JP2008144847A - Dynamic pressure bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance bearing performance by accurately positioning an end surface of a hub forming a thrust bearing clearance relative to a shaft member in an axial direction. <P>SOLUTION: The thrust bearing clearance is formed by an end surface 31a of a core metal 31, and the end surface 31a of the core metal 31 is abutted on a shoulder surface 2c of the shaft member 2. Thereby, since the thrust bearing surface can be positioned, with high precision, relative to the shaft member 2 in the axial direction, high accuracy of the clearance width of the thrust bearing clearance, reduction of rotation torque or miniaturization of the bearing device can be attained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device that rotatably supports a shaft member by a hydrodynamic action of a lubricating film generated in a bearing gap, and a manufacturing method thereof.

  This type of hydrodynamic bearing device includes information devices, for example, magnetic disk drive devices such as HDD, optical disk drive devices such as CD-ROM, CD-R / RW, DVD-ROM / RAM, and magneto-optical disks such as MD and MO. It can be suitably used for a spindle motor such as a driving device, a polygon scanner motor of a laser beam printer (LBP), a color wheel of a projector, or an electric device such as a small motor such as a fan motor.

  For example, a hydrodynamic bearing device shown in FIG. 6 of Patent Document 1 includes a shaft member, a flange portion provided at one end of the shaft member, and a flange-shaped hub (disc) provided at the other end of the shaft member. A hub), a bearing sleeve having a shaft member inserted into the inner periphery thereof, and a housing for holding the bearing sleeve. When the shaft member rotates, one thrust bearing gap is formed between the end face of the hub and the end face of the housing, and the other thrust bearing gap is formed between the end face of the flange portion and the end face of the bearing sleeve. The shaft member is supported in both thrust directions by the dynamic pressure action of the lubricating oil generated in these thrust bearing gaps.

  Further, FIG. 2 of the same document shows a hydrodynamic bearing device in which a shaft member is not provided with a flange portion and a thrust bearing gap is formed only at one location.

Japanese Patent Laying-Open No. 2005-337342 (FIGS. 2, 5, and 6)

  In the bearing device as described above, the positioning accuracy in the axial direction with respect to the shaft member of the hub is important. For example, in the hydrodynamic bearing device shown in FIG. 6 of Patent Document 1 above, the axial distance between the end surface of the hub facing one thrust bearing gap and the end surface of the flange portion facing the other thrust bearing gap is Directly linked to the width accuracy of each thrust bearing gap. For this reason, if the hub is not accurately positioned with respect to the shaft member in the axial direction, the width accuracy of the thrust bearing gap is lowered, and the supporting force in the thrust direction is lowered.

  Further, in the hydrodynamic bearing device shown in FIG. 2 of Patent Document 1 above, the positioning accuracy in the axial direction of the hub with respect to the shaft member is reflected in the axial distance between the lower end surface of the shaft member and the inner bottom surface of the housing. . If these axial distances are too small, the torque may increase when the shaft member rotates. On the other hand, if these axial distances are excessive, the space inside the bearing increases and the amount of lubricating oil to be filled also increases, so the volume of the seal space that absorbs the volume change accompanying the temperature change of the lubricating oil is expanded. Therefore, it is necessary to increase the size of the bearing device.

  By the way, in such a hydrodynamic bearing device, if the entire hub is made of a metal material, it becomes difficult to process, resulting in high costs. On the other hand, if the entire hub is formed of a resin material, sufficient strength cannot be obtained and the product life may be shortened. In view of this point, in the hydrodynamic bearing device shown in FIG. 5 of the same document, a hub is formed by inserting a metal core fitted to the outer peripheral surface of the shaft member and injection-molding it with resin. According to this configuration, the strength of the hub is enhanced by reinforcing with the core metal, and the moldability of the hub is enhanced by forming a complicated shape portion by injection molding.

  In this hydrodynamic bearing device, the shaft member is formed in a stepped shaft shape having a shoulder surface, and the core metal is positioned in the axial direction with respect to the shaft member by bringing the core metal into contact with the shoulder surface. . However, since the core is covered with the resin portion, even if the core is accurately positioned, the accuracy of the end face of the hub is reduced due to the molding shrinkage of the resin, and the desired width accuracy of the thrust bearing gap is reduced. There is a risk that it will not be obtained.

