JP2009068691A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device capable of accurately and inexpensively controlling an axially-movable distance of a shaft member. <P>SOLUTION: This fluid bearing device is provided with: a seal part 9 axially engaging with a shoulder surface 2c of a shaft member 2 to prevent coming-off of the shaft member 2; radial bearing parts R1 and R2 radially supporting the shaft member 2 with a fluid film generated in a radial bearing space between the outer peripheral surface of a large-diameter part 2a of the shaft member 2 and the inner peripheral surface 8a of a sleeve part 8; and a thrust bearing part T supporting the shaft member 2 in the thrust direction. In the fluid bearing device, a first axial space L1 is formed between the seal part 9 and the sleeve part 8. Thereby, the axially-movable distance of the shaft member 2 can be accurately set without relying on member accuracy of the sleeve part 8 and the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device that rotatably supports a shaft member with a fluid film generated in a bearing gap.

  Due to its high rotational accuracy and quietness, the hydrodynamic bearing device is an information device, for example, a magnetic disk drive device such as HDD, an optical disk drive device such as CD-ROM, CD-R / RW, DVD-ROM / RAM, MD, MO, etc. For spindle motors such as magneto-optical disk drive devices, etc., for polygon scanner motors of laser beam printers (LBP), for color wheel motors of projectors, or for small motors such as fan motors used for cooling electrical equipment, etc. It can be suitably used.

  For example, in the hydrodynamic bearing device disclosed in Patent Document 1, a radial bearing gap is formed between the outer peripheral surface of the shaft member and the inner peripheral surface of the sleeve portion, and the shaft member is formed by a fluid film generated in the radial bearing gap. While supporting in the radial direction, the shaft member is supported in the thrust direction by sliding the spherical convex portion provided at the lower end portion of the shaft member and the thrust plate provided on the inner bottom surface of the housing. In this hydrodynamic bearing device, the shaft member has a stepped shape having a small-diameter portion and a large-diameter portion, and an annular seal portion is provided on the inner periphery of the housing opening, and the seal portion is connected to the shoulder surface of the shaft member in the axial direction. The shaft member is prevented from coming off by being engaged with each other.

JP-A-2005-113987

  In this hydrodynamic bearing device, the shaft member is allowed to move in the axial direction by the amount of the axial clearance formed between the seal portion and the shoulder surface of the shaft member. If this axial clearance is too large, the axially movable amount of the shaft member will be excessive, causing an axial backlash in the HDD disk or the like attached to the shaft member, degrading the reading accuracy of the disk, There is a risk of causing interference with the head. Therefore, the axial gap formed between the seal portion and the shoulder surface of the shaft member needs to be set with high accuracy.

However, in the above hydrodynamic bearing device, since the seal portion is positioned by bringing the seal portion into contact with the sleeve portion, the accuracy of fixing the seal portion to the housing depends on the processing accuracy of the axial dimension of the sleeve portion. To do. For this reason, in order to manage the axially movable amount of the shaft member with high accuracy, it is necessary to process the sleeve portion with high accuracy, resulting in an increase in processing cost.

  An object of the present invention is to provide a hydrodynamic bearing device capable of controlling the axially movable amount of a shaft member with high accuracy and low cost.

  In order to solve the above problems, the present invention provides a shaft member having a small diameter portion, a large diameter portion, and a shoulder surface formed therebetween, and a sleeve portion in which the large diameter portion of the shaft member is inserted into the inner periphery. And the outer peripheral surface of the small-diameter portion of the shaft member, a seal space that prevents leakage of the lubricating fluid inside the bearing to the outside is formed, and the shaft member is engaged with the shoulder surface of the shaft member in the axial direction. A seal portion that prevents the shaft member from being removed, and a radial bearing portion that supports the shaft member in the radial direction with a fluid film generated in a radial bearing gap between the outer peripheral surface of the large-diameter portion of the shaft member and the inner peripheral surface of the sleeve portion, In the hydrodynamic bearing device including a thrust bearing portion that supports the shaft member in the thrust direction, a first axial gap is formed between the seal portion and the sleeve portion.

