JP2004116623A

JP2004116623A - Fluid bearing device

Info

Publication number: JP2004116623A
Application number: JP2002279476A
Authority: JP
Inventors: Fumitada Satoji; 里路　文規; Isao Komori; 古森　功; Masaji Shimizu; 清水　政次
Original assignee: NTN Corp; NTN Toyo Bearing Co Ltd
Current assignee: NTN Corp
Priority date: 2002-09-25
Filing date: 2002-09-25
Publication date: 2004-04-15
Anticipated expiration: 2022-09-25
Also published as: JP4152707B2; DE10344591A1; DE10344591B4

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a lifting phenomenon of a shaft member during rotation. <P>SOLUTION: Of a first radial bearing part R1 and a second radial bearing part R2 provided in two vertical positions, a dynamic pressure groove 8a2 of the second radial bearing part R2 of a lower side (a side near to a thrust bearing part) is formed in an axially asymmetric shape with respect to an axial center m2, and an axial dimension X1 of a lower side area (a side near the thrust bearing part) than the axial center m2 is larger than an axial dimension X2 of an upper side area (a side near a seal part). By this, pumping force of lubricant by the dynamic pressure groove 8a2 becomes relatively larger in the lower side area (the side near the thrust bearing part) with respect to the upper side area (the side near the seal part). By a differential pressure of the pumping force, a phenomenon of a pressure of the lubricant in a thrust bearing part T periphery becoming higher than a pressure of the lubricant in a periphery of the seal part is prevented. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ラジアル軸受隙間に生じる潤滑油の油膜によって回転部材を非接触支持する流体軸受装置に関する。この軸受装置は、情報機器、例えばＨＤＤ、ＦＤＤ等の磁気ディスク装置、ＣＤ−ＲＯＭ、ＣＤ−Ｒ／ＲＷ、ＤＶＤ−ＲＯＭ／ＲＡＭ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、レーザビームプリンタ（ＬＢＰ）のポリゴンスキャナモータ、あるいは電気機器、例えば軸流ファンなどの小型モータ用として好適である。
【０００２】
【従来の技術】
上記各種モータには、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、上記要求性能に優れた特性を有する流体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】
この種の流体軸受は、軸受隙間内の潤滑油に動圧を発生させる動圧発生手段を備えたいわゆる動圧軸受と、動圧発生手段を備えていないいわゆる真円軸受（軸受面が真円形状である軸受）とに大別される。
【０００４】
例えば、ＨＤＤ等のディスク装置のスピンドルモータに組込まれる流体軸受装置では、軸部材をラジアル方向に非接触支持するラジアル軸受部と、軸部材をスラスト方向に支持するスラスト軸受部とが設けられ、ラジアル軸受部として、軸受スリーブの内周面又は軸部材の外周面に動圧発生用の溝（動圧溝）を設けた動圧軸受が用いられる（例えば、特許文献１参照）。このラジアル軸受部は、高い軸受機能を得るため、軸方向に離隔して複数箇所に設けられる場合が多い。スラスト軸受部としては、例えば、軸部材の端面をハウジングの一端側に設けたスラスト軸受部でスラスト方向に支持する構造の軸受（いわゆるピボット軸受）が用いられる。通常、軸受スリーブはハウジングの内周の所定位置に固定され、また、ハウジングの内部空間に注油した潤滑油が外部に漏れるのを防止するため、ハウジングの他端側にシール部材を配設する場合が多い。
【０００５】
【特許文献１】
特開２００１―１２４０５７号公報
【０００６】
【発明が解決しようとする課題】
この種の流体軸受装置では、ラジアル軸受部の軸受隙間や動圧溝の形状・寸法誤差等の理由により、軸受回転時、ハウジング一端側のスラスト軸受部周辺において潤滑油の圧力が高まり、ハウジング他端側のシール部周辺の潤滑油と圧力差が生じる場合がある。例えば、ラジアル軸受面にヘリングボーン形状の動圧溝を設けた動圧軸受を例に取ると、動圧溝が軸方向中心に対して軸方向対称に精度良く形成されている場合、該動圧溝による潤滑油のポンピング力は軸方向中心に対してシール部側とスラスト軸受部側とでバランスするが、製造誤差等により、動圧溝の形状が軸方向非対称になり、軸方向中心に対してシール部側の軸方向寸法がスラスト軸受部側の軸方向寸法よりも大きくなると、該動圧溝による潤滑油のポンピング力はシール部側がスラスト軸受部側に対して相対的に大きくなる。そして、このポンピング力の差圧により、シール部側からスラスト軸受部側に向いた潤滑油の圧力が加わり、これがスラスト軸受部周辺の潤滑油の圧力を高め、シール部周辺の潤滑油との圧力差を生じる原因となる。
