JP2004163304A

JP2004163304A - Torque sensor

Info

Publication number: JP2004163304A
Application number: JP2002330462A
Authority: JP
Inventors: Naoki Nakane; 直樹中根; Shigetoshi Fukaya; 繁利深谷
Original assignee: Denso Corp; Nippon Soken Inc
Current assignee: Denso Corp; Soken Inc
Priority date: 2002-11-14
Filing date: 2002-11-14
Publication date: 2004-06-10

Abstract

<P>PROBLEM TO BE SOLVED: To provide a torque sensor 1 having a simple structure, no electrical contact point, and high accuracy near a neutral point. <P>SOLUTION: This torque sensor 1 is constituted of a torsion bar 4 for connecting coaxially an input shaft 2 to an output shaft 3, a ring magnet 5 mounted on the end of the input shaft 2, a pair of magnetic yokes 6 mounted on the end of the output shaft 3, a magnetic sensor 7 for detecting a magnetic flux density generated in the magnetic yokes 6, or the like. Each magnetic yoke 6 is provided with pawls 6a to the same number (twelve) as N-poles and S-poles of the magnet 5 at equal intervals on the whole circumference. The magnetic yokes 6 and the magnet 5 are arranged so that the center of each pawl 6a provided on the magnetic yokes 6 agrees with the boundary between the N-pole and the S-pole of the magnet 5 in the state where torsion is not generated in the torsion bar 4. The magnetic sensor 7 detects the magnetic flux density by being inserted into a gap provided between the magnetic yoke 6A and the magnetic yoke 6B facing in the axial direction. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば電動パワーステアリング装置等の回転動力を伝達する機構における軸トルクを検出するトルクセンサに関する。
【０００２】
【従来技術】
磁石と磁気センサを使った従来技術としては、磁石と磁気センサをトーションバーの両端に同定し、トルクが印加された際に、トーションバーが捩じれることによって磁石と磁気センサの位置関係が変化し、磁気センサからトルクに比例した出力を得るものがある（例えば、特許文献１参照。）。
【０００３】
また、磁石と磁気センサとトーションバーを使用する点で上記の特許文献１と同じであるが、トーションバーの捩じれをギヤを使って軸方向の運動に変える機構にして磁気センサをハウジングに固定させ、磁気センサヘの電力供給と信号の取り出しを行う電気的接触部を不要にしている（例えば、特許文献２参照。）。
【０００４】
【特許文献１】
特開平８−１５９８８７号公報
【特許文献２】
特開平６−２８１５１３号公報
【０００５】
【発明が解決しようとする課題】
ところが、特許文献１の方式では、磁石と磁気センサがトーションバーに固定されているため、磁気センサヘの電力供給と信号の取り出しを行うために電気的な接触部が必要となり、具体的にはスリップリングとブラシを使用しているため、接触部の信頼性が懸念される。
【０００６】
また、特許文献２の方式では、トーションバーの捩じれを軸方向の運動に変換するギヤ機構を有しているため、構造が複雑になり、且つギヤ機構のバックラッシやギヤの摩耗等により、誤差及び応答遅れ等が生じるため、性能面での懸念点がある。
【０００７】
本発明は、上記事情に基づいて成されたもので、その目的は、構造がシンプルで電気的な接触部を持たないトルクセンサを提供することにある。
【０００８】
【課題を解決するための手段】
上記課題を解決するために、請求項１では、第１の軸と第２の軸とを同軸上に連結し、第１の軸と第２の軸との間に捩じれトルクが入力されると、自身に捩じれを生じる弾性部材と、第１の軸に連結されて、周囲に磁界を形成する硬磁性体と、第２の軸に連結され、且つ硬磁性体により形成される磁界内に配置されて磁気回路を形成し、弾性部材の捩じれによって硬磁性体との相対位置が変化すると、磁気回路に発生する磁束密度が変化する構造を有する一組の軟磁性体と、軟磁性体と非接触に設置され、軟磁性体の磁気回路に発生する磁束密度を検出する磁気センサとを備え、硬磁性体は、周方向に着磁され、軟磁性体は、硬磁性体の外周に配置され、且つ軸方向にギャップを介して対向しており、磁石の極数と同数の爪が全周に等間隔に設けられ、且つ一方の軟磁性体に設けられる爪と他方の軟磁性体に設けられる爪とが周方向にずれて交互に配置され、爪は、根本部と先端部とを有し、根本部の周方向の幅が先端部の周方向の幅よりも大きく、根本部の周方向の幅Ａと、一方の軟磁性体の爪の根本部の周方向一端から隣り合う爪の根本部の周方向一端までの周方向の長さＰとの間に以下の関係が成立することを特徴としている。