  In view of this, the present invention provides a hydrodynamic bearing device having a hub having a cored bar, which improves the bearing performance by accurately positioning the end surface of the hub forming the thrust bearing gap in the axial direction with respect to the shaft member. The purpose is to plan.

  In order to achieve the above object, the present invention provides a stepped shaft-shaped shaft member having a shoulder surface, a core metal fitted to the outer peripheral surface of the shaft member, and a flange that is injection-molded by inserting the core metal. Of the shaft, a radial bearing gap that faces the outer peripheral surface of the shaft member, a radial bearing portion that supports the shaft member in the radial direction by the dynamic pressure action of the lubricating film generated in the radial bearing gap, and the end face of the hub faces In a hydrodynamic bearing device including a thrust bearing gap and a thrust bearing portion that supports a shaft member in a thrust direction by a dynamic pressure action of a lubricating film generated in the thrust bearing gap, an end surface of a core metal is used as a shoulder surface of the shaft member. A thrust bearing gap is formed at the end face of the cored bar as well as contacting.

  Thus, in the hydrodynamic bearing device of the present invention, since the thrust bearing gap is formed at the end face of the core metal, the end face accuracy is not reduced by molding shrinkage as in the conventional product coated with resin. Therefore, the end surface of the core bar is brought into contact with the shoulder surface of the shaft member, and the shaft member is accurately positioned in the axial direction, thereby improving the width accuracy of the thrust bearing gap, reducing the rotational torque, or the bearing device. Can be reduced in size.

  In addition, when an uneven portion is provided in a region in contact with the hub in the outer peripheral surface of the shaft member, an anchor effect caused by the injection molding material of the hub entering the uneven portion causes the injection molding material and the outer peripheral surface of the shaft member to Adhesion is improved, and the fixing strength between the hub and the shaft member is improved.

  Further, if the shoulder surface of the shaft member is processed with high accuracy by grinding, the positioning accuracy of the cored bar with respect to the shaft member can be further increased. The shoulder surface is preferably ground on the basis of one end surface of the shaft member. For example, when positioning a flange portion that forms a thrust bearing gap on this end face (see FIG. 2), the end face of the metal core that forms one thrust bearing gap and the flange portion that forms the other thrust bearing gap It is possible to set the axial distance L with respect to the end face with higher accuracy, and it is possible to further increase the accuracy of the width setting of the thrust bearing gap.

  In addition, when the outer peripheral surface facing the radial bearing gap and the shoulder surface of the shaft member are simultaneously ground, it is possible to reduce the number of steps and to process these grinding jigs with high accuracy. The perpendicularity and runout accuracy of the surface can be set with high accuracy. Therefore, the perpendicularity and runout accuracy between the radial bearing gap formed by the outer peripheral surface and the thrust bearing gap formed by the metal core in contact with the shoulder surface are set with high accuracy, and the bearing capacity is increased by improving the width accuracy of the bearing gap. In addition, the rotational accuracy of the bearing device can be improved.

  As described above, in the hydrodynamic bearing device of the present invention, the end face of the hub forming the thrust bearing gap can be accurately positioned in the axial direction with respect to the shaft member, so that the bearing performance can be improved.

  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 fluid dynamic bearing device 1 to which the present invention is applied. The spindle motor is used in a disk drive device such as an HDD, and is opposed to the hydrodynamic bearing device 1 that supports the shaft member 2 and the hub 3 in a non-contact manner so as to be relatively rotatable, for example, via a radial gap. A stator coil 4, a rotor magnet 5, and a bracket 6 are provided. The stator coil 4 is attached to the outer peripheral side inner peripheral surface 6 a of the bracket 6, and the rotor magnet 5 is fixed to the outer periphery of the hub 3. The hydrodynamic bearing device 1 is fixed to the inner periphery of the bracket 6. Although not shown, the hub 3 holds one or more disks as information recording media. In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 is rotated by an exciting force generated between the stator coil 4 and the rotor magnet 5, and accordingly, the hub 3 and the hub 3 are rotated. The disk held on the shaft rotates together with the shaft member 2.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a shaft member 2, a flange member 9 provided at one end of the shaft member 2, a flange-shaped hub 3 provided at the other end of the shaft member 2, and the shaft member 2 inserted into the inner periphery. The bearing sleeve 8, the housing 7 that holds the bearing sleeve 8 and opens on both sides in the axial direction, and the lid member 70 that closes one end opening of the housing 7 are mainly provided. For the sake of convenience of explanation, of the openings formed on both ends in the axial direction of the housing 7, the side closed by the lid member 70 will be described below, and the open side will be described below.

