JP3799176B2

JP3799176B2 - Hydrodynamic sintered oil-impregnated bearing unit

Info

Publication number: JP3799176B2
Application number: JP29254098A
Authority: JP
Inventors: 夏比古森; 嗣人中関; 一男岡村; 康裕山本
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 1998-02-24
Filing date: 1998-10-14
Publication date: 2006-07-19
Anticipated expiration: 2018-10-14
Also published as: JPH11311253A

Description

【０００１】
【発明の属する技術分野】
本発明は、高回転精度、高速安定性、高耐久性などに優れた特徴を有する動圧型焼結含油軸受および当該軸受ユニットに関し、特に情報機器におけるスピンドルモータ、例えばＤＶＤ−ＲＯＭ、ＤＶＤ−ＲＡＭなどの光ディスク、ＭＯなどの光磁気ディスク、ＨＤＤなどの磁気ディスクを駆動するモータ、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】
上記情報機器類のスピンドルモータには、高回転精度の他、さらなる高速化、低コスト化、低騒音化などが求められているが、これらの要求性能を決定づける構成要素の一つにモータのスピンドルを支持する軸受がある。従来では、この軸受としてボールベアリングか一般的な真円型の焼結含油軸受が用いられている。
【０００３】
【発明が解決しようとする課題】
しかしながら、この種のスピンドルモータは８０００〜１００００ｒｐｍ程度、特にＬＢＰに使用されるポリゴンスキャナモータでは、数万ｒｐｍの高速で使用される場合が多く、また、軸振れ、ＮＲＲＯ、ジッタなどの回転精度も考慮する必要があるため、ボールベアリングや焼結含油軸受では上記要求性能を満足することが難しくなっている。
【０００４】
以上の観点から、近年ではこの種の軸受として動圧型の焼結含油軸受を使用することが検討されている。この軸受は、焼結金属製の軸受本体に潤滑油または潤滑グリースを含浸させ、軸受面に設けた動圧溝の動圧効果で軸受隙間に潤滑油膜を形成してスピンドルを非接触支持するもので、上記要求性能にも十分に対応できる。
【０００５】
ところが、この軸受本体をハウジングに組み込んで縦軸姿勢で使用する場合には、モータ駆動時の圧力発生や熱膨張によって軸受本体から滲み出した油が軸受隙間内で飽和し、軸受隙間外へ漏れ出すおそれがある。図１６に示すように、軸受本体10の下方へ漏れ出た油16は、ハウジング1bの底部に溜まるが、軸受本体10の下面10ｆとハウジング1b底面との間の隙間14’が広いと軸受本体10は溜まった油16と接触しなくなる。モータが停止すると温度が下がり、軸受本体10の表面に付着した油は毛細管現象によって再び軸受本体10内部に吸収されるが、軸受本体10と接触しない油は二度と戻らず、これが繰り返されることによって潤滑油不足に至り、軸受性能の低下を招くおそれがある。潤滑油不足になると軸受隙間に形成された潤滑油膜中に空気が巻き込まれるようになり、本来の動圧効果が減じられてラジアル剛性が低下する一方、不安定な振動が発生するようになり、回転精度が悪化する。
【０００６】
以上の対策としては、隙間14’を予め潤滑油で満たしておくのが最も簡単であるが、これではスピンドル姿勢の変化（例えば上下逆向きにした場合）によって軸受本体10の反対側の端面から潤滑油が漏れ、周囲を汚染するおそれがある。
【０００７】
対策として接触シールの使用も考えられるが、トルクの上昇や変動等の要因となるので高精度の回転性能が要求される情報機器用のスピンドルモータには不向きである。図１７に示すような複雑なラビリンスシールを構成すれば油漏れ防止に一定の効果が認められるが、部品点数が多く、組立も極めて複雑なものとなるので、コストアップにつながる。
【０００８】
そこで、本発明は、ハウジング外への潤滑油の漏出による軸受性能の低下を確実に、かつ低コストに防止することを目的とする。
【０００９】
【課題を解決するための手段】
（１）上記目的を達成するため、本発明にかかる動圧型焼結含油軸受ユニットでは、焼結金属で形成され、かつ軸の外周面と軸受隙間を介して対向する複数のラジアル軸受面を軸方向に離隔して備えた軸受本体に、潤滑油または潤滑グリースを含浸させてなり、軸と軸受本体との相対回転時に、軸方向に対して傾斜した動圧溝で生じる動圧作用により軸を非接触支持する動圧型焼結含油軸受と、一端が開口で他端側が閉塞され、内径部に上記動圧型焼結含油軸受が内装されたハウジングと、軸をスラスト支持するスラスト軸受部とを備えるものにおいて、軸受本体のハウジング閉塞側端面と、当該端面に対向させてハウジングの閉塞側に設けられた対向面とを、両者間の隙間が１mm以下となるよう近接させ、当該隙間、および軸受本体の内周面と軸の外周面との間の隙間をそれぞれ油で満たすと共に、ハウジングの一端側開口部を毛細管現象によりシールした。
【００１１】
対向面は、ハウジングの他端を閉塞する底面で、あるいはハウジングの閉塞側に設けられたスペーサで構成することができる。また、スラスト軸受部を、軸端をハウジングの閉塞側に設けられたスラストワッシャで接触支持する構造とし、このスラストワッシャで上記対向面を構成することもできる。この場合、スラストワッシャに接触する軸の一端を球面状に形成すると共に、軸受本体のラジアル軸受面を軸の上記球面部よりも軸の他端側にずらせて設けるのがよい。これは、軸受本体のハウジング他端側の端面チャンファ部から環状の平滑部を隔ててラジアル軸受面を設けることによって実現できる。
【００１２】
▲２▼また、本発明にかかる動圧型焼結含油軸受ユニットは、焼結金属で形成され、かつ軸の外周面と軸受隙間を介して対向するラジアル軸受面を備えた軸受本体に潤滑油または潤滑グリースを含浸させてなり、軸と軸受本体との相対回転で生じる動圧作用により軸を非接触支持する動圧型焼結含油軸受と、一端が開口で他端が閉塞され、内径部に上記動圧型焼結含油軸受が内装されたハウジングと、軸をスラスト支持するスラスト軸受部とを備えるものにおいて、ハウジングの一端側開口部を、内周面を軸の外周面に近接させたシールワッシャでシールしたものである。シールワッシャの内周面と軸の外周面との間の隙間で生じる毛細管効果により当該隙間からの油漏れを防止することができる。
【００１３】
十分な毛細管効果を得るためには、シールワッシャの内周面と軸の外周面との間の隙間を０．１mm以下に設定するのが望ましい。また、軸の外周面のうち、少なくともシールワッシャの内周面との対向部を含む領域に撥油剤を塗布しておけば、油漏れをより確実に防止することができる。
【００１４】
シールワッシャとシールワッシャに対向する軸受端面との間の隙間は、１．０mm以下に設定するのがよい。
【００１５】
▲３▼ 上記▲１▼および▲２▼に挙げた各構成を適宜組合わせることもできる。この場合、シールワッシャとシールワッシャに対向する軸受端面との間の隙間を、軸受本体のハウジング閉塞側端面と、当該端面に対向する上記対向面との間の隙間よりも大きく設定しておけば、軸姿勢を変化させた場合（上下反転等）場合にも、シールワッシャと軸受端面との間の隙間が先に油で満たされ、逃げ場を失った空気が、対向面と軸受端面との間の隙間に入り込んで軸受隙間に巻き込まれる、という事態が防止される。
【００１６】
▲４▼ 動圧発生手段として、ラジアル軸受面に、軸方向に対して傾斜した動圧溝を設ければ、軸受隙間に剛性の高い安定した油膜が形成されるので、高精度が得られる。
【００１７】
▲５▼ 軸受本体の外径面とハウジングの内径面との間に、軸受本体の軸方向両端部に開口する通気路を設けておけば、軸の軸受内部への挿入時にハウジング内に閉じ込められた空気が通気路を通ってハウジング外に放出されるので、軸受隙間への空気の巻き込みを回避することができる。
【００１８】
▲６▼ 以上説明した動圧側焼結含油軸受ユニットは、軸と軸受本体との相対回転により磁気ディスクを回転させる磁気ディスクドライブのスピンドルモータや、軸と軸受本体との相対回転により、光ディスクを回転させる光ディスクドライブのスピンドルモータ、あるいは、軸と軸受本体との相対回転によりポリゴンミラーを回転させるレーザビームプリンタのポリゴンスキャナモータ等に用いられる。ここでいう「光ディスク」には光磁気ディスク（ＭＤ、ＭＯ等）も含まれる。
【００１９】
▲７▼ 本発明にかかる動圧型焼結含油軸受は、焼結金属からなり、軸の外周面と軸受隙間を介して対向するラジアル軸受面を軸方向に離隔させて有し、ラジアル軸受面に軸方向に対して傾斜した動圧溝が形成され、少なくとも一端内径部に端面チャンファ部が設けられた軸受本体と、軸受本体に含浸された潤滑油または潤滑グリースとを備えるものにおいて、端面チャンファ部から環状の平滑部を隔ててラジアル軸受面を形成したものである。
【００２０】
【発明の実施の形態】
以下、本発明の一実施形態を図１乃至図１５に基いて説明する。
【００２１】
図１は、情報機器の一種である光ディスクドライブ（ＤＶＤ−ＲＯＭ装置用）のスピンドルモータの断面図である。このスピンドルモータは、垂直の回転軸２を支持する軸受ユニット１と、回転軸２の上端に取り付けられ、ＤＶＤ−ＲＯＭ等の光ディスク３を支持固定するターンテーブル４およびクランパ８と、ラジアルギャップを介して対向させたステータ５およびロータマグネット６を有するモータ部Ｍとで構成される。ステータ５に通電すると、ステータ５との間に生じる励磁力でロータマグネット６が回転し、ロータマグネット６と一体になったロータケース７、ターンテーブル４、光ディスク３、クランパ８、および回転軸２が回転する。軸受ユニット１を他の情報機器用スピンドルモータ、例えば磁気ディスクドライブに用いる場合は、一または複数枚の磁気ディスクを保持するディスクハブ（図示省略）が回転軸２に装着され、ＬＢＰのポリゴンスキャナモータに用いる場合は、回転軸２にポリゴンミラー（図示省略）が装着される。
【００２２】
軸受ユニット１は、焼結含油軸受1aと、焼結含油軸受1aを内径部に固定したハウジング1bとを主要構成要素として構成される。ハウジング1bは一端を開口すると共に、他端を閉塞した有底円筒型に形成され、一端側の開口部を上にしてベース17に固定される。ハウジングの他端側は例えば図示のように、スラスト軸受部12で閉塞される。スラスト軸受部12は、図２（ａ）に示すように、例えば、円板状に形成された樹脂製のスラストワッシャ12ａと、これを支持する裏金12ｂとを積層した構造で、回転軸２は、その下端をスラストワッシャ12ａに接触させてスラスト方向で支持される。スラスト軸受部12の構造は任意であり、例えば図２（ｂ）に示すように、裏金12ｂの中心部に設けた凹所に樹脂製のスラストワッシャ12ａを埋設してもよい。また、スラストワッシャ12ａとハウジング1bとを一体成形してもよい。
【００２３】
焼結含油軸受1aは、図３に示すように、回転軸２の外周面と軸受隙間を介して対向するラジアル軸受面10ｂを有する焼結金属からなる円筒状の軸受本体10に、潤滑油あるいは潤滑グリース（低濃度の増稠剤を配合したものが望ましい）を含浸させて構成される。焼結金属からなる軸受本体10は、銅系あるいは鉄系、またはその双方を主成分とする焼結金属で形成され、望ましくは銅を20〜95％使用して成形される。軸受本体10の内周には、軸方向に離隔する２つの軸受面10ｂが形成され、２つの軸受面10ｂの双方に、それぞれ軸方向に対して傾斜した複数の動圧溝10ｃ（へリングボーン型）が円周方向に配列形成される。動圧溝10ｃは軸方向に対して傾斜して形成されていれば足り、この条件を満たす限りへリングボーン型以外の他の形状、例えばスパイラル型でもよい。動圧溝10ｃの溝深さは２〜６μｍ程度が適当で、例えば３μｍに設定される。
【００２４】
この焼結含油軸受1aでは、回転軸２の回転に伴う圧力発生と昇温による油の熱膨張によって軸受本体10の内部の潤滑剤（潤滑油または潤滑グリースの基油）が軸受本体10の表面からからにじみ出し、動圧溝の作用によって軸受隙間に引き込まれる。軸受隙間に引き込まれた油は潤滑油膜を形成して回転軸を非接触支持する。すなわち、ラジアル軸受面10ｂに、上記傾斜状の動圧溝10ｃを設けると、その動圧作用によってにじみ出した軸受本体10内部の潤滑剤が軸受隙間に引き込まれると共に、軸受面10ｂに潤滑剤が押し込まれ続けるので、油膜力が高まり、軸受の剛性を向上させることができる。
【００２５】
軸受隙間に正圧が発生すると、ラジアル軸受面10ｂの表面に孔（開孔部：多孔質体組織の細孔が外表面に開口した部分をいう）があるため、潤滑剤は軸受本体の内部に還流するが、次々と新たな潤滑剤が軸受隙間に押し込まれ続けるので油膜力および剛性は高い状態で維持される。この場合、連続しかつ安定した油膜が形成されるので、高回転精度が得られ、軸振れやＮＲＲＯ、ジッタ等が低減される。また、回転軸２と軸受本体10が非接触で回転するために低騒音であり、しかも低コストである。
【００２６】
この実施形態では、軸受本体10を１個とし、その内径面の複数箇所（本実施形態では２箇所）に動圧軸受面1bを設けているが、これは複数個の軸受１を別体に配置した場合に問題となる精度不良等の弊害を回避するためである。すなわち、仮にハウジング1bに複数個の軸受1aを収納すると、各軸受1aの同軸度、円筒度などの精度が問題となり、精度が悪い場合、回転軸２と軸受1aが線接触したり、最悪の場合には回転軸２が２個の軸受を貫通しない場合も起こり得る。これに対し、上記のように１つの軸受本体10に複数の軸受面10ｂを形成しておけば、この種の問題を回避することができる。
【００２７】
両ラジアル軸受面10ｂは、一方に傾斜する動圧溝10ｃが配列された第１の溝領域m1と、第１の溝領域m1から軸方向に離隔し、他方に傾斜する動圧溝10ｃが配列された第２の溝領域m2と、２つの溝領域m1、m2の間に位置する環状の平滑部ｎとを備えており、２つの溝領域m1、m2の動圧溝10ｃは平滑部ｎで区画されて非連続になっている。平滑部ｎと動圧溝10ｃ間の背の部分10ｅは同一レベルにある。この種の非連続型の動圧溝10ｃは、連続型、すなわち平滑部ｎを省略し、動圧溝10ｃを両溝領域m1、m2間で互いに連続するＶ字状に形成した場合に比べ、平滑部ｎを中心として油が集められるために油膜圧力が高く、また溝のない平滑部ｎを有するので軸受剛性が高いという利点を有する。
【００２８】
本発明においては、図４に示すように、軸受本体10のハウジング閉塞側の端面10f2を、この端面10f2に対向する対向面であるスラストワッシャ12ａの上面に接触させることとした。この場合、熱膨張などによって過剰に漏れ出した油は、軸受本体10の端面チャンファ部10ｇ（内径側）と回転軸２の外周面との間の空間、および端面チャンファ部10ｈ（外径側）とハウジング1bの内周面との間の空間にとどまり、駆動停止時の軸受本体10の温度低下により、軸受本体10内部に容易に吸収される（毛細管現象）。したがって、軸受内部には常に潤沢な油が保持されるので、駆動時には軸受隙間に十分な油を常時保持することができ、安定した軸受性能を長期間維持することができる。
【００２９】
もちろん、軸受本体10の上記端面10f2とスラストワッシャ12ａとが接触していなくても、十分に近接しているのであれば、すなわち、前記毛細管現象により溜まった油を吸収できる範囲内で近接しているのであれば、図５に示すように端面10f2とスラストワッシャ12の上面13（対向面）との間に軸方向の隙間14を介在させてもよい。
【００３０】
