JP2018165566A - Tapered-roller bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conical roller bearing capable of achieving both stabilization of rotational torque and seizure resistance and having durability in a high misalignment environment. An arithmetic average roughness Ra of a large flange surface 18 of an inner ring 13 is 0.1 μm or more and 0.2 μm or less. The distance from the outermost surface of at least one of the outer ring 11, the inner ring 13 and the plurality of rollers 12 of the rollers 12 to the bottom of the nitrogen-enriched layer is 0.2 mm or more. Crowning is formed on the rolling surface 12A of the roller 12. The sum of the dropping amounts of crowning is expressed by the following equation (1). [Selection diagram] FIG. 9

Description

  The present invention relates to a tapered roller bearing.

  In recent years, efforts have been made to reduce the size of bearings in transmissions and differentials for automobiles in accordance with efforts to reduce fuel consumption. Along with this, the space allowed for the bearing is reduced, and it is necessary to receive a high load with a small bearing. Furthermore, the use of an aluminum housing reduces the rigidity of the case included in the bearing and increases the shaft inclination. Therefore, the bearing is required to be durable even in a high misalignment environment. Due to the above background, there are an increasing number of cases in which tapered roller bearings that are small bearings and can receive a large load including misalignment are used.

  As a part of such fuel saving, for example, in bearing parts disclosed in Japanese Patent Application Laid-Open No. 2009-197904 (Patent Document 1), it is proposed to obtain a crowning contour line represented by a logarithmic function. . Further, for example, in Japanese Patent Application Laid-Open No. 2003-226918 (Patent Document 2), a nitride layer refined by a special heat treatment called FA treatment (crystal grain refinement strengthening treatment) is included in order to extend the life. A bearing component having a different configuration is disclosed.

JP 2009-197904 A JP 2003-226918 A

  However, a configuration having both a contour line of a crowning expressed by a logarithmic function and a nitrided layer refined by FA processing has not been proposed so far, and thus it cannot be said that the contribution to the fuel saving of an automobile is sufficient. It was.

  Further, it is desirable for the tapered roller bearing to stabilize the rotational torque within the range of the rotational speed under the condition for rotating the outer ring or the inner ring at a low speed. Furthermore, it is desirable that the tapered roller bearing be improved in seizure resistance because there is a possibility that the outer ring or the inner ring may seize due to the temperature rise during rotation. However, there has been no proposal for a technique that achieves both such stabilization of rotational torque and seizure resistance.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a tapered roller bearing that can achieve both rotational torque stabilization and seizure resistance and has durability even in a high misalignment environment.

The tapered roller bearing according to the present invention includes an outer ring, an inner ring, and a plurality of tapered rollers. The outer ring has an outer ring raceway surface on the inner peripheral surface. The inner ring has an inner ring raceway surface and a large collar surface disposed on the larger diameter side than the inner ring raceway surface on the outer peripheral surface, and is disposed radially inward with respect to the outer ring. The plurality of tapered rollers are arranged between the outer ring raceway surface and the inner ring raceway surface, and have rolling surfaces that contact the outer ring raceway surface and the inner ring raceway surface. The arithmetic mean roughness Ra of the large surface is 0.1 μm or more and 0.2 μm or less. At least one of the outer ring, the inner ring, and the plurality of tapered rollers includes a nitrogen-enriched layer formed on a surface layer of the outer ring raceway surface, the inner ring raceway surface, or the rolling surface. The distance from the outermost surface of the surface layer to the bottom of the nitrogen-enriched layer is 0.2 mm or more. Crowning is formed on the rolling surface of the tapered roller. The sum of the crowning drop amounts is defined as follows. In the yz coordinate system in which the generatrix of the rolling surface of the tapered roller is the y-axis and the direction orthogonal to the generatrix is the z-axis, K ₁ , K ₂ , and z _m are design parameters, and Q is Load, L is the length in the direction of the generatrix of the effective contact portion of the rolling surface of the tapered roller, E 'is the equivalent elastic modulus, and a is the origin on the generatrix of the rolling surface of the tapered roller to the end of the effective contact portion When A = 2K ₁ Q / πLE ′, the length is expressed by Expression (1).

  According to the present invention, it is possible to provide a tapered roller bearing that can achieve both stabilization of rotational torque and seizure resistance and has durability even in a high misalignment environment.

It is a schematic sectional drawing which shows the rough structure of the tapered roller bearing which concerns on this Embodiment. It is an expanded sectional view of the principal part of the tapered roller bearing shown in FIG. It is a partial cross section schematic diagram of the tapered roller of the tapered roller bearing shown in FIG. FIG. 4 is an enlarged partial cross-sectional schematic view of the tapered roller shown in FIG. 3. It is a yz coordinate diagram which shows an example of a crowning shape. It is the schematic diagram which illustrated the microstructure of bearing components, especially a prior austenite grain boundary. It is a figure which shows the roller which provided the crowning by which a contour line is represented by a logarithmic function. It is the figure which showed the contour line of the roller which provided the crowning of the partial arc, and the straight part, and the contact surface pressure in the rolling surface of a roller. FIG. 2 is a schematic cross-sectional view shown in more detail than FIG. 1 in order to define a large collar surface and a small collar surface of the tapered roller bearing of the present embodiment. It is an expanded sectional view of the principal part of FIG. It is a roughness curve which shows the skewness Rsk of the large collar surface of this Embodiment. It is a roughness curve which shows the kurtosis Rku of the large ridge surface of this Embodiment. FIG. 2 is a schematic cross-sectional view shown in more detail than FIG. 1 in order to define large ridges, small ridges and relief portions of the tapered roller bearing of the present embodiment. It is a figure which shows the crowning shape of the tapered roller bearing of FIG. It is a figure showing the relationship between the bus-line direction coordinate and drop amount of the tapered roller of FIG. It is a figure which shows the relationship between the maximum value of the equivalent stress of Mises, and a logarithmic crowning parameter. It is a figure which shows the crowning shape of the tapered roller contained in the tapered roller bearing which concerns on the 1st modification with respect to FIG. It is a figure which shows the crowning shape of the tapered roller contained in the tapered roller bearing which concerns on the 2nd modification with respect to FIG. It is a flowchart for demonstrating the manufacturing method of a tapered roller bearing. It is a schematic diagram which shows the heat processing pattern in the heat processing process of FIG. It is a schematic diagram which shows the modification of the heat processing pattern shown in FIG. It is the model which illustrated the microstructure of the bearing components as a comparative example, especially the prior austenite grain boundary. It is a graph which shows the result of the rotational torque test with respect to the tapered roller bearing of this Embodiment. It is a longitudinal cross-sectional view of the differential in which the gear-shaft support apparatus containing the tapered roller bearing of this Embodiment was integrated. It is a longitudinal section showing a transmission provided with a tapered roller bearing concerning this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Hereinafter, the tapered roller bearing of the present embodiment will be described step by step with a focus on FIG. 1 and FIG. 9 described later. First, with reference to FIGS. 1 to 4, features of portions of the tapered roller bearing according to the present embodiment other than the features that appear for the first time in FIG.

  A tapered roller bearing 10 shown in FIG. 1 mainly includes an outer ring 11, an inner ring 13, rollers 12 as a plurality of tapered rollers, and a cage 14. The outer ring 11 has a ring shape and has a raceway surface 11A as an outer ring raceway surface on the inner peripheral surface. The inner ring 13 has an annular shape, and has a raceway surface 13A as an inner ring raceway surface on the outer peripheral surface. The inner ring 13 is disposed on the inner diameter side of the outer ring 11 so that the raceway surface 13A faces the raceway surface 11A. In the following description, the direction along the central axis of the tapered roller bearing 10 is “axial direction”, the direction orthogonal to the central axis is “radial direction”, and the direction along the arc centered on the central axis is “circumferential direction”. "

  The roller 12 is disposed on the inner peripheral surface of the outer ring 11. The roller 12 has a rolling surface 12A as a roller rolling surface, and contacts the raceway surface 13A and the raceway surface 11A on the rolling surface 12A. The plurality of rollers 12 are arranged at a predetermined pitch in the circumferential direction by a cage 14 made of synthetic resin. As a result, the roller 12 is rotatably held on the annular raceway of the outer ring 11 and the inner ring 13. The tapered roller bearing 10 includes a cone including the raceway surface 11A, a cone including the raceway surface 13A, and a cone including the locus of the rotation axis when the roller 12 rolls at one point on the center line of the bearing. It is configured to cross. With such a configuration, the outer ring 11 and the inner ring 13 of the tapered roller bearing 10 are rotatable relative to each other. The cage 14 is not limited to resin, but may be made of metal.

