Lubricating oil composition

Abstract

A lubricating oil composition for use in an internal combustion engine contains a base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2), a thiadiazole compound (C), and an aromatic carboxylic acid ester having one or more hydroxyl groups (D), wherein the content of component (C) is 0.2 to 1.2 mass% based on the total amount of the lubricating oil composition, the content of zinc dithiophosphate, calculated as zinc atoms, is less than 500 ppm by mass based on the total amount of the lubricating oil composition, and the content of metal-based detergent, calculated as metal atoms, is less than 600 ppm by mass based on the total amount of the lubricating oil composition.

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil composition. [Background technology]

[0002] In recent years, automotive engines have been required to have higher engine power output and to comply with stricter exhaust gas regulations, and exhaust gas aftertreatment devices have been developed. Such exhaust gas aftertreatment devices employ oxidation catalysts, three-way catalysts, DPFs (diesel particulate filters), and the like to purify exhaust gases. However, it has been reported that phosphorus in engine oil poisons the catalytic active sites, reducing catalytic function, and that ash derived from metals accumulates in the DPF, shortening its lifespan.In addition, ash derived from metals accumulates on the top of the piston and accelerates the fouling of spark plugs. Therefore, there is a trend toward demand for automobile engine oils that contain reduced amounts of phosphorus-containing anti-wear agents and metal-based additives, which have been used conventionally.

[0003] There is also a demand for gas engine oils that contain reduced amounts of these additives and have reduced phosphorus and sulfated ash contents. Gas engines use natural gas, liquefied petroleum gas (LPG), autogas, etc. as fuel, and have good combustion characteristics and a higher combustion temperature than gasoline or diesel engines. As a result, the engine oil used in gas engines is used under high load conditions, which accelerates deterioration and can easily cause problems with its lifespan. Furthermore, in gas engines operated under high load conditions, the various additives in the engine oil used are prone to decomposition, and the decomposition products of these additives are likely to cause corrosion of the copper contained in the components that make up the engine. Therefore, engine oils used in gas engines are required to have resistance to deterioration and metal corrosion, and various engine oils are being developed.

[0004] For example, Patent Document 1 discloses an engine oil composition containing a base oil, a polyoxyethylene alkyl ether having an HLB value of 8 to 11, and a predetermined amount of an organic molybdenum complex, with the aim of providing an engine oil composition for gas engines that has excellent metal corrosion prevention properties, such as copper corrosion prevention properties, for bearing members of the gas engine, and also has a long life. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-209182 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the power output of automobile engines and gas engines has been increasing year by year. In these high-power automobile engines and gas engines, bearings and sliding parts such as piston pins reach high temperatures, so engine oils that lubricate these parts are required to maintain various performance characteristics when used in higher-temperature environments of over 160°C, which are higher than conventional temperatures. In high-temperature environments of over 160°C, engine oils are more susceptible to oxidation degradation, and the reduction in heat resistance becomes a major problem. It is conceivable to add a metallic detergent to engine oil to suppress oxidation degradation, but the inventors' investigations have revealed that adding a metallic detergent can sometimes cause a decrease in wear resistance.

[0007] Furthermore, metal parts that make up bearings and sliding parts, such as piston pins, in high-power automobile engines and gas engines are more susceptible to corrosion in high-temperature environments exceeding 160°C. In particular, when zinc dithiophosphate (ZnDTP) is contained in engine oil as an anti-wear agent, the decomposition of zinc dithiophosphate is accelerated in such a high-temperature environment of over 160°C, and it is likely to produce sulfuric acid and phosphoric acid, which are factors that accelerate the corrosion of metal parts.

[0008] Although Patent Document 1 also examines the metal corrosion resistance of engine oil, the temperature is 135°C, and no consideration is given to use in such high-temperature environments exceeding 160°C. Furthermore, according to the investigations of the present inventors, it has been found that the engine oil disclosed as a specific example in Patent Document 1 has problems with metal corrosion resistance in high temperature environments above 160°C.

[0009] As mentioned above, automobile engines and gas engines are becoming more powerful, and engines are becoming more highly supercharged. Laser spark plugs are being used in internal combustion engines because they are easier to ignite under high pressure than conventional spark plugs. However, ash derived from metals can be a factor in accelerating contamination of laser spark plugs, as well as conventional spark plugs.

[0010] The present invention has been made in view of the above problems, and has an object to provide a lubricating oil composition that has excellent wear resistance and is capable of exhibiting excellent metal corrosion resistance and heat resistance even when used in a high-temperature environment of above 160°C. [Means for solving the problem]

[0011] The present inventors have discovered that the above-mentioned problems can be solved by a lubricating oil composition that contains an ashless dispersant containing a non-boronated alkenyl succinimide and a boronated alkenyl succinimide, a thiadiazole compound, and an aromatic carboxylic acid ester having one or more hydroxyl groups, and that contains the thiadiazole compound in a specified range and the zinc dithiophosphate and metallic detergent in a specified amount or less, and have completed the present invention.

[0012] That is, the present invention provides the following [1]. [1] Base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2); Thiadiazole compounds (C), and Aromatic carboxylic acid ester having one or more hydroxyl groups (D) A lubricating oil composition comprising: the content of component (C) is 0.2 to 1.2 mass% based on the total amount of the lubricating oil composition; the content of zinc dithiophosphate in terms of zinc atoms is less than 500 ppm by mass based on the total amount of the lubricating oil composition; The content of the metal-based detergent in terms of metal atoms is less than 600 ppm by mass based on the total amount of the lubricating oil composition. A lubricating oil composition for use in an internal combustion engine. [Effects of the Invention]

[0013] The lubricating oil composition of the present invention has excellent anti-wear properties and can also exhibit excellent metal corrosion resistance and heat resistance even when used in high temperature environments above 160°C. DETAILED DESCRIPTION OF THE INVENTION

[0014] In this specification, the contents of boron atoms, phosphorus atoms, calcium atoms, zinc atoms, and molybdenum atoms refer to values measured in accordance with JPI-5S-38-03. The nitrogen atom content refers to a value measured in accordance with JIS K2609:1998. Furthermore, the content of sulfur atoms means a value measured in accordance with JIS K2541-6:2013.