【０００７】
そして、上記の圧力差により、軸部材はシール部側に押し上げられる方向の軸方向力を受ける（以下、この軸方向力を「押し上げ力」という。）。通常、この種の流体軸受装置が組み込まれるモータでは、マグネットの吸着力などにより、軸部材をスラスト軸受部に押し付ける構造になっているが、上記の押し上げ力がこの押し付け力よりも大きくなると、軸部材の浮き上がり現象が生じ、モータ及びその周辺部位に好ましくない影響を与える可能性がある。
【０００８】
本発明の課題は、上記の押し上げ力による軸部材の浮き上がり現象を防止することである。
【０００９】
【課題を解決するための手段】
上記課題を解決するため、本発明は、ハウジングと、ハウジングの内部に設けられた軸受スリーブと、軸受スリーブの内周面に挿入された軸部材と、軸受スリーブの内周面と軸部材の外周面との間に設けられ、軸受隙間に生じる潤滑油の油膜で軸部材をラジアル方向に支持するラジアル軸受部と、ハウジングの一端側に設けられ、軸部材の端面をスラスト方向に支持するスラスト軸受部と、ハウジングの他端側に設けられ、軸部材の外周面との間にシール空間を形成するシール部とを備えた流体軸受装置において、軸受スリーブと軸部材との相対回転時に、スラスト軸受部周辺の潤滑油の圧力Ｐｔが、シール部周辺の潤滑油の圧力Ｐｓに対して、Ｐｔ≦Ｐｓとなる構成を提供する。
【００１０】
スラスト軸受部周辺の潤滑油の圧力Ｐｔを、シール部周辺の潤滑油の圧力Ｐｓと同じか（Ｐｔ＝Ｐｓ）、これよりも低くすることにより（Ｐｔ＜Ｐｓ）、軸部材に対する上記押し上げ力の発生を回避して、軸部材の浮き上がり現象を防止することができる。
【００１１】
Ｐｔ≦Ｐｓにする手段として、ラジアル軸受部を軸方向に離隔して複数箇所に設けると共に、動圧溝を有する動圧軸受とし、スラスト軸受部に最も近い個所に設けられているラジアル軸受部の側から他の箇所に設けられているラジアル軸受部の方向に潤滑油の引き込みが生じるように構成することができる。このように構成することで、スラスト軸受部に最も近いラジアル軸受部側から他のラジアル軸受側に向かう潤滑油の流動、すなわち、スラスト軸受部側からシール部側に向かう潤滑油の流動が生じ、これにより、スラスト軸受部周辺の潤滑油の圧力がシール部周辺の潤滑油の圧力よりも高くなる現象が防止される。
【００１２】
より具体的には、次のような手段を採用することができる。
【００１３】
第１の手段は、スラスト軸受部に最も近い個所に設けられているラジアル軸受部において、該ラジアル軸受部の動圧溝による潤滑油のポンピング力がシール部側よりもスラスト軸受部側が大きくなるように構成することである。このように構成することで、スラスト軸受部側からシール部側に向かう潤滑油の流動が生じ、これにより、スラスト軸受部周辺の潤滑油の圧力がシール部周辺の潤滑油の圧力よりも高くなる現象が防止される。
【００１４】
第１の手段として、スラスト軸受部に最も近い個所に設けられているラジアル軸受部の動圧溝を軸方向非対称に形成することができる。例えば、該動圧溝をヘリングボーン形状とする場合、該動圧溝の軸方向中心に対して、スラスト軸受部側の軸方向寸法をシール部側の軸方向寸法よりも大きくし、若しくは、スラスト軸受部側の溝本数、溝角度、溝深さ等をシール部側と異ならせる。あるいは、第１の手段として、スラスト軸受部に最も近い個所に設けられているラジアル軸受部の動圧溝を軸方向対称に形成する一方、該動圧溝のシール部側端部領域と対向する相手部材の表面に軸受隙間よりも大きな隙間を形成する逃げ部を設けて、シール部側の軸方向寸法を擬似的にスラスト軸受部側の軸方向寸法よりも小さくしても良い。
【００１５】
第２の手段は、スラスト軸受部に最も近い個所に設けられているラジアル軸受部を、他の箇所に設けられているラジアル軸受部に対して、軸受隙間内に発生する潤滑油の動圧が高くなるように構成することである。このように構成することで、スラスト軸受部に最も近いラジアル軸受部側から他のラジアル軸受側に向かう潤滑油の流動、すなわち、スラスト軸受部側からシール部側に向かう潤滑油の流動が生じ、これにより、スラスト軸受部周辺の潤滑油の圧力がシール部周辺の潤滑油の圧力よりも高くなる現象が防止される。
【００１６】
第２の手段には、スラスト軸受部に最も近い個所に設けられているラジアル軸受部の軸受隙間を、他の個所に設けられているラジアル軸受部の軸受隙間よりも小さくする手段、スラスト軸受部に最も近い個所に設けられているラジアル軸受部の動圧溝と他のラジアル軸受部の動圧溝とで溝本数、溝角度、溝深さ等を異ならせる手段が含まれる。あるいは、第２の手段として、軸受スリーブを焼結金属等の多孔質体で形成すると共に、スラスト軸受部に最も近い個所に設けられているラジアル軸受部を構成する軸受スリーブの軸受面の表面開孔率（表面開孔とは多孔質体組織の内部気孔が外表面に開孔した部位をいい、表面開孔率とは単位面積当たりに占める表面開孔の総面積の比率をいう。）を、他の個所に設けられているラジアル軸受部を構成する軸受スリーブの軸受面の表面開孔率よりも小さくしても良い。
【００１７】
また、Ｐｔ≦Ｐｓ、特にＰｔ＝Ｐｓにする手段として、ラジアル軸受部を軸方向に離隔して複数箇所に設けると共に、スラスト軸受部に最も近い個所に設けられているラジアル軸受部とスラスト軸受部との間に、該ラジアル軸受部の軸受半径隙間よりも大きな隙間を有する空間部を設けることができる。該空間部を設けることにより、スラスト軸受部周辺における潤滑油の圧力の高まりが緩和され、シール部周辺における潤滑油の圧力よりも高くなる現象が防止される。この手段は、ラジアル軸受部をいわゆる真円軸受（軸受面に動圧溝を有しない軸受）として構成する場合、動圧軸受として構成する場合の双方に適用することができる。
【００１８】
上記空間部の隙間の最大値は軸受半径隙間の１０倍以上とするのが好ましい。これは次の理由による。一般に、流体軸受の負荷容量Ｗは下記の式で表すことができる。
