JP4987281B2 - Tapered roller bearing - Google Patents

Description

  The present invention relates to a tapered roller bearing and can be applied to a bearing that supports a power transmission shaft such as a differential of a self-propelled vehicle or a transmission.

    Tapered roller bearings have a raceway surface on the outer diameter surface, an inner ring with small and large collars arranged on both sides in the axial direction of the raceway surface, an outer ring with a raceway surface on the inner diameter surface, and raceway surfaces of the inner ring and the outer ring. The main components are a plurality of tapered rollers interposed between them and a retainer that stores and holds the tapered rollers in a pocket. The cage includes a small annular portion that is continuous on the small end surface side of the tapered roller, a large annular portion that is continuous on the large end surface side of the tapered roller, and a plurality of column portions that connect both annular portions. The pocket is formed between adjacent column portions, and has a trapezoidal shape in which a portion for storing the small diameter side of the tapered roller is a narrow side and a portion for storing the large diameter side is a wide side.

  Tapered roller bearings that support power transmission shafts such as differentials and transmissions of self-propelled vehicles are used with the lower part immersed in an oil bath, and the oil in the oil bath flows into the bearing as lubricating oil as it rotates. . In tapered roller bearings used for such applications, the lubricating oil flows into the bearing from the small diameter side of the tapered roller, and the lubricating oil flowing from the outer diameter side of the cage flows along the raceway surface of the outer ring. The lubricating oil that passes to the larger diameter side and flows from the inner diameter side to the cage passes along the raceway surface of the inner ring to the larger diameter side of the tapered roller.

In such a tapered roller bearing used for a portion where the lubricating oil flows from the outside, a notch is provided in the pocket of the cage, and the lubricating oil that flows into the outer diameter side and the inner diameter side of the cage is separated. There is one that passes through this notch to improve the flow of lubricating oil inside the bearing (see Patent Documents 1 and 2). As shown in FIG. 21 (A), in the one described in Patent Document 1, a notch 10d is provided in the central portion of the column portion 8 between the pockets 9 of the cage 5, and foreign matter mixed into the lubricating oil is caused inside the bearing. So that it does not stay. Moreover, in what was described in patent document 2, as shown to FIG. 21 (B), the notch 10e is provided in the small annular part 6 and the large annular part 7 of the axial direction both ends of the pocket 9 of the holder | retainer 5, and hold | maintained. The lubricating oil flowing in from the outer diameter side of the vessel is made easier to flow to the inner ring side. In addition, each dimension of the pocket 9 entered in each figure is the value used for the comparative example in the torque measurement test mentioned later.
Japanese Patent Application Laid-Open No. 09-032858 JP-A-11-2011149 JP 09-096352 A JP-A-11-210765 JP 2003-343552 A

  As described above, in the tapered roller bearing in which the lubricating oil is divided into the outer diameter side and the inner diameter side of the cage and flows into the bearing, the torque increases when the ratio of the lubricating oil flowing from the inner diameter side of the cage to the inner ring side increases. It turns out that the loss increases. The reason is considered as follows.

  That is, the lubricating oil flowing from the outer diameter side of the cage to the outer ring side smoothly passes to the large diameter side of the tapered roller along the raceway surface because there is no obstacle on the inner diameter surface of the outer ring. The lubricating oil flowing out from the inner diameter side of the cage to the inner ring side has a large flaw on the outer diameter surface of the inner ring, so when it passes along the raceway surface to the larger diameter side of the tapered roller It will be dammed up with a large spear and will easily stay inside the bearing. For this reason, when the ratio of the lubricating oil flowing from the inner diameter side to the inner ring side of the cage increases, the amount of the lubricating oil staying inside the bearing increases, and this staying lubricating oil becomes a flow resistance against the bearing rotation and generates torque. Loss is considered to increase.

  Therefore, it is necessary to reduce torque loss due to flow resistance of the lubricating oil in the tapered roller bearing in which the lubricating oil flows into the bearing. The above is a method for reducing the flow resistance of oil to reduce torque, but in order to significantly reduce torque, it is necessary to change the bearing specifications so that the rolling viscous resistance decreases. . However, in the conventional torque reduction method (see Patent Documents 3 to 5), torque reduction without reducing the rated load is possible, but the bearing rigidity is somewhat reduced.

  The main object of the present invention is to realize a low torque without reducing the bearing rigidity.

  The present invention solves the problem by reducing the PCD without decreasing or increasing the number of rollers. FIG. 23 shows the rigidity ratio (-●-) and torque ratio (-o-) when the roller pitch diameter (PCD) is changed in the tapered roller bearing. As shown in FIG. 23, when the PCD is reduced, the bearing torque is significantly reduced, but the bearing rigidity is not significantly reduced as a result of calculating and confirming the elastic deformation amount of the roller. Therefore, the torque can be reduced without reducing the rigidity by reducing the PCD while decreasing or increasing the number of rollers.

That is, the tapered roller bearing according to the present invention includes an inner ring, an outer ring, a plurality of tapered rollers arranged to roll between the inner ring and the outer ring, and a cage that holds the tapered rollers at a predetermined circumferential interval. The roller coefficient γ exceeds 0.94, and at least one member of the inner ring, the outer ring and the rolling element has a nitrogen-enriched layer, and the grain size of the austenite crystal grains in the nitrogen-enriched layer The number is in a range exceeding 10 and the retainer includes a small annular portion that is continuous on the small end face side of the tapered roller, a large annular portion that is continuous on the large end face side of the tapered roller, and a plurality of portions that connect these annular portions. A trapezoidal pocket is formed between the adjacent pillars, and the part that houses the small diameter side of the tapered roller is the narrow side, and the part that contains the large diameter side is the wide side. the central portion of the pillar portion and the small annular portion of the narrow side of the It is characterized in that the lubricating oil that has flowed into between the inner ring and the cage is provided notches for releasing quickly to the outer side.

