JP2005195180A - Dynamic oil-impregnated sintered bearing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To completely prevent degradation of bearing performance caused by lubricating oil leakage to the outside of a housing at a low cost. <P>SOLUTION: One end of the housing 1b is open and the other thereof is closed. A dynamic oil-impregnated sintered bearing 1a is provided in the inner-diameter portion of the housing 1b. A bearing 2 is supported in a non-contact manner with the dynamic oil-impregnated sintered bearing 1a. A seal washer 20 is fitted on an opening portion of the housing 1b on one end side, and an inner circumference of the seal washer 20 is adjacent to a circumference outer of the bearing 2. The opening portion of the housing 1b on one end side is sealed with the seal washer 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrodynamic sintered oil-impregnated bearing and a bearing unit having features excellent in high rotational accuracy, high-speed stability, high durability, and the like, and in particular, spindle motors in information equipment, such as DVD-ROM and DVD-RAM. It is suitable for supporting a spindle of an optical disk, a magneto-optical disk such as MO, a motor for driving a magnetic disk such as HDD, or a polygon scanner motor of a laser beam printer (LBP).

  The spindle motors of the above information devices are required to have higher speed, lower cost, lower noise, etc. in addition to high rotational accuracy. The motor spindle is one of the components that determine these required performances. There are bearings that support Conventionally, a ball bearing or a general circular oil-impregnated bearing is used as the bearing.

  However, this type of spindle motor is often used at a high speed of about 8000 to 10000 rpm, especially a polygon scanner motor used for LBP, at a high speed of several tens of thousands rpm, and also has rotational accuracy such as shaft runout, NRRO, and jitter. Since it is necessary to consider, it is difficult for ball bearings and sintered oil-impregnated bearings to satisfy the required performance.

  In view of the above, in recent years, it has been studied to use a hydrodynamic sintered oil-impregnated bearing as this type of bearing. In this bearing, a sintered metal bearing body is impregnated with lubricating oil or lubricating grease, and a lubricating oil film is formed in the bearing gap by the dynamic pressure effect of the dynamic pressure groove provided on the bearing surface to support the spindle in a non-contact manner. Thus, it can sufficiently cope with the required performance.

  However, when this bearing body is assembled in a housing and used in a vertical orientation, oil that has oozed out of the bearing body due to pressure generation or thermal expansion during motor drive is saturated within the bearing gap and leaks out of the bearing gap. There is a risk of release. As shown in FIG. 16, the oil 16 leaking downward from 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 of the housing 1b is wide, 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 contact the bearing body 10 never returns and is lubricated by repeating this process. Oil shortage may result in deterioration of bearing performance. When the lubricating oil is insufficient, air is entrained in the lubricating oil film formed in the bearing gap, the original dynamic pressure effect is reduced and the radial rigidity is lowered, while unstable vibrations are generated, Rotational accuracy deteriorates.

  As the above countermeasure, it is simplest to preliminarily fill the gap 14 'with lubricating oil. However, in this case, from the opposite end face of the bearing body 10 by changing the spindle posture (for example, when it is turned upside down) Lubricating oil may leak and contaminate the surroundings.

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

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

  In order to achieve the above object, the present invention is made by impregnating a bearing body, which is formed of a sintered metal and has a radial bearing surface facing the outer peripheral surface of the shaft through a bearing gap, with lubricating oil or lubricating grease. The hydrodynamic sintered oil-impregnated bearing that supports the shaft in a non-contact manner by the hydrodynamic action generated by the relative rotation of the shaft and the bearing body, and the hydrodynamic sintered oil-impregnated bearing having one end opened and the other end closed, In a dynamic pressure type sintered oil-impregnated bearing unit comprising an internal housing and a thrust bearing that thrust supports the shaft, the opening on 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. Provide the configuration. 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, it is desirable to set the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft to 0.1 mm or less. Moreover, if an oil repellent is applied to a region including at least a portion facing the inner peripheral surface of the seal washer on the outer peripheral surface of the shaft, oil leakage can be prevented more reliably.

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

  Further, if the gap between the seal washer and the bearing end face facing the seal washer is set larger than the gap between the housing closing side end face of the bearing body and the facing face facing the end face, Even when the shaft orientation 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 its escape space is removed between the opposing face and the bearing end face. The situation of entering the gap and being caught in the bearing gap is prevented.

