LUBRICATING OIL COMPOSITION FOR INTERNAL COMBUSTION ENGINES

Abstract

A lubricating oil composition for internal combustion engines, including: (A) a lubricating base oil; and (B) a metal-based detergent, wherein the component (B) contains: (B1) a calcium-based detergent in which a content of calcium based on a total mass of the composition is within a specific range; and (B2) a magnesium-based detergent in which a content of magnesium based on the total mass of the composition is within a specific range, the component (B1) contains (B1-1) a calcium-based detergent containing boron and calcium, a content of boron based on the total mass of the composition is 1000 mass ppm or less, a ratio (B(B1)/Ca(B1)) of B(B1) to Ca(B1) is 0.15 or more and 0.35 or less, and a ratio (B(B1)/[Ca(B1)+Mg(B2)]) of B(B1) to a total amount (Ca(B1)+Mg(B2)) of Ca(B1) and Mg(B2) is 0.13 or more and 0.29 or less.

Description

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for internal combustion engines.

BACKGROUND ART

Recently, along with increases in performances and outputs of internal combustion engines such as engines of automobiles, lubricating oils for internal combustion engines (engine oils) are required to have high performances, and various lubricating oil compositions obtained by blending lubricating base oils with various additives have been studied.

For example, International Publication No. WO2019/221295 (PTL 1) discloses a lubricating oil composition for internal combustion engines, comprising: a lubricating base oil; (A) a metal-based detergent containing calcium borate; and (B) a metal-based detergent containing magnesium, wherein the component (A) is one or more calcium-based detergents which are overbased with calcium borate or a combination of one or more calcium-based detergents which are overbased with calcium borate and one or more calcium-based detergents which are not overbased with calcium borate, and a molar ratio B/Ca between a total boron content B (unit: mol) derived from the metal-based detergents in the lubricating oil composition and a total calcium content Ca (unit: mol) derived from the metal-based detergents in the lubricating oil composition is 0.52 or more.

In addition, International Publication No. WO2018/212340 (PTL 2) discloses a lubricating oil composition for internal combustion engines, comprising: a lubricating base oil; (A) a metal-based detergent containing calcium borate; and (B) a metal-based detergent containing magnesium, and paragraph [0064] of this document discloses that a molar ratio B/Ca between a total boron content B (unit: mol) derived from the metal-based detergents in the lubricating oil composition and a total calcium content Ca (unit: mol) derived from the metal-based detergents in the lubricating oil composition is preferably 0.52 or more.

Moreover, Japanese Unexamined Patent Application Publication No. 2017-226793 (PTL 3) discloses a lubricating oil composition for internal combustion engines, comprising: (A) a lubricating base oil; and (B) a metal-based detergent in an amount of 500 to 2500 mass ppm in terms of calcium and in an amount of 100 to 1000 mass ppm in terms of magnesium based on a total mass of the composition, the metal-based detergent containing (B1) a metal-based detergent containing calcium and (B2) a metal-based detergent containing magnesium.

CITATION LIST

Patent Literature

• • [PTL 1] International Publication No. WO2019/221295
  • [PTL 2] International Publication No. WO2018/212340
  • [PTL 3] Japanese Unexamined Patent Application Publication No. 2017-226793

SUMMARY OF INVENTION

Technical Problem

However, even the conventional lubricating oil compositions for internal combustion engines as described in PTLs 1 to 3 still have room for improvements in terms of achieving excellent performance of suppressing LSPI (Low Speed Pre-Ignition) (LSPI suppressing performance) and also in terms of achieving excellent fuel saving performance by improving friction performance.

The present invention has been made in view of the above-described problem of the conventional techniques, and an object thereof is to provide a lubricating oil composition for internal combustion engines that is capable of achieving both excellent LSPI suppressing performance and excellent fuel saving performance.

Solution to Problem

As a result of conducting earnest studies in order to achieve the above-described object, the present inventors have found that when a lubricating oil composition for internal combustion engines, comprises: (A) a lubricating base oil; and (B) a metal-based detergent, wherein the component (B) contains: (B1) a calcium-based detergent in which a content of calcium based on a total mass of the composition is within a range of 1650 mass ppm or more and 2500 mass ppm or less; and (B2) a magnesium-based detergent in which a content of magnesium based on the total mass of the composition is within a range of 20 mass ppm or more and 400 mass ppm or less, the component (B1) contains (B1-1) a calcium-based detergent containing boron and calcium, a content of boron based on the total mass of the composition is 1000 mass ppm or less, and a ratio (B_(B1)/Ca_(B1)) of B_(B1) to Ca_(B1) is 0.15 or more and 0.35 or less, and a ratio (B_(B1)/[Ca_(B1)+Mg_(B2)]) of B_(B1) to a total amount (Ca_(B1)+Mg_(B2)) of Ca_(B1) and Mg_(B2) is 0.13 or more and 0.29 or less, where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, Ca_(B1) represents the content (mass ratio) of calcium in the component (B1) based on the total mass of the composition, and Mg_(B2) represents the content (mass ratio) of magnesium in the component (B2) based on the total mass of the composition, it becomes possible for the lubricating oil composition for internal combustion engines to have excellent LSPI suppressing performance, and also to have excellent fuel saving performance owing to improvement in friction performance, and have thus completed the present invention.

Specifically, a lubricating oil composition for internal combustion engines of the present invention is

• • a lubricating oil composition for internal combustion engines, comprising:
  • (A) a lubricating base oil; and
  • (B) a metal-based detergent, wherein
  • the component (B) contains:
  • (B1) a calcium-based detergent in which a content of calcium based on a total mass of the composition is within a range of 1650 mass ppm or more and 2500 mass ppm or less; and
  • (B2) a magnesium-based detergent in which a content of magnesium based on the total mass of the composition is within a range of 20 mass ppm or more and 400 mass ppm or less,
  • the component (B1) contains (B1-1) a calcium-based detergent containing boron and calcium,
  • a content of boron based on the total mass of the composition is 1000 mass ppm or less, and
  • a ratio (B_(B1)/Ca_(B1)) of B_(B1) to Ca_(B1) is 0.15 or more and 0.35 or less, and a ratio (B_(B1)/[Ca_(B1)+Mg_(B2)]) of B_(B1) to a total amount (Ca_(B1)+Mg_(B2)) of Ca_(B1)and Mg_(B2) is 0.13 or more and 0.29 or less, where B_(B1) represents the content of boron in the component (B1) based on the total mass of the composition, Ca_(B1)represents the content of calcium in the component (B1) based on the total mass of the composition, and Mg_(B2) represents the content of magnesium in the component (B2) based on the total mass of the composition. In descriptions “the content of boron in the component (B1) based on the total mass of the composition”, “the content of calcium in the component (B1) based on the total mass of the composition”, and “the content of magnesium in the component (B2) based on the total mass of the composition”, the description “content” means the proportion of the mass (mass ratio: mass-based content ratio) based on the total mass of the composition (the total amount of the composition).

It is preferable that in the lubricating oil composition for internal combustion engines of the present invention, the component (B1) contain calcium borate salicylate as the component (B1-1).

In addition, it is preferable that the lubricating oil composition for internal combustion engines of the present invention further comprise (C) a poly(meth)acrylate-based viscosity index improver. In addition, it is preferable that the component (C) contain a comb-shaped poly(meth)acrylate-based polymer.

Advantageous Effects of Invention

The present invention makes it possible to provide a lubricating oil composition for internal combustion engines that is capable of achieving both excellent LSPI suppressing performance and excellent fuel saving performance.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail based on preferred embodiments thereof. Note that in the present Description, regarding numerical values X and Y, description “X to Y” is intended to mean “X or more and Y or less” unless otherwise noted. In such description, in the case where unit is attached to only the numerical value Y, the unit is intended to apply also to the numerical value X.

A lubricating oil composition for internal combustion engines of the present invention comprises:

• • (A) a lubricating base oil; and
  • (B) a metal-based detergent, wherein
  • the component (B) contains:
  • (B1) a calcium-based detergent in which a content of calcium is within a range of 1650 mass ppm or more and 2500 mass ppm or less based on a total mass of the composition; and
  • (B2) a magnesium-based detergent in which a content of magnesium is within a range of 20 mass ppm or more and 400 mass ppm or less based on the total mass of the composition,
  • the component (B1) contains (B1-1) a calcium-based detergent containing boron and calcium,
  • a content of boron based on the total mass of the composition is 1000 mass ppm or less, and
  • a ratio (B_(B1)/Ca_(B1)) of B_(B1) to Ca_(B1) is 0.15 or more and 0.35 or less, and a ratio (B_(B1)/[Ca_(B1)+Mg_(B2)]) of B_(B1) to a total amount of Ca_(B1) and Mg_(B2) is 0.13 or more and 0.29 or less, where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, Ca_(B1) represents the content (mass ratio) of calcium in the component (B1) based on the total mass of the composition, and Mg_(B2) represents the content (mass ratio) of magnesium in the component (B2) based on the total mass of the composition. Hereinafter, each component which the lubricating oil composition for internal combustion engines of the present invention can contain will be first described.

<Component (A): Lubricating Base Oil>

In the present invention, the lubricating base oil used as the component (A) is not particularly limited, and a known base oil that can be used in the field of lubricating base oils can be used as appropriate, and for example, one or more mineral base oils, or one or more synthetic base oils, or mixed base oils of these can be used.

As a mineral base oil that can be used as the lubricating base oil, base oils of Group II, base oils of Group III, base oils of Group IV, or base oils of Group V in the base oil classification by API (American Petroleum Institute), or mixtures of two or more of these (mixed base oils) can be favorably used (hereinafter, the groups in the base oil classification by API are referred to simply as “API Groups”). Here, the base oils of API Group II are mineral base oils having a sulfur content of 0.03% by mass or less, a saturated content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. The base oils of API Group III are mineral base oils having a sulfur content of 0.03% by mass or less, a saturated content of 90% by mass or more, and a viscosity index of 120 or more. In addition, the base oils of API Group IV are poly-α-olefin base oils. Moreover, the base oils of API Group V are base oils other than those of API Groups I to IV, and preferred examples thereof include ester base oils.

In addition, as the mineral base oils, for example, paraffinic mineral oils, normal paraffinic base oils, isoparaffinic base oils, and mixtures thereof obtained by refining lubricating oil fractions that are obtained by atmospheric distillation and/or vacuum distillation of crude oils, through one or a combination of two or more refining processes selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, clay treatment, and the like can be used.

Preferred examples of mineral base oils include base oils which are obtained by using the following base oils (1) to (8) as raw materials, refining, through a predetermined refining method, these raw material oils and/or lubricating oil fractions recovered from these raw material oils, and recovering lubricating oil fractions:

• • (1) a distillate oil obtained by atmospheric distillation of paraffin-base crude oils and/or mixed-base crude oils;
  • (2) a distillate oil obtained by vacuum distillation of residual oils of paraffin-base crude oils and/or mixed-base crude oils (WVGO);
  • (3) a wax obtained through a lubricating oil dewaxing step (slack wax or the like) and/or a synthetic wax obtained through a gas to liquid (GTL) process or the like (Fischer-Tropsch wax, GTL wax, or the like);
  • (4) a mixed oil of one or two or more selected from the base oils (1) to (3) and/or a mild hydrocracked oil of the mixed oil;
  • (5) a mixed oil of two or more selected from the base oils (1) to (4);
  • (6) a deasphalted oil of the base oil (1), (2), (3), (4), or (5) (DAO);
  • (7) a mild hydrocracked oil of the base oil (6) (MHC); and
  • (8) a mixed oil of two or more selected from the base oils (1) to (7).

Note that the predetermined refining method is preferably hydrorefining such as hydrocracking or hydrofinishing; solvent refining such as furfural solvent extraction; dewaxing such as solvent dewaxing or catalytic dewaxing; clay refining using acid clay, activated clay, or the like; chemical (acid or alkali) washing such as sulfuric acid washing or caustic soda washing, or the like. One of these refining methods may be conducted alone or two or more of these may be conducted in combination. In addition, in the case where two or more refining methods are combined, the order of them is not particularly limited, and may be selected as appropriate.

