JP2009041744A - Rolling bearing for belt type continuously variable transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for a belt type continuously variable transmission capable of suppressing deterioration of surface roughness due to inclusion of foreign matters and fretting and suppressing tangential force applied between a rolling element and a bearing ring. <P>SOLUTION: In this rolling bearing for the belt type continuously variable transmission, at least one of an inner ring, an outer ring and the rolling element is formed by processing steel including 0.3-1.2 mass% of a carbon (C) content, 0.3-2.2 mass% of a silicon (Si) content and 0.2-2.0 mass% of a manganese (Mn) content to form a predetermined shape. Then, carbonitriding or nitriding is applied to a surface layer part of a raceway surface of the bearing. The nitrogen concentration of the surface layer part is set to be 0.2-2.0 mass%, and the area ratio of nitride including silicon (Si) and manganese (Mn) is set to be 1-20%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a belt-type continuously variable transmission used as, for example, a transmission unit of an automatic transmission of an automobile, and more particularly to improvement of a rolling bearing for supporting a rotating shaft of a belt-type continuously variable transmission.

Various belt type continuously variable transmissions of this type have been proposed, for example, as described in Patent Document 1, and some of them have been put into practical use. FIG. 11 schematically shows the basic structure of this type of belt-type continuously variable transmission.
As shown in the figure, this belt-type continuously variable transmission has an input side rotating shaft 1 and an output side rotating shaft 2 arranged in parallel to each other. Each of these rotating shafts 1 and 2 is rotatably supported via a pair of rolling bearings 3 and 3 inside a transmission case (not shown) which is a fixed portion.

  As shown in FIG. 12, each of the rolling bearings 3 and 3 has an outer ring 4 and an inner ring 5 provided concentrically with each other. Of these, the outer ring 4 has an outer ring raceway 6 on its inner peripheral surface, and the inner ring 5 has an inner ring raceway 7 on its outer peripheral surface as rolling surfaces. A plurality of rolling elements 8, 8 are interposed between the outer ring raceway 6 and the inner ring raceway 7 so as to roll freely while being held by a cage 9.

  Each of the rolling bearings 3, 3 supports the outer ring 4 by fitting inside a part of the transmission case, and supports the inner ring 5 by fitting to the input side rotating shaft 1 or the output side rotating shaft 2. The rotary shafts 1 and 2 are rotatably supported inside the transmission case. Conventionally, as the respective rolling bearings 3 and 3, the outer ring 4, the inner ring 5, and the respective rolling elements 8 and 8 made of two types of general bearing steel (SUJ2) have been used.

  Of the rotary shafts 1 and 2, the input-side rotary shaft 1 is rotationally driven by a driving source 10 such as an engine via a starting clutch 11 such as a torque converter or an electromagnetic clutch. In addition, a drive pulley 12 is provided in a portion located between the pair of rolling bearings 3 and 3 in the intermediate portion of the input side rotary shaft 1, and the drive side pulley 12 and the input side rotary shaft 1 are synchronized. To rotate. The distance between the pair of drive side pulley plates 13a and 13b constituting the drive side pulley 12 is adjusted by displacing one drive side pulley plate 13a in the axial direction by the drive side actuator 14 (left side in FIG. 11). It is free. That is, the groove width of the driving pulley 12 can be expanded and contracted by the driving actuator 14.

  On the other hand, a driven pulley 15 is provided at a middle portion of the output side rotating shaft 2 between the pair of rolling bearings 3 and 3, and the driven pulley 15 and the output side rotating shaft 2 are synchronized with each other. I try to rotate. The distance between the pair of driven pulley plates 16a and 16b constituting the driven pulley 15 is determined by displacing one (right side in FIG. 11) driven pulley plate 16a in the axial direction by the driven actuator 17. It is adjustable. That is, the groove width of the driven pulley 15 can be expanded and contracted by the driven actuator 17. An endless belt 18 is stretched between the driven pulley 15 and the driving pulley 12. As the endless belt 18, a metal belt is used.