  The facing surface can be constituted by a bottom surface that closes the other end of the housing, or a spacer provided on the closing side of the housing. Further, the thrust bearing portion may have a structure in which the shaft end is in contact with and supported by a thrust washer provided on the closed side of the housing, and the opposing surface may be configured by this thrust washer. In this case, it is preferable that one end of the shaft that contacts 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 toward the other end side of the shaft. This can be realized by providing a radial bearing surface across an annular smooth portion from an end surface chamfer portion on the other end side of the housing of the bearing body.

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

  If air passages that open at both ends in the axial direction of the bearing body are provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing, air trapped in the housing when the shaft is inserted into the bearing is removed. Since the air is discharged out of the housing through the air passage, air can be prevented from being caught in the bearing gap.

  The hydrodynamic side sintered oil-impregnated bearing unit described above includes a spindle motor of a magnetic disk drive that rotates a magnetic disk by relative rotation between a shaft and a bearing body, and an optical disk drive that rotates an optical disk by relative rotation between the shaft and the bearing body. And a polygon scanner motor of a laser beam printer that rotates a polygon mirror by relative rotation between a shaft and a bearing body. The “optical disk” here includes magneto-optical disks (MD, MO, etc.).

  In order to achieve the above object, the present invention is made of a sintered metal, and has a radial bearing surface that is opposed to the outer peripheral surface of the shaft via a bearing gap in the axial direction, and the radial bearing surface has an axial direction. In a hydrodynamic type sintered oil-impregnated bearing comprising a bearing body formed with a dynamic pressure groove inclined with respect to at least one end inner diameter portion and an end face chamfered portion and a lubricating oil or lubricating grease impregnated in the bearing body, Provided is a configuration in which a radial bearing surface is formed by separating an annular smooth portion from an end surface chamfer portion.

  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 bearing unit having high functionality at low cost. Further, since there is no oil leakage, a good oil film can be maintained for a long time, and the durability is dramatically improved. Moreover, the surroundings are not contaminated by oil leakage.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view of a spindle motor of an optical disc drive (for DVD-ROM device) which is a kind of information equipment. The spindle motor includes a bearing unit 1 that supports a vertical rotating shaft 2, a turntable 4 that is attached to the upper end of the rotating shaft 2 and supports and fixes an optical disk 3 such as a DVD-ROM, a clamper 8, and a radial gap. And a motor portion M having a stator 5 and a rotor magnet 6 opposed to each other. When the stator 5 is energized, the rotor magnet 6 is rotated by the exciting force generated between 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 rotated. Rotate. When the bearing unit 1 is used for a spindle motor for other information equipment, for example, a magnetic disk drive, a disk hub (not shown) that holds one or a plurality of magnetic disks is mounted on the rotary shaft 2 and is an LBP polygon scanner motor. In the case of using for the above, a polygon mirror (not shown) is mounted on the rotary 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 bottomed cylindrical shape with one end opened and the other end closed, and is fixed to the base 17 with the opening on one end side facing up. The other end side of the housing is closed by a thrust bearing portion 12 as shown in the figure, for example. As shown in FIG. 2 (a), the thrust bearing portion 12 has a structure in which, for example, a resin-made thrust washer 12a formed in a disk shape and a back metal 12b for supporting the same are laminated. The lower end is brought into contact with the thrust washer 12a and 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 in the central portion 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 a sintered metal having a radial bearing surface 10b opposed to the outer peripheral surface of the rotating shaft 2 through a bearing gap. It is constituted by impregnating a lubricating grease (preferably containing a low concentration thickener). The bearing body 10 made of sintered metal is formed of a sintered metal mainly composed of copper, iron, or both, and is preferably formed using 20 to 95% of copper. Two bearing surfaces 10b that are separated in the axial direction are formed on the inner periphery of the bearing body 10, and a plurality of dynamic pressure grooves 10c (herring bones) each inclined with respect to the axial direction are formed on both of the two bearing surfaces 10b. Mold) is 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, and other shapes other than the herringbone type, for example, a spiral type may be used as long as this condition is satisfied. The groove depth of the dynamic pressure groove 10c is suitably about 2 to 6 μm, and is set to 3 μm, for example.

  In this sintered oil-impregnated bearing 1a, the lubricant (lubricating oil or base oil of the lubricating grease) inside the bearing body 10 is generated on the surface of the bearing body 10 by the pressure generated by the rotation of the rotating shaft 2 and the thermal expansion of the oil due to the temperature rise. Oozes out of the bearing and is pulled 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. Therefore, the oil film force is increased and the rigidity of the bearing can be improved.