図６に、隙間14の軸方向幅（ｓ：図５参照）を変えた時（ｓ＝０mm、０．７mm、１．０mm、１．２mm）の軸振れ比と軸受本体10への注油量との関係を示す。軸受本体10は内径寸法をφ３mm、外径寸法をφ６mmとし、回転軸はアンバランス量０．５gr−cmを付与しつつ８０００ｒｐｍで回転させた。試験に先立ち、軸受本体10には十分な潤滑油を含ませた。
【００３１】
この試験より、隙間14の軸方向幅ｓが１．２mmの時には、ほぼ隙間14の容積分の追加給油が必要であり、給油量が少ない場合には軸振れ比が急激に大きくなるが、軸方向幅ｓが１mm以下であれば追加給油の有無にかかわらず、十分に低い軸振れ比を達成できることが判明した。したがって、隙間14の軸方向幅ｓは１mm以下とするのが好ましく、例えば０．４mm程度に設定される。
【００３２】
ところで、軸受ユニット１においては、図２（ａ）および図４に示すように、摩擦低減等の観点から回転軸２の下端を球面に形成する場合が多い。この場合、図４に示すように、回転軸２の球面部2aが軸受本体10のラジアル軸受面10ｂと重なっていると、軸受隙間が不均一となり、適正な動圧作用が得られない。従って、この場合には、図７に示すように、軸受本体10の内径チャンファ部10ｇから環状の平滑部10ｉを隔ててラジアル軸受面10ｂを設けることにより、軸受面10ｂを相対的に上方にずらせて、軸受面10ｂの全領域が回転軸２の球面部2aよりも上端側の円筒部2bと対向できるようにするとよい（図５参照）。この平滑部10ｉは、軸受本体10の両端部のうち、少なくとも一方の端部側、すなわちハウジング1bに組み込んだ際にハウジング1bの底部側に位置する端部（図７の左側）のみに形成すれば足りるが、他方の端部側（同右側）に同様の平滑部を設けても構わない。
【００３３】
以上の説明では、軸受本体10の閉塞側端面10f2と対向する対向面13としてスラストワッシャ12ａの上面を例示しているが、図９に示すように、スラストワッシャ12ａの上面と軸受本体10との間にリング状のスペーサ15を配置することにより、スペーサ15の上面を上記端面10f2に対向する対向面13としてもよい。この場合、軸受本体10とスペーサ15は、図４および図５と同様に互いに接触させ、または所定範囲内で近接させておく。また、スペーサ15の内径寸法は、トルクが上昇しないようにラジアル軸受面10ｂの内径寸法よりも僅かに大きくする。ハウジング1bの開口側にスラスト軸受部12を配置する場合、例えば図１８に示すように、軸２に設けた円板状のフランジ部2cを軸受本体10のハウジング開口側端面10f1に当接させてスラスト軸受部12を構成する場合は、ハウジング1bの底部を閉塞する底板16の上面（底面）を対向面13とし、この対向面13を軸受本体10のハウジング閉塞側端面10f2と接触させ、または所定範囲内で近接させる。
【００３４】
なお、以上の説明では、動圧溝10ｃを軸受本体10の軸受面10ｂに設けた場合を例示したが、本発明は回転軸２の外周面に動圧溝を設けた場合にも同様に適用することができる。
【００３５】
図５に示す軸受ユニット１を実施例とし、図１６に示す軸受ユニットを比較例として耐久試験を実施し、初期と２０００ｈ経過後の軸振れ特性をそれぞれ測定した。測定は何れも３台の軸受ユニットを用いて行った。また、実施例においては隙間14の幅ｓを０．２mm、平滑部10ｉの幅ｔを１mmとし、比較例においては隙間14’の幅ｓ’を３mmとした。試験条件は以下の通りである。
【００３６】
使用モータ：ポリゴンスキャナモータ（実機モータ）
回転数：２００００ｒｐｍ
雰囲気温度：５０℃
なお、通常、ポリゴンスキャナモータにおいては、ミラー面よりも上方に回転軸の上端が突出していないが、本実験用として軸の上端を突出させたロータを試作した。したがって、軸振れはミラー面よりもかなり上側で測定しており、測定結果は相対的な比較データである。
【００３７】
測定結果を図８に示す。図示のように、初期では実施例および比較例とも軸振れの値はほとんど大差がないが、２０００ｈ経過後には、比較例の軸振れが著しく大きくなり、実施例品の優位性が確認された。
【００３８】
図１０および図１１は、本発明の他の実施形態を示すもので、ハウジング1bの一端側開口部を非接触型のシール部材（シールワッシャ20）でシールしたものである。軸受ユニット１のうち、ハウジング1b上端のシール構造を除く他の構成要素、例えば動圧型焼結含油軸受1a、ハウジング1b、回転軸２、スラスト軸受部12等の構成は、以下に説明する事項を除き、図１乃至図９に示すものと同様の構成を適用することができる。
【００３９】
シールワッシャ20は、中心部に回転軸２の挿入孔を有する薄肉円板状をなすもので、例えば樹脂材料（例えばポリアミドなど）で形成され、接着等の手段でハウジング1bの一端開口部に固定される。シールワッシャ20はワッシャ状に形成されていれば足り、樹脂以外にも金属で形成することもできる。シールワッシャ20の内周面は回転軸２の外周面にできるだけ近接させて、毛細管現象によりハウジング1b内部からの油漏れを防止する構造とする。シールワッシャ20を軸２に接触させると、トルクの増大・変動を招き、高精度が要求される情報機器用スピンドルモータとしては好ましくない。したがって、シールワッシャ20は軸２に対して非接触とする。シールワッシャ20の内周面と回転軸２の外周面との間の隙間の幅u1が０．１mm以下、望ましくは０．０５mm以下であれば、たとえ軸姿勢を横向きや逆向きとした場合でも、毛細管現象により油漏れが確実に防止される。なお、隙間u1を介した空気の流通は確保されているので、ハウジング1b内からの空気の放出はスムーズに行われる。
【００４０】
回転軸２の外周面のうち、少なくともシールワッシャ20の内周面との対向部を含む領域（シールワッシャ20の厚みよりも大きな軸方向幅の領域）に、その全周にわって撥油剤21を塗布しておけば、軸２を伝わって漏れ出ようとする油をはじくことができ、油漏れを完全に防止することができる。撥油剤21としては、例えばパーフロロカーボンを主成分とするもの（ハーベスト社製、OS−90MF等）が使用可能である。
【００４１】
ところで、通常、回転軸２は、ハウジング1bにスラスト軸受部12を装着した状態で軸受1aの内径部に挿入される。軸２の挿入前には、図12に示すように、潤滑性向上のために予めハウジング1b内に油Ｏ（散点模様で示す）を注油する場合があるが、軸受1aと回転軸２の間の軸受隙間は数μｍ程度しかないため、軸端と注油した油Ｏの上面との間に閉じ込められた空気の逃げ場がなくなり、回転軸２の挿入が難しくなる。また、モータはその駆動時に発熱するが、発熱によって閉じ込められた空気が膨張し、回転軸２を押し上げて軸受性能を不安定化させたり、あるいは熱膨張した空気が油を軸受外に押し出して潤滑性を低下させるおそれもある。これらの問題は注油しない場合でも同様に生じる。
【００４２】
この対策として、図10および図11に示すように、軸受本体10の外径面とハウジング1bの内径面との間に、軸受本体10の軸方向両端に開口する通気路22を設け、この通気路22を通して閉じ込められた空気を軸受外に逃がすようにすればよい。この場合、油中に多少の空気が泡となって残存する場合もあるが、この種の泡は通気路22を通って浮き上がり、ハウジング1b外に放出される。従って、軸２の挿入後は、図１３に示すように、ハウジング1b内の空間（軸受1aと対向面13の間の空間14、シールワッシャ20と軸受端面10f1の間の空間23、軸受隙間、通気路22等）を油Ｏで満たすことが可能となる。通気路22は、図３に示すように、軸受本体1aの外周面に軸方向の溝10ｊを設けることによって形成することができるが、ハウジング1bの内周面に同様の溝10ｊを設けてもよい。また、通気路22は１箇所だけでなく、円周方向の複数箇所に設けてもよい。
【００４３】
シールワッシャ20とこれに対向する軸受端面10f1との間の隙間23（以下、一端側隙間と称する）が大きすぎると、注油量によってはハウジング1b内の空間を油で満たすことができず、ハウジング1b内に残る空気量が多くなり、軸姿勢を横向きや逆向きにした場合に空気がスラストワッシャ12ａと軸受端面10f2との間の隙間14（以下、他端側隙間と称する）に入り込むおそれがあって好ましくない。従って、一端側隙間23はできるだけ小さくするのが望ましく、その幅u2（図10参照）は例えば０．６mmに設定される。この隙間の幅u2は１．０mm以下であればよく、好ましくは０．５mm以下に設定されるが、他端側隙間14の幅ｓよりも大きく設定するのがよい（u2＞ｓ）。一端側隙間23が他端側隙間14よりも小さいと、軸姿勢を逆さまにした場合に、一端側隙間23が先に油で満たされ、逃げ場を失った空気が他端側隙間14に入り込む事態が予想されるためである。
【００４４】
この実施形態の効果を確認するため、以下のような試験を実施した。
【００４５】
・雰囲気：５０℃
・軸径：φ３
・軸姿勢：逆向き
・回転数：８０００ｒｐｍ
・試験時間：５００時間
・評価項目：油漏れの状況（目視観察）および性能の変化（軸振れ、電流値）試験に供した軸受ユニット１の寸法等は、図14に示す通りである。
【００４６】
試験結果を図15に示す。
【００４７】
比較例１のようにシールワッシャを設けていない場合、当然ながら注油した油が漏れ出てしまい、その部分に空気が巻き込まれるため、性能が大幅に低下した。電流値も大きくなっているので流体潤滑状態が損なわれ、金属接触を含む混合潤滑状態になっているものと推測される。
【００４８】
比較例２では、軸あるいはロータに油の付着が認められる程度ではあるが油漏れが認められる。電流値は若干小さくなったが、軸振れは初期に比べてかなり大きくなった。油漏れが発生したため、その部分に空気が侵入し、見かけ粘度が低下したため軸振れが大きくなったものと推測される。油漏れが生じた原因は、モータを逆向きにした際、軸受端面10f2とスラストワッシャ12ａ間の隙間14がシールワッシャ20と軸受端面10f1の間の隙間23よりも大きいため、シールワッシャ20と軸受端面10f1の間の隙間23が先に油で満たされ、逃げ場を失った空気が軸受端面10f2と対向面13の間の隙間14に入り込んだためと考えられる。軸受の温度が上昇すると気体の熱膨張の方が液体よりも大きいため、油が空気によって押し出されたものと思われる。
【００４９】
比較例３の場合も、軸あるいはロータに油の付着が認められる程度ではあったが油漏れが認められ、電流値は若干小さくなったが軸振れが初期に比べて大きくなった。シールワッシャ20と軸２の間の隙間が大きく、毛細管現象で油漏れを防止できなかったためと思われる。
【００５０】
比較例４の場合も、軸あるいはロータに油の付着が認められる程度ではあったが油漏れが認められ、電流値は若干小さくなったが、軸振れが初期に比べて大きくなった。シールワッシャ20と軸受端面10f1との隙間23が大きすぎたため、シールワッシャ20と軸受端面10f1間の毛細管現象が効かなかったためと考えられる。
【００５１】
これに対して実施例１ではほとんど油漏れは認められず、性能も初期の状態を維持しており、良好な結果となった。
【００５２】
また、実施例２では油漏れが全く認められなかった。実施例１では軸振れ等の性能に低下は認められなかったが、ＨＤＤ装置のようにオイルミストの飛散も問題になるような機種の場合は、より確実な油漏れ防止効果を有する実施例２が好ましいと考えられる。
【００５３】
【発明の効果】
以上のように本発明によれば、軸姿勢を問わず、簡単な構造で確実に油漏れを防止することができる。従って、低コストでかつ高機能を有する軸受ユニットを提供することができる。また、油漏れがないために長期間良好な油膜を維持することができ、耐久性が飛躍的に向上する。また、油漏れによって周囲を汚染することもない。
【図面の簡単な説明】
【図１】本発明にかかる軸受ユニットを用いたＤＶＤ−ＲＯＭ用スピンドルモータの軸方向の断面図である。
【図２】（ａ）図は軸受ユニット底部の拡大断面図であり、（ｂ）図はスラスト軸受部の他の例を示す断面図である。
【図３】焼結含油軸受の軸方向の断面図である。
【図４】上記軸受ユニットの一実施形態を示す軸方向の断面図である。
【図５】上記軸受ユニットの他の実施形態を示す軸方向の断面図である。
【図６】注油量と軸振れ比の測定データを示す図である。
【図７】焼結含油軸受の軸方向の断面図である。
【図８】本発明品と従来品における耐久試験の結果を示す図である。
【図９】上記軸受ユニットの他の実施形態を示す軸方向の断面図である。
【図１０】本発明にかかる軸受ユニットを用いたＤＶＤ−ＲＯＭ用スピンドルモータの軸方向断面図である。
【図１１】ハウジング開口部付近の拡大断面図である。
【図１２】軸の挿入中における軸受ユニットの軸方向断面図である。
【図１３】軸の挿入後における軸受ユニットの軸方向断面図である。
【図１４】油漏れ試験の条件を示す図である。
【図１５】実験結果を示す図である。
【図１６】従来の軸受ユニットを示す軸方向の断面図である。
【図１７】ラビリンスシールを適用した動圧型軸受ユニットの拡大断面図である。
【図１８】動圧型軸受ユニットの軸方向断面図である。
【符号の説明】
１軸受ユニット
1a 焼結含油軸受
1b ハウジング
２軸（回転軸）
３光ディスク
2a 球面部
10 軸受本体
10ｂラジアル軸受面
10ｃ動圧溝
10f1 軸受端面（一端側）
10f2 軸受端面（他端側）
10ｉ平滑部
10ｋ溝
12 スラスト軸受部
12ａスラストワッシャ
13 対向面
14 隙間（他端側）
15 スペーサ
16 底板
20 シールワッシャ
21 撥油剤
22 通気路
23 隙間（一端側）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic sintered oil-impregnated bearing and a bearing unit having features excellent in high rotational accuracy, high-speed stability, high durability, and the like, and in particular, spindle motors in information equipment, such as DVD-ROM and DVD-RAM. It is suitable for supporting a spindle of an optical disk, a magneto-optical disk such as MO, a motor for driving a magnetic disk such as HDD, or a polygon scanner motor of a laser beam printer (LBP).
[0002]
[Prior art]
The spindle motors of the above information devices are required to have higher speed, lower cost, lower noise, etc. in addition to high rotational accuracy. The motor spindle is one of the components that determine these required performances. There are bearings that support Conventionally, a ball bearing or a general circular oil-impregnated bearing is used as the bearing.
[0003]
[Problems to be solved by the invention]