  Although details will be described later in this hydrodynamic bearing device 1, the radial bearing portions R <b> 1 and R <b> 2 are separated in the axial direction between the large-diameter outer peripheral surface 2 a of the shaft member 2 and the inner peripheral surface 8 a of the bearing sleeve 8. Provided. A first thrust bearing portion T1 is provided between the upper end surface 7a of the housing 7 and the lower end surface 3a1 of the disk portion 3a of the hub 3, and the upper end surface 9a of the flange member 9 and the lower end surface of the bearing sleeve 8 are provided. A second thrust bearing portion T2 is provided between 8b and 8b.

  The bearing sleeve 8 is formed in a cylindrical shape, for example, of a sintered metal porous body mainly composed of copper, and is bonded, press-fitted (including press-fitting adhesion), and welded (ultrasonic welding) to the inner peripheral surface 7 c of the housing 7. ), Welding (including laser welding), or the like.

  As shown in FIG. 3, a region in which a plurality of dynamic pressure grooves 8a1 and 8a2 are arranged in a herringbone shape is formed in the entire surface of the inner peripheral surface 8a of the bearing sleeve 8 or a part of the cylindrical region. The The upper dynamic pressure groove 8a1 is formed in an asymmetric shape in the axial direction, and more specifically, the axial dimension X of the groove on the upper side of the annular smooth portion provided in the axially intermediate portion is equal to that of the lower groove. It is formed to be larger than the axial dimension Y. On the other hand, the lower dynamic pressure groove 8a2 is formed in a symmetrical shape in the axial direction.

  Although not shown, dynamic pressure grooves arranged in a spiral shape are formed on the entire lower surface 8b of the bearing sleeve 8 or a partial annular region. Further, one axial groove 8d1 or a plurality of axial grooves 8d1 are formed on the outer peripheral surface 8d of the bearing sleeve 8 at equal intervals in the circumferential direction.

  The housing 7 is formed in a substantially cylindrical shape with a metal material or a resin material, and the opening on the lower end side is closed with a lid member 70. The lid member 70 is in contact with a step 7f formed on the inner periphery of the lower part of the housing 7, and is fixed by means such as adhesion, press-fitting, welding, or welding. As shown in FIG. 4, a region in which a plurality of dynamic pressure grooves 7 a 1 are arranged in a spiral shape is formed on the entire upper surface 7 a of the housing 7 or a partial annular region. On the outer periphery of the upper portion of the housing 7, a first tapered surface 7 b that gradually increases in diameter upward is formed. The first taper surface 7b forms a seal space S between the first taper surface 7b and a second taper surface 3b1 formed on the hub 3 to be described later. A cylindrical surface 7e is formed on the outer periphery of the lower portion of the housing 7, and the cylindrical surface 7e is fixed to the inner periphery of the bracket 6 by means such as adhesion, press-fitting, welding, or welding.

  The shaft member 2 is formed in a stepped shaft shape with a metal material such as stainless steel, for example. Specifically, the large-diameter outer peripheral surface 2a, the small-diameter outer peripheral surface 2b provided on the upper side of the large-diameter outer peripheral surface 2a, and these And a radial shoulder surface 2c formed therebetween. The hub 3 is provided in a flange shape on the small-diameter outer peripheral surface 2 b of the shaft member 2, and the large-diameter outer peripheral surface 2 a forms a radial bearing gap with the inner peripheral surface 8 a of the bearing sleeve 8.