  The material constituting the outer ring 11, the inner ring 13, and the roller 12 may be steel. The steel is a portion other than the nitrogen-enriched layers 11B, 12B, and 13B, and at least carbon is 0.6 mass% to 1.2 mass%, silicon is 0.15 mass% to 1.1 mass%, manganese 0.3 mass% or more and 1.5 mass% or less. The steel may further contain 2.0% by mass or less of chromium.

  In the above configuration, if the carbon content exceeds 1.2% by mass, the material hardness is high even if spheroidizing annealing is performed, so that cold workability is hindered and sufficient cold work amount is obtained when performing cold work. The processing accuracy cannot be obtained. In addition, the carbonitriding process tends to become an excessively carburized structure, and there is a risk that the cracking strength is reduced. On the other hand, when the carbon content is less than 0.6% by mass, it takes a long time to secure the required surface hardness and the amount of retained austenite, or the necessary internal hardness is obtained by quenching after reheating. It becomes difficult to be.

  The reason why the Si content is 0.15 to 1.1% by mass is that Si increases resistance to tempering softening to ensure heat resistance, and can improve rolling fatigue life characteristics under lubrication mixed with foreign matter. It is. When the Si content is less than 0.15% by mass, the rolling fatigue life characteristics under lubrication with foreign matters are not improved. On the other hand, when the Si content exceeds 1.1% by mass, the hardness after normalization is too high. Impairs cold workability.

  Mn is effective for securing the quench hardening ability of the carbonitrided layer and the core. When the Mn content is less than 0.3% by mass, sufficient quenching and hardening ability cannot be obtained, and sufficient strength cannot be ensured in the core. On the other hand, if the Mn content exceeds 1.5% by mass, the curing ability becomes excessively high, the hardness after normalization becomes high, and the cold workability is hindered. In addition, the austenite is excessively stabilized and the amount of retained austenite in the core is excessively increased to promote a change in size over time. Further, when steel contains 2.0 mass% or less of chromium, chromium carbide and nitride are precipitated in the surface layer portion, and the hardness of the surface layer portion is easily improved. The Cr content is set to 2.0% by mass or less when the content exceeds 2.0% by mass, the cold workability is remarkably lowered, or even if the content exceeds 2.0% by mass, the hardness of the surface layer portion described above. This is because the improvement effect is small.

  Needless to say, the steel of the present disclosure may contain Fe as a main component and may contain inevitable impurities in addition to the above elements. Inevitable impurities include phosphorus (P), sulfur (S), nitrogen (N), oxygen (O), aluminum (Al), and the like. The amounts of these inevitable impurity elements are each 0.1% by mass or less.

  From a different point of view, the outer ring 11 and the inner ring 13 are preferably made of a steel material that is an example of a bearing material, for example, JIS standard SUJ2. The roller 12 may be made of a steel material that is an example of a bearing material, for example, JIS standard SUJ2. Moreover, the roller 12 may be comprised with other materials, for example, a sialon sintered compact.

  As shown in FIG. 2, nitrogen-enriched layers 11 </ b> B and 13 </ b> B are formed on the raceway surface 11 </ b> A of the outer ring 11 and the raceway surface 13 </ b> A of the inner ring 13. In the inner ring 13, the nitrogen-enriched layer 13 </ b> B extends from the raceway surface 13 </ b> A to the small surface and the large surface described later. The nitrogen-enriched layers 11B and 13B are regions where the nitrogen concentration is higher than the non-nitrided portion 11C of the outer ring 11 or the non-nitrided portion 13C of the inner ring 13, respectively. A nitrogen-enriched layer 12B is formed on the surface of the roller 12 including the rolling surface 12A. The nitrogen-enriched layer 12B of the roller 12 is a region where the nitrogen concentration is higher than that of the non-nitrided portion 12C of the roller 12. The nitrogen-enriched layers 11B, 12B, and 13B can be formed by any conventionally known method such as carbonitriding or nitriding.

  Note that the nitrogen-enriched layer 12B may be formed only on the roller 12, the nitrogen-enriched layer 11B may be formed only on the outer ring 11, or the nitrogen-enriched layer 13B may be formed only on the inner ring 13. Good. Alternatively, a nitrogen enriched layer may be formed on two of the outer ring 11, the inner ring 13, and the roller 12.

  As shown in FIG. 3, the rolling surface 12 </ b> A (see FIG. 2) of the roller 12 is positioned at both ends, and the crowning portions 22 and 24 where the crowning is formed, and the center connecting the crowning portions 22 and 24. Part 23. No crowning is formed in the central portion 23, and the shape of the central portion 23 in a cross section in the direction along the central line 26 that is the rotation axis of the roller 12 is linear. A chamfered portion 21 is formed between the small end surface 17 that is the left end surface of the roller 12 and the crowning portion 22. A chamfered portion 25 is also formed between the large end surface 16 which is the right end surface and the crowning portion 24.

  Here, in the manufacturing method of the roller 12, when performing the process (carbonitriding process) for forming the nitrogen-enriched layer 12B, no crowning is formed on the roller 12, and the outer shape of the roller 12 is a dotted line in FIG. It becomes the surface 12E before processing shown by these. After the nitrogen-enriched layer is formed in this state, as a finishing process, the side surface of the roller 12 is processed as indicated by the arrow in FIG. 4, and the crowning portion 22 in which the crowning is formed as shown in FIGS. , 24 is obtained.

  The depth of the nitrogen-enriched layer 12B in the roller 12, that is, the distance from the outermost surface of the nitrogen-enriched layer 12B to the bottom of the nitrogen-enriched layer 12B is 0.2 mm or more. Specifically, the first measurement point 31 that is a boundary point between the chamfered portion 21 and the crowning portion 22, the second measurement point 32 that is located at a distance W of 1.5 mm from the small end surface 17, and the rolling surface of the roller 12. At the third measurement point 33 that is the center of 12A, the depths T1, T2, and T3 of the nitrogen-enriched layer 12B at each position are 0.2 mm or more. Here, the depth of the nitrogen-enriched layer 12B means the thickness of the nitrogen-enriched layer 12B in the radial direction perpendicular to the center line 26 of the roller 12 and toward the outer peripheral side. The values of the depths T1, T2, and T3 of the nitrogen-enriched layer 12B depend on the process conditions such as the shape and size of the chamfered portions 21 and 25, the process of forming the nitrogen-enriched layer 12B, and the finishing process described above. It can be changed as appropriate. For example, in the configuration example shown in FIG. 4, the crowning 22A is formed after the nitrogen-enriched layer 12B is formed as described above. Therefore, as shown in FIG. 4, the depth T2 of the nitrogen-enriched layer 12B is smaller than the other depths T1 and T3. However, by changing the process conditions described above, the magnitude relationship between the values of the depths T1, T2, and T3 of the nitrogen-enriched layer 12B can be changed as appropriate.

  Further, regarding the nitrogen-enriched layers 11B and 13B in the outer ring 11 and the inner ring 13, the thickness of the nitrogen-enriched layers 11B and 13B, which is the distance from the outermost surface to the bottom of the nitrogen-enriched layers 11B and 13B, is 0.2 mm. That's it. Here, the thickness of the nitrogen-enriched layers 11B and 13B means the distance to the nitrogen-enriched layers 11B and 13B in the direction perpendicular to the outermost surface of the nitrogen-enriched layers 11B and 13B.

The shape of the crowning formed on the crowning portions 22, 24 of the roller 12 is defined as follows. That is, the sum of the amount of drop of crowning is K ₁ , K ₂ , z _m in the yz coordinate system in which the generatrix of the rolling surface 12A of the roller 12 is the y-axis and the direction orthogonal to the generatrix is the z-axis. , Q is the load, L is the length in the generatrix direction of the effective contact portion of the rolling contact surface 12A of the roller 12, E 'is the equivalent elastic modulus, and a is the effective contact portion from the origin on the generatrix of the rolling contact surface of the roller 12. When the length to the end of A is A = 2K ₁ Q / πLE ′, it is expressed by the following formula (1).

  In FIG. 5, the bus 12 has a y-axis, and the origin O is located at the center of the effective contact portion of the inner ring 13 or the outer ring 11 on the bus 12 and in the direction perpendicular to the bus (radial direction). An example of the crowning represented by the above formula (1) is shown in the yz coordinate system taking the z axis. In FIG. 5, the vertical axis is the z-axis and the horizontal axis is the y-axis. The effective contact portion is a contact portion with the inner ring 13 or the outer ring 11 when the crown 12 is not formed on the roller 12. Further, each crowning of the plurality of rollers 12 constituting the tapered roller bearing 10 is normally formed line-symmetrically with respect to the z axis passing through the central portion of the effective contact portion, and therefore only one crowning 22A is shown in FIG. ing.

  The load Q, the length L in the generatrix direction of the effective contact portion, and the equivalent elastic modulus E ′ are given as design conditions, and the length a from the origin to the end of the effective contact portion is a value determined by the position of the origin. It is.

