Lubricating oil composition for ammonia-fueled internal combustion engine

Abstract

A lubricating oil composition for an ammonia-fueled internal combustion engine, said lubricating oil composition containing a lubricating oil base oil and an anti-wear agent, wherein the lubricating oil base oil is at least one oil selected from the group consisting of mineral base oils and synthetic base oils, and the anti-wear agent is at least one of (A) a phosphorous-containing anti-wear agent that satisfies a specific condition and (B) a phosphorous-free anti-wear agent that satisfies a specific condition.

Description

Lubricating oil composition for ammonia-fueled internal combustion engines

[0001] The present invention relates to a lubricating oil composition for an ammonia-fueled internal combustion engine.

[0002] In recent years, reducing greenhouse gas (GHG) emissions to combat global warming has become a major challenge, and in the maritime sector in particular, the goal is to achieve net-zero GHG emissions by 2050 in both international and domestic shipping. To achieve this goal, it is considered essential to improve the fuel efficiency of internal combustion engines and to use low-carbon fuels, and the use of carbon-free fuels such as hydrogen and ammonia as fuel for internal combustion engines is being considered. Among these fuels for internal combustion engines, ammonia is expected to be a major decarbonization fuel, especially in the maritime sector where long-distance transport is the main focus, because its fuel density is higher than that of hydrogen.

[0003] In internal combustion engines that use ammonia as fuel, just as in conventional internal combustion engines that use hydrocarbons as fuel, it is necessary to use lubricating oil compositions to lubricate the sliding parts and fuel pumps, and the use of various lubricating oil compositions has been proposed.

[0004] For example, Japanese Patent Publication No. 2023-520938 (Patent Document 1) discloses an engine composition that is partially or completely fueled by bio-derived fuels, ethanol or methanol, ammonia, gaseous fuels, residual fuels, marine residual fuels, low-sulfur marine residual fuels, marine distillate fuels, low-sulfur marine distillate fuels, or high-sulfur fuels. Thus, Patent Document 1 exemplifies an ammonia-fueled engine as one of the various types of engines. Furthermore, in paragraph

[0054] , etc., Patent Document 1 exemplifies C8 primary dialkyldithiophosphate zinc (ZnDTP) as one of the wear-resistant additives that the lubricating oil composition may further contain.

[0005] Furthermore, Japanese Patent Publication No. 2024-056645 (Patent Document 2) discloses an invention relating to the use of metal alkanates such as zinc neodecanoate as additives in a lubricant composition having good wear resistance for application in large diesel engines, and paragraph

[0151] of that document discloses that the lubricant composition described in the document may be useful as a lubricant for hydrogen engines and ammonia engines, etc. Paragraph

[0139] of Patent Document 2 exemplifies zinc dialkyldithiophosphate as a useful wear-resistant agent.

[0006] Japanese Patent Publication No. 2023-520938, Japanese Patent Publication No. 2024-056645

[0007] The inventors investigated using conventional lubricating oil compositions used in general internal combustion engines for internal combustion engines that use ammonia as fuel. However, they found that when a lubricating oil composition containing zinc dialkyldithiophosphate, which is widely used as an anti-wear agent in the field of internal combustion engines and is considered particularly important in terms of availability and the balance between anti-wear properties and antioxidant properties, is used as a lubricating oil composition for an ammonia-fueled internal combustion engine, gel formation may occur in the system during use, leading to problems such as a decrease in the fluidity of the lubricating oil composition. Thus, the inventors found that simply applying lubricating oil compositions used in other engines is not necessarily sufficient to prevent gel formation in ammonia-fueled internal combustion engines.

[0008] In contrast, while Patent Documents 1 and 2 state that the lubricating oil compositions described in those documents can be used in engines that use ammonia as fuel, they do not mention the problems such as the formation of gel that may occur when a lubricating oil composition using zinc dialkyldithiophosphate, in which all alkyl groups in the compound are C8 alkyl groups, is used as an anti-wear agent in an internal combustion engine that uses ammonia as fuel. Nor do they consider any means to solve such problems.

[0009] The present invention aims to provide a lubricating oil composition for an ammonia-fueled internal combustion engine that can achieve a high level of wear resistance while highly preventing gel formation during use.

[0010] To achieve the above objective, the inventors first considered that since ammonia contamination is unavoidable when lubricating oil compositions used in sliding parts of ammonia-fueled internal combustion engines (including their fuel pumps, etc.) come into contact with ammonia fuel, a gel would be generated by the reaction between the components of the lubricating oil composition and ammonia, and proceeded to study various compositions. From this perspective, the present inventors have conducted extensive research on lubricating oil compositions for ammonia-fueled internal combustion engines that can exhibit high effectiveness in terms of wear resistance and prevention of gel formation without using zinc dialkyldithiophosphate (ZnDTP), which has been considered an important additive in conventional lubricating oil compositions. As a result, they have found that by providing a composition containing a lubricating oil base oil and an anti-wear agent, and by using at least one of the following components (A) and / or (B) as the anti-wear agent (by using at least one of the following components (A) and (B) as the anti-wear agent), it is possible to achieve a high level of wear resistance while highly preventing gel formation in the composition during use, thus completing the present invention.

[0011] In other words, the present invention provides the following embodiments.

[0012] [1] A lubricating oil composition for an ammonia fuel internal combustion engine, comprising a lubricating oil base oil and an anti-wear agent, wherein the lubricating oil base oil is at least one selected from the group consisting of mineral oil-based base oils and synthetic base oils, and the anti-wear agent is at least one of the following components (A) to (B): (A) A phosphorus-containing anti-wear agent that is at least one selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate ester, phosphate ester compound, and amine salt of a phosphate ester compound, and whose phosphorus content on a basis of the total mass of the lubricating oil composition is 100 ppm by mass or more and 3000 ppm by mass or less; (B) A phosphorus-free anti-wear agent that is molybdenum dithiocarbamate and whose molybdenum content on a basis of the total mass of the lubricating oil composition is 100 ppm by mass or more and 2000 ppm by mass or less;

[0013] [2] The lubricating oil composition according to [1], wherein the content of component (A) in terms of phosphorus element is 400 ppm by mass or more and 2000 ppm by mass or less, based on the total mass of the lubricating oil composition.

[0014] [3] The lubricating oil composition according to [1] or [2], further comprising a metal-based detergent.

[0015] [4] The lubricating oil composition according to any one of [1] to [3], further comprising an ashless dispersant.

[0016] According to the present invention, it is possible to provide a lubricating oil composition for an ammonia-fueled internal combustion engine that can achieve a high level of wear resistance while highly preventing the formation of gel during use.

[0017] The present invention will be described in detail below with reference to its preferred embodiments. In this specification, unless otherwise specified, the notation "X to Y" for numerical values ​​X and Y means "X or greater and Y or less". If a unit is attached only to the numerical value Y in such notation, that unit shall also apply to the numerical value X.

[0018] The lubricating oil composition for an ammonia-fueled internal combustion engine of the present invention contains a lubricating oil base oil and an anti-wear agent, wherein the lubricating oil base oil is at least one selected from the group consisting of mineral oil-based base oils and synthetic base oils, and the anti-wear agent is at least one of the following components (A) to (B): (A) A phosphorus-containing anti-wear agent that is at least one selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate esters, phosphate ester compounds, and amine salts of phosphate ester compounds, and whose phosphorus content, based on the total mass of the lubricating oil composition, is 100 ppm by mass or more and 3000 ppm by mass or less; (B) A phosphorus-free anti-wear agent that is molybdenum dithiocarbamate, and whose molybdenum content, based on the total mass of the lubricating oil composition, is 100 ppm by mass or more and 2000 ppm by mass or less;

[0019] In this specification, "ammonia-fueled internal combustion engine" refers to any internal combustion engine that uses ammonia as fuel, and is not particularly limited; it can be any internal combustion engine that uses known ammonia fuel (such as a so-called ammonia-fueled engine).

[0020] Furthermore, in this specification, "for ammonia fuel internal combustion engines" means that the product is intended for use in ammonia fuel internal combustion engines, and its uses are not particularly limited. Examples include its use in the ammonia fuel pump of an ammonia fuel internal combustion engine, its system oil, its cylinder oil, and, if the ammonia fuel internal combustion engine is a trunk piston type engine, its use in the trunk piston engine. Thus, in this specification, "for ammonia fuel internal combustion engines" means that the product is intended for use in ammonia fuel internal combustion engines and can be used without particular limitations for the various mechanisms of an ammonia fuel internal combustion engine.

[0021] Furthermore, unless otherwise specified in this specification, the phosphorus content and molybdenum content in the lubricating oil composition shall be those measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116. When the phosphorus element is introduced into the composition solely from the phosphorus-containing anti-wear agent, the phosphorus content in the lubricating oil composition, measured as described above, shall be adopted as the "phosphorus content on a basis of the total mass of the lubricating oil composition" of the phosphorus-containing anti-wear agent. Similarly, when the molybdenum element is introduced into the composition solely from the phosphorus-free anti-wear agent, the molybdenum content in the lubricating oil composition, measured as described above, shall be adopted as the "molybdenum content on a basis of the total mass of the lubricating oil composition" of the phosphorus-free anti-wear agent. Furthermore, when phosphorus or molybdenum is introduced into the composition from multiple components (for example, when molybdenum is present in the composition from two components by combining component (A) molybdenum dialkyldithiophosphate and component (B)), the value calculated from the elemental ratio of each component (the content ratio of phosphorus or molybdenum in that component) and the amount of that component added may be adopted as the phosphorus or molybdenum content of each component. Also, when an ashless dispersant is used in the lubricating oil composition, and a compound containing nitrogen (for example, succinimide) is used as the ashless dispersant, the nitrogen content derived from the ashless dispersant in the lubricating oil composition (the nitrogen content of the ashless dispersant) shall be a value calculated based on the amount of the ashless dispersant added and the nitrogen content (ratio: elemental ratio) relative to the total amount of constituent elements of the ashless dispersant.