  As described above, the hydrodynamic bearing device of the present invention forms the first axial gap between the seal portion and the sleeve portion, and makes the seal portion and the sleeve portion non-contact, thereby positioning accuracy of the seal portion. The shape accuracy of the sleeve portion can be excluded from the factors that determine the above. Therefore, the axially movable amount of the shaft member can be managed only by the position accuracy of the seal portion, regardless of the processing accuracy of the sleeve portion. Thereby, since the processing accuracy of the sleeve portion can be relaxed, the processing cost can be reduced.

  In this hydrodynamic bearing device, a second axial gap is formed between the seal portion and the shoulder surface of the shaft member. This second axial gap is preferably set to be equal to or smaller than the radial gap of the seal space. As a result, in the second axial clearance, the lubricating fluid is drawn in by the capillary force equivalent to or larger than the capillary force of the seal space, so that the lubricating fluid filled inside the bearing leaks to the outside. It is possible to reliably prevent the ejection.

  For example, when this hydrodynamic bearing device is used for a spindle motor of an HDD, it is necessary to suppress the axial movement of the shaft member as much as possible in order to prevent a disk attached to the shaft member from interfering with the head. At this time, if the second axial gap is set to 30 μm or less, interference between the disk and the head can be prevented even when used in the above applications.

  During the operation of such a hydrodynamic bearing device, a local negative pressure is generated in the lubricating fluid inside the bearing, particularly the lubricating fluid filled in the space facing the lower end of the shaft member, so that the fluid in the radial bearing gap Bubbles are generated in the membrane, and the supporting force of the shaft member by the fluid membrane may be reduced. Therefore, a communication path having one end opened in the first axial gap and the other end opened in the space facing the lower end of the shaft member between the sleeve portion and the housing housing the sleeve portion on the inner periphery. By providing, the space of the thrust bearing portion is communicated with the seal space via the communication path and the first axial gap, and generation of local negative pressure can be prevented, and the bearing is filled. It is possible to maintain a good pressure balance of the lubricating fluid and avoid a decrease in bearing performance.

  At this time, if a groove is formed in the end surface and the outer peripheral surface of the sleeve portion, and the communication path is configured by the groove, the inner bottom surface and the inner peripheral surface of the housing may have a simple shape such as a planar shape or a cylindrical surface shape. Therefore, the housing can be easily formed and the cost can be reduced.

  The stepped shaft member as described above may be formed integrally, but is not limited thereto, and is formed of, for example, a shaft portion and a hollow material fixed to the outer peripheral surface of the shaft portion, and the end surface of the hollow material You may comprise the shoulder surface of a shaft member. In this case, since the stepped shaft member can be configured by a simple shaft portion and a hollow material, the processing cost of the shaft member can be reduced.

  For example, when a thrust bearing portion is formed by a so-called pivot bearing in which a spherical convex portion is formed at the end of a shaft member, and the spherical convex portion is brought into contact sliding with a mating member (for example, the inner bottom surface of the housing) A space is formed between the spherical convex portion at the end of the member and the inner bottom surface of the housing (indicated by P in FIG. 2), and the space inside the bearing including this space is filled with the lubricant. At this time, when the shaft member is composed of the shaft portion and the hollow material, and the end of the hollow material is extended to the outer periphery of the spherical convex portion of the shaft portion, a part of the space that the spherical convex portion of the shaft portion faces is obtained. It can be filled with a hollow material (see FIG. 7). As a result, the amount of lubricant filled in the bearing can be reduced, so that it is possible to reduce the seal space that functions as a buffer that absorbs the thermal expansion of the lubricant, thereby reducing the thickness of the bearing device or the radial bearing. The bearing rigidity can be improved by expanding the bearing span of the part.

  Since the fluid dynamic bearing device as described above can control the axial movement of the shaft member with high accuracy, for example, it is desired to manage the axially movable amount of the shaft member such as a spindle motor for HDD as accurately as possible. It can be used suitably for a use.

  As described above, according to the present invention, it is possible to obtain a fluid dynamic bearing device capable of controlling the axially movable amount of the shaft member with high accuracy and low cost.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 conceptually shows a configuration example of a spindle motor for information equipment incorporating a hydrodynamic bearing device 1 according to an embodiment of the present invention. This spindle motor is used in a disk drive device such as an HDD, and is a stator that is opposed to a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 to which a disk hub 3 is attached, for example, via a radial gap. A coil 4 and a rotor magnet 5 and a motor bracket 6 are provided. The stator coil 4 is attached to the outer periphery of the motor bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is fixed to the inner periphery of the motor bracket 6. The disk hub 3 holds one or more (two in FIG. 1) disk-shaped information recording media (hereinafter simply referred to as disks) D such as magnetic disks. In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force generated between the stator coil 4 and the rotor magnet 5. The disk D held by the hub 3 rotates integrally with the shaft member 2.