Ｗ＝Ｗ１・｛αωＲ^４／（ΔＲ）^２｝・β
ここで、Ｗ：負荷容量、Ｗ１：軸受仕様によって決まる無次元負荷容量、α：潤滑油粘度、ω：回転角速度、Ｒ：軸受半径、ΔＲ：軸受半径隙間、β：偏心率である。
【００１９】
上記の式より、軸受半径隙間ΔＲが１０倍になると、負荷容量Ｗは１／１００になることが分かる。従って、上記空間部の隙間を軸受半径隙間の１０倍以上とすることで、上記空間部の負荷容量をラジアル軸受部の負荷容量の１／１００（１％）以下にすることができ、これにより、スラスト軸受部周辺における潤滑油の圧力の高まりを効果的に緩和することができる。
【００２０】
上記構成において、ハウジングは樹脂材料で形成することができる。樹脂製のハウジングは射出成形等の型成形で形成することができるので、旋削等の機械加工による金属製ハウジングに比べて低コストで製造することができると共に、プレス加工による金属製ハウジングに比べて比較的高い精度を確保することができる。特に、軸受スリーブをインサート部品として、ハウジングを樹脂材料で型成形することにより、ハウジングに対する軸受スリーブの接着等による固定作業を省略できるので、組立工程の簡素化に有利である。この場合、軸受スリーブを焼結金属で形成すると、型成形時に、溶融樹脂が軸受スリーブの固定面の表面開孔から内部気孔内に侵入して固化し、そして、内部気孔内で固化した部分が一種のアンカー効果によって、ハウジングと軸受スリーブとを強固に密着させるので、両者間の相対的な位置ずれが生じず、安定した固定状態が得られる。
【００２１】
【発明の実施の形態】
以下、本発明の実施形態を図１〜図５に基づいて説明する。
【００２２】
図１は、この実施形態に係る流体軸受装置１を組み込んだ情報機器用スピンドルモータの一構成例を示している。このスピンドルモータは、ＨＤＤ等のディスク駆動装置に用いられるもので、軸部材２を回転自在に支持する流体軸受装置１と、軸部材２に装着されたディスクハブ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とを備えている。ステータ４はケーシング６の外周に取付けられ、ロータ５はディスクハブ３の内周に取付けられる。流体軸受装置１のハウジング７は、ケーシング６の内周に装着される。ディスクハブ３には、磁気ディスク等のディスクＤが一又は複数枚保持される。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、それによってディスクハブ３および軸部材２が一体となって回転する。
【００２３】
図２は、第１の実施形態に係る流体軸受装置（流体動圧軸受装置）１を示している。この流体軸受装置１は、ハウジング７と、軸受スリーブ８と、軸部材２とを構成部品して構成される。
【００２４】
軸受スリーブ８の内周面８ａと軸部材２の外周面２ａとの間に第１ラジアル軸受部Ｒ１と第２ラジアル軸受部Ｒ２とが軸方向に離隔して設けられる。また、軸部材２の下側端面２ｂとハウジング７の底部７ｃの内底面７ｃ２との間にスラスト軸受部Ｔが設けられる。尚、説明の便宜上、スラスト軸受部Ｔの側を下側、スラスト軸受部Ｔと反対の側（シール部７ａの側）を上側として説明を進める。
【００２５】
軸受スリーブ８は、例えば、焼結金属からなる多孔質体、特に銅を主成分とする燒結金属の多孔質体で円筒状に形成される。この焼結金属で形成された軸受スリーブ８の内周面８ａには、第１ラジアル軸受部Ｒ１と第２ラジアル軸受部Ｒ２のラジアル軸受面となる上下２つの領域が軸方向に離隔して設けられ、該２つの領域には、例えば図３に示すようなヘリングボーン形状の動圧溝８ａ１、８ａ２がそれぞれ形成される。上側（シール部７ａに近い側）の動圧溝８ａ１は、軸方向中心ｍ１に対して軸方向対称形状に形成されているが（軸方向中心ｍ１からの軸方向寸法はＸ０）、下側（スラスト軸受部Ｔに近い側）の動圧溝８ａ２は、軸方向中心ｍ２に対して軸方向非対称形状に形成されている。この例では、軸方向中心ｍ２より下側領域（スラスト軸受部Ｔに近い側）の軸方向寸法Ｘ１を、上側領域（シール部７ａに近い側）の軸方向寸法Ｘ２よりも大きくしている（Ｘ１＞Ｘ２）。
【００２６】
軸部材２は、例えば、ステンレス鋼等の金属材で形成され、その下側端部に、ハウジング７の底部７ｃの内底面７ｃ２と協働してスラスト軸受部Ｔを構成する凸球状の下側端面２ｂを備えている。
【００２７】
ハウジング７は、焼結金属からなる軸受スリーブ８をインサート部品として、樹脂を射出成形（インサート成形）して形成され、円筒状の側部７ｂと、側部７ｂの上端から内径側に一体に延びた環状のシール部７ａと、側部７ｂの下端と一体に連続した底部７ｃとを備えている。シール部７ａの内周面７ａ１は、軸部材２の外周面２ａと所定のシール空間Ｓを介して対向する。上記のインサート成形により、側部７ｂの内周面７ｂ１は軸受スリーブ８の外周面８ｄと、シール部７ａの内側面７ａ２は軸受スリーブ８の上側端面８ｂと、内底面７ｃ１は軸受スリーブ８の下側端面８ｃと相互に密着した状態で結合される。軸受スリーブ８が多孔質の焼結金属で形成されているので、前述したアンカー効果により、ハウジング７と軸受スリーブ８とが強固に密着して、両者の安定した固定状態が得られる。
【００２８】
この実施形態の流体軸受装置１は、上記のインサート成形により相互に固定されたハウジング７および軸受スリーブ８に対して、軸部材２を装着することによって組立ることができる。すなわち、軸部材２を軸受スリーブ８の内周面８ａに挿入して、その下側端面２ｂをハウジング７の内底面７ｃ２に接触させる。そして、軸受スリーブ８の内部気孔を含め、シール部７ａで密封されたハウジング７の内部空間に潤滑油を充満する。この潤滑油の油面はシール空間Ｓ内に維持される。
【００２９】
軸部材２の回転時、軸受スリーブ８の内周面８ａのラジアル軸受面となる領域（上下２箇所の領域）は、それぞれ、軸部材２の外周面２ａとラジアル軸受隙間を介して対向する。そして、軸部材２の回転に伴い、上記軸受隙間に潤滑油の動圧が発生し、軸部材２が上記軸受隙間内に形成される潤滑油の油膜によってラジアル方向に回転自在に非接触支持される。これにより、軸部材２をラジアル方向に回転自在に非接触支持する第１ラジアル軸受部Ｒ１と第２ラジアル軸受部Ｒ２とが構成される。同時に、軸部材２の下側端面２ｂがハウジング７の内底面７ｃ２によって接触支持される。これにより、軸部材２をスラスト方向に回転自在に支持するスラスト軸受部Ｔが構成される。
