bearings

Abstract

To provide a bearing that ensures electrical conductivity. [Solution] A bearing is used for motors, reducers, and transmissions, comprising an outer ring 12 with an outer ring raceway surface 12a formed on its inner circumference, an inner ring 13 with an inner ring raceway surface 13a formed on its outer circumference, and a plurality of rolling elements 15 that are assembled at circumferential intervals in an annular bearing space 14 formed between the outer ring 12 and the inner ring 13 and roll in contact with the outer ring raceway surface 12a and the inner ring raceway surface 13a, wherein a solid lubricant 16 containing conductive grease is sealed in the bearing space 14.

Description

Technical Field

[0001] This invention relates to bearings; more specifically bearings such as main shaft bearings used in motors, speed reducers, and transmissions used in electric vehicles (EVs), hybrid cars (HEVs), etc.

Background Art

[0002] The electric motors (motors) used in electric vehicles (EVs), hybrid cars (HEVs), etc. may vary the frequency by inverter control for higher efficiency. However, when the frequency increases, current easily flows through the bearing, and electric corrosion may occur inside the bearing. As a countermeasure, there is a method of imparting electrical conductivity to the bearing by enclosing conductive grease inside the bearing.

[0003] As an example of a bearing with conductive grease enclosed inside, for example, the energized grease enclosed bearing described in Patent Document 1 can be cited. As shown in Fig. 4, this bearing 1 includes an outer ring 3 fitted to the inner periphery of a housing 2, an inner ring 5 fitted to the outer periphery of the axial end of a roll 4, a plurality of balls 6 interposed between the raceway surface 3a of the outer ring 3 and the raceway surface 5a of the inner ring 5, a cage 7 that holds the balls 6 at a predetermined circumferential interval, a seal member 8 that seals the inside of the bearing, and conductive grease 9 enclosed inside the bearing. This conductive grease 9 uses fluorine oil as the base oil and contains a predetermined amount of carbon black, which is a conductive substance, and can impart electrical conductivity to the bearing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, when electricity flows through the bearing 1 according to Patent Document 1, which is provided with the conductive grease 9, the electricity flows through the conductive substance, such as carbon black, which is a thickener constituting the conductive grease 9. However, if conductive grease 9 leaks out of the bearing space between the outer ring and the inner ring, or if the distribution of conductive material in the conductive grease 9 becomes uneven during the rotation of the bearing 1, and a portion of conductive material does not exist between the outer ring 3 and the inner ring 5, it may become difficult to form an electrical circuit and ensure conductivity. In this case, a discharge may occur between the outer ring 3 and the inner ring 5, and as a result, electrolytic corrosion may occur inside the bearing.

[0006] The inventors of this invention focused on the fact that conductive grease can leak out of the bearing space, and that conductive material can become unevenly distributed within the conductive grease during bearing rotation, making it impossible to ensure electrical conductivity. They then focused on the fact that if these issues could be suppressed, electrical conductivity could be ensured. [Means for solving the problem]

[0007] Based on this focus, this invention provides a bearing with the following configuration in order to solve the aforementioned problems. [Configuration 1] A rolling bearing used in motors, speed reducers, and transmissions, comprising an outer ring, an inner ring, and a plurality of rolling elements arranged at circumferential intervals in an annular bearing space formed between the outer ring and the inner ring, wherein a solid lubricant containing conductive grease is sealed in the bearing space.

[0008] By adopting this configuration, solidified conductive grease is used, which suppresses leakage and uneven distribution of conductive material. As a result, stable electrical conductivity can be maintained, and the electrical circuit within the bearing is maintained, ensuring conductivity. This suppresses discharge between the rolling elements and the inner and outer rings, thereby extending the lifespan of the bearing.

[0009] [Configuration 2] The rolling bearing according to [Configuration 1], wherein the solid lubricant is a lubricant having conductive grease and ultra-high molecular weight polyethylene. This configuration allows for the solidification of conductive grease.

[0010] [Configuration 3] The conductive substance contained in the conductive grease is a substance containing any of the following: carbon black, ionic liquid, graphite, metal, conductive carbon fiber, or graphite, as described in [Configuration 1] or [Configuration 2]. Adopting this configuration can further improve conductivity.

[0011] [Configuration 4] The rolling bearing according to [Configuration 3], wherein the content of conductive material in the solid lubricant is 5% by mass or more and 21% by mass or less. This configuration allows for a good balance between the conductivity and lubricity of the bearing.