In addition, as the mineral base oil, a base oil (9) or (10) described below, which is obtained by conducting a predetermined process on a base oil selected from the above-described base oils (1) to (8) or lubricating oil fractions recovered from the base oil is particularly preferable.

• • (9) a hydrocracked base oil obtained by: hydrocracking a base oil selected from the above-described base oils (1) to (8) or lubricating oil fractions recovered from the base oil; and conducting a dewaxing process such as solvent dewaxing or catalytic dewaxing on a product thereof or lubricating oil fractions recovered from the product by distillation or the like, or distilling the product thereof after the dewaxing process; and
  • (10) a hydroisomerized base oil obtained by: hydroisomerizing a base oil selected from the above-described base oils (1) to (8) or lubricating oil fractions recovered from the base oil; and conducting a dewaxing process such as solvent dewaxing or catalytic dewaxing on a product thereof or lubricating oil fractions recovered from the product by distillation or the like, or distilling the product thereof after the dewaxing process.

Note that as the lubricating base oils of the above-described (9) and (10), a lubricating base oil produced through a catalytic dewaxing process (step) as the dewaxing process is more preferable. In addition, when the lubricating base oil of the above-described (9) or (10) is obtained, a solvent refining process and/or hydrofinishing process step may be further conducted at an appropriate stage as necessary.

% C_P of the mineral base oil is preferably 70 to 99, more preferably 70 to 95, further preferably 75 to 95, and particularly preferably 75 to 94. When % C_P of the base oil is equal to or more than the above-described lower limit value, it becomes possible to enhance the viscosity-temperature properties and also to further enhance the fuel saving performance. In addition, in the case where the base oil is blended with an additive, it becomes possible to allow the additive to sufficiently exert the effectiveness. In addition, when % C_P of the base oil is equal to or less than the above-described upper limit value, it becomes possible to enhance the solubility of the additive.

% C_A of the mineral base oil is preferably 2 or less, more preferably 1 or less, further preferably 0.8 or less, and particularly preferably 0.5 or less. When % C_A of the base oil is equal to or less than the above-described upper limit value, it becomes possible to enhance the viscosity-temperature properties and also to further enhance the fuel saving performance.

% C_N of the mineral base oil is preferably 1 to 30, and more preferably 4 to 25. When % C_N of the base oil is equal to or less than the above-described upper limit value, it becomes possible to enhance the viscosity-temperature properties and also to further enhance the fuel saving performance. In addition, when % C_N is equal to or more than the above-described lower limit value, it becomes possible to enhance the solubility of the additive.

In the present Description, % C_P, % C_N, and % C_A mean the percentage of paraffinic carbons to the total carbons, the percentage of naphthenic carbons to the total carbons, and the percentage of aromatic carbons to the total carbons, respectively, which are obtained by a method according to ASTM D 3238-85 (n-d-M ring analysis). That is, the above-described preferred ranges of % C_P, % C_N, and % C_A are based on values obtained by the above-described method, and for example, even when a lubricating base oil does not contain a naphthene content, the % C_N obtained by the above-described method may represent a value exceeding 0.

The content of the saturated content in the mineral base oil is preferably 90% by mass or more, preferably 95% by mass or more, and more preferably 99% by mass or more, based on the total amount of the base oil. When the content of the saturated content is equal to or more than the above-described lower limit value, the viscosity-temperature properties can be improved. Note that in the present Description, the saturated content means a value measured in accordance with ASTM D 2007-93.

In addition, as the method for separating a saturated content, a similar method that can obtain the same result can be used. For example, besides the method described in ASTM D 2007-93, the method described in ASTM D 2425-93, the method described in ASTM D 2549-91, the method using high performance liquid chromatography (HPLC), or a method obtained by modifying these methods can be used.

The aromatic content in the mineral base oil is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and particularly preferably 0 to 1% by mass, and may be 0.1% by mass or more in one embodiment, based on the total amount of the base oil. When the content of the aromatic content is equal to or less than the above-described upper limit value, it becomes possible to enhance the viscosity-temperature properties and the low-temperature viscosity properties, also to further enhance the fuel saving performance, and to reduce evaporation loss of the lubricating oil to reduce the amount of the lubricating oil consumed. In addition, it becomes possible to allow the additive blended with the lubricating oil to efficiently exert the effectiveness. In addition, the lubricating base oil may not contain an aromatic content, but when the content of the aromatic content is equal to or more than the above-described lower limit value, it becomes possible to enhance the solubility of the additive. Note that in the present Description, the aromatic content means a value measured in accordance with ASTM D 2007-93. The aromatic content normally includes alkyl benzenes, alkyl naphthalenes, also anthracenes, phenanthrenes, and alkylated products of these, further compounds in which four or more benzene rings are condensed, aromatic compounds having heteroatoms such as pyridines, quinolines, phenols, and naphthols, and the like.

The synthetic base oil that can be used as the lubricating base oil is not particularly limited, and a known synthetic base oil can be used as appropriate. As such a synthetic base oil, for example, synthetic base oils of poly-α-olefins and hydrogenated products thereof, isobuten oligomers and hydrogenated products thereof, isoparaffinm, alkyl benzenes, alkyl naphthalenes, diesters (such as ditridecyl glutarate, bis-2-ethylhexyl azipate, diisodecyl azipate, ditridecyl azipate, and bis-2-ethylhexyl sebacate), polyol esters (such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate), polyoxyalkylene glycols, dialkyl diphenyl ethers, polyphenyl ethers, mixtures of these, and the like may be used, and among these, poly-α-olefin base oils are preferable. Typical examples of poly-α-olefin base oils include oligomers and co-oligomers of α-olefins having 2 to 32 carbon atoms, and preferably 6 to 16 carbon atoms (such as 1-octene oligomers, decene oligomers, and ethylene-propylene co-oligomers) and hydrogenated products thereof.

The kinematic viscosity at 100° C. of the lubricating base oil is preferably 2.0 to 5.0 mm²/s (more preferably 3.0 to 5.0 mm²/s, further preferably 4.0 to 4.8 mm²/s, and particularly preferably 4.1 to 4.7 mm²/s). When the kinematic viscosity at 100° C. of the lubricating base oil is equal to or more than the above-described lower limit value, it becomes possible to efficiently form an oil film at lubricating portions, and also to reduce evaporation loss of the lubricating oil composition to reduce the amount of the lubricating oil consumed, as compared with the case where the kinematic viscosity is less than the above-described lower limit value. In addition, when the kinematic viscosity at 100° C. of the lubricating base oil is equal to or less than the above-described upper limit, it becomes possible to achieve further excellent fuel saving performance as compared with the case where the kinematic viscosity is more than the above-described upper limit. Note that in the present Description, the “kinematic viscosity at 100° C.” means a kinematic viscosity at 100° C. measured in accordance with JIS K 2283-2000.

The kinematic viscosity at 40° C. of the lubricating base oil is preferably 9.0 to 36.0 mm²/s (more preferably 12.6 to 33.2 mm²/s, further preferably 15.8 to 25.2 mm²/s, particularly preferably 17.7 to 21.6 mm²/s, and most preferably 17.5 to 22.1 mm²/s). When the kinematic viscosity at 40° C. of the lubricating base oil is equal to or less than the above-described upper limit value, it becomes possible to achieve further excellent low-temperature viscosity properties and fuel saving performance of the lubricating oil composition as compared with the case where the kinematic viscosity is more than the above-described upper limit. In addition, when the kinematic viscosity at 40° C. of the lubricating base oil is equal to or more than the above-described lower limit value, it becomes possible to improve oil film formation at lubricating portions to achieve excellent lubricity, and also to reduce evaporation loss of the lubricating oil composition to reduce the amount of the lubricating oil consumed, as compared with the case where the kinematic viscosity is less than the above-described lower limit value. Note that in the present Description, the “kinematic viscosity at 40° C.” means a kinematic viscosity at 40° C. measured in accordance with JIS K 2283-2000.

The viscosity index of the lubricating base oil is preferably 100 or more (more preferably 105 or more, further preferably 110 or more, particularly preferably 115 or more, and most preferably 120 or more). When the viscosity index is equal to or more than the above-described lower limit value, it becomes possible to improve viscosity-temperature properties and anti-wear performance of the lubricating oil composition, and also to improve fuel saving performance, and further to reduce evaporation loss of the lubricating oil composition to reduce the amount of the lubricating oil consumed, as compared with the case where the viscosity index is less than the above-described lower limit value. Note that in the present Description, the “viscosity index” means a viscosity index measured in accordance with JIS K 2283-1993.

The NOACK evaporation loss at 250° C. of the lubricating base oil is preferably 30% by mass or less (more preferably 15% by mass or less). The lower limit of the NOACK evaporation loss at 250° C. of the lubricating base oil is not particularly limited, but is normally 3% by mass or more. Note that in the present Description, the “NOACK evaporation loss at 250° C.” is an evaporation loss at 250° C. of the lubricating base oil or the lubricating oil composition measured in accordance with ASTM D 5800.

The pour point of the lubricating base oil is preferably −10° C. or less (more preferably −12.5° C. or less, and further preferably −15° C. or less). When the pour point is equal to or less than the above-described upper limit value, it becomes possible to improve low-temperature fluidity of the whole lubricating oil composition as compared with the case where the pour point is more than the above-described upper limit. Note that in the present Description, the “pour point” means a pour point measured in accordance with JIS K 2269-1987.

The content of the sulfur content of the lubricating base oil depends on the content of the sulfur content of the raw materials. For example, in the case of using raw materials that substantially do not contain sulfur like a synthetic wax component obtained by the Fischer Tropsch reaction or the like, a lubricating base oil that substantially does not contain sulfur can be obtained. Note that in the present Description, the “sulfur content” means a sulfur content measured in accordance with JPI-5S-38. In addition, in the case of using raw materials that contain sulfur, such as slack wax obtained through the process of refining a lubricating base oil and microwax obtained through a wax refining process, the sulfur content in the obtained lubricating base oil is normally 100 mass ppm or more. From the viewpoint of reduction in the sulfur content of the lubricating oil composition, the content of the sulfur content of the lubricating oil composition is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, further preferably 10 mass ppm or less, and particularly preferably 5 mass ppm or less.

The content of a nitrogen content in the lubricating base oil is preferably 10 mass ppm or less, (more preferably 5 mass ppm, and further preferably 3 mass ppm or less). In the present Description, the nitrogen content means a nitrogen content measured in accordance with JIS K 2609-1990.

The content of the lubricating base oil (the whole base oil) in the lubricating oil composition is preferably 70 to 95% by mass (more preferably 75 to 85% by mass) based on the total mass of the composition.

<Component (B): Metal-Based Detergent>

The metal-based detergent used as the component (B) in the present invention contains:

• • (B1) a calcium-based detergent in which a content of calcium based on a total mass of the composition (the content of calcium derived from the component (B1) based on the total mass of the composition) is within a range of 1650 mass ppm or more and 2500 mass ppm or less; and
  • (B2) a magnesium-based detergent in which a content of magnesium based on the total mass of the composition (the content of magnesium derived from the component (B2) based on the total mass of the composition) is within a range of 20 mass ppm or more and 400 mass ppm or less.

Here, the “calcium-based detergent” is a metal-based detergent containing calcium as a metal, and the “magnesium-based detergent” is a metal-based detergent containing magnesium as a metal. As such metal-based detergents, metal-based detergents may be selected as appropriate from known metal-based detergents (such as, for example, sulfonate detergents, phenate detergents, and salicylate detergents each containing calcium or magnesium as a metal) and used such that the amounts of calcium, magnesium, and boron each satisfy a desired content ratio. Here, as “sulfonate detergents”, “phenate detergents”, and “salicylate detergents” given as examples of known metal-based detergents, for example, those described in paragraphs to of Japanese Unexamined Patent Application Publication No. 2020-76004 and those described in paragraphs to of International Publication No. WO2018/212340, and the like may be used as appropriate.

