JP7504270B2 - Tapered roller bearings - Google Patents

Description

This invention relates to a tapered roller bearing.

The rolling bearings that support the rotating parts must be suited to the direction and magnitude of the load they will receive, and the space in which they will be installed. When used to support the rotating parts of an automobile's transmission (MT, AT, DCT, CVT, hybrid, etc.) or differential, they must be compact, despite being subject to radial, axial and moment loads. For this reason, tapered roller bearings are used, which can withstand radial and axial loads and have excellent load capacity.

When a tapered roller bearing is in operation, a thrust force is generated that pushes the tapered rollers towards the larger diameter side. For this reason, the inner ring is formed with a large rib to support the large end faces of the tapered rollers while guiding them in the orbital direction (circumferential direction). The large rib has a large rib surface against which the large end faces of the tapered rollers slide. The inner ring is formed with a ground relief around the entire circumference that connects the large rib surface with the raceway surface.

In general, the shapes of the large end face of the tapered roller and the large rib surface of the inner ring are designed so that they geometrically contact at only one point. During operation, the large end face of the tapered roller slides in contact with the large rib surface of the inner ring in the direction of revolution, but due to the loads and thrust forces mentioned above, the sliding contact area generally occurs in an oblong area with a minor radial axis centered on the designed contact point. If the sliding contact area is not lubricated sufficiently, heat will be generated, leading to a rapid temperature rise.

When tapered roller bearings are operated at high speeds, such as in automobile transmissions, and the lubricating oil becomes hot, it is possible that a good lubrication mode cannot be maintained at the sliding contact area between the large end faces of the tapered rollers and the large rib surface of the inner ring, resulting in boundary lubrication and insufficient lubrication. In order to improve seizure resistance during such high-temperature operation, efforts have been made to improve the shapes and surface properties of the large end faces of the tapered rollers and the large rib surface of the inner ring (Patent Documents 1 to 3).

In Patent Document 1, when the radius of curvature of the large end face of the tapered roller is R and the distance from the apex of the cone angle of the tapered roller to the contact portion of the large rib surface is R _BASE , by setting R/R _BASE in the range of 0.75 to 0.87, the wedge effect when the lubricating oil is dragged between the large end face of the tapered roller and the large rib surface of the inner ring can be satisfactorily exerted, and the oil film thickness at the sliding contact portion can be improved (heat generation can be reduced).

In Patent Document 2, by forming a relief surface shaped to move away from the large end face of the tapered roller from the outer diameter side edge of the large rib surface toward the chamfered inner diameter side edge of the large rib, it is possible to increase the effect of drawing lubricating oil into the contact area between the large end face of the tapered roller and the large rib surface of the inner ring, thereby improving the oil film formation ability.

In Patent Document 3, the aforementioned R/R _BASE is set in the range of 0.75 to 0.87, and when the actual radius of curvature of the large end face of the tapered roller is R _ACTUAL , R _ACTUAL /R is set to 0.5 or more, thereby suppressing heat generation at the large end face of the tapered roller and the large rib face of the inner ring even under severe lubrication environments and improving seizure resistance, and in particular, by introducing the rib lubrication coefficient as an index that represents the level of severity of the lubrication condition, the practical range of the R _ACTUAL /R ratio is expanded, making it possible to select appropriate bearing specifications according to the usage conditions.

JP 2000-170774 A JP 2000-170775 A JP 2018-136027 A

However, there is a trend in automotive transmissions and differentials to reduce the viscosity of lubricating oil and the amount of lubricating oil in the unit in order to improve fuel efficiency, and this trend is expected to continue in the future. As a result, the lubrication conditions for rolling bearings will become even more severe. In particular, with tapered roller bearings, it is becoming increasingly important to ensure the oil film thickness in the sliding contact area between the large end face of the tapered roller and the large rib face of the inner ring, and to take care to suppress temperature rise due to the lubricating oil.

In view of the above background, the problem that this invention aims to solve is to prevent a sudden rise in temperature and ensure smooth rotation of the bearing even when the tapered roller bearing is used under severe lubrication conditions.

In order to achieve the above object, the present invention provides a tapered roller bearing comprising an inner ring, an outer ring, a plurality of tapered rollers arranged between the inner ring and the outer ring, and a cage that houses the tapered rollers, the tapered rollers having a rolling surface formed in a conical shape, a chamfer that continues to the large diameter side of the rolling surface, and a large end face that continues to the chamfer, the inner ring having a raceway surface formed in a conical shape, a large rib surface that receives the large end faces of the tapered rollers, and a ground relief formed in a groove that connects the large rib surface and the raceway surface, the generatrix of the raceway surface being aligned with the ground relief. The intersection point between an imaginary line extending to the large rib side and an imaginary line extending the generatrix of the large rib surface to the grinding relief side is taken as a reference point, the recess width from the reference point to the large rib surface is taken as A, and the width that the chamfer of the tapered roller has in the direction along the generatrix of the large rib surface is taken as RC. When the width RC is 0.7 mm or less and A < RC, the cone angle of the rolling surface is taken as β, and the acute angle that the imaginary line connecting the contact point between the large rib surface and the large end face of the tapered roller to the apex of the cone angle β forms with the generatrix of the raceway surface is taken as ρ, a configuration was adopted in which β/7 ≧ ρ.

According to the above configuration, by setting the width RC of the chamfer of the tapered roller to 0.7 mm or less and the grinding relief width A to be less than width RC, which is a particularly small dimension, the width of the large rib surface can be made wide enough to receive the large end face of the tapered roller. This optimizes the contact relationship between the large rib surface and the large end face of the tapered roller, effectively exerting the wedge effect acting between the large rib surface and the large end face of the tapered roller, and improving the oil film formation ability. In addition, by setting the angle ρ, which indicates the radial height of the contact point between the large rib surface and the large end face of the tapered roller relative to a reference point, to a range lower than β/7, it is possible to prevent an increase in the sliding speed at the sliding contact area, suppress the amount of heat generated by the large rib surface, and prevent a sudden rise in temperature.

Specifically, when the approach angle of the grinding relief relative to the large rib surface of the inner ring is a and the approach angle of the grinding relief relative to the raceway surface is b, a>b, and when the recess width from the reference point to the large rib surface is A and the recess width from the reference point to the raceway surface is B, A<B. In order to satisfy the recess width A of 0.5 mm or less in manufacturing, it is necessary to take into consideration that the width of the large rib surface changes depending on the approach angle a of the grinding relief when the grinding amount of the large rib surface changes during processing. The larger the approach angle a relative to the large rib surface, the smaller the change in the width of the large rib surface when the grinding amount of the large rib surface changes, so the larger the approach angle a, the better. Furthermore, considering the ease of chip discharge during turning of the grinding relief, it is preferable to satisfy the relationships a>b and A<B.

When the depth of the grinding relief relative to the raceway surface of the inner ring is c and the depth of the grinding relief relative to the large rib surface is d, it is preferable that c>d. In this way, the stress on the large rib generated by the load applied from the large end face of the tapered roller to the large rib surface of the inner ring can be reduced, and the strength of the large rib of the inner ring can be improved.

When the depth of the grinding relief relative to the large flange surface of the inner ring is d, it is preferable that the depth d be 0.3 mm or less. This ensures that the strength of the large flange of the inner ring is improved.