[0022] <Lubricating Oil Base Oil> The lubricating oil composition of the present invention contains "lubricating oil base oil" as an essential component. Furthermore, in the present invention, the lubricating oil base oil is at least one selected from the group consisting of mineral oil-based base oil and synthetic base oil. Thus, in the present invention, mineral oil-based base oil, synthetic base oil, or a mixture thereof is used as the lubricating oil base oil.

[0023] Examples of the mineral oil-based base oils include paraffinic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and naphthenic base oils, which are obtained by refining a lubricating oil fraction obtained by atmospheric distillation and / or vacuum distillation of crude oil using one or more refining treatments selected from solvent delamination, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, catalytic dewaxing, solvent refining, hydrorefining, chemical washing, and clay treatment; and mixtures of two or more of these.

[0024] Furthermore, as the mineral oil-based base oil, examples include a base oil obtained by using any of the following (1) to (8) as a raw material oil, and refining the raw material oil and / or the lubricating oil fraction recovered from the raw material oil by a predetermined refining method to recover the lubricating oil fraction. (1) Distillate of paraffin-based crude oil and / or mixed-based crude oil by atmospheric distillation (2) Distillate (WVGO) of atmospheric distillation residue of paraffin-based crude oil and / or mixed-based crude oil by vacuum distillation (3) Wax obtained by the lubricating oil dewaxing process (slack wax, etc.), and / or synthetic wax obtained by the Fischer-Tropsch (FT) process, Gas-to-Liquid (GTL) process, etc. (FT wax, GTL wax, etc.) (4) Mild hydrocracking oil selected from the raw material oils (1) to (3), and / or mild hydrocracking oil of a mixture of two or more selected from the raw material oils (1) to (3) (5) Mixture of two or more selected from the raw material oils (1) to (4) (6) Deflaxed oil (DAO) of raw material oil (1), (2), (3), (4) or (5) (7) Mild hydrocracking treated oil (MHC) of raw material oil (6) (8) A mixture of two or more oils selected from raw material oils (1) to (7).

[0025] The following are preferred purification methods: hydrogenation purification such as hydrocracking and hydrogenation finishing; solvent purification such as furfural solvent extraction; dewaxing such as solvent dewaxing and contact dewaxing; clay purification using acid clay or activated clay; and chemical (acid or alkali) washing such as sulfuric acid washing and caustic soda washing. One of these purification methods may be performed alone, or two or more may be performed in combination. When combining two or more purification methods, the order is not particularly limited and can be selected as appropriate.

[0026] Particularly preferred examples of mineral oil-based base oils include the base oils described in (9) or (10) below, which are obtained by performing a predetermined treatment on a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil. (9) Hydrocracking of a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil, and dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the product or the lubricating oil fraction recovered from the product by distillation, etc., or distillation after such dewaxing treatment. (10) Hydroisomerized base oil obtained by hydroisomerizing a raw material oil selected from (1) to (8) above or a lubricating oil fraction recovered from said raw material oil, and dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the product or the lubricating oil fraction recovered from the product by distillation, etc., or distillation after such dewaxing treatment (base oil produced via a catalytic dewaxing process is more preferred as the dewaxing process).

[0027] Furthermore, when obtaining the mineral oil-based base oil described in (9) or (10) above, a solvent refining treatment and / or a hydrogenation finishing treatment may be carried out at an appropriate stage as needed.

[0028] Furthermore, as the mineral oil base oil, you can use API Group I base oil (hereinafter referred to as "API Group I base oil" as it may be), Group II base oil (hereinafter referred to as "API Group II base oil" as it may be), or Group III base oil (hereinafter referred to as "API Group III base oil" as it may be), or a blended base oil obtained by combining these. Here, API Group I base oil is a mineral oil base oil having a sulfur content of more than 0.03% by mass and / or a saturation content of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API Group II base oil is a mineral oil base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. Furthermore, API Group III base oil is a mineral oil base oil having a sulfur content of 0.03% by mass or less, a saturation content of 90% by mass or more, and a viscosity index of 120 or more. API Group I base oils are typically produced through a solvent refining process, while API Group II and Group III base oils are typically produced through a hydrocracking process. In this specification, viscosity index means viscosity index measured in accordance with JIS K 2283-2000. In this specification, "sulfur content in lubricating base oil" shall be measured in accordance with JIS K 2541-2003. In this specification, "saturation content in lubricating base oil" means value measured in accordance with ASTM D 2007-93.

[0029] Furthermore, suitable synthetic base oils include hydrocarbon-based synthetic oils and ester-based base oils. Examples of such synthetic base oils include API base oil classification group IV base oils (poly-α-olefin base oils, hereinafter sometimes referred to as "API group IV base oils"; such base oils (hydrocarbon-based synthetic oils) are suitable as hydrocarbon-based base oils), API base oil classification group V base oils (hereinafter sometimes referred to as "API group V base oils"; such base oils include ester-based base oils as one type), or mixed base oils obtained by combining these.

[0030] Suitable API Group IV base oils that can be used as the aforementioned synthetic base oils include, for example, hydrocarbon base oils (hydrocarbon synthetic oils) consisting of α-olefin oligomers and co-oligomers having 2 to 32 carbon atoms (preferably 6 to 16 carbon atoms), such as ethylene-propylene copolymers, polybutene, 1-octene oligomers, and 1-decene oligomers, as well as their hydrogenation products.

[0031] Furthermore, suitable API group V base oils for use as the aforementioned synthetic base oils include, for example, ester-based base oils such as monoesters (e.g., butyl stearate, octyl laurate, 2-ethylhexyl oleate, etc.); diesters (e.g., ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.); polyesters (e.g., trimellitic acid esters, etc.); and polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate, etc.). Other examples of the aforementioned API group V base oils include aromatic synthetic base oils such as alkylbenzenes, alkylnaphthalenes, dialkyldiphenyl ethers, and polyphenyl ethers. Of these API base oil classification group V base oils, the ester-based base oils mentioned above are more preferred from the viewpoint of ease of availability.

[0032] Examples of such synthetic base oils include poly-α-olefins and their hydrogenates, isobutene oligomers and their hydrogenates, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, bis-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, bis-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene glycols, dialkyldiphenyl ethers, polyphenyl ethers, and mixtures thereof.

[0033] Thus, the lubricating oil base oil according to the present invention may be a mineral oil-based base oil, a synthetic base oil, or a mixture thereof. For example, API Group I base oils, API Group II base oils, API Group III base oils, API Group IV base oils, API Group V base oils, or mixtures thereof can be suitably used. Among such lubricating oil base oils, from the viewpoint of the difficulty in dissolving ammonia and the ability to obtain a lubricating oil composition more suitable for applications such as internal combustion engines and hydraulic fluids for fuel pumps, hydrocarbon base oils that are API Group I base oils, API Group II base oils, API Group III base oils, API Group IV base oils, API Group V base oils, ester base oils that are API Group V base oils, or mixtures thereof are more preferable.

[0034] Furthermore, among the lubricating oil base oils, mineral oil-based base oils are preferred from the viewpoint of being a base oil in which ammonia is less soluble.

[0035] The kinematic viscosity of the lubricating oil base oil (whole base oil) at 100°C is 2.0 mm². ２ / s or more 100mm ２ / s or less (more preferably 3.0 mm) ２ / s or more 75mm ２ / s or less, more preferably 4.0 mm ２ / s or more 50mm ２ / s or less, particularly preferably 6.0 mm２ 40 mm or more per s ２ It is preferably (40 mm or less per s). By setting the kinematic viscosity at 100°C to be not less than the lower limit, a higher effect can be obtained in terms of wear resistance. Further, by setting the kinematic viscosity at 100°C to be not more than the upper limit, a higher effect can be obtained in terms of energy conservation.

[0036] Further, when the kinematic viscosity at 100°C of the lubricating base oil (total base oil) is used as the working oil or system oil of the mechanism equipped with the ammonia fuel internal combustion engine, it is 2 mm ２ 15 mm or more per s ２ 4 mm or less per s (more preferably ２ 12 mm or more per s ２ 4 mm or less per s), and when the composition is used as trunk piston engine oil (TPEO), it is 4 mm ２ 18 mm or more per s ２ 5 mm or less per s (more preferably ２ 16.3 mm or more per s ２ 50 mm or less per s), and when the composition is used as cylinder oil, it is 12.5 mm ２ 50 mm or more per s ２ 16.3 mm or less per s (more preferably ２ 21.9 mm or more per s ２ 21.9 mm or less per s), which is preferable.

[0037] Further, the kinematic viscosity at 40°C of the lubricating base oil (total base oil) is 5.0 mm ２ 1500 mm or more per s ２ 10 mm or less per s (more preferably [[ID=3८]] ２ 1400 mm or more per s ２ 400 mm or less per s, more preferably ２ 20 mm or more per s ２ 400 mm or less per s, particularly preferably ２ 500 mm or more per s ２ 500 mm or less per s), which is preferable. By setting the kinematic viscosity at 40°C to be not less than the lower limit, a higher effect can be obtained in terms of wear resistance. Further, by setting the kinematic viscosity at 40°C to be not more than the upper limit, a higher effect can be obtained in terms of energy conservation.

