JP2005076651A - Rolling bearing and belt-type continuously variable transmission using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radial ball bearing to support a pulley shaft of a belt type continuously variable transmission, capable of securing a hardness and the dimensional stability even through the service in a high-temperature environment and securing a long life. <P>SOLUTION: The inner ring and outer ring of the rolling bearing 6a are made of an alloy steel containing by mass proportion 0.3-0.6% C, 0.5-2.0% Si, and 0.5-1.5% Si, wherein the total of Si and Mo is no less than 1.6%. The residual austenite amount of the surface layer constituting the raceway surface of the inner ring and outer ring made of such an alloy steel is made no more than 12 vol.%, and the carbon content of the surface layer is made 0.8-1.2% by mass. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３８】
各合金鋼を所定形状に成形加工した後に、熱処理として、８４０〜９２０℃に加熱して３〜２０時間の浸炭又は浸炭窒化処理を行った後、油焼入れを行った。その後、後述する表２に示す温度で、１．５〜２．０時間の焼戻しを行った。
熱処理後に、研削仕上げ加工と超仕上げ加工とを行い、内輪及び外輪の軌道面の表面粗さは０．０１〜０．０４μｍＲａ程度とした。
そして、完成させた内輪及び外輪と、ＳＵＪ２製で浸炭窒化処理がなされている玉と、金属製の保持器とを用いて試験軸受を組み立てた後、内輪及び外輪の間に形成され玉が内設された空隙部をシール部材で密封した。なお、ラジアル内部すきまは、「Ｃ３すきま」以下とした。
【００３９】
表２に、各試験軸受について、内輪及び外輪を形成した合金鋼の「鋼種記号」と、「焼戻し温度」と、「軌道面の表面Ｃ濃度（炭素含有率）」及び「軌道面の表面Ｎ濃度（窒素含有率）」と、「軌道面の表面残留γ（オーステナイト）量」と、「軌道面の表面硬さ（Ｈｖ）」とをそれぞれ示す。ここで、Ｃ濃度及びＮ濃度は発光分光分析装置を用いて測定し、同様に、残留γ量はＸ線分析装置、表面硬さはビッカース硬度計を用いてそれぞれ測定した。また、「表面」とは、仕上げ加工後の軌道面表面から２０μｍまでの表層部のことを指す。さらに、表２において、各構成が本発明の範囲から外れるものには下線を施した。
【００４０】
【表２】

【００４１】
次に、これらの試験軸受について、図１に示すベルト式無段変速機ユニットを用いて寿命試験を行った。このベルト式無段変速機ユニットでは、プライマリプーリ３の入力軸１及びセカンダリプーリ４の出力軸２が、それぞれ一対の転がり軸受６ａ，６ｂ，７ａ，７ｂで支持されている。この四個の転がり軸受のうち、プライマリフロント軸受（すなわち、プライマリプーリ３よりもエンジン側で入力軸１を支持する転がり軸受）６ａとして、各試験軸受を取り付けた。これ以外の転がり軸受６ｂ，７ａ，７ｂとしては、各試験で同じものを使用した。また、このベルト式無段変速機ユニットのベルト５は、図４と同様に、厚さ０．２ｍｍの鋼製薄板を１０枚重ねた構造の二条のリング５１に、２８０枚の厚さ２ｍｍの摩擦片５２を取り付けた構造であり、ベルト長は６００ｍｍである。
【００４２】
寿命試験は、下記に示す試験条件で試験軸受を回転させ、回転中の振動を測定した。そして、軸受の振動値が初期振動値の２倍となった時点で回転を終了し、この時点までの回転時間を寿命とした。結果は、表２に併せて示す。なお、表２中の寿命は、試験軸受Ｎｏ．３１の寿命を１とした場合の相対値で示す。
