Thrust roller bearing

Abstract

The thrust roller bearing (1) includes a plurality of rollers (2) arranged radially and a pair of annular washers (3, 4) having raceway surfaces (3a, 4a), and the rollers (2) roll on the raceway surfaces. The raceway surfaces (3a, 4a) are arranged to face each other. The rollers (2) are made of high-carbon chromium bearing steel and have a surface roughness of 0.01 to 0.10 in terms of Rvk and 0.01 to 0.08 in terms of Rk. At least one of the washers (3, 4) is made of carbon steel, the surface compressive residual stress of the raceway surfaces (3a, 4a) is -1400 MPa to -1000 MPa, and the Vickers hardness of the surface of the raceway surfaces (3a, 4a) is 850 to 900.

Description

Technical Field

[0001] The present invention relates to a thrust roller bearing. Background Art

[0002] A known thrust roller bearing includes a plurality of radially arranged rollers and a pair of annular washers having raceway surfaces, where the rollers roll on the raceway surfaces (for example, refer to Japanese Patent Application Laid-Open No. 2003-239981 (JP2003-239981A)). The thrust roller bearing is inserted, for example, between a non-rotating member and a rotating member in a transmission of a vehicle, and is used to smoothly rotate the rotating member while receiving a thrust in the bearing axis direction. Summary of the Invention

[0003] In a thrust roller bearing, wear tends to increase in a poor lubrication environment where the amount of lubricating oil is small. In recent years, the amount of lubricating oil supplied to transmissions of vehicles and the like has tended to decrease, and there is a need for a thrust roller bearing with high wear resistance, which can suppress wear even in a poor lubrication environment.

[0004] The present invention provides a thrust roller bearing with improved wear resistance.

[0005] An aspect of the present invention relates to a thrust roller bearing. The thrust roller bearing includes: a plurality of radially arranged rollers; and a pair of annular washers having raceway surfaces on which the plurality of rollers roll. These raceway surfaces are arranged to face each other. The rollers are made of high-carbon chromium bearing steel, and the rollers have a surface roughness of 0.01 to 0.10 in terms of Rvk and 0.01 to 0.08 in terms of Rk. At least one of the pair of washers is made of carbon steel, the surface compressive residual stress of the raceway surface is -1400 MPa to -1000 MPa, and the Vickers hardness of the surface of the raceway surface is 850 to 900.

[0006] According to this aspect, wear resistance can be improved. Brief Description of the Drawings

[0007] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the drawings, in which like reference numerals denote like elements, and in which:

[0008] Figure 1 is a cross-sectional view showing a cross-section including the bearing axis of a thrust roller bearing according to an embodiment of the present invention;

[0009] Figure 2 is a view showing the movement of lubricating oil in a poor lubrication environment;

[0010] Figure 3 is a graph showing Rvk and Rk as parameters representative of surface roughness;

[0011] Figure 4A is a view showing the temperature measurement positions in a test for evaluating wear resistance;

[0012] Figure 4B is a graph showing the start time of wear in a test for evaluating wear resistance;

[0013] Figure 5A is a graph showing the Rvk of the rollers in the examples of the present invention, the Rvk of the rollers in the conventional examples, and the Rvk of the rollers in the comparative examples;

[0014] Figure 5B is a graph showing the Rk of the rollers in the examples of the present invention, the Rk of the rollers in the conventional examples, and the Rk of the rollers in the comparative examples;

[0015] Figure 5C is a graph showing the hardness of the rollers in the examples of the present invention, the hardness of the rollers in the conventional examples, and the hardness of the rollers in the comparative examples;

[0016] Figure 5D is a graph showing the surface residual stress of the rollers in the examples of the present invention, the surface residual stress of the rollers in the conventional examples, and the surface residual stress of the rollers in the comparative examples;

[0017] Figure 6A is a graph showing the Rvk of the raceway surfaces in the examples of the present invention, the Rvk of the raceway surfaces in the conventional examples, and the Rvk of the raceway surfaces in the comparative examples;

[0018] Figure 6B is a graph showing the Rk of the raceway surfaces in the examples of the present invention, the Rk of the raceway surfaces in the conventional examples, and the Rk of the raceway surfaces in the comparative examples;

[0019] Figure 6C is a graph showing the hardness of the raceway surfaces in the examples of the present invention, the hardness of the raceway surfaces in the conventional examples, and the hardness of the raceway surfaces in the comparative examples;