  A flange member 9 is provided at the lower end of the shaft member 2. The flange member 9 is screwed into a screw hole provided in the lower end portion of the shaft member 2, and is positioned with respect to the shaft member 2 by contacting the lower end surface 2 d of the shaft member 2. A thrust bearing gap is formed between the upper end surface 9 a of the flange member 9 and the lower end surface 8 b of the bearing sleeve 8. In addition, the fixing method of the flange member 9 and the shaft member 2 is not limited to the above, and both members may be fixed by adhesion, for example.

  The hub 3 is provided in a flange shape on the small-diameter outer peripheral surface 2b of the shaft member 2, and is formed by injection molding in which a core metal 31 is inserted. The hub 3 includes a disk part 3a that covers the upper end opening of the housing 7, a cylindrical part 3b that extends downward in the axial direction from the outer peripheral part of the disk part 3a, and a flange part 3c that protrudes outward from the cylindrical part 3b. Is provided. A disc (not shown) is fitted on the outer periphery of the disc portion 3a and placed on a disc mounting surface 3d formed on the upper end surface of the flange portion 3c. Then, the disc is held on the hub 3 by an appropriate holding means (such as a clamper) not shown. As described above, since the resin hub 3 has the core 31, the strength of the hub 3 is increased, so that deformation of the hub 3 due to a clamping force or the like when the disk is mounted can be prevented.

  The core metal 31 is formed in a substantially disk shape by plastic processing (for example, press processing) of stainless steel, for example. The metal core 31 is press-fitted (including light press-fitting) with the inner peripheral surface 31b of the small-diameter outer peripheral surface 2b of the shaft member 2, and the lower end surface 31a is brought into contact with the shoulder surface 2c of the shaft member 2, Positioned in the axial direction. At this time, since the Nusumi portion 2e is formed at the boundary between the small-diameter inner peripheral surface 2b and the shoulder surface 2c of the shaft member 2 (see FIG. 5), the cored bar 31 is securely attached to the shoulder surface 2c of the shaft member 2. It can be adhered. In this state, the fitting surfaces of the cored bar 31 and the shaft member 2 are welded to fix both.

  The resin molding part 32 of the hub 3 is formed by inserting the cored bar 31 and the shaft member 2 fixed as described above and performing injection molding with resin. The resin molding part 32 includes, for example, a crystalline resin such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyphenyl sulfone (PPSU), polyether sulfone (PES), poly It is molded by injection molding of a resin composition having an amorphous resin such as etherimide (PEI) as a base resin. Also, fibrous or powder such as carbon fiber and glass fiber, whisker-like filler such as potassium titanate, scaly filler such as mica, carbon black, graphite, carbon nanomaterial, various metal powders, etc. A suitable amount of the conductive filler in the form of a base resin can be used depending on the purpose.

  The injection molding material for the hub 3 is not limited to resin, and molten metal can also be used. As the metal material, for example, a low-melting-point metal material such as a magnesium alloy or an aluminum alloy can be used, and in this case, strength and conductivity can be improved as compared with the case of using a resin material. In addition, so-called MIM molding in which degreasing and sintering are performed after injection molding with a mixture of metal powder and binder, or ceramic injection molding (so-called CIM molding) can also be employed.

  The resin molded portion 32 of the hub 3 is in contact with the small-diameter outer peripheral surface 2 b of the shaft member 2. By providing irregularities on the small-diameter outer peripheral surface 2b and allowing molten resin as an injection material to enter the irregular portions, the anchor effect is exerted, and the fixing force between the resin molded portion 32 and the shaft member 2 is enhanced. For example, as described later, the uneven portion can be formed by leaving a turning mark by turning of the shaft member 2 on the small-diameter outer peripheral surface 2b. For example, as shown in FIG. 6, the concavo-convex portion can be formed by the spline groove 2 b 1 formed on the small-diameter outer peripheral surface 2 b.

