JP2004232681A - Gas dynamic pressure bearing device, motor equipped with it, and information apparatus equipped with the motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas dynamic pressure bearing device and a motor equipped with it capable of widening the selectability of the material of the stationary side and the rotary side and reducing the change in the size of the gap generated by a temperature change. <P>SOLUTION: The gas dynamic pressure bearing device is equipped with shafts 22 and 23, a sleeve 32 whose inside surface confronts the outside surface of the shaft 23 through a micro-gap 32b to work as a gas dynamic pressure bearing, and a hub 31 approximately in a cylindrical shape fitted on the sleeve 32 while a surface pressure is applied and is structured so that dynamic pressure generating grooves 23a and 23b are formed at least at either of the outside surface of the shaft 23 and the inside surface of the sleeve 32, wherein the condition α<SB>1</SB><α<SB>0</SB><α<SB>2</SB>should be met, where α<SB>0</SB>, α<SB>1</SB>, and α<SB>2</SB>are the coefficients of linear expansion of the shaft 23, the sleeve 32, and the hub 31. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

で表すことができる。
【００１０】
Ｐｍによって、スリーブ内径は下記式（４）で表されるｕだけ収縮する。
【数２】

したがって、常温におけるラジアル隙間Ｃｒは
Ｃｒ＝Ｒ_１−Ｒ_０−ｕ・・・（５）
となる。
【００１１】
次に温度がΔＴだけ上昇したとすると、面圧Ｐｍ及びスリーブ内径の収縮量は下記式（６）及び（８）となる。
【数３】

【数４】

【数５】

【００１２】
また、温度上昇後のラジアル間隙Ｃｒ’は
Ｃｒ’＝Ｒ_１’−Ｒ_０’−ｕ’
＝（Ｒ_１α_１−Ｒ_０α_０）ΔＴ−ｕ’・・・（９）
となる。従って、ラジアル間隙の変化量は、
【数６】

