Hydrogen recirculation blower and rolling bearing

Abstract

[Problem] To provide a hydrogen recirculation blower that is for a fuel cell system and that comprises a bearing which has excellent durability in a high temperature humid environment , and in which lubrication performance is maintained even in an environment where water exists. [Solution] This hydrogen recirculation blower for a fuel cell system is provided with a rolling bearing. The rolling bearing has an inner ring, an outer ring, and rolling elements, has grease in an annular bearing space formed between the inner ring and the outer ring, and has a rubber seal for sealing the bearing space. The grease contains an organic acid metal salt at a proportion of 0.05-1 mass% with respect to the total amount of the grease. After a high-temperature and high-humidity test (1) under the conditions of 130°C and 100%RH for 48 hours, the grease exhibits a volume expansion rate of less than 60% as compared to before the test (1). After a high-temperature and high-humidity test (2) in which 1.3 g of the grease is made to coexist with 10 mL of pure water in a sealed container having a capacity of 100 mL and is left to stand for 48 hours under the condition of 120°C, the reduction rate of the organic acid metal salt from as compared to before the test (2) is not more than 50%. This rolling bearing is provided in said blower.

Description

Hydrogen recirculation blower and rolling bearings

[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.

[0002] Fuel cells are energy systems that directly convert 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 product produced during power generation is water (water vapor), not carbon dioxide. Furthermore, fuel cells have few moving parts, resulting in minimal noise and vibration, making them an environmentally friendly system. Furthermore, because electrical energy is directly extracted from the electrochemical reaction between hydrogen (fuel) and oxygen (oxidant), they are highly efficient and can produce electricity continuously as long as the fuel and oxygen are supplied. Furthermore, by effectively utilizing both the electricity and heat generated during the conversion process, overall energy efficiency can be further improved. Fuel cells, among other advantages, have been adopted as an alternative power source to internal combustion engines for automobiles due to their low (or zero) harmful emissions, high energy efficiency, compatibility with a variety of fuels and energy sources, low noise, and no need for charging. Various fuel cell vehicles have been proposed.

[0003] Fuel cell systems used in fuel cell vehicles and the like use blowers and compressors to pump hydrogen, which is the fuel, and oxygen, which is the oxidant, and one example of such a blower is an anode recirculation blower, which recirculates hydrogen that was not used in power generation. For example, Patent Document 1 proposes a rolling bearing to be incorporated into a fuel cell system compressor, a fuel cell system compressor equipped with such a bearing, and a fuel cell system equipped with such a compressor.

[0004] Japanese Patent Application Laid-Open No. 2004-190688 Japanese Patent Application Laid-Open No. 2013-35882 Japanese Patent Application Laid-Open No. 2013-173956 Japanese Patent No. 4883743 Japanese Patent No. 6646379

[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 the hydrogen, heat, water vapor, etc.

[0006] An 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 particularly durable in high-temperature and steam environments and that maintains its lubricating performance even in environments where water is present.

[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 having an inner ring, an outer ring, and rolling elements, grease in an annular bearing space formed between the inner ring and the outer ring, and a rubber seal sealing the bearing space, the grease containing an organic acid metal salt in a proportion of 0.05% by mass to 1% by mass of the total amount of the grease, and further characterized in that, after a high-temperature, high-humidity test (1) at 130°C, 100% RH, and 48 hours, the grease shows a volumetric expansion rate of less than 60% compared to before the test (1), and after a high-temperature, high-humidity test (2) in which 1.3 g of the grease is placed in a 100 mL sealed container and left at 120°C for 48 hours, the organic acid metal salt content decreases by 50% or less compared to before the test (2). The present invention also relates to a rolling bearing provided in the hydrogen recirculation blower.

