JPH11311253A - Dynamic pressure type oil-impregnated sintered bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a lowering of bearing performance caused by the leakage of lubricating oil to the outside of a bearing body, positively at a low cost. SOLUTION: An oil-impregnated sintered bearing 1a having dynamic pressure grooves on a bearing surface is fixed to an inner diameter part of a housing 1b, and a rotating shaft 2 is contact-supported by a thrust washer provided at a bottom part of the housing 1b to constitute a bearing unit 1. The lower end face of a bearing body 10 of the oil-impregnated sintered bearing 1a is disposed in proximity to the upper face of the thrust washer, and the width (s) of a clearance between both faces is set to 1 mm or less. An opening part of the housing 1b is sealed with a seal washer 20, and a clearance between the inner peripheral surface of the seal washer 20 and the outer peripheral surface of the rotating shaft 2 is set to 0.1 mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic sintered oil-impregnated bearing having excellent characteristics such as high rotational accuracy, high-speed stability, and high durability, and a bearing unit thereof. -ROM, D
It is suitable for supporting a spindle such as an optical disk such as a VD-RAM, a magneto-optical disk such as an MO, a magnetic disk such as an HDD, or a polygon scanner motor of a laser beam printer (LBP).

[0002]

2. Description of the Related Art In addition to high rotational accuracy, higher speed, lower cost, lower noise, and the like are required for spindle motors of the above information devices. One of the components that determine these required performances is as follows. One type is a bearing that supports a motor spindle. Conventionally, a ball bearing or a general round-shaped sintered oil-impregnated bearing is used as this bearing.

[0003]

However, this kind of spindle motor is often used at a high speed of about 8,000 rpm to 10,000 rpm, and especially for a polygon scanner motor used for LBP at tens of thousands of rpm.
Since it is necessary to consider rotation accuracy such as shaft run-out, NRRO, and jitter, it is difficult to satisfy the required performance in a ball bearing or a sintered oil-impregnated bearing.

In view of the above, the use of a dynamic pressure type sintered oil-impregnated bearing has been studied in recent years as this type of bearing. This bearing impregnates a sintered metal bearing body with lubricating oil or lubricating grease, forms a lubricating oil film in the bearing gap by the dynamic pressure effect of the dynamic pressure groove provided on the bearing surface, and supports the spindle in a non-contact manner. Thus, the above required performance can be sufficiently satisfied.

However, when this bearing body is incorporated in a housing and used in a vertical position, oil oozing out of the bearing body due to pressure generation or thermal expansion during motor driving is saturated in the bearing gap, and the bearing gap is saturated. There is a risk of leaking out. As shown in FIG. 16, the oil 16 leaking below the bearing body 10 accumulates at the bottom of the housing 1b. However, if the gap 14 ′ between the lower surface 10f of the bearing body 10 and the bottom surface of the housing 1b is large, the bearing body 10 no longer contacts the accumulated oil 16. When the motor stops, the temperature drops, and the oil adhering to the surface of the bearing body 10 is absorbed into the bearing body 10 again by capillary action, but the oil that does not come into contact with the bearing body 10 does not return again, and lubrication is repeated. There is a possibility that oil shortage will occur and the performance of the bearing will be reduced. When the lubricating oil becomes insufficient, air will be trapped in the lubricating oil film formed in the bearing gap, the original dynamic pressure effect will be reduced and the radial rigidity will decrease, but unstable vibration will occur, Rotational accuracy deteriorates.

As the above countermeasure, it is easiest to fill the gap 14 'with lubricating oil in advance. However, in this case, a change in the attitude of the spindle (for example, when the spindle 14 is turned upside down) causes the opposite side of the bearing body 10 to be closed. The lubricating oil may leak from the end face of the device and contaminate the surroundings.

As a countermeasure, the use of a contact seal is conceivable, but it is not suitable for a spindle motor for information equipment which requires high-precision rotation performance because it causes a rise or fluctuation of torque. If a complicated labyrinth seal as shown in FIG. 17 is formed, a certain effect can be recognized in preventing oil leakage, but the number of parts is large and assembly becomes extremely complicated, which leads to an increase in cost.

Accordingly, an object of the present invention is to reliably and at a low cost prevent deterioration of bearing performance due to leakage of lubricating oil out of a housing.

[0009]

In order to achieve the above object, a hydrodynamic sintered oil-impregnated bearing unit according to the present invention comprises:
Lubricating oil or lubricating grease is impregnated in a bearing body that is formed of sintered metal and has a radial bearing surface facing the outer peripheral surface of the shaft via a bearing gap, and is generated by relative rotation between the shaft and the bearing body. A dynamic pressure type oil-impregnated bearing that supports the shaft in a non-contact manner by dynamic pressure action, a housing in which one end is open and the other end is closed, and the above-mentioned dynamic pressure type oil-impregnated bearing is housed in the inner diameter portion, and the shaft is thrust supported. In the one provided with the thrust bearing portion, the end face of the housing close side of the bearing body and the opposing face provided on the close side of the housing so as to face the end face are brought close to or in contact with each other.

