JP4509650B2 - Hydrodynamic bearing device - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device. This bearing device is used for spindle motors of information equipment, for example, magnetic disk devices such as HDD, optical disk devices such as CD-ROM, CD-R / RW, DVD-ROM / RAM, and magneto-optical disk devices such as MD and MO. It is suitable for a polygon scanner motor of a laser beam printer (LBP), a color wheel of a projector, or a small motor such as an electric device such as an axial fan.

  A dynamic pressure bearing is a bearing that supports a shaft member in a non-contact state by a fluid dynamic pressure generated in a bearing gap. A bearing device (dynamic pressure bearing device) using this dynamic pressure bearing includes a contact type in which a radial bearing portion is constituted by a dynamic pressure bearing and a thrust bearing portion is constituted by a pivot bearing, and a radial bearing portion and a thrust bearing portion. They are roughly classified into non-contact types in which both are constituted by dynamic pressure bearings, and are properly used according to individual applications.

Among them, as an example of a non-contact type hydrodynamic bearing device, one in which a shaft member is constituted by a shaft portion and a flange portion is known. For example, Japanese Patent Laid-Open No. 2000-291648 discloses a shaft portion and a flange. A device in which both parts are formed of a metal material is disclosed (see Patent Document 1). Japanese Patent Application Laid-Open No. 2003-314537 discloses one in which a shaft portion is formed of a metal material and a flange portion is formed of a resin material (see Patent Document 2).
JP 2000-291648 A JP 2003-314537 A

  Among the hydrodynamic bearing devices configured as described above, in particular, according to the hydrodynamic bearing device including the shaft member in which the shaft portion is formed of a metal material and the flange portion is formed of a resin material, molding accuracy is improved and processing cost is reduced. Is planned. On the other hand, the base of the metal shaft portion and the resin flange portion is weaker in strength than other portions. Therefore, when a tensile load in the axial direction is applied to the shaft member, the shaft member may cause shear fracture mainly from the shaft portion that is the weakest portion and the base portion of the flange portion.

  Accordingly, an object of the present invention is to increase the strength of a shaft member in this type of hydrodynamic bearing device.

In order to solve the above problems, a hydrodynamic bearing device according to the present invention includes a shaft member, a radial bearing portion that non-contact-supports the shaft member in a radial direction by a dynamic pressure action of a fluid generated in the radial bearing gap, and a thrust bearing gap. In a hydrodynamic bearing device having a thrust bearing portion that supports the shaft member in the thrust direction in a non-contact manner by the dynamic pressure action of the fluid generated in the shaft, the shaft member has a metal shaft body having an outer peripheral surface facing the radial bearing gap And a core member fixed to the shaft main body and projecting to the outer diameter side of the shaft main body, and the end surface faces the thrust bearing gap by injection molding with the core member fixed to the shaft main body and covering the core material. and a resin portion forming a disk-shaped flange portion, core material is formed in a perforated disc shape having a hole in the center, it is fixed by being in contact with the end face of the shaft body, the core material A state where the hole provided in is closed by the resin part One end of the shaft body and the core member is characterized in that it is coated with a resin portion.

  With this configuration, according to the present invention, a part of the disk-shaped flange portion formed of resin is replaced with the core material. In this case, since the core material acts as a reinforcing material for the flange portion, the strength (rigidity) of the flange portion itself is increased. In addition, since the core material is fixed to the shaft body in a state of projecting to the outer diameter side of the shaft body, the strength of the shaft portion that becomes the weakest portion and the base of the flange portion can be improved, and the shear strength against the tensile load Improvement is achieved.

  The shape of the core material is arbitrary as long as it is fixed to the shaft body, but the thickness is uniform in the circumferential direction in order to prevent the occurrence of sink marks due to variations in the thickness of the resin part facing the thrust bearing gap. It is desirable to form in the shape of a disk having The shape of the shaft body is arbitrary as long as the outer peripheral surface of the shaft body facing the radial bearing gap is made of metal, and a hollow cylindrical shaft body can be used in addition to a solid shaft body. When a hollow cylindrical shaft main body is used, the shaft portion can be made into a composite structure of resin and metal by filling the inner peripheral hole of the shaft main body with a resin during injection molding.

  The shaft body and the core material are initially separate members that are individually formed and individually finished. Therefore, high finishing accuracy can be easily obtained as compared with the case where the shaft main body and the core material are formed as an integrated product from the beginning and finished.

