JP2008064268A

JP2008064268A - Rolling bearing unit for wheel support

Info

Publication number: JP2008064268A
Application number: JP2006245263A
Authority: JP
Inventors: Nancy Naoko Yokoyama; ナンシー尚子横山
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 2006-09-11
Filing date: 2006-09-11
Publication date: 2008-03-21
Anticipated expiration: 2026-09-11
Also published as: JP4797896B2

Abstract

<P>PROBLEM TO BE SOLVED: To realize structure which can enhance rigidity of moment by making the pitch circle diameter of an outside train larger than that of an inside train and furthermore can fully assure rolling fatigue life of a plurality of outer ring tracks 13a, 13b provided in the inner peripheral surface of an outer ring 3a. <P>SOLUTION: Heat treatment hardened layers 17a, 17b, 17c are formed on a portion which contains both of the outer ring tracks 13a, 13b in two positions in the axial direction of the inner peripheral surface of the outer ring 3a and a space portion 16 between these outer ring tracks 13a, 13b at a halfway part in the axial direction of the inner peripheral surface of the outer ring 3a. The heat treatment hardened layers 17a, 17b, 17c on these portions are integrated and are continuous with one another. By this configuration, the rolling bearing unit can transmit a force generated radially inwardly on an unhardened part 18 of the space portion 16 to the heat treatment hardened layers 17a, 17b of the outer ring tracks 13a, 13b, thereby enhancing the rolling fatigue life of both of these outer ring tracks 13a, 13b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

この発明は、自動車の車輪及びブレーキディスク等の制動用回転部材を懸架装置に対して回転自在に支持する為に使用する車輪支持用転がり軸受ユニットの改良に関する。 The present invention relates to an improvement of a rolling bearing unit for supporting a wheel used for rotatably supporting a rotating member for braking such as a wheel and a brake disk of an automobile with respect to a suspension device.

自動車の車輪及び制動用回転部材は、車輪支持用転がり軸受ユニットにより、懸架装置に対して回転自在に支持する。この様な車輪支持用転がり軸受ユニットには、自動車が旋回走行する際に大きなモーメントが加わる為、旋回走行時の安定性を確保する為には、大きなモーメント剛性を確保する必要がある。この為従来から、車輪支持用転がり軸受ユニットとして、転動体を複列に配置すると共に、これら両列の転動体に、予圧並びに背面組み合わせ型の接触角を付与した構造が、一般的に使用されている。更に近年、大型化を防止しつつ、より大きなモーメント剛性を確保する為に、例えば特許文献１〜５に記載されている様な、両列の転動体のピッチ円直径や転動体直径を異ならせた構造が提案されている。 The wheel of the automobile and the rotating member for braking are rotatably supported with respect to the suspension device by the wheel bearing rolling bearing unit. A large moment is applied to such a wheel-supporting rolling bearing unit when the automobile is turning. Therefore, in order to ensure stability during turning, it is necessary to ensure a large moment rigidity. For this reason, conventionally, as a rolling bearing unit for supporting a wheel, a structure in which rolling elements are arranged in a double row and a preload and a combined contact angle of the back surface are given to the rolling elements in both rows is generally used. ing. Furthermore, in recent years, in order to ensure a larger moment rigidity while preventing an increase in size, for example, as described in Patent Documents 1 to 5, the pitch circle diameters and the rolling element diameters of both rolling elements are made different. A proposed structure has been proposed.

図５は、このうちの特許文献４に記載された構造を示している。この車輪支持用転がり軸受ユニット１は、ハブ２と、外輪３と、それぞれが転動体である複数個の玉４、４とを備える。このうちのハブ２は、ハブ本体５と内輪６とを組み合わせて成る。更に、このハブ２は、外周面の軸方向外端（軸方向に関して外とは、自動車への組み付け状態で車両の幅方向外側を言い、各図の左側。反対に、車両の幅方向中央側となる各図の右側を、軸方向に関して内と言う。本明細書全体で同じ。）寄り部分に、車輪及び制動用回転部材を支持する為の取付フランジ７を、同じく中間部及び内端部に複列の内輪軌道８ａ、８ｂを、それぞれ形成している。これら両内輪軌道８ａ、８ｂのうち、軸方向外側の内輪軌道８ａの直径は、同内側の内輪軌道８ｂの直径よりも大きくしている。尚、上記取付フランジ７には、複数本のスタッド９の基端部を固定し、この取付フランジ７に、ディスク等の制動用回転体や、車輪を構成するホイールを支持固定できる様にしている。 FIG. 5 shows the structure described in Patent Document 4 among them. The wheel support rolling bearing unit 1 includes a hub 2, an outer ring 3, and a plurality of balls 4, 4 each of which is a rolling element. Of these, the hub 2 is formed by combining a hub body 5 and an inner ring 6. Further, the hub 2 is an outer end in the axial direction of the outer peripheral surface (outside with respect to the axial direction means the outer side in the width direction of the vehicle when assembled to the automobile, the left side of each figure. The right side of each figure is said to be inward with respect to the axial direction. The same throughout the present specification.) The mounting flange 7 for supporting the wheel and the rotating rotating member for braking is also provided at the intermediate portion and the inner end portion. Double row inner ring raceways 8a and 8b are formed respectively. Of these inner ring raceways 8a and 8b, the diameter of the inner ring raceway 8a on the outer side in the axial direction is larger than the diameter of the inner ring raceway 8b on the inner side. A base end portion of a plurality of studs 9 is fixed to the mounting flange 7 so that a braking rotator such as a disk or a wheel constituting a wheel can be supported and fixed to the mounting flange 7. .

上記両内輪軌道８ａ、８ｂの直径を異ならせる為に、図５に示した構造では、上記ハブ本体５の軸方向中間部外周面で上記外側の内輪軌道８ａよりも少し軸方向内側に寄った部分に、軸方向内側に向かう程外径が小さくなる方向に傾斜した、外周面側傾斜段部１０を形成している。又、この外周面側傾斜段部１０よりも軸方向内側に寄った、上記ハブ本体５の軸方向内端部に、小径段部１１を形成している。そして、この小径段部１１に、外周面に上記軸方向内側の内輪軌道８ｂを形成した、上記内輪６を外嵌し、上記ハブ本体５の軸方向内端部に形成したかしめ部１２により、この内輪６をこのハブ本体５に対し結合固定している。上記両内輪軌道８ａ、８ｂは、断面形状（母線形状）が円弧形で、互いに近付く程（ハブ２の軸方向中央に向う程）外径が小さくなる。 In order to make the diameters of the inner ring raceways 8a and 8b different, in the structure shown in FIG. 5, the outer circumferential surface of the hub body 5 is slightly closer to the inner side in the axial direction than the outer ring raceway 8a. An outer peripheral surface side inclined step portion 10 that is inclined in a direction in which the outer diameter decreases toward the inner side in the axial direction is formed in the portion. Further, a small-diameter step portion 11 is formed at the inner end portion in the axial direction of the hub body 5 which is closer to the inner side in the axial direction than the inclined step portion 10 on the outer peripheral surface side. The small-diameter step portion 11 is formed with the inner ring raceway 8b formed on the outer peripheral surface of the inner ring raceway 8b. The inner ring 6 is externally fitted, and the caulking portion 12 is formed on the inner end portion in the axial direction of the hub body 5. The inner ring 6 is coupled and fixed to the hub body 5. The inner ring raceways 8a and 8b have a circular cross-sectional shape (bus shape), and the outer diameter decreases as they approach each other (as they approach the center in the axial direction of the hub 2).