However, this type of spindle motor is often used at a high speed of about 8000 to 10000 rpm, especially a polygon scanner motor used for LBP, at a high speed of several tens of thousands rpm, and also has rotational accuracy such as shaft runout, NRRO, and jitter. Since it is necessary to consider, it is difficult for ball bearings and sintered oil-impregnated bearings to satisfy the required performance.
[0004]
In view of the above, in recent years, it has been studied to use a hydrodynamic sintered oil-impregnated bearing as this type of bearing. In this bearing, a sintered metal bearing body is impregnated with lubricating oil or lubricating grease, and a lubricating oil film is formed in the bearing gap by the dynamic pressure effect of the dynamic pressure groove provided on the bearing surface to support the spindle in a non-contact manner. Thus, it can sufficiently cope with the required performance.
[0005]
However, when this bearing body is assembled in a housing and used in a vertical orientation, oil that has oozed out of the bearing body due to pressure generation or thermal expansion during motor drive is saturated within the bearing gap and leaks out of the bearing gap. There is a risk of release. As shown in FIG. 16, the oil 16 leaking downward from the bearing body 10 accumulates at the bottom of the housing 1b. However, if the gap 14 'between the lower surface 10f of the bearing body 10 and the bottom of the housing 1b is wide, the bearing body 10 no longer contacts the accumulated oil 16. When the motor stops, the temperature drops, and the oil adhering to the surface of the bearing body 10 is absorbed into the bearing body 10 again by capillary action, but the oil that does not contact the bearing body 10 never returns and is lubricated by repeating this process. Oil shortage may result in deterioration of bearing performance. When the lubricating oil is insufficient, air is entrained in the lubricating oil film formed in the bearing gap, the original dynamic pressure effect is reduced and the radial rigidity is lowered, while unstable vibrations are generated, Rotational accuracy deteriorates.
[0006]
As the above countermeasure, it is simplest to preliminarily fill the gap 14 'with lubricating oil. However, in this case, from the opposite end face of the bearing body 10 by changing the spindle posture (for example, when it is turned upside down) Lubricating oil may leak and contaminate the surroundings.
[0007]
The use of a contact seal can be considered as a countermeasure, but it is not suitable for a spindle motor for information equipment that requires high-precision rotation performance because it causes an increase or fluctuation in torque. If a complex labyrinth seal as shown in FIG. 17 is configured, a certain effect can be recognized in preventing oil leakage, but the number of parts is large and the assembly is extremely complicated, leading to an increase in cost.
[0008]
Therefore, an object of the present invention is to reliably and at low cost prevent deterioration of bearing performance due to leakage of lubricating oil to the outside of the housing.
[0009]
[Means for Solving the Problems]
(1) In order to achieve the above object, the hydrodynamic sintered oil-impregnated bearing unit according to the present invention is formed of sintered metal and faces the outer peripheral surface of the shaft via a bearing gap.pluralRadial bearing surfaceAxially separatedThe bearing body is impregnated with lubricating oil or lubricating grease.Dynamic pressure grooves inclined with respect to the axial direction during rotationA hydrodynamic sintered oil-impregnated bearing that supports the shaft in a non-contact manner by the hydrodynamic action generated in the above, a housing in which one end is open and the other end is closed, and the above-mentioned hydrodynamic sintered oil-impregnated bearing is housed inside the inner diameter portion, and the shaft is thrust A bearing having a thrust bearing portion to support, a housing closing side end surface of the bearing body, and a facing surface provided on the closing side of the housing so as to face the end surfaceAnd the gap between them1mm or lessThe gap and the gap between the inner peripheral surface of the bearing body and the outer peripheral surface of the shaft were filled with oil, and the opening on the one end side of the housing was sealed by capillary action.
[0011]
The opposing surface can be constituted by a bottom surface that closes the other end of the housing, or a spacer provided on the closing side of the housing. Further, the thrust bearing portion may have a structure in which the shaft end is in contact with and supported by a thrust washer provided on the closed side of the housing, and the opposing surface may be configured by this thrust washer. In this case, it is preferable that one end of the shaft that contacts the thrust washer is formed in a spherical shape, and the radial bearing surface of the bearing body is shifted from the spherical portion of the shaft toward the other end side of the shaft. This can be realized by providing a radial bearing surface across an annular smooth portion from an end surface chamfer portion on the other end side of the housing of the bearing body.
[0012]
(2) Further, the hydrodynamic sintered oil-impregnated bearing unit according to the present invention is formed of a sintered metal and has a lubricating oil or a bearing on a bearing body having a radial bearing surface opposed to the outer peripheral surface of the shaft through a bearing gap. A hydrodynamic sintered oil-impregnated bearing that is impregnated with lubricating grease and supports the shaft in a non-contact manner by the dynamic pressure generated by the relative rotation of the shaft and the bearing body, and one end is open and the other end is closed, In a housing provided with a hydrodynamic sintered oil-impregnated bearing and a thrust bearing portion for thrust-supporting the shaft, the opening on the one end side of the housing is a seal washer whose inner peripheral surface is close to the outer peripheral surface of the shaft. It is sealed. Oil leakage from the gap can be prevented by the capillary effect generated in the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft.
[0013]
In order to obtain a sufficient capillary effect, it is desirable to set the gap between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft to 0.1 mm or less. Moreover, if an oil repellent is applied to a region including at least a portion facing the inner peripheral surface of the seal washer on the outer peripheral surface of the shaft, oil leakage can be prevented more reliably.
[0014]
The clearance between the seal washer and the bearing end face facing the seal washer is preferably set to 1.0 mm or less.
[0015]