[0012] [Configuration 5] The rolling bearing according to [Configuration 1] or [Configuration 2], wherein the proportion of the solid lubricant to the bearing space is 50% or more of the space volume. By adopting this configuration, it is possible to maintain the circumferential spacing of each rolling element and to have a large amount of conductive grease in the bearing space, thereby maintaining stable electrical conductivity.

[0013] [Configuration 6] The rolling bearing according to [Configuration 1] or [Configuration 2], wherein the circumferential spacing of each rolling element is equal. Adopting this configuration can further improve the rotational stability of the bearings. [Effects of the Invention]

[0014] Since the bearing of this invention uses a solid lubricant blended with a conductive grease, it is possible to prevent leakage of the conductive grease and prevent the conductive substance from being biased during bearing rotation, and it becomes possible to maintain stable electrical conduction performance. Therefore, compared with a conventional bearing filled with a conductive grease, it is possible to suppress electrical erosion due to discharge inside the bearing (for example, arc discharge that occurs when there is grease that has become an insulator due to the bias of the conductive substance between the rolling elements and the raceway ring), and it becomes possible to extend the life of the bearing. In addition, when the encapsulation rate of the solid lubricant is 50% or more of the bearing space, the circumferential intervals of the respective rolling elements can be maintained, and the rotation of the bearing can be made more stable. Also, a large amount of conductive grease will be present in the bearing space, making it possible to maintain stable electrical conduction performance. From these, the bearing of this invention can be usefully used as a bearing for a motor used in an electric vehicle (EV), a hybrid car (HEV), or the like.

Brief Description of the Drawings

[0015] [Figure 1] (a) Front view showing an example of a bearing according to an embodiment of this invention, (b) Cross-sectional view taken along line A-A of (a) [Figure 2] (a) Front view showing an example of another bearing according to an embodiment of this invention, (b) Cross-sectional view taken along line B-B of (a) [Figure 3] Cross-sectional view showing an example of another bearing according to an embodiment of this invention [Figure 4] Cross-sectional view showing an example of a conventional bearing

Mode for Carrying Out the Invention

[0016] In FIGS. 1(a)(b) and FIGS. 2(a)(b), bearings 11 and 11' according to embodiments of this invention are shown. These bearings 11 and 11' include an outer ring 12, an inner ring 13 coaxially provided inside the outer ring 12 in the radial direction, a plurality of rolling elements 15 incorporated in an annular bearing space 14 formed between the outer ring 12 and the inner ring 13 at regular intervals in the circumferential direction, and a cage 17 that holds the plurality of rolling elements 15.

[0017] The axial direction is parallel to the central axis of the outer ring 12 (the central axis of the bearing), the radial direction is perpendicular to the central axis of the outer ring 12, and the circumferential direction is along the circumference that revolves around the central axis of the outer ring 12.

[0018] As shown in FIGS. 1(a)(b) and FIGS. 2(a)(b), on the inner circumference of the outer ring 12, there are formed an outer ring raceway surface 12a where the rolling elements 15 rollingly contact, and a pair of outer ring shoulder surfaces 12b that axially adjoin both sides of the outer ring raceway surface 12a and extend circumferentially. The outer ring raceway surface 12a is the inner surface of a groove with a cross-sectional arc shape that extends circumferentially on the inner circumference of the outer ring 12, and the outer ring shoulder surface 12b is a cylindrical surface with a constant inner diameter along the axial direction.

[0019] On the outer circumference of the inner ring 13, there are formed an inner ring raceway surface 13a where the rolling elements 15 rollingly contact, and a pair of inner ring shoulder surfaces 13b that axially adjoin both sides of the inner ring raceway surface 13a and extend circumferentially. The inner ring raceway surface 13a is the outer surface of a groove with a cross-sectional arc shape that extends circumferentially on the outer circumference of the inner ring 13, and the inner ring shoulder surface 13b is a cylindrical surface with a constant outer diameter along the axial direction.

[0020] The rolling elements 15 are in rolling contact with the outer ring raceway surface 12a and the inner ring raceway surface 13a. The outer ring raceway surface 12a is formed symmetrically with respect to the axial center of the outer ring 12, and the inner ring raceway surface 13a is also formed symmetrically with respect to the axial center of the inner ring 13. This bearing 11 is a rolling bearing where the rolling elements 15 are balls or rollers. As a bearing where the rolling elements 15 are balls, ball bearings such as deep groove ball bearings can be cited.