[0015] [Lubricating oil composition] The lubricating oil composition of the present invention contains a base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2), a thiadiazole compound (C), and an aromatic carboxylic acid ester (D) having one or more hydroxyl groups, and is used in internal combustion engines. In this specification, the base oil (A), the ashless dispersant (B), the thiadiazole compound (C), and the aromatic carboxylic acid ester having one or more hydroxyl groups (D) are also referred to as "component (A)," "component (B)," "component (C)," and "component (D)," respectively. The non-boronated alkenyl succinimide (B1) and the boronated alkenyl succinimide (B2) are also referred to as "component (B1)" and "component (B2)", respectively.

[0016] The lubricating oil composition of one embodiment of the present invention may contain other lubricating oil additives that do not fall under the above-mentioned components, as long as the effects of the present invention are not impaired.

[0017] In the lubricating oil composition of one embodiment of the present invention, the total content of components (A), (B), (C), and (D) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 75 mass% or more, and still more preferably 80 mass% or more, and is usually 100 mass% or less, preferably 99.5 mass% or less, and more preferably 99.0 mass% or less. Each component contained in the lubricating oil composition of one embodiment of the present invention will now be described.

[0018] <Base oil (A)> The base oil (A) contained in the lubricating oil composition of the present invention may be any oil as long as it contains one or more types selected from mineral oils and synthetic oils.

[0019] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; mineral oils obtained by subjecting the distillates to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and mineral oils (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas to Liquids WAX)). The mineral oil used in one embodiment of the present invention is preferably a mineral oil classified into Group 2 or 3 of the base oil category of the API (American Petroleum Institute), and more preferably a mineral oil classified into Group 3.

[0020] Examples of synthetic oils include polyα-olefins such as α-olefin homopolymers or α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ethers; polyalkylene glycols; alkylbenzenes; and synthetic oils such as alkylnaphthalenes.

[0021] The kinematic viscosity of the base oil (A) at 40°C is preferably 10 to 150 mm 2 / s, preferably 12 to 120 mm 2 / s, more preferably 15 to 100 mm 2 / s.

[0022] The viscosity index of the base oil (A) is preferably 80 or more, more preferably 90 or more, even more preferably 100 or more, and even more preferably 105 or more.

[0023] In this specification, the kinematic viscosity and viscosity index refer to values measured or calculated in accordance with JIS K 2283:2000. When the base oil (A) is a mixed base oil of two or more kinds selected from mineral oils and synthetic oils, the kinematic viscosity and viscosity index of the mixed base oil may be within the above ranges.

[0024] In the lubricating oil composition of one embodiment of the present invention, the content of base oil (A) is, based on the total amount (100 mass%) of the lubricating oil composition, usually 55 mass% or more, preferably 60 mass% or more, more preferably 65 mass% or more, even more preferably 70 mass% or more, still more preferably 75 mass% or more, and is preferably 98 mass% or less, more preferably 97 mass% or less, even more preferably 95 mass% or less, and still more preferably 93 mass% or less.

[0025] <Ashless dispersant (B)> The lubricating oil composition of the present invention contains an ashless dispersant (B) comprising a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2). The combined use of component (B1) and component (B2) improves the dispersibility of components (C) and (D), resulting in a lubricating oil composition that can exhibit excellent metal corrosion resistance and heat resistance even when used in high-temperature environments above 160°C.

[0026] From the above viewpoints, the content ratio of boron atoms to nitrogen atoms [B / N] in component (B) is preferably 0.10 to 1.30, more preferably 0.20 to 1.20, even more preferably 0.20 to 1.10, still more preferably 0.30 to 1.10, and even more preferably 0.70 to 1.05, in mass ratio.

[0027] The content ratio of component (B1) to component (B2) [(B1) / (B2)] is preferably 0.01 to 6.00, more preferably 0.05 to 4.00, even more preferably 0.10 to 2.00, still more preferably 0.15 to 1.50, and even more preferably 0.20 to 0.95, in terms of mass ratio.

[0028] (Non-boronated alkenyl succinimide (B1)) Examples of the non-boronated alkenyl succinimide (B1) include alkenyl succinic acid monoimide represented by the following general formula (b-1) and alkenyl succinic acid bisimide represented by the following general formula (b-2).

[0029] [ka]

[0030] In the above general formulas (b-1) and (b-2), R A , R A1 and R A2are each independently an alkenyl group having a number average molecular weight (Mn) of 500 to 3000 (preferably 1000 to 3000, more preferably 1500 to 2500). Examples of the alkenyl group include a polybutenyl group, a polyisobutenyl group, an ethylene-propylene copolymer, and the like. Among these, a polybutenyl group or a polyisobutenyl group is preferred.

[0031] R B , R B1 and R B2 are each independently an alkylene group having 2 to 5 carbon atoms. R C represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or -(AO) n -H (wherein A is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 10). x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4. x2 is an integer of 0 to 10, preferably an integer of 1 to 4, and more preferably 2 or 3.

[0032] Component (B1) can be produced, for example, by reacting an alkenyl succinic anhydride obtained by reacting a polyolefin with maleic anhydride with a polyamine. The polyolefin may be, for example, a polymer obtained by polymerizing one or more α-olefins having 2 to 8 carbon atoms, and a copolymer of isobutene and 1-butene is preferred. Examples of the polyamine include single diamines such as ethylenediamine, propylenediamine, butylenediamine, and pentylenediamine; polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, di(methylethylene)triamine, dibutylenetriamine, tributylenetetramine, and pentapentylenehexamine; and piperazine derivatives such as aminoethylpiperazine.

[0033] The component (B1) used in one embodiment of the present invention may be a modified alkenyl succinimide obtained by reacting a compound represented by the general formulas (b-1) and (b-2) with a non-boron-containing compound such as an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, or an organic acid.

