Rolling bearing

Abstract

[Problem] To provide: a rolling bearing in which a grease composition containing molybdenum dithiocarbamate and triphenylphosphorothioate is sealed, said rolling bearing allowing friction qualities to be improved and acoustic-noise quality deterioration to be kept under control; and a motor with the bearing built-in. [Solution] Provided are a rolling bearing of 22 mm or less outer diameter and a motor comprising with the rolling bearing. The rolling bearing includes: an inner ring; an outer ring disposed coaxially with the inner ring along the outer periphery of the inner ring; a plurality of rolling elements disposed between the inner ring and the outer ring; a cage that retains the rolling elements; and a grease composition retained between the inner ring and the outer ring. The grease composition contains a base oil, a thickener, molybdenum dithiocarbamate containing an alkyl group with eight or more carbon atoms, and triphenylphosphorothioate. In a state in which a preload along the axial direction has been placed on the outer ring such that the average contact pressure on the inner ring will be 800 MPa, the roller bearing has a medium-band Anderon value of 1.2 or less after the inner ring has been rotated at a rotational speed of 1800 rpm for 30 seconds at room temperature under an atmospheric environment.

Description

Rolling bearings

[0001] The present invention relates to a rolling bearing in which a grease composition containing molybdenum dithiocarbamate and triphenyl phosphorothioate is enclosed, and to a motor equipped with the rolling bearing.

[0002] In the technical fields of greases and lubricating oils, thiophosphates such as triphenyl phosphorothioate (TPPT (CAS RN 597-82-0: triphenyl phosphorothioate, also known as triphenoxyphosphine sulfide)) have traditionally been used as anti-friction agents (anti-wear agents), and organic molybdenum compounds have traditionally been used as extreme pressure agents. A grease composition has been proposed that uses these in combination to improve the friction-reducing effect on sliding members (Patent Document 1).

[0003] Japanese Patent Application Publication No. 6-330072

[0004] In recent years, motors such as fan motors and cleaner motors used in automobiles, home appliances, etc., and the bearings used therein are desired to be not only durable but also quieter. Grease compositions applied to bearings used in such motors are also desired to have the ability to improve friction characteristics, which contribute to improved durability, without deteriorating acoustic characteristics. Although the grease composition shown in Patent Document 1 has been studied in terms of friction coefficient, wear resistance, temperature suppression ability, compatibility with sealing materials, and heat resistance, the document does not pay any attention to the acoustic characteristics of bearings to which the grease composition is applied.

[0005] The present invention aims to provide a rolling bearing packed with a grease composition containing molybdenum dithiocarbamate and triphenyl phosphorothioate, which can improve friction characteristics and suppress deterioration of acoustic characteristics, and to provide a motor incorporating such a bearing.

[0006] One aspect of the present invention relates to a rolling bearing having an outer diameter of 22 mm or less, comprising: an inner ring; an outer ring arranged coaxially around the inner ring and on the outer peripheral side of the inner ring; a plurality of rolling elements arranged between the inner ring and the outer ring; a cage for holding the rolling elements; and a grease composition held between the inner ring and the outer ring, the grease composition including a base oil, a thickener, a molybdenum dithiocarbamate having an alkyl group having 8 or more carbon atoms, and triphenyl phosphorothioate, wherein the inner ring is rotated at a rotational speed of 1,800 rpm for 30 seconds at room temperature in an atmospheric atmosphere with an axial preload applied to the outer ring so that the average surface pressure of the inner ring is 800 MPa. The present invention also relates to a motor equipped with the rolling bearing.

[0007] FIG. 1 is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. FIG. 2 is a schematic diagram illustrating an example of the structure of a motor according to the present invention. FIG. 3 is a diagram illustrating the measurement results of the friction coefficients of Example 1, Example 2, and Comparative Examples 1 and 2 in a friction characteristic evaluation (metal-metal). FIG. 4 is a diagram illustrating the measurement results of the Anderon values ​​(M band) of Example 1, Example 2, and Comparative Examples 1 and 2 in an acoustic evaluation. FIG. 5 is a diagram illustrating the measurement results of the Anderon values ​​(M band) of Examples 3-4 and Comparative Example 3, and Examples 5-6 and Comparative Example 4 in an acoustic evaluation.

