JP3782890B2 - Dynamic pressure type sintered grease bearing - Google Patents

Description

【００２６】
上記式中、Ｒはそれぞれ独立に水素又は炭化水素基又はアルコキシ基を示し、少なくとも１つは炭化水素基又はアルコキシ基である。
【００２７】
このリン酸エステルの基油に対する配合割合は、０．１〜１０重量％、好ましくは０．５〜３重量％とするのが良い。リン酸エステルの配合割合が０．１重量％未満であると耐摩耗性を改善することができず、１０重量％を超えて添加しても大幅な耐摩耗性の向上が認められない。
【００２８】
また、上記基油に粘度指数向上剤及び構造安定剤として、エチレン−α−オレフィン共重合体もしくはその水素化物、または、ポリメタクリレート系のものや、ポリブテン（ポリイソブチレン）系のものなどを添加しても良い。エチレン−α−オレフィン共重合体もしくはその水素化物は、例えばエチレンと１−デセン、イソブテン等をルイス酸等の触媒で重合させて得られた重合物を水素化することにより得られる。これらは、数平均分子量が２００〜４０００程度のものがあり、数平均分子量１４５０のものが好ましい。ポリメタクリレート系の平均分子量は２００００〜１５０００００程度である。せん断安定性との関係から平均分子量は２００００〜５００００が好ましい。また、ポリブテン系の平均分子量は５０００〜３０００００程度が良い。粘度指数向上剤及び構造安定剤の配合割合は、基油に対して１〜３０重量％、このましくは１〜５重量％の範囲が良い。
【００２９】
さらに、上記基油に酸化防止剤を配合することができる。酸化防止剤としては、遊離基連鎖反応停止剤として働くフェノール系、アミン系、及び過酸化物分解剤として働く硫黄系酸化防止剤からなる群から選択される１種以上の酸化防止剤を単独で又は混合して用いることができるが、アミン系とフェノール系を混合して用いることが好ましい。フェノール系酸化防止剤としては、例えば２，６−ジ−ｔ−ブチルフェノール、４，４’−メチレンビス（２，６−ジ−ｔ−ブチルフェノール）、２，６−ジ−ｔ−ブチル−４−エチルフェノール、２，６−ジ−ｔ−４−ｎ−ブチルフェノールが挙げられる。蒸発特性及び基油との相溶性の点からは、４，４’−メチレンビス（２，６−ジ−ｔ−ブチルフェノール）が好適である。また、アミン系酸化防止剤としては、ジオクチルジフェニールアミンやフェニル−α−ナフチルアミンが挙げられる。蒸発特性及び基油との相溶性の点からは、ジオクチルジフェニールアミンが好適である。その配合量は、基油に対しての溶解性を考慮して、基油に対して、アミン系酸化防止剤０．１〜１０重量％、フェノール系酸化防止剤０．１〜１０重量％が好ましい。単独使用の場合は、アミン系酸化防止剤０．１〜１０重量％が好適である。フェノール系酸化防止剤は併用の場合に効果がある。
【００３０】
さらに、本発明の基油には、本発明の目的・効果が損なわれない範囲で、必要に応じて、防錆剤、流動点降下剤、無灰系分散在、金属不活性剤、金属系洗浄剤、油性剤、界面活性剤、消泡剤、摩擦調整剤などを配合することができる。
【００３１】
【発明の実施の形態】
以下、本発明の実施形態について説明する。
【００３２】
図１は、情報機器の一種であるＤＶＤ−ＲＯＭ／ＲＡＭ装置のスピンドルモータを例示している。このスピンドルモータは、鉛直配置された回転軸４を回転自在に支持する軸受ユニットＡと、回転軸４の上端に装着されたＤＶＤ−ＲＯＭなどの光ディスク５を支持固定するターンテーブル６およびクランパー７と、例えばラジアルギャップを介して対向させたステータ８及びロータマグネット９を有するモータ部Ｂとを主要な構成要素とする。ステータ８は、軸受ユニットＡを構成するハウジング１の外周面に固定され、ロータマグネット９は、ターンテーブル６に装着されたロータケース１０の内周面に固定される。ステータ８に通電すると、ロータマグネット９と一体になったロータケース１０、ターンテーブル６、光ディスク５、クランパー７、及び回転軸４が回転する。
【００３３】
軸受ユニットＡは、筒状のハウジング１と、ハウジング１の内周面に固定され、回転軸４の外周面をラジアル方向に支持する動圧型焼結含グリース軸受２と、ハウジング１の下端開口部に固定され、回転軸４の下軸端面をスラスト方向に支持するスラスト軸受３とで構成される。この実施形態において、スラスト軸受３は、円板状の樹脂製スラストワッシャ３ａとこれを支持する裏金３ｂとからなり、樹脂スラストワッシャ３ａの上面で回転軸４の凸球状になった下軸端面をスラスト方向に接触支持する構成になっている。尚、樹脂製スラストワッシャ３ａは、回転軸４の下軸端面と接触するように、裏金３ｂの中心部分に埋設しても良い。
【００３４】
図２に示すように、動圧型焼結含グリース軸受２は、焼結金属からなる多孔質の軸受本体２ａに、潤滑剤として潤滑グリースを含浸させて自己潤滑機能を持たせたものである。軸受本体２ａは、銅、鉄、およびアルミニウの中から選択される１種以上の金属粉末を主原料とし、必要に応じてニッケル、すず、亜鉛、鉛、黒鉛の粉末又はこれらの合金粉末を混合し、焼結して得られた焼結金属で形成され、望ましくは銅を２０〜９７重量％配合し、密度が６．４〜７．２ｇ／ｃｍ³ となるように成形される。
【００３５】
この実施形態において、軸受本体２ａの内周面には、軸方向に離隔した２つの軸受面２ｂが形成され、２つの軸受面２ｂ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２ｃが形成される。各軸受面２ｂは、軸方向に対して一方に傾斜した複数の動圧溝２ｃを円周方向に配列形成した第１領域ｍ１と、第１領域ｍ１から軸方向に離隔し、軸方向に対して他方に傾斜した複数の動圧溝２ｃを円周方向に配列形成した第２領域ｍ２と、第１領域ｍ１と第２領域ｍ２との間に位置する環状の平滑領域ｎとを備えている。第１領域ｍ１の動圧溝２ｃと第２領域ｍ２の動圧溝２ｃは、平滑領域ｎで区画されて相互に非連続になっている。第１領域ｍ１の背２ｄ（動圧溝２ｃ間の領域）と第２領域ｍ２の背２ｄ（動圧溝２ｃ間の領域）は、平滑領域ｎと同一レベルにある。軸受面２ｂには、動圧溝２ｃの形成領域を含む全領域にわたって表面開孔がほぼ均一に分布している。
【００３６】
軸受本体２ａと軸４との間に相対回転が生じると、第１領域ｍ１と第２領域ｍ２にそれぞれ逆向きに傾斜形成された動圧溝２ｃによって、軸受隙間内の油が平滑領域ｎに向けて引き込まれ、油が平滑領域ｎに集められるため、平滑領域ｎにおける油膜圧力が高められる。そのため、高い軸受剛性が得られる。
【００３７】
動圧溝２ｃの傾斜角度は、任意の角度に設定すれば良いが、好ましくは軸方向と直交する方向との角度βが１５〜４０°、より好ましくは１５〜２５°になるように設定するのが良い。また、動圧溝２ｃと背２ｄとの幅比は０．８〜１．５、好ましくは１．０〜１．２の範囲内に設定するのが良い。さらに、平滑領域ｎの軸方向幅の比率Ｒは、各軸受面２ｂの軸方向幅を１として、Ｒ＝０．１〜０．６、好ましくはＲ＝０．２〜０．４の範囲内に設定するのが良い。Ｒが０．１未満では、平滑領域ｎを設けたことによる軸受剛性の増加効果が顕著に表れず、逆にＲが０．６を超えると、第１領域ｍ１および第２領域ｍ２の軸方向幅が小さくなり、動圧溝２ｃによる動圧効果が有効に発揮されない。
【００３８】
動圧溝２ｃの溝深さｈ（図４参照）と軸受半径すきまｃ（軸受面２ｂの背２ｄの部分の半径と回転軸４の外周面の半径との差）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。この最適範囲を明らかにすべく、ＤＶＤ−ＲＯＭ／ＲＡＭ用スピンドルモータを用いて軸振れを測定したところ、ｃ／ｈが０．５〜２．０の範囲内であれば軸振れを実用上充分なレベルに抑制できることが確認された。例えば、溝深さｈが２〜４μｍの場合は、軸受半径すきまｃは２〜４μｍの範囲内に設定すると良い。
【００３９】
また、軸受本体２ａにおける軸受面２ｂ間の領域の内径寸法は、軸受面２ｂの背２ｄの部分の内径寸法よりも大きく設定される。
【００４０】
尚、各軸受面２ｂの形状は図２（ａ）に示すものに限定されず、例えば、軸方向に対して一方に傾斜した動圧溝と他方に傾斜した動圧溝とを対にして軸方向にＶ字状に連続させたものでも良い（この場合、環状の平滑領域ｎは存在しない。）。回転体に殆どアンバランスがなく、軸受剛性が重要な要素とならないような使用条件等では、動圧溝が軸方向に連続した形状の軸受面の方が負圧が発生しにくく、むしろ好ましい場合もある。さらに、軸受面の動圧溝は軸方向に対して傾斜した形状であれば足り、この条件を満たす限り、任意の形状とすることができる。例えば、動圧溝はスパイラル状であっても良い。
【００４１】
