Grease composition and grease-filled bearing

Abstract

To provide: a grease composition capable of effectively suppressing early delamination due to hydrogen embrittlement ; and a grease-enclosed bearing in which the grease composition is enclosed.SOLUTION: There is provided a grease composition 7 comprising a base oil and a thickener and contains a hydrocarbon synthetic oil as the base oil, wherein at least a part of hydrogen atoms in the molecule of the hydrocarbon synthetic oil is replaced with deuterium atoms, the deuteration rate is 10% or more and the thickener contains at least one urea compound selected from an aliphatic diurea compound, an alicyclic diurea compound and an aromatic diurea compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a grease composition and a grease-encapsulated bearing in which the grease composition is encapsulated, and more particularly to a grease composition used for a bearing used in an environment where early peeling due to hydrogen embrittlement is likely to occur, and the grease-encapsulated bearing thereof.

Background Art

[0002] For example, rolling bearings are used in the rotating parts of various components such as electrical components and accessories in automobiles, and motors in industrial machines. Examples of automobile electrical components and accessories include an alternator, a pulley, an electromagnetic clutch for a car air conditioner, a fan coupling device, an electric fan motor, and the like. An automotive idler pulley is used as a belt tensioner for a drive belt that transmits the rotation of an engine to accessories of an automobile. Grease is encapsulated in these rolling bearings to impart lubricity.

[0003] In a rolling bearing, due to severe use conditions, there is a risk that a specific peeling accompanied by a white structure change occurs early on the rolling surface. This specific peeling is a fracture phenomenon that occurs from a relatively shallow part of the rolling surface, different from the peeling from the inside of the rolling surface caused by normal metal fatigue, and is considered to be hydrogen embrittlement caused by hydrogen. For example, it is considered that grease decomposes to generate hydrogen, which penetrates into the steel of the rolling bearing, causing early peeling due to hydrogen embrittlement. Since hydrogen significantly reduces the fatigue strength of steel, cracks occur and propagate near the inside of the rolling surface where the alternating shear stress is maximum even under conditions considered to be elastohydrodynamic lubrication where the contact elements are separated by an oil film, leading to early peeling.

[0004] Conventionally, various methods have been studied to prevent such a specific peeling phenomenon accompanied by a white structure change that occurs early. For example, a method of adding molybdate and organic acid salt as additives to grease has been proposed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-112902 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, the operating conditions for rolling bearings have become increasingly severe, with the addition of rapid acceleration and deceleration conditions to high temperatures and high speeds. Under these severe conditions, the surface pressure between the rolling elements and the raceways increases, and slippage due to rapid acceleration and deceleration increases, making the oil film more prone to breakdown (poor lubrication) in that area. Further methods are needed to prevent premature delamination even under such conditions.

[0007] In recent years, hydrogen has attracted attention as an alternative energy source to fossil fuels. Hydrogen is expected to be a clean energy source because, when used as an energy source, it only produces water and does not release carbon dioxide (CO2). In the future, it is expected that hydrogen use will advance throughout society, and along with that, hydrogen utilization equipment (for example, ball valves and compressors for hydrogen stations) will become widespread. Bearings used in such hydrogen utilization equipment may be used in environments exposed to hydrogen, and in such cases, the presence of hydrogen supplied from an external source may exacerbate premature delamination caused by the hydrogen embrittlement mentioned above.

[0008] This invention has been made in view of these circumstances, and aims to provide a grease composition that can effectively suppress premature delamination due to hydrogen embrittlement, and a grease-filled bearing containing the grease composition. [Means for solving the problem]

[0009] The grease composition of the present invention is a grease composition comprising a base oil and a thickener, wherein the base oil comprises a hydrocarbon-based synthetic oil, and at least a portion of the hydrogen atoms in the molecule of the hydrocarbon-based synthetic oil are substituted with deuterium atoms.

