JP4120147B2

JP4120147B2 - Method for manufacturing permanent magnet field type small DC motor

Info

Publication number: JP4120147B2
Application number: JP2000279693A
Authority: JP
Inventors: 文敏山下; 伸二戸田; 英史植西; 雄一朗佐々木
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1999-09-16
Filing date: 2000-09-14
Publication date: 2008-07-16
Anticipated expiration: 2020-09-14
Also published as: JP2001157419A

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば、ＭＤ、ＣＤ−ＲＯＭの光ピックアップなど音響映像機器に使用される始動電圧や始動電流を低く抑えて高精度回転するような円弧状希土類磁石を使った小型で高出力、且つ低コギングトルクの永久磁石界磁型小型直流モ−タに関する。
【０００２】
【従来の技術】
図１（ａ）、（ｂ）は本発明の対象となる永久磁石界磁型小型直流モ−タの要部断面と、それに使われる円弧状磁石を示す。図において１は一対の円弧状永久磁石、２は軟磁性フレ−ム、３はブラシ−整流子並びに電機子軸と軸受を含む電機子、４は一対の円弧状永久磁石１を軟磁性フレ−ム２に押圧固定するＵ字型状のバネである。このような永久磁石界磁型小型直流モ−タも他の永久磁石型モ−タと同様にモ−タの小型化と高出力化と高精度回転性能が求められている。
【０００３】
しかし、一般に永久磁石界磁型小型直流モ−タは電機子３の直径が小さくなるとモ−タの出力を維持して小型化することが困難であった。とくにフェライト系磁石では焼結、或いは樹脂を結合剤とした圧縮、射出、押出成形方式に拘わらず、最大エネルギ−積［ＢＨ］ｍａｘの低さから小型化すると永久磁石界磁１と電機子３との空隙に十分強い静磁界が得られず、モ−タの出力低下が著しかった。そこで、モ−タを小型化しても永久磁石界磁１と電機子３との空隙に強い静磁界が得られる、所謂高い［ＢＨ］ｍａｘを有する円弧状希土類磁石が求められていた。
【０００４】
永久磁石界磁型小型直流モ−タを小型化して、使用される最大厚さ１ｍｍ未満の円弧状希土類磁石となると磁石の製造方法が限られる。たとえば特開平６−２３６８０７号公報に記載の磁気的に異方性から等方性に至る多種類の希土類磁石粉末類と熱可塑性樹脂から成る溶融流動状態の材料を成形型中に送り込み、成形型中で熱可塑性樹脂の融点以下に冷却しながら押出成形する円弧状希土類磁石の製造方法が開示されている。それによれば、最大厚さ０．９ｍｍ±３０μｍの薄肉円弧状希土類磁石を押出成形で製造できる。
ところで、フェライト系磁石に比べると電機子３との空隙に強い静磁界が得られる上記のような円弧状希土類磁石を使用した永久磁石界磁型小型直流モ−タの問題点の一つにコギングトルクの増大がある。これは永久磁石界磁１と対向する電機子３の外周表面に電機子鉄心ティ−ス３１とスロット３２が存在するため、電機子３の回転に伴ってパ−ミアンスが変化することによるトルク脈動が発生するからである。とくにコギングトルクは本発明で対象とする小型高出力で、しかも高精度な回転性能が求められる永久磁石界磁型小型直流モ−タで問題となる。
【０００５】
希土類磁石に拘わらず永久磁石界磁型小型直流モ−タの円弧状磁石の形状によるコギングトルク低減手段は、当該円弧状磁石の内外周曲率半径を偏心させて不等肉厚とするか、または円弧状磁石の周方向両端面の角を落して不等肉厚とすることで磁極中心から周方向両端部にかけて一様な材質が一様に磁化されている磁石のパ−ミアンスを変化させることにより、空隙磁束密度分布を正弦波状に近づける手段が知られている（例えば、田中省吾「小型モ−タにおける永久磁石の応用」、小型モ−タ技術シンポジウム予稿集、ｐ７、昭５８年、特開平５−１６８２０１号公報）。
一方、例えば米国特許第４，７１０，２３９号公報のように、１０〜５０原子％の希土類元素ＲＥ（Ｎｄまたは／およびＰｒ）、１〜１０原子％のＢ、残部が遷移金属元素ＴＭで、遷移金属元素の少なくとも６０原子％がＦｅである非晶質希土類−鉄系急冷凝固薄片を出発原料とし、先ず磁石相ＲＥ₂ＴＭ₁₄Ｂの結晶化温度（約６００℃）以上、７５０℃以下で圧縮することにより、厚さの異なる等方性フル密度磁石を作成し、更に同様な加熱温度下での熱間塑性加工によって円弧状磁石に仕上げる。すると熱間塑性加工の程度に応じて塑性流れと直角方向に磁化容易軸が配列するためＲＥ₂ＴＭ₁₄Ｂは、もとが厚い部分で磁気的に強い異方性希土類磁石となる。このような異方性の強い部分と等方性部分とをもった円弧状磁石が開示されている。
【０００６】
このような異なった磁気性能部分を有する円弧状希土類磁石を永久磁石界磁型直流モ−タに使用して、磁極中心から周方向に減磁曲線自体を変化させることが可能となり、コギングトルクが低減するように界磁と電機子鉄心との空隙磁束密度分布変化をなだらかにすることも可能になる。
以上、円弧状希土類磁石を使用した永久磁石界磁型直流モ−タの内外周曲率半径を偏心させて不等肉厚とするか、または円弧状磁石の周方向両端面の角を落して不等肉厚とすることで磁極中心から周方向両端部にかけて磁石のパ−ミアンスを変化させ、更に磁極中心から周方向に磁石の磁気性自体を変化させ、異なる減磁曲線によってコギングトルクが低減するように界磁と電機子鉄心との空隙磁束密度分布を制御することが考えられる。
【０００７】
しかしながら、本発明が対象とする小型の永久磁石界磁型直流モ−タには非晶質希土類−鉄系急冷凝固薄片を出発原料とした厚さのことなるフル密度磁石を熱間加工して磁気性能の異なる部分を有する例えば厚さ１ｍｍ未満の円弧状希土類磁石を工業的規模で製造することは極めて難しい。また、異方性を強めると固有保磁力の温度係数が小さくなる。そのため異方性の強めた磁極中心部分の熱減磁が大きく、永久磁石界磁直流モ−タの熱減磁に伴うトルク低下が大きくなってしまうなどの欠点もある。
【０００８】
【発明が解決しようとする課題】
永久磁石界磁型小型直流モ−タを小型化して、使用される円弧状希土類磁石の最大厚さが１ｍｍ未満となると磁石の製造方法が限られる。たとえば特開平６−２３６８０７号公報に記載の磁気的に異方性から等方性に至る多種類の希土類磁石粉末類と熱可塑性樹脂から成る溶融流動状態の材料を成形型中に送り込み、成形型中で熱可塑性樹脂の融点以下に冷却しながら押出成形する円弧状希土類磁石の製造方法が開示されている。それによれば、例えば磁気的に等方性の希土類−鉄系急冷凝固薄片９５重量％と１２ナイロンを主とする熱可塑性樹脂との材料で最大厚さ０．９ｍｍ±３０μｍの薄肉円弧状希土類磁石を押出成形で製造できる。しかし、押出成形は熱可塑性樹脂が溶融状態で希土類−鉄系急冷凝固薄片のキャリアの役割を担わなければならない。
したがって、希土類−鉄系急冷凝固薄片を一般に３重量％以下の熱硬化性樹脂とともに圧縮成形する希土類磁石に比べると希土類−鉄系急冷凝固薄片の充填量を少なくせざるを得ず、その分［ＢＨ］ｍａｘが低くなり永久磁石界磁１と電機子３との空隙部分の静磁界が弱まる。磁気的に異方性の磁石粉末を使って高い［ＢＨ］ｍａｘの円弧状磁石にすることも考えられるが、本発明が解決すべき第一の課題は特開平６−２３６８０７号公報記載の「圧縮成形では最大厚さ１ｍｍ未満の薄肉円弧状磁石を±３０μｍ程度の寸法精度で得ることが成形時の秤量の変動が大きいために困難とされていた」点を解決することである。しかし、仮にこの課題が解決されても圧縮成形による希土類磁石は樹脂量が少ない分だけ機械的に脆い。
【０００９】
したがって、圧縮成形による円弧状希土類磁石を特開平１０−２０１２０６号公報や特開平１１−１８３９０号公報記載の「軟磁性フレ−ムの係合部分に円弧状希土類磁石を撓ませながら嵌合固定する」ことはできない。すなわち、本発明が解決すべき第二の課題は圧縮成形による円弧状希土類磁石の機械的性質に見合った軟磁性フレ−ムへの取付け手段となる。更にまた「押出成形による円弧状希土類磁石よりも、高［ＢＨ］ｍａｘになる」ため、本発明が解決すべき第三の課題はよく知られた磁石形状によるコギングトルク低減手段とともに、磁気的に等方性の希土類−鉄系急冷凝固薄片を円弧状に固めた永久磁石界磁の磁極中心と周方向両端部との減磁曲線が異なるような不飽和着磁をすることでコギングトルクを低減する永久磁石界磁型小型直流モ−タの製造方法の提供にある。
本発明は、電機子と界磁の空隙に、フェライト系磁石よりも強い静磁界が得られる磁気的に等方性の希土類−鉄系急冷凝固薄片を円弧状に固めた小型で高出力、かつ低コギングトルクの永久磁石界磁型直流モ−タの製造方法の提供を目的とする。
【００１０】
【課題を解決するための手段】
本発明は、希土類−鉄系急冷凝固薄片を主成分とする円弧状希土類磁石を軟磁性フレ−ム内周面に沿わせながら固定し、不飽和着磁することで、磁極中心部分の減磁曲線よりも周方向両端部分の減磁曲線を小さくした円弧状希土類磁石を、電機子を介して対向させた永久磁石界磁型小型直流モ−タの製造方法であり、外周部分の周方向両端面に軟磁性フレ−ムがバックヨ−クとして作用しない部分を形成し、球状断面の軟磁性材料を介した状態で不飽和着磁するとコギングトルクを更に低減することができる。
【００１１】
【発明の実施の形態】
本発明は希土類−鉄系急冷凝固薄片を主成分とする円弧状希土類磁石を軟磁性フレ−ム内周面に沿わせながら固定し、１５〜３０ｋＯｅの着磁界の強さで不飽和着磁することにより、磁極中心部分の減磁曲線よりも周方向両端部分の減磁曲線を小さくした円弧状希土類磁石を、電機子を介して対向させる永久磁石界磁型小型直流モ−タの製造方法が基本となる。（減磁曲線が大、減磁曲線が小の位置関係は図９に示す。）
なお、ここで言う不飽和着磁とは、永久磁石材に最大限の磁力を着磁してしまう飽和着磁に対し、永久磁石材に最大限の磁力を着磁しないことを言う。永久磁石材は一度着磁すると、その磁力は永久的に保持されるので、永久磁石に最大限の磁力を保持させて効率よく利用するのが一般的である。不飽和着磁とは、磁力の保持に余裕を持たせた状態で着磁することを言う。
【００１２】
ただし、円弧状希土類磁石の外周面を軟磁性フレ−ム内周面に沿わせながら固定し、当該磁石の外周部分の周方向両端面に軟磁性フレ−ムがバックヨ−クとして作用しない部分を形成し、球状または楕円状断面の軟磁性材料を介した状態で不飽和着磁する。或いはまた、円弧状希土類磁石の外周面を軟磁性フレ−ム内周面に沿わせながら固定し、当該磁石の周方向両端面に沿った軟磁性フレ−ムと着磁ヨ−ク先端面とに空隙部分を形成し、球状または楕円状断面の軟磁性材料を介した状態で不飽和着磁する。なお、円弧状希土類磁石の外周部分の周方向両端面を圧縮成形型の曲率面と角度θを５０〜８２度の直線面とし、外周部分の周方向両端面に軟磁性フレ−ムがバックヨ−クとして作用しない部分を形成し、球状断面の軟磁性材料を介した状態で不飽和着磁するとコギングトルクを更に低減することができる。
【００１３】
さらに、軟磁性フレ−ム内周面に沿わせて対向固定した一対の円弧状希土類磁石を不飽和着磁したのち、加熱して、磁極中心よりも周方向両端面の減磁率を大としてもコギングトルクを更に低減することができる。
上記、本発明で言う希土類−鉄系急冷凝固薄片とは、例えばＪ．Ｆ．Ｈｅｒｂｅｓｔ，ＲａｒｅＥａｒｔｈ−Ｉｒｏｎ−ＢｏｒｏｎＭａｔｅｒｉａｌｓ；ＡＮｅｗＥｒａｉｎＰｅｒｍａｎｅｎｔＭａｇｎｅｔｓ”Ａｎｎ．Ｒｅｖ．Ｓｃｉ．Ｖｏｌ−１６．（１９８６）に記載されているようにＮｄ：Ｆｅ：Ｂを２：１４：１に近い割合で含む溶湯合金を急冷凝固し、熱処理によって磁気的に等方性のＮｄ₂Ｆｅ₁₄Ｂ相を析出させたもので、Ｎｄ₂Ｆｅ₁₄Ｂ相は単磁区臨界寸法約３００ｎｍ以下であれば差し支えない。或いは、希土類−鉄系急冷凝固薄片が熱処理により例えばαＦｅ，Ｆｅ₃Ｂ系などのソフト磁性相とＮｄ₂Ｆｅ₁₄Ｂ，Ｓｍ₂Ｆｅ₁₇Ｎ₃系ハ−ド磁性相とが強い交換結合によって結ばれたナノコンポジット系であっても差し支えない。このような希土類−鉄系急冷凝固薄片に特定した理由は、この希土類磁石は着磁界の関数として残留磁束密度Ｂｒと保磁力Ｈｃとが同時に、次第に大きくなる性質をもっているからである。
したがって、仮に不飽和着磁状態でもバランスのよい減磁曲線が得られる。たとえば、着磁の際、円弧状希土類磁石の磁極中心と周方向両端部とでパ−ミアンスが異なるような磁気回路構成とし、例えば球状或いは楕円状断面の軟磁性材料を介した状態とすると、円弧状希土類磁石を着磁する際、球状或いは楕円状断面の軟磁性材料の反磁界作用で周方向端部は磁極中心よりも小さな減磁曲線（残留磁束密度Ｂｒと保磁力Ｈｃｂ）となる。このことは、希土類−鉄系急冷凝固薄片を使った不飽和着磁によって、磁極中心と周方向両端部とが同一材質であるにも拘わらず、あたかも異なる磁気性能をもった磁石で一体的な永久磁石界磁を形成すると言うこともできる。
【００１４】
ただし、本発明で言う磁気的に等方性の希土類−鉄系急冷凝固薄片が３００ｎｍ以下のＲＥ₂ＴＭ₁₄Ｂ（ＲＥはＮｄ，Ｐｒ．ＴＭはＦｅ，Ｃｏ）相からなる固有保磁力Ｈｃｉ８〜１０ｋＯｅ、残留磁化７．４〜８．６ｋＧであるか、或いはまた、αＦｅ，Ｆｅ₃Ｂ，Ｆｅ₂Ｂなどの軟磁性相とＲＥ₂ＴＭ₁₄Ｂなどの硬磁性相とを有するナノコンポジット構造の磁気的に等方性の希土類−鉄系急冷凝固薄片を含むもので、しかも希土類−鉄系急冷凝固薄片を結合剤とともに圧縮成形した一対の円弧状希土類磁石の場合には、外周面を軟磁性フレ−ム内周面に対向して沿わせ、当該磁石の周方向両端部をバネで押圧固定して永久磁石界磁型小型直流モ−タとする。すると機械的に脆い圧縮成形による円弧状希土類磁石でも軟磁性フレ−ムに欠落なく組込むことができる、また、希土類−鉄系急冷凝固薄片を結合剤とともに押出成形した一対の円弧状希土類磁石の場合には、若干撓む性質があるので外周面を軟磁性フレ−ム内周面に対向して沿わせ、当該磁石の周方向両端部と軟磁性フレ−ムに設けた係合突起で嵌合固定して永久磁石界磁型小型直流モ−タとしても差し支えない。
【００１５】
一方、希土類−鉄系急冷凝固薄片の合金組成がＮｄまたは／およびＰｒを１３〜１５原子％、Ｂを５〜１０原子％、Ｃｏを０〜２０原子％、残部がＦｅ製造上不可避な不純物を主成分とした非晶質または／および３００ｎｍ以下のＲＥ₂ＴＭ₁₄Ｂ（ＲＥはＮｄ，Ｐｒ．ＴＭはＦｅ，Ｃｏ）相を有する場合、結晶化温度以上７５０℃以下で圧縮成形した磁気的に等方性、または圧縮方向に僅かに異方化した磁気的に、ほぼ等方性のフル密度円弧状希土類磁石を使用した永久磁石界磁型小型直流モ−タではフル密度磁石の加熱手段が希土類−鉄系急冷凝固薄片への直接通電とすることが好ましく、フル密度磁石の周方向外周両端面を除く磁極中心外周面と軟磁性バックヨ−クとを直接通電により一体化することもできる。これらの円弧状希土類磁石も機械的には脆弱であるから、当該磁石の外周面を軟磁性フレ−ム内周面に対向して沿わせ、周方向両端部をバネで押圧固定することが好ましい。
【００１６】
以上のように、本発明は、着磁界の関数として残留磁束密度Ｂｒと保磁力Ｈｃとが同時に、次第に大きくなる性質をもち、仮に不飽和着磁状態でもバランスのよい減磁曲線が得られる希土類−鉄系急冷凝固薄片を利用するもので、例えば厚さ１ｍｍ未満の円弧状に固めて永久磁石界磁とし、着磁の際に磁極中心と周方向両端部とでパ−ミアンスが異なるような磁気回路構成とする、更に、球状または楕円状断面の軟磁性材料を一対の円弧状希土類磁石の中心に配置して、その反磁界を利用する。そして円弧状希土類磁石を着磁する際の反磁界反作用で磁極中心を周方向端部よりも大きな減磁曲線（残留磁束密度Ｂｒと保磁力Ｈｃｂ）とする。このことは、希土類−鉄系急冷凝固薄片を使った不飽和着磁によって、磁極中心と周方向両端部１１とが同一材質であるにも拘わらず、あたかも異なる磁気性能をもった磁石で一体的な永久磁石界磁を形成する効果があり、従来から知られている磁石形状によるコギングトルク低減手段と組合わせることで、より小型高出力で回転精度の高い永久磁石界磁型直流モ −タを製造することができる。
このように小型直流モータは、ＣＤ，ＭＤ等を備えるディスクフィーダ、光ピックアップ装置を用いるとよい。
ところで、本件発明は特公昭５８−１４０５４号の公報の着磁方法と一見似ているが、本件発明と特公昭５８−１４０５４号とは大きく異なるので、この相違点をここで主張しておく。
本件発明は、希土類磁石減磁曲線を部分的に変えるために、球状の断面を有する純鉄を希土類磁石の間に挟み、更にこの希土類磁石を着磁ヨークによって挟むため、純鉄から反磁界が発生し、希土類磁石の減磁曲線を、端部が低く中央部を高くすることができる。
このような方法を用いることで、希土類磁石の端部を不飽和着磁し、減磁曲線の波形をコントロールすることが可能となる。これは、保磁力の高い希土類磁石で可能なことであり、保磁力の低い磁石では、本実施例に示す方法を取ったとしても、中央部も端部も小さな着磁界により着磁してしまうので、端部の減磁曲線を低くした着磁は行えない。
なお、特公昭５８−１４５０５４号公報の出願日である１９８０年は、フェライト磁石が主流であり、１９９３年ころから使われ始めた、希土類磁石のように保磁力の高い磁石
はまだ開発されておりません。
特公昭５８−１４５０５４号公報の着磁方法は、公報中の第１図〜第７図（ａ）で示すような方法で着磁を行い、その結果磁束密度分布が第１図〜第７図（ｂ）の状態になっている。しかし、このような、永久磁石を二つの着磁ヨークの間に挟んで着磁する方法は、反磁界が発生するような方法ではないため、希土類磁石のように保持力が高い磁石を着磁しようとすると本件発明のように反磁界が発生しないため、本件発明のように、希土類磁石の端部を不飽和着磁状態にすることはできない。
【００１７】
【実施例】
以下、本発明を更に詳しく説明する。但し、本発明は実施例に限定されるものではない。
【００１８】
［結合剤を用いた円弧状希土類−鉄系磁石Ｍ１、Ｍ２の製造］
希土類−鉄系急冷凝固薄片はＭａｇｎｅｑｕｅｎｃｈＩｎｔｅｒｎａｔｉｏｎａｌＩｎ、Ｃｏ．製（商品名：ＭＱＰ−Ｂ）、合金組成Ｎｄ₁₂Ｆｅ₇₇Ｃｏ₅Ｂ₆、結晶粒子径２０〜５０ｎｍの磁気的に等方性のＮｄ₂Ｆｅ₁₄Ｂ相を有する厚さ２０〜３０μｍの薄片を用いた。先ずエポキシ樹脂のアセトン溶液（固形分換算で２．５重量％）と希土類−鉄系急冷凝固薄片９７．５重量％とを湿式混合し、アセトンを蒸発させ、室温で固体のブロックとした。次に室温で固体のブロックを解砕、分級し、粒子径を、それぞれ５００、３５０、２５０、２１２、１５０μｍの顆粒状コンパウンドとし、最後にステアリン酸カルシウム粉末を０．２〜０．６重量部添加した。
【００１９】
上記、粒子径を、それぞれ５００、３５０、２５０、２１２、１５０μｍ以下とした顆粒状コンパウンドを粉末成形機に供して体積秤量し、厚さ１ｍｍ未満の円弧状圧粉体を８ｔｏｎ／ｃｍ²で圧縮成形し、次に、それら円弧状圧粉体を１６０℃で２分間加熱硬化して、所謂圧縮成形による外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍの円弧状希土類磁石Ｍ１を各３０個作成した。
円弧状希土類磁石の最大厚さ０．９ｍｍに対する変動幅（ｎ＝３０）と、もとの顆粒状コンパウンドの粒子径上限とは、下式の関係にある（回帰式の相関係数は０．９８８）。
【００２０】
Ａ＝０．０００３Ｐ²−０．０７１８Ｐ＋２４．７４５ …… （１）
但し、上式中、Ａは厚さ変動幅±μｍ、Ｐは顆粒状コンパウンドの粒子径上限μｍである。回帰式から明らかなように、顆粒状コンパウンドの粒子径を２５０μｍ以下とすれば厚さ１ｍｍ未満の薄肉円弧状希土類磁石Ｍ１の厚さ変動幅は±３０μｍ以下、密度６．０ｇ／ｃｍ³となる。
【００２１】
一方、同じ希土類−鉄系急冷凝固薄片９５重量％と１２−ナイロン５重量％を２６０℃で混練したペレットを使い、特開平６−２３６８０７号公報に開示されている押出成形で成形ダイス先端温度を１２−ナイロンの融点以下の１７５℃に設定し、外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍの円弧状希土類磁石Ｍ２を製造したところ、最大肉厚０．９ｍｍ部分の厚さ変動は±３０μｍ、密度５．７ｇ／ｃｍ³であった。以上、顆粒状コンパウンドの圧縮成形による薄肉円弧状希土類磁石Ｍ１、押出成形による薄肉円弧状希土類磁石Ｍ２を製造した。
【００２２】
［結合剤を用いない円弧状希土類−鉄系磁石Ｍ３の製造］
希土類−鉄系急冷凝固薄片はＭａｇｎｅｑｕｅｎｃｈＩｎｔｅｒｎａｔｉｏｎａｌＩｎ，Ｃｏ．製（商品名：ＭＱＰ−Ｃ），合金組成Ｎｄ₁₄Ｆｅ₆₅Ｃｏ₁₅Ｂ₆、結晶粒子径２０〜５０ｎｍの磁気的に等方性のＮｄ₂Ｆｅ₁₄Ｂ相を有する厚さ２０〜３０μｍの薄片を用いた。この薄片を計量し、サイアロン製ダイと一対の電極を兼ねるＷＣ−Ｃｏ製パンチとで形成した成形型キャビティに充填した。次いで、ＷＣ−Ｃｏ製パンチを介してキャビティに充填した希土類−鉄系急冷凝固薄片を圧力３００ｋｇｆ／ｃｍ²で圧縮しながら電流密度１００Ａ／ｃｍ²のパルス電流を０．５ｓｅｃＯＮ−０．５ｓｅｃＯＦＦで１０回繰返し通電した。然る後３００Ａ／ｃｍ²の直流電流を通電した。直流電流による物体の温度上昇速度ΔＴ／Δｔ（℃／ｓｅｃ）は電流密度の二乗と電気抵抗に比例し、物体の比熱と比重に反比例する関係にあるから、温度上昇速度は、ほぼ電流密度の値で律則される。