(3) The configurations listed in (1) and (2) above can be combined as appropriate. In this case, the clearance between the seal washer and the bearing end surface facing the seal washer should be set larger than the clearance between the housing closing side end surface of the bearing body and the facing surface facing the end surface. Even when the shaft orientation is changed (upside down, etc.), the gap between the seal washer and the bearing end surface is filled with oil first, and the air that has lost its escape is between the opposing surface and the bearing end surface. It is possible to prevent the situation of entering the gap and getting caught in the bearing gap.
[0016]
(4) If a dynamic pressure groove inclined with respect to the axial direction is provided on the radial bearing surface as the dynamic pressure generating means, a highly stable and stable oil film is formed in the bearing gap, so that high accuracy can be obtained.
[0017]
(5) If an air passage that opens at both axial ends of the bearing body is provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing, it is confined in the housing when the shaft is inserted into the bearing. Since the discharged air is discharged out of the housing through the air passage, it is possible to avoid the air from being caught in the bearing gap.
[0018]
(6) The hydrodynamic side sintered oil-impregnated bearing unit described above rotates the optical disk by the spindle motor of the magnetic disk drive that rotates the magnetic disk by the relative rotation of the shaft and the bearing body, and the relative rotation of the shaft and the bearing body. It is used for a spindle motor of an optical disk drive to be driven or a polygon scanner motor of a laser beam printer that rotates a polygon mirror by relative rotation of a shaft and a bearing body. The “optical disk” here includes magneto-optical disks (MD, MO, etc.).
[0019]
(7) A hydrodynamic sintered oil-impregnated bearing according to the present invention is made of sintered metal, and has a radial bearing surface opposed to the outer peripheral surface of the shaft through a bearing gap in the axial direction. An end face chamfer part comprising a bearing body in which a dynamic pressure groove inclined with respect to the axial direction is formed and having an end face chamfer part at least at one inner diameter part, and a lubricating oil or grease impregnated in the bearing body. A radial bearing surface is formed with a ring-shaped smooth portion separated from each other.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0021]
FIG. 1 is a cross-sectional view of a spindle motor of an optical disc drive (for DVD-ROM device) which is a kind of information equipment. The spindle motor includes a bearing unit 1 that supports a vertical rotating shaft 2, a turntable 4 that is attached to the upper end of the rotating shaft 2 and supports and fixes an optical disk 3 such as a DVD-ROM, a clamper 8, and a radial gap. And a motor portion M having a stator 5 and a rotor magnet 6 opposed to each other. When the stator 5 is energized, the rotor magnet 6 is rotated by the exciting force generated between the stator 5, and the rotor case 7, the turntable 4, the optical disk 3, the clamper 8, and the rotating shaft 2 integrated with the rotor magnet 6 are rotated. Rotate. When the bearing unit 1 is used for a spindle motor for other information equipment, for example, a magnetic disk drive, a disk hub (not shown) that holds one or a plurality of magnetic disks is mounted on the rotary shaft 2 and is an LBP polygon scanner motor. In the case of using for the above, a polygon mirror (not shown) is mounted on the rotary shaft 2.
[0022]
The bearing unit 1 includes a sintered oil-impregnated bearing 1a and a housing 1b in which the sintered oil-impregnated bearing 1a is fixed to an inner diameter portion as main components. The housing 1b is formed in a bottomed cylindrical shape with one end opened and the other end closed, and is fixed to the base 17 with the opening on one end side facing up. The other end side of the housing is closed by a thrust bearing portion 12 as shown in the figure, for example. As shown in FIG. 2 (a), the thrust bearing portion 12 has a structure in which, for example, a resin-made thrust washer 12a formed in a disk shape and a back metal 12b for supporting the same are laminated. The lower end is brought into contact with the thrust washer 12a and supported in the thrust direction. The structure of the thrust bearing portion 12 is arbitrary. For example, as shown in FIG. 2B, a resin-made thrust washer 12a may be embedded in a recess provided in the central portion of the back metal 12b. Further, the thrust washer 12a and the housing 1b may be integrally formed.
[0023]
As shown in FIG. 3, the sintered oil-impregnated bearing 1a has a cylindrical bearing body 10 made of a sintered metal having a radial bearing surface 10b opposed to the outer peripheral surface of the rotating shaft 2 through a bearing gap. It is constituted by impregnating a lubricating grease (preferably containing a low concentration thickener). The bearing body 10 made of sintered metal is formed of a sintered metal mainly composed of copper, iron, or both, and is preferably formed using 20 to 95% of copper. Two bearing surfaces 10b that are separated in the axial direction are formed on the inner periphery of the bearing body 10, and a plurality of dynamic pressure grooves 10c (herring bones) each inclined with respect to the axial direction are formed on both of the two bearing surfaces 10b. Mold) is arranged in the circumferential direction. It is sufficient that the dynamic pressure groove 10c is formed to be inclined with respect to the axial direction, and other shapes other than the herringbone type, for example, a spiral type may be used as long as this condition is satisfied. The groove depth of the dynamic pressure groove 10c is suitably about 2 to 6 μm, and is set to 3 μm, for example.
[0024]
In this sintered oil-impregnated bearing 1a, the lubricant (lubricating oil or base oil of the lubricating grease) inside the bearing body 10 is generated on the surface of the bearing body 10 by the pressure generated by the rotation of the rotating shaft 2 and the thermal expansion of the oil due to the temperature rise. Oozes out of the bearing and is pulled into the bearing gap by the action of the dynamic pressure groove. The oil drawn into the bearing gap forms a lubricating oil film and supports the rotating shaft in a non-contact manner. That is, when the inclined dynamic pressure groove 10c is provided on the radial bearing surface 10b, the lubricant inside the bearing body 10 oozed out by the dynamic pressure action is drawn into the bearing gap and the lubricant is pushed into the bearing surface 10b. Therefore, the oil film force is increased and the rigidity of the bearing can be improved.
[0025]