  A second tapered surface 3b1 is formed in the upper portion of the inner peripheral surface of the cylindrical portion 3b of the hub 3 so as to gradually increase in diameter upward. The second taper surface 3b1 is set to have a smaller taper angle with respect to the axial direction than the first taper surface 7b. Accordingly, the seal space S formed between them is formed in a tapered shape with the radial dimension gradually reduced upward. In this way, by configuring the outer peripheral portion of the seal space S with the second tapered surface 3b1 whose diameter is increased upward, in addition to the pull-in action by the capillary force of the tapered seal space S when the hub 3 rotates, Since the lubricating oil in the seal space S is drawn upward by centrifugal force, that is, toward the bearing inner side, leakage of the lubricating oil to the outside can be prevented more reliably.

  The inside of the hydrodynamic bearing device 1 is filled with, for example, lubricating oil as a lubricant, and the oil level is always held in the seal space S. Various types of lubricating oil can be used, but the lubricating oil provided to the hydrodynamic bearing device for a disk drive device such as an HDD takes into account temperature changes during use or transportation. In addition, an ester-based lubricating oil excellent in low evaporation rate and low viscosity, for example, a lubricating oil using dioctyl sebacate (DOS), dioctyl azelate (DOZ) or the like as a base oil can be suitably used.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 rotates, the hydrodynamic groove 8a1 and 8a2 formation region formed on the inner peripheral surface 8a of the bearing sleeve 8 and the large-diameter outer peripheral surface 2a of the opposing shaft member 2 are formed. A radial bearing gap is formed between the two. As the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed toward the axial center of the dynamic pressure grooves 8a1 and 8a2, and the pressure rises. The first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in the radial direction without contact are configured by the dynamic pressure action of the lubricating oil generated by the dynamic pressure grooves 8a1 and 8a2.

  At the same time, a thrust bearing gap is formed between the region where the dynamic pressure groove 7a1 is formed on the upper end surface 7a of the housing 7 and the lower end surface 3a1 of the hub 3, and the dynamic pressure groove is formed on the lower end surface 8b of the bearing sleeve 8. A thrust bearing gap is formed between the formation region and the upper end surface 9 a of the flange member 9. The pressure of the lubricating oil film formed in these thrust bearing gaps is increased by the dynamic pressure action of each dynamic pressure groove, so that the first thrust bearing portion T1 that supports the shaft member 2 and the hub 3 in a non-contact manner in both thrust directions. And the 2nd thrust bearing part T2 is comprised.

  Further, by forming the axial groove 8d1 on the outer peripheral surface 8d of the bearing sleeve 8, the space on the outer diameter side of the second thrust bearing portion T2 communicates with the space on the inner diameter side of the first thrust bearing portion T1. Can do. Thereby, the production | generation of the bubble by a local negative pressure being applied to the internal space of a bearing can be prevented. In the present embodiment, as shown in FIG. 3, the dynamic pressure groove 8a1 of the first radial bearing portion R1 is formed in an asymmetric shape in the axial direction, so that the lubricating oil is pushed downward in the radial bearing gap. It is. As a result, the lubricating oil again passes through the radial bearing gap → the thrust bearing gap of the second thrust bearing portion T2 → the axial groove 8d1 → the space between the upper end surface 8c of the bearing sleeve 8 and the hub 3, and again the radial bearing. It is drawn into the gap. In this way, by forcibly circulating the lubricating oil inside the bearing, local negative pressure can be more reliably prevented. If such forced circulation is not particularly necessary, the dynamic pressure groove 8a1 may be formed in an axially symmetric shape.

  As described above, in the present invention, since the thrust bearing gap of the first thrust bearing portion T1 is formed by the core metal 31, the end face accuracy may be reduced by molding shrinkage as in the conventional product in which the core metal is coated with resin. No. Therefore, the end surface 31 a of the core metal 31 can be positioned with high accuracy in the axial direction with respect to the shaft member 2 by bringing the end surface 31 a of the core metal 31 into contact with the shoulder surface 2 c of the shaft member 2. In particular, the core metal 31 is accurately positioned with respect to the lower end surface 2d of the shaft member 2, so that the axial distance L from the flange member 9 positioned by contacting the lower end surface 2d (see FIG. 2). ) Can be set with high accuracy. Thereby, the total amount of the gap widths of the thrust bearing gaps of both thrust bearing portions T1, T2 is set with high accuracy, and the supporting force in the thrust direction can be increased.

