Angular ball bearing and rolling mechanism

Abstract

To provide an angular ball bearing and a rolling mechanism capable of reducing the cost in addition to suppressing the wear of balls even when the balls reversely slide with each other.SOLUTION: An angular ball bearing 1 is an angular ball bearing with no cage which includes an inner ring 2 and an outer ring 3, and a plurality of balls 4 laid between the inner ring 2 and the outer ring 3. The surface roughness of the ball 4 is 0.06 μmRa or less and the kinetic viscosity (40°C) of lubricant is 46 cst-220 cst. When the lubricant is grease, the consistency of the grease is No.1-No.00. It is preferable that the surface roughness of the ball 4 is 0.04 μmRa or less and the kinetic viscosity (40°C) of lubricant is 68 cst-150 cst.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an angular ball bearing and a rotation mechanism used, for example, in the main bearing portion of a reducer of a robot or construction machine, and relates to a technology specialized for achieving compactness, high load capacity, and high rigidity. [Background technology]

[0002] The following conventional technology exists as a cage-less (full ball) rolling bearing (Patent Document 1). This rolling bearing has only a large number of rolling elements arranged between an inner and outer ring, the rolling elements being made of martensitic stainless steel, and the surfaces of the rolling elements have nitrided layers with a hardness of Hv1200-1500. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-92686 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, bearings used in the main bearing parts of reducers in robots or construction machinery generally require a long life, high moment rigidity, and compactness. This means that there is a demand for improving the rated load within a certain bearing size, which necessitates an increase in the ball size or the number of balls. Increasing the ball size poses the problem of reduced bearing rigidity because the raceways become thinner. On the other hand, there is a method of using full ball bearings without a cage in order to increase the number of balls. However, with full ball bearings, the relative sliding speeds between adjacent balls in contact are in opposite directions, which causes "reverse sliding" in the contact area between the balls, making it a challenge to find ways to suppress ball wear.

[0005] The above-mentioned conventional technology solves this problem by providing a nitride layer on the surface of the ball, making the surface hardness extremely hard at HV1200 to 1500, thereby suppressing wear of the ball. However, a problem with nitrided balls with this surface hardness is that the heat treatment costs are high.

[0006] An object of the present invention is to provide an angular ball bearing and a rotation mechanism that are capable of suppressing ball wear even when reverse sliding occurs between the balls, and that can also reduce costs. [Means for solving the problem]

[0007] The angular contact ball bearing of the present invention is a cageless angular contact ball bearing including an inner ring, an outer ring, and a plurality of balls interposed between the inner ring and the outer ring, The surface roughness of the balls is 0.06 μmRa or less, and the kinetic viscosity of the lubricant (40° C.) is 46 cst or more and 220 cst or less.

[0008] By using a so-called full-ball angular contact ball bearing without a cage, the ball packing rate is improved compared to an angular contact ball bearing with a cage, which improves the relative load capacity and moment rigidity. When using a bearing without a cage, the balls come into contact with each other due to the relative difference in revolution speed, and the relative sliding speed between adjacent contacting balls is in the opposite direction, causing "reverse sliding" in the contact area between the balls.

[0009] With this configuration, it was found that wear on the ball surface can be suppressed by combining a lubricant with an optimal kinetic viscosity with an optimal ball surface roughness against "reverse slip." In other words, when the ball surface roughness is 0.06 μm or less in arithmetic mean roughness and the lubricant's kinetic viscosity (40°C) is in the range of 46 cst to 220 cst, an oil film is well formed between the balls, and wear on the balls is suppressed as feasible. This configuration, which combines a lubricant with an optimal kinetic viscosity with an optimal ball surface roughness, can reduce costs compared to conventional techniques such as applying special heat treatment to the ball surfaces.

[0010] The lubricant may be a grease, and the consistency of the grease may be from No. 1 to No. 00. The consistency is a value expressed in accordance with the JIS classification. It was found that when the lubricant is grease, grease that flows easily between the balls has a greater effect in suppressing ball wear. The ease with which grease can flow between the balls varies specifically with the consistency classification. The higher the consistency (softer), the easier it is for grease to flow between the balls, and the lower the consistency (harder), the worse it is for grease to flow. Greases with consistency classifications in the range of No. 1 to No. 00 have relatively good flowability between the balls, and can further increase the effect of suppressing ball wear.

