Rolling bearing, grease composition, and grease-filled bearing

Abstract

Provided is a rolling bearing capable of suppressing ridge marks caused by electrolytic corrosion. Rolling bearings 6, 7 are incorporated in an inverter-controlled motor 1, have an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and are lubricated by a lubricant. The lubricant contains a base oil having a relative dielectric constant higher than 2.5 and a phosphorus-based additive. The base oil is an ester oil, the phosphorus-based additive is an aliphatic phosphoric acid ester having a linear or branched alkyl group, the aliphatic phosphoric acid ester has three alkyl groups, and each of the alkyl groups has 2‒8 carbon atoms.

Description

Rolling bearings, grease compositions, and grease-filled bearings

[0001] The present invention relates to rolling bearings lubricated with a lubricant, and more particularly to rolling bearings incorporated into inverter-controlled devices. The present invention also relates to grease compositions and grease-filled bearings containing said grease compositions, and more particularly to rolling bearings used in automobiles, industrial machinery, wind turbines, and the like.

[0002] Rolling bearings are used in fan motors and servo motors used in industrial machinery, as well as in drive motors used in electric vehicles and hybrid vehicles. These rolling bearings are equipped with mechanisms that either contain a lubricant or allow a lubricant to penetrate the contact area to provide lubrication.

[0003] In recent years, most motors used in industrial machinery and drive motors are controlled by inverters to improve efficiency. Inverter control adjusts the voltage and frequency input to the motor according to the motor's set rotational speed. As the inverter's switching frequency increases, the frequency of motor shaft voltage generation also increases. As a result, a potential difference can occur between the outer and inner rings and the rolling elements in the rolling bearings incorporated into inverter-driven motors. If this potential difference becomes large and exceeds the dielectric breakdown voltage of the oil film formed between the raceway rings and rolling elements in the bearing, discharge can occur between the raceway rings and rolling elements, causing electrolytic corrosion inside the bearing. In addition, increasing the power supply voltage allows for a smaller current even at the same output, reducing copper losses in cables and inverter elements. However, this increases the potential difference between the shaft potential and the ground potential, making dielectric breakdown of the oil film more likely.

[0004] As this galvanic corrosion progresses, striped, uneven areas called ridge marks form on the racing surfaces of the outer and inner rings. These ridge marks can cause noise and vibration in the bearing. Therefore, efforts are underway to develop bearings that are designed to suppress the formation of ridge marks on the racing surfaces.

[0005] For example, Patent Document 1 describes a conductive grease containing a base oil consisting of at least one of perfluoropolyether and fluorosilicone, a thickener such as a fluorine compound, and carbon black. Patent Document 2 also describes the provision of a conductive seal as a seal to seal the end of the bearing space.

[0006] Patent No. 4599769 Patent No. 4177057

[0007] As described above, techniques for imparting conductivity to bearings are known. However, conductive greases and conductive seals, such as those described in Patent Documents 1 and 2, generally have a volume resistivity of 10. ４ ~10 ８ The resistance is high at Ωcm. Therefore, although it is effective in removing static electricity and preventing static charge buildup, if, for example, the shaft voltage of a motor caused by an inverter becomes a problem, it is difficult to suppress the generation of shaft voltage due to the high resistance, and as a result, dielectric breakdown of the oil film due to the grease composition may occur in rolling bearings.

[0008] This invention has been made in view of these circumstances, and aims to provide a rolling bearing capable of suppressing ridge marks caused by galvanic corrosion. Furthermore, even in rolling bearings where prevention of galvanic corrosion is required, durability such as wear resistance and grease life is also required. Therefore, this invention aims to provide a grease composition and a grease-filled bearing that suppress ridge marks caused by galvanic corrosion and have excellent wear resistance.

[0009] The rolling bearing of the present invention is incorporated into an inverter-controlled device and comprises an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and is lubricated with a lubricant, wherein the lubricant comprises a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive.

[0010] The above base oil is characterized by being an ester oil. The kinematic viscosity of the above base oil at 40°C is 10 mm². ２ / s ~ 80mm ２ It is characterized by being / s.

[0011] The phosphorus-based additive is characterized by being an aliphatic phosphate ester having a linear or branched alkyl group. The aliphatic phosphate ester is characterized by having three alkyl groups, each of which has 2 to 8 carbon atoms.

[0012] The above-mentioned phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three alkyl groups, each alkyl group having 2 to 8 carbon atoms, the phosphorus content relative to the total amount of the lubricant is 0.01% by mass or more and less than 2.0% by mass, and the lubricant does not contain sulfur-based additives.

[0013] The rolling bearing described above is characterized by having an oil film parameter Λ greater than 3 in steady-state operation. Furthermore, it is preferable that the ratio of the relative permittivity of the base oil to the oil film parameter Λ (relative permittivity / oil film parameter) is 0.4 or more and less than 0.8. Here, steady-state operation refers to the main operating conditions in which the rotational speed and load are generally stable.

[0014] The base oil is a polyol ester oil, the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three alkyl groups, each of which has 4 to 8 carbon atoms, the phosphorus content relative to the total amount of the lubricant is 0.01% by mass or more and less than 2.0% by mass, and the lubricant does not contain sulfur-based additives.

[0015] The above lubricant is characterized by being a lubricating oil composition.

[0016] In the above rolling bearing, the maximum surface pressure in steady-state operation is 0.3 GPa to 3 GPa, and the rotational speed is 500 min. －１ ~20,000 min －１ It is characterized by being such.

[0017] The grease composition of the present invention is characterized by comprising a base oil, a thickener, a phosphorus-based additive, and a metal powder having a melting point of 800°C or higher.

[0018] The above metal powder is copper powder, and is characterized in that the average particle diameter of the copper powder is 0.5 μm or more and less than 2.0 μm.

[0019] The above base oil is characterized in that the base oil has a relative permittivity higher than 2.5. The above base oil is an ester oil. The kinematic viscosity of the above base oil at 40 °C is 10 mm ２ / s to 80 mm ２ / s.

[0020] The above phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, and the aliphatic phosphate ester has three of the above alkyl groups, and each of the alkyl groups has 2 to 8 carbon atoms.

[0021] The above phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three of the above alkyl groups, and each of the alkyl groups has 2 to 8 carbon atoms. The above phosphorus-based additive is contained in an amount of 0.1 part by mass to 3.0 parts by mass with respect to 100 parts by mass of the base grease composed of the above base oil and the above thickener.

[0022] The above metal powder is copper powder, the above base oil is an ester oil, the kinematic viscosity of the base oil at 40 °C is 10 mm ２ / s to 80 mm ２ / s, the above phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, and the above grease composition does not contain an ionic liquid.

[0023] The grease-encapsulated bearing of the present invention has an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and is a grease-encapsulated bearing in which a grease composition is encapsulated, and the above grease composition is the grease composition of the present invention.

[0024] The ratio (average particle diameter of metal powder / oil film thickness) of the average particle diameter [unit: μm] of the above metal powder to the oil film thickness [unit: μm] of the above grease composition during use of the above grease-encapsulated bearing is greater than 1.

[0025] The above-described grease-filled bearing is characterized by having an oil film parameter Λ greater than 3 in steady-state operation. Here, steady-state operation refers to the main operating conditions in which the rotational speed and load are generally stable.

[0026] In the above-mentioned grease-filled bearing, the maximum surface pressure in steady-state operation is 0.3 GPa to 3 GPa, and the rotational speed is 500 min. －１ ~20,000 min －１ It is characterized by being such.

[0027] The rolling bearing of the present invention is incorporated into an inverter-controlled device and is lubricated with a lubricant. This lubricant contains a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive. The base oil lowers the dielectric breakdown voltage of the oil film, and the film derived from the phosphorus-based additive acts as an insulating film, thereby suppressing ridge marks caused by electrolytic corrosion.

