JP4954478B2 - Hydrodynamic bearing device - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device in which a rotating member is supported by a lubricating film of fluid generated in a bearing gap. This bearing device is a spindle motor such as an information device, for example, a magnetic disk device such as an HDD, an optical disk device such as a CD-ROM, CD-R / RW, DVD-ROM / RAM, or a magneto-optical disk device such as MD or MO, It is suitable for polygon scanner motors of laser beam printers (LBP) and other small motors.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a fluid bearing having characteristics excellent in the required performance has been studied or actually used. .

  This type of fluid dynamic bearing includes a dynamic pressure bearing having a dynamic pressure generating section that generates dynamic pressure in a fluid (for example, lubricating oil) in a bearing gap, and a so-called circular bearing (bearing) that does not include the dynamic pressure generating section. The bearings are roughly classified into bearings having a perfect circular cross section.

  For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk drive device such as an HDD, both a radial bearing portion that supports a shaft member in the radial direction and a thrust bearing portion that supports the shaft direction in a thrust direction may be configured by dynamic pressure bearings. is there. As a radial bearing part in this type of hydrodynamic bearing device, for example, a dynamic pressure groove as a dynamic pressure generating part is formed on either the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member facing the bearing sleeve. In addition, there is known one that forms a radial bearing gap between both surfaces (see, for example, Patent Document 1).

Further, in many cases, a bearing sleeve constituting the bearing is formed of a sintered metal for the purpose of circulating and supplying lubricating oil to the bearing portion to obtain stable bearing rigidity. This type of bearing sleeve is formed by compression-molding a metal powder mainly composed of Cu powder or Fe powder or both into a predetermined shape (mostly cylindrical) and then sintering. This bearing sleeve is used in a state in which internal holes are impregnated with lubricating oil (see, for example, Patent Document 2).
JP 2003-239951 A Japanese Patent Laid-Open No. 11-182551

  However, when the hydrodynamic bearing device is used in a high temperature atmosphere, for example, depending on the temperature or the type of the lubricating oil, the viscosity of the lubricating oil supplied to the bearing may decrease, and the bearing rigidity may be insufficient. is there. On the other hand, in a low temperature atmosphere, the viscosity of the lubricating oil increases, and the loss torque at the time of rotation (particularly at the start of rotation) may increase.

  In particular, in consideration of use under the action of axial compressive load or moment load, when the shaft member to be rotationally supported is formed of a high-strength material such as stainless steel (SUS), a bearing sleeve is formed. Often, the linear expansion coefficient of the material to be used exceeds the linear expansion coefficient of the material forming the shaft member. In this case, for example, when the temperature is high, the radial bearing gap is widened, which may further reduce the bearing rigidity. On the other hand, at low temperatures, the radial bearing gap is narrowed, and therefore, the torque loss during rotation may be further increased in combination with an increase in the viscosity of the lubricating oil.

  The subject of this invention is providing the hydrodynamic bearing apparatus which suppressed the fall of the bearing rigidity accompanying a temperature change, and reduced the loss torque at the time of rotation.

In order to solve the above-described problems, the present invention includes a shaft member and a bearing sleeve that rotatably supports the shaft member. The shaft member is formed of SUS, and the bearing sleeve is made of pure Cu powder with Ni content of 25 wt%. It was obtained by compressing and molding a mixed metal powder containing an Fe-Ni alloy powder containing 50 wt% or less and SUS powder, and then excluding the Fe-Ni alloy powder from the mixed metal powder. The powder is based on pure Cu powder and the balance is made of SUS powder, Sn powder, and graphite, and the proportion of pure Cu powder in the mixed metal powder is 30 wt% or more and 80 wt% or less, Fe-Ni alloy Provided is a hydrodynamic bearing device characterized in that the ratio of the powder is 10 wt% or more and less than 40 wt% .

Thus, by forming a bearing sleeve by mixing a metal powder exhibiting a low linear expansion coefficient (˜8.0 × 10 ⁻⁶ / ° C.) with Cu powder, the linear expansion coefficient of the bearing sleeve can be reduced by the conventional composition. This is smaller than that of the (Cu, Fe) bearing sleeve. For this reason, when the viscosity of the lubricating oil decreases, for example, at a high temperature, it is possible to suppress the radial bearing gap from spreading as much as possible. In addition, when the viscosity of the lubricating oil increases, such as at low temperatures, the radial bearing gap can be minimized as much as possible. Therefore, it is possible to suppress a decrease in bearing rigidity as much as possible even in a high / low temperature atmosphere or an atmosphere where temperature change is remarkable, and to reduce loss torque during rotation.