又、前記外輪３は、内周面に複列の外輪軌道１３ａ、１３ｂを、外周面にこの外輪３を懸架装置に結合固定する為の結合フランジ１４を、それぞれ設けている。又、上記両外輪軌道１３ａ、１３ｂのうち、軸方向外側の外輪軌道１３ａの直径は、同内側の外輪軌道１３ｂの直径よりも大きくしている。この為に図５に示した構造では、上記外輪３の軸方向中間部内周面で上記外側の外輪軌道１３ａよりも少し軸方向内側に寄った部分に、軸方向内側に向かう程内径が小さくなる方向に傾斜した、内周面側傾斜段部１５を形成している。上記両外輪軌道１３ａ、１３ｂは、断面形状（母線形状）が円弧形で、互いに近付く程（ハブ２の軸方向中央に向う程）内径が小さくなる。 The outer ring 3 is provided with double-row outer ring raceways 13a and 13b on the inner peripheral surface and a coupling flange 14 on the outer peripheral surface for coupling and fixing the outer ring 3 to a suspension device. Of the two outer ring raceways 13a and 13b, the diameter of the outer ring raceway 13a on the outer side in the axial direction is larger than the diameter of the outer ring raceway 13b on the inner side. For this reason, in the structure shown in FIG. 5, the inner diameter becomes smaller toward the inner side in the axial direction at a portion closer to the inner side in the axial direction than the outer outer ring raceway 13 a on the inner peripheral surface in the axial direction of the outer ring 3. An inner peripheral surface side inclined step portion 15 that is inclined in the direction is formed. Both the outer ring raceways 13a and 13b have a circular cross-sectional shape (bus shape), and the inner diameter decreases as they approach each other (as they approach the center in the axial direction of the hub 2).

前記各玉４、４は、前記両内輪軌道８ａ、８ｂと、上記両外輪軌道１３ａ、１３ｂとの間にそれぞれ複数個ずつ、転動自在に設けている。この状態で、複列に配置された上記各玉４、４には、予圧と共に背面組み合わせ型（ＤＢ型）の接触角を付与している。又、これら両列の玉４、４のピッチ円直径は、上記内輪軌道８ａ、８ｂ及び上記両外輪軌道１３ａ、１３ｂの直径の差に応じて互いに異なっている。即ち、軸方向外側の列の各玉４、４（外側列）のピッチ円直径ＰＣＤ_OUT が、軸方向内側の列の各玉４、４（内側列）のピッチ円直径ＰＣＤ_INよりも大きく（ＰＣＤ_OUT ＞ＰＣＤ_IN）なっている。尚、図示の例では、転動体として玉４、４を使用しているが、重量の嵩む自動車用の転がり軸受ユニットの場合には、転動体として円すいころを使用する場合もある。 A plurality of balls 4, 4 are provided between the inner ring raceways 8a, 8b and the outer ring raceways 13a, 13b, respectively, so that they can roll. In this state, a contact angle of a back combination type (DB type) is given to each of the balls 4 and 4 arranged in a double row together with a preload. The pitch circle diameters of the balls 4 and 4 in both rows differ from each other in accordance with the difference in diameter between the inner ring raceways 8a and 8b and the outer ring raceways 13a and 13b. That is, the pitch circle diameter PCD _OUT of each ball 4, 4 (outer row) in the axially outer row is larger than the pitch circle diameter PCD _IN of each ball 4, 4 (inner row) in the axially inner row ( PCD _OUT > PCD _IN ). In the illustrated example, balls 4 and 4 are used as rolling elements. However, in the case of a rolling bearing unit for automobiles that is heavy in weight, a tapered roller may be used as the rolling element.

特許文献１〜５に記載された、両列の転動体のピッチ円直径を異ならせた車輪支持用転がり軸受ユニットの構造は上述の通りである。この様な構造の場合には、外側列のピッチ円直径ＰＣＤ_OUT を大きくできる分、モーメント剛性を大きくして、旋回走行時の走行安定性向上と、車輪支持用転がり軸受ユニットの耐久性向上とを図る為の設計が容易である。一方、内側列のピッチ円直径ＰＣＤ_INを大きくする必要がないので、懸架装置の一部（ナックルの取付孔）を特に大径化する必要はない。従って、この懸架装置部分等を特に大型化しなくても、上記走行安定性、並びに、耐久性向上を図れる。 The structure of the rolling bearing unit for supporting a wheel described in Patent Documents 1 to 5 in which the pitch circle diameters of the rolling elements in both rows are made different is as described above. In the case of such a structure, the moment circle rigidity can be increased as much as the pitch circle diameter PCD _OUT of the outer row can be increased to improve the running stability during turning and the durability of the wheel bearing rolling bearing unit. Is easy to design. On the other hand, since it is not necessary to increase the pitch circle diameter PCD _IN of the inner row, it is not necessary to increase the diameter of a part of the suspension device (knuckle mounting hole). Therefore, the traveling stability and the durability can be improved without particularly increasing the size of the suspension device.

但し、この様な車輪支持用転がり軸受ユニットの耐久性を十分に確保する為には、一般的な（外側列のピッチ円直径と内側列のピッチ円直径とが等しい）車輪支持用転がり軸受ユニットの場合と同様に、上記両外輪軌道１３ａ、１３ｂの転がり疲れ寿命を確保する事が重要である。ところが、図５に示した様な、両列の転動体のピッチ円直径を異ならせた車輪支持用転がり軸受ユニットの場合には、次の様な理由から、上記両外輪軌道１３ａ、１３ｂの転がり疲れ寿命を確保する事が、上記一般的な車輪支持用転がり軸受ユニットの場合に比べて難しい場合がある。この理由に就いて、以下に説明する。 However, in order to sufficiently ensure the durability of such a wheel support rolling bearing unit, a general wheel support rolling bearing unit (the pitch circle diameter of the outer row is equal to the pitch circle diameter of the inner row) As in the case of the above, it is important to ensure the rolling fatigue life of the outer ring raceways 13a and 13b. However, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of both rows of rolling elements are different as shown in FIG. 5, the rolling of the outer ring raceways 13a and 13b is performed for the following reason. It may be difficult to secure the fatigue life as compared with the above-described general wheel bearing rolling bearing unit. The reason will be described below.

上記両外輪軌道１３ａ、１３ｂの転がり疲れ寿命を確保する為には、これら両外輪軌道１３ａ、１３ｂ部分に圧縮応力を残留させる事が好ましい。残留圧縮応力は、ピーリング等の発生を抑えて、上記両外輪軌道１３ａ、１３ｂに早期剥離等の損傷が発生する事を防止し、これら両外輪軌道１３ａ、１３ｂの転がり疲れ寿命を確保する面から有効である。一方、これら両外輪軌道１３ａ、１３ｂ部分に圧縮応力を残留させる為には、これら両外輪軌道１３ａ、１３ｂ部分に設けた焼き入れ硬化層の周囲（焼き入れ硬化層と前記外輪３の外周面との間部分）に、未焼き入れの非硬化部分を残留させる事が好ましい。 In order to ensure the rolling fatigue life of the outer ring raceways 13a and 13b, it is preferable to leave compressive stress in these outer ring raceways 13a and 13b. Residual compressive stress suppresses the occurrence of peeling and the like to prevent the occurrence of damage such as early separation on the outer ring raceways 13a and 13b, and from the aspect of ensuring the rolling fatigue life of both outer ring raceways 13a and 13b. It is valid. On the other hand, in order to leave compressive stress in both the outer ring raceways 13a, 13b, the periphery of the hardened hardening layer provided in the both outer ring raceways 13a, 13b (the quench hardened layer and the outer peripheral surface of the outer ring 3) It is preferable to leave an unquenched uncured part in the intermediate part).