[0038] Furthermore, the kinematic viscosity of the lubricating oil base oil (whole base oil) at 40°C should be 5 mm when the composition is used as hydraulic fluid or system oil for mechanisms in an ammonia-fueled internal combustion engine. ２ / s or more 165mm ２ / s or less (more preferably 20 mm) ２ / s or more 117mm ２ It is preferable to have a ratio of 0 / s or less, and when the composition is used as trunk piston engine oil (TPEO), it should be 20 mm ２ / s or more 220mm ２ / s or less (more preferably 30 mm) ２ / s or more 190mm ２ It is preferable to have a ratio of 0 / s or less, and furthermore, when the composition is used as cylinder oil, it should be 125 mm ２ / s or more 500mm ２ / s or less (more preferably 190 mm) ２ / s or more 295mm ２ It is preferable to set it to / s or less.

[0039] In this specification, "kinematic viscosity at 40°C" and "kinematic viscosity at 100°C" refer to the kinematic viscosity at each temperature (kinematic viscosity at 40°C or kinematic viscosity at 100°C), measured in accordance with JIS K 2283-2000 using an automatic viscometer (product name "CAV-2100", manufactured by Cannon Instruments).

[0040] The viscosity index of the lubricating oil base oil (whole base oil) is preferably 90 or higher, more preferably 95 or higher, even more preferably 100 or higher, particularly preferably 105 or higher, and most preferably 110 or higher, from the viewpoint of improving the viscosity-temperature characteristics of the composition, and further improving fuel efficiency and wear resistance. In this specification, "viscosity index" refers to the viscosity index measured using an automatic viscometer (product name "CAV-2100", manufactured by Cannon Instruments) as the measuring device, in accordance with JIS K 2283-2000.

[0041] The pour point of the lubricating oil base oil (whole base oil) is preferably -5°C or lower, more preferably -10°C or lower, even more preferably -12.5°C or lower, particularly preferably -15°C or lower, and most preferably -17.5°C or lower, from the viewpoint of the low-temperature fluidity of the entire lubricating oil composition. In this specification, "pour point" refers to the pour point measured in accordance with JIS K 2269-1987.

[0042] If the lubricating oil base oil (whole base oil) contains sulfur, it is preferable that the sulfur content be 2% by mass or less, and more preferably 1% by mass or less from the viewpoint of oxidation stability. In this specification, "sulfur content" in the base oil refers to the amount of sulfur measured in accordance with JIS K 2541-2003.

[0043] Furthermore, in the lubricating oil composition of the present invention, the content of the lubricating oil base oil (total base oil) is preferably 30% by mass or more and 99.5% by mass or less (more preferably 50% by mass or more and 99.5% by mass or less, and even more preferably 60% by mass or more and 99.5% by mass or less) based on the total mass of the lubricating oil composition.

[0044] <Anti-wear agent> The lubricating oil composition of the present invention contains an "anti-wear agent" as an essential component. Such an anti-wear agent must be component (A) and / or component (B) (at least one of component (A) and component (B)). Thus, the anti-wear agent may be at least one of component (A) and component (B), and both may be used in combination depending on the application, but it is preferable that it be either component (A) or component (B) to simplify the design (in other words, it is preferable that the anti-wear agent is either component (A) or component (B)). Component (A) and component (B) will be described separately below.

[0045] <Component (A): Phosphorus-containing abrasion-resistant agent> The component (A) that can be used as the abrasion-resistant agent is at least one phosphorus-containing abrasion-resistant agent selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate esters, phosphate ester compounds, and amine salts of phosphate ester compounds.

[0046] The zinc phosphate (ZP) that can be selected as component (A) is preferably a dialkyl zinc phosphate (zinc salt of dialkyl phosphate). For example, such a dialkyl zinc phosphate is the following formula (1):

[0047]

[0048] [In formula (1), R １ , R ２ , R ３ and R ４ Each of these independently represents an alkyl group. Examples of compounds represented by ] are given.

[0049] R in equation (1) １ , R ２ , R ３ and R ４ The alkyl group that can be selected may be linear or branched. Such alkyl groups may be primary, secondary, or tertiary alkyl groups, but primary alkyl groups are more preferred from the viewpoint of higher solubility in the base oil. Furthermore, such alkyl groups preferably have 1 to 24 carbon atoms (more preferably 2 to 18, even more preferably 3 to 12, and particularly preferably 4 to 8). Setting the carbon number above the lower limit provides an even higher effect in terms of wear resistance, while setting it below the upper limit provides an even higher effect in terms of solubility in the base oil.

[0050] Furthermore, there are no particular limitations on the molybdenum dialkyldithiophosphate that can be selected as component (A), and any known component can be used as appropriate. An example of such molybdenum dialkyldithiophosphate is given by the following formula (2):

[0051]

[0052] [In formula (2), R ５ , R ６ , R ７ and R ８ Each of these independently represents an alkyl group. Compounds represented by ] are preferred.

[0053] R in equation (2) ５ , R ６ , R ７ and R ８ The alkyl group that can be selected may be linear or branched. Such alkyl groups may be primary, secondary, or tertiary alkyl groups, but primary alkyl groups are more preferred from the viewpoint of friction reduction. Furthermore, such alkyl groups preferably have 1 to 30 carbon atoms (more preferably 2 to 30, even more preferably 3 to 30, and particularly preferably 3 to 8). Setting the carbon number above the lower limit provides an even higher effect in terms of wear resistance, while setting it below the upper limit provides an even higher effect in terms of friction reduction.

[0054] The copper dialkyldithiophosphate that can be selected as component (A) can be any known material as appropriate and is not particularly limited, but the following formula (3):

[0055]

[0056] [In formula (3), R ９ and R １０ Each of these independently represents an alkyl group. Compounds represented by ] are preferred.

[0057] R in equation (3) ９ ~R １０The alkyl group that can be selected may be linear or branched. Such alkyl groups may be primary, secondary, or tertiary alkyl groups, but primary alkyl groups are more preferred from the viewpoint of antioxidant properties. Furthermore, such alkyl groups preferably have 2 to 18 carbon atoms (more preferably 3 to 15, and even more preferably 4 to 12). Setting the carbon number above the lower limit provides an even higher effect in terms of wear resistance, while setting it below the upper limit provides an even higher effect in terms of antioxidant properties.

[0058] Such copper dialkyldithiophosphate can be obtained by, for example, employing the method described in Japanese Patent Publication No. 2022-73264. For example, a method for producing such copper dialkyldithiophosphate is R ９ ~R １０ Alcohols having an alkyl group corresponding to (R ９ -OH, R １０ -OH) and phosphorus pentasulfide (P ２ S ５ It can be produced by first synthesizing dialkyldithiophosphate through a reaction with ( ), and then reacting the dialkyldithiophosphate with a copper(II) compound. Examples of such alcohols include 2-ethylhexyl alcohol (C ８ H １７ OH), 2-methyl-1-propanol (C ４ H ９ OH), 2-methyl-1-butanol (C ５ H １１ OH), 1-pentanol (C ５ H １１Examples of copper(II) compounds include copper(II) OH, and one of these may be used alone or in combination of two or more. As the copper(II) compound, for example, copper(II) organic acid salts (for example, copper(II) acetate, etc.) are suitable. When reacting alkyldithiophosphate with the copper(II) compound, it is preferable to allow the reaction to proceed by mixing them in an organic solvent. As such an organic solvent, known organic solvents such as aliphatic hydrocarbons (hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, etc.) and aromatic hydrocarbons (benzene, toluene, xylene, etc.) can be used as appropriate.

[0059] The ashless dithiophosphate ester that can be selected as component (A) is not particularly limited, and known ashless dithiophosphate esters can be used as appropriate. As such ashless dithiophosphate esters, known compounds can be used as appropriate, for example, the "dithiophosphate ester" described in International Publication No. 2020 / 171133 and the "dithiophosphate ester derivative" described in Japanese Patent Application Publication No. 2021-147517 can be suitably used. As such ashless dithiophosphate esters, commercially available products (for example, BASF Japan Ltd., trade name: IRGALUBE 353 (3-(di-isobutoxythiophosphorylsulfanyl)-2-methyl-propionic acid), IRGALUBE 62, etc.) may be used.

[0060] Furthermore, the phosphate ester compound that can be selected as component (A) is not particularly limited, and known compounds used as additives in the field of lubricating oil compositions can be used as appropriate. Note that the term "phosphate ester compound" as used in this invention includes phosphate esters, acidic phosphate esters, and phosphite esters.

[0061] Examples of such phosphate esters include tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyldiphenyl phosphate, xylenyldiphenyl phosphate, and the like.

[0062] Furthermore, examples of the acidic phosphate esters include monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, monooctadecyl acid phosphate, monooleyl acid phosphate, and other mono-phosphates. Examples of dialkyl acid phosphates include alkyl acid phosphates, dibutyl acid phosphate, dipentyl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid phosphate, ditridecyl acid phosphate, ditetradecyl acid phosphate, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate, and dioleyl acid phosphate.

