JP7603538B2 - Lubricating oil composition for internal combustion engines - Google Patents

Description

The present invention relates to a lubricating oil composition for internal combustion engines. In particular, the present invention relates to a lubricating oil composition for internal combustion engines that has excellent fuel economy both at high oil temperatures and at low oil temperatures.

Since their invention, internal combustion engines have been the power source for various means of transportation for many years. In recent years, the fuel efficiency required of internal combustion engines has been increasing. To meet this demand, high fuel efficiency performance is also required of lubricating oils for internal combustion engines.

Various studies have been conducted to improve the fuel economy performance of lubricating oils for internal combustion engines. For example, Patent Document 1 discloses a lubricating oil for internal combustion engines that uses a specific blend of metal-based detergents to ensure LSPI suppression and cleaning performance while also improving fuel economy performance.

JP 2017-226793 A

The lubricating oil for internal combustion engines described in Patent Document 1 is intended to improve fuel efficiency at high oil temperatures, and no consideration has been given to improving fuel efficiency at low oil temperatures. By improving fuel efficiency not only at high oil temperatures but also at low oil temperatures, it is possible to obtain a lubricating oil for internal combustion engines with even better fuel efficiency.

The present inventors have conducted extensive research into lubricating oils for internal combustion engines that are excellent in fuel efficiency not only at high oil temperatures but also at low oil temperatures. In the prior art, it was believed that the greater the amount of calcium borate salicylate blended, the better the fuel efficiency at high oil temperatures. However, the present inventors have newly discovered that an excessive amount of calcium borate salicylate adversely affects fuel efficiency at low oil temperatures. The present inventors have also confirmed that by combining calcium borate salicylate and magnesium salicylate, it is possible to obtain lubricating oils for internal combustion engines that are excellent in fuel efficiency not only at high oil temperatures but also at low oil temperatures, and have thus completed the present invention.

The present invention has been made based on such findings and is as follows.
＜1＞
A lubricating oil composition for internal combustion engines, comprising: (A) a lubricating base oil; and (B) calcium borate salicylate and (C) magnesium salicylate as metal-based detergents, wherein the amount of calcium derived from the calcium borate salicylate (B) is 300 ppm by mass or more and 1,200 ppm by mass or less based on the total amount of the lubricating oil composition.
＜2＞
The lubricating oil composition for internal combustion engines according to <1>, having a HTHS viscosity at 150°C of 1.6 mPa·s or more and 2.3 mPa·s or less.
＜3＞
(B) The lubricating oil composition for internal combustion engines according to <1> or <2>, wherein the content of boron derived from calcium borate salicylate is 100 ppm by mass or more and 600 ppm by mass or less based on the total amount of the lubricating oil composition.
＜4＞
(C) The lubricating oil composition for internal combustion engines according to any one of <1> to <3>, wherein the content of magnesium derived from magnesium salicylate is 100 ppm by mass or more and 1000 ppm by mass or less based on the total amount of the lubricating oil composition.
＜5＞
(A) A lubricating oil composition for internal combustion engines according to any one of <1> to <4>, wherein the kinetic viscosity of the lubricating base oil at 100° C. is 3.0 mm ² /s or more and 5.0 mm ² /s or less.
＜6＞
The lubricating oil composition for internal combustion engines according to any one of <1> to <5>, further comprising (D) a molybdenum-based friction modifier in an amount of 100 ppm by mass or more and 1,000 ppm by mass or less in terms of molybdenum, based on the total amount of the composition.

The lubricating oil composition for internal combustion engines of the present invention can provide a lubricating oil for internal combustion engines that has excellent fuel economy not only at high oil temperatures but also at low oil temperatures.

[A] Lubricating base oil The lubricating base oil used in the present invention may be either a mineral oil or a synthetic base oil. In the present invention, it is preferable to use a mineral oil as the lubricating base oil.

As the mineral oil, a distillate oil obtained by distilling crude oil at atmospheric pressure can be used. In addition, a lubricating oil fraction prepared by subjecting the distillate oil obtained by further distilling the distillate oil at reduced pressure to various refining processes can also be used. The refining process can be a suitable combination of hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. By combining and processing these refining processes in a suitable order, a lubricating oil base oil that can be used in the present invention can be obtained. A mixture of multiple refined oils with different properties obtained by subjecting different crude oils or distillate oils to a combination of different refining processes can also be used.

The mineral base oil used in the lubricating oil composition of the present invention is preferably one belonging to API Group III base oil. API Group III base oil is a mineral base oil having a sulfur content of 0.03 mass% or less, a saturate content of 90 mass% or more, and a viscosity index of 120 or more. Multiple types of Group III base oils may be used, or only one type may be used.

The lubricating oil composition of the present invention may contain only mineral base oil as the lubricating oil base oil, or may contain other lubricating oil base oils. Specifically, the content of mineral base oil in the lubricating oil composition of the present invention may be, for example, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, 95 mass% or more, or 99 mass% or more based on the lubricating oil base oil.

