JP4048013B2

JP4048013B2 - Hydrodynamic bearing unit

Info

Publication number: JP4048013B2
Application number: JP36306699A
Authority: JP
Inventors: 嗣人中関; 一男岡村
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 1999-12-21
Filing date: 1999-12-21
Publication date: 2008-02-13
Anticipated expiration: 2019-12-21
Also published as: JP2001173645A

Description

【０００１】
【発明の属する技術分野】
本発明は、動圧型軸受ユニットに関する。この軸受ユニットは、特に情報機器、例えばＨＤＤ、ＦＤＤ等の磁気ディスク装置、ＣＤ−ＲＯＭ、ＤＶＤ−ＲＯＭ等の光ディスク装置、ＭＤ、ＭＯ等の光磁気ディスク装置などのスピンドルモータ、あるいはレーザビームプリンタ（ＬＢＰ）のポリゴンスキャナモータなどのスピンドル支持用として好適なものである。
【０００２】
【従来の技術】
上記各種情報機器のスピンドルモータには、高回転精度の他、高速化、低コスト化、低騒音化などが求められている。これらの要求性能を決定づける構成要素の一つに当該モータのスピンドルを支持する軸受があり、近年では、この種の軸受として、上記要求性能に優れた特性を有する動圧型軸受の使用が検討され、あるいは実際に使用されている。
【０００３】
図４はこの種のスピンドルモータの一例で、軸受ユニット21で回転自在に支持された軸部材22（軸22ａと、軸22ａへの装着によりフランジ部となるスラスト円盤22ｂとで構成される）を、軸受部材27側に固定したモータステータ４と、軸部材22側に装着したモータロータ５との間に生じる励磁力で回転駆動する構造である。軸受ユニット21には、軸部材22をラジアル方向で支持するラジアル軸受部30とスラスト円盤22ｂをスラスト方向で支持するスラスト軸受部31とが設けられ、これらの軸受部30、31は何れも軸受面に動圧発生用の溝（動圧溝）を有する動圧型軸受とされる。ラジアル軸受部30の動圧溝は、軸受部材27の内周面（あるいは軸22ａの外周面）に形成され、スラスト軸受部31の動圧溝は、軸部材22の下端に固定したスラスト円盤22ｂの両端面（あるいは当該端面に対向する面）にそれぞれ形成される。軸受部材27の底部には円板状のバックメタル33が嵌め込まれ、軸受部材27の底部側の開口部が封口されている。
【０００４】
軸部材22が回転すると、ラジアル軸受部30の軸受すきまＣｒ（軸22ａの外周面と軸受部材27の内周面との間のすきま）やスラスト軸受部31の軸受すきまＣs1、Ｃs2（スラスト円盤22ｂの両端面と、軸受部材24の端面およびバックメタル33の端面との間のすきま）に動圧油膜が形成され、軸部材２が非接触状態で回転自在に支持される。
【０００５】
スラスト軸受部31におけるスラスト軸受面（動圧溝を形成した面）の動圧溝の形状としては、図５（Ｃ）に示すへリングボーン型と図６（Ｃ）に示すスパイラル型とが代表的で、これら動圧溝35、35’の形状は用途に応じて適宜使い分けられている。へリングボーン型の動圧溝35は図示のように略Ｖ字状であり、外周部において流体を内径側に押し込むポンプイン部35ａと、その内周部において流体を外径側に押し込むポンプアウト部35ｂとを有する。ポンプイン部35ａで内径側に押し込まれた流体とポンプアウト部35ｂで外径側に押し込まれた流体とがＶ字の折り返し部分35ｃ付近で合流し、動圧を発生するため、スラスト軸受面での動圧の圧力分布は、図５（Ｂ）に示すようにリング状となる。この圧力分布から、へリングボーン型の動圧溝35では、図６（Ｂ）に示す圧力分布のスパイラル型の動圧溝35’に比べてモーメント荷重に対する負荷容量が大きく、それ故、薄型モータのようにラジアル軸受部30の軸方向長さを長くできず、モーメント負荷容量が小さくなるような場合には、へリングボーン型の動圧溝35を採用する場合が多い。
【０００６】
【発明が解決しようとする課題】
ところで、へリングボーン型の動圧溝35では、ポンプアウト部35ｂを流れる流体に軸部材22の回転に伴う遠心力が加わるため、スラスト軸受すきまの軸芯付近では流体を外径側に引き込もうとする力が強く働く。そのため、高速回転下では、図５（Ｂ）に示すようにポンプアウト部35ｂよりも内径側の領域で負圧の部分Ｎを生じ易い。かかる負圧下では流体中に気泡が発生しやく、この気泡が軸受性能、特にスラスト軸受性能の低下をおこすおそれがある。
【０００７】
この問題に対処するため、図４に示すように、軸部材22にスラスト軸受すきまＣs2の中心部とラジアル軸受すきまＣｒとに開口したバイパス孔36を設けることにより、スラスト軸受すきまＣs2（ラジアル軸受すきまＣｒも含めて）の圧力バランスを確保する提案もなされているが、バイパス孔36分の加工工数が増えるためにコスト高であり、また、バイパス孔36に残った異物が各軸受すきまＣｒ、Ｃs1、Ｃs2に入り込むおそれもある。
【０００８】
そこで、本発明は、バイパス孔を設けずとも、スラスト軸受すきまでの負圧発生を防止できる動圧型軸受ユニットの提供を目的とする。
【０００９】
【課題を解決するための手段】