軸受本体２ａに含浸する潤滑グリースの基油としては、４０°Ｃでの動粘度が５〜６０ｃＳｔに設定されたものを使用することができる。特に、ＤＶＤ−ＲＯＭ／ＲＡＭのように、ディスクが載ることによるアンバランス荷重に対するラジアル剛性が求められる機器では、１０〜５０ｃＳｔのものが好ましい。この実施形態では、４０°Ｃでの動粘度が４０ｃＳｔで、主成分をポリオールエステル油とし、粘度指数向上剤としてポリメタクリレート、酸化防止剤としてフェニル−α−ナフチルアミン、金属不活性剤としてベンゾトリアゾールの誘導体、耐摩耗剤としてりん酸トリオクチルを添加した潤滑油を基油として用いた。
【００４２】
上記潤滑グリースの増稠剤としては、リチウム石けん及びウレア化合物を用いた。
【００４３】
増稠剤のリチウム石けんは、ステアリン酸とＬｉＯＨ・Ｈ₂ Ｏを反応させてグリース化する。まず、反応容器に基油１／３量とステアリン酸を入れ、８０°Ｃに加熱する。溶媒がクリアーになったら、水とＬｉＯＨ・Ｈ₂ Ｏをよく混ぜて反応容器に投入する。その後約１時間かけて脱水を行う。脱水終了後、残りの基油を少しずつ温度が下がらないように投入し、１８５°Ｃに達した時点で反応終了とした。
【００４４】
増稠剤のモノウレアは、原料アミンとしてオクタデシルアミンを使用し、モノイソシアネートとしてはオクタデシルイソシアネートを使用した。ジウレアで示されるものは、末端基が芳香族基となる原料アミンとしてｐ−トルイジンを使用し、脂環族基となる原料アミンとしてｎ−オクチルアミンを使用し、脂肪族基となる原料アミンとしてシクロヘキシルアミンを使用した。また、ジイソシアネートは、ジフェニルメタン−４，４’−ジイソシアネートを使用した。トリウレアは、原料アミンにオクタデシルアミンを使用し、イソシアネートにトリレンジイソシアネートと水を使用した。ジウレアを例にとって具体的に説明すると、反応容器に基油半量と表１に示されるモノアミン全量を入れ、７０〜８０°Ｃに加熱した。別容器に基油の残りの半量とジフェニルメタン−４，４’−ジイソシアネートを入れ、７０〜８０°Ｃに加熱し、これを上記反応容器に加え攪拌した。約３０分間この状態で攪拌を続け、反応を充分に行った後、１７０〜１８０°Ｃまで昇温し、この温度に３０分間保持した。これを冷却したものを基グリースとした。
【００４５】
回転軸４を動圧型焼結含グリース軸受２の内周面に挿入してスピンドルモータを組立てる際、軸受本体２ａに含浸された潤滑グリースと同じ（あるいは同種の）潤滑グリース又はその基油を、含浸グリースとは別に、スラスト軸受３の軸受面が潤滑グリース又はその基油で濡れ、かつ、動圧型焼結含グリース軸受２の軸受隙間が潤滑グリース又はその基油で満たされてるように注油すると良い。この動圧型焼結含グリース軸受２では、回転軸４の回転に伴う発生圧力と温度上昇による油の熱膨張によって、軸受本体２ａの内部に含浸された潤滑グリースの基油が、ごく微小な増稠剤成分を含みながら軸受本体２ａの表面から滲み出し、動圧溝２ｃの作用によって軸受隙間内に引き込まれる。駆動初期に動圧型焼結含グリース軸受２の軸受隙間内が油で満たされていると、空気の巻き込みがなく、良好な潤滑油膜が形成され、安定した軸受機能が得られる。また、スラスト軸受３の軸受面が駆動初期時から油で濡れ、良好な潤滑状態になる。
【００４６】
また、通常、回転軸４はハウジング１の下端開口部にスラスト軸受３を装着した状態で、動圧型多孔質含グリース軸受２の内周面に挿入される。この挿入時には、軸受２と回転軸４との間の軸受隙間から空気が外部に逃げることになるが、軸受隙間は数μｍ程度しかないため、空気がハウジング１の下方空間に閉じ込められ、回転軸４の挿入作業が難しくなる場合がある。また、モータ回転時の発熱によって、ハウジング１の下方空間に閉じ込められた空気が膨張し、回転軸４を押し上げて軸受機能を不安定化させる可能性もある。この場合、図１及び図２に示すように、軸受２の外周面とハウジング１の内周面との間に、軸受本体２ａの軸方向両端に開口する空気通路Ｓを設けることにより、この空気通路Ｓを介して、ハウジング１の下方空間の空気を外部に逃がすようにすると良い。尚、この実施形態では、空気通路Ｓを軸受本体２ａの外周面に形成しているが、空気通路Ｓはハウジング１の内周面に形成しても良い。また、空気通路Ｓは１本でも良いし、円周方向に複数本形成しても良い。
【００４７】
動圧型焼結含グリース軸受２の軸受隙間内に正圧が発生すると、軸受面２ｂに表面開孔があるので、油は軸受面２ｂの表面開孔を介して軸受本体２ａの内部に還流する。その際、軸受面２ｂの表面開孔や、軸受面２ｂから所定深さの表層部分の細孔の大きさに大小があると、軸受隙間内の油が大きな孔を通って軸受本体２ａの内部に還流しやすくなる。そのため、軸受隙間内の圧力分布が不均一になり（局部的な圧力降下が生じる。）、回転精度に影響を及ぼす。この実施形態では、潤滑グリースの増稠剤が軸受本体２ａの大きな細孔に選択的に埋設され、表面開孔や細孔の大きさが見かけ上平均化されるので、軸受本体２ａの内部と軸受隙間との間の油の適切な循環が確保される。これにより、上記のような圧力分布の不均一化（局部的な圧力降下）の問題が解消され、また、動圧溝２ｃの動圧作用で次々と新たな油が軸受隙間に押し込まれつ続けるため、潤滑油膜の油膜力およびラジアル剛性が高い状態で維持される。この結果、回転軸４がホワール等の不安定振動を生じることなく動圧型焼結含グリース軸受２によって継続して非接触支持され、軸振れやＮＲＲＯ、ジッタなどが低減される。また、回転軸４と軸受本体２ａとが非接触で回転するため低騒音であり、しかも低コストである。
【００４８】
上記のような傾斜状の動圧溝２ｃを有する軸受面２ｂは、圧縮成形により形成することができる。例えば、焼結含グリース軸受の加工に用いられるサイジングピンなどのコアロッドの外周面に軸受面２ｂの形状に対応した成形型を形成し、コアロッドの外周面に軸受本体２ａの素材である円筒状の焼結金属素材を供給し、焼結金属素材に圧迫力を加えてその内周面をコアロッドの成形型に加圧し、成形型の形状を焼結金属素材の内周面に転写する。この時、軸受面２ｂにおける動圧溝２ｃの形成領域と、それ以外の領域（背２ｄおよび平滑領域ｎ）とを同時成形することができる。この場合、コアロッドの成形型を精度良く仕上ておけば、軸受面２ｂの成形精度も良くなる。コアロッドの成形型を必要とされる精度、例えば真円度１μｍ、円筒度２μｍ以内に仕上ることは比較的容易である。軸受面２ｂの成形後は、焼結金属素材のスプリングバックを利用して、さらには加熱によるコアロッドと焼結金属素材との熱膨張差をスプリングバックに付加して、動圧溝２ｃの形状を崩すことなく、コアロッドを焼結金属素材の内周面から離型することができる。
【００４９】
以上の軸受面成形を行う前に、焼結金属素材の内周面に回転サイジングを施し、内周面の表面開孔率を予め調整しておくのが好ましい。完成品としての軸受本体２ａの軸受面２ｂの表面開孔率は、動圧溝を有しない一般的な焼結含油軸受の軸受面の表面開孔率（通常２０〜３０％程度）よりも小さくするのが良い。例えば、軸受面２ｂの表面開孔率を３〜１５％に設定すると、グリース含浸による効果と相俟って、充分な油膜形成を維持しつつ、適切な油の循環を確保する上で有利である。尚、表面開孔率の調整は上記のような回転サイジングによる他、軸受本体２ａの密度設定により、あるいは表面処理と密度設定とを併用することにより行うこともできる。
【００５０】
【実施例】
図１に示すＤＶＤ−ＲＯＭ／ＲＡＭ用スピンドルモータを用いて回転軸４の軸振れの比較試験を行った。試験で用いた動圧型焼結含グリース／含油軸受には表１に示される潤滑剤を含浸させた。実施例１〜実施例７は潤滑グリースを含浸させたもの、比較例１は潤滑油を含浸させたものである。また、軸振れの測定は、図１に示す回転軸４を上端から突出する長いものに替え、非接触変位計でその挙動を測定することにより行った。
【００５１】
【表１】

【００５２】
試験は、回転数１０００〜８０００ｒｐｍ、回転体のアンバランス荷重１ｇ・ｃｍ、常温常湿環境下で実施した。軸受および軸受面の仕様は下記の通りである。
【００５３】
［軸受仕様］
軸径：φ３ｍｍ
軸受寸法：内径φ３×外径φ６×幅８．７ｍｍ
軸受面の数：上下に２個所
軸受面の軸方向幅：２．４ｍｍ
軸受隙間（直径）：４μｍ
「動圧溝仕様」（図２に示す形状）
溝深さ：３μｍ
溝角度β：２０°
溝本数：８本
比較試験の結果を図５にまとめて示す。図５に示すように、潤滑グリースを含浸した実施例１〜７では、いずれも比較例１に比べて軸振れが低減することが認められ、特に、増稠剤をウレアとした実施例４でその傾向が顕著であった。この試験結果から、この種の動圧型軸受において、潤滑油を含浸した構成に比べ、潤滑グリースを含浸した構成の方がより軸受剛性が向上し、軸振れの抑制に対して効果的であることが確認された。