【００２３】
通電約６０ｓｅｃ後には厚さ２ｍｍのダイ温度がＮｄ₂Ｆｅ₁₄Ｂ相の結晶化温度約６００℃を越え、薄片の軟化による塑性変形で圧縮方向の緻密化が始まったが、緻密化が終了した時点で通電を停止したときは通電後約８０ｓｅｃ、ダイ温度は７１０℃であった。冷却後に熱間圧縮成形した外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍの円弧状希土類磁石Ｍ３を取出すと、密度は７．５３〜７．５５ｇ／ｃｍ³であった。なお、このフル密度磁石は全ての厚み精度が、ほぼキャビティへの薄片充填量に単純に依存する。また、結合剤を含む磁石のような成形型から離型する際のスプリングバックがないので内半径や外半径寸法は型形状が、そのまま転写される。
【００２４】
［円弧状希土類磁石Ｍ１，Ｍ２，Ｍ３の押圧許容応力と軟磁性フレ−ムへの固定］
上記、希土類−鉄系急冷凝固薄片を外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍの固めた本発明の対象となる円弧状希土類磁石Ｍ１，Ｍ２，Ｍ３の、好ましい軟磁性フレ−ムへの固定の方法について以下に説明する。
【００２５】
図１は、円弧状希土類磁石Ｍ１，Ｍ２，Ｍ３の押圧許容応力の温度依存性を示す特性図である。但し、押圧許容応力は図中に示すように磁石の最大厚さ部分を押圧して磁石Ｍ１，Ｍ２，Ｍ３が破損したときの応力ｋｇｆである。また、図中Ｍ１は圧縮成形した円弧状希土類磁石、Ｍ２は押出成形した円弧状希土類磁石、Ｍ３は熱間圧縮成形した円弧状希土類磁石である。
図から明らかなように、Ｍ１は、Ｍ２に比べると室温の押圧許容応力が６０％未満と低く、しかも撓みなく脆い。したがって、Ｍ１は特開平１０−２０１２０６号公報や特開平１１−１８３９０号公報記載の軟磁性フレ−ムの係合部分に円弧状希土類磁石を撓ませながら嵌合固定すると、割れや欠落が生じるために工業的規模で歩留まりよく軟磁性フレ−ムに組込むことができない。Ｍ１と軟磁性フレ−ムとの接着は可能だが、特開平１０−２０１２０６号公報や特開平１１−１８３９０号公報にも記載されているように、この種の永久磁石界磁型小型直流モ−タでは接着によって磁石を軟磁性フレ−ムに組込むことは好まれない。
しかしながら、図のようにＭ１の室温での押圧許容応力は６ｋｇｆを越えている。また、Ｍ２と比べれば、概ね１２０℃の高温下まで押圧に対する許容応力は、ほぼ一定である。したがって、図１に示したように、軟磁性フレ−ム２の内周に沿って配置した一対の磁石Ｍ１の周方向両端部を、例えばＵ字形状のバネ４で押圧することで磁石Ｍ１を軟磁性フレ−ム２と固定する方法が好ましい。なお、軟磁性フレ−ムと磁石の固定の強さはバネの押圧力に依存する。一般に押圧力０．５ｋｇｆ以下で実使用条件に耐え得るから押圧許容応力と、押圧許容応力の温度依存性から永久磁石界磁型小型直流モ−タの１２０℃の最高温度に至る全実使用温度域で押圧許容応力に対する安全率は１０倍以上となる。
【００２６】
したがって磁石の固定に対する十分な信頼性を備えている。一方、Ｍ２は若干撓む性質があるため、撓ませて軟磁性フレ−ムに挿入し、その係合部を利用して嵌合固定することができる。更に、Ｍ３は押圧許容応力が高いが、Ｍ１と同様に機械的には脆弱であるから、Ｍ１と同様な軟磁性フレ−ムへの固定方法を採ることが好ましい。
【００２７】
［軟磁性フレ−ムに組込んだ円弧状希土類磁石Ｍ１の不飽和着磁とモ−タ特性］
上記、希土類−鉄系急冷凝固薄片を外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍに固めた本発明の対象となる円弧状希土類磁石Ｍ１を主体に反磁界を利用した不飽和着磁方法と永久磁石界磁型小型直流モ−タの特性について説明する。
【００２８】
（１）固有保磁力と着磁性
図３は合金組成Ｎｄ_X［Ｆｅ_0.8Ｃｏ_0.2］_1-XＢ₆の希土類−鉄系急冷凝固薄片を結合剤とともに、密度６ｇ／ｃｍ³に圧縮成形した磁石Ｍ１における固有保磁力Ｈｃｉと着磁性との関係を示す特性図である。ただし、着磁性は２４ｋＯｅまたは６０ｋＯｅでパルス着磁したΦ５ｍｍ（Ｌ／Ｄ＝１）磁石の［ＢＨ］ｍａｘの比とした。図のように、磁気的に等方性の希土類−鉄系急冷凝固薄片の固有保磁力Ｈｃｉが８ｋＯｅであっても２４ｋＯｅ程度の着磁界Ｈｍでは不飽和着磁である。また、固有保磁力Ｈｃｉが１０ｋＯｅを越えると着磁性が大きく低下する。本発明では、少なくとも磁極中心部分はフル着磁の９０％を越える程度が好ましく、そのためには希土類−鉄系急冷凝固薄片の固有保磁力Ｈｃｉが１０ｋＯｅ以下であることが好ましい。
【００２９】
熱間圧縮成形磁石Ｍ３はＮｄ₂Ｆｅ₁₄Ｂ相の結晶化温度以上での塑性変形能発現ため、希土類元素（Ｎｄ／Ｐｒ）の量をＮｄ₂Ｆｅ₁₄Ｂ化学量論組成より、やや多い１３原子％以上としなければならず、熱安定性確保の目安となるＮｄ₂Ｆｅ₁₄Ｂ相の単磁区臨界寸法内で固有保磁力Ｈｃｉを１０ｋＯｅ以下とすることが困難である。
【００３０】
熱安定性確保の目安となるＮｄ₂Ｆｅ₁₄Ｂ相の単磁区臨界寸法内で固有保磁力Ｈｃｉ８〜１０ｋＯｅが得られる希土類−鉄系急冷凝固薄片はＮｄ₂Ｆｅ₁₄Ｂ化学量論組成に近い合金組成のもので、希土類元素（Ｎｄ／Ｐｒ）の量を１２原子％以下とする必要がある。これを固めるには樹脂などの結合剤が必要で、そのような結合剤と共に所定形状に圧縮成形または押出成形した円弧状希土類磁石Ｍ１，Ｍ２が着磁性の観点からは好ましい。なお、圧縮成形の方が、押出成形よりも希土類−鉄系急冷凝固薄片をより高密度充填できるので、永久磁石界磁と電機子との空隙に、より強い静磁界を得るには固有保磁力Ｈｃｉ８〜１０ｋＯｅの希土類−鉄系急冷凝固薄片を結合剤とともに圧縮成形した円弧状希土類磁石Ｍ１が、本発明の永久磁石界磁型小型直流モ−タには好適である。
【００３１】
（２）着磁界の関数としての残留磁束密度と保磁力
図４は、上記希土類−鉄系急冷凝固薄片を固めた磁石の残留磁束密度Ｂｒ、保磁力Ｈｃｂ（Ｂ−Ｈ曲線の保磁力）の着磁界Ｈｍ依存性を示す。ただし、着磁界Ｈｍ５０ｋＯｅを１００％として規格化したものである。一般に永久磁石界磁型小型直流モ−タの界磁磁石の着磁に使用される１０〜４０ｋＯｅの範囲でみると、磁気的に等方性の希土類−鉄系急冷凝固薄片は、図のように固有保磁力Ｈｃｉに拘わらず、着磁界の関数として残留磁束密度Ｂｒや保磁力Ｈｃｂが次第に大きくなるため不飽和着磁状態であってもバランスのよい減磁曲線が得られる。なお、従来から永久磁石界磁型小型直流モ−タに一般的に用いられてきたフェライト系磁石では低い着磁界Ｈｍでも急峻に磁化される特性をもつ。したがって、不飽和着磁状態でバランスのよい安定した減磁曲線を得ることはできない。
【００３２】
（３）反磁界作用による永久磁石界磁の不飽和着磁
図５（ａ）、（ｂ）は反磁界を利用した軟磁性フレ−ムに組込んだ永久磁石界磁の不飽和着磁方法の一例を示す要部断面構成図であり、図５（ｃ）は通常の着磁方法を示す要部断面構成図である。ただし、図中１は円弧状希土類磁石、２は軟磁性フレ−ム、４は円弧状希土類磁石１を押圧固定するＵ字形状のバネ、５は一様な球状断面を有する純鉄である。図５（ａ）は円弧状希土類磁石１の外周面を軟磁性フレ−ム２の内周面に沿わせながら固定し、当該磁石１の外周部分の周方向両端面に軟磁性フレ−ム２がバックヨ−クとして作用しない部分を形成し、球状断面の軟磁性材料５を介した構成である、図５（ｂ）は、円弧状希土類磁石１の外周面を軟磁性フレ−ム２の内周面に沿わせながら固定し、当該磁石１の周方向両端面に沿った軟磁性フレ−ム２の中央部と着磁ヨ−ク６の先端部とを接し、軟磁性フレーム２の両端部と着磁ヨークとの間に空隙部分を形成する。更に、磁石１の間に球状断面の軟磁性材料５を介して、磁石１の端部と軟磁性材料５との間に空隙を設け、磁石１の中央部と軟磁性材料５とを接した状態にする。
【００３３】
着磁界Ｈｍが作用すると図５（ａ）、（ｂ）において、球状断面を有する純鉄５も磁化され、同時に一様な反磁界−ＮＩが発生する。発生した反磁界−ＮＩは球状断面を有する純鉄５に一様に発生し、その磁力線は表面磁極から湧き出し、磁束密度線の如く渦をつくらず、円弧状希土類磁石１の周方向両端部では着磁界Ｈｍに対して反作用する。なお、Ｕ字形状のバネを断面球状または楕円状の軟磁性材とすれば、円弧状希土類磁石１の周方向両端部に対して直接同様な反磁界作用が起こる。したがって、円弧状希土類磁石１を構成する個々の磁気的に等方性の希土類−鉄系急冷凝固薄片は、着磁界Ｈｍと反磁界−ＮＩに依存して着磁されることになり、図５（ｃ）のような一様な着磁界Ｈｍによる着磁状態とはＨｍの水準が同じでも全く異なるもので、本発明に係る永久磁石界磁型小型直流モ−タの製造方法の骨子となる。
【００３４】
（４）反磁界作用によるコギングトルク低減
希土類−鉄系急冷凝固薄片を外半径３．６５ｍｍ、内半径３．２５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍに圧縮成形し円弧状希土類磁石Ｍ１を軟磁性フレ−ムに組込んで、図５（ａ）、（ｂ）の着磁界Ｈｍ１５〜３０ｋＯｅの範囲で着磁した。次に、電機子３を組込んで永久磁石界磁型小型直流モ−タとし、それらの誘起電圧とコギングトルクを測定した。図６は誘起電圧とコギングトルクの関係を示す特性図である。ただし、図中の本発明例は図５（ａ）の着磁、比較例は図５（ｃ）の着磁によるものである。図から明らかなように、本発明例は軟磁性フレ−ムに組込んだ永久磁石界磁を、反磁界を利用して不飽和着磁する。すると同じ誘起電圧水準であっても明らかに、コギングトルクが４０％も少ない永久磁石界磁型小型直流モ−タが製造できる。
【００３５】
なお、上記永久磁石界磁型小型直流モ−タを分解し、円弧状磁石１を取出し、更に磁極中心部分と周方向両端部を切出した小片の固有保磁力ＨｃｉをＶＳＭで求めた。すると、比較例で示した図５（ｃ）の円弧状希土類磁石は部位による大きな差は見られず、Ｈｃｉは一様に７．９〜８．２ｋＯｅであった。一方、本発明例で示した図５（ａ）の円弧状希土類磁石の磁極中心部分は何れも比較例と同じ７．９〜８．２ｋＯｅであった。しかし、周方向両端部のＨｃｉは７．０〜７．５ｋＯｅと磁極中心部とは異なるＨｃｉ値を示した。このことは、本発明例における円弧状希土類磁石が磁極中心部と周方向両端部で、同じ性能をもつ一様な材質の磁石でありながら異なった減磁曲線（Ｂ−Ｈ曲線をもつ磁石であると言える。そして、磁極中心から周方向端部にかけて弱い減磁曲線を与えると、磁石の形状が同一であってもコギングトルクが低減することを示唆している。
【００３６】
（５）反磁界と磁石形状を組合わせたコギングトルク低減
図７は円弧状希土類磁石１のスラスト方向中央外周部分（距離１２．５ｍｍ）の周方向両端面を圧縮成形型の曲率面から角度θの直線面で軟磁性フレ−ムとの間にバックヨ−クのない空隙部を形成したとき、図１に示した角度θとコギングトルク、および誘起電圧の関係を示す特性図である。ただし、磁石の形状は外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍで、着磁は図５（ａ）の構成で、着磁界Ｈｍに対して反磁界−ＮＩによる反作用を伴う着磁を施している。なお、ここで使用した永久磁石界磁型小型直流モ−タにおいて角度θが９０度の場合の誘起電圧Ｖは０．２１８ｍＶ／ｒｐｍ、コギングトルクＣｔは１．１５ｇ−ｃｍで、これを基準に規格化した。
【００３７】
誘起電圧Ｖは図中に示す回帰式ように角度θに対して直線的に低下する。しかし、θが９０度から５０度になっても誘起電圧Ｖの低下は５％に過ぎない。一方のコギングトルクＣｔは角度θに対して大きく２次関数的な変化を示し、角度θが６５度程度でその変化が最大となる。この値は何と、基準とした９０度に対して７０％近いコギングトルク低下となる。また、８２度から５０度の範囲であっても角度９０度を基準として４０％以上のコギングトルクが低減される。
【００３８】
以上の効果は、着磁界の関数として残留磁化Ｂｒと保磁力Ｈｃがともに次第に増大し、不飽和着磁状態であってもバランスよい減磁曲線が得られる磁気的に等方性の希土類−鉄系急冷凝固薄片を固めた薄肉円弧状希土類磁石を、反磁界作用を利用して不飽和着磁する際、周方向両端部に軟磁性フレ−ムによるバックヨ−クのない部分があり、あたかも大きく異なる磁気性能をもった磁石を一体的に永久磁石界磁としたことによる。
【００３９】
（５）反磁界と熱減磁を組合わせたコギングトルク低減
図７は円弧状希土類磁石の外周部分（距離１２．５ｍｍ）の周方向両端面を圧縮成形型の曲率面から角度θ６２度の直線面でソフト磁性フレ−ムとの間にバックヨ−クのない空隙部を形成し、図５（ａ）の構成で、コンデンサ容量２０００μＦ、１５００〜２４００Ｖで４段階の不飽和着磁を施した。これを１４０℃に５分間暴露した熱減磁前後のコギングトルク、および誘起電圧の変化を示す特性図である。ただし、磁石の形状は外半径３．６５ｍｍ、内半径３．５５ｍｍ、最大厚さ０．９０ｍｍ、スラスト方向距離１５．５ｍｍであり、２０００μＦ、２４００Ｖの最大着磁界で熱減磁まえのコギングトルク、および誘起電圧を基準に規格化したものである。なお、ここで使用した永久磁石界磁型小型直流モ−タにおける基準の誘起電圧Ｖは０．２１４ｍＶ／ｒｐｍ、コギングトルクＣｔは０．４６ｇ−ｃｍであった。
【００４０】
図から明らかなように、本発明に掛かる永久磁石界磁型小型直流モ−タを熱減磁すると誘起電圧Ｖの低下は概ね０．５％以下であるにも拘わらず、コギングトルクを更に１０％近く低下させることができる。これは、軟磁性フレ−ム内周面に沿わせて押圧固定した円弧状希土類磁石を図５（ａ）の構成で反磁界を利用して着磁したのち、加熱による初期減磁を与える。すると、大きな減磁曲線（残留磁束密度Ｂｒと保磁力Ｈｃｂが大）の磁極中心部分の減磁率は小となり、周方向両端面の小さな減磁曲線の減磁率が大となる。その結果、空隙磁束密度分布はより正弦波状となり、減磁による誘起電圧の低下率よりも大きなコギングトルク低下率が得られる。
【００４１】
【発明の効果】
以上のように、本発明は、着磁界の関数として残留磁束密度Ｂｒと保磁力Ｈｃとが同時に、次第に大きくなる性質をもち、仮に不飽和着磁状態でもバランスのよい減磁曲線が得られる希土類−鉄系急冷凝固薄片を利用するもので、例えば厚さ１ｍｍ未満の円弧状に固めて永久磁石界磁とし、着磁の際に磁極中心と周方向両端部とでパ−ミアンスが異なるような磁気回路構成とする、とくに球状または楕円状断面の軟磁性材料を一対の円弧状希土類磁石の中心に配置する。そして円弧状希土類磁石を着磁する際の反磁界作用で周方向端部１１を磁極中心よりも、小さな減磁曲線（残留磁束密度Ｂｒと保磁力Ｈｃｂ）とする。このことは、希土類−鉄系急冷凝固薄片を使った不飽和着磁によって、磁極中心と周方向両端部１１とが同一材質であるにも拘わらず、あたかも異なる磁気性能をもった磁石で一体的な永久磁石界磁を形成する効果があり、従来から知られている磁石形状によるコギングトルク低減手段と組合わせることで、より小型高出力で回転精度の高い永久磁石界磁型直流モ−タを製造することができる。
【図面の簡単な説明】
【図１】（ａ）本発明例にかかるモ−タの要部断面図
（ｂ）本発明例にかかるモ−タの磁石の斜視外観図
【図２】押圧許容応力の温度依存性を示す特性図
【図３】固有保磁力と着磁性を示す特性図
【図４】着磁界の関数としての残留磁束密度と保磁力の関係を示す特性図
【図５】（ａ）、（ｂ）、（ｃ）は反磁界を利用した永久磁石界磁不飽和着磁の要部断面図
【図６】反磁界によるコギングトルク低減を示す特性図
【図７】反磁界と磁石形状によるコギングトルク低減を示す特性図
【図８】反磁界と熱減磁を組合わせたコギングトルク低減を示す図
【図９】減磁曲線の大小関係を示す図[0001]
BACKGROUND OF THE INVENTION
The present invention is, for example, a compact and high output using an arc-shaped rare earth magnet that rotates with high accuracy while suppressing a starting voltage and a starting current used in an audio visual device such as an optical pickup of MD, CD-ROM, and the like. The present invention relates to a small permanent magnet field type DC motor having a low cogging torque.
[0002]
[Prior art]
FIGS. 1A and 1B show a cross section of a main part of a permanent magnet field type small DC motor which is an object of the present invention, and an arc-shaped magnet used therefor. In the figure, 1 is a pair of arc-shaped permanent magnets, 2 is a soft magnetic frame, 3 is a brush-commutator, and an armature including an armature shaft and a bearing, 4 is a pair of arc-shaped permanent magnets 1 and a soft magnetic frame. This is a U-shaped spring that is pressed and fixed to the frame 2. Such permanent magnet field type small DC motors are required to have a smaller motor, higher output, and high precision rotation performance, as with other permanent magnet motors.
[0003]
However, in general, it has been difficult to reduce the size of the permanent magnet field type small DC motor while maintaining the output of the motor when the diameter of the armature 3 becomes small. In particular, in the case of ferrite magnets, the permanent magnet field 1 and armature 3 are reduced when the size is reduced from the low maximum energy product [BH] max regardless of sintering, compression, injection, or extrusion using resin as a binder. A sufficiently strong static magnetic field could not be obtained in the gap, and the motor output was significantly reduced. Therefore, there has been a demand for an arc-shaped rare earth magnet having a so-called high [BH] max that can obtain a strong static magnetic field in the gap between the permanent magnet field 1 and the armature 3 even if the motor is downsized.
[0004]
If the permanent magnet field type small DC motor is miniaturized to be an arc-shaped rare earth magnet having a maximum thickness of less than 1 mm, the magnet manufacturing method is limited. For example, a melt flow material composed of various kinds of rare earth magnet powders from thermoplastic anisotropy to isotropic described in JP-A-6-236807 and a thermoplastic resin is fed into a mold, and the mold In particular, a method of manufacturing an arc-shaped rare earth magnet that is extruded while being cooled below the melting point of a thermoplastic resin is disclosed. According to this, a thin arc-shaped rare earth magnet having a maximum thickness of 0.9 mm ± 30 μm can be manufactured by extrusion molding.