  Further, since the flange portion is molded by injecting resin with the core material and the shaft body fixed (insert molding or outsert molding), the molding accuracy of the flange portion, for example, the flatness of both end surfaces of the flange portion, The perpendicularity between the flange portion and the shaft portion depends on the molding surface accuracy of the mold. Therefore, as long as the mold accuracy is ensured, the fixing accuracy when fixing the core material to the shaft body is sufficient, and the fixing process can be simplified. By increasing the flatness and perpendicularity of the flange portion, the thrust bearing gap formed between the end surface of the flange portion and the surface facing the end surface can be managed with high accuracy.

  In addition to the core material, if the shaft end of the shaft body is covered with a resin portion, the covering portion of the shaft end of the shaft body can be used as a resin flow path in the mold. Thereby, for example, the gate can be disposed on the axis of the shaft main body. Since the resin supplied to the cavity from the gate on this axial center diffuses uniformly toward the outer diameter side, it is possible to prevent the occurrence of welds and increase the molding accuracy of the flange portion.

  As described above, since the fixing accuracy between the core material and the shaft main body is not so required, as a fixing means for the core material and the shaft main body, welding, welding, adhesion, or the like, as long as necessary strength is ensured. The existing fixing means can be widely adopted. In particular, when the core is made of metal, it is desirable to fix it by welding in consideration of strength and cost.

  The fixing portion between the core material and the shaft main body is preferably covered with a resin portion. According to this, since the welded portion, the welded portion, and the like are not exposed to the outside, the occurrence of contamination can be prevented.

  A groove (dynamic pressure groove) for generating dynamic pressure in the thrust bearing gap is formed in a portion facing the thrust bearing gap of the resin portion, and a corresponding groove shape is formed in advance on the mold surface of the resin portion. By setting, it can be molded simultaneously with the injection molding of the resin part (molding of the flange part). In this case, if the thickness of the portion of the resin portion that faces the thrust bearing gap varies, the occurrence of sink marks during solidification and variations in the amount of thermal expansion become a problem. The portion facing the bearing gap is preferably formed with a uniform thickness.

  The thickness of the portion of the resin portion facing the thrust bearing gap is preferably determined within the range of 0.2 mm to 1.0 mm. If the lower limit value is less than this, a decrease in the fluidity of the resin becomes a problem, and if the upper limit value is exceeded, the dimensional change due to sink marks or thermal expansion is not negligible. The upper limit is more preferably 0.5 mm or less.

  As described above, according to the present invention, since the flange portion formed of the resin portion is reinforced by the core material fixed to the shaft body, the strength of the shaft member, particularly the pull-out strength of the flange portion can be increased. Further, since the rigidity of the flange portion is increased, it is possible to avoid a decrease in accuracy of the thrust bearing gap due to deformation of the flange portion, and further a decrease in bearing performance.

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

  FIG. 2 conceptually shows a configuration example of a spindle motor for information equipment incorporating the fluid dynamic bearing device 1 according to one embodiment of the present invention. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 attached to the shaft member 2, A stator coil 4 and a rotor magnet 5 which are opposed to each other via a gap in the radial direction, and a casing 6 are provided. The stator coil 4 is attached to the outer periphery of the casing 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. A housing 7 that is one component of the hydrodynamic bearing device 1 is fixed to the inner periphery of the casing 6. The disk hub 3 holds one or more disk-shaped information recording media D such as magnetic disks. When the stator coil 4 is energized, the rotor magnet 5 is rotated by the magnetic force generated between the stator coil 4 and the rotor magnet 5, thereby rotating the disk hub 3 and the shaft member 2 together.

  For example, as shown in FIG. 3, the hydrodynamic bearing device 1 includes a housing 7 having an opening 7 a at one end and a bottom 7 c at the other end, and a cylindrical bearing sleeve 8 fixed to an inner peripheral surface 7 d of the housing 7. The shaft member 2 including the shaft portion 21 and the flange portion 22 and the seal member 9 fixed to the opening 7a of the housing 7 are configured as main members. For convenience of explanation, the following description will be made with the opening 7a side of the housing 7 as the upward direction and the bottom 7c side of the housing 7 as the downward direction.

