Hydrogen recirculation blower and rolling bearing

Abstract

To provide a hydrogen recirculation blower for a fuel cell system that has excellent durability under a high temperature / water vapor environment and comprises a bearing having lubrication performance preserved even under an environment in which water exists.SOLUTION: A hydrogen recirculation blower of a fuel cell system comprises a rolling bearing. The rolling bearing has: an inner ring, an outer ring, and a rolling element; grease in an annular bearing space formed between the inner ring and the outer ring; and a rubber seal that seals the bearing space. The grease contains organic acid metal salt at a ratio equal to or higher than 0.05 mass% and equal to or lower than 1 mass% of the total amount of the grease. After a high temperature and high humidity test (1) under a condition of 130°C, 100%RH, and 48 hours, the grease has a coefficient of cubical expansion lower than 60% as compared with that before the test (1). After a high temperature and high humidity test (2) that makes the grease 1.3 g coexist with pure water 10 mL in a sealed container whose capacity is 100 mL and holds the grease for 48 hours under a condition of 120°C, the grease has a reduction rate of the organic acid metal salt lower than 50% as compared with that before the test (2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hydrogen recirculation blower for a fuel cell system used in a high-temperature steam environment, and to a rolling bearing provided in the blower. [Background technology]

[0002] A fuel cell is an energy system that directly converts chemical energy into electrical and thermal energy through an electrochemical reaction between a fuel such as hydrogen and an oxidant such as oxygen (air). The only substance produced during power generation is water (water vapor), with no carbon dioxide. Furthermore, the fuel cell itself has few moving parts, resulting in little noise or vibration, making it a system with an extremely low environmental impact. Furthermore, because electrical energy is directly extracted from the electrochemical reaction between hydrogen (fuel) and oxygen (oxidant), the fuel cell has high power generation efficiency and can continuously generate electricity as long as these are supplied. Furthermore, by effectively utilizing both the electricity and heat generated during the conversion process, it is possible to further increase overall energy efficiency. Among these, fuel cells have been adopted as an alternative power source to internal combustion engines in automobiles due to their advantages such as low (or zero) harmful exhaust gases, high energy efficiency, availability of a variety of fuels and energy sources, low noise, and no need for charging, and various fuel cell vehicles have been proposed.

[0003] Fuel cell systems used in fuel cell vehicles, etc., use blowers and compressors to pressurize the fuel hydrogen and oxidant oxygen. One example is a blower (anode recirculation blower) that recirculates hydrogen that was not used in power generation. For example, Patent Document 1 proposes a rolling bearing to be incorporated into a pump for a fuel cell system, a pump for a fuel cell system equipped with the bearing, and a fuel cell system equipped with the pump. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-190688 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-35882 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-173956 [Patent Document 4] Patent No. 4883743 [Patent Document 5] Patent No. 6646379 Summary of the Invention [Problem to be solved by the invention]

[0005] Blowers used in the above fuel cell systems (e.g., hydrogen recirculation blowers (anode recirculation blowers)) are used in a hydrogen environment, and the environment in which the blowers are used is a hot and humid environment where heat and water vapor are generated during the fuel cell reaction process. Therefore, the various parts that make up the blower and the greases used for those parts must be able to withstand hydrogen, heat, water vapor, etc.

[0006] The object of the present invention is to provide a blower, particularly a hydrogen recirculation blower for a fuel cell system, equipped with a bearing that is highly durable, particularly in high-temperature and steam environments, and that maintains its lubricating performance even in environments where water is present. [Means for solving the problem]

[0007] One aspect of the present invention is a hydrogen recirculation blower for a fuel cell system equipped with a rolling bearing, the rolling bearing has an inner ring, an outer ring, and rolling elements, contains grease in an annular bearing space formed between the inner ring and the outer ring, and further has a rubber seal that seals the bearing space, the grease contains an organic acid metal salt in a proportion of 0.05 mass % or more and 1 mass % or less relative to the total amount of the grease, and further, the grease has a volume expansion rate of less than 60% from before high-temperature, high-humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, and after high-temperature, high-humidity test (2) in which 1.3 g of the grease is placed in a sealed container with a volume of 100 mL and left to stand at 120°C for 48 hours, the organic acid metal salt has a reduction rate of 50% or less from before test (2). The present invention also relates to a rolling bearing provided in the hydrogen recirculation blower. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram illustrating the structure of a hydrogen recirculation blower. [Figure 2] FIG. 2 is a schematic diagram illustrating the structure of a bearing provided in the hydrogen recirculation blower. [Figure 3] FIG. 1 is a conceptual diagram showing an example of the configuration of a fuel cell system using hydrogen. [Figure 4] FIG. 1 is a graph showing the volume expansion coefficient (vertical axis) of the grease after a high-temperature, high-humidity test versus the additive (disodium sebacate) concentration (horizontal axis). [Figure 5] FIG. 1 is a graph showing the additive (disodium sebacate) concentration (initial concentration) (horizontal axis) versus additive reduction rate (vertical axis) after a high-temperature, high-humidity test. [Figure 6] FIG. 10 is a diagram showing the Anderon values (M-band) after a durability test for each type of grease used in an acoustic evaluation test. DETAILED DESCRIPTION OF THE INVENTION