[0008] The present inventors focused on the acoustic properties of rolling bearings and conducted research into greases suitable for such bearings. They discovered that the grease composition used in the examples of Patent Document 1 (a urea grease composition containing a sulfurized dialkyldithiocarbamate having four carbon atoms, molybdenum, and triphenyl phosphorothioate) exhibited superior friction properties compared to a urea grease composition containing only triphenyl phosphorothioate, but that its acoustic properties were actually worse than those of a composition containing only triphenyl phosphorothioate. To address this issue of poor acoustic properties, the present inventors focused on the alkyl chain length contained in the molybdenum compound and discovered for the first time that the alkyl chain length changes acoustic properties without affecting frictional properties. Specifically, they discovered that the combined use of a molybdenum dithiocarbamate having an alkyl group containing eight or more carbon atoms and triphenyl phosphorothioate improves frictional properties without deteriorating acoustic properties, leading to the completion of the present invention. As shown in the results of the Examples described below, the present inventors have confirmed that the combination of molybdenum dithiocarbamate having an alkyl group with a specific number of carbon atoms and triphenyl phosphorothioate can suppress deterioration of acoustic properties without being affected by other components of the grease, such as the base oil, which is a new finding that has not been previously known.

[0009] [Rolling Bearing] First, preferred embodiments of the rolling bearing according to the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0010] FIG. 1 is a radial cross-sectional view of a rolling bearing 10 according to a preferred embodiment of the present invention. The rolling bearing 10 has the same basic structure as conventional rolling bearings, and includes an annular inner ring 11, an outer ring 12, multiple rolling elements 13, a cage 14, and a seal member 15. The inner ring 11 is a cylindrical structure that is installed coaxially with the center axis of a shaft (not shown) on the outer periphery of the shaft. The outer ring 12 is a cylindrical structure that is installed coaxially with the inner ring 11 on the outer periphery of the inner ring 11. Each of the multiple rolling elements 13 is a ball that is arranged in a raceway within an annular bearing space 16 formed between the inner ring 11 and the outer ring 12. In other words, the rolling bearing 10 according to this embodiment is a ball bearing. The cage 14 is arranged in the raceway and holds the multiple rolling elements 13. The cage 14 is an annular body installed coaxially with the central axis of the shaft. It has a structure in which it has multiple pockets on one side in the direction of the central axis for holding the rolling elements 13, with the rolling elements 13 housed in each pocket. The cage 14 holds the rolling elements 13 at predetermined intervals circumferentially around the inner ring 11 and the outer ring 12, thereby preventing the rolling elements 13 from falling off and preventing adjacent rolling elements 13 from coming into contact with each other. The shape (crown-shaped, corrugated, etc.) and material (steel plate, resin, etc.) of the cage 14 are optional and are not limited to a specific shape or material. The seal member 15 is fixed to the inner circumferential surface of the outer ring 12 and extends toward the inner ring 11, sealing the bearing space 16. A grease composition G is enclosed in the bearing space 16 sealed by the seal member 15. That is, the grease composition G is held between the inner ring 11 and the outer ring 12. The grease composition described below is used as the grease composition G. The amount of grease G enclosed within the bearing space 16 can be, for example, 5 to 50% of its volume. The sealing member 15 is formed, for example, from steel plate or rubber, and examples include a steel plate shield that does not contact the outer periphery of the inner ring 11, and a non-contact rubber seal that does not contact the outer periphery of the inner ring 11. Either the steel plate shield or the non-contact rubber seal can be used in the present invention. Note that while the drawing shows an embodiment that includes the sealing member 15, the rolling bearing of the present invention also covers embodiments of a rolling bearing that does not include a sealing member.In the rolling bearing 10 having the above configuration, the grease composition G acts to reduce friction between the rolling elements 13 and the cage 14, and between the rolling elements 13 and the inner ring 11 or outer ring 12. The reduction in friction reduces friction torque and suppresses the generation of frictional heat, promoting smooth rotation of the inner ring 11 and the outer ring 12. As can be seen from the configuration shown in Figure 1, the grease composition G sealed in the rolling bearing 10 lubricates the gap between the rolling elements 13 and the inner ring 11 or outer ring 12 when the rolling bearing 10 rotates.