When positive pressure is generated in the bearing gap, there is a hole in the surface of the radial bearing surface 10b (opening portion: a portion where the pores of the porous body structure are opened on the outer surface), so that the lubricant is inside the bearing body. However, since new lubricant continues to be pushed into the bearing gap one after another, the oil film force and rigidity are maintained in a high state. In this case, since a continuous and stable oil film is formed, high rotational accuracy is obtained, and shaft runout, NRRO, jitter, and the like are reduced. Further, since the rotary shaft 2 and the bearing body 10 rotate without contact, the noise is low and the cost is low.
[0026]
In this embodiment, a single bearing body 10 is provided, and the hydrodynamic bearing surface 1b is provided at a plurality of locations (two locations in the present embodiment) on its inner diameter surface. This is to avoid adverse effects such as inaccuracy and the like, which are problems when arranged. That is, if a plurality of bearings 1a are accommodated in the housing 1b, the accuracy of each bearing 1a, such as coaxiality and cylindricity, becomes a problem, and if the accuracy is poor, the rotating shaft 2 and the bearing 1a are in line contact, In some cases, the rotating shaft 2 may not pass through the two bearings. In contrast, if a plurality of bearing surfaces 10b are formed on one bearing body 10 as described above, this type of problem can be avoided.
[0027]
Both radial bearing surfaces 10b are arranged with a first groove region m1 in which a dynamic pressure groove 10c inclined on one side is arranged, and a dynamic pressure groove 10c which is axially separated from the first groove region m1 and inclined on the other side. Second groove region m2 and an annular smooth portion n positioned between the two groove regions m1 and m2, and the dynamic pressure groove 10c of the two groove regions m1 and m2 is the smooth portion n. Partitioned and discontinuous. The back portion 10e between the smooth portion n and the dynamic pressure groove 10c is at the same level. This type of non-continuous type dynamic pressure groove 10c is continuous type, that is, the smoothing portion n is omitted, and the dynamic pressure groove 10c is formed in a V-shape that is continuous between both groove regions m1 and m2. Since oil is collected around the smooth portion n, the oil film pressure is high, and since the smooth portion n without a groove is provided, the bearing rigidity is high.
[0028]
In the present invention, as shown in FIG. 4, the end surface 10f2 on the housing closing side of the bearing body 10 is brought into contact with the upper surface of the thrust washer 12a, which is a facing surface facing the end surface 10f2. In this case, the oil leaked excessively due to thermal expansion or the like is the space between the end surface chamfer portion 10g (inner diameter side) of the bearing body 10 and the outer peripheral surface of the rotary shaft 2, and the end surface chamfer portion 10h (outer diameter side). And the space between the inner peripheral surface of the housing 1b and easily absorbed into the bearing body 10 due to the temperature drop of the bearing body 10 when the drive is stopped (capillary phenomenon). Therefore, since abundant oil is always held inside the bearing, sufficient oil can always be held in the bearing gap during driving, and stable bearing performance can be maintained for a long time.
[0029]
Of course, even if the end face 10f2 of the bearing body 10 and the thrust washer 12a are not in contact with each other, if they are sufficiently close to each other, that is, within the range in which the oil accumulated by the capillary phenomenon can be absorbed. If so, an axial gap 14 may be interposed between the end face 10f2 and the upper surface 13 (opposing surface) of the thrust washer 12, as shown in FIG.
[0030]
6 shows the axial run-out ratio and the amount of lubrication to the bearing body 10 when the axial width of the gap 14 (s: see FIG. 5) is changed (s = 0 mm, 0.7 mm, 1.0 mm, 1.2 mm). Shows the relationship. The bearing body 10 had an inner diameter of φ3 mm and an outer diameter of φ6 mm, and the rotating shaft was rotated at 8000 rpm while applying an unbalance amount of 0.5 gr-cm. Prior to the test, the bearing body 10 contained sufficient lubricating oil.
[0031]
From this test, when the axial width s of the gap 14 is 1.2 mm, additional oil supply is required for the volume of the gap 14, and the shaft runout ratio increases rapidly when the amount of oil supply is small. It has been found that if the direction width s is 1 mm or less, a sufficiently low shaft runout ratio can be achieved regardless of the presence or absence of additional lubrication. Accordingly, the axial width s of the gap 14 is preferably 1 mm or less, and is set to about 0.4 mm, for example.
[0032]
Incidentally, in the bearing unit 1, as shown in FIGS. 2A and 4, the lower end of the rotary shaft 2 is often formed in a spherical surface from the viewpoint of reducing friction and the like. In this case, as shown in FIG. 4, if the spherical surface portion 2a of the rotating shaft 2 overlaps with the radial bearing surface 10b of the bearing body 10, the bearing gap becomes non-uniform and an appropriate dynamic pressure action cannot be obtained. Therefore, in this case, as shown in FIG. 7, by providing the radial bearing surface 10b with the annular smooth portion 10i separated from the inner diameter chamfered portion 10g of the bearing body 10, the bearing surface 10b is shifted relatively upward. Thus, the entire region of the bearing surface 10b may be opposed to the cylindrical portion 2b on the upper end side of the spherical portion 2a of the rotating shaft 2 (see FIG. 5). The smoothing portion 10i is formed only on at least one end side of the both ends of the bearing body 10, that is, only on the end portion (left side in FIG. 7) located on the bottom side of the housing 1b when assembled in the housing 1b. However, a similar smooth portion may be provided on the other end side (the right side).
[0033]
In the above description, the upper surface of the thrust washer 12a is illustrated as the facing surface 13 facing the closing side end surface 10f2 of the bearing body 10, but as shown in FIG. 9, the upper surface of the thrust washer 12a and the bearing body 10 By disposing the ring-shaped spacer 15 between them, the upper surface of the spacer 15 may be the facing surface 13 facing the end surface 10f2. In this case, the bearing body 10 and the spacer 15 are brought into contact with each other as in FIGS. 4 and 5, or close to each other within a predetermined range. The inner diameter of the spacer 15 is slightly larger than the inner diameter of the radial bearing surface 10b so that the torque does not increase. When the thrust bearing portion 12 is disposed on the opening side of the housing 1b, for example, as shown in FIG. 18, a disk-shaped flange portion 2c provided on the shaft 2 is brought into contact with the housing opening side end surface 10f1 of the bearing body 10. When the thrust bearing portion 12 is configured, the upper surface (bottom surface) of the bottom plate 16 that closes the bottom portion of the housing 1b is the facing surface 13, and the facing surface 13 is brought into contact with the housing closing side end surface 10f2 of the bearing body 10 or predetermined Close within range.