[0021] The cage 17 is a member that partially surrounds the rolling elements 15 and keeps them at regular intervals in the circumferential direction. This cage 17 may be formed of a metal plate such as an iron plate or resin, but since it will reach a high temperature when firing the solid lubricant 16 described later, it is preferably formed of a metal plate that is less likely to deform. Note that depending on the filling amount of the solid lubricant 16 described later, it may not be necessary to use the cage 17. This is because the solid lubricant 16 can keep the rolling elements 15 at regular intervals.

[0022] A solid lubricant 16 is placed in the bearing space 14 between the outer ring 12 and the inner ring 13. The proportion of this solid lubricant 16 to the bearing space 14 should be 50% or more of the space volume. By setting it to 50% or more, the circumferential spacing of each rolling element 15 can be maintained, and a large amount of conductive grease can be present in the bearing space 14, thereby maintaining stable electrical conductivity. Furthermore, in this case, the circumferential spacing of each rolling element 15 can be maintained even without providing the cage 17. Furthermore, by providing the solid lubricant 16, it is possible to arrange the circumferential spacing of each rolling element 15 at equal intervals, thereby further improving the rotational stability of the bearing.

[0023] Methods for filling the bearing space 14 with solid lubricant 16 include filling it in a spot-pack manner at multiple locations in the bearing space 14, as shown in Figures 1(a) and 1(b), and filling it in a full-pack manner that fills almost the entire bearing space 14, as shown in Figures 2(a) and 2(b).

[0024] Furthermore, both axial sides of the bearing space 14 between the outer ring 12 and the inner ring 13 may be sealed with a sealing member or the like, or they may be left open without a sealing member. As will be described later, the solid lubricant 16 placed in this bearing space 14 is solidified, so grease leakage does not occur, and there is no need to seal it. For this reason, if there is a possibility that foreign matter or dirt may enter the bearings 11 and 11' according to this invention, it is preferable to have a sealing member, but if there is no possibility of foreign matter or dirt entering, a sealing member is not necessary.

[0025] The solid lubricant 16 is a lubricant formed by solidifying a mixture of conductive grease as a lubricating component and ultra-high molecular weight polyolefin as a resin component. The conductive grease consists of a base oil and a thickener, with a conductive substance used as the thickener. Lubrication is provided by the seepage of the base oil contained in the conductive grease from the solid lubricant, and conductivity is also imparted to the solid lubricant 16 by the conductive substance.

[0026] As the base oil, a general non-aqueous lubricating oil can be used. For example, highly refined oils, mineral oils, ester oils, ether oils, PAO oils which are mixtures of α-olefins or oligomers or polymers of isomerized α-olefins, silicone oils, fluorine oils, etc., can be used. These may be used individually or in mixtures of two or more.

[0027] Examples of the aforementioned mineral oils include liquid paraffin oil and linear paraffin oil. Examples of the ester oils mentioned above include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, and dioctyl adipate, and aromatic ester oils such as trioctyl trimellitate and tridecyl trimellitate. Examples of the ether oil include monoalkyldiphenyl ether oil, dialkyldiphenyl ether oil, polyalkyldiphenyl ether oil, and other alkyldiphenyl ether oils, as well as polyphenyl ether oils. Examples of the PAO oil include oligomers such as 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-docosene, and 1-tetradocosene.

[0028] The kinematic viscosity of the aforementioned base oil at 40°C is 20-200 mm². 2 / s is preferred. More preferably 20-100 mm 2 / s, and more preferably 30-80 mm 2 It is / s.

[0029] A conductive substance is used as the thickener. This conductive substance only needs to be conductive, and examples include carbon black, ionic liquids, metals such as graphite and copper powder, conductive carbon fibers, and substances containing graphite. The ionic liquid refers to a salt that exists in liquid form, and examples include ionic liquids such as imidazolium salts, pyrrolidinium salts, pyridinium salts, piperidinium salts, ammonium salts, and phosphonium salts.

[0030] Examples of the ionic liquid imidazolium salt include 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-butylimidazolium bromide, and 1-allyl-3-butylimidazolium tetrafluoroborate. Examples of the pyrrolidinium salt ionic liquid include 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, and 1-butyl-1-methylpyrrolidinium chloride.

[0031] Examples of the pyridinium salt ionic liquid include 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, 1-butyl-2-methylpyridinium chloride, 1-butyl-2-methylpyridinium tetrafluoroborate, and 1-butylpyridinium bromide. Examples of the ionic liquid of the piperidinium salt include 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpiperidinium bromide, and 1-butyl-1-methylpiperidinium hexafluorophosphate.