  As shown in FIG. 2, the hydrodynamic bearing device 1 includes a shaft member 2, a sleeve portion 8 in which the shaft member 2 is inserted on the inner periphery, a bottomed cylindrical housing 7 that holds the sleeve portion 8 from the outer periphery, 7 is mainly provided with a seal portion 9 provided in the opening portion. In the following description, the opening side of the housing 7 is the upper side and the closing side is the lower side in the axial direction.

  The shaft member 2 is formed by turning a metal material such as SUS steel, for example, and includes a large diameter portion 2a disposed on the inner periphery of the sleeve portion 8 and a small diameter portion 2b provided on the upper side of the large diameter portion 2a. Have one. A shoulder surface 2 c is provided between the large-diameter portion 2 a and the small-diameter portion 2 b, and a spherical convex portion 2 a 2 is provided at the lower end portion of the shaft member 2.

  The sleeve portion 8 is formed in a cylindrical shape, for example, from a sintered metal porous body mainly composed of copper. In addition, the sleeve portion 8 can be formed of another metal, resin, ceramic, or the like.

  As shown in FIG. 3, for example, as shown in FIG. 3, a region where a plurality of dynamic pressure grooves 8 a 1 and 8 a 2 are arranged in a herringbone shape is formed on the entire inner surface or a part of the cylindrical region of the inner surface 8 a of the sleeve portion 8. Two places are formed apart in the axial direction. The formation region of the dynamic pressure grooves 8a1 and 8a2 is opposed to the outer peripheral surface 2a1 of the large-diameter portion 2a of the shaft member 2 as a radial bearing surface, and a radial bearing gap is formed between the outer peripheral surface 2a1 and the shaft member 2 when rotating. The radial bearing portions R1 and R2 described later are formed (see FIG. 2). Further, in the formation region of the upper dynamic pressure groove 8a1, the dynamic pressure groove 8a1 is formed axially asymmetric with respect to the annular smooth portion formed between the upper and lower inclined grooves, and the upper region from the annular smooth portion. Is larger than the axial dimension X2 of the lower region (X1> X2).

  On the outer peripheral surface 8d of the sleeve portion 8, one or a plurality of grooves 8d1 extending in the axial direction are formed over the entire length in the axial direction. One or more grooves 8c1 extending in the radial direction are formed on the lower end surface 8c of the sleeve portion 8. The axial groove 8d1 and the radial groove 8c1 provide a communication path for the lubricating oil between the inner peripheral surface 7a1 and the inner bottom surface 7b1 of the opposing housing 7 in a state where the sleeve portion 8 is fixed to the inner periphery of the housing 7. Configure (see FIG. 2). The axial groove 8d1 and the radial groove 8c1 are formed by providing portions corresponding to the axial groove 8d1 and the radial groove 8c1 in advance in a green compact forming die that forms the body of the sleeve portion 8, for example. It can be molded simultaneously with the green compact molding of the main body.

  The housing 7 is made of a crystalline resin such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), or polyphenylsulfone (PPSU), polyethersulfone (PES), polyetherimide ( It is injection molded with a resin composition having an amorphous resin such as PEI) as a base resin, and is formed into a bottomed cylindrical shape. In this embodiment, as shown in FIG. 2, the side part 7a and the bottom part 7b which obstruct | occludes the lower end part of the side part 7a are shape | molded integrally. Examples of the resin composition forming the housing 7 include fibrous fillers such as glass fibers, whisker-like fillers such as potassium titanate, scaly fillers such as mica, carbon fibers, carbon black, graphite, carbon Nanomaterials, fibrous or powdery conductive fillers such as various metal powders, and the like, which are blended in an appropriate amount with the base resin according to the purpose, can be used.