[0020] Figure 6D is a graph showing the surface residual stress of the raceway surfaces in the examples of the present invention, the surface residual stress of the raceway surfaces in the conventional examples, and the surface residual stress of the raceway surfaces in the comparative examples; and

[0021] Figure 7 is a graph showing the start time of wear in the examples of the present invention, the start time of wear in the conventional examples, and the start time of wear in the comparative examples. Detailed Description

[0022] Embodiment

[0023] Refer to Figures 1 to 7 Embodiments of the present invention will be described. It should be noted that the embodiments described below are shown as preferred specific examples for implementing the present invention. Although some technically preferred technical problems are specifically shown, the technical scope of the present invention is not limited to the specific embodiments.

[0024] Figure 1 FIG. is a cross-sectional view showing a cross-section of a bearing axis including a thrust roller bearing according to an embodiment of the present invention. The thrust roller bearing 1 includes: a plurality of radially arranged rollers 2; an annular first washer 3 having a first raceway surface 3a on which the rollers 2 roll; and an annular second washer 4 having a second raceway surface 4a on which the rollers 2 roll. The first washer 3 and the second washer 4 are arranged such that the first raceway surface 3a and the second raceway surface 4a face each other in the axial direction of the bearing axis O. In this thrust roller bearing, the first washer 3 and the second washer 4 rotate relative to each other about the bearing axis O.

[0025] The thrust roller bearing 1 is a bearing that, for example, is inserted between a rotating member and a non-rotating member in a transmission of a vehicle or industrial machinery, and is used to smoothly rotate the rotating member by rolling the rollers 2 while receiving thrust in the axial direction.

[0026] The rollers 2 are rotatably held by an annular cage 5 shown by a dashed line in Figure 1 . The rollers 2 rotate about the bearing axis O by being held by the cage 5, and at the same time rotate by the relative rotation between the first washer 3 and the second washer 4. The first washer 3 integrally has a circular flat raceway portion 31 perpendicular to the axial direction and a short cylindrical rib 32 extending from the radially inner end of the raceway portion 31 to the first side in the axial direction ( Figure 1 the right side in, the second washer 4 side). The surface of the raceway portion 31 on the first side in the axial direction is the first raceway surface 3a. The second washer 4 has a circular flat raceway portion 41 perpendicular to the axial direction. The surface of the raceway portion 41 on the second side in the axial direction ( Figure 1 the left side in, the first washer 3 side) is the second raceway surface 4a. In the present embodiment, the first washer 3 is provided on the rotating member, and the second washer 4 is provided on the non-rotating member.

[0027] The shapes of the first washer 3 and the second washer 4 are not limited to those shown. For example, the rib 32 of the first washer 3 may be omitted, or the second washer 4 may have a short cylindrical rib extending from the radially outer end of the raceway portion 41 to the second side in the axial direction.

[0028] As the roller 2, a roller made of high-carbon chromium bearing steel having high wear resistance can be used. In the present embodiment, the roller 2 in which special heat treatment is performed on the high-carbon chromium bearing steel to further increase the surface hardness is used. More specifically, the roller 2 contains 0.1 mass% to 0.6 mass% of carbon and 1.1 mass% to 1.6 mass% of nitrogen within a range of 0.1 mm from the surface. In the present embodiment, the surface compressive residual stress of the roller 2 is -1200 MPa or more and less than -900 MPa, and the surface Vickers hardness of the roller 2 is 700 to 850. It can be considered that the surface hardness of the roller 2 is further increased by performing shot peening on the roller 2. However, as described below, it has been confirmed that when shot peening is performed on the roller 2, the wear resistance of the thrust roller bearing 1 is reduced. Therefore, it is not preferable to perform shot peening on the roller 2. Like the first washer 3 and the second washer 4, washers made of carbon steel having relatively high hardness and high wear resistance are used.

[0029] As Figure 2 shown, in a poor lubrication environment where the amount of the lubricating oil 6 is small, the lubricating oil 6 moves between the first raceway surface 3a and the second raceway surface 4a via the roller 2. For example, the lubricating oil 6 supplied to the first raceway surface 3a moves to the surface of the roller 2 by the rotation of the roller 2, and is further supplied from the surface of the roller 2 to the second raceway surface 4a.