本発明にかかる動圧軸受ユニットは、軸および軸端に設けられたフランジ部を有する軸部材と、軸部材の外周にラジアル軸受すきまを介して配置された軸受部材と、内周面に軸受部材を固定したハウジングと、フランジ部の軸方向一方を密閉するスラスト支持部と、スラスト支持部の端面とフランジ部の一端面との間に形成された一方のスラスト軸受すきまと、フランジ部の他端面と軸受部材の端面との間に形成され、内径部がラジアル軸受すきまに連通すると共に、外径部が上記一方のスラスト軸受すきまの外径部に連通した他方のスラスト軸受すきまと、上記一方のスラスト軸受すきまに面してスラスト支持部またはフランジ部の何れか一方に設けられ、回転側部材の回転時に上記一方のスラスト軸受すきまに動圧を発生させる動圧溝を有するスラスト軸受面とを備え、上記動圧溝が、油を内径側に押し込むポンプイン部と、ポンプイン部の内周部で油を外径側に押し込むポンプアウト部とを有し、上記一方のスラスト軸受すきまが、ポンプアウト部よりも内径側の領域を有する動圧型軸受ユニットにおいて、
上記一方のスラスト軸受すきまが、ポンプアウト部よりも内径側の領域を含めて油で満たされ、上記一方のスラスト軸受すきまのポンプアウト部よりも内径側の領域がフランジ部とスラスト支持部とで密閉され、スラスト軸受面の動圧溝が、ポンプイン部のポンプ作用をポンプアウト部のポンプ作用よりも大きくすることで、ポンプアウト部よりも内径側の領域での負圧発生を防止する負圧発生防止機構を有し、軸受部材が油を保有した焼結金属で形成され、かつその端面がフランジ部の外周空間に面し、ハウジングがスラスト支持部を一体に有する有底円筒状であり、ハウジング内周面が段差のないストレート面であることを特徴とするものである。
【００１０】
この動圧型軸受ユニットにおいて、スラスト軸受面の動圧溝を、ポンプアウト部よりも内径側の領域での負圧発生を防止する負圧発生防止機構を有するものとすれば、当該内径側領域での気泡の発生を防止し、気泡発生による軸受性能の低下を回避することができる。
【００１１】
ポンプイン部のポンプ作用とポンプアウト部のポンプ作用との強弱調整は、例えば動圧溝形状を従来形状から変更することで実現できる。このような動圧溝の形状変更は、従来のようにバイパス孔を加工する場合に比べて加工コストを安価に抑えることができ、また、バイパス孔内での異物の残存も問題とはならない。
【００１２】
ポンプ作用の強弱調整は、ポンプイン部のポンプ作用を強化し、もしくはポンプアウト部のポンプ作用を弱化することによって行える。
【００１３】
ポンプイン部のポンプ作用の強化、もしくはポンプアウト部のポンプ作用の弱化は、ポンプイン部で押し込まれた流体とポンプアウト部で押し込まれた流体との合流部、例えばへリングボーン型動圧溝の折り返し部分を半径方向に変位させることで実現できる。この他、ポンプイン部を流れる流体の流量とポンプアウト部を流れる流体の流量とに差を設けてもよい。
【００１４】
上述の動圧型軸受ユニットには、固定側部材または回転側部材のうちの何れか一方の部材に含まれる軸部材と、他方の部材に含まれ、軸部材の外周にラジアル軸受すきまを介して配置された軸受部材とを備え、かつ軸受部材を、油を保有した焼結金属で形成した、いわゆる動圧型焼結含油軸受を適用することができる。軸受部材を含油焼結金属で形成した場合、軸受部材の内部で油が循環するため、ラジアル軸受すきまやスラスト軸受すきまでより一層負圧が生じにくくなる。
【００１５】
【発明の実施の形態】
以下、本発明の実施形態を図１〜図３に基いて説明する。
【００１６】
図１は、本発明にかかる動圧型軸受ユニット１を備える情報機器用スピンドルモータの断面図で、一例としてＨＤＤ（ハードディスクドライブ）スピンドルモータを示している。このスピンドルモータは、軸部材２（スピンドル）を回転自在に支持する軸受ユニット１と、軸部材２に取付けられ、磁気ディスクＤを一又は複数枚保持するディスクハブ３と、半径方向のギャップを介して対向させたモータステータ４およびモータロータ５とを有する。ステータ４は、軸受ユニット１を保持するケーシング９の円筒状外周部に取付けられ、ロータ５はディスクハブ３の内周面に取付けられている。ステータ４に通電すると、ステータ４とロータ５との間の励磁力でロータ５が回転し、ディスクハブ３および軸部材２が回転する。
【００１７】
軸受ユニット１は、軸部材２と、有底円筒状のいわゆる袋型ハウジング６と、ハウジング６の内周面に固定された厚肉円筒状の軸受部材７と、軸受部材７の一端側（ハウジング６の開口側）を密封するシールワッシャ等のシール部材８とを主な構成要素とする。軸部材２は、軸2aと軸2aの下端部に一体形成または圧入され、外径側に突出するスラスト円盤2b（フランジ部）とで構成される。この軸部材２は、軸2aを軸受部材７の内周部に、フランジ部2bを軸受部材７とハウジング６の底部との間に収容して配置される。
【００１８】
軸受部材７は、油を保有した焼結金属で形成される。軸受部材７の内周面には、複数の動圧溝を有するラジアル軸受面10ａが形成され、これより軸部材２と軸受部材７の相対回転時（本実施形態では軸部材２の回転時）には、固定側のラジアル軸受面10ａと回転側の軸2aの外周面との間のラジアル軸受すきまＣｒに潤滑油の動圧が発生し、軸2aをラジアル方向で非接触支持するラジアル軸受部10が構成される。ラジアル軸受面10ａは軸部材２の外周面に形成してもよい。
【００１９】