By the way, cogging is one of the problems of the permanent magnet field type small DC motor using the arc-shaped rare earth magnet as described above, which can obtain a stronger static magnetic field in the gap with the armature 3 than the ferrite magnet. There is an increase in torque. This is because the armature core teeth 31 and the slots 32 are present on the outer peripheral surface of the armature 3 facing the permanent magnet field 1, and therefore torque pulsation due to the change in permeance with the rotation of the armature 3. This is because. In particular, the cogging torque is a problem in a small permanent magnet field type DC motor that is required in the present invention to have a small, high output and highly accurate rotation performance.
[0005]
The cogging torque reducing means by the shape of the arc magnet of the permanent magnet field type small DC motor irrespective of the rare earth magnet is made to have an unequal thickness by decentering the inner and outer peripheral curvature radius of the arc magnet, or The permeance of a magnet in which a uniform material is uniformly magnetized from the center of the magnetic pole to both ends in the circumferential direction can be changed by dropping the corners at both ends in the circumferential direction of the arc-shaped magnet so as to have an unequal thickness. (See, for example, Shogo Tanaka “Application of Permanent Magnets in Small Motors”, Preliminary Proceedings of Small Motor Technology Symposium, p7, 1983. (Kaihei 168820).
On the other hand, as in US Pat. No. 4,710,239, for example, 10 to 50 atomic% of rare earth element RE (Nd or / and Pr), 1 to 10 atomic% of B, and the balance is transition metal element TM, Amorphous rare earth-iron rapidly solidified flakes in which at least 60 atomic percent of the transition metal element is Fe are used as starting materials, and first, the magnet phase RE ₂ TM ₁₄ Isotropic full-density magnets with different thicknesses are made by compression at a crystallization temperature of B (about 600 ° C) or higher and 750 ° C or lower, and arc-shaped by hot plastic working at the same heating temperature. Finish the magnet. Then, the easy axis of magnetization is arranged in a direction perpendicular to the plastic flow according to the degree of hot plastic working, so RE ₂ TM ₁₄ B becomes a magnetically strong anisotropic rare earth magnet in the originally thick part. An arc-shaped magnet having such a highly anisotropic portion and an isotropic portion is disclosed.
[0006]
Using such arc-shaped rare earth magnets with different magnetic performance parts for permanent magnet field type DC motors, the demagnetization curve itself can be changed from the center of the magnetic pole to the circumferential direction, and the cogging torque can be reduced. It is also possible to smooth the change in air gap magnetic flux density distribution between the field magnet and the armature core so as to reduce it.
As described above, the inner and outer peripheral radii of curvature of a permanent magnet field type DC motor using an arc-shaped rare earth magnet are decentered to have an unequal thickness, or the corners of both ends in the circumferential direction of the arc-shaped magnet are dropped. The constant thickness changes the magnet's permeance from the center of the magnetic pole to both ends in the circumferential direction, and further changes the magnet's magnetic properties from the center of the magnetic pole to the circumferential direction, thereby reducing the cogging torque by different demagnetization curves. Thus, it is conceivable to control the gap magnetic flux density distribution between the field magnet and the armature core.
[0007]
However, the small permanent magnet field type DC motor that is the subject of the present invention is obtained by hot working a full-density magnet with a thickness starting from amorphous rare earth-iron rapidly solidified flakes. It is extremely difficult to manufacture an arc-shaped rare earth magnet having a portion with different magnetic performance, for example, an arc-shaped rare earth magnet having a thickness of less than 1 mm on an industrial scale. Further, when the anisotropy is increased, the temperature coefficient of the intrinsic coercive force is reduced. For this reason, there is a disadvantage that the thermal demagnetization at the center portion of the magnetic pole with increased anisotropy is large, and the torque decrease due to the thermal demagnetization of the permanent magnet field DC motor becomes large.
[0008]
[Problems to be solved by the invention]
If the permanent magnet field type small DC motor is miniaturized and the maximum thickness of the arc-shaped rare earth magnet used is less than 1 mm, the manufacturing method of the magnet is limited. For example, a melt flow material composed of various kinds of rare earth magnet powders from thermoplastic anisotropy to isotropic described in JP-A-6-236807 and a thermoplastic resin is fed into a mold, and the mold In particular, a method of manufacturing an arc-shaped rare earth magnet that is extruded while being cooled below the melting point of a thermoplastic resin is disclosed. According to this, for example, a thin-walled arc-shaped rare earth magnet having a maximum thickness of 0.9 mm ± 30 μm made of a material of 95% by weight of a magnetically isotropic rare earth-iron rapidly solidified flake and a thermoplastic resin mainly composed of 12 nylon. Can be produced by extrusion. However, extrusion molding must play the role of a rare-earth-iron rapidly solidified flake carrier when the thermoplastic resin is in a molten state.
Therefore, compared with rare earth magnets in which rare earth-iron rapidly solidified flakes are generally compression-molded with 3% by weight or less of thermosetting resin, the amount of rare earth-iron rapidly solidified flakes must be reduced. BH] max is lowered, and the static magnetic field in the gap portion between the permanent magnet field 1 and the armature 3 is weakened. Although it is conceivable to use magnetically anisotropic magnet powder to form a high [BH] max arc-shaped magnet, the first problem to be solved by the present invention is described in JP-A-6-236807. In compression molding, it is difficult to obtain a thin arc magnet having a maximum thickness of less than 1 mm with a dimensional accuracy of about ± 30 μm due to a large variation in weighing during molding. However, even if this problem is solved, the rare earth magnet by compression molding is mechanically fragile by the amount of resin.
[0009]
Therefore, the arc-shaped rare earth magnet formed by compression molding is fitted and fixed while bending the arc-shaped rare earth magnet in the engaging portion of the soft magnetic frame described in JP-A-10-201206 and JP-A-11-18390. "It is not possible. That is, the second problem to be solved by the present invention is a means for attaching to a soft magnetic frame suitable for the mechanical properties of an arc-shaped rare earth magnet by compression molding. Furthermore, because it is [BH] max higher than the arc-shaped rare earth magnet by extrusion molding, the third problem to be solved by the present invention is magnetically coupled with the cogging torque reducing means by the well-known magnet shape. Cogging torque is reduced by unsaturated magnetization such that the demagnetization curves at the magnetic pole center and both ends in the circumferential direction of the permanent magnet field in which the isotropic rare earth-iron rapidly solidified flakes are arc-shaped are different. The present invention provides a method for manufacturing a permanent magnet field type small DC motor.
The present invention is a small, high-power, magnetically isotropic rare-earth-based rapidly solidified flake that is obtained in a gap between the armature and the magnetic field, and provides a stronger static magnetic field than a ferrite magnet. An object of the present invention is to provide a method of manufacturing a permanent magnet field type DC motor having a low cogging torque.
[0010]
[Means for Solving the Problems]
In the present invention, the arc-shaped rare earth magnet mainly composed of rare earth-iron rapid solidified flakes is fixed along the inner peripheral surface of the soft magnetic frame, and unsaturated magnetized, thereby demagnetizing the magnetic pole center portion. This is a method for manufacturing a permanent magnet field type small DC motor in which arc-shaped rare earth magnets having demagnetization curves at both ends in the circumferential direction smaller than the curve are opposed to each other via an armature. When a portion where the soft magnetic frame does not act as a back yoke is formed on the surface, and unsaturated magnetization is performed through a soft magnetic material having a spherical cross section, the cogging torque can be further reduced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, an arc-shaped rare earth magnet mainly composed of a rare earth-iron rapidly solidified flake is fixed along an inner peripheral surface of a soft magnetic frame, and unsaturated magnetized with a strength of a magnetic field of 15 to 30 kOe. Thus, there is provided a method of manufacturing a permanent magnet field type small DC motor in which arc-shaped rare earth magnets having a demagnetization curve at both ends in the circumferential direction smaller than a demagnetization curve at a magnetic pole center portion are opposed via an armature. Basic. (The positional relationship between the large demagnetization curve and the small demagnetization curve is shown in FIG. 9.)