  The injection material of the housing 7 is not limited to the above, and for example, a low melting point metal material such as a magnesium alloy or an aluminum alloy can be used. Alternatively, the housing 7 can be formed by so-called MIM molding in which degreasing and sintering are performed after injection molding with a mixture of a metal powder and a binder, or press molding of a soft metal such as a metal material such as brass. The housing bottom 7b is not necessarily integrated with the side 7b, and can be formed separately from the side 7a.

  The outer peripheral surface 8d of the sleeve portion 8 is fixed to the inner peripheral surface 7a1 of the housing 7 by an appropriate means such as bonding (including loose bonding or press-fitting bonding), press-fitting, or welding.

  The inner bottom surface 7 b 1 of the housing 7 functions as a thrust bearing portion T that contacts and supports the spherical convex portion 2 a 2 at the lower end portion of the shaft member 2. In the present embodiment, the thrust bearing portion T is formed directly on the housing 7 as described above. However, the present invention is not limited to this, and is separately formed of, for example, a resin material or a sintered material having good wear resistance and sliding characteristics. A thrust washer may be disposed on the inner bottom surface of the housing 7 and the thrust bearing portion T may be formed on the thrust washer. In this case, since the housing 7 does not slide in contact with the shaft member 2, the housing 7 does not need wear resistance, and the range of material selection for the housing 7 is widened.

  The seal portion 9 is formed in a ring shape with a metal material or a resin material, and is fixed to the inner periphery of the upper end portion of the side portion 7a of the housing 7 by, for example, press-fitting, press-fitting adhesion or the like. The inner peripheral surface 9a of the seal portion 9 is formed in a tapered surface shape whose diameter is gradually increased upward. In a state where the seal portion 9 is fixed to the inner periphery of the housing 7, the inner peripheral surface 9a of the seal portion 9 faces the outer peripheral surface 2b1 of the small diameter portion 2b of the shaft member 2, and the radial dimension is directed downward therebetween. An annular seal space S in which the diameter gradually decreases is formed. Lubricating oil, for example, is injected into the internal space of the housing 7 sealed by the seal portion 9 as a lubricating fluid, and the inside of the housing 7 is filled with the lubricating oil (a dotted area in FIG. 2). In this state, the oil level of the lubricating oil is maintained within the range of the seal space S. At this time, as shown in the enlarged view of FIG. 2, the space between the inner peripheral chamfer 9 b 1 of the lower end surface 9 b of the seal portion 9 and the outer peripheral surface 2 b 1 of the small diameter portion 2 b of the shaft member 2, or the upper side of the sleeve portion 8. The space between the inner peripheral chamfer 8c1 of the end surface 8b and the outer peripheral surface 2a1 of the large diameter portion 2a of the shaft member 2 is also filled with lubricating oil.

  A first axial gap L <b> 1 is formed between the lower end surface 9 b of the seal portion 9 and the upper end surface 8 b of the sleeve portion 8. Further, a second axial gap L2 is formed between the lower end surface 9b of the seal portion 9 and the shoulder surface 2c of the shaft member 2, and the second axial gap L2 moves in the axial direction of the shaft member 2. It becomes possible amount. Thus, by providing the first axial gap L1 between the seal portion 9 and the sleeve portion 8 and making them non-contact, the axially movable amount of the shaft member 2, that is, the second axial direction. The gap L2 can be managed only by the positional accuracy of the seal portion 9 regardless of the processing accuracy of the sleeve portion.

  Further, when the hydrodynamic bearing device 1 is used for a HDD spindle motor as in this embodiment, the second axial gap L2 is set to 30 μm or less, preferably in order to prevent interference between the disk and the head. It is desirable to set it to 20 μm or less. Furthermore, it is desirable to set the second axial gap L2 to be equal to or smaller than the smallest radial dimension L3 in the seal space S (L2 ≦ L3). Thereby, in the 2nd axial direction gap L2, since the capillary force equivalent to or larger than the seal space S is obtained, the leakage of the lubricating oil to the outside can be prevented more reliably.