  When 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 where the pores of the porous body structure are opened on the outer surface), so that the lubricant is inside the bearing body. However, since new lubricant continues to be pushed into the bearing gap one after another, the oil film force and 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, NRRO, jitter, and the like are reduced. Further, since the rotary shaft 2 and the bearing body 10 rotate without contact, the noise is low and the cost is low.

  In this embodiment, a single bearing body 10 is provided, and the hydrodynamic bearing surface 1b is provided at a plurality of locations (two locations in the present embodiment) on its inner diameter surface. This is to avoid adverse effects such as inaccuracy and the like, which are problems when arranged. That is, if a plurality of bearings 1a are accommodated in the housing 1b, the accuracy of each bearing 1a, such as coaxiality and cylindricity, becomes a problem, and if the accuracy is poor, the rotating shaft 2 and the bearing 1a are in line contact, In some cases, the rotating shaft 2 may not pass through the two bearings. In contrast, if a plurality of bearing surfaces 10b are formed on one bearing body 10 as described above, this type of problem can be avoided.

  Both radial bearing surfaces 10b are arranged with a first groove region m1 in which a dynamic pressure groove 10c inclined on one side is arranged, and a dynamic pressure groove 10c which is axially separated from the first groove region m1 and inclined on the other side. Second groove region m2 and an annular smooth portion n positioned between the two groove regions m1 and m2, and the dynamic pressure groove 10c of the two groove regions m1 and m2 is the smooth portion n. Partitioned and discontinuous. The back portion 10e between the smooth portion n and the dynamic pressure groove 10c is at the same level. This type of non-continuous type dynamic pressure groove 10c is continuous type, that is, the smoothing portion n is omitted, and the dynamic pressure groove 10c is formed in a V-shape that is continuous between both groove regions m1 and m2. Since oil is collected around the smooth portion n, the oil film pressure is high, and since the smooth portion n without a groove is provided, the bearing rigidity is high.

  In the present invention, as shown in FIG. 4, the end surface 10f2 on the housing closing side of the bearing body 10 is brought into contact with the upper surface of the thrust washer 12a, which is a facing surface facing the end surface 10f2. In this case, the oil leaked excessively due to thermal expansion or the like is the space between the end surface chamfer portion 10g (inner diameter side) of the bearing body 10 and the outer peripheral surface of the rotary shaft 2, and the end surface chamfer portion 10h (outer diameter side). And the space between the inner peripheral surface of the housing 1b and easily absorbed into the bearing body 10 due to the temperature drop of the bearing body 10 when the drive is stopped (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 and the thrust washer 12a are not in contact with each other, if they are sufficiently close to each other, that is, within the range in which the oil accumulated by the capillary phenomenon can be absorbed. If so, an axial gap 14 may be interposed between the end face 10f2 and the upper surface 13 (opposing surface) of the thrust washer 12, as shown in FIG.

  6 shows the axial run-out ratio and the amount of lubrication to the bearing body 10 when the axial width of the gap 14 (s: see FIG. 5) is changed (s = 0 mm, 0.7 mm, 1.0 mm, 1.2 mm). Shows the relationship. The bearing body 10 had an inner diameter of φ3 mm and an outer diameter of φ6 mm, and the rotating shaft was rotated at 8000 rpm while applying an unbalance amount of 0.5 gr-cm. Prior to the test, the bearing body 10 contained sufficient lubricating oil.

  From this test, when the axial width s of the gap 14 is 1.2 mm, additional oil supply is required for the volume of the gap 14, and the shaft runout ratio increases rapidly when the amount of oil supply is small. It has been found that if the direction width s is 1 mm or less, a sufficiently low shaft runout ratio can be achieved regardless of the presence or absence of additional lubrication. Accordingly, the axial width s of the gap 14 is preferably 1 mm or less, and is set to about 0.4 mm, for example.