[0030] At this time, when the surface of the roller 2 is rough, too much of the lubricating oil 6 remains on the surface of the roller 2, making it less likely for the lubricating oil 6 to be supplied to the raceway surfaces 3a, 4a. Therefore, it is desirable to make the surface of the roller 2 as smooth as possible and prevent the roller 2 from retaining too much of the lubricating oil 6. In addition, it is desirable to make the raceway surfaces 3a, 4a hard so that the raceway surfaces 3a, 4a do not wear even when the amount of the lubricating oil 6 is small. Therefore, in the present embodiment, the wear resistance is improved by making the surface of the roller 2 smooth and performing shot peening on the washers 3, 4 to increase the surface hardness of the raceway surfaces 3a, 4a.

[0031] Specifically, in the present embodiment, the surface roughness of the roller 2 is set to be 0.01 to 0.10 in terms of Rvk and 0.01 to 0.08 in terms of Rk. Further, in the present embodiment, by performing shot peening on the washers 3 and 4, the surface compressive residual stress of the raceway surfaces 3a and 4a is set to -1400 MPa to -1000 MPa, and the surface Vickers hardness of the raceway surfaces 3a and 4a is set to 850 to 900. Similar to the present embodiment, it is desirable to set the surface residual stress and hardness of the raceway surfaces 3a and 4a of both the first washer 3 and the second washer 4 within this numerical range. However, by setting the surface residual stress and hardness of at least one of the raceway surfaces 3a and 4a of the first washer 3 and the second washer 4 within this numerical range, an improved wear resistance effect can be obtained compared to the conventional case. In particular, in the first washer 3 that rotates as the rotating member rotates, the lubricating oil 6 may scatter due to centrifugal force, and lubrication failure may occur. Therefore, it is desirable to set at least the surface residual stress and hardness of the first raceway surface 3a of the first washer 3 within this numerical range.

[0032] Further, in order to suppress the scattering of the lubricating oil 6 due to centrifugal force, it is more desirable to make the surface roughness of the first raceway surface 3a of the first washer 3 relatively rough so that the lubricating oil 6 can be more easily retained on the first raceway surface 3a. It should be noted that if the surface roughness of the first raceway surface 3a is made too rough, the lubricating oil 6 will be difficult to move to the roller 2 or the second raceway surface 4a, and the wear resistance may be reduced. Therefore, it is desirable to adjust the surface roughness of the first raceway surface 3a to an appropriate roughness so that the lubricating oil 6 can be appropriately retained. In the present embodiment, the surface roughness of the first raceway surface 3a is set to be 0.05 to 0.22 in terms of Rvk and 0.05 to 0.15 in terms of Rk. In the present embodiment, the surface roughness of both the first raceway surface 3a and the second raceway surface 4a is set to be 0.05 to 0.22 in terms of Rvk and 0.05 to 0.15 in terms of Rk. The surface roughness of the roller 2 or the surface roughness of the raceway surfaces 3a and 4a can be appropriately adjusted under polishing conditions such as barrel polishing. Further, the surface compressive residual stress and the surface Vickers hardness of the raceway surfaces 3a and 4a can be appropriately adjusted by shot peening conditions.

[0033] Here, Rvk and Rk representing the surface roughness are lubricity evaluation parameters (load curve parameters) of the platform structure surface. As Figure 3 shown, the region between the height positions where the equivalent straight line 72 of the gentlest slope at the center of the load curve 71 as the surface unevenness intersects with the 0% and 100% load length ratios is defined as the core portion 73. The height of the core portion 73 (the height difference between the top and the bottom) is Rk. Rvk represents the depth of the protruding valley portion 74.