[0034] In the lubricating oil composition of one embodiment of the present invention, the content of component (B1) calculated as nitrogen atoms is preferably 400 to 3000 ppm by mass, more preferably 420 to 2500 ppm by mass, even more preferably 450 to 2200 ppm by mass, still more preferably 480 to 2000 ppm by mass, and even more preferably 500 to 1500 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0035] In the lubricating oil composition of one embodiment of the present invention, the content of component (B1) may be adjusted so that the content calculated as nitrogen atoms is within the above range, and is preferably 0.1 to 8.0 mass%, more preferably 0.2 to 6.0 mass%, and even more preferably 0.3 to 4.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0036] (Boronated alkenyl succinimide (B2)) Examples of the boronated alkenyl succinimide (B2) include boron-modified alkenyl succinimides represented by the following general formula (b-1) or (b-2) described above. The boronated alkenyl succinimide (B2) can be produced, for example, by reacting the alkenyl succinic anhydride obtained by the reaction of the above-mentioned polyolefin with maleic anhydride with the above-mentioned polyamine and boron compound. Examples of the boron compound include boron oxide, boron halides, boric acid, boric anhydride, boric acid esters, and ammonium salts of boric acid.

[0037] The content ratio of boron atoms to nitrogen atoms [B / N] in component (B2) used in one embodiment of the present invention is preferably 0.3 to 2.5, more preferably 0.5 to 2.0, and even more preferably 0.7 to 1.5, in mass ratio.

[0038] In the lubricating oil composition of one embodiment of the present invention, the content of component (B2) calculated as boron atoms is preferably 200 to 3000 ppm by mass, more preferably 400 to 2800 ppm by mass, even more preferably 600 to 2700 ppm by mass, still more preferably 700 to 2600 ppm by mass, and even more preferably 1100 to 2500 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0039] In the lubricating oil composition of one embodiment of the present invention, the content of component (B2) calculated as nitrogen atoms is preferably 250 to 3500 ppm by mass, more preferably 300 to 3200 ppm by mass, even more preferably 350 to 2800 ppm by mass, and still more preferably 400 to 2500 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0040] In the lubricating oil composition of one embodiment of the present invention, the content of component (B2) may be adjusted so that the contents in terms of boron atoms and nitrogen atoms are within the above-mentioned ranges, and is preferably 0.1 to 15.0 mass%, more preferably 0.5 to 13.0 mass%, and even more preferably 1.0 to 11.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0041] The lubricating oil composition of one embodiment of the present invention may contain, as component (B), an ashless dispersant other than components (B1) and (B2), as long as the effects of the present invention are not impaired. Examples of the ashless dispersant include benzylamines, boron-containing benzylamines, succinic acid esters, fatty acids, and mono- or di-carboxylic acid amides typified by succinic acid.

[0042] However, in the lubricating oil composition of one embodiment of the present invention, the total content of components (B1) and (B2) in the ashless dispersant (B) is preferably 70 to 100 mass%, more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, and still more preferably 95 to 100 mass%, relative to the total amount (100 mass%) of the ashless dispersant (B) contained in the lubricating oil composition.

[0043] In the lubricating oil composition of one embodiment of the present invention, the content of component (B) calculated as nitrogen atoms is preferably 600 to 6500 ppm by mass, more preferably 700 to 5200 ppm by mass, even more preferably 800 to 4000 ppm by mass, and still more preferably 850 to 3500 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0044] In the lubricating oil composition of one embodiment of the present invention, the content of component (B) is preferably 0.2 to 30.0 mass%, more preferably 0.7 to 27 mass%, even more preferably 1.5 to 25.0 mass%, and still more preferably 3.0 to 15.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0045] <Thiadiazole compounds (C)> The lubricating oil composition of the present invention contains a thiadiazole compound (C), and the content of component (C) is 0.2 to 1.2 mass % based on the total amount (100 mass %) of the lubricating oil composition. A lubricating oil composition containing less than 0.2% by mass of component (C) is unlikely to exhibit a friction-reducing effect and has problems with respect to wear resistance. On the other hand, lubricating oil compositions containing more than 1.2% by mass of component (C) are prone to corrosion of metal parts when used in high-temperature environments above 160°C, resulting in problems with metal corrosion resistance. Furthermore, when used in the same environment, they are prone to oxidative degradation, resulting in problems with heat resistance.

[0046] In the lubricating oil composition of one embodiment of the present invention, the content of component (C) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 0.22 mass% or more, more preferably 0.25 mass% or more, even more preferably 0.30 mass% or more, still more preferably 0.35 mass% or more, and even more preferably 0.40 mass% or more, from the viewpoint of improving wear resistance; and preferably 1.15 mass% or less, more preferably 1.10 mass% or less, even more preferably 1.00 mass% or less, and still more preferably 0.90 mass% or less, from the viewpoint of improving metal corrosion resistance and heat resistance.

[0047] In the lubricating oil composition of one embodiment of the present invention, the content of component (C) in terms of sulfur atoms, based on the total amount (100% by mass) of the lubricating oil composition, is preferably 500 ppm by mass or more, more preferably 700 ppm by mass or more, even more preferably 900 ppm by mass or more, and still more preferably 1200 ppm by mass or more, from the viewpoint of improving wear resistance, and is preferably 4000 ppm by mass or less, more preferably 3800 ppm by mass or less, even more preferably 3600 ppm by mass or less, and still more preferably 3000 ppm by mass or less, from the viewpoint of improving metal corrosion resistance and heat resistance.

[0048] The thiadiazole compound (C) used in one embodiment of the present invention may be any compound having a thiadiazole ring. From the viewpoint of providing a lubricating oil composition with excellent wear resistance, however, a compound having a 1,3,4-thiadiazole ring is preferred, and a compound represented by the following general formula (c-1) is more preferred. The component (C) may be used alone or in combination of two or more types.

[0049] [ka]

[0050] In the general formula (c-1), p and q each independently represent an integer of 0 to 5 (preferably an integer of 1 to 5, more preferably 1 or 2, and even more preferably 2), and p+q is 1 or greater. In one embodiment of the present invention, it is preferable that p=q. On the other hand, r and s each independently represent an integer of 1 to 5 (preferably 1 or 2, more preferably 1).

[0051] R a and R b are each independently a hydrogen atom, a hydrocarbon group, or a heteroatom-containing group containing one or more of an oxygen atom, a nitrogen atom, and a sulfur atom, and are preferably a hydrocarbon group.