In the above formula (1), z (y) indicates the drop amount of the crowning 22A at the position y in the generatrix direction of the roller 12, and the coordinates of the starting point O1 of the crowning 22A are (a−K ₂ a, 0). Therefore, the range of y in the formula (1) is y> (a−K ₂ a). In FIG. 5, since the origin O is located at the center of the effective contact portion, a = L / 2. Further, since the region from the origin O to the starting point O1 of the crowning 22A is the central portion (straight portion) where the crowning is not formed, when 0 ≦ y ≦ (a−K ₂ a), z (y) = 0.

Magnification design parameters K ₁ is a load Q, the geometric means the degree of curvature of the crowning 22A. Design parameters K _2, which means the ratio of the generatrix direction length ym of the crowning 22A against generatrix direction length a from the origin O to the end of the effective contact portions _{(K 2 = ym / a)} . The design parameter z _m means the drop amount at the end of the effective contact portion, that is, the maximum drop amount of the crowning 22A.

Here, the crowning of the roller shown in FIG. 7 to be described later is a full crowning having a design parameter K ₂ = 1 and no straight portion, and a sufficient drop amount that does not cause an edge load is secured. However, if the drop amount is excessive, the machining allowance generated from the material that has been removed during processing increases, leading to an increase in cost. Therefore, optimization of the design parameters K ₁ , K ₂ , and z _m in Expression (1) is performed as follows.

Various optimization methods for the design parameters K ₁ , K ₂ , and z _m can be adopted. For example, a direct search method such as Rosenblock method can be adopted. Here, since the damage at the rolling origin of the roller depends on the surface pressure, the crowning that prevents oil film breakage on the contact surface under dilute lubrication can be obtained by using the surface pressure as the optimization objective function. Can do.

In addition, when logarithmic crowning is applied to the rollers, it is preferable to provide a straight portion (center portion 23) at the center portion of the rolling surface in order to ensure the processing accuracy of the rollers. In this case, K ₂ may be a constant value, and K ₁ and z _m may be optimized.

  FIG. 6 shows the microstructure in the nitrogen-enriched layer 12B. The prior austenite crystal grain size in the nitrogen-enriched layer 12B in the present embodiment has a JIS standard grain size number of 10 or more, and is sufficiently refined as compared with a conventional general quenched product.

  Here, a method for measuring the nitrogen concentration will be described. About bearing parts, such as the outer ring | wheel 11, the roller 12, and the inner ring | wheel 13, about the cross section perpendicular | vertical to the surface of the area | region in which the nitrogen enriched layers 11B, 12B, and 13B were formed, respectively, it was lined by EPMA (Electron Probe Micro Analysis) in the depth direction. Perform analysis. In the measurement, each bearing part is cut from the measurement position in a direction perpendicular to the surface to expose the cut surface, and the measurement is performed on the cut surface. For example, with regard to the roller 12, the cut surface is exposed by cutting the roller 12 in a direction perpendicular to the center line 26 from the positions of the first measurement point 31 to the third measurement point 33 shown in FIG. On the cut surface, the nitrogen concentration is analyzed by the EPMA at a plurality of measurement positions that are 0.05 mm from the surface of the roller 12 toward the inside. For example, five measurement positions are determined, and the average value of the measurement data at the five positions is used as the nitrogen concentration of the roller 12.

  Further, for the outer ring 11 and the inner ring 13, after exposing the cross section along the radial direction perpendicular to the central axis and the central axis in the raceway surfaces 11A and 13A with the central portion in the central axis direction of the bearing as the measurement position, The nitrogen concentration is measured for the cross section by the same method as described above.

Method for measuring the distance from the outermost surface to the bottom of the nitrogen-enriched layer:
About the outer ring | wheel 11 and the inner ring | wheel 13, hardness distribution is measured in the depth direction from the surface about the cross section made into the measuring object in the measuring method of the said nitrogen concentration. A Vickers hardness measuring machine can be used as the measuring device. In the tapered roller bearing 10 after tempering at 500 ° C. × 1 h, hardness measurement is performed at a plurality of measurement points arranged in the depth direction, for example, measurement points arranged at intervals of 0.5 mm. And let the area | region whose Vickers hardness is HV450 or more be a nitrogen rich layer.

  For the roller 12, in the cross section at the first measurement point 31 shown in FIG. 3, the hardness distribution in the depth direction is measured as described above to determine the region of the nitrogen-enriched layer.

  As a method for measuring the prior austenite crystal grain size, a method defined in JIS standard G0551: 2013 is used. The cross section to be measured is the cross section measured by the method for measuring the distance to the bottom of the nitrogen-enriched layer. Thereby, the particle size number of the prior austenite crystal can be measured.

  The crowning shape of the roller 12 can be measured by any method. For example, the crowning shape may be measured by measuring the shape of the roller 12 with a surface texture measuring machine.

  As described above, the nitrogen-enriched layers 11B, 12B, and 13B in which the prior austenite crystal grain size is sufficiently refined are formed in at least one of the outer ring 11, the inner ring 13, and the roller 12 as the tapered roller. Therefore, it is possible to improve the Charpy impact value, the fracture toughness value, the crushing strength and the like while having a high rolling fatigue life.

  Further, since the rolling surface 12A of the roller 12 is provided with a crowning (so-called logarithmic crowning) in which the contour line is represented by a logarithmic function such that the sum of the drop amounts is represented by the above formula (1), A local increase in surface pressure can be suppressed as compared with the case where the crowning represented by the partial arc is formed, and the occurrence of wear on the rolling surface 12A of the roller 12 can be suppressed.

  Here, the effect of the logarithmic crowning described above will be described in more detail. FIG. 7 is a diagram in which the contour line of the roller provided with the crowning whose contour line is represented by a logarithmic function and the contact surface pressure on the rolling surface of the roller are overlapped. FIG. 8 is a diagram in which the contour line of the roller having an auxiliary arc between the crowning of the partial arc and the straight portion and the contact surface pressure on the rolling surface of the roller are overlapped. The vertical axis on the left side of FIGS. 7 and 8 shows the amount of crowning drop (unit: mm). The horizontal axis of FIG. 7 and FIG. 8 has shown the position (unit: mm) in the axial direction in a roller. The vertical axis on the right side of FIGS. 7 and 8 represents the contact surface pressure (unit: GPa).

  When the contour line of the rolling surface of the tapered roller is formed in a shape having a crown of a partial arc and a straight part, the gradient at the boundary between the straight part, the auxiliary arc and the crowning is continuous as shown in FIG. However, if the curvature is discontinuous, the contact surface pressure locally increases. As a result, the oil film may be cut or the surface may be damaged. If a lubricating film having a sufficient thickness is not formed, wear due to metal contact tends to occur. When wear occurs partially on the contact surface, metal contact is more likely to occur in the vicinity of the contact surface, so that wear on the contact surface is promoted and the tapered roller is damaged.

  Therefore, when the crowning whose contour line is represented by a logarithmic function is provided on the rolling surface of the tapered roller as the contact surface, for example, as shown in FIG. 7, the crowning represented by the partial arc of FIG. 8 is provided. Compared to the case, the local surface pressure becomes lower, and the contact surface can be made less likely to be worn. Therefore, even when the lubricant film thickness is reduced by reducing the amount of lubricant present on the rolling surface of the tapered roller or by reducing the viscosity, wear of the contact surface is prevented and damage to the tapered roller is prevented. Can do. 7 and 8 show an orthogonal coordinate system in which the roller generatrix direction is the horizontal axis and the generatrix orthogonal direction is the vertical axis, and the origin O of the horizontal axis is at the center of the effective contact portion of the inner ring or the outer ring. Is set to indicate the contour line of the roller, and the contact pressure is shown with the contact pressure as the vertical axis. Thus, the tapered roller bearing 10 which shows a long lifetime and high durability is realizable by employ | adopting the above structures.

  In the tapered roller bearing 10, the nitrogen concentration in the nitrogen-enriched layers 11B, 12B, and 13B at a depth of 0.05 mm from the outermost surface is 0.1% by mass or more. In this case, since the nitrogen concentration on the outermost surface of the nitrogen-enriched layers 11B, 12B, and 13B can be a sufficient value, the hardness of the outermost surface of the nitrogen-enriched layers 11B, 12B, and 13B can be made sufficiently high. Moreover, it is preferable that the above conditions such as the grain size of the prior austenite grain size, the distance to the bottom of the nitrogen-enriched layer, and the nitrogen concentration are satisfied at least at the first measurement point 31 in FIG.