A bearing body formed of a sintered metal and having a radial bearing surface opposed to the outer peripheral surface of the shaft via a bearing gap is impregnated with lubricating oil or lubricating grease. A dynamic pressure type sintered oil-impregnated bearing that supports the shaft in a non-contact manner by dynamic pressure action generated by the relative rotation of the bearing, a housing in which one end is open and the other end side is closed, and the dynamic pressure-type sintered oil-impregnated bearing is housed in the inner diameter portion, In a device having a thrust bearing portion for supporting a shaft in a thrust direction, a gap between an end face of a housing closed side of a bearing body and an opposing face provided on a closed side of the housing so as to face the end face is set to 1 mm or less. .

The opposing surface can be constituted by a bottom surface closing the other end of the housing or a spacer provided on the closing side of the housing. Also, the thrust bearing part
It is also possible to adopt a structure in which the shaft end is contacted and supported by a thrust washer provided on the closed side of the housing, and the thrust washer can constitute the above-mentioned facing surface. In this case, it is preferable that one end of the shaft that comes into contact with the thrust washer is formed in a spherical shape, and that the radial bearing surface of the bearing body is shifted from the spherical portion of the shaft to the other end of the shaft. This can be realized by providing a radial bearing surface with an annular smooth portion separated from an end surface chamfer portion on the other end side of the housing of the bearing body.

Further, the dynamic pressure type sintered oil-impregnated bearing unit according to the present invention provides lubricating oil or lubricating oil to a bearing body which is formed of sintered metal and has a radial bearing surface opposed to an outer peripheral surface of a shaft via a bearing gap. A dynamic pressure type sintered oil-impregnated bearing which is impregnated with lubricating grease and supports the shaft in a non-contact manner by the dynamic pressure action generated by the relative rotation of the shaft and the bearing body, one end is open and the other end is closed, In a housing including a dynamic pressure type sintered oil-impregnated bearing and a thrust bearing portion for supporting the shaft in a thrust direction, an opening at one end of the housing is provided with a seal washer having an inner peripheral surface close to an outer peripheral surface of the shaft. It is sealed. Oil leakage from the gap can be prevented by the capillary effect generated in the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft.

In order to obtain a sufficient capillary effect, the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft must be 0.1 mm.
It is desirable to set the following. In addition, if an oil repellent is applied to at least a region of the outer peripheral surface of the shaft that includes a portion facing the inner peripheral surface of the seal washer, oil leakage can be more reliably prevented.

The gap between the seal washer and the bearing end face facing the seal washer is preferably set to 1.0 mm or less.

[0015] Each of the above and above configurations can be appropriately combined. In this case, the gap between the seal washer and the bearing end face facing the seal washer may be set to be larger than the gap between the housing closing side end face of the bearing main body and the facing face facing the end face. ,
Even when the shaft attitude is changed (upside down, etc.), the gap between the seal washer and the bearing end face is filled with oil first, and the air that has lost the escape The situation of getting into the gap and getting caught in the bearing gap is prevented.

If a dynamic pressure groove which is inclined with respect to the axial direction is provided on the radial bearing surface as the dynamic pressure generating means, a highly rigid and stable oil film is formed in the bearing gap, so that high precision can be obtained.

If ventilation paths are provided at both ends in the axial direction of the bearing body between the outer diameter surface of the bearing body and the inner diameter surface of the housing, the shaft is confined in the housing when the shaft is inserted into the bearing. Since the exhausted air is discharged to the outside of the housing through the ventilation path, it is possible to avoid entrapment of air into the bearing gap.

The dynamic-pressure-side sintered oil-impregnated bearing unit described above rotates a magnetic disk by rotating the magnetic disk by the relative rotation of the shaft and the bearing body, and rotates the optical disk by the relative rotation of the shaft and the bearing body. It is used for a spindle motor of an optical disk drive to be driven, or a polygon scanner motor of a laser beam printer for rotating a polygon mirror by relative rotation between a shaft and a bearing body. The “optical disk” here includes a magneto-optical disk (MD, MO, etc.).