  The roller coefficient γ (roller filling ratio) is a parameter represented by (number of rollers × roller average diameter) / (π × PCD). When the average roller diameter is constant, the larger the value of γ, the greater the number of rollers. It means that there are many. In the conventional typical tapered roller bearing with a cage, the roller coefficient γ is usually designed to be 0.94 or less, whereas the roller coefficient γ exceeds 0.94. This means that the roller filling rate and thus the bearing rigidity is high.

The nitrogen-enriched layer is a layer with an increased nitrogen content formed on the raceway (outer ring or inner ring) or the surface layer of the rolling element, and can be formed by a process such as carbonitriding, nitriding, or nitriding. . Nitrogen content in the nitrogen-enriched layer is preferably Ru der range of 0.1% to 0.7%. If the nitrogen content is less than 0.1%, there will be no effect, and the rolling life will be reduced particularly under the foreign matter mixing conditions. When the nitrogen content is more than 0.7%, voids called voids are formed, or the retained austenite increases so much that the hardness does not come out, resulting in a short life. As for the nitrogen-enriched layer formed on the raceway, the nitrogen content is a value at the surface layer of 50 μm of the raceway surface after grinding, and can be measured by, for example, PMA (wavelength dispersion type X-ray microanalyzer).

  Also, the rolling fatigue life can be greatly improved by the finer austenite grain size as the grain size number of the austenite crystal grains exceeds 10. When the austenite grain size number is 10 or less, the rolling fatigue life is not greatly improved. Usually 11 or more. Although it is desirable that the austenite grain size is finer, it is usually difficult to obtain a grain size number exceeding 13. Note that the austenite grains of the bearing parts described above do not change even in the surface layer portion having the nitrogen-enriched layer or in the inside thereof. Therefore, the target position of the above crystal grain size number range is the surface layer portion and the inside. An austenite crystal grain is a crystal grain based on the trace of the austenite crystal grain boundary immediately before quenching, for example, after quenching.

Moreover, the following effect | action is acquired by providing a notch in the center part of the narrow pillar part and small annular part of the trapezoid shaped pocket of a holder | retainer. That is, the lubricating oil that has flowed into the inner side from the inner diameter side of the cage, can be released quickly to the outer ring side through the notch of these. As a result, the amount of lubricating oil reaching the large collar along the raceway surface of the inner ring is reduced, and the amount of lubricating oil staying inside the bearing is reduced. Therefore, torque loss due to the flow resistance of the lubricating oil is reduced.

More and this also notched in the small annular portion of the narrow side of the pocket is provided, it can also'll escape to the outer side of the lubricating oil flowing into the inner side from the inner diameter side of the cage from the notch . Accordingly, the amount of lubricating oil reaching the large collar along the raceway surface of the inner ring is reduced, and torque loss due to the flow resistance of the lubricating oil is further reduced.

According to this invention, a reduction in torque can be realized without reducing the bearing rigidity. That is, by providing a notch cut from the outer diameter side to the inner diameter side in the central part of the narrow side column part and small annular part of the trapezoidal pocket of the cage, the cage flows from the inner diameter side to the inner ring side. the lubricating oil, it is possible to escape quickly to the outer side through the notch of these, the amount of lubricating oil reaching the large flange along the inner ring raceway surface is reduced, the amount of lubricating oil staying inside the bearing The torque loss due to the flow resistance of the lubricating oil is reduced.

  By setting the roller coefficient γ to exceed 0.94, it is possible to prevent a decrease in rigidity. In addition, by setting the roller coefficient γ to γ> 0.94, not only the load capacity is increased, but also the maximum surface pressure of the raceway surface can be reduced, so that it has an extremely short life under severe lubrication conditions. Surface origin peeling can be prevented.

  Furthermore, the tapered roller bearing of the present invention has a nitrogen-enriched layer and further refines the austenite grain size to 11 or more in grain size number, so the rolling fatigue life is greatly improved, and excellent crack resistance strength and Aging dimensional change can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings. First, the tapered roller bearing 1 according to the embodiment shown in FIG. 1 includes an inner ring 2, an outer ring 3, a tapered roller 4, and a cage 5. The inner ring 2 has a conical track surface 2a on the outer periphery, and the outer ring 3 has a conical track surface 3a on the inner periphery. A plurality of tapered rollers 4 are interposed between the raceway surface 2a of the inner ring 2 and the raceway surface 3a of the outer ring 3 so as to roll freely. Each tapered roller 4 is accommodated in a pocket formed in the cage 5, and movement in the axial direction is restricted by a small brim 2 b and a large brim 2 c provided on both sides of the raceway surface 2 a of the inner ring 2.

Here, the tapered roller bearing 1 has a roller coefficient γ of γ> 0.94. The roller coefficient γ represents the filling rate of the roller and is defined by the following equation.
Roller coefficient γ = (Z · DA) / (π · PCD)
here,
Z: Number of rollers DA: Roller average diameter PCD: Roller pitch diameter.

  For comparison, referring to FIG. 22 and referring to the prior art, the tapered roller bearing shown in FIG. 22 is a typical tapered roller bearing with a cage in which the outer ring is separated from the cage. In order to ensure the column width of the retainer 72 and to obtain a proper rotation of the proper retainer 72, the roller coefficient γ is normally 0.94 or less. Designed. In FIG. 22, reference numerals 73, 74, and 75 denote a tapered roller, a column surface, and an inner ring, respectively, and reference sign θ represents a window angle.