[0010] The above-mentioned hydrocarbon-based synthetic oil is characterized in that it is a poly-α-olefin oil (hereinafter referred to as PAO oil) in which at least some of the hydrogen atoms in the molecule are replaced by deuterium atoms.

[0011] The above-mentioned hydrocarbon-based synthetic oil is characterized by having a deuterization rate of 10% or more.

[0012] The above thickener is characterized by containing at least one urea compound selected from aliphatic diurea compounds, alicyclic diurea compounds, and aromatic diurea compounds.

[0013] The above base oil is characterized by containing 50% by mass or more of the above hydrocarbon-based synthetic oil relative to the total amount of the base oil.

[0014] The kinematic viscosity of the above base oil at 40°C is 10 to 400 mm². 2 It is characterized by being / s.

[0015] The grease-filled bearing of the present invention is a grease-filled bearing having an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a grease composition sealed around the plurality of rolling elements, wherein the grease composition is the grease composition of the present invention. [Effects of the Invention]

[0016] The grease composition of the present invention contains a hydrocarbon-based synthetic oil as a base oil, and at least a part of the hydrogen atoms in the molecule of the hydrocarbon-based synthetic oil is replaced by deuterium atoms. Thus, by replacing a part of the carbon-hydrogen (C-H) bonds in the molecule of the hydrocarbon-based synthetic oil with carbon-deuterium (C-D) bonds having a greater binding force, chemical reactions are less likely to occur, and as a result, the generation amount of hydrogen (including H2, D2, and H-D) can be reduced. As a result, the amount of hydrogen (including H2, D2, and H-D) that penetrates into the steel is reduced, and early peeling due to hydrogen embrittlement can be effectively suppressed.

[0017] In addition, since the deuteration rate of the hydrocarbon-based synthetic oil is 10% or more, the generation amount of hydrogen (including H2, D2, and H-D) can be further reduced, and early peeling due to hydrogen embrittlement can be more effectively suppressed.

[0018] The grease-encased bearing of the present invention includes an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and the grease composition of the present invention is encapsulated around the rolling elements. Therefore, even under severe use conditions, early peeling caused by hydrogen embrittlement can be suppressed, and longer-term use can be achieved.

Brief Description of the Drawings

[0019] [Figure 1] It is a cross-sectional view of a deep groove ball bearing which is an example of the grease-encased bearing of the present invention. [Figure 2] It is a cross-sectional view showing an alternator using the grease-encased bearing of the present invention. [Figure 3] It is a cross-sectional view showing a hydrogen circulation pump using the grease-encased bearing of the present invention. [Figure 4] It is a graph showing the ratio of the hydrogen generation amount of each base oil.

Modes for Carrying Out the Invention

[0020] The grease composition of the present invention contains a base oil and a thickener, and various additives are blended as required. The above base oil includes a hydrocarbon-based synthetic oil, and at least a part of the hydrogen atoms in the molecules of the hydrocarbon-based synthetic oil are replaced by deuterium atoms. Here, replacing a hydrogen atom with a deuterium atom is called deuteration.

[0021] Hydrocarbon-based synthetic oils are easier to deuterate than other oils (such as ether oils and mineral oils), and have advantages in terms of production. For example, when deuterating ether oils, part or all of them are likely to decompose, while hydrocarbon-based synthetic oils do not change the structure of the oil and do not poison the catalyst. For example, since mineral oils contain sulfur components, there is a risk of poisoning the catalyst. Using hydrocarbon-based synthetic oils can also lead to the suppression of impurities, so it is considered preferable in terms of suppressing early peeling.

[0022] In the present invention, the hydrocarbon-based synthetic oil to be subjected to deuteration is not particularly limited. For example, aliphatic synthetic oils such as PAO oils, polybutene oils, and copolymers of α-olefins and olefins, and aromatic synthetic oils such as alkylbenzene oils and alkylnaphthalene oils can be used. These hydrocarbon-based synthetic oils may be used alone or in combination of two or more.