The hydrodynamic sintered oil-impregnated bearing according to the present invention is made of sintered metal, has a radial bearing surface opposed to an outer peripheral surface of a shaft via a bearing gap, and is spaced apart in the axial direction. A bearing body having a dynamic pressure groove inclined with respect to the axial direction, a bearing body provided with an end face chamfer at least at one end inner diameter part, and a lubricating oil or lubricating grease impregnated in the bearing body. The radial bearing surface is formed with an annular smooth portion separated from the radial bearing surface.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIGS.

FIG. 1 is a sectional view of a spindle motor of an optical disk drive (for a DVD-ROM device), which is a kind of information equipment. The spindle motor includes a bearing unit 1 for supporting a vertical rotating shaft 2, a turntable 4 and a clamper 8 attached to an upper end of the rotating shaft 2 for supporting and fixing an optical disk 3 such as a DVD-ROM, and a radial gap. And a motor unit M having a stator 5 and a rotor magnet 6 facing each other. When the stator 5 is energized, the rotor magnet 6 is rotated by an exciting force generated between the stator 5 and the stator 5, and the rotor case 7, the turntable 4, the optical disk 3, the clamper 8 and the rotating shaft 2 integrated with the rotor magnet 6 are formed. Rotate. When the bearing unit 1 is used for another information equipment spindle motor, for example, a magnetic disk drive, a disk hub (not shown) holding one or more magnetic disks is mounted on the rotating shaft 2 and an LBP polygon scanner motor is used. , A polygon mirror (not shown) is attached to the rotating shaft 2.

The bearing unit 1 includes a sintered oil-impregnated bearing 1a and a housing 1b in which the sintered oil-impregnated bearing 1a is fixed to an inner diameter portion as main components. The housing 1b is formed in a closed-end cylindrical shape with one end opened and the other end closed, and is fixed to the base 17 with the opening at one end facing upward. The other end of the housing is, for example, as shown in FIG.
Is closed. As shown in FIG. 2A, the thrust bearing portion 12 has, for example, a structure in which a resin-made thrust washer 12a formed in a disk shape and a back metal 12b supporting the same are laminated. , The lower end of which is a thrust washer 12a
And is supported in the thrust direction. The structure of the thrust bearing portion 12 is arbitrary. For example, as shown in FIG. 2B, a resin-made thrust washer 12a may be embedded in a recess provided at the center of the back metal 12b. Further, the thrust washer 12a and the housing 1b may be integrally formed.

As shown in FIG. 3, the sintered oil-impregnated bearing 1a has a cylindrical bearing body 10 made of sintered metal having a radial bearing surface 10b opposed to the outer peripheral surface of the rotating shaft 2 via a bearing gap.
And a lubricating oil or lubricating grease (preferably containing a low-concentration thickener). The bearing body 10 made of a sintered metal is formed of a copper-based or iron-based, or a sintered metal mainly containing both of them, and is desirably formed by using 20 to 95% of copper. On the inner periphery of the bearing body 10, two bearing surfaces 10b are formed, which are separated in the axial direction,
On both of the two bearing surfaces 10b, a plurality of dynamic pressure grooves 10c (herringbone type) each inclined with respect to the axial direction are arranged in the circumferential direction. It is sufficient that the dynamic pressure groove 10c is formed to be inclined with respect to the axial direction. As long as this condition is satisfied, a shape other than the herringbone type, for example, a spiral type may be used. The appropriate groove depth of the dynamic pressure groove 10c is about 2 to 6 μm,
For example, it is set to 3 μm.

In this sintered oil-impregnated bearing 1a, the lubricant (lubricating oil or base oil of lubricating grease) inside the bearing body 10 is generated by the pressure generation accompanying the rotation of the rotating shaft 2 and the thermal expansion of the oil due to the temperature rise. It oozes out of the surface of 10 and is drawn into the bearing gap by the action of the dynamic pressure groove. The oil drawn into the bearing gap forms a lubricating oil film and supports the rotating shaft in a non-contact manner. That is, when the inclined dynamic pressure groove 10c is provided on the radial bearing surface 10b, the lubricant inside the bearing body 10 oozed out by the dynamic pressure action is drawn into the bearing gap, and the lubricant is pushed into the bearing surface 10b. Since the oil film strength is continuously increased, the rigidity of the bearing can be improved.

When a positive pressure is generated in the bearing gap, there is a hole in the surface of the radial bearing surface 10b (opening portion: a portion in which the pores of the porous body structure are opened on the outer surface). Although the lubricant flows back into the main body, a new lubricant continues to be pushed into the bearing gap one after another, so that the oil film strength and the rigidity are maintained in a high state. In this case, since a continuous and stable oil film is formed, high rotational accuracy is obtained, and shaft runout and NRR
O, jitter and the like are reduced. Also, the rotating shaft 2 and the bearing body
10 is low-noise and low-cost because it rotates without contact.