焼結金属を使用する場合の動圧溝は、圧縮成形、すなわち、コアロッドの外周面にラジアル軸受面10ａの動圧溝形状（図２参照）に対応した凹凸形状の溝型を形成し、コアロッドの外周に焼結金属を供給して焼結金属を圧迫し、焼結金属の内周部に溝型形状に対応した動圧溝を転写することによって、低コストにかつ高精度に成形することができる。この場合、焼結金属の脱型は、圧迫力を解除することによる焼結金属のスプリングバックを利用して簡単に行える。脱型後の軸受部材７に潤滑剤、例えば潤滑油や潤滑グリースを含浸して油を保有させることにより、動圧型焼結含油軸受が構成される。なお、動圧溝サイジングを行う前に、多孔質材の内部に回転サイジングを施し、当該内径面の開孔率を抑えておくのが望ましい。
【００２０】
上記ラジアル軸受面10ａの動圧溝形状は任意に選択することができ、公知のへリングボーン型、スパイラル型、ステップ型、多円弧型等の何れかを選択し、あるいはこれらを適宜組合わせて使用することができる。図２は、ラジアル軸受面10ａの動圧溝形状の一例としてへリングボーン型を示す。図示のように、このラジアル軸受面10ａは、一方に傾斜する動圧溝13が形成された第一の溝領域m1と、第一の溝領域m1から軸方向に離隔し、他方に傾斜する動圧溝13が配列された第二の溝領域m2と、２つの溝領域間m1、m2間に位置する環状の平滑部ｎとを備え、平滑部ｎと動圧溝13間の背の部分14とは同一レベルにある。図２では、へリングボーン型動圧溝13を一列のみ表示しているが、モーメント荷重を受けるべく、通常は二列のへリングボーン型動圧溝13が設けられる。
【００２１】
フランジ部2bの軸方向両側には、軸方向のすきまであるスラスト軸受すきまＣs1、Ｃs2が設けられる。スラスト軸受すきまＣs1は、フランジ部2bの上端面とこれに対向する軸受部材７の端面との間に形成され、他方のスラスト軸受すきまＣs2は、フランジ部2bの下端面と、これに対向するスラスト支持部13の上面との間に形成される。本発明では、スラスト支持部13がハウジング６の他端開口を封口する底部となり、かつハウジング６と一体に形成される。一方のスラスト軸受すきまＣs1を臨む軸受部材７の下端面、および他方のスラスト軸受すきまＣs2を臨むスラスト支持部13の上面には、それぞれ動圧溝を有するスラスト軸受面11ａ、11ｂが形成され、これより軸部材２の回転時には、スラスト軸受すきまＣs1、Ｃs2に潤滑油の動圧が発生し、フランジ部2bをスラスト方向両側から非接触支持するスラスト軸受部11が構成される。スラスト軸受面11ａ、11ｂの何れか一方、あるいは双方は、フランジ部2bの一方の端面、あるいは両端面に形成することもできる。
【００２２】
スラスト軸受面11ａ、11ｂには、図３（Ｃ）に示すように、へリングボーン型に配列した複数の動圧溝15（クロスハッチングで示す）が形成される（図は一例としてハウジング６底部側、すなわちスラスト支持部13に設けられたスラスト軸受面11ｂを例示している）。スラスト軸受面11ａ、11ｂの動圧溝15は、同一径の円周方向線上に折り返し部分15ｃを有するほぼＶ字状をなし、折り返し部分15ｃを境とする外径側および内径側の何れの部分15ａ、15ｂも外径側を凸とする部分円弧状に形成される。動圧溝15のうち、折り返し部分15ｃの外径側はポンプイン部15ａで、軸部材２の回転に伴って作動流体である油を内径側に押し込み、折り返し部分15ｃの内径側はポンプアウト部15ｂで軸部材２の回転に伴って油を外径側に押し込む。ポンプイン部15ａとポンプアウト部15ｂによって押し込まれた油は、折り返し部分15ｃの近傍で合流し、所定の動圧を発生する。この時の圧力分布は、図示のように従来と同様のリング状となる。このスラスト軸受面11ａ、11ｂは、例えば上記動圧溝形状に対応した凹凸を有する型を用いてプレス等することにより、簡単かつ高精度に成形できる。
【００２３】
上記軸受ユニット１は、ハウジング６内にフランジ部2bを下にして軸部材２を挿入し、さらに所定幅のスラスト軸受すきまＣs1、Ｃs2が形成されるようにハウジング６内周部の所定位置に、軸受部材７を圧入あるいは接着することにより組立てられる。そして、この軸受ユニット１をケーシング９の円筒状内周部に圧入あるいは接着し、さらにロータ５やディスクハブ３からなるアッセンブリ（モータロータ）を軸2aの上端に圧入することにより、図１に示すスピンドルモータが組立てられる。なお、本実施形態は、上記のように軸部材２を回転させる構造であるから、軸部材２、ディスクハブ３等が回転側部材となり、ハウジング６、シール部材８、ケーシング９等が固定側部材となる。
【００２４】
本発明は、二つのスラスト軸受面11ａ、11ｂのうちの少なくとも一方、例えばハウジング底部側（スラスト支持部13側）のスラスト軸受面11ｂの動圧溝15に、負圧発生防止機構17を持たせたものである。負圧発生防止機構17は、スラスト軸受すきまＣs2のうち、ポンプアウト部15ｂよりも内径側の領域での負圧発生を防止するもので、本発明では、これをポンプイン部15ａとポンプアウト部15ｂの各ポンプ作用（油の押し込み力）の強弱を調整することで実現している。
【００２５】
