JP2004036756A

JP2004036756A - Motor using dynamic-pressure bearing, and disk drive device

Info

Publication number: JP2004036756A
Application number: JP2002194533A
Authority: JP
Inventors: Satoru Sodeoka; 袖岡　覚
Original assignee: Nidec Corp
Current assignee: Nidec Corp
Priority date: 2002-07-03
Filing date: 2002-07-03
Publication date: 2004-02-05

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a loss torque in a low temperature range while utilizing the advantages of a hybrid dynamic-pressure bearing in a motor having a pneumatic air-pressure bearing and a liquid dynamic-pressure bearing, i.e., the hybrid bearing. <P>SOLUTION: Air is used as a working fluid for a radial dynamic-pressure bearing part 51, and liquid is used as a working fluid for a thrust dynamic-pressure bearing part 52. The coefficient of thermal expansion of a shaft member 11b in the radial dynamic-pressure bearing part 51 is set larger than that of a surrounding member 24 opposed to the shaft member. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、動圧軸受を用いたモータ及びこれを用いたディスク駆動装置に関し、より詳細には動圧軸受の作動流体として液体と空気とを併用するいわゆるハイブリッド型の動圧軸受を用いたモータ及びディスク駆動装置に関するものである。
【０００２】
【従来の技術】
ハードディスクドライブ（ＨＤＤ）や高容量のフロッピィディスクドライブ（ＦＤＤ）などの磁気ディスク装置などに使用されるスピンドルモータは、年々高速化、小型化が進み、このようなスピンドルモータの軸受手段として、回転側部材と静止側部材との間に作動流体を介在させ、この作動流体中に発生する流体動圧を用いて回転側部材を非接触支持する動圧軸受が使用されるようになってきた。
【０００３】
このような動圧軸受としては、作動流体として液体を用いる液体動圧軸受と、作動流体として空気を用いる空気動圧軸受とに大きく分けられる。前者の軸受では小型化に対応可能となり、また静寂性と優れた振れ精度が得られる利点がある一方、高速回転時に潤滑液体が軸受外部に漏れるおそれがあり、また温度変化によって潤滑液体に体積変化が生じ、高温時には潤滑液体の漏れが促進されるだけでなく、潤滑液体の粘度の変化により軸受剛性、特にラジアル剛性が変化しやすい欠点がある。
【０００４】
他方、作動流体として空気を用いた後者の軸受では、潤滑液体の漏れの心配がなく、またシール機構も不要で、構造が簡単になるだけでなく、広い温度範囲で剛性変化が少ないといった利点がある一方、固定側部材と回転側部材とを空気を介在させて支持しているため、回転側部材に蓄積される静電荷を固定側部材に逃がすことができず各種の静電気障害が生じることがあった。また、空気動圧軸受を用いたスピンドルモータでは、作動流体が密度の低い空気であるためにダンピング定数を大きくすることが困難で、振動が発生した場合にこの振動が持続しやすく、安定性に懸念が存在する。特にディスク駆動装置に適用した場合に、このような問題が顕著になる。
【０００５】
そこで、高速回転時でも潤滑液体の漏れがなく、また剛性変化が少ないといった空気動圧軸受の利点を活かしつつ、回転側部材と固定側部材との間の電気的導通を確保し、さらにダンピング定数を適度に確保するため、空気動圧軸受と液体動圧軸受とを併用した、いわゆるハイブリッド型の動圧軸受が提案されている（例えば特開２０００−２１５５９０号公報など）。