[0023] As the hydrocarbon-based synthetic oil to be subjected to deuteration, PAO oil is preferred. PAO oil is a mixture of oligomers or polymers of α-olefins or isomerized α-olefins. Specific examples of α-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-docosene, 1-tetracosene, etc., and usually mixtures of these are used.

[0024] Deuterated hydrocarbon synthetic oils can be obtained, for example, by using hydrocarbon synthetic oil as a raw material and carrying out an HD exchange reaction by heating in the presence of a catalyst. As a catalyst, Pd / C, in which a noble metal is supported on a carbon (C) support, can be used. As a deuterium source in the HD exchange reaction, deuterium (D2) and heavy water (D2O) can be used.

[0025] The deuterated rate of the deuterated hydrocarbon synthetic oil is, for example, 2% or more, preferably 5% or more, more preferably 10% or more, and may be 20% or more. The above deuterated rate may be, for example, 80% or less, and may be 50% or less. The deuterated rate can be appropriately set by changing the reaction conditions of the HD exchange reaction (heating temperature, reaction time, etc.).

[0026] In this invention, the deuterated rate refers to the ratio (%) of the number of hydrogen atoms substituted with deuterium atoms to the total number of hydrogen atoms bonded to carbon atoms in a hydrocarbon synthetic oil. The deuterated rate can be calculated by NMR measurement. Specifically, NMR measurements are performed on both undeuterated and deuterated hydrocarbon synthetic oils, and the deuterated rate can be calculated from chemical shifts, coupling and bonding constants, peak areas, etc.

[0027] In the present invention, the deuterated hydrocarbon synthetic oil preferably reduces the amount of hydrogen (total amount of H2, D2, and HD) per unit of wear in the sliding test by 5% or more compared to the case of a non-deuterated hydrocarbon synthetic oil. A reduction of 10% or more is more preferable, and 20% or more is even more preferable.

[0028] Here, "hydrogen amount per unit of wear" is the value obtained by dividing the amount of hydrogen generated in the sliding test by the amount of wear determined from the wear marks on the ball produced in the sliding test. As the amount of wear on the ball, for example, the diameter of the wear marks that can be measured with an optical microscope can be used. The diameter of the wear marks on the ball is the average wear mark diameter (unit: μm) obtained by measuring the diameter of the circular scratches on the ball in the sliding direction and the diameter in the direction perpendicular to the sliding direction. In addition, the hydrogen (H2, D2, and HD) generated during the test can be measured using a quadrupole mass spectrometer. In this case, the amount of hydrogen (unit: A·s) is defined as the integral of the increased ion current value and the sliding time (seconds).

[0029] The above sliding test is conducted using Fe balls and Fe discs, in the presence of test oil, under the following conditions: surface pressure of 2.0 GPa, peripheral speed of 0.01 m / s, and sliding time of 3 minutes.

[0030] The base oil used in the grease composition of the present invention may be a mixture of a deuterated hydrocarbon synthetic oil and other oils. Preferably, the other oil is not deuterated. In this case, only hydrocarbon synthetic oil is used as the deuterated oil. The other oil mixed with the deuterated hydrocarbon synthetic oil can be any oil commonly used in the field of greases, without particular limitations. Examples include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, ester oils, ether oils, silicone oils, fluorinated oils, and hydrocarbon synthetic oils (non-deuterated). These oils may be used individually or in combination of two or more.

[0031] The above base oil preferably contains 50% by mass or more of deuterated hydrocarbon synthetic oil, and more preferably 70% by mass or more, relative to the total amount of base oil. The base oil may also consist solely of deuterated hydrocarbon synthetic oil (100% by mass).

[0032] The kinematic viscosity of the above base oil (or the kinematic viscosity of the mixed oil in the case of a mixed oil) is 10 to 400 mm at 40°C. 2 / s is preferred. More preferably 20-150 mm 2The interval is / s, and more preferably 20-100 mm 2 / s, 20~50mm 2 / s is also acceptable.