[0011] The present invention is particularly effective in rolling bearings with an outer diameter of 22 mm or less. The rolling bearing of the present invention can be used as a rolling bearing for motors (e.g., fan motors, cleaner motors) used in automobiles, home appliances, information devices, etc.

[0012] <Regarding Acoustic Properties> The rolling bearing according to the present invention is characterized in that by incorporating a molybdenum dithiocarbamate containing an alkyl group having 8 or more carbon atoms and triphenyl phosphorothioate in combination in the grease composition described below, not only is a bearing obtained with improved friction properties, but also a bearing in which deterioration of acoustic properties is suppressed. The rolling bearing according to the present invention is characterized in that the Anderon value of the M band is 1.2 or less after the inner ring is rotated at a rotational speed of 1,800 rpm for 30 seconds at room temperature and in the air, with an axial preload applied to the outer ring so that the average surface pressure of the inner ring is 800 MPa. In the present invention, the Anderon value is 1.2 or less, and from the perspective of acoustic properties, it is preferably 1.1 or less, and particularly preferably 1.0 or less.

[0013] [Motor] As an example, an embodiment of a motor equipped with the rolling bearing of this embodiment will be described in detail with reference to FIG. 2, but the present invention is not limited to the following embodiment.

[0014] 2 is a cross-sectional view of a motor according to one embodiment of the present invention taken along the shaft direction. Motor 20 has the same basic structure as conventional motors, and is composed of a housing 21, a stator 22, coils 23, a rotor magnet 24, a shaft 25, and a rolling bearing 26 that supports shaft 25. Motor 20 generates magnetic force by passing current supplied from a power source (not shown) via a drive circuit through coil 23 wound around stator 22, which rotates rotor magnet 24, and the rotation is transmitted to an external rotating body via shaft 25.

[0015] [Grease Composition] The grease composition used in the rolling bearing of the present invention contains a base oil, a thickener, molybdenum dithiocarbamate containing an alkyl group having 8 or more carbon atoms, and triphenyl phosphorothioate. The grease composition enclosed in the rolling bearing of the present invention will be described below.

[0016] <Base Oil> In the grease composition filled in the rolling bearing according to this embodiment, synthetic oils generally used as grease base oils, such as synthetic hydrocarbon oils, ether-based synthetic oils, and ester-based synthetic oils, can be used alone or in combination as the base oil. Examples of the synthetic hydrocarbon oils include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and polyalphaolefins (PAO) such as 1-decene and ethylene co-oligomer. Examples of the ester-based synthetic oils include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl phthalate, and methyl acetylsinolate, aromatic ester oils such as trioctyl trimellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate, and tetra-2-ethylhexyl pyromellitate, polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol pelargonate, and carbonate ester oils. Examples of the ether-based synthetic oils include alkyl ether oils such as monoalkyl diphenyl ether, dialkyl diphenyl ether, and polyalkyl diphenyl ether, and alkyl diphenyl ether oils.

[0017] The viscosity of the base oil used in the present invention is not particularly limited. However, taking into consideration the dispersion stability of the molybdenum dithiocarbamate and triphenyl phosphorothioate described below, the kinematic viscosity at 40° C. is preferably 20 to 150 mmHg. ２ / s range can be used.