[0063] Furthermore, as the phosphite esters, for example, dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, Examples of such phosphites include triundecyl phosphite, toridodecyl phosphite, trioleyl phosphite, triphenyl phosphite, tricresyl phosphite, monolauryl hydrogen phosphite, monooleyl hydrogen phosphite, monostearyl hydrogen phosphite, monophenyl hydrogen phosphite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite, diheptyl hydrogen phosphite, di-n-octyl hydrogen phosphite, and diethylhexyl hydrogen phosphite. Among these phosphite esters, dialkyl hydrogen phosphites having two alkyl groups are preferred, and dialkyl hydrogen phosphites having two alkyl groups with 4 to 12 carbon atoms are more preferred.

[0064] Among such phosphate ester compounds, from the viewpoint of providing higher wear resistance and stability, phosphite esters are preferred, dialkylhydrogen phosphites having two alkyl groups are more preferred, and dialkylhydrogen phosphites having two alkyl groups with 4 to 12 carbon atoms are even more preferred.

[0065] Furthermore, the amine salt of the phosphate ester compound that can be selected as component (A) is not particularly limited, and known salts can be used. As such an amine salt of a phosphate ester compound, a salt obtained by reacting an amine compound with a phosphate ester compound that contains acidic hydrogen (such as a monophosphate ester or diphosphate ester) to neutralize some or all of the remaining acidic hydrogen (a salt of the phosphate ester compound and the amine compound (reaction product)) can be suitably used. For example, the reaction product of the acidic phosphate ester and the amine compound can be cited.

[0066] Suitable amine compounds include monoalkylamines, dialkylamines, and trialkylamines. Examples of such amine compounds include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine, oleylamine, tetracosylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditri Examples include decylamine, ditetradecylamine, dipentadecylamine, dihexadecylamine, diheptadecylamine, dioctadecylamine, dioleylamine, ditetracosylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, tridodecylamine, tritridecylamine, tritetradecylamine, tripentadecylamine, trihexadecylamine, triheptadecylamine, trioctadecylamine, trioleylamine, and tritetracosylamine.

[0067] Furthermore, when forming the amine salt of the phosphate ester compound, one amine compound may be used alone, or two or more may be used in combination. Also, when forming the amine salt, one phosphate ester compound (preferably an acidic phosphate ester) may be used alone, or two or more may be used in combination.

[0068] In the present invention, the "phosphorus-containing wear-resistant agent" of component (A), which can be used as an wear-resistant agent, may be at least one selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate ester, phosphate ester compound, and amine salt of a phosphate ester compound, and is not particularly limited. One of these may be used alone, or two or more may be used in combination.

[0069] Furthermore, in the present invention, when component (A) is used as an anti-wear agent, the phosphorus content of component (A) based on the total mass of the lubricating oil composition (in other words, the phosphorus content derived from component (A) in the lubricating oil composition) must be 100 ppm by mass or more and 3000 ppm by mass or less. By keeping the phosphorus content of component (A) within the above range, it is possible to achieve high wear resistance while highly suppressing the generation of gel when the composition is used. Also, from the same viewpoint, a higher effect can be obtained, so it is preferable that the phosphorus content of component (A) is 400 ppm by mass or more and 2000 ppm by mass or less (more preferably 400 ppm by mass or more and 1500 ppm by mass or less) based on the total mass of the lubricating oil composition. Furthermore, the "phosphate content of component (A) in terms of the total mass of the lubricating oil composition" is synonymous with the phosphate content in the lubricating oil composition when component (A) is the only component containing phosphate present in the composition. Therefore, the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116 is adopted.

[0070] Furthermore, the content of component (A) is preferably 0.1% by mass or more and 6% by mass or less (more preferably 0.1% by mass or more and 4% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less) based on the total mass of the lubricating oil composition. By keeping the content of component (A) within the above range, it becomes possible to efficiently adjust the content of component (A) in terms of phosphorus element to the above range.

[0071] <Component (B): Phosphorus-free wear-resistant agent> The component (B) that can be used as the wear-resistant agent is a phosphorus-free wear-resistant agent which is molybdenum dithiocarbamate.

[0072] Such molybdenum dithiocarbamates can be, for example, any known ones used as friction modifiers in the field of lubricating oil compositions, and are not particularly limited, but for example, the following general formula (4):

[0073]

[0074] [In formula (4), R １１ , R １２ , R １３ and R １４ These may be the same or different, and each represents a hydrocarbon group (more preferably an alkyl group having 2 to 24 carbon atoms (even more preferably 4 to 13 carbon atoms) or an aryl group having 6 to 24 carbon atoms (even more preferably 8 to 15 carbon atoms) (including alkylaryl groups)). The alkyl group referred to here includes primary alkyl groups, secondary alkyl groups, and tertiary alkyl groups, and these alkyl groups may be linear or branched. Also, X １ , X ２ , X ３ and X ４ The atoms may be the same or different, and each represents either a sulfur atom or an oxygen atom. Compounds represented by [ ] can be suitably used.

[0075] R in equation (4) １１ , R １２ , R １３ and R １４Examples of the alkyl group that can be selected include an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and the like. These may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, and may be linear or branched.

[0076] R in formula (4) １１ , R １２ , R １３ and R １４ Examples of the aryl group (including an alkylaryl group) that can be selected include a phenyl group, a tolyl group, an ethylphenyl group, a propylphenyl group, a butylphenyl group, a pentylphenyl group, a hexylphenyl group, an octylphenyl group, a nonylphenyl group, a decylphenyl group, an undecylphenyl group, a dodecylphenyl group, and the like. When the aryl group is an alkylaryl group, the alkyl group may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, and may be linear or branched. Furthermore, the "alkylaryl group" herein includes all substitution isomers having different substitution positions of the alkyl group with respect to the aryl group.

[0077] X in formula (4) １ may be a sulfur atom or an oxygen atom, and is not particularly limited, but from the viewpoint of improving the wear resistance, a sulfur atom is more preferable. Also, X in formula (4) ２ may be a sulfur atom or an oxygen atom, and is not particularly limited, but from the viewpoint of improving the wear resistance, a sulfur atom is more preferable. Furthermore, X in formula (4) ３ may be a sulfur atom or an oxygen atom, and is not particularly limited, but from the viewpoint of improving the wear resistance, a sulfur atom is more preferable. Also, X in formula (4) ４ may be a sulfur atom or an oxygen atom, and is not particularly limited, but from the viewpoint of improving the wear resistance, a sulfur atom is more preferable.

[0078] Examples of such molybdenum dithiocarbamates include molybdenum diethyl dithiocarbamate sulfide, molybdenum dipropyl dithiocarbamate sulfide, molybdenum dibutyl dithiocarbamate sulfide, molybdenum dipentyl dithiocarbamate sulfide, molybdenum dihexyl dithiocarbamate sulfide, molybdenum dioctyl dithiocarbamate sulfide, molybdenum didecyl dithiocarbamate sulfide, molybdenum didodecyl dithiocarbamate sulfide, molybdenum di(butylphenyl) dithiocarbamate sulfide, molybdenum di(nonylphenyl) dithiocarbamate sulfide, and oxymolybdenum diethyl dithiocarbamate sulfide. Suitable examples include dithiocarbamates, oxymolybdenum dipropyl dithiocarbamate, oxymolybdenum dibutyl dithiocarbamate, oxymolybdenum dipentyl dithiocarbamate, oxymolybdenum dihexyl dithiocarbamate, oxymolybdenum dioctyl dithiocarbamate, oxymolybdenum didecyl dithiocarbamate, oxymolybdenum didecyl dithiocarbamate, oxymolybdenum di(butylphenyl) dithiocarbamate, oxymolybdenum di(nonylphenyl) dithiocarbamate, and mixtures thereof. Furthermore, in the present invention, a trinuclear molybdenum compound described in U.S. Patent No. 5,906,968 may be used as the molybdenum dithiocarbamate.

[0079] Among these molybdenum dithiocarbamates, sulfurized oxymolybdenum dithiocarbamate is more preferred from the viewpoint of obtaining higher solubility and a more advanced friction reduction effect, and among these, sulfurized oxymolybdenum dithiocarbamate having an alkyl chain length of 6 to 20 (more preferably 8 to 14) of hydrocarbon groups contained in the molecule is even more preferred.

[0080] Furthermore, when component (B) is used as an anti-wear agent in the present invention, the molybdenum content of component (B) based on the total mass of the lubricating oil composition (in other words, the molybdenum content derived from component (B) in the lubricating oil composition) must be 100 ppm by mass or more and 2000 ppm by mass or less. By keeping the molybdenum content of component (B) within the above range, it is possible to achieve high wear resistance while highly preventing the formation of gel when the composition is used. Also, from the perspective of obtaining a higher effect in the same respect, and obtaining an even higher effect in terms of friction reduction, etc., it is preferable that the molybdenum content of component (B) is 100 ppm by mass or more and 2000 ppm by mass or less (more preferably 200 ppm by mass or more and 1000 ppm by mass or less) based on the total mass of the lubricating oil composition. Furthermore, the "molybdenum content of component (B) in terms of the total mass of the lubricating oil composition" is synonymous with the molybdenum content in the lubricating oil composition when component (B) is the only component containing molybdenum present in the composition. Therefore, the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116 is adopted.

[0081] Furthermore, the content of component (B) is preferably 0.15% by mass or more and 6% by mass or less (more preferably 0.2% by mass or more and 5% by mass or less, and even more preferably 0.24% by mass or more and 2.5% by mass or less) based on the total mass of the lubricating oil composition. By keeping the content of component (B) within the above range, it becomes possible to efficiently adjust the content of component (B) in terms of molybdenum element to the above range.