  The setting of the second axial gap L2 can be performed as follows, for example. First, as shown in FIG. 4A, the sleeve portion 8 and the shaft member 2 are accommodated in the inner periphery of the housing 7. Specifically, the sleeve portion 8 is inserted into the inner periphery of the housing 7, the lower end surface 8 c of the sleeve portion 8 is brought into contact with the inner bottom surface 7 b 1 of the housing 7, and the sleeve portion 8 is brought into contact with the inner peripheral surface 7 a 1 of the housing 7. Fix it. The shaft member 2 is inserted into the inner periphery of the sleeve portion 8, and the spherical convex portion 2 a 2 at the lower end of the shaft member 2 is brought into contact with the inner bottom surface 7 b 1 of the housing 7. In this state, the axial dimensions of the large-diameter portion 2a and the sleeve portion 8 of the shaft member 2 are set so that the shoulder surface 2c of the shaft member 2 is positioned above the upper end surface 8b of the sleeve portion 8 (housing opening side). Design in advance.

  Next, as shown in FIG. 4B, the seal portion 9 is inserted into the inner peripheral surface 7 a 1 of the housing 7 from above, and the lower end surface 9 b is brought into contact with the shoulder surface 2 c of the shaft member 2. Thereafter, as shown by an arrow in FIG. 4B, the shaft member 2 is pulled up with respect to the housing 7 so that the seal portion 9 engaged with the shoulder surface 2c of the shaft member 2 becomes the second shaft shown in FIG. It is moved upward relative to the housing 7 by the direction gap L2. In this state, the second axial gap L2 is set by fixing the seal portion 9 to the inner peripheral surface 7a1 of the housing 7. The seal portion 9 and the housing 7 are fixed by, for example, press-fitting. In this case, the positioning and fixing of the seal portion 9 are completed when the shaft member 2 is pulled up by a predetermined amount. At this time, if an adhesive is interposed between the fitting surfaces of both, the fixing strength can be increased and oil leakage from the inside of the unit can be reliably prevented. Further, if an adhesive is applied before the seal portion 9 is inserted into the housing 7, the adhesive functions as a lubricant, and the insertion and movement of the seal portion 9 can be facilitated.

  According to this method, the second axial gap L <b> 2, which is the axially movable amount of the shaft member 2, can be set with high accuracy by the lifting amount of the shaft member 2. That is, the axially movable amount of the shaft member 2 can be directly managed not by the processing accuracy of the sleeve portion 8 but by the amount by which the shaft member 2 is pulled up. Accordingly, the axially movable amount of the shaft member 2 can be managed with high accuracy, the processing accuracy of the sleeve portion 8 can be relaxed, and the manufacturing cost can be reduced.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the radial bearing surface of the sleeve portion 8 (the dynamic pressure grooves 8a1 and 8a2 forming region of the inner peripheral surface 8a) is formed on the large-diameter portion 2a of the shaft member 2. It faces the outer peripheral surface 2a1 via a radial bearing gap. As the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed into the annular smooth portion at the axial center of the dynamic pressure grooves 8a1 and 8a2, and the pressure rises. By such dynamic pressure action of the dynamic pressure grooves 8a1 and 8a2, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner in the radial direction are configured.

  At the same time, when the spherical convex portion 2a2 provided at the lower end of the shaft member 2 and the inner bottom surface 7b1 of the housing 7 as the thrust bearing portion T are in contact sliding, the shaft member 2 is contacted and supported in the thrust direction.

  A communication path is formed between the sleeve portion 8 and the housing 7 by the axial groove 8d1 formed on the outer peripheral surface 8d of the sleeve portion 8 and the radial groove 8c1 formed on the lower end surface 8c. One end of this communication path opens into the first axial gap L1, and the other end is a space facing the lower end portion of the shaft member 2, more specifically, the inner bottom surface 7b1 of the housing 7 and the spherical convex portion 2a2 of the shaft member 2. It opens to the space P between. As a result, the space P formed on the housing closing side communicates with the seal space S via the communication path, the first axial gap L1, and further the second axial gap L2. A situation in which a local negative pressure is generated in the lubricating oil filled in is avoided, and deterioration in bearing performance due to the generation of bubbles can be prevented.