【０００９】
０．５×Ｐ＜Ａ＜Ｐ
本発明のトルクセンサは、第１の軸と第２の軸との間に捩じれトルクが入力されて弾性部材に捩じれが生じると、硬磁性体と軟磁性体との相対位置が変化することで、軟磁性体の磁気回路に発生する磁束密度が変化する。この磁束密度の変化を磁気センサで検出することにより、第１の軸と第２の軸との間に印加される捩じれトルクを求めることができる。この構成によれば、硬磁性体から発生する磁束を直接磁気センサで検出する必要がないので、非接触式の磁気センサを定位置に固定して使用することができる。その結果、磁気センサに対し電気的な接触部を設ける必要がないので、信頼性の高いトルクセンサを提供できる。
【００１０】
さらに、爪の根本部の周方向の幅Ａと、一方の軟磁性体の爪の根本部の周方向一端から隣り合う爪の根本部の周方向一端までの周方向の長さＰとの間に上記の関係式が成立することで、軟磁性体の大きさに関わらず、磁気センサが直線性の良い磁束密度を検出することができる。
【００１１】
また、請求項２では、第１の軸と第２の軸とを同軸上に連結し、第１の軸と第２の軸との間に捩じれトルクが入力されると、自身に捩じれを生じる弾性部材と、第１の軸に連結されて、周囲に磁界を形成する硬磁性体と、第２の軸に連結され、且つ硬磁性体により形成される磁界内に配置されて磁気回路を形成し、弾性部材の捩じれによって硬磁性体との相対位置が変化すると、磁気回路に発生する磁束密度が変化する構造を有する一組の軟磁性体と、軟磁性体に近接して配置され、軟磁性体から磁束を導くと共に、磁束を集める集磁部を有する補助軟磁性体と、集磁部を介して補助軟磁性体に生じる磁束密度を検出する磁気センサとを備え、硬磁性体は、周方向に着磁され、軟磁性体は、硬磁性体の外周に配置され、且つ軸方向にギャップを介して対向しており、磁石の極数と同数の爪が全周に等間隔に設けられ、且つ一方の軟磁性体に設けられる爪と他方の軟磁性体に設けられる爪とが周方向にずれて交互に配置され、爪は、根本部と先端部とを有し、根本部の周方向の幅が先端部の周方向の幅よりも大きく、根本部の周方向の幅Ａと、一方の軟磁性体の爪の根本部の周方向一端から隣り合う爪の根本部の周方向一端までの周方向の長さＰとの間に以下の関係が成立することを特徴としている。
【００１２】
０．５×Ｐ＜Ａ＜Ｐ
本発明のトルクセンサは、第１の軸と第２の軸との間に捩じれトルクが入力されて弾性部材に捩じれが生じると、硬磁性体と軟磁性体との相対位置が変化することで、軟磁性体の磁気回路に発生する磁束密度が変化する。さらに、軟磁性体に発生する磁束が補助軟磁性体に導かれて、その補助軟磁性体に設けられた集磁部に集められる。従って、集磁部を介して補助軟磁性体に生じる磁束密度を磁気センサで検出することにより、第１の軸と第２の軸との間に印加される捩じれトルクを求めることができる。この構成によれば、硬磁性体から発生する磁束を直接磁気センサで検出する必要がないので、非接触式の磁気センサを定位置に固定して使用することができる。その結果、磁気センサに対し電気的な接触郡を設ける必要がないので、信頼性の高いトルクセンサを提供できる。また、補助軟磁性体に生じる磁束を集磁部に集めることにより、軟磁性体の全周で発生する磁束密度の平均を磁気センサで検出することができる。これにより、磁気回路を構成する部品の製造ばらつきや組付け精度、センタずれ等による検出誤差を小さくできる。
【００１３】
さらに、爪の根本部の周方向の幅Ａと、一方の軟磁性体の爪の根本部の周方向一端から隣り合う爪の根本部の周方向一端までの周方向の長さＰとの間に上記の関係式が成立することで、軟磁性体の大きさに関わらず、磁気センサが直線性の良い磁束密度を検出することができる。
【００１４】
【発明の実施の形態】
以下、図に示す実施形態について説明する。
【００１５】
図１は、トルクセンサ１の分解斜視図である。図２は、トルクセンサ１の軸方向断面図である。図３は、磁石５と一組の磁気ヨーク６との位置関係を示す軸方向平面図（ａ）と側面図（ｂ）である。図４は、トーションバー４の捩じれ角（磁石５と磁気ヨーク６とのずれ角）と磁気ヨーク６に生じる磁束密度との関係を表すグラフである。図５は、一組の磁気ヨーク６の側面図である。図６は、トーションバー４の捩じれ角（磁石５と磁気ヨーク６とのずれ角）と磁気ヨーク６に生じる磁束密度との関係を表わすグラフである。
【００１６】
本実施形態のトルクセンサ１は、例えば車両の電動式パワーステアリング装置に用いられるもので、ステアリングシャフトを構成する入力軸２（第１の軸）と出力軸３（第２の軸）との間に設けられ、ステアリングシャフトに加わる操舵トルクを検出している。
【００１７】
そのトルクセンサ１は、入力軸２と出力軸３とを同軸上に連結するトーションバー４（弾性部材）、入力軸２の端部（またはトーションバー４の一端側）に取り付けられる磁石５（硬磁性体）、出力軸３の端部（またはトーションバー４の他端側）に取り付けられる一組の磁気ヨーク６（軟磁性体）、及びこの一組の磁気ヨーク６間に生じる磁束密度を検出する磁気センサ７等より構成される。
【００１８】
トーションバー４は、両端がそれぞれピン８により入力軸２と出力軸３とに固定され、目的に応じた捩じれ／トルク特性を持たせてある。従って、入力軸２と出力軸３は、トーションバー４が捩じれを生じることで相対的に回動することができる。
【００１９】
磁石５は、リング状に設けられて周方向にＳ極とＮ極とが交互に着磁され、例えば２４極に形成されている。
【００２０】
一組の磁気ヨーク６（６Ａ、６Ｂ）は、図１に示す様に、磁石５の外周に近接して配置される環状体で、それぞれ磁石５のＮ極及びＳ極と同数（１２個）の爪６ａが全周に等間隔に設けられている。この一組の磁気ヨーク６は、互いの爪６ａが周方向にずれて交互に配置される様に、固定部９（図２参照）により位置決めされている。
【００２１】
また、一組の磁気ヨーク６と磁石５は、トーションバー４に捩じれが生じていない状態（入力軸２と出力軸３との間に捩じれトルクが加わっていない時）で、各磁気ヨーク６に設けられた爪６ａの中心と磁石５のＮ極とＳ極との境界とが一致するように配置されている（図３参照）。
【００２２】
磁気センサ７は、図３に示す様に、軸方向に対向する一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂとの間に設けられるギャップＧ内に挿入され、両磁気ヨーク６間に生じる磁束密度を検出する。但し、この磁気センサ７は、磁気ヨーク６と接触することなく、図示しないハウジング等に固定されて、定位置に設けられている。