In this embodiment, a single bearing body 10 is provided, and a plurality of (two in this embodiment) hydrodynamic bearing surfaces 1b are provided on the inner diameter surface. This is to avoid adverse effects such as inaccuracy, which would be a problem when they are arranged separately. That is, if a plurality of bearings 1a are housed in the housing 1b, the accuracy of each bearing 1a, such as coaxiality and cylindricity, becomes a problem. If the accuracy is poor, the rotating shaft 2 and the bearing 1a come into line contact, In such a case, it may occur that the rotating shaft 2 does not pass through the two bearings. On the other hand, if a plurality of bearing surfaces 10b are formed on one bearing body 10 as described above, such a problem can be avoided.

The two radial bearing surfaces 10b are provided with a first groove region m1 in which a dynamic pressure groove 10c inclined on one side is arranged, and a dynamic pressure groove separated axially from the first groove region m1 and inclined on the other side. It has a second groove region m2 in which 10c are arranged, and an annular smooth portion n located between the two groove regions m1 and m2. The dynamic pressure groove 10c of the two groove regions m1 and m2 is smooth. It is partitioned by a section n and is discontinuous. The back portion 10e between the smooth portion n and the dynamic pressure groove 10c is at the same level. This type of discontinuous dynamic pressure groove 10c
Compared to the continuous type, that is, in which the smooth portion n is omitted and the dynamic pressure groove 10c is formed in a V-shape continuous with each other between the two groove regions m1 and m2, the oil film is collected because the oil is collected around the smooth portion n. Since the pressure is high and the smooth portion n having no groove is provided, there is an advantage that the bearing rigidity is high.

In the present invention, as shown in FIG. 4, the end face 10f2 of the bearing body 10 on the housing closed side is connected to the end face 10f.
The upper surface of the thrust washer 12a, which is the opposing surface facing f2, is brought into contact. In this case, the oil that excessively leaks due to thermal expansion or the like is removed from the space between the end face chamfer portion 10g (inner diameter side) of the bearing body 10 and the outer peripheral surface of the rotating shaft 2, and the end face chamfer portion 10h (outer diameter side). In the space between the housing 1b and the inner peripheral surface of the housing 1b.
Due to the temperature drop of 10, it is easily absorbed inside the bearing body 10 (capillary phenomenon). Therefore, since abundant oil is always held inside the bearing, sufficient oil can always be held in the bearing gap during driving, and stable bearing performance can be maintained for a long time.

Of course, even if the end face 10f2 of the bearing body 10 is not in contact with the thrust washer 12a, if the thrust washer is sufficiently close, that is, within a range in which the oil accumulated by the capillary action can be absorbed. If they are close to each other, as shown in FIG. 5, the end face 10f2 and the thrust washer 12
A gap 14 in the axial direction may be interposed between the upper surface 13 (opposing surface).

FIG. 6 shows that when the axial width (s: see FIG. 5) of the gap 14 is changed (s = 0 mm, 0.7 mm, 1.0 mm, 1.
The relationship between the shaft runout ratio of 2 mm) and the amount of lubrication to the bearing body 10 is shown. The bearing body 10 has an inner diameter of φ3 mm and an outer diameter of φ6 mm
The rotating shaft was rotated at 8000 rpm while giving an unbalance amount of 0.5 gr-cm. Prior to the test, the bearing body 10 was made to contain sufficient lubricating oil.

According to this test, the axial width s of the gap 14 was 1.
In the case of 2 mm, additional lubrication for the volume of the gap 14 is necessary, and when the amount of lubrication is small, the shaft runout ratio increases rapidly. However, if the axial width s is 1 mm or less, the presence or absence of additional lubrication is determined. Regardless, it has been found that a sufficiently low shaft runout ratio can be achieved. Therefore, the axial width s of the gap 14 is preferably set to 1 mm or less, for example, about 0.4 mm.

By the way, in the bearing unit 1, as shown in FIGS. 2A and 4, the lower end of the rotating shaft 2 is often formed into a spherical surface from the viewpoint of reducing friction and the like. In this case, as shown in FIG. 4, the spherical portion 2a of the rotating shaft 2 is
If the radial bearing surface 10b overlaps with 10, the bearing clearance becomes uneven, and an appropriate dynamic pressure action cannot be obtained. Therefore,
In this case, as shown in FIG. 7, by providing a radial bearing surface 10b with an annular smooth portion 10i separated from an inner diameter chamfer portion 10g of the bearing body 10, the bearing surface 10b is relatively shifted upward. It is preferable that the entire area of the bearing surface 10b can be opposed to the cylindrical portion 2b on the upper end side of the spherical portion 2a of the rotating shaft 2 (see FIG. 5). The smooth portion 10i is formed only on at least one end of both ends of the bearing main body 10, that is, only on the end located on the bottom side of the housing 1b when assembled into the housing 1b (left side in FIG. 7). Although it is sufficient, a similar smooth portion may be provided on the other end side (the right side).

