Rolling bearings

Abstract

To provide a rolling bearing that can suppress ridge marks caused by electrolytic corrosion. [Solution] The rolling bearings 6 and 7 are incorporated into an inverter-controlled motor 1 and have an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and are lubricated with a lubricant, the lubricant comprising a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive, the base oil being an ester oil, and the phosphorus-based additive being an aliphatic phosphate ester having a linear or branched alkyl group.

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing lubricated with a lubricant, and more particularly to a rolling bearing incorporated into an inverter-controlled device. [Background technology]

[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 composed of at least one of perfluoropolyether and fluorosilicone, a thickener such as a fluorine compound, and carbon black. Patent Document 2 also describes that a conductive seal is provided as a seal for sealing the end of a bearing space.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] As described above, techniques for imparting conductivity to bearings are known. However, the conductive greases and conductive seals described in Patent Document 1 and Patent Document 2 generally have a high volume resistivity of 10 4 ~10 8 Ω·cm. Therefore, although it is effective for removing static electricity and preventing charging, when the shaft voltage of the motor caused by the inverter becomes a problem, it is difficult to suppress the generation of shaft voltage due to the high resistance. As a result, dielectric breakdown of the oil film by the lubricant may occur in rolling bearings.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a rolling bearing capable of suppressing ridge marks due to electric corrosion.

Means for Solving the Problems

[0009] The rolling bearing of the present invention is incorporated in an inverter-controlled device, and 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 rolling bearing lubricated with a lubricant. The lubricant is characterized by containing a base oil having 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 is characterized by not containing 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 above lubricant is characterized by being a lubricating oil composition.

[0015] In the above rolling bearing, the maximum surface pressure under steady-state operation is 0.3 GPa to 3 GPa, and the rotational speed is 500 min⁻¹. -1 ~20,000 min -1 It is characterized by being such. [Effects of the Invention]

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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, the above-mentioned lubricant can suppress ridge marks. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic cross-sectional view of the motor. [Figure 2] This is a cross-sectional view of a deep groove ball bearing, which is an example of a rolling bearing of the present invention. [Figure 3] This diagram shows the structures of the phosphorus-based and sulfur-based additives used in the example. [Figure 4] These are observational photographs of the inner track surface for Reference Examples 1-5. [Figure 5] These are photographs of the inner raceway surfaces of Comparative Examples 1 and 2. [Figure 6] This is a diagram illustrating the Anderon trial. [Figure 7] This graph shows the results of the Anderon trial. [Figure 8] This is a schematic diagram of the SRV test machine. [Figure 9] This graph shows the changes in the coefficient of friction and electrical resistance values ​​during SRV testing. [Figure 10] This graph shows the electrical resistance values ​​when using each additive under different loads. [Figure 11] This is a schematic diagram of a device for measuring relative permittivity. [Figure 12] These are photographs of the inner ring raceway surfaces of Examples 1 and 2 and Comparative Example 1. [Modes for carrying out the invention]

[0021] The inventors of this invention have diligently studied how to suppress ridge marks caused by electrolytic corrosion in rolling bearings 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 knowledge showing 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.

[0022] The rolling bearing of the present invention will be described with reference to 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 according to the set rotational speed. When the switching frequency of the inverter increases, the frequency of shaft voltage generation increases accordingly. As a result, in a rolling bearing incorporated into an inverter-driven motor, for example, 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.

[0023] As shown in Figure 1, the motor 1 rotates a load by attaching a belt 9 to a pulley 8 that is linked to 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, 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.

[0024] 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.

[0025] 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. In addition, 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.

[0026] The lubricant for lubricating the rolling bearings 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.

[0027] 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.; JIS G4805), carburized steel (SCr420, SCM420, etc.; JIS G4053), stainless steel (SUS440C, etc.; JIS G4303), 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.

[0028] 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.

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[0029] 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 (see formula (2) below) (Reference: Chittenden, RJ, Dowson, D., Dunn, JF, Taylor, CM, Proc. Roy. Soc. London, A397 (1985) 271). As shown in formula (2) below, the oil film thickness depends on the velocity parameter, material parameter, and load parameter in the test.

