JP2004176903A

JP2004176903A - Gear device

Info

Publication number: JP2004176903A
Application number: JP2003039460A
Authority: JP
Inventors: Norio Usuki; 功雄臼杵; Masahiro Inoue; 昌弘井上; Takanori Kurokawa; 貴則黒川
Original assignee: Koyo Seiko Co Ltd
Current assignee: Koyo Seiko Co Ltd
Priority date: 2002-10-01
Filing date: 2003-02-18
Publication date: 2004-06-24

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a resin gear 20 from being pulled out of an outer cylindrical section 15 by achieving whirl-stop of the resin gear 20 to the peripheral direction of the outer cylindrical section 15 and preventing the resin gear 20 from moving axially to both sides, regarding a gear device applied to a ball screw device or the like. <P>SOLUTION: The resin gear 20 is formed on a cylindrical bracket 10 made of a thin steel by injection molding. The bracket 10 includes an annular section 14 being extended in a diameter direction; and the outer cylindrical section 15 being extended in an axial direction from the outer diameter end of the annular section 14. The cylindrical section 15 is set to be a corrugated sheet section 18, where a tip side as compared with the middle in the axial direction is expanded in the direction of an outer diameter, and a projection 18a and a recess 18b are alternately formed in the circumferential direction. The resin gear 20 is formed on an outer periphery surface 15a in the outer cylindrical section 15 in a form for coming into contact with both the ends in the axial direction of the corrugated sheet section 18. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ボールねじ装置等に適用される歯車装置に関する。
【０００２】
【従来の技術】
従来、保持体に樹脂歯車を射出成形してなる歯車装置を用いたパワーステアリング装置がある（例えば、特許文献１参照。）。
【０００３】
パワーステアリング装置に適用する歯車装置の場合、樹脂歯車は軸心回りに回転するが、軸方向に移動することはなく、軸心回りの回転に対して樹脂歯車が保持体の周方向にずれるのを防止するように構成されている。
【０００４】
しかし、歯車装置には、樹脂歯車が軸心回りに回転しながら軸方向にも移動する場合がある。
【０００５】
一例として、ナット部材とねじ軸との間でトルクを推力に変換したり、推力をトルクに変換したりする構成を有するボールねじ装置がある。
【０００６】
このボールねじ装置は、ナット部材と、このナット部材と同心に配置されるねじ軸と、ナット部材およびねじ軸に形成したねじ溝を転動自在なボール群とからなるボールねじを備える。
【０００７】
ボールねじのナット部材には、ブラケットが回転一体に連結されている。また、ブラケットおよびボールねじのねじ軸の内周面と、回転軸の外周面との間には転がり軸受が組付けられており、回転軸を軸心回りに回転自在に支持している。さらに、ブラケットの外周部には、回転動力が伝えられる樹脂歯車が射出成形により一体的に形成されている。
【０００８】
樹脂歯車に回転動力が伝えられて軸心回りに回転すると、ブラケットならびにナット部材が、ねじ軸の回りに回転し、ボールねじが伸び縮みする。このように、樹脂歯車はブラケットに一体成形されており、ブラケットと共に軸心回りに回転しながら軸方向に移動する。
【０００９】
【特許文献１】
特開２００２−１４５０８６号公報（図３）
【００１０】
【発明が解決しようとする課題】
ボールねじのブラケットに射出成形された樹脂歯車のように、軸心回りに回転しながら軸方向に移動する歯車装置の場合、樹脂歯車には周方向ならびに軸方向に力が作用する。
【００１１】
その結果、樹脂歯車がブラケットに対して周方向にずれたり、軸方向に移動してブラケットから抜けるおそれがあった。
【００１２】
【課題を解決するための手段】
本発明の歯車装置は、薄肉鋼板製の円筒状の保持体に、樹脂歯車を射出成形してなり、前記保持体は、径方向に延設された環状部と、前記環状部の外径端から軸方向に延設された筒部とを含み、前記筒部は、その軸方向途中よりも先端側を、外径方向に膨出させかつ周方向に凸部と凹部を交互に形成してなる波板部とし、前記樹脂歯車は、前記波板部の軸方向両端に当接する形態で前記筒部の外周面に射出成形されている。
【００１３】
樹脂歯車が成形される部位としては、軸心回りに回転しながら軸方向に移動するＣＶＴ用のボールねじ装置等が挙げられる。