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

[0009] As described above, the various components of hydrogen recirculation blowers used in fuel cell systems, such as motors, are required to have durability in environments containing hydrogen, heat, water vapor, and other elements. As described below, the blower uses bearings to support the rotating shaft of the impeller, and grease is used to lubricate the bearings. As described above, hydrogen recirculation blowers are used in high-temperature, high-humidity (water vapor) environments. In such environments, the grease may come into contact with moisture (water vapor) and absorb it, causing volumetric expansion. For example, if the grease expands in a bearing sealed with a rubber seal, the pressure in the space containing the grease (bearing space) increases, which can lead to grease leakage and, ultimately, poor lubrication due to grease depletion, thereby reducing the bearing's durability. Furthermore, in the high-temperature, high-humidity environment, hydrophilic additive components contained in the grease may dissolve in the absorbed moisture, significantly changing (decreasing) the concentration of the additive components in the grease and potentially impairing 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 also is resistant to volumetric expansion and suppresses changes in additive concentration. The inventors have discovered that greases containing a predetermined amount of organic acid metal salt exhibit minimal volumetric expansion and changes in the organic acid metal salt concentration even in high temperature and high humidity (water vapor) environments, while still maintaining lubricating performance. While 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 focused on suppressing the volumetric expansion of greases or suppressing changes in the metal salt concentration in high temperature and high humidity (water vapor) environments. The present invention will be described in detail below.

[0010] [Hydrogen Recirculation Blower] An embodiment of a blower according to the present invention will be described below with reference to the accompanying drawings. FIG. 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 a basic structure similar to that of 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) supporting shaft 15), an impeller 16, a housing 17, an intake port 18, and an exhaust port 19. The motor M generates magnetic force by passing current supplied from a power source (not shown) through the coil 13 wound around the stator 12 via a drive circuit, which rotates the rotor magnet 14. This rotation is transmitted to an external rotating body (impeller 16, described below) via the shaft 15, which serves as the rotation axis. Note that while the motor M in this figure is an inner rotor motor, it is not limited to this and may also be an outer rotor motor. In the case of an outer rotor motor, the stator 12 is arranged 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 exhausted from an exhaust port 19. In blowers and the like 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] [Bearing] A preferred embodiment of a bearing 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. More specifically, it is a bearing having an inner ring, an outer ring arranged coaxially with the inner ring on the outer periphery of the inner ring, and a plurality of rolling elements arranged between the inner ring and the outer ring, i.e., a rolling bearing. Note that the present invention is not limited to the following embodiment.

[0013] FIG. 2 is a radial cross-sectional view of a bearing (rolling bearing) 20 according to a preferred embodiment of the present invention. The bearing 20 has the same basic structure as a conventional rolling bearing, and includes an annular inner ring 21, an outer ring 22, multiple rolling elements 23, a cage 24, and a seal member 25. The inner ring 21 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 22 is a cylindrical structure that is installed coaxially with the inner ring 21 on the outer periphery of 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 according to this embodiment is a ball bearing. The cage 24 is arranged in the raceway and holds the multiple rolling elements 23. The cage 24 is an annular body installed coaxially with the central axis of the shaft. It has a plurality of pockets on one side in the direction of the central axis for holding the rolling elements 23, with the rolling elements 23 accommodated in each pocket. The cage 24 holds the rolling elements 23 at predetermined intervals circumferentially around the inner ring 21 and the outer ring 22, thereby preventing the rolling elements 23 from falling off and preventing adjacent rolling elements 23 from coming into contact with each other. The shape (crown-shaped, corrugated, etc.) and material (steel plate, resin, etc.) of the cage 24 are optional 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. Grease G is sealed in the bearing space 26 sealed by the seal member 25. That is, the grease G is held between the inner ring 21 and the outer ring 22. A mixed grease, as described below, is preferably used as the grease G. The amount of grease G enclosed within bearing space 26 can be, for example, 5 to 50% of its volume. 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 shown in the figure is a contact-type rubber seal in which a rubber seal insert-molded with 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, or a mixed grease of these. As described below, the grease used in the present invention preferably includes a fluorine-based grease having a fluorine oil as a base oil, and particularly 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 described below. The formulation of this mixed grease achieves excellent friction and wear resistance in the presence of water.

[0015] [Organic Acid Metal Salt] The grease used in the present invention essentially contains an organic acid metal salt, which is contained in an amount of 0.05 mass% or more and 1 mass% or less relative to the total amount of the grease, such as 0.05 mass% or more, more than 0.05 mass%, 0.1 mass% or more, more than 0.1 mass%, 0.2 mass% or more, or 1 mass% or less, less than 1 mass%, 0.5 mass% or less, or less than 0.5 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, monovalent saturated 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; monovalent unsaturated fatty acids such as acrylic acid, crotonic acid, undecylenic acid, oleic acid, and gadoleic acid; Examples of the metal salt 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; 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. Among these, sodium salts are preferred.