When the approach angle of the grinding relief with respect to the large rib surface of the inner ring is a, it is preferable that 20°≦a≦50°. In this way, it is easy to control the recess width A when grinding the large rib surface.

When the acute angle formed by the generatrix of the raceway surface with respect to the central axis of the inner ring is defined as θ, the large end diameter of the rolling surface of the tapered roller is defined as Dw, the roller length of the tapered roller is defined as L, and the width of the large rib surface is defined as W, it is preferable that the width W has a value that satisfies the following formula 1.
W≧{Dw×(1/2)×Tan θ/(L/Dw)} Equation 1
In this way, the large rib surface is sufficiently opposed to the large end face of the tapered roller, and good contact can be maintained even when the sliding contact area between the large end face of the tapered roller and the large rib surface of the inner ring moves up toward the outer diameter side of the large rib.

It is preferable that the grain size number of the prior austenite grains on the large rib surface of the inner ring is 6 or more. Such a large rib surface is suitable for delaying surface damage caused by metal contact with the large end surface of the tapered roller.

The large rib surface of the inner ring is preferably formed with a nitride layer having a nitrogen content of 0.05 wt% or more. Such a large rib surface is suitable for delaying surface damage caused by metal contact with the large end face of the tapered roller.

The surface roughness of the large rib surface of the inner ring is preferably 0.1 μm Ra or less, and the surface roughness of the large end surface of the tapered roller is preferably 0.12 μm Ra or less. This can improve the formation of an oil film between the large rib surface and the large end surface of the tapered roller.

When the set radius of curvature of the large end face of the tapered roller is R and the basic radius of curvature from the apex of the cone angle of the rolling surface to the large rib surface of the inner ring is R _BASE , R/R _BASE may be 0.70 or more and 0.95 or less, and when the actual radius of curvature of the large end face of the tapered roller is R _ACTUAL , R _ACTUAL /R of at least one tapered roller among the plurality of tapered rollers may be 0.3 or more and less than 0.5. In this invention, since the oil film forming ability can be improved on the large rib surface side, the ranges of R/R _BASE and R _ACTUAL /R can be relaxed compared to the tapered roller bearing of Patent Document 3. Since the yield of tapered rollers is improved accordingly, tapered roller bearings can be provided at relatively low cost.

The tapered roller bearing of this invention has excellent seizure resistance even under severe lubrication conditions, making it suitable for use in supporting rotating parts in automobile transmissions or differentials.

As described above, by adopting the above configuration, this invention optimizes the contact relationship between the large rib surface of the inner ring and the large end surface of the tapered roller, improves the oil film formation ability, and prevents an increase in the sliding speed at the sliding contact area, so that even when the tapered roller bearing is used under severe lubrication conditions, a sudden rise in temperature can be prevented and the bearing can rotate smoothly.

FIG. 1 is a diagram showing a generatrix shape near a large rib surface of a tapered roller bearing according to an embodiment of the present invention; 1 is a cross-sectional view of a tapered roller bearing according to this embodiment; FIG. 3 is a diagram showing the generatrix shape near the large rib surface in an ideal contact state between the large end face and the large rib surface of the tapered roller in FIG. 2. Half-longitudinal section showing the design specifications of the tapered roller bearing in Figure 2 Schematic diagram showing the detailed shape of the large end face of the tapered roller in FIG. 2 . 6 is a schematic diagram showing the machined shape of the large end face of the tapered roller in FIG. A graph showing the relationship between the radius of curvature of the large end face of the tapered roller in FIG. 2 and the oil film thickness FIG. 2 is a diagram showing an example of a modification of the generatrix shape in the vicinity of the large flange surface in FIG. 1. FIG. 3 is a cross-sectional view showing an example of an automobile differential incorporating the tapered roller bearing of FIG. 2. FIG. 3 is a cross-sectional view showing an example of an automobile transmission incorporating the tapered roller bearing of FIG. 2.

A tapered roller bearing according to an embodiment of the present invention will be described with reference to the attached drawings.

The tapered roller bearing shown in Figure 2 comprises an inner ring 10, an outer ring 20, a number of tapered rollers 30 arranged between the inner ring 10 and the outer ring 20, and a cage 40 that houses these tapered rollers 30. This tapered roller bearing is intended for use in automotive transmissions or differentials, primarily for passenger cars, and has an outer bearing diameter of 150 mm or less.

As shown in Figures 2 and 3, the inner ring 10 is a raceway ring having a conical raceway surface 11, a large flange 12 formed with a diameter larger than the large diameter side edge of the raceway surface 11, a grinding recess 13 formed from the base of the large flange 12 to the raceway surface 11, a small flange 14 formed with a diameter larger than the small diameter side edge of the raceway surface 11, and a small diameter side grinding recess 15 formed from the base of the small flange 14 to the raceway surface 11 on the outer periphery.

As shown in FIG. 2, the outer ring 20 is a raceway ring having a conical raceway surface 21 on the inner circumference. Lubricating oil is supplied from the outside to the bearing internal space between the inner ring 10 and the outer ring 20.

The tapered roller 30 is a rolling element having a rolling surface 31 formed in a conical shape, a chamfer 32 continuing with the large diameter side of the rolling surface 31, a large end face 33 continuing with the chamfer 32, and a small end face 34 formed on the opposite side of the large end face 33. The large end face 33 and the small end face 34 of the tapered roller 30 include both side ends that define the roller length L of the tapered roller 30.

The tapered rollers 30 are arranged in a single row between the inner and outer raceway surfaces 11, 21. The cage 40 is an annular bearing part that keeps the tapered rollers 30 spaced equally apart in the circumferential direction. Each tapered roller 30 is housed in a pocket formed in the cage 40 at equal intervals in the circumferential direction.

The cage 40 in the illustrated example is a punched cage-shaped cage, but the material and manufacturing method of the cage 40 are not particularly important.

Here, the direction along the central axis CL, which is the center of rotation of the inner ring 10, is called the "axial direction," the direction perpendicular to the central axis CL is called the "radial direction," and the circumferential direction going around the central axis CL is called the "circumferential direction." The central axis CL of the inner ring 10 corresponds to the design center of rotation of this tapered roller bearing.

The inner and outer raceway surfaces 11, 21 are surface portions that can be in rolling contact with the rolling surfaces 31 of the tapered rollers 30 and that receive the radial load from the rolling surfaces 31.

As shown in Figure 4, when the central axes of the inner ring 10, outer ring 20 and tapered roller 30 are included in the same imaginary axial plane and the central axis of the tapered roller 30 (not shown) is positioned directly opposite to point _O1 on the central axis CL of the inner ring 10, the apexes of the inner and outer raceway surfaces 11, 21 and the rolling surface 31 of the tapered roller 30 coincide with point _O1 . The large end face 33 of the tapered roller 30 is specified, in terms of design, based on a spherical shape with a set radius of curvature R centered on the straight line connecting point _O1 and the central axis of the tapered roller 30 in Figure 4.