  In the tapered roller bearing 10, at least one of the outer ring 11, the inner ring 13, and the roller 12 on which the nitrogen-enriched layers 11B, 12B, and 13B are formed is made of steel. In the steel, in portions other than the nitrogen-enriched layers 11B, 12B, and 13B, that is, in the non-nitrided portions 11C, 12C, and 13C, at least carbon (C) is 0.6 mass% or more and 1.2 mass% or less, silicon (Si ) 0.15 mass% to 1.1 mass%, and manganese (Mn) 0.3 mass% to 1.5 mass%. In the tapered roller bearing 10, the steel may further contain 2.0% by mass or less of chromium. In this case, the nitrogen-enriched layers 11B, 12B, and 13B having the structure defined in the present embodiment can be easily formed by using a heat treatment described later.

In the tapered roller bearing 10, at least one of the design parameters K ₁ , K ₂ , and z _m in the above formula (1) has the contact surface pressure between the roller 12 and the outer ring 11 or the roller 12 and the inner ring 13 as an objective function. Optimized.

The design parameters K ₁ , K ₂ , and z _m are determined by optimizing any one of the contact surface pressure, stress, and life as an objective function, and the damage at the surface starting point depends on the contact surface pressure. Here, according to the above embodiment, the contact surface pressure is optimized as an objective function and the design parameters K ₁ , K ₂ , and z _m are set, so that the contact surface is prevented from being worn even in a condition where the lubricant is lean. A possible crowning is obtained.

  In the tapered roller bearing 10, at least one of the outer ring 11 and the inner ring 13 includes nitrogen-enriched layers 11B and 13B. In this case, the outer ring 11 or the inner ring 13 having a long life and high durability is obtained by forming the nitrogen-enriched layers 11B and 13B having a refined crystal structure in at least one of the outer ring 11 and the inner ring 13. be able to.

  In the tapered roller bearing 10, the roller 12 includes a nitrogen-enriched layer 12B. In this case, the roller 12 having the long life and high durability can be obtained by forming the nitrogen-enriched layer 12B having a refined crystal structure in the roller 12.

  FIG. 9 is illustrated as an aspect having characteristics closer to those of the present embodiment on the premise of the basic configuration of FIG. Referring to FIG. 9, the tapered roller bearing 10 of the present embodiment is provided with a large collar surface 18 on the large diameter side of the raceway surface 13A of the inner ring 13 and a small collar surface 19 on the small diameter side. A large end surface 16 that contacts the large collar surface 18 is provided on the large diameter side of the roller 12, and a small end surface 17 that contacts the small collar surface 19 is provided on the small diameter side of the roller 12.

  The large collar surface 18 is formed via the large-diameter side end portion of the raceway surface 13A and the ground relief portion. The large collar surface 18 guides the roller 12 by contacting the large end surface 16 of the roller 12 when the tapered roller bearing 10 is used. The small flange surface 19 is formed through the small-diameter side end portion of the raceway surface 13A and a ground thin portion.

  Further, as shown in FIG. 10 in an enlarged manner, the small flange surface 19 of the inner ring 13 is finished to a ground surface that is parallel to the small end surface 17 of the roller 12, and in an initial assembly state indicated by a one-dot chain line in the drawing, the roller 12. Are in surface contact with the small end face 17. The small end surface 17 has a gap with the small flange surface 19 of the roller 12. The roller 12 indicated by a solid line is in a state where it is settled in a proper position, that is, in a state where the large end surface 16 of the roller 12 is in contact with the large collar surface 18 of the inner ring 13. A gap δ with the small end surface 17 is within a dimension regulation range of δ ≦ 0.4 mm. Thereby, the number of rotations required until the roller 12 in the habituation operation settles at the regular position can be reduced, and the habituation operation time can be shortened.

  In the tapered roller bearing 10 of the present embodiment, the arithmetic average roughness Ra of the large collar surface 18 is 0.1 μm or more and 0.2 μm or less, and the skewness Rsk of the roughness curve of the large collar surface 18 is −1.0. The kurtosis Rku of the roughness curve of the large ridge surface 18 is 3.0 or more and 5.0 or less. Here, the skewness Rsk of the roughness curve is the skewness Rsk of the roughness curve defined by 4.2.3 of Japanese Industrial Standard (JIS) B0601: 2013, and the kurtosis Rku of the roughness curve is Japan. It is the kurtosis Rku of the roughness curve defined by the industrial standard (JIS) B0601: 2013 4.2.4.

  In order to stabilize the rotational torque within the condition of rotating the outer ring 11 or the inner ring 13 of the tapered roller bearing 10 at a low speed, that is, within the range of the rotational speed of 200 r / min or less, the arithmetic average roughness Ra of the large collar surface 18 is 0. .1 μm or more and 0.2 μm or less.

  The skewness Rsk of the roughness curve is the cube average of z (x) at the reference length made dimensionless by the cube of the root mean square roughness Rq of the cross section curve, as shown in the following equation (2). . The skewness Rsk of the roughness curve is a numerical value indicating the degree of asymmetry of the probability density function of the contour curve, and is a parameter that is strongly influenced by the protruding peaks or valleys.

  FIG. 11 shows a roughness curve satisfying the skewness Rsk> 0 and a roughness curve satisfying the skewness Rsk <0.

  As is clear from the comparison of these two roughness curves, when the skewness Rsk> 0, there are many peaks that suddenly protrude upward in the drawing of FIG. 11, and in such a case, the seizure resistance of the large collar surface 18 is excessive. There is a possibility that it will be much worse than the roughness of the finishing level. However, in the case of skewness Rsk <0, the surface shape tends to have relatively few peaks sharply protruding upward in FIG. 11, so that the oil film is difficult to break, which is advantageous in preventing seizure. The larger the negative value of the skewness Rsk, the wider the valley width in the left-right direction in FIG. 11, and the surface of the protruding peak tends to be relatively small (in the tapered roller bearing 10, the large end face 16 of the roller 12). The width of the large collar surface 18) of the inner ring 13 in contact with the inner ring 13 becomes narrower. For this reason, stress concentration occurs at the boundary between the surface and the valley, so that oil film formation is inhibited. By setting the skewness Rsk of the roughness curve of the large collar surface 18 of the inner ring 13 to −1.0 or more and −0.3 or less, the large collar surface 18 has a smooth flat surface with relatively few protruding peaks. In the width direction of FIG. 11 and a surface shape that favors oil film formation.

  As shown on the right side of FIG. 11, the probability density function of Rsk is unevenly distributed above the average line extending in the horizontal direction along the dotted line in the figure when Rsk <0. For this reason, Rsk <0, and by setting this to −1.0 or more and −0.3 or less, the surface of the large collar surface 18 has a shape having a smooth mountain in a wide range.

  Further, the kurtosis Rku of the roughness curve is expressed by the mean square of z (x) at the reference length made dimensionless by the square of the root mean square roughness Rq of the cross section curve as shown in the following equation (3). It is. The kurtosis Rku of the roughness curve is a numerical value indicating the degree of sharpness (sharpness) of the probability density function of the contour curve, and is a parameter that is strongly influenced by protruding peaks or valleys.

  FIG. 12 shows a roughness curve satisfying Kurtosis Rku> 3 and a roughness curve satisfying Kurtosis Rku <3.

  As is apparent from the comparison of these two roughness curves, when Kurtosis Rku <3, there are few peaks or valleys sharply protruding on the curve, and in such a case, the rotational torque may not be stable. However, in the case of Kurtosis Rku> 3, there is a tendency that peaks and valleys protrude relatively rapidly in the upper and lower parts of the figure. As a result, the large flange surface 18 can be in appropriate contact with the metal, which is advantageous in stabilizing the rotational torque of the tapered roller bearing 10. However, if the positive value of the kurtosis Rku becomes excessively large, excessive metal contact of the large collar surface 18 occurs, and seizure resistance decreases. Therefore, by setting the kurtosis Rku of the roughness curve of the large collar surface 18 of the inner ring 13 to 3.0 or more and 5.0 or less, the large collar surface 18 can be used to stabilize the rotational torque during low-speed rotation. The surface texture has a protrusion.

  As described above, by adjusting the arithmetic average roughness Ra, the skewness Rsk of the roughness curve, and the kurtosis Rku of the roughness curve, the rotational torque of the tapered roller bearing 10 can be stabilized and seizure resistance can be improved. Coexistence can be realized.

  If grinding finish processing is used to process the large flange surface 18 of the inner ring 13 having the roughness characteristics described above, the specified range of roughness is too small and the processing resistance becomes too large. Problems such as grinding burn may occur, and it is difficult to perform the processing. Therefore, when machining the large flange surface 18 of the inner ring 13 having the above-described roughness characteristics, it is preferable to perform super finishing in an ultra-short time of, for example, 0.5 seconds to 2 seconds.