  In the belt-type continuously variable transmission having the above-described configuration, the power transmitted from the driving source 10 to the input side rotating shaft 1 via the starting clutch 11 is transmitted from the driving side pulley 12 via the endless belt 18 to the driven side pulley. 15 is transmitted. Conventionally, as the endless belt 18, one that transmits power in the pressing direction and one that transmits power in the pulling direction are known. In any case, the power transmitted to the driven pulley 15 is transmitted from the output side rotating shaft 2 to the drive wheels 21 and 21 via the reduction gear train 19 and the differential gear 20. When changing the gear ratio between the input-side rotating shaft 1 and the output-side rotating shaft 2, the groove widths of the pulleys 12 and 15 are expanded and contracted while being associated with each other.

  For example, when the reduction ratio between the input-side rotating shaft 1 and the output-side rotating shaft 2 is increased, the groove width of the driving pulley 12 is increased and the groove width of the driven pulley 15 is decreased. To do. As a result, the diameter of the part of the endless belt 18 that spans the pulleys 12 and 15 is small at the driving pulley 12 part and large at the driven pulley 15 part, and the input side rotation Deceleration is performed between the shaft 1 and the output side rotating shaft 2.

  On the other hand, when increasing the speed increasing ratio between the input side rotating shaft 1 and the output side rotating shaft 2 (decreasing the speed reducing ratio), the groove width of the driving pulley 12 is decreased and the driven side is also decreased. The groove width of the pulley 15 is increased. As a result, the diameter of the portion of the endless belt 18 that spans the pulleys 12 and 15 is larger at the driving pulley 12 portion and smaller at the driven pulley 15 portion, and the input side rotation The speed is increased between the shaft 1 and the output side rotating shaft 2.

  Here, during the operation of the belt-type continuously variable transmission, lubricating oil is supplied to each movable portion to lubricate each movable portion. CVT fluid (ATF combined oil) is used as the lubricating oil used in the belt type continuously variable transmission. The reason for this is to increase and stabilize the friction coefficient of the friction engagement portion between the metal endless belt 18 and both the drive side and driven side pulleys 12 and 15. The CVT fluid is circulated through the friction part at a flow rate of 300 cc / min or more to lubricate the friction part. Further, part of the CVT fluid passes through the inside of each of the rolling bearings 3 and 3 (for example, at a flow rate of 20 cc / min or more), and lubricates the rolling contact portion of each of the rolling bearings 3 and 3. Therefore, the wear powder generated due to the friction between the endless belt 18 and the pulleys 12 and 15 and the gear powder generated due to the friction in the reduction gear train 19 portion in each of the rolling bearings 3 and 3. There is a high possibility that foreign substances such as the like will enter the CVT fluid. Such foreign matters cause damage to the rolling contact portions of the respective rolling bearings 3 and 3 and reduce the durability thereof.

For this reason, conventionally, the basic dynamic rating of each rolling bearing 3, 3 is increased by increasing the bearing size of each rolling bearing 3, 3, or increasing the diameter (ball diameter) of each rolling element 8, 8. The load was increased so that the life of each of the rolling bearings 3 and 3 was given a margin. Further, in order to suppress the amount of the foreign matter flowing through the inside of each of the rolling bearings 3 and 3, each of the rolling bearings 3 and 3 is provided between the inner peripheral surface of the outer ring 4 and the outer peripheral surface of the inner ring 5. It is also conceivable to use one having sealing means for closing the opening portions at both ends of the rolling element installation portion where the moving bodies 8 and 8 are installed. In this case, the rolling element installation portion is filled with grease, and the rolling contact portions between the rolling surfaces of the rolling elements 8 and 8 and the outer ring raceway 6 and the inner ring raceway 7 are lubricated. However, even in this case, the CVT fluid does not circulate at all in the rolling element installation portion. That is, a relatively small amount of CVT fluid flows through the rolling element installation portion.
No. 8-30526

  By the way, the CVT fluid is required to have a function of transmitting power by smoothly operating a torque converter, a gear mechanism, a hydraulic mechanism, a wet clutch, and the like. For this reason, lubricating oil having a high traction coefficient (traction coefficient of 0.09 or more) is used, including the rolling bearing that supports the rotating shaft of each pulley described above. For this reason, the rolling bearing used in the belt-type continuously variable transmission has a large tangential force (traction) acting between the race and the rolling element, which causes a peculiar surface-origin separation and shortens its life. In addition, as described above, since wear powder such as gears enters the rolling bearing used in the continuously variable transmission, indentations are formed on the surfaces of the rolling elements and the races, and the surface properties of the rolling elements deteriorate.

