JP2004125008A

JP2004125008A - Boot for constant velocity joint

Info

Publication number: JP2004125008A
Application number: JP2002286952A
Authority: JP
Inventors: Masayuki Chokai; 鳥海　真幸
Original assignee: Toyoda Gosei Co Ltd
Current assignee: Toyoda Gosei Co Ltd
Priority date: 2002-09-30
Filing date: 2002-09-30
Publication date: 2004-04-22

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent a first valley portion from slipping out of place to an outer peripheral side of an outer race of a joint at a compression side when an operating angle is large. <P>SOLUTION: A boot provides a tapered portion 13 having a slant face 12 slanting from a shoulder portion 11 of a first cylinder portion to the first valley portion 30 on a boundary between the first cylinder portion and the first valley portion. A wall thickness t<SB>1</SB>of the tapered portion 13 and wall thickness t<SB>2</SB>of the shoulder portion are in a ratio of t<SB>1</SB>≤t<SB>2</SB>, the ratio d<SB>1</SB>/d<SB>2</SB>between an outer diameter d<SB>1</SB>of the shoulder portion 11 and an outer diameter d<SB>2</SB>of the first valley portion 30 is in a range of 1.1 to 1.3, and an angle θ formed by the slant face 12 and an outer peripheral surface of the shoulder portion 11 is 30° to 55°. When adapting a shape satisfying the aforementioned relationship, it is possible to surely prevent the first valley portion 30 from slipping out of place to the outer peripheral side of the outer race of the joint, and durability of a boot is improved. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、前輪駆動車のドライブシャフト用ジョイントなどに不可欠な等速ジョイントに被覆され、等速ジョイントのジョイント部への水や埃の侵入を阻止するブーツに関する。
【０００２】
【従来の技術】
等速ジョイントのジョイント部は従来より蛇腹形状のブーツで覆われ、水や埃の侵入を阻止することによって大角度で滑らかな回転が維持されている。この等速ジョイント用ブーツは、ジョイントアウターレースなどに保持される大径の第１筒部と、第１筒部より小径でシャフトに保持される第２筒部と、第１筒部と第２筒部を一体的に連結する略円錐台形状の蛇腹部とから構成されている。そして使用時には、ジョイントアウターレースなどとシャフトのなす角度の変化に応じて蛇腹部が変形するため、その作動角が大きくなってもブーツによってジョイント部を確実にシールすることができる。
【０００３】
従来の等速ジョイント用ブーツは、ジョイントアウターレースなどの中心軸とシャフトの中心軸とのなす作動角の変化への追従を容易とし、蛇腹部に発生する応力を小さくするために、蛇腹部の山部の外径が比較的大型に形成されている。ところが近年、自動車の軽量化が求められ、車体サイズのコンパクト化に伴って等速ジョイント用ブーツにも形状のコンパクト化が求められている。