【００１４】
波板部は、例えば、少なくとも凸部の一部が筒部の外径方向に膨出していればよく、その膨出部分の軸方向端面に樹脂歯車を当接させることで、樹脂歯車の軸方向の移動を防ぐことができる。
【００１５】
本発明の歯車装置によると、保持体の筒部の軸方向途中より先端側を、周方向に凸部と凹部を交互に形成してなる波板部とし、樹脂歯車を筒部の外周面に射出成形したことにより、保持体の周方向に対する樹脂歯車の回り止めが図れる。また、波板部を筒部の外周面より外径方向に膨出させ、樹脂歯車を波板部の軸方向両端に当接させて筒部の外周面に射出成形したので、樹脂歯車は、波板部の軸方向先端と軸方向基端に当接し、樹脂歯車が保持体に対して軸方向両側に移動するのを防止でき、樹脂歯車の抜け止めが図れる。
【００１６】
また、前記保持体の筒部は、その軸方向途中よりも先端側を外径側に屈曲させてなる拡径部を有しており、当該拡径部に前記波板部が形成されていてもよい。
【００１７】
このように、筒部の軸方向途中よりも先端側に拡径部を形成したので、樹脂歯車は波板部の軸方向基端において、拡径部ならびに波板部の端面に当接し、当該当接面積が大きくなる。よって、樹脂歯車が軸方向に移動するのをより一層防止でき、保持体に対する樹脂歯車の抜け止めが確実に図れる。
【００１８】
さらに、前記樹脂歯車が、前記保持体の筒部の軸方向先端から当該筒部の内周面にまで回り込む形態に射出成形されていてもよい。
【００１９】
このように、樹脂歯車を筒部の軸方向先端から内周面に回り込んで射出成形することで、樹脂歯車を筒部の外周面に射出成形する際に、当該射出圧によって薄肉鋼板製の筒部の内径が収縮するのを抑制でき、保持体の筒部のたわみを防止できる。
【００２０】
【発明の実施の形態】
本発明の実施形態に係る歯車装置を図面に基づいて説明する。
【００２１】
図１および図２は本実施形態の歯車装置の使用状態を示すボールねじ装置の全体断面図、図３はそのボールねじ装置の分解斜視図、図４は樹脂歯車を成形したブラケットの正面図、図５は図４の樹脂歯車を除いた状態のＶ−Ｖ断面図、図６は図４のVI-VI断面図、図７は樹脂歯車を成形したブラケットの部分断面図、図８はブラケットの部分拡大断面図、図９は図７のブラケット部分におけるIX矢視図である。
【００２２】
本発明の歯車装置が適用されるボールねじ装置１は、軸方向に一対のフランジを有するプーリ２における当該フランジ間の軸方向離隔距離を変更することで、プーリ２に巻掛られるベルト３の巻掛径を変更するために用いられる。
【００２３】
プーリ２は、回転軸４に軸心回りに回転一体に設けられる第一フランジ５と、回転軸４に軸心回りに回転一体かつ軸方向に沿って摺動自在に配置される第二フランジ６とを備える。
【００２４】
ボールねじ装置１は、保持体となるブラケット１０、合成樹脂製の樹脂歯車２０、ボールねじ３０を有する。
【００２５】
ブラケット１０は、薄肉鋼板をプレス加工することによって円筒形状に形成されている。
【００２６】
ブラケット１０は、内筒部１１と、この内筒部１１の軸方向一方側から内筒部１１の内周面に沿って重ねるように軸方向途中まで折返し形成された折返し筒部１２と、この折返し筒部１２の軸方向他方側端部から径方向内方に向けて折曲形成された隔壁１３と、内筒部１１の軸方向他方側端部から径方向外方に向けて折曲形成された環状部１４と、環状部１４の径方向外端から軸方向一方側に向けて折曲形成された外筒部１５とを備え、板金をプレス加工することによって製造されても、充分な剛性が得られる。
【００２７】
隔壁１３は、折返し筒部１２の円周方向等配位置に複数箇所形成されている。また、隔壁１３のうちの一個は、その先端部がさらに軸方向一方側に向けて折曲された折曲部１６が形成されている。
【００２８】
外筒部１５は、その軸方向途中よりも先端側を外径側に屈曲させてなる拡径部１７を有しており、その拡径部１７に波板部１８が形成されている。波板部１８は、外径方向に膨出させ、かつ、凸部１８ａと凹部１８ｂを周方向に交互にプレス形成してなる。これにより、波板部１８は外筒部１５の外周面１５ａより外径側に突出する。
【００２９】
図８に、ブラケット１０の外筒部１５の拡大断面図を示す。外筒部１５に形成された拡径部１７の基部における内径面が凸曲面１９ａ，外径面が凹曲面１９ｂに形成され、拡径部１７に形成された波板部１８の基部における内径面が凹曲面１９ｃ，外径面が凸曲面１９ｄに形成され、波板部１８の先端部における内径面および外径面がそれぞれ凸曲面１９ｅ，１９ｆに形成されている。
【００３０】
凸曲面１９ａ，１９ｄ，１９ｅ，１９ｆならびに凹曲面１９ｂ，１９ｃの曲率半径Ｒは、０．５ｍｍ以上とする。
【００３１】
図９に示すように、波板部１８の高さ寸法（谷部の内径と山部の外径との幅寸法）ｈは、２．０ｍｍ以上とする。また、凸部１８ａと凹部１８ｂの曲率半径Ｒは、０．５ｍｍ以上とする。さらに、凸部１８ａの数は、樹脂歯車２０の歯数の半分以上とする。
【００３２】
ブラケット１０の外筒部１５の凸曲面１９ａ，１９ｄ，１９ｅ，１９ｆならびに凹曲面１９ｂ，１９ｃ、波板部１８の凸部１８ａと凹部１８ｂを、それぞれ０．５ｍｍ以上の曲率半径Ｒとしたことにより、ヒートショック時における樹脂歯車２０への応力集中を防ぐことができる。
【００３３】
すなわち、雰囲気温度が下がり、金属製のブラケット１０と樹脂歯車２０の線膨張率の差から樹脂歯車２０が収縮することに基づいて、その境界部に残留応力（樹脂歯車２０にとっては引張方向）が集中する。ブラケット１０の角部の曲率半径Ｒが０．５ｍｍ未満であると、その角部に相対する樹脂歯車２０に大きな応力が集中して、割れ等の破損が発生し易くなる。
【００３４】
そこで、曲率半径Ｒを０．５ｍｍ以上とすることで、ブラケット１０と樹脂歯車２０の界面における応力集中を防止し、ヒートショックによる割れを防止することができる。
【００３５】
樹脂歯車２０は、外筒部１５の外周面１５ａに射出成形により一体的に形成され、ブラケット１０と樹脂歯車２０とが軸心回りに回転一体に設けられている。
【００３６】
樹脂歯車２０の外周端には、不図示の回転動力源から駆動力が伝達されて回転する減速歯車７の歯部７ａが噛合される歯部２１が形成されている。
【００３７】
