JP3607480B2

JP3607480B2 - Dynamic pressure type porous oil-impregnated bearing and bearing device

Info

Publication number: JP3607480B2
Application number: JP35553097A
Authority: JP
Inventors: 夏比古森; 康裕山本; 功古森; 一男岡村
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 1996-12-25
Filing date: 1997-12-24
Publication date: 2005-01-05
Anticipated expiration: 2017-12-24
Also published as: JPH10325416A

Description

【０００１】
【発明の属する技術分野】
本発明は、多孔質体に潤滑油あるいは潤滑グリースを含浸させて自己潤滑機能を持たせると共に、軸受隙間に介在する油の動圧油膜によって軸の摺動面を浮上支持する動圧型多孔質含油軸受及び軸受装置に関し、特にレーザビームプリンタのポリゴンミラーや磁気ディスクドライブ用のスピンドルモータなど、高速下で高回転精度が要求される機器の軸受として好適なものである。
【０００２】
【従来の技術】
多孔質含油軸受は、自己潤滑性を有する軸受として広く用いられているが、真円軸受の一種であるため、軸の偏心が小さいところでは、不安定振動が発生しやすく、回転速度の１／２の速度で振れ回るいわゆるホワールが発生しやすい欠点がある。この対策としては、軸受面にヘリングボーン型やスパイラル型などの動圧溝を設けることが挙げられる。多孔質含油軸受に動圧溝を形成し、その動圧作用によって軸を支持し、不安定振動を抑制しようとした従来例としては、特公昭６４−１１８４４号公報、あるいは実公昭６３−１９６２７号公報に記載のものがある。
【０００３】
特公昭６４−１１８４４号は、ヘリングボーン溝を有する多孔質含油部材を回転軸に嵌合し、円筒状のラジアル内周面を有するスリーブと組み合わせて軸受装置を構成したものである。一方、実公昭６３−１９６２７号は、多孔質含油軸受の軸受面に、表面目つぶし加工を施した動圧発生用の溝を設けたものである。
【０００４】
【発明が解決しようとする課題】
特公昭６４−１１８４４号は、回転軸にヘリングボーン溝を有する多孔質含油部材を嵌合し、軸の回転に伴う遠心力によって油を軸受隙間に滲出させようとするものである。このような構造では、以下の欠点がある。
【０００５】
▲１▼ 軸受装置の部品点数が通常の回転軸と軸受の２点から、回転軸、多孔質含油部材及びスリーブ（軸受）の３点になり、組立が繁雑化する上、コストが高くなる。
【０００６】
▲２▼ 動圧型の軸受装置の場合、高い寸法精度が要求されるが、部品点数が３点もあり、それぞれの精度が組み合わせ後の精度に影響するため、部品点数が２点のものに比べて精度を出しにくい。
【０００７】
▲３▼ 回転中は、多孔質含油部材には遠心力が加わり続ける。従って、油も滲み出し続け、軸受隙間はいずれ油で飽和し、さらに回転が続けば油は軸受隙間外に漏れ出さざるを得なくなる。そのため、油の流失が避けられない。
【０００８】
次に、実公昭６３−１９６２７号は、多孔質含油軸受の軸受面に、表面目つぶし加工を施した動圧発生用の溝を設けたものである。このような構造では、以下の欠点がある。
【０００９】
▲１▼ 溝部が完全に封孔されているので、溝部では多孔質含油軸受の最大の特徴である油の循環が阻害される。従って、一旦軸受隙間に滲み出した油はへリングボーン溝の作用によって溝の屈曲部に押し込まれ、そこにとどまることになる。軸受隙間内では大きな剪断作用が働いているので、その剪断力と摩擦熱によって溝部にとどまった油は変性しやすく、また、温度上昇によって酸化劣化が早まる傾向にある。従って、軸受寿命が短くなる。これに対し、通常の多孔質含油軸受では、含浸された油は、軸の回転に伴って常に軸受隙間および軸受内部を循環するため、軸受隙間内で連続的に剪断力を受けることはなく、いったん暖められても軸受内部で冷やされるので、温度上昇による酸化劣化の影響は受けにくい。
【００１０】
▲２▼ 溝部を封孔処理することは極めて困難である。当該公報では塑性加工により封孔できるとしているが、通常、動圧溝の溝深さはμｍオーダーのものであり、この程度の圧縮成形で表面の開孔部が封孔されることはない。また、塑性加工の他の手段としてコーティング等を挙げているが、コーティング被膜の厚さは溝深さよりも薄くする必要があり、数μｍのコーティング被膜を傾斜した溝部のみに施すのは極めて困難である。
【００１１】
このような状況に鑑み、本発明の解決しようとする課題は、
▲１▼ 軸受部の部品点数は２点とし、低コストなものとすると共に、精度が出しやすい、量産性に適したものとすること、
▲２▼ 通常の多孔質含油軸受のように含浸された油が軸受隙間と軸受内部を循環するようにし、それによって油が劣化しにくい構造とすること、
▲３▼ 工業的に実現可能なものとするため動圧溝に開孔部があっても動圧効果を発揮し得る軸受仕様を見出すこと
にある。
【００１２】
【課題を解決するための手段】
軸受本体（１）の軸受面に動圧溝（ヘリングボーン型やスパイラル型等の複数の傾斜した溝）を設けると、軸方向断面での油の流れは、例えば図２に示すようになる。油は、矢印で示すように軸受本体（１）の軸受面１７（内周表面）の開孔部から回転軸（２）との間の軸受隙間（４）に出入りするが、油の循環を適性に保とうとすれば、動圧溝（５）、及び当該溝以外の「背」の部分（６）（何れも図７参照）で開孔部がほぼ均一に分布しているのが望ましい。表面における開孔部の割合が小さくなると、油は動きにくくなり、逆に大きくなると油は動きやすくなる。また、含浸油の粘度も油の動きやすさに関係し、粘度が低いと動きやすく、粘度が高いと動きにくくなる。尚、本明細書において、「開孔部」とは多孔質体である軸受本体の多孔組織をなす細孔が外表面に開口した部分をいう。
【００１３】
開孔率が大きく、粘度が低い場合には、油は極めて動きやすくなるが、動圧溝（５）の作用によって軸受隙間（４）に滲み出した油は簡単に軸受本体（１）の内部に戻されるため、動圧効果が小さくなり、高回転精度を維持できないばかりか、軸（２）と軸受本体（１）とが接触することにより、軸受本体（１）が摩耗して軸受機能が損なわれるおそれがある。逆に開孔率が小さく、粘度が高い場合は、油は極めて動きにくくなるので、発生圧力は大きくなるが、適切な循環が阻害され、またトルクも大きくなるため、軸受部分の昇温によって油の劣化が促進される。
【００１４】
従って、開孔率と油の粘度には、軸を浮上支持するために必要な油の動圧油膜形成を確保し、同時に、油の適切な循環を確保し得る最適な範囲が存在する。
【００１５】
この最適範囲を明らかにすべく、図３及び図４に示すＬＢＰ実機モータを用いて評価試験を行った。両図において、（７）はハウジングであり、（８）は、軸（２）に固定された、ハブ（ロータ）である。また、（９）は軸（２）の先端と接触してスラスト負荷を支持するためのスラスト受けである。評価試験に用いた実機モータは、軸径がφ４のもので、ミラーを実装した状態であり、また、回転数は１００００ｒｐｍ、雰囲気温度は４０℃とした。
【００１６】
図５に評価試験の結果を示す。図５中、「○」は１０００時間連続運転した耐久試験で問題のなかったことを示す。「Δ」は５００〜１０００時間の間で軸振れ上昇（５μｍ以上）、トルク上昇＝回転数低下（１００００ｒｐｍまで回転数が上がらない）、異音発生などのトラブルを発生し、正常な運転が不可能になったことを示す。「×」は５００時間までに上記のようなトラブルが発生したことを示す。
【００１７】
以上の評価実験から、開孔率と油の粘度の最適範囲（「×」の存在しない範囲）は、図５に実線で区画する領域、すなわち、以下の条件
▲１▼ 動圧溝を含む軸受面における開孔部の表面積比率が２％以上２０％以下であり、
▲２▼ 含浸される油の４０℃での動粘度が２ｃＳｔ以上であり、
▲３▼ 軸受面における開孔部の表面積比率と油の４０℃での動粘度が
（３／５）Ａ−１ ≦ η ≦ （４０／６）Ａ＋（２０／３）
ここで、Ａ；開孔部の表面積率［％］
η；油の４０℃での動粘度［ｃＳｔ］
を満たす場合であることが理解できる。このような範囲で開孔率と油の粘度を選定することにより、軸を浮上支持するために充分な動圧油膜が形成されると同時に、油の適切な循環が確保されるので、高回転精度、長寿命を達成することができる。
【００１８】
なお、軸受面における開孔部の表面積比率は望ましくは２％以上、１５％以下とするのが良い。
【００１９】
動圧溝（５）の溝深さ（ｈ：図７参照）と軸受隙間（半径隙間：ｃ）との比には最適な範囲があり、この範囲外では充分な動圧効果が得られないと考えられる。この最適範囲を明らかにすべく、図６に示すように、図３に示すＬＢＰ実機モータの軸（２）を軸振れが測定できるように長いものに入れ替えて評価試験を行った。回転数は１００００ｒｐｍ、試験雰囲気は常温常湿であり、ＬＢＰ実機モータはφ４でミラー未実装としている。なお、（１０）は非接触型の変位計である。
【００２０】
以上の条件の下、ｃ／ｈ（ｃ；半径隙間、ｈ；溝深さ）に対する軸振れの値をそれぞれプロットしたところ、図８に示す結果を得た。図８より、ｃ／ｈが０．５〜４．０の範囲内であれば、軸振れは５μｍ以下になるが、０．５未満、あるいは４．０より大きくなると５μｍ以上となる。従って、高精度を維持するためには、ｃ／ｈ＝０．５〜４．０の範囲内とするのが望ましい。
【００２１】
多孔質含油軸受は、通常無給油で使用されるが、油の飛散、蒸発などにより油が徐々に消耗、流出することが避けられない。その場合には、油膜形成範囲が収縮するため、軸振れなどの回転精度の悪化を招く。特に軸姿勢が縦型で使用される場合が多く、毎分１万回転以上の高速で使用されるレーザビームプリンタ（ＬＢＰ）用モータ、あるいは磁気ディスクドライブ（ＨＤＤ）用モータ等では、図１２に示すように、遠心力の作用で油が流出し易く、油膜形成性等の潤滑性能の維持が難しかった。
【００２２】
ＬＢＰやＨＤＤでは、油膜切れを生じることは、高精度の回転を維持する上で、致命的となる。特に軸受本体を単独とした場合には、高速で回転すると、油は周囲の空気も巻き込んで軸受内部を循環するため、軸受隙間に空気が混入することがある。空気の混入を防止するためには、軸受本体の内部に少しでも空孔ができたら油を補給する部材（補油部材）を配置するのが有効な対策となる。
【００２３】
このような補油部材として、本発明では、図１に示すように、合成樹脂を基材とし、これに潤滑油又は潤滑グリースを配合あるいは含浸させ、少なくとも２０℃以上の温度では、静置した状態でも含有した油が表面に滲み出すようにした固形状の潤滑組成物（３）を軸受本体（１）と接触させて配置している。かかる構成により、軸受本体（１）の油が流失しても、当該軸受本体（１）に接触させて配置した潤滑組成物（３）から新たな油が毛細管現象によって軸受本体（１）の内部に補給されるので、回転軸（２）との間に常時良好な動圧油膜を形成することが可能となる。
【００２４】
具体的には、固形状の潤滑組成物（３）は、軸受本体が含有する潤滑油又は当該潤滑油を基油とする潤滑グリース５〜９９ｗｔ％に、平均分子量が１×１０^６〜５×１０^６である超高分子量ポリオレフィンの粉末９５〜１ｗｔ％を混合すると共に、超高分子量ポリオレフィン粉末のゲル化点以上、かつ、潤滑グリースを用いた場合はグリースの滴点以下の温度で分散保持させることにより、成形される。
【００２５】
このように、潤滑組成物を潤滑油あるいは潤滑グリースと超高分子量ポリオレフィン粉末との混合物で構成して固形状とすると、低コストで量産性に富み、取扱いが容易で組込み作業が簡単なものとなる。また、この固形状の潤滑組成物は、常温（２０℃程度）以上の温度で内部に含有した油をごく僅かずつ滲出させるので、連続的に軸受へ油を補給し続けることができる。図９は本発明における固形状の潤滑組成物（３）を静置し、放置時間と油分離率を調べた結果である。雰囲気が２０℃でも１０００時間にわたって僅かずつ油を分離し続けることが理解できる。雰囲気温度が上昇すれば、この分離量も増える。
【００２６】
図１０は、固形状の潤滑組成物を軸受に密着させた場合と、このような補油部材がなかった場合の比較であり、補油部材がない場合には（■で示す）、当初含まれていた油が２０００時間の運転で約３０％流失してしまうが、補油部材がある場合には（●で示す）、軸受本体から油が流失しても補油されるため、その損失量は僅か５％ほどに抑えられることが理解できる。
【００２７】
高温雰囲気下で使用される場合や、高速回転で使用され、摩擦による発熱が大きい場合には、固形状の潤滑組成物からの油の滲み出しが多すぎる場合が有るので、潤滑組成物の油滲出抑制剤として、固体ワックス、低分子量ポリエチレン、ポリアミド樹脂のうち１種以上を、１〜５０ｗｔ％の割合で添加混合するのが好ましい。
【００２８】
図１に示すように、軸受本体（１）（多孔質含油軸受Ａ）の軸方向一方側又は両側に、軸受本体（１）と同等若しくはこれよりも僅かに大きい内径を有する円筒状の油漏れ防止部材（１１）を配置し、この油漏れ防止部材（１１）の内周面に、軸（２）との相対回転に際して軸（２）との間の隙間に軸受本体側へ向けて流れる気流を発生させる気流発生溝（１２）を設けてもよい。この気流発生溝（１２）は、例えば複数の傾斜溝を設けることによって形成できる。図面では、上下二段に軸受本体（１）を配置し、上段の軸受本体（１）の外側に油漏れ防止部材（１１）を配置した場合を例示しているが、当該軸受本体（１）の内側にも油漏れ防止部材（１１）を配置することが可能であり、さらに下段の軸受本体（１）の一方側又は両側に油漏れ防止部材（１１）を配置することも可能である。
【００２９】