[0011] The ball may have a grade of 40 or less. The above grades are values ​​specified in JIS B1501. By limiting the ball grade to 40 or less, it is possible to select balls with a surface roughness of 0.06 μmRa or less.

[0012] The surface roughness of the balls may be 0.04 μmRa or less, and the kinetic viscosity of the lubricant (40° C.) may be 68 cst or more and 150 cst or less, in which case the oil film between the balls is more effectively formed, and the effect of suppressing the wear of the balls can be further improved.

[0013] The balls may be made of bearing steel, which can reduce manufacturing costs compared to using balls made of martensitic stainless steel, ceramics, etc.

[0014] When the material of the balls is bearing steel, the balls may be subjected to a surface hardening treatment, such as nitriding.

[0015] The rotation mechanism of the present invention includes any one of the angular contact ball bearings described above, and therefore the effects described above for the angular contact ball bearing of the present invention can be obtained. In the case of a rotation mechanism in which the inner ring and shaft are integrated, or a rotation mechanism in which the outer ring and housing are integrated, it is possible to achieve high rigidity and high load capacity without increasing the size. Effect of the Invention

[0016] The angular contact ball bearing of the present invention is a cageless, so-called full-ball angular contact ball bearing, in which the surface roughness of the balls is 0.06 μmRa or less and the kinetic viscosity of the lubricant (at 40°C) is 46 cst to 220 cst. As a result, even if the balls slide against each other in reverse, it is possible to suppress ball wear, and costs can be reduced compared to conventional technology. [Brief description of the drawings]

[0017] [Figure 1] 1 is a vertical sectional view of an angular ball bearing according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of the angular contact ball bearing. [Diagram 3] 4 is a conceptual diagram illustrating reverse sliding between balls in the angular contact ball bearing. FIG. [Figure 4] FIG. 4 is a vertical cross-sectional view showing an example of a back-to-back assembly of the angular ball bearings. [Diagram 5] FIG. 6 is a vertical sectional view of a rotation mechanism including an angular ball bearing according to a second embodiment of the present invention. [Figure 6] FIG. 11 is a vertical sectional view of a rotation mechanism including an angular ball bearing according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [First embodiment] An angular ball bearing according to an embodiment of the present invention will be described with reference to Figures 1 to 3. This angular ball bearing is used, for example, as a main bearing portion of a reducer in a robot or construction machine, etc. In this specification, the angular ball bearing may be simply referred to as a "bearing".

[0019] As shown in Fig. 1, the angular contact ball bearing 1 is a so-called full-ball angular contact ball bearing without a cage, which includes an inner ring 2, an outer ring 3, and a number of balls 4 interposed between raceway surfaces 2a, 3a of the inner and outer rings 2, 3. The inner and outer rings 2, 3 and the balls 4 are made of high carbon chromium bearing steel, such as SUJ2. In this specification, the "axial direction" refers to the direction along the bearing center line of the angular ball bearing 1. The "radial direction" refers to the direction perpendicular to the straight line that forms the "axial direction".

[0020] The raceway surface 3a is connected to the front surface of the outer ring 3 via a counterbore 3b. An inner peripheral surface 3d on the back side of the outer ring 3 is located radially inward from the counterbore 3b of the outer ring 3. The raceway surface 2a is connected to the front surface of the inner ring 2 via a counterbore 2b. An outer peripheral surface 2d on the back side of the inner ring 2 is formed between the raceway surface 2a of the inner ring 2 and the back surface 2c of the inner ring 2. The outer peripheral surface 2d of the inner ring 2 is located radially outward from the counterbore 2b of the inner ring 2. The front surfaces of the inner and outer rings 2 and 3 refer to the side surfaces that do not support an axial load, and the back surfaces 2c and 3c of the inner and outer rings 2 and 3 refer to the side surfaces that support an axial load.

[0021] <About parameters etc.> In order to improve the load capacity and moment rigidity of an angular contact ball bearing within a given size, there are two methods: (1) increasing the number of balls, and (2) increasing the ball diameter. As shown in Figure 2, the angular contact ball bearing 1 according to the embodiment of the present invention is cage-less (all balls) in order to increase the number of balls, and the improved ball packing rate improves the load capacity and moment rigidity compared to an angular contact ball bearing with a cage. The ball packing rate is calculated by the following formula: Packing rate = (ball diameter Dw x number) / (π x pitch circle diameter PCD). This indicates that the filling rate of the angular contact ball bearing of the present invention is 95% or more.