[0033] The above base oil is preferably contained in an amount of 60% to 95% by mass relative to the total amount of base oil and thickener (base grease). If the base oil content is less than 60% by mass, the lifespan may be reduced, and if it exceeds 95% by mass, the amount of thickener will be relatively small, which may make grease formation difficult. More preferably, the above base oil is contained in an amount of 70% to 90% by mass relative to the total amount of base oil and thickener.

[0034] The thickener used in the grease of the present invention is not particularly limited, and general thickeners commonly used in the field of grease can be used. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentone, silica gel, diurea compounds, triurea compounds, tetraurea compounds, and urea-urethane compounds can be used. Examples of metal soaps include sodium soap, calcium soap, and lithium soap, and examples of complex metal soaps include complex lithium soap. Among these, it is preferable to use a diurea compound as the thickener.

[0035] Diurea compounds are obtained by reacting a diisocyanate component with a monoamine component. Examples of diisocyanate components include phenylenediisocyanate and diphenylmethane diisocyanate (MDI). Diurea compounds include aliphatic diurea compounds, alicyclic diurea compounds, and aromatic diurea compounds, which are classified according to the type of substituent used in the monoamine component. In the case of aliphatic diurea compounds, an aliphatic monoamine (such as octylamine) is used as the monoamine component. In the case of alicyclic diurea compounds, an alicyclic monoamine (such as cyclohexylamine) is used as the monoamine component. In the case of aromatic diurea compounds, an aromatic monoamine (such as p-toluidine) is used as the monoamine component.

[0036] Base greases using diurea compounds as thickeners are prepared by reacting a diisocyanate component with a monoamine component in a base oil. The proportion of the thickener in the base grease is 5% to 40% by mass, preferably 10% to 30% by mass.

[0037] The grease composition of the present invention may further contain other additives, as long as they do not impair the objectives of the present invention. Examples include extreme pressure agents such as organozinc compounds and organomolybdenum compounds, antioxidants such as amine-based, phenol-based, and sulfur-based compounds, rust inhibitors such as sulfonates and polyhydric alcohol esters, and oily agents such as esters and alcohols. In particular, sulfur-based antioxidants such as phenothiazine and dilaurylthiodipropionate can be used as antioxidants.

[0038] The consistency of the grease composition of the present invention (JIS K 2220) 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 composition becomes soft and easily leaks out of the bearing, which is undesirable. The consistency is more preferably in the range of 250 to 300.

[0039] A grease-filled bearing containing the grease composition of the present invention will be described with reference to Figure 1. Figure 1 is a cross-sectional view of a deep groove ball bearing. The rolling bearing 1 has an inner ring 2 having an inner ring racing surface 2a on its outer circumference and an outer ring 3 having an outer ring racing surface 3a on its inner circumference, arranged concentrically, with a plurality of balls 4 arranged between the inner ring racing surface 2a and the outer ring racing surface 3a. These balls 4 are held by a cage 5. In addition, the axial openings 8a and 8b at both ends of the inner and outer rings are sealed by a sealing member 6, and the above-mentioned grease composition 7 is filled around at least the balls 4. The inner ring 2, outer ring 3 and balls 4 are made of an iron-based metal material, and the grease composition 7 is interposed on the racing surfaces with the balls 4 to lubricate them.

[0040] In the rolling bearing 1, the ferrous metal materials constituting the bearing components such as the inner ring 2, outer ring 3, and rolling elements 4 can be any material commonly used as a bearing material. Examples include high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; JIS G 4805), carburized steel (SCr420, SCM420, etc.; JIS G 4053), stainless steel (SUS440C, etc.; JIS G 4303), high-speed steel (M50, etc.), and cold-rolled steel. The sealing member 6 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.

[0041] Although Figure 1 illustrates a deep groove ball bearing as an example of a bearing, the grease-filled bearing of the present invention can also be used as an angular contact ball bearing, cylindrical roller bearing, tapered roller bearing, self-aligning roller bearing, needle roller bearing, thrust ball bearing (single-type flat seat, etc.), thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, thrust self-aligning roller bearing, and the like.