As shown in FIG. 1B, the cage 5 includes a small annular portion 6 that is continuous on the small end face side of the tapered roller 4, a large annular portion 7 that is continuous on the large end face side of the tapered roller 4, and these small annular portions. 6 and a plurality of pillars 8 that connect the macro-annular part 7. Then, as shown in FIG. 2, a pocket 9 is formed between the adjacent column portions 8.

The pocket 9 of the cage 9 has a trapezoidal shape, and the portion that stores the small diameter side of the tapered roller 4 is the narrow side, and the portion that stores the large diameter side is the wide side. On the narrow side and wide side of the pocket 9, two notches 10 a and 10 b that are cut from the outer diameter side to the inner diameter side are provided in each of the column portions 8 on both sides. Each notch 10a, 10b has a depth of 1.0 mm and a width of 4.6 mm. By providing the notches not only on the narrow side but also on the wide side, the tapered rollers can be brought into contact with the column portion in a balanced manner. The notch illustrated in the drawing is in the form of a groove cut in the radial direction of the cage 5, but allows the lubricating oil to pass smoothly by connecting the inner diameter side and the outer diameter side of the cage 5. As long as it can be done, the shape and dimensions are arbitrary.

3 and 4 show a modified example of the cage 5. In the modification shown in FIG. 3, a notch 10 c is also provided in the small annular portion 6 on the narrow side of the pocket 9. The total area of the three notches 10a and 10c on the narrow side is wider than the total area of the two notches 10b on the wide side. The notch 10c has a depth of 1.0 mm and a width of 5.7 mm. In the modification shown in FIG. 4, the depth of each notch 10a of the narrow column portion 8 is 1.5 mm, which is deeper than each notch 10b of the wide column portion 8, and each notch on the narrow side. The total area of 10a is wider than the total area of the notches 10b on the wide side. By adopting the configuration illustrated in FIG. 3 and FIG. 4, the amount of lubricating oil reaching the main shaft along the raceway surface of the inner ring is reduced, and torque loss due to the flow resistance of the lubricating oil is further reduced. be able to.

As shown in FIG. 5, a radially inward flange 11 is provided on the outer side in the axial direction of the small annular portion 6 of the cage 5 so as to face the outer diameter surface of the small collar 2 b of the inner ring 2. The clearance δ between the inner diameter surface of 11 and the outer diameter surface of the small collar 2b of the inner ring 2 is set narrowly to 2.0% or less of the outer diameter dimension of the small collar 2b. By adopting such a configuration, the amount of lubricating oil flowing from the inner diameter side of the cage to the inner ring side can be reduced, and torque loss due to the flow resistance of the lubricating oil can be further reduced.

Although not shown in the drawings, the entire surface of the tapered roller 4 is provided with an infinite number of minute concave recesses. The surface provided with the indentation has a surface roughness parameter Ryni of 0.4 μm ≦ Ryni ≦ 1.0 μm and a Sk value of −1.6 or less. By adopting such a configuration, even if the lubricating oil is evenly held on the surface of the tapered roller and the amount of lubricating oil staying inside the bearing is reduced, the contact portion between the tapered roller and the inner ring and the outer ring is sufficiently provided. Can be lubricated.
The parameter Ryni is the average value of the maximum height for each reference length, that is, the reference length is extracted from the roughness curve in the direction of the average line, and the interval between the peak line and the valley bottom line of this extracted part is set to the vertical line of the roughness curve. It is a value measured in the direction of magnification (ISO 4287: 1997). The Sk value is a value representing the degree of distortion of the roughness curve, that is, the asymmetry of the roughness unevenness distribution (ISO 4287: 1997), and the Sk value is close to 0 in a symmetric distribution such as a Gaussian distribution. When the concave and convex portions are deleted, a negative value is obtained. Conversely, when the concave and convex portions are deleted, a positive value is obtained. The Sk value can be controlled by selecting the rotational speed of the barrel polishing machine, the processing time, the workpiece input amount, the type and size of the polishing tip, etc., and by setting the Sk value to −1.6 or less, Lubricating oil can be held evenly in innumerable minute concave recesses.

  Tapered roller bearings (Example 1) using the cage shown in FIG. 2 and tapered roller bearings (Example 2) using the cage shown in FIG. 3 were prepared. Moreover, as a comparative example, a tapered roller bearing (Comparative Example 1) using a cage without a notch in a pocket and a tapered roller bearing (Comparative Example) using the cage shown in FIGS. 21 (A) and (B). 2, 3) were prepared. Each tapered roller bearing has an outer diameter of 100 mm, an inner diameter of 45 mm, and a width of 27.25 mm, and the portions other than the pocket notch are the same.

About the tapered roller bearing of an Example and a comparative example, the torque measurement test using the vertical torque tester was done. The test conditions are as follows.
Axial load: 300kgf
Rotational speed: 300-2000 rpm (100 rpm pitch)
Lubrication condition: oil bath lubrication (lubricating oil: 75W-90)

  FIG. 6 shows the test results. The vertical axis of the graph in the figure represents the torque reduction rate with respect to the torque of Comparative Example 1 using a cage with no notch in the pocket. Although the comparative example 2 which provided the notch in the center part of the pocket | column part of a pocket and the comparative example 3 which provided the notch in the small annular part and the large annular part of a pocket also show a torque reduction effect, the narrow part of a pocket In Example 1 in which a notch is provided in the column on the side, a torque reduction effect superior to those of the comparative examples is recognized, and a notch on the narrow side is provided with a notch in the small annular portion on the narrow side. In Example 2 in which the total area of these is wider than that on the wide side, a further excellent torque reduction effect is recognized.

