JP4556621B2 - Fluid dynamic pressure bearing and spindle motor - Google Patents

Description

  The present invention relates to a bearing device employing a fluid dynamic pressure bearing mechanism mounted on a signal recording / reproducing device such as a hard disk drive device, and a spindle motor equipped with the bearing device. In particular, the present invention relates to a thin bearing device having a small bearing height and a thin spindle motor.

  Conventionally, various fluid dynamic pressure bearings are used for spindle motors used in signal recording / reproducing apparatuses such as hard disk drives. A fluid dynamic pressure bearing is a bearing in which a lubricating liquid such as oil is interposed between a shaft and a sleeve, and the fluid pressure generated in the lubricating liquid has a supporting force.

  An example of a spindle motor using a conventional dynamic pressure bearing is shown in FIG. This spindle motor has a pair of radial bearing portions 137 and 137 between an outer peripheral surface of a shaft body 131 that is integral with the rotor 105 and an inner peripheral surface of a sleeve 133 through which the shaft body 131 is rotatably inserted. They are arranged apart from each other in the axial direction. The upper surface of the disc-shaped thrust plate 134 projecting radially outward from the outer peripheral surface of one end of the shaft 131 and the step formed on the sleeve 133, and the lower surface of the thrust plate 134 and one opening of the sleeve 133. A pair of thrust bearing portions 136 and 136 are formed between the thrust bush 132 and the thrust bush 132 for closing the shaft. A second taper seal portion 140 is formed on the peripheral surface of the shaft body 131 above the radial bearing portion.

  Such spindle motors are further required to be thinner. This is because the demand for small information devices is increasing, and accordingly, the hard disk drive and the like are also required to be small and thin.

  However, when the spindle motor as shown in FIG. 12 is made thin, severe restrictions are necessarily imposed on the height of the fluid dynamic bearing device. For this reason, the distance between the two radial bearing portions must be reduced, but this particularly reduces the rigidity against an external force that attempts to collapse the shaft body, making the bearing design extremely difficult.

  Patent Document 1 discloses a structure in which a thin plate is disposed on the end face of the sleeve and a taper seal is formed in the gap with the sleeve end face in order to realize a reduction in the size of the bearing. According to this configuration, the taper seal 140 in FIG. 12 is arranged in a shape lying in the radial direction, not in the axial direction. For this reason, it is possible to reduce the height of the entire bearing without reducing the distance between the two radial bearings.

  However, with this structure, it is not possible to sufficiently suppress the trouble that the lubricating liquid leaks through a small gap formed between the shaft body peripheral surface and the thin plate. For this reason, the bearing disclosed in Patent Document 1 has never been put to practical use.

Japanese Patent Application Laid-Open No. 08-331796

  An object of the present invention is to provide a thin fluid dynamic pressure bearing device with high bearing rigidity and a thin spindle motor equipped with the bearing device.

In order to solve the above problems, the fluid dynamic pressure bearing according to claim 1,
A shaft,
Shaft is inserted, and a stationary portion that rotatably supported by the central axis of the shaft,
A radial gap formed between the outer peripheral surface of the shaft body and the inner peripheral surface of the stationary portion facing the shaft body;
A lubricating liquid filled in the radial gap;
A radial dynamic pressure bearing formed in a first gap that constitutes a part of the radial gap, and having a radial dynamic pressure generating groove that induces a fluid dynamic pressure using a lubricating liquid as a working fluid when the shaft is rotated;
A second seal portion that is located radially outward from the radial gap and formed in a gap extending in the axial direction of the stationary portion, and connected to the radial gap;
A first seal portion formed in an axially extending gap located at an upper end portion of the radial gap, connected to the radial gap and the second seal portion, and having an axial length shorter than that of the second seal portion; ,
A second gas-liquid interface formed in the second seal portion;
Located above the second gas-liquid interface, the first gas-liquid interface formed in the first seal part; and
A communication path formed in the stationary portion, filled with a lubricating liquid, and connected to the second seal portion, the upper end portion of the first gap, and the first seal portion without going through the radial dynamic pressure bearing; ,
A part of the communication path formed in the stationary part, filled with the lubricating liquid, and connected to the second seal part, the communication path, and the lower end of the first gap without going through the radial dynamic pressure bearing; Have
The second seal portion is characterized by being positioned radially outward from a part of the communication path and the communication path.

In order to solve the above problems, the fluid dynamic pressure bearing according to claim 2 ,
The gap of the second seal portion is formed in a taper shape in which the gap dimension increases as it extends in the axial direction.