<Regarding the Component (B1)>

The “calcium-based detergent” used as the component (B1) is a metal-based detergent containing calcium as a metal, and contains at least a calcium-based detergent (a component (B1-1)) containing boron and calcium in the component. Causing the component (B1) to contain the component (B1-1) makes it possible to effectively reduce friction and also to improve the LSPI suppressing performance as compared with the case without the component (B1-1).

The “calcium-based detergent” to be used as the component (B1) needs to contain the component (B1-1) containing boron and calcium, but may contain a calcium-based detergent other than the component (B1-1). As such a calcium-based detergent other than the component (B1-1), a known calcium-based detergent that does not contain boron (a known metal-based detergent that does not contain boron and contains calcium as a metal) may be used as appropriate. As described above, as the component (B1), one composed of only the component (B1-1); or a mixture of the component (B1-1) and a calcium-based detergent that does not contain boron may be used as appropriate depending on the purpose.

The type of the calcium-based detergent used as the component (B1) is not particularly limited, and includes, for example, sulfonate detergents, phenate detergents, salicylate detergents, and the like each containing calcium as a metal. Among such calcium-based detergents, a salicylate detergent containing calcium as a metal is preferable from the viewpoint of friction reducing performance.

Such a sulfonate detergent containing calcium as a metal (a calcium sulfonate detergent) is not particularly limited, and a known one may be used as appropriate. Preferred examples of such a calcium sulfonate detergent include, for example, calcium salts of alkyl aromatic sulfonic acids obtained by sulfonating alkyl aromatic compounds having molecular weights of 300 to 1500 (more preferably 400 to 1300). The above-described alkyl aromatic sulfonic acids include, for example, petroleum sulfonic acids, synthetic sulfonic acids, and the like. Moreover, as the above-described petroleum sulfonic acid or synthetic sulfonic acid, a known one may be used as appropriate. In addition, as the calcium sulfonate detergent, a known one that can be used in lubricating oil compositions may be used as appropriate.

The salicylate detergent containing calcium as a metal (a calcium salicylate detergent) is not particularly limited, and a known one may be used as appropriate. Such a salicylate detergent includes, for example, calcium salts of alkyl salicylic acids each having one or two alkyl groups or alkenyl groups each having 4 to 36 (more preferably 14 to 30) carbon atoms as substituents, and mixtures of these. In addition, as the calcium salicylate detergent, a known one that can be used in lubricating oil compositions may be used as appropriate.

In addition, the component (B1-1) contained in the component (B1) is preferably a calcium-based detergent containing calcium borate, more preferably a calcium-based detergent overbased with calcium borate, and particularly preferably a calcium salicylate detergent overbased with calcium borate (calcium borate salicylate), from the viewpoint of friction reducing performance under particularly severe sliding conditions.

In addition, as the component (B1), a mixture of the component (B1-1) and (B1-2) a calcium-based detergent containing calcium carbonate may be favorably used from the viewpoint of improving the fuel saving performance depending on application conditions. The component (B1-2) (a calcium-based detergent containing calcium carbonate) is not particularly limited, and is more preferably a calcium-based detergent overbased with calcium carbonate, and particularly preferably a calcium salicylate detergent overbased with calcium carbonate.

In the case where the component (B1) is a mixture of the component (B1-1) and a calcium-based detergent other than the component (B1-1) (preferably the component (B1-2)), the content of the component (B1-1) in the component (B1) is not particularly limited, but the amount of the component (B1-1) is preferably 30 to 100% by mass (more preferably 45 to 100% by mass, and further preferably 67 to 100% mass) to the total amount of the component (B1). When the content of the component (B1-1) is equal to or more than the above-described lower limit, it becomes possible to further improve the friction reducing performance under particularly severe sliding conditions as compared with the case where the content is less than the above-described lower limit.

Regarding the component (B1-1) used as the component (B1), the content of boron in the component (B1-1) is preferably 1.0 to 5.0% by mass (more preferably 1.3 to 4.5% by mass, and further preferably 2.0 to 3.0% by mass) relative to the total amount of the component (B1-1). When the content of B in the component (B1-1) is equal to or more than the above-described lower limit, it becomes possible to further improve the friction reducing performance and the LSPI suppressing performance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to improve the stability of the lubricating oil composition as compared with the case where the content is more than the above-described upper limit.

The calcium-based detergent used as the component (B1) is such that for each calcium-based detergent contained in the component (B1) (in the case where the component (B1) is composed of one type, the one type), the content of calcium (Ca) is preferably 2.0 to 11.5% by mass (more preferably 4.0 to 10.0% by mass, and further preferably 5.7 to 7.2% by mass). When the content of calcium (Ca) in each calcium-based detergent is equal to or more than the above-described lower limit, it becomes possible to improve reduction in friction loss under low-temperature conditions as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to improve the stability of the lubricating oil composition as compared with the case where the content is more than the above-described upper limit.

The total base number (TBN) of each calcium-based detergent used as the component (B1) is not particularly limited, but the total base number of each calcium-based detergent is 50 to 500 mg KOH/g, more preferably 100 to 500 mg KOH/g, and particularly preferably 150 to 500 mg KOH/g. When the total base number of each calcium-based detergent used as the component (B1) is equal to or more than the above-described lower limit, it becomes possible to improve acid neutralizing performance as compared with the case where the total base number is less than the above-described lower limit, and when the total base number is equal to or less than the above-described upper limit, it becomes possible to improve the solubility of each additive in the lubricating oil composition as compared with the case where the total base number is more than the above-described upper limit. Note that in the present Description, the “total base number (TBN)” means a total base number measured by the perchloric acid method in accordance with JIS K 2501.

The component (B1) needs to be used such that the content (Ca_(B1)) of calcium derived from the component (B1) based on the total mass of the composition becomes within a range of 1650 mass ppm or more and 2500 mass ppm or less (more preferably 1650 mass ppm or more and 2200 mass ppm or less, further preferably 1700 mass ppm or more and 1900 mass ppm or less, and particularly preferably 1750 mass ppm or more and 1900 mass ppm or less). When the content (Ca_(B1)) of calcium is equal to or more than the above-described lower limit, it becomes possible to improve the detergency as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to improve both the LSPI suppressing performance and the fuel saving performance as compared with the case where the content is more than the above-described upper limit.

In addition, the content (B_(B1)) of boron derived from the component (B1) is preferably 50 mass ppm or more and 1000 mass ppm or less (more preferably 200 mass ppm or more and 700 mass ppm or less, further preferably 400 mass ppm or more and 700 mass ppm or less, and particularly preferably 400 mass ppm or more and 650 mass ppm or less) based on the total mass of the composition (based on the total amount of the lubricating oil composition). When the content (B_(B1)) of boron is equal to or more than the above-described lower limit, it becomes possible to further improve the friction reducing performance and LSPI suppressing performance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to further improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit.

In addition, the content of the component (B1) is preferably 1.5 to 3.5% by mass (more preferably 2.0 to 3.2% by mass, and further preferably 2.4 to 2.9% by mass) based on the total amount of the lubricating oil composition. When the content of the component (B1) is equal to or more than the above-described lower limit, it becomes possible to improve the detergency as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to further improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit.

Moreover, the content (B_(B1)) of boron derived from the component (B1) is preferably 50% by mass or more, more preferably 60% by mass to 100% by mass, and particularly preferably 70% by mass to 100% by mass, relative to the total amount of boron contained in the composition. When the proportion of B_(B1) to the total amount of boron in the composition is equal to or more than the above-described lower limit, it becomes possible to further improve the LSPI suppressing performance as compared with the case where the proportion is less than the above-described lower limit.

In addition, the content (Ca_(B1)) of calcium derived from the component (B1) is preferably 50% by mass or more, more preferably 75% by mass to 100% by mass, and particularly preferably 90% by mass to 100% by mass, relative to the total amount of calcium contained in the composition. When the proportion of Ca_(B1) to the total amount of calcium in the composition is equal to or more than the above-described lower limit, it becomes possible to further improve the LSPI suppressing performance as compared with the case where the proportion is less than the above-described lower limit.

Note that the content (B_(B1)) of boron derived from the component (B1) based on the total mass of the composition and the content (Ca_(B1)) of calcium derived from the component (B1) based on the total mass of the composition can be measured by the measurement method specified in JPI-5S-38.

<Regarding the Component (B2)>

The “magnesium-based detergent” used as the component (B2) is not particularly limited, and a known metal-based detergent containing magnesium as a metal may be used as appropriate. Such a magnesium-based detergent includes, for example, sulfonate detergents, phenate detergents, salicylate detergents, and the like each containing magnesium as a metal. Among such magnesium-based detergents, a sulfonate detergent containing magnesium as a metal and a salicylate detergent containing magnesium as a metal are preferable from the viewpoint of friction reducing performance.

Such a sulfonate detergent containing magnesium as a metal (a magnesium sulfonate detergent) is not particularly limited, and a known one may be used as appropriate. Preferred examples of such a magnesium sulfonate detergent include, for example, magnesium salts of alkyl aromatic sulfonic acids obtained by sulfonating alkyl aromatic compounds having molecular weights of 300 to 1500 (more preferably 400 to 1300). The above-described alkyl aromatic sulfonic acids include, for example, petroleum sulfonic acids, synthetic sulfonic acids, and the like. Moreover, as the above-described petroleum sulfonic acid or synthetic sulfonic acid, a known one may be used as appropriate. In addition, as the magnesium sulfonate detergent, a known one that can be used in lubricating oil compositions may be used as appropriate.

The salicylate detergent containing magnesium as a metal (a magnesium salicylate detergent) is not particularly limited, and a known one may be used as appropriate. Such a salicylate detergent includes, for example magnesium salts of alkyl salicylic acids each having one or two alkyl groups or alkenyl groups each having 4 to 36 (more preferably 14 to 30) carbon atoms as substituents, and mixtures of these. In addition, as the magnesium salicylate detergent, a known one that can be used in lubricating oil compositions may be used as appropriate.

In addition, the magnesium-based detergent is preferably a magnesium-based detergent containing magnesium carbonate. The magnesium-based detergent containing magnesium carbonate is not particularly limited, and is more preferably a magnesium-based detergent overbased with magnesium carbonate, and among these, a magnesium sulfonate detergent overbased with magnesium carbonate is particularly preferable from the viewpoint of suppressing loss of the total base number when water is mixed (loss of the total base number associated with coarse-graining, sedimentation, or precipitation of the magnesium-based detergent under hydrolytic conditions).

The content of magnesium (Mg) in the component (B2) is preferably 6.0 to 10.0% by mass (more preferably 7.5 to 9.5% by mass, and further preferably 7.5 to 9.1% by mass) relative to the total amount of the component (B2). When the content of magnesium in the component (B2) is equal to or more than the above-described lower limit, it becomes possible to reduce the viscosity resistance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to improve the stability of the lubricating oil composition as compared with the case where the content is more than the above-described upper limit.

The total base number (TBN) of each magnesium-based detergent used as the component (B2) is not particularly limited, but is preferably 50 to 500 mg KOH/g, more preferably 100 to 500 mg KOH/g, and particularly preferably 150 to 500 mg KOH/g. When the total base number of the component (B2) is equal to or more than the above-described lower limit, it becomes possible to further improve reduction in viscosity resistance as compared with the case where the total base number is less than the above-described lower limit, and when the total base number is equal to or less than the above-described upper limit, it becomes possible to improve the stability of the lubricating oil composition as compared with the case where the total base number is more than the above-described upper limit.

The component (B2) needs to be used such that the content (Mg_(B2)) of magnesium derived from the component (B2) based on the total mass of the composition becomes within a range of 20 mass ppm or more and 400 mass ppm or less (more preferably 20 mass ppm or more and 300 mass ppm or less, further preferably 100 mass ppm or more and 300 mass ppm or less, and particularly preferably 100 mass ppm or more and 200 mass ppm or less). When the content (Mg_(B2)) of magnesium is equal to or more than the above-described lower limit, it becomes possible to improve the LSPI suppressing performance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to improve the fuel saving performance as compared with the case where the content is more than the above-described upper limit. Note that the content (Mg_(B2)) of magnesium derived from the component (B2) based on the total mass of the composition can be measured by the measurement method described in JPI-5S-38.