【００５４】
【発明の効果】
本発明は以下の効果を有する。
【００５５】
（１）軸受面に設けた傾斜状の動圧溝の動圧効果により軸受隙間内に潤滑油膜を形成し、その潤滑油膜によって回転軸の摺動面を非接触支持するので、ホワール等の不安定振動が発生しにくく、高い回転精度が得られる。また、軸受本体の内部の細孔内に保有した油を軸受本体と軸受隙間との間で循環させながら潤滑作用を行うので、油の酸化劣化が生じにくく、高い軸受寿命が得られる。
【００５６】
（２）軸受本体に含浸する潤滑剤を潤滑グリースとすることにより、軸受面の表面開孔の一つ一つの面積が平均化され、また軸受面から所定深さの表層部分の一つ一つの細孔の断面積が平均化されるので、局部的な圧力降下が発生しにくくなると共に、軸受本体から軸受隙間への油の滲み出し、軸受隙間から軸受本体への油の戻りが適切量に調整される。そのため、動圧溝による潤滑油膜の形成効果が高められ、軸受剛性（軸受負荷容量）が向上すると同時に、油の適切な循環が確保され、軸受寿命が向上する。
【００５７】
（３）ウレア化合物は分子間の相互作用力が強いため、せん断安定性に優れ、金属表面に吸着しやすいという性質を有するため、これを潤滑グリースの増稠剤として用いることにより、潤滑効果をより一層高めることができる。
【００５８】
（４）軸受本体の内周面に複数の軸受面を軸方向に離隔形成することにより、軸受面相互間の同軸度を精度良く確保することができる。また、複数の軸受を配置する場合に比べ、部品点数、組立工数を減少することができる。
【００５９】
（５）上記のような動圧型焼結含グリース軸受で回転軸を非接触支持する本発明の情報機器のスピンドルモータは、軸振れ、ＮＲＲＯ、ジッタ等、搭載装置の高速・高性能化に伴って厳しさが増す諸要求特性を満足でき、情報機器の機能向上、高寿命化に寄与する。
【図面の簡単な説明】
【図１】実施形態に係わるＤＶＤ−ＲＯＭ／ＲＡＭ装置のスピンドルモータを示す断面図である。
【図２】動圧型焼結含グリース軸受の断面図（図ａ）、正面図（図ｂ：図ａにおけるｂ方向矢視図）である。
【図３】動圧型焼結含グリース軸受で軸を非接触支持する際の、軸方向断面での油の流れを模式的に示す図である。
【図４】動圧型焼結含グリース軸受における軸受面の動圧溝の深さｈと軸受隙間ｃとの関係を模式的に示す断面図である。
【図５】軸振れの比較試験の結果を示す図である。
【符号の説明】
２ 動圧型焼結含グリース軸受
２ａ 軸受本体
２ｂ 軸受面
２ｃ 動圧溝
４ 回転軸[0001]
BACKGROUND OF THE INVENTION
In the present invention, a porous bearing body made of sintered metal is impregnated with lubricating grease to have a self-lubricating function, and a lubricating oil film is formed in the bearing gap due to the dynamic pressure effect of the dynamic pressure groove on the bearing surface. The hydrodynamic sintered grease-containing bearing that supports the sliding surface of the rotating shaft in a non-contact manner by the lubricating oil film, especially for spindle motors for polygon mirrors of laser beam printers (LBP) and magnetic disk drives (HDD, etc.) A large unbalanced load is applied when a disk is mounted, such as a spindle motor for a device requiring high rotational accuracy, an optical disk device such as DVD-ROM or DVD-RAM, or a magneto-optical disk device such as MO. It is suitable for devices that drive at high speed under conditions.
[0002]
[Prior art]
Information devices can be broadly divided into two types: a main storage device that performs data processing and storage, and an auxiliary storage device that performs only storage. There are a memory part using a disk and a tape and a memory part using a semiconductor made of all electronic components. At present, the disk and tape are widely used from the viewpoint of cost. Examples of auxiliary storage devices that use disks and tapes include magnetic disk devices (HDD, FDD), optical disk devices (CD, DVD), magneto-optical disk devices (MO, ODD), and digital audio tape recorders (DAT). Furthermore, the information equipment includes a laser beam printer (LBP), digital FAX, digital PPC, and the like.
[0003]
The above-mentioned small spindle motors related to information equipment are required to further improve the rotational performance and reduce the cost. As a means for that purpose, the spindle bearing is replaced from a rolling bearing to a sintered oil-impregnated bearing. Is being considered. However, since ordinary sintered oil-impregnated bearings are a kind of perfect circular bearings, unstable vibrations are likely to occur where the shaft eccentricity is small, and so-called whirling occurs at about half the rotational speed. There is an easy defect (rotational accuracy deteriorates when unstable vibration such as whirl occurs). Therefore, a dynamic pressure groove such as a herringbone or spiral shape is provided on the bearing surface, and the dynamic pressure effect of the dynamic pressure groove along with the rotation of the shaft enhances the bearing function such as radial rigidity and eliminates shaft runout due to unstable vibration. Attempts have been made in the past (dynamic pressure type sintered oil-impregnated bearings).