[0052] R a and R b Examples of the hydrocarbon group that can be selected include linear or branched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1-dimethylhexyl, 2-ethylhexyl, nonyl, 1,1-dimethylheptyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; linear or branched alkenyl groups such as octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, and pentadecenyl; and cyclopropyl groups. cycloalkyl groups such as cyclobutyl, cyclopentyl, cyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, methylcyclohexylmethyl, cyclohexylethyl, propylcyclohexyl, butylcyclohexyl, and heptylcyclohexyl; aryl groups such as phenyl, naphthyl, anthracenyl, biphenyl, and terphenyl; alkylaryl groups such as tolyl, dimethylphenyl, butylphenyl, nonylphenyl, methylbenzyl, and dimethylnaphthyl; and arylalkyl groups such as phenylmethyl, phenylethyl, and diphenylmethyl. Among these, R a and R b The hydrocarbon group that can be selected as is preferably an alkyl group. The alkyl group may be a linear alkyl group or a branched alkyl group.

[0053] The hydrocarbon preferably has 1 to 30 carbon atoms, more preferably 1 to 24 carbon atoms, even more preferably 4 to 16 carbon atoms, and even more preferably 6 to 12 carbon atoms.

[0054] R a and R b Examples of the heteroatom-containing group that can be selected as the heteroatom include a hydroxyl group, an amino group, a nitro group, a carboxyl group, a sulfo group, a group represented by -COOR (where R is the above-mentioned hydrocarbon group), and hydrocarbon groups substituted with these groups. Among these, the heteroatom-containing group is preferably an alkyl group having 1 to 30 carbon atoms substituted with a hydroxyl group, or a group represented by -COOR (wherein R is the above-mentioned hydrocarbon group, preferably an alkyl group having 1 to 30 carbon atoms).

[0055] Component (C) used in one aspect of the present invention is a compound represented by the general formula (c-1) in which p and q are each independently 1 or 2, r and s are 1, and R a and R b are each independently a linear or branched alkyl group having 1 to 30 carbon atoms, more preferably a compound represented by the following general formula (c-11), and even more preferably a compound represented by the following general formula (c-12):

[0056] [ka]

[0057] In the general formula (c-11), R a1 and R b1 are each independently a linear or branched alkyl group having 1 to 30 carbon atoms, preferably a branched alkyl group having 4 to 16 carbon atoms, and more preferably a branched alkyl group having 6 to 12 carbon atoms.

[0058] In addition, in the general formula (c-12), R a2 and R b2are each independently a linear or branched alkyl group having 1 to 16 carbon atoms, more preferably a linear alkyl group having 1 to 16 carbon atoms, and even more preferably a linear alkyl group having 4 to 12 carbon atoms. R c , R d , R e and R f are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R c and R d At least one of the above and R e and R f At least one of them is an alkyl group having 1 to 6 carbon atoms. However, R c , R d , R e and R f are each independently preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.

[0059] <Aromatic carboxylic acid ester (D) having one or more hydroxyl groups> The lubricating oil composition of the present invention contains an aromatic carboxylic acid ester (D) having one or more hydroxyl groups. The component (D) may be used alone or in combination of two or more types. The lubricating oil composition of the present invention contains component (D), and therefore can exhibit excellent heat resistance even when used in high temperature environments above 160°C.

[0060] In particular, in the lubricating oil composition of the present invention, the presence of component (B2) makes it easier for component (D) to disperse, and the performance of component (D) can be more significantly exhibited, so that the composition has excellent heat resistance even when used in high-temperature environments above 160°C.

[0061] From the above viewpoints, in the lubricating oil composition of one embodiment of the present invention, the content ratio of component (D) to component (B2) [(D) / (B2)] is preferably 0.1 to 5.0, more preferably 0.15 to 4.0, even more preferably 0.2 to 3.0, and still more preferably 0.3 to 2.0, in mass ratio.

[0062] The aromatic carboxylic acid ester (D) having one or more hydroxyl groups used in one embodiment of the present invention is preferably one or more selected from the group consisting of a compound (D1) represented by the following general formula (d-1) and a compound (D2) represented by the following general formula (d-2), and more preferably includes at least the compound (D1).

[0063] [ka]

[0064] In the general formula (d-1) or (d-2), R 1 ~R 5 are each independently a hydrocarbon group having 1 to 50 carbon atoms. The hydrocarbon preferably has 1 to 50 carbon atoms, more preferably 4 to 40 carbon atoms, even more preferably 6 to 30 carbon atoms, and even more preferably 8 to 20 carbon atoms. The hydrocarbon group includes R a and R b Although the hydrocarbon groups that can be selected as the alkyl group include the same hydrocarbon groups as those that can be selected as the alkyl group, alkyl groups or alkenyl groups are preferred, and alkyl groups are more preferred. The alkyl group and the alkenyl group may be a straight chain or a branched chain.

[0065] In the general formula (d-1), a is an integer of 1 to 3 (preferably 1), b is an integer of 1 to 3 (preferably 1), c is an integer of 0 to 3 (preferably 0 or 1, more preferably 0), d is an integer of 1 to 3 (preferably 1), e is an integer of 1 to 3 (preferably 1), a+b+e is an integer of 3 to 6, and c+d is an integer of 1 to 5.

[0066] In the general formula (d-2), f is an integer of 0 to 3, g is an integer of 0 to 3, and f+g is an integer of 1 to 3. h is an integer of 0 to 4, i is an integer of 0 to 3, and h+i is an integer of 1 to 6. j is an integer of 0 to 3, k is an integer of 1 to 3, and j+k is an integer of 1 to 5. m is an integer of 1 to 3, and f+g+h+i+m is an integer of 3 to 8.

[0067] In the lubricating oil composition of one embodiment of the present invention, the content of component (D) is preferably 0.5 to 15.0 mass%, more preferably 0.7 to 13.0 mass%, even more preferably 1.0 to 12.0 mass%, and still more preferably 2.0 to 10.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition, from the viewpoint of providing a lubricating oil composition with excellent heat resistance even when used in a high-temperature environment of above 160°C.