【０００４】
このようなコンパクトなブーツとしては、ジョイントアウターレースに嵌着される大径リング部と、シャフトに嵌着される小径リング部と、両リング部間に介在する蛇腹部とからなり、蛇腹部は大径リング部から順に第１谷部，第１山部，第２谷部，第２山部・・と谷部及び山部が交互に連続したものが知られている。
【０００５】
ところがこのようなブーツでは、作動角が大きい時の圧縮側において、大径リング部の第１谷部に連接する肩部と第２山部との間に第１山部が挟まれて押圧されるため、第１山部の頂部付近の摩耗が促進されやすいという問題があった。また大径リング部の第１谷部に連接する肩部は一般にＲ（曲面）となっているが、作動角が大きい時の圧縮側において肩部と第１山部とが圧接したときの接触面積が小さいために、面圧が大きくなって肩部１１が外側に押し出され、その結果、図４に示すように、第１谷部３０がジョイントアウターレース５の外周側へずれ落ちる場合があった。
【０００６】
このようになると、ジョイントアウターレース５に大径リング部を嵌着している金属バンド４に対する肩部１１の曲折量が大きくなり、金属バンド４の周囲で亀裂が発生する恐れもある。特に小型ＣＶＪ用のブーツでは、ジョイントアウターレース５の径が小さいために、この問題が発生しやすい。
【０００７】
また肩部は蛇腹部に比べて変形しにくいため、作動角が大きい時の圧縮側において各山部が肩部で押し上げられる状態となり、第１山部の接触面圧が上昇するとともに蛇腹部に作用する応力も増大し、耐久性が低下する恐れもあった。
【０００８】
そこで実公平０３−０２８１８９号公報あるいは特開平０９−０９６３１８号公報には、肩部を面取り形状とした等速ジョイント用ブーツが開示されている。このような面取り部を形成することで、肩部と第１山部とが圧接したときの接触面積が大きくなり、接触面圧が低下するため、上記不具合の発生を未然に防止することができる。
【０００９】
【特許文献１】実公平０３−０２８１８９号
【特許文献２】特開平０９−０９６３１８号
【００１０】
【発明が解決しようとする課題】
ところが上記公報に記載されたブーツにおいても、作動角が大きい時の圧縮側において第１谷部がジョイントアウターレースの外周側へずれ落ちる場合があり、耐久性が低下する場合があった。
【００１１】
本発明はこのような事情に鑑みてなされたものであり、作動角が大きい時の圧縮側において第１谷部がジョイントアウターレースの外周側へずれ落ちるのを確実に防止し、耐久性を向上させることを目的とする。
【００１２】
【課題を解決するための手段】
上記課題を解決する本発明の等速ジョイント用ブーツの特徴は、大径の第１筒部と、第１筒部と離間して同軸的に配置され該第１筒部より小径でシャフトに保持される第２筒部と、第１筒部と第２筒部を一体的に連結する略円錐台形状の蛇腹部と、よりなる等速ジョイント用ブーツにおいて、
蛇腹部は第１筒部側から順に第１谷部，第１山部，第２谷部，第２山部，第３谷部，第３山部，第４谷部・・・と谷部と山部とが交互に連続してなり、
第１筒部と第１谷部との境界には第１筒部の肩部から第１谷部に向かって傾斜する傾斜面をもつテーパ部をもち、
テーパ部の肉厚ｔ_１と肩部の肉厚ｔ_２とがｔ_１≦ｔ_２の関係にあり、肩部の外径ｄ_１と第１谷部の外径ｄ_２との比ｄ_１／ｄ_２が　１．１〜　１．３の範囲にあり、かつ傾斜面と肩部の外周表面とのなす角度θが３０〜５５゜であることにある。
【００１３】
【発明の実施の形態】
本願発明者は、第１筒部（大径リング部）の肩部に面取り部をもつブーツにおいて、面取り部及びその近傍の部分の形状と、作動角が大きい場合に第１谷部がジョイントアウターレースの外周側へずれ落ちる不具合の発生率との関係を鋭意研究した。その結果、少なくとも３つの因子が大きく影響していることを見出し、その３つの因子を最適化することによって本発明を完成した。
【００１４】
すなわち本発明の等速ジョイント用ブーツの蛇腹部は、第１筒部の肩部から第１谷部に向かって傾斜する傾斜面をもつテーパ部をもち、テーパ部の肉厚ｔ_１と肩部の肉厚ｔ_２とがｔ_１≦ｔ_２の関係にあり、肩部の外径ｄ_１と第１谷部の外径ｄ_２との比ｄ_１／ｄ_２が　１．１〜　１．３の範囲にあり、かつ傾斜面と肩部の外周表面とのなす角度θが３０〜５５゜である。これらの関係が一つでも満足されないと、作動角が大きい場合に第１谷部がジョイントアウターレースの外周側へずれ落ちる不具合が発生する場合がある。
【００１５】
上記した構成以外においては、本発明の等速ジョイント用ブーツは従来と同様に構成することができる。その材質としてはＴＰＥ，ＴＰＯなどの熱可塑性エラストマーなどが用いられ、ブロー成形法あるいは射出ブロー成形法にて製造することができる。
【００１６】
【実施例】
以下、試験例により本発明を具体的に説明する。
【００１７】