  In this embodiment, the dynamic pressure groove 8a1 of the first radial bearing portion R1 is formed to be axially asymmetric (X1> X2) with respect to the annular smooth portion at the axially intermediate portion (see FIG. 3). When the shaft member 2 rotates, the lubricating oil pulling force (pumping force) by the dynamic pressure groove 8a1 is relatively larger in the upper region than in the lower region. Then, due to the differential pressure of the pulling force, the lubricating oil filled in the gap between the inner peripheral surface 8a of the sleeve portion 8 and the outer peripheral surface 2a1 of the large diameter portion 2a of the shaft member 2 flows downward, and the housing 7 Is circulated through a path of the closed side P → the radial groove 8c1 → the axial groove 8d1 → the first axial gap L1, and is drawn into the radial bearing gap of the first radial bearing portion R1 again. In this way, by forcibly flowing and circulating the lubricating oil inside the bearing, a situation in which a local negative pressure is generated in the lubricating oil can be more effectively prevented. In order to circulate the lubricating oil in the direction opposite to the above path, for example, the imbalance of the dynamic pressure groove 8a1 may be formed in the direction opposite to the example shown in FIG. 3, that is, X1 <X2. Further, when it is not necessary to forcibly circulate the lubricating oil inside the bearing as described above, both of the dynamic pressure grooves 8a1 and 8a2 may be formed symmetrically in the axial direction.

  The embodiment of the present invention is not limited to the above. In the following description, parts having the same configuration and function as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 5 shows a fluid dynamic bearing device 1 according to another embodiment. The hydrodynamic bearing device 1 has the same axial position of the shoulder surface 2c of the shaft member 2 and the upper end surface 8b of the bearing sleeve 8, and the lower end surface 8c of the bearing sleeve 8 and the inner bottom surface 7b1 of the housing 7. The configuration is different from that of the above-described embodiment in that an axial gap L4 is formed therebetween. If the axial gap L4 is appropriately set, this axial gap L4 can constitute a part of the communication path that connects the housing closing side space P and the seal space S. In this case, since the radial groove 8c1 formed in the lower end surface 8c of the bearing sleeve 8 in the embodiment of FIG. 2 is not necessary, the shape of the bearing sleeve 8 can be simplified.

  A method for assembling the above hydrodynamic bearing device 1 will be described with reference to FIG. First, the outer peripheral surface 2b1 of the small diameter portion 2b of the shaft member 2 and the inner peripheral surface 9a of the seal member 9 are fitted, and the end surface 9b of the seal member 9 and the shoulder surface 2c of the shaft member 2 are brought into contact with each other. The shaft member 2 and the seal member 9 are inverted so as to be upside down from the state shown in FIG. 5 and placed on the end surface 10a of the cylindrical base 10 (see FIG. 6A). Next, the outer peripheral surface 2a1 of the large-diameter portion 2a of the shaft member 2 and the inner peripheral surface 8a of the bearing sleeve 8 are fitted, and the end surface 8b of the bearing sleeve 8 and the end surface 9b of the seal member 9 are brought into contact with each other (FIG. 6). (See (b)). At this time, one end surface 8b of the bearing sleeve 8 and the shoulder surface 2c of the shaft member 2 are at the same axial position, and the spherical convex portion 2a2 of the shaft member 2 is slightly from the other end surface 8c of the bearing sleeve 8. It will be in the state of protruding.

Further, the outer peripheral surface 8d of the bearing sleeve 8 and the inner peripheral surface 7a1 of the housing 7 are fitted, and the spherical convex portion 2a2 of the shaft member 2 and the inner bottom surface 7b1 of the housing 7 are brought into contact with each other (FIG. 6C). reference). At this time, an axial gap L4 is formed between the end face 8c of the bearing sleeve 8 and the inner bottom face 7b1 of the housing 7. In this state, the housing 7 and the bearing sleeve 8 are fixed, and the unit is removed from the base 10 to obtain the state shown in FIG. Thereafter, the shaft member 2 is pulled toward the housing opening side to move the seal member 9, thereby forming a first axial gap L1 between the seal member 9 and the bearing sleeve 8, and the seal portion 9 and the shaft member. A second axial gap L2 is formed between the second shoulder surface 2c. At this time, since the shoulder surface 2c of the shaft member 2 and the upper end surface 8b of the bearing sleeve 8 are in the same axial position, the first axial clearance L1 and the second axial clearance L2 are equal (L1 = L2). . By fixing the seal member 9 to the housing 7 at this position, the first and second axial gaps L1 and L2 are determined.