[0068] <Zinc dithiophosphate> The lubricating oil composition of the present invention may further contain zinc dithiophosphate (ZnDTP), but the content of zinc dithiophosphate in terms of zinc atoms is limited to less than 500 ppm by mass based on the total amount (100% by mass) of the lubricating oil composition. A lubricating oil composition having a zinc dithiophosphate content of more than 500 ppm by mass has problems with metal corrosion resistance.

[0069] As mentioned above, ZnDTP decomposes more rapidly in high-temperature environments above 160°C, easily producing sulfuric acid and phosphoric acid, which can accelerate corrosion of metal parts. However, since the lubricating oil composition of the present invention contains components (B) to (D), it is possible to suppress the decomposition of ZnDTP to some extent even in high-temperature environments above 160° C. Therefore, if the ZnDTP content is less than 500 ppm by mass, it is possible to further improve wear resistance by the presence of ZnDTP while maintaining good metal corrosion resistance.

[0070] From the above viewpoints, in the lubricating oil composition of one embodiment of the present invention, the content of zinc dithiophosphate in terms of zinc atoms is preferably less than 400 ppm by mass, more preferably less than 350 ppm by mass, even more preferably less than 300 ppm by mass, and even more preferably less than 280 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition. Also, from the viewpoint of improving wear resistance, it is preferably 100 ppm by mass or more.

[0071] In the lubricating oil composition of one embodiment of the present invention, the zinc dithiophosphate content may be adjusted so that the content in terms of zinc atoms falls within the above range, but is preferably less than 0.50 mass%, more preferably less than 0.40 mass%, and even more preferably less than 0.30 mass%, based on the total amount (100 mass%) of the lubricating oil composition. From the viewpoint of improving wear resistance, it is preferably 0.10 mass% or more.

[0072] The zinc dithiophosphate used in one embodiment of the present invention includes a compound represented by the following general formula (e-1). [ka]

[0073] In the above formula (e-1), R 11 ~R 14 each independently represents a hydrocarbon group. The hydrocarbon group includes R a and R b The hydrocarbon groups that can be selected as the alkyl group include the same hydrocarbon groups as those that can be selected as the alkyl group, but alkyl groups are preferred. The alkyl group may be a linear alkyl group or a branched alkyl group, but is preferably a branched alkyl group. R 11 ~R 14 The hydrocarbon group that can be selected as the alkyl group preferably has 1 to 20 carbon atoms, more preferably 3 to 16 carbon atoms, even more preferably 4 to 12 carbon atoms, and even more preferably 5 to 10 carbon atoms.

[0074] <Metallic detergents> The lubricating oil composition of the present invention may contain a metallic detergent, but the content of the metallic detergent in terms of metal atoms is limited to less than 600 ppm by mass based on the total amount (100% by mass) of the lubricating oil composition. A lubricating oil composition with a content of 600 ppm by mass or more tends to have reduced wear resistance. However, since the lubricating oil composition of the present invention contains component (D), if the content of the metallic detergent is less than 600 ppm by mass, it is possible to suppress the deterioration of wear resistance to some extent, and the presence of the metallic detergent can further improve heat resistance.

[0075] In the lubricating oil composition of one embodiment of the present invention, the content of the metallic detergent, calculated as metal atoms, based on the total amount (100% by mass) of the lubricating oil composition, is preferably less than 550 ppm by mass, more preferably less than 500 ppm by mass, even more preferably less than 470 ppm by mass, and still more preferably less than 300 ppm by mass, from the viewpoint of maintaining good wear resistance.

[0076] Examples of metal-based detergents include organic acid metal salt compounds containing a metal atom selected from alkali metals and alkaline earth metals. Specific examples include metal salicylates, metal phenates, and metal sulfonates, each containing a metal atom selected from alkali metals and alkaline earth metals. As the metal atom contained in the metal-based detergent, sodium, calcium, magnesium, or barium is preferred, and calcium is more preferred, from the viewpoint of improving heat resistance. That is, the metallic detergent used in one embodiment of the present invention is preferably one or more selected from calcium salicylate, calcium phenate, and calcium sulfonate.

[0077] In one embodiment of the present invention, the metal-based detergent may be any of a neutral salt, a basic salt, an overbased salt, and a mixture thereof. The total base number of the metallic detergent is preferably 0 to 600 mgKOH / g. In one embodiment of the present invention, when the metallic detergent is a basic salt or an overbased salt, the total base number of the metallic detergent is preferably 10 to 600 mgKOH / g, more preferably 20 to 500 mgKOH / g. In this specification, the term "base number" refers to the base number measured by the perchloric acid method in accordance with JIS K2501 "Petroleum products and lubricants - Testing method for neutralization number" 7:2003.

[0078] <Other lubricating oil additives> The lubricating oil composition of one embodiment of the present invention may contain other lubricating oil additives in addition to the components described above, provided that the effects of the present invention are not impaired. In the following description, such other lubricating oil additives will also be referred to as "component (E)." Other lubricating oil additives include, for example, antioxidants, viscosity index improvers, pour point depressants, antiwear agents, extreme pressure agents, metal friction modifiers, rust inhibitors, metal deactivators, demulsifiers, and antifoaming agents. These lubricating oil additives may be used alone or in combination of two or more.

[0079] The content of each of these lubricating oil additives can be adjusted as appropriate within a range that does not impair the effects of the present invention, but is usually 0.001 to 15 mass%, preferably 0.005 to 10 mass%, more preferably 0.01 to 5 mass%, and even more preferably 0.03 to 2 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0080] In this specification, additives such as viscosity index improvers and antifoaming agents may be diluted and dissolved in a portion of the base oil (A) and blended with other components in the form of a solution, taking into account handling properties and solubility in the base oil (A). In such cases, the above-mentioned content of additives such as antifoaming agents and viscosity index improvers in this specification means the content in terms of active ingredients (resin content) excluding the diluent oil.

[0081] Examples of the antioxidant include amine-based antioxidants, phenol-based antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants. Among these, one or more selected from amine-based antioxidants and phenol-based antioxidants are preferred, and it is more preferred to use an amine-based antioxidant and a phenol-based antioxidant in combination.