図１に本発明の等速ジョイント用ブーツの半部断面で示す正面図を、図２に図１の丸で囲まれた部分の拡大図を示す。この等速ジョイント用ブーツは、第１筒部１と、第１筒部１より小径の第２筒部２と、第１筒部１と第２筒部２を一体的に連結する略円錐台形状の蛇腹部３とから構成され、第１筒部１及び蛇腹部３は熱可塑性エラストマーからブロー成形により形成され、第２筒部２は熱可塑性エラストマーから射出成形により蛇腹部３と一体的に製造されている。
【００１８】
第１筒部１，第２筒部２及び蛇腹部３は、負荷が作用しない状態において、それぞれ中心軸Ｌに対して同軸に位置している。また蛇腹部３は、第１筒部１側から順に第１谷部３０、第１山部３１、第２谷部３２、第２山部３３、第３谷部３４、第３山部３５、第４谷部３６、第４山部３７・・・と、山部及び谷部が交互に形成されている。
【００１９】
第１筒部１及び第２筒部２の外周表面には、金属バンド又はクランプが係合するクランプ溝１０，２０が形成され、第１筒部１の第１谷部３０側の端部には、中心軸Ｌと平行な円柱表面をもつ肩部１１が形成されている。そして肩部１１の端部から第１谷部３０に連接する部分には、肩部１１から第１谷部３０に向かって傾斜する傾斜面１２をもつ円錐台形状のテーパ部１３が形成されている。
【００２０】
ここで図２に拡大して示すように、テーパ部１３の肉厚をｔ_１とし、肩部１１の肉厚をｔ_２とする。また肩部１１の外径をｄ_１とし、第１谷部３０の外径をｄ_２とする。さらに傾斜面１２と肩部１１の外周表面とのなす角度をθとする。
【００２１】
表１に示すように、ｔ_１，ｔ_２，ｄ_１，ｄ_２及びθが種々異なる等速ジョイント用ブーツを作製し、作動角が大きい条件で用いた場合の変形状態をＦＥＡにて解析した。そして図３に示すように第１谷部３０がジョイントアウターレース５の内周側に位置する場合を○と評価し、図４に示すように第１谷部３０がジョイントアウターレース５の外周側にずれているものを×と評価して、結果を表１に合わせて示す。
【００２２】
×と評価されたものでは、図４に示すように第１谷部３０がジョイントアウターレース５の外周側にずり落ちている。そのため金属バンド４に対する肩部１１の曲折量が大きく、金属バンド４の周囲で亀裂が発生する恐れがある。また各山部が肩部１１で押し上げられる状態となり、第１山部３１の接触面圧が上昇するとともに蛇腹部３に作用する応力も増大し、耐久性が低下する。
【００２３】
しかし○と評価されたものでは、図３に示すように第１谷部３０がジョイントアウターレース５の内周側に位置し、ジョイントアウターレース５の座面内に位置している。そのため金属バンド４に対する肩部１１の曲折量も小さく、金属バンド４の周囲で亀裂が発生するような不具合が防止されている。さらに図４の場合に比べて蛇腹部３に作用する応力が小さいので、耐久性も向上する。
【００２４】
【表１】

【００２５】
表１より、ｔ_１≦ｔ_２，ｄ_１／ｄ_２＝　１．１〜　１．３，θ＝３０〜５５゜の三つの条件を全て満足するものが○と評価されていることがわかる。すなわち作動角が大きい時の圧縮側において、第１谷部３０がジョイントアウターレースの外周側へずれ落ちる現象には、ｔ_１とｔ_２の関係，ｄ_１／ｄ_２及び角度θの３つの因子が大きく影響し、これらを本願発明の範囲とすることでこの不具合を確実に防止できることが明らかである。
【００２６】
【発明の効果】
すなわち本発明の等速ジョイント用ブーツによれば、作動角が大きい時の圧縮側において、第１谷部３０がジョイントアウターレースの外周側へずれ落ちるのを確実に防止することができ、耐久性が大きく向上する。
【図面の簡単な説明】
【図１】本発明の等速ジョイント用ブーツの半部断面で示す正面図である。
【図２】図１の円で囲んだ部分を拡大して示す要部拡大図である。
【図３】本発明の等速ジョイント用ブーツを作動角が大きい条件で使用した場合のＦＥＡによる解析図である。
【図４】従来の等速ジョイント用ブーツを作動角が大きい条件で使用した場合のＦＥＡによる解析図である。
【符号の説明】
１：第１筒部　　　　　　２：第２筒部　　　　　　３：蛇腹部
１０：クランプ溝　　　　　１１：肩部　　　　　　　　１２：傾斜面
１３：テーパ部　　　　　　３０：第１谷部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a boot which is covered with a constant velocity joint which is indispensable for a drive shaft joint of a front wheel drive vehicle and prevents water and dust from entering a joint portion of the constant velocity joint.