樹脂歯車２０は、波板部１８の軸方向両端に当接すると共に、外筒部１５の先端から内周面１５ｂに回り込んで、外筒部１５の外周面１５ａに射出成形されている。内周面１５ｂに回り込んで樹脂歯車２０を成型する際に、樹脂はブラケット１０の環状部１４の表面１４ａ（図７参照）にまで達して止まることとなる。
【００３８】
すなわち、図７に示すように、外筒部１５の内周面１５ｂに沿って環状部１４にまで達する回り込み部２３と、波板部１８の先端１８ｃにおいて凸部１８ａならびに凹部１８ｂの端面に当接した先端当接部２４と、波板部１８の基端１８ｄにおいて拡径部１７の端面１７ａならびに波板部１８の端面に当接した基端当接部２５とを有している。
【００３９】
樹脂歯車２０を構成する樹脂材料としては、例えば、オレフィン系樹脂（ポリプロピレンなど）、フッ素樹脂、スチレン系樹脂（アクリロニトリル−スチレン共重合体、ＡＢＳ樹脂など）、アクリル系樹脂（ポリメタクリル酸メチルなど）、ポリエステル系樹脂（ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリエチレンナフタレートなどのポリアルキレンアリーレート（ホモポリエステル）、アルキレンアリレート単位を有するコポリエステル、ポリアリレート系樹脂、液晶性ポリエステルなど）、ポリカーボネート系樹脂（ビスフェノールＡ型ポリカーボネートなど）、ポリアミド系樹脂（６ナイロン、１１ナイロン、１２ナイロン、４６ナイロン、６６ナイロン、６Ｔナイロン、９Ｔナイロン、６１０ナイロン、６１２ナイロンなどの脂肪族ナイロン、芳香族ナイロンＭＸＤ−６など）、ポリアセタール系樹脂、ポリフェニレンエーテル系樹脂、ポリフェニレンスルフィド系樹脂、ポリスルホン系樹脂、ポリスルホンエーテル系樹脂、ポリフタルアミド系樹脂などが例示できる。
【００４０】
さらに、上記樹脂材料に補強繊維や固体潤滑剤が含まれていてもよい。
【００４１】
補強繊維としては、無機繊維（ガラス繊維、炭素繊維、金属繊維、チタン酸カリウム、チタン酸バリウム、アルミナ繊維、シリカ繊維、炭化ケイ素繊維、窒化ケイ素繊維等）、先進強化プラスチックや、有機繊維（アラミド繊維等）などが例示できる。
【００４２】
固体潤滑剤としては、二硫化モリブデン、高密度ポリエチレン（ＨＤＰＥ）、ＰＴＦＥ、超高分子量ポリエチレン（ＵＨＭＷＰＥ）などが例示できる。
【００４３】
外筒部１５の外周面１５ａに樹脂歯車２０が射出成形される際、当該射出圧によってプレス成形品である薄板の外筒部１５の内径が収縮し、樹脂金型に食い付くおそれがある。そこで、射出圧による収縮量を考慮して樹脂金型との隙間を大きくとると、ブラケット１０と樹脂歯車２０との心合わせができなくなったり、収縮により樹脂歯車２０が傾斜し、歯形精度が低下するおそれがある。そこで、外筒部１５の内周面１５ｂに沿う回り込み部２３を形成したことにより、当該回り込み部２３は、外筒部１５の内径の収縮を抑制する方向に作用し、当該収縮を抑えることができる。
【００４４】
先端当接部２４と基端当接部２５により、外筒部１５に対して樹脂歯車２０が軸方向に移動するのを防止できる。
【００４５】
ボールねじ３０は、保持器を有しない総ボール型のボールねじであり、ブラケット１０の軸方向一方側内周面に軸心回りに回転一体に嵌合される円筒状のナット部材３１を有する。このナット部材３１の端面に、各隔壁１３と嵌合する切欠き３２が形成され、これら各切欠き３２と隔壁１３とが軸方向で嵌合することにより、ナット部材３１がブラケット１０に軸心回りに確実に回転一体な構成となっている。ナット部材３１は、その切欠端面が隔壁１３の軸方向一方側端面に当接されている。ナット部材３１の内周面に、両端部間で連続した所定のリード角を有する一条のねじ溝３３が形成されている。
【００４６】
ボールねじ３０は、ナット部材３１の内径側に配置される円筒状のねじ軸３４を有する。ねじ軸３４は、図示しない所定の支持装置でもって軸心回りに非回転に支持されるとともに、軸方向に不動に支持されている。ねじ軸３４は、外周面に、互いに平行でそれぞれ独立の閉ループとした所定のリード角を有する２条のねじ溝３５を有する。各ねじ溝３５は、所定のリード角を有するねじ溝３５の端部どうしをリード角と異なる角度をもって連続させるボール循環溝３６を有し、このボール循環溝３６によって各ねじ溝３５は別個に閉ループとされる。
【００４７】
これらボール循環溝３６は、それぞれのねじ溝３５の上流側と下流側とを連通する部分である。すなわち、これらボール循環溝３６は、各ねじ溝３５の下流側に位置するボール３７をねじ軸３４の内径側に沈みこませて上流へ戻すよう、ねじ溝３５の他の部分に比べて深く形成されるとともに蛇行した形状に形成されている。これにより、ねじ溝３５に嵌合するボール３７をそれぞれ独立して転動循環させる構成となっている。
【００４８】
ねじ軸３４の軸方向他方側開口の外周面の一部が、所定周長を有するよう円周方向に沿って切欠かれ、当該切欠部３８と隔壁１３の折曲部１６とで、ナット部材３１が軸心回りに必要以上に回転するのを防止するためのストッパが構成される。
【００４９】
ねじ軸３４の内周面一方側に、転がり軸受（アンギュラ玉軸受）４０が嵌着されている。転がり軸受４０は、ねじ軸３４に嵌着された外輪部材４１と、回転軸４が挿通する内輪部材４２と、外輪部材４１と内輪部材４２との間に転動自在に配置された複数個の玉４３とを備える。
【００５０】
ブラケット１０の内周面他方側に、転がり軸受（アンギュラ玉軸受）５０が嵌着されている。転がり軸受５０は、ブラケット１０の内周面に嵌着される軸受部材としての外輪部材５１と、回転軸４に軸心回りに回転一体に組付けられるとともに第二フランジ６に一体形成された筒軸６ａの外周面に嵌着される内輪部材５２と、外輪部材５１および内輪部材５２の間に転動自在に配置された複数個の玉５３とを備える。転がり軸受５０における外輪部材５１の側面は、隔壁１３の側面に当接している。
【００５１】
図１は、ボールねじ３０が最も縮んで第一フランジ５と第二フランジ６とが軸方向に最も隔離した状態であり、ベルト３の巻掛径が小さい状態である。この状態では、切欠部３８の当接面に折曲部１６が当接し、ナット部材３１の回転が防止された状態にある。
【００５２】