[0028] Since the base oil is an ester oil, the dielectric breakdown voltage of the oil film tends to be lower, making it easier to suppress ridge marks.

[0029] Since the above phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, and furthermore, all three alkyl groups of the aliphatic phosphate ester have 2 to 8 carbon atoms, the insulating properties of the coating are high, and ridge marks can be suitably suppressed.

[0030] In the above-mentioned rolling bearing, the oil film parameter Λ in steady-state operation is greater than 3, and there is a concern that ridge marks may occur due to the presence of an oil film between the rolling elements and the raceways. However, ridge marks can be suppressed by the above-mentioned lubricant.

[0031] The grease composition of the present invention contains a phosphorus-based additive and further contains a metal powder with a melting point of 800°C or higher. As a result, the metal powder functions as a conductive additive, and a conductive path is formed through the grease composition, thereby suppressing discharge. Even if discharge occurs, an insulating film is formed by the phosphorus-based additive, which suppresses the occurrence of ridge marks due to electrolytic corrosion. Furthermore, by using a metal powder with a melting point of 800°C or higher, it is easier to maintain its function as a conductive additive, and increases in sound and vibration caused by the melting of the metal powder can also be suppressed.

[0032] The above metal powder is copper powder, and since copper is a soft metal, it can suppress aggressiveness towards other materials and reduce wear caused by conductive additives. In addition, among soft metals, it has particularly high conductivity, and the amount of energy generated during dielectric breakdown, which is thought to affect electrolytic corrosion, is small, resulting in even better low noise and wear resistance.

[0033] Since the above-mentioned base oil is a base oil with a relative permittivity higher than 2.5 (for example, an ester oil), the dielectric breakdown voltage of the oil film is lowered by this base oil, and in combination with the insulating film made by phosphorus-based additives, the occurrence of ridge marks due to electrolytic corrosion can be further suppressed.

[0034] Since the above phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, and furthermore, all three alkyl groups of the aliphatic phosphate ester have 2 to 8 carbon atoms, the insulating properties of the coating are high, and ridge marks can be suitably suppressed.

[0035] The grease-filled bearing of the present invention is filled with the grease composition of the present invention, and the ratio of the average particle size of the metal powder to the oil film thickness (average particle size of the metal powder / oil film thickness) is greater than 1. The metal powder imparts conductivity to the grease composition, and because the metal powder does not easily intervene in the sliding parts, it is easy to maintain its function as a conductive additive. Furthermore, it is possible to suppress the increase in noise and vibration caused by the melting of the metal powder, etc.

[0036] In the above-mentioned grease-filled bearing, the oil film parameter Λ in steady-state operation is greater than 3, and there is concern about the occurrence of ridge marks due to the interposition of an oil film between the rolling elements and the raceway rings. However, the above-mentioned grease composition can suppress the occurrence of ridge marks.

[0037] In the above-mentioned grease-filled bearing, the maximum surface pressure in steady-state operation is 0.3 GPa to 3 GPa, and the rotational speed is 500 min. －１ ~20,000 min －１ Therefore, it can be suitably used in motor bearings and other applications where electrolytic corrosion is a concern.

[0038] This is a schematic cross-sectional view of a motor. This is a cross-sectional view of a deep groove ball bearing, which is an example of a rolling bearing of the present invention. This is a diagram showing the structures of the phosphorus-based and sulfur-based additives used in the reference examples. These are observation photographs of the inner ring raceway surfaces of Reference Examples 1 to 5. These are observation photographs of the inner ring raceway surfaces of Comparative Examples 1 to 2. This is a schematic diagram of the Anderon test. This is a graph showing the results of the Anderon test. This is a schematic diagram of the SRV test machine. This is a graph showing the changes in the coefficient of friction and electrical resistance in the SRV test. This is a graph showing the electrical resistance when each additive is used for each load. This is a schematic diagram of the dielectric constant measuring device. These are observation photographs of the inner ring raceway surfaces of Test Examples A1 to A2 and Comparative Example 1. These are observation photographs of the inner ring raceway surfaces of Test Examples B1 to B4 and B6 to B7, etc.

[0039] The inventors of this invention have diligently studied how to suppress ridge marks caused by electrolytic corrosion in rolling bearings, particularly those incorporated into inverter-controlled devices. In their studies, they considered that the higher the dielectric breakdown voltage, the more likely ridge marks are to develop. Based on their knowledge of the relationship between dielectric breakdown voltage and polarity, they focused on the relative permittivity of the base oil and found that ridge marks could be suppressed by using a base oil with a relatively high relative permittivity. Furthermore, they discovered that when phosphorus-based additives, which are conventionally used as extreme pressure additives, are used, for example, under fluid lubrication conditions (oil film parameter Λ < 3), an insulating film is formed, and ridge marks caused by electrolytic corrosion can be suppressed. This invention is based on these findings.

[0040] Furthermore, the inventors have diligently studied additives in grease compositions in order to suppress ridge marks caused by electrolytic corrosion. To date, they have found that when phosphorus-based additives, which are conventionally used as extreme pressure additives, are used under fluid lubrication conditions (oil film parameter Λ < 3), an insulating film is formed, which can suppress ridge marks caused by electrolytic corrosion. Moreover, they have now found that by using metal powder with a melting point of 800°C or higher (preferably soft metal powder) as a conductive additive in a grease composition containing phosphorus-based additives, appropriate conductivity can be imparted to the grease composition, preventing electrolytic corrosion and effectively preventing damage caused by electrolytic corrosion. The present invention is based on these findings.

[0041] 1. Rolling Bearing First, the rolling bearing of the present invention will be explained based on Figure 1. The rolling bearing of the present invention is a rolling bearing incorporated into an inverter-controlled device. Here, inverter control controls the voltage and frequency in accordance with the set rotational speed. When the switching frequency of the inverter increases, the frequency of shaft voltage generation increases accordingly. As a result, for example, in a rolling bearing incorporated into an inverter-driven motor, a potential difference may occur between the raceways, which may lead to electrolytic corrosion. Examples of inverter-controlled devices include motors, reducers, and transmissions. Figure 1 shows a schematic cross-sectional view of an inverter-controlled motor.

[0042] As shown in Figure 1, the motor 1 rotates a load by attaching a belt 9 to a pulley 8 that is interlocked with the main shaft 2. A rotor 4 is attached to the main shaft 2, a pulley 8 is attached to one end of the rotor 4, and a belt 9 that rotates an air conditioning fan or the like is attached to it. The main shaft 2 is rotatably supported on a flange 5 by a first radial ball bearing 6 and a second radial ball bearing 7 attached to both ends of the rotor 4. A stator 3 is fixed to the flange 5, facing the rotor 4. Furthermore, a corrugated spring washer is positioned between the flange 5 and the second radial ball bearing 7 to provide preload. In Figure 1, the first radial ball bearing 6 and the second radial ball bearing 7 are rolling bearings of the present invention, and they support the rotor 4, which is the rotor, via the main shaft 2.

[0043] Figure 1 shows a method of preloading using springs, where a disc spring, corrugated spring washer, etc., are positioned between the flange 5 and the second radial ball bearing 7 to apply preload. The first radial ball bearing 6 and the second radial ball bearing 7 are each formed by an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a cage that holds the plurality of balls. Details are shown in Figure 2.