In addition, the content of the component (B2) is preferably 0.01 to 0.60% by mass (more preferably 0.01 to 0.40% by mass, and further preferably 0.10 to 0.27% by mass) based on the total amount of the lubricating oil composition. When the content of the component (B2) is equal to or more than the above-described lower limit, it becomes possible to improve the acid neutralizing performance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to further improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit.

In addition, the content (Mg_(B2)) of magnesium derived from the component (B2) is preferably 50% by mass, more preferably 75% by mass to 100% by mass, and particularly preferably 90% by mass to 100% by mass, relative to the total amount of magnesium contained in the composition. When the proportion of Mg_(B2) to the total amount of magnesium in the composition is equal to or more than the above-described lower limit, it becomes possible to further improve the fuel saving performance as compared with the case where the proportion is less than the above-described lower limit.

The component (B) may contain a metal-based detergent other than the component (B1) and the component (B2) as necessary. Note that the proportion of the total amount of the component (B1) and the component (B2) to the total amount of the component (B) is preferably 50 to 100% by mass (more preferably 75 to 100% by mass and particularly preferably 90 to 100% by mass). When the proportion of the total amount of the component (B1) and the component (B2) is equal to or more than the above-described lower limit, it becomes possible to further improve the LSPI suppressing performance and the friction reducing performance as compared with the case where the proportion is less than the above-described lower limit. The metal-based detergent other than the component (B1) and the component (B2) is not particularly limited, and a known metal-based detergent may be used as appropriate. Note that as the component (B), a mixture of the component (B1) and the component (B2) is more preferably used from the viewpoint of achieving both the LSPI suppressing performance and the friction reducing performance.

In addition, the content of the component (B) is preferably 1.0 to 4.0% by mass (more preferably 2.2 to 3.0% by mass, and further preferably 2.6 to 3.0% by mass) based on the total amount of the lubricating oil composition. When the content of the component (B) is equal to or more than the above-described lower limit, it becomes possible to improve the acid neutralizing performance as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to further improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit.

In addition, in the lubricating oil composition for internal combustion engines of the present invention, a ratio (B_(B1)/Ca_(B1)) of B_(B1) to Ca_(B1) is 0.15 or more and 0.35 or less (more preferably 0.21 or more and 0.30 or less, and particularly preferably 0.26 or more and 0.29 or less), where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, and Ca_(B1) represents the content (mass ratio) of calcium in the component (B1) based on the total mass of the composition. When B_(B1)/Ca_(B1) is equal to or more than the above-described lower limit, it becomes possible to achieve excellent LSPI suppressing performance, making it possible to achieve both excellent LSPI suppressing performance and excellent fuel saving performance as compared with the case where B_(B1)/Ca_(B1) is less than the above-described lower limit, and when B_(B1)/Ca_(B1) is equal to or less than the above-described upper limit, it becomes possible to make the friction coefficient have a small value, making it possible to achieve both excellent LSPI suppressing performance and excellent fuel saving performance as compared with the case where B_(B1)/Ca_(B1) is more than the above-described upper limit.

In the lubricating oil composition for internal combustion engines of the present invention, a ratio (B_(B1)/[Ca_(B)+Mg_(B2)]) of B_(B1) to a total amount (Ca_(B1)+Mg_(B2)) of Ca_(B1) and Mg_(B2) is 0.13 or more and 0.29 or less (more preferably 0.23 or more and 0.29 or less, and particularly preferably 0.25 or more and 0.29 or less), where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, Ca_(B1) represents the content (mass ratio) of calcium in the component (B1) based on the total mass of the composition, and Mg_(B2) represents the content (mass ratio) of magnesium in the component (B2) based on the total mass of the composition. When B_(B1)/[Ca_(B)+Mg_(B2)] is equal to or more than the above-described lower limit, it becomes possible to improve the LSPI suppressing performance as compared with the case where B_(B1)/[Ca_(B)+Mg_(B2)] is less than the above-described lower limit, and when B_(B1)/[Ca_(B)+Mg_(B2)] is equal to or less than the above-described upper limit, it becomes possible to improve the fuel saving performance as compared with the case where B_(B1)/[Ca_(B)+Mg_(B2)] is more than the above-described upper limit.

In addition, in the lubricating oil composition for internal combustion engines of the present invention, a ratio (B_(B1)/Ca) of B_(B1) to Ca is preferably 0.15 or more and 0.35 or less (more preferably 0.21 or more and 0.31 or less, and particularly preferably 0.26 or more and 0.30 or less), where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, and Ca represents the total amount (the content of all calcium: mass ratio) of calcium in the composition based on the total mass of the composition. When B_(B1)/Ca is equal to or more than the above-described lower limit, it becomes possible to further improve the LSPI suppressing performance as compared with the case where B_(B1)/Ca is less than the above-described lower limit, and when B_(B1)/Ca is equal to or less than the above-described upper limit, it becomes possible to further improve the fuel saving performance as compared with the case where B_(B1)/Ca is more than the above-described upper limit.

In the lubricating oil composition for internal combustion engines of the present invention, a ratio (B_(B1)/[Ca+Mg]) of B_(B1) to a total amount of Ca and Mg is preferably 0.13 or more and 0.29 or less (more preferably 0.23 or more and 0.29 or less, and particularly preferably 0.25 or more and 0.29 or less), where B_(B1) represents the content (mass ratio) of boron in the component (B1) based on the total mass of the composition, Ca represents the total amount (the content of all calcium: mass ratio) of calcium in the composition based on the total mass of the composition, and Mg represents the total amount (the content of all magnesium: mass ratio) of magnesium in the composition based on the total mass of the composition. When B_(B1)/[Ca+Mg] is equal to or more than the above-described lower limit, it becomes possible to further improve the LSPI suppressing performance as compared with the case where B_(B1)/[Ca+Mg] is less than the above-described lower limit, and when B_(B1)/[Ca+Mg] is equal to or less than the above-described upper limit, it becomes possible to further improve the fuel saving performance as compared with the case where B_(B1)/[Ca+Mg] is more than the above-described upper limit.

Note that the method for preparing a metal-based detergent used as the component (B) is not particularly limited, and a known method may be employed as appropriate.

In addition, the lubricating oil composition for internal combustion engines of the present invention may comprise a known additive used in general for lubricating oil compositions for internal combustion engines as appropriate depending on the purpose in order to improve the performance, besides the component (A) and the component (B) (the component including the component (B1) and the component (B2)). Hereinafter, components that can be favorably used as such additives will be described.

<Component (C): Poly(meth)acrylate-based Viscosity Index Improver>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention comprise (C) a poly(meth)acrylate-based viscosity index improver because this makes it possible to further improve the fuel saving performance. Here, as the “poly(meth)acrylate-based viscosity index improver”, a known poly(meth)acrylate-based compound used as a viscosity index improver (for example, a “viscosity index improver” described in International Publication No. WO 2019/221295, a “poly(meth)acrylate compound” described Japanese Unexamined Patent Application Publication No. 2018-177986, a “comb-shaped polymer” described in Japanese Unexamined Patent Application Publication No. 2017-101211, a “viscosity index improver” described in International Publication No. WO2016/159006, a “viscosity index improver” described in International Publication No. WO2017/099052, a “viscosity index improver” described in Japanese Unexamined Patent Application Publication No. 2017-110196, a “(co)polymer (A)” described in Japanese Unexamined Patent Application Publication No. 2017-110196, or the like) may be used as appropriate.

Regarding the poly(meth)acrylate-based polymer used as the component (C), the structure and the like are not particularly limited, and a so-called linear poly(meth)acrylate-based polymer or a so-called comb-shaped poly(meth)acrylate-based polymer may be used. Among these, as the component (C), a component containing a comb-shaped poly(meth)acrylate-based polymer is more preferable from the viewpoint of improvement in the fuel saving performance associated with improvement in the viscosity-temperature properties and oil film formation. In addition, it is particularly preferable that the poly(meth)acrylate-based viscosity index improver be a comb-shaped poly(meth)acrylate-based polymer. Here, as the comb-shaped poly(meth)acrylate-based polymer, a known poly(meth)acrylate-based polymer having a so-called comb-shaped structure (for example, a “comb-shaped polymer” described in Japanese Unexamined Patent Application Publication No. 2017-101211, a “comb-shaped poly(meth)acrylate” described in Japanese Unexamined Patent Application Publication No. 2018-177986, a “comb-shaped poly(meth)acrylate” described in International Publication No. WO 2016/159006, a “viscosity index improver” described in Japanese Unexamined Patent Application Publication No. 2017-110196, a “(co)polymer (A)” described in Japanese Unexamined Patent Application Publication No. 2017-110196, or the like) may be used as appropriate.

As such a comb-shaped poly(meth)acrylate-based polymer, a poly(meth)acrylate-based polymer having a comb-shaped structure that is a copolymer of a (meth)acrylate and a (meth)acrylate-based macromonomer may be used as appropriate. In addition, as such a comb-shaped poly(meth)acrylate-based polymer, a copolymer of a (meth)acrylate, a (meth)acrylate-based macromonomer, and another monomer (for example, ethylene, styrene, 1-butene, or the like) may be used. Note that in the present Description, the “(meth)acrylate” means an acrylate and/or a methacrylate.

In addition, as the comb-shaped poly(meth)acrylate-based polymer, a copolymer of a (meth)acrylate (hereinafter, referred to simply as a “monomer (M-1)” in some cases) represented by the following formula (1):

[in the formula (1), R¹ represents a hydrogen atom or a methyl group, and R² represents a linear or branched hydrocarbon group having 2 or more and 10 or less carbon atoms.], and
a (meth)acrylate-based macromonomer (hereinafter, referred to simply as a “macromonomer (M-2)” in some cases) represented by the following formula (2):

[in the formula (2), R³ represents a hydrogen atom or a methyl group, and R⁴ represents a hydrocarbon group having 12 or more and 24 or less carbon atoms.] are preferable.

R² in the formula (1) is a linear or branched hydrocarbon group (more preferably an alkyl group) having 2 or more and 10 or less carbon atoms. The number of carbon atoms of the hydrocarbon group selected as R² is preferably 4 or more and 10 or less (more preferably 4 or more and 8 or less, and particularly preferably 4 or more and 6 or less).

In addition, the number of carbon atoms of the hydrocarbon group selected as R⁴ in the formula (2) is preferably 12 or more and 24 or less (more preferably 12 or more and 20 or less, and particularly preferably 12 or more and 18 or less). When such number of carbon atoms is equal to or more than the lower limit, it becomes possible to increase the viscosity index, and when such number of carbon atoms is equal to or less than the upper limit, it becomes possible to achieve a favorable flow under low-temperature conditions. Note that the hydrocarbon groups may be linear or branched. Moreover, as the macromonomer (M-2), for example, a macromonomer derived from a hydrogenated product of a polyolefin obtained by copolymerizing butadiene and isoprene may be used. In addition, as such a macromonomer (M-2), for example, a known macromonomer (for example, a macromonomer described in Japanese Unexamined Patent Application Publication No. 2018-177986, a “monomer (a)” described in Japanese Unexamined Patent Application Publication No. 2017-110196, or the like) may also be used as appropriate.

In addition, in the copolymer of the monomer (M-1) and the macromonomer (M-2), a copolymerization molar ratio of these monomers is not particularly limited, but the monomer (M-1):the monomer (M-2) is preferably around 20:80 to 90:10 (more preferably 30:70 to 80:20, and further preferably 40:60 to 70:30).

In addition, the weight-average molecular weight (Mw) of a poly(meth)acrylate-based polymer (preferably, a comb-shaped poly(meth)acrylate-based polymer) to in the be contained poly(meth)acrylate-based viscosity index improver is preferably 100000 to 1000000 (more preferably 300000 to 1000000, and further preferably 600000 to 800000). When the weight-average molecular weight is equal to or more than the above-described lower limit, it becomes possible to improve the viscosity index when the poly(meth)acrylate-based polymer is dissolved into the lubricating base oil, thus achieving further excellent fuel saving performance and low-temperature viscosity properties as compared with the case where the weight-average molecular weight is less than the above-described lower limit, and when the weight-average molecular weight is equal to or less than the above-described upper limit, it becomes possible to achieve further excellent fuel saving performance and low-temperature viscosity properties and also to improve the shear stability, the solubility into the lubricating base oil, and the storage stability as compared with the case where the weight-average molecular weight is more than the above-described upper limit.