  In addition, the torque reduction rate at 2000 rpm, which is the maximum rotation speed of the test, was 9.5% in Example 1 and 11.5% in Example 2, which was excellent even under high-speed rotation conditions in a differential or transmission. A torque reduction effect can be obtained. In addition, the torque reduction rate in the rotational speed 2000rpm of the comparative example 2 and the comparative example 3 is 8.0% and 6.5%, respectively.

  The cage 5 is integrally formed of resin, and includes a small-diameter-side annular portion 6, a large-diameter-side annular portion 7, and a plurality of column portions 8 that connect the small-diameter-side annular portion 6 and the large-diameter-side annular portion 7. Yes. In addition to using super engineering plastics such as PPS, PEEK, PA, PPA, and PAI as the cage material, if necessary, these resin materials or other engineering plastics may be made of glass fiber or What mix | blended carbon fiber etc. may be used.

  Engineering plastics include general purpose engineering plastics and super engineering plastics. Typical examples are listed below, but these are examples of engineering plastics, and engineering plastics are not limited to the following.

  [General-purpose engineering plastics] Polycarbonate (PC), polyamide 6 (PA6), polyamide 66 (PA66), polyacetal (POM), modified polyphenylene ether (m-PPE), polybutylene terephthalate (PBT), GF reinforced polyethylene terephthalate (GF) -PET), ultra high molecular weight polyethylene (UHMW-PE)

  [Super Engineering Plastics] Polysulfone (PSF), Polyethersulfone (PES), Polyphenylene sulfide (PPS), Polyarylate (PAR), Polyamideimide (PAI), Polyetherimide (PEI), Polyetheretherketone ( PEEK), liquid crystal polymer (LCP), thermoplastic polyimide (TPI), polybenzimidazole (PBI), polymethylbenten (TPX), poly1,4-cyclohexanedimethylene terephthalate (PCT), polyamide 46 (PA46), polyamide 6T (PA6T), polyamide 9T (PA9T), polyamide 11,12 (PA11,12), fluororesin, polyphthalamide (PPA)

  Referring to FIGS. 7 and 8, the angle formed by the column part 5a, that is, the window angle θ will be described. The lower limit window angle θmin is 55 ° (FIG. 7), and the upper limit window angle θmax is 80 ° (FIG. 8). The window angle is at most about 50 ° for a typical tapered roller bearing with retainer (FIG. 22) where the retainer is spaced from the outer ring. The reason why the lower limit window angle θmin is set to 55 ° is to ensure a good contact state with the roller, and when the window angle is less than 55 °, the contact state with the roller is deteriorated. That is, when the window angle is 55 ° or more, the cage strength is secured and γ> 0.94 and a good contact state can be secured. Further, the upper limit window angle θmax is set to 80 ° because if it is larger than this, the pressing force in the radial direction increases, and there is a risk that smooth rotation cannot be obtained even with a self-lubricating resin material. It is.

  FIG. 9 shows the result of the bearing life test. In the same figure, “Comparative Example 1” in the “Bearing” column is a typical conventional tapered roller bearing (FIG. 22) in which the cage and the outer ring are separated, and “Comparative Example 2” is a tapered roller bearing of the present invention. A tapered roller bearing in which only the roller coefficient γ is γ> 0.94 with respect to the conventional product, “Example” has the roller coefficient γ> γ> 0.94, and the window angle is in the range of 55 ° to 80 °. This is a tapered roller bearing of the present invention. The test was conducted under severe lubrication and overload conditions. As is clear from the figure, “Comparative Example 2” has a lifetime that is at least twice that of “Comparative Example 1”. Further, the bearing of the “Example” has a roller coefficient of 0.96 which is the same as that of “Comparative Example 2”, but the life time is about five times or more that of “Comparative Example 2”. The dimensions of “Comparative Example 1”, “Comparative Example 2”, and “Example” are φ45 × φ81 × 16 (unit mm), and the number of rollers is 24 (“Comparative Example 1”) and 27 (“Comparative Example”). 2 ”,“ Example ”), and the oil film parameter Λ = 0.2.

In the modification shown in FIGS. 10 and 11, a protruding portion 5 b that is convex toward the raceway surface 3 a side of the outer ring 3 is formed on the outer diameter surface of the column portion 8 of the cage 5 that is integrally formed of engineering plastic. It is a thing. The rest is the same as the cage 5 described above. As shown in FIG. 11, the protruding portion 5b has a cross-sectional contour shape in the transverse direction of the column portion 8 forming an arc shape. The arc-shaped curvature radius R ₂ is smaller than the radius R ₁ of the raceway surface 3 a of the outer ring 3. This is so that good wedge oil film is formed between the raceway surface 3a of the protrusion 5b and the outer ring 3, preferably the radius of curvature R ₂ of the projecting portion 5b is of the raceway surface 3a of the outer ring 3 it may be formed in about 70% to 90% of the radius R _1. If it is less than 70%, the opening angle of the wedge-shaped oil film becomes too large, and the dynamic pressure decreases. If it exceeds 90%, the inlet angle of the wedge-shaped oil film becomes too small, and the dynamic pressure similarly decreases. Further, the lateral width W ₂ of the protruding portion 5b is desirably formed to be 50% or more of the lateral width W ₁ of the column portion 8 (W ₂ ≧ 0.5W ₁ ). This is because if it is less than 50%, it is impossible to ensure a sufficient height of the protrusion 5b for forming a good wedge-shaped oil film. Since the radius R ₁ of the raceway surface 3a of the outer ring 3 continuously changes from the large diameter side to the small diameter side, the curvature radius R ₂ of the projection portion 5b is correspondingly increased. It continuously changes from R ₂ to a small radius of curvature R ₂ of the small annular portion 6.