The conical shapes of the inner and outer raceway surfaces 11, 21 and the rolling surface 31 of the tapered roller 30 are not limited to shapes with a straight line as the generatrix, but are a concept that includes shapes with crowning. Here, the generatrix refers to a line segment that generates a certain curved surface as a trajectory due to movement around an axis. For example, the generatrix of the raceway surface 11 is a line segment that forms the raceway surface 11 on a virtual axial plane including the center axis CL of the inner ring 10, and the generatrix of the rolling surface 31 is a line segment that forms the rolling surface 31 on any virtual plane including the center axis of the tapered roller 30. As the crowning shape, the full crowning shape or cut crowning shape disclosed by the present applicant in Patent Document 3 can be adopted, and as the cut crowning shape of the rolling surface 31, a logarithmic crowning, for example, a shape defined by the formula in Patent Document 5037094 cited in Patent Document 3, may be adopted.

As shown in Figures 2 and 3, the large rib 12 of the inner ring 10 has a large rib surface 12a that receives the large end surface 33 of the tapered roller 30, an outer diameter surface 12b that defines the outer diameter of the large rib 12, and a rib side chamfer 12c that connects the outer diameter side edge of the large rib surface 12a and the outer diameter surface 12b around the entire circumference. The end face of the large rib 12 opposite the large rib surface 12a forms part of the side surface of the inner ring 10.

The large rib surface 12a is a surface portion for making sliding contact with the large end face 33 of the tapered roller 30 in the circumferential direction. The generatrix of the large rib surface 12a is a straight line inclined relative to the radial direction. Therefore, the large rib surface 12a is conical and coaxial with the raceway surface 11. The large rib surface 12a only needs to have a shape that can geometrically make contact with the large end face 33 of the tapered roller 30 at only one point, and the generatrix shape can be changed to a median concave shape (in this case, it is a contact with a contact surface, but for convenience, it is expressed as a point contact at the contact position between the median concave bottom and the roller large end face), a median convex shape, etc.

The grinding relief 13 of the inner ring 10 is formed as a groove connecting the large rib surface 12a and the raceway surface 11. The grinding relief 13 is a full-circumferential groove for grinding and super-finishing the raceway surface 11 and the large rib surface 12a, and has a depth relative to each of the raceway surface 11 and the large rib surface 12a.

As shown in FIG. 2, the small flange 14 of the inner ring 10 is a part that prevents the tapered rollers 30 from falling off the raceway surface 11 to the small diameter side, and is a part that forms an assembly with these tapered rollers 30, the cage 40, and the inner ring 10. The small flange 14 and the small diameter side grinding relief 15 used in forming it are not essential components of the inner ring.

The inner ring 10, outer ring 20, and tapered rollers 30 are each formed by machining the required parts in the following order: forging, turning, and grinding.

The raceway surface 11 and the large flange surface 12a of the inner ring 10 are formed by turning and grinding the forged body, and then polished by super-finishing.

As shown in Figures 1 and 3, the grinding relief 13 of the inner ring 10 is turned based on a predetermined generatrix shape. The generatrix in the turning of the grinding relief 13 is defined by a large diameter side straight section inclined from the large rib surface 12a, a small diameter side straight section inclined from the raceway surface 11, and an arc-shaped line section connecting these large diameter side straight section and small diameter side straight section. The grinding relief 13 is not actively ground or super-finished, but when the raceway surface 11 and the large rib surface 12a are ground, the grinding wheel slightly rounds the large diameter side end of the raceway surface grinding part and the inner diameter side end of the large rib surface grinding part. For this reason, almost the entire surface of the grinding relief 13 is a turned surface, but the connection part of the grinding relief 13 with the raceway surface 11 and the connection part with the large rib surface 12a are slightly rounded ground surfaces or super-finished surfaces.

Here, as shown in FIG. 1, the intersection of an imaginary line extending the generatrix of the raceway surface 11 of the inner ring 10 toward the grinding relief 13 side and an imaginary line extending the generatrix of the large rib surface 12a toward the grinding relief 13 side is defined as a reference point _O2 . The approach angle of the grinding relief 13 with respect to the large rib surface 12a is defined as a. The approach angle of the grinding relief 13 with respect to the raceway surface 11 is defined as b. The depth of the grinding relief 13 with respect to the raceway surface 11 is defined as c. The depth of the grinding relief 13 with respect to the large rib surface 12a is defined as d. The recess width from the reference point _O2 to the large rib surface 12a is defined as A. The recess width from the reference point _O2 to the raceway surface 11 is defined as B. Also, as shown in FIG. 3, the width of the chamfer 32 of the tapered roller 30 in the direction along the generatrix of the large rib surface 12a is defined as RC.

The approach angles a, b, recess widths A, B, and depths c, d shown in Figure 1 are physical quantities for defining the shape of the grinding relief 13. However, the connection between the grinding relief 13 and the raceway surface 11 and the large rib surface 12a is not stable in the rounding described above, so it is difficult to use these to define the approach angles a, b. For this reason, the inclination angle of the turned surface of the grinding relief 13 relative to the raceway surface 11 and the large rib surface 12a is used as the approach angles a, b.

Specifically, the approach angle a of the grinding relief 13 is an acute angle that the large-diameter side straight portion of the generating line of the grinding relief 13 forms with the inner-diameter side edge of the large flange surface 12a. The approach angle b of the grinding relief 13 is an acute angle that the small-diameter side straight portion of the generating line of the grinding relief 13 forms with the large-diameter side edge of the raceway surface 11.

The recess width A of the grinding relief 13 is the length from the inner diameter side edge of the large rib surface 12a in the direction along the generatrix of the large rib surface 12a to the reference point _O2 . The recess width B of the grinding relief 13 is the length from the large diameter side edge of the raceway surface 11 in the direction along the generatrix of the raceway surface 11 to the reference point _O2 .

The approach angle a of the grinding relief 13 is larger than the approach angle b. When the amount of grinding of the large rib surface 12a (the amount of cutting in a direction perpendicular to the generatrix of the large rib surface 12a) fluctuates from the target value during grinding, the width W of the large rib surface 12a shown in FIG. 3 changes depending on the approach angle a of the grinding relief 13. Here, the width W of the large rib surface 12a is the distance between both ends of the generatrix of the large rib surface 12a. In the illustrated example, since the generatrix of the large rib surface 12a is linear, the length of the generatrix corresponds to the width W. The amount of change in the width W of the large rib surface 12a can be reduced by increasing the approach angle a shown in FIG. 1. In other words, when the amount of grinding of the large rib surface 12a fluctuates, the effect on the dimension of the recess width A becomes less sensitive when the approach angle a is increased.

The approach angle a of the grinding relief 13 should be 20° or more and 50° or less. Within this range, even if the amount of grinding of the large flange surface 12a varies, the effect on the dimension of the recess width A is gradual, and it is easy to control the recess width A. It is more preferable to set the approach angle a to 30° or more and 40° or less.

The depth c of the grinding relief 13 is the depth of the grinding relief 13 considered in a direction perpendicular to an imaginary line extending from the generating line of the raceway surface 11, based on the large diameter side edge of the raceway surface 11. The depth d of the grinding relief 13 is the depth of the grinding relief 13 considered in a direction perpendicular to an imaginary line extending from the generating line of the large rib surface 12a, based on the inner diameter side edge of the large rib surface 12a.