  As the metal exhibiting the linear expansion coefficient, for example, an Fe—Ni alloy containing Ni in an amount of 25 wt% to 50 wt% can be used in addition to a single metal of Mo or Tw. Among these, those containing 30 wt% or more and 45 wt% or less of Ni can be used more preferably. Specific examples of the material include Invar type (Fe-36Ni) alloy powder, Super-Invar type (Fe-32Ni-4Co, Fe-31Ni-5Co) alloy powder, and Kovar type alloy powder. These materials have remarkable low linear expansion characteristics and can be used particularly preferably.

  As the mixed metal powder containing these Cu powder and low linear expansion metal powder, those containing 30 wt% or more and 90 wt% or less of Cu powder and 10 wt% or more and 70 wt% or less of low linear expansion metal powder can be preferably used. This is because if the content of the low linear expansion metal powder is less than 10 wt%, the effect of reducing the linear expansion coefficient by blending the low linear expansion metal powder may be insufficient. Also, if the Cu powder content is less than 30 wt%, the formability (workability) of the bearing sleeve is lowered, and the required dimensional accuracy cannot be ensured, or there is a risk of problems such as excessive wear of the mold. Because there is.

  Further, for the purpose of reinforcing the bearing sleeve 8, it is also possible to further mix SUS powder with the mixed metal powder including the Cu powder and the Fe-Ni alloy powder. As a result, the effect of reinforcing the bearing sleeve can be obtained, and the wear resistance of the bearing sleeve can be improved.

  The mixed metal powder containing SUS powder preferably contains 30 wt% or more and 80 wt% or less of Cu powder, 10 wt% or more and 65 wt% or less of low expansion metal powder, and 5 wt% or more and 60 wt% or less of SUS powder. By blending each powder within the above range, both the low linear expansion characteristic and the wear resistance of the bearing sleeve can be achieved at a high level.

  As described above, the bearing sleeve is formed of Cu powder and Fe—Ni alloy powder as low linear expansion metal powder, or mixed metal powder of Cu powder and Fe—Ni alloy powder, and SUS powder. A low melting point metal such as Sn or Zn can also be added to the metal powder. This low melting point metal melts (liquid phase) during sintering and functions as a binder for Cu powder or low linear expansion metal powder. In addition, the low melting point metal here refers to a metal that melts at a temperature (sintering temperature) or lower during sintering after compression molding of the mixed metal powder.

  The bearing sleeve formed of the mixed metal powder having the above composition may have a configuration in which a dynamic pressure generating portion is formed on the inner peripheral surface thereof. In this case, a fluid dynamic pressure action is generated in the radial bearing gap between the dynamic pressure generating portion forming region serving as the radial bearing surface of the bearing sleeve and the outer peripheral surface of the shaft member to be supported, and the shaft member is not rotatable. Contact supported.

  The hydrodynamic bearing device including the bearing sleeve can be provided as a spindle motor of a disk device incorporating the hydrodynamic bearing device, for example.

  As described above, according to the present invention, it is possible to provide a hydrodynamic bearing device that suppresses a decrease in bearing rigidity due to a temperature change and reduces a loss torque during rotation.

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

  FIG. 1 conceptually shows one configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device (dynamic pressure 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 includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 mounted on the shaft member 2, and a radial direction, for example. A stator coil 4 and a rotor magnet 5 are provided to face each other through a gap. The stator coil 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The disk hub 3 holds one or a plurality (two in FIG. 1) of a disk-shaped information storage medium (hereinafter simply referred to as a disk) D such as a magnetic disk on its outer periphery. 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.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a shaft member 2, a housing 7, a bearing sleeve 8 fixed to the housing 7, and a seal member 9 as main components. For convenience of explanation, the bottom 7b side of the housing 7 will be described below, and the side opposite to the bottom 7b will be described as the upper side.