The term “unsaturated magnetization” as used herein means that the maximum magnetic force is not magnetized in the permanent magnet material in contrast to the saturation magnetization in which the maximum magnetic force is magnetized in the permanent magnet material. Once a permanent magnet material is magnetized, its magnetic force is permanently retained. Therefore, the permanent magnet material is generally used efficiently by keeping the permanent magnet with the maximum magnetic force. Unsaturated magnetization refers to magnetization in a state where there is a margin for holding magnetic force.
[0012]
However, the outer peripheral surface of the arc-shaped rare earth magnet is fixed along the inner peripheral surface of the soft magnetic frame, and a portion where the soft magnetic frame does not act as a back yoke is formed on both end surfaces in the circumferential direction of the outer peripheral portion of the magnet. It is formed and unsaturated magnetized through a soft magnetic material having a spherical or elliptical cross section. Alternatively, the outer peripheral surface of the arc-shaped rare earth magnet is fixed along the inner peripheral surface of the soft magnetic frame, and the soft magnetic frame and the front end surface of the magnetized yoke along the circumferential end surfaces of the magnet are fixed. A void portion is formed in the substrate, and unsaturated magnetization is performed through a soft magnetic material having a spherical or elliptical cross section. Note that both end surfaces in the circumferential direction of the outer peripheral portion of the arc-shaped rare earth magnet are straight surfaces with a curvature surface of the compression mold and an angle θ of 50 to 82 degrees, and soft magnetic frames are placed on both end surfaces in the circumferential direction of the outer peripheral portion. Cogging torque can be further reduced by forming a portion that does not act as a hook and unsaturated magnetization through a soft magnetic material having a spherical cross section.
[0013]
Furthermore, after a pair of arc-shaped rare earth magnets fixed opposite to each other along the inner peripheral surface of the soft magnetic frame is unsaturated and heated, the demagnetization rate at both ends in the circumferential direction is larger than the center of the magnetic pole. The cogging torque can be further reduced.
The rare earth-iron-based rapidly solidified flakes referred to in the present invention are, for example, J. F. Near Nd: Fe: B as described in Herbest, Rare Earth-Iron-Boron Materials; A New Era in Permanent Magnets “Ann. Rev. Sci. Vol-16. (1986). Nd is magnetically isotropic by rapid solidification of the molten alloy containing a proportion and heat treatment ₂ Fe ₁₄ B phase is precipitated, Nd ₂ Fe ₁₄ The B phase may have a single domain critical dimension of about 300 nm or less. Alternatively, the rare earth-iron rapidly solidified flakes can be treated by heat treatment, for example, αFe, Fe _Three Bd soft magnetic phase and Nd ₂ Fe ₁₄ B, Sm ₂ Fe ₁₇ N _Three There may be a nanocomposite system in which the system hard magnetic phase is connected by strong exchange coupling. The reason for specifying such a rare earth-iron-based rapidly solidified flake is that this rare earth magnet has the property that the residual magnetic flux density Br and the coercive force Hc increase gradually as a function of the applied magnetic field.
Therefore, if Unsaturated A well-balanced demagnetization curve can be obtained even in a magnetized state. For example, when magnetizing, a magnetic circuit configuration in which the permeance differs between the magnetic pole center of the arc-shaped rare earth magnet and both ends in the circumferential direction, for example, a state through a soft magnetic material having a spherical or elliptical cross section, When magnetizing the arc-shaped rare earth magnet, the demagnetizing curve (residual magnetic flux density Br and coercive force Hcb) is smaller at the end in the circumferential direction than the magnetic pole center due to the demagnetizing effect of the soft magnetic material having a spherical or elliptical cross section. This is because unsaturation magnetization using rare earth-iron rapidly solidified flakes makes it possible to integrate the magnets with different magnetic performances even though the magnetic pole center and circumferential ends are the same material. It can also be said that a permanent magnet field is formed.
[0014]
However, the magnetically isotropic rare earth-iron rapidly solidified flakes referred to in the present invention are 300 nm or less in RE. ₂ TM ₁₄ B (RE is Nd, Pr.TM is Fe, Co) phase and has an intrinsic coercive force Hci8 to 10 kOe, residual magnetization 7.4 to 8.6 kG, or αFe, Fe _Three B, Fe ₂ RE and soft magnetic phase such as B ₂ TM ₁₄ A pair of magnetically isotropic rare earth-iron rapidly solidified flakes having a nanocomposite structure having a hard magnetic phase such as B, and a rare earth-iron rapidly solidified flakes compression-molded with a binder In the case of an arc-shaped rare earth magnet, the permanent magnet field type small DC motor is formed by placing the outer peripheral surface facing the inner peripheral surface of the soft magnetic frame and pressing and fixing both circumferential ends of the magnet with springs. And Then, even in the case of a pair of arc-shaped rare earth magnets in which arc-shaped rare earth magnets by mechanically brittle compression molding can be incorporated into the soft magnetic frame without loss, and a rare earth-iron rapidly solidified flake is extruded together with a binder. Has a slightly bendable nature so that the outer peripheral surface is opposed to the inner peripheral surface of the soft magnetic frame, and is engaged with both circumferential ends of the magnet by engaging protrusions provided on the soft magnetic frame. It can be fixed and used as a permanent magnet field type small DC motor.
[0015]
On the other hand, the alloy composition of the rare earth-iron rapidly solidified flakes is Nd or / and Pr is 13 to 15 atomic%, B is 5 to 10 atomic%, Co is 0 to 20 atomic%, and the balance is inevitable impurities in Fe production. Amorphous as a main component and / or RE of 300 nm or less ₂ TM ₁₄ When B (RE is Nd, Pr.TM is Fe, Co) phase, it is magnetically isotropically compression-molded above the crystallization temperature and below 750 ° C, or magnetically slightly anisotropic in the compression direction. In a permanent magnet field type small DC motor using a substantially isotropic full-density arc-shaped rare earth magnet, it is preferable that the heating means of the full-density magnet is a direct energization to the rare earth-iron rapidly solidified flakes, It is also possible to integrate the magnetic pole center outer peripheral surface excluding the circumferential outer peripheral end faces of the full density magnet and the soft magnetic back yoke by direct energization. Since these arc-shaped rare earth magnets are also mechanically fragile, it is preferable to place the outer peripheral surface of the magnet so as to face the inner peripheral surface of the soft magnetic frame and press and fix both ends in the circumferential direction with springs. .
[0016]
As described above, the present invention has the property that the residual magnetic flux density Br and the coercive force Hc gradually increase simultaneously as a function of the applied magnetic field. Unsaturated It uses rare earth-iron rapidly solidified flakes that provide a well-balanced demagnetization curve even in a magnetized state. For example, it is solidified into an arc shape with a thickness of less than 1 mm to form a permanent magnet field. The magnetic circuit configuration has different permeances at both ends in the circumferential direction, and a soft magnetic material with a spherical or elliptical cross section is placed at the center of a pair of arc-shaped rare earth magnets, and its demagnetizing field is used. To do. Then, the demagnetizing reaction when magnetizing the arc-shaped rare earth magnet makes the magnetic pole center a demagnetization curve (residual magnetic flux density Br and coercive force Hcb) larger than the circumferential end. This is because unsaturation magnetization using rare earth-iron rapidly solidified flakes makes it possible to integrate the magnets with different magnetic performances even though the magnetic pole center and the circumferential ends 11 are made of the same material. In combination with a conventionally known cogging torque reduction means with a magnet shape, a smaller permanent magnet field type DC motor with higher rotation accuracy and higher rotation accuracy can be obtained. Can be manufactured.