  Furthermore, a rolling bearing for a belt-type continuously variable transmission receives a load due to belt tension even when it is stopped, and when vibration is transmitted from an engine or the like in that state, fretting (Mindlin slip) occurs between the rolling elements and the raceway. ) Is generated. In that case, the rolling surface and the raceway surface roughness of the part where the Mindlin slip occurs are deteriorated. And if the surface property between a rolling element and a bearing ring deteriorates, since the tangential force which acts between a rolling element and a bearing ring will become large, a lifetime will become short. Therefore, in order to achieve a longer life of the rolling bearing for the belt type continuously variable transmission, it is possible to suppress the deterioration of the surface roughness due to foreign matter contamination or Mindlin slip, and to act between the rolling elements and the raceway. It is important to suppress the tangential force.

As described above, the functions necessary for extending the life of the belt-type continuously variable transmission rolling bearing are required to prevent formation of indentation due to foreign object biting and to suppress the Mindlin slip.
Therefore, the present inventors have conducted intensive research on extending the life of rolling bearings for belt-type continuously variable transmissions used in an environment where the surface-originated peeling life is shortened, and the surface properties of the rolling elements and the raceway are deteriorated. To achieve long life.

  That is, the belt-type continuously variable transmission rolling bearing according to the present invention includes a fixed portion and a rotating portion that rotatably supports a pulley for continuously variable transmission with respect to the fixed portion. Used in a transmission, an outer ring having a rolling surface on the inner peripheral surface, an inner ring having a rolling surface on the outer peripheral surface, and a rollable arrangement between the rolling surface of the outer ring and the rolling surface of the inner ring. A rolling bearing in which the outer ring is fitted and supported by the fixed portion, and the inner ring is fitted and supported by the rotating portion together with the pulley, the inner ring and the outer ring. And at least one of the rolling elements has a carbon (C) content of 0.3 to 1.2 mass%, a silicon (Si) content of 0.3 to 2.2 mass%, and manganese (Mn). A steel material comprising 0.2 to 2.0 mass% of the content of iron, the remaining iron and unavoidable impurities After processing into a shape, the surface layer portion of the raceway surface is obtained by carbonitriding or nitriding treatment, and the nitrogen concentration of the surface layer portion is 0.2 to 2.0 mass%, and silicon (Si ) And manganese (Mn) -containing nitride have an area ratio of 1% to 20%. Although the specific reason for limiting the numerical value will be described later, according to the rolling bearing for a belt-type continuously variable transmission according to the present invention, it is possible to suppress the deterioration of the surface properties of the rolling elements and the raceway to achieve a long life. it can.

In the rolling bearing for a belt type continuously variable transmission according to the present invention, the amount of retained austenite on the inner and outer ring raceway surfaces is γrAB (volume%), and the amount of retained austenite on the rolling element rolling surface is γr _C (volume%). In this case, by setting γr _AB −15 ≦ γr _C ≦ γr _AB +15 (where 0 (volume%) ≦ γr _AB , γr _C ≦ 50 (volume%)), without significant cost increase, High-performance rolling bearings for belt-type continuously variable transmissions can be realized.

  In addition, when the surface roughness of the rolling element and the race is reduced, the present inventors reduce the surface roughness of the rolling element (surface roughness) compared to the case where the surface roughness of the race is reduced.・ When the deterioration of the surface shape was suppressed), it was clarified that the surface-origin type peeling can be effectively suppressed. That is, the life of the entire bearing can be effectively extended by suppressing the deterioration of the surface roughness and surface shape of the rolling elements rather than the race.

[Action]
The operation of the above-described belt-type continuously variable transmission rolling bearing according to the present invention will be described.
[Nitride concentration in the surface layer portion of the rolling surface is 0.2 to 2.0% by mass and further contains silicon (Si) and manganese (Mn) (hereinafter referred to as “Si · Mn nitride”) The area ratio is also 1% or more and 20% or less]
In the rolling bearing for a belt type continuously variable transmission according to the present invention, carbonitriding is performed in order to enrich the surface layer of the raceway or rolling element with predetermined nitrogen. Nitrogen, like carbon, not only acts to strengthen the solid solution of martensite and to ensure the stability of retained austenite, but also forms nitrides or carbonitrides to improve the pressure resistance and wear resistance.