In order to solve the above problems, the fluid dynamic pressure bearing according to claim 3 ,
The gap of the first seal portion is formed in a tapered shape in which the gap dimension increases toward the upper side,
The taper angle of the first seal part is larger than the taper angle of the second seal part.

In order to solve the above problem, the fluid dynamic pressure bearing according to claim 4 ,
The width of the second gas-liquid interface is characterized by being wider than the width of the first gas-liquid interface.

In order to solve the above problems, the fluid dynamic pressure bearing according to claim 5 ,
An oil repellent film is formed on at least one of the outer peripheral surface of the shaft body and the surface of the stationary portion located above the first gas-liquid interface.

In order to solve the above problems, the fluid dynamic pressure bearing according to claim 6 ,
The gas-liquid interface of the lubricating liquid is characterized by only the second gas-liquid interface and the first gas-liquid interface.

In order to solve the above problem, the fluid dynamic pressure bearing according to claim 7 ,
A rotor including a shaft body and a rotor magnet;
A stator attached to the stationary part;
A fluid dynamic pressure bearing according to any one of claims 1 to 12.

According to the fluid dynamic pressure bearing of claim 1, a fluid dynamic pressure bearing is obtained in which the axial height is small, the bearing rigidity is high, and occurrence of problems due to leakage of lubricating liquid or residual bubbles is suppressed. .
This is due to the following reason.

  In the fluid dynamic pressure bearing of the present invention, conventionally, the taper seal formed along the peripheral surface of the shaft body is removed, and the lubricating liquid is supported by the first interface formed at the end portion of the bearing cavity. This interface hardly moves because the adjacent portion has oil repellency. Since a length like a taper seal is not required, the bearing can be lowered, while the radial dynamic pressure bearing portion does not have to be reduced in size in the axial direction.

  Changes in the volume of the lubricating liquid due to thermal expansion or the like are absorbed by a taper seal formed on the side surface of the sleeve. By forming on the side surface of the sleeve, bubbles taken in or generated in the lubricating liquid are more easily discharged.

The fluid dynamic pressure bearing of the present invention has a communication passage that communicates two places separated in the axial direction of the first gap, and a dynamic pressure bearing mechanism is located between the two places.
According to this configuration, since the lubricating liquid can flow between both ends of the gap that holds the lubricating liquid through a path other than the bearing surface, uneven generation of pressure is suppressed, the characteristics of the bearing device are stabilized, and reliability is increased. .

In the fluid dynamic pressure bearing of the present invention, the shaft body peripheral surface and the bearing cavity inner peripheral surface are oleophilic from the portion adjacent to one end side of the dynamic pressure bearing mechanism to the vicinity of the first interface.
According to this configuration, bubbles taken into the lubricating liquid at the time of rotation are reduced, the performance of the bearing is stabilized, and a long-life bearing device can be realized. The reason for this will be described with reference to FIG.

FIGS. 1A and 1B are schematic sectional views of the bearing device from the vicinity of the first interface to the region where the radial dynamic pressure bearing mechanism is formed.
a) is a sleeve near the first interface 51, and the shaft surface is oleophilic. (In the figure, the wall having oil repellency is represented by a double line). b) is a comparative example, and the first interface 51 is formed between wall surfaces having oil repellency.

  In order for the support force by dynamic pressure to act on the shaft body, a flow having a component perpendicular to the peripheral surface of the shaft body must be generated in the lubricating fluid. When such a flow occurs, the fluid exhibits a complex flow. At this time, there may be a moment when the hydrodynamic bearing portion acts to draw the lubricating liquid from the first interface side. As in b), when the oil repellent film formed on the outer surface of the first interface extends to the vicinity of the hydrodynamic bearing, the curvature of the interface is small. In such a situation, when the pulling force as described above is applied, the interface is pulled to the back of the bearing gap, and there is a possibility that bubbles and voids are formed in the lubricating liquid.

The fluid dynamic pressure bearing of the present invention is configured to act so as to increase the pressure of the lubricating liquid held in the first gap in a direction away from one end side of the bearing.
According to this configuration, since the lubricating liquid inside the bearing can be circulated, accumulation of bubbles in the bearing gap (first gap) is suppressed, and the performance of the bearing device is stabilized.

In the fluid dynamic pressure bearing of the present invention, chamfering is applied to the edge portion forming the open end of the bearing cavity.
According to this configuration, the first interface is more stable and the lubricating liquid is less likely to leak. This is due to the following reason.