【０００６】
【発明が解決しようとする課題】
このハイブリッド型の動圧軸受において、空気動圧軸受部では作動流体である空気の温度による粘性変化がないため、温度によらず一定の軸受特性が得られるものの、液体動圧軸受部では作動流体である潤滑液体の温度による粘性変化が大きく、高温で充分な軸受負荷を負えるようにした場合には、低温時の粘度が大きくなるため、この動圧軸受を用いたモータでは低温域での損失トルクが大きくなり、モータの駆動電流値が大きくなる問題があった。
【０００７】
本発明はこのような従来の問題に鑑みてなされたものであり、その目的とするところは、ハイブリッド型の動圧軸受を用いたモータにおいて、ハイブリッド型の動圧軸受の従来の利点をそのまま生かしながら、低温域での損失トルクを小さくすることにある。
【０００８】
また本発明の目的は、小型で高速回転し、また優れた振れ精度と静寂性を有すると共に、低温域での損失トルクの小さいディスク駆動装置を提供することにある。
【０００９】
【課題を解決するための手段】
前記目的を達成するため本発明のモータでは、軸部材と、微小間隙を有して該軸部材を取り囲む囲繞部材とが動圧軸受部を介して回転自在に係合した動圧軸受装置であって、前記動圧軸受部は、空気を作動流体とするラジアル動圧軸受部と、液体を作動流体とするスラスト動圧軸受部とからなり、前記ラジアル動圧軸受部における軸部材の熱膨張率を、対向する囲繞部材のそれよりも大きくした構成とした。
【００１０】
ここで、前記軸部材は、軸部と該軸部から半径方向外方に突出するスラストプレート部とを有し、前記囲繞部材は、前記軸部と前記スラストプレート部に対し微小間隙を有して周設されてなり、前記ラジアル動圧軸受部は、前記軸部およびこの軸部と対向する前記囲繞部材の内周面の少なくとも一方に設けられた、ラジアル荷重を支持するためのラジアル動圧発生溝と空気とから構成され、前記スラスト動圧軸受部は、前記スラストプレート部の上下面およびこの上下面と対向する前記囲繞部材の内側面の少なくとも一方に設けられた、スラスト荷重を支持するためのスラスト動圧発生溝と、この対向面間に充填された潤滑液体とから構成されているようにしてもよい。
【００１１】
低温域での損失トルクをより低減する観点から、前記軸部材の主材料をステンレス鋼とし、前記囲繞部材の主材料をセラミック材としてもよい。
【００１２】
また、本発明のディスク駆動装置では、情報を記録できる円板状記録媒体が装着されるディスク駆動装置において、筐体と、該筐体の内部に固定され、前記記録媒体を回転させるスピンドルモータと、前記記録媒体の所望の位置に情報を書き込み又は読み出すための情報アクセス手段とを有するディスク駆動装置であって、前記スピンドルモータとして前記記載のモータを用いる構成とした。
【００１３】
【発明の実施の形態】
本発明者は、ハイブリッド型の動圧軸受を用いたモータにおいて、ハイブリッド型の動圧軸受の利点を存置しながら低温域での損失トルクを低減すべく鋭意検討を重ねた結果、意外にも、温度によって粘度がほとんど変化しない空気を用いた空気動圧軸受部での低温域における損失トルクを小さくすることにより、モータ全体としての損失トルクを低減できることを見出し本発明をなすに至った。すなわち、本発明のモータの大きな特徴は、空気を作動流体とするラジアル動圧軸受部における軸部材の熱膨張率を、対向する囲繞部材のそれよりも大きくしたことにある。かかる構成により、低温になったときラジアル軸受部の軸部材と、対向する囲繞部材との間隙が広くなり、損失トルクが低減される。また、ラジアル軸受部の間隙が広くなることによって低温域での軸受特性は低下するものの、スラスト軸受部では液体粘度が増加しているので軸受の剛性が高くなり、これにより回転部の姿勢は安定化される。
【００１４】
以下、図に基づいて本発明のモータについて説明する。なお、本発明はこれらに何ら限定されるものではない。
【００１５】
本発明に係るモータの組立断面図例を図１に示し、その組立後の断面図を図２に示す。図１および図２に示したモータでは、ブラケット６は中心部に設けられた基部６１と、この基部６１の外周方向に設けられた周壁６２と、この周壁６２からさらに外方向に延設された鍔部６３と、基部６１の中心部に形成された環状突部６４とからなり、これらが一体且つ同心状に形成されている。
【００１６】
一方、軸部材は、軸部１１と、この軸部１１と別体のスラストプレート部１２とからなる。軸部１１は、先端部側が小径とされた円柱状軸部１１ａを円筒状軸部１１ｂの中心孔に嵌合させてなり、円柱状軸部１１ａの底面を円筒状軸部１１ｂの底面から奥まった所に位置させることにより、軸部材１１の底面に穴１１１を形成し、ブラケット６の中心部に形成された環状突部６４にこの穴１１１を填め込み、軸部材１１をブラケット６に立設させている。