上記状態から減速歯車７が軸心回りに回転して歯部７ａが回転すると、減速歯車７の回転とともに樹脂歯車２０が軸心回りに回転する。樹脂歯車２０の回転に伴なって、ブラケット１０ならびにナット部材３１が、ねじ軸３４の回りに回転すると共に、図２に示すように、軸方向（図の左方）に移動する。これにより、ブラケット１０に一体成形された樹脂歯車２０も軸方向に移動する。そして、第一フランジ５および第二フランジ６の径方向内方部位どうしが軸方向で当接した時点で、ナット部材１３は軸方向の移動を停止し、ベルト３はフランジ５，６間を拡径するようにせり上がり巻掛径が最大となる。
【００５３】
再び、ベルト３の巻掛径を小さくする場合は、上記と反対方向の回転力を減速歯車７から樹脂歯車２０に対して付与することで、ナット部材３１は軸方向（図の右方）に移動し、図１のように、切欠部３８の当接面に折曲部１６が当接した時点で、ナット部材３１は軸方向の移動を停止する。
【００５４】
このように構成された歯車装置によると、外筒部１５の軸方向途中より先端側を、周方向に凸部１８ａと凹部１８ｂを交互に形成してなる波板部１８とし、樹脂歯車２０を外筒部１５の外周面１５ａに射出成形したことにより、外筒部１５の周方向に対する樹脂歯車２０の回り止めが図れる。しかも、プレス成形により簡単に波板部１８を形成でき、コストの低減が図れる。
【００５５】
また、波板部１８を外筒部１５の外周面１５ａより外径側に膨出させ、樹脂歯車２０を波板部１８の軸方向両端に当接させて外筒部１５の外周面１５ａに成形したので、樹脂歯車２０の先端当接部２４が波板部１８の軸方向先端１８ｃに当接し、基端当接部２５が波板部１８の軸方向基端１８ｄに当接し、樹脂歯車２０が外筒部１５に対して軸方向両側に移動するのを防止でき、樹脂歯車２０の抜け止めが図れる。しかも、波板部１８の高さ寸法ｈを２ｍｍ以上としたので、樹脂歯車２０が当接する軸方向先端１８ｃならびに軸方向基端１８ｄの当接面積が増え、抜け荷重が大きくなり、樹脂歯車２０の抜け止めが確実に行える。
【００５６】
また、外筒部１５の軸方向途中よりも先端側に拡径部１７を形成したので、樹脂歯車２０は波板部１８の軸方向基端１８ｄにおいて、拡径部１７ならびに波板部１８の端面に当接し、当該当接面積が大きくなる。よって、樹脂歯車２０が軸方向に移動するのをより一層防止でき、外筒部１５に対する樹脂歯車２０の抜け止めが確実に図れる。
【００５７】
また、外筒部１５の凸曲面１９ａ，１９ｄ，１９ｅ，１９ｆならびに凹曲面１９ｂ，１９ｃの曲率半径Ｒ、凸部１８ａと凹部１８ｂの曲率半径Ｒを、それぞれ０．５ｍｍ以上としたことで、ブラケット１０と樹脂歯車２０の界面における応力集中を防止し、ヒートショックによる割れを防止できる。
【００５８】
また、樹脂歯車２０を外筒部１５の軸方向先端から内周面１５ｂに回り込んで成形することで、樹脂歯車２０を外筒部１５の外周面１５ａに射出成形する際に、当該射出圧によって薄肉鋼板製の外筒部１５の内径が収縮するのを抑制でき、外筒部１５のたわみを防止できる。よって、射出成形時に樹脂金型に食い付くのを防止でき、ブラケット１０と樹脂歯車２０との心合わせが容易に行えて歯形精度が向上し、生産性の向上ならびにコストの低減が図れる。
【００５９】
さらに、外筒部１５の軸方向途中より先端側を波板部１８としたので、外筒部１５の外周面１５ａに樹脂歯車２０を成形することで、波板部１８の軸方向両端に樹脂歯車２０を当接させることができ、環状部１４にまで渡って樹脂歯車２０を成形する必要がなく、射出成形時における樹脂金型の形状の簡素化が図れ、簡単かつ安価に樹脂歯車２０を射出成形できる。
【００６０】
図１０に、樹脂歯車２０を成形したブラケット１０の変形例を示す。
【００６１】
この例は、ブラケット１０の外筒部１５が平坦な筒状に形成されており、その軸方向途中より先端側を波板部１８としたものである。
【００６２】
樹脂歯車２０は、波板部１８の軸方向両端に当接させて外筒部１５の外周面１５ａに成形される。すなわち、波板部１８の先端１８ｃに当接した先端当接部２４と、波板部１８の基端１８ｄに当接した基端当接部２５とを有している。
【００６３】
このように構成された歯車装置においても、外筒部１５の軸方向途中より先端側を、周方向に凸部１８ａと凹部１８ｂを交互に形成してなる波板部１８とし、樹脂歯車２０を外筒部１５の外周面１５ａに成形したことにより、外筒部１５の周方向に対する樹脂歯車２０の回り止めが図れる。
【００６４】
また、先端当接部２４と基端当接部２５により、樹脂歯車２０が外筒部１５に対して軸方向両側に移動するのを防止できて抜け止めが図れる。
【００６５】
なお、樹脂歯車２０に、外筒部１５の先端から内周面１５ｂにまで回り込んでなる回り込み部２３を形成してもよい。
【００６６】
【発明の効果】
本発明の歯車装置によると、保持体の周方向に対する樹脂歯車の回り止めが図れ、かつ、樹脂歯車が軸方向両側に移動するのを防止できて保持体に対する樹脂歯車の抜け止めが図れるという効果が得られる。
【図面の簡単な説明】
【図１】本発明の実施形態における歯車装置の使用状態を示すボールねじ装置の全体断面図
【図２】本発明の実施形態における歯車装置の使用状態を示すボールねじ装置の全体断面図
【図３】図１のボールねじ装置の分解斜視図
【図４】本発明の実施形態を示す樹脂歯車を成形したブラケットの正面図
【図５】図４の樹脂歯車を除いた状態のＶ−Ｖ断面図
【図６】図４のVI-VI断面図
【図７】本発明の実施形態を示す樹脂歯車を成形したブラケットの部分断面図
【図８】本発明の実施形態を示すブラケットの部分拡大断面図
【図９】図７のブラケット部分におけるIX矢視図
【図１０】本発明の樹脂歯車を成形したブラケットの変形例の部分断面図
【符号の説明】
１ボールねじ装置
１０ブラケット（保持体）
１４環状部
１５外筒部
１５ａ外周面
１５ｂ内周面
１７拡径部
１８波板部
１８ａ凸部
１８ｂ凹部
２０樹脂歯車
３０ボールねじ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gear device applied to a ball screw device and the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is a power steering device using a gear device formed by injection molding a resin gear on a holder (for example, see Patent Document 1).