で求められる。但し、ｕ’は、式（６）及び式（８）に式群（７）の各式を代入して定まる値である。
【００１３】
この発明の軸受け装置は上記の作用を生じることから、この軸受け装置と、前記シャフトを固定するブラケットと、ブラケットに取り付けられたステータと、ステータと対向するようにハブに取り付けられたマグネットとを備えたモータは、安定して動作する。
【００１４】
【発明の実施の形態】
この発明の実施形態を図面と共に説明する。図１は、実施形態に係るハードディスク装置（情報機器に相当）を模式的に示す回転中心軸方向（以下、軸方向という。）断面図である。ハードディスク装置１０は、内部が清浄に保たれたハウジング１１と、ハウジング１１内に設置された動圧軸受けモータ（以下、単にモータという。）１及びアクチュエータ１２を備えている。モータ１には複数枚（図示では４枚）の磁気ディスク６が軸方向に搭載されている。磁気ディスク６はモータ１の駆動によって所定方向に回転する。他方、アクチュエータ１２には、磁気ディスク６に対して磁気ヘッド１３を有するアーム１４が径方向に延びるように取り付けられている。磁気ヘッド１３は、この装置の非使用時はアーム１４とともに磁気ディスク６から離れた位置に退避しており、モータ１の駆動とともにアクチュエータ１２の作動によって旋回し、磁気ディスク６に接近して情報を読み書きする。
【００１５】
図２は、そのハードディスク装置１０に用いられているモータ１を示す軸方向断面図である。但し、破断線Ｘ−Ｘを境として一部は正面図で示す。モータ１は、ハウジング１１の内面に固定された静止部材２と、後述の気体動圧軸受けを介して静止部材２に対して回転可能に支持されている回転部材３と、ステータ４と、マグネット５とを備えている。
【００１６】
静止部材２は、凹部を有するほぼ円盤状のブラケット２１、インナーシャフト２２、アウターシャフト２３、上スラスト板２４及び下スラスト板２５から主になる。ブラケット２１の中央には図略の貫通孔が形成され、その孔の周縁が肉厚となってボス２１ａを形成している。また、ブラケット２１は、周縁に肉厚の壁２１ｂを有し、その壁２１ｂの内面にステータ４が取り付けられている。ステータ４のコイルは、ブラケット２１の所定部に設けられたフレキシブル回路基板（図示省略）を通じて外部電源から電流が供給される。インナーシャフト２２は、円柱状で、下端が上記貫通孔に嵌合されてボス２１ａによって支持されている。アウターシャフト２３は、円筒状で、ボス２１ａより露出したインナーシャフト２２の外周に嵌合されている。下スラスト板２５は、アウターシャフト２３よりも径方向に張り出しており、アウターシャフト２３の下端面とボス２１ａとで挟持するようにインナーシャフト２２に嵌合されている。上スラスト板２４もアウターシャフト２３よりも径方向に張り出しており、アウターシャフト２３の上端面に接してインナーシャフト２２に嵌合されている。
【００１７】
回転部材３は、貫通孔３１ｂを有する以外は上端が閉じたほぼ円筒状のハブ３１、ハブ３１の内周面に焼きばめされた円筒状のスリーブ３２、クランパ３３ａ及び複数（図示では４個）のスペーサ３３からなる。スリーブ３２は、その上下端面が微小間隙（以下、スラスト間隙という。）３２ａ，３２ｃを介して上下のスラスト板２４，２５と対向するように挟まれるとともに、その内周面が微小間隙（以下、ラジアル間隙という。）３２ｂを介してアウターシャフト２３の外周面と対向している。ハブ３１は、スリーブ３２の上下に露出する内周面にて上下のスラスト板２４，２５及びボス２１ａを包囲し、下端付近の外周面に鍔３１ａを有し、その鍔３１ａより下の外周面にてマグネット５を保持している。ハブ３１は、鍔３１ａより上位において一様な外径を有する。上記インナーシャフト２２の上端付近は、貫通孔３１ｂを通ってハブ３１の外部に露出している。マグネット５はステータ４と対向している。スペーサ３３は、ハブ３１の鍔３１ａより上位の外周面に各々張り出して磁気ディスク６同士の軸方向間隔を定めるものである。クランパ３３ａは、ハブ３１に対して複数（図示では４枚）の磁気ディスク６およびスペーサ３３を固定するための固定手段である。
【００１８】
上スラスト板２４の下面及び下スラスト板２５の上面には、各々内側から外側に向かって湾曲した円弧状で深さ数μｍの多数の溝２４ａ，２５ａが周方向に同一間隔をあけて形成されている。これらの溝２４ａ，２５ａは、回転部材３の回転時にスラスト間隙３２ａに存在する空気を内側に向かって送るポンプ作用を生じ、それによってスラスト間隙３２ａ，３２ｃの動圧を発生させ、静止部材２と回転部材３との軸方向における非接触状態を保つ。また、アウターシャフト２３の外周面の上半分及び下半分には、各々「く」の字状で深さ数μｍの多数の溝２３ａ，２３ｂが周方向に同一間隔をあけて形成されている。これらの溝２３ａ，２３ｂは、回転部材３の回転時にラジアル間隙３２ｂに存在する空気を各溝の折り返し点に向かって送るポンプ作用を生じ、それによってラジアル間隙３２ｂの動圧を発生させ、静止部材２と回転部材３との径方向における非接触状態を保つ。こうしてスラスト間隙３２ａ，３２ｃ及びラジアル間隙３２ｂを構成する部位が、動圧気体軸受けとして機能する。
【００１９】
次にモータ１の動作について説明する。
ステータ４のコイルに給電すると、ステータ４とマグネット５との間で磁力が発生し、この磁力によりハブ３１がスリーブ３２とともに回転し始める。すると上記の通りスラスト間隙３２ａ，３２ｃ及びラジアル間隙３２ｂに動圧が発生し、回転部材３が静止部材２に対して非接触状態を保って回転し続ける。
【００２０】
静止部材２及び回転部材３は、回転部材３の回転に伴い、給電によるコイルからの発熱、あるいは環境温度の上昇によって、各部材の熱膨張係数に応じて膨張しようとする。この実施形態では、アウターシャフト２３が熱膨張係数α_０＝６．２×１０^−６／℃のＡｌ_２Ｏ_３−ＴｉＣ系セラミックからなる。スリーブ３２及びハブ３１は各々熱膨張係数α１＝５．１×１０^−６／℃のＡｌ_２Ｏ_３及び熱膨張係数α_２＝１０．１×１０^−６／℃のフェライト系ステンレス鋼からなる。そして、スリーブ３２と対向する部分におけるアウターシャフト２３の外径２Ｒ_０を９．９９４ｍｍ、スリーブ３２の内径２Ｒ_１を１０ｍｍ、スリーブ３２とハブ３１との嵌合径２Ｒ_２を１７．５ｍｍ、鍔３１ａより上位におけるハブ３１の外径２Ｒ_３を２０ｍｍとし、ハブ３１とスリーブ３２との嵌合部の締め代δを１０μｍと設定した。この仕様で温度２０℃の状態と８０℃の状態のラジアル間隙の径方向変化量を上記式（１０）に従って求めると、０．０２μｍ以下であった。また、上記式（１）の左辺の値を求めると５．２５μｍとなり、ハブ３１の肉厚ｔ_２とスリーブ３２の肉厚ｔ_１の比ｔ_２／ｔ_１＝０．３３となり、上記式（１）及び（２）を充足するとともに、嵌合部に必要な面圧がかかっていた。
【００２１】
比較のために、スリーブ３２の材料をアウターシャフト２３と同一にすると、ラジアル間隙の径方向変化量は、０．３μｍとなった。
尚、上記の各寸法及び物性は一例であって、この発明はこれらに限定されるものではない。
【００２２】
【発明の効果】
以上の通り、この発明によれば、軸受面近傍の部材の熱膨張係数を所定の不等関係に設定するだけで、ラジアル間隙の変化量を低減するとともに、スリーブとハブとの嵌合部の面圧を確保することができるから、部材の選択肢を拡げることができる。このため、気体動圧軸受け装置を適用する種々の機器に有益である。
【図面の簡単な説明】
【図１】実施形態に係るハードディスク装置を模式的に示す回転中心軸方向断面図である。
【図２】上記ハードディスク装置に用いられているモータを示す軸方向断面図である。
【符号の説明】
１ モータ
２ 静止部材
３ 回転部材
４ ステータ
５ マグネット
６ 磁気ディスク
２２ インナーシャフト
２３ アウターシャフト
３１ ハブ