[0018] Among the above organic acid metal salts, preferred examples include sodium benzoate, monosodium sebacate, disodium sebacate, monosodium succinate, and disodium succinate, and particularly sodium sebacate (monosodium sebacate, disodium sebacate).

[0019] [Fluorine-based grease] <Base oil> The base oil in fluorine-based grease is fluorine oil. Examples of fluorine oil include those containing perfluoropolyether (PFPE) as the main component. PFPE has the general formula: RfO(CF ２ O) ｐ (C ２ F ４ O) ｑ (C ３ F ６ O) ｒIt 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, and the straight-chain type has 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 suppressing the outflow of grease from the application location and the accompanying depletion, that is, the use of straight-chain perfluoropolyether is preferred. The fluorine oil can 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. As the fluorine-based thickener, fluororesin particles are preferred, and for example, polytetrafluoroethylene (PTFE) particles are preferably used. PTFE is a polymer of tetrafluoroethylene and is represented by the general formula: [C ２ F ４ ] ｎ (n: degree of polymerization). Other fluorine-based thickeners that can be used 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. Furthermore, 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 % based on the total amount of the fluorine-based grease.

[0022] [Non-fluorine-based 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 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 oils include polyalphaolefins (PAOs) such as normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and 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. 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 Thickeners> Urea compounds have excellent heat resistance and water resistance, and good stability at high temperatures, so they are suitable for use as thickeners in applications where high temperatures or water is present. Urea compounds such as diurea compounds, triurea compounds, and polyurea compounds can be used as urea-based thickeners. From the standpoint 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. Conventionally known urea compounds can be used as these urea-based thickeners.

[0025] As an example of a urea-based thickener, a diurea compound represented by the following general formula (1) can be mentioned: １ -NHCONH-R ２ -NHCONH-R ３ ... (1) In the above formula (1), R １ and R ３ each independently represents a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group, or a monovalent aromatic hydrocarbon group, and R １ and R ３ At least one of R represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group. ２ represents a divalent aromatic hydrocarbon group.

[0026] 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.

[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, as well as alicyclic amines such as cyclohexylamine, and aromatic amines such as aniline, p-toluidine, and ethoxyphenylamine. Examples of the isocyanate compound 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.

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

[0029] <Soap-based thickeners> 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, sodium soap, etc. The soap thickeners 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 with a fluorine-based oil as a base oil, and particularly to use a mixed grease of a fluorine-based grease with a fluorine-based oil as a base oil and a non-fluorine-based grease with 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 with a fluorine-based oil as a base oil and a non-fluorine-based grease with a synthetic hydrocarbon oil as a base oil and a urea compound as a thickener, and can be obtained by blending other additives described below as desired. The above-mentioned various base oils (fluorine-based oils and synthetic hydrocarbon oils) and various thickeners (fluorine-based thickeners, urea compounds) can be mixed in a predetermined ratio, and other additives can be blended as desired to produce a mixed grease. 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 can contain additives commonly used in greases as needed, as long as the effects of the present invention are not impaired. Examples of such additives include antioxidants, extreme pressure agents, 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 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- 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 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] [Regarding the Volumetric Expansion Rate and the 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 of the blower is required to have a low volumetric expansion rate and a low reduction rate of organic acid metal salts after a specified high-temperature, high-humidity test. That is, after subjecting the grease to a high-temperature, high-humidity test (1) at 130°C, 100% RH, and 48 hours, the volumetric expansion rate of the grease compared to 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 100-mL container with 10 mL of pure water and left at 120°C for 48 hours, the reduction rate of the organic acid metal salts in the grease compared to before the test (2) is 50% or less. The volumetric expansion rate of the grease from 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 from before the above test (2) can be preferably 35% or less, or 20% or less. After the above-mentioned specified high-temperature, high-humidity test, the volumetric expansion of the grease is suppressed, and the change in the 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 can be expected that a hydrogen recirculation blower using the grease will have good durability in the above-mentioned environment.