  In the invention relating to this configuration, a taper seal is not provided at the bearing gap opening at the shaft end. When there is a taper seal, leakage of the lubricant can be avoided by moving the interface inside the second taper seal even when a force for pushing out the lubricant is applied due to the impact or thermal expansion applied to the bearing. Even in the present invention, the second tapered seal portion is provided, but at the same time, since the first interface is also provided on one end side of the bearing, the stability of the interface with respect to impact and vibration must be considered. I don't get it.

  In general, an interface maintained by surface tension tends to be stronger and less likely to collapse as the width is narrower. In the bearing device of the present invention, the first interface of the bearing gap end is narrower than the second interface formed in the second taper seal, so basically the influence of impact and vibration is not Absorbed by the second taper seal. However, there may be situations where the interface is momentarily pushed beyond the end of the cylindrical cavity.

  In such a case, if the cavity end is not chamfered, part of the lubricating liquid may be cut off by the corners or burrs generated during processing, and may remain outside the gap. If the opening edge of the cavity is chamfered, the burr is removed and the corner is removed, so that such a situation is less likely to occur.

In the fluid dynamic pressure bearing of the present invention, the length in the axial direction of the chamfered portion is larger than half the width of the first interface and smaller than the width of the second interface.
According to this configuration, the first interface is further stabilized, and the height of the bearing device can be suppressed, and the leakage of the lubricating liquid can be further prevented.

  If the chamfering of the opening edge described above is too large, the axial length becomes long and the height of the bearing device increases, but if it is too small, the effect decreases. As a lower limit of this chamfering amount, it is reasonable to use the curvature of the first interface as a guide. The upper limit is half the width of the second interface constituting the taper seal. This is because the first interface becomes larger than the second interface at a temperature higher than this.

  Here, the size of the chamfer is defined by the axial length r, and the radial direction is not defined in the claims. This is because in normal chamfering, the axial direction and the radial direction are almost equal in size. Even if the asymmetric chamfering is used, the effect of stabilizing the interface is obtained, but it is reduced. When the ratio of the chamfer size in the axial direction and the radial direction exceeds 1: 3 or 3: 1, it is desirable to add a measure such as further chamfering to the corner portion generated by chamfering.

In the fluid dynamic pressure bearing of the present invention, at least a region on the radially outer side of the surface of the chamfered portion has oil repellency.
According to this configuration, the first interface is further stabilized, and the lubricating liquid is less likely to leak. This is because in order to prevent the lubricating liquid from flowing out from the opening edge, it is desirable that the lubricating liquid be repelled on the surface of the chamfered portion and the lubricating liquid be pulled back into the gap. In order to obtain such an effect, the half of the chamfered portion far from the bearing gap needs to be given oil repellency. On the other hand, in the bearing gap, it is desirable that the surfaces constituting the gap have lipophilicity. In the present specification, “having oil repellency” means that the contact angle of the lubricating liquid is larger than 45 degrees. More preferably, it is 90 degrees or more.

In the fluid dynamic pressure bearing according to the present invention, the first gap is a first taper seal portion in which the gap is enlarged toward one end side, and the taper angle is larger than the taper angle of the second taper seal portion. large.
According to this configuration, the first interface formed in the gap can be further stabilized by forming the first tapered seal portion as a structure in which the gap is enlarged toward the one end side. I can do it. However, the first taper seal portion taper angle (hereinafter referred to as the first taper angle) is made larger than the taper angle of the second taper seal portion (hereinafter referred to as the second taper angle). This is because if the first taper angle is reduced, the length of the taper seal portion in the shaft body direction is increased, which hinders downsizing of the bearing device. The first taper angle is more preferably twice or more the second taper angle.

In the fluid dynamic pressure bearing of the present invention, a radially enormous portion is formed at the other end of the shaft body, and the bearing cavity of the sleeve has a radially enlarged portion that accommodates the radially enlarging portion, And a thrust dynamic pressure bearing having a bearing surface that is an axial surface of the portion and an axial surface of the radially enlarged portion facing the axial surface.
According to this configuration, since the axial load is supported by the thrust dynamic pressure bearing, the support of the bearing is stabilized.

In the fluid dynamic bearing of the present invention, at least a part of the sleeve is made of an oil-containing porous material.
According to this configuration, since the porous body can store a large amount of the lubricating liquid, the amount of the lubricating liquid retained in the bearing device is increased, and it is difficult for the lubricating liquid to be exhausted due to evaporation or the like. I can get it. In addition, since the porous body can trap dust generated in the bearing gap, trouble due to dust accumulation is also suppressed.