[0004]
On the other hand, this type of hydrodynamic sintered oil-impregnated bearing has a high effect on suppressing shaft runout, but on the other hand, the oil in the bearing clearance escapes into the bearing through the surface opening of the bearing surface. There is a problem that there is a phenomenon of reducing the effect (pressure drop), and it is difficult to obtain the expected dynamic pressure effect. Conventionally, as a means for solving the problem of the pressure drop, a configuration is known in which the dynamic pressure groove on the bearing surface is subjected to surface crushing to seal the formation region of the dynamic pressure groove (Japanese Utility Model Publication No. 63-19627). issue).
[0005]
[Problems to be solved by the invention]
In the configuration in which the formation region of the dynamic pressure groove is sealed, the following problems occur.
[0006]
(1) Since the formation area of the dynamic pressure groove is completely sealed, the circulation of oil, which is the greatest feature of the sintered grease-containing bearing, is inhibited in that area. Therefore, the oil that has once oozed into the bearing gap is pushed into the axial center of the bearing surface by the action of the dynamic pressure groove, and remains in the bearing gap. Since a large shearing action is acting in the bearing gap, the oil remaining in the bearing gap 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.
[0007]
(2) As other means for crushing the surface, coating etc. are mentioned, but the thickness of the coating film needs to be thinner than the groove depth, and a coating film of several μm is applied only to the formation area of the dynamic pressure groove It is extremely difficult to apply.
[0008]
Further, techniques (sintered grease bearings) in which a sintered body is impregnated with lubricating grease are described in JP-A-63-195416 and JP-A-7-42740. It is intended for a perfect circular bearing having no dynamic pressure groove, and has a low radial rigidity in a region where the eccentricity is small, so that unstable vibration such as whirl cannot be effectively suppressed.
[0009]
Therefore, the present invention eliminates the problem of pressure drop in the bearing gap while ensuring proper circulation of oil between the inside of the bearing body and the bearing gap in this type of bearing, The main purpose is to further improve the bearing function, particularly the bearing rigidity (bearing load capacity) and the bearing life by increasing the pressure effect.
[0010]
[Means for Solving the Problems]
FIG. 3 shows the flow of oil in the axial section when the rotary shaft 4 is supported by the hydrodynamic sintered grease-containing bearing 2 having the bearing surface 2b in which the inclined dynamic pressure groove 2c of the present invention is formed. Show. With the rotation of the rotating shaft 4, oil (in the present specification, "pores" refers to pores that the porous body has as a structure) within the bearing body 2a (rotation of the lubricating grease). Base oil) oozes out from the both sides in the axial direction of the bearing surface 2b (and around the chamfer portion) into the bearing gap, and is further drawn toward the axial center of the bearing gap by the dynamic pressure groove 2c. The oil pulling action (dynamic pressure action) increases the pressure of the oil interposed in the bearing gap, thereby forming a lubricating oil film. Due to the lubricating oil film formed in the bearing gap, the rotating shaft 4 is supported in a non-contact manner on the bearing surface 2b without causing unstable vibration such as whirl. The oil that has oozed into the bearing gap is caused by the surface opening of the bearing surface 2b due to the pressure generated by the rotation of the rotating shaft 4 (in this specification, “surface opening” means that the pores of the porous body tissue are the outer surface From the bearing surface 2b (and around the chamfer portion) again to the bearing gap.
[0011]
As described above, this type of hydrodynamic bearing is lubricated in the bearing gap by the action of the hydrodynamic groove while circulating the oil retained in the pores inside the bearing body between the bearing body and the bearing gap. The oil film is formed and the rotating oil shaft is continuously supported by the lubricating oil film in a non-contact manner. In order to exert such a stable bearing function, proper circulation of the oil, shaft It is necessary to ensure the formation of a lubricating oil film necessary for support. In particular, the oil circulation has the effect of suppressing the deterioration of the oil and extending the bearing life, and also works complementarily and reciprocally with respect to the formation of the lubricating oil film. Whether to make it suitable is a very important issue in this type of hydrodynamic bearing. In other words, in order to always form a lubricating oil film having sufficient pressure and oil film thickness in the bearing gap, a fresh and appropriate amount of oil constantly oozes out from the bearing body into the bearing gap to form a lubricating oil film. It is essential that the oil circulation cycle of returning from the gap to the bearing body works properly. If the amount of circulating oil is too small, oil oozes out into the bearing gap and the formation of the lubricating oil film becomes insufficient. At the same time, the oil stays in the bearing gap, causing oxidative degradation due to temperature rise. . On the other hand, if the amount of oil circulation is excessive, the return of oil from the bearing gap to the bearing body becomes excessive, and the above-described pressure drop problem occurs.
[0012]
Examples of means for controlling the amount of oil circulation include adjustment of the surface opening ratio (area ratio of surface opening in a unit area) and adjustment of oil kinematic viscosity. However, adjustment of surface area ratio Only However, since it is not possible to control the size of the surface openings and pores, if there is a large surface opening on the bearing surface, or if there is a large hole in the surface layer at a predetermined depth from the bearing surface, Inevitable pressure drop occurs. Moreover, excessive adjustment of the kinematic viscosity of the oil causes a torque increase. Therefore, these means have limitations, and in consideration of the recent trend of higher-speed rotation and higher performance of the spindle motor, it is often impossible to obtain a sufficient bearing function.
[0013]
Therefore, in the present invention, a dynamic pressure groove inclined with respect to the axial direction is provided on the bearing surface of the porous bearing body, and a lubricant impregnated in the bearing body is provided. The kinematic viscosity of the base oil at 40 ° C. is 5 to 60 cSt, Lubricating grease in which the blending ratio of the thickener is 0.1 to 5.0% by weight And the surface area of the bearing surface of the bearing body is 3 to 15%. It was.
[0014]
By using the lubricating grease impregnated in the bearing body as the lubricating grease, the thickener contained in the lubricating grease does not enter the very small pores but is selectively embedded in the relatively large pores. Therefore, the area of each surface opening on the bearing surface is averaged, and the cross-sectional area of each pore in the surface layer portion of a predetermined depth from the bearing surface is averaged, so that a local pressure drop is generated. In addition to being less likely to occur, oil oozes from the bearing body into the bearing gap, and the return of oil from the bearing gap to the bearing body is adjusted to an appropriate amount. Therefore, the formation effect of the lubricating oil film by the dynamic pressure grooves is enhanced, the bearing rigidity (bearing load capacity) is improved, and at the same time, proper circulation of the oil is ensured, and the bearing life is improved. Here, “oil” is a base oil of lubricating grease impregnated in the bearing body, and normally circulates between the bearing body and the bearing gap while containing a very small thickener component.
[0015]
If the blending ratio of the thickener is less than 0.1% by weight, the above-mentioned effect does not appear remarkably. Conversely, if it exceeds 5.0% by weight, the consistency of the lubricating grease becomes too high, and the impregnation step. Work in is complicated. That is, the bearing does not sink into the grease instantaneously, and after impregnation, it takes time to remove the grease adhering to the bearing surface.
[0016]
The bearing surface provided with the inclined dynamic pressure groove as described above can be formed by simultaneously molding the formation region of the dynamic pressure groove and the other region by a molding die having a shape corresponding to the bearing surface. it can. As a means for that purpose, for example, a concave and convex mold corresponding to the shape of the bearing surface is formed on the outer peripheral surface of the core rod, and a porous material is supplied to the mold for forming the core rod to apply a compression force. It is possible to employ a means for pressurizing the inner peripheral surface of the material to the core rod mold and plastically deforming it. After forming the bearing surface, the core rod forming die can be released from the porous material by utilizing the spring back of the porous material by releasing the compression force.