[0009] As mentioned above, the motor and other components of the hydrogen recirculation blower used in fuel cell systems are required to have the performance to withstand environments containing hydrogen, heat, water vapor, etc. As will be described later, the blower uses bearings to support the rotating shaft of the impeller, and grease is used to lubricate the bearings. As mentioned above, hydrogen recirculation blowers are used in high-temperature, high-humidity (water vapor) environments, and in such environments, the grease can come into contact with moisture (water vapor) and absorb it, causing the grease to expand in volume. For example, if the grease expands in volume in a bearing sealed with a rubber seal, the pressure in the space where the grease is sealed (the bearing space) increases, which can lead to grease leakage and, ultimately, to poor lubrication due to grease depletion, which can reduce the durability of the bearing. Furthermore, in the above-mentioned high-temperature and high-humidity environment, the hydrophilic additive components contained in the grease may dissolve in the absorbed water, causing a significant change (decrease) in the concentration of the additive components in the grease, which may impair the desired performance. Thus, for blowers and motors equipped therewith that are expected to operate under high temperature and high humidity conditions, such as hydrogen recirculation blowers used in fuel cell systems, it is desirable to have bearings filled with grease that not only maintains its lubricating performance even in high temperature and high humidity (water vapor) environments, but is also resistant to volume expansion and suppresses changes in additive concentration. The present inventors have discovered that greases containing a predetermined amount of organic acid metal salts exhibit little volume expansion or change in the concentration of the organic acid metal salts even in high-temperature, high-humidity (water vapor) environments, and still retain lubricating properties. Although organic acid metal salts have been used as grease additives in the past as anti-peeling additives and corrosion inhibitors (e.g., Patent Documents 2 to 5), no proposals have been made to date that focus on suppressing the volume expansion of greases or the change in the concentration of the metal salts in high-temperature, high-humidity (water vapor) environments. The present invention will be described in detail below.

[0010] [Hydrogen recirculation blower] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a blower according to the present invention will be described below with reference to the accompanying drawings. 1 is a cross-sectional view of an impeller-type blower, an example of a hydrogen recirculation blower for a fuel cell system according to the present invention, taken along the shaft direction. The hydrogen recirculation blower 10 has the same basic structure as a conventional impeller-type blower, and is composed of a motor M (housing 11, stator 12, coil 13, rotor magnet 14, shaft 15, and bearing 20 (rolling bearing) that supports shaft 15), an impeller 16, a housing 17, an intake port 18, and an exhaust port 19. In the motor M, a magnetic force is generated by passing current supplied from a power source (not shown) via a drive circuit through coils 13 wound around a stator 12, which rotates a rotor magnet 14, and the rotation is transmitted to an external rotating body (impeller 16, described below) via a shaft 15, which is the rotation axis. Note that while the motor M is shown as an inner rotor type motor in this figure, it is not limited to this and may also be an outer rotor type motor. In the case of an outer rotor type motor, the stator 12 is configured to be located on the inner periphery of the rotor magnet 14. An impeller 16 is attached to the shaft 15, and when the impeller 16 rotates at high speed in conjunction with the high speed rotation of the shaft 15, water vapor drawn in through an intake port 18 is pressurized by the centrifugal force of the impeller 16 and is exhausted from an exhaust port 19. In blowers used in high temperature and high humidity environments, a dynamic seal member S is normally provided between the rolling bearing 20 of the motor M and the impeller 16 to prevent the flow of gases such as water vapor from the impeller 16 side (blower portion) to the rolling bearing 20 side (motor portion).

[0011] Although the impeller-type blower shown in FIG. 1 has been given as a specific example of a hydrogen recirculation blower, the hydrogen recirculation blower according to the present invention is not limited to the above embodiment and may be of a scroll type or screw type.

[0012] [Bearings] Preferred embodiments of the bearings provided in the hydrogen recirculation blower of the present invention will be described below with reference to the accompanying drawings. The bearing used in the present invention is a bearing having an inner ring, an outer ring, and rolling elements, and more specifically, a bearing having an inner ring, an outer ring arranged coaxially with the inner ring on the outer peripheral side of the inner ring, and a plurality of rolling elements arranged between the inner ring and the outer ring, i.e., a rolling bearing. It should be noted that the present invention is not limited to the following embodiments.