【００３０】
上述したように、上下２箇所に設けられた第１ラジアル軸受部Ｒ１と第２ラジアル軸受部Ｒ２のうち、下側（スラスト軸受部Ｔに近い側）の第２ラジアル軸受部Ｒ２の動圧溝８ａ２は、軸方向中心ｍ２に対して軸方向非対称形状に形成されており、軸方向中心ｍ２より下側領域（スラスト軸受部Ｔに近い側）の軸方向寸法Ｘ１が、上側領域（シール部７ａに近い側）の軸方向寸法Ｘ２よりも大きくなっている。そのため、軸部材２の回転時、動圧溝８ａ２による潤滑油のポンピング力は下側領域（スラスト軸受部Ｔに近い側）が上側領域（シール部７ａに近い側）に対して相対的に大きくなる。そして、このポンピング力の差圧により、第２ラジアル軸受部Ｒ２の側から第１ラジアル軸受部Ｒ１の側に向かう潤滑油の流動、すなわち、スラスト軸受部Ｔ側からシール部７ａ側に向かう潤滑油の流動が生じ、これにより、スラスト軸受部Ｔの周辺における潤滑油の圧力がシール部７ａの周辺における潤滑油の圧力よりも高くなる現象が防止される。
【００３１】
図４は、第２の実施形態に係る流体軸受装置（流体動圧軸受装置）１１を示している。この流体軸受装置１１では、第１ラジアル軸受部Ｒ１の動圧溝８ａ１’と第２ラジアル軸受部Ｒ２の動圧溝８ａ２’を共に軸方向対称に形成する一方、第２ラジアル軸受部Ｒ２については、その動圧溝８ａ２’のシール部７ａ側の端部領域を、軸部材２の外周面２ａに設けた逃げ部２ｃに対向させている。軸部材２の逃げ部２ｃは、第１ラジアル軸受部Ｒ１と第２ラジアル軸受部Ｒ２との間の領域に設けられ、逃げ部２ｃと軸受スリーブ８の内周面８ａとの間の隙間は、第２ラジアル軸受部Ｒ２（及び第１ラジアル軸受部Ｒ１）の軸受隙間よりも大きい。従って、動圧溝８ａ２’のシール部７ａ側の端部領域をこの逃げ部２ｃに対向させることにより、動圧溝８ａ２’のシール部７ａ側の軸方向寸法は擬似的にスラスト軸受部Ｔ側の軸方向寸法よりも小さくなる。そのため、軸部材２の回転時、動圧溝８ａ２’による潤滑油のポンピング力は下側領域（スラスト軸受部Ｔに近い側）が上側領域（シール部７ａに近い側）に対して相対的に大きくなる。そして、このポンピング力の差圧により、第２ラジアル軸受部Ｒ２の側から第１ラジアル軸受部Ｒ１の側に向かう潤滑油の流動、すなわち、スラスト軸受部Ｔ側からシール部７ａ側に向かう潤滑油の流動が生じ、これにより、スラスト軸受部Ｔの周辺における潤滑油の圧力がシール部７ａの周辺における潤滑油の圧力よりも高くなる現象が防止される。
【００３２】
図５は、第３の実施形態に係る流体軸受装置（流体動圧軸受装置）におけるスラスト軸受部Ｔの周辺を示している。この流体軸受装置では、第２ラジアル軸受部Ｒ２とスラスト軸受部Ｔとの間に、第２ラジアル軸受部Ｒ２の軸受半径隙間Ｃ０よりも大きな隙間Ｃ１を有する空間部Ｓ１を設けている。
【００３３】
この実施形態において、軸部材２の下側端面２ｂは凸球状に形成され、下側端面２ｂの曲率半径よりも小さな曲率半径を有する繋ぎ部２ｄを介して外周面２ａと滑らかに連続している。また、空間部Ｓ１の隙間Ｃ１の最大値は、第２ラジアル軸受部Ｒ２の軸受半径隙間Ｃ０の１０倍以上となるように設定されている。また、第１ラジアル軸受部Ｒ１の動圧溝と第２ラジアル軸受部Ｒ２の動圧溝は共に軸方向対称に形成されている。その他の構成は、図２に示す実施形態と同様である。
【００３４】
第２ラジアル軸受部Ｒ２とスラスト軸受部Ｔとの間に、第２ラジアル軸受部Ｒ２の軸受半径隙間Ｃ０よりも大きな隙間Ｃ１を有する空間部Ｓ１を設けることにより、特に、空間部Ｓ１の隙間Ｃ１の最大値を第２ラジアル軸受部Ｒ２の軸受半径隙間Ｃ０の１０倍以上となるように設定することにより、スラスト軸受部Ｔ周辺における潤滑油の圧力の高まりが緩和され、シール部７ａ周辺における潤滑油の圧力よりも高くなる現象が防止される。
【００３５】
【発明の効果】
本発明によれば、軸受スリーブと軸部材との相対回転時に、スラスト軸受部周辺の潤滑油の圧力Ｐｔがシール部周辺の潤滑油の圧力Ｐｓに対してＰｔ≦Ｐｓとなる構成としたので、軸部材の浮き上がり現象を防止することができる。
【図面の簡単な説明】
【図１】本発明に係る流体軸受装置を使用した情報機器用スピンドルモータの断面図である。
【図２】第１の実施形態に係る流体軸受装置を示す断面図である。
【図３】軸受スリーブの断面図である。
【図４】第２の実施形態に係る流体軸受装置を示す断面図である。
【図５】第３の実施形態に係る流体軸受装置におけるスラスト軸受部の周辺を示す拡大断面図である。
【符号の説明】
１　　　流体軸受装置（動圧軸受装置）
１１　　　流体軸受装置（動圧軸受装置）
２　　　軸部材
２ａ　　外周面
２ｂ　　端面
２ｃ　　逃げ部
７　　　ハウジング
７ａ　　シール部
８　　　軸受スリーブ
８ａ　　内周面
８ａ１、８ａ１’　動圧溝
８ａ２　８ａ２’　動圧溝
Ｒ１　　第１ラジアル軸受部
Ｒ２　　第２ラジアル軸受部
Ｔ　　　スラスト軸受部
Ｓ　　　シール空間
Ｓ１　　空間部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrodynamic bearing device that supports a rotating member in a non-contact manner by an oil film of lubricating oil generated in a radial bearing gap. This bearing device is a spindle for information equipment, for example, a magnetic disk device such as an HDD or FDD, an optical disk device such as a CD-ROM, a CD-R / RW, a DVD-ROM / RAM, or a magneto-optical disk device such as an MD or MO. It is suitable for a motor, a polygon scanner motor of a laser beam printer (LBP), or a small motor such as an electric device such as an axial fan.