FIG. 4 shows the results of the influence of the surface nitrogen concentration on the pressure scar resistance and wear resistance. In addition, the same figure (a) shows the influence of nitrogen on the indentation resistance determined by the indentation resistance test shown in FIG. 1, and the same figure (b) shows the resistance to resistance determined by the two-cylinder abrasion test shown in FIG. The influence of nitrogen on wear is shown.
The pressure dent test was performed by pressing a steel ball having a diameter of 2 mm against a sample at 5 GPa and then measuring the depth of the dent. On the other hand, in the two-cylinder wear test, the driving side (high speed side) is rotated at 10 min ⁻¹ under the condition of a surface pressure of 0.8 GPa, the gear is decelerated and the driven side (low speed side) is rotated at 7 min ^−1. This was a method for forcibly giving a slip, and the average value of the amount of wear of the driving side and driven side test pieces 20 hours after the start of the test was measured. An electron beam microanalyzer (EPMA) was used for the measurement of the surface nitrogen amount. In order to investigate only the effect of the nitrogen concentration, the hardness other than the surface nitrogen concentration and the amount of retained austenite are kept constant.

As shown in FIG. 4 (a), the higher the surface nitrogen concentration, the better the pressure scar resistance, and as shown in FIG. 4 (b), the higher the surface nitrogen concentration, the better the wear resistance. . As shown in FIG. 4, both the indentation resistance and the abrasion resistance are remarkably effective when the surface nitrogen concentration exceeds 0.2% by mass, but more preferably 0.45% by mass or more.
On the other hand, if the nitrogen concentration is too high, there is a drawback that toughness and static strength are lowered. Since the toughness and static strength are necessary performances for rolling elements of a rolling bearing, it is not preferable that the nitrogen concentration is too high. FIG. 5 shows the result of the Charpy impact test. As shown in FIG. 5, it can be seen that when the nitrogen concentration exceeds 2.0 mass%, the toughness rapidly decreases. Therefore, the upper limit of the nitrogen concentration of the present invention is set to 2.0% by mass.
As described above, it has been clarified that the higher the nitrogen concentration on the surface, the higher the pressure scar resistance and wear resistance of the material.

However, the present inventors have further found that the pressure resistance and wear resistance change depending on the presence of nitrogen inside the material even when the nitrogen concentration is the same. Nitrogen may be present as a solid solution in the material or may be precipitated as a nitride. Although detailed numerical values will be described later, when carbonitriding a material containing a large amount of Si · Mn, the surface of the Si · Mn system is larger than the amount of nitrogen present in solid solution in the material even at the same nitrogen concentration. The amount of nitrogen present by precipitation of nitride increases.
FIG. 6 shows the influence of the area ratio of the Si / Mn nitride on the pressure scar resistance and the wear resistance obtained by the pressure scar resistance test shown in FIG. 1 and the two-cylinder wear test shown in FIG. The figure (a) shows the relationship between the area ratio of Si / Mn nitride and the depth of indentation, and the figure (b) shows the relation between the area ratio of Si / Mn nitride and the amount of wear. ing.

In order to investigate only the effect of the Si / Mn nitride, the hardness other than the area ratio of the Si / Mn nitride, the amount of retained austenite, and the nitrogen concentration are kept constant. The area ratio of the Si / Mn nitride was measured using a field emission scanning electron microscope (FE-SEM) by observing the rolling surface at an acceleration voltage of 10 kV and at least 3 fields of view at a magnification of 5000 times. After taking a photograph as described above, the area ratio was calculated using a surface image analyzer after binarizing the photograph.
As shown in FIG. 6 (a), the higher the area ratio of the Si / Mn nitride, the better the pressure resistance, and as shown in FIG. 6 (b), the area of the Si / Mn nitride. The higher the rate, the better the wear resistance. As shown in FIG. 6, both the indentation resistance and the wear resistance are remarkably effective when the area ratio of the Si · Mn nitride exceeds 1%, but more preferably 2% or more.

On the other hand, similarly to the nitrogen concentration described above, there is a drawback that the toughness and the static strength are lowered when the amount of Si · Mn-based nitride deposited becomes too large. Since the toughness and static strength are necessary performances for rolling elements of a rolling bearing, it is not preferable that the amount of Si / Mn nitride precipitates is excessive.
FIG. 7 shows the result of the Charpy impact test. As shown in the figure, it can be seen that when the area ratio of the Si · Mn nitride exceeds 20%, the toughness rapidly decreases. Therefore, the upper limit of the area ratio of the Si / Mn nitride of the present invention is set to 20%, more preferably 10%.

