JP2005214390A - Needle bearing, planetary gear mechanism and pinion shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a needle bearing having a cage, a planetary gear mechanism and a pinion shaft, striking a balance between load capacity and durability in a high level. <P>SOLUTION: This needle bearing 10 is used in a planetary gear mechanism 14 to support a planetary gear 14c on a pinion shaft 14h to freely rotate, and a cage 12 retaining rollers 11a to 11c is provided. Thus, the frictional resistance can be reduced as compared with the so-called full type roller needle bearing. The outside diameters of the rollers 11a to 11c are set 10 to 20% of the outside diameter of the pinion shaft 14h, whereby while bending of the pinion shaft 14h is restrained, decrease in load capacity of the rollers 11a to 11c can be restrained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a planetary gear mechanism, and more particularly to a planetary gear mechanism suitable for use in an automatic transmission of a vehicle, a needle bearing and a pinion shaft used therefor.

  In an automatic transmission mounted on a vehicle or the like, a planetary gear mechanism is generally used. By the way, in recent years, there is a tendency to increase the number of stages in an automatic transmission for the purpose of improving fuel consumption. However, there is an attempt to use a so-called Ravigneaux type planetary gear mechanism in order to reduce the size of the automatic transmission, which currently has the mainstream of the fourth speed, to, for example, the fifth speed or the sixth speed. The Ravigneaux type planetary gear mechanism is a combination of two planetary gear mechanisms that share a planetary gear, and is described in Patent Document 1, for example.

Here, one feature of the Ravigneaux type planetary gear mechanism is that a short gear with a short axial length and a long gear with a long axial length are used. Particularly, a pinion shaft that supports a long gear has a long axial length with respect to the diameter. That is, it becomes elongated.
JP-A-6-200998

  However, in the Ravigneaux type planetary gear mechanism, when the pinion shaft diameter is reduced, the bending of the pinion shaft increases with respect to the load direction, and the roller of the needle bearing that rolls on the outer periphery thereof may be biased. There is a risk of shortening the service life.

  On the other hand, if the pinion shaft diameter is increased, its bending with respect to the load direction can be reduced, but the maximum outer diameter of the Ravigneaux planetary gear mechanism is limited, so the pinion shaft has a larger diameter. The roller diameter of the needle bearing must be reduced, and there is a problem that the load capacity is reduced.

  On the other hand, in order to increase the load capacity of the needle bearing, it is conceivable to use a so-called full roller type bearing that does not use a cage. However, in the case of the full roller type, the frictional resistance between the rollers increases. It is not preferable. Therefore, it is necessary to use a needle bearing having a cage.

  Furthermore, in the Ravigneaux type planetary gear mechanism, the planetary gear revolves around the sun gear while rotating, and at this time, the needle bearing supporting the planetary gear also rotates and revolves around the sun gear. The centrifugal force obtained by synthesizing is applied to the needle bearing. Accordingly, when the needle bearing is provided with a cage, a large centrifugal force is applied to the cage, and an excessive stress is generated, which may cause breakage.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a needle bearing having a cage, a planetary gear mechanism, and a pinion shaft that balances load capacity and durability at a high level. And

The needle bearing of the present invention is used in a planetary gear mechanism, and supports a planetary gear rotatably with respect to a pinion shaft.
It has a roller and a retainer for holding the roller, and the outer diameter of the roller is 10 to 20% of the outer diameter of the pinion shaft.

  Needless to say, special attention may be required when designing a needle bearing for use in a Ravigneaux planetary gear mechanism having a longer pinion shaft. In general, it is known that the dynamic load rating of a needle bearing is maximized when the roller diameter is 30 to 50% of the shaft diameter. However, the present inventor has discovered that when a needle bearing designed in such a ratio is used in a Ravigneaux type planetary gear mechanism, a short life is caused due to a long pinion shaft bending. Based on this discovery, the present inventors have made further studies and found that when the roller diameter is 10 to 20% of the shaft diameter, the load capacity and life of the needle bearing can be balanced in a high dimension.

  That is, according to the needle bearing of the present invention, it is possible to reduce the frictional resistance by providing a cage for holding the roller as compared with a so-called full roller type needle bearing. Further, by setting the outer diameter of the roller to 10 to 20% of the outer diameter of the pinion shaft, it is possible to suppress a decrease in the load capacity of the roller while suppressing the bending of the pinion shaft.

