Rolling bearings

Abstract

The rolling bearing comprises: a first raceway surface (11); a second raceway surface (12); and a plurality of rolling elements rotatably arranged between the first raceway surface (11) and the second raceway surface (12). A plurality of recesses (20) are provided on at least one of the first raceway surface (11), the second raceway surface (12) and the rolling surfaces of the plurality of rolling elements. The area ratio of the opening of the recess (20) to the at least one surface is in the range of 5% to 37%. The equivalent circular diameter of the opening of each recess (20) is in the range of 1 μm to 27 μm. The depth of each recess (20) in a direction perpendicular to the at least one surface is in the range of 3 μm to 10 μm. The surface waviness of the at least one surface excluding the recess (20) is less than or equal to 0.2 μm.

Description

Technical Field

[0001] The invention relates to rolling bearings. Background Art

[0002] For example, the planetary gears used in the planetary gear mechanism in the transmission are rotatably supported on the support shaft of the planetary carrier via needle roller bearings. The needle roller bearings are lubricated by forcibly supplying lubricating oil from the support shaft side (refer to Japanese Unexamined Patent Application Publication No. 2015-083861 (JP 2015-083861 A)).

[0003] In recent years, the amount of lubricating oil in the bearings tends to decrease due to the reduction in the amount of lubricating oil forcibly supplied to the bearings for the purpose of saving natural resources and energy, and further, the lubricating oil is dispersed by the centrifugal force generated by the bearings rotating at a higher speed. When the amount of lubricating oil in the bearings decreases, insufficient oil film occurs, which causes a temperature rise and bearing seizure. Summary of the invention

[0004] The present invention provides a rolling bearing capable of suppressing temperature rise and improving seizure resistance.

[0005] As a result of intensive research, the inventors have found that by providing a plurality of recesses on at least one of the rolling surface of the rolling element and the raceway surface on which the rolling element rolls and setting the area ratio of the opening of the recesses, the equivalent circle diameter and depth of each recess, and the surface waviness of the surface excluding the recesses within an appropriate range, lubricating oil can be easily accumulated in the recesses, and the oil film thickness on the surface (i.e., the thickness of the oil film) can be increased. The inventors have completed the present invention based on this finding.

[0006] One aspect of the present invention relates to a rolling bearing, which includes: a first raceway surface; a second raceway surface; and a plurality of rolling elements, which are arranged between the first raceway surface and the second raceway surface in a rotatable manner. A plurality of recesses are provided on at least one of the first raceway surface, the second raceway surface, and the rolling surfaces of the plurality of rolling elements. The area ratio of the openings of the plurality of recesses to the at least one surface is in the range of 5% to 37%. The equivalent circular diameter of the opening of each of the plurality of recesses is in the range of 1 μm to 27 μm. The depth of each of the plurality of recesses in a direction perpendicular to the at least one surface is in the range of 3 μm to 10 μm. The surface waviness of the at least one surface excluding the plurality of recesses is less than or equal to 0.2 μm.

[0007] In the rolling bearing according to the above aspect of the present invention, lubricating oil can easily accumulate in the recessed portion provided on at least one of the first raceway surface, the second raceway surface, and the rolling surface of the rolling element, and the thickness of the oil film on the at least one surface can be increased. With this configuration, it is possible to suppress the lack of oil film on the at least one surface. Therefore, the temperature rise of the rolling bearing can be suppressed, and the seizure resistance can be improved.

[0008] The rolling element may be a roller. In this case, a temperature rise of the rolling bearing including the roller as the rolling element can be suppressed, and the seizure resistance can be improved.

[0009] Each rolling element may be any one of a needle roller, a cylindrical roller, and a long cylindrical roller. In this case, the temperature rise of the rolling bearing including any one of the needle roller, the cylindrical roller, and the long cylindrical roller (i.e., the rod roller) as the rolling element can be suppressed, and the anti-seizure property can be improved.

[0010] According to the rolling bearing of the above aspect of the present invention, it is possible to suppress a temperature rise and improve seizure resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0012] Figure 1 is a partial cross-sectional view of a planetary gear mechanism including a rolling bearing according to an embodiment of the present invention;

[0013] Figure 2 is along Figure 1 A cross-sectional view taken along line II-II in FIG.