The depth c of the grinding recess 13 is greater than the depth d. This is to avoid the thickness between the grinding recess 13 and the side surface of the inner ring 10 becoming thin. To make this thickness sufficiently large, it is preferable that the depth d be 0.3 mm or less.

The recess width A of the grinding relief 13 is smaller than the recess width B. If the recess width A is smaller than the recess width B, it is advantageous to make the approach angle a larger than the approach angle b. The grinding relief 13 is machined by turning. In this case, it is easier to discharge the chips from the raceway surface 11 side, which has a relatively large space, than to discharge them to the large flange surface 12a side of the grinding relief 13. Therefore, discharging the chips to the raceway surface 11 side makes the turning process more efficient. By satisfying the approach angle a>b and the recess width A<B of the grinding relief 13, the discharge pressure of the chips on the approach angle b and the recess width B side during turning becomes relatively small, and the chips are easily discharged to the raceway surface 11 side. Therefore, the turning process is improved and the processing cost can be reduced.

3, the width RC of the chamfer 32 of the tapered roller 30 is the length from the outer diameter side edge of the large end face 33 to the large end side edge of the rolling surface 31 in the direction along the generatrix of the large rib surface 12a. In the illustrated example, the width RC of the chamfer 32 coincides with the length from the outer diameter side edge of the large end face 33 to the reference point _O2 . The width RC of the chamfer 32 of the tapered roller 30 is 0.7 mm or less.

On the other hand, the recess width A of the grinding relief 13 is smaller than the width RC of the chamfer 32 of the tapered roller 30. The reason for adopting such a small recess width A is to make the inner diameter of the large rib surface 12a small and to make the width W of the large rib surface 12a facing the large end face 33 of the tapered roller 30 sufficiently wide as shown in FIG. 3, so that the sliding contact portion between the large end face 33 of the tapered roller 30 and the large rib surface 12a does not reach the inner diameter side edge of the large rib surface 12a. Increasing the width W of the large rib surface 12a is advantageous in maintaining a good contact state between the large end face 33 of the tapered roller 30 and the large rib surface 12a even if the position of the sliding contact portion between the large end face 33 of the tapered roller 30 and the large rib surface 12a moves. The recess width A can be, for example, 0.5 mm or less.

2 and 4, the acute angle formed by the generatrix of raceway surface 11 with respect to the central axis CL of inner ring 10 is defined as θ. Furthermore, the large end diameter Dw of rolling surface 31 of tapered roller 30 is defined as Dw. In the geometric relationship between the inclination angle θ of raceway surface 11, the large end diameter Dw of rolling surface 31, and the roller length L shown in Fig. 2, the width W of large rib surface 12a shown in Fig. 3 is a value that satisfies the following formula 1.
W≧{Dw×(1/2)×Tan θ/(L/Dw)} Equation 1

The above formula 1 is for determining the lower limit of the appropriate width W of the large rib surface 12a so that the large end surface 33 of the tapered roller 30 and the large rib surface 12a of the inner ring 10 shown in Figures 2 and 3 can be kept in good contact with each other. That is, when a radial load (dynamic equivalent load when combined with an axial load) is applied to this tapered roller bearing, the load is distributed to the raceway surface 11 and the large rib surface 12a according to the inclination angle θ of the raceway surface 11. The ratio of this distribution is expressed as Tan θ, which is multiplied by the large end diameter Dw of the rolling surface 31, which is closely related to the bearing load capacity. Normally, the load applied during operation of a tapered roller bearing is approximately half or less of the bearing load capacity, so the large end diameter Dw of the rolling surface 31 is multiplied by (1/2) to take this into account. Furthermore, taking into consideration that if the roller length L is long, the bearing rate on the raceway surface 11 in the aforementioned distribution ratio becomes large, the relationship between the roller length L and the large end diameter Dw of the rolling surface 31 is also taken into consideration as (L/Dw) ^-1 . Using this formula 1, the lower limit of the width W of the large rib surface 12a according to the applied load is set. As a result, good contact can be maintained even when skewing of the tapered roller 30 or tilting of the large rib 12 of the inner ring 10 due to a large moment load occurs and the sliding contact portion between the large end face 33 and the large rib surface 12a moves up toward the large rib outer diameter side.

The upper limit of the width W of the large rib surface 12a can be any number of millimeters for the purpose of supporting and guiding the large end face 33 of the tapered roller 30, but is preferably no more than three times the lower limit calculated by formula 1. If the width W of the large rib surface 12a is too large (i.e., the outer diameter of the large rib surface 12a is too large), it becomes difficult for the lubricating oil to reach the sliding contact area between the large end face 33 of the tapered roller 30 and the large rib surface 12a, making it impossible to ensure good lubrication.

Here, as shown in Fig. 3, the acute angle that the large rib surface 12a forms with respect to the radial direction is defined as a rib surface angle α. The difference in height in the radial direction between the contact point between the large rib surface 12a and the large end face 33 of the tapered roller 30 and the reference point _O2 is defined as a contact point height H. The contact point height H is uniquely determined by a combination of the basic radius of curvature R _BASE at the large end face 33 of the tapered roller 30 and the rib surface angle α. As shown in Figs. 2 and 4, the cone angle of the rolling surface 31 of the tapered roller 30 is defined as β. The cone angle β of the rolling surface 31 is the central angle formed by the cone shape of the rolling surface 31 with its apex _O1 as the center. Also, ρ is the acute angle that an imaginary line connecting the contact point between the large rib surface 12a of the inner ring 10 and the large end face 33 of the tapered roller 30 to the apex _O1 of the cone angle β forms with the generatrix of the raceway surface 11. The angle ρ corresponds to the contact height H as shown in Figure 3. Here, when the large rib surface has a curvature on the convex side toward the large end face of the tapered roller or on the concave side away from the large end face, ρ is the angle connecting the deepest or highest part of the large rib surface and the contact point with the large end face.

The circumferential sliding speed at the contact point between the large rib surface 12a and the large end face 33 of the tapered roller 30 depends on the contact height H. If the aforementioned contact point exists at the reference point _O2 , which is the virtual intersection point between the raceway surface 11 of the inner ring 10 and the large rib surface 12a (contact height H = 0), the sliding speed is zero, and the higher the contact height H from the reference point _O2 , the higher the sliding speed at the contact point. As described above, by adopting a small recess width A, it is possible to widen the large rib surface 12a toward the grinding relief 13 side and lower the contact height H. For this reason, the contact point between the large rib surface 12a and the large end face 33 of the tapered roller 30 is set at a low position that satisfies β/7 ≧ ρ. Setting the contact point at such a low position is effective in slowing down the sliding speed at the sliding contact area between the large rib surface 12a and the large end face 33 of the tapered roller 30, thereby suppressing heat generation at the large rib surface 12a and preventing a rapid rise in temperature of the large rib surface 12a.

For the ratio R/R _BASE of the set radius of curvature R at the large end face 33 of the tapered roller 30 shown in Figure 4 to the basic radius of curvature R BASE from the apex _O1 of the cone angle β of the rolling _surface 31 to the large rib surface 12a of the inner ring 10, and the ratio R _ACTUAL /R of the actual radius of curvature R _ACTUAL of the large end face 33 to the set radius of curvature R, it is possible to adopt the numerical ranges disclosed by the present applicant in Patent Document 3. The details and technical significance of R/R _BASE and R _ACTUAL /R are as disclosed in Patent Document 3, so the explanation of this embodiment will be limited to the gist of R/R _BASE and R _ACTUAL /R.