図３（Ａ）（Ｃ）は、ポンプ作用強弱調整手段の一例を示すもので、この例では、動圧溝15の折り返し径ｄ、すなわち各動圧溝15の折り返し部分15ｃを結んでできる円の直径を図５（Ｃ）に示す従来品の折り返し径d'よりも小さくしている。この場合も、ポンプイン部15ａに押し込まれた油とポンプアウト部15ｂに押し込まれた油は折り返し部分15ｃ付近で合流するが、この合流部分が従来品よりも内径側に変位しているため、ポンプアウト部15ｂのポンプ作用は弱くなる（反対にポンプイン部15ａのポンプ作用は強くなる）。そのため、高速回転時においてもポンプアウト部15ｂで過剰の油が外径側に押し込まれることはなく、これより同図（Ｂ）に示すように、ポンプアウト部15ｂよりも内径側のスラスト軸受すきまＣs2、特にその軸芯周辺での負圧発生を防止することができる。なお、この負圧発生防止機構17は、従来のプレス型を対応品に交換するだけで動圧溝15と同時に成形可能であり、低コストに加工可能である。
【００２６】
負圧発生防止機構17におけるポンプ作用の強弱の程度は、軸受ユニット１の使用回転数に応じて定められ、例えば本実施形態では、最大使用回転数下においても負圧が発生しないように折り返し径ｄが設定される。
【００２７】
上記と同様の効果は、ポンプイン部15ａを流れる油の流量とポンプアウト部15ｂを流れる油の流量とに差を設けることによって得ることができる。流量の調整手段としては、例えばポンプアウト部15ｂの溝深さをポンプイン部15ａよりも浅くすることが考えられる。その他、ポンプアウト部15ｂの溝幅をポンプイン部15ａのそれよりも小さくしてもよい（何れも図示は省略）。
【００２８】
ポンプ作用の強弱調整は、ポンプイン部15ａのポンプ作用を強化し、もしくはポンプアウト部15ｂのポンプ作用を弱化すればよいので、これを実現できる限り、上記以外の他の構成を採用することも可能である。
【００２９】
なお、軸受部材７を上記含油焼結金属で形成した場合、軸受部材７の内部で油が循環するため、ラジアル軸受すきまＣｒやスラスト軸受すきまＣs1、Ｃs2での負圧発生防止により有効となる。
【００３０】
【発明の効果】
このように本発明によれば、スラスト軸受面の動圧溝に負圧発生防止機構を設けているので、スラスト軸受すきま、特にポンプアウト部の内径側領域での負圧の発生を防止することができる。従って、スラスト軸受すきまへの気泡の混入を防止することができ、安定した軸受性能（特にスラスト負荷能力）が確保される。この負圧発生防止機構は、動圧溝の成形と同時にプレス等で簡単に加工することができるので、従来のようにバイパス孔を貫通形成する場合に比べて加工コストの低減が図られる。また、バイパス孔を加工する場合のように狭い孔内での異物の残存、および当該異物の軸受すきまへの侵入が生じることはなく、軸受性能を長期間安定して維持することができる。
【図面の簡単な説明】
【図１】本発明にかかる動圧型軸受ユニットの断面図である。
【図２】軸受部材の部分拡大断面図であって、ラジアル軸受面は展開した状態を示す。
【図３】（Ａ）図は軸部材の側面図、（Ｂ）図は圧力分布を示す図、（Ｃ）図はスラスト軸受面の平面図である。）図１の要部拡大断面図である。
【図４】従来の動圧型軸受ユニットの断面図である。
【図５】図４に示す軸受ユニットにおける、軸部材の側面図（Ａ図）、動圧の圧力分布図（Ｂ図）、およびへリングボーン型の動圧溝を有するスラスト軸受面の平面図（Ｃ図）である。
【図６】図４に示す軸受ユニットにおける、軸部材の側面図（Ａ図）、動圧の圧力分布図（Ｂ図）、およびスパイラル型の動圧溝を有するスラスト軸受面の平面図（Ｃ図）である。
【符号の説明】
１軸受ユニット
２軸部材
６ハウジング
７軸受部材
10ａラジアル軸受面
11ａスラスト軸受面
11ｂスラスト軸受面
13 ラジアル軸受面の動圧溝
15 スラスト軸受面の動圧溝
15ａポンプイン部
15ｂポンプアウト部
15ｃ折り返し部分（合流部）
17 負圧発生防止機構
Ｃｒラジアル軸受すきま
Ｃs1 スラスト軸受すきま
Ｃs2 スラスト軸受すきま
ｄ折り返し径[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dynamic pressure type bearing unit. This bearing unit is particularly suitable for information equipment, for example, a spindle motor such as a magnetic disk device such as HDD or FDD, an optical disk device such as CD-ROM or DVD-ROM, a magneto-optical disk device such as MD or MO, or a laser beam printer ( It is suitable for supporting a spindle such as a polygon scanner motor of LBP).
[0002]
[Prior art]
In addition to high rotational accuracy, spindle motors of the various information devices 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 hydrodynamic bearing having characteristics excellent in the required performance has been studied as this type of bearing. Or it is actually used.