In addition, when (C) the poly(meth)acrylate-based viscosity index improver contains a comb-shaped poly(meth)acrylate-based polymer, the content of the comb-shaped poly(meth)acrylate-based polymer relative to the total amount of the component (C) is preferably 30% by mass or more (more preferably 50 to 100% by mass, further preferably 95 to 100% by mass, and particularly preferably 98 to 100% by mass). When the content of the comb-shaped poly(meth)acrylate-based polymer in the component (C) is equal to or more than the above-described lower limit, it becomes possible to further improve the fuel saving performance owing to improvements in the viscosity-temperature properties and the oil film formation as compared with the case where the content is less than the above-described lower limit. Note that as the component (C), it is more preferable to use a component containing only a comb-shaped poly(meth)acrylate-based polymer from the viewpoint of improvements in the viscosity-temperature properties and the oil film formation.

In addition, the content of the component (C) is preferably 5 to 15% by mass (more preferably 7 to 11% by mass, and further preferably 9 to 11% by mass) based on the total amount of the lubricating oil composition. When the content of the component (C) is equal to or more than the above-described lower limit, it becomes possible to improve the viscosity-temperature properties and to improve the anti-wear performance owing to oil film formation as compared with the case where the content is less than the above-described lower limit, and when the content is equal to or less than the above-described upper limit, it becomes possible to further improve the fuel saving performance by suppressing excessive thickening as compared with the case where the content is more than the above-described upper limit.

The method for preparing a poly(meth)acrylate-based polymer used in the component (C) is not particularly limited, and a known method may be employed as appropriate. As such a preparation method, for example, a method for obtaining a poly(meth)acrylate-based polymer by polymerizing the monomer (M-1) and the macromonomer (M-2), and another monomer as necessary, under the presence of a polymerization initiator (for example, benzoyl peroxide or the like) through radical solution polymerization may be employed.

<Component (D): Ashless Dispersant>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention further comprise (D) an ashless dispersant because it becomes possible to highly disperse a metal powder generated by wear during use, to improve the anti-wear performance, and also to improve the oxidation stability. As the component (D), a known compound used as an ashless dispersant in the field of lubricating oil compositions (for example, besides a “nitrogen-containing ashless dispersant” described in International Publication No. WO2019/221295, ashless dispersants described in Japanese Unexamined Patent Application Publication No. 2003-155492, Japanese Unexamined Patent Application Publication No. 2020-76004, and International Publication No. WO2013/147262, or the like) may be favorably used.

The ashless dispersant includes, for example, a mono-or bis-succinimide having at least one linear or branched alkyl group or alkenyl group in its molecule, a benzylamine having at least one alkyl group or alkenyl group in its molecule, or a polyamine having at least one alkyl group or alkenyl group in its molecule, or modified products of these with boron compounds, carboxylic acid, phosphoric acid, and the like, and the like. Note that in the component (D), the linear or branched alkyl group or alkenyl group is preferably a linear or branched alkyl group or alkenyl group having 40 to 400 (more preferably 60 to 350) carbon atoms.

In addition, as the component (D), (D1) a boronated succinimide (a boron-modified compound of the aforementioned mono-or bis-succinimide, or the like), (D2) a non-boronated succinimide (the aforementioned mono- or bis-succinimide or the like), and mixtures of these are favorably used from the viewpoint of adding more excellent dispersibility on a metal powder or the like.

In addition, as each of the component (D1) and the component (D2), a known boronated succinimide or non-boronated succinimide used as an ashless dispersant may be used as appropriate. In addition, as each of the component (D1) and the component (D2), the content of nitrogen atoms is preferably 0.5 to 3.0% by mass based on the total amount of the component (the component (D1) or the component (D2)). In addition, as the component (D1), the content of boron is preferably 0.1 to 5.0% by mass (more preferably 0.1 to 3.0% by mass) based on the total amount of the component (D1). Moreover, the weight-average molecular weight of each of the component (D1) and the component (D2) is preferably 1000 to 20000 (more preferably 2000 to 20000, and further preferably 4000 to 15000). Note that as the component (D), one type may be used alone or two or more types may be used in combination.

When the component (D) is added to the lubricating oil composition of the present invention, the content of the component (D) is not particularly limited, but is preferably 0.1 to 5.0% by mass (more preferably 1.0 to 2.5% by mass) based on the total amount of the lubricating oil composition. Setting the content of the component (D) within the above-described range makes it possible to improve the dispersion performance when insoluble contents are generated.

In addition, when the component (D) contains the component (D1), the content of boron (B_(D1)) derived from the component (D1) is preferably 90% by mass or less (more preferably 70% by mass or less, and further preferably 27% by mass or less) relative to the total amount of boron contained in the composition. When the proportion of B_(D1) to the total amount of boron in the composition is equal to or less than the above-described upper limit, it becomes possible to suppress excessive generation of ash contents as compared with the case where the proportion is more than the above-described upper limit.

<Component (E): Antioxidant>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention further comprise (E) an antioxidant because it becomes possible to improve the oxidation stability. The component (E) is not particularly limited, and a known one used as an antioxidant in the field of lubricating oil compositions may be used as appropriate, and for example, (E1) a phenol antioxidant, (E2) an amine antioxidant, (E3) a metal antioxidant (a copper antioxidant, a molybdenum antioxidant, or the like), or the like may be used.

As the component (E1), a known one may be used as appropriate, and for example, esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid; and hindered phenol compounds and bisphenol compounds such as methyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate may be used.

As the component (E2), for example, known compounds as amine antioxidants such as aromatic amine antioxidants and hindered amine antioxidants (for example, compounds presented as examples in International Publication No. WO2020/095970) may be used as appropriate. Among the aromatic amine antioxidants, alkylated diphenylamine and alkylated phenyl-α-naphthylamine may be favorably used. In addition, as the hindered amine antioxidants, for example, compounds having 2,2,6,6-tetraalkylpiperidine skeletons (2,2,6,6-tetraalkylpiperidine derivatives) may be favorably used. As the amine antioxidants, aromatic amine antioxidants may be more favorably used.

The component (E3) includes, for example, organic molybdenum antioxidants such as alkylamine complexes of oxymolybdenum sulfide or oxymolybdenum, alkenyl succinimide complexes of oxymolybdenum sulfide or oxymolybdenum, sulfurized oxymolybdenum dithiocarbamates, and sulfurized oxymolybdenum dithiophosphates, and the like. Among such molybdenum antioxidants, oxymolybdenum sulfide-or oxymolybdenum-di(tridecyl)amine complex and oxymolybdenum sulfide-or oxymolybdenum-alkenyl succinimide complexes are more preferable because these are capable of easily suppressing increase in viscosity and maintaining the fuel saving performance over a long period of time and are also more excellent in high-temperature detergency.

In addition, as the component (E), one type may be used alone or two or more types may be used in combination. Moreover, as the component (E), the component (E1), the component (E2), and the component (E3) may be used in combination as appropriate, among such combinations, it is preferable to use the component (E2) and the component (E3) in combination because it becomes possible to suppress oxidation degradation of the lubricating oil composition over a long period of time.

When the component (E) is added to the lubricating oil composition for internal combustion engines of the present invention, the content of the component (E) is preferably 1.5% by mass or more and 2.5% by mass or less (more preferably 1.7% by mass or more and 2.0% by mass or less) based on the total amount of the lubricating oil composition. Setting the content of the component (E) within the above-described range makes it possible to improve the capability of suppressing degradation of the lubricating oil composition while maintaining the solubility of the component (E).

In addition, when the component (E1) is added to the lubricating oil composition for internal combustion engines of the present invention, the content of the component (E1) is preferably 2.0% by mass or less (more preferably 0.5% by mass or less) based on the total amount of the lubricating oil composition. Setting the content of the component (E1) within the above-described range makes it possible to improve the capability of suppressing degradation of the lubricating oil composition while maintaining the solubility of the component.

In addition, when the component (E2) is added to the lubricating oil composition for internal combustion engines of the present invention, the content of the component (E2) is preferably 1.3% by mass or more and 2.3% by mass or less (more preferably 1.5% by mass or more and 1.9% by mass or less) based on the total amount of the lubricating oil composition. Setting the content of the component (E2) within the above-described range makes it possible to improve the capability of suppressing degradation of the lubricating oil composition while maintaining the solubility of the component.

Moreover, when the component (E3) is added to the lubricating oil composition for internal combustion engines of the present invention, the content of the component (E3) is preferably 0.3% by mass or less (more preferably 0.1% by mass or more and 0.2% by mass or less) based on the total amount of the lubricating oil composition. Setting the content of the component (E3) within the above-described range makes it possible to improve the capability of suppressing degradation of the lubricating oil composition while maintaining the solubility of the component.

<(F) Molybdenum Friction Modifier>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention comprise (F) a molybdenum friction modifier (an oil-soluble organic molybdenum compound). As such a molybdenum friction modifier, a known one used as a molybdenum friction modifier in the field of lubricating oil compositions may be used as appropriate.

In addition, the component (F) is more preferably a molybdenum dithiocarbamate (a sulfurized molybdenum dithiocarbamate or a sulfurized oxymolybdenum dithiocarbamate) from the viewpoint of friction reduction under boundary lubrication conditions. As the molybdenum dithiocarbamate (MoDTC), for example, a compound represented by the following general formula (3):

[in the formula (3), R¹⁰ to R¹³ each independently represent an alkyl group having 2 to 24 carbon atoms or an (alkyl)aryl group having 6 to 24 carbon atoms, and

Y¹ to Y⁴ each independently represent a sulfur atom or an oxygen atom, and at least one of Y¹ to Y⁴ represents a sulfur atom.]

may be used as appropriate.

R¹⁰ to R¹³ in the general formula (3) may be the same or different, and each represent an alkyl group having 2 to 24 carbon atoms or an (alkyl)aryl group having 6 to 24 carbon atoms (preferably an alkyl group having 4 to 13 carbon atoms or an (alkyl)aryl group having 10 to 15 carbon atoms). The alkyl group that can be selected as such R¹⁰ to R¹³ may be any of a primary alkyl group, a secondary alkyl group, and a tertiary alkyl group, and may be linear or branched.

Note that the “(alkyl)aryl group” mentioned herein means an “aryl group or alkylaryl group”. In an alkylaryl group, the substitution position of an alkyl group in an aromatic ring is optional. In addition, Y¹ to Y⁴ in the general formula (3) are each independently a sulfur atom or an oxygen atom, and at least one of Y¹ to Y⁴ is a sulfur atom.

The oil-soluble organic molybdenum compound other than molybdenum dithiocarbamate includes, for example, sulfur-containing organic molybdenum compounds such as molybdenum dithiophosphate; complexes of molybdenum compounds (for example, molybdenum oxides such as molybdenum dioxide and molybdenum trioxide, molybdic acids such as orthomolybdic acid, paramolybdic acid, and sulfurized (poly)molybdic acid, molybdic acid salts such as metal salts and ammonium salts of these molybdic acids, molybdenum sulfides such as molybdenum disulfide, molybdenum trisulfide, molybdenum pentasulfide, and molybdenum polysulfide, sulfurized molybdic acid, metal salts or amine salts of sulfurized molybdic acid, molybdenum halides such as molybdenum chloride, and the like) and sulfur-containing organic compounds (for example, alkyl(thio)xanthate, thiadiazole, mercaptothiadiazole, thiocarbonate, tetrahydrocarbylthiuram disulfide, bis(di(thio)hydrocarbyldithiophosphonate)disulfide, organic (poly)sulfide, sulfurized esters, and the like) or other organic compounds; and complexes of sulfur-containing molybdenum compounds such as sulfurized molybdic acid, and alkenyl succinimide. Note that the organic molybdenum compound may be a mononuclear molybdenum compound, or may be a polynuclear molybdenum compound such as a binuclear molybdenum compound or a trinuclear molybdenum compound.