[0034] Evaluation of wear resistance

[0035] The thrust roller bearing 1 of this embodiment was manufactured as a prototype and used in the example, and its wear resistance was evaluated. The thrust roller bearing 1 of the example was manufactured as follows. A bar line of JIS SUJ2 was cut to obtain the roller workpieces of the example. The roller workpieces of the example were carbonitrided at a temperature of 820°C to 870°C for one hour in an atmosphere with a carbon potential of 1.2 to 1.6 and an ammonia concentration of 0.1 vol% to 0.5 vol%. Then, the roller workpieces were immersed in oil at 80°C, rapidly cooled, and quenched. After quenching, the roller workpieces were tempered at 200°C for one hour. Then, polishing was performed, and barrel polishing was performed for two hours. As a result, the rollers 2 of the example were obtained. In the range of 0.1 mm from the surface of the rollers 2 of the example, 1.1 mass% to 1.6 mass% of carbon and 0.1 mass% to 0.6 mass% of nitrogen were contained. The SAE1075 steel plate was punched into a ring shape and forged to produce the workpiece of the first washer of the example and the workpiece of the second washer of the example. The workpiece of the first washer of the example and the workpiece of the second washer of the example were held at a temperature of 760°C to 830°C for 0.5 hour, and then they were immersed in oil at 80°C, rapidly cooled, and quenched. After quenching, the workpieces were tempered at 200°C for one hour. Then, shot peening was performed, polishing was performed, and barrel polishing was performed for five hours. As a result, the first washer 3 of the example and the second washer 4 of the example were obtained. The shot peening conditions are as follows.

[0036] · Shot peening particle diameter: 100 μm or less

[0037] · Shot peening particle material: iron

[0038] · Shot peening pressure: 0.5 MPa

[0039] The SPCD steel plate was punched into a ring shape to remove the part that would become the pocket. Thus, the cage 5 was obtained. The thrust roller bearing 1 was manufactured by combining the rollers 2 of the example, the first washer 3 of the example, the second washer 4 of the example, and the cage 5. As a result, the thrust roller bearing 1 of the example was obtained.

[0040] As Figure 4A shown, the test was carried out by attaching the first washer 3 and the second washer 4 to the fixture 70, and 0.05 g of lubricating oil 6 was dripped onto the first raceway surface 3a with an axial load of 9 kN and a rotational speed of 2000 rpm. In this test, the temperature of the area represented by A in Figure 4A was measured, that is, the temperature of the back surface of the fixture 70 holding the second washer 4 was measured, and the test was terminated when the temperature rose to 80°C.

[0041] Figure 4Bshows the change in temperature measured during the test. As Figure 4B shown, the change in temperature over time can be divided into: a first region in which the temperature gradually increases after the start of the test; a second region in which the temperature is substantially constant and stable; and a third region in which wear occurs and the temperature increases. The start time of the third region is defined as the wear start time. In this embodiment, the wear resistance is evaluated based on the wear start time. The number of tests is three.

[0042] In addition, for comparison with the example, a thrust roller bearing of a conventional example was prepared, in which a roller 2 made of a quenched and tempered material of high-carbon chromium bearing steel was used, and adjustment of the surface roughness of the roller 2 and the surface roughness of the raceway surfaces 3a, 4a or shot peening was not performed. Evaluation of the wear resistance was performed in the same manner as in the example.

[0043] The thrust roller bearing 1 according to the conventional example was manufactured as follows. A bar stock of JIS SUJ2 was cut to obtain a roller workpiece of the conventional example. The roller workpiece of the conventional example was held at a temperature of 820 °C to 850 °C for 0.5 hours, immersed in oil at 80 °C, rapidly cooled and quenched. After quenching, the roller workpiece was tempered at 200 °C for one hour. Then polishing was performed, and barrel polishing was performed for one hour. As a result, the roller 2 of the conventional example was obtained. An SAE1075 steel plate was punched into a ring shape and forged to produce a workpiece of the first washer of the conventional example and a workpiece of the second washer of the conventional example. The workpiece of the first washer of the conventional example and the workpiece of the second washer of the conventional example were held at a temperature of 760 °C to 830 °C for 0.5 hours, then immersed in oil at 80 °C, rapidly cooled and quenched. After quenching, the workpiece was tempered at 200 °C for one hour. Then polishing was performed, and barrel polishing was performed for one hour. As a result, the first washer 3 of the conventional example and the second washer 4 of the conventional example were obtained. An SPCD steel plate was punched into a ring shape to remove a part that would become a pocket. Thus, the cage 5 was obtained. The thrust roller bearing 1 was manufactured by combining the roller 2 of the conventional example, the first washer 3 of the conventional example, the second washer 4 of the conventional example, and the cage 5. As a result, the thrust roller bearing 1 of the conventional example was obtained.

[0044] In addition, a thrust roller bearing of Comparative Example 1 was prepared, in which the same roller 2 as in the example was used, and only the surface roughness of the raceway surfaces 3a, 4a was adjusted, and shot peening was not performed. A thrust roller bearing of Comparative Example 2 was prepared, in which the roller 2 used was made of high-carbon chromium bearing steel subjected to shot peening, and the same washers 3, 4 as in the example were used. Evaluation of the wear resistance was performed in the same manner as in the example.