即ち、上記両外輪軌道１３ａ、１３ｂ部分に、高周波焼き入れ等の熱処理により硬化層を形成すると、この硬化層部分の金属組織が、マルテンサイト変態により僅かとは言え膨張する。この場合に、この硬化層の周囲部分に（マルテンサイト変態による膨張をしない）非硬化部分が存在すると、この硬化層がこの非硬化部分により抑え付けられて、内部に残留圧縮応力が発生する。この残留圧縮応力は、上述の様に転がり疲れ寿命の確保の面からも有利に働くが、この残留圧縮応力の大きさは、上記硬化層の周囲の非硬化部分の厚さが大きい程大きくなる。 That is, when a hardened layer is formed on both the outer ring raceways 13a and 13b by heat treatment such as induction hardening, the metal structure of the hardened layer expands albeit slightly due to martensitic transformation. In this case, if there is an uncured portion (which does not expand due to martensite transformation) in the peripheral portion of the cured layer, the cured layer is suppressed by the uncured portion, and residual compressive stress is generated inside. This residual compressive stress works advantageously from the aspect of securing the rolling fatigue life as described above, but the magnitude of the residual compressive stress increases as the thickness of the non-hardened portion around the hardened layer increases. .

ところが、図５に示した様な、両列の転動体のピッチ円直径を異ならせた車輪支持用転がり軸受ユニットの場合には、上記外輪３の形状が特有である為、上記両外輪軌道１３ａ、１３ｂ同士の間部分の径方向に関する厚さ寸法を大きくできる（この間部分の厚さ寸法が大きくなる）反面、上記両外輪軌道１３ａ、１３ｂを設けた部分で、径方向の厚さを確保する事が難しい場合がある。即ち、上記外輪３の外径に関しては、この外輪３の軸方向内端寄り部分を懸架装置を構成するナックルの支持孔に内嵌固定する必要上、この軸方向内端寄り部分で小さくなっている。これに対して、上記外輪３の内径に関しては、前記外側列のピッチ円直径ＰＣＤ_OUT を大きくする必要上、軸方向外端寄り部分で大きくなっている。一方、上記外輪３の軸方向内端寄り部分の内径を小さくする程度、並びに、この外輪３の軸方向外端寄り部分の外径を大きくする程度は、軽量化等、他の条件により限られている。従って、上記両列の転動体のピッチ円直径を異ならせた車輪支持用転がり軸受ユニットの場合には、上記外輪３の軸方向両端寄り部分で上記両外輪軌道１３ａ、１３ｂを設けた部分の厚さを確保する事が、一般的な車輪支持用転がり軸受ユニットに比べて難しくなる場合がある。 However, in the case of a rolling bearing unit for supporting a wheel in which the pitch circle diameters of the rolling elements in both rows are different as shown in FIG. 5, the shape of the outer ring 3 is unique. , 13b can be increased in thickness in the radial direction (the thickness of the portion in between is increased). On the other hand, the thickness in the radial direction is ensured in the portion where the outer ring raceways 13a and 13b are provided. Things can be difficult. That is, the outer diameter of the outer ring 3 is smaller at the portion near the inner end in the axial direction because the portion near the inner end in the axial direction of the outer ring 3 needs to be fitted and fixed in the support hole of the knuckle that constitutes the suspension device. Yes. In contrast, with respect to the inner diameter of the outer ring 3, on necessary to increase the pitch circle diameter PCD _OUT of the outboard row is larger in the axial direction outer end portion close. On the other hand, the extent to which the inner diameter of the outer ring 3 near the inner end of the outer ring 3 is reduced and the extent of the outer diameter of the outer ring 3 closer to the outer end in the axial direction are limited by other conditions such as weight reduction. ing. Accordingly, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of the rolling elements in both rows are different, the thickness of the portion where the outer ring raceways 13a and 13b are provided at both ends in the axial direction of the outer ring 3 is provided. It may be difficult to secure the thickness as compared with a general rolling bearing unit for supporting a wheel.

この結果、上記両列の転動体のピッチ円直径を異ならせた車輪支持用転がり軸受ユニットの場合には、上記両外輪軌道１３ａ、１３ｂの周囲部分に存在する非硬化部分の厚さを確保する事が難しくなる場合がある。これら両外輪軌道１３ａ、１３ｂの転がり疲れ寿命の確保は、これら両外輪軌道１３ａ、１３ｂ部分に熱処理硬化層を形成する事で図るが、単に熱処理硬化層を形成しただけで、この熱処理硬化層に十分な残留圧縮応力を発生させない場合には、十分な転がり疲れ寿命を確保する事が難しい。前記特許文献１〜５の何れにも、この様な点に就いて記載されていない。特許文献６には、両列の転動体のピッチ円直径が等しい構造で、両外輪軌道部分に形成する熱処理硬化層を独立させる構造、並びに両外輪軌道部分に形成する熱処理硬化層を連続させる構造が記載されている。但し、上記特許文献６に記載された技術にしても、両列の転動体のピッチ円直径が異なる構造で、両列の外輪軌道部分の熱処理硬化層に十分な残留圧縮応力を発生させる事を示唆するものではない。 As a result, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of the rolling elements in both rows are different, the thickness of the non-hardened portion existing in the peripheral portions of the outer ring raceways 13a and 13b is ensured. Things can be difficult. The rolling fatigue life of both the outer ring raceways 13a and 13b is ensured by forming a heat treatment hardened layer on both the outer ring raceways 13a and 13b. However, the heat treatment hardened layer is simply formed on the heat treated hardened layer. If sufficient residual compressive stress is not generated, it is difficult to ensure a sufficient rolling fatigue life. None of Patent Documents 1 to 5 describe such a point. Patent Document 6 discloses a structure in which the pitch circle diameters of the rolling elements in both rows are equal, a structure in which the heat treatment hardened layers formed on both outer ring raceway portions are independent, and a structure in which the heat treatment hardened layers formed on both outer ring raceway portions are continuous. Is described. However, even with the technique described in Patent Document 6, it is possible to generate sufficient residual compressive stress in the heat-treated hardened layer of the outer ring raceway portions of both rows with a structure in which the pitch circle diameters of both rows of rolling elements are different. It is not a suggestion.

特開２００３−２３２３４３号公報JP 2003-232343 A 特開２００４−１０８４４９号公報JP 2004-108449 A 特開２００４−３４５４３９号公報JP 2004-345439 A 特開２００６−１３７３６５号公報JP 2006-137365 A 国際公開ＷＯ２００５／０６５０７７International Publication WO2005 / 065077 実開平３−２２１２４号公報Japanese Utility Model Publication No. 3-22124

本発明の車輪支持用転がり軸受ユニットは、上述の様な事情に鑑み、外側列のピッチ円直径を内側列のピッチ円直径よりも大きくして、モーメント剛性を向上させる事ができ、しかも外輪の内周面に設けた複列の外輪軌道同士の間に位置し、径方向に関する厚さ寸法を十分に確保できる部分を有効利用して、これら両外輪軌道の転がり疲れ寿命を十分に確保できる構造を実現すべく発明したものである。 In consideration of the above-described circumstances, the wheel bearing rolling bearing unit of the present invention can increase the moment rigidity by making the pitch circle diameter of the outer row larger than the pitch circle diameter of the inner row. A structure that is located between the double row outer ring raceways provided on the inner peripheral surface, and that can effectively secure the rolling fatigue life of both outer ring raceways by effectively using the part that can sufficiently secure the thickness dimension in the radial direction. Invented to realize the above.