[0002]
[Prior art]
The above various motors are required to have high speed, low cost, low noise, etc. in addition to high rotational accuracy. One of the components that determine the required performance is a bearing that supports the spindle of the motor.In recent years, the use of a fluid bearing having characteristics excellent in the required performance has been studied or actually used. .
[0003]
Fluid bearings of this type include a so-called dynamic pressure bearing having a dynamic pressure generating means for generating dynamic pressure in lubricating oil in a bearing gap, and a so-called circular bearing without a dynamic pressure generating means (the bearing surface is a perfect circle). Bearings).
[0004]
For example, in a fluid bearing device incorporated in a spindle motor of a disk device such as an HDD, a radial bearing portion that supports a shaft member in a non-contact manner in a radial direction and a thrust bearing portion that supports the shaft member in a thrust direction are provided. As the bearing portion, a dynamic pressure bearing in which a groove (dynamic pressure groove) for generating dynamic pressure is provided on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member is used (for example, see Patent Document 1). This radial bearing portion is often provided at a plurality of locations separated in the axial direction in order to obtain a high bearing function. As the thrust bearing, for example, a bearing (so-called pivot bearing) having a structure in which the end surface of the shaft member is supported in the thrust direction by a thrust bearing provided on one end side of the housing is used. Normally, the bearing sleeve is fixed at a predetermined position on the inner periphery of the housing, and a seal member is provided at the other end of the housing to prevent the lubricating oil injected into the internal space of the housing from leaking outside. There are many.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-124057
[Problems to be solved by the invention]
In this type of hydrodynamic bearing device, when the bearing rotates, the pressure of the lubricating oil increases around the thrust bearing at one end of the housing due to the bearing gap of the radial bearing and the shape and dimensional error of the dynamic pressure groove. There may be a pressure difference between the lubricating oil around the end seal and the lubricating oil. For example, taking a dynamic pressure bearing in which a herringbone-shaped dynamic pressure groove is provided on a radial bearing surface as an example, if the dynamic pressure groove is formed with high accuracy in an axially symmetric manner with respect to the axial center, the dynamic pressure The pumping force of the lubricating oil by the groove is balanced between the seal portion side and the thrust bearing portion side with respect to the axial center, but due to manufacturing errors, the shape of the dynamic pressure groove becomes axially asymmetric, and When the axial dimension on the seal portion side becomes larger than the axial dimension on the thrust bearing portion side, the pumping force of the lubricating oil by the dynamic pressure grooves becomes relatively larger on the seal portion side than on the thrust bearing portion side. Due to the differential pressure of the pumping force, the pressure of the lubricating oil from the seal portion side to the thrust bearing portion side is applied, which increases the pressure of the lubricating oil around the thrust bearing portion, and the pressure with the lubricating oil around the seal portion. It causes a difference.
[0007]
Then, the shaft member receives an axial force in a direction in which the shaft member is pushed up toward the seal portion due to the pressure difference (hereinafter, this axial force is referred to as a "push-up force"). Usually, in a motor in which this type of hydrodynamic bearing device is incorporated, a structure is used in which a shaft member is pressed against a thrust bearing portion by an attraction force of a magnet or the like. A lifting phenomenon of the member may occur, which may have an undesired effect on the motor and its surrounding parts.
[0008]
An object of the present invention is to prevent the shaft member from being lifted by the above-described pushing force.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a housing, a bearing sleeve provided inside the housing, a shaft member inserted into an inner peripheral surface of the bearing sleeve, an inner peripheral surface of the bearing sleeve, and an outer periphery of the shaft member. A radial bearing portion provided between the first and second surfaces and radially supporting the shaft member with a lubricating oil film generated in a bearing gap; and a thrust bearing provided on one end side of the housing and supporting the end surface of the shaft member in the thrust direction. And a seal part provided on the other end side of the housing and forming a seal space between the outer peripheral surface of the shaft member and the bearing member. A configuration is provided in which the pressure Pt of the lubricating oil around the part is Pt ≦ Ps with respect to the pressure Ps of the lubricating oil around the seal part.
[0010]
By setting the pressure Pt of the lubricating oil around the thrust bearing portion to be equal to (Pt = Ps) or lower than the pressure Ps of the lubricating oil around the seal portion (Pt <Ps), the push-up force of the shaft member is reduced. It is possible to prevent the shaft member from lifting up by avoiding the occurrence.
[0011]
As means for satisfying Pt ≦ Ps, a radial bearing portion is provided at a plurality of locations spaced apart in the axial direction, a dynamic pressure bearing having a dynamic pressure groove is provided, and a radial bearing portion provided at a location closest to the thrust bearing portion is provided. The lubricating oil can be drawn from the side in the direction of the radial bearing provided at another location. With this configuration, the flow of the lubricating oil from the radial bearing portion side closest to the thrust bearing portion toward the other radial bearing side, that is, the flow of the lubricating oil flowing from the thrust bearing portion side to the seal portion side is generated, This prevents a phenomenon in which the pressure of the lubricating oil around the thrust bearing is higher than the pressure of the lubricating oil around the seal.
[0012]
More specifically, the following means can be adopted.