[0003]
FIG. 4 shows an example of this type of spindle motor. A shaft member 22 (comprised of a shaft 22a and a thrust disk 22b that becomes a flange portion when mounted on the shaft 22a) is rotatably supported by a bearing unit 21. In this structure, the motor stator 4 fixed on the bearing member 27 side and the motor rotor 5 mounted on the shaft member 22 side are rotationally driven by an exciting force. The bearing unit 21 is provided with a radial bearing portion 30 for supporting the shaft member 22 in the radial direction and a thrust bearing portion 31 for supporting the thrust disk 22b in the thrust direction. These bearing portions 30, 31 are both bearing surfaces. The hydrodynamic bearing has a dynamic pressure generating groove (dynamic pressure groove). The dynamic pressure groove of the radial bearing portion 30 is formed on the inner peripheral surface of the bearing member 27 (or the outer peripheral surface of the shaft 22 a), and the dynamic pressure groove of the thrust bearing portion 31 is fixed to the lower end of the shaft member 22. Are formed on both end faces (or faces facing the end faces). A disc-shaped back metal 33 is fitted into the bottom of the bearing member 27, and the opening on the bottom side of the bearing member 27 is sealed.
[0004]
When the shaft member 22 rotates, the bearing clearance Cr of the radial bearing portion 30 (the clearance between the outer peripheral surface of the shaft 22a and the inner peripheral surface of the bearing member 27) and the bearing clearances Cs1 and Cs2 of the thrust bearing portion 31 (thrust disk 22b) Are formed between the two end surfaces and the end surface of the bearing member 24 and the end surface of the back metal 33), and the shaft member 2 is rotatably supported in a non-contact state.
[0005]
As the shape of the dynamic pressure groove on the thrust bearing surface (surface on which the dynamic pressure groove is formed) in the thrust bearing portion 31, the herringbone type shown in FIG. 5 (C) and the spiral type shown in FIG. 6 (C) are representative. Therefore, the shapes of the dynamic pressure grooves 35 and 35 ′ are properly used depending on the application. The herringbone-type dynamic pressure groove 35 is substantially V-shaped as shown in the figure, and a pump-in portion 35a for pushing the fluid to the inner diameter side at the outer peripheral portion and a pump-out for pushing the fluid to the outer diameter side at the inner peripheral portion. Part 35b. The fluid pushed into the inner diameter side by the pump-in portion 35a and the fluid pushed to the outer diameter side by the pump-out portion 35b merge near the V-shaped folded portion 35c and generate dynamic pressure. The pressure distribution of the dynamic pressure is a ring shape as shown in FIG. From this pressure distribution, the herringbone type dynamic pressure groove 35 has a larger load capacity with respect to moment load than the spiral type dynamic pressure groove 35 ′ having the pressure distribution shown in FIG. When the axial length of the radial bearing portion 30 cannot be increased as described above and the moment load capacity is reduced, the herringbone type dynamic pressure groove 35 is often employed.
[0006]
[Problems to be solved by the invention]
By the way, in the herringbone type dynamic pressure groove 35, a centrifugal force accompanying the rotation of the shaft member 22 is applied to the fluid flowing through the pump-out portion 35b, so that the fluid is drawn to the outer diameter side in the vicinity of the axial center of the thrust bearing clearance. Power to work strongly. Therefore, under high-speed rotation, as shown in FIG. 5B, a negative pressure portion N is likely to be generated in the inner diameter side region from the pump-out portion 35b. Under such a negative pressure, bubbles are likely to be generated in the fluid, and these bubbles may cause deterioration in bearing performance, particularly thrust bearing performance.
[0007]
In order to cope with this problem, as shown in FIG. 4, a thrust bearing clearance Cs2 (radial bearing clearance) is provided in the shaft member 22 by providing a bypass hole 36 opened in the central portion of the thrust bearing clearance Cs2 and the radial bearing clearance Cr. Proposals have been made to ensure the pressure balance (including Cr), but the cost is high because the number of processing steps for the bypass hole 36 is increased, and the foreign matter remaining in the bypass hole 36 causes the bearing clearances Cr, Cs1. There is also a risk of entering Cs2.
[0008]
Therefore, an object of the present invention is to provide a dynamic pressure type bearing unit that can prevent generation of negative pressure up to a thrust bearing clearance without providing a bypass hole.
[0009]
[Means for Solving the Problems]
A hydrodynamic bearing unit according to the present invention includes a shaft member having a shaft and a flange portion provided at a shaft end, a bearing member disposed on the outer periphery of the shaft member via a radial bearing clearance, and a bearing member on an inner peripheral surface. , A thrust support portion that seals one axial direction of the flange portion, one thrust bearing clearance formed between the end surface of the thrust support portion and one end surface of the flange portion, and the other end surface of the flange portion And the end surface of the bearing member, the inner diameter portion communicates with the radial bearing clearance, the outer diameter portion communicates with the outer diameter portion of the one thrust bearing clearance, and the other thrust bearing clearance. A dynamic pressure groove is provided on either the thrust support portion or the flange portion facing the thrust bearing clearance, and generates dynamic pressure in the one thrust bearing clearance when the rotating side member rotates. The dynamic pressure groove has a pump-in portion that pushes oil into the inner diameter side, and a pump-out portion that pushes oil into the outer diameter side at the inner peripheral portion of the pump-in portion, In the dynamic pressure type bearing unit in which the thrust bearing clearance has a region on the inner diameter side of the pump-out portion,
The above-mentioned one thrust bearing clearance is filled with oil including the region on the inner diameter side from the pump-out portion, and the region on the inner diameter side from the pump-out portion of the above-mentioned one thrust bearing clearance is formed by the flange portion and the thrust support portion. Sealed and the dynamic pressure groove on the thrust bearing surface makes the pumping action of the pump-in part larger than the pumping action of the pump-out part, thereby preventing negative pressure generation in the region on the inner diameter side of the pump-out part. It has a pressure generation prevention mechanism, the bearing member is made of sintered metal holding oil , its end face faces the outer peripheral space of the flange part, and the housing is a bottomed cylindrical shape integrally having a thrust support part The inner peripheral surface of the housing is a straight surface without a step.