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[0030] h min : Minimum oil film thickness U: Velocity 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

[0031] In the above formula (2), R x is the equivalent radius of curvature in the flow direction, and R y is the equivalent radius of curvature in the direction perpendicular to the flow. R x is 1 / R x =(1 / R x1 )+(1 / R x2 ) and is calculated thereby, and R y is 1 / R y =(1 / R y1 )+(1 / R y2 ) and is calculated thereby. R x1 is the radius of curvature in the flow direction of one cylindrical body, and R x2 is the radius of curvature in the flow direction of the other cylindrical body, and R y1 is the radius of curvature in the direction perpendicular to the flow of one cylindrical body, and R y2 is the radius of curvature in the direction perpendicular to the flow of the other cylindrical body. Also, in the above formula (2), U is the velocity parameter and is calculated by (η0×u) / (E′×R x ). η0 is the atmospheric pressure viscosity. η0 is calculated by ρ×ν. 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 cylindrical body and the peripheral speed of the other cylindrical body. E′ is the equivalent Young's modulus. E′ is calculated by 2 / E′={(1 - ν1 2 ) / E1}+{(1 - ν2 2 ) / E2}. E1 is the Young's modulus of one cylindrical body, E2 is the Young's modulus of the other cylindrical body. ν1 is the Poisson's ratio of one cylindrical body, and ν2 is the Poisson's ratio of the other cylindrical body.

[0032] 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 { 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 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 2 It is calculated by ), where w is the load.

[0033] 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.

[0034] 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.

[0035] 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 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.

[0036] Examples of base oils with a dielectric constant 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.

[0037] 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.

[0038] 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.

[0039] 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 for 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.

[0040] 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). r It is possible to find this.

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[0041] C: Capacitance [F] S: Area of ​​electrode [m²] 2 ] d: Electrode spacing [m] ε r Relative permittivity of lubricating oil ε0: 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]

[0042] 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.

[0043] 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 is 10mm 2 / s~50mm 2 It is preferable that it be / s, which is 20mm 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.

[0044] 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.

[0045] 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.

[0046] Among the above, phosphate esters are preferred because they readily form an insulating film. Phosphate esters are 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. 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. 1These 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.

[0047] 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 of the alkyl groups 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.

[0048] The phosphorus content of the above lubricant is preferably, 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. The phosphorus content may also 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 is preferably derived solely from phosphorus-based additives contained in the lubricant.

[0049] 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.

[0050] 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 can be any common one used in the field of rolling bearings. 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.

[0051] 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.

[0052] In the above grease composition, the thickener is preferably present in an amount of 10% to 30% by mass, and more preferably in an amount of 10% to 20% by mass, relative to the total amount (100% by mass) of the base oil and the thickener.

[0053] 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.

[0054] The above lubricant may further contain other additives, as long as they do not impair the objectives of the present invention.

[0055] 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.

[0056] 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.

[0057] In rolling bearings, 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. -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.

[0058] 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.

[0059] The rolling bearing of the present invention is a bearing incorporated into inverter-controlled devices, and is suitable for use in motors, reducers, transmissions, and the like. It can also be used as a motor bearing in electric vehicles (EVs) and hybrid electric vehicles (HEVs). [Examples]

[0060] 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.

[0061] Reference Examples 1-5 and Comparative Examples 1-2 First, in order to investigate the effect of additives in lubricants, lubricants with the compositions shown in Table 1 were prepared. These lubricants are lubricating oil compositions consisting of a base oil and additives. In Table 1, the values ​​in the column for each additive represent the mass percentage of phosphorus (P) or sulfur (S) relative to the total amount of lubricant.

[0062] The structural formulas of the phosphorus-based and sulfur-based additives used in this example are shown in Figure 3. For example, phosphate esters were used as phosphorus-based additives; more specifically, trioctyl phosphate was used as a branched alkyl group, trimethyl phosphate and tributyl phosphate were used as linear alkyl groups, and tricresyl phosphate was used as an aromatic group.

[0063] [Electrolytic corrosion test] A rolling bearing (inner ring, outer ring, and steel balls made of bearing steel SUJ2) supporting the rotating shaft, simulating an industrial motor, was sealed with various lubricants and tested under the following conditions: combined load of 59N, rotational speed of 1600 min⁻¹. -1 The operating conditions were set, and the test was conducted with a constant current of 5.0A flowing through the test bearing (6206). The bearing was subjected to constant current control, applying the set current (the voltage was adjusted to achieve the set current).

[0064] <Test Conditions> Bearing: 6206T2X2CMLLU Rolling element: Steel ball (standard bearing) Power supply current: 5.0A Test machine rotation speed: 1600 min⁻¹ -1 Radial load: 38.2N Axial load: 101N Maximum surface pressure: 0.74GPa Oil film parameter Λ(35℃): 6.56 Exam duration: 7 hours Number of test samples: 1 each

[0065] 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 Cittenden's formula, 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.