As described above, the small DC motor may be a disc feeder equipped with a CD, MD, or the like, or an optical pickup device.
By the way, although the present invention is similar to the magnetizing method disclosed in Japanese Patent Publication No. 58-14054, the present invention and Japanese Patent Publication No. 58-14054 are greatly different, so this difference will be claimed here.
In the present invention, in order to partially change the rare-earth magnet demagnetization curve, pure iron having a spherical cross section is sandwiched between rare-earth magnets, and further, this rare-earth magnet is sandwiched between magnetized yokes. And the demagnetization curve of the rare earth magnet can be lowered at the end and raised at the center.
By using such a method, the end of the rare earth magnet can be unsaturated and magnetized, and the waveform of the demagnetization curve can be controlled. This is possible with a rare earth magnet having a high coercive force, and a magnet having a low coercive force is magnetized by a small magnetizing field at the center and at the end even if the method shown in this embodiment is used. Therefore, magnetization with a low demagnetization curve at the end cannot be performed.
In 1980, the filing date of Japanese Patent Publication No. 58-14504, ferrite magnets were the mainstream, and magnets with a high coercive force, such as rare earth magnets, started to be used around 1993.
Has not been developed yet.
The magnetizing method disclosed in Japanese Patent Publication No. 58-14504 is performed by the method shown in FIGS. 1 to 7 (a) of the gazette, and as a result, the magnetic flux density distribution is shown in FIGS. It is in the state of (b). However, this method of magnetizing a permanent magnet between two magnetized yokes is not a method that generates a demagnetizing field, so magnetize a magnet with high holding power such as a rare earth magnet. If an attempt is made, no demagnetizing field is generated as in the present invention, so that the end portion of the rare earth magnet cannot be in an unsaturated magnetization state as in the present invention.
[0017]
【Example】
Hereinafter, the present invention will be described in more detail. However, the present invention is not limited to the examples.
[0018]
[Manufacture of arc-shaped rare earth-iron magnets M1 and M2 using a binder]
Rare earth-iron rapidly solidified flakes are available from Magneque International In, Co. (Product name: MQP-B), alloy composition Nd ₁₂ Fe ₇₇ Co _Five B ₆ Magnetically isotropic Nd with a crystal grain size of 20-50 nm ₂ Fe ₁₄ Thin pieces having a B phase and a thickness of 20 to 30 μm were used. First, an acetone solution of epoxy resin (2.5% by weight in terms of solid content) and 97.5% by weight of rare earth-iron rapidly solidified flakes were wet-mixed to evaporate acetone to form a solid block at room temperature. Next, the solid block is pulverized and classified at room temperature to form granular compounds having particle sizes of 500, 350, 250, 212, and 150 μm, respectively, and finally 0.2 to 0.6 parts by weight of calcium stearate powder is added. did.
[0019]
The above-mentioned granular compounds having particle diameters of 500, 350, 250, 212, and 150 μm or less are subjected to volume weighing using a powder molding machine, and an arc compact of less than 1 mm thickness is 8 ton / cm. ² Then, these arc-shaped green compacts were heat-cured at 160 ° C. for 2 minutes, so-called compression molding, outer radius 3.65 mm, inner radius 3.55 mm, maximum thickness 0.90 mm, thrust direction Thirty arc-shaped rare earth magnets M1 each having a distance of 15.5 mm were prepared.
The fluctuation range (n = 30) with respect to the maximum thickness of 0.9 mm of the arc-shaped rare earth magnet and the upper limit of the particle diameter of the original granular compound have the following relationship (the correlation coefficient of the regression equation is 0. 0). 988).
[0020]
A = 0.0003P ² -0.0718P + 24.745 (1)
In the above formula, A is the thickness variation width ± μm, and P is the particle diameter upper limit μm of the granular compound. As is apparent from the regression equation, if the particle diameter of the granular compound is 250 μm or less, the thickness fluctuation range of the thin arc-shaped rare earth magnet M1 having a thickness of less than 1 mm is ± 30 μm or less, and the density is 6.0 g / cm. ^Three It becomes.
[0021]
On the other hand, by using pellets obtained by kneading 95% by weight of the same rare earth-iron rapidly solidified flakes and 5% by weight of 12-nylon at 260 ° C., the temperature at the tip of the forming die is set by extrusion disclosed in JP-A-6-236807. When the arc-shaped rare earth magnet M2 having an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, and a thrust direction distance of 15.5 mm was manufactured, the temperature was set to 175 ° C. below the melting point of 12-nylon. Thickness variation of 0.9mm thick part is ± 30μm, density 5.7g / cm ^Three Met. As described above, the thin arc-shaped rare earth magnet M1 by the compression molding of the granular compound and the thin arc rare earth magnet M2 by the extrusion molding were manufactured.
[0022]
[Production of arc-shaped rare earth-iron magnet M3 without using a binder]
Rare earth-iron rapidly solidified flakes are available from Magnequench International In, Co. (Product name: MQP-C), alloy composition Nd ₁₄ Fe ₆₅ Co ₁₅ B ₆ Magnetically isotropic Nd with a crystal grain size of 20-50 nm ₂ Fe ₁₄ Thin pieces having a B phase and a thickness of 20 to 30 μm were used. The flakes were weighed and filled into a mold cavity formed by a sialon die and a WC-Co punch that also served as a pair of electrodes. Next, the rare earth-iron rapidly solidified flake filled in the cavity through the punch made of WC-Co was pressured at 300 kgf / cm. ² Current density 100A / cm while compressing ² The pulse current was repeatedly applied 10 times with 0.5 sec ON-0.5 sec OFF. Then 300A / cm ² Of direct current was applied. The temperature rise rate ΔT / Δt (° C / sec) of the object due to the direct current is proportional to the square of the current density and the electrical resistance, and is inversely proportional to the specific heat and specific gravity of the object. Ruled by value.
[0023]
After energization of about 60 sec, the die temperature of 2 mm thickness is Nd ₂ Fe ₁₄ The crystallization temperature of the B phase exceeded about 600 ° C., and densification in the compression direction started due to plastic deformation due to softening of the flakes. When energization was stopped when densification was completed, about 80 sec after energization, the die temperature was It was 710 ° C. When the arc-shaped rare earth magnet M3 having an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, and a thrust direction distance of 15.5 mm is taken out after cooling, the density is 7.53 to 7. 55 g / cm ^Three Met. In this full density magnet, the accuracy of all thicknesses is simply dependent on the amount of flakes filled in the cavity. In addition, since there is no spring back when releasing from a mold such as a magnet containing a binder, the inner and outer radius dimensions are transferred as they are.
[0024]
[Pressure allowable stress of arc-shaped rare earth magnets M1, M2, M3 and fixing to soft magnetic frame]
The above-mentioned rare earth-iron rapidly solidified flakes are solidified into an arc-shaped rare earth magnet M1, subject to the present invention having an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, and a thrust direction distance of 15.5 mm. A method of fixing M2 and M3 to a preferable soft magnetic frame will be described below.
[0025]
FIG. 1 is a characteristic diagram showing the temperature dependence of the allowable pressure stress of the arc-shaped rare earth magnets M1, M2, M3. However, the allowable pressure stress is the stress kgf when the magnet M1, M2, M3 is damaged by pressing the maximum thickness portion of the magnet as shown in the figure. In the figure, M1 is a compression-formed arc-shaped rare earth magnet, M2 is an extrusion-formed arc-shaped rare earth magnet, and M3 is a hot-compression arc-shaped rare earth magnet.
As is apparent from the figure, M1 has a lower allowable stress at room temperature of less than 60% compared to M2, and is brittle without bending. Therefore, when M1 is fitted and fixed while bending an arc-shaped rare earth magnet to the engaging portion of the soft magnetic frame described in JP-A-10-201206 and JP-A-11-18390, cracks and omissions occur. However, it cannot be incorporated into a soft magnetic frame with a high yield on an industrial scale. Although M1 can be bonded to the soft magnetic frame, as described in Japanese Patent Application Laid-Open No. 10-201206 and Japanese Patent Application Laid-Open No. 11-18390, this kind of permanent magnet field type small DC mode is also available. It is not preferred that the magnet be incorporated into the soft magnetic frame by bonding.