[0003]
In the case of a gear device applied to a power steering device, the resin gear rotates around the axis, but does not move in the axial direction, and the resin gear shifts in the circumferential direction of the holder with respect to the rotation around the axis. It is configured to prevent
[0004]
However, in some gear devices, the resin gear may move in the axial direction while rotating about the axis.
[0005]
As an example, there is a ball screw device having a configuration for converting torque into thrust between a nut member and a screw shaft, or converting thrust into torque.
[0006]
The ball screw device includes a ball screw including a nut member, a screw shaft arranged concentrically with the nut member, and a ball group that can roll a screw groove formed in the nut member and the screw shaft.
[0007]
A bracket is rotationally connected to the nut member of the ball screw. A rolling bearing is mounted between the inner peripheral surface of the screw shaft of the bracket and the ball screw and the outer peripheral surface of the rotating shaft, and supports the rotating shaft so as to be rotatable around the axis. Further, a resin gear to which rotational power is transmitted is integrally formed on the outer peripheral portion of the bracket by injection molding.
[0008]
When the rotational power is transmitted to the resin gear and rotates around the axis, the bracket and the nut member rotate around the screw shaft, and the ball screw expands and contracts. As described above, the resin gear is integrally formed with the bracket, and moves in the axial direction while rotating around the axis with the bracket.
[0009]
[Patent Document 1]
JP-A-2002-145086 (FIG. 3)
[0010]
[Problems to be solved by the invention]
In the case of a gear device that moves in the axial direction while rotating about an axis, such as a resin gear injection molded on a bracket of a ball screw, a force acts on the resin gear in both the circumferential direction and the axial direction.
[0011]
As a result, the resin gear may be displaced in the circumferential direction with respect to the bracket, or may move in the axial direction and fall out of the bracket.
[0012]
[Means for Solving the Problems]
The gear device of the present invention is obtained by injection molding a resin gear on a cylindrical holding body made of a thin steel plate, wherein the holding body has an annular portion extending in a radial direction, and an outer diameter end of the annular portion. And a cylindrical portion extending in the axial direction, and the cylindrical portion is formed such that the distal end side of the cylindrical portion in the axial direction swells in the outer diameter direction and alternately forms convex portions and concave portions in the circumferential direction. The resin gear is injection-molded on the outer peripheral surface of the cylindrical portion so as to abut on both axial ends of the corrugated plate portion.
[0013]
Examples of the portion where the resin gear is formed include a ball screw device for a CVT that moves in the axial direction while rotating around the axis.
[0014]
The corrugated plate portion may be, for example, at least a portion of the convex portion swelling in the outer diameter direction of the cylindrical portion. By bringing the resin gear into contact with the axial end surface of the swelling portion, the shaft of the resin gear The movement in the direction can be prevented.
[0015]
According to the gear device of the present invention, the distal end side of the cylindrical portion of the cylindrical portion of the holding member in the axial direction is a corrugated plate portion formed by alternately forming convex portions and concave portions in the circumferential direction, and the resin gear is provided on the outer peripheral surface of the cylindrical portion. By the injection molding, the rotation of the resin gear in the circumferential direction of the holding body can be prevented. In addition, since the corrugated plate portion is bulged in the outer diameter direction from the outer peripheral surface of the cylindrical portion, and the resin gear is made to abut against both axial ends of the corrugated plate portion and injection molded on the outer peripheral surface of the cylindrical portion, the resin gear is By contacting the axial end and the axial base end of the corrugated plate portion, it is possible to prevent the resin gear from moving to both sides in the axial direction with respect to the holder, and to prevent the resin gear from falling off.
[0016]
Further, the cylindrical portion of the holding body has a diameter-enlarging portion formed by bending the distal end side to the outer diameter side from the middle in the axial direction, and the corrugated plate portion is formed in the diameter-enlarging portion. Is also good.
[0017]
As described above, since the enlarged diameter portion is formed on the distal end side in the axial direction of the cylindrical portion, the resin gear abuts on the enlarged diameter portion and the end face of the corrugated plate portion at the axial base end of the corrugated plate portion. The contact area increases. Therefore, the resin gear can be further prevented from moving in the axial direction, and the resin gear can be reliably prevented from coming off the holder.
[0018]
Further, the resin gear may be injection-molded so as to extend from the axial end of the cylindrical portion of the holding body to the inner peripheral surface of the cylindrical portion.
[0019]
In this way, by injecting and molding the resin gear from the axial end of the cylindrical portion to the inner peripheral surface, when the resin gear is injection-molded on the outer peripheral surface of the cylindrical portion, the injection pressure is used to make a thin steel plate. It is possible to prevent the inner diameter of the cylindrical portion from shrinking, and to prevent the cylindrical portion of the holder from bending.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
A gear device according to an embodiment of the present invention will be described with reference to the drawings.
[0021]
1 and 2 are overall sectional views of a ball screw device showing a use state of the gear device of the present embodiment, FIG. 3 is an exploded perspective view of the ball screw device, FIG. 4 is a front view of a bracket formed of a resin gear, 5 is a sectional view taken along the line VV of FIG. 4 excluding the resin gear, FIG. 6 is a sectional view taken along the line VI-VI of FIG. 4, FIG. 7 is a partial sectional view of a bracket formed from the resin gear, and FIG. FIG. 9 is a partial enlarged cross-sectional view, and FIG.
[0022]
In the ball screw device 1 to which the gear device of the present invention is applied, the belt 3 wound around the pulley 2 is changed by changing the axial separation distance between the flanges in the pulley 2 having a pair of flanges in the axial direction. Used to change the hanging diameter.
[0023]
The pulley 2 includes a first flange 5 provided integrally with the rotation shaft 4 so as to rotate about the axis, and a second flange 6 provided integrally with the rotation shaft 4 so as to rotate about the axis and slide in the axial direction. And
[0024]
The ball screw device 1 includes a bracket 10 serving as a holder, a resin gear 20 made of synthetic resin, and a ball screw 30.
[0025]
The bracket 10 is formed in a cylindrical shape by pressing a thin steel plate.
[0026]
The bracket 10 includes an inner cylindrical portion 11, a folded cylindrical portion 12 that is formed by being folded halfway in the axial direction so as to overlap along the inner peripheral surface of the inner cylindrical portion 11 from one side in the axial direction of the inner cylindrical portion 11. A partition wall 13 bent radially inward from the other axial end of the folded tubular portion 12 and a radially outward bent portion from the other axial end of the inner cylindrical portion 11. An annular portion 14 is provided, and an outer cylindrical portion 15 bent from the radially outer end of the annular portion 14 toward one side in the axial direction is provided. Rigidity is obtained.