３２ スリーブ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention belongs to a gas dynamic pressure bearing device, a motor including the same, and an information device including the motor, and is suitably applied to a motor for rotating a magnetic disk such as a hard disk or a DVD, a disk device including the same, and a laser printer. Can be used.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Application Laid-Open No. 10-89345 [Patent Document 2] Japanese Patent Application Laid-Open No. 11-159524 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-33725 As a motor requiring high-speed and high-precision rotation, for example, a hard disk There is a motor for rotating a magnetic disk as described above. As a bearing means of a motor for rotating this magnetic disk, a fluid dynamic pressure bearing device capable of obtaining a stable rotational motion has begun to spread. In general, a radial gap and a thrust gap are formed on a first member in which a disc-shaped thrust plate is disposed at one end or both ends of a cylindrical shaft, and on the outer peripheral surface of the shaft and a plane of the thrust plate, respectively. And a second member, such as a cylindrical sleeve, which is disposed to face through the gap, and a herringbone-shaped or spiral-shaped groove for generating dynamic pressure is formed on a surface (referred to as a bearing surface) forming the gap therebetween. In these gaps, a lubricating fluid such as air or oil is interposed. When one of the first and second members rotates relative to the other, the lubricating fluid increases the fluid pressure in each of the radial gap and the thrust gap by the pumping action of the hydrodynamic groove, At the same time, the rotating sides of the first and second members float with respect to the stationary side, and the non-contact state between them is maintained during rotation.
[0003]
The gas dynamic pressure bearing device in which gas is used for the lubricating fluid is applied taking advantage of the advantage that there is no problem of leakage of the lubricating fluid unlike the liquid dynamic pressure bearing device in which oil or the like is used for the lubricating fluid, If the size of the gap changes due to a difference in thermal expansion between the stationary side and the rotating side due to a temperature change, there is a possibility that a desired fluid pressure becomes too large or too small and rotation is hindered. Therefore, various proposals have been made to prevent this change. One of them is that a copper alloy is selected as a material used for a sleeve and an austenitic stainless steel is selected as a material used for a shaft so that the thermal expansion coefficients of the two are almost the same (Patent Document 1). The other is that when one material of the bearing surface forming the thrust gap is a metal such as stainless steel, the other material is formed of ceramics such as zirconia so that the thermal expansion coefficients of the two substantially match. At the same time, the amount of wear of the mating material is reduced (Patent Document 2).
[0004]
[Problems to be solved by the invention]
However, since each of the prior arts is a material selected within a constraint that the thermal expansion coefficients on the stationary side and the rotating side are almost the same, from other viewpoints such as workability, price, and lubricity, Not necessarily the right combination.
SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a gas dynamic pressure bearing device capable of expanding a choice of materials on a stationary side and a rotating side and reducing a change in a size of a gap due to a temperature change, a motor including the same, and information. To provide equipment.
[0005]
[Means for Solving the Problems]
In order to solve the problem, the gas dynamic pressure bearing device of the present invention is:
A shaft, a sleeve having an inner peripheral surface facing the outer peripheral surface of the shaft via a minute gap serving as a gas dynamic pressure bearing, and a substantially cylindrical hub fitted to the outside of the sleeve by applying a surface pressure. In a gas dynamic pressure bearing device (hereinafter referred to as a bearing device) in which a groove for generating dynamic pressure is formed on at least one of an outer peripheral surface of a shaft and an inner peripheral surface of a sleeve,
When the linear expansion coefficients of the shaft, sleeve, and hub are α ₀ , α _1, and α ₂ , respectively, the relationship is α ₁ <α ₀ <α ₂ .
[0006]
In the bearing device of the present invention, at normal temperature (20 ° C.), the sleeve is compressed and fixed to the inner diameter side by fitting with the hub. When the temperature rises, the radial gap between the shaft and the sleeve tends to be narrowed from the relationship α ₁ <α ₀ (this gap change amount is assumed to be A). However, the interference between the sleeve and the hub is reduced due to the relationship of α ₁ <α ₂ , whereby the surface pressure between the sleeve and the hub is reduced, and the sleeve tends to expand (this expansion amount is B). As a result, the expansion amount B absorbs the gap change amount A, and reduces or suppresses the actual change in the radial gap. Moreover, since it is sufficient to satisfy the above inequality, it is possible to apply the most suitable material to each member in terms of workability, cost, lubricity and the like.
[0007]
When the interference between the sleeve and the hub is δ, the fitting radius is R ₂ , and the difference between the maximum operating temperature and 20 ° C. is ΔT, the following relational expression (1) is satisfied:
When the thickness of the sleeve is t ₁ and the thickness of the hub is t ₂ , it is preferable that the following relational expression (2) is satisfied.
2R ₂ ΔT (α ₂ −α ₁ ) ≦ δ (1)
_{t 2 / t 1 ≧ 0.25 ···} (2)
[0008]
By satisfying the relational expression (1), the interference is secured even if the sleeve expands in the operating temperature range of the bearing device. On the other hand, if the thickness of the hub is too thin compared to the sleeve even when the interference is secured in this way, only the hub is deformed in a direction in which only the hub expands at the time of fitting such as shrink fit or press fitting, and a predetermined surface is formed on the sleeve. No pressure is applied. Therefore, the setting is made so as to satisfy the relational expression (2). Thus, when the sleeve and the hub are fitted with the interference that satisfies the relational expression (1), a predetermined surface pressure is applied between the sleeve and the hub. As a result, loosening of the fitting portion is prevented while reducing the change in the radial gap as described above.
[0009]
The amount of change in the radial gap when the shaft, sleeve, and hub are made of a material that satisfies the above conditions can be obtained by the following formula.
First, the outer radius of the shaft, the inner radius of the sleeve, the fitting radius of the sleeve and the hub, and the outer radius of the hub are R ₀ , R ₁ , R _2, and R ₃ , respectively, and the longitudinal elastic modulus of the sleeve material and the hub material. each and E ₁ and E _2, and each [nu ₁ and [nu ₂ Poisson's ratio of the sleeve member and the hub member. The surface pressure Pm generated on the fastening surface by press fitting or shrink fitting between the hub and the sleeve is expressed by the following equation (3) at normal temperature.
(Equation 1)