【００１７】
また、略円筒状のロータハブ（囲繞部材）２の上面中央部には、大小２つの環状溝２１，２２と貫通孔２３とが同心状に形成され、この貫通孔２３に軸部１１の先端部側の小径部分１１２を挿通させることにより、ロータハブ２は軸部１１を覆うように装着される。そして、ロータハブ２の環状溝２２にスラストプレート部１２を嵌入した後、軸部１１の小径部分１１２に固定する。さらに、ロータハブ２の環状溝２１にスラストプレート部１２の上側に蓋をするように円盤状のキャップ部材３が嵌入し、ロータハブ２に固着する。したがって、キャップ部材３はロータハブ２と共に回転するようになる。
【００１８】
ロータハブ２の内周面には、スリーブ２４が円筒状軸部１１ｂの外周面に対向するよう取り付けられている。また、ロータハブ２の外周中間部には鍔部２５が形成され、ここにハードディスクＤが装着される。具体的にはロータハブ２の外周により位置決めされて、鍔部２５の上に１又は複数のハードディスクＤが装着された後、クランプ部材（不図示）などにより軸部１１の先端面に穿設された孔部Ｈにネジ止めされて、ハードディスクＤはロータハブ２に対して保持固定される。さらに、ロータハブ２の外周下側には周方向に多極着磁されたロータマグネット２６が全周にわたり配設されている。またロータマグネット２６の半径方向外方には、ロータマグネット２６に対向して、ステータコア４ａの周りにステータコイル４ｂを巻着したステータ４がブラケット６の周壁６４に配設されている。
【００１９】
図２において、ラジアル動圧軸受部５１は、円筒状軸部１１ｂの外周面とこの外周面に対向したスリーブ２４の内周面との間に、軸方向に離隔して２つ形成されている。どちらも作動流体として対向面間に存在する空気と、円筒状軸部１１ｂの外周面に形成されたヘリングボーン状の動圧発生溝Ｇ_１，Ｇ_１’とから構成されている。一方、スラスト動圧軸受部５２は、キャップ部材３の下面とスラストプレート部１２の上面との間、及びスラストプレート部１２の下面とロータハブ２上面の環状溝２２の底面との間に形成され、作動流体として介在する潤滑液体と、スラストプレート部１２の上下面側に形成されたヘリングボーン状の動圧発生溝Ｇ_２，Ｇ_２’とから構成されている。なお、ロータハブ２などの回転部材に蓄積される静電荷を軸部材側に逃がして静電気障害の発生を防止するためには、潤滑液体として導電性液体を用い、回転部材と軸部材とを導通可能とすることが推奨される。
【００２０】
ここでスラストプレート部１２の一例を図３に示す。図３のスラストプレート部１２では、動圧発生溝Ｇ_２としてのヘリングボーン状溝が同心状に形成されており、またスラストプレート部１２の中央部には中央孔１２ａが設けられ、この中央孔１２ａに軸部１１の小径部分１１２が挿通される。そして、この中央孔１２ａの内周側に半円形の切り欠き部１２ｂが対向位置に設けられており、この切り欠き部１２ｂを介してラジアル動圧軸受部５１と軸受外部との間で空気の流通が行われる。またスラストプレート部１２には潤滑液体を循環させるために、スラストプレート部１２の上下面を繋ぐ循環孔１２ｃと、この循環孔１２ｃに接続し、スラストプレート部１２の周面に通じる循環孔（図１及び図２に図示）１２ｄとが穿設されている。
【００２１】
このような構成のモータＭにおいてステータコイル４ｂに通電すると、ステータ４及びロータマグネット２６の磁気回路部の駆動で、ラジアル動圧軸受部５１及びスラスト動圧軸受部５２で支持されたロータハブ２及びキャップ部材３が、軸部材１に対して記録ディスクＤと共に回転する。この時、ラジアル動圧軸受部５１では、円筒状軸部１１ｂの外周面とスリーブ２４の内周面との間隙内の空気が、ヘリングボーン状の動圧発生溝Ｇ_１，Ｇ_１’の作用により、「く」の字状の屈曲部分に向けて両方から流動しラジアル荷重支持圧を発生させる。一方、スラスト動圧軸受部５２でも同様に、ヘリングボーン状の動圧発生溝Ｇ_２，Ｇ_２’の作用により、「く」の字状の屈曲部分に向けて両方から潤滑液体が流動してスラスト荷重支持圧を発生させる。
【００２２】
ここで本発明におけるラジアル動圧軸受部５２では、軸部材１の熱膨張率を、対向する囲繞部材（ロータハブ２とスリーブ２４）のそれよりも大きくしているので、高温域では軸部材１とこれに対向する囲繞部材との間隙が狭くなり軸受特性が高くなる一方、低温域では前記間隙は広くなり損失トルクが低減される。この結果、本発明のモータでは、モータ駆動開始・停止時の低速回転における損失トルクは従来のモータに比べ低く抑えられる。また前記間隙が広くなることによって低温域での軸受特性は低下するものの、スラスト動圧軸受部５２は低温域では液体粘度が増加しているので軸受の剛性が高くなり、これにより回転部の姿勢は安定化される。