[0013]
The first means is that, in a radial bearing portion provided at a position closest to the thrust bearing portion, the pumping force of the lubricating oil by the dynamic pressure groove of the radial bearing portion is larger on the thrust bearing portion side than on the seal portion side. Is to be configured. With such a configuration, the flow of the lubricating oil from the thrust bearing portion side to the seal portion side occurs, whereby the pressure of the lubricating oil around the thrust bearing portion becomes higher than the pressure of the lubricating oil around the seal portion. The phenomenon is prevented.
[0014]
As a first means, a dynamic pressure groove of a radial bearing portion provided at a position closest to the thrust bearing portion can be formed asymmetrically in the axial direction. For example, when the dynamic pressure groove has a herringbone shape, the axial dimension on the thrust bearing portion side is larger than the axial dimension on the seal portion side with respect to the axial center of the dynamic pressure groove, or The number of grooves, the groove angle, the groove depth, etc. on the bearing part side are different from those on the seal part side. Alternatively, as a first means, a dynamic pressure groove of a radial bearing portion provided at a position closest to the thrust bearing portion is formed symmetrically in the axial direction, while facing the seal portion side end region of the dynamic pressure groove. A clearance may be provided on the surface of the mating member to form a clearance larger than the bearing clearance, and the axial dimension on the seal part side may be artificially made smaller than the axial dimension on the thrust bearing part side.
[0015]
The second means is that the dynamic pressure of the lubricating oil generated in the bearing gap is changed between the radial bearing portion provided at the location closest to the thrust bearing portion and the radial bearing portion provided at another location. It is configured to be higher. With this configuration, the flow of the lubricating oil from the radial bearing portion side closest to the thrust bearing portion toward the other radial bearing side, that is, the flow of the lubricating oil flowing from the thrust bearing portion side to the seal portion side is generated, This prevents a phenomenon in which the pressure of the lubricating oil around the thrust bearing is higher than the pressure of the lubricating oil around the seal.
[0016]
The second means includes a means for reducing a bearing gap of a radial bearing portion provided at a position closest to the thrust bearing portion to a bearing clearance of a radial bearing portion provided at another position, and a thrust bearing portion. Means for making the number of grooves, the groove angle, the groove depth, and the like different between the dynamic pressure groove of the radial bearing portion provided at the position closest to the above and the dynamic pressure groove of the other radial bearing portion. Alternatively, as a second means, the bearing sleeve is formed of a porous body such as a sintered metal and the surface of the bearing surface of the bearing sleeve constituting the radial bearing portion provided at a position closest to the thrust bearing portion. The porosity (the surface porosity refers to the site where the internal pores of the porous body tissue are opened on the outer surface, and the surface porosity refers to the ratio of the total area of the surface pores per unit area). Alternatively, the opening ratio may be smaller than the surface porosity of the bearing surface of the bearing sleeve constituting the radial bearing portion provided at another location.
[0017]
As means for setting Pt ≦ Ps, particularly Pt = Ps, radial bearings are provided at a plurality of locations spaced apart in the axial direction, and a radial bearing and a thrust bearing provided at a location closest to the thrust bearing are provided. And a space having a gap larger than the bearing radial gap of the radial bearing. By providing the space, the increase in the pressure of the lubricating oil around the thrust bearing portion is reduced, and the phenomenon that the pressure of the lubricating oil around the seal portion becomes higher than the lubricating oil is prevented. This means can be applied to both cases where the radial bearing portion is configured as a so-called perfect circular bearing (a bearing having no dynamic pressure groove on the bearing surface) and when configured as a dynamic pressure bearing.
[0018]
It is preferable that the maximum value of the gap in the space is 10 times or more the bearing gap. This is for the following reason. Generally, the load capacity W of a fluid bearing can be expressed by the following equation.
W = W1 · {αωR ⁴ / (ΔR) ² } · β
Here, W: load capacity, W1: dimensionless load capacity determined by bearing specifications, α: lubricating oil viscosity, ω: rotational angular velocity, R: bearing radius, ΔR: bearing radius gap, β: eccentricity.
[0019]
From the above equation, it can be seen that the load capacity W becomes 1/100 when the bearing radial gap ΔR increases tenfold. Therefore, the load capacity of the space can be reduced to 1/100 (1%) or less of the load capacity of the radial bearing by setting the gap of the space to be at least 10 times the bearing radial gap. Thus, it is possible to effectively reduce the increase in the pressure of the lubricating oil around the thrust bearing.
[0020]
In the above configuration, the housing can be formed of a resin material. Since the resin housing can be formed by injection molding or other mold forming, it can be manufactured at a lower cost than a metal housing made by machining such as turning, and also compared to a metal housing made by pressing. Relatively high accuracy can be secured. In particular, by molding the housing with a resin material using the bearing sleeve as an insert part, the work of fixing the bearing sleeve to the housing by bonding or the like can be omitted, which is advantageous in simplifying the assembly process. In this case, if the bearing sleeve is formed of a sintered metal, at the time of molding, the molten resin penetrates into the internal pores from the surface opening of the fixing surface of the bearing sleeve and solidifies, and the solidified portion in the internal pores is formed. Since the housing and the bearing sleeve are firmly adhered to each other by a kind of anchor effect, relative displacement between the two does not occur and a stable fixed state can be obtained.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0022]
FIG. 1 shows an example of the configuration of a spindle motor for information equipment incorporating a hydrodynamic bearing device 1 according to this embodiment. This spindle motor is used in a disk drive device such as an HDD, and includes a fluid bearing device 1 that rotatably supports a shaft member 2, a disk hub 3 mounted on the shaft member 2, and a radial gap. And a motor stator 4 and a motor rotor 5 that face each other. The stator 4 is attached to the outer periphery of the casing 6, and the rotor 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the casing 6. The disk hub 3 holds one or more disks D such as magnetic disks. When the stator 4 is energized, the rotor 5 rotates by the exciting force between the stator 4 and the rotor 5, whereby the disk hub 3 and the shaft member 2 rotate integrally.