[0022] Without a cage, the balls come into contact with each other in the circumferential direction due to the difference in their relative revolution speeds, as shown in Figure 3, and the relative sliding velocities R1 and R2 between the contacting balls 4, 4 are in the opposite directions. This causes "reverse sliding" in the contact area between the balls. The thick arrow A1 in Figure 3 indicates the direction of ball movement. It was found that in angular contact ball bearings without a cage, wear on the ball surface can be suppressed by combining a lubricant with an optimal dynamic viscosity and an optimal ball surface roughness against "reverse slip." In addition, when the lubricant is grease, it was found that ball wear can be further suppressed by combining it with an optimal consistency in addition to the above.

[0023] The consistency is a value determined by the test method of JIS K2220, and in this embodiment, it is expressed by the JIS classification. The kinetic viscosity is the value at 40°C determined by the test method of JIS K2283. EXAMPLES

[0024] A rotation durability test was conducted on angular contact ball bearings under the following conditions, and evaluation was performed for each combination of the arithmetic mean surface roughness (μmRa) of the balls and the kinetic viscosity of the lubricant. <Condition> Ball diameter Dw / Pitch circle diameter PCD: 0.07 Ball filling rate: 98% dmn value: 50000 dmn={(D+d) / 2}×n

[0025] [Table 1] Table 1: Relationship between ball surface roughness, lubricant kinetic viscosity and ball wear suppression effect D: outer diameter of outer ring (mm), d: inner diameter of inner ring (mm), n: rotation speed (min -1 ) Load: Under load conditions of 10% to 20% of basic dynamic load rating (Cr) Ball: Bearing steel In Table 1, regarding ball wear, those which were feasible and had a high wear-inhibiting effect were rated as O, those which were feasible but had a lower wear-inhibiting effect than O were rated as △, and those which had a low wear-inhibiting effect were rated as ×.

[0026] <Action and effect> In an angular contact ball bearing without a cage, when the surface roughness of the balls is 0.06 μm or less in arithmetic mean roughness and the kinetic viscosity of the lubricant (40°C) is in the range of 46 cst to 220 cst as in Examples 1 to 5, an oil film is formed well between the balls and ball wear is suppressed as feasible. If the surface roughness of the balls is 0.04 μmRa or less and the kinetic viscosity of the lubricant (40°C) is in the range of 68 cst to 150 cst as in Examples 2 to 4, an oil film is formed even better between the balls and the effect of suppressing ball wear can be further improved.

[0027] This configuration, which combines a lubricant with an optimum kinetic viscosity and an optimum ball surface roughness, can reduce costs compared to the conventional technique of providing a nitride layer on the surface of the ball. When the kinetic viscosity of the lubricant (40°C) is 320 cst, regardless of the surface roughness of the balls, heat generation increases and an oil film is difficult to form, resulting in a low wear-suppression effect.

[0028] If the surface roughness of the ball is 0.04 μmRa or less, balls of grade 24 or less may be selected, and if the surface roughness of the ball is 0.06 μmRa or less, balls of grade 40 or less may be selected. It was found that when the lubricant is grease, those that allow the grease to easily flow between the balls have a greater effect in suppressing ball wear. The ease with which grease can flow between the balls varies specifically with the consistency classification. The higher the consistency (softer), the better the ability of grease to flow between the balls, and the lower the consistency (harder), the worse the ability of grease to flow. Greases with consistency classifications in the range of No. 1 to No. 00 have relatively good ability to flow between the balls, further enhancing the effect of suppressing ball wear. With a consistency classification lower than No. 2, the grease is hard and the grease does not flow easily, which may conversely result in a lower effect in suppressing wear.

[0029] By keeping the surface roughness of the balls and the kinetic viscosity (40°C) of the lubricant, and in the case of grease, the consistency classification, within the above ranges, it is possible to enhance the effect of suppressing ball wear without having to subject the balls to special heat treatment.

[0030] <Rear combination, etc.> Moment loads are often applied to industrial machinery. Under operating conditions where moment loads are applied by angular contact ball bearings, the angular contact ball bearings 1 can be arranged in a back-to-back configuration as shown in Fig. 4 to increase the distance between the bearing load points, so that the allowable radial load and allowable moment load can be increased even if the angular contact ball bearings 1 are made smaller, i.e., more compact. Furthermore, by arranging the angular contact ball bearings 1 in a back-to-back configuration, they can withstand axial loads in both directions, and the rigidity of the bearing portion can be increased by adding preload. In the example shown in Fig. 4, an inner ring spacer 7 and an outer ring spacer 8 are interposed between the angular contact ball bearings 1, 1 adjacent to each other in the axial direction, but it is also possible to omit these spacers 7, 8 and arrange the angular contact ball bearings 1, 1 in a back-to-back configuration.