【００２３】
磁気センサ７としては、例えばホール素子、ホールＩＣ、磁気抵抗素子等を使用することができ、検出した磁束密度を電気信号（例えば電圧信号）に変換して出力する。
【００２４】
次に、本実施形態の作動を説明する。
【００２５】
入力軸２と出力軸３との間に捩じれトルクが印加されていない状態、つまりトーションバー４が捩じれていない中立位置では、図４（ｂ）に示す様に、磁気ヨーク６に設けられた爪６ａの中心と磁石５のＮ極とＳ極との境界とが一致している。この場合、各磁気ヨーク６の爪６ａには、磁石５のＮ極とＳ極から同数の磁力線が出入りするため、一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂの内部でそれぞれ磁力線が閉じている。従って、磁気ヨーク６Ａと磁気ヨーク６Ｂとの間（ギャップＧ）に磁束が洩れることはなく、磁気センサ７で検出する磁束密度は０となる（図４参照）。
【００２６】
入力軸２と出力軸３との間に捩じれトルクが印加されて、トーションバー４に捩じれが生じると、入力軸２に固定された磁石５と出力軸３に固定された一組の磁気ヨーク６との相対位置が周方向に変化する。これにより、図４（ａ）または（ｃ）に示す様に、磁気ヨーク６に設けられた爪６ａの中心と磁石５のＮ極とＳ極との境界とが一致しなくなるため、各磁気ヨーク６には、ＮまたはＳの極性を有する磁力線が増加する。
【００２７】
この時、一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂは、それぞれ逆の極性を有する磁力線が増加するので、一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂとの間（ギャップＧ）に磁束密度が発生する。この磁束密度は、図４に示す様に、トーションバー４の捩じれ量に略比例し、且つトーションバー４の捩じれ方向に応じて極性が反転する。この磁束密度を磁気センサ７で検出し、電圧信号として取り出すことができる。
【００２８】
本実施形態のトルクセンサ１は、トーションバー４に捩じれが生じて、磁石５と一組の磁気ヨーク６との相対位置が周方向に変化すると、一組の磁気ヨーク６間の全周で磁束密度が変化する。即ち、一組の磁気ヨーク６間の全周で同一強度の磁束密度を検出できる。従って、一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂとが対向するギャップＧ内に磁気センサ７を挿入することで、磁気ヨーク６に接触することなく、磁気ヨーク６間の磁束密度を検出することができる。これにより、磁気センサ７に対し電気的な接触部（例えばスリップリングとブラシ）を設ける必要がないので、信頼性の高いトルクセンサ１を提供できる。
【００２９】
また、磁気センサ７の検出トルク範囲において、磁気ヨーク６で発生する磁束密度の直線性を向上させるための磁気ヨーク６の形状の求め方について実験データに基づいて以下に説明する。
【００３０】
爪６ａは、図５に示すように、根本部６ａ１と先端部６ａ２とを有し、根本部６ａ１の周方向の幅Ａが先端部６ａ２の周方向の幅Ｂよりも大きく、周方向の中心に沿って対称である略台形形状を呈している。
【００３１】
そして、磁石５の極数ｎを２４極、磁気ヨーク６の内径ｒを３１ｍｍ、一方の磁気ヨーク６Ａから他方の磁気ヨーク６Ｂまでの軸方向の距離Ｆを８ｍｍとし、表１に示すように、爪６ａの根本部６ａ１の周方向の幅Ａを第１から第３水準の値に、根本部６ａ１から先端部６ａ２までの軸方向の長さＬを第１から第４水準の値にそれぞれ設定した。そして、磁気ヨーク６を磁石５との中立位置から周方向に２．５度回転させた場合の磁気ヨーク６で発生する磁束密度をそれぞれ測定した。
【００３２】
【表１】

【００３３】
他方の磁気ヨーク６Ｂの爪６ａは、図５に示すように、周方向に隣り合う第１の爪６１と第２の爪６２とを有しており、根本部６ａ１の周方向の幅Ａと第１の爪６１の根本部６ａ１の周方向一端（周方向右側一端）から第２の爪６２の根本部６ａ１の周方向一端（周方向右側一端）までの周方向の距離Ｐとが変化することで、第１の爪６１と第２の爪６２との周方向の間隔が変化し、磁石５と磁気ヨーク６との間を出入りする磁束の量が変化することから、磁気ヨーク６で発生する磁束密度の直線性を向上させるための理論を以下に説明する。
【００３４】
第１の爪６１の根本部６ａ１の周方向一端から第２の爪６２の根本部６ａ１の周方向一端までの周方向の距離Ｐは、一方の磁気ヨーク６Ａと他方の磁気ヨーク６Ｂとのそれぞれの爪６ａの極数ｎが１２極数であることから、以下の関係式▲１▼で求められる。
【００３５】
Ｐ［ｍｍ］＝π×ｒ（３１ｍｍ）／ｎ（１２）≒８．１１・・・・・・・▲１▼
また、根本部６ａ１の周方向の幅Ａが第３水準（４．２ｍｍ）の時に、図６に示す正弦波である実線の波形になり、且つ、表２より根本部６ａ１から先端部６ａ２までの軸方向の長さＬが第２水準（７．０ｍｍ）、根本部６ａ１の周方向の幅Ａが第２水準（３．７ｍｍ）の時に、磁気ヨーク６で発生する磁束密度を最も大きくすることができると共に、図６に示す点線の波形になることがわかった。この点線の波形では、磁束密度の変化が少ない不感帯領域を生じるため、磁気角±９０ｄｅｇ付近の磁気ヨーク６で発生する磁束密度を直線性にできない。
【００３６】
このことから、本発明では、第３水準（４．２ｍｍ）を根本部６ａ１の周方向の幅Ａの閾値とした。また、本実施形態では、第１の爪６１の根本部６ａ１の周方向一端から第２の爪６２の根本部６ａ１の周方向一端までの周方向の距離Ｐを固定させている。そのため、根本部６ａ１の周方向の幅Ａを上述の関係式▲４▼で求めた距離Ｐで割ることで、根本部６ａ１の周方向の幅Ａと第１の爪６１の根本部６ａ１の周方向一端から第２の爪６２の根本部６ａ１の周方向一端までの周方向の距離Ｐとの比例定数を求めることができる（関係式▲２▼参照）。
【００３７】
Ａ（４．２ｍｍ）／Ｐ（８．１１ｍｍ）≒０．５１７・・・・・・・・▲２▼
以上説明したように、以下の関係式▲２▼から数値Ａを以下の関係式▲３▼の範囲に設定することによって、磁気ヨーク６で発生する磁束密度は、図６の実線の波形のように、正弦波にすることができ、磁気センサ７が直線性の良い磁束密度を検出することができる。なお、実験データに若干の誤差があることを考慮して比例定数を決定した。