[0023]
FIG. 2 shows a hydrodynamic bearing device (fluid dynamic bearing device) 1 according to the first embodiment. The hydrodynamic bearing device 1 includes a housing 7, a bearing sleeve 8, and a shaft member 2 as components.
[0024]
A first radial bearing portion R1 and a second radial bearing portion R2 are provided between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a of the shaft member 2 so as to be separated in the axial direction. A thrust bearing portion T is provided between the lower end surface 2b of the shaft member 2 and the inner bottom surface 7c2 of the bottom 7c of the housing 7. For convenience of explanation, the description will be made with the side of the thrust bearing portion T being the lower side and the side opposite to the thrust bearing portion T (the side of the seal portion 7a) being the upper side.
[0025]
The bearing sleeve 8 is formed of, for example, a porous body made of a sintered metal, in particular, a porous body of a sintered metal containing copper as a main component. On the inner peripheral surface 8a of the bearing sleeve 8 formed of this sintered metal, two upper and lower regions serving as radial bearing surfaces of a first radial bearing portion R1 and a second radial bearing portion R2 are provided axially separated. In these two regions, for example, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 as shown in FIG. 3, respectively, are formed. The dynamic pressure groove 8a1 on the upper side (closer to the seal portion 7a) is formed symmetrically in the axial direction with respect to the axial center m1 (the axial dimension from the axial center m1 is X0), but on the lower side (X0). The dynamic pressure groove 8a2 on the side close to the thrust bearing portion T) is formed in an asymmetric shape in the axial direction with respect to the axial center m2. In this example, the axial dimension X1 in the region below the axial center m2 (the side closer to the thrust bearing portion T) is larger than the axial dimension X2 in the upper region (the side closer to the seal portion 7a) ( X1> X2).
[0026]
The shaft member 2 is formed of, for example, a metal material such as stainless steel. An end face 2b is provided.
[0027]
The housing 7 is formed by injection-molding (insert molding) a resin using a bearing sleeve 8 made of a sintered metal as an insert part, and extends integrally from the upper end of the cylindrical side part 7b to the inner diameter side. It has an annular seal portion 7a and a bottom portion 7c integrally connected to the lower end of the side portion 7b. The inner peripheral surface 7a1 of the seal portion 7a faces the outer peripheral surface 2a of the shaft member 2 via a predetermined seal space S. By the insert molding described above, the inner peripheral surface 7b1 of the side portion 7b is the outer peripheral surface 8d of the bearing sleeve 8, the inner surface 7a2 of the seal portion 7a is the upper end surface 8b of the bearing sleeve 8, and the inner bottom surface 7c1 is the lower portion of the bearing sleeve 8. It is joined with the side end face 8c in a state of being in close contact with each other. Since the bearing sleeve 8 is formed of a porous sintered metal, the housing 7 and the bearing sleeve 8 are firmly adhered to each other by the above-described anchor effect, and a stable fixed state of both is obtained.
[0028]
The hydrodynamic bearing device 1 of this embodiment can be assembled by mounting the shaft member 2 to the housing 7 and the bearing sleeve 8 fixed to each other by the insert molding described above. That is, the shaft member 2 is inserted into the inner peripheral surface 8a of the bearing sleeve 8, and the lower end surface 2b is brought into contact with the inner bottom surface 7c2 of the housing 7. Then, lubricating oil is filled in the internal space of the housing 7 including the internal pores of the bearing sleeve 8 and sealed by the seal portion 7a. The oil level of the lubricating oil is maintained in the seal space S.
[0029]
When the shaft member 2 rotates, the regions (two upper and lower regions) of the inner peripheral surface 8a of the bearing sleeve 8 to be radial bearing surfaces respectively oppose the outer peripheral surface 2a of the shaft member 2 via the radial bearing gap. Then, with the rotation of the shaft member 2, a dynamic pressure of the lubricating oil is generated in the bearing gap, and the shaft member 2 is rotatably and non-contactly supported in the radial direction by an oil film of the lubricating oil formed in the bearing gap. You. Thus, a first radial bearing portion R1 and a second radial bearing portion R2 that rotatably support the shaft member 2 in the radial direction in a non-contact manner are configured. At the same time, the lower end surface 2b of the shaft member 2 is contacted and supported by the inner bottom surface 7c2 of the housing 7. Thus, a thrust bearing portion T that rotatably supports the shaft member 2 in the thrust direction is configured.
[0030]
As described above, of the first radial bearing portion R1 and the second radial bearing portion R2 provided at the upper and lower two places, the dynamic pressure groove of the lower (closer to the thrust bearing portion T) second radial bearing portion R2. 8a2 is formed in an asymmetric shape in the axial direction with respect to the axial center m2, and the axial dimension X1 in a region below the axial center m2 (closer to the thrust bearing portion T) is in the upper region (seal portion 7a). Is larger than the axial dimension X2 on the side closer to (). Therefore, when the shaft member 2 rotates, the pumping force of the lubricating oil by the dynamic pressure groove 8a2 is relatively larger in the lower region (the side closer to the thrust bearing portion T) than in the upper region (the side closer to the seal portion 7a). Become. The differential pressure of the pumping force causes the flow of the lubricating oil from the second radial bearing portion R2 to the first radial bearing portion R1, ie, the lubricating oil flowing from the thrust bearing portion T to the seal portion 7a. This prevents the phenomenon that the pressure of the lubricating oil around the thrust bearing portion T becomes higher than the pressure of the lubricating oil around the seal portion 7a.