  Further, when the bearing device is started and stopped at a low speed, the dynamic pressure action by the dynamic pressure groove is not sufficiently exhibited, so that the lower end surface 3a1 of the disk portion 3a of the hub 3 faces through the thrust bearing gap. It slides in contact with the upper end surface 7 a of the housing 7. For this reason, high wear resistance is required for the lower end surface 3a1 of the disk portion 3a of the hub 3 forming the thrust bearing gap. As described above, by forming the lower end surface 3a1 of the disk portion 3a of the hub 3 with the lower end surface 31a of the cored bar 31, the wear resistance of the portion that contacts and slides during low-speed rotation can be improved.

  Below, the processing method of the shaft member 2 is demonstrated using FIG.

  First, a cylindrical shaft member made of stainless steel is cut into a predetermined length, and the outer peripheral surface of this shaft member is turned so that the shaft member 2 has a large-diameter outer peripheral surface 2a, a small-diameter outer peripheral surface 2b, and A shoulder surface 2c is formed. These surfaces are rough surfaces on which turning lines are formed. Simultaneously with this turning process, a pusmy part 2e is formed at the boundary between the small-diameter outer peripheral surface 2b and the shoulder surface 2c.

  Thereafter, the large-diameter outer peripheral surface 2a and the shoulder surface 2c of the shaft member 2 are ground to improve the surface accuracy of these surfaces. In this grinding process, an angular grinding wheel 40 that rotates about an axis inclined with respect to the central axis of the shaft member 2 and a positioning jig 50 that contacts the lower end surface 2d of the shaft member 2 are used (see FIG. 5). ). The grinding wheel 40 includes a first grinding surface 41 that grinds the large-diameter outer circumferential surface 2a of the shaft member 2, a second grinding surface 42 that grinds the shoulder surface 2c of the shaft member 2, and a small-diameter outer circumferential surface 2b of the shaft member 2. And an opposing third grinding surface 43. The radial dimension L1 of the second grinding surface 42 (dimension in the radial direction of the shaft member 2) is set smaller than the radial dimension L2 of the shoulder surface 2c of the shaft member 2 (L1 <L2). When the shaft member 2 is ground by rotating such a grinding wheel 40, the large-diameter outer peripheral surface 2a and the shoulder surface 2c of the shaft member 2 are ground by the first grinding surface 41 and the second grinding surface 42, while the small-diameter outer periphery is ground. The surface 2b and the 3rd grinding surface 43 can be made non-contact. As a result, the large-diameter outer peripheral surface 2a and the shoulder surface 2c can be made to be a ground surface processed with high precision, and the small-diameter outer peripheral surface 2b can be made to be a rough surface leaving a turning line by turning.

  In addition, as shown in FIG. 5, the shoulder surface 2c is the second ground surface in a state where the positioning jig 50 is in contact with the lower end surface 2d of the shaft member 2, that is, with the lower end surface 2d of the shaft member 2 as a reference. By grinding at 42, the axial distance L3 between the shoulder surface 2c and the lower end surface 2d of the shaft member 2 can be set with high accuracy. In addition, since the lower end surface 2d of the shaft member 2 is ground in advance to increase the surface accuracy of this surface, the axial positioning by the contact with the positioning jig 50 is performed more accurately. The axial distance between the second shoulder surface 2c and the lower end surface 2d is set with higher accuracy.

  As described above, by grinding the shoulder surface 2c of the shaft member 2 and increasing the surface accuracy of this surface, the positioning accuracy of the cored bar 31 with respect to the shaft member 2 is increased. Furthermore, by grinding the shoulder surface 2c of the shaft member 2 with the lower end surface 2d as a reference, the axial distance L3 between the shoulder surface 2c and the lower end surface 2d is set with high accuracy. Thereby, the setting accuracy of the axial distance L between the metal core 31 and the flange member 9 is further increased, the width accuracy of the thrust bearing gap is improved, and the supporting force in the thrust direction is further increased.