この構成であれば、図１１に示すように、回転軸（２）と油漏れ防止部材（１２）の内周面との間の隙間（１３）に、軸（２）の回転に伴って軸受本体（１）の方向（図面下方）へ流れる気流が発生するので、軸受部から油が漏れ出たとしても、軸（２）と油漏れ防止部材（１１）との間の隙間（１３）を通過できない。この作用によって油漏れが防止される。また、静止時には、当該隙間（１３）の毛細管力で油を保持するので、回転が止まっても油が漏れ出ることはない。
【００３０】
この場合、油漏れ防止部材（１１）を多孔質体とし、且つ隣接する軸受本体（１）との間に空間（１４）を設けるとよい。この構成であれば、漏れ出てきた油を多孔質体からなる油漏れ防止部材（１１）に吸収することができる。また、静止時には油漏れ防止部材（１１）と軸（２）との間の油も吸収できるので、大気にさらされる部分が減り、油の蒸発や発塵を減少させることができる。油漏れ防止部材（１１）に吸収された油は、回転に伴って隙間（１３）内に引き出され、気流発生溝（１２）の作用で生じた気流により空間（１４）を介して軸受本体（１）側に返される。
【００３１】
図１に示すように、油漏れ防止部材（１１）の、軸受本体（１）と反対側の端面（１１ａ）及びチャンファ部（１１ｂ）に目潰し加工を施し、この部分の表面開孔率が面積比で５％以下、望ましくは完全に封孔すれば、油漏れ防止部材（１１）に吸収された油の蒸発、発塵をさらに減少させることができる。
【００３２】
図１に示すように、一端が開放され、他端が閉塞されている円筒状のハウジング（７）内に、軸受本体（１）を圧入固定すると共に、この軸受本体（１）に接触させて固形状の潤滑組成物（３）を収納し、かつ、軸受本体（１）の外側に油漏れ防止部材（１１）を配置してハウジング（７）の開口部を閉塞する。この場合、上述のように、軸受に動圧作用があり、さらに潤滑組成物（３）から常時油が補給されるので、常に良好な動圧油膜形成を維持することができ、長期間にわたって高回転精度を維持することができる。また、軸受部からの油の漏洩は、油漏れ防止部材（１１）によって補足され、流出することもない。
【００３３】
ハウジング（７）の底面（７ａ）と、これに対向する軸受本体（１）の内側端面（１ａ）との間に空間（１５）を設け、この空間（１５）とハウジング外部とが軸受隙間（４）以外の箇所で連通するように空気流通路（１６）を設けると、この空気流路（１６）は空気抜きとして機能する。これにより、組立時に軸（２）が挿入し易くなる。また、回転時には発熱によって内圧が高まり、軸（ロータ）が押し上げられて回転が不安定となる場合があるが、かかる事態も防止可能となる。
【００３４】
回転軸（２）に回転部材、例えばロータ（８）を取り付けると共に、このロータと対向する軸受本体（１）の端面にヘリングボーン型、あるいはスパイラル型等の動圧溝を設け、回転軸（２）の回転時にこの動圧溝で生じる動圧によりスラスト負荷を支持するようにすれば、ラジアル負荷のみならずスラスト負荷も支持できるようになり、スラスト受け（９）が不要となる。
【００３５】
この場合、動圧溝を設けた軸受本体（１）の端面における開孔部の表面積比率は、２％以上で２０％以下とするのが好ましい。
【００３６】
【発明の実施の形態】
以下、本発明の一実施形態を説明する。
【００３７】
図１は、本発明にかかる動圧型多孔質含油軸受装置の一例を示すもので、一端が開放され、他端が閉塞されているハウジング（７）内に、軸受面（１７）を有する２つの軸受本体（１）を圧入固定し、この軸受本体（１）の内周部に軸（２）（回転軸）を挿入して軸方向に離隔する２つの多孔質含油軸受（Ａ）を構成したものである。軸受本体（１）の材質は特に限定されるものではなく、粉末冶金により、あるいは、鋳鉄、セラミックなどを焼結又は発泡成形することにより、多数の気孔を有する周知の多孔質体状に形成されたものであれば良いが、望ましくは、銅又は鉄、あるいはその両者を主成分とする焼結金属、さらに望ましくは銅を２０〜９５ｗｔ％含有する焼結金属で形成するのが良い。
【００３８】
両軸受本体（１）の間には、合成樹脂を基材とし、これに潤滑油又は潤滑グリースを配合した固形状の潤滑組成物（３）が配置され、かつ、開放側（上段）の軸受本体（１）の上方には油漏れ防止部材（１１）が配置されていてハウジング（７）の上端開口部を閉塞している。油漏れ防止部材（１１）の上側端面（１１ａ）及び上側のチャンファ部（１１ｂ）は、封孔処理がなされている。また、閉塞側（下段）の軸受本体（１）の端面（１ａ）と、ハウジング（７）の底面（７ａ）との間に空間（１５）が設けられ、この空間（１５）と外部とが連通するように空気の流通路（１６）が設けられている。この空気流通路（１６）は、例えば軸受本体（１）、潤滑組成物（３）、及び油漏れ防止部材（１１）の外形面の一部に軸方向の切欠きを設けることにより形成される。軸受本体（１）及び油漏れ防止部材（１１）の内周面には、複数の傾斜した溝（動圧溝５及び気流発生溝１２）が設けられる。油漏れ防止部材（１１）は多孔質体で形成されており、潤滑油などは含浸されていない。油漏れ防止部材（１１）の材質は、特に限定されるものではなく、粉末冶金により、あるいは、鋳鉄、合成樹脂、セラミックなどを焼結または発泡成形することにより、多数の気孔を有する周知の多孔質体状に成形される。
【００３９】
図１に示すように、軸受本体（１）の軸受面（１７）に例えばへリングボーン型の動圧溝（５）を設けることによって、回転軸（２）との相対回転時に軸受隙間（４）に動圧油膜が形成され、ホワールなどの不安定振動を効果的に抑制することができる。尚、図１に示す軸受面（１７）（図４に示す軸受面も同じ）においては、溝領域５（黒く塗りつぶした部分）が軸方向両側に向かって相反した向きに傾斜し、かつ、相反した向きに傾斜した溝領域５間に環状の背６（白い部分）が設けられている（同図では、環状の背６は軸受面の軸方向中央に位置している。）。軸受隙間（４）の幅（ｃ）は、軸（２）の半径をＲとした場合に、
ｃ／Ｒ＝１／２０００〜１／４００
とするのが望ましい。また、溝深さをｈとした場合、
ｃ／ｈ＝０．５〜４．０
とするのが良いが、さらに望ましくは、
ｃ／ｈ＝０．５〜３．０
とするのが良い。
【００４０】
また、軸受本体（１）の軸受面の開孔率は、表面積比で、２〜２０％とするのが望ましい。２％以下では油の循環が阻害され、２０％以上では動圧効果が発揮されず、満足な動圧油膜が形成されないためである。この表面開孔率に応じて油の粘度が選択される。
【００４１】
軸受本体（１）に接触させて配置される補油部材（３）は、金属や樹脂などの多孔質体、あるいはフェルトなどの繊維物質に油を含ませた周知のものでもよいが、固形状であり、少なくとも２０℃以上の温度で含有する油を表面に滲み出し続ける固形状の潤滑組成物を用いるのが好ましい。この潤滑組成物は、ごく簡単な方法で製作することができる。例えば、所定量の潤滑グリースあるいは潤滑油と、所定量の超高分子量オレフィン粉末とを均一に混合し、所定形状の型に流し込んで、超高分子量ポリオレフィン粉末のゲル化点以上の温度で、さらに潤滑グリースを用いる場合はその滴点以下の温度で分散保持させ、常温で冷却することによって得られる。この発明における超高分子量ポリオレフィン粉末は、ポリエチレン、ポリプロピレン、ポリブデン若しくはこれらの共重合体からなる粉末、またはそれぞれ単独の粉末を配合した混合粉末であり、各粉末の分子量は、粘度法により測定される平均分子量が１×１０^６〜５×１０^６になるように選択される。このような平均分子量の範囲にあるポリオレフィンは、剛性及び保油性において低分子量のポリオレフィンよりも優れ、高温に加熱してもほとんど流動することがない。このような超高分子量ポリオレフィンの潤滑組成物中の配合割合は、９５〜１ｗｔ％とする。なお、その量は組成物に要求される離油度、粘り強さ及び硬さに左右される。超高分子量ポリオレフィンの量が多いほど、所定の温度で分散保持させた後のゲルの硬さが大きくなる。
【００４２】
また、この発明に用いる潤滑グリースは、特に限定されるものではなく、石鹸または非石鹸で増ちょうした潤滑グリースとして、リチウム石鹸−ジエステル系、リチウム石鹸−鉱油系、ナトリウム石鹸−鉱油系、アルミニウム石鹸−鉱油系、リチウム石鹸ージエステル鉱油系、非石鹸−ジエステル系、非石鹸−鉱油系、非石鹸−ポリオールエステル系、リチウム石鹸−ポリオールエステル系などのグリースが挙げられる。同じく潤滑油も特に限定されるものではなく、ジエステル系、鉱油系、ジエステル鉱油系、ポリオールエステル系などの潤滑油を挙げることができる。なお、潤滑グリースの基油あるいは潤滑油は、当初軸受本体（１）に含浸される潤滑油と同じものであることが望ましいが、潤滑特性を損なわない限りにおいて多少異なるものであってもよい。
【００４３】
上記した超高分子量ポリオレフィンの融点は、その平均分子量に対応して変化するために一定ではないが、例えば粘度法による平均分子量が２×１０^６のものの融点は１３６℃である。同平均分子量の市販品としては、三井石油化学工業株式会社製の「ミペロン（登録商標）ＸＭ−２２０」などがある、
従って、潤滑グリースあるいは潤滑油に超高分子量ポリオレフィンを分散保持させるには、上記した材料を混合した後、超高分子量ポリオレフィンがゲル化を起こす温度以上で、且つ潤滑グリースを用いた場合はその滴点未満の温度、例えば１５０〜２００℃に加熱する。
【００４４】
このような軸受装置は、レーザビームプリンタのポリゴンミラーモータや磁気ディスクドライブ用のスピンドルモータなどの他、軸流ファンや換気扇、扇風機などの電気製品、自動車用電装品など、各種のモータに広範囲に利用することができ、軸受部周辺を油で汚染させることなく、特にその耐久性を著しく向上させることができる。すなわち、当初多孔質含油軸受内に保持されていた油が流失しても、油漏れ防止部材（１１）があるため軸受部の外には流出せず、また、軸受には固形状の潤滑組成物（３）から油が補給されるので、油膜が常に維持され、軸受本体（１）の軸受面に設けた動圧溝（５）の動圧効果によって高い回転精度を常に維持することができる。さらに、起動時の油切れによる摩耗などを防止し、耐久寿命を大幅に向上させることができるのである。この固形状の潤滑組成物は、フェルトと違って繊維状のものを含まないので、軸受隙間内に繊維等のごみが入り込むことがない。さらにグリースと違って固形状であるため、回転する軸（２）にまとわりついたりすることがなく、回転変動の原因とならない。そして、固形状であるため取扱いが極めて容易で組立時の効率が良い。
【００４５】
また、磁性流体シールで密封するような構造ではないため、油漏れ防止部材（１１）、軸受本体（１）、補油部材（潤滑組成物３）をそれぞれハウジング（７）に圧入等の手段によって固定するだけでよいから、組立時の効率が良く、コストが安い利点がある。
【００４６】
【発明の効果】
以上の説明から明らかなように、本発明によれば、
ａ）油の流失、飛散、蒸発等による周囲の汚染を著しく軽減することができる。
ｃ）ホワールなどの不安定振動を抑制することができ、軸振れを小さくして高い回転精度を達成することができる。
ｂ）常時、良好な動圧油膜形成を維持することができる。
ｄ）耐久性を大幅に向上させることができる。
という効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施形態を示す軸方向断面図である。
【図２】ヘリングボーン型動圧溝を設けた多孔質含油軸受における油の動きを示す軸方向断面図である。
【図３】評価試験用の多孔質含油軸受の軸方向断面図である。
【図４】評価試験用の多孔質含油軸受の軸方向断面図である。
【図５】評価試験の結果を示す図である。
【図６】評価試験用の多孔質含油軸受の軸方向断面図である。
【図７】多孔質含油軸受の半径方向断面図である。
【図８】ｃ／ｈと軸振れとの関係を求める評価試験の結果を示す図である。
【図９】本発明にかかる固形状潤滑組成物の油分離率の経時変化を示す図である。
【図１０】固形状潤滑組成物の有無による比較試験の結果を示す図である。
【図１１】油漏れ防止部材を有する多孔質含油軸受における油の動きを示す軸方向断面図である。
【図１２】一般的な多孔質含油軸受の軸方向断面図である。
【符号の説明】
１軸受本体
２回転軸
３潤滑組成物
４軸受隙間
５動圧溝
７ハウジング
８ロータ（ハブ）
１１油漏れ防止部材
１２気流発生溝
１６空気流通路
１７軸受面
Ａ多孔質含油軸受[0001]
BACKGROUND OF THE INVENTION
The present invention provides a dynamic pressure type porous oil impregnated with a porous body impregnated with lubricating oil or lubricating grease and having a self-lubricating function, and a sliding surface of a shaft is levitated and supported by a dynamic pressure oil film of oil interposed in a bearing gap. The present invention relates to a bearing and a bearing device, and is particularly suitable as a bearing for equipment that requires high rotational accuracy at high speed, such as a polygon mirror of a laser beam printer and a spindle motor for a magnetic disk drive.
[0002]
[Prior art]