【００３８】
０．５×Ｐ＜Ａ＜Ｐ・・・・・・・・・・・・・・・・・・・・・・・▲３▼
また、本実施形態では、磁気ヨーク６もしくは磁石５の極数ｎを２４極、磁気ヨーク６の内径ｒを３１ｍｍ、一方の磁気ヨーク６Ａから他方の磁気ヨーク６Ｂまでの軸方向の距離Ｆを８ｍｍとしているが、磁気ヨーク６の大きさが変化して極数ｎ、内径ｒ、距離Ｆの値が比例的に変わったとしても、磁石５と磁気ヨーク６との間を流れる磁束の量及び磁束の経路が変わらないため、上記の関係式▲３▼の関係を満たすことで、図６に示す正弦波の波形にできる。
【００３９】
なお、本実施形態では、例えば根本部６ａ１の周方向の幅Ａが３．７ｍｍである場合に、最も磁気センサ６の磁束密度が大きくできると説明したが、３．７ｍｍ付近の値でさらに磁気センサ６の磁束密度を大きくできる値があることも考えられる。
【００４０】
なお、本実施形態での爪６ａは、根本部６ａ１の周方向の幅Ａが先端部６ａ２の周方向の幅Ｂよりも大きい略台形形状を呈しているが、先端部６ａ２の周方向の幅Ｂが０である略三角形形状であってもよい。
【００４１】
なお、図７に示すように、磁気ヨーク６Ａ、６Ｂの外周に近接してリング状の集磁リング１０（補助軟磁性体）が設けられていてもよい。この集磁リング１０は、磁気ヨーク６Ａ，６Ｂと同じ軟磁性体であって、周方向の一箇所に平板状の集磁部１０ａが設けられ、互いの集磁部１０ａ同士が軸方向に対向して配置される。但し、集磁部１０ａは、集磁リング１０の他の部位より軸方向に接近して設けられる。さらに、軸方向に対向する集磁部１０ａ同士の間に磁気センサ７が挿入され、その両集磁部１０ａ間に発生する磁束密度を検出する。
【００４２】
この構成によれば、集磁リング１０が磁気回路の一部を形成するため、磁石５から発生した磁束が磁気ヨーク６を通って集磁リング１０に導かれ、その集磁リング１０に設けられた集磁部１０ａに優先的に集まる。この集磁部１０ａ間に発生する磁束密度を磁気センサ７で検出することにより、磁気ヨーク６の全周で発生する磁束密度の平均を取ることができるので、磁気回路を構成する部品の製造ばらつきや組み付け誤差、及び入力側と出力側とのセンタずれ等による検出誤差を抑えることができる。
【図面の簡単な説明】
【図１】トルクセンサの分解斜視図である。
【図２】トルクセンサの軸方向断面図である。
【図３】磁石と一組の磁気ヨークとの位置関係を示す軸方向平面図（ａ）と側面図（ｂ）である。
【図４】トーションバーの捩じれ角（磁石と磁気ヨークとのずれ角）と磁気ヨークに生じる磁束密度との関係を表すグラフである。
【図５】一組の磁気ヨークの側面図である。
【図６】トーションバーの捩じれ角（磁石と磁気ヨークとのずれ角）と磁気ヨークに生じる磁束密度との関係を表わすグラフである。
【図７】トルクセンサの分解斜視図である。（他の実施例）
【符号の説明】
１…トルクセンサ、
２…入力軸、
３…出力軸、
４…トーションバー、
５…磁石、
６…磁気ヨーク、
７…磁気センサ、
８…ピン、
９…固定部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a torque sensor that detects a shaft torque in a mechanism that transmits rotational power, such as an electric power steering device.
[0002]
[Prior art]
As a conventional technique using a magnet and a magnetic sensor, the magnet and the magnetic sensor are identified at both ends of the torsion bar, and when a torque is applied, the torsion bar is twisted to change the positional relationship between the magnet and the magnetic sensor. There is one that obtains an output proportional to torque from a magnetic sensor (for example, see Patent Document 1).
[0003]
Also, it is the same as Patent Document 1 described above in that a magnet, a magnetic sensor, and a torsion bar are used, but a mechanism that changes the torsion of the torsion bar into an axial movement using a gear is used to fix the magnetic sensor to the housing. In addition, an electric contact portion for supplying power to the magnetic sensor and extracting a signal is not required (for example, see Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 8-15987 [Patent Document 2]
JP-A-6-281513
[Problems to be solved by the invention]
However, in the method of Patent Literature 1, since the magnet and the magnetic sensor are fixed to the torsion bar, an electric contact portion is required to supply power to the magnetic sensor and take out a signal. Since the ring and brush are used, there is concern about the reliability of the contact part.