＜試験条件＞
回転速度：１０００〜１００００ｍｉｎ^−１
Ｐ（負荷荷重）／Ｃ（動定格荷重）：ｍａｘ０．２
潤滑油：無段変速機用潤滑油（昭和シェル製、ＮＳ−１）
油温度：１００〜１６０℃
【００４３】
また、各試験軸受の内輪及び外輪を形成した合金鋼中のＳｉとＭｏとの合計の含有量と、得られた寿命比との関係を、図２にグラフで示す。
さらに、各試験軸受の内輪及び外輪の軌道面の表面残留γ量と、得られた寿命比との関係を、図３にグラフで示す。なお、図３では、ＳｉとＭｏとの合計の含有量が本発明の範囲内の試験軸受についてのみ示した。
これらの結果から分かるように、Ｎｏ．１〜２０の試験軸受は、内輪及び外輪を、合金成分が本発明の範囲内である合金鋼で形成し、軌道面の表面Ｃ濃度が０．８〜１．２質量％で、且つ、軌道面の残留γ量が１２体積％以下であるため、これら全てを満たしていないＮｏ． ２１〜３２の試験軸受よりも、軸受寿命を長くすることができる。
【００４４】
Ｎｏ．１〜２０のうち、Ｎｏ．１〜９、Ｎｏ．１１、Ｎｏ．１３〜１５、及びＮｏ．１８〜２０は、いずれも寿命が５以上とより長寿命となっているが、Ｎｏ．１０、Ｎｏ．１２、及びＮｏ．１６、Ｎｏ． １７は、いずれも寿命が５未満となっていた。この結果より、軌道面の残留γ量が６体積％以下とすると、より長寿命な軸受が得られることが分かる。
【００４５】
これに対して、Ｎｏ．２１〜２３、Ｎｏ．２５〜２７、及びＮｏ．３１では、いずれもＳｉとＭｏとの合計の含有量が本発明の範囲を外れているため、高温環境下での硬さ及び寸法安定性を十分に確保できないため、短寿命となっていた。また、Ｎｏ．２４では、焼戻し温度及び残留γ量が本発明の範囲を外れているため、寸法安定性の劣化及び凝着の促進が起こり、短寿命となっていた。さらに、Ｎｏ．２８では、表面Ｃ濃度が本発明の範囲よりも低いため、十分な表面硬さが得られず、短寿命となっていた。さらに、Ｎｏ．２９では、表面Ｃ濃度が本発明の範囲よりも高いため、表面に粗大な炭化物が生成されるため、短寿命となっていた。また、Ｎｏ． ３２は、Ｓｉの含有率が本発明の範囲より高いため、機械的強度が低下し、短寿命となっていた。
【００４６】
このように、Ｓｉ及びＭｏの合計の含有量が高い合金鋼を用いたことで高温での硬さ及び寸法安定性を向上させるとともに、高温での焼戻しにより残留オーステナイト量を低減させたことで高温での耐表面疲労を向上させることができる。すなわち、内輪及び外輪が本発明の範囲を満たすＮｏ．１〜２０の構成とすることにより、高温環境下及び厳しい潤滑条件下で使用されるベルト式無段変速機に使用しても、長寿命な転がり軸受が得られる。
【００４７】
【発明の効果】
以上説明したように、本発明の転がり軸受によれば、内輪、外輪、及び転動体の少なくとも一つを、特定の合金鋼で形成するとともに、転がり面をなす表層部の残留オーステナイト量及び炭素含有率を特定の範囲に限定することにより、高温環境下で使用される場合であっても、硬さ及び寸法安定性が確保され、寿命が長くなる。
また、本発明のベルト式無段変速機によれば、高温環境下でも長寿命な転がり軸受でプーリの回転軸を支持することによって、長期間安定してプーリを回転させることができるため、耐久性を長期間保持することができる。
【図面の簡単な説明】
【図１】実施形態で寿命試験に使用したベルト式無段変速機を示す概略構成図である。
【図２】実施形態の結果から得られた、合金鋼中のＳｉとＭｏとの合計の含有量と寿命との関係を示すグラフである。
【図３】実施形態の結果から得られた、内輪及び外輪の軌道面の残留オーステナイト量と寿命との関係を示すグラフである。
【図４】車両のベルト式無段変速機の一例を示す断面図である。
【符号の説明】
１ 入力軸（駆動軸）
２ 出力軸（従動軸）
３ 入力軸プーリ（プライマリプーリ）
３１ 固定円錐板
３２ 可動円錐板
４ 出力軸プーリ（セカンダリプーリ）
４１ 固定円錐板
４２ 可動円錐板
５ ベルト
５１ リング
５２ 摩擦片
６，７ ラジアル玉軸受[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rolling bearing suitable for use in supporting a pulley shaft of a belt type continuously variable transmission of a vehicle.