In the lubricating oil composition of the present invention, a synthetic base oil may be used as the lubricating oil base oil. Examples of synthetic base oils include poly-α-olefins and their hydrogenated products, isobutene oligomers and their hydrogenated products, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene glycols, dialkyl diphenyl ethers, polyphenyl ethers, and mixtures thereof. Among these, poly-α-olefins are preferred. Polyα-olefins typically include oligomers or co-oligomers of α-olefins having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms (such as 1-octene oligomers, decene oligomers, and ethylene-propylene co-oligomers) and their hydrogenated products.

The kinematic viscosity at 100 ° C. of the lubricating base oil contained in the lubricating oil composition of the present invention is preferably 3.0 mm ² /s or more and 5.0 mm ² /s or less. The kinematic viscosity at 100 ° C. of the lubricating base oil of the present invention is preferably 3.2 mm ² /s or more, more preferably 3.5 mm ² /s or more, and even more preferably 4.0 mm ² /s or more. The upper limit is preferably 4.8 mm ² /s or less, more preferably 4.6 mm ² /s or less, even more preferably 4.5 mm ² /s or less, and most preferably 4.3 mm ² /s or less. The specific range is preferably 3.2 mm ² /s or more and 4.8 mm ² /s or less, more preferably 3.5 mm ² /s or more and 4.6 mm ² /s or less, even more preferably 4.0 mm ² /s or more and 4.5 mm ² /s or less, and most preferably 4.0 mm ² /s or more and 4.3 mm ² /s or less. When the kinematic viscosity of the lubricating base oil at 100° C. is 5.0 mm ² /s or less, sufficient fuel saving performance can be obtained. Also, when the kinematic viscosity of the lubricating base oil at 100° C. is 3.0 mm ² /s or more, oil film formation at lubricated points can be ensured and evaporation loss of the lubricating oil composition can be reduced.
The kinematic viscosity at 100° C. refers to the kinematic viscosity of all the lubricating base oils mixed together, that is, the kinematic viscosity of the base oil as a whole. In other words, it does not refer to the kinematic viscosity of a specific lubricating base oil when multiple base oils are included.
In this specification, the term "kinematic viscosity at 100° C." means the kinematic viscosity at 100° C. measured in accordance with ASTM D-445.

The viscosity index of the lubricating base oil contained in the lubricating oil composition of the present invention is preferably 110 or more, more preferably 120 or more. By having the viscosity index of the lubricating base oil be equal to or more than the lower limit, it is possible to improve fuel economy. The upper limit of the viscosity index of the lubricating base oil is not particularly limited, but it can usually be 160 or less.
In this specification, the viscosity index means the viscosity index defined in JIS K 2283:2000.

In the lubricating oil composition of the present invention, the content of the lubricating base oil is, for example, 50% by mass or more and 95% by mass or less, preferably 60% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 95% by mass or less, even more preferably 80% by mass or more and 95% by mass or less, and most preferably 85% by mass or more and 95% by mass or less, based on the total amount of the lubricating oil composition.

[B] Calcium Borate Salicylate The lubricating oil composition of the present invention contains calcium borate salicylate as a metal detergent.

Calcium borate salicylate is calcium salicylate that has been overbased with boric acid or a borate salt. An example of calcium salicylate is the compound represented by the following formula (1).

In the formula (1), R ¹ each independently represents an alkyl group or alkenyl group having 14 to 30 carbon atoms, and n represents 1 or 2. Ca represents calcium. n is preferably 1. When n=2, R ¹ may be a combination of different groups.

The amount of calcium derived from calcium borate salicylate contained in the lubricating oil composition of the present invention is 300 ppm by mass or more and 1200 ppm by mass or less based on the total amount of the lubricating oil composition. The amount of calcium derived from calcium borate salicylate is preferably 400 ppm by mass or more, more preferably 500 ppm by mass or more. The upper limit is preferably 1100 ppm by mass or less, more preferably 1000 ppm by mass or less. The specific range is preferably 400 ppm by mass or more and 1100 ppm by mass or less, more preferably 500 ppm by mass or more and 1000 ppm by mass or less. By setting the content of calcium derived from calcium borate salicylate within the above range, fuel efficiency can be ensured not only at high oil temperatures but also at low oil temperatures. In this specification, unless otherwise specified, the contents of calcium, magnesium, zinc, boron, and molybdenum in oil are measured by inductively coupled plasma atomic emission spectrometry (intensity ratio method (internal standard method)) in accordance with JPI-5S-62.

The amount of boron derived from calcium borate salicylate contained in the lubricating oil composition of the present invention is preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, and even more preferably 200 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 800 ppm by mass or less, more preferably 600 ppm by mass or less, even more preferably 500 ppm by mass or less, and most preferably 400 ppm by mass or less. The specific range is preferably 50 ppm by mass or more and 800 ppm by mass or less, more preferably 100 ppm by mass or more and 600 ppm by mass or less, even more preferably 200 ppm by mass or more and 500 ppm by mass or less, and most preferably 200 ppm by mass or more and 400 ppm by mass or less.