  Further, nitrides exceeding 1 μm do not contribute much to the strengthening of the material. The one where fine nitride is dispersed is strengthened. The reason for this is that, in the theory of precipitation strengthening, the smaller the distance between the precipitate particles, the better the strengthening ability. Therefore, even if the area ratio of the Si / Mn nitride is the same, if the number of precipitated particles is large, the relative In addition, the interparticle distance is shortened and strengthened. That is, the number of fine nitrides having an average particle size of 0.05 μm or more and 1 μm or less is used in a range where the area ratio of Si / Mn nitride is 1 to 20%, using steel with a high content of Si and Mn. It is good to increase. Further, among Si / Mn nitrides having a thickness of 0.05 μm or more, the ratio of the number of Si / Mn nitrides having a thickness of 0.05 μm to 0.50 μm is set to 20% or more, so that it can be further strengthened. Become.

Specifically, it is preferable that there are 100 or more Si · Mn nitrides having an area of 375 μm ² and 0.05 μm or more and 1 μm or less. It is preferable that the temperature is 800 ° C. or higher and 870 ° C. or lower. When this temperature is exceeded, the nitride becomes coarse and the number of fine Si · Mn nitrides decreases. Further, when the temperature is higher than the treatment temperature, the solid solubility limit of nitrogen is increased, so that the amount of nitride is reduced and a desired area ratio may not be obtained. From the initial stage of the carbonitriding process, it is preferable that the mixed gas atmosphere of RX gas, enriched gas, and ammonium gas is used, the CP value is 1.2 or more, and the flow rate of ammonia gas is at least 1/5 of the RX gas flow rate. Moreover, it is preferable to perform the quenching after carbonitriding at an oil temperature in the range of 60 ° C to 120 ° C. If it is higher than this temperature, sufficient hardness may not be obtained. Tempering is performed at a temperature of 160 ° C. to 270 ° C., and the surface hardness range is HV 740 or more, preferably HV 780 or more. Moreover, you may perform a subzero process after a quenching process as needed.

FIG. 10 shows the relationship between the number of Si · Mn nitrides of 0.05 μm to 1 μm and the life ratio. As can be seen from the figure, by dispersing 100 or more Si · Mn nitrides within a measurement area of 375 μm ² , the base structure is strengthened and the life under lubrication with foreign matter is extended.
[Carbon (C) content is 0.3 to 1.2% by mass]
Carbon is an important element for obtaining the strength and life required for steel. If the amount of carbon is too small, not only a sufficient strength cannot be obtained, but also the heat treatment time required to obtain the hardened layer depth required for carbonitriding described later will be increased, leading to an increase in the heat treatment cost. Therefore, the carbon content is 0.3% by mass or more, preferably 0.5% by mass or more. In addition, if the carbon content is too large, giant carbides are produced during steelmaking, which adversely affects the subsequent quenching characteristics and rolling fatigue life, and the header property may be reduced, leading to an increase in cost. .2% by mass.
[Content of silicon (Si) is 0.3 to 2.2% by mass, content of manganese (Mn) is 0.2 to 2.0% by mass]

As described above, in order to sufficiently precipitate the Si · Mn nitride, it is necessary to use a steel material containing a large amount of Si and Mn. In the case of SUJ2 (Si content 0.25%, Mn content 0.4%) which is a general bearing material, even if nitrogen is excessively added by carbonitriding or the like, the amount of Si · Mn nitride is small. For this reason, content of Si and Mn makes the following values critical values.
<Si content: 0.3 to 2.2% by mass>