  Incidentally, in the bearing unit 1, as shown in FIGS. 2A and 4, the lower end of the rotary shaft 2 is often formed in a spherical surface from the viewpoint of reducing friction and the like. In this case, as shown in FIG. 4, if the spherical surface portion 2a of the rotating shaft 2 overlaps with the radial bearing surface 10b of the bearing body 10, the bearing gap becomes non-uniform and an appropriate dynamic pressure action cannot be obtained. Therefore, in this case, as shown in FIG. 7, by providing the radial bearing surface 10b with the annular smooth portion 10i separated from the inner diameter chamfered portion 10g of the bearing body 10, the bearing surface 10b is shifted relatively upward. Thus, the entire region of the bearing surface 10b may 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 smoothing portion 10i is formed only on at least one end side of the both ends of the bearing body 10, that is, only on the end portion (left side in FIG. 7) located on the bottom side of the housing 1b when assembled in the housing 1b. However, a similar smooth portion may be provided on the other end side (the right side).

  In the above description, the upper surface of the thrust washer 12a is illustrated as the facing surface 13 facing the closing side end surface 10f2 of the bearing body 10, but as shown in FIG. 9, the upper surface of the thrust washer 12a and the bearing body 10 By disposing the ring-shaped spacer 15 between them, the upper surface of the spacer 15 may be the facing surface 13 facing 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 close to each other within a predetermined range. The inner diameter of the spacer 15 is slightly larger than the inner diameter of the radial bearing surface 10b so that the torque does not increase. When the thrust bearing portion 12 is disposed on the opening side of the housing 1b, for example, as shown in FIG. 18, a disk-shaped flange portion 2c provided on the shaft 2 is brought into contact with the housing opening side end surface 10f1 of the bearing body 10. When the thrust bearing portion 12 is configured, the upper surface (bottom surface) of the bottom plate 16 that closes the bottom portion of the housing 1b is the facing surface 13, and the facing surface 13 is brought into contact with the housing closing side end surface 10f2 of the bearing body 10 or predetermined Close within 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 is illustrated, but the present invention is similarly applied to the case where the dynamic pressure groove is provided on the outer peripheral surface of the rotating shaft 2. can do.

  An endurance test was conducted using the bearing unit 1 shown in FIG. 5 as an example and the bearing unit shown in FIG. 16 as a comparative example, and the shaft run-out characteristics after the initial and 2000-hour elapsed were measured. All measurements were performed using three bearing units. In the embodiment, the width s of the gap 14 is 0.2 mm, the width t of the smooth portion 10i is 1 mm, and in the comparative example, the width s 'of the gap 14' is 3 mm. The test conditions are as follows.

Motor used: Polygon scanner motor (actual motor)
Rotational speed: 20000 rpm
Ambient temperature: 50 ° C
Normally, in the polygon scanner motor, the upper end of the rotating shaft does not protrude above the mirror surface, but a rotor with the upper end of the shaft protruding was made for the purpose of this experiment. Therefore, the axial run-out is measured substantially above the mirror surface, and the measurement result is relative comparison data.

  The measurement results are shown in FIG. As shown in the drawing, although the shaft runout values in the example and the comparative example are almost the same at the initial stage, the shaft runout in the comparative example became remarkably large after 2000 hours, and the superiority of the example product was confirmed.

  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). In the bearing unit 1, the components other than 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, a configuration similar to 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 rotary shaft 2 at the center, and is formed of, for example, a resin material (for example, polyamide) and fixed to one end opening of the housing 1b by means of adhesion or the like. Is done. The seal washer 20 need only be formed in a washer shape, and can be formed of metal other than resin. The inner peripheral surface of the seal washer 20 is as close as possible to the outer peripheral surface of the rotating shaft 2 so that oil leakage from the inside of the housing 1b is prevented by capillary action. When the seal washer 20 is brought into contact with the shaft 2, torque is increased or fluctuated, which is not preferable as a spindle motor for information equipment that requires high accuracy. Therefore, the seal washer 20 is not in contact with the shaft 2. If 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 or less, even if the shaft orientation is in the horizontal direction or the reverse direction, Oil leakage is surely prevented by capillary action. Since air circulation through the gap u1 is ensured, the air is smoothly released from the housing 1b.

  Of the outer peripheral surface of the rotating shaft 2, an oil repellent 21 is applied to the region including at least a portion facing the inner peripheral surface of the seal washer 20 (region having an axial width larger than the thickness of the seal washer 20) over the entire periphery. If oil is applied, the oil that is about to leak through the shaft 2 can be repelled, and oil leakage can be completely prevented. As the oil repellent 21, for example, a material mainly composed of perfluorocarbon (manufactured by Harvest, OS-90MF, etc.) can be used.