【００２３】
軸部材および囲繞部材の熱膨張率は、ラジアル動圧発生部の軸受間隙や軸部材の径、モータの使用環境温度などから適宜決定すればよい。例えば、軸部材の直径をＤ（ｍｍ）、熱膨張率をα（／℃）、囲繞部材の熱膨張率をβ（／℃）、軸受間隙Ｃ（ｍｍ、ａｔ２０℃）、モータの使用環境の温度上昇が８０℃、軸受の限界間隙が０．００１（ｍｍ）とすると下記不等式が成立し、この不等式を満たす範囲で（α−β）が最も高くなるように軸部材および囲繞部材の熱膨張率を決めればよい。
０＜（α−β）＜２×（Ｃ−０．００１）／（８０×Ｄ）
ここで、Ｃ＝０．００４ｍｍ、Ｄ＝１０ｍｍの場合には
０＜（α−β）＜７．５×１０^−６
となる。
【００２４】
ラジアル動圧軸受部における軸部材と囲繞部材との好ましい組み合わせとしては、例えば表１の組み合わせが挙げられる。
【００２５】
【表１】

【００２６】
本発明者は実際に、軸部材として熱膨張率が１０×１０^−６（／℃）のＳＵＳ４００系を用い、スリーブ部材（囲繞部材）として熱膨張率が７．８×１０^−６（／℃）のアルミナを用いたモータＩの駆動電流値を測定した。また比較として、軸部材として熱膨張率が１０×１０^−６（／℃）のＳＵＳ４００系を用い、スリーブ部材として熱膨張率が９．６×１０^−６（／℃）のジルコニアを用いたモータＩＩの駆動電流値も測定した。その結果、６０℃以上の温度域では両モータの駆動電流値に差異は見られなかったが、低温ではモータＩの駆動電流値はモータＩＩよりも数十ｍＡ低くなっていた。このことから軸部材と囲繞部材との熱膨張率の差が大きいほど低温域におけるモータの損失トルクを低減できることがわかる。
【００２７】
次に、本発明のディスク駆動装置について以下説明する。図４に、一般的なディスク駆動装置７の内部構成を模式図として示す。ハウジング（筐体）７１の内部は塵・埃などが極端に少ないクリーンな空間を形成しており、その内部に情報を記憶する円板状のディスク板（記録媒体）７３が装着されたモータ７２が設置されている。加えてハウジング７１の内部には、ディスク板７３に対して情報を読み書きするヘッド移動機構（情報アクセス手段）が配置され、このヘッド移動機構はディスク板７３上の情報を読み書きするヘッド７６、このヘッド７６を支えるアーム７５，およびヘッド７６並びにアーム７５をディスク板７３上の所要位置に移動させるアクチュエータ部７４により構成される。
【００２８】
【発明の効果】
本発明のモータでは、空気を作動流体とするラジアル動圧軸受部と、液体を作動流体とするスラスト動圧軸受部とを有し、ラジアル動圧軸受部における軸部材の熱膨張率を、対向するスリーブ部材（囲繞部材）のそれよりも大きくしたので、ハイブリッド型の動圧軸受の利点をそのまま生かしながら、低温域における損失トルクを小さくできる。
【００２９】
また、本発明のディスク駆動装置では、情報を記録できる円板状記録媒体を回転させるスピンドルモータとして前記のモータを用いるので、小型で高速回転が可能となり、また優れた振れ精度と静寂性を有すると共に、低温域での損失トルクが小さい。
【図面の簡単な説明】
【図１】本発明のモータの一例を示す組立断面図である。
【図２】図１のモータの組立後の断面図である。
【図３】スラストプレート部の一例を示す平面図である。
【図４】本発明のディスク駆動装置の一例を示す概略構成図である。
【符号の説明】
１　軸部材
２　ロータハブ（囲繞部材）
３　キャップ部材
７　ディスク駆動装置
１１　軸部
１１ａ　円柱状軸部
１１ｂ　円筒状軸部
１２　スラストプレート部
２４　スリーブ部材（囲繞部材）
５１　ラジアル動圧軸受部
５２　スラスト動圧軸受部
７１　筐体
７３　記録媒体
Ｄ　ハードディスク（記録媒体）
Ｍ　モータ
Ｇ_１，Ｇ_１’　ラジアル動圧発生溝
Ｇ_２，Ｇ_２’　スラスト動圧発生溝[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor using a dynamic pressure bearing and a disk drive device using the same, and more particularly to a motor using a so-called hybrid type dynamic pressure bearing that uses both liquid and air as working fluids for the dynamic pressure bearing. And a disk drive device.