A spindle motor according to the present invention includes a base, a stator fixed to the base, a rotor supported rotatably with respect to the base by the fluid dynamic pressure bearing described above, and attached to the rotor circumferential surface facing the stator. Rotor magnet.
According to this configuration, by adopting the fluid dynamic pressure bearing described above, it is possible to obtain a spindle motor that has less vibration and has a long life and a low height.

  Examples suitable for carrying out the fluid dynamic pressure bearing and the spindle motor according to the present invention are shown in Examples 1 to 3 below.

(1-1) Description of Spindle Motor FIG. 2 is a schematic cross-sectional view of the spindle motor 1 according to the present invention. The spindle motor 1 includes a bearing device 3 according to the present invention attached to a base plate 2, a stator 4 installed on the base plate 2 so as to surround the bearing device 3, and a rotor 5 attached to one end of a shaft 31. Consists of. The rotor 5 includes a hub 6 and a rotor magnet 7. The rotor magnet 7 is attached to the inner peripheral surface of the cylindrical portion of the hub 6 and has a positional relationship facing the magnetic poles of the stator 4. When the stator 4 is energized, a rotational driving force is generated. The spindle motor 1 is attached to a housing such as a hard disk device via a base plate 2.

(1-2) Overall Configuration of Bearing Device FIG. 3A is a schematic cross-sectional view of the bearing device 3, and b) is a perspective view.

  The bearing device 3 includes a substantially cylindrical sleeve 33, a shaft 31 fitted in the cylindrical portion, and a bottomed cylindrical housing 32 that accommodates the sleeve 33 as main components.

  In the drawing, a thrust plate 34 is formed at the lower end portion of the shaft 31 and faces the lower end surface of the sleeve 33 on its upper surface. In FIG. 3, a step portion 41 is formed on the bottom surface of the inner periphery of the housing to accommodate the thrust plate 34, but when the outer diameter of the thrust plate 34 and the outer diameter of the sleeve 33 are substantially equal. Such a step 41 is not necessary.

(1-3) Lubricating liquid and communication path A minute first gap is formed between the outer peripheral surface of the shaft 31 and the inner peripheral surface of the sleeve 33. Similarly, a second gap is also maintained between the thrust plate 34 and the inner peripheral surface of the housing 32 and the lower end surface of the sleeve 33. These bearing gaps are filled with the lubricant without being interrupted. The first gap lower portion and the upper portion communicate with each other through a communication passage 42 described later.

A cover member 35 is fitted on the upper end side of the sleeve 33. Between the outer peripheral side surface of the cover member 35 and the inner peripheral surface of the housing 32, a second taper seal portion 40 is formed in which the gap increases toward the opening end of the housing.
Further, the cover member 35 has a convex portion 43 formed by pressing and extending in the radial direction, and a gap secured between the concave portion on the back surface and the upper end surface of the sleeve 33 serves as a communication path 42a for the lubricating liquid. . The communication path 42a forms part of the communication path 42.

  On the side surface of the sleeve 33, flat portions 44 extending in the axial direction are formed at three locations in the circumferential direction (FIG. 4). The flat portion 44 is apparently a flat portion, but is substantially a recess in that the distance from the central axis of the sleeve is the smallest at the central portion. It becomes a part 42b of the passage.

  FIG. 5 a) shows an aspect when the bearing device 3 is looked down from the upper side of FIG. 3. FIG. 5b) shows a state before the cover member 35 is attached. The dotted line in FIG. 5 a) shows the position of the flat part 44 of the sleeve 33. The radially outer end of the convex portion 43 formed on the upper surface of the cover member 35 is located on the flat portion 44, and the communication path 42a and the communication path portion 42b are connected here. , One communication path 42 is formed. The communication path 42 is filled with the lubricating liquid like the bearing gap, and allows the lubricating liquid to pass back and forth between the first gap and the upper side.

  As shown in FIG. 3 a), when the step 41 is formed at the bottom of the housing, the communication passage 42 b formed on the side surface of the sleeve 33 is blocked by the step 41. In order to avoid this, a recess is provided on the upper surface of the step portion 41 at a position corresponding to the lower end of the communication path 42b, and the communication path 42b and the bearing gap are connected.