[0032] Examples of the ionic liquid ammonium salt include butyltriethylammonium bis(trifluoromethylsulfonyl)imide, diethylmethylammonium methanesulfonate, and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide. Examples of the ionic liquid phosphonium salt include methyltributylphosphonium bis(trifluoromethylsulfonyl)imide, tetrabutylphosphonium chloride, tributylethylphosphonium diethyl phosphate, and tributyltetradecylphosphonium chloride.

[0033] Conductive grease is obtained by blending a thickener consisting of a conductive substance with a base oil. The content of the conductive substance in the conductive grease is preferably between 10% and 30%. Within this range, it is possible to maintain both the lubricity and electrical conductivity of the bearing.

[0034] The consistency of the grease used in this invention (JIS K2220) is preferably in the range of 200 to 350. If the consistency is less than 200, oil separation is poor and lubrication may be inadequate. On the other hand, if the consistency exceeds 350, the grease becomes soft and easily leaks out of the bearing, which is undesirable.

[0035] Examples of ultra-high molecular weight polyolefins used as the resin component include powders made from polyethylene, polypropylene, polybutene, or copolymers thereof, or mixed powders containing each of these powders individually. Here, the average molecular weight of each powder, as measured by the viscosity method, is 1 × 10⁻⁶. 6 The above is preferable. This is because polyolefins within this molecular weight range are superior to low molecular weight polyolefins in terms of rigidity and oil retention. Furthermore, among ultra-high molecular weight polyolefins, it is preferable to use ultra-high molecular weight polyethylene. An example of such a solid lubricant is "Polyloop" manufactured by NTN Corporation.

[0036] In the solid lubricant described above, ultra-high molecular weight polyolefin is contained in an amount of 20 to 50% by mass, and conductive grease is contained in an amount of 80 to 50% by mass. Preferably, ultra-high molecular weight polyolefin is contained in an amount of 30 to 50% by mass, and conductive grease is contained in an amount of 70 to 50% by mass. This configuration allows for a moderate suppression of oil separation. Therefore, considering the above-mentioned description of the content of conductive substances in the conductive grease (10% to 30%), the proportion of conductive substances in the solid lubricant is preferably 5 to 21% by mass. The proportion of conductive substances can be calculated by thermogravimetric analysis, which removes substances other than the conductive substances from the solid lubricant.

[0037] When the solid lubricant is heated at 160°C for 30 minutes, it is preferable that the oil separation rate, defined by the following formula, is 7 to 12% by mass. Oil separation rate (mass%) = {(weight before heating - weight after heating) / weight before heating} x 100 Various organic or inorganic additives may be added to the solid lubricant. The conductive grease used in this invention may also contain additives such as antioxidants, rust inhibitors, extreme pressure agents, wear modifiers, and pH adjusters.

[0038] The solid lubricant is obtained by uniformly mixing the conductive grease and the ultra-high molecular weight polyolefin, directly filling the mixture into a mold or bearing of a predetermined shape, heating it to a temperature above the gelation point (melting temperature) of the ultra-high molecular weight polyolefin, and then cooling it to solidify it. The method of mixing the conductive grease and the ultra-high molecular weight polyolefin is not particularly limited, and commonly used agitators such as Henschel mixers and ribbon mixers can be used. Furthermore, the heating (firing) conditions are preferably above the gelation point and below the dropping point of the grease. For example, if the average molecular weight of the ultra-high molecular weight polyolefin is 1 × 10⁻⁶ 6 ~3×10 6 In that case, it is preferable to heat at a temperature of 150-200°C. Since the resulting solid lubricant is solidified by the method described above, the thickener (conductive substance) of the conductive grease is immobilized, preventing the thickener (conductive substance) from leaking out of the bearing space 14 or from becoming unevenly distributed within the conductive grease during bearing rotation, thereby maintaining the conductivity of the bearing.

[0039] An example of a rolling bearing filled with the solid lubricant of the present invention will be described with reference to Figures 1(a)(b) and 2(a)(b). Figures 1(a)(b) are a front view and a partial cross-sectional view of a rolling bearing in which the solidified lubricant is filled in a spot pack, and Figures 2(a)(b) are a front view and a partial cross-sectional view of a rolling bearing in which the solidified lubricant is filled in a full pack. The rolling bearings 11 and 11' have an outer ring 12 having an outer ring racing surface on its inner circumferential surface and an inner ring 13 having an inner ring racing surface on its outer circumferential surface arranged concentrically, with a plurality of rolling elements 15 arranged between the inner ring racing surface and the outer ring racing surface. A cage 17 holds these plurality of rolling elements 15. In the rolling bearing 11 shown in Figures 1(a) and 1(b), solid lubricant 16 is filled in a spot pack around the rolling elements 15, while in the rolling bearing 11' shown in Figures 2(a) and 2(b), solid lubricant 16 is filled in a full pack around the rolling elements 15. Depending on the amount of solid lubricant 16 filled, the cage 17 may not be necessary.