  The shaft member 2 is formed of a metal material such as stainless steel, for example, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. In addition, the shaft member 2 can also have a hybrid structure of a metal material and a resin material. In this case, the sheath portion including at least the outer peripheral surface 2a1 of the shaft portion 2a is formed of the metal, and the remaining portion (for example, the shaft portion) The core part of the part 2a and the flange part 2b) are formed of resin. In order to secure the strength of the flange portion 2b, the flange portion 2b can be made of a resin / metal hybrid structure, and the core portion of the flange portion 2b can be made of metal together with the sheath portion of the shaft portion 2a.

  The housing 7 is injection-molded with a resin composition having LCP, PPS, PEEK or the like as a base resin. For example, as shown in FIG. 2, a cylindrical portion 7 a and a bottom portion 7 b integrally formed at the lower end of the cylindrical portion 7 a Consists of. Examples of the resin composition constituting 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 A material in which an appropriate amount of a fibrous or powdery conductive filler such as nanomaterials or various metal powders is blended with the base resin according to the purpose can be used.

  For example, although not shown, a region in which a plurality of dynamic pressure grooves are arranged in a spiral shape is formed on the entire upper surface 7b1 of the bottom 7b or a partial annular region as a thrust dynamic pressure generating portion. This dynamic pressure groove forming region faces the lower end surface 2b2 of the flange portion 2b, and forms a thrust bearing gap of the second thrust bearing portion T2 between the lower end surface 2b2 and the shaft member 2 when the shaft member 2 rotates (see FIG. 2). reference). This type of dynamic pressure groove is formed at the same time as the housing 7 by forming a groove mold for forming the dynamic pressure groove in a required part of the mold for molding the housing 7 (a part for molding the upper end surface 7b1). can do. Further, a step portion 7d that engages with the lower end surface 8c of the bearing sleeve 8 and performs axial positioning is integrally formed at a position that is separated from the upper end surface 7b1 in the axial direction by a predetermined dimension.

  The bearing sleeve 8 is formed of a sintered metal porous body mainly composed of Cu and a low linear expansion metal and is formed in a cylindrical shape, and is fixed to the inner peripheral surface 7 c of the housing 7.

  A dynamic pressure groove as a radial dynamic pressure generating portion is formed on the entire inner surface 8a of the bearing sleeve 8 or a partial cylindrical region. In this embodiment, for example, as shown in FIG. 3A, two regions having a plurality of dynamic pressure grooves 8a1 and 8a2 arranged in a herringbone shape are formed apart from each other in the axial direction. In the formation region of the upper dynamic pressure groove 8a1, the dynamic pressure groove 8a1 is formed to be axially asymmetric with respect to the axial center m (the axial center of the upper and lower inclined groove regions). The axial dimension X1 of the upper region is larger than the axial dimension X2 of the lower region.

  For example, as shown in FIG. 3B, a region where a plurality of dynamic pressure grooves 8c1 are arranged in a spiral shape is formed as a thrust dynamic pressure generating portion on the entire lower surface 8c of the bearing sleeve 8 or a partial annular region. Is done.

  The bearing sleeve 8 includes, for example, pure Cu powder, Super-Invar type alloy powder (hereinafter simply referred to as S. Invar powder) as low linear expansion metal powder, and SUS powder (in some cases, a low melting point metal). It is obtained by compressing and molding a mixed metal powder containing Sn powder, P powder, or an alloy powder thereof as a powder into a cylindrical shape and sintering it at a predetermined sintering temperature. In this embodiment, dimension sizing, rotational sizing, and groove sizing are further performed in this order, whereby the sintered body is sized to a predetermined size, and dynamic pressure grooves 8a1, 8c1, etc. are formed on the surface of the sintered body. The In addition, for the purpose of improving the moldability at the time of compression molding or the sliding characteristics of the finished product, a solid lubricant such as graphite can be further blended with the mixed metal powder.