  On the other hand, the roughness of the large end surface 16 of the roller 12 has less influence on the function of the tapered roller bearing 10 than the roughness of the large collar surface 18 of the inner ring 13. For this reason, the condition of the roughness of the large end surface 16 of the roller 12 is gentler than that of the large collar surface 18. Specifically, the arithmetic average roughness Ra of the large end face 16 of the roller 12 may be set to 0.1 μm or less from the viewpoint of obtaining a good lubricating oil wedge effect. Moreover, when the large end surface 16 of the roller 12 and the large flange surface 18 of the inner ring 13 are ideally in a contact relationship between a spherical surface and a flat surface, particularly good seizure resistance can be realized. For this reason, when the large collar surface 18 has a bus bar shape having irregularities, the maximum height of the irregularities on the large collar surface 18 is preferably 1 μm or less.

In summary, for example, the tapered roller bearing 10 according to the present embodiment shown in FIG. 9 includes an outer ring 11, an inner ring 13, and a plurality of rollers 12. The outer ring 11 has a raceway surface 11A on the inner peripheral surface. The inner ring 13 has a raceway surface 13 </ b> A and a large flange surface 18 disposed on the larger diameter side than the raceway surface 13 </ b> A on the outer peripheral surface, and is disposed radially inward with respect to the outer ring 11. Here, the arithmetic average roughness Ra of the large collar surface 18 is 0.1 μm or more and 0.2 μm or less. The plurality of rollers 12 are arranged between the raceway surface 11A and the raceway surface 13A, and have a raceway surface 12A that contacts the raceway surface 11A and the raceway surface 13A. At least one of the outer ring 11, the inner ring 13, and the plurality of rollers 12 includes nitrogen-enriched layers 11B, 12B, and 13B formed on the surface layer of the raceway surface 11A, the raceway surface 13A, or the rolling surface 12A. . The distance from the outermost surface of the surface layer to the bottom of the nitrogen-enriched layers 11B, 12B, 13B is 0.2 mm or more. Crowning portions 22 and 24 are formed on the rolling surface 12 </ b> A of the roller 12. The sum of the drop amounts of the crowning portions 22 and 24 is designed as K ₁ , K ₂ , and z _m in the yz coordinate system in which the generatrix of the rolling surface of the tapered roller is the y-axis and the direction orthogonal to the generatrix is the z-axis. Parameters, Q is the load, L is the length in the direction of the generatrix of the effective contact portion of the rolling surface of the tapered roller, E 'is the equivalent elastic modulus, and a is the effective contact portion from the origin on the generatrix of the rolling surface of the tapered roller Is represented by the above formula (1), where A = 2K ₁ Q / πLE ′. Both the above description and the following description are based on the premise that the tapered roller bearing 10 of the present embodiment has the characteristics described above in this paragraph.

  As shown in FIGS. 13 and 14, in the tapered roller bearing of the present embodiment, a first grinding relief portion 43 is formed at a corner where the raceway surface 13A and the large collar 41 intersect, and the raceway surface 13A and A second grinding relief 44 is formed at the corner with the gavel 42. The raceway surface 13A has a straight line extending in the inner ring axial direction. A raceway surface 11A facing the raceway surface 13A is formed on the inner periphery of the outer ring 2, and there is no wrinkle. The raceway surface 11A has a straight line extending in the outer ring axial direction.

  As shown in FIGS. 13 and 14, crowning surfaces 22 </ b> A and 22 </ b> B as the crowning portion 22 and crownings 24 </ b> A and 24 </ b> B as the crowning portion 24 are formed on the rolling surface 12 </ b> A on the outer periphery of the roller 12. Chamfered portions 21 and 25 are provided on the surface. The crowning portions 22 and 24 of the rolling surface 12A can be considered as crowning forming portions where crowning is formed. Here, the crowning formation portion is specifically formed as a contact portion crowning portion 27 and a non-contact portion crowning portion 28. Among these, the contact portion crowning portion 27 is in the axial range of the raceway surface 13A and is in contact with the raceway surface 13A. The non-contact portion crowning portion 28 is out of the axial range of the raceway surface 13A and is not in contact with the raceway surface 13A.

  The contact portion crowning portion 27 and the non-contact portion crowning portion 28 are lines in which the buses extending in the roller axis direction are expressed by different functions and smoothly continue at the connection point P1. In the vicinity of the connection point P1, the curvature R8 of the bus of the non-contact portion crowning portion 28 is set smaller than the curvature R7 of the bus of the contact portion crowning portion 27. The term “smoothly continuous” refers to continuous without generating a corner. Ideally, the bus bar of the contact portion crowning portion 27 and the bus bar of the non-contact portion crowning portion 28 are mutually continuous points. In FIG. 4, the continuation has a common tangent, that is, the bus is a function that can be continuously differentiated at the continuous points.

  According to this configuration, since the crowning portion is formed on the rolling surface 12A on the outer periphery of the roller 12, the grindstone can be applied to the rolling surface 12A as necessary and sufficiently as compared with the case where the crowning portion is formed only on the raceway surface 13A. Therefore, the processing defect with respect to 12 A of rolling surfaces can be prevented beforehand. The crowning portions 22 and 24 formed on the rolling surface 12A can reduce the surface pressure and the stress at the contact portion, thereby extending the life of the tapered roller bearing 10. Further, in the vicinity of the connection point P1 between the contact portion crowning portion 27 and the non-contact portion crowning portion 28, the curvature R8 of the non-contact portion crowning portion 28 is smaller than the curvature R7 of the contact portion crowning portion 27. Therefore, it is possible to reduce the drop amount at both ends of the roller 12. Therefore, for example, the amount of grinding can be suppressed from that of the conventional single arc crowning, the processing efficiency of the roller 12 can be improved, and the manufacturing cost can be reduced.

  The bus bar of the contact portion crowning portion 27 is formed by a logarithmic curve of logarithmic crowning represented by the following equation.

  The contact portion crowning portion 27 represented by the logarithmic crowning can reduce the surface pressure and the stress at the contact portion, thereby extending the life of the tapered roller bearing 10.

By the way, when the crowning is optimized using the mathematical optimization method for K ₁ and z _m in the above formula (1), the crowning as shown in “logarithm” in FIG. 15 is obtained under this condition. At this time, the maximum drop amount of the crowning of the roller 12 is 69 μm. However, the region G in FIG. 15 is the crowning portion 24B facing the first grinding relief portion 43 and the second grinding relief portion 44 of the inner ring 13 in FIG. For this reason, the G region of the roller 12 does not need to be logarithmic crowning, and may be a straight line, a circular arc, or other functions. Even if the G region of the roller 12 is a straight line, an arc, or other functions, the entire surface of the roller 12 has the same surface pressure distribution as in the case of logarithmic crowning, and there is no functional difference.

A mathematical optimization method for logarithmic crowning is described.
An optimal logarithmic crowning can be designed by appropriately selecting K ₁ and z _m in the functional expression representing the logarithmic crowning.

Crowning is generally designed to reduce the maximum surface pressure or stress at the contact. Here, it is considered that the rolling fatigue life occurs according to the yield condition of Mises, and K ₁ and z _m are selected so as to minimize the maximum value of the equivalent stress of Mises.

K ₁ and z _m can be selected using an appropriate mathematical optimization method. Various algorithms for mathematical optimization methods have been proposed. One of the direct search methods is that optimization can be performed without using the derivative of the function. Useful when functions and variables cannot be directly represented by mathematical expressions. Here, the optimum values of K ₁ and z _m are obtained using the Rosenbrock method, which is one of the direct search methods.

Under the above conditions, that is, when a radial load of 35% of the basic dynamic load rating acts on the tapered roller bearing, nominal number 30316, and the misalignment is 1/600, the maximum value sMises_max of the equivalent stress of Mises and the logarithmic crowning parameter K ₁ and z _m have a relationship as shown in FIG. Giving an appropriate initial value K _1, z _m, As you modify the K _1, z _m according to the rules of Rosenbrok method to reach the optimum combination of values in FIG. 16, SMises_max is minimized.

  As long as the contact between the roller 12 and the inner ring 13 is considered, the crowning in the region G in FIG. 15 may have any shape, but considering the contact with the outer ring 2 and the formability of the grindstone during processing, In the connection point P1 with the logarithmic crowning part, it is not desirable that the slope is smaller than that of the logarithmic crowning part. Giving a gradient larger than the gradient of the logarithmic crowning portion for the crowning in the region G is not desirable because the drop amount increases. That is, it is desirable that the crowning and logarithmic crowning in the region G are designed so that the gradients coincide at the connection point P1 and are smoothly connected. In FIG. 15, the case where the crowning of the G region of the roller 12 is a straight line is illustrated by a dotted line, and the case of an arc is illustrated by a thick solid line. When the crowning of the region G is a straight line, the drop amount Dp of the crowning of the roller 12 is, for example, 36 μm. When the crowning in the region G is an arc, the crowning drop amount Dp of the roller 12 is, for example, 40 μm.