[0006]
In addition, the method disclosed in Patent Document 2 has a gear mechanism for converting the torsion of the torsion bar into an axial movement. Therefore, the structure is complicated, and errors and errors are caused by backlash of the gear mechanism and wear of the gear. Since a response delay occurs, there is a concern in terms of performance.
[0007]
SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances, and an object of the present invention is to provide a torque sensor having a simple structure and no electrical contact.
[0008]
[Means for Solving the Problems]
In order to solve the above problem, in claim 1, the first shaft and the second shaft are connected coaxially, and when a torsional torque is input between the first shaft and the second shaft. An elastic member that causes twisting in itself, a hard magnetic body connected to the first shaft to form a magnetic field around it, and a hard magnetic body connected to the second shaft and arranged in a magnetic field formed by the hard magnetic body. And a magnetic circuit is formed, and when the relative position with respect to the hard magnetic material changes due to the torsion of the elastic member, a set of soft magnetic material having a structure in which the magnetic flux density generated in the magnetic circuit changes, A magnetic sensor installed in contact and detecting a magnetic flux density generated in a magnetic circuit of the soft magnetic material, the hard magnetic material is magnetized in the circumferential direction, and the soft magnetic material is disposed on the outer periphery of the hard magnetic material. , And face each other with a gap in the axial direction. The claw provided on one soft magnetic body and the claw provided on the other soft magnetic body are alternately arranged so as to be displaced in the circumferential direction, and the claw has a root portion and a tip portion; Is larger than the circumferential width of the tip portion, and the circumferential width A of the root portion is equal to the circumferential width of one of the soft magnetic nails. The following relationship is established with the circumferential length P up to one end in the direction.
[0009]
0.5 × P <A <P
According to the torque sensor of the present invention, when a torsional torque is input between the first shaft and the second shaft and the elastic member is twisted, the relative position between the hard magnetic material and the soft magnetic material changes. The magnetic flux density generated in the magnetic circuit of the soft magnetic material changes. By detecting the change in the magnetic flux density with a magnetic sensor, the torsional torque applied between the first axis and the second axis can be obtained. According to this configuration, the magnetic flux generated from the hard magnetic material does not need to be directly detected by the magnetic sensor, so that the non-contact type magnetic sensor can be fixed and used at a fixed position. As a result, there is no need to provide an electrical contact portion for the magnetic sensor, so that a highly reliable torque sensor can be provided.
[0010]
Further, between the circumferential width A of the base of the nail and the circumferential length P from one circumferential end of the base of one soft magnetic body to one circumferential end of the base of the adjacent nail. By satisfying the above relational expression, the magnetic sensor can detect a magnetic flux density with good linearity regardless of the size of the soft magnetic material.
[0011]
In the second aspect, the first shaft and the second shaft are coaxially connected, and when a torsional torque is input between the first shaft and the second shaft, the first shaft and the second shaft are twisted. A hard magnetic body connected to the elastic member and the first shaft to form a magnetic field around the elastic member; and a magnetic circuit connected to the second shaft and arranged in the magnetic field formed by the hard magnetic body to form a magnetic circuit. Then, when the relative position with respect to the hard magnetic material changes due to the torsion of the elastic member, a set of soft magnetic materials having a structure in which the magnetic flux density generated in the magnetic circuit changes, and An auxiliary soft magnetic body having a magnetic flux collecting part that guides magnetic flux from the magnetic body and collects the magnetic flux, and a magnetic sensor that detects a magnetic flux density generated in the auxiliary soft magnetic body via the magnetic collecting part, Circumferentially magnetized, the soft magnetic material is arranged on the outer periphery of the hard magnetic material, and the gap is And the same number of claws as the number of poles of the magnet are provided at equal intervals on the entire circumference, and the claw provided on one soft magnetic body and the claw provided on the other soft magnetic body are arranged in the circumferential direction. The nails have a root portion and a tip portion, and are arranged alternately and shifted. The circumferential width of the root portion is larger than the circumferential width of the tip portion, and the circumferential width A of the root portion is one. The following relationship is established between the soft magnetic material and the circumferential length P from one circumferential end of the base of the claw to one circumferential end of the base of the adjacent claw.
[0012]
0.5 × P <A <P
According to the torque sensor of the present invention, when a torsional torque is input between the first shaft and the second shaft and the elastic member is twisted, the relative position between the hard magnetic material and the soft magnetic material changes. The magnetic flux density generated in the magnetic circuit of the soft magnetic material changes. Further, the magnetic flux generated in the soft magnetic material is guided to the auxiliary soft magnetic material, and is collected in a magnetic flux collecting unit provided in the auxiliary soft magnetic material. Therefore, the torsion torque applied between the first axis and the second axis can be obtained by detecting the magnetic flux density generated in the auxiliary soft magnetic body via the magnetic flux collecting part by the magnetic sensor. According to this configuration, the magnetic flux generated from the hard magnetic material does not need to be directly detected by the magnetic sensor, so that the non-contact type magnetic sensor can be fixed and used at a fixed position. As a result, there is no need to provide an electrical contact group for the magnetic sensor, and a highly reliable torque sensor can be provided. Further, by collecting the magnetic flux generated in the auxiliary soft magnetic material in the magnetic flux collecting part, the average of the magnetic flux density generated in the entire circumference of the soft magnetic material can be detected by the magnetic sensor. As a result, it is possible to reduce a detection error due to manufacturing variations, assembly accuracy, center deviation, and the like of components constituting the magnetic circuit.