  The size of the pure Cu powder particles used as the material of the bearing sleeve 8 is preferably equal to or smaller than that of S. Invar powder or SUS powder. Further, the blending ratio of the pure Cu powder to the S. Invar powder and the SUS powder in this embodiment is as follows: pure Cu powder: 30 wt% to 80 wt%, S. Invar powder: 10 wt% to 65 wt%, SUS powder: It is preferably 5 wt% or more and 60 wt% or less. This is because if the blending amount of the SUS powder is less than 5 wt%, the reinforcing effect and the wear resistance improving effect by the SUS powder may be insufficient. In addition, pure Cu powder is excellent in spreadability and is a preferable material for enhancing the moldability of the sintered body, particularly sizing workability after sintering, but when its blending ratio is reduced, sizing processing after sintering, In particular, the sizing of the dynamic pressure grooves 8a1, 8c1, etc. may be difficult. From such a viewpoint, the blending ratio of the pure Cu powder is preferably 30 wt% or more.

  The temperature during sintering (sintering temperature) is preferably 750 ° C. or higher and 1000 ° C. or lower, and more preferably 800 ° C. or higher and 950 ° C. or lower. This is because when the sintering temperature is less than 750 ° C., the sintering action between the powders is not sufficient, so the strength of the sintered body is reduced. When the sintering temperature exceeds 1000 ° C., for the same reason as described above, that is, during sizing processing This is because there is a risk of disturbing the groove formability.

  Moreover, when mix | blending Sn powder with the said mixed metal powder, the mixture ratio is good to set it as 0.2 wt% or more and 10 wt% or less with respect to all the mixed metal powders. Within this blending range, the Sn powder melts (liquid phase) at the sintering temperature and functions as a binder between other powders (pure Cu powder, S. Invar powder, etc.). Further, by alloying with pure Cu powder within the above blending range, the excellent workability (especially plastic deformability) inherent in pure Cu is moderately maintained while improving the wear resistance of the sintered body. be able to.

In this way, by using a mixed metal powder including a predetermined proportion of pure Cu powder and low expansion metal powder (S. Invar powder), and further SUS powder and Sn powder, it is high in addition to a low linear expansion coefficient. It is possible to obtain a bearing sleeve 8 having mechanical strength and excellent in sliding characteristics (wear resistance, conformability) and dimensional accuracy of the bearing surface. The density of the bearing sleeve 8 as a finished product is, for example, 7.0 to 7.4 [g / cm ³ ], and the surface opening ratio is 2 to 10 [vol%]. As an example, the pure Cu powder, S.I. FIG. 11 shows a micrograph of the inside of the bearing sleeve 8 when the bearing sleeve 8 is formed of a mixed metal powder containing Invar powder, SUS powder, and Sn powder.

  The seal member 9 is formed in an annular shape with, for example, a resin material or a metal material, and is disposed on the inner periphery of the upper end portion of the cylindrical portion 7 a of the housing 7. An inner peripheral surface 9a of the seal member 9 is opposed to a tapered surface 2a2 provided on the outer periphery of the shaft portion 2a via a predetermined seal space S. The tapered surface 2a2 of the shaft portion 2a is gradually reduced in diameter toward the upper side (outside of the housing 7), and also functions as a capillary force seal and a centrifugal force seal when the shaft member 2 rotates.

  After the shaft member 2 and the bearing sleeve 8 are inserted into the inner periphery of the housing 7 and the bearing sleeve 8 is positioned in the axial direction by the step portion 7d, the bearing sleeve 8 is placed on the inner peripheral surface 7c of the housing 7, for example, Fix by means of adhesion, press-fitting, welding, etc. The seal member 9 is fixed to the inner peripheral surface 7 c of the housing 7 with the lower end surface 9 b abutting against the upper end surface 8 b of the bearing sleeve 8. Then, the assembly of the hydrodynamic bearing device 1 is completed by filling the internal space of the housing 7 with lubricating oil. At this time, the oil level of the lubricating oil filled in the internal space of the housing 7 (including the internal holes of the bearing sleeve 8) sealed by the seal member 9 is maintained within the range of the seal space S.

  When the shaft member 2 rotates, a region (a region where the dynamic pressure grooves 8a1 and 8a2 are formed in the upper and lower portions) of the inner peripheral surface 8a of the bearing sleeve 8 is a radial bearing gap between the outer peripheral surface 2a1 of the shaft portion 2a. Opposite through. As the shaft member 2 rotates, the lubricating oil in the radial bearing gap is pushed toward the axial center m of the dynamic pressure grooves 8a1 and 8a2, and the pressure rises. The dynamic pressure action of the dynamic pressure grooves 8a1 and 8a2 constitutes a first radial bearing portion R1 and a second radial bearing portion R2 that support the shaft portion 2a in a non-contact manner (see FIG. 2).