[0082] <Regarding other additives, etc.> The lubricating oil composition of the present invention preferably does not contain zinc dialkyldithiophosphate (so-called ZnDTP), which is suitably used as an anti-wear agent in conventional lubricating oil compositions. This is because if zinc dialkyldithiophosphate (particularly zinc dialkyldithiophosphate having an alkyl group with 8 or more carbon atoms), which has been conventionally and suitably used as an anti-wear agent, is used in place of the anti-wear agent according to the present invention (component (A) or component (B)), it may become impossible to prevent the formation of gel in the composition, and it may become difficult to prevent the formation of gel during use. The present inventors have found through research that gel may form when ZnDTP is simply used as an anti-wear agent, and from the viewpoint of solving such a problem, the present invention proposes using the anti-wear agent, which is component (A) and / or component (B), instead of ZnDTP (using at least one of components (A) and (B) so as to satisfy the conditions of a specific content).

[0083] The term "zinc dialkyldithiophosphate" used herein can refer to known zinc dialkyldithiophosphates, which are commonly known as anti-wear agents, for example, the following general formula (5):

[0084]

[0085] [In formula (5), R ａ ~R ｄ Each of these independently represents an alkyl group (preferably a linear or branched alkyl group having 1 to 24 carbon atoms). Examples of compounds represented by ] include:

[0086] Furthermore, the lubricating oil composition of the present invention may contain the lubricating oil base oil and the anti-wear agent, and may appropriately contain other known additives used in the field of lubricating oil compositions (except for the aforementioned ZnDTP) to the extent that it does not impair the effects of the present invention. As such other additives, for example, various additives described in International Publication No. 2013 / 147162, International Publication No. 2017 / 073748, Japanese Patent Publication No. 2018-177875, Japanese Patent Publication No. 2020-76004, International Publication No. 2020 / 095969, International Publication No. 2020 / 095970, Japanese Patent Publication No. 2022-158121, Japanese Patent Publication No. 2022-158124, Japanese Patent Publication No. 2022-090378, etc. (except for the aforementioned zinc dialkyldithiophosphate) can be appropriately used.

[0087] Other additives, though not particularly limited, include metal-based detergents, ashless dispersants, antioxidants, metal deactivators, anti-emulsifiers, rust inhibitors, defoamers, friction modifiers such as dithiocarbamite (ZnDTC) and glycerol monooleate (GMO), and amine-based friction modifiers (oleylamine, oleylamine ethylene oxide adduct, oleylamide, etc.).

[0088] Furthermore, among the other additives mentioned above, the lubricating oil composition of the present invention preferably further contains a metal-based detergent from the viewpoint of improving engine cleanliness. Such a metal-based detergent is not particularly limited, and known metal-based detergents such as alkali or alkaline earth metal alkyl salicylates, alkali or alkaline earth metal alkylbenzene sulfonates, and alkali or alkaline earth metal alkylphenates can be used as appropriate. Sodium or potassium is preferred as the alkali metal, and calcium or magnesium is preferred as the alkaline earth metal. In addition, the metal-based detergent may be over-basified with a carbonate (for example, alkali metal carbonates such as sodium carbonate or potassium carbonate, or alkaline earth metal carbonates such as calcium carbonate or magnesium carbonate), or it may be over-basified with a borate (for example, alkali metal borates such as sodium borate or potassium borate, or alkaline earth metal borates such as calcium borate or magnesium borate).

[0089] Furthermore, calcium sulfonate detergents, calcium salicylate detergents, and calcium phenate detergents are preferred as the metal-based detergents. These calcium sulfonate detergents, calcium salicylate detergents, and calcium phenate detergents may be neutral or overbasic from the viewpoint of improving their cleaning ability, and are not particularly limited in this respect. However, from the viewpoint of improving the neutralization of acidic components, they are preferably overbasicated with calcium carbonate. Thus, the metal-based detergents are preferably overbasic calcium sulfonate detergents, overbasic calcium salicylate detergents, and overbasic calcium phenate detergents. Herein, "overbasic" means that the base number (perchloric acid method) is 60 mg KOH / g or higher.

[0090] Furthermore, the base number (perchloric acid method) of such metal-based detergents can be appropriately determined according to the application of the lubricating oil composition and is not particularly limited, but is preferably 60 mg KOH / g or more and 1000 mg KOH / g or less, more preferably 100 mg KOH / g or more and 500 mg KOH / g or less, and even more preferably 150 mg KOH / g or more and 400 mg KOH / g or less. In this specification, "base number (perchloric acid method)" refers to the value measured according to JIS K 2501:2003, item 9. Such metal-based detergents may be used individually or in combination of two or more types.

[0091] Furthermore, the content of such metal-based detergents is preferably 0.1% by mass or more and 70% by mass or less (more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 40% by mass or less) based on the total mass of the lubricating oil composition. Moreover, when the metal-based detergent is a calcium sulfonate detergent, a calcium salicylate detergent, or a calcium phenate detergent, the content of such metal-based detergents in terms of calcium element is preferably 500 ppm by mass or more and 80,000 ppm by mass or less (even more preferably 1,000 ppm by mass or more and 75,000 ppm by mass or less) based on the total mass of the lubricating oil composition. Setting the content above the lower limit tends to yield an even higher effect in terms of improving the neutralization of acidic components, while setting it below the upper limit tends to yield an even higher effect in terms of suppressing piston deposits. Furthermore, this "calcium element content" refers to the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116.

[0092] Furthermore, when the lubricating oil composition is used as hydraulic fluid or system oil for a mechanism in an ammonia fuel internal combustion engine, it is preferable that the content of the metal-based detergent be 0.1% by mass or more and 20% by mass or less (more preferably 0.5% by mass or more and 15% by mass or less). When the composition is used as trunk piston engine oil (TPEO), it is preferable that the content of the metal-based detergent be 1% by mass or more and 35% by mass or less (more preferably 2% by mass or more and 30% by mass or less). Furthermore, when the composition is used as cylinder oil, it is preferable that the content of the metal-based detergent be 1% by mass or more and 70% by mass or less (more preferably 2% by mass or more and 60% by mass or less).

[0093] Furthermore, the lubricating oil composition of the present invention preferably further contains an ashless dispersant among the other additives mentioned above. The ashless dispersant is not particularly limited, but for example, succinic acid-based ashless dispersants can be suitably used. Suitable succinic acid-based ashless dispersants include, for example, alkyl succinic acid, alkenyl succinic acid and their ester compounds; succinimide and its derivatives; and the like. Among such succinic acid-based ashless dispersants, for example, succinimide and its derivatives (succinimide-based ashless dispersants) can be suitably used. Suitable succinimide-based ashless dispersants include, specifically, non-boronated succinimide, boronated succinimide (boron-modified succinimide compounds), and mixtures thereof. Suitable succinimide-based ashless dispersants include succinimides and their derivatives having hydrocarbon groups with 40 to 400 carbon atoms (e.g., alkyl groups, alkenyl groups). For such non-boronated succinimides, boronated succinimides, or mixtures thereof, a nitrogen atom content of 0.5 to 4.8% by mass (more preferably 1.0 to 3.0% by mass, and even more preferably 1.2 to 2.4% by mass) is preferred. The ashless dispersants may be used individually or in combination of two or more types.

[0094] Further, the content of such an ashless dispersant is preferably 0.1% by mass or more and 25% by mass or less (more preferably 0.5% by mass or more and 20% by mass or less, still more preferably 0.8% by mass or more and 15% by mass or less) based on the total mass of the lubricating oil composition. Further, when the ashless dispersant is a succinimide-based ashless dispersant, the content of such a succinimide-based ashless dispersant in terms of nitrogen element is preferably 10 ppm by mass or more and 6000 ppm by mass or less (still more preferably 50 ppm by mass or more and 3000 ppm by mass or less) based on the total mass of the lubricating oil composition. By setting such a content to be not less than the lower limit, a higher effect can be obtained in terms of the dispersibility of combustion residue and degraded products. On the other hand, by setting it to be not more than the upper limit, a higher effect can be obtained in terms of fuel economy. The content of such an ashless dispersant (succinimide-based ashless dispersant) in terms of nitrogen element can be obtained by calculating based on the addition amount of the ashless dispersant and the content (ratio) of nitrogen to the total amount of the constituent elements of the ashless dispersant.

[0095] Further, among the other additives, the lubricating oil composition of the present invention preferably further contains an antioxidant. As such an antioxidant, components known in the field of lubricating oil compositions can be appropriately used and are not particularly limited, and examples thereof include diphenylamine, naphthylamine, phenolic antioxidants, and the like. Further, the content of such an antioxidant is preferably 0.01% by mass or more and 3% by mass or less (more preferably 0.1% by mass or more and 2% by mass or less, still more preferably 0.2% by mass or more and 1% by mass or less) based on the total mass of the lubricating oil composition.

[0096] <Regarding suitable conditions for characteristics of the composition, etc.> The lubricating oil composition of the present invention has a kinematic viscosity at 40°C of 12.5 mm ２ / s or more and 750 mm ２ / s or less (more preferably 30 mm ２ / s or more and 750 mm ２ / s or less, still more preferably 35 mm ２ / s or more and 700 mm ２ / s or less, particularly preferably 40 mm <​​It is preferable that the kinematic viscosity of the composition at 40°C is less than or equal to the upper limit. By setting the kinematic viscosity of the composition at 40°C to less than or equal to the upper limit, it is possible to further improve fuel efficiency. Furthermore, by setting the kinematic viscosity of the composition at 40°C to or greater than the lower limit, it is possible to achieve a high degree of oil film formation, thereby increasing its reliability as a lubricant.