  Further, as described above, by simultaneously grinding the large-diameter outer peripheral surface 2a and the shoulder surface 2c of the shaft member 2 with the grinding wheel 40, the number of steps can be reduced, and the squareness and vibration of these surfaces can be reduced. The accuracy can be set with high accuracy. Thereby, the perpendicularity and runout accuracy between the radial bearing gap formed by the large-diameter outer peripheral surface 2a and the thrust bearing gap formed by the cored bar 31 positioned by the shoulder surface 2c can be set with high accuracy. Therefore, the bearing force can be increased by improving the width accuracy of the bearing gap, and the rotation accuracy of the shaft member 2 can be improved.

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

  FIG. 7 shows a hydrodynamic bearing device 101 according to another embodiment of the present invention. In the hydrodynamic bearing device 101, the flange member provided at the lower end of the shaft member 2 in the above embodiment and the second thrust bearing portion formed by the flange member are omitted. A retaining member 10 is fixed to the step portion 3e provided at the upper part of the inner periphery of the cylindrical portion 3b of the hub 3 by means such as adhesion or welding. The retaining member 10 is formed in a substantially L-shaped cross section by, for example, pressing a metal material, and the upper end surface 10a and the radial shoulder surface provided on the outer periphery of the housing 7 are engaged in the axial direction. The hub 3 and the shaft member 2 are prevented from coming off. The inner peripheral surface 10 b of the retaining member 10 is formed in a tapered shape that gradually increases in diameter upward, and forms a seal space S with the first tapered surface 7 b of the housing 7. That is, the inner peripheral surface 10b of the retaining member 10 plays the same role as the second tapered surface 3b1 provided on the hub 3 of the above embodiment. The housing 7 is formed in a bottomed cylindrical cup shape, and the lower end surface 8b of the bearing sleeve 8 is in contact with the inner bottom surface 7d thereof. The lower end surface 2d of the shaft member 2 is opposed to the inner bottom surface 7d of the housing 7 in the axial direction with a certain gap.

  In this hydrodynamic bearing device 101, as in the above-described embodiment, the axial distance between the shoulder surface 2c and the lower end surface 2d is accurately determined by grinding the shoulder surface 2c of the shaft member 2 with the lower end surface 2d as a reference. It is set. Accordingly, the axial distance between the lower end surface 2d of the shaft member 2 and the inner bottom surface 7d of the housing 7 is set with high accuracy in a state where the hub 3 and the shaft member 2 are supported in the thrust direction by the thrust bearing portion T1. can do. Therefore, the rotational torque increases when the lower end surface 2d of the shaft member 2 and the inner bottom surface 7d of the housing 7 are excessively approached, and the seal space S is generated when these surfaces are excessively separated to increase the bearing internal space. Therefore, it is possible to avoid an increase in the capacity of the bearing device and an increase in the size of the bearing device.

  In the above embodiment, the hub is injection-molded by inserting an integral part of the cored bar 13 and the shaft member 2, but not limited thereto, for example, after the hub is injection-molded using the cored bar as an insert part, This hub may be fixed to the shaft member

  In the above embodiment, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are exemplified by the configuration in which the dynamic pressure action of the lubricating oil is generated by the dynamic pressure grooves having a herringbone shape or a spiral shape. However, the present invention is not limited to this.

  For example, although not shown as radial bearing portions R1 and R2, a so-called step-like dynamic pressure generating portion in which axial grooves are formed at a plurality of locations in the circumferential direction, or a plurality of circular arc surfaces in the circumferential direction. And a so-called multi-arc bearing in which a wedge-shaped radial gap (bearing gap) is formed between the opposing shaft member 2 and the large circular outer peripheral surface 2a.

  Alternatively, the inner peripheral surface 8a of the bearing sleeve 8 is a perfect circular inner peripheral surface not provided with a dynamic pressure groove or a circular arc surface as a dynamic pressure generating portion, and the perfect circular shape of the shaft member 2 facing the inner peripheral surface 8a. The large-diameter outer peripheral surface 2a can constitute a so-called circular bearing.

  Moreover, in the above description form, 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 the radial bearing portions R1 and R2 may be provided.