[0031] <Other embodiments> In the following description, parts corresponding to matters previously described in each embodiment are given the same reference numerals, and duplicated description is omitted. When only a part of the configuration is described, the other parts of the configuration are the same as the previously described embodiment unless otherwise specified. The same configuration has the same action and effect. It is possible to combine not only the parts specifically described in each embodiment, but also partially combine embodiments together, provided that there is no particular problem with the combination.

[0032] [Second embodiment: Inner ring and shaft integrated] As shown in Fig. 5, a rotation mechanism 9 may be provided with an angular contact ball bearing 1 in which the inner ring 2 and the shaft are integrated. The term "integrated" means that the inner ring 2 and the shaft are not formed by combining multiple elements but are formed as a part or the whole of a single object from a single material by, for example, forging or machining.

[0033] <Axle unit> This rotation mechanism 9 is a vehicle power unit, a so-called axle unit, that is provided on a vehicle and includes a double-row angular ball bearing 1 assembled back-to-back and a drive motor M with a power generating function. The outer ring 3 of the angular ball bearing 1 is a rotating ring, and the inner ring 2 integrated with the shaft is a fixed ring. A brake rotor 12 and a wheel (not shown) are attached to a wheel mounting flange 11 provided on the outboard end of the outer ring 3 in a state where they overlap in the axial direction. In the case of the rotation mechanism 9 in which the inner ring 2 and the shaft are integrated, it is possible to achieve high rigidity and high load capacity without increasing the size.

[0034] [Third embodiment: Outer ring and housing integrated] As shown in Fig. 6, a rotation mechanism 9A may be provided with an angular ball bearing 1 in which the outer ring 3 and the housing 14 are integrated. Even in the case of the rotation mechanism 9A in which the outer ring 3 and the housing 14 are integrated, it is possible to achieve high rigidity and high load capacity without increasing the size.

[0035] At least one of the inner and outer rings and the balls may be made of a material other than bearing steel, such as martensitic stainless steel or ceramics. It is also possible to use angular contact ball bearings in face-to-face combination, parallel combination, etc. It is also possible to use angular contact ball bearings in multiple rows (three or more rows). The angular ball bearing and the rotation mechanism can also be used for purposes other than the reducer.

[0036] When the material of the balls is bearing steel, the balls may be subjected to a surface hardening treatment, such as nitriding.

[0037] Although the embodiment for carrying out the present invention has been described above, the embodiment disclosed herein is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0038] 1...angular contact ball bearing, 2...inner ring, 3...outer ring, 4...ball, 9,9A...rotation mechanism

Claims

1. A cageless angular contact ball bearing including an inner ring, an outer ring, and a plurality of balls interposed between the inner ring and the outer ring, The angular contact ball bearing has a surface roughness of 0.06 μm Ra or less and a kinetic viscosity (40° C.) of the lubricant of 46 cst or more and 220 cst or less.

2. 2. The angular ball bearing according to claim 1, wherein the lubricant is grease, and the consistency of the grease is from No. 1 to No.

00.

3. 3. The angular ball bearing according to claim 1, wherein the balls have a class of 40 or less.

4. 3. An angular contact ball bearing according to claim 1, wherein the surface roughness of the balls is 0.04 μm Ra or less, and the kinetic viscosity (40° C.) of the lubricant is 68 cst or more and 150 cst or less.

5. 3. The angular contact ball bearing according to claim 1, wherein the material of the balls is bearing steel.

6. 6. The angular contact ball bearing according to claim 5, wherein said balls are subjected to a surface hardening treatment.

7. 7. The angular contact ball bearing according to claim 6, wherein said surface hardening treatment is a nitriding treatment.

8. A rotation mechanism comprising the angular ball bearing according to any one of claims 1 to 7.

9. 9. The rotation mechanism according to claim 8, wherein the inner ring and the shaft are integrated together.

10. 9. The rotation mechanism according to claim 8, wherein the outer ring and a housing are integrated together.

11. A reducer comprising the rotation mechanism according to any one of claims 8 to 10.

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