[0034]
In the above description, the case where the dynamic pressure groove 10c is provided on the bearing surface 10b of the bearing body 10 is illustrated, but the present invention is similarly applied to the case where the dynamic pressure groove is provided on the outer peripheral surface of the rotating shaft 2. can do.
[0035]
An endurance test was conducted using the bearing unit 1 shown in FIG. 5 as an example and the bearing unit shown in FIG. 16 as a comparative example, and the shaft run-out characteristics after the initial and 2000-hour elapsed were measured. All measurements were performed using three bearing units. In the embodiment, the width s of the gap 14 is 0.2 mm, the width t of the smooth portion 10i is 1 mm, and in the comparative example, the width s 'of the gap 14' is 3 mm. The test conditions are as follows.
[0036]
Motor used: Polygon scanner motor (actual motor)
Rotational speed: 20000 rpm
Ambient temperature: 50 ° C
Normally, in the polygon scanner motor, the upper end of the rotating shaft does not protrude above the mirror surface, but a rotor with the upper end of the shaft protruding was made for this experiment. Therefore, the axial run-out is measured substantially above the mirror surface, and the measurement result is relative comparison data.
[0037]
The measurement results are shown in FIG. As shown in the drawing, although the shaft runout values in the example and the comparative example are almost the same at the initial stage, the shaft runout in the comparative example became remarkably large after 2000 hours, and the superiority of the example product was confirmed.
[0038]
10 and 11 show another embodiment of the present invention, in which the opening at one end of the housing 1b is sealed with a non-contact type sealing member (seal washer 20). In the bearing unit 1, the components other than the seal structure at the upper end of the housing 1b, for example, the configuration of the hydrodynamic sintered oil-impregnated bearing 1a, the housing 1b, the rotating shaft 2, the thrust bearing portion 12, and the like are as described below. Except for this, a configuration similar to that shown in FIGS. 1 to 9 can be applied.
[0039]
The seal washer 20 is formed in a thin disk shape having an insertion hole for the rotary shaft 2 at the center, and is formed of, for example, a resin material (for example, polyamide) and fixed to one end opening of the housing 1b by means of adhesion or the like. Is done. The seal washer 20 need only be formed in a washer shape, and can be formed of metal other than resin. The inner peripheral surface of the seal washer 20 is as close as possible to the outer peripheral surface of the rotating shaft 2 so that oil leakage from the inside of the housing 1b is prevented by capillary action. When the seal washer 20 is brought into contact with the shaft 2, torque is increased or fluctuated, which is not preferable as a spindle motor for information equipment that requires high accuracy. Therefore, the seal washer 20 is not in contact with the shaft 2. If the width u1 of the gap between the inner peripheral surface of the seal washer 20 and the outer peripheral surface of the rotary shaft 2 is 0.1 mm or less, preferably 0.05 mm or less, even if the shaft orientation is in the horizontal direction or the reverse direction, Oil leakage is surely prevented by capillary action. Since air circulation through the gap u1 is ensured, the air is smoothly released from the housing 1b.
[0040]
Of the outer peripheral surface of the rotating shaft 2, an oil repellent 21 is applied to the region including at least a portion facing the inner peripheral surface of the seal washer 20 (region having an axial width larger than the thickness of the seal washer 20) over the entire periphery. If oil is applied, the oil that is about to leak through the shaft 2 can be repelled, and oil leakage can be completely prevented. As the oil repellent 21, for example, a material mainly composed of perfluorocarbon (manufactured by Harvest, OS-90MF, etc.) can be used.
[0041]
By the way, the rotating shaft 2 is normally inserted into the inner diameter portion of the bearing 1a with the thrust bearing portion 12 mounted on the housing 1b. Before the shaft 2 is inserted, as shown in FIG. 12, oil O (indicated by a dotted pattern) may be injected into the housing 1b in advance to improve lubricity. Since the bearing gap between them is only a few μm, there is no escape space for air trapped between the shaft end and the upper surface of the oil O that has been lubricated, making it difficult to insert the rotating shaft 2. The motor generates heat when it is driven, but the trapped air expands and pushes up the rotating shaft 2 to destabilize the bearing performance, or the thermally expanded air pushes oil out of the bearing and lubricates it. There is also a risk of reducing the properties. These problems occur similarly even when not lubricating.
[0042]
As a countermeasure against this, as shown in FIGS. 10 and 11, an air passage 22 opened at both axial ends of the bearing body 10 is provided between the outer diameter surface of the bearing body 10 and the inner diameter surface of the housing 1b. The air trapped through the path 22 may be released to the outside of the bearing. In this case, some air may remain in the oil as bubbles, but this type of bubbles floats up through the air passage 22 and is released out of the housing 1b. Therefore, after the shaft 2 is inserted, as shown in FIG. 13, the space in the housing 1b (the space 14 between the bearing 1a and the facing surface 13, the space 23 between the seal washer 20 and the bearing end surface 10f1, the bearing gap, It is possible to fill the air passage 22 and the like with the oil O. As shown in FIG. 3, the air passage 22 can be formed by providing an axial groove 10j on the outer peripheral surface of the bearing body 1a. However, the same groove 10j may be provided on the inner peripheral surface of the housing 1b. Good. Moreover, you may provide the ventilation path 22 not only in one place but in the multiple places of the circumferential direction.
[0043]