Porous oil-impregnated bearings are widely used as self-lubricating bearings, but since they are a kind of perfect circular bearings, unstable vibrations are likely to occur where the shaft eccentricity is small. There is a drawback that a so-called whirl that swings at a speed of 2 is likely to occur. As a countermeasure, a dynamic pressure groove such as a herringbone type or a spiral type is provided on the bearing surface. As a conventional example of forming a dynamic pressure groove in a porous oil-impregnated bearing and supporting the shaft by its dynamic pressure action to suppress unstable vibration, Japanese Patent Publication No. 64-11844 or Japanese Utility Model Publication No. 63-19627. Some are described in the publication.
[0003]
Japanese Examined Patent Publication No. 64-11844 is configured by fitting a porous oil-containing member having a herringbone groove to a rotating shaft and combining it with a sleeve having a cylindrical radial inner peripheral surface. On the other hand, Japanese Utility Model Publication No. 63-19627 is provided with a dynamic pressure generating groove having a crushing process on the bearing surface of a porous oil-impregnated bearing.
[0004]
[Problems to be solved by the invention]
In Japanese Patent Publication No. 64-11844, a porous oil-containing member having a herringbone groove is fitted to a rotating shaft, and oil is oozed into a bearing gap by a centrifugal force accompanying the rotation of the shaft. Such a structure has the following drawbacks.
[0005]
(1) The number of parts of the bearing device is changed from two points of the normal rotating shaft and the bearing to three points of the rotating shaft, the porous oil-impregnated member and the sleeve (bearing), and the assembly becomes complicated and the cost increases.
[0006]
(2) In the case of a dynamic pressure type bearing device, high dimensional accuracy is required, but there are also 3 parts, and each precision affects the accuracy after combination. Compared to those with 2 parts. It is difficult to obtain accuracy.
[0007]
(3) Centrifugal force continues to be applied to the porous oil-impregnated member during rotation. Accordingly, the oil continues to bleed out, the bearing gap is eventually saturated with oil, and if the rotation continues, the oil must be leaked out of the bearing gap. Therefore, oil loss is inevitable.
[0008]
Next, Japanese Utility Model Publication No. 63-19627 is provided with a dynamic pressure generating groove having a clogged surface on the bearing surface of a porous oil-impregnated bearing. Such a structure has the following drawbacks.
[0009]
(1) Since the groove is completely sealed, the circulation of oil, which is the most characteristic feature of the porous oil-impregnated bearing, is inhibited in the groove. Accordingly, the oil that has once oozed into the bearing gap is pushed into the bent portion of the groove by the action of the herringbone groove and remains there. Since a large shearing action is acting in the bearing gap, the oil remaining in the groove is easily denatured by the shearing force and frictional heat, and oxidation deterioration tends to be accelerated due to temperature rise. Therefore, the bearing life is shortened. On the other hand, in a normal porous oil-impregnated bearing, the impregnated oil constantly circulates in the bearing gap and the inside of the bearing as the shaft rotates. Even if it is once warmed, it is cooled inside the bearing, so it is less susceptible to oxidative degradation due to temperature rise.
[0010]
(2) It is extremely difficult to seal the groove. In this publication, it is said that the hole can be sealed by plastic working. However, the groove depth of the dynamic pressure groove is usually on the order of μm, and the opening portion on the surface is not sealed by this degree of compression molding. In addition, although coating or the like is cited as another means of plastic working, it is necessary to make the thickness of the coating film thinner than the groove depth, and it is extremely difficult to apply a coating film of several μm only to the inclined groove portion. is there.
[0011]
In view of such a situation, the problem to be solved by the present invention is:
(1) The number of parts of the bearing should be two, low cost, easy to get accuracy, suitable for mass production,
(2) The impregnated oil circulates between the bearing gap and the inside of the bearing as in the case of a normal porous oil-impregnated bearing, thereby making the oil resistant to deterioration.
(3) To find a bearing specification capable of exerting a dynamic pressure effect even if there is an opening in the dynamic pressure groove in order to make it industrially feasible.
It is in.
[0012]
[Means for Solving the Problems]
When dynamic pressure grooves (a plurality of inclined grooves such as herringbone type and spiral type) are provided on the bearing surface of the bearing body (1), the oil flow in the axial section is as shown in FIG. The oil enters and exits the bearing gap (4) between the bearing shaft 17 (inner peripheral surface) of the bearing body (1) and the rotary shaft (2) as shown by the arrows. In order to maintain appropriateness, it is desirable that the apertures are almost uniformly distributed in the dynamic pressure groove (5) and the “back” part (6) other than the groove (see FIG. 7). When the ratio of the opening portion on the surface becomes small, the oil becomes difficult to move, and conversely, when it becomes large, the oil becomes easy to move. Also, the viscosity of the impregnated oil is related to the ease of movement of the oil. When the viscosity is low, it is easy to move, and when the viscosity is high, it is difficult to move. In the present specification, the “open portion” refers to a portion where the pores forming the porous structure of the bearing body, which is a porous body, are opened on the outer surface.
[0013]