本発明の車輪支持用転がり軸受ユニットは、前述の図５に示した従来構造と同様に、外輪と、ハブと、複数個の転動体とを備える。
このうちの外輪は、炭素鋼製で、内周面に複列の外輪軌道を有する。
又、上記ハブは、外周面の軸方向外端部に車輪を支持固定する為の取付フランジを、同じく軸方向に関する中間部及び内端部に複列の内輪軌道を、それぞれ有する。
又、上記各転動体は、これら両内輪軌道と上記両外輪軌道との間に各列毎に複数個ずつ、予圧と背面組み合わせ型の接触角とを付与された状態で設けられている。
そして、軸方向外側の列のピッチ円直径が、同じく内側の列のピッチ円直径よりも大きい。
特に、本発明の車輪支持用転がり軸受ユニットに於いては、上記外輪の内周面のうちで、上記両外輪軌道部分と、上記外輪の内周面の軸方向中間部でこれら両外輪軌道同士の間部分とに、熱処理硬化層を形成している。そして、これら各部分の熱処理硬化層が連続して一体の（非硬化層により分割されていない）熱処理硬化層を形成している。 The wheel-supporting rolling bearing unit of the present invention includes an outer ring, a hub, and a plurality of rolling elements as in the conventional structure shown in FIG.
Out of these, the outer ring is made of carbon steel and has a double row outer ring raceway on the inner peripheral surface.
The hub has a mounting flange for supporting and fixing the wheel at the axially outer end portion of the outer peripheral surface, and double row inner ring raceways at the intermediate and inner end portions in the axial direction.
Each of the rolling elements is provided with a preload and a back contact type contact angle between each of the inner ring raceways and the outer ring raceways for each row.
The pitch circle diameter of the outer row in the axial direction is larger than the pitch circle diameter of the inner row.
In particular, in the rolling bearing unit for supporting a wheel of the present invention, the outer ring raceways are arranged between the outer ring raceway portions and the axially intermediate portion of the outer circumference of the outer race. A heat-treated and hardened layer is formed between the intermediate portions. And the heat-treatment hardening layer of these each part forms the heat treatment hardening layer continuously (it is not divided | segmented by the non-hardening layer) continuously.

上述の様な本発明の車輪支持用転がり軸受ユニットを実施する場合に好ましくは、請求求項２に記載した様に、上記両外輪軌道同士の間部分の熱処理硬化層を、上記両列の外輪軌道の断面形状に共通する接線を母線とする仮想円すい筒面よりも、径方向内側部分にのみ存在させる。
或いは、請求項３に記載した様に、上記外輪の内周面のうちで両外輪軌道同士の間部分の断面形状を、直線又は滑らかな曲線を連続させた形状とする。 When the rolling bearing unit for supporting a wheel according to the present invention as described above is implemented, preferably, the heat treatment hardened layer between the outer ring raceways is formed as the outer ring in both rows as described in claim 2. It exists only in the radially inner portion of the virtual conical cylindrical surface having a tangent common to the cross-sectional shape of the track as a generating line.
Alternatively, as described in claim 3, the cross-sectional shape of the portion between the outer ring raceways in the inner peripheral surface of the outer ring is a shape in which straight lines or smooth curves are continuous.

上述の様に構成する本発明の車輪支持用転がり軸受ユニットによれば、外側列のピッチ円直径を内側列のピッチ円直径よりも大きくして、モーメント剛性を向上させる事ができる構造で、外輪の内周面に設けた複列の外輪軌道同士の間部分を有効利用する事により、これら両外輪軌道部分に形成した熱処理硬化層に十分な残留圧縮応力を発生させて、これら両外輪軌道の転がり疲れ寿命を十分に確保できる。この理由に就いて、以下に説明する。 According to the rolling bearing unit for supporting a wheel of the present invention configured as described above, the outer ring has a structure that can increase the moment stiffness by making the pitch circle diameter of the outer row larger than the pitch circle diameter of the inner row. By effectively using the portion between the double row outer ring raceways provided on the inner peripheral surface of the outer circumferential raceway, sufficient residual compressive stress is generated in the heat treatment hardened layer formed on both outer ring raceway portions, A sufficient rolling fatigue life can be secured. The reason will be described below.

上記外輪の内周面部分に、高周波焼き入れ等の熱処理により硬化層を形成すると、前述した様に、この硬化層部分の金属組織が、マルテンサイト変態により僅かとは言え膨張する。そして、この硬化層の周囲部分に非硬化部分が存在すると、この硬化層がこの非硬化部分により抑え付けられて、内部に残留圧縮応力が発生する。前述した様に、上記両外輪軌道部分に形成した熱処理硬化層に十分な残留圧縮応力を発生させる為には、上記外輪の周囲部分に十分な厚さを有する非硬化部分を存在させれば良いが、やはり前述した理由により、この周囲部分の非硬化部分の厚さを確保する事は難しい場合がある。 When a hardened layer is formed on the inner peripheral surface portion of the outer ring by heat treatment such as induction hardening, as described above, the metal structure of the hardened layer portion expands albeit slightly due to martensitic transformation. And when a non-hardened part exists in the surrounding part of this hardened layer, this hardened layer will be suppressed by this non-hardened part, and a residual compressive stress will generate | occur | produce inside. As described above, in order to generate a sufficient residual compressive stress in the heat-treated hardened layer formed on both outer ring raceway portions, it is only necessary to have a non-hardened portion having a sufficient thickness around the outer ring. However, for the reasons described above, it may be difficult to ensure the thickness of the uncured portion in the surrounding portion.

一方、複列に配置した転動体に背面組み合わせ型の接触角を付与する車輪支持用転がり軸受ユニットの場合、上記外輪の軸方向中間部で上記両外輪軌道の間部分の厚さは、これら両外輪軌道の厚さに比べて大きくできる。そこで、これら両外輪軌道部分だけでなく上記間部分の内周面にも熱処理硬化層を形成すれば、この間部分を利用して、上記両外輪軌道部分に生じる残留圧縮応力を大きくできる。即ち、この間部分の内周面に熱処理硬化層を形成すると、この間部分に関しても、熱処理硬化層の周囲部分が外径側に押される状態となり、その反作用として、この周囲部分から径方向内方に向いた力が加わる。そして、この径方向内方に向いた力は、上記間部分の内周面に形成した熱処理硬化層だけでなく、上記両外輪軌道部分に形成した熱処理硬化層にも伝わる。この結果、これら両外輪軌道部分の残留圧縮応力がその分だけ（各外輪軌道部分に形成した熱処理硬化層により生じる残留圧縮応力に、上記間部分から伝わる、径方向内方に向いた力により生じる残留圧縮応力が足される分だけ）増大し、これら両外輪軌道の転がり疲れ寿命が向上する。尚、熱処理硬化層の厚さとは、上記外輪の内周面（外輪軌道に関しては、転動体の転動面と転がり接触する部分）から、予め設定した所定の硬さの値となる深さ迄の距離（例えば、表面部分の、より高い硬度が、次第に低下してＨｖ５００となる迄の距離）とする。 On the other hand, in the case of a rolling bearing unit for supporting a wheel that gives a contact angle of the rear combination type to rolling elements arranged in a double row, the thickness of the portion between the outer ring raceways in the axial direction intermediate part of the outer ring It can be made larger than the thickness of the outer ring raceway. Therefore, if a heat treatment hardened layer is formed not only on the outer ring raceway portions but also on the inner peripheral surface of the intermediate portion, the residual compressive stress generated in the outer ring raceway portions can be increased using the intermediate portion. That is, when the heat treatment cured layer is formed on the inner peripheral surface of the intermediate portion, the peripheral portion of the heat treatment hardened layer is also pushed to the outer diameter side with respect to the intermediate portion, and as a reaction, the peripheral portion is radially inward from the peripheral portion. Adds the right power. The force directed inward in the radial direction is transmitted not only to the heat treatment hardened layer formed on the inner peripheral surface of the intermediate portion but also to the heat treatment hardened layer formed on both outer ring raceway portions. As a result, the residual compressive stress of these outer ring raceway portions is generated by that amount (the residual compressive stress generated by the heat-treated hardened layer formed on each outer ring raceway portion is caused by the radially inward force transmitted from the above-mentioned portion. As the residual compressive stress is added, the rolling fatigue life of both outer ring raceways is improved. The thickness of the heat-treated hardened layer is from the inner peripheral surface of the outer ring (for the outer ring raceway, the portion that is in rolling contact with the rolling surface of the rolling element) to a depth at which a predetermined hardness value is set. (For example, the distance until the higher hardness of the surface portion gradually decreases to Hv500).