That is, the set radius of curvature R of the large end face 33 of the tapered roller 30 shown in Fig. 4 is the R dimension when the large end face 33 is made of an ideal spherical surface determined in design. As shown in Fig. 5, considering points _P1 , _P2 , _P3 , _P4 at the end of the large end face 33, the midpoint _P5 between points _P1 and _P2 , the midpoint _P6 between points _P3 and _P4 , the radius of curvature _R152 passing through points _P1 , _P5 , _P2 , the radius of curvature _R364 passing through points _P3 , _P6 , P4, and the radius of curvature _R1564 passing through points _P1 , _P5 , _P6 , _P4 , ideally, R= _R152 = _R364 = _R1564 . Points _{P1 and P4} are connection points between the large end face 33 and the chamfer 32. Points _P2 and _P3 are connection points between the large end face 33 and the relief portion 35. In reality, as shown in Fig. 6, both ends of the large end face 33 droop during grinding, so that _R152 and R364 on one side cannot be made the same relative to _R1564 of the entire large end face 33, _and are made smaller. The _R152 and _R364 on one side of the large end face 33 after machining are called the actual radius of curvature _RACTUAL .

The set radius of curvature R and the actual radius of curvature _RACTUAL are obtained as follows. The radius of curvature _R1564 in Fig. 6 is an approximation circle passing through the four points _P1 , _P5 , _P6 , and _P4 shown in Fig. 5. _R152 = _R364 = _R1564 was measured using a "Surf Test Surface Roughness Measuring Instrument manufactured by Mitutoyo Corporation", model name: SV-3100. The measurement method was to use the above measuring instrument to obtain the shape in the direction along the generatrix of the large end face 33 of the tapered roller 30, plot the points _P1 , _P2 , _P3 , and _P4 , and then plot the midpoints _P5 and _P6 . The radius of curvature _R152 was calculated as the radius of the circular arc passing through the points _P1 , _P5 , and _P2 (the same applies to the radius of curvature _R364 ). The radius of curvature R ₁₅₆₄ was calculated by taking values from four points using the command "multiple inputs". The shape of the large end face 33 in the direction along the generatrix was measured once in the diameter direction.

The large rib surface 12a of the inner ring 10 shown in Fig. 3 is in sliding contact only with the portion of the large end face 33 of the tapered roller 30 shown in Fig. 6 that has a radius of curvature R ₁₅₂ and a radius of curvature R ₃₆₄ on one side. The actual sliding contact between the large end face 33 and the large rib surface 12a has an actual radius of curvature R _ACTUAL (R ₁₅₂ , R ₃₆₄ ) that is smaller than the set radius of curvature R (R ₁₅₆₄ ). As a result, the actual contact surface pressure between the large end face 33 and the large rib surface 12a and the skew angle of the tapered roller 30 are larger than their respective ideal design values. If the skew angle and contact surface pressure become large in an environment in which the oil film is insufficient, the sliding contact between the large end face 33 and the large rib surface 12a becomes unstable, and the oil film parameters decrease. When the oil film parameter is less than 1, the large end face 33 and the large rib surface 12a enter boundary lubrication where metal contact begins, and the risk of seizure increases. Here, the oil film parameter is Λ (=h/σ), which is defined as the ratio of the oil film thickness h calculated from the elastic fluid lubrication theory to the composite roughness σ of the root mean square roughness of the large end face 33 and the large rib surface 12a. The verification of the practical range of the ratio of the actual radius of curvature R _ACTUAL to the set radius of curvature R is affected by the severity of the lubrication condition between the large end face 33 and the large rib surface 12a at the peak of the lubricating oil use temperature.

When the generatrix shape of the large flange surface 12a is linear and constant, the lubrication state between the large end face 33 and the large flange surface 12a is determined by the actual radius of curvature R _ACTUAL and the operating temperature of the lubricant. In the case of transmissions and differentials, the lubricant used is basically fixed, so the viscosity of the lubricant is also determined. Assuming an extremely severe temperature condition of 120°C continuing for 3 minutes (180 seconds) as the maximum condition at the peak of the lubricant operating temperature, and taking into account the viscosity characteristics of the lubricant to this assumed peak temperature condition, the threshold value for setting the ratio R _ACTUAL /R of the actual radius of curvature R _ACTUAL and the set radius of curvature R that does not cause a sudden rise in temperature in the lubricated state is obtained as the flange lubrication coefficient. The flange lubrication coefficient is obtained by 120°C viscosity x (oil film thickness h) ² /180 seconds. The oil film thickness h is obtained from the Karna formula. From the viewpoints of the contact surface pressure between the large end face 33 and the large rib face 12a, the oil film thickness h, the skew angle, and the oil film parameters, it is practical to set R _ACTUAL /R so that the value of the rib lubrication coefficient exceeds 8×10 ⁻⁹ (threshold value).

Turbine oil ISO viscosity grade VG32, a lubricant often used in transmissions, has a viscosity of 7.7 cSt (=7.7 ^mm2 /s) at 120°C. VG32 has a low viscosity at 120°C, and the lubrication conditions, taking into account the expected peak temperature conditions and the viscosity of the lubricant, are extremely severe. For this reason, the aforementioned _RACTUAL /R is preferably 0.8 or greater. In addition, in the case of SAE 75W-90, a gear lubricant often used in differentials, _RACTUAL /R is preferably 0.5 or greater.

The ratio R/R _BASE of the set radius of curvature R of the large end face 33 of the tapered roller 30 shown in Fig. 4 to the basic radius of curvature R _BASE from the apex _O1 of the cone angle β of the rolling surface 31 to the large rib surface 12a of the inner ring 10 is related to the oil film formation ability in the sliding contact area between the large end face 33 and the large rib surface 12a, as shown in Fig. 7. The maximum Hertz stress p in the sliding contact area between the large rib surface 12a and the large end face 33 decreases as R/R _BASE increases. Also, the smaller R/R _BASE becomes, the larger the skew angle becomes.

If the oil film thickness formed in the sliding contact portion between the large end face 33 and the large rib face 12a shown in Fig. 4 is denoted as t, the vertical axis of Fig. 7 indicates the ratio t/ _t0 to the oil film thickness _t0 when R/R _BASE is 0.76. From Fig. 7, it can be seen that the oil film thickness t is maximum when R/R _BASE is 0.76, and when R/R _BASE exceeds 0.9, the oil film thickness t decreases rapidly. In terms of the optimum value of the oil film thickness, it is particularly preferable that R/R _BASE be 0.75 or more and 0.87 or less.

In this tapered roller bearing, as described above, the recess width A of the grinding recess 13 is reduced and the width W of the large rib surface 12a is made wider toward the grinding recess 13 side, thereby optimizing the large rib surface 12a to maintain good contact with the large end face 33 of the tapered roller 30, and it is also possible to widen the allowable ranges for each of R/R _BASE and R _ACTUAL /R.

Specifically, R/R _BASE may be 0.70 or more and 0.95 or less, preferably 0.70 or more and 0.90 or less, and most preferably 0.75 or more and 0.87 or less.