However, as shown in the drawing, the allowable pressure stress of M1 at room temperature exceeds 6 kgf. Further, compared with M2, the allowable stress for pressing is almost constant up to a high temperature of approximately 120 ° C. Accordingly, as shown in FIG. 1, the magnet M1 is pressed by pressing both ends in the circumferential direction of the pair of magnets M1 arranged along the inner circumference of the soft magnetic frame 2 with, for example, a U-shaped spring 4. A method of fixing to the soft magnetic frame 2 is preferable. The fixing strength between the soft magnetic frame and the magnet depends on the pressing force of the spring. Generally, it can withstand actual usage conditions with a pressing force of 0.5 kgf or less, so that the actual operating temperature reaches the maximum temperature of 120 ° C for permanent magnet field type small DC motors because of the allowable pressure stress and the temperature dependence of the allowable pressure stress. The safety factor against the pressure allowable stress in the region is 10 times or more.
[0026]
Therefore, it has sufficient reliability for fixing the magnet. On the other hand, since M2 has a property of being slightly bent, it can be bent and inserted into a soft magnetic frame, and can be fitted and fixed using the engaging portion. Further, although M3 has a high pressure allowable stress, it is mechanically fragile like M1, and therefore, it is preferable to adopt the same fixing method to the soft magnetic frame as M1.
[0027]
[Unsaturated magnetization and motor characteristics of arc-shaped rare earth magnet M1 incorporated in soft magnetic frame]
The above-mentioned rare earth-iron rapid solidified flakes are arcuate in shape, which is the object of the present invention, solidified to an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, and a thrust direction distance of 15.5 mm. The characteristics of the unsaturated magnetization method using a demagnetizing field mainly with the rare earth magnet M1 and the permanent magnet field type small DC motor will be described.
[0028]
(1) Intrinsic coercivity and magnetization
FIG. 3 shows the alloy composition Nd. _X [Fe _0.8 Co _0.2 ] _1-X B ₆ Rare earth-iron rapidly solidified flakes together with binder, density 6g / cm ^Three It is a characteristic view which shows the relationship between the intrinsic coercive force Hci and the magnetism in the magnet M1 compression-molded. However, the magnetization was the ratio of [BH] max of a Φ5 mm (L / D = 1) magnet pulse-magnetized at 24 kOe or 60 kOe. As shown in the figure, even if the intrinsic coercive force Hci of the magnetically isotropic rare earth-iron rapidly solidified flakes is 8 kOe, the magnetization is unsaturated at a magnetic field Hm of about 24 kOe. On the other hand, when the intrinsic coercive force Hci exceeds 10 kOe, the magnetization is greatly reduced. In the present invention, at least the central portion of the magnetic pole preferably exceeds 90% of full magnetization, and for that purpose, the intrinsic coercive force Hci of the rare earth-iron rapidly solidified flake is preferably 10 kOe or less.
[0029]
Hot compression molded magnet M3 is Nd ₂ Fe ₁₄ In order to develop plastic deformability above the crystallization temperature of the B phase, the amount of rare earth element (Nd / Pr) is changed to Nd. ₂ Fe ₁₄ Bd must be 13 atom% or more, slightly higher than the stoichiometric composition, and Nd is a measure for ensuring thermal stability. ₂ Fe ₁₄ It is difficult to set the intrinsic coercive force Hci to 10 kOe or less within the B domain single domain critical dimension.
[0030]
Nd, which is a measure for ensuring thermal stability ₂ Fe ₁₄ Rare earth-iron rapidly solidified flakes with an intrinsic coercive force Hci8-10 kOe within the single domain critical dimension of the B phase are Nd ₂ Fe ₁₄ The alloy composition is close to the B stoichiometric composition, and the amount of rare earth element (Nd / Pr) needs to be 12 atomic% or less. In order to harden this, a binder such as a resin is required, and arc-shaped rare earth magnets M1 and M2 compression-molded or extruded into a predetermined shape together with such a binder are preferable from the viewpoint of magnetization. In addition, compression molding can fill rare-earth / iron-based rapidly solidified flakes more densely than extrusion molding, so to obtain a stronger static magnetic field in the gap between the permanent magnet field and the armature, the intrinsic coercive force An arc-shaped rare earth magnet M1 obtained by compression-molding a rare earth-iron rapidly solidified flake of Hci 8-10 kOe together with a binder is suitable for the permanent magnet field type small DC motor of the present invention.
[0031]
(2) Residual magnetic flux density and coercivity as a function of the applied magnetic field
FIG. 4 shows the dependence of the residual magnetic flux density Br and the coercive force Hcb (coercive force of the BH curve) on the magnetized magnetic field Hm of the magnet obtained by solidifying the rare earth-iron rapid solidified flakes. However, the magnetic field Hm50 kOe is standardized as 100%. When viewed in the range of 10 to 40 kOe generally used for magnetizing field magnets of permanent magnet field type small DC motors, the magnetically isotropic rare earth-iron rapidly solidified flakes are as shown in the figure. Regardless of the intrinsic coercive force Hci, the residual magnetic flux density Br and the coercive force Hcb gradually increase as a function of the applied magnetic field, so that a well-balanced demagnetization curve can be obtained even in the unsaturated magnetization state. A ferrite magnet that has been generally used for permanent magnet field type small DC motors has a characteristic of being rapidly magnetized even with a low applied magnetic field Hm. Therefore, it is impossible to obtain a stable demagnetization curve with good balance in the unsaturated magnetization state.
[0032]
(3) Unsaturated magnetization of permanent magnet field by demagnetizing field action
FIGS. 5 (a) and 5 (b) are cross-sectional views showing the principal part of an example of a method for unsaturated magnetization of a permanent magnet field incorporated in a soft magnetic frame using a demagnetizing field. ) Is a cross-sectional configuration diagram of a main part showing a normal magnetization method. In the figure, 1 is an arc-shaped rare earth magnet, 2 is a soft magnetic frame, 4 is a U-shaped spring for pressing and fixing the arc-shaped rare earth magnet 1, and 5 is pure iron having a uniform spherical cross section. FIG. 5A shows that the outer peripheral surface of the arc-shaped rare earth magnet 1 is fixed along the inner peripheral surface of the soft magnetic frame 2, and the soft magnetic frame 2 is attached to both end surfaces in the circumferential direction of the outer peripheral portion of the magnet 1. 5 (b) is a configuration in which a portion that does not act as a back yoke is formed and a soft magnetic material 5 having a spherical cross section is interposed, FIG. 5 (b) shows the outer peripheral surface of the arc-shaped rare earth magnet 1 within the soft magnetic frame 2. The soft magnetic frame 2 is fixed along the peripheral surface, and the center portion of the soft magnetic frame 2 and the tip end portion of the magnetized yoke 6 along the circumferential end surfaces of the magnet 1 are in contact with each other. A gap is formed between the magnetized yoke and the magnetized yoke. Further, a gap is provided between the end portion of the magnet 1 and the soft magnetic material 5 via the soft magnetic material 5 having a spherical cross section between the magnets 1 and the central portion of the magnet 1 and the soft magnetic material 5 are in contact with each other. Put it in a state.
[0033]
5A and 5B, the pure iron 5 having a spherical cross section is magnetized and a uniform demagnetizing field -NI is generated at the same time. The generated demagnetizing field -NI is uniformly generated in pure iron 5 having a spherical cross section, and the lines of magnetic force spring out from the surface magnetic poles and do not form vortices like the magnetic flux density lines. Then, it reacts against the magnetic field Hm. If the U-shaped spring is made of a soft magnetic material having a spherical or elliptical cross section, the same demagnetizing field action occurs directly on both ends in the circumferential direction of the arc-shaped rare earth magnet 1. Therefore, the individual magnetically isotropic rare earth-iron rapidly solidified flakes constituting the arc-shaped rare earth magnet 1 are magnetized depending on the magnetic field Hm and the demagnetizing field-NI. The magnetized state by the uniform magnetized magnetic field Hm as in (c) is completely different even if the level of Hm is the same, and becomes the essence of the method for manufacturing the permanent magnet field type small DC motor according to the present invention. .
[0034]
(4) Cogging torque reduction by demagnetizing field action