[0002]
[Prior art]
Spindle motors used in hard disk drives (HDDs) and magnetic disk drives such as high-capacity floppy disk drives (FDDs) are becoming faster and smaller year by year. A dynamic pressure bearing has been used in which a working fluid is interposed between a member and a stationary-side member, and a rotating-side member is supported in a non-contact manner by using a fluid dynamic pressure generated in the working fluid.
[0003]
Such dynamic pressure bearings are broadly divided into liquid dynamic pressure bearings using liquid as working fluid and air dynamic pressure bearings using air as working fluid. The former has the advantage of being able to respond to miniaturization and has the advantages of quietness and excellent runout accuracy.However, the lubricating liquid may leak out of the bearing during high-speed rotation. This has the disadvantage that not only the leakage of the lubricating liquid is promoted at high temperatures, but also the bearing stiffness, especially the radial stiffness, tends to change due to the change in the viscosity of the lubricating liquid.
[0004]
On the other hand, the latter bearing, which uses air as the working fluid, has the advantage that there is no need to worry about leakage of lubricating liquid, no seal mechanism is required, the structure is simple, and there is little change in rigidity over a wide temperature range. On the other hand, since the fixed-side member and the rotating-side member are supported with air interposed therebetween, electrostatic charges accumulated in the rotating-side member cannot be released to the fixed-side member, and various kinds of static electricity troubles may occur. there were. Also, with a spindle motor using an air dynamic pressure bearing, it is difficult to increase the damping constant because the working fluid is low-density air. Concerns exist. In particular, such a problem becomes remarkable when applied to a disk drive.
[0005]
Therefore, while taking advantage of the advantages of the pneumatic hydrodynamic bearing such that there is no leakage of the lubricating liquid even during high-speed rotation and little change in rigidity, electrical conduction between the rotating side member and the fixed side member is ensured, and the damping constant is further increased. In order to ensure the appropriate performance, a so-called hybrid type dynamic pressure bearing using both an air dynamic pressure bearing and a liquid dynamic pressure bearing has been proposed (for example, Japanese Patent Application Laid-Open No. 2000-215590).
[0006]
[Problems to be solved by the invention]
In this hybrid type dynamic pressure bearing, although there is no change in viscosity due to the temperature of the air as the working fluid in the air dynamic pressure bearing, constant bearing characteristics can be obtained regardless of the temperature. If the lubricating fluid has a large viscosity change due to the temperature and a sufficient bearing load can be applied at high temperatures, the viscosity at low temperatures will increase. There is a problem that the torque increases and the drive current value of the motor increases.
[0007]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a motor using a hybrid type dynamic pressure bearing while keeping the conventional advantages of the hybrid type dynamic pressure bearing. However, the object is to reduce torque loss in a low temperature range.
[0008]
It is another object of the present invention to provide a disk drive device which is small in size, rotates at high speed, has excellent runout accuracy and quietness, and has small loss torque in a low temperature range.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a motor according to the present invention is a dynamic pressure bearing device in which a shaft member and a surrounding member having a minute gap and surrounding the shaft member are rotatably engaged via a dynamic pressure bearing portion. The dynamic pressure bearing portion includes a radial dynamic pressure bearing portion using air as a working fluid, and a thrust dynamic pressure bearing portion using a liquid as a working fluid, and a thermal expansion coefficient of a shaft member in the radial dynamic pressure bearing portion. Was made larger than that of the surrounding member facing it.
[0010]
Here, the shaft member has a shaft portion and a thrust plate portion protruding radially outward from the shaft portion, and the surrounding member has a minute gap between the shaft portion and the thrust plate portion. The radial dynamic pressure bearing portion is provided on at least one of the shaft portion and the inner peripheral surface of the surrounding member opposed to the shaft portion, the radial dynamic pressure bearing portion supporting a radial load. The thrust dynamic pressure bearing portion, which includes a generating groove and air, supports a thrust load provided on at least one of the upper and lower surfaces of the thrust plate portion and the inner surface of the surrounding member facing the upper and lower surfaces. And a lubricating liquid filled between the opposed surfaces.
[0011]
From the viewpoint of further reducing the torque loss in a low temperature range, the main material of the shaft member may be stainless steel, and the main material of the surrounding member may be a ceramic material.