[0017]
As the material of the bearing body, one or more kinds of metal powder selected from copper, iron and aluminum are used as the main raw material, and tin, zinc, lead, graphite powder or alloy powder thereof is used as required. It can be a sintered metal obtained by mixing and sintering. When such a sintered metal is used as the material of the bearing body, the bearing body can be manufactured with high accuracy and low cost by the compression molding method as described above.
[0018]
The number of bearing surfaces may be one or more for one bearing, but a plurality of bearing surfaces are formed on the inner peripheral surface of the bearing body so as to be separated from each other in the axial direction, and the region between the bearing surfaces It can be set as the structure which made the internal diameter dimension larger than the internal diameter dimension of area | regions other than the dynamic pressure groove of a bearing surface. By forming a plurality of bearing surfaces on one bearing, it is possible to solve the problem of the coaxiality between the bearing surfaces when incorporating a plurality of bearings. In order to ensure the rotational accuracy of the shaft, a plurality of, for example, two bearings are usually used in combination. Further, the bearing is often used by being press-fitted into the housing. Therefore, conventionally, in order to ensure the coaxiality of the two bearings, a method of simultaneously press-fitting the two bearings after inserting the correction pins into the housing has been adopted. However, in the configuration of the present invention in which the inclined dynamic pressure groove is provided on the bearing surface, if the correction pin is forcibly corrected, the dynamic pressure groove on the bearing surface is crushed due to the biting of the correction pin, and stable. The dynamic pressure effect cannot be obtained. In this case, by forming a plurality of bearing surfaces on one bearing as described above, the problem of the coaxiality between the bearing surfaces can be solved, and the coaxiality is ensured with a correction pin as in the prior art. There is no need. Accordingly, there is no inconvenience that the dynamic pressure grooves on the bearing surface are crushed. In addition, the number of parts and the number of assembling steps are reduced as compared with the case where a plurality of bearings are arranged. Furthermore, an increase in torque can be suppressed by making the inner diameter dimension of the area between the bearing surfaces larger than the inner diameter dimension of the area other than the dynamic pressure groove on the bearing surface.
[0019]
The thickener for the lubricating grease used in the present invention may be either soap-based or non-soap-based, but it is preferable to use a urea compound as the thickener. Since the urea compound has a strong intermolecular interaction force, it has excellent shear stability, is easily adsorbed on the metal surface, and has an effect of enhancing the lubricating effect. Urea compounds have chemical structural formulas
-NHCONH-, for example, monourea, diurea, triurea and the like. Monourea is obtained from the reaction of monoamine and monoisocyanate, diurea is obtained from the reaction of monoamine and diisocyanate, and triurea is obtained from the reaction of monoamine, tolylene diisocyanate, and water. Among urea compounds, diurea is preferable from the viewpoint of availability of raw materials and manufacturability.
[0020]
In addition, general formula (1): R1-NHCONH-R2-NHCONH-R3
{R2 represents an aromatic hydrocarbon group having 6 to 15 carbon atoms;
R1 and R3 represent an aromatic hydrocarbon group having 6 to 12 carbon atoms or an alkyl group having 8 to 20 carbon atoms, and the proportion of the aromatic hydrocarbon group in R1 and R3 is 0 to 100 mol%. It is. }
The structure of the micelle can be freely changed by adjusting the ratio of the aromatic hydrocarbon group in R1 and R3 of the urea compound represented by the formula 0 to 100 mol%. In the urea compound group included in the general formula (1), it is impossible to finely adjust the molar ratio with only one kind of diurea, but two or more kinds of amines giving R1 and R3 are used. By adjusting the ratio, adjustment becomes possible. In the case of hydrodynamic sintered grease-containing bearings, it is possible to suppress pressure drop and heat generation to some extent by adjusting the surface opening ratio, etc., but higher performance can be achieved by adjusting the lubricating grease micelle structure. Thus, a hydrodynamic sintered grease-containing bearing having excellent durability can be obtained.
[0021]
In order to suppress shaft runout and oil leakage, it can be dealt with by increasing the proportion of aromatic hydrocarbon groups in R1 and R3 of the above general formula (1). The greater the proportion of aromatic hydrocarbon groups, the thicker and shorter the urea micelles. Therefore, compared with other thickeners having the same viscosity, the amount of thickener is increased, which is effective in suppressing axial runout and improving durability. On the other hand, when low current performance is required, the short fiber / thick micelle has an adverse effect and may cause heat generation. In that case, since the amount of the thickener can be reduced by reducing the mol% of the aromatic hydrocarbon group in R1 and R3, it is possible to cope with a reduction in current value. Therefore, by using a urea compound as a thickener for lubricating grease impregnated in a hydrodynamic sintered grease-containing bearing, it is possible to satisfy a wide range of required characteristics, which is extremely advantageous as a spindle motor bearing. Needless to say, the aromatic hydrocarbon group contained in R1 and R3 can be adjusted according to the application and use conditions in which the hydrodynamic sintered grease-containing bearing is used.
[0022]
The urea compound is obtained by the reaction of an isocyanate and a monoamine. Examples of the isocyanate used include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmetallene-4,4′-diisocyanate, and naphthylene- Aromatic diisocyanates such as 1,5-diisocyanate, tolylene diisocyanate, triazine-derived groups and mixtures thereof may be mentioned. Monoamines include aromatic amines such as aniline, benzylamine, toluidine, chloroaniline and octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine. And aliphatic amines such as heptadecylamine, octadecylamine, nonadecylamine, eicodecylamine, and cyclohexylamine.
[0023]
Although the base oil of the lubricating grease used in the present invention is not particularly limited, it is a mineral oil, paraffinic mineral oil, hydrogenated paraffin mineral oil, hydrogenated paraffin mineral oil, refined naphthenic mineral oil, high viscosity index paraffin mineral oil And polyalphaolefin-based, ester-based, ether-based, polyglycol-based, aromatic hydrocarbon oil, fluorine-based lubricating oil, and mixed oils thereof, which are synthetic lubricating oils, are preferable.
[0024]
Various additives can be added to the base oil to improve wear resistance, thermal stability, etc., but it is preferable to add a phosphate ester represented by the following general formula (2). is there. Examples of the phosphoric acid ester include phosphoric acid triesters such as trioctyl phosphate and tricresyl phosphate, acidic phosphoric acid esters such as monooctyl phosphate, and dioctyl phosphate, and alkyl phosphate amine salts (some amine groups). Among them, phosphoric acid triesters are preferable. By using phosphate ester, the oil film forming ability can be increased.
[0025]
[Chemical 1]

[0026]
In the above formula, each R independently represents hydrogen, a hydrocarbon group or an alkoxy group, and at least one is a hydrocarbon group or an alkoxy group.
[0027]
The blending ratio of the phosphate ester to the base oil is 0.1 to 10% by weight, preferably 0.5 to 3% by weight. When the blending ratio of the phosphoric ester is less than 0.1% by weight, the wear resistance cannot be improved, and even when the content exceeds 10% by weight, no significant improvement in wear resistance is observed.
[0028]
In addition, as a viscosity index improver and a structural stabilizer, an ethylene-α-olefin copolymer or a hydride thereof, a polymethacrylate type, or a polybutene (polyisobutylene) type is added to the base oil. May be. The ethylene-α-olefin copolymer or a hydride thereof can be obtained, for example, by hydrogenating a polymer obtained by polymerizing ethylene and 1-decene, isobutene or the like with a catalyst such as a Lewis acid. These have a number average molecular weight of about 200 to 4000, and preferably have a number average molecular weight of 1450. The average molecular weight of the polymethacrylate series is about 20000 to 1500,000. The average molecular weight is preferably 20000 to 50000 in relation to shear stability. The average molecular weight of the polybutene system is preferably about 5000 to 300000. The blending ratio of the viscosity index improver and the structure stabilizer is 1 to 30% by weight, preferably 1 to 5% by weight, based on the base oil.