  The thrust bearing portions T1 and T2 are not shown in the figure, but a plurality of radial groove-shaped dynamic pressure grooves are circumferentially formed in a region where the dynamic pressure generating portion is formed (for example, the upper end surface 7a of the housing 7). A so-called step bearing provided at a predetermined interval in the direction, or a corrugated bearing (one in which the step mold is corrugated) may be used.

  In the above embodiment, the radial dynamic pressure generating portion (dynamic pressure grooves 8a1 and 8a2) is provided on the bearing sleeve 8 side, and the thrust dynamic pressure generating portion (dynamic pressure groove is provided on the housing 7 or the bearing sleeve 8 side. 7a1) has been described, the regions where these dynamic pressure generating portions are formed are, for example, the large-diameter outer peripheral surface 2a of the shaft member 2 opposed to them, the lower end surface 3a1 of the hub 3, or the flange. It can also be provided on the member 9 side.

  Further, in the above description, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and causes the hydrodynamic action in the radial bearing gap or the thrust bearing gap. A fluid capable of generating a dynamic pressure action, for example, a gas such as air, a magnetic fluid, or lubricating grease may be used.

  In the above embodiment, a disk is placed on the hub 3 and the hydrodynamic bearing device 1 is used as a spindle motor used in a disk drive device such as an HDD. However, the present invention is not limited to this. For example, a polygon mirror can be mounted on the hub 3 and the hydrodynamic bearing device 1 can be used for supporting the rotating shaft of a polygon scanner motor of a laser beam printer. Alternatively, a color wheel can be mounted on the hub 3 and the dynamic pressure bearing device 1 can be used for supporting the rotating shaft of the color wheel of the projector. Alternatively, a fan can be installed (integrated) in the hub 3 and the hydrodynamic bearing device 1 can be used as a fan motor.

It is sectional drawing of the spindle motor incorporating the dynamic pressure bearing apparatus. 1 is a cross-sectional view of a fluid dynamic bearing device 1 according to the present invention. 3 is a cross-sectional view of a bearing sleeve 8. FIG. FIG. 6 is a top view of the housing 7. 5 is a front view showing a processing step of the shaft member 2. FIG. It is a front view which shows the other example of the uneven | corrugated | grooved part of the shaft member. It is sectional drawing of the hydrodynamic bearing apparatus 101 which shows other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic-pressure bearing apparatus 2 Shaft member 2a Large diameter outer peripheral surface 2b Small diameter outer peripheral surface 2c Shoulder surface 2d Lower end surface 3 Hub 31 Core metal 32 Resin molding part 7 Housing 8 Bearing sleeve 9 Flange member 40 Grinding wheel 41 First grinding surface 42 First 2 Grinding surface 43 Non-grinding surface 50 Positioning jig R1, R2 Radial bearing portion T1, T2 Thrust bearing portion S Seal space

Claims (5)

A stepped shaft-shaped shaft member having a shoulder surface, a core metal fitted to the outer peripheral surface of the shaft member, a flange-shaped hub inserted by injection of the core metal, and the outer peripheral surface of the shaft member A radial bearing gap, a radial bearing portion that supports the shaft member in the radial direction by the dynamic pressure action of the lubricating film generated in the radial bearing gap, a thrust bearing gap facing the end surface of the hub, and a lubricating film generated in the thrust bearing gap In the hydrodynamic bearing device comprising a thrust bearing portion that supports the shaft member in the thrust direction by the hydrodynamic action of
A hydrodynamic bearing device characterized in that an end surface of a core metal is brought into contact with a shoulder surface of a shaft member, and a thrust bearing gap is formed on the end surface of the core metal.   2. The hydrodynamic bearing device according to claim 1, wherein an uneven portion is provided in a region of the outer peripheral surface of the shaft member in contact with the hub.   2. The hydrodynamic bearing device according to claim 1, wherein a shoulder surface of the shaft member is a ground surface.   4. The hydrodynamic bearing device according to claim 3, wherein the grinding of the shoulder surface of the shaft member is performed with reference to one end surface of the shaft member.   4. The hydrodynamic bearing device according to claim 3, wherein an outer peripheral surface and a shoulder surface that form a radial bearing gap are ground simultaneously in the shaft member.

Images