特に、請求項２に記載した様に、上記両外輪軌道同士の間部分の熱処理硬化層を、上記両外輪軌道の断面形状に共通する接線を母線とする仮想円すい筒面よりも径方向内側部分にのみ存在させれば、上記間部分に生じた、径方向内方に向いた力を、上記両外輪軌道部分に形成した熱処理硬化層のうちで各転動体と転がり接触する部分に効果的に伝達できる。即ち、本発明の対象となる車輪支持用転がり軸受ユニットの場合には、上記各転動体に背面組み合わせ型の接触角を付与しており、これら各転動体は、上記両外輪軌道のうちで上記間部分寄り部分に転がり接触する。この間部分の非硬化部分に生じた、径方向内方に向いた力を、上記両外輪軌道のうちでこの間部分寄り部分に伝達する為には、この間部分の未硬化部分（残留圧縮応力を生じた部分）を、できるだけ径方向内側寄り部分に迄設ける事が好ましい。逆に言えば、上記間部分の熱処理硬化層が上記仮想円すい筒面よりも径方向外側に迄存在すると、この熱処理硬化層にブロックされる形で、上記非硬化部分に生じた、径方向内方に向いた力が、上記両外輪軌道のうちでこの間部分寄り部分に伝達されにくくなる。 In particular, as described in claim 2, the heat treatment hardened layer between the two outer ring raceways is a radially inner portion of a virtual conical cylindrical surface having a tangent line common to the cross-sectional shape of the two outer ring raceways as a generating line. In the heat treatment hardened layer formed on the outer ring raceway portions, the radially inwardly generated force generated in the intermediate portion is effectively applied to the portions that are in rolling contact with the rolling elements. Can communicate. That is, in the case of a rolling bearing unit for supporting a wheel that is a subject of the present invention, a contact angle of a back combination type is given to each of the rolling elements, and each of these rolling elements is the above-mentioned among the both outer ring raceways. Rolling contact with the part near the gap. In order to transmit the radially inward force generated in the non-hardened part of the intermediate part to the part near the intermediate part of the outer ring raceway, the unhardened part (residual compressive stress is generated) It is preferable to provide the portion as far as possible in the radially inner portion. In other words, if the heat-treated cured layer in the intermediate portion exists to the outside in the radial direction with respect to the virtual conical cylindrical surface, the heat-cured layer is blocked by the heat-cured cured layer and is generated in the non-cured portion. The force directed in the direction is less likely to be transmitted to a portion closer to the portion between the outer ring raceways.

但し、上記間部分の内周面部分に設ける熱処理硬化層の厚さが、この間部分の未硬化部分に、十分に大きな、径方向内方に向いた力を生じさせられる程度の寸法（例えば、一般的な乗用車用の車輪支持用転がり軸受ユニットの場合で、１〜２mm程度）である事が条件となる。これらの事を考慮すれば、上記間部分の熱処理硬化層を上記仮想円すい筒面よりも径方向内側部分にのみ設ける事により、上記目的を高次元で達成する事ができる。尚、上記間部分に形成する熱処理硬化層の厚さを過度に（上記仮想円すい筒面よりも径方向外側に達する程度に迄）大きくする事は、この間部分の未硬化部分の厚さを確保する面と、この間部分と上記両外輪軌道との境界部（溝肩部）にオーバーヒートによる粗大な結晶粒が生じるのを防止する面からも好ましくない。因に、この粗大な結晶粒の出現は、上記溝肩部の脆化による耐久性低下の原因となる等、品質保持の面から好ましくない。 However, the thickness of the heat-cured layer provided on the inner peripheral surface portion of the intermediate portion is sufficiently large to generate a radially inward force on the uncured portion of the intermediate portion (for example, It is a condition that it is about 1 to 2 mm in the case of a rolling bearing unit for supporting a wheel for a general passenger car. If these things are considered, the said objective can be achieved in a high dimension by providing the heat treatment hardening layer of the said intermediate part only in the radial direction inner side rather than the said virtual conical cylinder surface. It should be noted that excessively increasing the thickness of the heat-treated cured layer formed in the intermediate portion (to the extent that it reaches the outside in the radial direction from the virtual conical cylinder surface) ensures the thickness of the uncured portion in the intermediate portion. This is also undesirable from the viewpoint of preventing the formation of coarse crystal grains due to overheating at the boundary surface (groove shoulder) between this surface and the outer ring raceway. For this reason, the appearance of the coarse crystal grains is not preferable from the standpoint of maintaining the quality, for example, causing a decrease in durability due to the embrittlement of the groove shoulder.

又、本発明を実施する場合に、請求項３に記載した様に、前記外輪の内周面のうちで上記両外輪軌道同士の間部分の断面形状を、直線又は滑らかな曲線を連続させた形状とすれば、これら両外輪軌道同士の間部分の熱伝達長さを短く、且つ、この間部分の放熱面積を狭くして、これら両外輪軌道及び間部分を、同時に且つ均一に加熱し易くできる。そして、これら両外輪軌道及び間部分に、均一な熱処理硬化層を形成し易くできる。 Further, when carrying out the present invention, as described in claim 3, the cross-sectional shape of the portion between the outer ring raceways in the inner peripheral surface of the outer ring is made continuous with a straight line or a smooth curve. If the shape is adopted, the heat transfer length between the two outer ring raceways can be shortened, and the heat radiation area between the two outer ring raceways can be narrowed to easily heat both the outer ring raceways and the intermediate portion simultaneously and uniformly. . A uniform heat-treated hardened layer can be easily formed on both the outer ring raceways and the intermediate portions.

図１〜３は、全部の請求項に対応する、本発明の実施の形態の第１例を示している。尚、本発明の特徴は、外輪３ａの内周面に形成した複列の外輪軌道１３ａ、１３ｂ部分及びこれら両外輪軌道１３ａ、１３ｂの間部分１６に、熱処理硬化層１７ａ、１７ｂ、１７ｃを互いに連続させて（これら各熱処理硬化層１７ａ、１７ｂ、１７ｃを一体として）形成する点にある。又、本例の場合には、上記外輪３ａの軸方向中間部内周面で上記間部分１６に対応する部分の断面形状（母線形状）を直線としている。従って、この内周面の形状は、軸方向外側に向かう程内径が大きくなる方向に傾斜した、部分円すい状凹面である。尚、上記間部分１６の両端部と上記両外輪軌道１３ａ、１３ｂの端部との連続部にそれぞれ存在する折れ曲がり部の角度は、できるだけ大きく（鈍角に）する事が好ましい。この理由は、上記各熱処理硬化層１７ａ、１７ｂ、１７ｃの焼き入れの際に、上記連続部がオーバーヒートして、前述の様な粗大な結晶粒が生じるのを防止する為である。 1 to 3 show a first example of an embodiment of the present invention corresponding to all claims. The feature of the present invention is that the heat treatment hardened layers 17a, 17b, 17c are formed on the outer ring raceways 13a, 13b of the double row formed on the inner peripheral surface of the outer ring 3a and the portion 16 between these outer ring raceways 13a, 13b. It is in the point that it forms continuously (these heat treatment hardening layers 17a, 17b, and 17c are united). In the case of this example, the cross-sectional shape (bus shape) of the portion corresponding to the intermediate portion 16 on the inner circumferential surface in the axial direction of the outer ring 3a is a straight line. Therefore, the shape of the inner peripheral surface is a partial conical concave surface that is inclined in a direction in which the inner diameter increases toward the outer side in the axial direction. In addition, it is preferable that the angle of the bent part which exists in the continuous part of the both ends of the said intermediate part 16 and the edge part of the said both outer ring track 13a, 13b is made as large as possible (an obtuse angle). The reason for this is to prevent the above-described continuous portion from overheating and quenching of the heat-treated cured layers 17a, 17b, and 17c to generate coarse crystal grains as described above.