When the hole area ratio is large and the viscosity is low, the oil is very easy to move, but the oil that has oozed out into the bearing gap (4) by the action of the dynamic pressure groove (5) is easily inside the bearing body (1). Therefore, not only can the dynamic pressure effect be reduced and high rotational accuracy cannot be maintained, but also the shaft (2) and the bearing body (1) come into contact with each other, so that the bearing body (1) is worn and the bearing function is improved. There is a risk of damage. On the other hand, when the hole area ratio is small and the viscosity is high, the oil becomes extremely difficult to move, so the generated pressure increases, but proper circulation is hindered and torque increases. Degradation is promoted.
[0014]
Therefore, there is an optimum range for the hole area ratio and the viscosity of the oil, which can ensure the formation of a dynamic pressure oil film necessary for floatingly supporting the shaft, and at the same time, the proper circulation of the oil.
[0015]
In order to clarify this optimum range, an evaluation test was conducted using the LBP actual motor shown in FIGS. In both figures, (7) is a housing, and (8) is a hub (rotor) fixed to the shaft (2). (9) is a thrust receiver for contacting the tip of the shaft (2) to support the thrust load. The actual motor used in the evaluation test has a shaft diameter of φ4, a mirror mounted state, a rotation speed of 10,000 rpm, and an ambient temperature of 40 ° C.
[0016]
FIG. 5 shows the results of the evaluation test. In FIG. 5, “◯” indicates that there was no problem in the durability test that was continuously operated for 1000 hours. “Δ” indicates a problem such as an increase in shaft runout (5 μm or more), torque increase = rotational speed decrease (the rotational speed does not increase up to 10,000 rpm), abnormal noise generation, etc. during 500 to 1000 hours. Indicates that it is possible. “X” indicates that the above-described trouble occurred up to 500 hours.
[0017]
From the above evaluation experiment, the optimum range of the open area ratio and the viscosity of the oil (the range where “x” does not exist) is the region defined by the solid line in FIG.
(1) The surface area ratio of the hole in the bearing surface including the dynamic pressure groove is 2% or more and 20% or less,
(2) The kinematic viscosity at 40 ° C. of the impregnated oil is 2 cSt or more,
(3) The surface area ratio of the hole in the bearing surface and the kinematic viscosity of the oil at 40 ° C
(3/5) A-1 ≦ η ≦ (40/6) A + (20/3)
Here, A: the surface area ratio of the aperture [%]
η: Kinematic viscosity of oil at 40 ° C. [cSt]
It can be understood that this is the case. By selecting the hole area ratio and the viscosity of the oil within such a range, a sufficient dynamic pressure oil film is formed to support the shaft so that it can be supported. Accuracy and long life can be achieved.
[0018]
In addition, the surface area ratio of the opening portion on the bearing surface is desirably 2% or more and 15% or less.
[0019]
The ratio between the groove depth (h: see FIG. 7) of the dynamic pressure groove (5) and the bearing clearance (radial clearance: c) has an optimum range, and a sufficient dynamic pressure effect cannot be obtained outside this range. it is conceivable that. In order to clarify this optimum range, as shown in FIG. 6, an evaluation test was conducted by replacing the shaft (2) of the LBP actual motor shown in FIG. 3 with a long one so that the shaft runout can be measured. The rotation speed is 10,000 rpm, the test atmosphere is normal temperature and humidity, and the LBP actual machine motor is φ4 and is not mounted with a mirror. In addition, (10) is a non-contact type displacement meter.
[0020]
Under the above conditions, the values of axial runout against c / h (c: radial gap, h: groove depth) were plotted, and the results shown in FIG. 8 were obtained. From FIG. 8, if c / h is in the range of 0.5 to 4.0, the shaft runout is 5 μm or less, but if it is less than 0.5 or greater than 4.0, it becomes 5 μm or more. Therefore, in order to maintain high accuracy, it is desirable that c / h = 0.5 to 4.0.
[0021]
Porous oil-impregnated bearings are usually used without lubrication, but it is inevitable that the oil gradually wears out and flows out due to scattering and evaporation of the oil. In such a case, the oil film formation range contracts, leading to deterioration in rotational accuracy such as shaft runout. In particular, the shaft orientation is often used in a vertical type. For a laser beam printer (LBP) motor or a magnetic disk drive (HDD) motor used at a high speed of 10,000 revolutions per minute or more, FIG. As shown, the oil easily flows out by the action of centrifugal force, and it is difficult to maintain the lubricating performance such as oil film formation.
[0022]
In LBP and HDD, the occurrence of oil film breakage is fatal in maintaining high-precision rotation. In particular, when the bearing main body is used alone, when the oil is rotated at high speed, the oil also circulates inside the bearing by surrounding air, and thus air may be mixed into the bearing gap. In order to prevent air from being mixed in, it is effective to arrange a member (oil replenishing member) for replenishing oil if any hole is formed in the bearing body.
[0023]
As such a bunkering member, in the present invention, as shown in FIG. 1, a synthetic resin is used as a base material, and this is blended or impregnated with lubricating oil or lubricating grease, and left at a temperature of at least 20 ° C. or more. The solid lubricating composition (3) in which the oil contained in the state is oozed out to the surface is arranged in contact with the bearing body (1). With this configuration, even if the oil in the bearing body (1) is washed away, new oil is generated inside the bearing body (1) by capillary action from the lubricating composition (3) disposed in contact with the bearing body (1). Therefore, it is possible to always form a good dynamic pressure oil film with the rotary shaft (2).
[0024]