[0044] Figure 2 is a cross-sectional view of a deep groove ball bearing. The rolling bearing 11 has an inner ring 12 having an inner ring raceway surface 12a on its outer circumference and an outer ring 13 having an outer ring raceway surface 13a on its inner circumference, arranged concentrically. Multiple rolling elements 14 are arranged between the inner ring raceway surface 12a and the outer ring raceway surface 13a. These rolling elements 14 are held by a cage 15. The axial openings 18a and 18b at both ends of the inner and outer rings are sealed by a sealing member 16, and a grease composition 17 is sealed in the bearing space, at least around the rolling elements 14. The inner ring 12, outer ring 13 and rolling elements 14 are made of steel, and the grease composition 17 is interposed between them as a lubricant to provide lubrication.

[0045] The lubricant used to lubricate the rolling bearing of the present invention can be of two types: (A) a lubricating oil composition comprising a base oil and additives as essential components, and (B) a grease composition comprising a base oil, a thickener, and additives as essential components. In the case of the grease-filled bearing of the present invention, lubrication is provided by the grease composition.

[0046] In the rolling bearing 11, the steel materials constituting the bearing members such as the inner ring 12, outer ring 13, and rolling elements 14 can be any material commonly used as a bearing material. Examples include high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; ISO 683-17), carburized steel (SCr420, SCM420, etc.; ISO 683-5), stainless steel (SUS440C, etc.; ISO 16143-2), high-speed steel (M50, etc.), and cold-rolled steel. The sealing member 16 may be made of metal or a rubber molded body alone, or it may be a composite of a rubber molded body and a metal plate, plastic plate, or ceramic plate. A composite of a rubber molded body and a metal plate is preferred due to its durability and ease of adhesion.

[0047] In this invention, the rolling bearing is lubricated with a lubricant, and it is preferable that the oil film parameter Λ in steady-state operation is greater than 3. This oil film parameter Λ is a parameter that gives the degree of inter-projection interference in the elastohydrodynamic lubrication (EHL) region, and as shown in the following equation (1), the oil film thickness h ｍｉｎ This is calculated by the ratio of the standard deviations of the surface roughness σ1 and σ2. The symbol in equation (1) is h ｍｉｎ : Oil film thickness [μm], σ1, σ2: Mean square roughness [μm] of the two contacting surfaces (rolling contact surfaces of the rolling element and the raceway).

[0048] The oil film thickness can be calculated using a theoretical formula. When using a theoretical formula, it can be calculated using base oil data and test conditions, using Cittenden's formula shown in equation (2) below (Reference: Cittenden, R.J., Downon, D., Dunn, J.F., Taylor, C.M., Proc. Roy. Soc. London, A397 (1985) 271). As shown in equation (2) below, the oil film thickness depends on the velocity parameter, material parameter, and load parameter in the test.

[0049] h ｍｉｎ : Minimum oil film thickness U: Speed ​​parameter G: Material parameter W: Load parameter R ｘ : Equivalent radius of curvature in the flow direction R ｙ : Equivalent radius of curvature in the direction perpendicular to the flow

[0050] In the above formula (2), R ｘ R is the equivalent radius of curvature in the direction of flow. ｙ R is the equivalent radius of curvature in the direction perpendicular to the flow. ｘ is 1 / R ｘ = (1 / R) ｘ１ ) + (1 / R ｘ２ ) is calculated by R ｙ is 1 / R ｙ = (1 / R) ｙ１ ) + (1 / R ｙ２ It is calculated by R. ｘ１ R is the radius of curvature in the flow direction of one of the cylindrical bodies. ｘ２R is the radius of curvature in the flow direction of the other cylindrical body. ｙ１ R is the radius of curvature in the direction perpendicular to the flow of one of the cylindrical bodies. ｙ２ is the radius of curvature in the direction perpendicular to the flow of the other cylindrical body. Also, in equation (2) above, U is the velocity parameter, and (η ０ ×u) / (E'×R ｘ It is calculated by η. ０ This is the viscosity at atmospheric pressure. η ０ It is calculated by ρ × ν, where ρ is the density of the lubricating oil and ν is the kinematic viscosity of the lubricating oil. u is the average value of the peripheral speed of one cylinder and the peripheral speed of the other cylinder. E' is the equivalent Young's modulus. E' is given by 2 / E' = {(1 - ν １ ２ ) / E １} + {(1-ν) ２ ２ ) / E ２ It is calculated by}. E １ E is the Young's modulus of one of the cylinders. ２ ν is the Young's modulus of the other cylinder. １ ν is the Poisson ratio of one of the cylinders, ２ This is the Poisson ratio of the other cylinder.

[0051] In equation (2) above, G is a material parameter and is calculated by α × E'. α is the viscosity-pressure coefficient. α is calculated by the Wu-Klaus-Duda equation. More specifically, α is (0.1657 + 0.2332 × log １０ ν) × m × 10 －８ It is calculated by the following: ν is the kinematic viscosity of the lubricating oil. m is a constant determined by the lubricating oil and is calculated by the Walther-ASTM formula. More specifically, m is log １０ {log} １０ (ν+0.7)}=-m×log １０ It is calculated by T + K. T is the temperature, and K is a constant determined by the lubricating oil. By substituting the two temperatures and the kinematic viscosity at those two temperatures into the Walther-ASTM equation and solving the simultaneous equations, the values ​​of m and K can be calculated. W is the load parameter, and w / (E' × R ｘ ２It is calculated by the formula shown, where w is the load.

[0052] The rolling bearing of the present invention is preferably operated under conditions that form an oil film thicker than the surface roughness of the rolling elements and raceways in a steady-state operation. In the case of metal rolling bearings, under boundary lubrication conditions (oil film parameter Λ < 1) and mixed lubrication conditions (1 < oil film parameter Λ < 3), current is conducted by the contact between the rolling elements and raceways, so electrolytic corrosion due to discharge is unlikely to occur (see, for example, the lower part of Figure 5). On the other hand, under fluid lubrication conditions (3 < oil film parameter Λ), an oil film is interposed between the rolling elements and raceways, and if the potential difference between the two becomes large and exceeds the dielectric breakdown voltage of the oil film, discharge may occur and ridge marks may be generated due to electrolytic corrosion.

[0053] Incidentally, considering the above-mentioned mechanism of ridge mark formation, it is thought that the higher the dielectric breakdown voltage of the oil film, the larger the current that flows during discharge, and as a result, ridge marks are more likely to develop. On the other hand, there are reports that the dielectric breakdown voltage of organic materials tends to be lower for polar materials than for nonpolar materials.

[0054] Taking these factors into consideration, the present invention focuses on relative permittivity as an indicator of polarity, and uses a base oil with a relative permittivity higher than 2.5 as the base oil for the lubricant used to lubricate rolling bearings. Relative permittivity is a parameter that indicates the degree of polarization inside a dielectric, and is defined as the ratio of the dielectric constant of the substance to the dielectric constant in a vacuum. The relative permittivity of the above base oil may be 2.8 or higher, or 3.0 or higher. The upper limit of the relative permittivity is, for example, 4.0.

[0055] Examples of base oils with a relative permittivity higher than 2.5 include ester oils and ether oils. With such polar oils, the dielectric breakdown voltage of the oil film is lower, and it is thought that polar groups are more likely to adsorb onto the orbital surface and form a protective film. As shown in the examples described later, for example, when ester oil is used, ridge marks are less likely to form compared to non-polar oils.

[0056] Examples of ester oils include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methyl acetyl cinolate; aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromelitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane veralgonate, and pentaerythritol ester oil; carbonate ester oils; phosphate ester oils; polymer ester oils; and polyglycol oils. Among these, pentaerythritol ester oil is preferred.

[0057] Examples of ether oils include polyphenyl ether oil, alkyl diphenyl ether oil, alkyl triphenyl ether oil, and alkyl tetraphenyl ether oil. Examples of alkyl diphenyl ether oils include monoalkyl diphenyl ether oil, dialkyl diphenyl ether oil, and polyalkyl diphenyl ether oil.