[0010]
In this dynamic pressure type bearing unit, if the dynamic pressure groove on the thrust bearing surface has a negative pressure generation preventing mechanism that prevents the generation of negative pressure in the region on the inner diameter side from the pump-out portion, Generation of bubbles can be prevented, and deterioration of bearing performance due to generation of bubbles can be avoided.
[0011]
The strength adjustment between the pumping action of the pump-in part and the pumping action of the pump-out part can be realized , for example, by changing the dynamic pressure groove shape from the conventional shape. Such a change in the shape of the dynamic pressure groove can reduce the processing cost at a lower cost than the case of processing the bypass hole as in the prior art, and the remaining foreign matter in the bypass hole is not a problem.
[0012]
The adjustment of the pump action can be performed by strengthening the pump action of the pump-in part or weakening the pump action of the pump-out part.
[0013]
The pumping action of the pump-in part is strengthened or the pumping action of the pump-out part is weakened. The merged part of the fluid pushed in the pump-in part and the fluid pushed in the pump-out part, for example, a herringbone type dynamic pressure groove This can be realized by displacing the folded portion of the substrate in the radial direction. In addition, a difference may be provided between the flow rate of the fluid flowing through the pump-in portion and the flow rate of the fluid flowing through the pump-out portion.
[0014]
The above-described dynamic pressure type bearing unit includes a shaft member included in one of the fixed side member and the rotation side member and the other member, and is disposed on the outer periphery of the shaft member via a radial bearing clearance. A so-called dynamic pressure type sintered oil-impregnated bearing, which is formed of a sintered metal having oil, can be applied. When the bearing member is formed of oil-impregnated sintered metal, oil circulates inside the bearing member, and therefore, negative pressure is less likely to be generated up to the radial bearing clearance and the thrust bearing clearance.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0016]
FIG. 1 is a sectional view of a spindle motor for information equipment provided with a hydrodynamic bearing unit 1 according to the present invention, and shows an HDD (Hard Disk Drive) spindle motor as an example. The spindle motor includes a bearing unit 1 that rotatably supports a shaft member 2 (spindle), a disk hub 3 that is attached to the shaft member 2 and holds one or more magnetic disks D, and a radial gap. The motor stator 4 and the motor rotor 5 are opposed to each other. The stator 4 is attached to the cylindrical outer peripheral portion of the casing 9 that holds the bearing unit 1, and the rotor 5 is attached to the inner peripheral surface of the disk hub 3. When the stator 4 is energized, the rotor 5 is rotated by the exciting force between the stator 4 and the rotor 5, and the disk hub 3 and the shaft member 2 are rotated.
[0017]
The bearing unit 1 includes a shaft member 2, a so-called bag-shaped housing 6 having a bottomed cylindrical shape, a thick cylindrical bearing member 7 fixed to the inner peripheral surface of the housing 6, and one end side of the bearing member 7 (housing 6 and the sealing member 8 such as a seal washer that seals the opening side). The shaft member 2 includes a shaft 2a and a thrust disk 2b (flange portion) that is integrally formed or press-fitted into the lower end portion of the shaft 2a and protrudes toward the outer diameter side. The shaft member 2 is arranged with the shaft 2 a accommodated in the inner peripheral portion of the bearing member 7 and the flange portion 2 b accommodated between the bearing member 7 and the bottom portion of the housing 6.
[0018]
The bearing member 7 is formed of a sintered metal having oil . A radial bearing surface 10 a having a plurality of dynamic pressure grooves is formed on the inner peripheral surface of the bearing member 7, and thereby the shaft member 2 and the bearing member 7 are rotated relative to each other (in this embodiment, the shaft member 2 is rotated). Includes a radial bearing portion in which dynamic pressure of lubricating oil is generated in the radial bearing clearance Cr between the fixed-side radial bearing surface 10a and the outer peripheral surface of the rotating-side shaft 2a, and the shaft 2a is supported in a non-contact manner in the radial direction. 10 is configured. The radial bearing surface 10 a may be formed on the outer peripheral surface of the shaft member 2.
[0019]
When using sintered metal, the dynamic pressure groove is compression-molded, that is, an irregular groove shape corresponding to the dynamic pressure groove shape (see FIG. 2) of the radial bearing surface 10a is formed on the outer peripheral surface of the core rod. Sintered metal is supplied to the outer periphery of the metal, pressed against the sintered metal, and a dynamic pressure groove corresponding to the groove shape is transferred to the inner peripheral portion of the sintered metal, thereby forming at low cost and with high accuracy. Can do. In this case, demolding of the sintered metal can be easily performed using a spring back of the sintered metal by releasing the pressing force. A hydrodynamic sintered oil-impregnated bearing is configured by impregnating the bearing member 7 after demolding with a lubricant, for example, lubricating oil or lubricating grease, and retaining the oil. In addition, before performing dynamic pressure groove sizing, it is desirable to perform rotational sizing inside the porous material to suppress the open area ratio of the inner diameter surface.
[0020]
The dynamic pressure groove shape of the radial bearing surface 10a can be arbitrarily selected, and a known herringbone type, spiral type, step type, multi-arc type, or the like is selected, or these are appropriately combined. Can be used. FIG. 2 shows a herringbone type as an example of the dynamic pressure groove shape of the radial bearing surface 10a. As illustrated, the radial bearing surface 10a includes a first groove region m1 in which a dynamic pressure groove 13 inclined on one side is formed, and an axially separated movement from the first groove region m1 and inclined on the other side. A second groove region m2 in which the pressure grooves 13 are arranged; and an annular smooth portion n positioned between the two groove regions m1 and m2. A back portion 14 between the smooth portion n and the dynamic pressure groove 13 Are at the same level. In FIG. 2, only one row of herringbone type dynamic pressure grooves 13 is shown, but usually two rows of herringbone type dynamic pressure grooves 13 are provided to receive moment load.