[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 a configuration of a fuel cell system using hydrogen. The fuel cell system 30 shown in FIG. 3 includes a fuel cell stack 32. The fuel cell stack 32 is the smallest power generation unit and is composed of individual fuel cells 34 (mostly flat cells). The fuel cell stack 32 includes a cathode terminal 36 and an anode terminal 38 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. Air (oxygen) as an oxidant flows into the fuel cell stack 32 through a cathode gas inlet 44, while pressurized hydrogen as a fuel flows into the fuel cell stack 32 through an anode gas inlet 46. In the fuel cells (cells) 34 that constitute the fuel cell stack 32, hydrogen supplied as fuel dissociates into hydrogen ions and electrons at the fuel electrode (anode). The electrons move to the oxygen electrode (cathode), generating electricity, which is then supplied to the outside (for external consumption) via the external circuit. The fuel cell stack 32 includes internal flow paths 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 (H ２ O), nitrogen (N ２ ), unreacted hydrogen (H ２) is transported through a first conduit 56, a portion of which is vented through an exhaust valve 60 into an exhaust line 58. The remaining anode gas flow passes through a recycle line 62 and is returned to the fuel cell stack 32 via a blower 64 (described later). 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 pressure loss caused by its own ventilation and friction loss within the internal flow path (anode gas flow path) 50 within the fuel cell stack 32. To address these pressure losses, the fuel cell system 30 uses a blower portion 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 according to the present invention described above. A heat exchanger (not shown) removes excess heat generated by the blower motor 66 while the blower 64 is operating. For clarity, blower 64 is shown in dashed lines in FIG. 3 to indicate that a rigid shaft 70 transmits torque between blower motor 66 and blower section 68. As indicated by arrow 72, dynamic seal 74 reduces, but does not eliminate, the flow of anode gas from blower section 68 to blower motor 66. The pressurized anode recirculation gas exits blower 66 through outlet 76 to exhaust line 78, which introduces the anode recirculation gas (anode gas recycle stream) to the anode gas inlet 46 of fuel cell stack 32. Make-up hydrogen is introduced into blower exhaust line 78 from 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 controller (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 their acoustic characteristics. As one example, it is desirable to use a bearing in which the Anderon value of the M band after rotating the inner ring against the outer ring of the bearing filled with grease containing the above-mentioned specified organic acid metal salt at a rotation speed of 2500 rpm for two hours at room temperature in an atmospheric atmosphere under an axial preload of 75 N (maximum surface pressure 1.5 GPa) is 5 or less, for example 2.5 or less.

[0040] The present invention is not limited to the embodiments and specific examples described in this specification, and various modifications and variations are possible within the scope of the technical concept 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 used in a hydrogen environment, such as a hydrogen fuel engine system that directly combusts hydrogen in an internal combustion engine and uses the resulting thermal energy as power, or a blower in a hydrogen supply system. Furthermore, the hydrogen recirculation blower according to the present invention 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 used in relatively sealed environments, such as high-temperature, high-humidity environments.

[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 disodium sebacate (0 mass %), and then subjected to the tests described below. In the following explanation, the example numbers of the test greases will also be used as example numbers for the evaluation of various tests. <Mixed Grease> 80 wt % fluorine grease (base oil: perfluoropolyether (PFPE), kinematic viscosity at 40°C: 85 mm 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, High-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% by mass (Example 1), 0.2% by mass (Example 2), 0.5% by mass (Example 3), 1% by mass (Example 4), 2% by mass (Example 5), or 5% by mass (Example 6) relative to the total amount.

[0044] (1) Volumetric Expansion Coefficient Each of the greases from Examples 1 to 6 was filled into a rubber shielded ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm) at a volume of 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 being placed in the test tank, and the volumetric expansion coefficient (%) was calculated from the increase in mass. The results are shown in Table 1 and Figure 4.