[0045] The thrust roller bearing 1 of Comparative Example 1 was manufactured as follows. A bar stock of JIS SUJ2 was cut to obtain the roller workpiece of Comparative Example 1. The roller workpiece of Comparative Example 1 was carbonitrided by holding it at a temperature of 820°C to 870°C for one hour in an atmosphere with a carbon potential of 1.2 to 1.6 and an ammonia concentration of 0.1 vol% to 0.5 vol%. Then, the roller workpiece was immersed in oil at 80°C, rapidly cooled, and quenched. After quenching, the roller workpiece was tempered at 200°C for one hour. Then, polishing was performed, and barrel polishing was performed for two hours. As a result, the roller 2 of Comparative Example 1 was obtained. In the range within 0.1 mm from the surface of the roller 2 of Comparative Example 1, it contains 1.1 mass% to 1.6 mass% of carbon and 0.1 mass% to 0.6 mass% of nitrogen. The SAE1075 steel plate was punched into a ring shape and forged to produce the workpiece of the first washer of Comparative Example 1 and the workpiece of the second washer of Comparative Example 1. The workpiece of the first washer of Comparative Example 1 and the workpiece of the second washer of Comparative Example 1 were held at a temperature of 760°C to 830°C for 0.5 hour, and then immersed in oil at 80°C, rapidly cooled, and quenched. After quenching, the workpiece was tempered at 200°C for one hour. Then, polishing was performed, and barrel polishing was performed for five hours. As a result, the first washer 3 of Comparative Example 1 and the second washer 4 of Comparative Example 1 were obtained. The SPCD steel plate was punched into a ring shape to remove the part that would become the pocket. Thus, the cage 5 was obtained. The thrust roller bearing 1 was made by combining the roller 2 of Comparative Example 1, the first washer 3 of Comparative Example 1, the second washer 4 of Comparative Example 1, and the cage 5. As a result, the roller bearing 1 of Comparative Example 1 was obtained.

[0046] The thrust roller bearing 1 of Comparative Example 2 was manufactured as follows. A bar stock of JIS SUJ2 was cut to obtain the roller workpiece of Comparative Example 2. The roller workpiece of Comparative Example 2 was carbonitrided by holding it at a temperature of 820°C to 870°C for one hour in an atmosphere with a carbon potential of 1.2 to 1.6 and an ammonia concentration of 0.1 vol% to 0.5 vol%. Then, the roller workpiece was immersed in oil at 80°C, rapidly cooled, and quenched. After quenching, the roller workpiece was tempered at 200°C for one hour. Then, shot peening was performed, polishing was performed, and barrel polishing was performed for two hours. As a result, the roller 2 of Comparative Example 2 was obtained. In the range within 0.1 mm from the surface of the roller 2 of Comparative Example 2, it contains 1.1 mass% to 1.6 mass% of carbon and 0.1 mass% to 0.6 mass% of nitrogen. The shot peening conditions are as follows.

[0047] · Shot peening particle diameter: 100 μm or less

[0048] · Shot peening particle material: iron

[0049] · Shot peening pressure: 0.5 MPa

[0050] The SAE1075 steel plate was annularly punched and forged to produce the workpiece of the first washer of Comparative Example 2 and the workpiece of the second washer of Comparative Example 2. The workpiece of the first washer of Comparative Example 2 and the workpiece of the second washer of Comparative Example 2 were held at a temperature of 760 °C to 830 °C for 0.5 hour, and then immersed in oil at 80 °C, rapidly cooled and quenched. After quenching, the workpiece was tempered at 200 °C for one hour. Then, shot peening treatment was performed, polishing was performed, and barrel polishing was performed for five hours. As a result, the first washer 3 of Comparative Example 2 and the second washer 4 of Comparative Example 2 were obtained. The shot peening treatment conditions are as follows.

[0051] · Shot peening particle diameter: 100 μm or less

[0052] · Shot peening particle material: iron

[0053] · Shot peening pressure: 0.5 MPa

[0054] The SPCD steel plate was annularly punched to remove the part that would become the pocket hole. Thus, the cage 5 was obtained. The thrust roller bearing 1 was made by combining the roller 2 of Comparative Example 2, the first washer 3 of Comparative Example 2, the second washer 4 of Comparative Example 2, and the cage 5. As a result, the roller bearing 1 of Comparative Example 2 was obtained.