[0058] The above base oils may be used alone or in combination of two or more. When two or more are used in combination, the dielectric constant of the mixed oil must be higher than 2.5, and oils other than those mentioned above may be mixed in. For example, examples of oils that can be mixed in include synthetic hydrocarbon oils, paraffinic mineral oils, naphthenic mineral oils, and other mineral oils. As synthetic hydrocarbon oils, aliphatic synthetic hydrocarbon oils such as normal paraffin oil, polybutene oil, polyisobutylene oil, and poly-α-olefin (PAO) oil, and aromatic synthetic hydrocarbon oils such as alkylbenzene oil and alkylnaphthalene oil can be used.

[0059] The relative permittivity of the above base oil can be measured by well-known methods such as the capacitance method. For example, in the capacitance method, an impedance meter is used as the measuring instrument. Specifically, a capacitor is formed by sandwiching the lubricating oil between two electrodes, an alternating current of voltage or current is applied to the lubricating oil, and the amplitude and phase difference of the responding alternating current or voltage are measured to determine the impedance Z. Then, the relative permittivity ε is calculated based on the following equations (3) and (4). ｒIt is possible to find this.

[0060] C: Capacitance [F] S: Electrode area [m²] ２ ] d: Electrode spacing [m] ε ｒ : Relative permittivity of lubricating oil ε ０ : Permittivity of vacuum (8.85 × 10⁻⁶) －１２ [F / m]) |Z|: absolute value of impedance [Ω] ω: angular frequency (=2πf), f is the measured frequency [Hz]

[0061] Furthermore, it is preferable that the ratio of the relative permittivity of the base oil to the oil film parameter Λ (relative permittivity / oil film parameter) is 0.4 or more and less than 0.8.

[0062] The kinematic viscosity of the base oil at 40°C (or the kinematic viscosity of the mixed oil in the case of a mixed oil; the same applies hereinafter) is not particularly limited, but for example, 10 mm ２ / s ~ 80mm ２ / s, 10mm ２ / s ~ 50mm ２ It is preferable that it be / s, and 20 mm ２ / s ~ 40mm ２ It may also be / s. Furthermore, the kinematic viscosity of the above base oil at 100°C is, for example, 5.0 mm. ２ / s ~ 12mm ２ It is / s.

[0063] The lubricant in the rolling bearing of the present invention preferably contains a phosphorus-based additive along with the base oil. This phosphorus-based additive forms an insulating film, which suppresses the occurrence of ridge marks.

[0064] The phosphorus-based additives contained in the above lubricants are additives that contain phosphorus (P) in their molecular structure. Examples of phosphorus-based additives include phosphate esters, acidic phosphate esters, phosphite esters, acidic phosphite esters, thiophosphates, thiophosphites, zinc alkyldithiophosphate (ZnDTP), and molybdenum alkyldithiophosphate (MoDTP). These can be used individually or in combination.

[0065] Among the above, phosphate esters are preferred because they readily form an insulating film. A phosphate ester is represented by the following formula (5). (R １ O) ｎ P(=O)H ３－ｎ ... (5) In the above formula (5), n is 1 to 3, preferably 2 to 3, and more preferably 3. R １ R are independent alkyl groups or aromatic groups having 1 to 12 carbon atoms. For example, when n is 2 or 3, １ They may be the same or different. １ These are, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a phenyl group, a tolyl group, a tert-butylphenyl group, or a naphthyl group, and may be branched, and may have substituents including an oxygen atom, a nitrogen atom, a fluorine atom, etc.

[0066] R １ It is preferable that the aliphatic phosphate ester has a linear or branched alkyl group. Furthermore, since the electrical resistance of the insulating film formed on the metal surface tends to be higher, it is more preferable that the aliphatic phosphate ester has three alkyl groups (n=3), and that each alkyl group has 2 to 8 carbon atoms. Examples of such phosphate esters include triethyl phosphate, tributyl phosphate, and trioctyl phosphate. The number of carbon atoms may be 2 to 6. Also, each alkyl group may have 4 to 8 carbon atoms.

[0067] The above lubricant preferably has a phosphorus content of, for example, 0.01% by mass or more and 5.0% by mass or less, and 0.01% by mass or more and less than 2.0% by mass, relative to the total amount of the lubricant. Furthermore, the phosphorus content may be 1.8% by mass or less, 1.5% by mass or less, 0.3% by mass or more, or 0.5% by mass or more. The above phosphorus content preferably originates solely from phosphorus-based additives contained in the lubricant.

[0068] Furthermore, it is preferable that the above lubricant does not contain sulfur-based additives (especially sulfur-based extreme pressure agents) as additives. Sulfur-based additives are additives that contain sulfur (S) in their molecules, and examples include sulfur-based extreme pressure agents such as sulfide compounds.

[0069] When the above lubricant is used as a grease composition (form (B)), the lubricant further contains a thickener. The thickener is not particularly limited, and common thickeners used in the field of rolling bearings can be used. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentonite, silica gel, urea compounds, and urea-urethane compounds can be used. Examples of metal soaps include sodium soap, calcium soap, aluminum soap, and lithium soap, while examples of urea compounds and urea-urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds.

[0070] For example, diurea compounds are obtained by reacting a diisocyanate component with a monoamine component. Examples of diisocyanate components include phenylenediisocyanate and diphenylmethane diisocyanate (MDI). Examples of monoamine components include alicyclic monoamines such as cyclohexylamine, aromatic monoamines such as p-toluidine, and aliphatic monoamines such as octylamine.

[0071] In the above grease composition, the thickener is preferably present in an amount of 10% to 30% by mass, more preferably 10% to 20% by mass, and may also be 10% to 14% by mass, based on the total amount (100% by mass) of the base oil and the thickener.

[0072] In the case of the above grease composition, its mixed consistency (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.

[0073] The above lubricant may further contain other additives, as long as they do not impair the objectives of the present invention. For example, it may contain metal powders as described in section 2 below.

[0074] The rolling bearing of the present invention may have an oil film parameter Λ of 4 or higher, or 5 or higher, in a steady-state operating condition. As the oil film parameter Λ increases, the oil film becomes thicker, making it more difficult for current to flow and thus easier to suppress the occurrence of ridge marks. On the other hand, if the oil film parameter Λ becomes too high, the bearing torque will increase, which may increase, for example, the power consumption of the motor. The oil film parameter Λ may be, for example, 10 or less, 8 or less, or 6 or less.

[0075] In the rolling bearing of the present invention, the mean square roughness of the raceway surface is preferably 0.01 μm or less. Furthermore, the mean square roughness of the surface of the rolling elements is preferably about 0.001 μm.

[0076] In a rolling bearing, the maximum surface pressure in steady-state operation is, for example, 0.3 GPa to 3 GPa, and may also be 0.15 GPa to 4 GPa. Furthermore, the rotational speed in steady-state operation is, for example, 500 min. －１ ~30,000 min －１ And, 500 min －１ ~20,000 min －１ It may also be 1000 min －１ ~20,000 min －１ That's fine.

[0077] Figure 2 illustrates a deep groove ball bearing as an example of the rolling bearing of the present invention, but the form of the rolling bearing of the present invention is not limited to this. For example, it can also be used as an angular contact ball bearing, cylindrical roller bearing, tapered roller bearing, self-aligning roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, thrust self-aligning roller bearing, etc.

[0078] The rolling bearing of the present invention is a bearing incorporated into inverter-controlled devices, and is suitable for use in motors, speed reducers, transmissions, and the like. It can also be used as a motor bearing in electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0079] 2. Grease Composition The present invention provides a grease composition for lubricating rolling bearings, which contains a predetermined metal powder and a phosphorus-based additive. The metal powder functions as a conductive additive, while the insulating film formed by the phosphorus-based additive during discharge comprehensively prevents the occurrence of ridge marks.