[0040] The bearings 11 and 11' according to this invention are electrically conductive, with current flowing from the outer ring 12 of the bearings 11 and 11' towards the inner ring 13 via the conductive substance of the solid lubricant 16 and, optionally, the rolling elements 15, or from the inner ring 13 of the bearings 11 and 11' towards the outer ring 12 via the conductive substance of the solid lubricant 16 and, optionally, the rolling elements 15. Therefore, in EVs and HEVs, when current flows through the bearing, the current flows through this path, preventing discharge inside the bearing and suppressing electrolytic corrosion. Generally, when a voltage is applied with an insulator placed between the rolling elements and the raceway, arc discharge occurs and leads to electrolytic corrosion. However, as in the present invention, when conductive grease is placed between the rolling elements and the raceway, this arc discharge can be suppressed. Furthermore, if the width of the solid lubricant 16 filled in the bearings 11 and 11' according to this invention is close to the width of the bearings 11 and 11', for example, if the bearings 11 and 11' have a cage 17 and the width of the solid lubricant 16 is longer in the width direction than the width of the cage 17, then, as shown in Figure 3, it is possible to conduct electricity from the width direction of the housing 18, etc., through the conductive material of the solid lubricant 16, and possibly through the rolling elements 15, toward the member on the opposite side in the width direction, thereby further suppressing the occurrence of electrolytic corrosion.

[0041] Incidentally, reducing the groove curvature between the outer ring 12 and the rolling element 15, and between the inner ring 13 and the rolling element 15, increases the elliptical contact area between the outer ring raceway surface 12a and the inner ring raceway surface 13a and the rolling element 15, thereby improving conductivity. For this reason, the groove curvature between the outer ring 12 and the rolling element 15 is preferably 1.03 to 1.07, and the groove curvature between the inner ring 13 and the rolling element 15 is preferably 1.02 to 1.06.

[0042] Furthermore, it is preferable that the roughness of the outer ring shoulder 12b and inner ring shoulder 13b is rougher than the roughness of the transfer surfaces of the outer ring raceway surface 12a and inner ring raceway surface 13a, and it is also preferable that the roughness of the outer ring shoulder 12b is rougher than the roughness of the inner ring shoulder 13b. As a result, when filling the bearing space 14 with solid lubricant before it hardens, the adhesion to each shoulder tends to be higher than that to each raceway surface, and the adhesion to the outer ring shoulder 12b tends to be higher than that to the inner ring shoulder 13b. Therefore, the conductivity can be further improved.

[0043] The bearing according to this invention can be used as a motor bearing in electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like. [Explanation of symbols]

[0044] 1 bearing 2 Housing 3 Outer ring 3a Outer ring raceway surface 4 rolls 5. Inner Ring 5a Inner ring raceway surface 6 balls 7 Cage 8. Sealing member 9. Conductive grease 11, 11' bearing 12 Outer ring 12a Outer ring raceway 12b Outer ring shoulder surface 13 Inner circle 13a Inner ring raceway surface 13b Inner shoulder surface 14. Bearing space 15 Rolling element 16. Solid lubricants 17 Cage 18 Housing

Claims

1. Outer ring (12), Internal circle (13), The bearing has an annular bearing space (14) formed between the outer ring (12) and the inner ring (13), in which a plurality of rolling elements (15) are incorporated at circumferential intervals. Bearings used in motors, reducers, and transmissions, A rolling bearing in which a solid lubricant (16) containing conductive grease is sealed in the bearing space (14).

2. The rolling bearing according to claim 1, wherein the solid lubricant (16) is a lubricant having conductive grease and ultra-high molecular weight polyethylene.

3. The rolling bearing according to claim 1 or 2, wherein the conductive substance contained in the conductive grease is a substance that includes any of carbon black, ionic liquid, graphite, metal, conductive carbon fiber, or graphite.

4. The rolling bearing according to claim 3, wherein the content of conductive material in the solid lubricant (16) is 5% by mass or more and 21% by mass or less.

5. The rolling bearing according to claim 1 or 2, wherein the proportion of the solid lubricant (16) to the bearing space (14) is 50% or more of the space volume.

6. The rolling bearing according to claim 1 or 2, wherein the circumferential spacing of each rolling element (15) is equal.

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