[0045] (2) Additive (organic acid metal salt) reduction rate: A 100 mL cylindrical PTFE sealed container was prepared, 1.3 g of each grease from Examples 1 to 6 was applied to the inner wall of the container, and 10 mL of pure water was poured into the bottom of the container and sealed. The pure water and the grease applied to the inner wall 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 recovered, and the sodium (Na) concentration (ppm) contained in the recovered 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, releasing water vapor that came into contact with the grease on the inner wall of the container. The evaporated water caused the sealed container to reach saturated water vapor pressure. The hydrophilic component in the grease (organic acid metal salt: disodium sebacate) is easily dissolved by water vapor it comes into contact with, and therefore, when the water vapor liquefies after the test, the hydrophilic component is extracted into the water inside the container. The additive reduction rate was calculated by calculating 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) placed in the sealed container. A 100% additive reduction rate was considered to indicate that all of the additive (disodium sebacate) added was extracted into the water. The results are shown in Table 1 and Figure 5.

[0046]

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

[0048] [Durability Test of Water-Filled Bearings] Test greases of Examples 7 to 9 were prepared by adding disodium sebacate in an amount of 0% by mass (Example 7), 0.2% by mass (Example 8), or 2% by 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 water-filled ball bearings was evaluated by measuring the Anderon value in the M band (300 to 1800 Hz) using an Anderon meter. Each of the greases of 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. The filled portion (bearing space) of the ball bearing was then sealed with the rubber shield. 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 coupled to the rotating shaft of the test motor so that the ball bearing rotated around the inner ring. The bearing was then rotated at 25,000 rpm for two hours in an air atmosphere at room temperature, after which an acoustic evaluation test was conducted using the following procedure. However, if the ball bearing vibrated significantly during the test and stopped rotating before the end of the two-hour rotation test, the following acoustic evaluation test was conducted 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 in room temperature and ambient air. A velocity pickup was then placed in radial contact with the outer periphery of the outer ring of the bearing to detect mechanical vibrations transmitted to the outer ring and calculate the Anderon value. The acoustic performance of each test was evaluated according to the following criteria (maximum measured Anderon value: 50). For each of the ball bearings in Examples 7 to 9, two tests were conducted, and the average Anderon value was calculated (the same average was calculated even when rotation stopped before the end of the two-hour rotation test). The results are shown in Table 2 and Figure 6. Note that frequencies in the M-band between 300 and 1,800 Hz are considered harsh to the human ear.

[0050]

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

[0053] REFERENCE SIGNS LIST 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...retainer, 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, wherein the rolling bearing has an inner ring, an outer ring, and rolling elements, and 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, and the grease contains an organic acid metal salt in a proportion of 0.05 mass % to 1 mass % of the total amount of the grease, and further, after a high-temperature, high-humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, the grease has a volume expansion rate of less than 60% from before the test (1), 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 metal salt has a reduction rate of 50% or less from before the test (2).

2. A hydrogen recirculation blower for a fuel cell system as described in claim 1, wherein the grease contains the organic acid metal salt in a proportion of 0.1 mass % or more and 0.5 mass % or less relative to the total amount of the grease, and after the high-temperature, high-humidity test, the organic acid metal salt is reduced by 35% or less from the amount before the test.

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

4. The hydrogen recirculation blower for a fuel cell system according to claim 1, wherein the grease comprises 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.

5. The hydrogen recirculation blower of a fuel cell system according to claim 4, wherein the mixed grease comprises a base oil containing perfluoropolyether and polyalphaolefin, and a thickener containing polytetrafluoroethylene and a urea compound.

6. The hydrogen recirculation blower for a fuel cell system according to claim 4, wherein the mixture ratio of the fluorine-based grease to the non-fluorine-based grease is 7:3 to 9:1 by mass.

7. A rolling bearing provided in a hydrogen recirculation blower of a fuel cell system, the rolling bearing having an inner ring, an outer ring, and rolling elements, 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 containing an organic acid metal salt in a proportion of 0.05 mass % to 1 mass % of the total amount of the grease, and further, after a high-temperature, high-humidity test (1) under conditions of 130°C, 100% RH, and 48 hours, the grease has a volume expansion rate of less than 60% from before the test (1), and after a high-temperature, high-humidity test (2) in which 1.3 g of the grease is coexisted with 10 mL of pure water in a 100 mL sealed container and left for 48 hours at 120°C, the organic acid metal salt has a reduction rate of 50% or less from before the test (2).

Images