It is an element necessary for the precipitation of the nitride according to the present invention, and due to the presence of Mn, it effectively reacts with nitrogen and precipitates significantly when added in an amount of 0.3% by mass or more.
<Mn content: 0.2 to 2.0 mass%>
It is an element necessary for precipitation of nitride according to the present invention, and has the effect of promoting the precipitation of Si · Mn nitride when added in an amount of 0.2% by mass or more by coexistence with Si. Further, since Mn has a function of stabilizing austenite, it is set to 2.0% by mass or less in order to prevent the problem that the retained austenite increases more than necessary after the heat treatment for curing.
[When the amount of retained austenite on the raceway surfaces of the inner ring and the outer ring is γr _AB (volume%) and the amount of retained austenite on the rolling surface of the rolling element is γr _C (volume%), γr _AB −15 ≦ γr _C ≦ γr _AB +15 (where 0 (volume%) ≦ γr _AB , γr _C ≦ 50 (volume%))]

  As described above, it has been clarified that when the amount of retained austenite is reduced, the pressure scar resistance and wear resistance are improved, while the peel life is extended as the amount of retained austenite on the surface is increased. In other words, considering rolling elements, the smaller the amount of austenite on the surface of the rolling elements, the better the pressure resistance and wear resistance of the rolling elements, and the life of the bearing rings is extended, but the life of the rolling elements themselves is reduced. . Accordingly, there is an optimum amount of retained austenite of the rolling elements to achieve the longest bearing life, but the optimum range varies depending on the amount of retained austenite of the race. When the amount of retained austenite in the raceway is large, the life of the raceway is prolonged, the pressure resistance of the raceway is reduced, and the tangential force acting between the raceway and the rolling element is also increased. It is necessary to extend the life of the rolling element rather than to improve the scratch resistance and wear resistance. Therefore, when the amount of retained austenite of the race is large, the amount of retained austenite of the rolling elements must also be increased.

That is, since the range of the retained austenite amount (γr _C ) of the rolling element that achieves the longest bearing life varies depending on the retained austenite amount (γr _AB ) of the raceway, γr _AB −15 ≦ γr _C ≦ γr _AB +15 (however, 0 (volume%) ≦ γr _AB , γr _C ≦ 50 (volume%)) (the reason for the numerical limitation will be described later).
In addition, when the amount of retained austenite is too large, not only the hardness is lowered and the pressure resistance and wear resistance is lowered, but also the dimensional stability when used at a high temperature is deteriorated, so the upper limit is set to 50% by volume.

  In the present invention, the hardness of the rolling contact surface is preferably HV ≧ 750. Surface hardness is a material factor that improves pressure scar resistance and wear resistance. In order to investigate the effect of surface hardness on pressure scar resistance and wear resistance, the pressure scar resistance test and chart shown in FIG. A two-cylinder abrasion test shown in FIG. FIG. 3 shows the influence of the surface hardness on the pressure scar resistance and wear resistance. In addition, the same figure (a) shows the relationship between surface hardness and indentation depth, and the same figure (b) shows the relationship between surface hardness and wear amount.

  As shown in FIG. 3 (a), the greater the surface hardness, the better the pressure resistance, and as shown in FIG. 3 (b), the greater the surface hardness, the better the wear resistance. I understand that. In particular, when the surface hardness is HV750 or more in both wear resistance and pressure scar resistance, the effect of surface hardness is remarkably obtained. In addition, it is known that the higher the hardness, the higher the fatigue strength. By increasing the surface hardness of the rolling surface, it is possible to increase not only the scratch resistance and wear resistance but also the peel strength. is there.

  As described above, according to the present invention, it is possible to suppress the deterioration of the surface roughness due to foreign matter contamination and Mindlin slip, and to suppress the tangential force acting between the rolling elements and the raceway, thereby further extending the life. It is possible to provide a rolling bearing for a belt type continuously variable transmission.

Hereinafter, one example of a rolling bearing for a belt-type continuously variable transmission according to the present invention, an example thereof, and a life test performed on a comparative example will be described.
This rolling bearing for a belt-type continuously variable transmission is used in a belt-type continuously variable transmission having the same basic structure as the belt-type continuously variable transmission shown in FIG. 11 described above, and has the structure shown in FIG. Is. Specifically, it is a deep groove ball bearing (6206), and of the inner ring 5, the outer ring 4, and the rolling element 8, in the example of the present embodiment, the belt type continuously variable transmission according to the present invention is used as the rolling element 8. Rolling bearings were used. Further, for the inner and outer rings 5, 4, after carbonitriding for 1 to 3 hours in an atmosphere of Rx gas + enrich gas + ammonia gas at 830 to 850 ° C. using high carbon chromium bearing steel (SUJ2), The tempering at 180 to 240 ° C. was performed, and three types of bearing rings having residual austenite of the inner and outer ring raceway surfaces of about 10, 20, and 30% were prepared.
Table 1 shows the components of the rolling element material used in this life test and the quality of the finished rolling element.