[0002]
[Prior art]
The joint portion of the constant velocity joint is covered with a bellows-shaped boot, and smooth rotation at a large angle is maintained by preventing water and dust from entering. The constant velocity joint boot has a large-diameter first tubular portion held by a joint outer race, a second tubular portion smaller in diameter than the first tubular portion and held by a shaft, a first tubular portion and a second tubular portion. And a bellows portion having a substantially truncated cone shape that integrally connects the cylindrical portions. In use, since the bellows portion is deformed in accordance with a change in the angle formed between the shaft and the joint outer race or the like, the boot can reliably seal the joint portion even when the operating angle increases.
[0003]
Conventional constant-velocity joint boots are designed to make it easier to follow the change in the operating angle between the central axis of the joint outer race and the central axis of the shaft, and to reduce the stress generated in the bellows. The outer diameter of the peak is formed relatively large. However, in recent years, the weight of automobiles has been required to be reduced, and as the size of the vehicle body has been reduced, the boots for constant velocity joints have also been required to be downsized.
[0004]
Such a compact boot includes a large-diameter ring portion fitted to the joint outer race, a small-diameter ring portion fitted to the shaft, and a bellows portion interposed between the two ring portions. It is known that a first valley portion, a first ridge portion, a second valley portion, a second valley portion,.
[0005]
However, in such boots, on the compression side when the operating angle is large, the first ridge is sandwiched and pressed between the shoulder connected to the first valley of the large diameter ring and the second ridge. Therefore, there is a problem that the wear near the top of the first peak is easily promoted. The shoulder connected to the first valley of the large-diameter ring is generally R (curved surface). However, the contact when the shoulder and the first ridge are pressed against each other on the compression side when the operating angle is large. Due to the small area, the surface pressure increases and the shoulder portion 11 is pushed outward, and as a result, the first valley portion 30 may be shifted toward the outer peripheral side of the joint outer race 5 as shown in FIG. Was.
[0006]
In this case, the amount of bending of the shoulder portion 11 with respect to the metal band 4 in which the large-diameter ring portion is fitted to the joint outer race 5 increases, and there is a possibility that a crack may be generated around the metal band 4. Particularly, in a boot for a small CVJ, this problem is likely to occur because the diameter of the joint outer race 5 is small.
[0007]
Also, since the shoulder is less deformable than the bellows, each peak is pushed up by the shoulders on the compression side when the operating angle is large, and the contact surface pressure of the first peak rises and the bellows There is also a risk that the acting stress increases and the durability decreases.
[0008]
Thus, Japanese Utility Model Publication No. 03-028189 or Japanese Patent Application Laid-Open No. 09-096318 discloses boots for constant velocity joints having chamfered shoulders. By forming such a chamfered portion, the contact area when the shoulder portion and the first mountain portion are pressed against each other is increased, and the contact surface pressure is reduced, so that the above-described problem can be prevented from occurring. .
[0009]
[Patent Document 1] Japanese Utility Model Publication No. 03-28189 [Patent Document 2] Japanese Patent Application Laid-Open No. 09-096318
[Problems to be solved by the invention]
However, even in the boots described in the above publication, the first valley may be shifted to the outer peripheral side of the joint outer race on the compression side when the operating angle is large, and the durability may be reduced.
[0011]
The present invention has been made in view of such circumstances, and reliably prevents the first valley from falling to the outer peripheral side of the joint outer race on the compression side when the operating angle is large, thereby improving durability. The purpose is to let them.
[0012]
[Means for Solving the Problems]
A feature of the constant velocity joint boot of the present invention that solves the above-mentioned problems is that a large-diameter first cylindrical portion and a coaxially spaced apart from the first cylindrical portion are held on the shaft with a smaller diameter than the first cylindrical portion. A constant-velocity joint boot comprising: a second cylindrical portion to be formed; and a substantially frustoconical bellows portion integrally connecting the first cylindrical portion and the second cylindrical portion.