[0014] Figure 3 is an enlarged cross-sectional view showing a rolling bearing;

[0015] Figure 4 is a graph showing the results of the evaluation test. In the graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the area ratio of the concave portion;

[0016] Figure 5 is a graph showing the results of the evaluation test. In the graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the equivalent circle diameter of the concave portion;

[0017] Figure 6 is a graph showing the results of the evaluation test. In the graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the depth of the recessed portion;

[0018] Figure 7 is a graph showing the results of the evaluation test. In the graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the surface waviness of the surface excluding the concave portion; and

[0019] Figure 8 is a table showing the results of the evaluation test. DETAILED DESCRIPTION

[0020] Figure 1 is a partial cross-sectional view of a planetary gear mechanism including a rolling bearing according to an embodiment of the present invention. Figure 2 is along Figure 1 A cross-sectional view taken along line II-II in FIG. Figure 1 and Figure 2 The planetary gear mechanism 50 is used in, for example, a transmission of a vehicle (eg, an automobile). The planetary gear mechanism 50 includes a sun gear 51 , an internal gear (ring gear) 52 , a plurality of planetary gears 53 , and a planet carrier 54 .

[0021] The sun gear 51 is assembled to the outer periphery of the rotating shaft 61 and is rotatable integrally with the rotating shaft 61. The internal gear 52 is arranged radially outside the sun gear 51 so as to be concentric with the sun gear 51. A plurality of planetary gears 53 (three planetary gears in the present embodiment) are arranged along the circumferential direction of the sun gear 51 and mesh with the outer periphery of the sun gear 51. In addition, each planetary gear 53 meshes with the inner periphery of the internal gear 52.

[0022] The planet carrier 54 includes a plurality of shafts 55 and a pair of planet carrier bodies 56. Each shaft 55 supports a corresponding one of the planetary gears 53 so that the corresponding one of the planetary gears 53 can rotate via the rolling bearing 10. The planet carrier body 56 supports the respective ends of the shafts 55. With this configuration, each planetary gear 53 rotates around the axis of the corresponding shaft 55 supporting the planetary gear 53, and also rotates around the outer periphery of the sun gear 51.

[0023] Figure 3 1 is an enlarged cross-sectional view showing a rolling bearing. The rolling bearing 10 is a needle roller bearing and includes a first raceway surface 11, a second raceway surface 12, a plurality of needle rollers (rolling elements) 13, and a cage 15. The first raceway surface 11 is provided at the axial center portion of the outer peripheral surface of the shaft 55. The second raceway surface 12 is provided on the inner peripheral surface of the planetary gear 53.

[0024] exist Figure 2 and Figure 3, the needle roller 13 is arranged to be able to roll between the first raceway surface 11 and the second raceway surface 12. The outer peripheral surface of the needle roller 13 serves as a rolling surface 14 that rolls on the first raceway surface 11 and the second raceway surface 12. The retainer 15 has an annular shape and retains the needle roller 13 at a predetermined interval in the axial direction. The outer peripheral surface of the retainer 15 slidably contacts the inner peripheral surface of the planetary gear 53, so that the rotation of the retainer 15 is guided.

[0025] An oil passage 57 is provided in the shaft 55 for forcibly supplying lubricating oil to the interior of the rolling bearing 10. The oil passage 57 extends from one axial end ( Figure 3 The washer 58 is disposed between each planet carrier body 56 and the corresponding planetary gear 53.

[0026] A plurality of minute recesses 20 for accumulating lubricating oil are provided on the rolling surface 14 of each needle roller 13. These minute recesses 20 are formed, for example, by performing sandblasting on the rolling surface 14 to form minute uneven portions, and then performing roller finishing to remove protrusions of the uneven portions. The shape of the recesses 20 is set as described below so that lubricating oil can be easily accumulated.

[0027] The ratio of the area of ​​the opening of the recess 20 to the area of ​​the rolling surface 14, that is, the area ratio of the opening of the recess 20 to the rolling surface 14 (hereinafter referred to as the area ratio A of the recess 20), is set to be greater than or equal to 5% and less than or equal to 37% (preferably, greater than or equal to 8% and less than or equal to 30%). In other words, the area ratio A of the recess 20 is set within the range of 5% to 37% (preferably, within the range of 8% to 30%). The area ratio A of the recess 20 can be obtained by measuring the area of ​​the opening of the recess 20 in one field of view when observing the rolling surface 14 and calculating the percentage (%) of the area of ​​the opening to the area of ​​the observation field of view. The area of ​​one observation field of view is, for example, 0.4 mm 2 .