In the above description, the closed side end face of the bearing body 10
Although the upper surface of the thrust washer 12a is illustrated as the opposing surface 13 facing 10f2, as shown in FIG. The upper surface of the spacer 15 may be the opposing surface 13 opposing the end surface 10f2. in this case,
The bearing body 10 and the spacer 15 are brought into contact with each other as in FIGS. 4 and 5, or are brought close to each other within a predetermined range. The inner diameter of the spacer 15 is made slightly larger than the inner diameter of the radial bearing surface 10b so as not to increase the torque. When the thrust bearing portion 12 is arranged on the opening side of the housing 1b, for example, as shown in FIG. 18, the disk-shaped flange portion 2c provided on the shaft 2 is connected to the end face of the bearing body 10 on the housing opening side.
When forming the thrust bearing part 12 by abutting on 10f1,
The upper surface (bottom surface) of the bottom plate 16 for closing the bottom of the housing 1b is defined as an opposing surface 13, and the opposing surface 13 is brought into contact with the housing closing side end surface 10f2 of the bearing main body 10 or is brought close within a predetermined range.

In the above description, the case where the dynamic pressure groove 10c is provided on the bearing surface 10b of the bearing body 10 has been exemplified. However, the present invention is also applicable to the case where the dynamic pressure groove is provided on the outer peripheral surface of the rotary shaft 2. The same can be applied.

The bearing unit 1 shown in FIG.
A durability test was performed using the bearing unit shown in FIG. 16 as a comparative example, and shaft runout characteristics were measured at the initial stage and after a lapse of 2,000 hours. Each measurement was performed using three bearing units. In the embodiment, the width s of the gap 14 is set to 0.2 m.
m, the width t of the smooth portion 10i was 1 mm, and the width s 'of the gap 14' was 3 mm in the comparative example. The test conditions are as follows.

Motor used: Polygon scanner motor (actual machine motor) Revolution: 20,000 rpm Atmospheric temperature: 50 ° C. Normally, in a polygon scanner motor, the upper end of the rotating shaft does not protrude above the mirror surface. For use, a rotor with the upper end of the shaft protruding was prototyped.
Therefore, the axial runout is measured significantly above the mirror surface, and the measurement results are relative comparison data.

FIG. 8 shows the measurement results. As shown in the figure, the value of the axial run-out is almost not greatly different between the example and the comparative example at the initial stage, but after 2000 hours, the axial run-out of the comparative example is significantly increased, and the superiority of the product of the example was confirmed.

FIGS. 10 and 11 show another embodiment of the present invention, in which the opening at one end of the housing 1b is sealed with a non-contact type sealing member (seal washer 20). Other components of the bearing unit 1 except for the seal structure at the upper end of the housing 1b, for example, the configuration of the hydrodynamic sintered oil-impregnated bearing 1a, the housing 1b, the rotating shaft 2, the thrust bearing portion 12, and the like, are as described below. Except for this, the same configuration as that shown in FIGS. 1 to 9 can be applied.

The seal washer 20 is formed in a thin disk shape having an insertion hole for the rotating shaft 2 at the center, and is formed of, for example, a resin material (eg, polyamide), and is opened at one end of the housing 1b by means such as bonding. Fixed to the part. The seal washer 20 only needs to be formed in a washer shape, and may be formed of metal other than resin. The inner peripheral surface of the seal washer 20 is made as close as possible to the outer peripheral surface of the rotating shaft 2 so as to prevent oil leakage from the inside of the housing 1b due to a capillary phenomenon. When the seal washer 20 is brought into contact with the shaft 2, the torque increases and fluctuates, which is not preferable as a spindle motor for information equipment requiring high accuracy. Therefore, the seal washer 20 does not contact the shaft 2. The width u1 of the gap between the inner peripheral surface of the seal washer 20 and the outer peripheral surface of the rotary shaft 2 is 0.1 mm or less, preferably 0.05 mm
If it is below, even if the shaft posture is set to the sideways or reverse direction, oil leakage is surely prevented by the capillary phenomenon.
In addition, since the flow of the air through the gap u1 is ensured, the air is smoothly discharged from the inside of the housing 1b.

In the outer peripheral surface of the rotary shaft 2, at least a region (a region having an axial width larger than the thickness of the seal washer 20) including a portion facing the inner peripheral surface of the seal washer 20 is formed along the entire circumference. If the oil repellent 21 is applied, oil which is transmitted along the shaft 2 and leaks can be repelled, and oil leakage can be completely prevented. As the oil repellent 21, for example, a substance containing perfluorocarbon as a main component (manufactured by Harvest Corporation, OS-90MF, etc.) can be used.