If the gap 23 between the seal washer 20 and the bearing end face 10f1 opposite to the seal washer 20 (hereinafter referred to as a gap on one end side) is too large, the space in the housing 1b cannot be filled with oil depending on the amount of lubrication. The amount of air remaining in 1b increases, and there is a risk of air entering the gap 14 between the thrust washer 12a and the bearing end face 10f2 (hereinafter referred to as the other end side gap) when the shaft orientation is set to the horizontal or reverse direction. It is not preferable. Accordingly, it is desirable to make the one end side gap 23 as small as possible, and its width u2 (see FIG. 10) is set to 0.6 mm, for example. The width u2 of the gap may be 1.0 mm or less, and is preferably set to 0.5 mm or less, but is preferably set to be larger than the width s of the other end side gap 14 (u2> s). If the one-end-side gap 23 is smaller than the other-end-side gap 14, the one-end-side gap 23 will be filled with oil first and the air that has lost its escape will enter the other-end-side gap 14 when the shaft posture is reversed. This is because it is expected.
[0044]
In order to confirm the effect of this embodiment, the following tests were conducted.
[0045]
・ Atmosphere: 50 ℃
・ Shaft diameter: φ3
・ Axis posture: Reverse
・ Rotation speed: 8000rpm
・ Test time: 500 hours
Evaluation items: The oil leakage situation (visual observation) and the performance change (shaft runout, current value) dimensions of the bearing unit 1 subjected to the test are as shown in FIG.
[0046]
The test results are shown in FIG.
[0047]
When the seal washer was not provided as in Comparative Example 1, the oil that was lubricated naturally leaked out, and air was caught in that portion, so the performance was greatly reduced. Since the current value is also increased, the fluid lubrication state is impaired, and it is presumed that the mixed lubrication state including the metal contact is achieved.
[0048]
In Comparative Example 2, oil leakage is recognized although the adhesion of oil to the shaft or rotor is recognized. Although the current value was slightly smaller, the shaft runout was considerably larger than the initial value. Since oil leakage occurred, air intruded into that part, and the apparent viscosity decreased, so it is presumed that the shaft runout increased. The cause of the oil leakage is that when the motor is reversed, the gap 14 between the bearing end face 10f2 and the thrust washer 12a is larger than the gap 23 between the seal washer 20 and the bearing end face 10f1, so the seal washer 20 and the bearing This is presumably because the gap 23 between the end faces 10f1 was first filled with oil, and the air that lost the escape area entered the gap 14 between the bearing end face 10f2 and the facing surface 13. As the temperature of the bearing rises, the thermal expansion of the gas is greater than that of the liquid, so the oil appears to have been pushed out by the air.
[0049]
In the case of Comparative Example 3 as well, although oil adhesion was recognized to the shaft or rotor, oil leakage was observed, and the current value was slightly smaller but the shaft runout was larger than the initial value. This is probably because the gap between the seal washer 20 and the shaft 2 was large and oil leakage could not be prevented by capillary action.
[0050]
In the case of Comparative Example 4 as well, although oil adhesion was recognized to the shaft or rotor, oil leakage was recognized and the current value was slightly smaller, but the shaft runout was larger than the initial value. This is probably because the gap 23 between the seal washer 20 and the bearing end face 10f1 was too large, and the capillary phenomenon between the seal washer 20 and the bearing end face 10f1 did not work.
[0051]
On the other hand, almost no oil leakage was observed in Example 1, and the performance was maintained at the initial state, and a good result was obtained.
[0052]
In Example 2, no oil leakage was observed. In the first embodiment, no deterioration was observed in the performance such as shaft runout. However, in the case of a model in which oil mist scattering is a problem as in the HDD apparatus, the second embodiment has a more reliable oil leakage prevention effect. Is considered preferable.
[0053]
【The invention's effect】
As described above, according to the present invention, oil leakage can be reliably prevented with a simple structure regardless of the shaft posture. Therefore, it is possible to provide a bearing unit having high functionality at low cost. Further, since there is no oil leakage, a good oil film can be maintained for a long time, and the durability is dramatically improved. Moreover, the surroundings are not contaminated by oil leakage.
[Brief description of the drawings]
FIG. 1 is a sectional view in the axial direction of a spindle motor for DVD-ROM using a bearing unit according to the present invention.
2A is an enlarged cross-sectional view of a bottom portion of a bearing unit, and FIG. 2B is a cross-sectional view showing another example of a thrust bearing portion.
FIG. 3 is a sectional view in the axial direction of a sintered oil-impregnated bearing.
FIG. 4 is an axial sectional view showing an embodiment of the bearing unit.
FIG. 5 is an axial sectional view showing another embodiment of the bearing unit.
FIG. 6 is a diagram showing measurement data of the amount of lubrication and the shaft runout ratio.
FIG. 7 is a sectional view in the axial direction of a sintered oil-impregnated bearing.
FIG. 8 is a diagram showing the results of a durability test on the product of the present invention and a conventional product.
FIG. 9 is an axial sectional view showing another embodiment of the bearing unit.
FIG. 10 is an axial sectional view of a DVD-ROM spindle motor using the bearing unit according to the present invention.
FIG. 11 is an enlarged cross-sectional view in the vicinity of the housing opening.
FIG. 12 is an axial sectional view of a bearing unit during shaft insertion.
FIG. 13 is an axial sectional view of the bearing unit after the shaft is inserted.
FIG. 14 is a diagram showing conditions for an oil leakage test.
FIG. 15 is a diagram showing experimental results.
FIG. 16 is an axial sectional view showing a conventional bearing unit.
FIG. 17 is an enlarged cross-sectional view of a hydrodynamic bearing unit to which a labyrinth seal is applied.
FIG. 18 is an axial sectional view of a dynamic pressure type bearing unit.
[Explanation of symbols]
1 Bearing unit
1a Sintered oil-impregnated bearing
1b housing
2 axis (rotary axis)
3 Optical disc
2a Spherical surface
10 Bearing body
10b Radial bearing surface
10c Dynamic pressure groove
10f1 Bearing end face (one end side)
10f2 Bearing end face (other end side)
10i smooth part
10k groove
12 Thrust bearing
12a Thrust washer
13 Opposite surface
14 Clearance (other end side)
15 Spacer
16 Bottom plate
20 Seal washer
21 Oil repellent
22 Ventilation path
23 Clearance (one end side)