[0013] 2 is a radial cross-sectional view of a bearing (rolling bearing) 20 according to a preferred embodiment of the present invention. Bearing 20 has the same basic structure as prior art rolling bearings, and includes an annular inner ring 21, an outer ring 22, a plurality of rolling elements 23, a cage 24, and a seal member 25. The inner ring 21 is a cylindrical structure that is installed on the outer periphery of a shaft (not shown) and coaxially with its center axis. The outer ring 22 is a cylindrical structure that is installed on the outer periphery of the inner ring 21 and coaxially with the inner ring 21. Each of the multiple rolling elements 23 is a ball that is arranged in a raceway within an annular bearing space 26 formed between the inner ring 21 and the outer ring 22. In other words, the rolling bearing 20 in this embodiment is a ball bearing. The cage 24 is disposed within the raceway and holds the plurality of rolling elements 23. The cage 24 is an annular body installed coaxially with the central axis of the shaft, and is provided with a plurality of pockets for holding the rolling elements 23 on one side in the direction of the central axis, with the rolling elements 23 housed in each pocket. The rolling elements 23 are held at predetermined intervals in the circumferential direction of the inner ring 21 and the outer ring 22 by the cage 24, thereby preventing the rolling elements 23 from falling off and preventing contact between adjacent rolling elements 23. The shape (crown-shaped, corrugated, etc.) and material (steel plate, resin, etc.) of the cage 24 are arbitrary and are not limited to a specific shape or material. The seal member 25 is fixed to the inner peripheral surface of the outer ring 22 and extends toward the inner ring 21, sealing the bearing space 26. The bearing space 26 sealed by the seal member 25 is filled with grease G. That is, the grease G is held between the inner ring 21 and the outer ring 22. The grease G As the grease, a mixed grease, which will be described later, is preferably used. The amount of grease G enclosed inside the bearing space 26 can be set to, for example, 5 to 50% of the volume thereof. Sealing member 25 is generally made of steel plate or rubber, and examples include a steel plate shield that does not contact the outer periphery of inner ring 21, and a contact / non-contact rubber seal that may or may not contact the outer periphery of inner ring 21. The embodiment in the figure shows a contact-type rubber seal in which a rubber seal (rubber seal) insert-molded into a core metal 25a (made of steel plate) is used as sealing member 25, and the sealing member is in contact with the outer periphery of inner ring 21. In the rolling bearing 20 having the above configuration, the grease G acts to reduce friction between the rolling elements 23 and the cage 24, and between the rolling elements 23 and the inner ring 21 or outer ring 22. The reduction in friction reduces friction torque and suppresses the generation of frictional heat, promoting smooth rotation of the inner ring 21 and the outer ring 22. As can be seen from the configuration shown in Figure 2, the grease G sealed in the rolling bearing 20 lubricates the spaces between the rolling elements 23 and the inner ring 21 or outer ring 22 when the rolling bearing 20 rotates.

[0014] [Grease] The grease sealed in the bearings provided in the hydrogen recirculation blower of the present invention is not particularly limited as long as it contains a predetermined amount of an organic acid metal salt described below, and may be any of fluorine-based grease, non-fluorine-based grease, and a mixed grease of these. As will be described later, the grease used in the present invention preferably contains a fluorine-based grease having a fluorine oil as a base oil, and in particular, is preferably a mixed grease of a fluorine-based grease having a fluorine oil as a base oil and a non-fluorine-based grease having a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener, as will be described later. The formulation of this mixed grease achieves excellent friction and wear resistance in the presence of water.

[0015] [Organic acid metal salts] The grease used in the present invention essentially contains an organic acid metal salt. The organic acid metal salt is contained in a proportion of 0.05% by mass or more and 1% by mass or less relative to the total amount of the grease, and is contained in a proportion of 0.05% by mass or more, more than 0.05% by mass, 0.1% by mass or more, more than 0.1% by mass, 0.2% by mass or more, or 1% by mass or less, less than 1% by mass, 0.5% by mass or less, or less than 0.5% by mass.

[0016] The organic acid metal salt used in the present invention may be any metal salt of an aromatic organic acid, an aliphatic organic acid, or an alicyclic organic acid, and the organic acid may be either a monobasic acid or a polybasic acid such as a dibasic acid.