Specifically, the solid lubricating composition (3) has an average molecular weight of 1 × 10 5 to 5 to 99 wt% of the lubricating oil contained in the bearing body or the lubricating grease containing the lubricating oil as a base oil. ⁶ ~ 5x10 ⁶ By mixing 95 to 1 wt% of the ultrahigh molecular weight polyolefin powder and dispersing and holding at a temperature not lower than the gel point of the ultrahigh molecular weight polyolefin powder and, if lubricating grease is used, not higher than the dropping point of the grease. Molded.
[0025]
In this way, when the lubricating composition is composed of a mixture of lubricating oil or lubricating grease and ultra-high molecular weight polyolefin powder and made into a solid form, it is low-cost, high in mass productivity, easy to handle, and easy to install. Become. Further, since this solid lubricating composition exudes the oil contained therein at a temperature of ordinary temperature (about 20 ° C.) or more little by little, the oil can be continuously supplied to the bearing. FIG. 9 shows the results of standing the solid lubricating composition (3) in the present invention and examining the standing time and the oil separation rate. It can be seen that the oil continues to be separated little by little over 1000 hours even at 20 ° C. As the ambient temperature increases, the amount of separation increases.
[0026]
FIG. 10 is a comparison between the case where the solid lubricating composition is in close contact with the bearing and the case where there is no such lubricating oil member. When there is no lubricating oil member (indicated by ■), it is initially included. About 30% of the oil was lost after 2000 hours of operation, but if there is an oil filler (indicated by ●), it will be lost even if oil is lost from the bearing body. It can be seen that the amount is limited to only 5%.
[0027]
When used in a high temperature atmosphere, or when used at high speed rotation and generates a large amount of heat due to friction, there may be excessive oil oozing from the solid lubricating composition. As the exudation inhibitor, it is preferable to add and mix one or more of solid wax, low molecular weight polyethylene, and polyamide resin at a ratio of 1 to 50 wt%.
[0028]
As shown in FIG. 1, a cylindrical oil leak having an inner diameter that is equal to or slightly larger than that of the bearing body (1) on one or both sides in the axial direction of the bearing body (1) (porous oil-impregnated bearing A). An airflow that flows toward the bearing body in the gap between the shaft (2) and the shaft (2) on the inner peripheral surface of the oil leakage prevention member (11) when the member is disposed relative to the shaft (2). An air flow generating groove (12) for generating This air flow generation groove (12) can be formed, for example, by providing a plurality of inclined grooves. In the drawing, the case where the bearing body (1) is arranged in two upper and lower stages and the oil leakage preventing member (11) is arranged outside the upper stage bearing body (1) is illustrated. The oil leakage prevention member (11) can also be disposed inside, and the oil leakage prevention member (11) can also be disposed on one side or both sides of the lower bearing body (1).
[0029]
If it is this structure, as shown in FIG. 11, it will be bearing in a clearance gap (13) between a rotating shaft (2) and the internal peripheral surface of an oil leak prevention member (12) with rotation of a shaft (2). Since an airflow flowing in the direction of the main body (1) (downward in the drawing) is generated, even if oil leaks from the bearing portion, a gap (13) between the shaft (2) and the oil leakage prevention member (11) is formed. I can't pass. This action prevents oil leakage. Moreover, since oil is hold | maintained with the capillary force of the said clearance gap (13) at the time of stillness, even if rotation stops, oil does not leak.
[0030]
In this case, the oil leakage prevention member (11) may be a porous body and a space (14) may be provided between the adjacent bearing body (1). If it is this structure, the oil which leaked can be absorbed in the oil leak prevention member (11) which consists of a porous body. Moreover, since the oil between the oil leakage preventing member (11) and the shaft (2) can be absorbed when stationary, the portion exposed to the air is reduced, and the evaporation of oil and the generation of dust can be reduced. The oil absorbed in the oil leakage prevention member (11) is drawn into the gap (13) as it rotates, and the bearing body (via the air flow generated by the action of the air flow generation groove (12) through the space (14) ( 1) Returned to the side.
[0031]
As shown in FIG. 1, the end face (11a) and the chamfer part (11b) on the opposite side of the bearing main body (1) of the oil leakage prevention member (11) are subjected to crushing processing. If the ratio is 5% or less, preferably completely sealed, the evaporation and dust generation of the oil absorbed by the oil leakage prevention member (11) can be further reduced.
[0032]
As shown in FIG. 1, a bearing body (1) is press-fitted and fixed in a cylindrical housing (7) having one end opened and the other end closed, and is brought into contact with the bearing body (1). The solid lubricating composition (3) is accommodated, and an oil leakage prevention member (11) is disposed outside the bearing body (1) to close the opening of the housing (7). In this case, as described above, the bearing has a dynamic pressure action, and oil is always replenished from the lubricating composition (3), so that a good dynamic pressure oil film formation can always be maintained, and a high level is maintained over a long period of time. Rotational accuracy can be maintained. Moreover, the oil leakage from the bearing portion is supplemented by the oil leakage preventing member (11) and does not flow out.
[0033]
A space (15) is provided between the bottom surface (7a) of the housing (7) and the inner end surface (1a) of the bearing body (1) facing the housing (7). When the air flow path (16) is provided so as to communicate with other places than 4), the air flow path (16) functions as an air vent. This facilitates the insertion of the shaft (2) during assembly. Further, during rotation, the internal pressure increases due to heat generation, and the shaft (rotor) may be pushed up to make the rotation unstable. However, such a situation can be prevented.