[0018] The base oil may be contained in a proportion of, for example, 70 mass % or more based on the total mass of the grease composition used in the present invention, and may be contained in a proportion of, for example, 70 mass % to 90 mass % based on the total mass of the grease composition.

[0019] <Thickener> In the grease composition used in the present invention, the type of thickener is not particularly limited, but for example, a urea-based thickener can be preferably used. Urea compounds have excellent heat resistance and water resistance, and are particularly stable at high temperatures, so they are preferably used as thickeners in applications under high-temperature environments. As the urea-based thickener, urea compounds such as diurea compounds, triurea compounds, and polyurea compounds can be used. From the viewpoint of acoustic properties (silence), it is preferable to use a diurea compound. Furthermore, the type of urea compound preferably includes at least one of aliphatic-aromatic urea, alicyclic-aliphatic urea, and aliphatic urea. As these urea-based thickeners, conventionally known urea compounds can be used.

[0020] An example of a diurea compound used in a urea-based thickener is a diurea compound represented by the following formula (2): ５ -NHCONH-R ６ -NHCONH-R ７ ...Formula (2) In the above formula (2), R ５ and R ７ each independently represents a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and R ５ and R ７ At least one of R represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. ５ and R ７ one of R may represent an aliphatic hydrocarbon group and the other may represent a monovalent alicyclic hydrocarbon group or a monovalent aromatic hydrocarbon group, and alternatively R ５ and R ７ One of R may represent an aliphatic hydrocarbon group, and the other may represent a monovalent aromatic hydrocarbon group. ６ represents a divalent aromatic hydrocarbon group. The diurea compound represented by formula (2) may be a mixture of a plurality of types. For example, R ５ and R ７ and a compound in which both R represent a monovalent aliphatic hydrocarbon group. ５ and R ７and a compound in which both R represent a monovalent aromatic hydrocarbon group. ５ and R ７ It is also possible to use a mixture of compounds in which one of the groups represents an aliphatic hydrocarbon group and the other represents a monovalent aromatic hydrocarbon group.

[0021] Examples of the monovalent aliphatic hydrocarbon groups include linear or branched, saturated or unsaturated alkyl groups having 6 to 26 carbon atoms. Examples of the monovalent alicyclic hydrocarbon groups include cycloalkyl groups having 5 to 12 carbon atoms. Examples of the aromatic hydrocarbon groups include monovalent or divalent aromatic hydrocarbon groups having 6 to 20 carbon atoms.

[0022] The urea compound used as a urea-based thickener can be synthesized using an amine compound and an isocyanate compound. Examples of the amine compound include aliphatic amines such as hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine (stearylamine), behenylamine, and oleylamine, as well as alicyclic amines such as cyclohexylamine, and aromatic amines such as aniline, p-toluidine, and ethoxyphenylamine. Two or more of these amine compounds can also be used in combination when synthesizing the urea compound. Examples of isocyanate compounds that can be used include aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate (TDI), diphenyl diisocyanate, diphenylmethane diisocyanate (MDI), and dimethylbiphenyl diisocyanate (TODI), as well as aliphatic diisocyanates such as octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. In addition, when an aromatic diurea compound obtained by using an aromatic monoamine and an aromatic diisocyanate as amine raw materials is used as a urea-based thickener, there is a risk of abnormal noise being generated, so its use should be considered.

[0023] The urea-based thickener (urea compound) can be blended in an amount of, for example, 10 to 20 mass % based on the total amount of the grease composition used in the present invention.

[0024] <Molybdenum dithiocarbamate (MoDTC)> The grease composition used in the present invention is characterized by containing molybdenum dithiocarbamate (MoDTC) as an essential component together with triphenyl phosphorothioate, which will be described later. The molybdenum dithiocarbamate used in the present invention contains an alkyl group having 8 or more carbon atoms, and for example, a molybdenum dithiocarbamate containing an alkyl group having 13 or more carbon atoms can be used.