  As for the bus line of the non-contact part crowning part 28, either one or both of the large diameter part and the small diameter part may be circular. In this case, the drop amount Dp can be reduced more than that in which the generatrix of the entire roller rolling surface is represented by a logarithmic curve, for example. Therefore, the amount of grinding can be reduced. As shown in FIG. 17, the generatrix of the non-contact portion crowning portion 28 may have either a large-diameter side portion or a small-diameter side portion or both straight lines (in the example of FIG. 17, the large-diameter side portion). Only the straight line). In this case, the drop amount Dp can be further reduced as compared with the case where the bus of the non-contact portion crowning portion 28 is an arc.

  A part or all of the bus of the contact portion crowning portion 27 may be represented by logarithmic crowning represented by the above formula (1). The contact portion crowning portion 27 represented by the logarithmic crowning can reduce the surface pressure and the stress at the contact portion, thereby extending the life of the tapered roller bearing.

  As shown in FIG. 18, the generating line of the contact portion crowning portion 27 is formed by a straight portion 27A (synonymous with the central portion 23 in FIG. 3) formed flat along the roller axis direction and a logarithmic curve of logarithmic crowning. And may be represented by the portion 27B.

In order to ensure the processing accuracy of the crowning, it is desirable that the straight portion 27 </ b> A exists on the outer periphery of the roller 12. Accordingly, if the crowning portions 22 and 24 are symmetrical with respect to the small-diameter side portion and the large-diameter side portion with respect to the center in the roller axial direction, among the design parameters in the logarithmic crowning equation (1), K ₂ is It is fixed, and K ₁ and z _m are objects of design.

Hereafter, the manufacturing method of a tapered roller bearing is demonstrated using FIGS.
As shown in FIG. 19, a component preparation step (S100) is first performed. In this step (S100), members to be bearing parts such as the outer ring 11, the inner ring 13, the roller 12, and the cage 14 are prepared. In addition, the crowning is not yet formed on the member to be the roller 12, and the surface of the member is a pre-processed surface 12E indicated by a dotted line in FIG. Further, the roller 12 is formed to have a large end surface 16 and a small end surface 17 as shown in FIG. 9, and the inner ring 13 is formed to have a large collar surface 18 and a small collar surface 19 as shown in FIG. .

Next, a heat treatment step (S200) is performed. In this step (S200), a predetermined heat treatment is performed to control the characteristics of the bearing component. For example, in order to form the nitrogen-enriched layers 11B, 12B, and 13B according to the present embodiment in at least one of the outer ring 11, the roller 12, and the inner ring 13, a carbonitriding process or a nitriding process, a quenching process, and a tempering process are performed. Perform processing. An example of the heat treatment pattern in this step (S200) is shown in FIG. FIG. 20 shows a heat treatment pattern showing a method of performing primary quenching and secondary quenching. Figure 21 is a material in the course quenching cooled to below the A ₁ transformation point temperature, then, it shows a heat treatment pattern reheated shows the final quenching Ru method. In these figures, it was sufficiently the penetration of addition of carbon to diffuse carbon and nitrogen in the matrix of the treated T ₁ steel is cooled below the A ₁ transformation point. Next, in the process T ₂ of the in the figure, than the processing T ₁ is reheated to a low temperature, subjected to oil quenching from there. Thereafter, for example, a tempering process at a heating temperature of 180 ° C. is performed.

  According to the above heat treatment, it is possible to improve the cracking strength and reduce the aging rate of dimensional change while carbonitriding the surface layer portion of the bearing component, rather than normal quenching, that is, carbonitriding once after the carbonitriding treatment. Can do. According to the heat treatment step (S200), in the nitrogen-enriched layers 11B, 12B, and 13B having a quenched structure, the grain size of the prior austenite crystal grains is compared with the microstructure in the conventional quenched structure shown in FIG. As a result, a microstructure as shown in FIG. 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.

  Next, a processing step (S300) is performed. In this step (S300), finishing is performed so that the final shape of each bearing component is obtained. For the roller 12, the crowning 22A and the chamfered portion 21 are formed by machining such as cutting as shown in FIG.

  Next, an assembly process (S400) is performed. In this step (S400), the tapered roller bearing 10 shown in FIG. 9 is obtained by assembling the bearing components prepared as described above. In this way, the tapered roller bearing 10 shown in FIG. 1 can be manufactured.

From the viewpoint of verifying the rotational driving force, a rotational torque test was performed on each of a plurality of types of tapered roller bearings having different inner ring large collar surfaces. The test model number of the tapered roller bearing 10 is 30307D, and the rust preventive oil has a kinematic viscosity at 40 ° C. of 16.5 mm ² / s and a kinematic viscosity at 100 ° C. of 3.5 mm ² / s. I used something.

  As the tapered roller bearing as the test object, the arithmetic mean roughness Ra of the large flange surface 18 according to the present embodiment is 0.149 μm, the skewness Rsk of the roughness curve is −0.96, A sample of the tapered roller bearing 10 having a curvature curve kurtosis Rku of 4.005 was used. On the other hand, as a comparative prior art sample, there are two types, a sample having an arithmetic average roughness Ra of the large corrugated surface 18 of 0.2 μm and a sample having an arithmetic average roughness Ra of the large corrugated surface 18 of 0.08 μm. Used. Note that the arithmetic average roughness Ra, skewness Rsk, and kurtosis Rku on the large surface can all be measured by a surface roughness measuring machine.

  The test was performed by measuring the rotational torque when the rotational speed of the tapered roller bearing was changed from 0 r / min to 200 r / min. The measurement results are shown in FIG.

  As shown in FIG. 23, the product of the present invention, which is a sample of the present embodiment, has a stable torque characteristic substantially equal to that of a conventional product having an Ra of 0.2 μm. This is because the wedge effect of the lubricating oil is small in the low rotational speed region of 200 r / min or less, and the lubricating oil film is thin and boundary lubrication is performed up to a condition of 200 r / min.

  On the other hand, in the conventional product with Ra of 0.08 μm, the rotational torque value suddenly decreases even at a rotational speed of 50 r / min or less. This is a result of a sufficient oil film thickness being formed before reaching 50 r / min because the roughness of the large ridge surface is finer than the others. In the conventional product with Ra of 0.08 μm, when it is 50 r / min or more, the rolling resistance of the rolling surface becomes dominant.

  Preload management (or torque check) after assembling the actual machine is often performed under conditions of a rotational speed in the range of 10 r / min to 50 r / min. It can be said that the present invention product capable of stabilizing the torque in this range has good assembling performance.

  From the viewpoint of verifying seizure resistance, a temperature rise test was performed on a test object of the same type, that is, the same lot sample as the tapered roller bearing subjected to the rotational torque test. The test model number of the tapered roller bearing 10 is 30307D, and the radial load is 17 kN and the radial load is 1.5 kN. Turbine oil VG56 was used as a hot water bath for raising the temperature. And the temperature of the outer ring | wheel of each sample was measured and temperature rising was confirmed. The test results are as shown in Table 1 below. In the table, “◯” indicates that the temperature of the outer ring was 120 ° C. or lower, and “Δ” indicates that the temperature of the outer ring was 120 ° C. or higher and lower than 150 ° C. Furthermore, the “x” mark indicates that the temperature of the outer ring was 150 ° C. or higher.

  As shown in Table 1, the product of the present invention has the same seizure resistance as that of the conventional product with Ra of 0.08 μm.

  In order to have such characteristics, it is preferable that the contact relationship between the large end surface of the tapered roller and the large collar surface of the inner ring is a “contact relationship between a sphere and a flat surface”. From this viewpoint, it is preferable that the large collar surface 18 of the inner ring 13 of the present embodiment is a substantially straight plane to the extent that it can be obtained from industrial products.

  Tables 2 to 5 show the results of evaluation according to the above-described temperature increase test and rotational torque test in various combinations of arithmetic average roughness Ra, roughness curve skewness Rsk, and roughness curve kurtosis Rku. In each table, “◎” indicates very good, “◯” indicates good, “△” indicates not good but not bad, “×” indicates Indicates a failure.

  As shown in Table 2, when the arithmetic average roughness Ra on the large corrugated surface is 0.05 μm, the large corrugated surface is finished with a particularly smooth surface property, so that the skewness Rsk of the roughness curve on the large corrugated surface is Regardless of whether it is in the range of -1.0 or more and -0.3 or less, and whether or not the kurtosis Rku of the roughness curve is in the range of 3.0 or more and 5.0 or less, It can be seen that the tackiness is particularly good while the torque stability is particularly bad.