In addition, as the oil-soluble organic molybdenum compound other than molybdenum dithiocarbamate, it is also possible to use an organic molybdenum compound that does not contain sulfur. Examples of organic molybdenum compounds that do not contain sulfur include molybdenum-amine complex, molybdenum-succinimide complex, molybdenum salts of organic acids, molybdenum salts of alcohols, and the like, and among these, molybdenum-amine complex, molybdenum salts of organic acids, and molybdenum salts of alcohols are preferable.

The content of the component (F) in the lubricating oil composition is preferably such an amount that the content of molybdenum becomes 100 to 2000 mass ppm (more preferably 300 to 1500 mass ppm, further preferably 500 to 1200 mass ppm, and particularly preferably 700 to 1000 mass ppm) based on the total amount of the lubricating oil composition. When the content of the component (F) is equal to or more than the above-described lower limit value, it becomes possible to further enhance the fuel saving performance and the LSPI suppressing performance. In addition, when the content of the component (F) is equal to or less than the above-described upper limit value, it becomes possible to enhance the storage stability of the lubricating oil composition.

<(G) Anti-Wear Agent>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention comprise (G) an anti-wear agent. The anti-wear agent is not particularly limited, and a known compound used as an anti-wear agent in lubricating oil compositions may be used. As the anti-wear agent, for example, sulfur-based, phosphorus-based, and sulfur-phosphorus-based anti-wear agents, and the like may be used. Specifically, the anti-wear agent includes phosphite esters, thiophosphite esters, dithiophosphite esters, trithiophosphite esters, phosphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts of these, metal salts of these, derivatives of these, dithiocarbamates, zinc dithiocarbamate, disulfides, polysulfides, olefin sulfides, sulfurized oils and fats, and the like.

Among these anti-wear agents, phosphorus-based anti-wear agents are preferable, zinc-containing phosphorus-based anti-wear agents are more preferable, and among these, a zinc dialkyldithiophosphate (ZnDTP) represented by the following formula (4):

[in the formula (4), R¹⁴ to R¹⁷ each independently represent a linear or branched alkyl group having 1 to 24 carbon atoms.]
is particularly preferable.

R¹⁴ to R¹⁷ in the general formula (4) each independently represent a linear or branched alkyl group having 1 to 24 carbon atoms, and may be a combination of different groups. In addition, the number of carbon atoms of each of R¹⁴ to R¹⁷ is preferably 3 or more, and preferably 12 or less, and more preferably 8 or less. In addition, R¹⁴ to R¹⁷ may be any of primary alkyl groups, secondary alkyl groups, and tertiary alkyl groups, but are preferably primary alkyl groups or secondary alkyl groups, or a combination of these, and further, a molar ratio between primary alkyl groups and secondary alkyl groups (primary alkyl groups:secondary alkyl groups) is preferably 0:100 to 30:70. This ratio may be a combination ratio between alkyl chains in a molecule, or may be a mixture ratio between ZnDTP having only primary alkyl groups and ZnDTP having only secondary alkyl groups. When secondary alkyl groups are a majority, it becomes possible to further improve the fuel saving performance. In addition, the method for producing ZnDTP is not particularly limited, and a known method may be used as appropriate, and for example, a method for synthesizing ZnDTP, including: reacting an alcohol having alkyl groups corresponding to R¹⁴ to R¹⁷ with phosphorus pentasulfide to synthesize dithiophosphoric acid; and neutralizing dithiophosphoric acid with zinc oxide may be employed.

The content of the anti-wear agent is preferably 0.1 to 5.0% by mass or less (more preferably 0.5 to 3.0% by mass or less) based on the total amount of the lubricating oil composition. When the content of the anti-wear agent is within the above-described numerical range, it is possible to achieve sufficient anti-wear effect.

<(H) Pour Point Depressant>

It is preferable that the lubricating oil composition for internal combustion engines of the present invention comprise (H) a pour point depressant. Such a pour point depressant is not particularly limited, and a known pour point depressant used in lubricating oil compositions may be used as appropriate. Such a pour point depressant includes, for example, poly(meth)acrylate, ethylene-vinyl acetate copolymer, and the like, and among these, polymethacrylate is preferable. The weight-average molecular weight of poly(meth)acrylate (more preferably polymethacrylate) used as the pour point depressant is preferably 20,000 to 100,000 (more preferably 20,000 to 80,000) from the viewpoint of pour point depressing action and shear stability.

As the pour point depressant, one type may be used alone or two or more types may be used in combination. When a pour point depressant is used, the content of the pour point depressant is preferably 0.01 to 1.0% by mass (more preferably 0.03 to 0.6% by mass) based on the total amount of the lubricating oil composition.

<(I) Other Components>

The lubricating oil composition for internal combustion engines of the present invention may further comprise other additives that can be used in lubricating oil compositions besides the above-described components. Such other components are not particularly limited, but include, for example, defoaming agents, anti-rust agents, demulsifiers, metal deactivators, and the like. As such other components, known ones may be used as appropriate, and for example, the defoaming agents include silicone oil having a kinematic viscosity at 25° C. of 1,000 to 100,000 mm²/s, alkenylsuccinimide derivatives, esters of polyhydroxy aliphatic alcohols and long-chain fatty acids, methyl salicylate, o-hydroxybenzylalcohol, and the like. In addition, the contents of such other components may be designed as appropriate such that the content of each component becomes the most appropriate amount depending on the application, and are not particularly limited, but the content of each component is preferably set to 0.001 to 5% by mass based on the total amount of the lubricating oil composition. In addition, the content of each component used as the component (I) is preferably 0.001 to 0.05 parts by mass when the total mass of the components other than the each component in the lubricating oil composition is considered as 100 parts by mass.

[Regarding the Lubricating Oil Composition]

In the lubricating oil composition for internal combustion engines of the present invention, the content of boron based on the total mass of the composition (the content of boron based on the total amount of the lubricating oil composition) is 1000 mass ppm or less (more preferably 200 mass ppm or more and 700 mass ppm or less, and further preferably 400 mass ppm or more and 650 mass ppm or less). When the content of boron based on the total amount of the composition is equal to or less than the above-described upper limit, it becomes possible to improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit, and when the content is equal to or more than the above-described lower limit, it becomes possible to improve the LSPI suppressing performance as compared with the case where the content is less than the above-described lower limit.

In the lubricating oil composition for internal combustion engines of the present invention, the content of calcium based on the total amount of the lubricating oil composition is preferably 1650 mass ppm or more and 2500 mass ppm or less (more preferably 1700 mass ppm or more and 1900 mass ppm or less, and further preferably 1750 mass ppm or more and 1900 mass ppm or less). When the content of calcium based on the total amount of the composition is equal to or less than the above-described upper limit, it becomes possible to achieve both the LSPI suppressing performance and the friction reducing performance as compared with the case where the content is more than the above-described upper limit, and when the content is equal to or more than the above-described lower limit, it becomes possible to improve the detergency owing to improvement in the acid neutralizing performance as compared with the case where the content is less than the above-described lower limit.

In the lubricating oil composition for internal combustion engines of the present invention, the content of magnesium based on the total amount of the lubricating oil composition is preferably 20 mass ppm or more and 400 mass ppm or less (more preferably 20 mass ppm or more and 300 mass ppm or less, and further preferably 100 mass ppm or more and 200 mass ppm or less). When the content of magnesium based on the total amount of the composition is equal to or less than the above-described upper limit, it becomes possible to improve the friction reducing performance as compared with the case where the content is more than the above-described upper limit, and when the content is equal to or more than the above-described lower limit, it becomes possible to improve the acid neutralizing performance as compared with the case where the content is less than the above-described lower limit.

In the lubricating oil composition for internal combustion engines of the present invention, when molybdenum is contained in the composition, the content of molybdenum based on the total amount of the lubricating oil composition is preferably 100 mass ppm or more and 1200 mass ppm or less (more preferably 700 mass ppm or more and 1000 mass ppm or less). Setting the content of molybdenum based on the total amount of the lubricating oil composition within the above-described range makes it possible to further improve the friction reducing performance while maintaining the solubility of the additives in the composition.

In the lubricating oil composition for internal combustion engines of the present invention, when phosphorus is contained in the composition, the content of phosphorus based on the total amount of the lubricating oil composition is preferably 600 mass ppm or more and 800 mass ppm or less (more preferably 700 mass ppm or more and 800 mass ppm or less). Setting the content of phosphorus based on the total amount of the lubricating oil composition within the above-described range makes it possible to avoid excessive catalyst poisoning and also to achieve both the friction reducing performance and the anti-wear performance.

In the lubricating oil composition for internal combustion engines of the present invention, when sulfur is contained in the composition, the content of sulfur based on the total amount of the lubricating oil composition is preferably 500 mass ppm or more and 3000 mass ppm or less (more preferably 1000 mass ppm or more and 2700 mass ppm or less). Setting the content of sulfur based on the total amount of the lubricating oil composition within the above-described range makes it possible to improve anti-seizure performance.

In the lubricating oil composition for internal combustion engines of the present invention, when zinc is contained in the composition, the content of zinc based on the total amount of the lubricating oil composition is preferably 500 mass ppm or more and 1300 mass ppm or less (more preferably 700 mass ppm or more and 900 mass ppm or less). Setting the content of zinc based on the total amount of the lubricating oil composition within the above-described range makes it possible to improve the anti-wear performance.

Note that the contents of boron, calcium, magnesium, molybdenum, zinc, sulfur, and phosphorus in the lubricating oil composition can be measured in accordance with JPI-5S-62.

In the lubricating oil composition for internal combustion engines of the present invention, a ratio between the content of boron based on the total amount of the lubricating oil composition and the content of calcium based on the total amount of the lubricating oil composition (mass ratio: [boron]/[calcium]) is preferably 0.15 to 0.35 (more preferably 0.25 to 0.35, and further preferably 0.26 to 0.30). Setting the mass ratio within the above-described range makes it possible to improve the LSPI suppressing performance while maintaining the friction reducing performance.

In addition, in the lubricating oil composition for internal combustion engines of the present invention, a ratio of the content of boron based on the total amount of the lubricating oil composition to the total amount (sum amount) of calcium based on the total amount of the lubricating oil composition and magnesium based on the total amount of the lubricating oil composition [mass ratio: [boron]/([calcium]+[magnesium]) is preferably 0.13 to 0.29 (more preferably 0.20 to 0.29, and further preferably 0.25 to 0.28). Setting the mass ratio within the above-described range makes it possible to improve the LSPI suppressing performance while maintaining the friction reducing performance.

The kinematic viscosity at 100° C. of the lubricating oil composition for internal combustion engines of the present invention is more preferably 4.0 to 9.3 mm²/s (further preferably 6.5 to 8.0 mm²/s). In addition, the kinematic viscosity at 40° C. of the lubricating oil composition of the present invention is more preferably 23.0 to 40.0 mm²/s (further preferably 26.0 to 30.0 mm²/s). When these kinematic viscosities are equal to or lower than the upper limit values, it becomes possible to further improve the fuel saving performance in either case as compared with the case where the kinematic viscosities are more than the upper limit values. On the other hand, when these kinematic viscosities are equal to or more than the lower limit values, it becomes possible to improve the anti-wear performance owing to the holding of oil films in either case as compared with the case where the kinematic viscosities are less than the lower limit values.

The viscosity index of the lubricating oil composition for internal combustion engines of the present invention is preferably 180 or more (more preferably 200 or more, further preferably 220 or more, and particularly preferably 225 or more). When the viscosity index is equal to or more than the above-described lower limit value, it becomes possible to improve the viscosity-temperature properties and anti-wear performance of the lubricating oil composition, and also to further improve the fuel saving performance, as compared with the case where the viscosity index is less than the above-described lower limit value. In addition, when the viscosity index is equal to or more than the above-described lower limit value, it becomes possible to reduce evaporation loss of the lubricating oil to reduce the amount of the lubricating oil consumed.