  A hole 46 for passing the shaft 31 is formed on the upper surface of the cover member 35. The inner peripheral surface 47 of this hole maintains a minute gap with the peripheral surface of the shaft 31, and the first interface 51 is formed here. The second taper seal portion 40 is connected to the communication path 42 at the lower end edge of the cover member 35. The second taper seal portion is partially filled with the lubricating liquid, and a second interface 52 is formed. An oil repellent made of a fluororesin is applied to the outer peripheral surface of the shaft adjacent to the first interface and the surface of the cover member 35 to impart oil repellency.

  In this bearing device 3, the lubricating liquid that fills the gap between the outer peripheral surface of the shaft 31 and the inner peripheral surface of the sleeve 32 is not in contact with the surrounding air except for these first and second interfaces. .

(1-4) Dynamic Pressure Bearings In FIG. 3, dynamic pressure generating grooves 37 and 38 are formed on the cylindrical inner peripheral surface of the sleeve 33 at two locations separated in the axial direction. Configure the bearing. These dynamic pressure generating grooves provide a portion that acts to increase the pressure toward the lower side in the axial direction and the pressure toward the upper side in the axial direction with respect to the lubricating liquid held in the bearing gap when the shaft 31 rotates. The part which acts to raise is provided as a pair and faces each other, generates a high dynamic pressure between the two parts, and supports the bearing.

  In the figure, double lines drawn obliquely to the bearing surface indicate the presence of these dynamic pressure generating grooves, and the pressure of the lubricating liquid increases toward the side where the double line goes away from the bearing surface. It means being done. The double line in the figure is bent halfway and is farthest from the bearing surface at this part, which indicates that the highest pressure is generated at this part.

  Of the two radial dynamic pressure generating grooves 37, 38, the upper 37 is not symmetrical in the vertical direction, and has a larger portion for increasing the pressure toward the lower side. For this reason, the dynamic pressure generating groove 37 acts to push the lubricating liquid downward of the bearing while generating a radial shaft supporting force. The other radial dynamic pressure generating groove 38 is symmetrical, and the two thrust dynamic pressure generating grooves 36, 36 are configured symmetrically in the radial direction.

  In the entire dynamic pressure generating groove, due to the action of the radial dynamic pressure generating groove 37, the lubricant flows downward through the radial bearing gap, which is the first gap, and passes through the communication path 42 to the upper end of the radial bearing surface. The flow which recirculates to the 1st interface 51 vicinity which is a part arises. This flow prevents the lubricant from leaking from the first interface 51. Further, it helps to discharge bubbles generated inside the bearing to the outside of the bearing through the communication path 42 and the second taper seal portion 40.

(1-5) Manufacturing Method The cover member 35 and its mounting method will be described with reference to FIGS.

  FIG. 6 shows an example of the manufacturing process of the cover member 35. First, a metal plate material is punched and formed into a covered cylindrical shape by pressing, and a hole 46 is punched out in the center of the lid portion. At the same time, a convex portion 43 extending in the radial direction is formed on the lid portion by pressing (FIG. 6a).

  Next, two cuts extending in the axial direction are made in the side peripheral surface of the member at a position shifted by 60 degrees from the position of the convex portion with respect to the central axis of the cover member. The member 48 between the cuts is lifted horizontally to form the slit 47 (FIG. 6b).

  The member 48 is cut and molded to a length in contact with the inner peripheral surface of the housing to form a connection portion 49 (FIG. 6c).

  After the machining is completed, an oil repellent is applied around the hole 46 in the lid to impart oil repellency. At this time, care should be taken so that the oil repellent agent does not enter the inner peripheral surface of the hole or the back side of the lid (the side in contact with the sleeve).

  The cover member 35 is welded and fixed to the housing at the distal end portion of the connection portion 49. As the welding method, directional beam welding such as laser welding or electron beam welding is suitable. Moreover, you may fix by adhesion instead of welding. As another method, the cylindrical portion of the cover member 35 may be lightly press-fitted and fixed to the sleeve 33.

  Note that the lubricating liquid is injected into the bearing device after the cover member 35 is welded, and the lubricating liquid may be dropped on the second taper seal portion and spread in the bearing. The cover member 35 may be welded (FIG. 7).

  In the bearing device of the present invention, since the interface between the lubricating liquid and the surrounding air is at two locations on the bearing, when the lubricating liquid is injected, the replacement of the lubricating liquid with the air in the bearing gap is relatively smooth and poor injection occurs. Hard to occur. However, when the lubricating liquid is injected after the cover member 35 is attached, the ratio of injection failure increases.