又、図示の例では、外側列の玉４ａ、４ａの直径（例えば、約１０．３mm）を、内側列の玉４ｂ、４ｂの直径（例えば、約１１．１mm）よりも小さくして、外側列の玉４ａ、４ａの数（例えば１５個）を、内側列の玉４ｂ、４ｂの数（例えば１１個）よりも多くしている。これに合わせて、外側列の内輪軌道８ａ及び外輪軌道１３ａの断面形状（母線形状）の曲率半径を、内側列の内輪軌道８ｂ及び外輪軌道１３ｂの断面形状の曲率半径よりも小さくしている。又、外側列の玉４ａ、４ａのピッチ円直径を例えば６０mmとし、内側列の玉４ｂ、４ｂのピッチ円直径を例えば５０mmとしている。要するに、本発明は、外側、内側両列の玉４ａ、４ｂに関して、何れも、ピッチ円直径が玉の直径の６倍未満である構造に適用して、両列の外輪軌道１３ａ、１３ｂの転がり疲れ寿命確保を図る面から有効である。逆に言えば、ピッチ円直径を玉の直径の６倍以上に大きくできる様な、比較的大型の車輪支持用転がり軸受ユニットの場合には、両列の外輪軌道の周囲に、十分な厚さの未硬化部分を設け易いので、本発明によらなくても（勿論、本発明を適用する事で、より優れた耐久性を確保する事は自由であるが）、転がり疲れ寿命の確保を行なう設計は、比較的容易である。その他の部分の構成及び作用は、前述の図５に示した従来構造と同様であるから、同等部分に関する説明は省略若しくは簡略にし、以下、本発明及び本例の特徴部分を中心に説明する。 In the illustrated example, the outer rows 4a and 4a have a diameter (for example, about 10.3 mm) smaller than the inner rows 4b and 4b (for example, about 11.1 mm). The number of balls 4a, 4a in the row (for example, 15) is made larger than the number of balls (4b, 4b) in the inner row (for example, 11). Accordingly, the curvature radii of the cross-sectional shapes (bus shape) of the inner ring raceway 8a and the outer ring raceway 13a in the outer row are made smaller than the curvature radii of the cross-sectional shapes of the inner ring raceway 8b and the outer ring raceway 13b in the inner row. The pitch circle diameter of the balls 4a and 4a in the outer row is set to 60 mm, for example, and the pitch circle diameter of the balls 4b and 4b in the inner row is set to 50 mm, for example. In short, the present invention is applied to a structure in which both the outer and inner rows of balls 4a and 4b have a pitch circle diameter of less than 6 times the diameter of the balls, and the outer ring raceways 13a and 13b of both rows are rolled. This is effective from the viewpoint of ensuring fatigue life. Conversely, in the case of a relatively large wheel-supporting rolling bearing unit that can increase the pitch circle diameter to more than six times the ball diameter, a sufficient thickness is provided around the outer ring raceways in both rows. Since it is easy to provide the uncured portion, it is possible to secure a rolling fatigue life even if not according to the present invention (although it is of course free to secure superior durability by applying the present invention). Design is relatively easy. Since the configuration and operation of the other parts are the same as those of the conventional structure shown in FIG. 5 described above, explanations of the equivalent parts will be omitted or simplified, and the following description will focus on the features of the present invention and this example.

図２に示す様に、上記外輪３ａの内周面の軸方向両端部を除く部分で、上記複列の外輪軌道１３ａ、１３ｂ及び上記間部分１６を含む部分に上記熱処理硬化層１７ａ、１７ｂ、１７ｃ（斜格子で示した部分）を、高周波焼き入れにより、それぞれ全周に亙って形成している。これら各熱処理硬化層１７ａ、１７ｂ、１７ｃは、上記外輪３ａの内周面に倣う外周面形状を有する一体型の高周波加熱コイルにより、上記両外輪軌道１３ａ、１３ｂ及び上記間部分１６を同時に加熱する、高周波熱処理により形成している。説明の為、上記各熱処理硬化層１７ａ、１７ｂ、１７ｃに別個の符号を付しているが、これら各熱処理硬化層１７ａ、１７ｂ、１７ｃは互いに連続した一体型で、各部の厚さが異なる以外、均質である。 As shown in FIG. 2, the heat treatment hardened layers 17 a, 17 b, 17 b, 17 b, 17 b, and a portion including the double row outer ring raceways 13 a, 13 b and the intermediate portion 16, except for both axial ends of the inner peripheral surface of the outer ring 3 a 17c (portions indicated by oblique lattices) are formed over the entire circumference by induction hardening. These heat treatment hardened layers 17a, 17b, and 17c simultaneously heat both the outer ring raceways 13a and 13b and the intermediate portion 16 by an integrated high-frequency heating coil having an outer peripheral surface shape that follows the inner peripheral surface of the outer ring 3a. It is formed by high frequency heat treatment. For the purpose of explanation, the heat treatment cured layers 17a, 17b, and 17c are given a separate reference numeral, but the heat treatment cured layers 17a, 17b, and 17c are integrated with each other except that the thicknesses of the respective parts are different. Is homogeneous.

上記各熱処理硬化層１７ａ、１７ｂ、１７ｃのうち、上記両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂを形成する範囲は、車輪支持用転がり軸受ユニットに加わるモーメントやアキシアル荷重に拘らず、上記各玉４ａ、４ｂの転動面と上記両外輪軌道１３ａ、１３ｂとの転がり接触部に存在する接触楕円が上記両熱処理硬化層１７ａ、１７ｂからはみ出さない様に、その範囲を規制している。又、上記両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂの厚さは、これら両外輪軌道１３ａ、１３ｂの転がり疲れ寿命及び耐圧痕性を確保する面から規制している。これら両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂの厚さＴａ、Ｔｂは、転がり軸受の技術分野で広く知られているＨｅｒｔｚの理論等により決定するが、例えば、一般的な乗用車用の車輪支持用転がり軸受ユニットの場合で、２〜３mm程度とする。 Of the heat treatment hardened layers 17a, 17b, and 17c, the range in which the heat treatment hardened layers 17a and 17b of the outer ring raceways 13a and 13b are formed, regardless of the moment and the axial load applied to the wheel support rolling bearing unit, The range is regulated so that the contact ellipse existing at the rolling contact portion between the rolling surfaces of the balls 4a and 4b and the outer ring raceways 13a and 13b does not protrude from the heat-treated cured layers 17a and 17b. Yes. Further, the thickness of the heat-treated hardened layers 17a and 17b of both the outer ring raceways 13a and 13b is restricted from the viewpoint of ensuring the rolling fatigue life and pressure proof property of both the outer ring raceways 13a and 13b. The thicknesses Ta and Tb of the heat-treated hardened layers 17a and 17b in the outer ring raceways 13a and 13b are determined by Hertz's theory, which is widely known in the technical field of rolling bearings. In the case of the rolling bearing unit for supporting the wheel, it is set to about 2 to 3 mm.