[0080] The additives (metal powders, phosphorus-based additives), base oil, and thickeners of the grease composition will be described in detail below.

[0081] [Metal Powder] The metal powder contained in the above grease composition is a metal powder with a melting point of 800°C or higher. This metal powder contributes to imparting conductivity to the grease composition and improving wear resistance. The melting point of the metal powder may be 900°C or higher, 1000°C or higher, or 1200°C or lower. Furthermore, from the viewpoint of ensuring conductivity, it is preferable to have a large number of free electrons, and it is preferable to include metals of group 11 to 13 elements. The type of metal powder is not particularly limited as long as it has a melting point of 800°C or higher (preferably including group 11 to 13 elements), but soft metal powder is preferred when considering the aggressiveness towards the rolling surface and raceway surface. Soft metal powder has a Mohs hardness of, for example, 4 or less, and preferably 3.5 or less.

[0082] As soft metal powders with a melting point of 800°C or higher and containing elements from groups 11 to 13, powders of copper (melting point: approximately 1084°C), silver (approximately 961°C), gold (melting point: approximately 1064°C), and their alloy powders can be used. Each of these metal powders may be used alone or in combination of two or more types. In general, aluminum (melting point: approximately 660°C) and zinc (approximately 419°C) are also known as soft metal powders, but these do not fall under the category of metal powders with a melting point of 800°C or higher. In other words, it is preferable that the grease composition of the present invention does not contain metal powders with a melting point of less than 800°C. For example, if metal powders with a melting point of less than 800°C are used, under conditions where the sliding parts of a rolling bearing become hot, it becomes difficult to maintain the particle shape of the metal powder, and the powder adheres to the sliding parts. As a result, this may lead to an increase in noise and vibration.

[0083] The Mohs hardness scale is a measure of hardness in which a material is judged to be less hard than a standard material if it is scratched sequentially against one of ten standard materials. For example, if a material is scratched without being scratched by calcite (Mohs hardness 3) but scratched by fluorite (Mohs hardness 4), its hardness is expressed as 3.5. The Mohs hardness scale indicates the degree of hardness when a force is applied in the lateral direction and is suitable as a measure of wear on sliding surfaces. The Mohs hardness scale can be measured using a known Mohs hardness tester.

[0084] As the soft metal powder with a melting point of 800°C or higher, it is preferable to use copper-based powder, which has excellent conductivity and is relatively inexpensive. As the copper-based powder, copper powder (elemental copper powder) or copper alloy powder containing copper as the main component can be used. As the copper alloy powder, for example, copper-zinc alloy (brass) powder or copper-tin alloy (bronze) powder can be used. In addition, each alloy powder may contain a third compounding element. Furthermore, the metal powder may be composed of group 11 to 13 elements with a melting point of 800°C or higher.

[0085] Various shapes of metal powders, such as spherical or flaky, can be used. However, from the viewpoint of dispersibility and fluidity in the grease composition, spherical powders are preferable. For example, metal powders produced by atomization or other methods can be used, or commercially available products may be used.

[0086] Average particle size of metal powder (D ５０ The average particle size (D) of the metal powder is not particularly limited, but is, for example, 0.1 μm to 10 μm, preferably 0.5 μm to 5.0 μm, and may be 0.5 μm or more and less than 2.0 μm. Furthermore, in relation to the oil film, the average particle size is preferably larger than the oil film thickness. Note that the average particle size (D) of the metal powder is not particularly limited, but is, for example 0.1 μm to 10 μm, preferably 0.5 μm to 5.0 μm, and may be 0.5 μm or more and less than 2.0 μm. ５０ This refers to the particle size at the point where the cumulative value reaches 50% when the particle size distribution is expressed as a volume-based cumulative distribution, and can be measured using a particle size distribution measuring device that utilizes laser light scattering.

[0087] In a rolling bearing containing the above-mentioned grease composition, it is preferable that the ratio of the average particle size of the metal powder [unit: μm] to the oil film thickness [unit: μm] of the grease composition during use (average particle size of metal powder / oil film thickness) is greater than 1. When this ratio is greater than 1, the metal powder has difficulty intervening in the sliding part, which is considered unfavorable for the formation of conductive paths. However, it is easier to maintain the particle shape (especially in the case of soft metal powder), thus enabling a long-term anti-corrosion effect. In this case, it is considered that the conductive paths are mainly formed outside the contact ellipse. The above ratio may be, for example, 1.2 or more and 10 or less, or 1.5 or more and 5.0 or less.

[0088] The metal powder content is, for example, 0.1 to 10 parts by mass, preferably 0.5 to 10 parts by mass, and may be 0.5 to 5 parts by mass, per 100 parts by mass of base grease consisting of base oil and thickener. By setting the content within this range, conductivity that is effective in preventing galvanic corrosion is ensured, and wear resistance is also improved.

[0089] [Phosphorus-based additives] The phosphorus-based additives contained in the above grease composition are additives that contain phosphorus (P) in their molecular structure. As the phosphorus-based additive, the phosphorus-based additives described in 1. above for rolling bearings can be used, and among them, phosphate esters are preferred (see formula (5) above).

[0090] The phosphorus-based additive is included in an amount of, for example, 0.01 to 10 parts by mass, preferably 0.05 to 5.0 parts by mass, more preferably 0.05 to 2.0 parts by mass, and may also be 0.1 to 2.0 parts by mass, per 100 parts by mass of the base grease consisting of the base oil and the thickener. In terms of phosphorus content, the phosphorus content of the grease composition is, for example, 0.01% by mass or more and 2.0% by mass relative to the total amount of the grease composition. The phosphorus content may be 1.8% by mass or less, 1.5% by mass or less, 0.3% by mass or more, or 0.5% by mass or more. Preferably, the phosphorus content is derived solely from the phosphorus-based additive contained in the grease composition.

[0091] Furthermore, it is preferable that the above grease composition does not contain sulfur-based additives (especially sulfur-based extreme pressure agents) as additives. Sulfur-based additives are additives that contain sulfur (S) in their molecules, and examples include sulfur-based extreme pressure agents such as sulfide compounds.

[0092] [Base Oil] The base oil can be any type commonly used in rolling bearings, without any particular restrictions. Examples include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as poly-α-olefin (PAO) oil and alkylbenzene oil, ester oils, ether oils, silicone oils, and fluorinated oils. These oils may be used individually or in combination of two or more types.

[0093] Incidentally, considering the mechanism of the generation of ridge marks, it is preferable to use a base oil having a relative dielectric constant higher than 2.5 as the base oil of the grease composition, and it may be 2.8 or more, or may be 3.0 or more. The upper limit of the relative dielectric constant is, for example, 4.0. Examples of the base oil having a relative dielectric constant higher than 2.5 include ester oil and ether oil. The oil mentioned in the rolling bearing of 1. above can be used. When two or more kinds of oils are used in combination as the base oil, it is preferable that the relative dielectric constant of the mixed oil is higher than 2.5.

[0094] The kinematic viscosity of the above base oil at 40°C (in the case of a mixed oil, the kinematic viscosity of the mixed oil, the same applies hereinafter) is not particularly limited, but for example, it is 10 mm ２ / s to 80 mm ２ / s, and it is preferably 10 mm ２ / s to 50 mm ２ / s, and may be 20 mm ２ / s to 40 mm ２ / s. Further, the kinematic viscosity of the above base oil at 100°C is, for example, 5.0 mm ２ / s to 12 mm ２ / s.

[0095] [Thickener] The types and contents of the thickeners described in the rolling bearing of 1. above can be applied.

[0096] The consistency (JIS K2220) of the grease composition is preferably in the range of 200 to 350. When the consistency is less than 200, there is a risk of poor lubrication due to small oil separation. On the other hand, when the consistency exceeds 350, the grease becomes soft and easily flows out of the bearing, which is not preferable.