  The housing 7 is formed of, for example, a soft metal such as brass or resin, and includes a cylindrical side portion 7b and a disc-shaped bottom portion 7c as separate structures. At the lower end of the inner peripheral surface 7d of the housing 7, a large-diameter portion 7e having a larger diameter than other portions is formed, and a lid-like member that becomes the bottom portion 7c is, for example, caulked, bonded, or press-fitted to the large-diameter portion 7e. It is fixed by means such as. In addition, the side part 7b and the bottom part 7c of the housing 7 can also be integrally formed with a metal material or a resin material. Alternatively, the seal member 9 and the housing 7 can be integrally formed.

  The bearing sleeve 8 is formed in a cylindrical shape, for example, with a porous body made of sintered metal, in particular, a sintered metal porous body mainly composed of copper. As shown in FIG. 3, the inner peripheral surface 8a of the bearing sleeve 8 is provided with two upper and lower regions which are the radial bearing surfaces of the first radial bearing portion R1 and the second radial bearing portion R2, spaced apart in the axial direction. ing.

  For example, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 as shown in FIG. 4 are formed in the two regions. The upper dynamic pressure groove 8a1 is formed axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions), and the axial dimension X1 of the upper region is lower than the axial center m. It is larger than the axial dimension X2 of the side region. The axial length of the upper radial bearing surface (distance from the upper end to the lower end of the dynamic pressure groove 8a1) is larger than the axial length (distance from the upper end to the lower end of the dynamic pressure groove 8a2) of the lower radial bearing surface. In addition to this, the radial bearing surface may have a shape in which the first radial bearing portion R1 and the second radial bearing portion R2 are continuous, or may have an inner diameter cross-section arc shape or a step shape.

  As shown in FIG. 3, the sealing member 9 as a sealing means has an annular shape and is fixed to the inner peripheral surface of the opening 7 a of the housing 7 by means such as press-fitting and bonding. In this embodiment, the inner peripheral surface 9 a of the seal member 9 is formed in a cylindrical shape, and the lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 b of the bearing sleeve 8.

  A tapered surface is formed on the outer peripheral surface 21 a of the shaft portion 21 that faces the inner peripheral surface 9 a of the seal member 9, and a bottom portion of the housing 7 is provided between the tapered surface and the inner peripheral surface 9 a of the seal member 9. An annular seal space S in which the radial dimension gradually increases from the 7c side toward the opening 7a side is formed. Lubricating oil is injected into the internal space of the housing 7 sealed with the seal member 9, and the inside of the housing 7 is filled with the lubricating oil. In this state, the oil level of the lubricating oil is maintained within the range of the seal space S.

  As shown in FIG. 1A, the shaft member 2 includes a shaft portion 21 and a flange portion 22 that protrudes to the outer diameter side of the shaft portion 21 when viewed from the shape. On the other hand, the shaft member 2 forms a composite structure of resin and metal from the structural aspect. That is, the shaft member 2 includes a metal shaft main body 23 having an outer peripheral surface 23a facing the radial bearing gap, a disk-shaped core member 24 fixed to the shaft main body 23 and protruding toward the outer diameter side of the shaft main body 23, In a state where the core material 24 is covered, the end surfaces (the upper end surface 22a and the lower end surface 22b) have a resin portion 25 that forms a flange portion 22 that faces the thrust bearing gap. The outer peripheral surface 23 a forms the outer peripheral surface 21 a of the shaft portion 21.

  In this embodiment, the shaft body 23 is formed in a solid shape having a cylindrical outer peripheral surface. A fitting portion 23b is provided at the lower end of the shaft body 23 by annularly cutting the outer peripheral portion of the end surface, and the inner peripheral surface 24a of the core member 24 is fitted to the cylindrical surface of the inner diameter portion of the fitting portion 23b. Thus, the core member 24 is positioned in the inner and outer diameter directions. In this case, in the subsequent injection molding process, the core material 24 and the shaft main body 23 are positioned and are carried into the molding die, and the assembly accuracy of both is maintained even within the die by this positioning. Increased product quality stability.

  The core material 24 is formed of a metal material, ceramic, or a resin that is superior in strength to the resin that forms the resin portion 25. In this embodiment, the core member 24 is made of stainless steel having a rust prevention effect, and is formed into a perforated disk shape by plastic working such as press working.