[0021]
Thrust bearing clearances Cs1 and Cs2 extending to the axial clearance are provided on both axial sides of the flange portion 2b. The thrust bearing clearance Cs1 is formed between the upper end surface of the flange portion 2b and the end surface of the bearing member 7 facing this, and the other thrust bearing clearance Cs2 is the lower end surface of the flange portion 2b and the thrust facing this. It is formed between the upper surface of the support part 13. In the present invention, the thrust supporting portion 13 is a bottom for sealing the other open end of the housing 6, and is formed integrally with the housing 6. Thrust bearing surfaces 11a and 11b having dynamic pressure grooves are formed on the lower end surface of the bearing member 7 facing one thrust bearing clearance Cs1 and the upper surface of the thrust support portion 13 facing the other thrust bearing clearance Cs2. Further, when the shaft member 2 rotates, a dynamic pressure of lubricating oil is generated in the thrust bearing clearances Cs1 and Cs2, and the thrust bearing portion 11 is configured to support the flange portion 2b in a non-contact manner from both sides in the thrust direction. Either one or both of the thrust bearing surfaces 11a and 11b can be formed on one end surface or both end surfaces of the flange portion 2b.
[0022]
As shown in FIG. 3C, the thrust bearing surfaces 11a and 11b are formed with a plurality of dynamic pressure grooves 15 (indicated by cross hatching) arranged in a herringbone shape (the figure shows the bottom of the housing 6 as an example). The thrust bearing surface 11b provided on the side, that is, the thrust support portion 13 is illustrated). The dynamic pressure grooves 15 of the thrust bearing surfaces 11a and 11b have a substantially V shape having a folded portion 15c on the circumferential line of the same diameter, and any portion on the outer diameter side and the inner diameter side with the folded portion 15c as a boundary. 15a and 15b are also formed in a partial arc shape with the outer diameter side convex. Of the dynamic pressure groove 15, the outer diameter side of the folded portion 15c is a pump-in portion 15a, and the working fluid oil is pushed into the inner diameter side as the shaft member 2 rotates, and the inner diameter side of the folded portion 15c is the pump-out portion. In 15b, oil is pushed into the outer diameter side as the shaft member 2 rotates. The oil pushed in by the pump-in portion 15a and the pump-out portion 15b merges in the vicinity of the turned-up portion 15c and generates a predetermined dynamic pressure. The pressure distribution at this time has a ring shape similar to the conventional one as shown. The thrust bearing surfaces 11a and 11b can be easily and highly accurately formed by, for example, pressing using a mold having irregularities corresponding to the dynamic pressure groove shape.
[0023]
In the bearing unit 1, the shaft member 2 is inserted into the housing 6 with the flange portion 2b facing downward, and thrust bearing clearances Cs1 and Cs2 having predetermined widths are formed at predetermined positions on the inner peripheral portion of the housing 6. The bearing member 7 is assembled by press-fitting or bonding. Then, the bearing unit 1 is press-fitted or bonded to the cylindrical inner peripheral portion of the casing 9, and an assembly (motor rotor) including the rotor 5 and the disk hub 3 is press-fitted to the upper end of the shaft 2a, whereby the spindle shown in FIG. The motor is assembled. In this embodiment, since the shaft member 2 is rotated as described above, the shaft member 2, the disc hub 3 and the like serve as the rotation side members, and the housing 6, the seal member 8, the casing 9 and the like serve as the fixed side members. It becomes.
[0024]
In the present invention, a negative pressure generation preventing mechanism 17 is provided in at least one of the two thrust bearing surfaces 11a and 11b, for example, the dynamic pressure groove 15 of the thrust bearing surface 11b on the housing bottom side (thrust support portion 13 side). It is a thing. The negative pressure generation prevention mechanism 17 prevents the generation of negative pressure in the thrust bearing clearance Cs2 in the region on the inner diameter side of the pump out portion 15b. In the present invention, the negative pressure generation prevention mechanism 17 is connected to the pump in portion 15a and the pump out portion. This is realized by adjusting the strength of each pump action (oil pushing force) of 15b.
[0025]
FIGS. 3A and 3C show an example of the pump action strength adjusting means. In this example, the turning diameter d of the dynamic pressure groove 15, that is, a circle formed by connecting the turning portions 15c of the dynamic pressure grooves 15 is shown. Is made smaller than the folded diameter d ′ of the conventional product shown in FIG. Also in this case, the oil pushed into the pump-in portion 15a and the oil pushed into the pump-out portion 15b merge in the vicinity of the folded portion 15c, but this merged portion is displaced to the inner diameter side than the conventional product. The pumping action of the pump-out part 15b becomes weak (in contrast, the pumping action of the pump-in part 15a becomes strong). Therefore, excessive oil is not pushed into the outer diameter side at the pump-out portion 15b even during high-speed rotation, and as shown in FIG. 5B, the thrust bearing clearance on the inner-diameter side than the pump-out portion 15b. It is possible to prevent negative pressure from being generated around Cs2, particularly around the axis. The negative pressure generation preventing mechanism 17 can be formed simultaneously with the dynamic pressure groove 15 simply by replacing the conventional press die with a corresponding product, and can be processed at low cost.