[0013]
Further, between the circumferential width A of the base of the nail and the circumferential length P from one circumferential end of the base of one soft magnetic body to one circumferential end of the base of the adjacent nail. By satisfying the above relational expression, the magnetic sensor can detect a magnetic flux density with good linearity regardless of the size of the soft magnetic material.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the embodiment shown in the drawings will be described.
[0015]
FIG. 1 is an exploded perspective view of the torque sensor 1. FIG. 2 is an axial sectional view of the torque sensor 1. FIG. 3 is an axial plan view (a) and a side view (b) showing the positional relationship between the magnet 5 and a set of magnetic yokes 6. FIG. 4 is a graph showing the relationship between the torsion angle of the torsion bar 4 (the angle of deviation between the magnet 5 and the magnetic yoke 6) and the magnetic flux density generated in the magnetic yoke 6. FIG. 5 is a side view of a pair of magnetic yokes 6. FIG. 6 is a graph showing the relationship between the torsion angle of the torsion bar 4 (the deviation angle between the magnet 5 and the magnetic yoke 6) and the magnetic flux density generated in the magnetic yoke 6.
[0016]
The torque sensor 1 according to the present embodiment is used, for example, in an electric power steering device for a vehicle, and is provided between an input shaft 2 (first shaft) and an output shaft 3 (second shaft) constituting a steering shaft. And detects the steering torque applied to the steering shaft.
[0017]
The torque sensor 1 includes a torsion bar 4 (elastic member) for connecting the input shaft 2 and the output shaft 3 coaxially, and a magnet 5 (hard) attached to an end of the input shaft 2 (or one end of the torsion bar 4). A magnetic body), a set of magnetic yokes 6 (soft magnetic body) attached to the end of the output shaft 3 (or the other end of the torsion bar 4), and a magnetic flux density generated between the set of magnetic yokes 6 And the like.
[0018]
Both ends of the torsion bar 4 are fixed to the input shaft 2 and the output shaft 3 by pins 8, respectively, and have torsional / torque characteristics according to the purpose. Therefore, the input shaft 2 and the output shaft 3 can relatively rotate due to the torsion bar 4 being twisted.
[0019]
The magnet 5 is provided in a ring shape, and the S pole and the N pole are alternately magnetized in the circumferential direction, and are formed to have, for example, 24 poles.
[0020]
As shown in FIG. 1, the pair of magnetic yokes 6 (6A, 6B) is an annular body disposed close to the outer periphery of the magnet 5, and has the same number (12) as the N and S poles of the magnet 5, respectively. Are provided at equal intervals around the entire circumference. The set of magnetic yokes 6 is positioned by the fixing portion 9 (see FIG. 2) such that the claws 6a are alternately arranged while being shifted in the circumferential direction.
[0021]
The pair of magnetic yokes 6 and the magnets 5 are applied to the respective magnetic yokes 6 in a state where the torsion bar 4 is not twisted (when no torsional torque is applied between the input shaft 2 and the output shaft 3). It is arranged so that the center of the provided claw 6a and the boundary between the N pole and the S pole of the magnet 5 coincide (see FIG. 3).
[0022]
As shown in FIG. 3, the magnetic sensor 7 is inserted into a gap G provided between one magnetic yoke 6A and the other magnetic yoke 6B opposed in the axial direction, and the magnetic flux density generated between the two magnetic yokes 6 Is detected. However, the magnetic sensor 7 is fixed to a housing or the like (not shown) without being in contact with the magnetic yoke 6, and is provided at a fixed position.
[0023]
As the magnetic sensor 7, for example, a Hall element, a Hall IC, a magnetic resistance element, or the like can be used, and the detected magnetic flux density is converted into an electric signal (for example, a voltage signal) and output.
[0024]
Next, the operation of the present embodiment will be described.
[0025]
In a state where no torsional torque is applied between the input shaft 2 and the output shaft 3, that is, in a neutral position where the torsion bar 4 is not twisted, the claw provided on the magnetic yoke 6 as shown in FIG. The center of 6a coincides with the boundary between the north pole and the south pole of the magnet 5. In this case, since the same number of lines of magnetic force enter and exit from the N pole and the S pole of the magnet 5 to the claws 6a of each magnetic yoke 6, the lines of magnetic force are closed inside one magnetic yoke 6A and the other magnetic yoke 6B. . Therefore, no magnetic flux leaks between the magnetic yoke 6A and the magnetic yoke 6B (gap G), and the magnetic flux density detected by the magnetic sensor 7 becomes 0 (see FIG. 4).
[0026]
When a torsion torque is applied between the input shaft 2 and the output shaft 3 and the torsion bar 4 is twisted, a pair of magnets 5 fixed to the input shaft 2 and a pair of magnetic yokes 6 fixed to the output shaft 3 are formed. Relative position changes in the circumferential direction. As a result, as shown in FIG. 4A or 4C, the center of the claw 6a provided on the magnetic yoke 6 does not coincide with the boundary between the N pole and the S pole of the magnet 5, so that each magnetic yoke In 6, the number of lines of magnetic force having N or S polarity increases.
[0027]
At this time, since the magnetic lines of force having the opposite polarities increase in one magnetic yoke 6A and the other magnetic yoke 6B, the magnetic flux density is present between one magnetic yoke 6A and the other magnetic yoke 6B (gap G). appear. As shown in FIG. 4, the magnetic flux density is substantially proportional to the amount of twist of the torsion bar 4, and the polarity is reversed according to the direction of twist of the torsion bar 4. This magnetic flux density can be detected by the magnetic sensor 7 and taken out as a voltage signal.