[0012]
Further, in the disk drive device of the present invention, in a disk drive device on which a disk-shaped recording medium capable of recording information is mounted, a housing, a spindle motor fixed inside the housing and rotating the recording medium, A disk drive device having information access means for writing or reading information at a desired position on the recording medium, wherein the spindle motor uses the motor described above.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventor, in a motor using a hybrid type dynamic pressure bearing, as a result of intensive studies to reduce the loss torque in the low temperature range while maintaining the advantages of the hybrid type dynamic pressure bearing, surprisingly, The inventors have found that the loss torque of the motor as a whole can be reduced by reducing the loss torque in a low-temperature region in an air dynamic pressure bearing portion using air whose viscosity hardly changes with temperature, and have accomplished the present invention. That is, a major feature of the motor of the present invention is that the coefficient of thermal expansion of the shaft member in the radial dynamic pressure bearing portion using air as the working fluid is larger than that of the surrounding member facing the same. With this configuration, when the temperature becomes low, the gap between the shaft member of the radial bearing portion and the surrounding member facing each other is widened, and the torque loss is reduced. In addition, although the bearing characteristics in the low temperature range are degraded due to the increase in the gap between the radial bearings, the rigidity of the bearings is increased due to the increase in the liquid viscosity in the thrust bearings. Be converted to
[0014]
Hereinafter, the motor of the present invention will be described with reference to the drawings. Note that the present invention is not limited to these.
[0015]
FIG. 1 shows an example of an assembled sectional view of the motor according to the present invention, and FIG. 2 shows a sectional view after the assembly. In the motor shown in FIGS. 1 and 2, the bracket 6 has a base 61 provided in the center, a peripheral wall 62 provided in the outer peripheral direction of the base 61, and further extended outward from the peripheral wall 62. A flange 63 and an annular projection 64 formed at the center of the base 61 are formed integrally and concentrically.
[0016]
On the other hand, the shaft member includes a shaft portion 11 and a thrust plate portion 12 separate from the shaft portion 11. The shaft portion 11 is formed by fitting a cylindrical shaft portion 11a having a small diameter at the tip end side into a center hole of the cylindrical shaft portion 11b, and the bottom surface of the cylindrical shaft portion 11a is recessed from the bottom surface of the cylindrical shaft portion 11b. A hole 111 is formed in the bottom surface of the shaft member 11, and the hole 111 is inserted into an annular protrusion 64 formed at the center of the bracket 6, and the shaft member 11 is erected on the bracket 6. Let me.
[0017]
At the center of the upper surface of the substantially cylindrical rotor hub (surrounding member) 2, two large and small annular grooves 21, 22 and a through hole 23 are formed concentrically. The rotor hub 2 is mounted so as to cover the shaft portion 11 by inserting the small-diameter portion 112 on the side. Then, after the thrust plate portion 12 is fitted into the annular groove 22 of the rotor hub 2, it is fixed to the small-diameter portion 112 of the shaft portion 11. Further, the disk-shaped cap member 3 is fitted into the annular groove 21 of the rotor hub 2 so as to cover the upper side of the thrust plate portion 12, and is fixed to the rotor hub 2. Therefore, the cap member 3 rotates with the rotor hub 2.
[0018]
A sleeve 24 is attached to the inner peripheral surface of the rotor hub 2 so as to face the outer peripheral surface of the cylindrical shaft portion 11b. In addition, a flange 25 is formed at an intermediate portion of the outer periphery of the rotor hub 2, and a hard disk D is mounted here. Specifically, after one or more hard disks D are mounted on the flange 25 and positioned on the outer periphery of the rotor hub 2, the hard disk D is pierced on the distal end surface of the shaft 11 by a clamp member (not shown) or the like. The hard disk D is held and fixed to the rotor hub 2 by being screwed to the hole H. Further, a rotor magnet 26, which is multipolarly magnetized in the circumferential direction, is provided over the entire circumference below the outer circumference of the rotor hub 2. A stator 4 around which a stator coil 4b is wound around a stator core 4a is disposed on a peripheral wall 64 of the bracket 6 outside the rotor magnet 26 in the radial direction.