  The weight of the roller is preferably 1 g or less. In the cage, one of the parts that are easily damaged by fatigue is the base of the pillar. In particular, when the cage is manufactured by a punching process, cracks are easily generated from the fractured surface having a cut surface. The stress at the base is related to the collision force (proportional to the centrifugal force to the roller) on the roller column and the collision position. The smaller the impact force, the more advantageous against fatigue damage. According to the study by the present inventors, it has been found that if it is 2 g or less (preferably 1 g or less), the collision force due to the centrifugal force is reduced and the stress is effectively suppressed.

  The difference between the axial width of the cage and the axial length of the roller is preferably 2.7 mm or less because the load capacity of the roller can be increased as much as possible.

  The amount of retained austenite on the rolling surface of the roller is preferably 15 to 40%. This is because when the surface retained austenite amount is less than 15%, the rolling fatigue strength of the roller becomes insufficient, and when it exceeds 40%, the hardness of the roller becomes insufficient and the wear amount becomes large.

  The cage is preferably carbonitrided and quenched. Carbonitriding that can be performed at a quenching temperature of 840 to 860 ° C. is advantageous in terms of countermeasures against deformation of the cage.

  The surface hardness of the cage is preferably lower than the surface hardness of the roller and Hv 600 or more. When the roller is incorporated into the cage, if the roller is harder, the surface (rolling surface) is prevented from being damaged, and flaking of the roller can be prevented. However, if the surface hardness is lower than Hv600, the fatigue strength is lowered, so that it is preferable to be higher.

  The surface retained austenite amount of the cage is preferably 5% or less. This is because it is effective to reduce the surface retained austenite amount to 5% or less in order to suppress the deformation of the cage due to the decomposition of the retained austenite.

  The surface of the cage preferably has a chemical conversion film. In order to achieve high-speed rotation under centrifugal force in the planetary gear mechanism, the cage is preferably an outer ring guide. In such a case, in order to prevent seizure of the outer ring outer diameter surface and the gear inner diameter surface, This is because chemical conversion coating treatment such as acid salt coating and manganese phosphate coating is effective.

  It is preferable that the cage is formed by bending a single plate member, and a relief that does not contact the rollers is formed at the center of the cage. As described above, in the cage, one of the parts that are easily damaged by fatigue is the base of the column, and the stress at the base is a collision force to the column of the roller (proportional to the centrifugal force to the roller), and It is related to the collision position. Here, in a so-called M-shaped cage that is formed by bending a single plate material and has an M-shaped axial cross section, the roller is usually held at the center of the bent shape. Since it is advantageous to make the collision position as close as possible to the flange position, the stress at the base of the column portion can be reduced by forming a relief at the center of the cage as in the present invention.

  In the planetary gear mechanism including the needle bearing described above, when the rollers of the needle bearing are arranged in a double row, the lubricant supply holes provided on the outer peripheral surface of the pinion shaft are at least at both ends. It is preferable if it is formed at a position facing the roller row. The planetary gear mechanism has a characteristic that the lubricant flows in the centrifugal force direction and hardly flows in the axial direction due to the revolution of the planetary gear. In particular, in the Ravigneaux type planetary gear mechanism, in the case of a long gear with a long axial direction length, it may be supported by double row rollers, but in that case, if the hole for lubricant supply is opened in the center of the pinion shaft, There is a risk that the lubricity of the rollers at both ends will deteriorate. On the other hand, if the holes for supplying the lubricant are formed at least at positions facing the roller rows at both ends as in the present invention, the lubricity can be improved. When the roller rows are one or two rows, it is preferable that the holes are present in all rows. On the other hand, when the number of rollers is three or more, the load on the both end rows becomes larger than that of the center row due to the bending of the pinion shaft, and therefore a hole for supplying the lubricant is provided at least at a position facing the both end rows. Is extremely effective. It is more preferable that the hole for supplying the lubricant is at a position of ± 90 ° from the shaft position closest to the center of revolution.

  In the planetary gear mechanism provided with the needle bearing described above, the surface roughness of the inner raceway surface of the planetary gear, the rolling surface of the roller of the needle bearing, and the outer raceway surface of the pinion shaft is 0.1 μmRa or less. It is preferable that the superfinishing process is performed. In order to suppress flaking of the inner raceway surface of the planetary gear, the rolling surface of the roller of the needle bearing, and the outer raceway surface of the pinion shaft, it is necessary to form a sufficient oil film and avoid metal contact as much as possible. It is valid. According to experiments by the present inventors, it has been found that a desired life can be obtained when the surface roughness is 0.1 μmRa or less. Such surface roughness can be obtained by superfinishing.