  At the same time, the thrust bearing gap between the upper end surface 2b1 of the flange portion 2b and the region (the dynamic pressure groove 8c1 formation region) that becomes the thrust bearing surface of the lower end surface 8c of the bearing sleeve 8 facing the flange portion 2b, and the flange portion 2b. An oil film of lubricating oil is formed in the thrust bearing gap between the lower end surface 2b2 of the upper portion and the region (dynamic pressure groove forming region) of the upper end surface 7b1 of the bottom portion 7b opposite to the thrust bearing surface by the dynamic pressure action of the dynamic pressure groove. Are formed respectively. The pressure of these oil films forms a first thrust bearing portion T1 and a second thrust bearing portion T2 that support the flange portion 2b in a non-contact manner so as to be rotatable in both thrust directions (see FIG. 2).

  When used in a high temperature atmosphere, the shaft member 2 and the bearing sleeve 8 both expand, and the outer peripheral surface 2a1 of the shaft portion 2a and the inner peripheral surface 8a including the radial bearing surface of the bearing sleeve 8 are displaced to the outer diameter side. Here, since the bearing sleeve 8 is formed of a mixed metal powder containing S. Invar powder, the displacement amount of the inner peripheral surface 8a of the bearing sleeve 8 with the temperature rise is the displacement of the outer peripheral surface 2a1 of the shaft portion 2a. It is almost equal to or smaller than the amount. Thereby, the radial bearing gap between the radial bearing surface of the inner circumferential surface 8a and the outer circumferential surface 2a1 facing the radial bearing surface can be kept at least at the same level as the gap before the temperature rises. Therefore, even when the viscosity of the lubricating oil is reduced due to a temperature rise, the reduction in bearing rigidity can be suppressed as much as possible. Further, when the temperature is lowered, the radial bearing gap between the inner peripheral surface 8a and the outer peripheral surface 2a1 can be kept at least at the same level as before the decrease. Therefore, even when the viscosity of the lubricating oil increases as the temperature decreases, the loss torque at the time of rotation (particularly at the start of rotation) can be reduced as much as possible.

  In addition to the S. Invar powder, the SUS powder is mixed with the mixed metal powder, whereby the hardness of the region (dynamic pressure groove 8a1, 8a2 forming region) that becomes the radial bearing surface of the inner peripheral surface 8a is increased. As a result, the difference in hardness between the opposing surfaces 2a1 and 8a is reduced, and even when the bearing sleeve 8 and the shaft portion 2a slide in contact with each other (for example, at the start of rotation), either one or both members Can be prevented as much as possible.

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

  In the above embodiment, the cylindrical portion 7a and the bottom portion 7b are integrally molded with the resin as the housing 7. However, for example, although not shown, the cylindrical portion 7a is separated from the bottom portion 7b. It can also be molded with resin. In this case, for example, the seal member 9 can be molded integrally with the cylindrical portion 7a from resin, and according to this, the axial positioning of the bearing sleeve 8 can be performed under the seal portion molded integrally with the cylindrical portion 7a. This can be done by bringing the upper end surface 8b of the bearing sleeve 8 into contact with the end surface. The housing 7 is not limited to an injection-molded product made of a resin material, and may be, for example, a turning product of a metal material or a pressed product.

  In the above embodiment, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are configured to generate the dynamic pressure action of the lubricating fluid by the herringbone shape or spiral shape dynamic pressure grooves. However, the present invention is not limited to this.

  For example, so-called step bearings or multi-arc bearings may be employed as the radial bearing portions R1 and R2.

  FIG. 4 shows an example in which one or both of the radial bearing portions R1 and R2 are constituted by multi-arc bearings. In the same figure, the area | region used as the radial bearing surface of the internal peripheral surface 8a of the bearing sleeve 8 is comprised by several arc surface 8a3 (this figure 3 arc surface). Each arc surface 8a3 is an eccentric arc surface centered at a point offset from the rotation axis O by an equal distance, and is formed at equal intervals in the circumferential direction. An axial separation groove 8a4 is formed between each eccentric arc surface 8a3.