[0082] Examples of viscosity index improvers include polymers such as non-dispersant polymethacrylate, dispersant polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymers), dispersant olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers). The weight average molecular weight (Mw) of these viscosity index improvers is usually 3,000 to 1,000,000, preferably 5,000 to 800,000, and more preferably 10,000 to 700,000, but is set appropriately depending on the type of polymer.

[0083] Examples of pour point depressants include ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates, and polyalkylstyrenes.

[0084] Examples of anti-wear agents or extreme pressure agents include sulfur-containing compounds such as molybdenum dithiocarbamates, molybdenum dithiophosphates, disulfides, sulfurized olefins, sulfurized fats and oils, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphates, phosphonates, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing compounds such as thiophosphites, thiophosphates, thiophosphonates, and amine salts or metal salts thereof.

[0085] Examples of metal-based friction modifiers include molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdic acid.

[0086] Examples of the rust inhibitor include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers.

[0087] Examples of metal deactivators include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds.

[0088] Examples of demulsifiers include anionic surfactants such as castor oil sulfate ester salts and petroleum sulfonates; cationic surfactants such as quaternary ammonium salts and imidazolines; polyoxyalkylene polyglycols and their dicarboxylic acid esters; alkylene oxide adducts of alkylphenol-formaldehyde polycondensates; and the like.

[0089] Examples of the antifoaming agent include silicone oil, fluorosilicone oil, and fluoroalkyl ether.

[0090] In addition, from the viewpoint of reducing the ash content derived from metal components, the lubricating oil composition of one embodiment of the present invention preferably contains as little molybdenum compound as possible as an additive. Specifically, the content of the molybdenum-based compound, calculated as molybdenum, is preferably less than 100 ppm by mass, more preferably less than 50 ppm by mass, and even more preferably less than 10 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0091] [Method for producing lubricating oil composition] The method for producing the lubricating oil composition of the present invention is not particularly limited, but examples thereof include a production method comprising the following step (I): Step (I): A step of blending a base oil (A) with an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2), a thiadiazole compound (C), and an aromatic carboxylic acid ester (D) having one or more hydroxyl groups.

[0092] In step (I), component (E) may be added simultaneously with components (A) to (D). However, in step (I), the content of the metallic detergent in terms of metal atoms is adjusted to be less than 600 ppm by mass based on the total amount of the lubricating oil composition.

[0093] In this step, the components to be mixed are as described above, and the types of suitable components and the contents of each component are also as described above. Furthermore, each component to be blended in step (I) may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. After blending the components, it is preferable to stir them by a known method to uniformly disperse them.

[0094] [Various properties of lubricating oil composition] The kinematic viscosity at 100°C of the lubricating oil composition of one embodiment of the present invention is preferably 8.0 to 20.0 mm 2 / s, more preferably 9.3 to 18.0 mm 2 / s, more preferably 9.3 to 16.3 mm 2 / s. The kinematic viscosity at 100°C is preferably 8.0 to 20 mm 2 / s, preferably 8.0 to 16.3 mm 2 / s, more preferably 8.0 to 12.5 mm 2 / s.

[0095] The viscosity index of the lubricating oil composition of one embodiment of the present invention is preferably 100 or greater, more preferably 110 or greater, and even more preferably 120 or greater.

[0096] In the lubricating oil composition of one embodiment of the present invention, the content of phosphorus atoms is preferably less than 400 ppm by mass, more preferably less than 350 ppm by mass, even more preferably less than 300 ppm by mass, and still more preferably less than 250 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of reducing the load on an exhaust gas aftertreatment device.

[0097] In the lubricating oil composition of one embodiment of the present invention, the content of sulfur atoms is preferably 500 to 5000 ppm by mass, more preferably 700 to 4500 ppm by mass, even more preferably 900 to 4000 ppm by mass, and still more preferably 1050 to 3500 ppm by mass, based on the total amount (100% by mass) of the lubricating oil composition.

[0098] In the lubricating oil composition of one embodiment of the present invention, the sulfated ash content is preferably less than 0.30 mass%, more preferably less than 0.25 mass%, even more preferably less than 0.20 mass%, and still more preferably less than 0.05 mass%, based on the total amount (100 mass%) of the lubricating oil composition. If the sulfated ash content is less than 0.30 mass%, it is possible to suppress the deterioration of the function of the catalyst installed in the exhaust gas aftertreatment device, and also to prevent the accumulation of ash derived from metal components in the DPF. In this specification, the sulfated ash content refers to a value measured in accordance with JIS K2272:1998.

[0099] When a metal corrosion test is performed on the lubricating composition of one embodiment of the present invention at a temperature of 100°C in accordance with the test tube method of JIS K2513:2000, the specified discoloration number is preferably 1 or 2, and more preferably 1. Furthermore, when the lubricating composition of one embodiment of the present invention is subjected to a test in accordance with the test tube method of JIS K2513:2000 at a temperature of 165.5°C, the specified discoloration number is preferably 1 or 2. In this specification, detailed conditions for the test in accordance with the test tube method of JIS K2513:2000 are as described in the Examples below.

[0100] In the lubricating oil composition of one embodiment of the present invention, the wear scar diameter measured according to the method and conditions in the Examples described below is preferably 450 μm or less, more preferably 440 μm or less, even more preferably 435 μm or less, and still more preferably 430 μm or less.

[0101] When the lubricating oil composition of one embodiment of the present invention is subjected to a hot tube test in accordance with JPI-5S-55-99 at a temperature of 280°C, the specified merit score is preferably 8.0 or higher, more preferably 8.5 or higher, even more preferably 9.0 or higher, and still more preferably 9.5 or higher.

[0102] Furthermore, when the lubricating oil composition of one embodiment of the present invention is subjected to an ISOT test in accordance with JIS K 2514-1:2013 at 165.5°C for 72 hours, and the resulting deteriorated oil is subjected to a hot tube test in accordance with JPI-5S-55-99 at a temperature of 280°C, the determined merit score is preferably 7.0 or higher, more preferably 7.5 or higher, even more preferably 8.0 or higher, and even more preferably 8.5 or higher. In the present invention, detailed conditions for the hot tube test and the ISOT test in accordance with JIS K 2514-1:2013 are as described in the examples below.