Rare earth-iron-based rapidly solidified flakes are compression molded to an outer radius of 3.65 mm, an inner radius of 3.25 mm, a maximum thickness of 0.90 mm, and a thrust direction distance of 15.5 mm to convert the arc-shaped rare earth magnet M1 into a soft magnetic frame. The magnetic field was magnetized in the range of 15 to 30 kOe in the magnetic field Hm of FIGS. Next, the armature 3 was incorporated into a permanent magnet field type small DC motor, and their induced voltage and cogging torque were measured. FIG. 6 is a characteristic diagram showing the relationship between the induced voltage and the cogging torque. However, the example of the present invention in the figure is based on the magnetization of FIG. 5A, and the comparative example is based on the magnetization of FIG. 5C. As is apparent from the figure, in the example of the present invention, the permanent magnet field incorporated in the soft magnetic frame is unsaturated-magnetized using a demagnetizing field. This clearly makes it possible to manufacture a permanent magnet field type compact DC motor having a cogging torque as low as 40% even at the same induced voltage level.
[0035]
The permanent magnet field type small DC motor was disassembled, the arc-shaped magnet 1 was taken out, and the intrinsic coercive force Hci of the small piece obtained by cutting out the magnetic pole center portion and both ends in the circumferential direction was obtained by VSM. Then, the arc-shaped rare earth magnet of FIG. 5C shown in the comparative example did not show a large difference depending on the part, and Hci was uniformly 7.9 to 8.2 kOe. On the other hand, the magnetic pole center portion of the arc-shaped rare earth magnet of FIG. 5A shown in the present invention example was 7.9 to 8.2 kOe, which is the same as the comparative example. However, Hci at both ends in the circumferential direction was 7.0 to 7.5 kOe, indicating a different Hci value from the magnetic pole center. This is because the arc-shaped rare earth magnet in the example of the present invention is a magnet having a uniform demagnetization curve (BH curve), although it is a uniform material magnet having the same performance at the magnetic pole center portion and both ends in the circumferential direction. When a weak demagnetization curve is given from the center of the magnetic pole to the end in the circumferential direction, it is suggested that the cogging torque is reduced even if the shape of the magnet is the same.
[0036]
(5) Cogging torque reduction combining demagnetizing field and magnet shape
FIG. 7 shows the back end of the arc-shaped rare earth magnet 1 between the back end of the circumferential outer peripheral portion (distance: 12.5 mm) between the curvature surface of the compression mold and the soft magnetic frame at a straight surface at an angle θ. FIG. 2 is a characteristic diagram showing a relationship between an angle θ, a cogging torque, and an induced voltage shown in FIG. 1 when a void-free gap is formed. However, the shape of the magnet is an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, a thrust direction distance of 15.5 mm, and the magnetization is the configuration shown in FIG. On the other hand, the magnetic field accompanied by the reaction by the demagnetizing field-NI is applied. In the permanent magnet field type small DC motor used here, the induced voltage V when the angle θ is 90 degrees is 0.218 mV / rpm, and the cogging torque Ct is 1.15 g-cm. Standardized.
[0037]
The induced voltage V decreases linearly with respect to the angle θ as shown in the regression equation shown in the figure. However, the reduction of the induced voltage V is only 5% even when θ is changed from 90 degrees to 50 degrees. One cogging torque Ct shows a large quadratic function change with respect to the angle θ, and the change becomes maximum when the angle θ is about 65 degrees. This value is almost 70% lower than the standard 90 degree cogging torque. Further, even in the range of 82 degrees to 50 degrees, the cogging torque of 40% or more is reduced with the angle 90 degrees as a reference.
[0038]
The above effect is that the remanent magnetization Br and the coercive force Hc gradually increase as a function of the magnetizing field, and a magnetically isotropic rare earth-iron that provides a well-balanced demagnetization curve even in the unsaturated magnetization state. When a thin-walled arc-shaped rare earth magnet with hardened rapidly solidified flakes is magnetized in an unsaturated manner using the demagnetizing field, there are portions that do not have back yoke due to soft magnetic frames at both ends in the circumferential direction. This is because magnets having different magnetic performances are integrated into a permanent magnet field.
[0039]
(5) Cogging torque reduction combining demagnetizing field and thermal demagnetization
FIG. 7 shows the back yoke of the arc-shaped rare earth magnet between the soft magnetic frame with both ends in the circumferential direction (distance 12.5 mm) being a straight surface with an angle θ62 degrees from the curvature surface of the compression mold. A void portion was formed, and four stages of unsaturated magnetization were performed with a capacitor capacity of 2000 μF and 1500 to 2400 V in the configuration of FIG. It is a characteristic view which shows the cogging torque before and behind the thermal demagnetization which exposed this to 140 degreeC for 5 minute (s), and the change of an induced voltage. However, the magnet has an outer radius of 3.65 mm, an inner radius of 3.55 mm, a maximum thickness of 0.90 mm, a thrust direction distance of 15.5 mm, a cogging torque before thermal demagnetization with a maximum magnetic field of 2000 μF and 2400 V, And normalized based on the induced voltage. The reference induced voltage V in the permanent magnet field type small DC motor used here was 0.214 mV / rpm, and the cogging torque Ct was 0.46 g-cm.
[0040]
As is apparent from the figure, when the permanent magnet field type small DC motor according to the present invention is thermally demagnetized, the cogging torque is further increased by 10 even though the decrease in the induced voltage V is approximately 0.5% or less. % Can be reduced. In this method, an arc-shaped rare earth magnet pressed and fixed along the inner peripheral surface of the soft magnetic frame is magnetized using a demagnetizing field with the configuration shown in FIG. As a result, the demagnetization factor of the magnetic pole center portion of the large demagnetization curve (residual magnetic flux density Br and coercive force Hcb is large) becomes small, and the demagnetization factor of the small demagnetization curve on both end faces in the circumferential direction becomes large. As a result, the gap magnetic flux density distribution becomes more sinusoidal, and a cogging torque reduction rate larger than the reduction rate of the induced voltage due to demagnetization can be obtained.
[0041]
【The invention's effect】
As described above, the present invention has the property that the residual magnetic flux density Br and the coercive force Hc gradually increase simultaneously as a function of the applied magnetic field. Unsaturated It uses rare earth-iron rapidly solidified flakes that provide a well-balanced demagnetization curve even in a magnetized state. For example, it is solidified into an arc shape with a thickness of less than 1 mm to form a permanent magnet field. And a magnetic circuit configuration having different permeances at both ends in the circumferential direction, in particular, a soft magnetic material having a spherical or elliptical cross section is arranged at the center of a pair of arc-shaped rare earth magnets. The demagnetizing curve (residual magnetic flux density Br and coercive force Hcb) of the circumferential end portion 11 is smaller than that of the magnetic pole center due to the demagnetizing field action when magnetizing the arc-shaped rare earth magnet. This is because the magnets having different magnetic performances are integrated by the unsaturated magnetization using rare earth-iron rapidly solidified flakes, although the magnetic pole center and the circumferential end portions 11 are made of the same material. The permanent magnet field type DC motor with a smaller size, higher output and higher rotation accuracy can be obtained by combining with the cogging torque reducing means with the conventionally known magnet shape. Can be manufactured.
[Brief description of the drawings]
FIG. 1A is a cross-sectional view of a main part of a motor according to an example of the present invention.
(B) Perspective perspective view of motor magnet according to an example of the present invention.
FIG. 2 is a characteristic diagram showing the temperature dependence of allowable pressure stress.
FIG. 3 is a characteristic diagram showing intrinsic coercivity and magnetization.
FIG. 4 is a characteristic diagram showing the relationship between residual magnetic flux density and coercivity as a function of the applied magnetic field.
FIGS. 5A, 5B, and 5C are cross-sectional views of main parts of permanent magnet field unsaturated magnetization using a demagnetizing field.
FIG. 6 is a characteristic diagram showing cogging torque reduction by a demagnetizing field.
FIG. 7 is a characteristic diagram showing cogging torque reduction by demagnetizing field and magnet shape.
FIG. 8 is a diagram showing cogging torque reduction by combining demagnetizing field and thermal demagnetization.
FIG. 9 is a diagram showing the magnitude relationship of the demagnetization curve.