[0017] Examples of the organic acid include, but are not limited to, monosaturated fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and arachic acid; monounsaturated fatty acids such as acrylic acid, crotonic acid, undecylenic acid, oleic acid, and gadoleic acid; Examples of the fatty acids include divalent saturated fatty acids such as malonic acid, methylmalonic acid, succinic acid, methylsuccinic acid, dimethylmalonic acid, ethylmalonic acid, glutaric acid, adipic acid, dimethylsuccinic acid, pimelic acid, tetramethylsuccinic acid, suberic acid, azelaic acid, and sebacic acid; divalent unsaturated fatty acids such as fumaric acid, maleic acid, and oleic acid, and fatty acid derivatives such as tartaric acid and citric acid; and aromatic organic acids such as benzoic acid, phthalic acid, trimellitic acid, and pyromellitic acid. Examples of the metal salt include alkali metal salts such as lithium salt, sodium salt, and potassium salt, and alkaline earth metal salts such as calcium salt and magnesium salt, with sodium salt being preferred among them.

[0018] Among the above organic acid metal salts, preferred examples include sodium benzoate and sebacin. Examples of suitable salts include monosodium sebacate, disodium sebacate, monosodium succinate, and disodium succinate, and in particular sodium sebacate (monosodium sebacate, disodium sebacate).

[0019] [Fluorine-based grease] <Base oil> The base oil in fluorine-based grease is fluorine oil. An example of a fluorine oil is one whose main component is perfluoropolyether (PFPE). PFPE has the general formula: RfO(CF2O) p (C2F4O) q (C3F6O) r It is a compound represented by Rf (Rf: perfluoro lower alkyl group, p, q, r: integers). Perfluoropolyethers are broadly classified into straight-chain and side-chain types, with the straight-chain type having a smaller temperature dependency of kinematic viscosity than the side-chain type. This means that the straight-chain type has a lower viscosity than the side-chain type in low-temperature environments and a higher viscosity than the side-chain type in high-temperature environments. For example, when assuming use in high-temperature environments, a high viscosity in high-temperature environments is desirable from the viewpoint of preventing the grease from leaking from the application area and the resulting depletion, which means that the use of straight-chain perfluoropolyethers is preferable. The fluorine oil may be contained in a proportion of, for example, 60% to 90% by mass relative to the total amount of the fluorine-based grease.

[0020] <Fluorine-based thickener> The thickener for fluorine-based grease is a fluorine-based thickener. Fluorine-based thickeners are preferably fluororesin particles, such as polytetrafluoroethylene (PTFE) particles. PTFE is a polymer of tetrafluoroethylene and has the general formula: [C2F4] n (n: degree of polymerization). Other usable fluorine-based thickeners include perfluoroethylene propylene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), and tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA). The size of the PTFE particles is not particularly limited, but for example, polytetrafluoroethylene with an average particle size of 0.5 to 100 μm can be used. The shape of the PTFE particles is not particularly limited, and they may be spherical, polyhedral, acicular, etc.

[0021] The fluorine-based thickener can be blended in an amount of, for example, 10 to 30 mass % relative to the total amount of the fluorine-based grease.

[0022] [Non-fluorine grease] Examples of non-fluorine-based grease include urea-based grease that uses a urea compound as a thickener, and soap-based grease that contains a soap-based thickener.

[0023] <Base oil> As the base oil for the non-fluorinated grease, 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. Examples of the synthetic hydrocarbon oil 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 dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl phthalate, and methyl acetylsinolate. diester oils, 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 oil include alkyl ether oils such as monoalkyldiphenyl ether, dialkyldiphenyl ether, and polyalkyldiphenyl ether, and alkyldiphenyl ether oils. The base oil may be contained in a proportion of, for example, 70 to 90% by mass based on the total amount of the non-fluorine-based grease, for example, the total amount of the urea-based grease or the total amount of the soap-based grease.

[0024] <Urea-based thickener> Urea compounds have excellent heat resistance and water resistance, and are stable at high temperatures, so they are suitable for use as thickeners in applications where they are used at high temperatures or in environments where water is present. Urea compounds such as diurea compounds, triurea compounds, and polyurea compounds can be used as urea-based thickeners. From the viewpoints of heat resistance and acoustic properties (silence), it is preferable to use diurea compounds. Furthermore, it is preferable that the type of urea compound 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.

[0025] An example of a urea-based thickener is a diurea compound represented by the following general formula (1). R1-NHCONH-R2-NHCONH-R3...(1) In the above formula (1), R1 and R3 each independently represent a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and at least one of R1 and R3 represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. Furthermore, R2 represents a divalent aromatic hydrocarbon group.

[0026] Examples of the monovalent aliphatic hydrocarbon group include linear or branched, saturated or unsaturated alkyl groups having 6 to 26 carbon atoms. The monovalent alicyclic hydrocarbon group may, for example, be a cycloalkyl group having 5 to 12 carbon atoms. The aromatic hydrocarbon group may be, for example, a monovalent or divalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0027] The urea compound used as the 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; alicyclic amines such as cyclohexylamine; and aromatic amines such as aniline, p-toluidine, and ethoxyphenylamine. As the isocyanate compound, aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate (TDI), diphenyl diisocyanate, diphenylmethane diisocyanate (MDI), and dimethylbiphenyl diisocyanate (TODI), and aliphatic diisocyanates such as octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate can be used. In addition, the amine raw material is an aromatic monoamine and an aromatic diisocyanate. When aromatic diurea compounds are used as urea-based thickeners, there is a risk of abnormal noise being generated, so their use should be considered.