[0028]
In the torque sensor 1 according to the present embodiment, when the torsion bar 4 is twisted and the relative position between the magnet 5 and the set of magnetic yokes 6 changes in the circumferential direction, the magnetic flux is generated all around the set of magnetic yokes 6. Density changes. That is, the magnetic flux density having the same intensity can be detected in the entire circumference between the pair of magnetic yokes 6. Therefore, by inserting the magnetic sensor 7 into the gap G where one magnetic yoke 6A and the other magnetic yoke 6B face each other, it is possible to detect the magnetic flux density between the magnetic yokes 6 without contacting the magnetic yoke 6. Can be. Accordingly, it is not necessary to provide an electrical contact portion (for example, a slip ring and a brush) to the magnetic sensor 7, so that the highly reliable torque sensor 1 can be provided.
[0029]
In addition, how to determine the shape of the magnetic yoke 6 for improving the linearity of the magnetic flux density generated in the magnetic yoke 6 in the detection torque range of the magnetic sensor 7 will be described below based on experimental data.
[0030]
As shown in FIG. 5, the claw 6a has a root portion 6a1 and a tip portion 6a2. The circumferential width A of the root portion 6a1 is larger than the circumferential width B of the tip portion 6a2, and the center in the circumferential direction. Has a substantially trapezoidal shape that is symmetrical along the line.
[0031]
Then, the number of poles n of the magnet 5 is 24, the inner diameter r of the magnetic yoke 6 is 31 mm, and the axial distance F from one magnetic yoke 6A to the other magnetic yoke 6B is 8 mm, as shown in Table 1. The circumferential width A of the base 6a1 of the claw 6a is set to the first to third levels, and the axial length L from the base 6a1 to the tip 6a2 is set to the first to fourth levels. did. Then, the magnetic flux density generated in the magnetic yoke 6 when the magnetic yoke 6 was rotated 2.5 degrees in the circumferential direction from the neutral position with respect to the magnet 5 was measured.
[0032]
[Table 1]

[0033]
As shown in FIG. 5, the claw 6a of the other magnetic yoke 6B has a first claw 61 and a second claw 62 that are adjacent in the circumferential direction, and has a width A in the circumferential direction of the root portion 6a1. The circumferential distance P from one circumferential end of the root 6a1 of the first claw 61 (one right end in the circumferential direction) to one circumferential end of the root 6a1 of the second claw 62 (one right in the circumferential direction) changes. As a result, the circumferential distance between the first claw 61 and the second claw 62 changes, and the amount of magnetic flux entering and exiting between the magnet 5 and the magnetic yoke 6 changes. The theory for improving the linearity of the magnetic flux density will be described below.
[0034]
The circumferential distance P from one circumferential end of the root 6a1 of the first claw 61 to one circumferential end of the root 6a1 of the second claw 62 is the distance P between one magnetic yoke 6A and the other magnetic yoke 6B. Since the number of poles n of the nail 6a is 12 poles, it can be obtained by the following relational expression (1).
[0035]
P [mm] = π × r (31 mm) / n (12) ≒ 8.11 (1)
Further, when the circumferential width A of the root 6a1 is at the third level (4.2 mm), the waveform becomes a solid line waveform as a sine wave shown in FIG. 6, and from Table 2, from the root 6a1 to the tip 6a2. When the axial length L is at the second level (7.0 mm) and the circumferential width A of the root 6a1 is at the second level (3.7 mm), the magnetic flux density generated in the magnetic yoke 6 is maximized. It was found that the waveforms indicated by dotted lines in FIG. In the waveform of the dotted line, a dead zone region where the change of the magnetic flux density is small is generated, so that the magnetic flux density generated in the magnetic yoke 6 near the magnetic angle of ± 90 deg cannot be made linear.
[0036]
For this reason, in the present invention, the third level (4.2 mm) is set as the threshold value of the circumferential width A of the root portion 6a1. In the present embodiment, the circumferential distance P from one circumferential end of the root 6a1 of the first claw 61 to one circumferential end of the root 6a1 of the second claw 62 is fixed. Therefore, by dividing the circumferential width A of the root 6a1 by the distance P obtained by the above-described relational expression (4), the circumferential width A of the root 6a1 and the circumference of the root 6a1 of the first claw 61 are obtained. A proportionality constant with the circumferential distance P from one end in the direction to one end in the circumferential direction of the root 6a1 of the second claw 62 can be obtained (see relational expression (2)).
[0037]
A (4.2 mm) / P (8.11 mm) ≒ 0.517
As described above, by setting the numerical value A from the following relational expression (2) to the range of the following relational expression (3), the magnetic flux density generated in the magnetic yoke 6 becomes as shown by the solid line waveform in FIG. In addition, a sine wave can be obtained, and the magnetic sensor 7 can detect a magnetic flux density with good linearity. The proportionality constant was determined in consideration of a slight error in the experimental data.
[0038]
0.5 × P <A <P ・・・・・・・・・ 3
In the present embodiment, the number of poles n of the magnetic yoke 6 or the magnet 5 is 24, the inner diameter r of the magnetic yoke 6 is 31 mm, and the axial distance F from one magnetic yoke 6A to the other magnetic yoke 6B is 8 mm. However, even if the size of the magnetic yoke 6 changes and the values of the number of poles n, the inner diameter r, and the distance F change proportionally, the amount and magnetic flux of the magnetic flux flowing between the magnet 5 and the magnetic yoke 6 Since the path does not change, the sine wave waveform shown in FIG. 6 can be obtained by satisfying the above relation (3).
[0039]
In the present embodiment, for example, it has been described that the magnetic flux density of the magnetic sensor 6 can be maximized when the circumferential width A of the root part 6a1 is 3.7 mm. It is conceivable that there is a value that can increase the magnetic flux density of the sensor 6.