  When the lubricating liquid is dropped onto the second taper seal portion 40 after the cover member 35 is attached, the lubricating liquid is divided into two directions and spreads in the bearing device. First, there is a path that travels along the part 42b of the communication path, reaches the periphery of the thrust plate 34 at the lower part of the bearing, and then extends toward the upper part of the bearing through the first minute gap in which the radial dynamic pressure bearing is configured. The other is via a connecting path 42a formed between the cover member 35 and the sleeve 33 and reaches the upper portion of the first gap, and the inner peripheral surface 50 of the hole 46 of the cover member and the outer peripheral surface of the shaft 31 are connected. This is a path that fills the gap between them and forms the first interface.

  When comparing the former with the latter, the former progresses faster. For this reason, before the air inside the bearing is sufficiently discharged, the first interface is formed, the air escape path is blocked, and bubbles may remain inside the bearing. On the other hand, as shown in FIG. 7, such a problem does not occur when the cover member 35 is attached after the lubricating liquid is injected into the bearing device.

  The shaft 31b of the bearing device of FIG. 7 has a reduced diameter portion protruding from the hole 46 of the cover member 35, so that the outer peripheral surface of the shaft and the inner peripheral surface 50 of the hole 46 are difficult to contact when the cover member is attached. It has become. The diameter of the hole 46 is larger than the outer diameter of the portion of the shaft accommodated in the bearing cavity, but the difference is slight. If the diameter is not reduced, This is because the inner peripheral surface 50 may be damaged. The reduced diameter portion does not need to continue over the entire region from the end of the shaft to the vicinity of the opening of the hole, and even if it ends at a position slightly away from the opening, the effect of preventing damage can be obtained. . However, as shown in FIG. 7, if the inclined portion 80 is provided in the vicinity of the opening, even if the oil repellent film near the opening is lost and the lubricating liquid leaks, the angle of the wall surface that supports the interface increases. , Leakage of the lubricating liquid can be suppressed to a small level.

In addition, when the cover member is welded and fixed after injecting the lubricating liquid, there is a concern about the deterioration of the lubricating liquid due to heat and the adverse effect on the dynamic pressure bearing surface due to thermal expansion. Then there is no problem.

  First, most of the heat applied during welding is dissipated to the housing portion having a large heat capacity, and the lubricating liquid in the second taper seal portion 40 is hardly heated. With respect to the lubricating liquid between the cover member 35 and the sleeve 33, since the connecting portion 49 is small, heat transmitted to the cover member is small, and no problem occurs. The influence on the hydrodynamic bearing surface can be ignored because the welded part is far away from the bearing surface.

(1-6) Material The material constituting the bearing device described in this embodiment can basically be selected as long as it has the required strength and rigidity. Since the metal material generally has sufficient strength and rigidity and is also oleophilic, it is suitable as a material constituting the bearing device of the present invention.

  In the bearing device shown in FIGS. 2 to 7, the housing is made of an aluminum-based alloy. The sleeve is made of free-cutting stainless steel, and inclusions are removed from the surface by surface treatment after machining. The shaft is made of martensitic stainless steel, and the cover member is made of a copper alloy or a synthetic resin material. Among the synthetic resin materials, a liquid crystal polymer that can easily form a fine structure is particularly suitable. The inner peripheral surface 50 of the hole 46 of the cover member 35 may be subjected to a treatment for enhancing the lipophilicity as necessary.

  The oil repellent film applied in the vicinity of the first interface opening uses a perfluoro resin. The lubricating liquid uses an ester compound as a base oil.

  A modification 3 ′ of the bearing device 3 will be described with reference to FIGS. 8 and 9. FIG. 8 a) is a view of the bearing device 3 ′ looking down from above the bearing. FIG. 8b) shows a state before the cover member 35 'is further attached.

  Unlike the bearing device 3, the connecting portion 49 is located immediately above the flat portion 44 of the sleeve 33. The convex portion 43 ′ is divided into two portions 43 ′ a and 43 ′ b, and a connection portion 49 is formed between them.

  FIG. 9a) is a perspective view of the cover member 35 '. Since the cover member 35 is formed by the same method, the slit 47 formed along with the connecting portion 49 is also located between the two convex portions 43 ′ a and 43 ′ b and extends in the axial direction.