[0103] [Uses of lubricating oil composition] The lubricating oil composition of the present invention has excellent anti-wear properties and can also exhibit excellent metal corrosion resistance and heat resistance even when used in high temperature environments above 160°C. The lubricating oil composition of the present invention is used in internal combustion engines, and is particularly preferably used in internal combustion engines equipped with components whose maximum temperature exceeds 160°C. Examples of the internal combustion engine include gasoline engines, diesel engines, gas engines, etc. that are mounted on motorcycles, automobiles, generators, ships, etc. Since the lubricating oil composition of the present invention has a reduced metal content, it is also preferable for use in internal combustion engines equipped with exhaust gas after-treatment devices, spark-ignition internal combustion engines equipped with spark plugs, and laser-ignition internal combustion engines equipped with laser spark plugs.

[0104] The present invention can also provide an internal combustion engine as shown in [1] below and a method of use as shown in [2] below. [1] A lubricating oil composition comprising a base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2), a thiadiazole compound (C), and an aromatic carboxylic acid ester (D) having one or more hydroxyl groups, The content of component (C) is 0.2 to 1.2 mass %, The content of zinc dithiophosphate in terms of zinc atom is less than 500 ppm by mass, The content of metal-based detergents in terms of metal atoms is less than 600 ppm by mass. An internal combustion engine using a lubricating oil composition. [2] A lubricating oil composition comprising a base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2), a thiadiazole compound (C), and an aromatic carboxylic acid ester (D) having one or more hydroxyl groups, The content of component (C) is 0.2 to 1.2 mass %, The content of zinc dithiophosphate in terms of zinc atom is less than 500 ppm by mass, The content of metal-based detergents in terms of metal atoms is less than 600 ppm by mass. A method of using a lubricating oil composition, comprising using the lubricating oil composition in an internal combustion engine.

[0105] Regarding the lubricating oil compositions used in [1] and [2] above, the preferred embodiments of each component and the preferred properties of the lubricating oil compositions are as described above. Furthermore, the internal combustion engines described in [1] and [2] above are preferably internal combustion engines equipped with components whose maximum temperature exceeds 160°C, and more preferably internal combustion engines equipped with components whose maximum temperature exceeds 160°C and also equipped with an exhaust gas aftertreatment device. Also, it is preferable that the internal combustion engines are spark-ignition internal combustion engines equipped with spark ignition plugs and laser-ignition internal combustion engines equipped with laser ignition plugs. [Example]

[0106] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. The various properties of the components used in the examples and comparative examples and the resulting lubricating oil compositions were measured according to the methods described below.

[0107] <Kinematic viscosity, viscosity index> Measured or calculated in accordance with JIS K 2283:2000. <Content of boron atoms, phosphorus atoms, calcium atoms, zinc atoms, and molybdenum atoms> Measurements were performed in accordance with JPI-5S-38-03. <Nitrogen atom content> Measurement was carried out in accordance with JIS K2609:1998. <Sulfur atom content> Measurements were performed in accordance with JIS K2541-6:2013. <Sulfated ash> Measurement was carried out in accordance with JIS K2272:1998.

[0108] Examples 1 to 12, Comparative Examples 1 to 8 The base oils and various additives shown below were added in the amounts shown in Tables 1 to 3 and mixed thoroughly to produce a kinematic viscosity of 12.0 to 13.0 mm at 100°C. 2 Lubricating oil compositions having the following compositions were prepared: Details of the base oils and various additives used in the examples and comparative examples are as follows.

[0109] (Component (A)) "Base oil (a)": 500N mineral oil that has been hydrotreated and is classified as Group 2 in the API base oil category, with a kinematic viscosity of 89.3 mm at 40°C 2 / s, 100℃ kinematic viscosity=10.9mm 2 / s, viscosity index=107. (Component (B1)) "Non-boronated alkenyl succinic acid monoimide (b1)": an alkenyl succinic acid monoimide represented by the general formula (b-1) (R A is a polybutenyl group having a number average molecular weight (Mn) of 1000, and the nitrogen atom content is 2.0% by mass. (Component (B2)) "Boronated alkenyl succinic acid monoimide (b2-1)": a boron-modified alkenyl succinic acid monoimide represented by the general formula (b-1) (R A is a polybutenyl group having a number average molecular weight (Mn) of 1000), nitrogen atom content=1.8 mass %, boron atom content=2.0 mass %, B / N=1.11. "Boronated alkenyl succinic acid monoimide (b2-2)": a boron-modified alkenyl succinic acid monoimide represented by the general formula (b-1) (R A is a polybutenyl group having a number average molecular weight (Mn) of 1000), nitrogen atom content=1.2 mass%, boron atom content=1.3 mass%, B / N=1.08.

[0110] (Component (C)) Thiadiazole compound (c1): a compound represented by the following formula (ci), sulfur atom content: 35.0 mass %. Thiadiazole compound (c2): a compound represented by the following formula (c-ii), sulfur atom content: 33.6% by mass. [ka]

[0111] (Component (D)) Aromatic carboxylic acid ester (d1): dodecylsalicylic acid dodecylphenyl ester, R in the general formula (d-1)1 and R 2 is a dodecyl group (-C 12 H 25 ), a=b=d=e=1, c=0.

[0112] (Other ingredients) ZnDTP: zinc dithiophosphate, R in the general formula (e-1) 11 ~R 14 is a 2-ethylhexyl group, the phosphorus atom content=8.2 mass%, the zinc atom content=9.0 mass%, and the sulfur atom content=17.1 mass%. · Calcium-based detergent: Ca phenate, calcium atom content = 9.25 mass%. · Antioxidant: A mixture of amine-based antioxidants and phenol-based antioxidants. · Mixed additives: Mixed additives including antifoaming agents, pour point depressants, etc.

[0113] The prepared lubricating oil compositions were subjected to the following tests (1) to (3) in this order. The results are shown in Tables 1 to 3. If the results of the (1) metal corrosion test were poor, the subsequent (2) abrasion resistance test and (3) hot tube test were not conducted. Also, if the results of the (2) abrasion resistance test were poor, the (3) hot tube test was not conducted.