[0028] The urea thickener (urea compound) can be blended in an amount of, for example, 10 to 20 mass % relative to the total amount of the non-fluorine-based grease.

[0029] <Soap-based thickener> Examples of soap-based thickeners include metal complex soap thickeners selected from lithium, sodium, barium, calcium, etc.; and simple metal soap thickeners such as lithium soap, calcium soap, barium soap, and sodium soap. The soap thickener can be blended in an amount of, for example, 10 to 20% by mass based on the total amount of the non-fluorine-based grease.

[0030] In the present invention, it is preferable to use a fluorine-based grease having a fluorine oil as a base oil, and in particular to use a mixed grease of a fluorine-based grease having a fluorine oil as a base oil and a non-fluorine-based grease having a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener. The mixed grease can be obtained by mixing a fluorine-based grease having a fluorine oil as a base oil with a non-fluorine-based grease having a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener, and can also be obtained by blending other additives described below as desired. Mixed greases may be prepared by mixing the above-mentioned various base oils (fluorinated oils and synthetic hydrocarbon oils) with various thickeners (fluorinated thickeners, urea compounds) in a predetermined ratio, and adding other additives as desired. The mixing ratio of the fluorine-based grease to the non-fluorine-based grease in the mixed grease can be, for example, 9:1 to 7:3 (mass ratio).

[0031] [Other additives] The grease used in the present invention may contain additives that are normally used in greases, as needed, within the range that does not impair the effects of the present invention. Examples of such additives include antioxidants, extreme pressure agents, metal deactivators, anti-friction agents (anti-wear agents), rust inhibitors, oiliness improvers, viscosity index improvers, and thickeners. When these other additives are contained, the amount (total amount) of them added is usually about 0.1 to 10 mass % of the total amount of the grease used.

[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- Examples of antioxidants include hindered phenol-based antioxidants such as 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide), 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, diarylamine, triphenylamine, 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 paraffin and chlorinated diphenyl; and metal salts of sulfur compounds such as zinc dialkyldithiophosphate and molybdenum dialkyldithiocarbamate.

[0034] Examples of metal deactivators 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 anti-friction agent (anti-wear agent) include tricresyl phosphate and polymer ester. Examples of the polymer ester include esters of aliphatic monocarboxylic acids and dicarboxylic acids with polyhydric alcohols. Specific examples of the polymer ester include, but are not limited to, the PRIOLUBE (registered trademark) series manufactured by Croda Japan.

[0036] [Volume expansion rate and reduction rate of organic acid metal salts] In the hydrogen recirculation blower of the fuel cell system according to the present invention, the grease sealed in the rolling bearings provided in the blower is required to have a low volume expansion rate and a low rate of reduction in the organic acid metal salt content after a specified high-temperature, high-humidity test. That is, the grease is used in the hydrogen recirculation blower if, after subjecting the grease to a high-temperature, high-humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, the volume expansion rate of the grease from before the test (1) is less than 60%, and after subjecting the grease to a high-temperature, high-humidity test (2) in which 1.3 g of the grease is placed in a sealed container with a volume of 100 mL and left to stand at 120°C for 48 hours, the reduction rate of the organic acid metal salt in the grease from before the test (2) is 50% or less. The volume expansion rate of the grease before the above test (1) is preferably 30% or less, 20% or less, or 10% or less, and the reduction rate of the organic acid metal salt in the grease before the above test (2) can be preferably 35% or less, or 20% or less. After the specified high-temperature, high-humidity test, the volume expansion of the grease is suppressed and the change in concentration of the additive (organic metal salt) in the grease is suppressed, so that lubricating performance is maintained even in a high-temperature, high-humidity environment, and it is expected that the durability of a hydrogen recirculation blower using this grease in the above environment will be good.

[0037] [Fuel cell system] An example of a fuel cell system incorporating the hydrogen recirculation blower of the present invention will be described below, but the fuel cell system is not limited to the following embodiment.