The bellows are in the order of the first cylindrical portion, the first valley portion, the first valley portion, the second valley portion, the second valley portion, the third valley portion, the third valley portion, the fourth valley portion, and the valley portion. And mountains alternately and continuously,
At the boundary between the first tubular portion and the first valley portion, there is a tapered portion having a slope inclined from the shoulder of the first tubular portion toward the first valley portion,
There the wall thickness _{t 2} of the thickness _{t 1} and the shoulder of the tapered portion to the relationship _{t 1} ≦ _{t 2,} the ratio between the outer diameter _{d 1} of the shoulder portion and the outer diameter _{d 2} of the first valley _d 1 / in the range of d ₂ is from 1.1 to 1.3, and the angle θ between the inclined surface and the shoulder portion outer peripheral surface of the is that it is 30 to 55 °.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The inventor of the present application has proposed a boot having a chamfered portion on a shoulder of a first cylindrical portion (large-diameter ring portion). The relationship between the rate of occurrence of the problem of slipping to the outer peripheral side of the race was studied diligently. As a result, it was found that at least three factors had a great influence, and the present invention was completed by optimizing the three factors.
[0014]
That constant velocity bellows portion of the joint boot of the present invention has a tapered portion having an inclined surface inclined from the shoulder portion of the first cylindrical portion toward the first valley, the thickness t ₁ of the tapered portion and the shoulder portion the thickness _{t 2} and are in the relationship of _{t 1} ≦ _{t 2,} the ratio _d 1 / _{d 2} between the outer diameter _{d 1} of the shoulder portion and the outer diameter _{d 2} of the first valley from 1.1 to 1.3 And the angle θ between the inclined surface and the outer peripheral surface of the shoulder is 30 to 55 °. If at least one of these relationships is not satisfied, a problem may occur in which the first valley shifts toward the outer peripheral side of the joint outer race when the operating angle is large.
[0015]
Except for the configuration described above, the constant velocity joint boot of the present invention can be configured in the same manner as the conventional one. As the material, a thermoplastic elastomer such as TPE or TPO is used, and it can be manufactured by a blow molding method or an injection blow molding method.
[0016]
【Example】
Hereinafter, the present invention will be described specifically with reference to test examples.
[0017]
FIG. 1 is a front view showing a half section of the constant velocity joint boot of the present invention, and FIG. 2 is an enlarged view of a portion surrounded by a circle in FIG. The boot for a constant velocity joint includes a first tubular portion 1, a second tubular portion 2 having a smaller diameter than the first tubular portion 1, and a substantially truncated cone that integrally connects the first tubular portion 1 and the second tubular portion 2. The first cylindrical portion 1 and the bellows portion 3 are formed by blow molding from a thermoplastic elastomer, and the second cylindrical portion 2 is formed integrally with the bellows portion 3 by injection molding from a thermoplastic elastomer. Being manufactured.
[0018]
The first tubular portion 1, the second tubular portion 2, and the bellows portion 3 are coaxially located with respect to the central axis L when no load is applied. The bellows portion 3 includes a first valley portion 30, a first ridge portion 31, a second valley portion 32, a second ridge portion 33, a third valley portion 34, a third ridge portion 35, in that order from the first cylindrical portion 1 side. Fourth troughs 36, fourth peaks 37,..., And peaks and troughs are formed alternately.
[0019]
Clamp grooves 10 and 20 are formed on the outer peripheral surfaces of the first tubular portion 1 and the second tubular portion 2 so as to engage with a metal band or a clamp. Is formed with a shoulder 11 having a cylindrical surface parallel to the central axis L. A frusto-conical taper portion 13 having an inclined surface 12 inclined from the shoulder portion 11 toward the first valley portion 30 is formed in a portion connected from the end of the shoulder portion 11 to the first valley portion 30. I have.
[0020]
Here, as shown enlarged in FIG. 2, the thickness of the tapered portion 13 and t _1, the thickness of the shoulder portion 11 and t _2. The outer diameter of the shoulder portion 11 and _{d 1,} the outer diameter of the first valley 30 and _{d 2.} Further, an angle between the inclined surface 12 and the outer peripheral surface of the shoulder 11 is defined as θ.
[0021]
As shown in Table 1, boots for constant velocity joints having various t ₁ , t ₂ , d ₁ , d _2, and θ were manufactured, and the deformation state when used under the condition of a large operating angle was analyzed by FEA. . The case where the first valley portion 30 is located on the inner peripheral side of the joint outer race 5 as shown in FIG. 3 is evaluated as ○, and the first valley portion 30 is located on the outer peripheral side of the joint outer race 5 as shown in FIG. Are evaluated as x, and the results are shown in Table 1.
[0022]
In the case of the evaluation of ×, the first valley portion 30 slips down to the outer peripheral side of the joint outer race 5 as shown in FIG. Therefore, the amount of bending of the shoulder portion 11 with respect to the metal band 4 is large, and there is a possibility that a crack may be generated around the metal band 4. Further, each peak is pushed up by the shoulder 11, the contact surface pressure of the first peak 31 increases, the stress acting on the bellows 3 increases, and the durability decreases.