Furthermore, R _ACTUAL /R may be 0.3 or more, preferably 0.5 or more, and most preferably 0.8 or more. For the finished tapered rollers 30 for which R _ACTUAL /R is in the range of 0.3 or more and less than 0.5, even if there is some disturbance that causes the sliding contact portion to move, such as skew of the tapered rollers 30 or tilting of the large rib 12 due to a large moment load, good contact with the large end face 33 of the tapered roller 30 can be maintained by optimizing the large rib surface 12a as described above.

Therefore, by allowing the plurality of tapered rollers 30 to include finished tapered rollers 30 having R/R _BASE of 0.70 or more and 0.95 or less and R _ACTUAL /R of 0.3 or more and less than 0.5, the yield of tapered rollers 30 can be improved.

The oil film parameters mentioned above depend on the composite roughness of the large end face 33 of the tapered roller 30 and the large rib surface 12a of the inner ring 10. By mirror finishing the large end face 33 and the large rib surface 12a, the oil film can be formed well and a good oil film thickness can be maintained. Specifically, the surface roughness of the large rib surface 12a is 0.1 μmRa or less, and preferably 0.08 μmRa or less. The surface roughness of the large end face 33 is 0.12 μmRa or less, and preferably 0.1 μmRa or less. Here, the surface roughness refers to the arithmetic mean roughness Ra defined in JIS standard B0601:2013 "Geometric characteristics specifications for products (GPS) - Surface quality: Profile curve method - Terms, definitions and surface quality parameters".

In order to prevent the large end face 33 of the tapered roller 30 from sliding contact (edge contact) with the outer diameter side edge of the large rib surface 12a of the inner ring 10, a flank may be formed between the large rib surface 12a and the rib side chamfer 12c shown in FIG. 1. An example of such a modification is shown in FIG. 8. As shown in the figure, a flank 12d is formed between the large rib surface 12a and the rib side chamfer 12c. The flank 12d curves toward the outer diameter surface 12b as it moves from the outer diameter side edge of the large rib surface 12a toward the rib side chamfer 12c. The generatrix of the flank 12d is an arc line with a radius of curvature Rd.

Here, a virtual intersection between a virtual line extending from the generatrix of the large rib surface 12a and a virtual line extending from the generatrix of the rib side chamfer 12c is considered, and the distance from the virtual intersection in the direction along the generatrix of the large rib surface 12a to a position having the same diameter as the outer diameter surface 12b is defined as the width _L1 of the rib side chamfer 12b, and the distance from the outer diameter side edge of the large rib surface 12a to the virtual intersection in the direction along the generatrix of the large rib surface 12a is defined as the width _L2 of the relief surface 12d. In order to prevent the width _L2 of the relief surface 12d from becoming too small, it is preferable that the radius of curvature Rd of the relief surface 12d is 2 mm or less. In addition, in order to secure the width _L2 of the relief surface 12d, it is preferable that the width _L1 of the rib side chamfer 12c is 1 mm or less.

It is also preferable to further improve the performance by combining the optimization of the large rib surface 12a of the inner ring 10 as shown in Figures 1, 3, and 8 with the heat treatment characteristics of the inner ring 10. In other words, when the lubrication conditions for the sliding contact between the large end face 33 of the tapered roller 30 and the large rib surface 12a are severe, there is concern that surface damage may occur due to metal contact, so it is advisable to give the large rib surface 12a a characteristic that delays surface damage.

Specifically, the grain size number of the prior austenite grains on the large rib surface 12a of the inner ring 10 should be 6 or more. Here, the grain size number of the prior austenite grains refers to the number specified in JIS standard G0551:2013 "Steel - Microscopic test method for grain size". Prior austenite grains refer to the austenite grains after quenching. The boundary (grain boundary) between prior austenite grains is called the prior austenite grain boundary, and the prior austenite grains are those surrounded by the prior austenite grain boundaries. The finer the prior austenite grain size (the larger the grain size number), the more the grain boundary can slow the progression of damage. For this reason, for a metal base material structure that comes into sliding contact, such as the large rib surface 12a, a grain size number of 6 or more is suitable, more preferably 10 or more, and even more preferably 11 or more.

In addition, the large rib surface 12a of the inner ring 10 may be formed by a nitrided layer having a nitrogen content of 0.05 wt% or more, or the nitrogen penetration depth may be 0.1 mm or more. A nitrided layer having a nitrogen content of 0.05 wt% or more has resistance to tempering softening due to its nitrogen enrichment effect. Therefore, the resistance to local heat generation during sliding contact of the large rib surface 12a is increased. The nitrided layer is a layer with an increased nitrogen content formed on the surface layer of the large rib surface 12a, and is realized by processes such as carbonitriding, nitriding, and nitriding. The nitrogen content of the nitrided layer is preferably 0.1 wt% or more and 0.7 wt% or less. If the nitrogen content is 0.1 wt% or more, it is possible to expect an improvement in rolling life, especially under conditions of foreign matter contamination, and if it exceeds 0.7 wt%, there is a high concern about a short life due to the formation of holes called voids or the excessive amount of retained austenite, which results in a loss of hardness. The nitrogen content is the value in the surface layer of 10 μm of the large flange surface 12a after grinding, and can be measured, for example, with an EPMA (wavelength dispersive X-ray microanalyzer).

The inner ring 10, outer ring 20, and tapered rollers 30 shown in FIG. 2 are made of high carbon chromium bearing steel (e.g., SUJ2 material). The inner ring 10, outer ring 20, and tapered rollers 30 are heat treated to form a nitride layer. This heat treatment method may be the method disclosed in Patent Document 3, or other methods. The material of the inner ring 10, outer ring 20, and tapered rollers 30 is not limited to high carbon chromium bearing steel. For example, the inner ring 10 and outer ring 20 may be made of carburizing steel such as chromium steel or chromium molybdenum steel, and conventional carburizing, quenching, and tempering may be applied as the heat treatment.

Tests were carried out to verify the effectiveness of this tapered roller bearing. The verification conditions and basic specifications of the test specimen in the first test were as follows (see Figures 1 to 3 as appropriate below).
<Verification conditions>
Test bearing: Model 32007X (JIS millimeter standard tapered roller bearing)
- Bearing size: φ35×φ62×18
Lubricating oil: Turbine oil ISO VG32 (viscosity ³² mm2/s@40
°C, 5.5 ^mm2 /s @ 100 °C)
Load conditions: Radial load = 0.3Cr (Cr is the basic dynamic load rating)
Rotation speed: 4000 r/min
Lubricating oil quantity: Dripping oil supply amount 8 mL/min
<Results of the test product>
_RACTUAL / R = 0.54
Width W of the large flange surface 12a = 1.69
Surface roughness of the large flange surface 12a = 0.039 μm Ra
Surface roughness of the large end face 33 = 0.032 μm Ra
R/R _BASE = 0.75

In the first test, in addition to the basic specifications described above, various specifications were evaluated in which the ratio of the cone angle β to the angle ρ was kept constant and the width RC of the chamfer 32 of the tapered roller 30 and the recess width A of the grinding relief 13 were varied, as shown below. The evaluation results are shown in Table 1.