[0002]
[Prior art]
The belt-type continuously variable transmission has a mechanism for continuously changing the radius of a belt-driven pulley as a transmission mechanism of an automatic transmission. For example, as shown in FIG. 4, pulleys 3 and 4 are provided on an input shaft (drive shaft) 1 and an output shaft (driven shaft) 2 that are arranged in parallel, and a metal made between these pulleys 3 and 4. The belt 5 is wound. This belt 5 has a structure in which a large number of thin (about 2 mm thick) friction pieces 52 are attached to two rings 51 having a structure in which about 10 thin plates having a thickness of about 0.2 mm are stacked. Power is transmitted by the pressing force when the friction pieces 52 are pressed against each other.
[0003]
The driving force is transmitted from the input shaft pulley (primary pulley) 3 to the output shaft pulley (secondary pulley) 4 via the belt 5. Both pulleys 3 and 4 are composed of fixed conical plates 31 and 41 fixed to the respective shafts 1 and 2 and movable conical plates 32 and 42 movable in the axial direction by a hydraulic mechanism. Thus, a V-shaped pulley groove is formed.
[0004]
By moving the movable conical plates 32 and 42 of these pulleys 3 and 4 in the axial direction to change the groove width, and changing the position where the belt 5 contacts the pulleys 3 and 4 (effective rotation radius of the pulley), The gear ratio can be changed steplessly. For example, if the groove width of the input shaft pulley is reduced and the groove width of the output shaft pulley is increased, the effective rotation radius of the input shaft pulley decreases and the effective rotation radius of the output shaft pulley increases. can get.
[0005]
Shaft portions (pulley shafts) 31 a and 41 a in which the fixed conical plates 31 and 41 of the pulleys 3 and 4 are integrated are supported by radial ball bearings 6 and 7. These pulley shafts 31a and 41a receive a thrust load as a reaction force when the shaft output is transmitted to the subsequent stage. Therefore, the radial ball bearings 6 and 7 are displaced in the axial direction by this thrust load, and the center in the groove width direction is shifted between the input shaft pulley 3 and the output shaft pulley 4 (so-called “center misalignment” occurs). There is a need to prevent. If the misalignment becomes large, the belt 9 may meander and damage may be caused by improper contact between the ring 51 and the friction piece 52, or the radial ball bearings 6 and 7 may slip and generate heat. Sometimes it grows.
[0006]
As a countermeasure, Patent Document 1 describes a ratio (R / D) of a radius of curvature (R) of a raceway groove (R) of an inner ring and an outer ring to a ball diameter (D) for a ball bearing that supports a pulley shaft. It is described that the value is smaller than the value (0.53) (50.1 to 50.9% for the inner ring and 50.1 to 51.9% for the outer ring). As the ratio (R / D) is smaller, the ball bearing is less likely to be displaced in the axial direction due to the thrust load.
[0007]
On the other hand, as a lubricating oil for a belt type continuously variable transmission, a lubricating oil for an automatic transmission having a high traction coefficient (in order to transmit power by smoothly operating a torque converter, a gear mechanism, a hydraulic mechanism, a wet clutch, etc.) Special oils such as ATF (Automatic Transmission Fluid) and continuously variable transmission lubricating oil (CVTF) are used.
[0008]
In the case of rolling bearings used in these lubricating oils, the tangential force generated between the bearing ring and the rolling element increases, and the center of the contact ellipse where the normal contact surface pressure is the largest (the groove width of the raceway groove). The lubricant film is destroyed at a part away from the center of the direction), that is, a part where the PV value (product of contact surface pressure and speed) is the largest, and heat is generated by increasing the frequency of metal contact. There are many.
[0009]
In particular, in recent years, a belt-type continuously variable transmission that can be applied to a large engine exceeding 2.5L has been eagerly desired. In the case of a rolling bearing used in such a belt-type continuously variable transmission, It is estimated that high torque is applied and heat generation is likely to occur. Also, in the case of a rolling bearing used in a dry belt type continuously variable transmission made of resin, torque lubrication by the belt is performed in an oil-free environment, so oil lubrication is difficult. However, heat generation is likely to occur compared to oil lubrication.
[0010]
Such heat generation causes a decrease in bearing hardness and a decomposition of retained austenite. Therefore, a rolling bearing applied to a belt-type continuously variable transmission requires maintenance of hardness and dimensional stability in a high temperature environment. Further, in rolling bearings applied in belt type continuously variable transmissions, in addition to the above-described problems under high temperature environments, peeling fatigue due to use under severe lubricating conditions is also a problem.