[0029]
Furthermore, antioxidant can be mix | blended with the said base oil. As the antioxidant, one or more antioxidants selected from the group consisting of phenolic, amine-based, which functions as a free radical chain terminator, and sulfur-based antioxidant, which functions as a peroxide decomposer, are used alone. Alternatively, a mixture of an amine and a phenol can be used. Examples of phenolic antioxidants include 2,6-di-t-butylphenol, 4,4′-methylenebis (2,6-di-t-butylphenol), and 2,6-di-t-butyl-4-ethyl. Examples include phenol and 2,6-di-t-4-n-butylphenol. From the viewpoint of evaporation characteristics and compatibility with the base oil, 4,4′-methylenebis (2,6-di-t-butylphenol) is preferable. Examples of amine-based antioxidants include dioctyl diphenylamine and phenyl-α-naphthylamine. Dioctyl diphenylamine is preferred from the viewpoint of evaporation characteristics and compatibility with the base oil. The blending amount is 0.1 to 10% by weight of amine-based antioxidant and 0.1 to 10% by weight of phenol-based antioxidant in consideration of solubility in base oil. preferable. When used alone, 0.1 to 10% by weight of an amine-based antioxidant is suitable. Phenolic antioxidants are effective when used in combination.
[0030]
Furthermore, the base oil of the present invention includes a rust inhibitor, a pour point depressant, an ashless dispersion, a metal deactivator, a metal system, as long as the purpose and effect of the present invention are not impaired. A cleaning agent, an oily agent, a surfactant, an antifoaming agent, a friction modifier, and the like can be blended.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0032]
FIG. 1 illustrates a spindle motor of a DVD-ROM / RAM device which is a kind of information equipment. This spindle motor includes a bearing unit A that rotatably supports a rotary shaft 4 arranged vertically, a turntable 6 that supports and fixes an optical disk 5 such as a DVD-ROM mounted on the upper end of the rotary shaft 4, and a clamper 7. For example, a motor part B having a stator 8 and a rotor magnet 9 opposed to each other through a radial gap is a main component. The stator 8 is fixed to the outer peripheral surface of the housing 1 constituting the bearing unit A, and the rotor magnet 9 is fixed to the inner peripheral surface of the rotor case 10 mounted on the turntable 6. When the stator 8 is energized, the rotor case 10, the turntable 6, the optical disk 5, the clamper 7, and the rotating shaft 4 integrated with the rotor magnet 9 rotate.
[0033]
The bearing unit A includes a cylindrical housing 1, a hydrodynamic sintered grease-containing bearing 2 that is fixed to the inner peripheral surface of the housing 1 and supports the outer peripheral surface of the rotating shaft 4 in the radial direction, and a lower end opening of the housing 1. And a thrust bearing 3 that supports the lower shaft end surface of the rotary shaft 4 in the thrust direction. In this embodiment, the thrust bearing 3 includes a disc-shaped resin thrust washer 3a and a back metal 3b that supports the disk-shaped resin thrust washer 3a. The lower shaft end surface of the upper surface of the resin thrust washer 3a is a convex spherical shape of the rotary shaft 4. It is configured to contact and support in the thrust direction. The resin thrust washer 3a may be embedded in the center portion of the back metal 3b so as to come into contact with the lower shaft end surface of the rotary shaft 4.
[0034]
As shown in FIG. 2, the hydrodynamic sintered grease-containing bearing 2 is obtained by impregnating a porous bearing body 2a made of sintered metal with a lubricating grease as a lubricant to have a self-lubricating function. The bearing body 2a is made of one or more kinds of metal powder selected from copper, iron, and aluminum as a main raw material, and optionally mixed with nickel, tin, zinc, lead, graphite powder or alloy powder thereof. And sintered metal obtained by sintering, preferably 20 to 97% by weight of copper, and a density of 6.4 to 7.2 g / cm. ^Three It is shape | molded so that it may become.
[0035]
In this embodiment, two bearing surfaces 2b spaced apart in the axial direction are formed on the inner peripheral surface of the bearing body 2a, and a plurality of dynamic pressures inclined with respect to the axial direction are provided on both of the two bearing surfaces 2b. A groove 2c is formed. Each bearing surface 2b is separated from the first region m1 in the axial direction by a first region m1 in which a plurality of dynamic pressure grooves 2c inclined in one direction with respect to the axial direction are arranged in the circumferential direction. A second region m2 in which a plurality of hydrodynamic grooves 2c inclined to the other side are arranged in the circumferential direction, and an annular smooth region n positioned between the first region m1 and the second region m2. . The dynamic pressure groove 2c in the first region m1 and the dynamic pressure groove 2c in the second region m2 are partitioned by the smooth region n and are discontinuous with each other. The back 2d of the first region m1 (region between the dynamic pressure grooves 2c) and the back 2d of the second region m2 (region between the dynamic pressure grooves 2c) are at the same level as the smooth region n. On the bearing surface 2b, the surface openings are distributed almost uniformly over the entire region including the region where the dynamic pressure groove 2c is formed.
[0036]
When relative rotation occurs between the bearing main body 2a and the shaft 4, the oil in the bearing gap is transferred to the smooth region n by the dynamic pressure grooves 2c formed in the first region m1 and the second region m2 so as to incline in opposite directions. Since the oil is drawn toward and collected in the smooth region n, the oil film pressure in the smooth region n is increased. Therefore, high bearing rigidity can be obtained.
[0037]
The inclination angle of the dynamic pressure groove 2c may be set to an arbitrary angle, but is preferably set so that the angle β with the direction orthogonal to the axial direction is 15 to 40 °, more preferably 15 to 25 °. Is good. Further, the width ratio between the dynamic pressure groove 2c and the spine 2d is set within the range of 0.8 to 1.5, preferably 1.0 to 1.2. Furthermore, the ratio R of the axial width of the smooth region n is within the range of R = 0.1 to 0.6, preferably R = 0.2 to 0.4, where the axial width of each bearing surface 2b is 1. It is good to set to. If R is less than 0.1, the effect of increasing the bearing rigidity due to the provision of the smooth region n does not appear remarkably. Conversely, if R exceeds 0.6, the axial direction of the first region m1 and the second region m2 The width is reduced, and the dynamic pressure effect by the dynamic pressure groove 2c is not effectively exhibited.
[0038]
Optimal for the ratio between the groove depth h of the dynamic pressure groove 2c (see FIG. 4) and the bearing radius clearance c (the difference between the radius of the back 2d portion of the bearing surface 2b and the radius of the outer peripheral surface of the rotary shaft 4). There is a range, and outside this range, a sufficient dynamic pressure effect cannot be obtained. In order to clarify this optimum range, the shaft runout was measured using a spindle motor for DVD-ROM / RAM. When c / h was in the range of 0.5 to 2.0, the runout was practically sufficient. It was confirmed that it can be controlled to a certain level. For example, when the groove depth h is 2 to 4 μm, the bearing radius clearance c is preferably set within a range of 2 to 4 μm.
[0039]
Further, the inner diameter dimension of the region between the bearing surfaces 2b in the bearing body 2a is set larger than the inner diameter dimension of the back 2d portion of the bearing surface 2b.
[0040]
The shape of each bearing surface 2b is not limited to that shown in FIG. 2 (a). For example, a pair of a dynamic pressure groove inclined to one side and a dynamic pressure groove inclined to the other side in the axial direction is used as a shaft. It may be continuous in a V shape in the direction (in this case, there is no annular smooth region n). Under operating conditions where there is almost no unbalance in the rotating body and bearing rigidity is not an important factor, the bearing surface with a dynamic pressure groove continuous in the axial direction is less likely to generate negative pressure. There is also. Furthermore, the dynamic pressure groove on the bearing surface only needs to be inclined with respect to the axial direction, and can have any shape as long as this condition is satisfied. For example, the dynamic pressure groove may be spiral.
[0041]
As the base oil of the lubricating grease impregnated in the bearing body 2a, one having a kinematic viscosity at 40 ° C. set to 5 to 60 cSt can be used. In particular, in a device such as a DVD-ROM / RAM that requires radial rigidity against an unbalanced load due to the loading of a disk, a device having 10 to 50 cSt is preferable. In this embodiment, the kinematic viscosity at 40 ° C. is 40 cSt, the main component is polyol ester oil, the viscosity index improver is polymethacrylate, the antioxidant is phenyl-α-naphthylamine, and the metal deactivator is benzotriazole. A lubricating oil to which trioctyl phosphate was added as a derivative and an antiwear agent was used as a base oil.