Claims

A bearing body made of sintered metal and having a plurality of radial bearing surfaces opposed to the outer peripheral surface of the shaft through bearing clearances in the axial direction is impregnated with lubricating oil or lubricating grease. And a hydrodynamic sintered oil-impregnated bearing that supports the shaft in a non-contact manner by a hydrodynamic action generated by a hydrodynamic groove inclined with respect to the axial direction during relative rotation between the bearing body and the bearing body, and one end is open and the other end is closed, In a part provided with a housing in which the above-mentioned hydrodynamic sintered oil-impregnated bearing is housed, and a thrust bearing portion for thrust-supporting the shaft,
The housing main body closing side end surface of the bearing body and the opposing surface provided on the housing closing side facing the end surface are brought close to each other so that the gap between them is 1 mm or less , and the inner surface of the bearing main body A hydrodynamic sintered oil-impregnated bearing unit characterized in that the gap between the surface and the outer peripheral surface of the shaft is filled with oil, and the opening at one end of the housing is sealed by capillary action.

Hydrodynamic type oil-impregnated sintered bearing unit according to claim 1, wherein the forming the opposing surfaces at the bottom which closes the other end of the housing.

Thrust bearing portion is intended to contact the support with a thrust washer provided the shaft end on the closed side of the housing, hydrodynamic type oil-impregnated sintered bearing unit according to claim 1, wherein the thrust washer is constructed of the opposing surfaces.

Hydrodynamic type oil-impregnated sintered bearing unit according to claim 1, wherein the forming the opposing surfaces at the spacer provided on the closed side of the housing.

4. The hydrodynamic sintered oil-impregnated oil-impregnated structure according to claim 3 , wherein one end of the shaft contacting the thrust washer is formed in a spherical shape, and the radial bearing surface of the bearing body is shifted from the other spherical surface of the shaft toward the other end side of the shaft. Bearing unit.

The hydrodynamic sintered oil-impregnated bearing unit according to claim 5, wherein a radial bearing surface is provided with an annular smooth portion separated from an end surface chamfer portion on the other end side of the housing of the bearing body.

The hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 6 , wherein the opening at one end of the housing is sealed with a seal washer whose inner peripheral surface is close to the outer peripheral surface of the shaft.

The hydrodynamic sintered oil-impregnated bearing unit according to claim 7 , wherein a clearance between the inner peripheral surface of the seal washer and the outer peripheral surface of the shaft is set to 0.1 mm or less.

The hydrodynamic sintered oil-impregnated bearing unit according to claim 7 , wherein a clearance between the seal washer and the bearing end face facing the seal washer is set to 1.0 mm or less.

8. The hydrodynamic sintered oil-impregnated bearing unit according to claim 7 , wherein a gap between the seal washer and the bearing end face facing the seal washer is set larger than a gap between the housing closing side end face of the bearing body and the facing face. .

8. The hydrodynamic sintered oil-impregnated bearing unit according to claim 7, wherein an oil repellent is applied to a region including at least a portion facing the inner peripheral surface of the seal washer in the outer peripheral surface of the shaft.

The hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 11, wherein a hydrodynamic groove inclined with respect to the axial direction is provided on the radial bearing surface.

The hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 12, wherein a vent path is provided between the outer diameter surface of the bearing body and the inner diameter surface of the housing.

The spindle motor of an optical disc drive having a hydrodynamic type oil-impregnated sintered bearing unit according to any one of claims 1 to 13 for rotating the optical disc by the relative rotation between the shaft and the bearing body.

Axis and the spindle motor of the magnetic disk drive having a hydrodynamic type oil-impregnated sintered bearing unit according to any one of claims 1 to 13 to rotate the magnetic disk by relative rotation of the bearing body.

A polygon scanner motor for a laser beam printer comprising the hydrodynamic sintered oil-impregnated bearing unit according to any one of claims 1 to 13, wherein the polygon mirror is rotated by relative rotation between the shaft and the bearing body.

The hydrodynamic sintered oil-impregnated bearing according to claim 1 , wherein an end face chamfer portion is provided at least at one inner diameter portion of the bearing body, and a radial bearing surface is formed by separating an annular smooth portion from the end face chamfer portion .