[0027]
The partition walls 13 are formed at a plurality of positions at equal positions in the circumferential direction of the folded tube portion 12. One of the partition walls 13 is formed with a bent portion 16 whose tip is further bent toward one side in the axial direction.
[0028]
The outer cylindrical portion 15 has an enlarged diameter portion 17 formed by bending the distal end side toward the outer diameter side from the middle in the axial direction, and the corrugated plate portion 18 is formed in the enlarged diameter portion 17. The corrugated plate portion 18 is formed by swelling in the outer diameter direction and press forming the convex portions 18a and the concave portions 18b alternately in the circumferential direction. Thereby, the corrugated plate portion 18 protrudes from the outer peripheral surface 15 a of the outer cylindrical portion 15 to the outer diameter side.
[0029]
FIG. 8 shows an enlarged cross-sectional view of the outer cylindrical portion 15 of the bracket 10. The inner diameter surface at the base of the enlarged diameter portion 17 formed on the outer cylinder portion 15 is formed as a convex curved surface 19a, and the outer diameter surface is formed as a concave curved surface 19b, and the inner diameter surface at the base of the corrugated plate portion 18 formed at the enlarged diameter portion 17 is formed. Are formed with a concave curved surface 19c and an outer diameter surface with a convex curved surface 19d, and an inner diameter surface and an outer diameter surface at a distal end portion of the corrugated plate portion 18 are formed with convex curved surfaces 19e and 19f, respectively.
[0030]
The curvature radii R of the convex curved surfaces 19a, 19d, 19e, 19f and the concave curved surfaces 19b, 19c are 0.5 mm or more.
[0031]
As shown in FIG. 9, the height dimension (the width dimension between the inner diameter of the valley and the outer diameter of the crest) h of the corrugated plate section 18 is 2.0 mm or more. The radius of curvature R of the convex portion 18a and the concave portion 18b is 0.5 mm or more. Further, the number of the convex portions 18a is set to be at least half of the number of teeth of the resin gear 20.
[0032]
The convex curved surfaces 19a, 19d, 19e, 19f and the concave curved surfaces 19b, 19c of the outer cylindrical portion 15 of the bracket 10 and the convex portion 18a and the concave portion 18b of the corrugated plate portion 18 each have a curvature radius R of 0.5 mm or more. In addition, stress concentration on the resin gear 20 during heat shock can be prevented.
[0033]
That is, based on the fact that the ambient temperature decreases and the resin gear 20 contracts due to the difference in the linear expansion coefficient between the metal bracket 10 and the resin gear 20, residual stress (the tensile direction for the resin gear 20) is generated at the boundary. concentrate. When the radius of curvature R of the corner of the bracket 10 is less than 0.5 mm, a large stress is concentrated on the resin gear 20 facing the corner, and breakage or the like is likely to occur.
[0034]
Therefore, by setting the radius of curvature R to 0.5 mm or more, stress concentration at the interface between the bracket 10 and the resin gear 20 can be prevented, and cracking due to heat shock can be prevented.
[0035]
The resin gear 20 is integrally formed on the outer peripheral surface 15a of the outer cylindrical portion 15 by injection molding, and the bracket 10 and the resin gear 20 are integrally provided so as to rotate about the axis.
[0036]
On the outer peripheral end of the resin gear 20, there is formed a tooth portion 21 with which the tooth portion 7a of the reduction gear 7 that rotates upon transmission of a driving force from a rotation power source (not shown).
[0037]
The resin gear 20 abuts on both ends in the axial direction of the corrugated plate portion 18, wraps around the inner peripheral surface 15 b from the tip of the outer cylindrical portion 15, and is injection-molded on the outer peripheral surface 15 a of the outer cylindrical portion 15. When the resin gear 20 is formed around the inner peripheral surface 15b, the resin reaches the surface 14a of the annular portion 14 of the bracket 10 (see FIG. 7) and stops.
[0038]
That is, as shown in FIG. 7, the wraparound portion 23 reaching the annular portion 14 along the inner peripheral surface 15b of the outer cylindrical portion 15 and the end surfaces of the convex portion 18a and the concave portion 18b at the tip 18c of the corrugated plate portion 18. It has a distal end contact portion 24 in contact with it, and a base end contact portion 25 in contact with the end surface 17 a of the enlarged diameter portion 17 and the end surface of the corrugated plate portion 18 at the base end 18 d of the corrugated plate portion 18.
[0039]
Examples of the resin material constituting the resin gear 20 include an olefin resin (eg, polypropylene), a fluororesin, a styrene resin (eg, an acrylonitrile-styrene copolymer, an ABS resin), and an acrylic resin (eg, polymethyl methacrylate). , Polyester resins (polyalkylene arylate (homopolyester) such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, copolyester having alkylene arylate unit, polyarylate resin, liquid crystalline polyester, etc.), polycarbonate resin (bisphenol A type polycarbonate, etc., polyamide resin (6 nylon, 11 nylon, 12 nylon, 46 nylon, 66 nylon, 6T nylon, 9T nylon, 610 nylon, 61 Aliphatic nylons such as nylon and aromatic nylon MXD-6), polyacetal resin, polyphenylene ether resin, polyphenylene sulfide-based resins, polysulfone resins, polysulfone ether resin, polyphthalamide resin can be exemplified.
[0040]
Further, the resin material may contain a reinforcing fiber or a solid lubricant.
[0041]
The reinforcing fibers include inorganic fibers (glass fibers, carbon fibers, metal fibers, potassium titanate, barium titanate, alumina fibers, silica fibers, silicon carbide fibers, silicon nitride fibers, etc.), advanced reinforced plastics, and organic fibers (aramids). And the like.
[0042]
Examples of the solid lubricant include molybdenum disulfide, high density polyethylene (HDPE), PTFE, ultra high molecular weight polyethylene (UHMWPE), and the like.