  Since the tapered roller bearing 1 of FIGS. 10 and 11 is configured as described above, when the bearing 1 rotates and the cage 5 starts to rotate, the space between the outer ring raceway surface and the protrusion 5b of the cage 5 is increased. A wedge-shaped oil film is formed. Since this wedge-shaped oil film generates a dynamic pressure substantially proportional to the rotational speed of the bearing 1, even if the pitch diameter (PCD) of the cage 5 is made larger than that of the conventional one and brought closer to the raceway surface 3 a of the outer ring 3, the bearing 1 Can be rotated without causing great wear or torque loss, and the number of rollers can be increased without difficulty.

FIG. 12 exemplifies the configuration of a vehicle differential that can use the tapered roller bearing described above. This differential is connected to a propeller shaft (not shown), and a drive pinion 22 inserted into the differential case 21 meshes with a ringing gear 24 attached to the differential gear case 23, and a pinion gear 25 attached to the inside of the differential gear case 23. However, the driving force of the engine is transmitted from the propeller shaft to the left and right drive shafts by meshing with a side gear 26 that couples a drive shaft (not shown) inserted into the differential gear case 23 from the left and right. In this differential, a drive pinion 22 that is a power transmission shaft and a differential gear case 23 are supported by a pair of tapered roller bearings 1a and 1b, respectively.

  The differential case 21 is sealed with seal members 27a, 27b, and 27c, and the lubricating oil is stored inside. Each tapered roller bearing 1a, 1b rotates with its lower part immersed in this lubricating oil bath. When each tapered roller bearing 1a, 1b rotates at high speed and its lower part is immersed in an oil bath, the lubricating oil in the oil bath is drawn from the small diameter side of the tapered roller 4 to the outer diameter of the cage 5 as shown by arrows in FIG. The lubricating oil that flows into the bearing divided into the inner diameter side and the inner diameter side and flows into the outer ring 3 from the outer diameter side of the cage 5 passes along the raceway surface 3 a of the outer ring 3 to the larger diameter side of the tapered roller 4. Out of the bearing. On the other hand, the lubricating oil flowing from the inner diameter side of the cage 5 to the inner ring 2 side is far less than the lubricating oil flowing from the outer diameter side of the cage 5, and most of the lubricating oil flowing from this clearance δ is Then, it passes through the notch 10 a provided in the column portion 8 on the narrow side of the pocket 9 and moves to the outer diameter side of the cage 5. Therefore, the amount of the lubricating oil that reaches the large collar 2c along the raceway surface 2a of the inner ring 2 becomes very small, and the amount of the lubricating oil staying inside the bearing can be reduced.

  FIG. 13 exemplifies a configuration of an automobile transmission that can use the tapered roller bearing described above. This transmission is of a synchronous mesh type, and the left side of the figure is the engine side and the right side is the drive wheel side. A tapered roller bearing 43 is disposed between the main shaft 41 and the main drive gear 42. In this example, the outer ring raceway surface of the tapered roller bearing 43 is formed directly on the inner periphery of the main drive gear 42. The main drive gear 42 is rotatably supported with respect to the casing 45 by a tapered roller bearing 44. A clutch gear 46 is connected to the main drive gear 42, and a synchronization mechanism 47 is disposed in the vicinity of the clutch gear 46.

  The synchronizer 47 includes a sleeve 48 that moves in the axial direction (left and right in the figure) by the operation of a selector (not shown), a synchronizer key 49 that is mounted on the inner periphery of the sleeve 48 so as to be axially movable, and a main shaft. The hub 50 fitted to the outer periphery of the 41, the synchronizer ring 51 slidably mounted on the outer periphery (cone portion) of the clutch gear 46, and the synchronizer key 49 are elastically pressed against the inner periphery of the sleeve 48. A holding pin 52 and a spring 53 are provided.

  In the state shown in the figure, the sleeve 48 and the synchronizer key 49 are held in the neutral position by the pressing pin 52. At this time, the main drive gear 42 idles with respect to the main shaft 41. On the other hand, when the sleeve 48 is moved to the left side in the axial direction, for example, by the operation of the selector, the synchronizer key 49 is moved to the left side in the axial direction following the sleeve 48 and the synchronizer ring 51 is moved to the clutch gear 46. Press against the inclined surface of the cone. As a result, the rotational speed of the clutch gear 46 decreases, and conversely, the rotational speed on the synchro mechanism 47 side is increased. When the rotational speeds of the two are synchronized, the sleeve 48 further moves to the left in the axial direction, engages with the clutch gear 46, and the main shaft 41 and the main drive gear 42 are connected via the sync mechanism 47. . Thereby, the main shaft 41 and the main drive gear 42 rotate synchronously.

  At least one bearing component of the inner ring 2, outer ring 3 and rolling element 4 of the tapered roller bearing 1 described above has a nitrogen-enriched layer. A heat treatment including a carbonitriding process will be described as a specific example of the process for forming the nitrogen-enriched layer.

  FIG. 14 is a diagram for explaining a heat treatment method for a rolling bearing according to the embodiment of the present invention, and FIG. 15 is a diagram for explaining a modification thereof. FIG. 14 is a heat treatment pattern showing a method of performing primary quenching and secondary quenching, and FIG. 15 shows a method of cooling the material to below the A1 transformation point temperature during quenching, and then reheating and finally quenching. It is a heat treatment pattern. In these figures, in the treatment T1, the carbon is sufficiently melted while diffusing carbon and nitrogen in the steel substrate, and then cooled to less than the A1 transformation point. Next, in the process T2 in the figure, it is reheated to a temperature equal to or higher than the A1 transformation point temperature and lower than the process T1, and oil quenching is performed from there.