[0025] The molybdenum dithiocarbamate may, for example, be a compound represented by the following formula (1): In the above formula (1), R １ ~R ４ each independently represents a hydrocarbon group having 8 to 14 carbon atoms; １ ~X ４ each independently represents an oxygen atom or a sulfur atom.

[0026] R １ ~R ４ Examples of the hydrocarbon group having 8 to 14 carbon atoms in R include alkyl groups having 8 to 14 carbon atoms and aromatic hydrocarbon groups having 8 to 14 carbon atoms, and among these, alkyl groups having 8 to 14 carbon atoms such as octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, and tetradecyl groups can be mentioned. The alkyl group may be linear, branched, cyclic, or a combination thereof. １ ~R ４ At least one of X may be an alkyl group having 13 to 14 carbon atoms. １ ~X ４ represents an oxygen atom or a sulfur atom, for example, X １ ~X ４ Two or three of the X may be sulfur atoms and the rest may be oxygen atoms, １ ~X ４ In the above, the sulfur atom and the oxygen atom may be 2 each, and for example, X １ and X ２ is a sulfur atom, and X ３ and X ４may be an oxygen atom.

[0027] The molybdenum dithiocarbamate represented by the formula (1) may be a molybdenum dithiocarbamate having a symmetric hydrocarbon group, or may be a molybdenum dithiocarbamate having an asymmetric hydrocarbon group. １ ~R ４ are all the same hydrocarbon group, or １ and R ２ are the same hydrocarbon group, and R ３ and R ４ is R １ and R ２ As the molybdenum dithiocarbamate having an asymmetric hydrocarbon group, there may be mentioned molybdenum dithiocarbamates having the same hydrocarbon group but different from R １ ~R ４ molybdenum dithiocarbamate, R １ ~R ３ are the same hydrocarbon groups and R ４ and molybdenum dithiocarbamate, wherein at least R １ and R ２ are different hydrocarbon groups, or R ３ and R ４ Molybdenum dithiocarbamates (e.g., R １ and R ３ are the same hydrocarbon group, and R ２ and R ４ are the same hydrocarbon group, and R １ and R ２ molybdenum dithiocarbamates, in which the hydrocarbon group is different from the molybdenum dithiocarbamates.

[0028] The molybdenum dithiocarbamate used in the present invention may be, for example, a compound represented by the general formula (1) in which R １ ~R ４ are all alkyl groups having 8 carbon atoms, １ ~R ４are each independently a group selected from an alkyl group having 8 carbon atoms and an alkyl group having 13 carbon atoms (R １ ~R ４ are all alkyl groups having 8 carbon atoms, and １ ~R ４ and R are each an alkyl group having 13 carbon atoms. １ ~R ４ at least one of which is an alkyl group having 8 carbon atoms and the remaining are alkyl groups having 13 carbon atoms, and a mixture thereof).

[0029] The molybdenum dithiocarbamate may be blended in an amount such that the content of molybdenum atoms contained in the molybdenum dithiocarbamate is, for example, 0.01 to 0.5 mass % relative to the total amount of the grease composition used in the present invention.

[0030] <Triphenyl phosphorothioate (TPPT)> The grease composition used in the present invention is characterized by containing triphenyl phosphorothioate (TPPT) as an essential component together with the molybdenum dithiocarbamate described above. Triphenyl phosphorothioate can be blended in an amount of, for example, 0.1 to 10 mass % based on the total amount of the grease composition used in the present invention.

[0031] <Other Additives> The grease composition used in the present invention can contain additives commonly used in grease compositions as needed, within the range that does not impair the effects of the present invention. Examples of such additives include antioxidants, extreme pressure agents (extreme pressure additives), metal deactivators, antifriction agents (antiwear agents), rust inhibitors, oiliness improvers, viscosity index improvers, thickeners, etc. When these other additives are contained, the amount added (total amount) is usually 0.1 to 10 mass% of the total amount of the grease composition.