[0011]
As a countermeasure, Patent Document 2 uses a four-point contact ball bearing in which the total amount of retained austenite of the inner ring and ball is 5% or less and the amount of retained austenite on the raceway surface of the inner ring or outer ring is 10% or more. It is described. Here, by setting the total retained austenite amount to 5% or less, the dimensional change due to decomposition of the retained austenite during heat generation is reduced, and by increasing the retained austenite amount on the raceway surface to 10% or more, surface fatigue is reduced. Suppressed.
[0012]
[Patent Document 1]
Japanese Patent Publication No. 8-30526 [Patent Document 2]
Japanese Patent Laid-Open No. 10-292859
[Problems to be solved by the invention]
However, since the technique described in Patent Document 1 described above has been made to increase the durability of the belt of the belt-type continuously variable transmission, the life of the rolling bearing that supports the rotating shaft of the pulley is mentioned. Not.
Moreover, since the technique described in Patent Document 2 described above does not have resistance to structural changes in a high-temperature environment, wear, peeling fatigue, and the like due to hardness reduction and dimensional stability deterioration at high temperatures. However, there is still room for improvement in terms of suppressing the fatigue characteristic of belt type continuously variable transmissions.
Therefore, the present invention has been made in view of the above circumstances, and has a long life that can be suitably used for a belt-type continuously variable transmission by ensuring hardness and dimensional stability in a high-temperature environment. It is an object to provide a rolling bearing.
[0014]
[Means for Solving the Problems]
In order to solve such a problem, the present invention provides a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to roll between the inner ring and the outer ring. At least one of the inner ring, the outer ring, and the rolling element has a mass ratio of C of 0.3 to 0.6%, Si of 0.5 to 2.0%, and Mo of 0.5 to 1.5. %, By processing alloy steel containing 1.6% or more of Si and Mo into a predetermined shape, and then performing carburizing or carbonitriding treatment and quenching treatment, and high temperature tempering treatment at 200 to 400 ° C., There is provided a rolling bearing characterized in that the amount of retained austenite in a surface layer part forming a rolling surface is 12% by volume or less and the carbon content of the surface layer part is 0.8 to 1.2% by mass.
[0015]
The present invention also relates to a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are freely rollable between the inner ring and the outer ring, the inner ring, the outer ring, and the rolling element. At least one of the mass ratio is 0.3 to 0.6% for C, 0.5 to 2.0% for Si, 0.5 to 1.5% for Mo, and Si and Mo in total Residual austenite in the surface layer part forming the rolling surface by performing carburizing or carbonitriding treatment, quenching treatment and high-temperature tempering treatment at 240 to 400 ° C. after processing alloy steel contained in 1.6% or more Provided is a rolling bearing characterized in that the amount is 6% by volume or less, and the carbon content of the surface layer part is 0.8 to 1.2% by mass.
[0016]
According to the rolling bearing of the present invention, at least one of the inner ring, the outer ring, and the rolling element is formed of the specific alloy steel, and the amount of retained austenite and the carbon content of the rolling surface are configured as described above. Even when used in a high temperature environment, the hardness and dimensional stability can be ensured, so the life can be extended.
[0017]
In the rolling bearing of the present invention, it is preferable that the alloy steel includes Cr in a range of 0.5 to 3.0%, and the balance is Fe and inevitable impurities.
Furthermore, in the rolling bearing of the present invention, the nitrogen content is preferably 0.5% by mass or less. According to this, since the wear resistance and seizure resistance of the rolling bearing can be further improved, the life can be further extended.
[0018]
Furthermore, in the rolling bearing according to the present invention, it is preferable that a gap formed between the inner ring and the outer ring and in which the rolling element is provided is sealed with a shield member or a seal member. According to this, since it becomes possible to prevent wear metal powder and the like from being mixed inside the rolling bearing, the life of the rolling bearing can be further extended.
[0019]
The present invention further includes a belt-type continuously variable transmission including a pulley around which a belt is wound and a bearing that supports a rotating shaft of the pulley, wherein the bearing is the rolling bearing according to the present invention. Provided is a belt type continuously variable transmission.
According to the belt type continuously variable transmission of the present invention, even if the belt type continuously variable transmission is used in a high-temperature environment, the long-life rolling bearing supports the rotating shaft of the pulley, so that durability can be maintained for a long time.
[0020]
In addition, the “rolling surface” in the rolling bearing of the present invention indicates the raceway surfaces of the inner ring and the outer ring and the rolling surface of the rolling element. The “surface layer portion” indicates a portion from the surface to a depth of 20 μm. Furthermore, “residual austenite amount”, “carbon content”, and “nitrogen content” all indicate values on the rolling surface in a finished state after grinding finish.