[0066] Then, the surface properties of the inner ring raceway were optically observed after 7 hours of testing. Observation photographs of Reference Examples 1-5 are shown in Figure 4, and observation photographs of Comparative Examples 1-2 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.

[0067] 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. 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 were designated as "B," and cases where ridge marks were formed but little suppression was confirmed were designated as "C." The results are shown in Table 1.

[0068] [Table 1]

[0069] 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.

[0070] 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).

[0071] [Anderon test] The 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 for every 10 seconds of rotation, and the average value of five samples was calculated for each band. The results are shown in Figure 7.

[0072] Since the Anderon H band (frequency 1800Hz to 10000Hz) is particularly useful for evaluating electrolytic corrosion, the calculated Anderon values ​​were categorized as follows: less than 100 was designated as "A", 100 to less than 200 as "B", and 200 or more as "C".

[0073] 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).

[0074] Below, in order to consider 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.

[0075] The wear test 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 PAO10 alone, or a lubricating oil composition in which various sulfur-based or phosphorus-based additives were added to PAO10. The sulfur-based additive was added to the total amount of lubricant to a ratio of 0.5 mass% in sulfur equivalent, and the phosphorus-based additive was added to a ratio of 0.2 mass% in phosphorus equivalent. The test conditions were as follows.

[0076] <Test Conditions> Temperature: 40℃ Load: 50N / 5min, up to 200N Initial surface pressure: 1.7 GPa, 2.2 GPa, 2.5 GPa, 2.8 GPa Frequency: 50Hz Amplitude: 1mm Exam time: 20 minutes Ball: Made of SUJ2 (φ9.525mm) Disc: Made of SUJ2 (φ24mm)

[0077] 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.

[0078] Figures 9(b) and (c) show the changes in electrical resistance values ​​when each additive is used. It can be seen that the phosphorus-based additives maintain higher electrical resistance values ​​compared to the sulfur-based additives. Figure 10 shows a bar graph of the average values ​​for the last minute at each load.

[0079] 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.

[0080] 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.

[0081] 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).

[0082] 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.

[0083] Examples 1 to 3 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, 200kHz).

[0084] For measuring the relative permittivity of the lubricating oil, a capacitance transducer MC-130 and electrode cell manufactured by YEI Corporation were used. Figure 11 shows a schematic diagram of the measurement 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. For the measurement method, a metal container was prepared with the electrode cell 43 and a thermocouple for measuring the temperature of the sample fixed in it, and the output voltage V0 of the capacitance transducer 42 in air was obtained. Next, the metal container was heated with a ring heater 44 to adjust the temperature of the sample 45 to an arbitrary value. The voltage value V1 output by the capacitance transducer 42 was converted to the relative permittivity using the following formula (6).

number

[0085] The obtained lubricants were tested 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 Examples 1-3 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. Figure 12 shows the observation photographs of Examples 1-2 and Comparative Example 1. As shown in Figure 12, even with only the ester oil of Example 1 (no additives added), 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 of Example 2, no ridge marks were formed. In this evaluation, no difference in results was confirmed between Examples 1-2, 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.

[0086] 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 three of Examples 1 to 3.

[0087] [Table 2]

[0088] Thus, the above tests showed 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. [Industrial applicability]

[0089] The rolling bearing of the present invention can suppress ridge marks caused by electrolytic corrosion, making it suitable for use in environments where electrolytic corrosion is likely to occur. For example, it is suitable for rolling bearings used in motors for automotive auxiliary equipment and industrial machinery, as well as for rolling bearings used in motor drive systems of electric vehicles and hybrid vehicles. [Explanation of symbols]

[0090] 1 motor 2 spindle 3 stata 4. Rotor 5 Flange 6. First radial ball bearing 7. Second radial ball bearing 8 Pulley 9 belts 11 Rolling bearings 12 Inner Ring 13 Outer ring 14 Balls (rolling elements) 15 Cage 16. Sealing member 17. Grease composition (lubricant) 18a opening 18b opening 21 Rolling bearings 22 Inner Ring 23 Outer ring 24 Rolling elements 25 Crown retainer 31 SRV Test Machine 32 balls 33 Arms 34 discs 35 Lubricant 41 Measuring device 42 Capacitive Converters 43 Electrode Cells 44 Ring Heater 45 samples

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 lubricated with a lubricant, The rolling bearing is characterized in that 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 or 2, 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 or 2, 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 or 2, 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.

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