[0019]
In FIG. 2, two radial dynamic pressure bearing portions 51 are formed axially separated between the outer peripheral surface of the cylindrical shaft portion 11b and the inner peripheral surface of the sleeve 24 facing the outer peripheral surface. . Both are composed of air existing between the opposing surfaces as working fluid, and herringbone-shaped dynamic pressure generating grooves G ₁ , G ₁ ′ formed on the outer peripheral surface of the cylindrical shaft portion 11b. On the other hand, the thrust dynamic pressure bearing portion 52 is formed between the lower surface of the cap member 3 and the upper surface of the thrust plate portion 12, and between the lower surface of the thrust plate portion 12 and the bottom surface of the annular groove 22 on the upper surface of the rotor hub 2, It comprises a lubricating liquid interposed as a working fluid, and herringbone-shaped dynamic pressure generating grooves G ₂ , G ₂ ′ formed on the upper and lower surfaces of the thrust plate portion 12. In order to prevent static electricity from accumulating in the rotating member such as the rotor hub 2 to the shaft member and to prevent the occurrence of static electricity, a conductive liquid is used as a lubricating liquid, and the rotating member and the shaft member can be electrically connected. It is recommended that
[0020]
Here, an example of the thrust plate portion 12 is shown in FIG. The thrust plate 12 of FIG. 3, the herringbone grooves as dynamic pressure generating groove G ₂ is formed coaxially and center hole 12a is provided in the central portion of the thrust plate 12, the central bore The small diameter portion 112 of the shaft portion 11 is inserted through 12a. A semicircular notch 12b is provided on the inner peripheral side of the center hole 12a at an opposing position, and air flows between the radial dynamic pressure bearing 51 and the outside of the bearing via the notch 12b. Distribution takes place. Further, in order to circulate the lubricating liquid in the thrust plate portion 12, a circulation hole 12c connecting the upper and lower surfaces of the thrust plate portion 12, and a circulation hole connected to the circulation hole 12c and communicating with the peripheral surface of the thrust plate portion 12 (FIG. 1 and FIG. 2) 12d.
[0021]
When the stator coil 4b is energized in the motor M having such a configuration, the rotor 4 and the cap supported by the radial dynamic pressure bearing portion 51 and the thrust dynamic pressure bearing portion 52 are driven by driving the magnetic circuit portion of the stator 4 and the rotor magnet 26. The member 3 rotates together with the recording disk D with respect to the shaft member 1. At this time, in the radial dynamic pressure bearing portion 51, the air in the gap between the outer peripheral surface of the cylindrical shaft portion 11b and the inner peripheral surface of the sleeve 24 acts on the herringbone-shaped dynamic pressure generating grooves G ₁ , G ₁ ′. As a result, the fluid flows from both sides toward the "-"-shaped bent portion to generate a radial load supporting pressure. On the other hand, similarly in the thrust dynamic pressure bearing portion 52, by the action of the herringbone dynamic pressure generating grooves G _2, G 2 _', "V" lubricating fluid from both toward-shaped bent portion of the flowing Generates thrust load support pressure.
[0022]
Here, in the radial dynamic pressure bearing portion 52 according to the present invention, the thermal expansion coefficient of the shaft member 1 is made larger than that of the surrounding members (the rotor hub 2 and the sleeve 24) facing each other. On the other hand, the gap between the opposing surrounding member and the bearing member is narrowed, and the bearing characteristics are improved. On the other hand, in a low temperature range, the gap is widened and the torque loss is reduced. As a result, in the motor of the present invention, the torque loss at low speed rotation at the start and stop of motor driving is suppressed to be lower than that of the conventional motor. Further, although the bearing characteristics in the low temperature range are degraded by the widening of the gap, the rigidity of the thrust hydrodynamic bearing portion 52 is increased in the low temperature range because the liquid viscosity is increased in the low temperature range. Is stabilized.
[0023]
The coefficient of thermal expansion of the shaft member and the surrounding member may be appropriately determined based on the bearing gap of the radial dynamic pressure generating portion, the diameter of the shaft member, the operating temperature of the motor, and the like. For example, the diameter of the shaft member is D (mm), the coefficient of thermal expansion is α (/ ° C.), the coefficient of thermal expansion of the surrounding member is β (/ ° C.), the bearing gap C (mm, at 20 ° C.), When the temperature rise is 80 ° C. and the limit gap of the bearing is 0.001 (mm), the following inequality is satisfied, and the thermal expansion of the shaft member and the surrounding member is set so that (α−β) becomes highest within a range satisfying the inequality. You can decide the rate.
0 <(α−β) <2 × (C−0.001) / (80 × D)
Here, when C = 0.004 mm and D = 10 mm, 0 <(α−β) <7.5 × 10 ^−6.
It becomes.
[0024]
Preferred combinations of the shaft member and the surrounding member in the radial dynamic pressure bearing portion include, for example, the combinations shown in Table 1.