[0042]
Lithium soap and urea compounds were used as thickeners for the lubricating grease.
[0043]
Thickener lithium soap is stearic acid and LiOH.H. ₂ React with O to make grease. First, 1/3 of the base oil and stearic acid are placed in a reaction vessel and heated to 80 ° C. When the solvent is clear, water and LiOH · H ₂ Mix O well into the reaction vessel. Thereafter, dehydration is performed for about 1 hour. After the dehydration was completed, the remaining base oil was added gradually so that the temperature did not decrease, and the reaction was terminated when the temperature reached 185 ° C.
[0044]
As the thickener monourea, octadecylamine was used as a raw material amine, and octadecyl isocyanate was used as a monoisocyanate. What is shown by diurea uses p-toluidine as a raw material amine whose end group becomes an aromatic group, uses n-octylamine as a raw material amine that becomes an alicyclic group, and as a raw material amine that becomes an aliphatic group Cyclohexylamine was used. Further, diphenylmethane-4,4′-diisocyanate was used as the diisocyanate. Triurea used octadecylamine as a raw material amine and tolylene diisocyanate and water as isocyanate. Specifically, diurea will be described as an example. A reaction vessel was charged with half of the base oil and all of the monoamine shown in Table 1, and heated to 70 to 80 ° C. In a separate container, the remaining half of the base oil and diphenylmethane-4,4′-diisocyanate were added and heated to 70 to 80 ° C., which was added to the reaction container and stirred. Stirring was continued in this state for about 30 minutes, and after the reaction was sufficiently performed, the temperature was raised to 170 to 180 ° C. and kept at this temperature for 30 minutes. The cooled product was used as a base grease.
[0045]
When the spindle motor is assembled by inserting the rotating shaft 4 into the inner peripheral surface of the hydrodynamic sintered grease-containing bearing 2, the same (or the same type) lubricating grease or its base oil as the lubricating grease impregnated in the bearing body 2a is used. In addition to the impregnated grease, when the bearing surface of the thrust bearing 3 is wetted with the lubricating grease or its base oil and the bearing gap of the hydrodynamic sintered grease-containing bearing 2 is filled with the lubricating grease or its base oil, good. In this hydrodynamic sintered grease-containing bearing 2, the base oil of the lubricating grease impregnated inside the bearing body 2 a is increased by a very small amount due to the thermal expansion of the oil due to the pressure generated by the rotation of the rotating shaft 4 and the temperature rise. It exudes from the surface of the bearing body 2a while containing the thickener component, and is drawn into the bearing gap by the action of the dynamic pressure groove 2c. If the inside of the bearing gap of the hydrodynamic sintered grease-containing bearing 2 is filled with oil in the initial stage of driving, air is not involved, a good lubricating oil film is formed, and a stable bearing function is obtained. Further, the bearing surface of the thrust bearing 3 is wetted with oil from the initial stage of driving and is in a good lubricating state.
[0046]
In general, the rotating shaft 4 is inserted into the inner peripheral surface of the dynamic pressure type porous grease-containing bearing 2 with the thrust bearing 3 attached to the lower end opening of the housing 1. At the time of this insertion, air escapes from the bearing gap between the bearing 2 and the rotary shaft 4, but since the bearing gap is only about several μm, the air is confined in the lower space of the housing 1, and the rotary shaft 4 may be difficult to insert. Moreover, the heat confined in the space below the housing 1 may expand due to the heat generated when the motor rotates, and the rotating shaft 4 may be pushed up to destabilize the bearing function. In this case, as shown in FIGS. 1 and 2, this air passage S is provided between the outer peripheral surface of the bearing 2 and the inner peripheral surface of the housing 1 so as to open at both ends in the axial direction of the bearing body 2 a. The air in the lower space of the housing 1 may be released to the outside through the passage S. In this embodiment, the air passage S is formed on the outer peripheral surface of the bearing body 2 a, but the air passage S may be formed on the inner peripheral surface of the housing 1. Further, the number of air passages S may be one, or a plurality of air passages S may be formed in the circumferential direction.
[0047]
When a positive pressure is generated in the bearing gap of the hydrodynamic sintered grease-containing bearing 2, since the bearing surface 2b has a surface opening, oil flows back into the bearing body 2a through the surface opening of the bearing surface 2b. . At that time, if the surface opening of the bearing surface 2b or the size of the pore in the surface layer portion of a predetermined depth from the bearing surface 2b is large, the oil in the bearing gap passes through the large hole and the inside of the bearing body 2a. It becomes easy to reflux. Therefore, the pressure distribution in the bearing gap becomes non-uniform (a local pressure drop occurs), which affects the rotation accuracy. In this embodiment, the thickener of the lubricating grease is selectively embedded in the large pores of the bearing body 2a, and the surface openings and pore sizes are apparently averaged. Proper circulation of oil between the bearing gaps is ensured. As a result, the problem of non-uniform pressure distribution (local pressure drop) as described above is solved, and new oil continues to be pushed into the bearing gap one after another by the dynamic pressure action of the dynamic pressure groove 2c. The oil film force and radial rigidity of the lubricating oil film are maintained in a high state. As a result, the rotating shaft 4 is continuously supported in a non-contact manner by the hydrodynamic sintered grease-containing bearing 2 without causing unstable vibration such as whirl, and shaft runout, NRRO, jitter, and the like are reduced. Further, since the rotating shaft 4 and the bearing body 2a rotate without contact, the noise is low and the cost is low.
[0048]
The bearing surface 2b having the inclined dynamic pressure groove 2c as described above can be formed by compression molding. For example, a molding die corresponding to the shape of the bearing surface 2b is formed on the outer peripheral surface of a core rod such as a sizing pin used for processing a sintered grease-containing bearing, and a cylindrical shape that is a material of the bearing body 2a is formed on the outer peripheral surface of the core rod. A sintered metal material is supplied, a pressing force is applied to the sintered metal material, and the inner peripheral surface thereof is pressed against the core rod mold, and the shape of the mold is transferred to the inner peripheral surface of the sintered metal material. At this time, the formation region of the dynamic pressure groove 2c on the bearing surface 2b and the other region (the back 2d and the smooth region n) can be simultaneously formed. In this case, if the core rod mold is finished with high accuracy, the molding accuracy of the bearing surface 2b is improved. It is relatively easy to finish the core rod mold within required accuracy, for example, roundness within 1 μm and cylindricity within 2 μm. After forming the bearing surface 2b, the shape of the dynamic pressure groove 2c is changed by using a spring back of a sintered metal material and further adding a thermal expansion difference between the core rod and the sintered metal material by heating to the spring back. The core rod can be released from the inner peripheral surface of the sintered metal material without breaking.
[0049]
Before carrying out the above bearing surface molding, it is preferable to perform rotational sizing on the inner peripheral surface of the sintered metal material and adjust the surface open area ratio of the inner peripheral surface in advance. The surface opening ratio of the bearing surface 2b of the bearing body 2a as a finished product is smaller than the surface opening ratio (usually about 20 to 30%) of the bearing surface of a general sintered oil-impregnated bearing having no dynamic pressure grooves. Good to do. For example, when the surface area ratio of the bearing surface 2b is set to 3 to 15%, combined with the effect of the grease impregnation, it is advantageous for ensuring adequate oil circulation while maintaining sufficient oil film formation. is there. The surface opening ratio can be adjusted by the above-described rotational sizing, by setting the density of the bearing body 2a, or by combining surface treatment and density setting.
[0050]
【Example】
Using a DVD-ROM / RAM spindle motor shown in FIG. The dynamic pressure type sintered grease-containing / oil-impregnated bearing used in the test was impregnated with the lubricant shown in Table 1. Examples 1 to 7 were impregnated with lubricating grease, and Comparative Example 1 was impregnated with lubricating oil. The shaft runout was measured by replacing the rotating shaft 4 shown in FIG. 1 with a long one protruding from the upper end and measuring its behavior with a non-contact displacement meter.
[0051]
[Table 1]

[0052]
The test was carried out in an environment with a rotational speed of 1000 to 8000 rpm, an unbalanced load of the rotating body of 1 g · cm, and a normal temperature and humidity environment. The specifications of the bearing and the bearing surface are as follows.