[0032] Examples of the antioxidant include octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thiazolinone, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene ...1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) hindered phenol-based antioxidants such as N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyphenyl)propionate and N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamic acid; other phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-t-butylphenol); and amine-based antioxidants such as diphenylamine, alkylated diphenylamine, triphenylamine, hindered amine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, and alkylated phenothiazine.

[0033] Examples of extreme pressure agents include phosphorus compounds such as phosphate esters, phosphites, and phosphate amine salts; sulfur compounds such as sulfides and disulfides; chlorine compounds such as chlorinated paraffins and chlorinated diphenyls; and metal salts of sulfur compounds such as zinc dialkyldithiophosphates.

[0034] Examples of the metal deactivator include benzotriazole-based compounds such as benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]-benzotriazole, and 1-[N,N-bis(2-ethylhexyl)aminomethyl]-4-methylbenzotriazole; thiadiazole-based compounds such as thiadiazole, 2-mercaptothiadiazole, and 2,5-bis(alkyldithio)-1,3,4-thiadiazole; benzimidazole-based compounds such as benzimidazole, 2-mercaptobenzimidazole, and 2-(decyldithio)-benzimidazole; and sodium nitrite.

[0035] Examples of the antifriction agent (antiwear agent) include tricresyl phosphate and polymer esters. Examples of the polymer esters include esters of aliphatic monocarboxylic acids and dicarboxylic acids with polyhydric alcohols. Specific examples of the polymer esters include, but are not limited to, the PRIOLUBE (registered trademark) series manufactured by Croda Japan.

[0036] The grease composition used in the present invention can be obtained by blending the above-mentioned base oil with a thickener, a molybdenum dithiocarbamate containing an alkyl group having 8 or more carbon atoms, triphenyl phosphorothioate, and, if desired, other additives. Alternatively, a grease composition can be obtained by blending a grease (base grease) consisting of the above-mentioned base oil and thickener with a molybdenum dithiocarbamate containing an alkyl group having 8 or more carbon atoms, triphenyl phosphorothioate, and, if desired, other additives. Typically, the content of the thickener relative to the base grease is about 10 to 30% by mass. For example, the content of the diurea compound (urea-based thickener) relative to the above-mentioned urea-based grease can be, for example, about 10 to 25% by mass, or about 10 to 20% by mass.

[0037] The present invention is not limited to the embodiments and specific examples described in this specification, and various changes and modifications are possible within the scope of the technical idea described in the claims.

[0038] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0039] Grease compositions of Examples 1 to 6 and Comparative Examples 1 to 4 were prepared with the compositions shown in Table 1 below, and various evaluations were carried out according to the procedures described below. In the following explanation, the example numbers of the grease compositions will also be used as the example numbers of the ball bearings in which they are packed, and the example numbers of the evaluations of each test. Details of the components used in preparing the grease compositions and their abbreviations are as follows: <Base oil> PAO: Polyalphaolefin [kinematic viscosity at 40°C: 48 mm ２ / s] Ether + PAO: mixed oil of alkyl diphenyl ether oil and polyalphaolefin [kinematic viscosity at 40 ° C: 80 mm ２ / s] Ether + ester: mixed oil of alkyl diphenyl ether oil and aromatic ester oil [kinematic viscosity at 40 ° C: 80 mm ２ / s] The blending amount of base oil is the balance of the thickeners and additives (TPPT, MoDTC1-3, other additives) listed below. <Thickeners> Diurea compound: Aliphatic-aromatic diurea compound (a diurea compound obtained by reacting a mixture of an aliphatic amine and an aromatic amine with a diisocyanate compound) The thickener was added to each grease composition in an amount of 12% by mass. <Additives> TPPT: Triphenyl phosphorothioate (IRGALUBE TPPT manufactured by BASF Japan Ltd.) The TPPT was added to each grease composition in an amount of 2% by mass. MoDTC1: Molybdenum dithiocarbamate containing alkyl groups having 8 and 13 carbon atoms (Sakuralube (registered trademark) 525, manufactured by ADEKA Corporation) MoDTC2: Molybdenum dithiocarbamate containing alkyl groups having 8 carbon atoms (Sakuralube (registered trademark) 200, manufactured by ADEKA Corporation) MoDTC3: Molybdenum dithiocarbamate containing alkyl groups having 4 carbon atoms (Sakuralube (registered trademark) 600, manufactured by ADEKA Corporation) MoDTC1 to MoDTC3 were added so that the molybdenum (MO) content was 0.1% by mass of the total grease composition. Other additives: Antioxidant and rust inhibitor were added so that the total amount was 3% by mass of each grease composition (total mass: 100% by mass).