Claims

An arc-shaped rare earth magnet mainly composed of a rare earth-iron rapidly solidified flake is fixed along the inner peripheral surface of the soft magnetic frame, and the soft magnetic frame is attached to both ends of the outer peripheral portion of the magnet in the circumferential direction. -Demagnetization curves at both ends in the circumferential direction than the demagnetization curve at the center of the magnetic pole by forming a portion that does not act as a core and unsaturated magnetization through a soft magnetic material with a spherical or elliptical cross section A method of manufacturing a small permanent magnet field type DC motor in which a reduced arc-shaped rare earth magnet is opposed to an armature.

2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein a demagnetizing field larger than the central portion is generated at an end portion in the circumferential direction of the rare earth magnet to perform unsaturated magnetization.

Fix the outer surface of the arc-shaped rare earth magnet along the inner surface of the soft magnetic frame, and place it between the soft magnetic frame and the tip of the magnetized yoke along the circumferential ends of the magnet. 2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the gap portion is formed and unsaturated magnetization is performed through a soft magnetic material having a spherical or elliptical cross section.

Both ends in the circumferential direction of the outer peripheral portion of the arc-shaped rare earth magnet are straight surfaces with an angle of 50 to 82 degrees with the curvature surface of the compression mold, and the soft magnetic frame does not act as a back yoke on both ends in the circumferential direction of the outer peripheral portion. 2. A method of manufacturing a permanent magnet field type compact DC motor according to claim 1 , wherein the portion is formed and unsaturated magnetization is performed through a soft magnetic material having a spherical or elliptical cross section.

2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the intensity of the unsaturated magnetic field applied to the arc-shaped rare earth magnet is 15 to 30 kOe.

A pair of arc-shaped rare earth magnets fixed opposite to each other along the inner surface of the soft magnetic frame is unsaturated magnetized through a soft magnetic material having a spherical or elliptical cross section, and then heated to heat the magnetic pole center. 2. The method for manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the demagnetization rate of both end faces in the circumferential direction is larger than that of the permanent magnet field type.

RE ₂ TM ₁₄ B with rare earth-iron rapidly solidified flakes of 300 nm or less
(RE is Nd, Pr.TM is Fe, Co) intrinsic coercive force Hci8~10kOe consisting phase, the residual magnetization 7.4～8.6KG, moreover No mounting 請 Motomeko 1 SL is magnetically isotropic A method for manufacturing a permanent magnet field type small DC motor.

Magnetically isotropic rare earth-iron with a nanocomposite structure in which a rare earth-iron rapidly solidified flake has a soft magnetic phase such as αFe, Fe ₃ B, Fe ₂ B and a hard magnetic phase such as RE ₂ TM ₁₄ B system rapidly solidified flakes permanent magnet field type miniature DC 請 Motomeko 1 comprising a motor - motor manufacturing method of.

The outer peripheral surface of a pair of arc-shaped rare earth magnets compression-molded with rare earth-iron rapidly solidified flakes together with a binder is opposed to the inner peripheral surface of the soft magnetic frame, and both ends in the circumferential direction of the magnet are pressed with springs. 2. A method of manufacturing a permanent magnet field type small DC motor according to claim 1, which is fixed.

2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the spring for pressing and fixing both ends in the circumferential direction is a soft magnetic material having a spherical or elliptical cross section.

The outer peripheral surface of a pair of arc-shaped rare earth magnets formed by extruding rare earth-iron rapidly solidified flakes together with a binder is opposed to the inner peripheral surface of the soft magnetic frame, and both ends of the magnet in the circumferential direction are connected to the soft magnetic frame. A manufacturing method of a permanent magnet field type small DC motor according to claim 1, wherein the fixing is performed by an engagement protrusion provided on the frame.

The arc-shaped rare earth magnet is Nd or / and Pr is 13 to 15 atomic%, B is 5 to 10 atomic%, Co is 0 to 20 atomic%, and the balance is Fe or amorphous having impurities inevitable in production, and / or A rare-earth / iron-based rapidly solidified flake having a RE ₂ TM ₁₄ B (RE is Nd, Pr. TM is Fe, Co) phase of 300 nm or less is a full-density magnet formed by hot compression molding at a crystallization temperature of 750 ° C. or less. there 請 Motomeko first permanent magnet field type miniature DC motor as claimed - data producing method.

2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the heating means for the full density magnet is direct energization to the rare earth-iron rapidly solidified flake.

2. The method of manufacturing a permanent magnet field type compact DC motor according to claim 1, wherein the outer peripheral surface of the magnetic pole center and the soft magnetic back yoke, excluding both circumferential outer peripheral end faces of the full density magnet, are integrated by direct energization.

The outer peripheral surface of a pair of arc-shaped rare earth magnets with a rare-earth-iron rapidly solidified flake made of full-density magnets is placed facing the inner peripheral surface of the soft magnetic frame, and both circumferential ends of the magnet are pressed and fixed with springs. A method of manufacturing a permanent magnet field type small DC motor according to claim 1.

A permanent magnet, a soft magnetic frame for fixing the permanent magnet to the inner peripheral surface, and an armature disposed in the soft magnetic frame are provided. The permanent magnet is softened on both circumferential end surfaces of the outer peripheral portion of the magnet. A part where the magnetic frame does not act as a back yoke is formed, and unsaturated end magnetization is performed via a soft magnetic material having a spherical or elliptical cross section, so that the end part in the circumferential direction is more than the demagnetization curve of the magnetic pole center part. Permanent magnet field type small DC motor with reduced demagnetization curve.

The permanent magnet field type compact DC motor according to claim 16 , wherein both end portions in the circumferential direction of the permanent magnet are in a state of being unsaturated magnetized.

The permanent magnet field type small DC motor according to claim 16 , wherein the permanent magnet is a rare earth magnet mainly composed of a rare earth-iron rapidly solidified flake.

The permanent magnet field small motor according to claim 16 , wherein the rare earth magnet has a constant thickness.

The permanent magnet field type small DC motor according to claim 16 , wherein the permanent magnet is obtained by compression molding, and the rare earth permanent magnet has a thickness of less than 1 mm.

A disk feeder comprising the permanent magnet field type small DC motor according to claim 16 .

A pickup device comprising the permanent magnet field small DC motor according to claim 16 .