In addition, the HTHS viscosity at 150° C. of the lubricating oil composition for internal combustion engines of the present invention is preferably 1.7 mPa˜s or more and 2.9 mPa˜s or less (more preferably 2.3 mPa˜s or more and 2.8 mPa˜s or less, further preferably 2.6 mPa˜s or more and 2.8 mPa˜s or less, and particularly preferably 2.6 mPa˜s). When the HTHS viscosity at 150° C. is equal to or more than the lower limit value, it becomes possible to improve the anti-wear performance under high-shear conditions as compared with the case where the HTHS viscosity at 150° C. is less than the lower limit value, and when the HTHS viscosity at 150° C. is equal to or less than the upper limit value, it becomes possible to further improve the fuel saving performance by reducing the viscosity resistance as compared with the case where the HTHS viscosity at 150° C. is more than the upper limit value. Note that in the present Description, the “HTHS viscosity at 150° C.” means a high temperature high shear viscosity at 150° C. measured in accordance with ASTM D-4683.

The method for producing the lubricating oil composition for internal combustion engines of the present invention is not particularly limited, and the lubricating oil composition may be prepared by selecting and mixing the components to be added as appropriate such that the lubricating oil composition of the present invention can be obtained (such that the above-described conditions are satisfied).

EXAMPLES

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples; however, the present invention is not limited to Examples given below.

(Regarding Components Used in Each Example and the Like)

First, lubricating base oils and additives used in Examples and the like will be presented below.

<Component (A): Lubricating Base Oil>

(A-1)

A base oil of API Group II (a hydrocracked mineral base oil, Yubase (Registered Trademark) 3 produced by SK Lubricants Co., Ltd.), kinematic viscosity (100° C.): 3.05 mm²/s, kinematic viscosity (40° C.): 12.3 mm²/s, viscosity index: 105, NOACK evaporation loss (250° C., 1 h): 40% by mass, % C_P: 72.6, % C_N: 27.4, % C_A: 0, saturated content: 99.6% by mass, aromatic content: 0.3% by mass

(A-2)

A base oil of API Group III (a hydrocracked mineral base oil, Yubase (Registered Trademark) 4+ produced by SK Lubricants Co., Ltd.), kinematic viscosity (100° C.): 4.2 mm²/s, kinematic viscosity (40° C.): 17.9 mm²/s, viscosity index: 134, NOACK evaporation loss (250° C., 1 h): 13.5% by mass, % C_P: 87.2, % C_N: 12.8, % C_A: 0, saturated content: 99.8% by mass, aromatic content: 0.1% by mass

(A-3)

A base oil of API Group III (a hydrocracked mineral base oil, Yubase (Registered Trademark) 6+ produced by SK Lubricants Co., Ltd.), kinematic viscosity (100° C.): 6.4 mm²/s, kinematic viscosity (40° C.): 33.8 mm²/s, viscosity index: 145, NOACK evaporation loss (250° C., 1 h): 8% by mass, % C_P: 85%, C_N: 15%, C_A: 0%, saturated content: 99.5% by mass, aromatic content: 0.2% by mass

<Component (B): Metal-Based Detergent>

<Component (B1): Calcium-Based Detergent>

(B1-i)

Calcium borate-overbased calcium salicylate, content of calcium: 6.8% by mass, content of boron: 2.7% by mass, base number (perchloric acid method): 190 mg KOH/g

(B1-ii)

Calcium carbonate-overbased calcium salicylate, content of calcium: 8.0% by mass, base number (perchloric acid method): 210 mg KOH/g

<Component (B2): Magnesium-Based Detergent>

(B2-i)

Magnesium carbonate-overbased magnesium salicylate, content of magnesium: 7.5% by mass, base number (perchloric acid method): 350 mg KOH/g

(B2-ii)

Magnesium carbonate-overbased magnesium sulfonate, content of magnesium: 9.1% by mass, base number (perchloric acid method): 400 mg KOH/g

<Component (C): Viscosity Index Improver (poly(meth)acrylate-based Viscosity Index Improver)>

(C-1)

Comb-shaped polymethacrylate-based polymer (produced by Sanyo Chemical Industries, Ltd., product name: ACLUBE V-7030, Mw: 520000, Mn: 220000, Mw/Mn: 2.4)

(C-2)

Linear polymethacrylate-based polymer (produced by Sanyo Chemical Industries, Ltd., product name: ACLUBE V-5090, Mw: 480000, Mn: 170000, Mw/Mn: 2.8)

<Component (D): Ashless Dispersant>

(D-1)

Non-boronated succinimide (content of nitrogen: 1.6% by mass, Mw: 6000)

(D-2)

Boronated succinimide (content of nitrogen: 1.2% by mass, content of boron: 0.5% by mass, Mw: 7000)

<Component (E): Antioxidant>

(E-1)

Amine antioxidant (produced by BASF, product name: IRGANOX (Registered Trademark) L67, bis(nonylphenyl)amine, content of nitrogen: 3.6% by mass)

(E-2)

Molybdenum antioxidant (dialkylamine salt of molybdic acid, content of molybdenum: 10% by mass, content of nitrogen: 3.6% by mass).

<Component (F): Friction Modifier (Molybdenum Friction Modifier)>

(F-1)

Molybdenum dithiocarbamate (MoDTC, produced by ADEKA Corporation, product name: ADEKA SAKURA-LUBE 525, content of molybdenum (theoretical value): 10.0% by mass)

<(G) Anti-Wear Agent>

(G-1)

Zinc dialkyldithiophosphate (ZnDTP, secondary alkyl group type, a compound represented by the above-described formula (4), where R¹⁴ to R¹⁷ in the formula (4) are each any one of secondary alkyl groups having 4 or 6 carbon atoms, content of zinc: 8.0% by mass, content of phosphorus: 7.0% by mass, content of sulfur: 14% by mass)

(G-2)

Zinc dialkyldithiophosphate (ZnDTP, primary alkyl group type, a compound represented by the above-described formula (4), where R¹⁴ to R¹⁷ in the formula (4) are each a primary alkyl group having 8 carbon atoms, content of zinc: 8.0% by mass, content of phosphorus: 7.0% by mass, content of sulfur: 15% by mass)

(G-3)

Zinc dialkyl phosphate (ZnP, primary alkyl group type having 8 carbon atoms, content of zinc: 5.3% by mass, content of phosphorus: 5.2% by mass).

<Component (H): Pour Point Depressant>

(H-1)

Polymethacrylate (produced by Evonik Industries, product name: Viscoplex 1-300, Mw: 60000, Mn: 32000, Mw/Mn: 1.9).

<Component (I): Other Components>

(I-1)

Defoaming agent (produced by Shin-Etsu Chemical Co., Ltd., product name “KF-96H”).

Examples 1 to 5 and Comparative Examples 1 to 10

Lubricating oil compositions of Examples 1 to 5 and Comparative Examples 1 to 10 were prepared by using the aforementioned components to obtain compositions shown in Tables 1 to 3. Note that in the item “Composition” in Tables 1 to 3, “-” indicates that the corresponding component was not used. In addition, in the item “Composition” in Tables 1 to 3, “mass %” of the unit of the content of the component (A) represents the content of each base oil component relative to the total amount of the lubricating base oil (% by mass), “inmass %” of the unit of the contents of the components (B) to (H) represents the content of each additive relative to the total amount of the lubricating oil composition (% by mass), and “Parts by mass” represents the proportion (parts by mass) of the component (I-1) in the case where the total mass of the components in the lubricating oil composition except for the component (I-1) is considered as 100 parts by mass. In addition, in Tables 1 to 3, “massppm” of the unit of [B_(B1)] represents the parts per million by mass (mass ppm) of boron derived from the component (B1) based on the total amount of the lubricating oil composition, “massppm” of the unit of [Ca_(B1)] represents the parts per million by mass (mass ppm) of calcium derived from the component (B1) based on the total amount of the lubricating oil composition, and “massppm” of the unit of [Mg_(B2)] represents the parts per million by mass (mass ppm) of magnesium derived from the component (B2) based on the total amount of the lubricating oil composition. Moreover, in the item “The content of each element in the composition” in Tables 1 to 3, “massppm” of the unit regarding the contents of B, Ca, Mg, Mo, P, S, and Zn represents the parts per million by mass (mass ppm) of the respective elements (B, Ca, Mg, Mo, P, S, and Zn) based on the total amount of the lubricating oil composition. Note that the numerical values of the contents of B, Ca, Mg, Mo, P, S, and Zn in the item “The content of each element in the composition” in Tables 1 to 3 are each a value measured in accordance with JPI-5S-62.

[Evaluation on the Properties of the Lubricating Oil Composition Obtained in Each Example and the Like]

<LSPI Performance Evaluation Test (LSPI Test)>

A test for evaluating an LSPI suppressing performance was conducted on each lubricating oil composition in accordance with ASTM D8291 [Test method: Sequence IX test (Seq. IX ASTM D8291), used engine: an engine manufactured by Ford Motor Company in 2012 (2000 CC, 4 cylinders, GDTI engine)]. An average value of the number of occurrences of LSPI of each lubricating oil composition obtained by such measurement was shown in Tables 1 to 3 as results of the LSPI test. In addition, it was evaluated whether or not the result of the LSPI test (the average value of the number of occurrences of LSPI) satisfied the condition “5”, which is the standard value of “API SP/ILSAC GF-6” of the engine oil standard, or lower, and in Tables 1 to 3, “S” is shown in the case where the result was equal to or less than the standard value (in the case where the standard was satisfied), and “F” is shown in the case where the result was more than the standard value (in the case where the standard was not satisfied). Note that in the case where the result of the LSPI test satisfies the condition of 5, which is the standard value of “API SP/ILSAC GF-6”, or lower, it can be evaluated that the lubricating oil composition is excellent in LSPI suppressing performance.

<SRV Test (Test for Evaluating Fuel Saving Performance)>

By using each lubricating oil composition, the SRV test was conducted by using a cylinder-on-disk reciprocating tribometer (SRV manufactured by Optimol Instruments) under test conditions of load: 100 N, disk temperature: 100° C., frequency: 50 Hz, amplitude: 1 mm, and test time: 15 minutes, to measure the friction coefficient between metals. The results thus obtained are shown in 10 Tables 1 to 3. Note that in the case where the value of the friction coefficient is 0.060 or less, since it is obvious that the lubricating oil composition is excellent in friction properties, it can be evaluated that the lubricating oil composition is excellent in fuel saving performance.

	TABLE 1
	Example 1	Example 2	Example 3	Example 4	Example 5
Composition	(A) Lubricating base oil	(A-1)	mass %	7	7	7	7	7
			(A-2)	mass %	93	93	93	93	93
			(A-3)	mass %	—	—	—	—	—
	(B) Metal-based	(B1)	(B1-i)	inmass %	2.1	1.7	1.9	2.2	2.1
	detergent		(B1-ii)	inmass %	0.55	0.71	0.93	0.61	0.55
		(B2)	(B2-i)	inmass %	—	—	—	—	—
			(B2-ii)	inmass %	0.16	0.11	0.11	0.11	0.16
	(C) Viscosity index improver	(C-1)	inmass %	10.5	7	7	7	10.5
	(C-2)	inmass %	—	—	—	—	—
	(D) Ashless dispersant	(D-1)	inmass %	2.4	2.4	2.4	2.4	2.4
	(D-2)	inmass %	—	—	—	—	—
	(E) Antioxidant	(E-1)	inmass %	1.7	1.7	1.7	1.7	1.7
	(E-2)	inmass %	0.2	0.2	0.2	0.2	0.2
	(F) Friction modifier	(F-1)	inmass %	0.8	0.8	0.8	0.8	0.8
	(G) Anti-wear agent	(G-1)	inmass %	0.7	0.7	0.7	0.7	0.55
	(G-2)	inmass %	0.4	0.4	0.4	0.4	0.35
	(G-3)	inmass %	—	—	—	—	—
	(H) Pour point depressant	(H-1)	inmass %	0.3	0.3	0.3	0.3	0.3
	(I) Other component	(I-1)	Parts	0.002	0.002	0.002	0.002	0.002
	(defoaming agent)		by mass
The content of B derived from the component (B1) [B(B1)]	massppm	550	450	500	600	550
The content of Ca derived from the component (B1) [Ca(B1)]	massppm	1850	1700	2000	2000	1850
The content of Mg derived from the component (B2) [Mg(B2)]	massppm	150	100	100	100	150
[B(B1)]/[Ca(B1)]	Mass ratio	0.30	0.26	0.25	0.30	0.30
[B(B1)]/([Ca(B1)] + [Mg(B2)])	Mass ratio	0.28	0.25	0.24	0.29	0.28
The content of each element	B	massppm	550	450	500	600	550
in the composition	Ca	massppm	1850	1700	2000	2000	1850
(based on the total amount	Mg	massppm	150	100	100	100	150
of the composition)	Mo	massppm	1000	1000	1000	1000	1000
	P	massppm	770	770	770	770	600
	S	massppm	2500	2500	2500	2500	2200
	Zn	massppm	880	880	880	880	720
Physical properties	Kinematic viscosity at 100° C.	mm2/s	4.1	4.1	4.1	4.1	4.1
of the base oil
Physical properties	Kinematic viscosity at 40° C.	mm2/s	27.6	27.3	26.4	26.4	27.6
of the composition	Kinematic viscosity at 100° C.	mm2/s	7.6	6.8	6.6	6.6	7.6
	HTHS viscosity at 150° C.	mPa · s	2.6	2.3	2.3	2.3	2.6
	Viscosity index		267	225	223	223	267
Results of evaluations on	Result of the LSPI test	1.9	2.3	1.5	2.5	4.1
the physical properties	(Seq. IX, ASTM D8291)
of the composition	Evaluation for the standard value	S	S	S	S	S
	of API SP/ILSAC GF-6
	Result of the SRV test	0.051	0.058	0.054	0.057	0.054
	(friction coefficient)