[0055] As shown in Table 1, Comparative Example 1 was the same as the example except that shot peening treatment was not performed on the washers 3 and 4; Comparative Example 2 was the same as the example except that shot peening treatment was not performed on the roller 2.

[0056] Table 1

[0057]

[0058] Regarding the example, the conventional example, and Comparative Examples 1 and 2, respectively Figure 5A It shows Rvk on the surface of the roller 2, Figure 5B It shows Rk on the surface of the roller 2, Figure 5C It shows the Vickers hardness on the surface of the roller 2, Figure 5D It shows the surface residual stress of the roller 2. In addition, regarding the example, the conventional example, and Comparative Examples 1 and 2, respectively Figure 6A It shows Rvk on the raceway surfaces 3a and 4a of the washers 3 and 4, Figure 6B It shows Rk on the raceway surfaces 3a and 4a of the washers 3 and 4, Figure 6C It shows the Vickers hardness of the raceway surfaces 3a and 4a, Figure 6D It shows the surface residual stress of the raceway surfaces 3a and 4a.

[0059] As Figure 5AAs shown in [reference], in the conventional example, the surface Rvk of the roller 2 is greater than 0.1, while in the examples and Comparative Examples 1 and 2 in which the surface roughness is improved, Rvk is from 0.01 to 0.10. In addition, as Figure 5B shown in [reference], in the conventional example, the surface Rk of the roller 2 is greater than 0.1, while in the examples and Comparative Examples 1 and 2 in which the surface roughness is improved, Rk is from 0.01 to 0.08. As described above, in the examples according to the present invention (and in Comparative Examples 1 and 2), both the Rvk and Rk of the surface of the roller 2 are smaller than those in the conventional example, and the surface roughness is also smaller.

[0060] In addition, as Figure 5C shown in [reference], in Comparative Example 2 in which shot peening is performed, there are samples in which the surface Vickers hardness of the roller 2 is greater than 850. On the other hand, in the examples (and Comparative Example 1) in which shot peening is not performed, the surface Vickers hardness of the roller 2 is from 700 to 850. In addition, as Figure 5D shown in [reference], in the conventional example, the surface compressive residual stress of the roller 2 is -900 MPa. On the other hand, the surface compressive residual stress of the roller 2 is less than -1200 in Comparative Example 2, and is -1200 MPa or greater and less than -900 MPa in the examples (and Comparative Example 1). That is, in the examples according to the present invention (and Comparative Example 1), the surface compressive residual stress has an intermediate value between the conventional example and Comparative Example 2.

[0061] In addition, as Figure 6A shown in [reference], the surface Rvk of the raceway surfaces 3a, 4a is greater than 0.22 in the conventional example, while it is from 0.05 to 0.22 in the examples and Comparative Examples 1 and 2 in which the surface roughness is improved. In addition, as Figure 6B shown in [reference], the surface Rk of the raceway surfaces 3a, 4a is 0.2 or greater in the conventional example, while it is from 0.05 to 0.15 in the examples. As described above, in the examples according to the present invention (and Comparative Examples 1 and 2), both the surface Rvk and Rk of the raceway surfaces 3a, 4a are smaller than those in the conventional example, and the surface roughness is also smaller.

[0062] In addition, as Figure 6C shown in [reference], the surface Vickers hardness of the raceway surfaces 3a, 4a is less than 850 in the conventional example and Comparative Example 1 in which shot peening is not performed. On the other hand, the surface Vickers hardness of the raceway surfaces 3a, 4a is from 850 to 900 in the examples and Comparative Example 2 in which shot peening is performed. In addition, as Figure 6DAs shown, in the conventional example and Comparative Example 1 where shot peening is not performed, the surface compressive residual stress of the raceway surfaces 3a and 4a is -600 MPa or greater, while in the examples (and Comparative Example 2) it is -1400 MPa to -1000 MPa. That is, in the examples (and Comparative Example 2) according to the present invention, compared with the conventional example and Comparative Example 1, the raceway surfaces 3a and 4a are hard on the surface and the absolute value of the surface compressive residual stress is large.