  As shown in Table 3 and Table 4, when the arithmetic average roughness Ra on the large ridge surface is 0.1 μm or 0.2 μm, the seizure resistance tends to deteriorate compared to the case of Ra = 0.05, Torque stability shows a trend of improvement. Here, it is understood that when the skewness Rsk <−1.0 of the roughness curve on the large ridge surface, an oil film is hardly formed, which is disadvantageous for seizure resistance. On the other hand, when the skewness Rsk of the roughness curve on the large ridge surface is greater than −0.3, the seizure resistance and the stability of the torque are obtained by balancing with the characteristics of the kurtosis Rku of the roughness curve on the large ridge surface shown below. Cannot balance. Further, it is understood that when the kurtosis Rku <3 of the roughness curve on the large ridge surface, an oil film is formed too much, which is disadvantageous for torque stability. On the other hand, when the kurtosis Rku> 5 of the roughness curve on the large ridge surface, the minute peaks on the surface are too sharp and it is easy to make metal contact with the roller large end surface, making it difficult to form an oil film, which is disadvantageous for seizure resistance. I understand.

  As shown in Table 5, when the arithmetic average roughness Ra on the large surface is 0.25 μm, the seizure resistance is further worse than in Table 3 and Table 4, and the torque stability is good. Specifically, regardless of whether the skewness Rsk of the roughness curve on the large surface is in the range of −1.0 or more and −0.3 or less, the kurtosis Rku of the roughness curve is 3.0 or more. Regardless of whether it is in the range of 5.0 or less, it can be seen that the seizure resistance is particularly poor, while the torque stability is particularly good.

  Therefore, as described above, in the product of the present invention, when the arithmetic average roughness Ra of the large collar surface 18 is 0.1 μm ≦ Ra ≦ 0.2 μm, the skewness Rsk of the roughness curve of the large collar surface 18 is −1.0. ≦ Rsk ≦ −0.3, and if the kurtosis Rku of the roughness curve of the large rib surface 18 is 3.0 ≦ Rku ≦ 5.0, it is possible to achieve both seizure resistance and torque stability. I understand that.

<Sample>
As a sample, Sample No. Four types of tapered rollers 1 to 4 were prepared as samples. The model number of the tapered roller was 30206. As the material of the tapered roller, JIS standard SUJ2 material (1.0 mass% C-0.25 mass% Si-0.4 mass% Mn-1.5 mass% Cr) was used.

  Sample No. For No. 1, after carbonitriding and quenching, logarithmic crowning according to the present embodiment shown in FIG. 5 was formed at both ends. The carbonitriding temperature was 845 ° C. and the holding time was 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. Sample No. For sample 2, sample no. After performing carbonitriding and quenching in the same manner as in No. 1, the partial arc crowning shown in FIG. 8 was formed.

  Sample No. For No. 3, after performing the heat treatment pattern shown in FIG. 20, logarithmic crowning according to the present embodiment shown in FIG. 5 was formed at both ends. The carbonitriding temperature was 845 ° C. and the holding time was 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. The final quenching temperature was 800 ° C.

  Sample No. For No. 4, after performing the heat treatment pattern shown in FIG. 20, logarithmic crowning according to the present embodiment shown in FIG. 5 was formed at both ends. In order to set the nitrogen concentration in the nitrogen-enriched layer at a depth of 0.05 mm from the outermost surface of the sample to 0.1% by mass or more, the carbonitriding temperature was 845 ° C. and the holding time was 150 minutes. The atmosphere of the carbonitriding process was RX gas + ammonia gas. Furthermore, the furnace atmosphere was strictly controlled. Specifically, the furnace temperature unevenness and the ammonia gas atmosphere unevenness were suppressed. The final quenching temperature was 800 ° C. Sample No. mentioned above. 3 and sample no. 4 corresponds to the embodiment of the present invention. Sample No. 1 and sample no. 2 corresponds to the comparative example.

<Experiment details>
Experiment 1: Life test A life test apparatus was used. As test conditions, test load: Fr = 18 kN, Fa = 2 kN, lubricating oil: turbine oil 56, lubrication method: oil bath lubrication were used. In the life test apparatus, two tapered roller bearings as test objects are arranged so as to support both ends of a support shaft. A cylindrical roller bearing for applying a radial load to the tapered roller bearing via the support shaft is disposed at the center in the extending direction of the support shaft, that is, the center of the two tapered roller bearings. A radial load is applied to the tapered roller bearing as a test object by applying a radial load to the cylindrical roller bearing for load application. The axial load is transmitted from one tapered roller bearing to the support shaft through the housing of the life test apparatus, and the other tapered roller bearing is loaded with the axial load. Thereby, the life test of the tapered roller bearing is performed.

Experiment 2: Life test under uneven load The same test equipment as the life test of Experiment 1 was used. The test conditions were basically the same as those in Experiment 1 described above, but the test was performed with an axial load of 2/1000 rad applied to the center axis of the roller and an unbalanced load applied.

Experiment 3: Rotational torque test Sample No. About 1-4, the torque measurement test using the vertical torque tester was done. As test conditions, test load: Fa = 7000N, lubricating oil: turbine oil 56, lubrication method: oil bath lubrication, rotation speed: 5000 rpm were used.

<Result>
Experiment 1: Life test Sample No. 4 showed the best results and was considered to have a long life. Sample No. 2 and Sample No. 3 is sample No. Although it did not reach the result of 4, it showed a good result and was judged to be sufficiently practical. On the other hand, sample No. For 1, the result showed the shortest life.

Experiment 2: Life test under unbalanced load 4 and sample no. 3 showed the best results and was considered to have a long life. Next, sample No. 1 is Sample No. 4 and sample no. Although it was less than 3, comparatively good results were shown. On the other hand, sample No. No. 2 shows a result worse than the result in Experiment 1 above, and it is considered that the life was shortened by the uneven load condition.

Experiment 3: Rotational torque test Sample No. 1, sample no. 3, Sample No. No. 4 showed a sufficiently small rotational torque, which was a good result. On the other hand, sample No. No. 2 had a rotational torque greater than that of the other samples.

  From the above results, the sample No. No. 4 showed a good result in any test, and it was the best overall result. Sample No. 3 also sample No. 1 and sample no. The result was better than 2.

  Below, an example of the use of the tapered roller bearing 10 which concerns on this Embodiment is demonstrated. The above-described tapered roller bearing 10 is suitable, for example, for an automobile differential or transmission. That is, it is preferable to use the tapered roller bearing 10 as a tapered roller bearing for automobiles. An example in which the tapered roller bearing 10 of the above-described embodiment is applied to an automotive differential will be described with reference to FIG. FIG. 24 shows an automobile differential using the tapered roller bearing 10 described above. This differential is connected to a propeller shaft (not shown), and a drive pinion 122 inserted through the differential case 121 is engaged with a ring gear 124 attached to the differential gear case 123 and attached to the inside of the differential gear case 123. The pinion gear 125 is engaged with a side gear 126 connected to a drive shaft (not shown) inserted through the differential gear case 123 from the left and right, and the driving force of the engine is transmitted from the propeller shaft to the left and right drive shafts. It is like that. In this differential, a drive pinion 122 and a differential gear case 123, which are power transmission shafts, are supported by a pair of tapered roller bearings 10a and 10b, respectively.

  In addition, the tapered roller bearing 10 of this Embodiment may be integrated for the gear shaft support of power transmission devices, such as a transmission. Referring to FIG. 25, manual transmission 100 is a constant-mesh manual transmission, and includes input shaft 111, output shaft 112, counter shaft 113, gears (gears) 114 a to 114 k, and housing 115. It has.

  The input shaft 111 is rotatably supported with respect to the housing 115 by the tapered roller bearing 10. A gear 114a is formed on the outer periphery of the input shaft 111, and a gear 114b is formed on the inner periphery.

  On the other hand, the output shaft 112 is rotatably supported on the housing 115 by the tapered roller bearing 10 on one side (right side in the figure), and can be rotated on the input shaft 111 by the rolling bearing 120A on the other side (left side in the figure). It is supported by. Gears 114c to 114g are attached to the output shaft 112.

  The gear 114c and the gear 114d are respectively formed on the outer periphery and the inner periphery of the same member. The member in which the gear 114c and the gear 114d are formed is rotatably supported with respect to the output shaft 112 by the rolling bearing 120B. The gear 114e is attached to the output shaft 112 so as to rotate integrally with the output shaft 112 and to be slidable in the axial direction of the output shaft 112.

  Each of the gear 114f and the gear 114g is formed on the outer periphery of the same member. The member in which the gear 114f and the gear 114g are formed is attached to the output shaft 112 so as to rotate integrally with the output shaft 112 and to be slidable in the axial direction of the output shaft 112. When the member on which the gear 114f and the gear 114g are formed slides to the left in the figure, the gear 114f can mesh with the gear 114b. When the member slides to the right in the figure, the gear 114g and the gear 114d Engageable.