[0038] FIG. 3 is a conceptual diagram showing an example of the configuration of a fuel cell system using hydrogen. The fuel cell system 30 shown in Figure 3 includes a fuel cell stack 32. The fuel cell stack 32 is the smallest power generation unit and is made up of individual fuel cells 34 (mostly flat cells). The fuel cell stack 32 includes a cathode terminal 36 and an anode terminal 38 that are electrically connected via an external circuit 40. The external circuit 40 includes a load (e.g., an electric motor, not shown) that consumes the power generated by the fuel cell stack 32. The oxidant, air (oxygen), enters the fuel cell stack 32 through the cathode gas inlet 44, while the fuel, pressurized hydrogen, enters the fuel cell stack 32 through the anode gas inlet 46. In the fuel cell (cell) 34, which is a constituent unit of the fuel cell stack 32, hydrogen supplied as fuel dissociates into hydrogen ions and electrons at the fuel electrode (anode), and electricity is generated in the process of the electrons moving to the oxygen electrode (cathode), which is then supplied to the outside (to be consumed externally) via an external circuit. The fuel cell stack 32 includes internal flow channels 48, 50 that distribute air (oxygen) and hydrogen to the cathode and anode of each fuel cell 34. Oxygen-depleted air exits the fuel cell stack 32 through a cathode gas outlet 52, while water, nitrogen, and unreacted hydrogen exit the fuel cell stack 32 through an anode gas outlet 54. The anode gas stream [water (H2O), nitrogen (N2), and unreacted hydrogen (H2)] discharged from the fuel cell stack 32 is transported via a first conduit 56, and a portion of it is vented through an exhaust valve 60 into an exhaust line 58. The remaining anode gas stream passes through a recycle line 62 and is returned to the fuel cell stack 32 via a blower 64 (described below). The hydrogen recirculation path is indicated by an outline arrow in the figure. The anode gas experiences pressure drops across the fuel cell stack 32 due to friction losses within the internal flow path (anode gas flow path) 50 within the fuel cell stack 32, in addition to pressure losses due to its own ventilation. To address these pressure losses, the fuel cell system 30 uses a blower section 68 of a blower 64, driven by a blower motor 66, to increase the pressure of the anode gas in the recycle line 62. The blower 64 used here can be the hydrogen recirculation blower of the present invention described above. During operation, a heat exchanger (not shown) removes excess heat generated by the blower motor 66. For clarity, FIG. 3 shows the blower 64 with a dashed line to indicate that a rigid shaft 70 transfers torque between the blower motor 66 and the blower section 68. As indicated by arrow 72, a dynamic seal 74 can reduce, but not eliminate, the flow of anode gas from the blower section 68 to the blower motor 66. The pressurized anode recycle gas exits blower 66 through outlet 76 to discharge line 78 , which introduces the anode recycle gas (anode gas recycle stream) into anode gas inlet 46 of fuel cell stack 32 . Meanwhile, make-up hydrogen is introduced into the blower exhaust line 78 from a hydrogen gas reservoir 82 or other hydrogen source via a second conduit 80 in communication therewith. A control valve 84 in communication with a flow control device (not shown) regulates the amount of hydrogen added to the anode gas recycle stream.

[0039] <Acoustic characteristics> The durability and / or deterioration of the motor and bearings incorporated in the hydrogen recirculation blower according to the present invention can be evaluated, for example, by acoustic characteristics. As an example, it is desirable to use a bearing whose M-band Anderon value is 5 or less, for example 2.5 or less, after rotating the inner ring against the outer ring of the bearing, which is filled with grease containing the above-mentioned specified organic acid metal salt, at room temperature in an atmospheric atmosphere at a rotational speed of 2500 rpm for 2 hours under an axial preload of 75 N (maximum surface pressure 1.5 GPa).

[0040] 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. For example, the hydrogen recirculation blower of the fuel cell system according to the present invention can be used in any blower that is used in a hydrogen environment, such as a hydrogen fuel engine system that directly burns hydrogen in an internal combustion engine and uses the resulting thermal energy as power, or a blower in a hydrogen supply system.The hydrogen recirculation blower according to the present invention also has improved durability in high-temperature, high-humidity environments, and the motor, bearings, and grease sealed in the bearings that make up the blower can be used in motors that are used in relatively sealed environments and in high-temperature, high-humidity environments. [Example]

[0041] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0042] [Test grease] In the examples, test greases were prepared by adding 0.1 mass % to 5 mass % of disodium sebacate to the total amount of the following mixed grease (a mixture of fluorine-based grease and non-fluorine-based grease), or by not adding any (0 mass %), and then subjected to the tests described below. In the following description, the example numbers of the test greases will also be used as example numbers for the evaluation of various tests. <Mixed grease> 80wt% fluorine grease (base oil: perfluoropolyether (PFPE), kinematic viscosity at 40°C: 85mm 2 / s), thickener: polytetrafluoroethylene (PTFE)) + 20 wt% urea grease (base oil: synthetic hydrocarbon oil (PAO, kinematic viscosity at 40°C: 46 mm 2 / s))

[0043] [High temperature and humidity test] Test greases of Examples 1 to 6 were prepared by adding disodium sebacate to the above mixed grease in an amount of 0.1 mass % (Example 1), 0.2 mass % (Example 2), 0.5 mass % (Example 3), 1 mass % (Example 4), 2 mass % (Example 5), or 5 mass % (Example 6) relative to the total amount.