[0021]
Hereinafter, the critical significance of each numerical limitation in the present invention will be described.
[C: 0.3 to 0.6% by mass]
C (carbon) is an element necessary for improving the hardness after quenching and tempering. When C is less than 0.3%, it is necessary to lengthen the time for carburizing or carbonitriding to reduce the heat treatment productivity in order to obtain the necessary hardness up to the depth at which shear stress acts when used as a bearing. In addition, it is disadvantageous in terms of cost. On the other hand, if the C content exceeds 0.6%, the amount of retained austenite increases not only to the surface layer portion but also to the core portion, so that dimensional stability in a high temperature environment may be hindered. In addition, since a large amount of carbide is generated at the material stage, the machinability and toughness are lowered.
[0022]
[Si: 0.5 to 2.0% by mass]
Si (silicon) is an element effective for delaying the division of retained austenite at high temperature, stabilizing the structure, and improving resistance to temper softening. In order to acquire this effect, it is necessary to contain 0.3% or more of Si. However, if the content is too large, the mechanical strength decreases, the machinability decreases, and the carbonitridability decreases, so the upper limit is made 2.0% or less.
[0023]
[Mo: 0.5 to 1.5% by mass]
Mo (molybdenum) is an element having an excellent solid solution strengthening ability higher than that of Cr described above and effective in improving the temper softening resistance. Further, Mo is an element that can form fine carbides even at high temperatures, and is therefore an essential element for obtaining sufficient hardness at high temperatures. In order to acquire this effect, it is necessary to contain Mo 0.5% or more. However, if the content is too large, the mechanical strength decreases, the machinability decreases, and the carbonitridability decreases, so the upper limit is made 1.5% or less.
[0024]
[Total content of Si and Mo: 1.6% by mass or more]
A material used as a bearing for supporting a pulley shaft of a belt type continuously variable transmission is required to have excellent dimensional stability and high hardness at a high temperature. Therefore, it is an essential condition to add Si in which dimensional stability at high temperature is obtained and Mo in which high hardness is obtained in combination. The present inventors need to make the total content of Si and Mo contained in the alloy steel 1.6% or more in order to sufficiently bring out the performance improvement effect of both Si and Mo. I found out.
[0025]
[Carburizing or carbonitriding, quenching, and tempering at high temperatures]
It is known that peeling resistance is improved by generating a compressive residual stress in the vicinity of the surface of a material made of alloy steel (see, for example, JP-A-5-288257). In the present invention, medium carbon alloy steel and medium carbon alloy steel are subjected to carburizing or carbonitriding treatment, thereby providing a gradient of carbon content in the vicinity of the surface and improving the peel resistance by applying a compressive residual stress on the surface. I planned.
[0026]
That is, by subjecting the alloy steel of the present invention to carburizing or carbonitriding treatment, quenching treatment, and tempering treatment at a high temperature, it is possible to impart compressive residual stress to the surface layer portion and reduce the amount of retained austenite in the surface layer portion. It becomes possible to do. Residual austenite is transformed into martensite in a high temperature environment, and a dimensional change occurs during this transformation. This reduces the gap between the inner ring and the outer ring of the bearing and increases peeling fatigue. For this reason, by performing a tempering process at a high temperature, the surface layer portion where the amount of retained austenite is the largest is 12 volume% or less, more preferably 6 volume% or less. The tempering temperature is preferably 200 to 400 ° C. to make the amount of retained austenite in the surface layer portion 12% or less, and 240 to 400 ° C. to make the amount of retained austenite in the surface layer portion 6% or less. Is preferred.
[0027]
[Carbon content of the surface layer portion forming the rolling surface: 0.8 to 1.2% by mass]
In order to obtain sufficient rolling fatigue strength as a bearing, it is necessary that the carbon content of the surface layer portion forming the rolling surface of the member after the alloy steel is processed into a predetermined shape and heat-treated is 0.8% or more. is there. On the other hand, if the carbon content of the surface layer portion exceeds 1.2%, giant carbides are likely to be formed, and such giant carbides may become defects and the rolling fatigue life may be reduced.
[0028]
[Nitrogen content of the surface layer portion forming the rolling surface: 0.5% by mass or less]
N (nitrogen) is an effective element for improving the wear resistance and seizure resistance. Therefore, it is effective to distribute it in the surface layer portion forming the rolling surface of the member by carburizing or carbonitriding. . However, if the N content exceeds 0.5%, it is necessary to lengthen the time for the carburizing or carbonitriding treatment, which decreases the heat treatment productivity and is disadvantageous in terms of cost. Further, since it becomes difficult to grind after the heat treatment, the productivity of the polishing process, which is a finishing process of the bearing, is lowered.