[0042] In the grease composition of the present invention, at least some of the hydrogen (H) atoms in the hydrocarbon synthetic oil molecule are replaced with deuterium (D) atoms. By replacing the hydrogen (H) atoms in the hydrocarbon synthetic oil molecule with deuterium (D) atoms, the number of hydrogen (H) atoms in the hydrocarbon synthetic oil is relatively reduced, and the carbon-deuterium (CD) bond, which has greater bonding strength, increases. Therefore, as shown in the examples, the amount of hydrogen (including H2, D2, and HD) generated by the deuterated hydrocarbon synthetic oil is reduced compared to the non-deuterated hydrocarbon synthetic oil, and consequently, the amount of hydrogen (including H2, D2, and HD) that penetrates the steel is also reduced. Furthermore, the carbon-deuterium (CD) bond is more difficult to break than the carbon-hydrogen (CH) bond, and the amount of deuterium generated is less than that of hydrogen. In addition, since deuterium (D) atoms have a larger atomic radius than hydrogen (H) atoms, they are less likely to penetrate the steel. For these reasons, it is believed that hydrogen embrittlement delamination in steel materials is suppressed.

[0043] The grease-filled bearing of the present invention contains the above-mentioned grease composition and can suppress premature delamination caused by hydrogen embrittlement. Therefore, the grease-filled bearing is suitable for use in environments where premature delamination due to hydrogen embrittlement is likely to occur.

[0044] The grease-filled bearing of the present invention can be used, for example, in bearings for the following applications.

[0045] Grease-filled bearings are used, for example, in the transaxles of vehicles (fuel cell vehicles (FCVs), electric vehicles (EVs), etc.), in vehicle transmissions (continuously variable transmissions, etc.), and in vehicle motors (for drive units and transmissions). Bearings in these applications require performance capable of withstanding rapid changes in rotational speed due to speed changes, high rotations, and high loads. In addition, these devices use low-viscosity lubricants to reduce power loss. In such harsh operating environments, wear of the raceways and rolling elements is easily accelerated by sliding. When a new steel surface is formed due to this wear, water and lubricant components decompose, generating hydrogen, which penetrates the steel, making premature delamination due to hydrogen embrittlement likely to occur. Furthermore, in fuel cell vehicles, it is possible that hydrogen leakage from hydrogen equipment may also contribute to hydrogen embrittlement of rolling bearings.

[0046] Furthermore, grease-filled bearings are used as bearings for high-pressure hydrogen pressure reducing valves in fuel cell vehicles and for hydrogen circulation pumps in fuel cell vehicles. In these operating environments, wear of the raceways and rolling elements is easily accelerated by sliding, and as a result, premature delamination due to hydrogen embrittlement is likely to occur, as described above. In addition, in fuel cell vehicles, it is possible that hydrogen leakage from hydrogen equipment may also contribute to hydrogen embrittlement of rolling bearings.

[0047] Furthermore, grease-filled bearings are used as bearings for vehicle electrical components and auxiliary equipment (alternators, electromagnetic clutches for car air conditioners, fan coupling devices, intermediate pulleys, electric fan motors, compressors, etc.). In recent years, in order to make vehicles smaller, lighter, and quieter, the miniaturization and weight reduction of electrical components and auxiliary equipment, as well as the sealing of the engine compartment, have been promoted. To prevent the decrease in output that comes with miniaturization, electrical components and auxiliary equipment in the engine compartment are being made to rotate at high speeds, and furthermore, rapid speed changes and high-temperature conditions are being added to the mix. In such harsh operating environments, wear of raceways and rolling elements is easily accelerated due to sliding, and as a result, premature delamination due to hydrogen embrittlement is likely to occur, as described above.