  FIG. 9b) is an enlarged view of a part of the second interface, and is a cross-sectional view in a plane perpendicular to the axial direction including the cover member 35 '. An interface between the lubricating liquid and air is formed in the second taper seal portion 40 formed on the outer periphery of the housing inner peripheral surface 32 and the cover member 35 ', but the interface between the inner peripheral surface of the cover member and the outer peripheral surface of the sleeve. A second taper seal portion 40 ′ is also formed therebetween, and a part 52 ′ of the second interface appears.

  The lubricating fluid circulating in the bearing flows from the narrow portion of the second taper seal portion 40 ′ into the communication path 42 a and returns to the upper portion of the bearing. Even if bubbles are included in the lubricating liquid, it is difficult for the bubbles to enter the area where the width of the second taper seal portion is narrow. Therefore, the interface 52 located at the second taper seal portion 40 '. 'It is driven to the side and discharged through the slit 47. Thus, since the second taper seal portion 40 ′ functions as an efficient sieve that separates the bubbles in the lubricating liquid, the bearing device 3 ′ discharges the bubbles in the lubricating liquid very efficiently. I can do it.

  Other modifications 83 and 93 of the bearing device 3 will be described with reference to FIGS. 10a) and 10b).

  In FIG. 10a), the outer diameter of one end of the sleeve 33 'is reduced to form a second taper seal without forming a taper on the inner periphery of the housing 32'. In this case, the sleeve 33 ′ uses a copper-based porous sintered body and forms a tapered shape during sintering. It is not necessary to make a taper by machine cutting, and processing costs can be reduced.

  In FIG. 10 b), the communication path 42 ′ is formed by opening an axial through hole in the sleeve 33. Since the extension of the distance through which the lubricating liquid circulates becomes shorter, the lubricating liquid circulates more quickly and the bearing performance is stabilized.

  A modification 73 of the bearing device 3 will be described with reference to FIGS.

  FIG. 11 a) is an axial sectional view of the bearing device 73, and particularly shows an enlarged view of a portion including the cover member 35 b, the first interface 51, and the second interface 52. Further, FIGS. 11b) and 11c) are enlarged views of the vicinity of the first interface 51 and the second interface 52. FIG.

  The cover member 35 b has a chamfered inner side surface of the hole, and the first taper seal portion 39 is formed by facing the outer peripheral surface of the shaft 31. The taper angle θa of the first taper seal portion 39 is 34 degrees, and the taper angle θb of the second taper seal portion 40 is 5 degrees, and θa is set to be larger. In order to stabilize the interface, it is desirable that the wall surface of the taper seal part is sufficiently wettable. In this case, the width W1 of the first interface 51 is larger than the width W2 of the second interface 52. Always narrower. The magnitudes of θa and θb may be other than the above values. However, good characteristics can be obtained when θa is approximately 15 to 50 degrees and θb is approximately 3 to 10 degrees.

  Unlike the second interface 52, the first interface 51 is subjected to stress that disturbs the interface because the outer peripheral surface of the inner shaft of the wall surface constituting the tapered seal portion is relatively rotated. However, the width W1 is configured to be relatively narrow, and the narrower the width, the stronger the interface, so that the interface is prevented from being destroyed by this stress.

  An oil repellent film is applied to the outside of the first taper seal portion. In FIG. 11, the surface to which the oil repellent film is applied is represented by a double line. An annular recess 81 is formed on the outer peripheral surface of the shaft 31, and an oil repellent film is formed in the recess. This function is similar to the inclined portion in FIG. When attaching the cover member 35b through the shaft 31, the oil repellent film on the outer peripheral surface of the shaft may be damaged due to contact with the inner peripheral surface of the hole portion. The problem can be avoided.

  In FIG. 11, the oil repellent film on the surface of the cover member 35b is not applied to the inside of the first gap (including the first taper seal portion 39). Further, the end of the first interface 51 does not reach the portion where the oil repellent film is applied.

  In the bearing device 73, the outflow of the lubricating liquid from the first gap is first suppressed by the first taper seal portion. The oil-repellent film suppresses further outward movement when the interface moves to the vicinity of the opening of the taper seal portion due to sudden pressure applied to the lubricating liquid. It also has the function of preventing the lubricant from diffusing through the wall surface and leaking outside. Thus, since it is guarded by both the taper seal and the oil repellent film, it is more resistant to lubricant leakage than the bearing device 3 of the first embodiment. However, since the axial length of the first gap portion is long, it is somewhat disadvantageous for miniaturization.