[0034]
A rotary member, for example, a rotor (8) is attached to the rotary shaft (2), and a dynamic pressure groove such as a herringbone type or a spiral type is provided on the end face of the bearing body (1) facing the rotor. If the thrust load is supported by the dynamic pressure generated in the dynamic pressure groove during the rotation of), not only the radial load but also the thrust load can be supported, and the thrust receiver (9) becomes unnecessary.
[0035]
In this case, it is preferable that the surface area ratio of the opening portion in the end face of the bearing body (1) provided with the dynamic pressure groove is 2% or more and 20% or less.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
[0037]
FIG. 1 shows an example of a dynamic pressure type porous oil-impregnated bearing device according to the present invention, and includes two bearing surfaces (17) in a housing (7) having one end opened and the other end closed. The bearing body (1) is press-fitted and fixed, and the two porous oil-impregnated bearings (A) are formed by inserting the shaft (2) (rotating shaft) into the inner peripheral portion of the bearing body (1) and separating in the axial direction. Is. The material of the bearing body (1) is not particularly limited, and is formed into a well-known porous body shape having a large number of pores by powder metallurgy, or by sintering or foam molding of cast iron, ceramic or the like. However, it is desirable to form the sintered metal containing copper or iron or both of them as a main component, and more desirably a sintered metal containing 20 to 95 wt% of copper.
[0038]
Between both bearing bodies (1), a solid lubricating composition (3) comprising a synthetic resin as a base material and blended with lubricating oil or lubricating grease is disposed, and the open side (upper) bearing An oil leakage prevention member (11) is disposed above the main body (1) and closes the upper end opening of the housing (7). The upper end face (11a) and the upper chamfer part (11b) of the oil leakage prevention member (11) are sealed. A space (15) is provided between the end surface (1a) of the bearing body (1) on the closing side (lower stage) and the bottom surface (7a) of the housing (7). An air flow passage (16) is provided so as to communicate with each other. The air flow passage (16) is formed, for example, by providing an axial notch in a part of the outer surface of the bearing body (1), the lubricating composition (3), and the oil leakage prevention member (11). . A plurality of inclined grooves (dynamic pressure grooves 5 and airflow generation grooves 12) are provided on the inner peripheral surfaces of the bearing body (1) and the oil leakage prevention member (11). The oil leakage prevention member (11) is formed of a porous body and is not impregnated with lubricating oil or the like. The material of the oil leakage prevention member (11) is not particularly limited, and is a well-known porous material having a large number of pores by powder metallurgy, or by sintering or foam molding of cast iron, synthetic resin, ceramic or the like. Molded into a solid body.
[0039]
As shown in FIG. 1, by providing, for example, a herringbone type dynamic pressure groove (5) on the bearing surface (17) of the bearing body (1), a bearing clearance (4) is obtained during relative rotation with the rotating shaft (2). ) Is formed, and unstable vibration such as whirl can be effectively suppressed. Incidentally, in the bearing surface (17) shown in FIG. 1 (the bearing surface shown in FIG. 4 is the same), the groove region 5 (the blacked-out portion) is inclined in opposite directions toward both sides in the axial direction. An annular spine 6 (white portion) is provided between the groove regions 5 inclined in the above direction (in the figure, the annular spine 6 is located at the axial center of the bearing surface). The width (c) of the bearing gap (4) is determined by assuming that the radius of the shaft (2) is R,
c / R = 1/2000 to 1/400
Is desirable. If the groove depth is h,
c / h = 0.5-4.0
Is better, but more desirable,
c / h = 0.5-3.0
It is good to do.
[0040]
Further, the hole area ratio of the bearing surface of the bearing body (1) is desirably 2 to 20% in terms of the surface area ratio. If it is 2% or less, the circulation of oil is inhibited, and if it is 20% or more, the dynamic pressure effect is not exhibited and a satisfactory dynamic pressure oil film is not formed. The viscosity of the oil is selected according to the surface area ratio.
[0041]
The oil filler member (3) disposed in contact with the bearing body (1) may be a porous material such as metal or resin, or a well-known one in which oil is contained in a fiber material such as felt. It is preferable to use a solid lubricating composition that continues to exude oil containing at least at a temperature of 20 ° C. or more to the surface. This lubricating composition can be made in a very simple manner. For example, a predetermined amount of lubricating grease or lubricating oil and a predetermined amount of ultrahigh molecular weight olefin powder are uniformly mixed, poured into a mold having a predetermined shape, and at a temperature equal to or higher than the gel point of the ultrahigh molecular weight polyolefin powder. When lubricating grease is used, it is obtained by dispersing and holding at a temperature below the dropping point and cooling at room temperature. The ultra-high molecular weight polyolefin powder in this invention is a powder made of polyethylene, polypropylene, polybudene or a copolymer thereof, or a mixed powder in which individual powders are blended, and the molecular weight of each powder is measured by a viscosity method. Average molecular weight is 1 × 10 ⁶ ~ 5x10 ⁶ Selected to be. A polyolefin having such an average molecular weight range is superior to a low molecular weight polyolefin in rigidity and oil retention, and hardly flows even when heated to a high temperature. The blending ratio of such ultrahigh molecular weight polyolefin in the lubricating composition is 95 to 1 wt%. The amount depends on the degree of oil separation, tenacity and hardness required for the composition. The greater the amount of ultrahigh molecular weight polyolefin, the greater the hardness of the gel after being dispersed and held at a predetermined temperature.