[0029]
Moreover, you may make it add the element shown below to the alloy steel of this invention in the range which does not impair the effect of this invention.
[Cr: 0.5 to 3.0% by mass]
Cr (chromium) is an effective element for improving hardenability and temper softening resistance. Further, by precipitation hardening that uniformly forms fine carbides, sufficient surface hardness can be obtained even when high-temperature tempering is performed, and the toughness of the base can be improved. Furthermore, wear resistance can be improved by the hard and fine Cr carbide. Furthermore, since Cr is a carbide forming element and can increase the C content of the carbonitriding layer, the carbonitriding property of the alloy steel can be increased even if the Si content having carburization inhibition is increased.
[0030]
In order to obtain these effects and to ensure an HRC (Rockwell hardness) of 60 or more as a necessary surface hardness, the lower limit of the Cr content is set to 0.5% or less. On the other hand, if the content exceeds 3.0% by mass, giant carbides are generated at the stage of the material made of alloy steel, and stress concentration occurs around the giant carbides, so that the life of the bearing is reduced. When trying to refine this giant carbide, quenching at a high temperature is required, and the heat treatment productivity is lowered. However, from the viewpoint of reducing giant carbides, the upper limit value of Cr is preferably 1.8% or less.
[0031]
[Mn: 0.2 to 2.0% by mass]
Mn (manganese) acts as a deoxidizer and desulfurizer during steel making and is an effective element for improving hardenability. In order to acquire this effect, it is necessary to contain 0.2% or more of Mn. However, if the content is too large, the amount of non-metallic inclusions increases, so that the life is shortened and the machinability such as forgeability and machinability is lowered. Therefore, the upper limit of the Mn content is set to 2.0%.
[0032]
[O: 10 ppm or less]
O (oxygen) is an oxide-based non-metallic inclusion (in particular, Al ₂ O ₃ ) generating element and has a function of reducing the life, so that its content needs to be 10 ppm or less.
[Al: 100 to 400 ppm]
Al (aluminum) produces oxide-based non-metallic inclusions such as Al ₂ O _{3 in the same} manner as O, but Al itself has an action of preventing the coarsening of crystal grains, so it is contained in the range of 100 to 400 ppm. It is preferable to do.
[0033]
[P: 0.02% by mass or less]
P (phosphorus) is an element that decreases rolling life and toughness. For this reason, the P content is preferably 0.02% or less.
[S: 0.02 mass% or less]
S (sulfur) is an element that improves machinability, but combines with Mn to form sulfide inclusions that reduce the rolling fatigue life. Since this machinability can be improved by adding an element other than S, the S content is preferably 0.02% or less.
[0034]
[Ni: 2.0% by mass or less]
Ni (nickel) is a strong austenite stabilizing element and has the effect of improving high temperature characteristics by suppressing the formation of δ-ferrite and improving toughness by solid solution in the matrix. However, if the content is too large, retained austenite is generated and sufficient quenching hardness cannot be obtained, so the Ni content is preferably 2.0% or less.
[0035]
[Cu: 0.05 to 2.0% by mass]
Cu (copper) is an element having an austenite stabilizing action like Ni, and has an action of suppressing the formation of δ-ferrite which lowers the quenching hardness and improving the corrosion resistance and acid resistance. In order to obtain this effect, Cu is preferably contained in an amount of 0.05% or more, preferably 5.0% or more. However, if the content is too large, hot cracking may occur in the hot forging process in the bearing manufacturing process, so the upper limit is made 2.0% or less.
[Other inevitable impurities: 100 ppm or less]
As elements other than the above elements and Fe (iron), the contents of inevitable impurities such as Ti (titanium) and Nb (niobium) are preferably 100 ppm or less, respectively.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, inner and outer rings for a radial ball bearing (inner ring 35 mm, outer ring 72 mm, width 17 mm) having a nominal number 6207 were produced using alloy steels A to S made of the alloy components shown in Table 1. At this time, the ratio (R1 / D) of the curvature radius R1 of the raceway groove of the inner ring and the diameter D of the ball and the ratio (R2 / D) of the curvature radius R2 of the raceway groove of the outer ring and the diameter D of the ball are both. It was formed to be 51%.