  By the way, the rotating shaft 2 is normally inserted into the inner diameter portion of the bearing 1a with the thrust bearing portion 12 mounted on the housing 1b. Before the shaft 2 is inserted, as shown in FIG. 12, oil O (indicated by a dotted pattern) may be injected into the housing 1b in advance to improve lubricity. Since the bearing gap between them is only a few μm, there is no escape space for air trapped between the shaft end and the upper surface of the oil O that has been lubricated, making it difficult to insert the rotating shaft 2. The motor generates heat when it is driven, but the trapped air expands and pushes up the rotating shaft 2 to destabilize the bearing performance, or the thermally expanded air pushes oil out of the bearing and lubricates it. There is also a risk of reducing the properties. These problems occur similarly even when not lubricating.

  As a countermeasure against this, as shown in FIGS. 10 and 11, an air passage 22 opened at both axial ends of the bearing body 10 is provided between the outer diameter surface of the bearing body 10 and the inner diameter surface of the housing 1b. The air trapped through the path 22 may be released to the outside of the bearing. In this case, some air may remain in the oil as bubbles, but this type of bubbles floats up through the air passage 22 and is released out of 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 surface 10f1, the bearing gap, It is possible to fill the air passage 22 and the like with the 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. However, the same groove 10j may be provided on the inner peripheral surface of the housing 1b. Good. Further, the air passage 22 may be provided not only at one place but at a plurality of places in the circumferential direction.

  If the gap 23 between the seal washer 20 and the bearing end face 10f1 opposite to the seal washer 20 (hereinafter referred to as a gap on one end side) is too large, the space in the housing 1b cannot be filled with oil depending on the amount of lubrication. The amount of air remaining in 1b increases, and there is a risk of air entering the gap 14 between the thrust washer 12a and the bearing end face 10f2 (hereinafter referred to as the other end side gap) when the shaft posture is set to the horizontal or reverse direction. It is not preferable. Accordingly, 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 0.6 mm, for example. The width u2 of the gap may be 1.0 mm or less, and is preferably set to 0.5 mm or less, but is preferably set to be larger than the width s of the other end side gap 14 (u2> s). If the one-end-side gap 23 is smaller than the other-end-side gap 14, the one-end-side gap 23 will be filled with oil first and the air that has lost its escape will enter the other-end-side gap 14 when the shaft posture is reversed. This is because it is expected.

  In order to confirm the effect of this embodiment, the following tests were conducted.

・ Atmosphere: 50 ℃
・ Shaft diameter: φ3
・ Axis posture: Reverse direction ・ Rotation speed: 8000rpm
Test time: 500 hours Evaluation items: Oil leakage status (visual observation) and performance changes (shaft runout, current value) The dimensions and the like of the bearing unit 1 subjected to the test are as shown in FIG.

  The test results are shown in FIG.

  When the seal washer was not provided as in Comparative Example 1, the oil that was lubricated naturally leaked out, and air was caught in that portion, so the performance was greatly reduced. Since the current value is also increased, the fluid lubrication state is impaired, and it is presumed that the mixed lubrication state including the metal contact is achieved.

  In Comparative Example 2, oil leakage is recognized although the adhesion of oil to the shaft or rotor is recognized. Although the current value was slightly smaller, the shaft runout was considerably larger than the initial value. Since oil leakage occurred, air intruded into that part, and the apparent viscosity decreased, so it is presumed that the shaft runout increased. The cause of the oil leakage is that when the motor is reversed, the gap 14 between the bearing end face 10f2 and the thrust washer 12a is larger than the gap 23 between the seal washer 20 and the bearing end face 10f1, so the seal washer 20 and the bearing This is presumably because the gap 23 between the end faces 10f1 was first filled with oil, and the air that lost the escape area entered the gap 14 between the bearing end face 10f2 and the facing surface 13. As the temperature of the bearing rises, the thermal expansion of the gas is greater than that of the liquid, so the oil appears to have been pushed out by the air.

  In the case of Comparative Example 3 as well, although oil adhesion was recognized to the shaft or rotor, oil leakage was observed, and the current value was slightly smaller 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 as well, although oil adhesion was recognized to the shaft or rotor, oil leakage was recognized and the current value was slightly smaller, but the shaft runout was larger than the initial value. This is probably because the gap 23 between the seal washer 20 and the bearing end face 10f1 was too large, and the capillary phenomenon between the seal washer 20 and the bearing end face 10f1 did not work.