[0048] Here, Figure 2 shows a cross-sectional view of an alternator in which a grease-filled bearing is applied. In the alternator, a rotor shaft 13, on which a rotor 12 is mounted, is rotatably supported by rolling bearings 18 and 19 on a pair of frames 11a and 11b that form a housing, which are stationary members. At least one of these rolling bearings is used as the grease-filled bearing of the present invention. A rotor coil 14 is attached to the rotor 12, and a stator coil 16 with 3 turns at a 120° phase is attached to a stator 15 located on the outer circumference of the rotor 12. The rotor shaft 13 is rotationally driven by rotational torque transmitted by a belt (not shown) to a pulley 17 attached to its tip. The pulley 17 is attached to the rotor shaft 13 in a cantilevered state, and vibrations are generated as the rotor shaft 13 rotates at high speed, so the rolling bearing 18 that supports the pulley 17 side in particular is subjected to a severe load.

[0049] Furthermore, grease-filled bearings are used as hub bearings. Hub bearings are susceptible to water intrusion into the bearing space due to rain, rough roads, or driving on coastlines. In addition, sudden gear changes and shocks promote wear of the raceway rings and rolling elements due to sliding, and when a new steel surface is formed due to this wear, water and lubricant components decompose, generating hydrogen, which penetrates into the steel, making premature delamination due to hydrogen embrittlement likely to occur.

[0050] Furthermore, grease-filled bearings are used in machine tools (such as spindles), wind power generation equipment (such as speed increasers), railway vehicles (such as axles, drive systems, and main motors), construction machinery (such as axles), paper machines, and transmissions. The rapid speed changes, high-speed rotation, and distortion of the housing and raceways associated with these operating environments tend to accelerate wear of the raceways and rolling elements due to sliding, resulting in premature delamination due to hydrogen embrittlement, as described above. Premature delamination is particularly likely to occur in environments where water is easily introduced, such as outdoors.

[0051] Furthermore, grease-filled bearings are used as bearings for hydrogen-utilizing equipment. They are particularly useful as bearings used in environments exposed to externally supplied hydrogen. In the future, with the advancement of hydrogen utilization, it is expected that the number of cases in which bearings are used under a hydrogen atmosphere (including mixed atmospheres containing hydrogen) will increase. In such cases, in addition to hydrogen generated due to the decomposition of grease (hydrogen from internal factors), it is thought that hydrogen supplied from external factors (hydrogen from external factors) will also affect premature delamination due to hydrogen embrittlement. The grease-filled bearing of the present invention can effectively suppress premature delamination by using the grease composition described above, even when premature delamination due to hydrogen embrittlement is a greater concern than with conventional bearings.

[0052] Examples of hydrogen utilization equipment include ball valves and compressors for hydrogen refueling stations. The type of compressor is not particularly limited and may be reciprocating, rotary (screw), centrifugal, or axial flow. Hydrogen utilization equipment also includes high-pressure hydrogen pressure reducing valves and hydrogen circulation pumps for fuel cell vehicles, as mentioned above.

[0053] Here, Figure 3 shows a cross-sectional view of a hydrogen circulation pump in which grease-filled bearings are applied. The hydrogen circulation pump 21 includes a motor housing 22, a pump housing 23, rotating shafts 24 and 25, a motor stator 26, a motor rotor 27, gears 28 and 29, rotors 30 and 31, and rolling bearings 32, 33, 34, 35, 36, and 37.

[0054] The motor housing 22 is attached to the pump housing 23. One end of the rotating shaft 24 is located inside the motor housing 22, and the other end of the rotating shaft 24 is located inside the pump housing 23. The one end and the other end of the rotating shaft 24 are rotatably supported by a rolling bearing 32 located inside the motor housing 22 and a rolling bearing 33 located inside the pump housing 23, respectively. The rotating shaft 24 is also rotatably supported between the one end and the other end by rolling bearings 34 and 35 located inside the pump housing 23.

[0055] The rotating shaft 25 is located within the pump housing 23. One end of the rotating shaft 25 is rotatably supported by a rolling bearing 36 located within the pump housing 23. The rotating shaft 25 is also rotatably supported at a position away from the other end by a rolling bearing 37 located within the pump housing 23.