[0040]
The claw 6a in the present embodiment has a substantially trapezoidal shape in which the circumferential width A of the root portion 6a1 is larger than the circumferential width B of the distal end portion 6a2, but the circumferential width of the distal end portion 6a2. A substantially triangular shape in which B is 0 may be used.
[0041]
As shown in FIG. 7, a ring-shaped magnetic flux collecting ring 10 (auxiliary soft magnetic material) may be provided near the outer periphery of the

magnetic yokes

6A and 6B. The magnetic flux collecting ring 10 is a soft magnetic material similar to the

magnetic yokes

6A and 6B, and is provided with a flat magnetic flux collecting portion 10a at one circumferential position, and the magnetic flux collecting portions 10a are opposed to each other in the axial direction. Placed. However, the magnetic flux collecting part 10a is provided closer to the axial direction than other parts of the magnetic flux collecting ring 10. Further, the magnetic sensor 7 is inserted between the magnetic flux collecting portions 10a facing each other in the axial direction, and detects the magnetic flux density generated between the magnetic flux collecting portions 10a.
[0042]
According to this configuration, since the magnetic flux collection ring 10 forms a part of a magnetic circuit, the magnetic flux generated from the magnet 5 is guided to the magnetic flux collection ring 10 through the magnetic yoke 6 and provided on the magnetic flux collection ring 10. It gathers preferentially in the magnetic flux collecting part 10a. By detecting the magnetic flux density generated between the magnetic flux collecting portions 10a with the magnetic sensor 7, the average of the magnetic flux density generated over the entire circumference of the magnetic yoke 6 can be obtained, so that manufacturing variations of the components constituting the magnetic circuit can be obtained. And an assembly error, and a detection error due to a center shift between the input side and the output side can be suppressed.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a torque sensor.
FIG. 2 is an axial sectional view of a torque sensor.
3A and 3B are an axial plan view and a side view showing a positional relationship between a magnet and a set of magnetic yokes.
FIG. 4 is a graph showing a relationship between a torsion angle of a torsion bar (a deviation angle between a magnet and a magnetic yoke) and a magnetic flux density generated in the magnetic yoke.
FIG. 5 is a side view of a set of magnetic yokes.
FIG. 6 is a graph showing a relationship between a torsion angle of a torsion bar (a deviation angle between a magnet and a magnetic yoke) and a magnetic flux density generated in the magnetic yoke.
FIG. 7 is an exploded perspective view of the torque sensor. (Other embodiments)
[Explanation of symbols]
1: Torque sensor,
2. Input shaft,
3 ... output shaft,
4 ... torsion bar
5 ... magnet,
6 ... magnetic yoke,
7 ... magnetic sensor,
8 ... pin,
9 ... fixed part

Claims

An elastic member that connects the first shaft and the second shaft coaxially, and when a torsional torque is input between the first shaft and the second shaft, the elastic member generates a torsion;
A hard magnetic body connected to the first shaft and forming a magnetic field around the first shaft;
The magnetic member is connected to the second shaft and arranged in a magnetic field formed by the hard magnetic material to form a magnetic circuit, and when the relative position with respect to the hard magnetic material changes due to the torsion of the elastic member, the magnetic force is reduced. A set of soft magnetic materials having a structure in which the magnetic flux density generated in the circuit changes,
A magnetic sensor that is installed in non-contact with the soft magnetic body and detects a magnetic flux density generated in a magnetic circuit of the soft magnetic body,
The hard magnetic material is magnetized in a circumferential direction,
The soft magnetic material is arranged on the outer periphery of the hard magnetic material, and is opposed to each other via a gap in the axial direction, and the same number of claws as the number of poles of the magnet are provided at equal intervals on the entire circumference. The claw provided on the soft magnetic body and the claw provided on the other soft magnetic body are alternately arranged so as to be shifted in the circumferential direction,
The claw has a root portion and a tip portion, and a circumferential width of the root portion is larger than a circumferential width of the tip portion,
Between the circumferential width A of the root portion and the circumferential length P from one circumferential end of the root portion of the claw of one soft magnetic material to one circumferential end of the root portion of the adjacent claw. A torque sensor, wherein the following relationship is established.
0.5 × P <A <P

An elastic member that connects the first shaft and the second shaft coaxially, and when a torsional torque is input between the first shaft and the second shaft, the elastic member generates a torsion;
A hard magnetic body connected to the first shaft and forming a magnetic field around the first shaft;
The magnetic member is connected to the second shaft and arranged in a magnetic field formed by the hard magnetic material to form a magnetic circuit, and when the relative position with respect to the hard magnetic material changes due to the torsion of the elastic member, the magnetic force is reduced. A set of soft magnetic materials having a structure in which the magnetic flux density generated in the circuit changes,
An auxiliary soft magnetic body that is arranged close to the soft magnetic body, guides magnetic flux from the soft magnetic body, and has a magnetic flux collecting unit that collects the magnetic flux;
A magnetic sensor that detects a magnetic flux density generated in the auxiliary soft magnetic body through the magnetic flux collection unit,
The hard magnetic material is magnetized in a circumferential direction,
The soft magnetic material is arranged on the outer periphery of the hard magnetic material, and is opposed to each other via a gap in the axial direction, and the same number of claws as the number of poles of the magnet are provided at equal intervals on the entire circumference. The claw provided on the soft magnetic body and the claw provided on the other soft magnetic body are alternately arranged so as to be shifted in the circumferential direction,
The claw has a root portion and a tip portion, and a circumferential width of the root portion is larger than a circumferential width of the tip portion,
Between the circumferential width A of the root portion and the circumferential length P from one circumferential end of the root portion of the claw of one soft magnetic material to one circumferential end of the root portion of the adjacent claw. A torque sensor, wherein the following relationship is established.
0.5 × P <A <P