[0053]
[Bearing specifications]
Shaft diameter: φ3mm
Bearing dimensions: inner diameter φ3 × outer diameter φ6 × width 8.7 mm
Number of bearing surfaces: 2 on top and bottom
Axial width of bearing surface: 2.4 mm
Bearing gap (diameter): 4μm
"Dynamic pressure groove specification" (shape shown in Fig. 2)
Groove depth: 3 μm
Groove angle β: 20 °
Number of grooves: 8
The results of the comparative test are summarized in FIG. As shown in FIG. 5, in Examples 1 to 7 impregnated with lubricating grease, it was recognized that the axial runout was reduced as compared with Comparative Example 1, and in particular, in Example 4 where the thickener was urea. The tendency was remarkable. From this test result, in this type of hydrodynamic bearing, compared to the configuration impregnated with lubricating oil, the configuration impregnated with lubricating grease improves the bearing rigidity and is more effective in suppressing shaft runout. Was confirmed.
[0054]
【The invention's effect】
The present invention has the following effects.
[0055]
(1) A lubricating oil film is formed in the bearing gap due to the dynamic pressure effect of the inclined dynamic pressure groove provided on the bearing surface, and the sliding surface of the rotating shaft is supported in a non-contact manner by the lubricating oil film. Stable vibration hardly occurs and high rotation accuracy can be obtained. Further, since the lubricating action is performed while the oil retained in the pores inside the bearing body is circulated between the bearing body and the bearing gap, oxidation deterioration of the oil hardly occurs and a long bearing life can be obtained.
[0056]
(2) By using the lubricating grease impregnated in the bearing body as a lubricating grease, the area of each surface opening of the bearing surface is averaged, and each surface layer portion of a predetermined depth from the bearing surface Since the cross-sectional area of the pores is averaged, local pressure drop is unlikely to occur, and oil oozes out from the bearing body to the bearing gap and returns to the bearing body from the bearing gap to an appropriate amount. Adjusted. Therefore, the formation effect of the lubricating oil film by the dynamic pressure grooves is enhanced, the bearing rigidity (bearing load capacity) is improved, and at the same time, proper circulation of the oil is ensured, and the bearing life is improved.
[0057]
(3) Since the urea compound has a strong interaction force between molecules, it has excellent shear stability and is easily adsorbed on the metal surface. Therefore, by using this as a thickener for lubricating grease, a lubricating effect can be obtained. It can be further increased.
[0058]
(4) By forming a plurality of bearing surfaces spaced apart in the axial direction on the inner peripheral surface of the bearing body, the coaxiality between the bearing surfaces can be ensured with high accuracy. Further, the number of parts and the number of assembly steps can be reduced as compared with the case where a plurality of bearings are arranged.
[0059]
(5) The spindle motor of the information equipment according to the present invention in which the rotating shaft is supported in a non-contact manner by the dynamic pressure type sintered grease-containing bearing as described above is accompanied by high speed and high performance of the mounted device such as shaft runout, NRRO, and jitter. Satisfying the increasingly demanding characteristics, contributing to improved functionality and long life of information equipment.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a spindle motor of a DVD-ROM / RAM device according to an embodiment.
FIG. 2 is a cross-sectional view (FIG. A) and a front view (FIG. B: view in the direction of arrow b in FIG. A) of a hydrodynamic sintered grease-containing bearing.
FIG. 3 is a diagram schematically showing an oil flow in an axial section when a shaft is supported in a non-contact manner by a hydrodynamic sintered grease-containing bearing.
FIG. 4 is a cross-sectional view schematically showing a relationship between a depth h of a dynamic pressure groove on a bearing surface and a bearing gap c in a dynamic pressure type sintered grease-containing bearing.
FIG. 5 is a diagram showing the results of a shaft runout comparison test.
[Explanation of symbols]
2 Dynamic pressure type sintered grease bearing
2a Bearing body
2b Bearing surface
2c Dynamic pressure groove
4 Rotating shaft

Claims (10)

A porous bearing made of sintered metal having a bearing surface facing the sliding surface of the rotating shaft to be supported via a bearing gap, and provided with dynamic pressure grooves inclined with respect to the axial direction on the bearing surface A main body and a lubricant impregnated in pores inside the bearing main body,
Lubricants impregnated in the bearing body, Ri Oh lubricating grease kinematic viscosity at 40 ° C of the base oil is 5～60CSt, and 0.1 to 5.0 wt% blending ratio of the thickener,
The surface area of the bearing surface of the bearing body is 3 to 15%,
While the base oil of the lubricating grease circulates between the inside of the bearing body and the bearing gap through the surface opening including the bearing surface, the lubricating oil film is formed in the bearing gap by the dynamic pressure effect of the dynamic pressure groove. forming a dynamic pressure type sintered Yui含grease bearing characterized that you contact manner the sliding surface of the rotary shaft relative to the bearing surface by the lubricant film.   2. The hydrodynamic sintered grease-containing bearing according to claim 1, wherein the sintered metal is mainly composed of one or more materials selected from copper, iron, and aluminum.   The hydrodynamic sintered grease-containing bearing according to claim 1, wherein the thickener of the lubricating grease is a urea compound. 4. The hydrodynamic sintered grease-containing bearing according to claim 3, wherein the urea compound is at least one compound selected from the group represented by the following formula (1).
R1-NHCONH-R2-NHCONH-R3 (1)
In the above formula, R2 represents an aromatic hydrocarbon group having 6 to 15 carbon atoms, and R1 and R3 represent an aromatic hydrocarbon group having 6 to 12 carbon atoms or an alkyl group having 8 to 20 carbon atoms. The ratio of the aromatic hydrocarbon group in R1 and R3 is 0-100 mol%.   A plurality of bearing surfaces are formed on the inner peripheral surface of the bearing body so as to be spaced apart from each other in the axial direction. The hydrodynamic sintered grease-containing bearing according to claim 1. In a spindle motor of an information device including a rotation shaft that rotates together with a rotation element of the information device, a bearing that supports the rotation shaft, and a rotor and a stator that are arranged to face each other with a predetermined gap therebetween.
The above-mentioned bearing has a bearing surface facing the sliding surface of the rotating shaft through a bearing gap, and the bearing surface is a porous metal made of sintered metal provided with dynamic pressure grooves inclined with respect to the axial direction. A bearing body, and a lubricant impregnated in pores inside the bearing body, the lubricant having a kinematic viscosity at 40 ° C. of the base oil of 5 to 60 cSt, and a blending ratio of the thickener of 0. .1～5.0 Ri Oh in weight percent and the lubricating grease,
The surface area of the bearing surface of the bearing body is 3 to 15%,
While the base oil of the lubricating grease circulates between the inside of the bearing body and the bearing gap through the surface opening including the bearing surface, the lubricating oil film is formed in the bearing gap by the dynamic pressure effect of the dynamic pressure groove. forming a spindle motor of an information device which is characterized that you contact manner the sliding surface of the rotary shaft relative to the bearing surface by the lubricant film. The spindle motor for information equipment according to claim 6 , wherein the sintered metal is mainly composed of one or more materials selected from copper, iron, and aluminum. 7. The spindle motor for information equipment according to claim 6 , wherein the thickener for the lubricating grease is a urea compound. 9. The spindle motor for information equipment according to claim 8, wherein the urea compound is one or more compounds selected from the group represented by the following formula (1).
R1-NHCONH-R2-NHCONH-R3 (1)
In the above formula, R2 represents an aromatic hydrocarbon group having 6 to 15 carbon atoms, and R1 and R3 represent an aromatic hydrocarbon group having 6 to 12 carbon atoms or an alkyl group having 8 to 20 carbon atoms. The ratio of the aromatic hydrocarbon group in R1 and R3 is 0-100 mol%. A plurality of bearing surfaces are formed on the inner peripheral surface of the bearing body so as to be separated from each other in the axial direction, and the inner diameter dimension of the area between the bearing surfaces is larger than the inner diameter dimension of the area other than the dynamic pressure groove on the bearing surface. A spindle motor for an information device according to claim 6 .

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