[0028] The equivalent circular diameter of the opening of each recess 20 (hereinafter referred to as the equivalent circular diameter B of the recess 20) is set to be greater than or equal to 1 μm and less than or equal to 27 μm (preferably, greater than or equal to 8 μm and less than or equal to 27 μm). In other words, the equivalent circular diameter B of the recess 20 is set within the range of 1 μm to 27 μm (preferably, within the range of 8 μm to 27 μm). The equivalent circular diameter B of the recess 20 can be obtained by measuring the area S of the opening of each recess 20 in the rolling surface 14 by processing a captured image of the rolling surface 14 and using the following formula.

[0029] B=2×(S / π)^(1 / 2)

[0030] The depth from the opening of the recess 20 to the bottom in the direction perpendicular to the rolling surface 14 (hereinafter referred to as the depth C of the recess 20) is set to be greater than or equal to 3 μm and less than or equal to 10 μm (preferably, greater than or equal to 3 μm and less than or equal to 9.6 μm). In other words, the depth C of the recess 20 is in the range of 3 μm to 10 μm (preferably, in the range of 3 μm to 9.6 μm). Note that the value of the depth C of the recess 20 represents the maximum valley depth Pv specified in Japanese Industrial Standard (JIS) B0601-2001. The surface waviness of the rolling surface 14 excluding the recess 20 (hereinafter referred to as the surface waviness D) is set to be less than or equal to 0.2 μm (preferably, less than or equal to 0.16 μm). In other words, the surface waviness D is set in the range of 0.2 μm or less (preferably, in the range of 0.16 μm or less). The value of the surface waviness D represents the arithmetic mean waviness Wa specified in JIS B 0601-2001.

[0031] Next, an evaluation test conducted by the inventors will be described to verify the effect obtained by the rolling bearing of the present invention. In the evaluation test, nine groups of samples (bearing steel balls) were used. One group includes three samples. Each group of samples is processed to have a plurality of recesses on a portion of the surface of the sample. Basically, as described above, the samples are processed by first performing sandblasting finishing and then performing roller finishing.

[0032] Under the condition that a small amount of lubricating oil was applied (5 μl of low-viscosity oil was applied to the sample surface), the three samples in each group were rotated at different rotation speeds (0.1 m / s, 1.0 m / s, and 2.0 m / s) from each other. Then, the change in the oil film thickness was measured at the central portion of the sample where the sample was in contact with the mating member (i.e., the counterpart member) of each sample, and the area ratio of the recessed portion, the equivalent circle diameter and depth of the recessed portion, and the surface waviness of the processed surface were also measured.

[0033] The change in oil film thickness is measured by using a known three-wavelength optical interferometer (e.g., refer to Japanese Unexamined Patent Application Publication No. 2017-207316) to simultaneously measure the oil film thickness on a processed surface on which a recess is provided (i.e., the thickness of the oil film) and the oil film thickness on an unprocessed surface on which a recess is not provided, and calculating the difference between the measured oil film thicknesses. The difference between the oil film thicknesses is a value obtained by subtracting the oil film thickness on the unprocessed surface from the oil film thickness on the processed surface. This value will be referred to as the oil film thickness variation hereinafter. The oil film thickness variation indicates that the oil film thickness on the processed surface increases as the value of the oil film thickness variation increases.

[0034] Figure 4 is a graph showing the results of the above evaluation test. In this graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the area ratio of the concave portion. Figure 4 As shown in , when the area ratio of the recessed portion is within the range of 5% to 37% (in other words, when the area ratio of the recessed portion is greater than or equal to 5% and less than or equal to 37%), the value of the oil film thickness variation amount is generally large, and the oil film thickness of the processed surface on which the recessed portion is provided is large. Therefore, as can be seen from this graph, by setting the area ratio of the recessed portion within the range of 5% to 37%, the lubricating oil can be more easily accumulated in the recessed portion, and the oil film thickness can be made larger (that is, the oil film thickness can be increased).

[0035] Figure 5 is a graph showing the results of the above evaluation test. In this graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the equivalent circle diameter of the concave portion. Figure 5 As shown in , when the equivalent circle diameter of the recessed portion is within the range of 1 μm to 27 μm, the value of the oil film thickness variation amount is generally large, and the oil film thickness of the processed surface on which the recessed portion is provided is large. Therefore, as can be seen from this graph, by setting the equivalent circle diameter of the recessed portion within the range of 1 μm to 27 μm, the lubricating oil can be more easily accumulated in the recessed portion, and the oil film thickness can be made larger (that is, the oil film thickness can be increased).

[0036] Figure 6 is a graph showing the results of the above evaluation test. In this graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the depth of the recess. Figure 6 As shown in , when the depth of the recessed portion is within the range of 3 μm to 10 μm, the value of the oil film thickness variation is generally large, and the oil film thickness of the processed surface on which the recessed portion is provided is large. Therefore, as can be seen from this graph, by setting the depth of the recessed portion within the range of 3 μm to 10 μm, the lubricating oil can be more easily accumulated in the recessed portion, and the oil film thickness can be made larger (that is, the oil film thickness can be increased).