[0097] The above grease composition may further contain other additives as long as the object of the present invention is not impaired. The grease composition preferably does not contain an ionic liquid. Here, the ionic liquid refers to a substance that becomes a liquid near room temperature (for example, 25°C) although it is an ionic bonding compound composed of a cation component and an anion component.

[0098] 3. Grease-Sealed Bearings The grease-sealed bearing of the present invention is one in which the grease composition described in 2. above is sealed. The oil film parameter Λ of this grease-sealed rolling bearing may be 4 or higher, or 5 or higher, in steady-state operation. As the oil film parameter Λ increases, the oil film becomes thicker, making it more difficult for current to flow and making it easier to suppress the occurrence of ridge marks. On the other hand, if the oil film parameter Λ becomes too high, the bearing torque will increase, which may increase the power consumption of the motor, for example. The oil film parameter Λ may be, for example, 10 or less, 8 or less, or 6 or less.

[0099] In the grease-filled bearing of the present invention, the mean square roughness of the raceway surface is preferably 0.01 μm. Furthermore, the mean square roughness of the rolling element surface is preferably about 0.001 μm.

[0100] In the above-described grease-filled bearing, the maximum surface pressure in steady-state operation is, for example, 0.3 GPa to 3 GPa, and may also be 0.15 GPa to 4 GPa. Furthermore, the rotational speed in steady-state operation is, for example, 500 min. －１ ~30,000 min －１ And, 500 min －１ ~20,000 min －１ It may also be 1000 min －１ ~20,000 min －１ That's fine.

[0101] The grease-filled bearings described above are suitable as rolling bearings for use in environments and applications where electrolytic corrosion is likely to occur. For example, they are suitable as bearings that rotatably support the rotating shafts of motors and refrigerant compressors, and as bearings incorporated into inverter-controlled devices (see, for example, Figure 1).

[0102] The present invention will be described in detail by reference to examples and comparative examples, but is not limited in any way by these examples.

[0103] Reference Examples 1 to 5 and Comparative Examples 1 and 2 First, in order to examine the influence of additives in lubricants, lubricants having the compositions shown in Table 1 were prepared respectively. These lubricants are lubricating oil compositions comprising a base oil and additives. In Table 1, the numerical values in the columns of each additive indicate the mass % in terms of phosphorus (P) or sulfur (S) relative to the total amount of the lubricant.

[0104] The structural formulas of the phosphorus-based additives and sulfur-based additives used in this reference example are shown in FIG. 3. For example, as the phosphorus-based additive, a phosphate ester was used. More specifically, as the branched-chain alkyl type, trioctyl phosphate was used, as the straight-chain alkyl type, trimethyl phosphate and tributyl phosphate were used, and as the aromatic type, tricresyl phosphate was used.

[0105] [Erosion Test] Each lubricant was enclosed in a rolling bearing with an inner ring rotation that supports a rotating shaft, which simulated an industrial motor (the inner ring, outer ring, and steel balls are bearing steel SUJ2), and an operation test was conducted under the following conditions. The combined load was 59 N, and the rotational speed was 1600 min －１ The operating conditions were set, and further, the test was carried out with a constant current of 5.0 A flowing in the test bearing (6206). A set current was applied to the bearing under constant current control (the voltage was adjusted so that the set current was obtained).

[0106] <Test Conditions> Bearing: 6206T2X2CMLCLU Rolling element: Steel ball (standard bearing) Power supply current: 5.0 A Test machine rotation speed: 1600 min －１ Radial load: 38.2 N Axial load: 101 N Maximum surface pressure: 0.74 GPa Oil film parameter Λ (35°C): 6.56 Test time: 7 hours Number Number of tests: 1 each

[0107] The oil film parameter Λ under the above test conditions was calculated using equation (1) above. The oil film thickness in equation (1) was calculated using Cittender's equation (see equation (2) above) with the base oil data and test conditions. The surface roughness (mean square roughness) of the rolling elements and the inner ring was measured using a stylus-type surface roughness measuring instrument for the rolling elements and inner ring before the test. Under these test conditions, the oil film parameter Λ is 3 or greater. Generally, when the oil film parameter Λ is 3 or greater, fluid lubrication occurs between the two surfaces, resulting in non-contact. Therefore, under the above test conditions, it can be said that the steel balls do not come into contact with the inner and outer rings and wear down.

[0108] Then, the surface properties of the inner ring raceway were optically observed after 7 hours of testing. Observation photographs of Reference Examples 1 to 5 are shown in Figure 4, and observation photographs of Comparative Examples 1 and 2 are shown in Figure 5. First, as shown in Comparative Example 1 in Figure 5, when no additive was added (only PAO oil), ridge marks (striped irregularities) were clearly formed on the inner ring raceway surface.

[0109] On the other hand, in the cases where additives were added (Comparative Example 2 and Reference Examples 1-5), the suppression of ridge mark formation was evaluated in comparison to the ridge marks formed in Comparative Example 1. In this test, based on observation of surface properties, cases where no ridge marks were formed were designated as "A", cases where ridge marks were formed but sufficient suppression was confirmed as "B", and cases where ridge marks were formed but little suppression was confirmed as "C". The results are shown in Table 1.

[0110]

[0111] As shown in Figure 5, in Comparative Example 2, which had a sulfur-based additive added, the ridge marks themselves were thinner than in Comparative Example 1, but the suppression of ridge mark formation was not very noticeable. In contrast, as shown in Figure 4, in Reference Examples 1 to 5, which had a phosphorus-based additive added, no ridge marks were formed, or sufficient suppression of ridge mark formation was observed. It was found that the phosphorus-based additive was effective regardless of whether it was branched-chain alkyl, linear alkyl, or aromatic (Reference Examples 1, 4, and 5). Furthermore, even when the base oil viscosity was increased and the oil film thickness was increased, although ridge marks were formed, a sufficient suppressive effect was observed (Reference Example 3). In addition, a sufficient suppressive effect was observed even when the concentration of the phosphorus-based additive was increased.

[0112] Furthermore, when the same test was performed using the lubricant of Comparative Example 1 under the condition of oil film parameter Λ = 1.6, no ridge marks were formed. This is thought to be because current was conducted due to metal-to-metal contact between the rolling elements and the inner ring (see Figure 5, lower diagram).

[0113] [Anderon Test] An inner ring after the electrolytic corrosion test, a new outer ring, a crown-type cage, and ceramic rolling elements were prepared. They were ultrasonically cleaned using petroleum benzine and assembled so that the outer ring markings, inner ring markings, and the openings of the retaining claws of the crown-type cage were on the same plane (see Figure 6). 10 μL of PAO6 was dropped onto the raceway surface and the inner ring 22 was rotated gently. The crown-type cage 25 was placed on the shaft of the anderon measuring machine so that its opening was facing forward. An axial load of 100 N was applied to the outer ring 23 of the rolling bearing 21 and the anderon value was measured while rotating at a rotation speed of 1800 rpm. The frosted portion of the inner ring 22 is shown with cross-hatching. Sampling was performed by acquiring one data point every 10 seconds of rotation, and the average value of five samples was calculated for each band. The results are shown in Figure 7.

[0114] For evaluating electrolytic corrosion, the Anderon H band (frequency 1800 Hz to 10000 Hz) is particularly useful. Therefore, calculated Anderon values ​​of less than 100 were classified as "A", values ​​between 100 and 200 as "B", and values ​​of 200 or more as "C".