[0040] <Various Evaluations> (1) Frictional Property Evaluation (Metal-Metal: Friction Test) A metal-metal friction and wear test was conducted using a vibration friction tester (product name: SRV) manufactured by Optimol. The test was conducted using a ball-on-disk method, using a ball (material: SUJ2, φ10 mm) and a disk (material: SUJ2, φ24 mm). The test conditions were a load of 100 N, a measurement temperature of 50°C, a sliding distance of 1 mm, a vibration frequency of 50 Hz, and a test time of 20 minutes (1200 seconds). Five mg of each grease composition was supplied at the start of the test, and the friction coefficient was measured over time during the test. Figure 3 shows the measurement results of the friction coefficient versus test time (seconds) for Examples 1 and 2, and Comparative Examples 1 and 2.

[0041] (2) Acoustic Evaluation The acoustic performance of ball bearings filled with each test grease composition was evaluated by measuring the Anderon value in the M band (300 to 1800 Hz) using an Anderon meter. Each grease composition from Examples 1 to 6 and Comparative Examples 1 to 4 was filled into a steel-shielded ball bearing (inner diameter 3 mm, outer diameter 8 mm, width 4 mm) at 25% to 35% of the bearing volume. After applying a preload of 10 N to the outer ring of this ball bearing in the axial direction, the shaft was coupled to the rotating shaft of a test motor so that the inner ring of the ball bearing rotated. Under these preload conditions, the average surface pressure of the inner ring of this ball bearing was approximately 800 MPa. The ball bearing was then rotated at 1800 rpm in an atmospheric atmosphere at room temperature. In this state, a velocity pickup was brought into radial contact with the outer periphery of the outer ring of the ball bearing to detect mechanical vibrations transmitted to the outer ring, and the Anderon value 30 seconds after the start of rotation was calculated (maximum measured Anderon value: 50). Tests were conducted three times for each of the ball bearings in Examples 1 to 6 and Comparative Examples 1 to 4, and the average Anderon value was calculated. The results are shown in Table 1. FIG. 4 shows the Anderon values ​​(M band) 30 seconds after the start of rotation for grease compositions containing PAO as the base oil: Examples 1 to 2, Comparative Example 1, and Comparative Example 2. FIG. 5 shows the Anderon values ​​(M band) 30 seconds after the start of rotation for grease compositions containing a mixed oil of ether and PAO as the base oil: Examples 3 to 4 and Comparative Example 3, and for grease compositions containing a mixed oil of ether and ester as the base oil: Examples 5 to 6 and Comparative Example 4. Incidentally, the M band frequencies of 300 to 1,800 Hz are said to be harsh to the human ear.

[0042]

[0043] Regarding the evaluation of friction characteristics, as shown in FIG. 3, compared to the grease composition of Comparative Example 1, which contained only triphenyl phosphorothioate (TPPT), in Examples 1, 2, and Comparative Example 2, which also contained molybdenum dithiocarbamate, the friction coefficient was kept low regardless of the number of carbon atoms in the alkyl group in the molybdenum dithiocarbamate, confirming that the friction characteristics could be improved.