[0031]
FIG. 4 shows a hydrodynamic bearing device (fluid dynamic bearing device) 11 according to the second embodiment. In this hydrodynamic bearing device 11, the dynamic pressure groove 8a1 'of the first radial bearing portion R1 and the dynamic pressure groove 8a2' of the second radial bearing portion R2 are both formed axially symmetrically, while the second radial bearing portion R2 is An end region of the dynamic pressure groove 8a2 'on the seal portion 7a side is opposed to a relief portion 2c provided on the outer peripheral surface 2a of the shaft member 2. The relief portion 2c of the shaft member 2 is provided in a region between the first radial bearing portion R1 and the second radial bearing portion R2, and the clearance between the relief portion 2c and the inner peripheral surface 8a of the bearing sleeve 8 is: It is larger than the bearing clearance of the second radial bearing portion R2 (and the first radial bearing portion R1). Accordingly, by making the end region of the dynamic pressure groove 8a2 'on the seal portion 7a side to face the relief portion 2c, the axial dimension of the dynamic pressure groove 8a2' on the seal portion 7a side is pseudo-thrust bearing portion T side. Is smaller than the dimension in the axial direction. Therefore, when the shaft member 2 rotates, the pumping force of the lubricating oil by the dynamic pressure grooves 8a2 'is such that the lower region (the side closer to the thrust bearing portion T) is relatively to the upper region (the side closer to the seal portion 7a). growing. The differential pressure of the pumping force causes the flow of the lubricating oil from the second radial bearing portion R2 to the first radial bearing portion R1, ie, the lubricating oil flowing from the thrust bearing portion T to the seal portion 7a. This prevents the phenomenon that the pressure of the lubricating oil around the thrust bearing portion T becomes higher than the pressure of the lubricating oil around the seal portion 7a.
[0032]
FIG. 5 shows the periphery of a thrust bearing portion T in a hydrodynamic bearing device (fluid dynamic pressure bearing device) according to the third embodiment. In this hydrodynamic bearing device, a space portion S1 having a gap C1 larger than a bearing radial gap C0 of the second radial bearing portion R2 is provided between the second radial bearing portion R2 and the thrust bearing portion T.
[0033]
In this embodiment, the lower end surface 2b of the shaft member 2 is formed in a convex spherical shape, and is smoothly connected to the outer peripheral surface 2a via a connecting portion 2d having a radius of curvature smaller than the radius of curvature of the lower end surface 2b. . The maximum value of the gap C1 in the space S1 is set to be 10 times or more the bearing radius gap C0 of the second radial bearing R2. The dynamic pressure grooves of the first radial bearing portion R1 and the dynamic pressure grooves of the second radial bearing portion R2 are both formed symmetrically in the axial direction. Other configurations are the same as those of the embodiment shown in FIG.
[0034]
By providing a space S1 having a gap C1 larger than the bearing radial gap C0 of the second radial bearing R2 between the second radial bearing R2 and the thrust bearing T, the gap C1 of the space S1 is particularly provided. Is set to be 10 times or more the bearing radial gap C0 of the second radial bearing portion R2, so that the increase in the pressure of the lubricating oil around the thrust bearing portion T is reduced, and the lubrication around the seal portion 7a is reduced. The phenomenon that the pressure becomes higher than the oil pressure is prevented.
[0035]
【The invention's effect】
According to the present invention, at the time of relative rotation between the bearing sleeve and the shaft member, the pressure Pt of the lubricating oil around the thrust bearing portion satisfies Pt ≦ Ps with respect to the pressure Ps of the lubricating oil around the seal portion. The floating phenomenon of the shaft member can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a spindle motor for information equipment using a hydrodynamic bearing device according to the present invention.
FIG. 2 is a cross-sectional view illustrating the hydrodynamic bearing device according to the first embodiment.
FIG. 3 is a sectional view of a bearing sleeve.
FIG. 4 is a sectional view showing a hydrodynamic bearing device according to a second embodiment.
FIG. 5 is an enlarged cross-sectional view illustrating the periphery of a thrust bearing in a hydrodynamic bearing device according to a third embodiment.
[Explanation of symbols]
1 Fluid bearing device (dynamic bearing device)
11 Hydrodynamic bearing device (dynamic pressure bearing device)
2 Shaft member 2a Outer peripheral surface 2b End surface 2c Relief portion 7 Housing 7a Seal portion 8 Bearing sleeve 8a Inner peripheral surface 8a1, 8a1 'Dynamic pressure groove 8a2 8a2' Dynamic pressure groove R1 First radial bearing portion R2 Second radial bearing portion T Thrust Bearing S Seal space S1 Space

Claims

A housing, a bearing sleeve provided inside the housing, a shaft member inserted into an inner peripheral surface of the bearing sleeve, and a shaft member provided between an inner peripheral surface of the bearing sleeve and an outer peripheral surface of the shaft member. A radial bearing portion that radially supports the shaft member with an oil film of lubricating oil generated in a bearing gap, a thrust bearing portion provided at one end of the housing, and supporting an end surface of the shaft member in a thrust direction; A fluid bearing device provided on the other end side of the housing, and a seal portion forming a seal space between the housing and the outer peripheral surface of the shaft member.
When the bearing sleeve and the shaft member rotate relative to each other, the pressure Pt of the lubricating oil around the thrust bearing portion satisfies Pt ≦ Ps with respect to the pressure Ps of the lubricating oil around the seal portion. Fluid bearing device.

The radial bearing portion is provided at a plurality of locations apart from each other in the axial direction, the radial bearing portion has a dynamic pressure groove, and the radial bearing portion provided at a location closest to the thrust bearing portion is different from the radial bearing portion. The hydrodynamic bearing device according to claim 1, wherein lubricating oil is drawn in the direction of the radial bearing portion provided at the location.

The radial bearing portion provided at a position closest to the thrust bearing portion is configured such that the pumping force of the lubricating oil by the dynamic pressure groove is larger on the thrust bearing portion side than on the seal portion side. The hydrodynamic bearing device according to claim 2, wherein:

The radial bearing portion is provided at a plurality of locations apart from each other in the axial direction, and between the radial bearing portion and the thrust bearing portion provided at a position closest to the thrust bearing portion, the radial bearing portion is provided. 2. The hydrodynamic bearing device according to claim 1, wherein a space having a gap larger than the bearing radius gap is provided.

The hydrodynamic bearing device according to claim 4, wherein the maximum value of the gap in the space is at least 10 times the bearing radial gap.

The hydrodynamic bearing device according to any one of claims 1 to 5, wherein the bearing sleeve is formed of a sintered metal.

7. The hydrodynamic bearing device according to claim 1, wherein the housing is formed of a resin material.