As shown in Table 1 above, when β/ρ is 8.0, test pieces 1 to 3, in which the width RC of the chamfer 32 is ≦ 0.69 mm and the recess width A is < width RC, can suppress temperature rise and obtain sufficient bearing life even under severe lubrication conditions. In test piece 4, the width RC is set to 0.65 mm, which is smaller than that of test piece 3, but the recess width A is set to 0.77 mm, which is larger than the width RC, and although the temperature rise is easier, it does not reach a temperature that adversely affects the bearing life. In test pieces 5 and 6, in which the width RC is further reduced and the recess width A is further increased, the temperature rise cannot be suppressed and a long bearing life cannot be expected. In other words, when β/ρ = 8.0 (β/8 = ρ), it is considered that setting the width RC to 0.7 mm or less and the recess width A < width RC is effective in suppressing temperature rise even under severe lubrication conditions.

The verification conditions and basic specifications of the test items in the second test are as follows:
<Verification conditions>
Test bearing: Model 32007X (JIS millimeter standard tapered roller bearing)
- Bearing size: φ35×φ62×18
Lubricating oil: Turbine oil ISO VG32 (viscosity ³² mm2/s@40
°C, 5.5 ^mm2 /s @ 100 °C)
Load conditions: Radial load = 0.3Cr (Cr is the basic dynamic load rating)
Rotation speed: 4000 r/min
Lubricating oil quantity: Dripping oil supply amount 8 mL/min
<Results of the test product>
_RACTUAL / R = 0.61
Width W of the large flange surface 12a = 1.71
Surface roughness of the large flange surface 12a = 0.023 μm Ra
Surface roughness of the large end face 33 = 0.025 μm Ra
R/R _BASE = 0.76

In the second test, in addition to the basic specifications mentioned above, various specifications were evaluated in which the width RC of the chamfer 32 of the tapered roller 30 and the ratio of the cone angle β to the angle ρ were varied while the recess width A was kept constant, as shown below. The evaluation results are shown in Table 2.

As shown in Table 2 above, when the recess width A is 0.7 mm, test pieces 7 to 9, in which the width RC of the chamfer 32 is 0.65 mm or less and β/ρ is 7.1 or more, can suppress temperature rise and obtain sufficient bearing life even under severe lubrication conditions. Test piece 10 has a width RC of 0.55 mm, which is smaller than test pieces 7 to 9, and a β/ρ of 6.7, which is smaller than test pieces 7 to 9, so that the temperature rise is easier, but it does not reach a temperature that adversely affects the bearing life. Test pieces 11 and 12, in which the width RC is further reduced and β/ρ is further reduced, cannot suppress temperature rise and cannot be expected to have a long bearing life. In other words, when the recess width A is 0.7 mm, it is considered that a width RC of less than 0.7 mm and a β/ρ of 7 or more (β/7 ≧ ρ) are effective in suppressing temperature rise even under severe lubrication conditions.

Considering the results of the first and second tests together, it appears that setting width RC to 0.7 mm or less, recess width A < width RC, and β/7 ≥ ρ is particularly effective in suppressing temperature rise even under severe lubrication conditions.

As described above, this tapered roller bearing has a particularly small dimension of width RC of chamfer 32 of tapered roller 30 of 0.7 mm or less, and grinding relief width A < width RC, making it possible to widen width W of large rib surface 12a and make it wide enough to receive large end surface 33 of tapered roller 30. This optimizes the contact relationship between large rib surface 12a and large end surface 33, effectively exerts the wedge effect acting between large rib surface 12a and large end surface 33, and improves the oil film formation ability at the sliding contact area between large rib surface 12a and large end surface 33.

Furthermore, in this tapered roller bearing, the cone angle β/7 of the tapered rollers 30 is equal to or greater than angle ρ, and therefore the radial contact height H of the large rib surface 12a of the inner ring 10 and the large end face 33 with respect to reference point _O2 is low, preventing an increase in the sliding speed at the sliding contact portion between the large rib surface 12a and the large end face 33 and suppressing the amount of heat generated by the large rib surface 12a to prevent a sudden rise in temperature.

In this way, this tapered roller bearing optimizes the contact relationship between the large rib surface 12a of the inner ring 10 and the large end surface 33 of the tapered roller 30, improving the oil film formation ability at the sliding contact area and preventing an increase in the sliding speed at the sliding contact area, so that even when the tapered roller bearing is used under severe lubrication conditions, a sudden rise in temperature can be prevented and the bearing can rotate smoothly.

For example, when the lubrication conditions are particularly severe and the lubrication at the sliding contact area between the large rib surface 12a and the large end face 33 is at the level of a boundary film, it is possible that the large rib surface 12a side will wear out. If the wear of the large rib surface 12a reaches the grinding relief 13 and the large end face 33 and the inner diameter side edge of the large rib surface 12a come into contact at a corner, causing a large stress concentration, causing instability in the sliding behavior of the tapered roller 30 and raising concerns about a sudden rise in temperature. In contrast, in this tapered roller bearing, even if the large rib surface 12a wears, the width W of the large rib surface 12a is wide, and it faces the large end face 33 sufficiently, and the grinding relief 13 (recess width A) is small, so the wear of the large rib surface 12a does not reach the boundary with the grinding relief 13 (the inner diameter side edge of the large rib surface 12a), and the end area on the inner diameter side of the large rib surface 12a is maintained, so that the large rib surface 12a and the large end face 33 can maintain proper contact even under such particularly severe lubrication conditions.

In addition, this tapered roller bearing has an approach angle of a>b for the grinding recess 13 of the inner ring 10, and a recess width A<B, so that the grinding recess 13 has excellent turning workability, and the amount of grinding of the large rib surface 12a is not easily affected by the amount of change in the width W of the large rib surface 12a (the dimension of the recess width A) when the amount of grinding of the large rib surface 12a varies, and grinding of the large rib surface 12a is not difficult. For this reason, this tapered roller bearing does not require any concerns about processing costs, and is not particularly expensive.

In addition, in this tapered roller bearing, the depth of the grinding relief 13 of the inner ring 10 is c>d, so that the stress on the large rib 12 caused by the load applied from the large end face 33 of the tapered roller 30 to the large rib surface 12a of the inner ring 10 can be reduced, improving the strength of the large rib 12. This is advantageous in preventing the large rib 12 from falling due to external disturbances, etc., and in maintaining an appropriate contact state between the large rib surface 12a and the large end face 33.

In addition, the depth d of the grinding recess 13 of the inner ring 10 of this tapered roller bearing is 0.3 mm or less, which ensures that the strength of the large flange 12 is improved.

In addition, this tapered roller bearing has an approach angle a of the grinding relief 13 of the inner ring 10 in the range of 20°≦a≦50°, so even if the amount of grinding of the large rib surface 12a varies, the effect on the dimension of the change in the width W of the large rib surface 12a (recess width A) is moderate, making it easy to control the width W of the large rib surface 12a (recess width A).

In addition, in this tapered roller bearing, the width W of the large rib surface 12a of the inner ring 10 is a value that satisfies the above formula 1, so that the large rib surface 12a is fully opposed to the large end surface 33 of the tapered roller 30, and good contact can be maintained even when an external disturbance causes the sliding contact area between the large end surface 33 and the large rib surface 12a to rise to the outer diameter side of the large rib.