  The configuration of the hydrodynamic bearing device 1 according to the embodiment of the present invention is not limited to the above. In the above-described embodiment, the stepped shaft member 2 is integrally formed. However, the present invention is not limited to this, and for example, as shown in FIG. 7, the shaft member 2 includes a straight shaft-shaped shaft portion 21 and a hollow material 22. You may comprise. In the illustrated example, a spherical convex portion 21 b is formed at the lower end portion of the shaft portion 21, and the inner peripheral surface 22 b of the cylindrical hollow material 22 is fixed to the outer peripheral surface 21 a of the shaft portion 21. The outer peripheral surface 22 a of the hollow member 22 faces the radial bearing gap, and the upper end surface 22 c of the hollow member 22 constitutes the shoulder surface of the shaft member 2. The lower end portion of the hollow member 22 extends downward beyond the lower end portion of the outer peripheral surface 21 a of the shaft portion 21 and reaches the outer periphery of the spherical convex portion 21 b of the shaft portion 21. Thereby, a part of the space P between the lower end portion of the shaft member 2 and the inner bottom surface 7b1 of the housing 7 is filled with the hollow material 22, for example, the lubricating oil filled in the bearing as compared with the configuration shown in FIG. The amount can be reduced. Accordingly, the seal space S that absorbs the volume change of the lubricating oil filled in the bearing is reduced, and the axial dimension of the seal member 9 can be reduced, whereby the axial direction of the bearing device 1 is maintained while maintaining the bearing performance. The dimensions can be reduced. Alternatively, without increasing the axial dimension of the bearing device 1, the space between the radial bearing portions R1 and R2 (bearing span) can be expanded to improve the bearing rigidity.

The shaft member 2 composed of the shaft portion 21 and the hollow material 22 is fixed by an arbitrary method such as press-fitting, adhesion, or welding. For example, when fixing by welding, if the boundary portion between the outer diameter end of the spherical convex portion 21b at the lower end of the shaft portion 21 and the inner peripheral surface 22b of the hollow member 22 is welded, the molten material is converted into the spherical convex portion 21b. It can be captured by the recess Q formed by the inner peripheral surface 22 b of the hollow material 22. Moreover, since the amount of lubricating oil inside the bearing can be further reduced by filling the concave portion Q with the melted material, the seal space S is further reduced, and the bearing device can be further reduced or the bearing rigidity can be improved. It can be further enhanced.

  2 and 5, the shaft member 2 is integrally processed, and then the outer peripheral surface 2a1 of the large diameter portion 2a, the outer peripheral surface 2b1 of the small diameter portion 2b, and the shoulder surface 2c are ground. And finished. At this time, if the Nusumi 2d is formed at the boundary between the outer peripheral surface 2b1 and the shoulder surface 2c of the small diameter portion 2b, the outer peripheral surface 2b1 and the shoulder surface 2c of the small diameter portion 2b can be reliably ground to the end. It becomes. On the other hand, if the shaft member 2 is composed of two members of the shaft portion 21 and the hollow member 22 as shown in FIG. 7, both can be fixed in advance after being processed with high accuracy. Absent. In this case, if the shaft 21 and the hollow member 22 are fixed and then the outer peripheral surface 22a of the hollow member 22 facing the radial bearing gap is ground, the assembly error between the shaft 21 and the hollow member 22 is taken into consideration. Thus, the outer peripheral surface 22a can be finished with high accuracy.

Although the housing 7 and the sleeve portion 8 are formed separately, they may be integrally formed. For example, if the housing 7 and the sleeve portion 8 are integrally formed by injection molding, the manufacturing process can be omitted, so that the cost can be reduced.

  Further, in the above embodiment, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed on the inner peripheral surface 8a of the sleeve portion 8 as a dynamic pressure generating portion that generates a dynamic pressure action on the lubricating fluid in the radial bearing gap. However, the present invention is not limited to this, and for example, a spiral dynamic pressure groove, a step bearing, or a multi-arc bearing may be employed. Alternatively, both the inner peripheral surface 8a of the sleeve portion 8 and the outer peripheral surface 2a1 of the large diameter portion 2a of the shaft member 2 may be formed into a cylindrical surface to constitute a so-called circular bearing.

In the above-described embodiment, the configuration in which the shaft member 2 is contact-supported by the thrust bearing portion T is shown, but the present invention is not limited to this. For example, a thrust bearing gap T is formed between the lower end surface of the shaft member 2 and the inner bottom surface 7b1 of the housing 7, and the shaft member 2 is supported in a non-contact manner by the dynamic pressure action of lubricating oil in the thrust bearing gap. May be configured.