[0037]
[Table 1]

[0038]
After forming each alloy steel into a predetermined shape, as a heat treatment, it was heated to 840 to 920 ° C. and subjected to carburizing or carbonitriding treatment for 3 to 20 hours, followed by oil quenching. Thereafter, tempering was performed at a temperature shown in Table 2 described later for 1.5 to 2.0 hours.
After the heat treatment, grinding finishing and super finishing were performed, and the surface roughness of the raceway surfaces of the inner ring and the outer ring was set to about 0.01 to 0.04 μmRa.
Then, after assembling the test bearing using the completed inner and outer rings, balls made of SUJ2 and carbonitrided, and a metal cage, the balls formed between the inner and outer rings The provided gap was sealed with a sealing member. The radial internal clearance was set to “C3 clearance” or less.
[0039]
Table 2 shows the “steel type symbol”, “tempering temperature”, “surface C concentration (carbon content) of the raceway surface”, and “surface N of the raceway surface” for each test bearing. “Concentration (nitrogen content)”, “Surface residual γ (austenite) amount of raceway surface”, and “Surface hardness (Hv) of raceway surface” are shown. Here, the C concentration and the N concentration were measured using an emission spectroscopic analyzer, and similarly, the residual γ amount was measured using an X-ray analyzer, and the surface hardness was measured using a Vickers hardness meter. Further, the “surface” refers to a surface layer portion from the surface of the raceway surface after finishing to 20 μm. Further, in Table 2, those components that are out of the scope of the present invention are underlined.
[0040]
[Table 2]

[0041]
Next, a life test was conducted on these test bearings using the belt type continuously variable transmission unit shown in FIG. In this belt type continuously variable transmission unit, the input shaft 1 of the primary pulley 3 and the output shaft 2 of the secondary pulley 4 are supported by a pair of rolling bearings 6a, 6b, 7a, 7b, respectively. Of these four rolling bearings, each test bearing was attached as a primary front bearing (that is, a rolling bearing that supports the input shaft 1 on the engine side relative to the primary pulley 3) 6a. As the other rolling bearings 6b, 7a, 7b, the same bearings were used in each test. Also, the belt 5 of this belt type continuously variable transmission unit has 280 sheets of 2 mm thickness in a two-ring ring 51 having a structure in which ten steel thin plates having a thickness of 0.2 mm are stacked, as in FIG. The friction piece 52 is attached, and the belt length is 600 mm.
[0042]
In the life test, the test bearing was rotated under the test conditions shown below, and vibration during rotation was measured. Then, the rotation was terminated when the vibration value of the bearing became twice the initial vibration value, and the rotation time up to this point was regarded as the life. The results are also shown in Table 2. The life in Table 2 is the test bearing no. The relative value when the lifetime of 31 is set to 1 is shown.
<Test conditions>
Rotational speed: 1000 to 10000 min ⁻¹
P (load load) / C (dynamic load rating): max0.2
Lubricating oil: Lubricating oil for continuously variable transmission (made by Showa Shell, NS-1)
Oil temperature: 100-160 ° C
[0043]
FIG. 2 is a graph showing the relationship between the total content of Si and Mo in the alloy steel forming the inner and outer rings of each test bearing and the obtained life ratio.
Furthermore, the relationship between the surface residual γ amount on the raceway surfaces of the inner and outer rings of each test bearing and the obtained life ratio is shown in a graph in FIG. In FIG. 3, only the test bearings in which the total content of Si and Mo is within the scope of the present invention are shown.
As can be seen from these results, no. In the test bearings 1 to 20, the inner ring and the outer ring are made of alloy steel whose alloy component is within the range of the present invention, the surface C concentration of the raceway surface is 0.8 to 1.2% by mass, and the raceway. Since the amount of residual γ on the surface is 12% by volume or less, no. The bearing life can be made longer than that of the test bearings 21 to 32.
[0044]
No. 1-20, no. 1-9, no. 11, no. 13-15, and Nos. 18 to 20 all have a longer life of 5 or more. 10, no. 12, and no. 16, no. No. 17 had a lifetime of less than 5. From this result, it can be seen that when the residual γ amount on the raceway surface is 6% by volume or less, a bearing having a longer life can be obtained.