[0115] As shown in Figure 7(a), it was found that sulfur-based and phosphorus-based additives suppressed the rise in the anderone H band. Furthermore, in Reference Example 3, which has a higher base oil viscosity, the rise in the anderone H band was suppressed more than in Reference Example 1. Among the phosphate esters, trioctyl phosphate (branched-chain alkyl) showed the most suppression, followed by trimethyl phosphate (linear alkyl) and tricresyl phosphate (aromatic).

[0116] In the following section, in order to examine the differences in results between phosphorus-based and sulfur-based additives, the electrical resistance (insulating properties) of each coating formed under abrasion test conditions was evaluated.

[0117] [SRV Test] As an abrasion test, the product was evaluated using an SRV testing machine. Figure 8 shows an overview of the SRV testing machine. Using the SRV testing machine 31, a load F was applied to a disc 34 coated with lubricant 35, and an arm 33 holding a ball 32 was vibrated horizontally in a reciprocating direction. The lubricant 35 used was either PAO 10 alone, or a lubricating oil composition in which various sulfur-based or phosphorus-based additives were added to PAO 10. The sulfur-based additive was added to the total amount of lubricant so as to be 0.5% by mass in terms of sulfur, and the phosphorus-based additive was added to the total amount of phosphorus so as to be 0.2% by mass. The test conditions were as follows.

[0118] <Test Conditions> Temperature: 40°C Load: 50 N / 5 min, up to 200 N Initial surface pressure: 1.7 GPa, 2.2 GPa, 2.5 GPa, 2.8 GPa Frequency: 50 Hz Amplitude: 1 mm Test time: 20 minutes Ball: SUJ2 (φ9.525 mm) Disc: SUJ2 (φ24 mm)

[0119] Figure 9(a) shows the change in the coefficient of friction when tert-butyl disulfide is used as an additive. As shown in Figure 9(a), the coefficient of friction decreases as the load increases, indicating that tert-butyl disulfide forms a film and exhibits extreme pressure action.

[0120] Figures 9(b) and 9(c) show the changes in electrical resistance values ​​when each additive is used. It can be seen that the phosphorus-based additive maintains a higher electrical resistance value compared to the sulfur-based additive. Figure 10 shows a bar graph of the average value over the last minute for each load.

[0121] As shown in Figure 10, in the case of PAO oil alone, the electrical resistance decreased as the load increased. On the other hand, when a sulfur-based additive was added, the electrical resistance remained low regardless of the load.

[0122] When phosphorus-based additives were added, all phosphate esters exhibited higher electrical resistance values ​​compared to when sulfur-based additives were added. In particular, the three phosphate esters excluding trimethyl phosphate showed high electrical resistance values ​​and small changes with load. Furthermore, linear alkyl and branched alkyl phosphate esters had even higher electrical resistance values ​​than aromatic phosphate esters.

[0123] Thus, the addition of additives shows different trends compared to the case with PAO oil alone, suggesting that these additives contribute to the early formation of a protective film. Furthermore, the difference in electrical resistance between the addition of sulfur-based and phosphorus-based additives is thought to have influenced the suppression of ridge marks in the electrolytic corrosion test described above. In other words, the film based on phosphorus-based additives has high insulating properties (is non-conductive), while the film based on sulfur-based additives has low insulating properties (is conductive).

[0124] Based on the SRV test results, the film formed by the phosphorus-based extreme pressure additive is considered to be an insulating film. Furthermore, although extreme pressure additives generally do not act when the oil film parameter is greater than 3, the discharge during dielectric breakdown generates high heat of several thousand joules. Therefore, it is thought that the heat generated during discharge brings the rolling surface to the operating temperature of the extreme pressure additive, forming an insulating film, and as a result, suppressing the occurrence of ridge marks.

[0125] [Test Examples A1 to A3] Next, lubricants with the compositions shown in Table 2 were prepared. These lubricants are lubricating oil compositions consisting of lubricating oil and additives. As lubricating oils, an ester oil with a relative permittivity of 3.16 and a PAO oil with a relative permittivity of 2.18 were used. The relative permittivity of each lubricating oil was measured using a commercially available capacitance transducer (30°C, 200 kHz).

[0126] For measuring the dielectric constant of the lubricating oil, a capacitance transducer MC-130 and electrode cell manufactured by Y.E.I. Co., Ltd. were used. Figure 11 shows a schematic diagram of the measuring apparatus 41. The capacitance transducer 42 used corresponds to a capacitor component fluctuation of 1 pF at an output of 1 V. The capacitance value of the electrode cell 43 used is 5.17 pF. The measurement method involves preparing a metal container with the electrode cell 43 and a thermocouple for measuring the temperature of the sample fixed in it, and measuring the output voltage V of the capacitance transducer 42 in air. ０ Next, the metal container was heated by the ring heater 44 to adjust the temperature of the sample 45 to an arbitrary value. The voltage value V output by the capacitance converter 42 was obtained. １ This was converted to relative permittivity using the following formula (6).

[0127] The obtained lubricants were used to conduct tests under the same conditions as the electrolytic corrosion test described above. In this test, the ratio of the relative permittivity of the base oils in Test Examples A1 to A3 to the oil film parameter Λ in the test (relative permittivity / oil film parameter) was 0.48. The surface properties of the inner ring raceway were optically observed after 7 hours of testing. Observation photographs of Test Examples A1 to A2 and Comparative Example 1 are shown in Figure 12. As shown in Figure 12, even in the case of Test Example A1 with only ester oil (no additives), no ridge marks were formed, indicating that the influence of the difference in base oil (relative permittivity) is involved. Furthermore, even when a phosphorus-based additive was added to the ester oil in Test Example A2, no ridge marks were formed. In this evaluation, no difference in results was confirmed between Test Examples A1 and A2, but from the results of the reference examples described above, it can be said that adding a phosphorus-based additive is even more effective in suppressing the occurrence of ridge marks.

[0128] Furthermore, Table 2 shows the results of tests conducted under the same conditions as the Anderon test described above. As shown in Table 2, the Anderon values ​​were low in all of the cases of test examples A1 to A3.

[0129]

[0130] Thus, the results of Test Example A above show that using a base oil with a high dielectric constant can suppress the occurrence of ridge marks even when the test is conducted for a long period of time. Furthermore, adding a phosphorus-based extreme pressure additive to the base oil can be expected to further suppress the occurrence of ridge marks.

[0131] [Test Examples B1 to B9] Next, grease compositions with the compositions shown in Table 3 were prepared. Trioctyl phosphate, which yielded good results in the above-mentioned tests, was used as an additive, and copper powder or aluminum powder was used as a conductive additive. Ester oil (with a dielectric constant higher than 2.5) and PAO oil (with a dielectric constant of 2.5 or less) were used as base oils. As a thickener, a diurea compound (lipid-alicyclic diurea) obtained by reacting a diisocyanate component with an aliphatic monoamine and an alicyclic monoamine (with a molar ratio of monoamines of 1:1) was used as a monoamine component. In Table 3, the content of base oil and thickener is shown in mass% relative to 100 mass% of base grease (base oil + thickener). The content of trioctyl phosphate, copper powder, and aluminum powder is shown in parts by mass relative to 100 parts by mass of base grease.

[0132] Using the obtained grease composition, tests were conducted under the same conditions as the electrolytic corrosion test described above, and the surface properties of the inner ring raceway after 30 hours were optically observed. The results for test examples B1 to B4 and B6 to B7 are shown in Figure 13(a). In Figure 13(a), for each test example, from top to bottom, the observed image, the roughness curve along the circumferential direction of the inner ring raceway and its maximum height roughness Rz, and the cross-sectional curve along the radial direction of the inner ring raceway and its depth are shown.