  In the above embodiment, the dynamic pressure grooves 8a1 and 8a2 are formed on the inner peripheral surface 8a of the sleeve portion 8, but the outer periphery of the large-diameter portion 2a of the shaft member 2 facing this surface through a bearing gap. A dynamic pressure groove may be formed on the surface 2a1.

  Moreover, in said embodiment, although radial bearing part R1, R2 is spaced apart and provided in the axial direction, you may provide these continuously in an axial direction. Alternatively, only one of these may be provided.

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and generates the hydrodynamic action in the radial bearing gap. However, the hydrodynamic action is also generated in each bearing gap. Possible fluids, for example, a gas such as air, a magnetic fluid, or lubricating grease can also be used.

  Further, the hydrodynamic bearing device of the present invention is not limited to the spindle motor used in the disk drive device such as the HDD as described above, but is used for information used under high-speed rotation, such as a spindle motor for driving a magneto-optical disk of an optical disk. It can also be suitably used as a fan motor for rotating shaft support in a small motor for equipment, a polygon scanner motor of a laser beam printer, or a cooling fan for electrical equipment.

It is sectional drawing which shows the spindle motor for HDD incorporating the hydrodynamic bearing apparatus. It is sectional drawing of a hydrodynamic bearing apparatus. It is sectional drawing of a sleeve part. (A), (b) is sectional drawing which shows the setting method of the 2nd axial direction clearance gap. It is sectional drawing of the hydrodynamic bearing apparatus of another example. (A)-(d) is sectional drawing which shows the other example of the assembly method of a hydrodynamic bearing apparatus. It is sectional drawing of the hydrodynamic bearing apparatus of another example. It is sectional drawing which expands and shows the shoulder surface vicinity of a shaft member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrodynamic bearing device 2 Shaft member 2a Large diameter part 2b Small diameter part 2c Shoulder surface 7 Housing 8 Sleeve part 8c1 Radial direction groove 8d1 Axial direction groove 9 Seal part L1 1st axial direction clearance L2 2nd axial direction clearance L3 Seal space Radial dimension R1, R2 Radial bearing part T Thrust bearing part S Seal space

Claims (8)

Between the small-diameter portion, the large-diameter portion, and the shaft member having a shoulder surface formed between them, the sleeve portion in which the large-diameter portion of the shaft member is inserted on the inner periphery, and the outer peripheral surface of the small-diameter portion of the shaft member A seal space that prevents leakage of the lubricating fluid inside the bearing to the outside, and a seal portion that engages the shoulder surface of the shaft member in the axial direction to prevent the shaft member from coming off, and a large shaft member A radial bearing portion that supports the shaft member in the radial direction with a fluid film generated in a radial bearing gap between the outer peripheral surface of the diameter portion and the inner peripheral surface of the sleeve portion, and a thrust bearing portion that supports the shaft member in the thrust direction. In the hydrodynamic bearing device provided,
A hydrodynamic bearing device, wherein a first axial gap is formed between a seal portion and a sleeve portion.   The hydrodynamic bearing device according to claim 1, wherein a second axial gap formed between the seal portion and the shoulder surface of the shaft member is equal to or smaller than a radial dimension of the seal space.   The hydrodynamic bearing device according to claim 1, wherein the second axial clearance is 30 μm or less.   A communication path is provided between the sleeve portion and the housing housing the sleeve portion on the inner periphery, with one end opened in the first axial gap and the other end opened in a space facing the lower end of the shaft member. The hydrodynamic bearing device according to claim 1.   The hydrodynamic bearing device according to claim 4, wherein the communication path is configured by grooves formed in an end surface and an outer peripheral surface of the sleeve portion.   The hydrodynamic bearing device according to claim 1, wherein the shaft member is formed of a shaft portion and a hollow material fixed to the outer peripheral surface of the shaft portion, and a shoulder surface of the shaft member is configured by an end surface of the hollow material.   A spherical convex portion is formed at the end of the shaft portion, and this spherical convex portion is contact-supported to constitute a thrust bearing portion, and the end of the hollow material is extended to the outer periphery of the spherical convex portion of the shaft portion. The hydrodynamic bearing device according to claim 6.   The hydrodynamic bearing device according to claim 1, which is used for a HDD spindle motor.

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