これに対して、上記間部分１６の熱処理硬化層１７ｃの厚さＴｃに関しては、この間部分１６のうちでこの熱処理硬化層１７ｃの周囲に存在する未硬化部分１８に、この熱処理硬化層１７ｃの加工に伴って生じ、且つ、上記両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂに伝達される、径方向内方に向いた力をできるだけ大きくする面から規制する。これらの事を考慮すれば、上記熱処理硬化層１７ｃの厚さＴｃは、前述した通り、一般的な乗用車用の車輪支持用転がり軸受ユニットの場合で、１〜２mm程度が適切である。少なくとも、上記熱処理硬化層１７ｃの厚さＴｃは、この熱処理硬化層１７ｃが、上記両外輪軌道１３ａ、１３ｂの断面形状に共通する接線αを母線とする仮想円すい筒面よりも径方向外方に迄達しない程度に収める。 On the other hand, regarding the thickness Tc of the heat treatment hardened layer 17c in the intermediate portion 16, the heat treatment hardened layer 17c is processed into the uncured portion 18 around the heat treatment hardened layer 17c in the intermediate portion 16. Therefore, the force directed inward in the radial direction that is transmitted to the heat-treated and hardened layers 17a and 17b of both the outer ring raceways 13a and 13b is restricted from the aspect of increasing as much as possible. In consideration of these matters, the thickness Tc of the heat-treated cured layer 17c is appropriately about 1 to 2 mm in the case of a general rolling bearing unit for supporting a wheel for a passenger car as described above. At least the thickness Tc of the heat-treated hardened layer 17c is such that the heat-treated hardened layer 17c is radially outward from the virtual conical cylinder surface whose tangent line α is common to the cross-sectional shapes of the outer raceways 13a and 13b. Keep it to the extent that it does not reach.

一方、やはり炭素鋼製であるハブ本体５の外周面に関しては、図３に示す様に、取付フランジ７の基端部内側面から小径段部１１にかけての部分に熱処理硬化層１９（斜格子で示した部分）を、軸方向外側の内輪軌道８ａ部分を含めて、軸方向に連続した状態で、全周に亙り形成している。上記焼き入れ硬化層１９に関しても、高周波焼き入れにより形成している。上記小径段部１１には、図１に示す様に、軸受鋼製で全体を焼き入れ硬化した（所謂ズブ焼きした）内輪６を外嵌し、かしめ部１２により上記ハブ本体５に対し結合固定している。 On the other hand, as shown in FIG. 3, the outer peripheral surface of the hub body 5, which is also made of carbon steel, is a heat treatment hardened layer 19 (indicated by a slanted lattice) in a portion extending from the inner side surface of the mounting flange 7 to the small diameter step portion 11. And the inner ring raceway 8a on the outer side in the axial direction are formed over the entire circumference in a state of being continuous in the axial direction. The quench hardened layer 19 is also formed by induction hardening. As shown in FIG. 1, an inner ring 6 made of bearing steel and hardened and hardened (so-called baked) is externally fitted to the small diameter step portion 11, and the caulking portion 12 is coupled and fixed to the hub body 5. is doing.

上述の様に構成する本例の車輪支持用転がり軸受ユニットは、前述の［発明の効果］部分で説明した理由により、外側列のピッチ円直径を内側列のピッチ円直径よりも大きくし、モーメント剛性を向上させる事ができる構造で、外輪３ａの内周面に形成した複列の外輪軌道１３ａ、１３ｂの転がり疲れ寿命を十分に確保できる。要約すれば、十分な厚さ寸法を有する前記間部分１６の内周面部分に熱処理硬化層１７ｃを形成し、この間部分１６でこの熱処理硬化層１７ｃの周囲に存在する未硬化部分１８に、十分に大きな、径方向内方に向いた力を発生させ、この力を、図２に複数の矢印で示す様に、上記未硬化部分１８から径方向内方に向け作用させる。即ち、この未硬化部分１８部分で発生した力が、上記間部分１６の熱処理硬化層１７ｃだけでなく、上記両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂも、径方向内方に押圧する。この結果、これら両外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂにも残留圧縮応力が発生し、これら両外輪軌道１３ａ、１３ｂの転がり疲れ寿命が向上する。 The wheel support rolling bearing unit of the present example configured as described above has a pitch circle diameter of the outer row larger than that of the inner row for the reason explained in the above [Effects of the invention], and a moment With the structure capable of improving the rigidity, it is possible to sufficiently ensure the rolling fatigue life of the double row outer ring raceways 13a and 13b formed on the inner peripheral surface of the outer ring 3a. In summary, a heat-treated cured layer 17c is formed on the inner peripheral surface portion of the intermediate portion 16 having a sufficient thickness dimension, and the uncured portion 18 existing around the heat-treated cured layer 17c is sufficiently formed in the intermediate portion 16 in the intermediate portion. A large force directed radially inward is generated, and this force is applied radially inward from the uncured portion 18 as indicated by a plurality of arrows in FIG. That is, the force generated in the uncured portion 18 is pressed not only in the heat-treated hardened layer 17c in the intermediate portion 16 but also in the heat-treated hardened layers 17a and 17b in the outer ring raceways 13a and 13b. To do. As a result, residual compressive stress is also generated in the heat-treated hardened layers 17a and 17b of both the outer ring raceways 13a and 13b, and the rolling fatigue life of both the outer ring raceways 13a and 13b is improved.

この為、比較的小型で、これら外輪軌道１３ａ、１３ｂ部分の熱処理硬化層１７ａ、１７ｂの周囲に存在する未硬化部分の厚さ寸法を十分に確保できない車輪支持用転がり軸受ユニットの場合にも、当該車輪支持用転がり軸受ユニットを組み込んだ自動車の車輪支持部の耐久性向上を図れる。特に、上記間部分１６は、全体に亙って、外側列の外輪軌道１３ａに向う程内径が大きくなる方向に傾斜している為、図２の各矢印の分力が軸方向外方に作用する事から明らかな様に、上記外側列の外輪軌道１３ａ部分に形成した熱処理硬化層１７ａに、大きな残留圧縮応力を生じさせる事ができる。そして、この外側列の外輪軌道１３ａ部分の径方向に関する厚さを小さく抑え、車輪支持用転がり軸受ユニットの為の設計を行ない易くできる。 For this reason, even in the case of a wheel bearing rolling bearing unit that is relatively small and cannot sufficiently secure the thickness dimension of the uncured portion existing around the heat-treated cured layers 17a and 17b of the outer ring raceways 13a and 13b, It is possible to improve the durability of the wheel support portion of an automobile incorporating the wheel support rolling bearing unit. In particular, since the intermediate portion 16 is inclined in a direction in which the inner diameter increases toward the outer ring raceway 13a in the outer row, the component force of each arrow in FIG. 2 acts outward in the axial direction. As is clear from this, a large residual compressive stress can be generated in the heat-treated hardened layer 17a formed in the outer ring raceway 13a portion of the outer row. And the thickness regarding the radial direction of the outer ring raceway 13a part of this outer side row | line | column can be suppressed small, and it can be made easy to design for the rolling bearing unit for wheel support.