[0037] Figure 7 is a graph showing the results of the above evaluation test. In this graph, the vertical axis represents the amount of change in oil film thickness, and the horizontal axis represents the surface waviness of the surface excluding the concave portion. Figure 7As shown in , when the surface waviness of the surface excluding the recessed portion is within a range of 0.2 μm or less, the value of the oil film thickness variation amount is generally large, and the oil film thickness of the processed surface on which the recessed portion is provided is large. Therefore, as can be seen from this graph, by setting the surface waviness of the surface excluding the recessed portion within a range of 0.2 μm or less, the lubricating oil can be easily accumulated in the recessed portion, and the oil film thickness can be made larger (that is, the oil film thickness can be increased).

[0038] Figure 8 is a table showing the results of the above evaluation test. Figure 8 As shown in , among the nine groups of samples A to J, only sample G (G-1, G-2, G-3) shows that all the oil film thickness changes have positive values, which means that the oil film thickness on the processed surface on which the recess is provided is increased. Then, in each sample G, the area ratio of the recess has a value (15%) in the range of 5% to 37%, and the equivalent circle diameter of the recess is a value (15.31 μm) in the range of 1 μm to 27 μm. The depth of the recess has a value (4.788 μm) in the range of 3 μm to 10 μm, and the surface waviness of the surface excluding the recess has a value (0.148 μm) in the range of 0.2 μm or less. Therefore, as can be seen from the test results, by setting the area ratio of the recess, the equivalent circle diameter and depth of the recess, and the surface waviness of the surface excluding the recess within the corresponding ranges as described above, the lubricating oil can be easily accumulated in the recess, and the oil film thickness on the processed surface on which the recess is provided can be increased.

[0039] As described above, in the rolling bearing 10 of the present embodiment, lubricating oil can be easily accumulated in the plurality of recesses 20 provided on the rolling surface 14 of the needle roller 13, and the thickness of the oil film on the rolling surface 14 can be increased. With this configuration, it is possible to suppress the shortage of the oil film on the rolling surface 14. Therefore, the temperature rise of the rolling bearing 10 can be suppressed, and the seizure resistance can be improved.

[0040] In all respects, the above-described embodiments should be considered as illustrative rather than restrictive. That is, the rolling bearing according to the present invention is not limited to those described in the above-described embodiments shown in the accompanying drawings, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiments, the recess 20 is provided on the rolling surface 14 of all the needle rollers 13. However, the recess 20 may be provided on the rolling surface 14 of at least one needle roller 13. In addition, the recess 20 may be provided on at least one of the first raceway surface 11, the second raceway surface 12, and the rolling surface 14 of the needle roller 13.

[0041] The rolling bearing of the present invention may be other roller bearings other than needle roller bearings, such as self-aligning roller bearings or cylindrical roller bearings. The rolling elements of the rolling bearing may be other cylindrical rollers or long cylindrical rollers (i.e., rod rollers) other than needle rollers. In addition, in addition to being a rolling bearing including rollers as rolling elements, the rolling bearing may also be a ball bearing including balls as rolling elements. Further, an example of applying the rolling bearing of the present invention to a planetary gear mechanism in a transmission is described. However, the application of the rolling bearing is not limited to this.

Claims

1. A rolling bearing, characterized in that include: A first raceway surface (11); A second raceway surface (12); and a plurality of rolling elements, the plurality of rolling elements being rotatably arranged between the first raceway surface (11) and the second raceway surface (12), wherein A plurality of recesses (20) are provided on at least one of the first raceway surface (11), the second raceway surface (12) and the rolling surfaces of the plurality of rolling elements, The area ratio of the openings of the plurality of recesses (20) to the at least one surface is in the range of 5% to 37%, The equivalent circle diameter of the opening of each of the plurality of recesses (20) is in the range of 1 μm to 27 μm, Each of the plurality of recesses (20) has a depth in a direction perpendicular to the at least one surface in a range of 3 μm to 10 μm, and The surface waviness of the at least one surface excluding the plurality of recesses (20) is less than or equal to 0.2 μm.

2. The rolling bearing according to claim 1, characterized in that The rolling elements are rollers.

3. The rolling bearing according to claim 2, characterized in that Each of the plurality of rolling elements is any one of a needle roller, a cylindrical roller, and a long cylindrical roller.

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