[0042]
Further, the lubricating grease used in the present invention is not particularly limited, and as a lubricating grease increased with soap or non-soap, lithium soap-diester, lithium soap-mineral oil, sodium soap-mineral oil, aluminum soap -Grease of mineral oil type, lithium soap-diester mineral oil type, non-soap-diester type, non-soap-mineral oil type, non-soap-polyol ester type, lithium soap-polyol ester type, and the like. Similarly, the lubricating oil is not particularly limited, and examples thereof include lubricating oils such as diester, mineral oil, diester mineral oil, and polyol ester. The base oil or lubricating oil of the lubricating grease is preferably the same as the lubricating oil initially impregnated in the bearing body (1), but may be slightly different as long as the lubricating characteristics are not impaired.
[0043]
The melting point of the above-described ultrahigh molecular weight polyolefin is not constant because it changes corresponding to the average molecular weight. For example, the average molecular weight by the viscosity method is 2 × 10 ⁶ Its melting point is 136 ° C. Examples of commercially available products having the same average molecular weight include “Miperon (registered trademark) XM-220” manufactured by Mitsui Petrochemical Co., Ltd.
Therefore, in order to disperse and maintain the ultrahigh molecular weight polyolefin in the lubricating grease or lubricating oil, after mixing the above-mentioned materials, when the ultrahigh molecular weight polyolefin is at or above the temperature at which gelation occurs and the lubricating grease is used, its drops are used. Heat to a temperature below the point, for example 150-200 ° C.
[0044]
Such bearings are widely used in various motors such as polygon mirror motors for laser beam printers and spindle motors for magnetic disk drives, as well as electrical products such as axial fans, ventilation fans and fans, and electrical equipment for automobiles. In particular, the durability can be significantly improved without contaminating the periphery of the bearing with oil. That is, even if the oil originally retained in the porous oil-impregnated bearing is lost, the oil leakage prevention member (11) prevents the oil from flowing out of the bearing portion, and the bearing has a solid lubricating composition. Since oil is replenished from the object (3), the oil film is always maintained, and high rotational accuracy can always be maintained by the dynamic pressure effect of the dynamic pressure groove (5) provided on the bearing surface of the bearing body (1). . Furthermore, wear due to running out of oil at the start-up can be prevented, and the durability life can be greatly improved. Unlike the felt, this solid lubricating composition does not include a fibrous material, so that dust such as fibers does not enter the bearing gap. Furthermore, unlike grease, it is solid, so it does not cling to the rotating shaft (2) and does not cause rotational fluctuations. And since it is solid, handling is very easy and the efficiency at the time of an assembly is good.
[0045]
Further, since the structure is not sealed with a magnetic fluid seal, the oil leakage prevention member (11), the bearing body (1), and the oil filler member (lubricating composition 3) are respectively pressed into the housing (7) by means such as press fitting. Since it only needs to be fixed, there are advantages in that the efficiency during assembly is high and the cost is low.
[0046]
【The invention's effect】
As is clear from the above description, according to the present invention,
a) It is possible to remarkably reduce surrounding pollution due to oil spill, scattering, evaporation and the like.
c) Unstable vibrations such as whirl can be suppressed, and shaft rotation can be reduced to achieve high rotational accuracy.
b) A good dynamic pressure oil film formation can always be maintained.
d) Durability can be greatly improved.
The effect is obtained.
[Brief description of the drawings]
FIG. 1 is an axial sectional view showing an embodiment of the present invention.
FIG. 2 is an axial sectional view showing the movement of oil in a porous oil-impregnated bearing provided with a herringbone type dynamic pressure groove.
FIG. 3 is an axial sectional view of a porous oil-impregnated bearing for evaluation tests.
FIG. 4 is an axial sectional view of a porous oil-impregnated bearing for an evaluation test.
FIG. 5 is a diagram showing the results of an evaluation test.
FIG. 6 is an axial sectional view of a porous oil-impregnated bearing for evaluation tests.
FIG. 7 is a radial sectional view of a porous oil-impregnated bearing.
FIG. 8 is a diagram showing the results of an evaluation test for determining the relationship between c / h and shaft runout.
FIG. 9 is a graph showing the change over time in the oil separation rate of the solid lubricating composition according to the present invention.
FIG. 10 is a diagram showing the results of a comparative test with and without a solid lubricating composition.
FIG. 11 is an axial sectional view showing the movement of oil in a porous oil-impregnated bearing having an oil leakage preventing member.
FIG. 12 is an axial sectional view of a general porous oil-impregnated bearing.
[Explanation of symbols]
1 Bearing body
2 Rotating shaft
3 Lubricating composition
4 Bearing clearance
5 Dynamic pressure groove
7 Housing
8 Rotor (hub)
11 Oil leakage prevention member
12 Air flow generation groove
16 Air flow passage
17 Bearing surface
A Porous oil-impregnated bearing