By the way, usually, the rotating shaft 2 is
The thrust bearing portion 12 is attached to the inner diameter portion of the bearing 1a with the thrust bearing portion 12 attached to the 1b. Before inserting the shaft 2, as shown in FIG.
Oil O (indicated by a dotted pattern) may be previously injected into the housing 1b in order to improve lubricity.
Between the shaft ends and the upper surface of the lubricated oil O, there is no escape space for the air trapped between the shaft end and the upper surface of the oil O, and the insertion of the rotating shaft 2 becomes difficult. In addition, the motor generates heat when it is driven, but the air trapped by the heat expands and pushes up the rotary shaft 2 to destabilize the bearing performance, or the thermally expanded air pushes oil out of the bearing to lubricate the oil. There is also a possibility that the property may be reduced. These problems also occur without lubrication.

As a countermeasure for this, as shown in FIGS. 10 and 11, between the outer diameter surface of the bearing body 10 and the inner diameter surface of the housing 1b, there are provided ventilation passages 22 opened at both axial ends of the bearing body 10. What is necessary is just to make the air trapped through the ventilation path 22 escape to the outside of the bearing. In this case, some air may remain as bubbles in the oil, but such bubbles float up through the ventilation path 22 and are discharged outside the housing 1b. Therefore, after the shaft 2 is inserted, as shown in FIG. 13, the space in the housing 1b (the space 14 between the bearing 1a and the facing surface 13,
The space 23 between the seal washer 20 and the bearing end face 10f1, the bearing gap, the ventilation path 22, etc.) can be filled with oil O. As shown in FIG. 3, the air passage 22 can be formed by providing an axial groove 10j on the outer peripheral surface of the bearing body 1a, but it is also possible to provide a similar groove 10j on the inner peripheral surface of the housing 1b. Good. Further, the ventilation path 22 may be provided not only at one place but also at a plurality of places in the circumferential direction.

If the gap 23 between the seal washer 20 and the bearing end face 10f1 facing the seal washer 20 (hereinafter referred to as one end gap) is too large, the space in the housing 1b can be filled with oil depending on the amount of lubrication. The amount of air remaining in the housing 1b increases, and when the shaft is turned sideways or in the opposite direction, air flows between the thrust washer 12a and the bearing end face 10f2.
14 (hereinafter referred to as the other end side gap), which is not preferable. Therefore, it is desirable to make the one end side gap 23 as small as possible, and its width u2 (see FIG. 10) is set to, for example, 0.6 mm. The width u2 of this gap may be 1.0 mm or less, preferably 0.5 mm or less, but is preferably set to be larger than the width s of the other end gap 14 (u2> s). If the one end side gap 23 is smaller than the other end side gap 14, when the shaft posture is reversed, the one end side gap 23 is filled with oil first, and the air that has lost the escape space enters the other end side gap 14. Is expected.

In order to confirm the effect of this embodiment, the following test was conducted.

・ Atmosphere: 50 ° C. ・ Shaft diameter: φ3 ・ Shaft attitude: reverse ・ Rotation speed: 8000 rpm ・ Test time: 500 hours ・ Evaluation items: Oil leak status (visual observation) and performance change (shaft runout, (Current value) The dimensions and the like of the bearing unit 1 subjected to the test are as shown in FIG.

FIG. 15 shows the test results.

When the seal washer was not provided as in Comparative Example 1, naturally, the injected oil leaked out.
The performance was greatly reduced because air was trapped in the area. It is presumed that the fluid lubrication state is impaired because the current value is also large, and a mixed lubrication state including metal contact is present.

In Comparative Example 2, oil leakage was observed although oil adhesion was observed on the shaft or the rotor. The current value was slightly smaller, but the shaft runout was considerably larger than in the initial stage. It is presumed that the oil leak occurred, air entered the part, and the apparent viscosity decreased, and the shaft runout increased. The cause of the oil leak is that when the motor is reversed, the bearing end face 10f2 and the thrust washer
Since the gap 14 between the seal washers 20 and the bearing end face 10f1 is larger than the gap 23 between the seal washer 20 and the bearing end face 10f1, the gap 23 between the seal washer 20 and the bearing end face 10f1 is first filled with oil, and the air that has lost the escape space It is considered that the gap entered the gap 14 between the end face 10f2 and the facing face 13. As the temperature of the bearing rises, the thermal expansion of the gas is greater than that of the liquid, so it is likely that the oil was pushed out by the air.