  Gears 114 h to 114 k are formed on the countershaft 113. Two thrust needle roller bearings are disposed between the countershaft 113 and the housing 115, thereby supporting an axial load (thrust load) of the countershaft 113. The gear 114h always meshes with the gear 114a, and the gear 114i always meshes with the gear 114c. The gear 114j can mesh with the gear 114e when the gear 114e slides to the left side in the drawing. Furthermore, the gear 114k can mesh with the gear 114e when the gear 114e slides to the right in the drawing.

  Next, the shifting operation of the manual transmission 100 will be described. In the manual transmission 100, the rotation of the input shaft 111 is transmitted to the countershaft 113 by meshing between the gear 114 a formed on the input shaft 111 and the gear 114 h formed on the countershaft 113. The rotation of the countershaft 113 is transmitted to the output shaft 112 by meshing the gears 114 i to 114 k formed on the countershaft 113 with the gears 114 c and 114 e attached to the output shaft 112. Thereby, the rotation of the input shaft 111 is transmitted to the output shaft 112.

  When the rotation of the input shaft 111 is transmitted to the output shaft 112, the gear meshing between the input shaft 111 and the counter shaft 113 and the gear meshing between the counter shaft 113 and the output shaft 112 are changed. The rotational speed of the output shaft 112 can be changed stepwise with respect to the rotational speed of the input shaft 111. Further, the rotation of the input shaft 111 can be directly transmitted to the output shaft 112 by directly meshing the gear 114 b of the input shaft 111 and the gear 114 f of the output shaft 112 without using the counter shaft 113.

  Hereinafter, the shifting operation of the manual transmission 100 will be described more specifically. When the gear 114f does not mesh with the gear 114b, the gear 114g does not mesh with the gear 114d, and the gear 114e meshes with the gear 114j, the driving force of the input shaft 111 is the gear 114a, the gear 114h, the gear 114j, and It is transmitted to the output shaft 112 via the gear 114e. This is the first speed, for example.

  When the gear 114g meshes with the gear 114d and the gear 114e does not mesh with the gear 114j, the driving force of the input shaft 111 is transmitted via the gear 114a, the gear 114h, the gear 114i, the gear 114c, the gear 114d, and the gear 114g. It is transmitted to the output shaft 112. This is the second speed, for example.

  When the gear 114f meshes with the gear 114b and the gear 114e does not mesh with the gear 114j, the input shaft 111 is directly coupled to the output shaft 112 by meshing with the gear 114b and the gear 114f, and the driving force of the input shaft 111 is Directly transmitted to the output shaft 112. This is the third speed, for example.

  As described above, the manual transmission 100 includes the tapered roller bearing 10 in order to rotatably support the input shaft 111 and the output shaft 112 as rotating members with respect to the housing 115 disposed adjacent thereto. Yes. As described above, the tapered roller bearing 10 according to the above embodiment can be used in the manual transmission 100. The tapered roller bearing 10 with reduced torque loss and improved seizure resistance and life is suitable for use in the manual transmission 100 in which high surface pressure is applied between the rolling elements and the raceway member. .

  By the way, in transmissions or differentials that are power transmission devices for automobiles, in order to save fuel consumption, in addition to using low-viscosity lubricating oil, there is a tendency to reduce the amount of oil. An oil film may be difficult to form. Further, when the transmission or differential is used in a low temperature environment (for example, −40 ° C. to −30 ° C.), the viscosity of the lubricating oil increases. Oil may not be sufficiently supplied to the tapered roller bearing. For this reason, tapered roller bearings for automobiles are required to be improved in seizure resistance and life. Therefore, the above requirements can be satisfied by incorporating the tapered roller bearing 10 having improved seizure resistance and life into a transmission or a differential.

  You may apply so that the characteristic described in each example contained in embodiment described above may be combined suitably in the range with no technical contradiction.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. 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.

  1 housing, 2, 3 tapered roller bearing, 4 drive pinion, 5 ring gear, 7 differential gear case, 8 pinion, 9 side gear, 10 tapered roller bearing, 11 outer ring, 11A, 13A raceway surface, 11B, 12B, 13B nitrogen rich 11C, 12C, 13C Non-nitrided portion, 12 rollers, 12A rolling surface, 12E surface before processing, 13 inner ring, 14 cage, 16 large end surface, 17 small end surface, 18 large collar surface, 19 small collar surface, 21, 25 Chamfered portion, 22, 24 Crowned portion, 22A Crowned portion, 23 Center portion, 26 Center line, 27 Contact portion crowned portion, 27A Straight portion, 27B Portion formed by logarithmic curve, 28 Non-contact portion crowned portion, 31 First measurement point, 32 Second measurement point, 33 Third measurement point, 41 Oiso, 42 Oiso, 43 First Cutting relief portion, 44 second grinding relief portion, 111 an input shaft, 112 output shaft 113 counter shaft, 114A～114k gear, 115 housing, 190 stealing, 200 contact ellipse.

Claims (11)

An outer ring having an outer ring raceway surface on the inner circumferential surface;
An inner ring disposed on a radially inner side with respect to the outer ring, the outer ring having an inner ring raceway surface and a large flange surface disposed on a larger diameter side than the inner ring raceway surface;
A plurality of tapered rollers arranged between the outer ring raceway surface and the inner ring raceway surface and having rolling surfaces that contact the outer ring raceway surface and the inner ring raceway surface;
Arithmetic mean roughness Ra of the large ridge surface is 0.1 μm or more and 0.2 μm or less,
At least any one of the outer ring, the inner ring, and the plurality of tapered rollers includes a nitrogen-enriched layer formed on a surface layer of the outer ring raceway surface, the inner ring raceway surface, or the rolling surface,
The distance from the outermost surface of the surface layer to the bottom of the nitrogen-enriched layer is 0.2 mm or more,
Crowning is formed on the rolling surface of the tapered roller,
The sum of the amount of drop of the crowning is K ₁ , K ₂ , z _m in the yz coordinate system in which the generatrix of the rolling surface of the tapered roller is the y axis and the z axis is the generatrix orthogonal direction. , Q is a load, L is a length in a generatrix direction of an effective contact portion of the rolling surface of the tapered roller, E ′ is an equivalent elastic modulus, and a is an origin on a generatrix of the rolling surface of the tapered roller A tapered roller bearing represented by the formula (1) when the length to the end of the effective contact portion is A = 2K ₁ Q / πLE ′.

  2. The tapered roller bearing according to claim 1, wherein the prior austenite crystal grain size in the nitrogen-enriched layer has a JIS standard grain size number of 10 or more.   The tapered roller bearing according to claim 1 or 2, wherein a nitrogen concentration in the nitrogen-enriched layer at a depth of 0.05 mm from the outermost surface is 0.1 mass% or more. At least one, but is optimized surface pressure as an objective function, the tapered roller bearing according to any one of claims 1 to 3 K _1, K _2, z _m of the formula (1). The crowning forming portion in which the crowning is formed on the rolling surface of the tapered roller is a contact portion crowning portion that is in an axial range of the inner ring raceway surface and is in contact with the inner ring raceway surface, and an axial direction of the inner ring raceway surface. A non-contact portion crowning portion that is out of range and is non-contact with the inner ring raceway surface,
In the contact portion crowning portion and the non-contact portion crowning portion, the generatrix extending in the roller axis direction is a line that is represented by a function different from each other and smoothly connected to each other at a connection point,
The tapered roller bearing according to any one of claims 1 to 4, wherein a curvature of a bus of the non-contact portion crowning portion is smaller than a curvature of a bus of the contact portion crowning portion in the vicinity of the connection point.   The tapered roller bearing according to claim 5, wherein one or both of the large-diameter side portion and the small-diameter side portion of the bus bar of the non-contact portion crowning portion is a straight line.   The tapered roller bearing according to claim 5 or 6, wherein a part or all of the bus bar of the contact portion crowning portion is represented by logarithmic crowning.   The tapered roller bearing according to claim 7, wherein a connecting portion with a portion formed by a logarithmic curve of the logarithmic crowning among buses of the non-contact portion crowning portion is matched with a slope of the logarithmic curve.   The skewness Rsk of the roughness curve of the large ridge surface is -1.0 or more and -0.3 or less, and the kurtosis Rku of the roughness curve of the large ridge surface is 3.0 or more and 5.0 or less. The tapered roller bearing according to any one of 1 to 8. The tapered roller further has a large end surface that contacts the large collar surface,
The tapered roller bearing according to any one of claims 1 to 9, wherein an arithmetic average roughness Ra of a large end surface included in the tapered roller is 0.1 µm or less.   The tapered roller bearing according to claim 9 or 10, wherein the maximum height of the irregularities on the large collar surface is 1 µm or less.

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