  By the above heat treatment, the crack strength can be improved and the aging rate of dimensional change can be reduced while carbonitriding the surface layer portion as compared with conventional carbonitriding and quenching, that is, carbonitriding as it is, followed by quenching as it is. The rolling bearing of the present invention manufactured by the heat treatment pattern shown in FIG. 14 or FIG. 15 has a microstructure in which the grain size of austenite crystal grains is less than half that of the prior art. The bearing component subjected to the above heat treatment has a long life against rolling fatigue, can improve the cracking strength, and can also reduce the rate of dimensional change over time. Since a heat treatment step for lowering the secondary quenching temperature is performed to refine the crystal grains, the amount of retained austenite is reduced in the surface layer and inside, and as a result, excellent crack strength and aging resistance can be obtained.

  FIG. 16 is a diagram showing the microstructure of bearing parts, particularly austenite grains. FIG. 16A shows a bearing component of the present invention example, and FIG. 16B shows a conventional bearing component. That is, FIG. 16A shows the austenite grain size of the bearing ring of the rolling bearing according to the embodiment of the present invention to which the heat treatment pattern shown in FIG. 14 is applied. For comparison, FIG. 16B shows the austenite grain size of the bearing steel obtained by the conventional heat treatment method. FIGS. 17A and 17B show austenite grain sizes illustrating the above FIGS. 16A and 16B. From the structure showing the austenite crystal grain size, the conventional austenite grain size is No. 10 in the JIS standard grain size number, and according to the heat treatment method according to FIG. 14 or FIG. 15, No. 12 fine grains can be obtained. The average particle diameter in FIG. 16 (A) was 5.6 μm as a result of measurement by the intercept method.

Next, examples of the present invention will be described.
Example 1
Using JIS standard SUJ2 material (1.0 wt% C-0.25 wt% Si-0.4 wt% Mn-1.5 wt% Cr), (1) measurement of hydrogen content, (2) crystal grain size (3) Charpy impact test, (4) measurement of fracture stress value, and (5) rolling fatigue test. Table 1 shows the results.

The manufacturing history of each sample is as follows.
Samples A to D (examples of the present invention): carbonitriding 850 ° C., holding time 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. In the heat treatment pattern shown in FIG. 14, primary quenching was performed from a carbonitriding temperature of 850 ° C., followed by secondary quenching by heating to a temperature range of 780 ° C. to 830 ° C. lower than the carbonitriding temperature. However, Sample A having a secondary quenching temperature of 780 ° C. was excluded from the test because of insufficient quenching.
Samples E and F (comparative examples): The carbonitriding process was performed with the same history as that of Examples A to D of the present invention, and the secondary quenching temperature was 850 ° C to 870 ° C which is a carbonitriding temperature of 850 ° C or higher.
Conventional carbonitrided product (comparative example): carbonitrided at 850 ° C., holding time of 150 minutes. The atmosphere was a mixed gas of RX gas and ammonia gas. Quenching was performed directly from the carbonitriding temperature, and secondary quenching was not performed.
Normal hardened product (comparative example): without quenching and carbonitriding, it was heated to 850 ° C. and quenched. Secondary quenching was not performed.

Next, the test method will be described.
(1) Measurement of hydrogen amount The amount of hydrogen was determined by analyzing the amount of non-diffusible hydrogen in the steel using a DH-103 type hydrogen analyzer manufactured by LECO. The amount of diffusible hydrogen is not measured. The specifications of the LECO DH-103 hydrogen analyzer are as follows.
Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: Thermal conductivity method Sample weight size: 10 mg to 35 mg (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone Mg (ClO ₄ ) ₂ , Ascarite NaOH
Carrier gas: Nitrogen gas, Gas dosing gas: Hydrogen gas, all gases have a purity of 99.99% or more, pressure 40 psi (2.8 kgf / cm ² )

  The outline of the measurement procedure is as follows. A sample collected with a dedicated sampler is inserted into the hydrogen analyzer together with the sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this example. Next, a sample is taken out from the sampler, heated in a resistance heating furnace, and non-diffusible hydrogen is guided to a thermal conductivity detector by nitrogen carrier gas. The amount of non-diffusible hydrogen can be known by measuring the thermal conductivity with a thermal conductivity detector.

(2) Measurement of crystal grain size The crystal grain size was measured based on the JIS G 0551 steel austenite grain size test method.

(3) Charpy impact test The Charpy impact test was performed based on the Charpy impact test method of the metal material of JISZ2242. As a test piece, a U-notch test piece (JIS No. 3 test piece) shown in JIS Z 2202 was used.

(4) Measurement of Fracture Stress Value FIG. 18 is a diagram showing a test piece for a static crush strength test (measurement of a fracture stress value). The load until it is broken by applying a load in the P direction in the figure is measured. Thereafter, the obtained fracture load is converted into a stress value by the following stress calculation formula of the curved beam. In addition, a test piece is not restricted to the test piece shown in FIG. 18, You may use the test piece of another shape.