  In the planetary gear mechanism using the needle bearing described above, the pinion shaft includes a Cr concentration of 1.3 to 2%, further has a surface retained austenite amount of 15 to 40%, and a core portion retained austenite amount of 0%. Preferably there is. According to the inventor's research, it was found that when the Cr concentration of the pinion shaft is less than 1.3%, the rolling fatigue strength is insufficient, and when it exceeds 2%, the cost increases. Further, it was found that when the surface retained austenite amount of the pinion shaft is less than 15%, the rolling fatigue strength is insufficient, and when it exceeds 40%, the hardness is insufficient. Furthermore, it is effective that the amount of retained austenite in the pinion shout core is 0% in order to suppress the bending. That is, a martensite structure is desirable.

  In the planetary gear mechanism using the needle bearing described above, when the rollers of the needle bearing are provided in a double row, the austenite of the rolling surface of the pinion shaft that faces the outer half in the axial direction of the rollers of the both ends row The amount is preferably larger than the amount of austenite at the center. In recent years, the carrier supporting the pinion shaft of the planetary gear mechanism has a tendency to rotate at a high speed, thereby applying a large centrifugal force to the planetary gear. In such a case, the pinion shaft undergoes plastic deformation due to elastic deformation and thermal decomposition of retained austenite. In the case of a single row, the rolling surface edge portion, and in the case of multiple rows or more, about half of the rolling on the end side of both end rows The load is received only on the surface, and the load is not received much on the other rolling surfaces. Therefore, a rolling surface with a small load does not require much rolling fatigue strength. Therefore, it is possible to extend the life by reducing the amount of retained austenite on the surface of the central portion to less than about half of the end portion side of both end rows, reducing plastic deformation, and making the contact stress more uniform as a result.

  In the planetary gear mechanism using the needle bearing described above, the surface hardness of the pinion shaft is preferably higher than the surface hardness of the roller. For example, in the Ravigneaux type planetary gear mechanism, the rolling part having the largest contact surface pressure and stress repetition number is the pinion shaft of the long gear, and therefore the weakest part is the pinion shaft. In a normal needle bearing, the roller is hardest, but in the Ravigneaux planetary gear mechanism, the rolling fatigue resistance can be improved by making the pinion shaft the hardest.

  In the planetary gear mechanism using the needle bearing described above, the difference between the inner diameter of the planetary gear and the outer diameter of the cage is preferably 0.1 to 0.2 mm. In order to form an oil film, it is desirable that the difference between the inner diameter of the gear and the outer diameter of the cage be as small as possible, but on the other hand, the gear and the cage are deformed during use. The surface pressure is excessively increased and burned. According to the research result of the present inventor, it was found that the value for achieving the balance was 0.1 to 0.2 mm.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an automatic transmission 10 for an FF vehicle equipped with a Ravigneaux type planetary gear mechanism according to the present embodiment. In FIG. 1, power from an engine (not shown) is input to an automatic transmission 10 via a torque converter 11 and an input shaft 12. The inputted power is transmitted to the Ravigneaux planetary gear mechanism 14 through the brake clutch group 13 including the brake 13a, the rear clutch 13b, the reverse clutch 13c, and the forward clutch 13d.

  The rotational output decelerated by the Ravigneaux type planetary gear mechanism 14 is transmitted from the drive gear 16 to the driven gear 17, and further from the counter shaft 18 to which the driven gear 17 is attached to the differential gear mechanism 19, and further to the differential gear mechanism 19. The power is transmitted from a driving wheel (not shown).

  FIG. 2 is a perspective view showing the configuration of the Ravigneaux planetary gear mechanism 14, but it is different from the actual shape for easy understanding. In FIG. 2, a first sun gear 14b connected to a first drive shaft 14a that selectively receives power from the brake clutch group 13 meshes with a planetary gear (long gear) 14c having a long axis, and this planetary gear 14c is connected to a ring gear 14e. Is engaged. On the other hand, the second sun gear 14f connected to the second drive shaft 14a 'that selectively receives power from the brake clutch group 13 meshes with a planetary gear (short gear) 14d having a short axis. The planetary gear 14d is further meshed with the planetary gear 14c.