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

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

It is sectional drawing of the axial direction of the spindle motor for DVD-ROM using the bearing unit concerning this invention. (A) A figure is an expanded sectional view of a bearing unit bottom, and (b) figure is a sectional view showing other examples of a thrust bearing part. It is sectional drawing of the axial direction of a sintered oil-impregnated bearing. It is sectional drawing of the axial direction which shows one Embodiment of the said bearing unit. It is sectional drawing of the axial direction which shows other embodiment of the said bearing unit. It is a figure which shows the measurement data of a lubrication amount and a shaft runout ratio. It is sectional drawing of the axial direction of a sintered oil-impregnated bearing. It is a figure which shows the result of the endurance test in this invention product and a conventional product. It is sectional drawing of the axial direction which shows other embodiment of the said bearing unit. It is an axial sectional view of a spindle motor for DVD-ROM using a bearing unit according to the present invention. It is an expanded sectional view near a housing opening. It is an axial sectional view of the bearing unit during the insertion of the shaft. It is an axial sectional view of the bearing unit after the shaft is inserted. It is a figure which shows the conditions of an oil leak test. It is a figure which shows an experimental result. It is sectional drawing of the axial direction which shows the conventional bearing unit. It is an expanded sectional view of a dynamic pressure type bearing unit to which a labyrinth seal is applied. It is an axial sectional view of a dynamic pressure type bearing unit.

Explanation of symbols

1 Bearing unit
1a Sintered oil-impregnated bearing
1b Housing 2 axis (rotary axis)
3 Optical disc
2a Spherical surface
10 Bearing body
10b Radial bearing surface
10c Dynamic pressure groove
10f1 Bearing end face (one end side)
10f2 Bearing end face (other end side)
10i smooth part
10k groove
12 Thrust bearing
12a Thrust washer
13 Opposite surface
14 Clearance (other end side)
15 Spacer
16 Bottom plate
20 Seal washer
21 Oil repellent
22 Ventilation path
23 Clearance (one end side)

Claims (11)

A bearing body made of sintered metal and having a radial bearing surface facing the outer peripheral surface of the shaft through a bearing gap is impregnated with lubricating oil or lubricating grease, and is generated by relative rotation between the shaft and the bearing body. A hydrodynamic sintered oil-impregnated bearing that supports the shaft in a non-contact manner by a dynamic pressure action, a housing in which one end is open and the other end is closed, and the dynamic pressure-type sintered oil-impregnated bearing is housed in the inner diameter portion, and the shaft is thrust-supported In a thing provided with a thrust bearing part,
A hydrodynamic sintered oil-impregnated bearing unit characterized in that one end side opening of the housing is sealed with a seal washer whose inner peripheral surface is close to the outer peripheral surface of the shaft.   The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein a 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.   The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein a clearance between the seal washer and the bearing end face facing the seal washer is set to 1.0 mm or less.   The hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein a lubricant is applied to a region including at least a portion facing the inner peripheral surface of the seal washer in the outer peripheral surface of the shaft.   The clearance between the seal washer and the bearing end surface facing the seal washer is larger than the clearance between the housing closing side end surface of the bearing body and the facing surface provided on the housing closing side facing the end surface. The hydrodynamic sintered oil-impregnated bearing unit according to claim 3, which is set.   The hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 5, wherein a hydrodynamic groove inclined with respect to the axial direction is provided on the radial bearing surface.   The hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 6, wherein a vent path that opens at both axial ends of the bearing body is provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing.   8. 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 relative rotation between a shaft and a bearing body.   8. A spindle motor for a magnetic disk drive comprising the hydrodynamic sintered oil-impregnated bearing unit according to claim 1, wherein the magnetic disk is rotated by relative rotation between a shaft and a bearing body.   A polygon scanner motor for a laser beam printer comprising the hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 7, wherein the polygon mirror is rotated by relative rotation between a shaft and a bearing body. A radial bearing surface that is made of a sintered metal and is opposed to the outer peripheral surface of the shaft via a bearing gap in the axial direction, and a dynamic pressure groove that is inclined with respect to the axial direction is formed on the radial bearing surface, and at least In one provided with a bearing main body provided with an end face chamfered portion at one end inner diameter portion, and lubricating oil or lubricating grease impregnated in the bearing main body,
A hydrodynamic sintered oil-impregnated bearing in which a radial bearing surface is formed across an annular smooth portion from an end surface chamfer portion.

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