[0056] The motor stator 26 is located inside the motor housing 22. The motor rotor 27 is mounted on the rotating shaft 24 so as to face the motor stator 26. The motor stator 26 and motor rotor 27 rotate the rotating shaft 24. Gears 28 and 29 are mounted on the rotating shaft 24 and the rotating shaft 25, respectively. The rotation of the rotating shaft 24 is transmitted to the rotating shaft 25 by gears 28 and 29. Gear 28 is located between rolling bearings 34 and 35, and gear 29 is located between rolling bearings 36 and 37.

[0057] A pump chamber 23a is formed inside the pump housing 23. Rotors 30 and 31 are arranged inside the pump chamber 23a. Rotors 30 and 31 are attached to the rotating shafts 24 and 25, respectively. As rotor 30 rotates with the rotation of the rotating shaft 24, and rotor 31 rotates with the rotation of the rotating shaft 25, hydrogen is drawn into the pump chamber 23a and discharged from the pump chamber 23a.

[0058] In Figure 3, rolling bearings 32, 33, 34, and 36 are deep groove ball bearings. Rolling bearing 33 is used in an environment exposed to hydrogen supplied from an external source (for example, under a hydrogen atmosphere). Rolling bearings 35 and 37 are double-row angular contact ball bearings. In the configuration shown in Figure 3, at least one of the rolling bearings 32, 33, 34, 35, 36, and 37 is used as the grease-filled bearing of the present invention. [Examples]

[0059] The present invention will be specifically described by examples and comparative examples, but the invention is not limited in any way by these examples.

[0060] For the sliding tests described below, we used base oils with different deuterization (HD exchange) rates, as shown in Table 1. Base oils B to D are deuterized versions of base oil A (PAO oil).

[0061] [Table 1]

[0062] Sliding tests were conducted using base oils A to D to evaluate hydrogen generation. An iron ball was pressed against an iron disc coated with the base oil and slid in a vacuum chamber. The test conditions were a surface pressure of 2.0 GPa, a peripheral speed of 0.01 m / s, and a sliding time of 3 minutes. The hydrogen generated during the test was measured using a quadrupole mass spectrometer, and the hydrogen amount was defined as the integral of the increased ion current value and the sliding time. Hydrogen was evaluated as follows: "m / z=2" was classified as H2 molecules, "m / z=3" as HD molecules, and "m / z=4" as D2 molecules. After the test, the diameter of the wear marks on the ball was measured using an optical microscope to determine the amount of wear. The obtained hydrogen amounts were divided by the amount of wear to calculate the hydrogen amount per unit of wear (unit: A·s / μm). The same sliding test was performed twice for each base oil, and the average value was calculated.

[0063] For "m / z=2", "m / z=3", "m / z=4", and "m / z=2,3,4" (total), the ratio of hydrogen per unit of wear amount for base oils B, C, and D was calculated based on the hydrogen per unit of wear amount for base oil A. The results are shown in Figure 4.

[0064] As shown in Figure 4(a), the amount of hydrogen (H2) generated was similar for base oil A and base oil B, but decreased for base oil C and base oil D as the deuterization rate increased. As shown in Figures 4(b) and 4(c), the amount of hydrogen (HD) and hydrogen (D2) produced increased as the deuteration rate increased. Furthermore, the amount of hydrogen (HD) produced was about an order of magnitude less than the amount of hydrogen (H2) produced, and the amount of hydrogen (D2) produced was about two orders of magnitude less than the amount of hydrogen (H2) produced. As shown in Figure 4(d), the total amount of hydrogen (sum of H2, HD, and D2) generated was similar for base oil A and base oil B, but decreased for base oil C and base oil D as the deuteration rate increased.

[0065] Next, grease compositions with the compositions shown in Table 2 were prepared. The grease compositions shown in Table 2 consist only of a base oil and a thickener (aromatic diurea compound).