  The planetary gear 14c is supported by a pinion shaft 14h that is bridged with a pair of carriers 14g via a radial needle bearing (not shown). Thus, it is supported via a radial needle bearing (not shown). The carrier 14g is coaxially attached to the driven shaft 14j. That is, the rotational force input to the drive shafts 14a and 14a 'is decelerated by the combination of gears and output to the driven shaft 14j. One feature of the Ravigneaux planetary gear mechanism 14 is that the pinion shaft 14h that supports the long gear 14c is longer in axial length than the other planetary gear mechanisms, and the pinion shaft 14i that supports the short gear 14d is cantilevered. Sometimes it is.

  FIG. 3 is an axial sectional view showing the periphery of the pinion shaft 14h of the present embodiment in an enlarged manner. As shown in FIG. 3, the radial needle bearing 10 is disposed between the pinion shaft 14h and the planetary gear 14c, and rotatably supports the planetary gear 14c. The radial needle bearing 10 includes rollers 11a, 14b, and 14c arranged in three rows, and a cage 12 that holds them. The cage 12 is a so-called M-type cage formed by bending a single plate material. In the shaft 14h, there are a bag hole 14k extending along the axis from the right end surface in FIG. 3, and two radial holes (both ends) extending in the radial direction from the bag hole 14k and opening on the peripheral surface of the shaft 14h. 14m) for supplying a lubricant facing the roller row. The needle bearing 10 is lubricated by lubricating oil supplied from the outside of the shaft 14h through the bag hole 14k and the diameter hole 14m.

  4A is a cross-sectional view of the central row of the radial needle bearing 10, and FIG. 4B is a view of the radial needle bearing 10 as viewed from the outer peripheral side (in the direction of arrow B). As shown in FIG. 4, the retainer 12 has a shape in which a pair of annular portions 12a are connected by a plurality of column portions 12b. A space between the adjacent column portions 12b is a pocket portion for accommodating the rollers 11b. Further, in the present embodiment, the column portion 12b has a reduced diameter portion 12c whose diameter is reduced so that the central portion approaches the axis as shown in FIG. 3, but the central portion of the reduced diameter portion 12c. A recess (relief) 12d that is recessed in the circumferential direction is formed.

  According to the present embodiment, since the concave portion 12d is formed, the central portion of the roller 11b in the central row is avoided from coming into contact with the column portion 12b, whereby the root of the column portion 12b due to the impact force of the roller is avoided. Since the stress applied to is relaxed, the column portion 12b can be made thinner to increase the fatigue strength, and the load capacity can be increased by increasing the roller diameter. A similar configuration may be provided for the cage 12 with which the rollers 11a and 11c in the both end rows contact.

  In the present embodiment, the outer diameter d of the rollers 11a to 11c is 10 to 20% of the outer diameter D of the pinion shaft 14h. The weight of the rollers 11a to 11c is 1 g or less.

  In FIG. 3, the plate thickness t of the cage 12 needs to be about 1 mm in order to ensure its strength. In addition, the distance s from the flange end surface to the pocket portion is effectively 0.2 mm or less in order to prevent the rollers 11a and 11c from entering. Further, the effect of the backlash in the axial direction of the pocket portions 11a to 11c that improve the lubricity becomes less than 0.3 mm. In order to ensure the above reason and load capacity, it is effective that the difference between the axial width L of the cage 12 and the axial length La + Lb + Lc of the rollers 11a to 11c is 2.7 mm or less.

  The amount of surface retained austenite on the rolling surfaces of the rollers 11a to 11c is 15 to 40%. The cage 12 is subjected to carbonitriding and quenching treatment, and the surface hardness of the cage 12 is lower than the surface hardness of the rollers 11a to 11c and is equal to or higher than Hv600.

  The amount of retained austenite on the surface of the cage 12 is 5% or less, and the surface of the cage 12 has a chemical conversion coating (phosphate coating, manganese phosphate coating).

  In the present embodiment, the surface roughness of the inner raceway surface of the long gear 14c, the rolling surfaces of the rollers 11a to 11c of the needle bearing 10 and the outer raceway surface of the pinion shaft 14h is superfinished to be 0.1 μmRa or less. Has been processed. The pinion shaft 14h includes a Cr concentration of 1.3 to 2%, further has a surface retained austenite amount of 15 to 40%, and a core portion retained austenite amount of 0%.