[0044] (1) Volume expansion rate A rubber shielded ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm) was filled with each of the greases from Examples 1 to 6 at 35% of the bearing space volume. The bearing was placed in a test tank at 130°C and 100% RH, and removed from the test tank after 48 hours. The mass of the bearing was measured before and after it was placed in the test tank, and the volume expansion rate (%) was calculated from the increased mass. The results obtained are shown in Table 1 and FIG.

[0045] (2) Reduction rate of additives (organic acid metal salts) A 100 mL cylindrical PTFE sealed container was prepared, 1.3 g of each of the greases from Examples 1 to 6 was applied to the inner wall surface of the container, and 10 mL of pure water was poured into the bottom of the container, which was then sealed. Note that the pure water and the grease applied to the inner wall surface were positioned so that they did not come into contact with each other (before the test, the concentration of grease-derived components in the pure water at the bottom of the container was 0). The PTFE sealed container was placed in an oven at 120°C and removed after 48 hours. The water inside the PTFE sealed container was collected, and the sodium (Na) concentration (ppm) in the collected water was quantitatively analyzed using ICP atomic emission spectrometry. Heating at 120°C for 48 hours caused the water inside the sealed container to evaporate and spread throughout the container, and the resulting water vapor came into contact with the grease on the inner wall of the container. The evaporated water then caused the sealed container to reach saturated water vapor pressure. The hydrophilic component in the grease (organic acid metal salt: disodium sebacate) was easily dissolved by the water vapor it came into contact with. Therefore, when the water vapor liquefied after the test, the hydrophilic component was extracted into the water inside the container. The additive reduction rate (%) for each test grease was calculated as the ratio of the measured Na concentration in the collected water (obtained by quantitative analysis using ICP atomic emission spectrometry) to the Na concentration assumed to be contained in the water (10 mL) containing the entire amount of disodium sebacate added. An additive reduction rate of 100% is considered to indicate that all of the added additive (disodium sebacate) has been extracted into the water. The results obtained are shown in Table 1 and FIG.

[0046] [Table 1]

[0047] Figure 4 shows the volume expansion rate of the grease (vertical axis) after the high-temperature, high-humidity test versus the additive (disodium sebacate) concentration (horizontal axis) in the test grease, and Figure 5 shows the additive reduction rate (vertical axis) after the high-temperature, high-humidity test versus the additive (disodium sebacate) concentration (initial concentration) (horizontal axis) in the test grease. As shown in Table 1, FIGS. 4 and 5, the greases (Examples 1 to 4) with a disodium sebacate concentration (amount added) of 0.1 to 1 mass % had a volumetric expansion rate of less than 60% and an additive reduction rate of 50% or less after the high-temperature, high-humidity test. In particular, the greases (Examples 1 to 3) with a disodium sebacate concentration (amount added) of 0.5 mass % or less had a volumetric expansion rate of less than 10% and an additive reduction rate of less than 20% after the high-temperature, high-humidity test.

[0048] [Water-filled bearing durability test] Test greases of Examples 7 to 9 were prepared by adding disodium sebacate in an amount of 0 mass % (Example 7), 0.2 mass % (Example 8), or 2 mass % (Example 9) relative to the total amount of the mixed grease. The acoustic performance of the test greases of Examples 7 to 9 and the ball bearings filled with water was evaluated by measuring the anderon values in the M band (300 to 1800 Hz) using an anderon meter. Each grease from Examples 7 to 9 was filled into a rubber-shielded ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm) at 6% to 9% of the bearing space volume, and 200 μL of water was then filled in, and the filled area (bearing space) was sealed with the rubber shield of the ball bearing. This ball bearing was set in the housing of a test motor, and a preload of 75 N (maximum surface pressure 1.5 GPa) was applied to the outer ring in the axial direction.A shaft was then inserted into the inner diameter of the bearing and connected to the rotating shaft of the test motor so that the ball bearing rotated around the inner ring. Next, after rotating at a rotation speed of 25,000 rpm for 2 hours in an air atmosphere at room temperature, an acoustic evaluation test was carried out according to the following procedure. However, if the ball bearing vibrated significantly during the test and the rotation stopped before the end of the 2-hour rotation test, the following acoustic evaluation test was carried out at that point.