[0066] An alternator, an example of an electrical auxiliary component, was simulated, and each prepared grease composition was sealed in a rolling bearing with an inner ring rotation supporting the rotating shaft (inner ring, outer ring, and steel balls are made of bearing steel SUJ2), and a rapid acceleration / deceleration test was performed. The load on the pulley attached to the tip of the rotating shaft was set to 2334N, and the rotation speed was set to 0rpm to 18000rpm. Furthermore, the test was conducted with a current of 1.0A flowing through the test bearing (6203). The time at which abnormal delamination occurred in the bearing and the vibration of the vibration detector exceeded the set value and stopped (delamination occurrence time, h) was measured. Table 2 shows the ratio of the delamination occurrence time of each example to the delamination occurrence time of Comparative Example 1.

[0067] [Table 2]

[0068] As shown in Table 2, in Example 2 (base oil C: deuterization rate 13%), the delamination time was extended by 1.3 times compared to Comparative Example 1 (base oil A: non-deuterized). In Example 3 (base oil D: deuterization rate 24%), the delamination time was extended by 1.5 times compared to Comparative Example 1 (base oil A: non-deuterized). Thus, the bearing life improved as the deuterization rate of the hydrocarbon synthetic oil increased. [Industrial applicability]

[0069] The grease composition of the present invention effectively suppresses the unique premature peeling accompanied by a change in white structure that occurs on the rolling surface, thus providing excellent bearing life for rolling bearings. It is particularly suitable for bearings in transaxles of fuel cell vehicles and electric vehicles, transmissions of vehicles, motors of vehicles, high-pressure hydrogen pressure reducing valves of fuel cell vehicles, hydrogen circulation pumps of fuel cell vehicles, and bearings for automotive electrical components and auxiliary equipment such as alternators, electromagnetic clutches for car air conditioners, intermediate pulleys, and electric fan motors. [Explanation of symbols]

[0070] 1. Rolling bearings (grease-filled bearings) 2 Inner ring 3 Outer ring 4 Rolling elements 5 Cage 6. Sealing member 7. Grease Composition 8a, 8b opening 11a, 11b frames 12 rotors 13 Rotor rotation shaft 14 Rotor coil 15 stata 16 Stator Coil 17 Pulley 18 Rolling bearings 19 Rolling bearings 21 Hydrogen circulation pump 22 Motor Housing 23 Pump Housing 24, 25 Rotation axis 26 Motor Stator 27 Motor Rotor 28, 29 gear 30, 31 rotors 32, 33, 34, 35, 36, 37 Rolling bearings

Claims

1. A grease composition comprising a base oil and a thickener, The base oil comprises a poly-α-olefin oil, wherein at least some of the hydrogen atoms in the molecule of the poly-α-olefin oil are substituted with deuterium atoms. The deuteration rate of the poly-α-olefin oil is 10% or more and 50% or less. The grease composition is characterized in that, in a sliding test using Fe balls and Fe discs, under the conditions of a surface pressure of 2.0 GPa, peripheral speed of 0.01 m / s, and sliding time of 3 minutes, the amount of hydrogen per unit of wear (total amount of H2, D2, and H-D) is reduced by 10% or more compared to the case where the poly-α-olefin oil is not deuterated.

2. The grease composition according to claim 1, characterized in that the thickener comprises at least one urea compound selected from aliphatic diurea compounds, alicyclic diurea compounds, and aromatic diurea compounds.

3. The grease composition according to claim 1 or 2, characterized in that the base oil contains 50% by mass or more of the poly-α-olefin oil relative to the total amount of the base oil.

4. The kinematic viscosity of the base oil at 40°C is 10 to 400 mm². ２ The grease composition according to claim 1 or 2, characterized in that it is / s.

5. A grease-filled bearing comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed around the plurality of rolling elements, A grease-filled bearing characterized in that the grease composition is the grease composition according to claim 1 or claim 2.

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