[0097] Furthermore, the kinematic viscosity of the lubricating oil composition of the present invention at 40°C is 12.5 mm when the composition is used as a hydraulic fluid or system oil for a mechanism in an ammonia fuel internal combustion engine. ２ / s or more 165mm ２ / s or less (more preferably 20 mm) ２ / s or more 117mm ２ It is preferable to have a ratio of 0 / s or less, and when the composition is used as trunk piston engine oil (TPEO), it should be 20 mm ２ / s or more 220mm ２ / s or less (more preferably 30 mm) ２ / s or more 190mm ２ It is preferable to have a ratio of 0 / s or less, and furthermore, when the composition is used as cylinder oil, it should be 125 mm ２ / s or more 750mm ２ / s or less (more preferably 190 mm) ２ / s or more 295mm ２ It is preferable to set it to / s or less.

[0098] Furthermore, the lubricating oil composition of the present invention has a kinematic viscosity of 3.0 mm at 100°C. ２ / s or more 40.0mm ２ / s or less (more preferably 7.0 mm) ２ / s or more 40.0mm ２ / s or less, more preferably 8.0 mm ２ / s or more 35.0mm ２ / s or less, particularly preferably 9.3 mm ２ / s or more 30.0mm ２It is preferable that the kinematic viscosity of the composition at 100°C is less than or equal to the upper limit. By setting the kinematic viscosity of the composition at 100°C to less than or equal to the upper limit, it is possible to further improve fuel efficiency. Furthermore, by setting the kinematic viscosity of the composition at 100°C to more than or equal to the lower limit, it is possible to achieve a high degree of oil film formation, thereby increasing its reliability as a lubricant.

[0099] The kinematic viscosity of the lubricating oil composition of the present invention at 100°C is 3 mm when the composition is used as a hydraulic fluid or system oil for a mechanism in an ammonia fuel internal combustion engine. ２ / s or more 15mm ２ / s or less (more preferably 4 mm) ２ / s or more 12mm ２ It is preferable to have a ratio of 0 / s or less, and when the composition is used as trunk piston engine oil (TPEO), 4 mm ２ / s or more 18mm ２ / s or less (more preferably 5 mm) ２ / s or more 16.3mm ２ It is preferable to have a ratio of 0 / s or less, and furthermore, when the composition is used as cylinder oil, it should be 12.5 mm. ２ / s or more 40mm ２ / s or less (more preferably 16.3 mm) ２ / s or more 21.9mm ２ It is preferable to set it to / s or less.

[0100] The lubricating oil composition of the present invention preferably has a viscosity index of 90 or higher (more preferably 95 or higher, and even more preferably 100 or higher). By setting the viscosity index of the composition to be above the lower limit, it is possible to achieve a higher level of fuel efficiency.

[0101] Furthermore, the lubricating oil composition of the present invention preferably has a base number (perchloric acid method) of 0 mg KOH / g or more and 300 mg KOH / g or less (more preferably 5 mg KOH / g or more and 200 mg KOH / g or less, and even more preferably 7 mg KOH / g or more and 150 mg KOH / g or less). Setting the base number (perchloric acid method) above the lower limit tends to yield an even higher effect in terms of neutralization of acidic components, while setting it below the upper limit tends to yield an even higher effect in terms of suppressing piston deposits.

[0102] Furthermore, the method for producing the lubricating oil composition of the present invention is not particularly limited. For example, a method can be employed in which each component to be included is appropriately selected and mixed so as to satisfy the above conditions, thereby producing the lubricating oil composition of the present invention.

[0103] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0104] [Regarding the components used in each example] First, the components of the base oil, etc., used in each example and their abbreviations are shown below. In the table of examples shown below, each component will be expressed using the abbreviations listed below (base oil (1) to (3), ZP (1) to (2), etc.).

[0105] [Lubricating oil base oil] ・Base oil (1): Mineral oil-based base oil [Hydrogenated refined base oil, API Group I base oil, kinematic viscosity at 40°C: 97.5 mm] ２ kinematic viscosity at 100°C (k / s): 10.9 mm² ２ / s, viscosity index: 96, sulfur content in base oil (sulfur content in base oil): 0.32% by mass, manufactured by ENEOS Corporation, product name: Super Oil M100] ・Base oil (2): mineral oil-based base oil [hydrogenated refined base oil, API Group I base oil, kinematic viscosity at 40°C: 110.6 mm] ２ kinematic viscosity at 100°C (k / s): 11.9 mm² ２ / s, viscosity index: 95, sulfur content in base oil (sulfur content in base oil): 0.58 mass%, manufactured by ExxonMobil, product name: AP / E CORE600] • Base oil (3): Mineral oil-based base oil [hydrogenated refined base oil, API Group I base oil, kinematic viscosity at 40°C: 155.6 mm] ２ kinematic viscosity at 100°C ( / s): 15.01 mm² ２ [Fluid: / s, Viscosity index: 96, Sulfur content in base oil: 0.80% by mass, Manufactured by ENEOS Corporation, Product name: Super Oil K170].

[0106] [Anti-wear agent] <Phosphorus-containing anti-wear agent: component (A)> <Zinc phosphate> ・ZP(1) [Zinc phosphate (dialkyl zinc phosphate), manufactured by Johoku Chemical Industry Co., Ltd., product name: DBP-Zn-50L, alkyl group: butyl group, phosphorus element content: 6.5% by mass, zinc element content: 6.6% by mass, acid value: 5.2] ・ZP(2) [Zinc phosphate (dialkyl zinc phosphate), manufactured by Johoku Chemical Industry Co., Ltd., product name: DHP-Zn50L, alkyl group: hexyl group, phosphorus element content: 5.3% by mass, zinc element content: 5.3% by mass, acid value: 1.9].

[0107] <Molybdenum dialkyldithiophosphate> ・MoDTP(1) [Molybdenum dialkyldithiophosphate, manufactured by ADEKA Corporation, product name: Sakura Lube 300, alkyl group: C8 (carbon 8) alkyl group (primary alkyl group), phosphorus element content: 3.4 mass%, molybdenum element content: 9.1 mass%, sulfur element content: 9.7 mass%] ・MoDTP(2) [Molybdenum dialkyldithiophosphate, manufactured by Vanderbilt Chemicals, product name: MOLYVAN L, alkyl group: C8 alkyl group (primary alkyl group), phosphorus element content: 6.3 mass%, molybdenum element content: 8.8 mass%, sulfur element content: 13.3 mass%].

[0108] <Copper Dialkyldithiophosphate> ・CuDTP(1) [Copper dialkyldithiophosphate, compound obtained by the method described in Synthesis Example 1 below, alkyl groups contained in the total synthesized compound: C4 alkyl group (primary alkyl group) and C5 alkyl group (primary alkyl group), phosphorus element content: 9.5% by mass, sulfur element content: 20% by mass] (Synthesis Example 1: Method for producing CuDTP(1)) First, phosphorus pentasulfide (P ２ S ５ ) 0.1 mol and; 2-methyl-1-propanol (C ４ H ９ OH) 0.32 mol, 2-methyl-1-butanol (C ５ H １１ OH) 0.04 mol and 1-pentanol (C) ５ H １１ An alcohol consisting of 0.04 mol of OH was introduced into a flask to obtain a mixture. This mixture was then stirred at 70°C for 15 hours to obtain approximately 0.2 mol of chemically mixed dialkyldithiophosphate as a reaction product. Next, 0.1 mol of the obtained dialkyldithiophosphate was introduced into a beaker, and 150 mL of hexane was added to the beaker to dissolve the dialkyldithiophosphate in the hexane, thereby preparing a solution of dialkyldithiophosphate. Separately, 0.05 mol of copper(II) acetate was dissolved in 150 mL of water to prepare an aqueous solution of copper(II) acetate. Then, the aqueous solution of copper(II) acetate was added to the solution of dialkyldithiophosphate and stirred at 70°C for 1 hour to obtain a two-layer liquid separated into a hexane layer and an aqueous layer. Next, the hexane layer and the aqueous layer were separated from the two-layer liquid obtained in this way using a separatory funnel. Subsequently, the obtained hexane layer was washed twice with 150 mL of water, and the hexane was removed by distillation using an evaporator to obtain the target product, copper dialkyldithiophosphate. It is clear from the method of production that this copper dialkyldithiophosphate is the compound represented by formula (3). Here, R in formula (3) ９ and R １０It is clear from the type of raw material (alcohol) used that each of these groups can independently become one of the following groups: 2-methyl-1-propyl group, 2-methyl-1-butyl group, and pentyl group.

[0109] • CuDTP(2) [copper dialkyldithiophosphate, compound obtained by the method described in Synthesis Example 2 below, alkyl group: C8 alkyl group (primary alkyl group), phosphorus element content: 7.4% by mass, sulfur element content: 17.8% by mass] (Synthesis Example 2: Method for producing CuDTP(2)) First, phosphorus pentasulfide (P ２ S ５ ) 0.1 mol and 2-ethylhexyl alcohol (C ８ H １７ 0.4 mol of OH) was introduced into a flask to obtain a mixture. The mixture was then stirred at 70°C for 15 hours to obtain approximately 0.2 mol of di-2-ethylhexyldithiophosphate as a reaction product. Next, 0.1 mol of di-2-ethylhexyldithiophosphate was introduced into a beaker, and 150 mL of hexane was added to the beaker to dissolve the dialkyldithiophosphate in the hexane, thereby preparing a solution of dialkyldithiophosphate. Separately, 0.05 mol of copper(II) acetate was dissolved in 150 mL of water to prepare an aqueous solution of copper(II) acetate. Then, the aqueous solution of copper(II) acetate was added to the solution of dialkyldithiophosphate and stirred at 70°C for 1 hour to obtain a two-layered liquid separated into a hexane layer and an aqueous layer. Next, the hexane layer and the aqueous layer were separated from the two-layered liquid obtained in this way using a separatory funnel. Subsequently, the obtained hexane layer was washed twice with 150 mL of water, and the hexane was removed by distillation using an evaporator to obtain the target product, copper dialkyldithiophosphate. This copper dialkyldithiophosphate, based on its manufacturing method (raw materials used, etc.), is represented by formula (3) and R ９ and R １０ It is clear that all of these are compounds that are C8 alkyl groups.