  The core member 24 is integrally fixed to the shaft main body 23 by fixing the inner peripheral surface 24a to the fitting portion 23b of the shaft main body 23 by means such as welding, welding, or adhesion. For example, means such as arc welding or laser welding are used as welding, and means such as ultrasonic welding or laser welding are used as welding. In this embodiment, arc welding is performed in consideration of strength and cost. Used. Further, for example, as shown in FIG. 1B, a welding projection 24b is provided in advance on the inner peripheral surface 24a of the core member 24, and the core member 24 is fixed to the shaft main body by melting the projection 24b. 23 can be integrally fixed. The protrusion 24b is processed at the same time when the core member 24 is formed by plastic processing such as press processing. In this case, since it is not necessary to bother to form the fitting portion 23b in the shaft body 23, the processing can be made easier. The core member 24 may have a hollow washer shape as shown in FIG. 1B or a disk shape.

  The resin part 25 is injection-molded using the core member 24 fixed to the shaft body 23 as an insert part. Thereby, the resin part 25 forms the flange part 22 in the state which coat | covered the fixing | fixed part of the core material 24 and the core material 24, and the shaft main body 23, and coat | covered the lower end of the shaft main body 23. In this state, the axial thickness of the resin portion 25 that covers the core member 24 and forms the upper end surface 22a and the lower end surface 22b of the flange portion 22 is uniform, and escapes and sink marks due to shrinkage during molding occur. It has become difficult to do. Specifically, the thickness is preferably set within a range of 0.2 mm to 1.0 mm, and the upper limit is more preferably 0.5 mm or less. This is because if the wall thickness is less than 0.2 mm, the fluidity of the resin in the mold during molding deteriorates. If it exceeds 0.5 mm, especially if it exceeds 1.0 mm, the resin molded part shrinks when solidified. Or it is because the dimensional change accompanying the temperature change after shaping | molding becomes remarkable. In FIG. 1A, the resin portion 25 that forms the outer peripheral surface of the flange portion 22 has the same thickness as the resin portion 25 that forms the upper and lower end surfaces 22a and 22b. Since the influence of bearings and sink marks on the bearing performance is small, the wall thickness may be different from these.

  In this embodiment, since the lower end of the shaft body 23 is covered with the resin portion 25, for example, a gate for filling the molten resin is provided at a position corresponding to the axis of the shaft body 23 of the molding die. Can do. According to this, since the molten resin supplied from the gate to the cavity of the molding die is uniformly diffused toward the outer diameter side, the generation of welds is suppressed and the molding accuracy of the flange portion is increased. In addition, LCP, PPS, etc. can be used as resin of the flange part 22, and fillers, such as glass fiber and carbon fiber, are mix | blended with these resin in a suitable quantity according to a use.

  Thus, in the present invention, since the core member 24 is fixed to the shaft main body 23 in a state of projecting to the outer diameter side of the shaft main body 23, the shear load acting on the flange portion 22 is applied to the flange portion 22. Instead of the resin portion 25 to be formed, the core material 24 can be mainly used. Thereby, the fracture | rupture of the shaft member 2 which makes the origin the edge part 26 between the shaft part 21 and the flange part 22 used as the weakest part at the time of the tension | pulling of the shaft member 2 can be suppressed, and the drawing strength of the flange part 22 is suppressed. Improvement is achieved. Further, by disposing the core member 24 protruding to the outer diameter side of the shaft main body 23 in the flange portion 22, the proof stress (bending rigidity) against bending deformation of the flange portion 22 is improved. As a result, the bending deformation of the flange portion 22 is suppressed, and it is possible to prevent the accuracy of the thrust bearing gaps respectively facing the upper end surface 22a or the lower end surface 22b of the flange portion 22 from being lowered. Further, the molding accuracy of the flange portion 22, for example, the flatness of the flange portion end faces 22 a and 22 b and the perpendicularity between the flange portion 22 and the shaft portion 21 depend on the molding surface accuracy of the molding die. Therefore, if the mold accuracy is sufficiently ensured, when fixing the core member 24 to the shaft body 23, a particularly high fixing accuracy is not required, and the fixing process between them can be simplified.

  Dynamic pressure groove regions serving as thrust bearing surfaces for generating dynamic pressure are formed on both end faces (axial end faces of the resin part 25) 22a and 22b of the flange part 22, respectively. Although not shown, for example, a plurality of dynamic pressure grooves having a spiral shape or a herringbone shape are formed on the thrust bearing surface, and this dynamic pressure groove region is formed simultaneously with the insert molding of the flange portion 22 (resin portion 25). Molded.