  Furthermore, in the pinion shaft 14h, the amount of austenite on the rolling surfaces facing the outer half in the axial direction of the rollers 11a and 11c in both ends of the row is larger than the amount of austenite in the central portion. Further, the surface hardness of the pinion shaft 14h is higher than the surface hardness of the rollers 11a to 11c. Further, the difference between the inner diameter of the long gear 14c and the outer diameter of the cage 12 is 0.1 to 0.2 mm.

The inventor manufactured Examples 1 and 2 and Comparative Examples 1, 2 and 3 having different roller diameters and pinion shaft diameters, and used them in an evaluation test under the following conditions.
Test conditions (1) Long gear inner diameter: φ21 (mm)
(2) Roller length: 18 (mm)
(3) Long gear revolutions: 8000 (min ⁻¹ )
(4) Long gear rotation speed: 13050 (min ⁻¹ )
(5) Test lubricant: ATF oil (6) Test lubricant temperature: 80 ° C
(7) Test time: 200hour
Table 1 shows the roller diameters and pinion shaft diameters of Examples 1 and 2 and Comparative Examples 1, 2 and 3, and the test results.

  FIG. 5 is a diagram plotting the values of Examples 1 and 2 and Comparative Examples 1, 2 and 3 with the dynamic load rating on the vertical axis and the roller diameter / pinion shaft diameter on the horizontal axis. According to FIG. 5, since the dynamic load rating C is the highest in Comparative Example 2, it can be said that it was common sense to adopt the needle bearing of Comparative Example 2 according to the conventional design method.

  However, according to the test conducted by the present inventor, the conventional common sense was overturned. As shown in Table 1, in Comparative Example 1 (Roller Diameter / Pinion Shaft Diameter: 0.38) and Comparative Example 2 (Roller Diameter / Pinion Shaft Diameter: 0.31), peeling due to excessive edge load was caused after the test. Recognized on the pinion shaft. On the other hand, in the case of Comparative Example 3 (roller diameter / pinion shaft diameter: 0.08), the dynamic load rating C was lowered, and the roller was peeled off. On the other hand, in the case of Example 1 (roller diameter / pinion shaft diameter: 0.20) and Example 2 (roller diameter / pinion shaft diameter: 0.12), defects such as peeling were not recognized.

Furthermore, the present inventor manufactured Example 1 and Comparative Examples 1, 2, and 3 used in the same pinion shaft and having different roller weights, and used them in an evaluation test under the following conditions.
Test conditions (1) Long gear revolutions: 7000 (min ⁻¹ )
(2) Long gear rotation speed: 13500 (min ⁻¹ )
(3) Test lubricant: ATF oil (4) Test lubricant temperature: 80 ° C
(5) Test time: 200hour
The test results are shown in Table 2.

  As is apparent from the above test results, in the case of Comparative Examples 1 to 3 in which the roller weight is 1.11 g or more, a tendency for the cage to break in a short time as the weight increases was observed. On the other hand, in Example 1 where the roller weight was 0.99 g, the cage was not damaged.

Furthermore, the inventor manufactured Examples 1 and 2 and Comparative Examples 1 and 2 in which the roughness of the roller rolling surface, the pinion shaft rolling surface, and the long gear inner diameter surface was changed, and used for the evaluation test under the following conditions. did.
Test conditions (1) Long gear inner diameter: φ21 (mm)
(2) Pinion shaft diameter: φ15 (mm)
(3) Roller length: 18 (mm)
(4) Roller diameter: φ3.5 (mm)
(5) Long gear revolutions: 8000 (min ⁻¹ )
(6) Long gear rotation speed: 13050 (min ⁻¹ )
(7) Test lubricant: ATF oil (8) Test lubricant temperature: 80 ° C
The test results are shown in Table 3.

  As is clear from the above test results, in Comparative Example 1 in which the roughness of the inner surface of the long gear is 0.11 μmRa and in Comparative Example 2 in which the roughness of the rolling surface of the pinion shaft is 0.12 μmRa, the calculated life is reduced. There is a problem that the actual durability time is 60% or less. On the other hand, when the roughness of the roller rolling surface, the pinion shaft rolling surface, and the long gear inner diameter surface was all suppressed to 0.09 μmRa or less, the result was that the actual durability exceeded the calculated life by 5% or more.