[0133] The maximum height (rz) of the roughness curve and the depth of the cross-sectional curve were measured using a stylus-type surface roughness measuring instrument. Rz is defined in ISO 4287. In this test, Rz less than 0.5 μm was classified as "A", 0.5 μm or more and less than 0.7 μm as "B", and 0.7 μm or more as "C". Similarly, wear depth less than 1 μm was classified as "A", 1 μm or more and less than 2 μm as "B", and 2 μm or more as "C". Measurements were taken at five locations, and the average value was used to evaluate from A to C. The results are shown in Table 3.

[0134] The following conditions were used to obtain all roughness profiles, including the circumferential roughness profile and the axial cross-sectional roughness profile: Measurement length: 7.0 mm Measurement pitch: 0.0005 mm Roughness analysis measurement pitch: 0.0005 mm Measurement speed: 0.2 mm / sec Reference length: 0.8 mm Number of sections: 5 λs: 0.0025 mm Correction: R correction (automatic) based on the non-sliding surface was performed.

[0135]

[0136] As shown in Figure 13(a), test examples B1 and B2, which used grease compositions containing phosphorus-based additives and copper powder, showed no observed ridge marks and low roughness Rz within the contact ellipse. Furthermore, wear on the inner ring raceway surface was suppressed, resulting in overall excellent results. In test examples B1 and B2, the "average particle size of metal powder / oil film thickness" was greater than 1, suggesting that copper powder was less likely to intervene in the sliding part. However, compared to cases without copper powder (test examples B3-B4, B6-B7), the adverse effects of galvanic corrosion were prevented due to the creation of conductive paths. In addition, as shown in Figure 13(b), improvement in wear resistance was confirmed by adding copper powder to the grease composition containing phosphorus-based additives.

[0137] Table 3 shows that there was no significant difference in ridge mark evaluation between Test Example B1 and Test Example B2. However, comparing the results of Test Example B3 and Test Example B6, and Test Example B4 and Test Example B7, ester oil showed a better tendency in ridge mark evaluation compared to synthetic hydrocarbon oil. This suggests that the influence of differences in base oil (relative permittivity) is involved in suppressing ridge marks. Therefore, it is preferable to use a base oil with a high relative permittivity.

[0138] Furthermore, as shown in the results in Table 3, good results were obtained in ridge mark evaluation even with only the addition of copper powder as an additive (Test Examples B5 and B8). This is thought to be because the addition of copper particles forms conductive paths, making it difficult for a potential difference to occur between the raceway and rolling elements, thus suppressing discharge in the first place. On the other hand, it is conceivable that the discharge-suppressing effect of copper particles may decrease due to prolonged operation. In contrast, with the grease compositions of Test Examples B1 and B2, even if discharge occurs, the insulating film formed by the added phosphorus-based extreme pressure agent is formed within the contact ellipse, maintaining the discharge-suppressing effect of the copper particles and suppressing the progression of electrolytic corrosion. Thus, by combining metal powder and phosphorus-based additives, different approaches to the mechanism of electrolytic corrosion progression can be taken.

[0139] Furthermore, the grease composition in test example B2 uses an oil with a high dielectric constant as the base oil, which can be expected to further stabilize the suppression of electrolytic corrosion.

[0140] Next, test examples B1 to B9 were also tested under the same conditions as the Anderon test described above. The results are shown in Table 4 and Figure 13(c). In this test, the calculated Anderon value was classified as "A" if it was less than 50, "B" if it was 50 or more but less than 100, and "C" if it was 100 or more.

[0141]

[0142] As shown in Table 4, in all cases of test examples B1 and B2, the anderon value was low, less than 100. Furthermore, as shown in Figure 13(c), the increase in the anderon H band was suppressed by adding copper powder to the grease composition containing a phosphorus-based additive.

[0143] As shown in Table 4, the aluminum powder used in Test Example B9 is a soft metal and is conductive, but it showed a high anderon value. To investigate this result, elemental mapping was performed on the central and end portions of the frosting on the inner ring raceway surface. It was found that in Test Example B9, aluminum adhesion to the inner ring raceway surface was significant (i.e., aluminum was deposited) compared to the other test examples. In contrast, copper has a higher melting point than aluminum, and no significant adhesion to the raceway surface was observed. As a result, the particle shape was maintained, which is thought to have led to the favorable results.

[0144] The rolling bearings of the present invention can suppress ridge marks caused by galvanic corrosion, making them suitable for use in environments where galvanic corrosion is likely to occur. Furthermore, the grease-filled bearings of the present invention suppress ridge marks caused by galvanic corrosion and also have excellent wear resistance, making them suitable for use in environments where galvanic corrosion is likely to occur. These bearings are suitable, for example, for rolling bearings used in automotive auxiliary equipment and motors for industrial machinery, as well as for rolling bearings used in motor drive systems of electric vehicles and hybrid vehicles.

[0145] 1 Motor 2 Main shaft 3 Stator 4 Rotor 5 Flange 6 First radial ball bearing 7 Second radial ball bearing 8 Pulley 9 Belt 11 Rolling bearing 12 Inner ring 13 Outer ring 14 Balls (rolling elements) 15 Cage 16 Seal member 17 Grease composition (lubricant) 18a Opening 18b Opening 21 Rolling bearing 22 Inner ring 23 Outer ring 24 Rolling elements 25 Crown-type cage 31 SRV tester 32 Ball 33 Arm 34 Disc 35 Lubricant 41 Measuring device 42 Capacitance transducer 43 Electrode cell 44 Ring heater 45 Sample

Claims

1. A rolling bearing incorporated into an inverter-controlled device, having an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and being lubricated with a lubricant, wherein the lubricant comprises a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive.

2. The rolling bearing according to claim 1, characterized in that the base oil is an ester oil.

3. The rolling bearing according to claim 1, characterized in that the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group.

4. The rolling bearing according to claim 1, characterized in that the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three alkyl groups, each alkyl group having 2 to 8 carbon atoms, the phosphorus content relative to the total amount of the lubricant is 0.01% by mass or more and less than 2.0% by mass, and the lubricant does not contain a sulfur-based additive.

5. The rolling bearing according to claim 1, characterized in that the oil film parameter Λ in a steady-state operating condition is greater than 3, and the ratio of the relative permittivity of the base oil to the oil film parameter Λ (relative permittivity / oil film parameter) is 0.4 or more and less than 0.

8.

6. The rolling bearing according to claim 1, characterized in that the base oil is a polyol ester oil, the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three alkyl groups, each alkyl group having 4 to 8 carbon atoms, the phosphorus content relative to the total amount of the lubricant is 0.01% by mass or more and less than 2.0% by mass, and the lubricant does not contain a sulfur-based additive.

7. A grease composition characterized by comprising a base oil, a thickener, a phosphorus-based additive, and a metal powder having a melting point of 800°C or higher.

8. The grease composition according to claim 7, characterized in that the metal powder is copper powder.

9. The grease composition according to claim 7, characterized in that the base oil is a base oil with a relative permittivity higher than 2.

5.

10. The base oil is an ester oil, and the kinematic viscosity of the base oil at 40°C is 10 mm². ２ / s ~ 80mm ２ The grease composition according to claim 7, characterized in that it is / s.

11. The grease composition according to claim 7, characterized in that the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester having three alkyl groups, each alkyl group having 2 to 8 carbon atoms.

12. The metal powder is copper powder, the base oil is ester oil, and the kinematic viscosity of the base oil at 40°C is 10 mm². ２ / s ~ 80mm ２ The grease composition according to claim 7, wherein the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, and the grease composition does not contain an ionic liquid.

13. A grease-filled bearing having an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, wherein a grease composition is sealed inside, and the grease composition is the grease composition described in claim 7.

14. The grease-filled rolling bearing according to claim 13, characterized in that the ratio of the average particle size [unit: μm] of the metal powder to the oil film thickness [unit: μm] of the grease composition when the grease-filled bearing is used (average particle size of metal powder / oil film thickness) is greater than 1.

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