[0063] Figure 7 The measurement results of the wear start times of the examples, the conventional example, and Comparative Examples 1 and 2 are shown. Figure 7 The measurement results in represent the average value of three tests. It can be considered that, as Figure 7 shown, in Comparative Example 1, by improving the surface roughness of the roller 2, the wear start time is slightly longer than that in the conventional example. However, due to the insufficient hardness of the raceway surfaces 3a and 4a, the wear increases. It can be considered that, in Comparative Example 2, by performing shot peening on the roller 2, the raceway surfaces 3a and 4a are relatively prone to wear, and thus a sufficient wear start time cannot be obtained. On the other hand, in the examples according to the present invention, the wear start time is five times or longer compared with the conventional example. As a result, it should be understood that the wear resistance in a poor lubrication environment is significantly improved.

[0064] Functions and effects of the embodiments

[0065] As described above, in the thrust roller bearing 1 according to the present embodiment, the roller 2 is made of high-carbon chromium bearing steel, and the roller 2 has a surface roughness of 0.01 to 0.10 in terms of Rvk and 0.01 to 0.08 in terms of Rk. At least one of the washers 3 and 4 is made of carbon steel, the surface compressive residual stress of the raceway surfaces 3a and 4a is -1400 MPa to -1000 MPa, and the surface Vickers hardness of the raceway surfaces 3a and 4a is 850 to 900.

[0066] By reducing the surface roughness of the roller 2, the lubricating oil 6 easily circulates between the first raceway surface 3a and the second raceway surface 4a by the rotation of the roller 2, and the wear resistance can be improved even in a poor lubrication environment. In addition, by increasing the surface hardness of the raceway surfaces 3a and 4a by means of shot peening, the wear can be suppressed even in a state where the lubricating oil 6 is very little, and the wear resistance can be further improved.

[0067] Supplementary description

[0068] Although the present invention has been described above based on the embodiments, the embodiments do not limit the present invention according to the claims. It should be noted that not all combinations of the features described in the embodiments are essential for the means of solving the problems of the present invention.

[0069] In addition, the present invention can be appropriately modified and implemented without departing from the spirit of the present invention. For example, in the embodiments, the case where the rollers 2 are arranged in a row in the circumferential direction is described, but the arrangement of the rollers 2 is not limited thereto. For example, the rollers 2 can be arranged in two rows or more rows.

Claims

1. A thrust roller bearing (1), characterized in that it comprises: a plurality of rollers (2) arranged radially; and a pair of annular washers (3, 4), the pair of washers (3, 4) having raceway surfaces (3a, 4a) on which the plurality of rollers (2) roll, the raceway surfaces (3a, 4a) being arranged to face each other, wherein: the rollers (2) are made of high-carbon chromium bearing steel, and the rollers (2) have a surface roughness of 0.01 to 0.10 in terms of Rvk and 0.01 to 0.08 in terms of Rk; and at least one of the pair of washers (3, 4) is made of carbon steel, the surface compressive residual stress of the raceway surfaces (3a, 4a) is -1400 MPa to -1000 MPa, and the Vickers hardness of the surface of the raceway surfaces (3a, 4a) is 850 to 900.

2. The thrust roller bearing (1) according to claim 1, characterized in that: the pair of washers (3, 4) includes a first washer (3) and a second washer (4), the first washer (3) is provided on a rotating member and rotates with the rotation of the rotating member, the second washer (4) is provided on a non-rotating member and does not rotate with the rotation of the rotating member; and the first washer (3) is made of carbon steel, the surface compressive residual stress of the raceway surface (3a) is -1400 MPa to -1000 MPa, and the Vickers hardness of the surface of the raceway surface (3a) is 850 to 900.

3. The thrust roller bearing (1) according to claim 2, characterized in that in the first washer (3), the surface roughness of the raceway surface (3a) is 0.05 to 0.22 in terms of Rvk and 0.05 to 0.15 in terms of Rk.

4. The thrust roller bearing (1) according to any one of claims 1 to 3, characterized in that both of the pair of washers (3, 4) are made of carbon steel, the surface compressive residual stress is -1400 MPa to -1000 MPa, and the Vickers hardness of the surface is 850 to 900.

5. The thrust roller bearing (1) according to any one of claims 1 to 3, characterized in that the rollers (2) contain 0.1 mass% to 0.6 mass% of carbon and 1.1 mass% to 1.6 mass% of nitrogen within a range of 0.1 mm from the surface, and the surface compressive residual stress of the rollers (2) is -1200 MPa or greater and less than -900 MPa.

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