  In this rolling element 8, first, wire rods having the components shown in Table 1 above are manufactured by header processing and rough grinding, and carbonitriding and quenching (830 ° C. X 5 to 20 hr, Rx gas + enrich gas + ammonia gas atmosphere), 180 A heat treatment and post-process of ˜270 ° C. tempering were performed. For the measurement of the surface nitrogen amount of the rolling element, an electron beam microanalyzer (EPMA) was used for quantitative analysis. The amount of retained austenite in the surface layer was measured by an X-ray diffraction method. In both cases, the rolling element surface was directly analyzed and measured. Furthermore, the area ratio of the Si / Mn nitride was measured using a field emission scanning electron microscope (FE-SEM) by observing the rolling surface at an acceleration voltage of 10 kV and at least 3 fields of view at a magnification of 5000 times. After taking a photograph as described above, the area ratio was calculated using a surface image analyzer after binarizing the photograph.

Using this deep groove ball bearing 6206, a life test was conducted under the contamination with foreign matter. Prior to the life test, a Mindlin slip was formed on the rolling elements and the races under the following conditions using a hydraulic fatigue tester.
[Mindrin slip formation conditions]
Load: Repetitive load of 20 kN and 5 kN is applied. Number of repetitions: 20 Hz
Number of repetitions: 1.0 × 10 ⁵ cycle

The life test conditions are as follows.
[Life test conditions]
Test load: Fr = 6.4 kN
Rotation speed: 0 (3 sec) ⇔ 3000 min ⁻¹ (30 sec)
Lubricant: CVT fluid NS2
Hardness of foreign matter: HV870
Foreign material size: 74-147 μm
Foreign matter contamination: 0.05g

  Table 1 shows the life test results together with the components and quality of the rolling element materials of Examples and Comparative Examples. The life test was performed for each sample n = 10, the life time until peeling occurred was investigated, a Weibull plot was created, the L10 life was obtained from the results of the Weibull distribution, and the life value was obtained. The lifetime is shown as a ratio value, with the value of Comparative Example 1 having the shortest lifetime as 1. FIG. 8 summarizes the relationship between the area ratio and the life ratio of Si / Mn nitrides.

  From Table 1, the life of Comparative Example 6 is not extended because of insufficient hardness. From Table 1 and FIG. 8, the steel material within the scope of the present invention was used, and the surface layer portion of the raceway surface thereof had a nitrogen concentration of 0.2% by mass to 2.0% by mass, a Si / Mn nitride area ratio of 1 It was confirmed that the examples according to the present invention having a ratio of not less than 20% and not more than 20% have a longer life extension effect than the comparative example. In Comparative Example 5, steel within the scope of the present invention was used, and the nitrogen content was further 0.2 mass% or more, but the Si / Mn nitride protrusions were 1% or less in area ratio. Therefore, the lifetime has not been extended.

FIG. 9 shows the relationship between the remaining austenite of the rolling element rolling surface and the life ratio when the retained austenite of the raceway surface is 10, 20, and 30%.
As shown in the figure, the longer the retained austenite on the raceway surface, the longer the life expectancy.The lifetime depends on the amount of retained austenite on the rolling element rolling surface. By defining within the scope of the present invention, a long life is achieved as a whole bearing. In addition, when the amount of retained austenite of the rolling element is less than the range specified in the present invention, the rolling element is all damaged, and when it is more than the range specified in the present invention, all the raceway rings are damaged. It can be seen that the lifespan of the rolling elements and the bearing rings is extended in a well-balanced manner, and a long life can be achieved for the entire bearing.

  As described above, according to the rolling bearing for the belt type continuously variable transmission according to the present invention, the deterioration of the surface roughness due to foreign matter contamination and Mindlin slip is suppressed, and the tangential force acting between the rolling element and the raceway is reduced. It can suppress and can achieve further life extension. In addition, although the said Example showed the example which applied this invention with respect to the rolling element, the same effect is acquired even if it applies to either an inner ring and an outer ring, or all of an inner ring, an outer ring, and a rolling element.