In the case of Comparative Example 3, oil leakage was observed, although the amount of oil adhering to the shaft or the rotor was recognized, and the current value was slightly reduced, but the shaft runout was larger than the initial value. This is probably because the gap between the seal washer 20 and the shaft 2 was large and oil leakage could not be prevented by capillary action.

In the case of Comparative Example 4, oil leakage was observed, although the amount of oil adhering to the shaft or rotor was recognized, and the current value was slightly reduced, but the shaft runout was larger than in the initial stage. . Because the gap 23 between the seal washer 20 and the bearing end face 10f1 was too large, the seal washer 20 and the bearing end face
This is probably because the capillary action during 10f1 did not work.

On the other hand, in Example 1, almost no oil leakage was observed, and the performance was maintained in the initial state, and good results were obtained.

In Example 2, no oil leakage was observed. In the first embodiment, no reduction in performance such as shaft runout was observed. However, in the case of a model such as an HDD device in which scattering of oil mist is a problem, a second embodiment having a more reliable oil leakage prevention effect is provided. Is considered preferable.

[0053]

As described above, according to the present invention, oil leakage can be reliably prevented with a simple structure regardless of the shaft posture. Therefore, it is possible to provide a low-cost and high-performance bearing unit. Further, since there is no oil leakage, a good oil film can be maintained for a long time, and the durability is dramatically improved. Further, the surroundings are not polluted by the oil leak.

[Brief description of the drawings]

FIG. 1 shows a DVD- using a bearing unit according to the present invention.
FIG. 3 is an axial sectional view of a ROM spindle motor.

FIG. 2A is an enlarged cross-sectional view of a bottom portion of a bearing unit, and FIG. 2B is a cross-sectional view illustrating another example of a thrust bearing portion.

FIG. 3 is an axial sectional view of a sintered oil-impregnated bearing.

FIG. 4 is an axial sectional view showing an embodiment of the bearing unit.

FIG. 5 is an axial sectional view showing another embodiment of the bearing unit.

FIG. 6 is a diagram showing measurement data of an oiling amount and a shaft runout ratio.

FIG. 7 is an axial sectional view of a sintered oil-impregnated bearing.

FIG. 8 is a diagram showing the results of endurance tests on a product of the present invention and a conventional product.

FIG. 9 is an axial sectional view showing another embodiment of the bearing unit.

FIG. 10 shows a DVD using the bearing unit according to the present invention.
FIG. 3 is an axial sectional view of a spindle motor for ROM.

FIG. 11 is an enlarged cross-sectional view near a housing opening.

FIG. 12 is an axial sectional view of the bearing unit during insertion of the shaft.

FIG. 13 is an axial sectional view of the bearing unit after insertion of the shaft.

FIG. 14 is a diagram showing conditions of an oil leak test.

FIG. 15 is a view showing an experimental result.

FIG. 16 is an axial sectional view showing a conventional bearing unit.

FIG. 17 is an enlarged sectional view of a dynamic pressure bearing unit to which a labyrinth seal is applied.

FIG. 18 is an axial sectional view of a dynamic pressure type bearing unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bearing unit 1a Sintered oil-impregnated bearing 1b Housing 2 shaft (rotating shaft) 3 Optical disk 2a Spherical part 10 Bearing body 10b Radial bearing surface 10c Dynamic pressure groove 10f1 Bearing end surface (one end) 10f2 Bearing end surface (other end) 10i Smooth part 10k groove 12 Thrust bearing 12a Thrust washer 13 Opposite surface 14 Gap (other end) 15 Spacer 16 Bottom plate 20 Seal washer 21 Oil repellent 22 Ventilation passage 23 Gap (One end)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuhiro Yamamoto

Claims (22)