Claims

A bearing body made of a porous body and having a bearing surface facing a sliding surface of a shaft to be supported via a bearing gap, lubricating oil or lubricating grease impregnated in the bearing body, and a bearing surface of the bearing body In a dynamic pressure type porous oil-impregnated bearing having an inclined dynamic pressure groove formed in
The openings are distributed almost uniformly on the bearing surface including the dynamic pressure grooves,
The surface area ratio of the hole portion in the bearing surface is 2% or more and 15% or less,
The kinematic viscosity at 40 ° C. of the oil contained is 2 cSt or more,
The surface area ratio and the kinematic viscosity are as follows:
(3/5) A-1 ≦ η ≦ (40/6) A + (20/3)
Where, A: the surface area ratio of the aperture [%]
η: Kinematic viscosity of oil at 40 ° C. [cSt]
Satisfied,
The sliding surface of the shaft is levitated and supported by a hydrodynamic oil film of oil intervening in the bearing gap, and oil is supplied to the interior of the bearing body and the bearing gap through an opening portion of the bearing surface including the hydrodynamic groove. Dynamic pressure type porous oil-impregnated bearing that circulates between.

The ratio between the groove depth (h) of the dynamic pressure groove and the bearing gap (c) is c / h = 0.5 to 4.0.
Hydrodynamic type porous oil-impregnated bearings according to claim 1, wherein a is in the range of.

The dynamic pressure type porous oil-impregnated bearing according to claim 1 or 2, wherein the bearing body is formed of a sintered metal.

4. The dynamic pressure type porous oil-impregnated bearing according to claim 3 , wherein the sintered metal is mainly composed of copper, iron, or both.

A cylindrical oil leakage preventing member having an inner diameter that is equal to or slightly larger than the bearing body is disposed on one or both sides in the axial direction of the hydrodynamic porous oil-impregnated bearing according to any one of claims 1 to 4. And a fluid pressure type porous oil-impregnated bearing provided with an airflow generating groove on the inner peripheral surface of the oil leakage preventing member for generating an airflow flowing toward the bearing main body in a gap between the shaft and the shaft relative to the shaft. apparatus.

The dynamic pressure type porous oil-impregnated bearing device according to claim 5, wherein the oil leakage preventing member is a porous body, and a space is provided between the oil leakage preventing member and the bearing body.

Of the oil leakage prevention member is subjected to a blinding machining the end surface and the chamfer portion on the opposite side to the bearing body, according to claim 6, wherein the sealing as surface porosity of this portion is less than 5% by area ratio Dynamic pressure type porous oil-impregnated bearing device.

The bearing body is fixed in a cylindrical housing whose one end is open and the other end is closed, and the solid lubricating composition is stored in contact with the bearing body, and the bearing body The dynamic pressure type porous oil-impregnated bearing device according to claim 6 or 7 , wherein the oil leakage preventing member is disposed outside the housing to close the opening of the housing.

The space provided between the inner end surface of the bearing body to the bottom surface facing thereto of the housing, according to claim 8, wherein the the space and outside the housing is provided with an air flow passage so as to communicate with places other than the bearing gap Dynamic pressure type porous oil-impregnated bearing device.

A rotary member is attached to the rotary shaft, and a dynamic pressure groove is provided on an end surface of the bearing body facing the rotary member, and a thrust load is supported by a dynamic pressure generated in the dynamic pressure groove when the rotary shaft rotates. Item 5. The dynamic pressure type porous oil-impregnated bearing according to any one of Items 1 to 4 .

The dynamic pressure type porous oil-impregnated bearing according to claim 10 , wherein a surface area ratio of an opening portion in an end face of the bearing body provided with the dynamic pressure groove is 2% or more and 20% or less.