  In addition, the Example demonstrated above does not limit embodiment of this invention to these. For example, as the thrust side bearing mechanism, there is only a description about the thrust dynamic pressure bearing mechanism, but this may be a dynamic pressure bearing mechanism that also uses the static pressure of the lubricating liquid. Alternatively, the thrust plate may be omitted and the shaft end may be point-supported. Moreover, it is free to use a synthetic resin or the like as a material, and the effect of the present invention is not lost by changing them.

Explanatory drawing of the first interface and radial dynamic pressure groove Schematic sectional view of the spindle motor 1 according to the present invention Schematic sectional view (a) and perspective view (b) of the bearing device Perspective view of sleeve Top view of bearing device Explanatory drawing of manufacturing process of cover member Explanatory drawing of how to install cover member Modification 1 of bearing device Explanatory drawing of modification of cover member Second and third modifications of the bearing device Fourth modification of bearing device Spindle motor with conventional bearing device

DESCRIPTION OF SYMBOLS 1 Spindle motor 2 Base plate 3, 3 ', 73, 83, 93 Bearing apparatus 31, 31b, 131 Shaft 32 Housing 33, 33', 133 Sleeve 34, 134 Thrust plate 35, 35 'Cover member 36, 136 Thrust dynamic pressure generation Grooves 37, 38, 137 Radial dynamic pressure generating groove 39 First taper seal part 4 Stator 40, 40 ', 140 Second taper seal part 41 Step part 42, 42' Communication path 42a Communication path 42b Part of communication path 43, 43 ′, 43′a, 43′b Radial convex portion 44 Sleeve flat portion 47 Slit 48 Member 49 between cuts Connection portion 5, 105 Rotor 50 Hole inner peripheral surface 51 First interface 52, 52 ′ Second interface 6 Hub 7 Rotor magnet 80 Shaft side inclined portion 81 Shaft side concave portion r Chamfered portion axial length W1 First Taper angle θb width W2 width θa first tapered seal portion of the second interface surface second taper angle 132 thrust bush of the tapered seal portion

Claims (7)

A shaft,
A stationary portion in which the shaft body is inserted and rotatably supported with the shaft body as a central axis;
A radial gap formed between the outer peripheral surface of the shaft body and the inner peripheral surface of the stationary part opposite to the outer peripheral surface;
A lubricating liquid filled in the radial gap;
A radial dynamic pressure bearing formed in a first gap constituting a part of the radial gap and having a radial dynamic pressure generating groove for inducing fluid dynamic pressure using the lubricating liquid as a working fluid when the shaft is rotated;
A second seal portion that is positioned radially outward from the radial gap and formed in a gap extending in the axial direction of the stationary portion, and connected to the radial gap;
Formed in an axially extending gap located at the upper end of the radial gap, connected to the radial gap and the second seal part, and the axial length is shorter than the second seal part. A seal part;
A second gas-liquid interface formed in the second seal portion;
A first gas-liquid interface located above the second gas-liquid interface and formed in the first seal part; and
The second seal portion, the upper end portion of the first gap, and the first seal portion are formed in the stationary portion, filled with the lubricating liquid, and not via the radial dynamic pressure bearing. and a communication path that connects,
The continuous portion is formed in the stationary portion, is filled with the lubricating liquid, and connects the second seal portion, the communication path, and the lower end portion of the first gap without going through the radial dynamic pressure bearing. A part of the passage, and
The fluid dynamic pressure bearing according to claim 2, wherein the second seal portion is located radially outside the communication path and a part of the communication path.   The fluid dynamic pressure bearing according to claim 1, wherein the gap of the second seal portion is formed in a taper shape in which the gap size increases as it extends in the axial direction.   The gap of the first seal part is formed in a tapered shape in which the gap dimension increases toward the upper side,
  The fluid dynamic pressure bearing according to claim 2, wherein a taper angle of the first seal portion is larger than a taper angle of the second seal portion.   The fluid dynamic pressure bearing according to any one of claims 1 to 3, wherein a width of the second gas-liquid interface is wider than a width of the first gas-liquid interface.   5. The oil repellent film is formed on at least one of the outer peripheral surface of the shaft body and the surface of the stationary portion located above the first gas-liquid interface. The fluid dynamic pressure bearing according to any one of the above.   The fluid dynamic pressure bearing according to any one of claims 1 to 5, wherein a gas-liquid interface of the lubricating liquid is only the second gas-liquid interface and the first gas-liquid interface.   A rotor including a shaft body and a rotor magnet;
  A stator attached to the stationary part;
A spindle motor comprising: the fluid dynamic pressure bearing according to claim 1.

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