[0110] <Ashless dithiophosphate ester> Ashless DTP [3-(di-isobutoxythiophosphorylsulfanil)-2-methylpropionic acid, manufactured by BASF Japan Ltd., product name: IRGALUBE 353, phosphorus content: 9% by mass, sulfur content: 19.4% by mass, acid value: 161].

[0111] <Phosphate ester compounds> • Phosphite ester [di-2-ethylhexyl hydrozen phosphite, manufactured by Osaki Industries Co., Ltd., product name: Chelex H-8, alkyl group: C8 alkyl group (primary alkyl group), phosphorus element content: 10% by mass, acid value: 2.3].

[0112] <Amine salts of phosphate ester compounds> - Amine salt of phosphate ester [reaction product of acidic phosphate ester (a mixture of 2-ethylhexyl acid phosphate C8 monoester and C8 diester, Osaki Industries Co., Ltd., product name: Phoslex A-8) and oleylamine, phosphorus element content: 5.7% by mass, acid value: 162].

[0113] <Phosphorus-free anti-wear agent: component (B)> MoDTC [Molybdenum dithiocarbamate, manufactured by ADEKA Corporation, product name: Sakura Lube 100, alkyl group: C8 alkyl group (primary alkyl group), molybdenum element content: 4.2% by mass].

[0114] [Comparative wear-resistant agent] ZnDTP [represented by the above formula (5) and R in the formula] ａ ~R ｄ Compounds in which all are primary alkyl groups having 8 carbon atoms, manufactured by Chevron Japan Co., Ltd., product name: OLOA269RJ.

[0115] [Metal-based cleaning agents] ・Metal-based cleaning agent (1) [Perbasic calcium salicylate, manufactured by Osca Chemical Co., Ltd., product name: OSCA463, base number (perchloric acid method): 170 mg KOH / g, calcium element content: 6.3% by mass] ・Metal-based cleaning agent (2) [Perbasic calcium salicylate, manufactured by Osca Chemical Co., Ltd., product name: OSCA438B, base number (perchloric acid method): 320 mg KOH / g, calcium element content: 11.4% by mass] ・Metal-based cleaning agent (3) [Perbasic calcium phenate, manufactured by Chevron Japan Co., Ltd., product name: OLOA219, base number (perchloric acid method): 250 mg KOH / g, calcium element content: 9.25% by mass] - Metal-based cleaning agent (4) [Perbasic calcium sulfonate, manufactured by Lubrizol Japan Co., Ltd., product name: Lubrizol 6446, base number (perchloric acid method): 400 mg KOH / g, calcium element content: 9.25% by mass].

[0116] [Ashless Dispersant] Succinimide-based ashless dispersant [Borated polybutenyl succinimide (boron-modified compound of polybutenyl succinimide), manufactured by Chevron Japan Co., Ltd., product name: OLOA5096, base number (perchloric acid method): 32 mg KOH / g, nitrogen element content: 1.5% by mass, boron content: 0.5% by mass].

[0117] [Antioxidant] Antioxidant [Diphenylamine, manufactured by BASF Japan Ltd., product name: IRGANOX L57].

[0118] [Regarding lubricating oil compositions for ammonia fuel internal combustion engines containing phosphorus-containing anti-wear agents] (Examples 1 to 27 and Comparative Examples 1 to 19) Lubricating oil compositions were prepared by mixing the above-mentioned components to obtain the compositions shown in Tables 1 to 3.

[0119] In Tables 1 to 13, a blank space in the "Composition" column indicates that the component was not used. Furthermore, in the "Composition" column in the tables below, "mass%" represents the mass-based content (mass%) of the lubricating oil composition. In each example and comparative example, the lubricating oil base oil and additives were used so that the total amount of the lubricating oil base oil and additives was 100 mass% (mass%). Also, in the "Composition" column of Tables 1 to 13, "Base Number (Perchloric Acid Method)" indicates the value obtained by measuring the composition in accordance with JIS K 2501:2003, Section 9. Furthermore, in the "Composition" section of Tables 1 to 13, "Content of nitrogen element derived from ashless dispersant" represents the content of nitrogen element in the ashless dispersant on a mass basis relative to the total amount of the lubricating oil composition (content of ashless dispersant in the lubricating oil composition in terms of nitrogen element, unit: mass ppm), and "Content of phosphorus element" represents the content of phosphorus element on a mass basis relative to the total amount of the lubricating oil composition (unit: mass ppm). The "Content of phosphorus element" is the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116, and the "Content of nitrogen element derived from ashless dispersant" is the value obtained by calculation based on the amount of ashless dispersant added and the nitrogen content (ratio) relative to the total amount of constituent elements of the ashless dispersant. In addition, in the compositions shown in Tables 1 to 13, the only component containing phosphorus element is the phosphorus-containing anti-wear agent, so the "Content of phosphorus element" for each composition is synonymous with the phosphorus-containing anti-wear agent's phosphorus-equivalent content.

[0120] <Evaluation Test of Lubricating Oil Compositions Obtained in Examples 1-27 and Comparative Examples 1-19> <Observation of the Appearance of the Composition After the Ammonia Injection Test (Confirmation Test for the Presence or Absence of Gel Formation)> 200 g of the lubricating oil composition was placed in a 500 mL four-necked flask, and the opening of a gas injection nozzle was placed in the composition. Then, ammonia gas was injected through the nozzle into the composition with the nozzle opening introduced into the liquid at room temperature (approximately 25°C) for 90 minutes. The amount of ammonia injected in this manner was 37 L per 200 g of lubricating oil composition over 90 minutes. After the ammonia injection test (ammonia injection test) was performed in this manner, the appearance of the lubricating oil composition was visually observed to confirm whether or not gel formation occurred in the lubricating oil composition. As a result of this appearance observation, lubricating oil compositions in which gel formation was confirmed after the ammonia injection test were evaluated as "present," and lubricating oil compositions in which gel formation was not confirmed were evaluated as "absent." The results are shown in Tables 1-3.

[0121] <High-Speed ​​Four-Ball Test> The wear resistance of each lubricating oil composition was evaluated by a high-speed four-ball test in accordance with ASTM D4172-94. The test conditions for the high-speed four-ball test were as follows: SUJ2 was used as the rigid ball, rotation speed 1800 rpm, load 294 N, test temperature (composition temperature) 80°C, and test time 30 minutes. The average value (unit: mm) of the wear mark diameter of the fixed ball was measured. The obtained average values ​​are shown in Tables 1 to 3 as wear mark diameter (unit: mm) (however, the wear resistance was not specifically evaluated for compositions in which gel formation occurred in the aforementioned gel formation confirmation test). In this test, the smaller the wear mark diameter measured, the better the wear resistance, and in particular, if it is 0.7 mm or less, it can be evaluated as having a high level of wear resistance.

[0122]

[0123]

[0124]

[0125] As is clear from the results shown in Tables 1 to 3, the lubricating oil compositions obtained in Examples 1 to 27, which contain a base oil and a phosphorus-containing anti-wear agent and have a phosphorus element content (corresponding to the phosphorus element content of the phosphorus-containing anti-wear agent relative to the total amount of the composition) of 100 ppm by mass or more and 3000 ppm by mass or less, all showed no gel formation after the ammonia injection test, and the wear mark diameter in the high-speed four-ball test was 0.48 mm or more and 0.60 mm or less, confirming that they possess a high level of excellent wear resistance. From these results, it was found that the lubricating oil compositions obtained in Examples 1 to 27 are suitable for use in lubricating internal combustion engines that use ammonia as fuel.

[0126] In contrast, the lubricating oil compositions obtained in Comparative Examples 1, 3, 5, 7, 9, 11, 13, 15, and 17, which contained 50 ppm by mass (less than 100 ppm by mass) of phosphorus (converted to phosphorus content in the phosphorus-containing anti-wear agent), all showed wear marks of 1.2 mm in the high-speed four-ball test, indicating insufficient wear resistance. Furthermore, the lubricating oil compositions obtained in Comparative Examples 2, 4, 6, 8, 10, 12, 14, 16, and 18, which contained 4000 ppm by mass (converted to 3000 ppm by mass) of phosphorus (converted to phosphorus content in the phosphorus-containing anti-wear agent), all showed wear marks of 1.0 mm or more in the high-speed four-ball test, indicating insufficient wear resistance. It should be noted that the lubricating oil compositions obtained in Comparative Examples 1 to 18, which utilized a specific phosphorus-containing anti-wear agent, were confirmed not to produce gel after the ammonia injection test.

[0127] Furthermore, in Comparative Example 19, which used zinc dialkyldithiophosphate having a C8 alkyl group as a comparative anti-wear agent instead of the phosphorus-containing anti-wear agent, the lubricating oil composition obtained showed gel formation after the ammonia injection test, indicating that it is unsuitable for lubricating internal combustion engines that use ammonia as fuel.