[0114] [(1) Metal Corrosion Test] The temperature conditions were set at 100°C and 165.5°C, and the test was conducted in accordance with the test tube method of JIS K2513:2000. After the test, the copper plate was removed and the degree of discoloration of the copper plate was determined according to the copper plate evaluation method specified in JIS K2513:2000, and a discoloration number was assigned to each temperature condition. The discoloration number is given in four levels, from 1 to 4, and the smaller the number, the more the discoloration is suppressed, and the greater the effect of suppressing metal corrosion. Under both the temperature conditions of 100°C and 165.5°C, a lubricating oil composition was judged to have good metal corrosion resistance if the discoloration number was 1 or 2. Then, only those lubricating oil compositions judged to have good metal corrosion resistance were subjected to the following (2) wear resistance test.

[0115] [(2) Abrasion resistance test] Using a high-speed reciprocating friction tester TE77 (manufactured by Phoenix Tribology), the lubricating oil composition was introduced between the test plate and the test ball, and the test was performed by moving the test ball under the conditions below, and the wear scar diameter of the test ball after the test was measured. Test plate Material: SUJ2, Shape: Length 58mm x Width 38mm x Thickness 3.9mm Test ball: Material: SUJ2, diameter 10mm ·Lubricating conditions: oil bath, oil amount 3mL Load: 50N (5 minutes) → 100N (5 minutes) → 150N (5 minutes) → 200N (5 minutes) ·Temperature: 100℃ Frequency: 10Hz The smaller the wear scar diameter, the more excellent the wear resistance of the lubricating oil composition. When the wear scar diameter was 450 μm or less, the wear resistance was judged to be good.Then, only those lubricating oil compositions judged to have good wear resistance were subjected to the following (3) hot tube test.

[0116] (3) Hot tube test The prepared lubricating oil composition was placed in a glass tube and subjected to a hot tube test in accordance with JPI-5S-55-99 at a test temperature of 280°C. After the test, the glass tube was rated in increments of 0.5 from 0 (black) to 10 (colorless) (merit rating), and the new oil was given a rating on a 21-point scale. The higher the rating, the better the high-temperature detergency. In addition, copper and iron pieces were added as catalysts to the test oil (lubricating oil composition), and the test oil was subjected to the ISOT test in accordance with JIS K 2514-1:2013 at 165.5°C for 72 hours to forcibly degrade the test oil to obtain a degraded oil. The degraded oil was then subjected to a hot tube test under the same conditions as above, and the degraded oil was evaluated. When the rating of the new oil was 8.0 or higher and the rating of the deteriorated oil was 7.0 or higher, the heat resistance was judged to be good.

[0117] [Table 1]

[0118] [Table 2]

[0119] [Table 3]

[0120] The lubricating oil compositions prepared in Examples 1 to 12 had excellent wear resistance, and were also able to exhibit excellent metal corrosion resistance and heat resistance even when used in high temperature environments above 160°C. On the other hand, the lubricating oil compositions prepared in Comparative Examples 2 to 5 and 7 gave poor results in the metal corrosion test, which assumes use in a high-temperature environment above 160°C, and were found to have poor metal corrosion resistance. The lubricating oil compositions prepared in Comparative Examples 6 and 8 had good metal corrosion resistance but poor wear resistance. Furthermore, the lubricating oil composition prepared in Comparative Example 1 received a low score in the hot tube test, indicating a problem with heat resistance.

Claims

1. Base oil (A), an ashless dispersant (B) containing a non-boronated alkenyl succinimide (B1) and a boronated alkenyl succinimide (B2); a thiadiazole compound (C), and Aromatic carboxylic acid ester (D) having one or more hydroxyl groups A lubricating oil composition comprising: the content of component (B1) in terms of nitrogen atoms is 2000 ppm by mass or less based on the total amount of the lubricating oil composition; the content of component (B2) in terms of boron atoms is 200 to 3,000 ppm by mass based on the total amount of the lubricating oil composition; The content ratio of boron atoms to nitrogen atoms [B / N] in component (B) is 0.30 or more in mass ratio, Component (C) is a compound represented by the following general formula (c-11): 【Chemical 1】 [In the general formula (c-11), R ａ1 and R ｂ1 are each independently a linear or branched alkyl group having 6 to 12 carbon atoms. the content of component (C) is 0.2 to 1.2 mass% based on the total amount of the lubricating oil composition; Component (D) is a compound (D1) represented by the following general formula (d-1): 【Chemistry 2】 [In the general formula (d-1), R １ and R ２ are each independently a hydrocarbon group having 8 to 20 carbon atoms. In the general formula (d-1), a is 1, b is 1, c is 0, d is 1, and e is 1. The content of component (D) is 0.7 to 12.0 mass% based on the total amount of the lubricating oil composition, the content of zinc dithiophosphate in terms of zinc atoms is less than 500 ppm by mass based on the total amount of the lubricating oil composition; The content of the metal-based detergent in terms of metal atoms is less than 600 ppm by mass based on the total amount of the lubricating oil composition. A lubricating oil composition for use in an internal combustion engine.

2. 2. The lubricating oil composition according to claim 1, wherein the content ratio of component (D) to component (B2) [(D) / (B2)] is 0.1 to 5.0 by mass.

3. 3. The lubricating oil composition according to claim 1, wherein the ratio of boron atoms to nitrogen atoms [B / N] in component (B2) is 0.3 to 2.5 in mass ratio.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the content of component (B1) in terms of nitrogen atoms is 400 to 2000 ppm by mass based on the total amount of the lubricating oil composition.

5. 5. The lubricating oil composition according to claim 1, wherein the content ratio of boron atoms to nitrogen atoms in component (B) [B / N] is, in mass ratio, from 0.30 to 1.

30.

6. 6. The lubricating oil composition according to claim 1, wherein the content of the molybdenum-based compound in terms of molybdenum is less than 100 ppm by mass based on the total amount of the lubricating oil composition.

7. 7. The lubricating oil composition according to claim 1, wherein the phosphorus atom content is less than 400 ppm by mass based on the total amount of the lubricating oil composition.

8. The lubricating oil composition according to any one of claims 1 to 7, wherein the sulfated ash content is less than 0.30 mass % based on the total amount of the lubricating oil composition.

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