Furthermore, this inventor produced Example 1, 2 and Comparative Example 1, 2, 3, 4 which changed chromium concentration and a retained austenite, and used for the evaluation test on the following conditions.
Test conditions (1) Long gear inner diameter: φ21 (mm)
(2) Pinion shaft diameter: φ15 (mm)
(3) Roller length: 18 (mm)
(4) Roller diameter: φ3.5 (mm)
(5) Long gear revolutions: 8000 (min ⁻¹ )
(6) Long gear rotation speed: 13050 (min ⁻¹ )
(7) Test lubricant: ATF oil (8) Test lubricant temperature: 80 ° C
The test results are shown in Table 4.

  Considering the above test results, the Cr concentration is 0.5%, the surface residual austenite amount is 16%, the Cr concentration is 1.2%, and the surface residual austenite amount is 13%. In Comparative Example 2, there is a problem that the actual durability is 60% or less with respect to the calculated life. In Comparative Example 4 in which the Cr concentration is 1.5% and the surface retained austenite amount is 14%, there is a problem that the actual durability time is 70% with respect to the calculated life. Incidentally, even if the Cr concentration is 1.5% and the surface retained austenite amount is 22%, in Comparative Example 4 in which the core portion retained austenite amount is 10%, the actual durability time is 40% with respect to the calculated life. In addition, peeling due to edge loading occurred.

  On the other hand, in Examples 1 and 2 in which the Cr concentration is 1.3 to 1.8%, the surface retained austenite amount is 17 to 18%, and the core portion retained austenite amount is 0%, the calculated lifetime As a result, the actual durability time exceeded 30 to 50% or more.

Furthermore, the present inventor manufactured Examples 1, 2, and 3 and Comparative Examples 1, 2 and 3 in which the amount of retained austenite on the rolling surface of the roller was changed, and was subjected to an evaluation test under the following conditions.
Test conditions (1) Long gear inner diameter: φ21 (mm)
(2) Pinion shaft diameter: φ15 (mm)
(3) Roller length: 18 (mm)
(4) Roller diameter: φ3.5 (mm)
(5) Long gear revolutions: 8000 (min ⁻¹ )
(6) Long gear rotation speed: 13050 (min ⁻¹ )
(7) Test lubricant: ATF oil (8) Test lubricant temperature: 80 ° C
The test results are shown in Table 5.

  Considering the above test results, in Comparative Example 1 in which the amount of surface retained austenite is 7% and in Comparative Example 2 in which the amount of surface retained austenite is 14%, the actual durability time is 80% or less with respect to the calculated life. There is. Further, in Comparative Example 3 where the surface retained austenite amount is 41%, there is a problem that the actual durability time is 70% with respect to the calculated life.

  In contrast, in Examples 1, 2, and 3 in which the amount of retained austenite on the roller rolling surface was 15 to 39%, a result that the actual durability exceeded 10 to 20% or more with respect to the calculated life was obtained.

  In FIG. 6, the vertical axis indicates (actual durability time / calculated life), the surface retained austenite of the roller rolling surface, and the values of Examples 1, 2, 3 and Comparative Examples 1, 2, 3 are plotted. FIG. According to FIG. 5, it can be seen that the actual durability time is equal to or longer than the calculated life when the amount of retained austenite on the roller rolling surface is 15 to 40%.

  As the heat treatment of the cage, the present inventor manufactured Comparative Example 1 that was carburized (heated to 950 ° C.) and Example 1 that was carbonitrided (heated to 840 to 860 ° C.). It was measured. Table 6 shows the measurement results.

  Considering the above measurement results, the roundness of Comparative Example 1 subjected to the carburizing treatment was as large as 40 μm, whereas the roundness of Example 1 subjected to the carbonitriding treatment could be suppressed to a small value of 25 μm.

Furthermore, the inventor manufactured Example 1 and Comparative Examples 1 and 2 in which the amount of retained austenite of the cage was changed, and was subjected to an evaluation test under the following conditions.
Test conditions (1) Long gear inner diameter: φ21 (mm)
(2) Pinion shaft diameter: φ15 (mm)
(3) Roller length: 18 (mm)
(4) Roller diameter: φ3.5 (mm)
(5) Long gear revolutions: 8000 (min ⁻¹ )
(6) Long gear rotation speed: 13050 (min ⁻¹ )
(7) Test lubricant: ATF oil (8) Test lubricant temperature: 80 ° C
The test results are shown in Table 7.