  By inserting the shaft portion 2a of the shaft member 2 into the inner peripheral surface 8a of the bearing sleeve 8, the eccentric arc surface 8a3 and the separation groove 8a4 of the bearing sleeve 8 and the perfect circular outer peripheral surface 2a1 of the shaft portion 2a are interposed. The radial bearing gaps of the first and second radial bearing portions R1 and R2 are respectively formed. In the radial bearing gap, a region formed by the eccentric arc surface 8a3 and the perfect circular outer peripheral surface 2a1 is a wedge-shaped gap 8a5 in which the gap width is gradually reduced in the circumferential direction. The reduction direction of the wedge-shaped gap 8a5 coincides with the rotation direction of the shaft member 2.

  FIG. 5 shows another embodiment of the multi-arc bearing constituting the first and second radial bearing portions R1 and R2. In this embodiment, in the configuration shown in FIG. 4, the predetermined region θ on the minimum gap side of each eccentric arc surface 8 a 3 is configured by concentric arcs with the rotation axis O as the center. Accordingly, the radial bearing gap (minimum gap) 8a6 in each predetermined region θ is constant. The multi-arc bearing having such a configuration may be referred to as a tapered flat bearing.

  In FIG. 6, a region that becomes a radial bearing surface of the inner peripheral surface 8 a of the bearing sleeve 8 is formed by three arc surfaces 8 a 7, and the centers of the three arc surfaces 8 a 7 are offset from the rotation axis O by an equal distance. Yes. In each region defined by the three eccentric arc surfaces 8a7, the radial bearing gap 8a8 has a shape that is gradually reduced with respect to both circumferential directions.

  The multi-arc bearings of the first and second radial bearing portions R1 and R2 described above are all so-called three-arc bearings, but are not limited thereto, so-called four-arc bearings, five-arc bearings, and more than six arcs. You may employ | adopt the multi-arc bearing comprised by the several circular arc surface. Further, in addition to the configuration in which the two radial bearing portions are separated from each other in the axial direction as in the radial bearing portions R1 and R2, one radial bearing portion extends over the upper and lower regions of the inner peripheral surface 8a of the bearing sleeve 8. It is good also as a structure which provided.

  One or both of the thrust bearing portions T1 and T2, for example, are not shown in the figure, but a plurality of radial groove-shaped dynamic pressure grooves are provided at predetermined intervals in the circumferential direction in a region serving as a thrust bearing surface. It can also be constituted by a step bearing, a so-called corrugated bearing (the corrugated step mold) or the like.

  Moreover, although the radial bearing part R1 and R2 and the thrust bearing part T1 and T2 were comprised by the dynamic pressure bearing in the above embodiment, it can also comprise by bearings other than this. For example, the inner peripheral surface 8a of the bearing sleeve 8 serving as a radial bearing surface is a perfect circular inner peripheral surface not provided with the dynamic pressure groove 8a1 or the circular arc surface 8a3 as a dynamic pressure generating portion, and the shaft portion opposed to the inner peripheral surface A so-called perfect circle bearing can be constituted by the perfect circular outer peripheral surface 2a1 of 2a.

  Further, in the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and forms a lubricating film in the radial bearing gap or the thrust bearing gap. A fluid capable of forming a lubricating film, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or lubricating grease may be used.

  In order to demonstrate the effect of the present invention, a test body (Examples 1 to 4) formed of a mixed metal powder containing Cu powder and a low expansion metal powder, and a metal powder (Cu powder and Fe powder of conventional composition) With respect to the test body (comparative example) formed with the mixed powder), a linear expansion coefficient measurement test was performed, and the linear expansion coefficient was evaluated and compared. Moreover, among the above test bodies (Examples 1 to 4), in addition to the Cu powder and the low expansion metal powder, the test body (Examples 2 to 4) formed of a mixed metal powder further containing a SUS powder and the conventional product. A wear test was conducted on (Comparative Example), and the wear resistance was evaluated and compared.