	TABLE 2
	Compar-	Compar-	Compar-	Compar-	Compar-
	ative	ative	ative	ative	ative
	Exam-	Exam-	Exam-	Exam-	Exam-
	ple 1	ple 2	ple 3	ple 4	ple 5
Composition	(A) Lubricating base oil	(A-1)	mass %	7	—	—	—	—
			(A-2)	mass %	93	70	70	70	70
			(A-3)	mass %	—	30	30	30	30
	(B) Metal-based	(B1)	(B1-i)	inmass %	2.1	2.1	0.8	—	2.9
	detergent		(B1-ii )	inmass %	1.5	—	1.2	1.3	—
		(B2)	(B2-i)	inmass %	—	0.65	0.65	1.3	—
			(B2-ii )	inmass %	0.16	—	—	—	—
	(C) Viscosity index improver	(C-1)	inmass %	10.5	—	—	—	—
	(C-2)	inmass %	—	13	13	13	13
	(D) Ashless dispersant	(D-1)	inmass %	2.4	0.8	0.8	0.8	0.8
	(D-2)	inmass %	—	4	4	4	4
	(E) Antioxidant	(E-1)	inmass %	1.7	1.7	1.7	1.7	1.7
	(E-2)	inmass %	0.2	0.15	0.15	0.15	0.15
	(F) Friction modifier	(F-1)	inmass %	0.8	—	—	—	—
	(G) Anti-wear agent	(G-1)	inmass %	0.7	—	—	—	—
	(G-2)	inmass %	0.4	—	—	—	—
	(G-3)	inmass %	—	1.3	1.3	1.3	1.3
	(H) Pour point depressant	(H-1)	inmass %	0.3	0.3	0.3	0.3	0.3
	(I) Other component	(I-1)	Parts	0.002	0.002	0.002	0.002	0.002
	(defoaming agent)		by mass
The content of B derived from the component (B1) [B(B1)]	massppm	550	550	200	0	800
The content of Ca derived from the component (B1) [Ca(B1)]	massppm	2600	1400	1500	1000	2000
The content of Mg derived from the component (B2) [Mg(B2)]	massppm	150	500	500	950	10
[B(B1)]/[Ca(B1)]	Mass ratio	0.21	0.39	0.13	0.00	0.40
[B(B1)]/([Ca(B1)] + [Mg(B2)])	Mass ratio	0.20	0.29	0.10	0.00	0.40
The content of each element	B	massppm	550	750	400	200	1000
in the composition	Ca	massppm	2600	1400	1500	1000	2000
(based on the total amount	Mg	massppm	150	500	500	950	10
of the composition)	Mo	massppm	1000	150	150	150	150
	P	massppm	770	700	700	700	700
	S	massppm	2500	800	800	800	800
	Zn	massppm	880	690	690	690	690
Physical properties	Kinematic viscosity at 100° C.	mm2/s	4.1	4.7	4.7	4.7	4.7
of the base oil
Physical properties	Kinematic viscosity at 40° C.	mm2/s	28.3	39.2	39.2	39.2	39.4
of the composition	Kinematic viscosity at 100° C.	mm2/s	7.7	9	9	9	9
	HTHS viscosity at 150° C.	mPa · s	2.6	2.9	2.9	2.9	2.9
	Viscosity index	263	221	221	221	220
Results of evaluations on	Result of the LSPI test	8.1	5.1	7.7	5.1	5.9
the physical properties	(Seq. IX, ASTM D8291)
of the composition	Evaluation for the standard value	F	F	F	F	F
	of API SP/ILSAC GF-6
	Result of the SRV test	0.065	0.137	0.133	0.138	0.130
	(friction coefficient)

	TABLE 3
	Compar-	Compar-	Compar-	Compar-	Compar-
	ative	ative	ative	ative	ative
	Exam-	Exam-	Exam-	Exam-	Exam-
	ple 6	ple 7	ple 8	ple 9	ple 10
Composition	(A) Lubricating base oil	(A-1)	mass %	—	—	—	—	—
			(A-2)	mass %	70	70	70	70	70
			(A-3)	mass %	30	30	30	30	30
	(B) Metal-based	(B1)	(B1-1)	inmass %	—	—	1.4	—	2.2
	detergent		(B1-ii)	inmass %	2.5	3.2	—	1.8	—
		(B2)	(B2-i)	inmass %	0.4	—	1.2	0.4	0.65
			(B2-ii)	inmass %	—	—	—	—	—
	(C) Viscosity index improver	(C-1)	inmass %	—	—	—	—	11
	(C-2)	inmass %	13	13	13	13	—
	(D) Ashless dispersant	(D-1)	inmass %	0.8	0.8	0.8	0.8	0.8
	(D-2)	inmass %	4	4	4	4	4
	(E) Antioxidant	(E-1)	inmass %	1.7	1.7	1.7	1.7	1.7
	(E-2)	inmass %	0.15	0.15	0.15	0.15	0.15
	(F) Friction modifier	(F-1)	inmass %	—	—	—	—	—
	(G) Anti-wear agent	(G-1)	inmass %	—	—	—	—	—
	(G-2)	—	—	—	—	—	—
	(G-3)	inmass %	1.3	1.3	1.3	1.3	1.3
	(H) Pour point depressant	(H-1)	inmass %	0.3	0.3	0.3	0.3	0.3
	(I) Other component	(I-1)	Parts	0.002	0.002	0.002	0.002	0.002
	(defoaming agent)		by mass
The content of B derived from the component (B1) [B(B1)]	massppm	0	0	400	0	600
The content of Ca derived from the component (B1) [Ca(B1)]	massppm	2000	2500	950	1500	1500
The content of Mg derived from the component (B2) [Mg(B2)]	massppm	300	10	900	300	500
[B(B1)]/[Ca(B1)]	Mass ratio	0.00	0.00	0.42	0.00	0.40
[B(B1)]/([Ca(B1)] + [Mg(B2)])	Mass ratio	0.00	0.00	0.22	0.00	0.30
The content of each element	B	massppm	200	200	600	200	800
in the composition	Ca	massppm	2000	2500	950	1500	1500
(based on the total amount	Mg	massppm	300	10	900	300	500
of the composition)	Mo	massppm	150	150	150	150	150
	P	massppm	700	700	700	700	700
	S	massppm	800	800	800	800	800
	Zn	massppm	690	690	690	690	690
Physical properties	Kinematic viscosity at 100° C.	mm2/s	4.7	4.7	4.7	4.7	4.7
of the base oil
Physical properties	Kinematic viscosity at 40° C.	mm2/s	39.3	39.4	39.3	39.4	34.4
of the composition	Kinematic viscosity at 100° C.	mm2/s	8.9	8.9	9	9	8.5
	HTHS viscosity at 150° C.	mPa · s	2.9	2.9	2.9	2.9	2.9
	Viscosity index		217	216	220	220	239
Results of evaluations on	Result of the LSPI test	23.8	21.5	1.8	21.3	5.0
the physical properties	(Seq. IX, ASTM D8291)
of the composition	Evaluation for the standard value	F	F	S	F	S
	of API SP/ILSAC GF-6
	Result of the SRV test	0.116	0.112	0.139	0.118	0.140
	(friction coefficient)

As is clear from the results shown in Table 1, it was confirmed that the lubricating oil compositions obtained in Examples 1 to 5, each comprising: (A) the lubricating base oil; and (B) the metal-based detergent, wherein the component (B) contained: the calcium-based detergent (the component (B1)); and the metal-based detergent (the component (B2)), the content of calcium derived from the component (B1) was within a range of 1650 mass ppm or more and 2500 mass ppm or less based on the total mass of the composition, the content of magnesium derived from the component (B2) was within a range of 20 mass ppm or more and 400 mass ppm or less based on the total mass of the composition, the component (B1) contained the component (B1-i) (the component containing boron and calcium), the total amount of B in the composition was 1000 mass ppm or less, B_(B1)/Ca_(B1) was 0.15 or more and 0.35 or less, and B_(B1)/[Ca_(B1)+Mg_(B2)] was 0.13 or more and 0.29 or less, were excellent in both LSPI suppressing performance and fuel saving performance (friction properties). Note that the lubricating oil compositions obtained in Comparative Example 2 and Comparative Example 9 in which although B_(B1)/[Ca_(B1)+Mg_(B2)] was 0.29, B_(B1)/Ca_(B1) was out of the range of 0.15 or more and 0.35 or less particularly had larger friction coefficients than those of the lubricating oil compositions obtained in Examples 1 to 5.

INDUSTRIAL APPLICABILITY

As described above, the present invention makes it possible to provide a lubricating oil composition for internal combustion engines that is capable of achieving both excellent LSPI suppressing performance and excellent fuel saving performance. Therefore, the lubricating oil composition for internal combustion engines of the present invention is particularly useful as a lubricating oil composition for internal combustion engines such as gasoline engines and diesel engines, and the like.

Claims

1. A lubricating oil composition for internal combustion engines, comprising:

(A) a lubricating base oil; and

(B) a metal-based detergent, wherein

the component (B) contains:

(B1) a calcium-based detergent in which a content of calcium based on a total mass of the composition is within a range of 1650 mass ppm or more and 2500 mass ppm or less; and

(B2) a magnesium-based detergent in which a content of magnesium based on the total mass of the composition is within a range of 20 mass ppm or more and 400 mass ppm or less,

the component (B1) contains (B1-1) a calcium-based detergent containing boron and calcium,

a content of boron based on the total mass of the composition is 1000 mass ppm or less, and

a ratio (B(B1)/Ca(B1)) of B(B1) to Ca(B1) is 0.15 or more and 0.35 or less, and a ratio (B(B1)/[Ca(B1)+Mg(B2)]) of B(B1) to a total amount (Ca(B1)+Mg(B2) of Ca(B1) and Mg(B2) is 0.13 or more and 0.29 or less, where B(B1) represents the content of boron in the component (B1) based on the total mass of the composition, Ca(B1) represents the content of calcium in the component (B1) based on the total mass of the composition, and Mg(B2) represents the content of magnesium in the component (B2) based on the total mass of the composition.

2. The lubricating oil composition for internal combustion engines according to claim 1, wherein

the component (B1) contains calcium borate salicylate as the component (B1-1).

3. The lubricating oil composition for internal combustion engines according to claim 1, further comprising:

a poly(meth)acrylate-based viscosity index improver.

4. The lubricating oil composition for internal combustion engines according to claim 3, wherein

the component (C) contains a comb-shaped poly(meth)acrylate-based polymer.