[0043]
When the resin gear 20 is injection-molded on the outer peripheral surface 15a of the outer cylindrical portion 15, the inner pressure of the thin outer cylindrical portion 15 which is a press-formed product may contract due to the injection pressure, and may bite into the resin mold. Therefore, if the gap between the resin mold and the resin mold is increased in consideration of the contraction amount due to the injection pressure, the alignment between the bracket 10 and the resin gear 20 cannot be performed, or the resin gear 20 is inclined due to the contraction, and the tooth profile accuracy decreases. There is a possibility that. Therefore, by forming the wraparound portion 23 along the inner peripheral surface 15b of the outer cylinder portion 15, the wraparound portion 23 acts in a direction to suppress the shrinkage of the inner diameter of the outer cylinder portion 15, and the shrinkage can be suppressed. it can.
[0044]
The distal contact portion 24 and the proximal contact portion 25 can prevent the resin gear 20 from moving in the axial direction with respect to the outer cylindrical portion 15.
[0045]
The ball screw 30 is a full ball type ball screw having no retainer, and has a cylindrical nut member 31 that is fitted around the inner peripheral surface of the bracket 10 on one side in the axial direction so as to rotate integrally around the axis. A notch 32 is formed on the end surface of the nut member 31 to be fitted to each partition 13. The notch 32 and the partition 13 are fitted in the axial direction, so that the nut member 31 It is a configuration that is surely integrated around the rotation. The cutout end surface of the nut member 31 is in contact with one axial end surface of the partition wall 13. A single thread groove 33 having a predetermined lead angle continuous between both ends is formed on the inner peripheral surface of the nut member 31.
[0046]
The ball screw 30 has a cylindrical screw shaft 34 arranged on the inner diameter side of the nut member 31. The screw shaft 34 is supported non-rotatably around the axis by a predetermined support device (not shown), and is supported immovably in the axial direction. The screw shaft 34 has, on its outer peripheral surface, two thread grooves 35 having a predetermined lead angle which are parallel to each other and are independent closed loops. Each screw groove 35 has a ball circulation groove 36 that connects the ends of the screw groove 35 having a predetermined lead angle to each other at an angle different from the lead angle. Each of the screw grooves 35 is separately closed by the ball circulation groove 36. It is said.
[0047]
These ball circulation grooves 36 are portions that connect the upstream side and the downstream side of each screw groove 35. That is, these ball circulation grooves 36 are formed deeper than other portions of the screw grooves 35 so that the balls 37 located on the downstream side of the respective screw grooves 35 are sunk on the inner diameter side of the screw shaft 34 and returned upstream. And a meandering shape. Thus, the balls 37 fitted into the thread grooves 35 are independently rolled and circulated.
[0048]
A part of the outer peripheral surface of the other opening in the axial direction of the screw shaft 34 is cut out along the circumferential direction so as to have a predetermined circumferential length, and the notch 38 and the bent portion 16 of the partition wall 13 form the nut member 31. A stopper is configured to prevent the shaft from rotating more than necessary around the axis.
[0049]
A rolling bearing (angular ball bearing) 40 is fitted to one inner peripheral surface of the screw shaft 34. The rolling bearing 40 includes an outer ring member 41 fitted to the screw shaft 34, an inner ring member 42 through which the rotating shaft 4 is inserted, and a plurality of rollingly arranged between the outer ring member 41 and the inner ring member 42. The ball 43 is provided.
[0050]
A rolling bearing (angular ball bearing) 50 is fitted on the other side of the inner peripheral surface of the bracket 10. The rolling bearing 50 is an outer ring member 51 as a bearing member fitted on the inner peripheral surface of the bracket 10, and a cylinder integrally rotatably mounted on the rotating shaft 4 around the axis and integrally formed on the second flange 6. The vehicle includes an inner ring member 52 fitted on the outer peripheral surface of the shaft 6a, and a plurality of balls 53 rotatably arranged between the outer ring member 51 and the inner ring member 52. The side surface of the outer ring member 51 in the rolling bearing 50 is in contact with the side surface of the partition wall 13.
[0051]
FIG. 1 shows a state in which the ball screw 30 is most contracted and the first flange 5 and the second flange 6 are most separated in the axial direction, and a state in which the belt 3 has a small winding diameter. In this state, the bent portion 16 is in contact with the contact surface of the notch 38 so that the nut member 31 is prevented from rotating.
[0052]
When the reduction gear 7 rotates about the axis from the above state and the tooth portion 7a rotates, the resin gear 20 rotates about the axis together with the rotation of the reduction gear 7. As the resin gear 20 rotates, the bracket 10 and the nut member 31 rotate around the screw shaft 34 and move in the axial direction (leftward in the figure) as shown in FIG. Thereby, the resin gear 20 integrally formed with the bracket 10 also moves in the axial direction. When the radially inner portions of the first flange 5 and the second flange 6 contact each other in the axial direction, the nut member 13 stops moving in the axial direction, and the belt 3 expands between the flanges 5 and 6. The diameter is raised to the maximum diameter.
[0053]
When the winding diameter of the belt 3 is reduced again, a rotational force in the opposite direction is applied from the reduction gear 7 to the resin gear 20 so that the nut member 31 moves in the axial direction (rightward in the figure). The nut member 31 stops moving in the axial direction when the bent portion 16 moves and comes into contact with the contact surface of the cutout portion 38 as shown in FIG.
[0054]
According to the gear device configured as described above, the distal end side of the outer cylindrical portion 15 from the middle in the axial direction is the corrugated plate portion 18 in which the convex portions 18a and the concave portions 18b are alternately formed in the circumferential direction, and the resin gear 20 is formed. By performing injection molding on the outer peripheral surface 15a of the outer cylindrical portion 15, the rotation of the resin gear 20 in the circumferential direction of the outer cylindrical portion 15 can be prevented. In addition, the corrugated plate portion 18 can be easily formed by press molding, and the cost can be reduced.
[0055]
Further, the corrugated plate portion 18 is bulged to the outer diameter side from the outer peripheral surface 15 a of the outer cylindrical portion 15, and the resin gear 20 is brought into contact with both ends of the corrugated plate portion 18 in the axial direction, so that the outer peripheral surface 15 a of the outer cylindrical portion 15 is formed. Since the resin gear 20 is formed, the distal end contact portion 24 of the resin gear 20 contacts the axial distal end 18 c of the corrugated plate portion 18, and the proximal contact portion 25 contacts the axial proximal end 18 d of the corrugated plate portion 18. 20 can be prevented from moving in the axial direction with respect to the outer cylindrical portion 15, and the resin gear 20 can be prevented from coming off. In addition, since the height h of the corrugated plate portion 18 is set to 2 mm or more, the contact area of the axial distal end 18c and the axial base end 18d with which the resin gear 20 contacts increases, and the unloading load increases. Can be reliably prevented.