Can be represented by
[0010]
By Pm, the inner diameter of the sleeve contracts by u represented by the following equation (4).
(Equation 2)

Therefore, the radial gap Cr at normal temperature is Cr = R ₁ −R ₀ −u (5)
It becomes.
[0011]
Next, assuming that the temperature rises by ΔT, the surface pressure Pm and the contraction amount of the sleeve inner diameter are represented by the following equations (6) and (8).
[Equation 3]

(Equation 4)

(Equation 5)

[0012]
Also, the radial gap Cr after temperature rise 'is _{Cr' = R 1 '-R 0} ' -u '
= (R ₁ α ₁ -R ₀ α ₀ ) ΔT-u ′ (9)
It becomes. Therefore, the amount of change in the radial gap is
(Equation 6)

Is required. Here, u ′ is a value determined by substituting each of the equations (7) into the equations (6) and (8).
[0013]
Since the bearing device according to the present invention produces the above-described effects, the bearing device includes the bearing device, a bracket for fixing the shaft, a stator attached to the bracket, and a magnet attached to the hub so as to face the stator. The motor operates stably.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically illustrating a hard disk device (corresponding to an information device) according to an embodiment in a rotation center axis direction (hereinafter, referred to as an axial direction). The hard disk device 10 includes a housing 11 whose inside is kept clean, a dynamic pressure bearing motor (hereinafter simply referred to as a motor) 1 and an actuator 12 installed in the housing 11. A plurality of (four in the figure) magnetic disks 6 are mounted on the motor 1 in the axial direction. The magnetic disk 6 is rotated in a predetermined direction by driving the motor 1. On the other hand, an arm 14 having a magnetic head 13 with respect to the magnetic disk 6 is attached to the actuator 12 so as to extend in the radial direction. When the apparatus is not used, the magnetic head 13 is retracted to a position away from the magnetic disk 6 together with the arm 14. The magnetic head 13 is turned by the operation of the actuator 12 when the motor 1 is driven, and approaches the magnetic disk 6 to read information. Read and write.
[0015]
FIG. 2 is an axial sectional view showing the motor 1 used in the hard disk device 10. However, a part is shown in a front view with respect to a break line XX. The motor 1 includes a stationary member 2 fixed to the inner surface of the housing 11, a rotating member 3 rotatably supported by the stationary member 2 via a gas dynamic pressure bearing described later, a stator 4, and a magnet 5 And
[0016]
The stationary member 2 mainly includes a substantially disk-shaped bracket 21 having a concave portion, an inner shaft 22, an outer shaft 23, an upper thrust plate 24, and a lower thrust plate 25. An unillustrated through-hole is formed at the center of the bracket 21, and the periphery of the hole is thick to form a boss 21 a. The bracket 21 has a thick wall 21b on the periphery, and the stator 4 is mounted on the inner surface of the wall 21b. An electric current is supplied to the coil of the stator 4 from an external power supply through a flexible circuit board (not shown) provided at a predetermined portion of the bracket 21. The inner shaft 22 has a columnar shape, and has a lower end fitted in the through hole and supported by the boss 21a. The outer shaft 23 has a cylindrical shape and is fitted on the outer periphery of the inner shaft 22 exposed from the boss 21a. The lower thrust plate 25 projects more radially than the outer shaft 23 and is fitted to the inner shaft 22 so as to be sandwiched between the lower end surface of the outer shaft 23 and the boss 21a. The upper thrust plate 24 also projects more radially than the outer shaft 23, and is fitted on the inner shaft 22 in contact with the upper end surface of the outer shaft 23.
[0017]
The rotating member 3 includes a substantially cylindrical hub 31 whose upper end is closed except for having the through hole 31b, a cylindrical sleeve 32 shrink-fitted on the inner peripheral surface of the hub 31, a clamper 33a, and a plurality (four in the figure). ) Spacers 33). The upper and lower end surfaces of the sleeve 32 are sandwiched between the upper and lower thrust plates 24 and 25 via minute gaps (hereinafter referred to as thrust gaps) 32a and 32c. It is opposed to the outer peripheral surface of the outer shaft 23 via a radial gap 32b. The hub 31 surrounds the upper and lower thrust plates 24, 25 and the boss 21a on the inner peripheral surface exposed above and below the sleeve 32, has a flange 31a on the outer peripheral surface near the lower end, and has an outer peripheral surface below the flange 31a. Holds the magnet 5. The hub 31 has a uniform outer diameter above the flange 31a. The vicinity of the upper end of the inner shaft 22 is exposed to the outside of the hub 31 through the through hole 31b. The magnet 5 faces the stator 4. The spacers 33 protrude from the outer peripheral surface of the hub 31 above the flange 31a to determine the axial distance between the magnetic disks 6. The clamper 33a is fixing means for fixing a plurality (four in the drawing) of the magnetic disks 6 and the spacers 33 to the hub 31.