  The shaft portion 21 of the shaft member 2 is inserted into the inner periphery of the bearing sleeve 8, and the flange portion 22 is accommodated between the lower end surface 8 c of the bearing sleeve 8 and the inner bottom surface 7 c 1 of the housing 7. Two radial bearing surfaces on the upper and lower sides of the inner peripheral surface 8a of the bearing sleeve 8 are opposed to the outer peripheral surface 21a of the shaft portion 21 (the outer peripheral surface 23a of the shaft main body 23) via a radial bearing gap, respectively, and the radial bearing portion R1 and A radial bearing portion R2 is configured. The thrust bearing surface formed on the upper end surface 22a of the flange portion 22 is opposed to the lower end surface 8c of the bearing sleeve 8 via a thrust bearing gap, thereby forming a thrust bearing portion T1. The thrust bearing surface formed on the lower end surface 22b of the flange portion 22 is opposed to the inner bottom surface 7c1 of the bottom portion 7c of the housing 7 through a thrust bearing gap, thereby forming the thrust bearing portion T2.

  From the above configuration, when the shaft member 2 rotates, the dynamic pressure of the lubricating oil is generated in the radial bearing gaps of the radial bearing portions R1 and R2 by the action of the dynamic pressure grooves 8a1 and 8a2 as described above. The shaft portion 21 is supported in a non-contact manner rotatably in the radial direction by an oil film of lubricating oil formed in each radial bearing gap. At the same time, the dynamic pressure of the lubricating oil is generated in the thrust bearing gaps of the thrust bearing portions T1 and T2 by the action of the dynamic pressure grooves formed on both end faces 22a and 22b of the flange portion 22, and the flange portion 22 of the shaft member 2 is It is supported in a non-contact manner so as to be rotatable in both thrust directions by an oil film of lubricating oil formed in each thrust bearing gap.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

  In this embodiment, the metal shaft main body 23 has a solid shape. However, the shaft main body 23 has a hollow shape, and the resin shown in FIG. The unit 25 may be integrated.

  The present invention is applicable to all the hydrodynamic bearing devices including the shaft member 2 having the shaft portion 21 and the flange portion 22. That is, in the above embodiment, the example in which the dynamic pressure grooves are formed in the both end faces 22a and 22b of the flange portion has been described. However, the present invention is not limited to this, and the face facing the both end faces 22a and 22b (for example, the bottom of the bearing sleeve 8). A dynamic pressure groove may be formed on the side end face 8 c or the inner bottom face 7 c 1 of the bottom 7 c of the housing 7.

(A) is sectional drawing of the shaft member which concerns on one Embodiment of this invention, (b) is sectional drawing of the core material of the other example provided in the end of a shaft member. It is sectional drawing of the spindle motor incorporating the dynamic pressure bearing apparatus provided with the shaft member. It is sectional drawing of a hydrodynamic bearing apparatus. It is sectional drawing of a bearing sleeve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 6 Casing 7 Housing 7a Opening part 7c Bottom part 8 Bearing sleeve 8a1, 8a2 Dynamic pressure groove 9 Seal member 21 Shaft part 22 Flange part 22a Upper side end surface 22b Lower side End surface 23 Shaft body 24 Core material 25 Resin portion 26 Edge portions R1, R2 Radial bearing portions T1, T2 Thrust bearing portions

Claims (4)

A shaft member, a radial bearing that supports the shaft member in the radial direction in a non-contact manner by the dynamic pressure action of the fluid generated in the radial bearing gap, and a shaft member in the thrust direction in a non-contact manner by the fluid pressure action of the fluid generated in the thrust bearing gap. In the hydrodynamic bearing device having a thrust bearing portion to support,
In a state where the shaft member is made of a metal shaft main body having an outer peripheral surface facing the radial bearing gap, a core member fixed to the shaft main body and protruding to the outer diameter side of the shaft main body, and the core member fixed to the shaft main body. A resin part that is injection-molded and covers the core material to form a disc-shaped flange part whose end face faces the thrust bearing gap;
The core material is formed in a perforated disk shape having a hole in the center, and is fixed in a state where it is in contact with one end surface of the shaft body, and the hole provided in the core material is closed with a resin portion . One end and a core material are coat | covered with the resin part, The dynamic pressure bearing apparatus characterized by the above-mentioned. 2. The hydrodynamic bearing device according to claim 1, wherein the core material is made of metal and is fixed to the shaft body by welding. 2. The hydrodynamic bearing device according to claim 1, wherein a portion of the resin portion facing the thrust bearing gap has a uniform thickness. 4. The hydrodynamic bearing device according to claim 3, wherein a thickness of a portion of the resin portion facing the thrust bearing gap is 0.2 mm or more and 1.0 mm or less.