[0056]
In addition, since the enlarged diameter portion 17 is formed on the distal end side of the outer cylindrical portion 15 with respect to the axial direction, the resin gear 20 is formed at the axial base end 18d of the corrugated plate portion 18 with the enlarged diameter portion 17 and the corrugated plate portion 18. It comes into contact with the end face, and the contact area increases. Therefore, the resin gear 20 can be further prevented from moving in the axial direction, and the resin gear 20 can be reliably prevented from coming off with respect to the outer cylindrical portion 15.
[0057]
Also, the radius of curvature R of the convex curved surfaces 19a, 19d, 19e, 19f and the concave curved surfaces 19b, 19c of the outer cylindrical portion 15 and the radius of curvature R of the convex portion 18a and the concave portion 18b are 0.5 mm or more, respectively. Stress concentration at the interface between the resin gear 10 and the resin gear 20 can be prevented, and cracking due to heat shock can be prevented.
[0058]
Further, by molding the resin gear 20 by wrapping around the inner circumferential surface 15b from the axial end of the outer cylindrical portion 15, the injection pressure is increased when the resin gear 20 is injection-molded on the outer circumferential surface 15a of the outer cylindrical portion 15. Accordingly, the inner diameter of the outer cylindrical portion 15 made of a thin steel plate can be suppressed from shrinking, and the outer cylindrical portion 15 can be prevented from bending. Accordingly, it is possible to prevent the resin mold from biting during the injection molding, to easily align the bracket 10 with the resin gear 20, to improve the tooth profile accuracy, and to improve the productivity and reduce the cost.
[0059]
Further, since the distal end side of the outer cylindrical portion 15 from the middle in the axial direction is the corrugated plate portion 18, the resin gear 20 is formed on the outer peripheral surface 15 a of the outer cylindrical portion 15, so that the resin is formed on both ends of the corrugated plate portion 18 in the axial direction. The gear 20 can be brought into contact, and there is no need to mold the resin gear 20 over the annular portion 14, so that the shape of the resin mold during injection molding can be simplified, and the resin gear 20 can be easily and inexpensively formed. Can be injection molded.
[0060]
FIG. 10 shows a modified example of the bracket 10 in which the resin gear 20 is formed.
[0061]
In this example, the outer cylindrical portion 15 of the bracket 10 is formed in a flat cylindrical shape, and the front end side of the outer cylindrical portion 15 is formed as a corrugated plate portion 18 in the axial direction.
[0062]
The resin gear 20 is formed on the outer peripheral surface 15 a of the outer cylindrical portion 15 by making contact with both ends in the axial direction of the corrugated plate portion 18. That is, it has a distal end contact portion 24 in contact with the distal end 18c of the corrugated plate portion 18 and a proximal end contact portion 25 in contact with the proximal end 18d of the corrugated plate portion 18.
[0063]
Also in the gear device configured as described above, the distal end side of the outer cylindrical portion 15 from the middle in the axial direction is a corrugated plate portion 18 in which convex portions 18a and concave portions 18b are alternately formed in the circumferential direction, and the resin gear 20 is formed. The resin gear 20 can be prevented from rotating in the circumferential direction of the outer cylinder 15 by being formed on the outer peripheral surface 15 a of the outer cylinder 15.
[0064]
Further, the distal end contact portion 24 and the proximal end contact portion 25 can prevent the resin gear 20 from moving in both axial directions with respect to the outer cylindrical portion 15 and can prevent the resin gear 20 from coming off.
[0065]
Note that the resin gear 20 may be provided with a wraparound portion 23 wrapping around from the tip of the outer cylindrical portion 15 to the inner peripheral surface 15b.
[0066]
【The invention's effect】
Advantageous Effects of Invention According to the gear device of the present invention, the resin gear can be prevented from rotating in the circumferential direction of the holder, and the resin gear can be prevented from moving to both sides in the axial direction, so that the resin gear can be prevented from falling out of the holder. Is obtained.
[Brief description of the drawings]
FIG. 1 is an overall sectional view of a ball screw device showing a use state of a gear device according to an embodiment of the present invention. FIG. 2 is an overall sectional view of a ball screw device showing a use state of a gear device according to an embodiment of the present invention. 3 is an exploded perspective view of the ball screw device of FIG. 1; FIG. 4 is a front view of a bracket on which a resin gear is formed according to an embodiment of the present invention; FIG. FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 4 FIG. 7 is a partial cross-sectional view of a bracket on which a resin gear is formed according to the embodiment of the present invention. FIG. FIG. 9 is a view of the bracket portion of FIG. 7 as viewed in the direction of arrow IX. FIG. 10 is a partial cross-sectional view of a modified example of the bracket formed by molding the resin gear of the present invention.
1 ball screw device 10 bracket (holding body)
14 annular portion 15 outer cylindrical portion 15a outer peripheral surface 15b inner peripheral surface 17 enlarged diameter portion 18 corrugated plate portion 18a convex portion 18b concave portion 20 resin gear 30 ball screw

Claims

In a gear device formed by injection molding a resin gear on a cylindrical holding body made of a thin steel plate,
The holding body includes an annular portion extending in a radial direction, and a tubular portion extending in an axial direction from an outer diameter end of the annular portion,
The tubular portion is a corrugated plate portion formed by alternately forming convex portions and concave portions in the circumferential direction by swelling in the outer diameter direction and bulging in the outer diameter direction, in the axial direction,
The gear device according to claim 1, wherein the resin gear is injection-molded on an outer peripheral surface of the cylindrical portion so as to abut on both axial ends of the corrugated plate portion.

The gear device according to claim 1, wherein
The cylindrical portion of the holding body has a diameter-enlarging portion formed by bending the distal end side to the outer diameter side from the middle in the axial direction, and the corrugated plate portion is formed in the diameter-enlarging portion. A gear device characterized by the above-mentioned.

The gear device according to claim 1, wherein
A gear device, wherein the resin gear is injection-molded in such a manner as to extend from an axial end of a cylindrical portion of the holding body to an inner peripheral surface of the cylindrical portion.