[0023]
However, in the case of the evaluation of ○, the first valley portion 30 is located on the inner peripheral side of the joint outer race 5 as shown in FIG. Therefore, the amount of bending of the shoulder portion 11 with respect to the metal band 4 is small, and a problem that a crack occurs around the metal band 4 is prevented. Further, since the stress acting on the bellows portion 3 is smaller than in the case of FIG. 4, the durability is also improved.
[0024]
[Table 1]

[0025]
From Table 1, it can be seen that those satisfying all three conditions of t ₁ ≦ t ₂ , d ₁ / d ₂ = 1.1 to 1.3, θ = 30 to 55 ° are evaluated as ○. That is, on the compression side when the operating angle is large, the phenomenon in which the first valley portion 30 is shifted toward the outer peripheral side of the joint outer race is caused by three factors of the relationship between t ₁ and t ₂ , d ₁ / d ₂ and the angle θ. It is clear that this problem can be surely prevented by setting them within the scope of the present invention.
[0026]
【The invention's effect】
That is, according to the constant velocity joint boot of the present invention, on the compression side when the operating angle is large, the first valley portion 30 can be surely prevented from falling to the outer peripheral side of the joint outer race, and durability can be improved. Is greatly improved.
[Brief description of the drawings]
FIG. 1 is a front view showing a half section of a constant velocity joint boot of the present invention.
FIG. 2 is an enlarged view of a main part, showing an encircled portion of FIG. 1 in an enlarged manner.
FIG. 3 is an analysis diagram by FEA when the constant velocity joint boot of the present invention is used under the condition that the operating angle is large.
FIG. 4 is an analysis diagram by FEA when a conventional constant velocity joint boot is used under the condition of a large operating angle.
[Explanation of symbols]
1: First cylindrical portion 2: Second cylindrical portion 3: Bellows portion 10: Clamp groove 11: Shoulder portion 12: Inclined surface 13: Tapered portion 30: First valley portion

Claims

大径の第１筒部と、該第１筒部と離間して同軸的に配置され該第１筒部より小径でシャフトに保持される第２筒部と、該第１筒部と該第２筒部を一体的に連結する略円錐台形状の蛇腹部と、よりなる等速ジョイント用ブーツにおいて、
該蛇腹部は該第１筒部側から順に第１谷部，第１山部，第２谷部，第２山部，第３谷部，第３山部，第４谷部・・・と谷部と山部とが交互に連続してなり、
該第１筒部と該第１谷部との境界には該第１筒部の肩部から該第１谷部に向かって傾斜する傾斜面をもつテーパ部をもち、
該テーパ部の肉厚ｔ_１と該肩部の肉厚ｔ_２とがｔ_１≦ｔ_２の関係にあり、該肩部の外径ｄ_１と該第１谷部の外径ｄ_２との比ｄ_１／ｄ_２が　１．１〜　１．３の範囲にあり、かつ該傾斜面と該肩部の外周表面とのなす角度θが３０〜５５゜であることを特徴とする等速ジョイント用ブーツ。A first cylindrical portion having a large diameter, a second cylindrical portion which is coaxially spaced apart from the first cylindrical portion and has a smaller diameter than the first cylindrical portion and is held by a shaft; In a constant velocity joint boot composed of a substantially frusto-conical bellows part integrally connecting two cylinder parts,
The bellows portion includes a first valley portion, a first valley portion, a second valley portion, a second valley portion, a third valley portion, a third valley portion, a fourth valley portion, and the like in this order from the first cylindrical portion side. The valley and the mountain are alternately continuous,
A boundary between the first cylindrical portion and the first valley portion has a tapered portion having a slope inclined from the shoulder of the first cylindrical portion toward the first valley portion,
The thickness t _{1 of the} tapered portion and the thickness t _{2 of} the shoulder have a relationship of t ₁ ≦ t ₂ , and the outer diameter d ₁ of the shoulder and the outer diameter d ₂ of the first valley are different. constant velocity joints the ratio _d 1 / _{d 2} is in the range of 1.1 to 1.3, and the angle θ between the inclined surface and the shoulder portion outer peripheral surface of the is characterized in that 30 to 55 ° Boots.