Assuming that the fiber stress on the convex surface of the test piece in FIG. 18 is σ ₁ and the fiber stress on the concave surface is σ ₂ , σ ₁ and σ ₂ are obtained by the following formulas (Mechanical Engineering Handbook A4 Knitting Material Dynamics A4-40) . Here, N is the axial force of the cross section including the axis of the annular specimen, A is the cross-sectional area, e ₁ is the outer radius, and e ₂ is the inner radius. Further, κ is a section modulus of the curved beam.
σ ₁ = (N / A) + {M / (Aρ ₀ )} [1 + e ₁ / {κ (ρ ₀ + e ₁ )}]
σ ₂ = (N / A) + {M / (Aρ ₀ )} [1-e ₂ / {κ (ρ ₀ −e ₂ )}]
κ = − (1 / A) ∫A {η / (ρ ₀ + η)} dA

(5) Rolling fatigue life Table 2 shows the test conditions for the rolling fatigue life test. 19 is a schematic view of a rolling fatigue life tester, FIG. 19A is a front view, and FIG. 19B is a side view. In FIG. 19A and FIG. 19B, the rolling fatigue life test piece 18 is driven by the drive roll 12 and rotates in contact with the ball 16. The ball 16 is a 3/4 inch ball and rolls while being applied to the rolling fatigue life test piece 18 by being guided by the guide roll 14 while exerting a high surface pressure.

The test results of Example I shown in Table 1 will be described as follows.
-Hydrogen content Conventional carbonitrided products that have been carbonitrided have a very high value of 0.72 ppm. This is thought to be because ammonia (NH ₃ ) contained in the atmosphere of carbonitriding decomposed and hydrogen entered the steel. On the other hand, in Samples B to D, the hydrogen content is reduced to almost half of 0.37 to 0.40 ppm. This amount of hydrogen is at the same level as that of ordinary hardened products.

・ Grain size When the secondary quenching temperature is lower than the quenching (primary quenching) temperature during carbonitriding, that is, in the case of Samples B to D, the austenite grains are remarkably fine with grain size numbers 11 to 12. It has become. The austenite grains of the samples E and F, the conventional carbonitrided product and the normal quenching product have a crystal grain size number 10, and are coarser than the samples B to D of the examples of the present invention.

-Charpy impact test According to Table 1, the Charpy impact value of the conventional carbonitrided product is 5.33 J / cm ² , whereas the Charpy impact values of the samples B to D of the examples of the present invention are 6.30 to A high value of 6.65 J / cm ² is obtained. Among these, the one where secondary quenching temperature is low shows the tendency for a Charpy impact value to become high. The normally hardened product has a high Charpy impact value of 6.70 J / cm ² .

(4) Measurement of fracture stress value The fracture stress value corresponds to the crack resistance strength. According to Table 1, the conventional carbonitrided product has a fracture stress value of 2330 MPa. Compared to this, the fracture stress values of Samples B to D were improved to 2650 to 2840 MPa. The fracture stress value of the normal quenching product is 2770 MPa, and the improved cracking resistance strength of Samples B to D is estimated to have a great effect by reducing the hydrogen content, along with the refinement of austenite crystal grains.

(5) According to the rolling contact fatigue test Table 1, normally hardened product to reflect to have no carbonitrided layer in the surface layer portion, the rolling fatigue life L ₁₀ is the lowest. Compared to this, the rolling fatigue life of the conventional carbonitrided product is 3.1 times. The rolling fatigue life of Samples B to D is significantly improved as compared with the conventional carbonitrided product. Samples E and F are almost equivalent to conventional carbonitrided products.

  In summary, Samples B to D of the present invention have a reduced hydrogen content, an austenite crystal grain size of 11 or more, and improved Charpy impact value, crack resistance strength and rolling fatigue life. .

Example II
Next, Example II will be described. A series of tests were performed on the following X material, Y material, and Z material. JIS standard SUJ2 material (1.0% by weight C-0.25% by weight Si-0.4% by weight Mn-1.5% by weight Cr) is used for the heat treatment material. did. The manufacturing history of the X material to the Z material is as follows.
X material (comparative example): Normal quenching only (not carbonitriding)
Y material (comparative example): quenching directly after carbonitriding (conventional carbonitriding quenching). Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas.
Z material (example of the present invention): bearing steel subjected to the heat treatment pattern of FIG. Carbonitriding temperature 845 ° C, holding time 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. The final quenching temperature was 800 ° C.

(1) Rolling fatigue life Test conditions and test equipment for rolling fatigue life are as shown in Table 2 and FIG. 19, as described above. The results of this rolling fatigue life test are shown in Table 3. According to Table 3, the Y material of the comparative example shows 3.1 times the L ₁₀ life of the X material that has been subjected only to normal quenching in the comparative example (the life that one of the 10 test pieces breaks). In addition, the effect of extending the life by carbonitriding is recognized. On the other hand, the Z material of the present invention example has a long life of 1.74 times that of the B material and 5.4 times that of the X material. The main reason for this improvement is thought to be the refinement of the microstructure.

(2) Charpy impact test The Charpy impact test was performed by the method according to the above-mentioned JISZ2242 using the U notch test piece. The test results are shown in Table 4. The Charpy impact value of the Y material (comparative example) subjected to carbonitriding was not higher than that of the normal quenching X material (comparative example), but the Z material obtained the same value as the X material.

(3) Test of Static Fracture Toughness Value FIG. 20 is a diagram showing a test piece of a static fracture toughness test. After introducing a pre-row about 1 mm into the notch portion of the test piece, a static load by three-point bending was applied to determine the breaking load P. The following formula (I) was used for calculation of the fracture toughness value (K1c value). The test results are shown in Table 5. Since the precrack depth is larger than the carbonitrided layer depth, there is no difference between the X material and the Y material of the comparative example. However, the Z material of the present invention example was able to obtain a value about 1.2 times that of the comparative example.
K1c = (PL√a / BW ² ) {5.8−9.2 (a / W) +
^{43.6 (a / W) 2 -75.3} (a / W) 3 +77.5 (a / W) 4} ...... (I)

(4) Static Crush Strength Test The static crush strength test used the shape shown in FIG. 20 as described above. In the figure, a static crushing strength test was performed by applying a load in the P direction. The test results are shown in Table 6. The Y material subjected to the carbonitriding process has a slightly lower value than the normal quenching X material. However, the Z material of the example of the present invention has a static crushing strength higher than that of the Y material, and a level comparable to that of the X material is obtained.