  In consideration of the above test results, in Comparative Examples 1 and 2 in which the surface retained austenite amount is 6 to 10%, the roundness was changed by 5 to 15 μm before and after the treatment, whereas the surface retained austenite amount was 4%. %, The change in roundness before and after the treatment could be suppressed to 1 μm.

  The present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. The present invention can also be applied to Ravigneaux type planetary gear mechanisms and other types of planetary gear mechanisms. The rollers are not limited to double rows but may be single rows.

It is sectional drawing of the automatic transmission 1 of the vehicle containing the needle bearing concerning this Embodiment. FIG. 2 is a perspective view of a Ravigneaux type planetary gear mechanism that can be used in the automatic transmission 1 of FIG. 1. It is an axial direction sectional view expanding and showing the circumference of the pinion shaft of this embodiment. It is the figure which looked at the radial needle bearing 10 from the outer peripheral side. It is a figure which plots and shows the value of Example 1, 2, and Comparative Example 1, 2, 3 by taking a dynamic load rating on a vertical axis | shaft and taking a roller diameter / pinion shaft diameter on a horizontal axis. FIG. 4 is a graph plotting the values of Examples 1, 2, 3 and Comparative Examples 1, 2, 3 by taking (actual durability time / calculated life) on the vertical axis and taking the surface retained austenite of the roller rolling surface. .

Explanation of symbols

14 Ravigneaux type planetary gear mechanism 14c Planetary gear 14h Pinion shaft 10 Needle bearing

Claims (16)

In a needle bearing used for a planetary gear mechanism and rotatably supporting a planetary gear with respect to a pinion shaft,
A needle bearing comprising a roller and a cage for holding the roller, wherein the outer diameter of the roller is 10 to 20% of the outer diameter of the pinion shaft.   2. The needle bearing according to claim 1, wherein the weight of the roller is 1 g or less.   The needle bearing according to claim 1 or 2, wherein a difference between an axial width of the cage and an axial length of the roller is 2.7 mm or less.   The needle bearing according to any one of claims 1 to 3, wherein a surface retained austenite amount of a rolling surface of the roller is 15 to 40%.   The needle bearing according to any one of claims 1 to 4, wherein the cage is subjected to a carbonitriding quenching process.   The needle bearing according to any one of claims 1 to 5, wherein the surface hardness of the cage is lower than the surface hardness of the roller and is Hv 600 or more.   The needle bearing according to any one of claims 1 to 6, wherein a surface retained austenite amount of the cage is 5% or less.   The needle bearing according to claim 1, wherein a surface of the cage has a chemical conversion film.   9. The retainer according to claim 1, wherein the retainer is formed by bending a single plate member, and a relief is formed in a central portion of the retainer so as not to contact the roller. The needle bearing in any one. In the planetary gear mechanism provided with the needle bearing according to any one of claims 1 to 9,
When the rollers of the needle bearing are arranged in double rows, the lubricant supply holes provided on the outer peripheral surface of the pinion shaft are formed at positions facing at least the roller rows at both ends. Planetary gear mechanism characterized by In the planetary gear mechanism provided with the needle bearing according to any one of claims 1 to 9,
The surface roughness of the inner raceway surface of the planetary gear, the rolling surface of the roller of the needle bearing, and the outer raceway surface of the pinion shaft is superfinished so as to be 0.1 μmRa or less. Planetary gear mechanism. In the planetary gear mechanism using the needle bearing according to any one of claims 1 to 9,
The pinion shaft includes a Cr concentration of 1.3 to 2%, further has a surface retained austenite amount of 15 to 40%, and a core portion retained austenite amount is 0%. In the planetary gear mechanism using the needle bearing according to any one of claims 1 to 9,
When the rollers of the needle bearing are provided in double rows, the amount of austenite on the rolling surface facing the outer half in the axial direction of the rollers in both ends of the pinion shaft is larger than the amount of austenite in the center portion. Planetary gear mechanism characterized by In the planetary gear mechanism using the needle bearing according to any one of claims 1 to 9,
A planetary gear mechanism characterized in that the surface hardness of the pinion shaft is higher than the surface hardness of the roller. In the planetary gear mechanism using the needle bearing according to any one of claims 1 to 9,
A planetary gear mechanism characterized in that a difference between an inner diameter of the planetary gear and an outer diameter of the cage is 0.1 to 0.2 mm. A pinion shaft characterized by being used in the planetary gear mechanism according to any one of claims 11 to 14.

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