In addition, in this tapered roller bearing, the grain size number of the prior austenite crystal grains on the large rib surface 12a of the inner ring 10 is 6 or more, which can delay surface damage caused by metal contact with the large end surface 33 of the tapered roller 30.

In addition, in this tapered roller bearing, the large rib surface 12a of the inner ring 10 is formed with a nitride layer with a nitrogen content of 0.05 wt% or more, which can delay surface damage caused by metal contact with the large end surface 33 of the tapered roller 30.

In addition, this tapered roller bearing has a surface roughness of 0.1 μm Ra or less on the large rib surface 12a of the inner ring 10, and a surface roughness of 0.12 μm Ra or less on the large end surface 33 of the tapered roller 30, improving the oil film parameters between the large rib surface 12a and the large end surface 33 and improving oil film formation.

Furthermore, this tapered roller bearing has an R/R _BASE of 0.70 or more and 0.95 or less, and even if R _ACTUAL /R for at least one of the multiple tapered rollers 30 is 0.3 or more and less than 0.5, it can be used under severe lubrication conditions, and yet, compared to the tapered roller bearing disclosed in Patent Document 3, the yield of the tapered rollers 30 is improved and it can be provided relatively cheaply.

This tapered roller bearing is suitable for use in supporting the rotating shaft of an automobile transmission or differential, and for applications in which lubricating oil is supplied from the outside to the inside of the bearing by splash or oil bath lubrication. An example of its use is explained with reference to Figure 9. Figure 9 shows an example of an automobile differential.

The differential shown in FIG. 9 comprises a drive pinion 104 supported rotatably by two tapered roller bearings 102, 103 in a housing 101, a ring gear 105 that meshes with the drive pinion 104, and a differential gear mechanism (not shown), all of which are housed in a housing 101 filled with gear lubricating oil. This gear lubricating oil also serves as the lubricating oil for each of the tapered roller bearings 102, 103, and is supplied to the bearing sides by splashing or oil bath lubrication.

Another example of the use of this tapered roller bearing is explained with reference to Figure 10. Figure 10 shows an example of an automobile transmission.

The transmission shown in FIG. 10 is a multi-speed transmission that changes the gear ratio in stages, and includes tapered roller bearings according to any of the above-mentioned embodiments as tapered roller bearings 202-205 that rotatably support the rotating shaft (e.g., input shaft 201 to which engine rotation is input). The illustrated transmission switches between gear trains 206, 207 used by selectively engaging a clutch (not shown), thereby changing the gear ratio of the rotation transmitted from the input shaft 201 to the output shaft. In addition, this transmission is designed so that lubricating oil (transmission lubricating oil) is splashed onto the sides of each of the tapered roller bearings 202-205 as the gears rotate.

The tapered roller bearings 102, 103, 202-205 shown in Figures 9 and 10 correspond to the tapered roller bearings shown in Figure 1, etc., and therefore prevent rapid temperature rises due to sliding contact between the large rib surface of the inner ring and the large end surfaces of the tapered rollers during initial lubrication at the start of operation, even in a lean lubrication environment for fuel saving purposes, and maintain stable sliding contact to form a good oil film even if the operating temperature rises and the viscosity of the lubricating oil decreases, preventing damage to both surfaces.

However, this tapered roller bearing is not limited to transmission applications, but can be used in other applications with extremely severe lubrication conditions. The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. Therefore, the scope of the present invention is indicated by the claims rather than the above description, and it is intended to include all modifications within the meaning and scope of the claims.

10 Inner ring 11 Raceway surface 12 Large flange 12a Large flange surface 13 Grinding relief 20 Outer ring 30 Tapered roller 31 Rolling surface 32 Chamfer 33 Large end surface 102, 103, 202 to 205 Tapered roller bearing 104 Drive pinion (rotating part)
201 Input shaft (rotating part)

Claims (11)

The bearing comprises an inner ring, an outer ring, a plurality of tapered rollers disposed between the inner ring and the outer ring, and a cage that houses the tapered rollers,
The tapered roller has a rolling surface formed in a conical shape,
In a tapered roller bearing, the inner ring has a raceway surface formed in a conical shape and a large rib surface that receives the large end surfaces of the tapered rollers,
a large end diameter of the rolling surface of the tapered roller is Dw, a roller length of the tapered roller is L, and a width of the large rib surface is W, wherein the acute angle formed by the generatrix of the raceway surface with respect to the central axis of the inner ring is θ, the large end diameter of the rolling surface of the tapered roller is Dw, the roller length of the tapered roller is L, and the width of the large rib surface is W, said width W is a value that satisfies the following formula 1 .
W≧{Dw×(1/2)×Tan θ/(L/Dw)} Equation 1 2. The tapered roller bearing according to claim 1, wherein β is a cone angle of the rolling surfaces, and ρ is an acute angle formed by an imaginary line connecting from the point of contact between the large rib surface and the large end face of the tapered roller to the apex of the cone angle β with a generatrix of the raceway surface, such that β/7 ≧ ρ . the inner ring has a ground relief formed in a groove shape connecting the large rib surface and the raceway surface,
3. A tapered roller bearing according to claim 1, wherein the depth of the grinding relief from the raceway surface of the inner ring is c and the depth of the grinding relief from the large rib surface is d, such that c>d. 4. The tapered roller bearing according to claim 3 , wherein the depth of the grinding relief from the large rib surface of the inner ring is d, and the depth d is 0.3 mm or less. 5. A tapered roller bearing according to claim 3 , wherein an approach angle of the grinding relief with respect to the large rib surface of the inner ring is defined as a, and 20°≦a≦50° is satisfied. an approach angle of the grinding relief with respect to the large rib surface of the inner ring is defined as a and an approach angle of the grinding relief with respect to the raceway surface is defined as b, wherein a>b;
A virtual line extending the generatrix of the raceway surface to the grinding relief side and a virtual line extending the generatrix of the large flange surface to the grinding relief side are
6. A tapered roller bearing according to claim 3, wherein a reference point is an intersection with a virtual line extended toward the relief side, a recess width from said reference point to said large rib surface is defined as A, and a recess width from said reference point to said raceway surface is defined as B, such that A<B . A tapered roller bearing according to any one of claims 1 to 6, in which the grain size number of the prior austenite grains on the large rib surface of the inner ring is 6 or more. A tapered roller bearing according to any one of claims 1 to 7, in which the large rib surface of the inner ring is formed of a nitride layer having a nitrogen content of 0.05 wt% or more. A tapered roller bearing according to any one of claims 1 to 8, in which the surface roughness of the large rib surface of the inner ring is 0.1 μm Ra or less, and the surface roughness of the large end surface of the tapered roller is 0.12 μm Ra or less. when a set radius of curvature of the large end face of the tapered roller is R and a base radius of curvature from an apex of the cone angle of the rolling surface to a large rib surface of the inner ring is R _BASE , R/R _BASE is 0.70 or more and 0.95 or less,
10. A tapered roller bearing according to claim 1, wherein when the actual radius of curvature of the large end face of said tapered roller is R _ACTUAL , R _ACTUAL /R of at least one tapered roller among said plurality of tapered rollers is 0.3 or more. A tapered roller bearing according to any one of claims 1 to 10, which supports a rotating part in an automobile transmission or differential.

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