［実施の形態の第２例］
図４は、やはり全部の請求項に対応する、本発明の実施の形態の第２例を示している。本例の場合には、両列の外輪軌道１３ａ、１３ｂの端部と間部分１６ａの両端部との間に、それぞれ円筒面部２０ａ、２０ｂを形成している。これら両円筒面部２０ａ、２０ｂのうち、内側列の外輪軌道１３ｂに隣接して設けた円筒面部２０ｂの存在により、この内側列の外輪軌道１３ｂの端部に存在する連続部の折れ曲がり部の角度を、上述した第１例の場合よりも大きくできる。そして、各熱処理硬化層１７ａ、１７ｂ、１７ｃの焼き入れの際に、上記連続部がオーバーヒートする事を防止できる。尚、以上の説明から明らかな通り、外側列の外輪軌道１３ａに隣接して設けた円筒面部２０ａに関しては、オーバーヒート防止の面からは、省略しても良い。要は、外輪３ａの内周面のうちで上記各熱処理硬化層１７ａ、１７ｂ、１７ｃを形成する部分に、急な｛折れ曲がり角度が９０度以下で、曲率半径が極く小さい（例えば１mm以下）である｝変曲点を設けずに、上記オーバーヒートを防止する。但し、上記外側の円筒面部２０ａに関しては、設ける事で、上記外側列の外輪軌道１３ａの肩高さを確保して、玉の転動面の乗り上げを防止する面からは有効である。その他の構成及び作用は、上述した実施の形態の第１例の場合と同様であるから、重複する図示並びに説明は省略する。 [Second Example of Embodiment]
FIG. 4 shows a second example of an embodiment of the invention which also corresponds to all claims. In the case of this example, cylindrical surface portions 20a and 20b are formed between the ends of the outer ring raceways 13a and 13b in both rows and the both ends of the intermediate portion 16a, respectively. Of these cylindrical surface portions 20a and 20b, the presence of the cylindrical surface portion 20b provided adjacent to the inner row outer ring raceway 13b allows the angle of the bent portion of the continuous portion present at the end of the inner row outer ring raceway 13b to be determined. It can be made larger than in the case of the first example described above. And it can prevent that the said continuous part overheats at the time of quenching of each heat processing hardening layer 17a, 17b, 17c. As is clear from the above description, the cylindrical surface portion 20a provided adjacent to the outer ring raceway 13a in the outer row may be omitted from the viewpoint of preventing overheating. In short, the steep {bending angle is 90 degrees or less and the radius of curvature is extremely small (for example, 1 mm or less) in the portion of the inner peripheral surface of the outer ring 3a where the heat treatment hardened layers 17a, 17b, 17c are formed. The overheating is prevented without providing an inflection point. However, the outer cylindrical surface portion 20a is effective in terms of providing the shoulder height of the outer ring raceway 13a in the outer row and preventing the ball from rolling on the rolling surface. Other configurations and operations are the same as in the case of the first example of the above-described embodiment, and thus overlapping illustrations and descriptions are omitted.

本発明の実施の形態の第１例を示す断面図。Sectional drawing which shows the 1st example of embodiment of this invention. 外輪軌道部分の熱処理硬化層の範囲を説明する為、外輪のみを取り出して示す部分断面図。FIG. 4 is a partial cross-sectional view showing only the outer ring in order to explain the range of the heat-treated hardened layer in the outer ring raceway portion. 内輪軌道及び小径段部の熱処理硬化層の範囲を説明する為、ハブ本体のみを取り出して示す部分断面図。FIG. 4 is a partial cross-sectional view showing only the hub body in order to explain the range of the heat-treated hardened layer of the inner ring raceway and the small-diameter stepped portion. 本発明の実施の形態の第２例を示す、図２と同様の図。The figure similar to FIG. 2 which shows the 2nd example of embodiment of this invention. 従来構造の１例を示す断面図。Sectional drawing which shows an example of a conventional structure.

符号の説明Explanation of symbols

１車輪支持用転がり軸受ユニット
２ハブ
３、３ａ外輪
４、４ａ、４ｂ玉
５ハブ本体
６内輪
７取付フランジ
８ａ、８ｂ内輪軌道
９スタッド
１０外周面側傾斜段部
１１小径段部
１２かしめ部
１３ａ、１３ｂ外輪軌道
１４結合フランジ
１５内周面側傾斜段部
１６、１６ａ間部分
１７ａ、１７ｂ、１７ｃ熱処理硬化層
１８未硬化部分
１９熱処理硬化層
２０ａ、２０ｂ円筒面部 DESCRIPTION OF SYMBOLS 1 Wheel support rolling bearing unit 2 Hub 3, 3a Outer ring 4, 4a, 4b Ball 5 Hub main body 6 Inner ring 7 Mounting flange 8a, 8b Inner ring track 9 Stud 10 Outer peripheral surface side inclined step part 11 Small diameter step part 12 Caulking part 13a, 13b Outer ring raceway 14 Coupling flange 15 Inner peripheral surface side inclined step portion 16, 16a Between portions 17a, 17b, 17c Heat-treated cured layer 18 Uncured portion 19 Heat-treated cured layer 20a, 20b Cylindrical surface portion

Claims

内周面に複列の外輪軌道を有する、炭素鋼製の外輪と、外周面の軸方向外端部に車輪を支持固定する為の取付フランジを、同じく軸方向に関する中間部及び内端部に複列の内輪軌道を、それぞれ有するハブと、これら両内輪軌道と上記両外輪軌道との間に各列毎に複数個ずつ、背面組み合わせ型の接触角を付与された状態で設けられた転動体とを備え、軸方向外側の列のピッチ円直径が軸方向内側の列のピッチ円直径よりも大きい車輪支持用転がり軸受ユニットに於いて、上記外輪の内周面のうちで、上記両外輪軌道部分と、この外輪の内周面の軸方向中間部でこれら両外輪軌道同士の間部分とに、熱処理硬化層が形成されており、これら各部分の熱処理硬化層が連続して一体の熱処理硬化層を形成している事を特徴とする車輪支持用転がり軸受ユニット。 A carbon steel outer ring having a double-row outer ring raceway on the inner peripheral surface, and a mounting flange for supporting and fixing the wheel on the outer peripheral end in the axial direction on the outer peripheral surface, also in the intermediate and inner end portions in the axial direction. A hub having double-row inner ring raceways, and a rolling element provided with a contact angle of a back combination type between each of the inner ring raceways and the outer ring raceways. In the rolling bearing unit for supporting a wheel having a pitch circle diameter of the outer row in the axial direction larger than the pitch circle diameter of the row in the axial direction, the outer ring raceway of the inner race surface of the outer ring. A heat-treated and hardened layer is formed between the outer ring raceway and a portion between the outer ring raceways in the axially intermediate portion of the inner peripheral surface of the outer ring. Wheel-supporting rolling characterized by forming a layer Receiving unit.

両外輪軌道同士の間部分の熱処理硬化層が、両列の外輪軌道の断面形状に共通する接線を母線とする仮想円すい筒面よりも径方向内側部分にのみ存在する、請求項１に記載した車輪支持用転がり軸受ユニット。 The heat treatment hardened layer in a portion between both outer ring raceways is present only in a radially inner portion of a virtual conical cylindrical surface having a tangent common to the cross-sectional shape of both rows of outer ring raceways as a generating line. Rolling bearing unit for wheel support.

外輪の内周面のうちで両外輪軌道同士の間部分の断面形状を、直線又は滑らかな曲線を連続させた形状とした、請求項１〜２のうちの何れか１項に記載した車輪支持用転がり軸受ユニット。 The wheel support according to any one of claims 1 to 2, wherein a cross-sectional shape of a portion between both outer ring raceways in the inner peripheral surface of the outer ring is a shape in which a straight line or a smooth curve is continuous. Rolling bearing unit for use.