[0018]
On the lower surface of the upper thrust plate 24 and the upper surface of the lower thrust plate 25, a large number of grooves 24a and 25a each having a depth of several μm and having an arc shape curved from inside to outside are formed at equal intervals in the circumferential direction. ing. These grooves 24a, 25a generate a pumping action for sending air existing in the thrust gap 32a inward when the rotating member 3 rotates, thereby generating dynamic pressure in the thrust gaps 32a, 32c, and A non-contact state in the axial direction with the rotating member 3 is maintained. In the upper half and the lower half of the outer peripheral surface of the outer shaft 23, a large number of grooves 23a and 23b each having a U shape and a depth of several μm are formed at equal intervals in the circumferential direction. These grooves 23a and 23b generate a pumping action for sending air existing in the radial gap 32b toward the turning point of each groove when the rotating member 3 rotates, thereby generating a dynamic pressure in the radial gap 32b, and A non-contact state in the radial direction between the rotating member 2 and the rotating member 3 is maintained. In this way, the parts constituting the thrust gaps 32a and 32c and the radial gap 32b function as dynamic pressure gas bearings.
[0019]
Next, the operation of the motor 1 will be described.
When power is supplied to the coil of the stator 4, a magnetic force is generated between the stator 4 and the magnet 5, and the hub 31 starts rotating together with the sleeve 32 due to the magnetic force. Then, as described above, dynamic pressure is generated in the thrust gaps 32a and 32c and the radial gap 32b, and the rotating member 3 keeps rotating while keeping the non-contact state with the stationary member 2.
[0020]
The stationary member 2 and the rotating member 3 tend to expand in accordance with the thermal expansion coefficient of each member due to the heat generated from the coil by the power supply or the rise in the environmental temperature with the rotation of the rotating member 3. In this embodiment, the outer shaft 23 is made of an Al ₂ O ₃ —TiC-based ceramic having a thermal expansion coefficient α ₀ = 6.2 × 10 ⁻⁶ / ° C. The sleeve 32 and the hub 31 are made of Al ₂ O _{3 having a} thermal expansion coefficient α1 = 5.1 × 10 ⁻⁶ / ° C. and a ferritic stainless steel having a thermal expansion coefficient α ₂ = 10.1 × 10 ⁻⁶ / ° C., respectively. Then, 9.994Mm the outer diameter 2R ₀ of the outer shaft 23 at a portion facing the sleeve 32, 10 mm inner diameter 2R ₁ of the sleeve 32, 17.5 mm the fitting diameter 2R ₂ of the sleeve 32 and the hub 31, the flange 31a the outer diameter 2R ₃ of the hub 31 in a higher and 20 mm, setting the interference δ of the fitting portion between the hub 31 and the sleeve 32 and 10 [mu] m. When the radial change amount of the radial gap at the temperature of 20 ° C. and the temperature of 80 ° C. was determined according to the above equation (10), it was 0.02 μm or less. Also, the value on the left side of the above equation (1) is 5.25 μm, and the ratio t ₂ / t _{1 of the} thickness t ₂ of the hub 31 to the thickness t ₁ of the sleeve 32 is 0.32 / 0.33. In addition to satisfying 1) and (2), necessary surface pressure was applied to the fitting portion.
[0021]
For comparison, when the material of the sleeve 32 was the same as that of the outer shaft 23, the radial change amount of the radial gap was 0.3 μm.
The above dimensions and physical properties are merely examples, and the present invention is not limited to these.
[0022]
【The invention's effect】
As described above, according to the present invention, by merely setting the thermal expansion coefficients of the members near the bearing surface to a predetermined unequal relationship, the amount of change in the radial gap can be reduced, and the fitting portion between the sleeve and the hub can be reduced. Since the surface pressure can be ensured, the choice of members can be expanded. Therefore, it is useful for various devices to which the gas dynamic pressure bearing device is applied.
[Brief description of the drawings]
FIG. 1 is a sectional view in the direction of a rotation center axis schematically showing a hard disk device according to an embodiment.
FIG. 2 is an axial sectional view showing a motor used in the hard disk device.
[Explanation of symbols]
Reference Signs List 1 motor 2 stationary member 3 rotating member 4 stator 5 magnet 6 magnetic disk 22 inner shaft 23 outer shaft 31 hub 32 sleeve