[Claims] A bearing body formed of sintered metal and having a radial bearing surface opposed to an outer peripheral surface of a shaft through a bearing gap is impregnated with lubricating oil or lubricating grease. A dynamic pressure type sintered oil-impregnated bearing that supports the shaft in a non-contact manner by the dynamic pressure action generated by the relative rotation of the bearing; A thrust bearing portion for supporting the shaft in a thrust direction, wherein an end surface of the housing closed side of the bearing body and an opposing surface provided on the closed side of the housing in opposition to the end surface are brought close to or in contact with each other. Pressure type sintered oil-impregnated bearing unit. 2. A bearing body formed of sintered metal and having a radial bearing surface opposed to an outer peripheral surface of a shaft via a bearing gap is impregnated with lubricating oil or lubricating grease. A dynamic pressure type sintered oil-impregnated bearing that supports the shaft in a non-contact manner by dynamic pressure action generated by the relative rotation of the bearing, a housing in which one end is open and the other end side is closed, and the dynamic pressure-type sintered oil-impregnated bearing is housed in the inner diameter portion, A thrust bearing portion for supporting the shaft in a thrust direction, wherein a gap between an end face of the housing closed side of the bearing body and an opposing face provided on the closed side of the housing in opposition to the end face is set to 1 mm or less. A hydrodynamic sintered oil-impregnated bearing unit characterized by the above-mentioned. 3. The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the opposed surface is constituted by a bottom surface closing the other end of the housing. 4. The dynamic pressure type sintering device according to claim 1, wherein the thrust bearing portion supports the shaft end in contact with a thrust washer provided on the closed side of the housing, and the opposed surface is constituted by a thrust washer. Oil-impregnated bearing unit. 5. The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the opposed surface is constituted by a spacer provided on the closed side of the housing. 6. The shaft according to claim 4, wherein one end of the shaft contacting the thrust washer is formed in a spherical shape, and the radial bearing surface of the bearing body is shifted from the spherical portion of the shaft to the other end of the shaft. Dynamic pressure type oil-impregnated bearing unit. 7. The hydrodynamic sintered oil-impregnated bearing unit according to claim 6, wherein a radial bearing surface is provided with an annular smooth portion separated from an end surface chamfer portion on the other end side of the housing of the bearing body. 8. A bearing body formed of sintered metal and having a radial bearing surface opposed to an outer peripheral surface of a shaft with a bearing gap therebetween being impregnated with lubricating oil or lubricating grease. A dynamic pressure type sintered oil-impregnated bearing that supports the shaft in a non-contact manner by the dynamic pressure action generated by the relative rotation of the bearing, a housing in which one end is open and the other end is closed, and the dynamic pressure type oil-impregnated bearing is housed in the inner diameter portion, A thrust bearing portion for supporting the shaft in a thrust direction, wherein an opening at one end of the housing is sealed with a seal washer whose inner peripheral surface is close to the outer peripheral surface of the shaft. unit. 9. The hydrodynamic sintered oil-impregnated bearing unit according to claim 8, wherein the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft is set to 0.1 mm or less. 10. The hydrodynamic sintered oil-impregnated bearing unit according to claim 8, wherein a gap between the seal washer and a bearing end face opposed to the seal washer is set to 1.0 mm or less. 11. The hydrodynamic sintered oil-impregnated bearing unit according to claim 8, wherein a lubricating agent is applied to at least a region of the outer peripheral surface of the shaft including a portion facing the inner peripheral surface of the seal washer. 12. The hydrodynamic sintered oil-impregnated bearing according to claim 1, wherein an opening on one end side of the housing is sealed with a seal washer whose inner peripheral surface is close to the outer peripheral surface of the shaft. unit. 13. The hydrodynamic sintered oil-impregnated bearing unit according to claim 12, wherein the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft is set to 0.1 mm or less. 14. The hydrodynamic sintered oil-impregnated bearing unit according to claim 12, wherein a gap between the seal washer and a bearing end face facing the seal washer is set to 1.0 mm or less. 15. The dynamic pressure type according to claim 14, wherein a gap between the seal washer and the bearing end face facing the seal washer is set to be larger than a gap between the housing closing side end face of the bearing body and the facing face. Sintered oil-impregnated bearing unit. 16. The hydrodynamic sintered oil-impregnated bearing unit according to claim 12, wherein an oleophobic agent is applied to at least a region of the outer peripheral surface of the shaft that faces the inner peripheral surface of the seal washer. 17. The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein a hydrodynamic groove inclined with respect to the axial direction is provided on the radial bearing surface. 18. The hydrodynamic sintered oil-impregnated product according to claim 1, wherein ventilation passages are provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing, the ventilation passages being opened at both axial ends of the bearing body. Bearing unit. 19. A spindle motor for an optical disk drive comprising the hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the optical disk is rotated by a relative rotation between the shaft and the bearing body. 20. A spindle motor for a magnetic disk drive equipped with a hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the magnetic disk is rotated by a relative rotation between a shaft and a bearing body. 21. A polygon scanner motor for a laser beam printer equipped with a hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the polygon mirror is rotated by relative rotation between the shaft and the bearing body. 22. A dynamic pressure groove made of a sintered metal and having a radial bearing surface opposed to an outer peripheral surface of a shaft via a bearing gap in an axial direction, and being inclined with respect to the axial direction in the radial bearing surface. And a lubricating oil or lubricating grease impregnated in the bearing body, at least at one end having an inner diameter portion provided with an end surface chamfer portion, wherein the radial bearing is separated from the end surface chamfer portion by an annular smooth portion. A hydrodynamic sintered oil-impregnated bearing with a surface formed.