[0025]
[Table 1]

[0026]
The inventor actually used a SUS400 system having a thermal expansion coefficient of 10 × 10 ⁻⁶ (/ ° C.) as a shaft member and a thermal expansion coefficient of 7.8 × 10 ⁻⁶ (/ ° C.) as a sleeve member (surrounding member). The drive current value of the motor I using alumina was measured. For comparison, a motor using a SUS400 series having a thermal expansion coefficient of 10 × 10 ⁻⁶ (/ ° C.) as a shaft member and using zirconia having a thermal expansion coefficient of 9.6 × 10 ⁻⁶ (/ ° C.) as a sleeve member. The driving current value of II was also measured. As a result, no difference was found in the drive current values of both motors in the temperature range of 60 ° C. or higher, but at low temperatures, the drive current value of motor I was several tens mA lower than that of motor II. From this, it is understood that the larger the difference in the coefficient of thermal expansion between the shaft member and the surrounding member, the more the motor torque loss in the low temperature range can be reduced.
[0027]
Next, the disk drive of the present invention will be described below. FIG. 4 is a schematic diagram showing the internal configuration of a general disk drive 7. The interior of the housing (housing) 71 forms a clean space with extremely little dust and dirt, and a motor 72 on which a disk-shaped disk (recording medium) 73 for storing information is mounted. Is installed. In addition, a head moving mechanism (information access means) for reading / writing information from / to the disk plate 73 is disposed inside the housing 71. The head moving mechanism includes a head 76 for reading / writing information on the disk plate 73, The head 75 includes an arm 75 for supporting the head 76 and an actuator 74 for moving the arm 75 to a required position on the disk plate 73.
[0028]
【The invention's effect】
The motor of the present invention has a radial dynamic pressure bearing portion using air as a working fluid, and a thrust dynamic pressure bearing portion using a liquid as a working fluid. Since it is larger than that of the sleeve member (surrounding member), the loss torque in the low temperature range can be reduced while keeping the advantage of the hybrid type dynamic pressure bearing.
[0029]
Further, in the disk drive device of the present invention, since the above-described motor is used as the spindle motor for rotating the disc-shaped recording medium on which information can be recorded, the disk drive device can be rotated at a small size and at a high speed, and has excellent runout accuracy and quietness. In addition, the torque loss in the low temperature range is small.
[Brief description of the drawings]
FIG. 1 is an assembled sectional view showing an example of a motor of the present invention.
FIG. 2 is a sectional view of the motor of FIG. 1 after assembly.
FIG. 3 is a plan view showing an example of a thrust plate portion.
FIG. 4 is a schematic configuration diagram showing one example of a disk drive device of the present invention.
[Explanation of symbols]
1 shaft member 2 rotor hub (surrounding member)
3 Cap member 7 Disk drive 11 Shaft 11a Columnar shaft 11b Cylindrical shaft 12 Thrust plate 24 Sleeve member (surrounding member)
51 Radial dynamic pressure bearing part 52 Thrust dynamic pressure bearing part 71 Housing 73 Recording medium D Hard disk (recording medium)
M Motor G ₁ , G ₁ ′ Radial dynamic pressure generating groove G ₂ , G ₂ ′ Thrust dynamic pressure generating groove

Claims

A motor in which a shaft member and a surrounding member having a minute gap and surrounding the shaft member are rotatably engaged via a dynamic pressure bearing portion,
The dynamic pressure bearing portion includes a radial dynamic pressure bearing portion using air as a working fluid, and a thrust dynamic pressure bearing portion using liquid as a working fluid,
A motor, wherein a coefficient of thermal expansion of a shaft member in the radial dynamic pressure bearing portion is larger than that of an opposing surrounding member.

The shaft member has a shaft portion and a thrust plate portion protruding radially outward from the shaft portion, and the surrounding member is provided with a small gap between the shaft portion and the thrust plate portion. Have been
The radial dynamic pressure bearing portion is provided on at least one of the shaft portion and the inner peripheral surface of the surrounding member facing the shaft portion, and includes a radial dynamic pressure generating groove for supporting a radial load and air. And
The thrust dynamic pressure bearing portion is provided on at least one of the upper and lower surfaces of the thrust plate portion and the inner surface of the surrounding member facing the upper and lower surfaces, a thrust dynamic pressure generating groove for supporting a thrust load, 2. The motor according to claim 1, wherein said motor is constituted by a lubricating liquid filled between said opposed surfaces.

3. The motor according to claim 1, wherein a main material of the shaft member is stainless steel, and a main material of the surrounding member is a ceramic material.

In a disk drive device on which a disc-shaped recording medium capable of recording information is mounted, a housing, a spindle motor fixed inside the housing and rotating the recording medium, and information stored in a desired position on the recording medium A disk drive device having information access means for writing or reading data, wherein the motor according to any one of claims 1 to 3 is used as the spindle motor.