having the properties of both. The surface porosity of the bearing surface, hydrodynamic type porous oil-impregnated bearing unit as set forth in any one of claims 2 to 7 was smaller than the surface porosity of the region between the bearing surfaces. The hydrodynamic porous oil-impregnated bearing unit according to any one of claims 1 to 8, wherein ventilation passages are provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing, the ventilation paths being open at both axial ends of the bearing body. Hydrodynamic type porous oil-impregnated bearing unit as set forth in any one of claims 1 to 9 to form an identification mark for identifying the one assembly direction on the end face of the bearing body.

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