(5) Aged dimensional change rate The measurement results of the aged dimensional change rate at a holding temperature of 130 ° C. and a holding time of 500 hours are shown in Table 7 together with the surface hardness and the retained austenite amount (50 μm depth). It can be seen that the Z material of the example of the present invention is suppressed to half or less compared to the dimensional change rate of the Y material having a large amount of retained austenite.

(6) Rolling life test under the presence of foreign matter Using a ball bearing 6206, the rolling fatigue life under the presence of foreign matter mixed with a predetermined amount of standard foreign matter was evaluated. Table 8 shows the test conditions and Table 9 shows the test results. Compared to the X material, the Y material subjected to the conventional carbonitriding treatment is about 2.5 times longer, and the Z material of the present invention example has a long life of about 2.3 times. Although the Z material of the present invention example has a small amount of retained austenite as compared with the Y material of the comparative example, a substantially equivalent long life is obtained due to the intrusion of nitrogen and the influence of the refined microstructure.

  From the above results, the Z material, that is, the present invention example, simultaneously satisfies the three items of the rolling fatigue life extension, crack strength improvement, and reduction of aging dimensional change rate, which were difficult in the conventional carbonitriding process. I found out that I could do it.

Example III
Table 10 shows the results of tests conducted on the relationship between the nitrogen content and the rolling life under the contamination condition. Comparative Example 1 is a standard quenched product, and Comparative Example 2 is a standard carbonitrided product. Comparative Example 3 is a case where only the amount of nitrogen was excessive although the same treatment as that of the inventive example was performed. The test conditions are as follows.
Test bearing: Tapered roller bearing 30206 (both inner and outer rings and rollers are made of JIS high carbon chrome bearing steel class 2 (SUJ2))
Radial load: 17.64kN
Axial load: 1.47kN
Rotation speed: 2000rpm
1g / L of hard foreign matter

  From Table 10, regarding Examples 1 to 5, it can be seen that the nitrogen content and the foreign substance lifetime are in a substantially proportional relationship. However, in Comparative Example 3 where the nitrogen content is 0.72, the upper limit of the nitrogen content is preferably 0.7 in light of the fact that the rolling life under the mixing of foreign matters is extremely reduced.

  The embodiments disclosed herein are illustrative in all aspects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

(A) is a cross-sectional view of a tapered roller bearing showing an embodiment of the present invention (B) is a vertical cross-sectional view of the bearing Fig. 1 is a developed plan view of a cage in the tapered roller bearing of Fig. 1. An expanded plan view similar to FIG. 2 showing a modified example of the cage Fig. 2 is a developed plan view similar to Fig. 2 showing another modified example of the cage. Partial enlarged view of FIG. Graph showing results of torque measurement test Partial enlarged sectional view of tapered roller bearing with lower window angle Partial enlarged sectional view of a tapered roller bearing with an upper window angle Diagram showing results of bearing life test Partial cross-sectional view of tapered roller bearing showing modified examples of cage Partial enlarged view of FIG. Cross section of a typical automobile transmission Cross section of a typical automobile differential Diagram explaining heat treatment method for tapered roller bearing Diagram showing a variation of the heat treatment method for tapered roller bearings (A) is a microstructure of the bearing part of the present invention example, especially a structure diagram showing austenite grain boundaries (B) is a microstructure of a conventional bearing part, particularly a structure diagram showing austenite grain boundaries. (A) is a structure diagram illustrating an austenite grain boundary illustrated in FIG. 16 (A). (B) is a structure diagram illustrating an austenite grain boundary illustrated in FIG. 16 (B). Diagram showing test piece for static crushing strength test (measurement of fracture stress value) (A) is a schematic view of a rolling fatigue life tester. (B) is a side view of a rolling fatigue life tester. Diagram showing test piece for static fracture toughness test (A) is a development plan view of a cage showing a conventional technique (B) is a development plan view of a cage showing a conventional technique Partial enlarged cross-sectional view of a tapered roller bearing showing conventional technology Diagram showing changes in stiffness ratio (-●-) and torque ratio (-○-) when changing the roller pitch diameter (PCD) in tapered roller bearings

Explanation of symbols

1, 1a, 1b Tapered roller bearing 2 Inner ring 2a Raceway surface 2b Small brim 2c Large brim 3 Outer ring 3a Raceway surface 4 Tapered roller 5 Cage 6 Small ring part 7 Large ring part 8 Column part 9 Pocket 10a, 10b, 10c Notch 11 collar

Claims (1)

An inner ring, an outer ring, a plurality of tapered rollers arranged to roll between the inner ring and the outer ring, and a cage that holds the tapered rollers at a predetermined circumferential interval,
Roller coefficient γ exceeds 0.94,
At least one member of the inner ring, the outer ring and the rolling element has a nitrogen-enriched layer, and the austenite grain size number in the nitrogen-enriched layer is in a range exceeding 10;
The retainer is composed of a small annular portion that is continuous on the small end face side of the tapered roller, a large annular portion that is continuous on the large end face side of the tapered roller, and a plurality of pillar portions that connect these annular portions, and adjacent pillar portions. A trapezoidal pocket is formed in which the portion that stores the small diameter side of the tapered roller is the narrow side and the portion that stores the large diameter side is the wide side, and the column portion on the narrow side of the pocket and the small ring A tapered roller bearing in which a notch is provided in the central part of the part to quickly release the lubricating oil flowing between the cage and the inner ring to the outer ring side .

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