[0026]
The degree of strength of the pumping action in the negative pressure generation preventing mechanism 17 is determined according to the operating rotational speed of the bearing unit 1. For example, in this embodiment, the turning diameter is set so that negative pressure is not generated even under the maximum operating rotational speed. d is set.
[0027]
The same effect as described above can be obtained by providing a difference between the flow rate of oil flowing through the pump-in portion 15a and the flow rate of oil flowing through the pump-out portion 15b. As a means for adjusting the flow rate, for example, it is conceivable to make the groove depth of the pump-out portion 15b shallower than the pump-in portion 15a. In addition, the groove width of the pump-out portion 15b may be smaller than that of the pump-in portion 15a (both are not shown).
[0028]
In order to adjust the strength of the pump action, it is only necessary to strengthen the pump action of the pump-in part 15a or weaken the pump action of the pump-out part 15b, so that other configurations than the above may be adopted as long as this can be realized. Is possible.
[0029]
When the bearing member 7 is formed of the oil-impregnated sintered metal, the oil circulates inside the bearing member 7 and is effective in preventing the generation of negative pressure in the radial bearing clearance Cr and the thrust bearing clearances Cs1 and Cs2.
[0030]
【The invention's effect】
Thus, according to the present invention, since the negative pressure generation prevention mechanism is provided in the dynamic pressure groove of the thrust bearing surface, it is possible to prevent the generation of negative pressure in the thrust bearing clearance, particularly in the inner diameter side region of the pump-out portion. Can do. Accordingly, air bubbles can be prevented from being mixed into the thrust bearing clearance, and stable bearing performance (especially thrust load capability) can be ensured. Since this negative pressure generation preventing mechanism can be easily processed by a press or the like simultaneously with the formation of the dynamic pressure groove, the processing cost can be reduced as compared with the case where the bypass hole is formed through as in the prior art. Further, the foreign matter does not remain in the narrow hole and the foreign matter does not enter the bearing clearance as in the case of processing the bypass hole, and the bearing performance can be stably maintained for a long time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a hydrodynamic bearing unit according to the present invention.
FIG. 2 is a partially enlarged cross-sectional view of a bearing member, showing a state in which a radial bearing surface is unfolded.
3A is a side view of a shaft member, FIG. 3B is a view showing pressure distribution, and FIG. 3C is a plan view of a thrust bearing surface. FIG. 2 is an enlarged cross-sectional view of a main part of FIG. 1.
FIG. 4 is a cross-sectional view of a conventional hydrodynamic bearing unit.
5 is a side view of the shaft member (FIG. A), a dynamic pressure distribution diagram (FIG. B), and a plan view of a thrust bearing surface having a herringbone type dynamic pressure groove in the bearing unit shown in FIG. (Fig. C).
6 is a side view of a shaft member (FIG. A), a distribution diagram of dynamic pressure (FIG. B), and a plan view of a thrust bearing surface having spiral dynamic pressure grooves in the bearing unit shown in FIG. 4 (C). Figure).
[Explanation of symbols]
1 Bearing unit 2 Shaft member 6 Housing 7 Bearing member
10a Radial bearing surface
11a Thrust bearing surface
11b Thrust bearing surface
13 Dynamic pressure groove on radial bearing surface
15 Dynamic pressure groove on thrust bearing surface
15a Pump-in part
15b Pump-out part
15c Folding part (merge part)
17 Negative pressure prevention mechanism Cr Radial bearing clearance Cs1 Thrust bearing clearance Cs2 Thrust bearing clearance d Folding diameter

Claims

A shaft member having a flange portion provided at the shaft and the shaft end, a bearing member disposed on the outer periphery of the shaft member via a radial bearing clearance, a housing having a bearing member fixed to the inner peripheral surface, and a shaft of the flange portion A thrust support part that seals one of the directions, one thrust bearing clearance formed between the end face of the thrust support part and one end face of the flange part, and formed between the other end face of the flange part and the end face of the bearing member The inner diameter portion communicates with the radial bearing clearance, the outer diameter portion communicates with the outer diameter portion of the one thrust bearing clearance, and the thrust support portion facing the one thrust bearing clearance. Or a thrust bearing surface having a dynamic pressure groove that is provided on any one of the flange portions and generates dynamic pressure in the one thrust bearing clearance when the rotation side member rotates. The pressure groove has a pump-in portion that pushes oil into the inner diameter side, and a pump-out portion that pushes oil into the outer diameter side at the inner peripheral portion of the pump-in portion, and the one thrust bearing clearance from the pump-out portion In the hydrodynamic bearing unit also having a region on the inner diameter side,
The above-mentioned one thrust bearing clearance is filled with oil including the region on the inner diameter side from the pump-out portion, and the region on the inner diameter side from the pump-out portion of the above-mentioned one thrust bearing clearance is formed by the flange portion and the thrust support portion. Sealed and the dynamic pressure groove on the thrust bearing surface makes the pumping action of the pump-in part larger than the pumping action of the pump-out part, thereby preventing negative pressure generation in the region on the inner diameter side of the pump-out part. It has a pressure generation prevention mechanism, the bearing member is made of sintered metal holding oil , its end face faces the outer peripheral space of the flange part, and the housing is a bottomed cylindrical shape integrally having a thrust support part The hydrodynamic bearing unit is characterized in that the inner peripheral surface of the housing is a straight surface having no step .

The hydrodynamic bearing unit according to claim 1, wherein a joining portion of the oil pushed into the pump-in portion and the oil pushed into the pump-out portion is displaced in the radial direction.

The hydrodynamic bearing unit according to claim 1, wherein a difference is provided between a flow rate of oil flowing through the pump-in portion and a flow rate of oil flowing through the pump-out portion.