Claims (4)

A shaft, a sleeve having an inner peripheral surface facing the outer peripheral surface of the shaft via a minute gap serving as a gas dynamic pressure bearing, and a substantially cylindrical hub fitted to the outside of the sleeve by applying a surface pressure. In a gas dynamic pressure bearing device in which a groove for generating dynamic pressure is formed on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve,
When the linear expansion coefficients of the shaft, the sleeve, and the hub are α ₀ , α _1, and α ₂ , respectively, the relationship of α ₁ <α ₀ <α ₂ is satisfied. When the interference between the sleeve and the hub is δ, the fitting radius is R ₂ , and the difference between the maximum operating temperature and 20 ° C. is ΔT, the following relational expression (1) is satisfied:
T ₁ the thickness of the _sleeve, when the thickness of the hub and t _2, the gas dynamic pressure bearing device according to claim 1, satisfying the following relational expression (2).
2R ₂ ΔT (α ₂ −α ₁ ) ≦ δ (1)
_{t 2 / t 1 ≧ 0.25 ···} (2) A motor comprising: the gas dynamic pressure bearing device according to claim 1 or 2; a bracket for fixing the shaft; a stator mounted on the bracket; and a magnet mounted on a hub so as to face the stator. An information device comprising the motor according to claim 3.

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