[0049] <Acoustic evaluation test> After rotating each ball bearing for a predetermined period of time using the above procedure, a preload of 20 N was applied and the bearing was rotated at 1,800 rpm at room temperature and in an air atmosphere. In this state, a velocity pickup was brought into contact with the outer periphery of the outer ring of the ball bearing in the radial direction to detect mechanical vibrations transmitted to the outer ring and calculate the Anderon value, and the acoustic performance in each test was evaluated according to the following criteria (maximum Anderon value measured: 50). For the ball bearings of Examples 7 to 9, the test was carried out twice each, and the average Anderon value was calculated (the average was also calculated in the same way if the rotation stopped before the end of the 2-hour rotation test). The results obtained are shown in Table 2 / Figure 6. The M-band frequencies of 300 to 1800 Hz are said to be harsh to the ears of humans.

[0050] [Table 2]

[0051] As shown in Table 2, when the amount of disodium sebacate blended into the test grease was 0.2 mass% (Example 8, Anderon value: 1.0), the acoustic properties were improved compared to when no disodium sebacate was blended (Example 7, Anderon value: 4.5). On the other hand, when the blending amount of disodium sebacate was increased to 2.0 mass % (Example 9, Anderon value: 1.0), the acoustic properties were deteriorated.

[0052] 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. [Explanation of symbols]

[0053] 10...hydrogen recirculation blower, 11...housing, 12...stator, 13...coil, 14...rotor magnet, 15...shaft, 16...impeller, 17...housing, 18...inlet port, 19...exhaust port, M...motor, S...dynamic seal 20...Bearing, 21...Inner ring, 22...Outer ring, 23...Rolling element, 24...Cage, 25...Sealing member (rubber seal), 25a...Core metal, 26...Bearing space G...Grease 30... fuel cell system, 32... fuel cell stack, 34... fuel cell (cell), 36... cathode terminal, 38... anode terminal, 40... external circuit, 44... cathode gas inlet, 46... anode gas inlet, 48... internal flow path (cathode gas flow path), 50... internal flow path (anode gas flow path), 52... cathode gas outlet, 54... anode gas outlet, 56...first conduit, 58...exhaust line, 60...exhaust valve, 62...recycle line, 64...blower, 66...blower motor, 68...blower section, 70...rigid shaft, 72...arrow, 74...dynamic seal, 76...outlet, 78...exhaust line, 80...second conduit, 82...hydrogen gas reservoir, 84...control valve

Claims

1. A hydrogen recirculation blower for a fuel cell system equipped with a rolling bearing, comprising: The rolling bearing is It has an inner ring, an outer ring, and rolling elements, grease is disposed in an annular bearing space formed between the inner ring and the outer ring; and a rubber seal for sealing the bearing space; The grease contains an organic acid metal salt in a proportion of 0.05% by mass or more and 1% by mass or less relative to the total amount of the grease, and further contains The grease is After a high temperature and high humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, the volume expansion rate from before the test (1) is less than 60%; and After a high-temperature, high-humidity test (2) in which 1.3 g of the grease is placed in a sealed container having a volume of 100 mL and left to stand for 48 hours at 120°C, the organic acid metal salt is reduced by 50% or less from the amount before the test (2). Hydrogen recirculation blower for fuel cell systems.

2. the grease contains the organic acid metal salt in an amount of 0.1% by mass or more and 0.5% by mass or less based on the total amount of the grease, After the high-temperature, high-humidity test, the organic acid metal salt is reduced by 35% or less from the amount before the test.

10. The hydrogen recirculation blower of claim 1.

3. 2. The hydrogen recirculation blower of claim 1, wherein said organic acid metal salt is sodium sebacate.

4. The grease contains a mixed grease of a fluorine-based grease having a fluorine oil as a base oil and a non-fluorine-based grease having a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener, and the organic acid metal salt.

10. The hydrogen recirculation blower of claim 1.

5. The mixed grease is The base oil comprises perfluoropolyether and polyalphaolefin, The thickener contains polytetrafluoroethylene and a urea compound.

5. The hydrogen recirculation blower of claim 4.

6. The mixing ratio of the fluorine-based grease to the non-fluorine-based grease is 7:3 to 9:1 by mass.

5. The hydrogen recirculation blower of claim 4.

7. A rolling bearing provided in a hydrogen recirculation blower of a fuel cell system, The rolling bearing has an inner ring, an outer ring, and rolling elements, grease is disposed in an annular bearing space formed between the inner ring and the outer ring; a rubber seal for sealing the bearing space; The grease contains an organic acid metal salt in a proportion of 0.05% by mass or more and 1% by mass or less relative to the total amount of the grease, and further contains The grease has a volume expansion rate of less than 60% from before the test (1) after a high-temperature, high-humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, and after a high-temperature, high-humidity test (2) in which 1.3 g of the grease is placed in a sealed container with a volume of 100 mL and left to stand at 120°C for 48 hours, the organic acid content of the grease is less than that of the organic acid content of the organic acid before the test (2). The reduction rate of metal salts is 50% or less. Rolling bearing.

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