[0128] These results confirm that no gel formation occurred after the ammonia injection test in the system composition utilizing the phosphorus-containing abrasion resistant agent. Furthermore, it was confirmed that by setting the phosphorus content of the phosphorus-containing abrasion resistant agent to between 100 ppm by mass and 3000 ppm by mass, it is possible to achieve excellent abrasion resistance.

[0129] Furthermore, the phosphorus-containing abrasion-resistant agents used in Tables 1 to 3, regardless of their type, all exhibited similarly high levels of excellent abrasion resistance when their phosphorus content (in terms of elemental phosphorus) was between 100 ppm and 3000 ppm by mass. Therefore, it is clear that excellent abrasion resistance is exhibited when the elemental phosphorus content falls within the aforementioned range.

[0130] (Examples 28-163 and Comparative Examples 20-45) Lubricating oil compositions were prepared by mixing the aforementioned components to obtain the compositions shown in Tables 4-13.

[0131] Furthermore, the lubricating oil compositions obtained in Examples 28 to 163 and Comparative Examples 20 to 45 were used to check for the presence or absence of gel formation in the lubricating oil compositions, using the same method as employed in the "Visual Observation of Compositions After Ammonia Injection Test (Confirmation Test for Presence or Absence of Gel Formation)" described above. The results are shown in Tables 4 to 13, respectively.

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142] As is clear from the results shown in Tables 4 to 13, the lubricating oil compositions obtained in Examples 28 to 163, which contain a base oil and a phosphorus-containing anti-wear agent and have a phosphorus content (corresponding to the phosphorus content of the phosphorus-containing anti-wear agent relative to the total amount of the composition) of 100 ppm by mass or more and 3000 ppm by mass or less, all showed no gel formation after the ammonia injection test. Furthermore, considering the results shown in Tables 1 to 3 together, it is clear that the lubricating oil compositions obtained in Examples 28 to 163, which have the compositions shown in Tables 4 to 13, all have excellent abrasion resistance because the phosphorus content of the phosphorus-containing anti-wear agent is in the range of 100 ppm by mass or more and 3000 ppm by mass or less. In addition, although the lubricating oil compositions obtained in Examples 29 to 31 do not utilize metal-based detergents or ashless dispersants, no gel formation occurred after the ammonia injection test in these compositions, indicating that gel formation can be suppressed when the anti-wear agent described in the present invention is used.

[0143] On the other hand, as is clear from the descriptions in Tables 12-13, the lubricating oil compositions obtained in Comparative Examples 20-45, which utilized zinc dialkyldithiophosphate (ZnDTP) having a C8 alkyl group, exhibited gel formation after the ammonia injection test.

[0144] Considering these results, it is clear that even if the composition differs in terms of the type and amount of base oil used, the type and amount of phosphorus-containing anti-wear agent used, the presence or absence of ashless dispersant, the type and presence or absence of metal liquid detergent, and the presence or absence of antioxidant, by using at least one phosphorus-containing anti-wear agent selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate esters, phosphate ester compounds, and amine salts of phosphate ester compounds, such that the phosphorus content is between 100 ppm by mass and 3000 ppm by mass, the wear resistance of the lubricating oil composition can be made to a high level, and it is also possible to highly prevent the formation of gel in the lubricating oil composition when it is used under conditions in contact with ammonia. From these results, it is clear that the lubricating oil composition of the present invention is useful as a component for lubricating the sliding parts of an ammonia-fueled internal combustion engine.

[0145] [Regarding lubricating oil compositions for ammonia-fueled internal combustion engines containing phosphorus-free wear-resistant agents] (Examples 164-166 and Comparative Examples 46-47) Lubricating oil compositions were prepared by mixing the aforementioned components to obtain the compositions shown in Table 14.

[0146] Furthermore, using the lubricating oil compositions obtained in Examples 164-166 and Comparative Examples 46-47, the presence or absence of gel formation in the lubricating oil compositions was confirmed in the same manner as the method used in the "Visual Observation of Compositions After Ammonia Injection Test (Confirmation Test for Presence or Absence of Gel Formation)" described above, and the average value (unit: mm) of the wear mark diameter of the fixed balls was measured in the same manner as the method used in the "High-Speed ​​Four-Ball Test" described above. The results are shown in Table 14 (note that the wear mark diameters listed as results of the High-Speed ​​Four-Ball Test are the average values ​​measured as described above). For reference, Table 14 also shows the composition and measurement results of Comparative Example 19.

[0147] Here, in the "Composition" column of Table 14, a blank space indicates that the component was not used. Also, in the "Composition" column of Table 14, "mass%" represents the mass-based content (mass%) of the total amount of the lubricating oil composition. In each example and comparative example, the lubricating oil base oil and additives were used so that the total amount of the lubricating oil base oil and additives was 100 mass% (mass%). Also, in the "Composition" column of Table 14, "Base number (perchloric acid method)" shows the value measured for the composition in accordance with JIS K 2501:2003-9. Also, in the "Composition" column of Table 14, "Content of nitrogen element derived from ashless dispersant" represents the mass-based content of nitrogen element in the ashless dispersant relative to the total amount of the lubricating oil composition (nitrogen element content of the ashless dispersant in the lubricating oil composition, unit: mass ppm), and "Content of molybdenum element" represents the mass-based content of molybdenum element relative to the total amount of the lubricating oil composition (unit: mass ppm). The "molybdenum content" refers to the value measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JIS K0116, and the "nitrogen content derived from the ashless dispersant" refers to the value calculated based on the amount of ashless dispersant added and the nitrogen content (ratio) to the total amount of constituent elements of the ashless dispersant. In the compositions shown in Table 14, the only component containing molybdenum is the phosphorus-free abrasion resistant agent (MoDTC), therefore, the "molybdenum content" for each composition is synonymous with the molybdenum content of the phosphorus-free abrasion resistant agent in the composition.

[0148]

[0149] As is clear from the results shown in Table 14, the lubricating oil compositions obtained in Examples 164 to 166, which contain a base oil and an anti-wear agent (phosphorus-free anti-wear agent) consisting of MoDTC, and whose molybdenum content in the composition (corresponding to the molybdenum content of the phosphorus-free anti-wear agent relative to the total amount of the composition) is 100 ppm by mass or more and 2000 ppm by mass or less, all showed no gel formation after the ammonia injection test, and the wear mark diameter in the high-speed four-ball test was 0.51 mm or more and 0.60 mm or less, confirming that they possess a high level of excellent wear resistance. From these results, it was found that the lubricating oil compositions obtained in Examples 164 to 166 are suitable for use in lubricating internal combustion engines that use ammonia as fuel.

[0150] In contrast, the lubricating oil composition obtained in Comparative Example 46, in which the molybdenum content of the composition (molybdenum content in the phosphorus-free anti-wear agent) was 50 ppm by mass (less than 100 ppm by mass), showed a wear mark diameter of 1.20 mm in the high-speed four-ball test, indicating insufficient wear resistance. Furthermore, the lubricating oil composition obtained in Comparative Example 47, in which the molybdenum content of the composition (molybdenum content in the phosphorus-free anti-wear agent) was 3000 ppm by mass (a value exceeding 2000 ppm by mass), showed a wear mark diameter of 0.90 mm in the high-speed four-ball test, indicating insufficient wear resistance.

[0151] Considering these factors together, it was found that by using an anti-wear agent consisting of MoDTC with a molybdenum content in the range of 100 ppm to 2000 ppm by mass, it is possible to create a lubricating oil composition with a high level of wear resistance while highly preventing gel formation during use.

[0152] As described above, the present invention makes it possible to provide a lubricating oil composition for ammonia-fueled internal combustion engines that can highly prevent gel formation during use while maintaining a high level of wear resistance. Therefore, the lubricating oil composition for ammonia-fueled internal combustion engines of the present invention is particularly excellent in preventing gel formation when in contact with ammonia, while maintaining a high level of wear resistance, and is therefore useful as a lubricating oil composition for lubricating various mechanisms of ammonia-fueled internal combustion engines, such as for ammonia fuel pumps, system oils, cylinder oils, and trunk piston engines.

Claims

1. A lubricating oil composition for an ammonia fuel internal combustion engine, comprising a lubricating oil base oil and an anti-wear agent, wherein the lubricating oil base oil is at least one selected from the group consisting of mineral oil-based base oils and synthetic base oils, and the anti-wear agent is at least one of the following components (A) to (B): (A) A phosphorus-containing anti-wear agent that is at least one selected from the group consisting of zinc phosphate, molybdenum dialkyldithiophosphate, copper dialkyldithiophosphate, ashless dithiophosphate ester, phosphate ester compound, and amine salt of a phosphate ester compound, and whose phosphorus content, on a basis of the total mass of the lubricating oil composition, is 100 ppm by mass or more and 3000 ppm by mass or less; (B) A phosphorus-free anti-wear agent that is molybdenum dithiocarbamate, and whose molybdenum content, on a basis of the total mass of the lubricating oil composition, is 100 ppm by mass or more and 2000 ppm by mass or less; 2. The lubricating oil composition according to claim 1, wherein the content of component (A) in terms of phosphorus element is 400 ppm by mass or more and 2000 ppm by mass or less, based on the total mass of the lubricating oil composition.

3. The lubricating oil composition according to claim 1, further comprising a metal-based detergent.

4. The lubricating oil composition according to claim 1, further comprising an ashless dispersant.

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