  Further, as described in Japanese Patent Laid-Open No. 5-25609, the result of extending the life in a foreign matter-mixed lubricating environment when the retained austenite increases is also obtained in this test result. However, that alone is not sufficient, and it is possible to extend the life as shown in the above embodiment by defining the amount of retained austenite of the counterpart material. In addition, the present invention provides a method for extending the life effectively by specifying a range for effectively extending the life even when the retained austenite cannot be increased due to cost reasons and problems in use conditions, and the life can not be extended. is there.

It is a figure for demonstrating the method of a pressure | voltage resistant test. It is a figure for demonstrating the method of an abrasion resistance test. It is a graph which shows the result of the influence of the surface hardness which gives to an impression resistance and abrasion resistance, The figure (a) shows the relationship between surface hardness and indentation depth, The figure (b) shows surface hardness and The relationship with the amount of wear is shown. It is a graph which shows the result of the influence of surface nitrogen concentration on pressure dent resistance and abrasion resistance, the figure (a) shows the relationship between surface nitrogen concentration and dent depth, and the figure (b) shows surface nitrogen. The relationship between the concentration and the amount of wear is shown. It is a graph which shows the relationship between surface nitrogen concentration and shock absorption energy. It is a graph which shows the result of the influence of the area ratio of the Si / Mn nitride on the indentation resistance and the wear resistance. FIG. (A) shows the relationship between the area ratio of the Si / Mn nitride and the indentation depth. FIG. 4B shows the relationship between the area ratio of Si / Mn nitride and the amount of wear. It is a graph which shows the relationship between the area ratio of Si * Mn type nitride, and impact absorption energy. It is a graph which shows the relationship between the area ratio and lifetime ratio of Si * Mn type nitride. It is a graph which shows the relationship between the amount of retained austenite of the raceway surface layer part of an inner and outer ring based on the data obtained by embodiment, the amount of retained austenite of the rolling surface surface layer part of a rolling element, and the lifetime of a bearing. It is a graph which shows the relationship between the number of the Si * Mn type nitride of 0.05 micrometer-1 micrometer, and a lifetime ratio. It is explanatory drawing which shows an example of the structure of a belt-type continuously variable transmission. It is sectional drawing which shows an example of the structure of the rolling bearing for belt type continuously variable transmissions.

Explanation of symbols

1, 2 Rotating shaft 3 Rolling bearing 4 Outer ring 5 Inner ring 6 Outer ring raceway (rolling surface)
7 Inner ring raceway (rolling surface)
8 Rolling elements 9 Cage 10 Drive source 11 Starting clutch 12 Drive pulley (pulley)
15 Driven pulley (pulley)

Claims (2)

An outer ring that is used in a belt-type continuously variable transmission that includes a fixed portion and a rotating portion that rotatably supports a pulley for continuously variable transmission with respect to the fixed portion, and that has a rolling surface on an inner peripheral surface thereof. And an inner ring having a rolling surface on the outer peripheral surface, and a plurality of rolling elements arranged to roll between the rolling surface of the outer ring and the rolling surface of the inner ring, and the outer ring on the fixed portion Is a rolling bearing in which the inner ring is supported by the rotating portion together with the pulley.
At least one of the inner ring, the outer ring, and the rolling element has a carbon (C) content of 0.3 to 1.2 mass%, a silicon (Si) content of 0.3 to 2.2 mass%, After processing a steel material having a manganese (Mn) content of 0.2 to 2.0 mass%, the balance iron and inevitable impurities into a predetermined shape, carbonitriding or nitriding is performed on the surface layer of the raceway surface. The nitrogen concentration of the surface layer portion is 0.2 to 2.0% by mass, and the area ratio of the nitride containing silicon (Si) and manganese (Mn) is 1% or more. A rolling bearing for a belt-type continuously variable transmission, characterized by being 20% or less. When the amount of retained austenite on the raceway surfaces of the inner ring and the outer ring is γr _AB (volume%) and the amount of retained austenite on the rolling surface of the rolling element is γr _C (volume%), the following equation (1) is obtained: The rolling bearing for a belt type continuously variable transmission according to claim 1, wherein:
γr _AB −15 ≦ γr _C ≦ γr _AB +15 (1)
However, 0 (volume%) ≦ γr _AB and γr _C ≦ 50 (volume%).

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