  As test materials, CE-15 manufactured by Fukuda Metal Foil Powder Co., Ltd. was used as pure Cu powder, and S.P. SUPER INVAR manufactured by Atmix Co., Ltd. was used as the Invar powder, DAP410L (SUS410L) manufactured by Daido Steel Co., Ltd. as the SUS powder, and NC100.24 manufactured by Heganes Co., Ltd. as the Fe powder. . In addition, Sn-At-W350 manufactured by Fukuda Metal Foil Powder Co., Ltd. is used for Sn powder as a low melting point metal, and ECB-250 manufactured by Nippon Graphite Industry Co., Ltd. is used for graphite as a solid lubricant. It was. The sintering temperature of the test piece (sintered metal material) was 870 ° C. in both the comparative example and the example. The composition of the mixed metal powders of the comparative example and the example are as shown in FIG. Further, the particle size distribution of each powder is as shown in FIG.

The linear expansion coefficient measurement test was performed under the following conditions in both the comparative example and the example.
Test piece: outer diameter φ7.5 mm × axial width 10 mm
Measurement temperature: -40 ° C to 120 ° C
Temperature increase rate: 5 ° C / min
Load: 10 gf
Nitrogen gas flow rate: 200 ml / min

The abrasion test was performed under the following conditions in both the comparative example and the example.
Test piece: outer diameter φ7.5 mm × axial width 10 mm
Counter specimen: Outer diameter 40 mm x Axial width 4 mm
Peripheral speed: 50 m / min
Surface pressure: 1.3 MPa
Lubricating oil: Ester oil (12mm ² / s)
Test time: 3 hrs

  FIG. 9 shows the linear expansion coefficient measurement test results. As shown in FIG. The test body not containing Invar powder (comparative example) showed a high linear expansion coefficient. On the other hand, S.M. In the specimens (Examples 1 to 4) containing Invar powder, the value of the linear expansion coefficient was small.

  FIG. 10 shows the wear test results. As shown in the figure, remarkable wear was confirmed in the test body (comparative example) not containing SUS powder. On the other hand, the amount of wear (wear depth and wear scar area) in the specimens containing SUS powder (Examples 2 to 4) was much smaller than that of the specimen having the conventional composition (Comparative Example). It was.

  From the above, it was confirmed that any combination of the tested S. Invar powder and SUS powder (Examples 2 to 4) satisfied both the linear expansion coefficient reduction effect and the wear resistance improvement effect. It was.

It is sectional drawing of the spindle motor for information devices incorporating the hydrodynamic bearing apparatus which concerns on one Embodiment of this invention. It is sectional drawing of a hydrodynamic bearing apparatus. They are (a) longitudinal cross-sectional view and (b) bottom view of the bearing sleeve, respectively. It is sectional drawing which shows the other structural example of a radial bearing part. It is sectional drawing which shows the other structural example of a radial bearing part. It is sectional drawing which shows the other structural example of a radial bearing part. It is a figure which shows the composition of a test material. It is a figure which shows the particle size distribution of a powder particle. It is a figure which shows a linear expansion coefficient measurement test result. It is a figure which shows an abrasion test result. It is a microscope picture which shows the inside of a bearing sleeve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid dynamic bearing apparatus 2 Shaft member 3 Disc hub 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 8 Bearing sleeve 8a1, 8a2 Dynamic pressure groove 8c1 Dynamic pressure groove 9 Seal member S Seal space R1, R2 Radial bearing part T1, T2 Thrust bearing Part

Claims (4)

In a hydrodynamic bearing device including a shaft member and a bearing sleeve that rotatably supports the shaft member,
The shaft member is made of SUS,
The bearing sleeve is obtained by compressing and molding a mixed metal powder in which pure Cu powder is mixed with Fe-Ni alloy powder containing Ni in an amount of 25 wt% to 50 wt% and SUS powder ,
Of the mixed metal powder, the powder excluding the Fe-Ni alloy powder is based on pure Cu powder, and the balance is composed of SUS powder, Sn powder, and graphite. A hydrodynamic bearing device , wherein the ratio is 30 wt% or more and 80 wt% or less, and the ratio of the Fe—Ni alloy powder is 10 wt% or more and less than 40 wt% . The Fe-Ni alloy powder is an Invar type alloy powder or Super-Invar.
The hydrodynamic bearing device according to claim 1, which is a mold alloy powder.   The hydrodynamic bearing device according to claim 1, wherein a dynamic pressure generating portion is provided on an inner peripheral surface of the bearing sleeve. The motor provided with the hydrodynamic bearing apparatus in any one of Claims 1-3 .