[0044] On the other hand, with regard to acoustic properties, as shown in Table 1 and Figure 4, Comparative Example 2, which used a grease composition formulated with molybdenum dithiocarbamate containing an alkyl group with 4 carbon atoms, showed a significant increase in anderon value after 30 seconds. In contrast, Examples 1 and 2, which were formulated with molybdenum dithiocarbamate containing an alkyl group with 8 or more carbon atoms, showed anderon values ​​similar to those of Comparative Example 1, which also contained molybdenum dithiocarbamate. Similarly, in the cases where the base oil was changed from a PAO oil alone to a blend of ether and PAO (Examples 3, 4, and Comparative Example 3) and the cases where the base oil was changed to a blend of ether and ester (Examples 5, 6, and Comparative Example 4), the acoustic properties also changed significantly depending on the alkyl group contained in the molybdenum dithiocarbamate. That is, Examples 3 and 4 and Examples 5 and 6, which were formulated with molybdenum dithiocarbamate containing an alkyl group with 8 or more carbon atoms, showed lower anderon values ​​after 30 seconds than Comparative Examples 3 and 4, which were formulated with molybdenum dithiocarbamate containing an alkyl group with 4 carbon atoms.

[0045] The above results demonstrate that the use of a grease composition containing a molybdenum dithiocarbamate containing an alkyl group having 8 or more carbon atoms in combination with triphenyl phosphorothioate in the rolling bearing according to the present invention makes it possible to achieve excellent friction characteristics and to suppress deterioration of acoustic characteristics.

[0046] The best mode for carrying out the invention has been described in detail above, but the invention is not limited to the above mode for carrying out the invention, and modifications and improvements within the scope of achieving the object of the invention are included in the invention.

[0047] 10... rolling bearing, 11... inner ring, 12... outer ring, 13... rolling element, 14... retainer, 15... sealing member, 16... bearing space, 20... motor, 21... housing, 22... stator, 23... coil, 24... rotor magnet, 25... shaft, 26... bearing

Claims

1. A rolling bearing having an outer diameter of 22 mm or less comprising: an inner ring; an outer ring arranged coaxially with the inner ring on the outer peripheral side of the inner ring; a plurality of rolling elements arranged between the inner ring and the outer ring; a cage for holding the rolling elements; and a grease composition held between the inner ring and the outer ring, the grease composition comprising a base oil, a thickener, a molybdenum dithiocarbamate having an alkyl group having 8 or more carbon atoms, and triphenyl phosphorothioate, wherein the rolling bearing has an Anderon value of M band of 1.2 or less after the inner ring is rotated for 30 seconds at a rotational speed of 1,800 rpm at room temperature in an atmospheric environment with a preload applied to the outer ring in the axial direction so that the average surface pressure of the inner ring is 800 MPa.

2. The rolling bearing according to claim 1, wherein the molybdenum dithiocarbamate includes a molybdenum dithiocarbamate having an alkyl group having 13 or more carbon atoms.

3. The molybdenum dithiocarbamate is a compound represented by the following formula (1): (In the formula, R １ ~R ４ each independently represents a hydrocarbon group having 8 to 14 carbon atoms; １ ~X ４ Each of the radicals independently represents an oxygen atom or a sulfur atom. The rolling bearing according to claim 1 .

4. The molybdenum dithiocarbamate is represented by the formula (1), １ ~R ４ 4. The rolling bearing according to claim 3, wherein at least one of the above is an alkyl group having 13 to 14 carbon atoms.

5. The molybdenum dithiocarbamate is represented by the formula (1), １ ~R ４ The rolling bearing according to claim 3 , wherein is a compound in which is an alkyl group having 8 carbon atoms.

6. The molybdenum dithiocarbamate is represented by the formula (1), １ ~R ４ The rolling bearing according to claim 3 , wherein each of the formulas is independently a group selected from an alkyl group having 8 carbon atoms and an alkyl group having 13 carbon atoms.

7. A motor equipped with a rolling bearing according to any one of claims 1 to 6.

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