[0045]
In contrast, no. 21-23, no. 25-27 and No. In No. 31, the total content of Si and Mo is out of the scope of the present invention, so that the hardness and dimensional stability under a high temperature environment cannot be sufficiently ensured, resulting in a short life. No. In No. 24, the tempering temperature and the amount of residual γ were outside the range of the present invention, so that the dimensional stability was deteriorated and the adhesion was promoted, resulting in a short life. Furthermore, no. In No. 28, since the surface C concentration was lower than the range of the present invention, sufficient surface hardness could not be obtained and the life was short. Furthermore, no. In No. 29, since the surface C concentration was higher than the range of the present invention, coarse carbides were generated on the surface, so the life was short. No. In No. 32, since the Si content was higher than the range of the present invention, the mechanical strength was lowered and the life was short.
[0046]
In this way, the use of alloy steel with a high total content of Si and Mo improves the hardness and dimensional stability at high temperatures and reduces the amount of retained austenite by tempering at high temperatures. Can improve surface fatigue resistance. That is, No. 1 in which the inner ring and the outer ring satisfy the scope of the present invention. With the configuration of 1 to 20, a long-life rolling bearing can be obtained even when used in a belt-type continuously variable transmission that is used under a high temperature environment and severe lubrication conditions.
[0047]
【The invention's effect】
As described above, according to the rolling bearing of the present invention, at least one of the inner ring, the outer ring, and the rolling element is formed of a specific alloy steel, and the amount of retained austenite and carbon content in the surface layer portion that forms the rolling surface. By limiting the rate to a specific range, even when used in a high temperature environment, the hardness and dimensional stability are ensured and the life is extended.
Further, according to the belt type continuously variable transmission of the present invention, the pulley can be stably rotated for a long period of time by supporting the pulley rotating shaft with a long-life rolling bearing even in a high temperature environment. Sex can be maintained for a long time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a belt type continuously variable transmission used for a life test in an embodiment.
FIG. 2 is a graph showing the relationship between the total content of Si and Mo in alloy steel and the life obtained from the results of the embodiment.
FIG. 3 is a graph showing the relationship between the amount of retained austenite on the raceway surfaces of the inner and outer rings and the life obtained from the results of the embodiment.
FIG. 4 is a cross-sectional view showing an example of a belt type continuously variable transmission of a vehicle.
[Explanation of symbols]
1 Input shaft (drive shaft)
2 Output shaft (driven shaft)
3 Input shaft pulley (primary pulley)
31 Fixed conical plate 32 Movable conical plate 4 Output shaft pulley (secondary pulley)
41 Fixed conical plate 42 Movable conical plate 5 Belt 51 Ring 52 Friction piece 6, 7 Radial ball bearing

Claims (6)

In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to roll between the inner ring and the outer ring,
At least one of the inner ring, the outer ring, and the rolling element has a mass ratio of C of 0.3 to 0.6%, Si of 0.5 to 2.0%, and Mo of 0.5 to 1.5. %, By processing alloy steel containing 1.6% or more of Si and Mo into a predetermined shape, and then performing carburizing or carbonitriding treatment and quenching treatment, and high temperature tempering treatment at 200 to 400 ° C., A rolling bearing characterized in that the amount of retained austenite in a surface layer portion forming a rolling surface is 12% by volume or less, and the carbon content of the surface layer portion is 0.8 to 1.2% by mass. In a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that are arranged to roll between the inner ring and the outer ring,
At least one of the inner ring, the outer ring, and the rolling element has a mass ratio of C of 0.3 to 0.6%, Si of 0.5 to 2.0%, and Mo of 0.5 to 1.5. %, After processing alloy steel containing Si and Mo in total 1.6% or more into a predetermined shape, carburizing or carbonitriding treatment and quenching treatment, and high-temperature tempering treatment at 240 to 400 ° C., A rolling bearing characterized in that the amount of retained austenite in the surface layer portion forming the rolling surface is 6% by volume or less, and the carbon content of the surface layer portion is 0.8 to 1.2% by mass. The rolling bearing according to claim 1 or 2, wherein the alloy steel includes Cr in a range of 0.5 to 3.0%, and the balance is Fe and inevitable impurities. The rolling bearing according to any one of claims 1 to 3, wherein the surface layer portion has a nitrogen content of 0.5 mass% or less. 5. The gap formed between the inner ring and the outer ring and in which the rolling element is provided is sealed with a shield member or a seal member. Rolling bearing. In a belt-type continuously variable transmission including a pulley around which a belt is wound and a bearing that supports a rotating shaft of the pulley,
The belt-type continuously variable transmission according to any one of claims 1 to 5, wherein the bearing is a rolling bearing according to any one of claims 1 to 5.

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