(Base Number of Calcium Borate Salicylate)
The base number of the calcium borate salicylate contained in the lubricating oil composition of the present invention is preferably 140 mgKOH/g or more, more preferably 160 mgKOH/g or more, and even more preferably 180 mgKOH/g or more. The upper limit is preferably 500 mgKOH/g or less, more preferably 400 mgKOH/g or less, and even more preferably 300 mgKOH/g or less. The specific range is preferably 140 mgKOH/g or more and 500 mgKOH/g or less, more preferably 160 mgKOH/g or more and 400 mgKOH/g or less, and even more preferably 180 mgKOH/g or more and 300 mgKOH/g or less. The base number is a value measured according to JIS K 2501:2003-9.

[C] Magnesium Salicylate An example of magnesium salicylate is a compound represented by the following formula (2).

In the formula (2), R ² each independently represents an alkyl group or alkenyl group having 14 to 30 carbon atoms, and n represents 1 or 2. Mg represents magnesium. n is preferably 1. When n=2, R ² may be a combination of different groups. The magnesium salicylate may be overbased with a carbonate or a borate.

The amount of magnesium derived from magnesium salicylate contained in the lubricating oil composition of the present invention is preferably 50 ppm by mass or more, more preferably 100 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 ppm by mass or less, more preferably 1000 ppm by mass or less. The specific range is preferably 50 ppm by mass or more and 2000 ppm by mass or less, more preferably 100 ppm by mass or more and 1000 ppm by mass or less. By setting the content of magnesium derived from magnesium salicylate within the above range, fuel efficiency can be further improved not only at high oil temperatures but also at low oil temperatures.

(Base Number)
The base number of the magnesium salicylate contained in the lubricating oil composition of the present invention is preferably 200 mgKOH/g or more, more preferably 250 mgKOH/g or more, and even more preferably 300 mgKOH/g or more. The upper limit is preferably 600 mgKOH/g or less, more preferably 500 mgKOH/g or less, and even more preferably 400 mgKOH/g or less. The specific range is preferably 200 mgKOH/g or more and 600 mgKOH/g or less, more preferably 250 mgKOH/g or more and 500 mgKOH/g or less, and even more preferably 300 mgKOH/g or more and 400 mgKOH/g or less.

(Calcium Salicylate)
The lubricating oil composition of the present invention may further contain calcium salicylate as a metal detergent. In this specification, "calcium salicylate" means calcium salicylate that does not contain boron or has a very low boron content (specifically, the amount contained in the metal detergent is, for example, 0.1 mass % or less). In this specification, "calcium salicylate" includes calcium salicylate overbased with carbonate. In addition, in this specification, "calcium salicylate" does not include calcium borate salicylate.
An example of calcium salicylate is the compound represented by the above formula (1).

When the lubricating oil composition of the present invention contains calcium salicylate, the amount of calcium derived from calcium salicylate is preferably 100 ppm by mass or more, more preferably 300 ppm by mass or more, and even more preferably 500 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 1500 ppm by mass or less, more preferably 1200 ppm by mass or less, and even more preferably 1000 ppm by mass or less. The specific range is preferably 100 ppm by mass or more and 1500 ppm by mass or less, more preferably 300 ppm by mass or more and 1200 ppm by mass or less, and even more preferably 500 ppm by mass or more and 1000 ppm by mass or less.

When the lubricating oil composition of the present invention contains calcium salicylate, the content thereof is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and even more preferably 0.5 mass% or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less. The specific range is preferably 0.1 mass% or more and 10 mass% or less, more preferably 0.2 mass% or more and 5 mass% or less, and even more preferably 0.5 mass% or more and 2 mass% or less.

(Base Number of Calcium Salicylate)
The base number of the calcium salicylate contained in the lubricating oil composition of the present invention is preferably 140 mgKOH/g or more, more preferably 170 mgKOH/g or more, and even more preferably 200 mgKOH/g or more. The upper limit is preferably 500 mgKOH/g or less, more preferably 400 mgKOH/g or less, and even more preferably 300 mgKOH/g or less. The specific range is preferably 140 mgKOH/g or more and 500 mgKOH/g or less, more preferably 170 mgKOH/g or more and 400 mgKOH/g or less, and even more preferably 2000 mgKOH/g or more and 300 mgKOH/g or less.

When the lubricating oil composition of the present invention contains calcium salicylate, the total amount of calcium derived from calcium borate salicylate and the total amount of calcium derived from calcium salicylate is preferably 400 ppm by mass or more, more preferably 700 ppm by mass or more, and even more preferably 1000 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 1800 ppm by mass or less, more preferably 1600 ppm by mass or less. The specific range is preferably 400 ppm by mass or more and 1800 ppm by mass or less, more preferably 700 ppm by mass or more and 1600 ppm by mass or less, and even more preferably 1000 ppm by mass or more and 1600 ppm by mass or less.

The calcium content derived from calcium salicylate relative to the calcium content derived from calcium salicylate borate (Ca content derived from calcium salicylate/Ca content derived from calcium salicylate borate) is preferably 0.40 or more and 4.0 or less, more preferably 0.50 or more and 3.0 or less, and even more preferably 0.55 or more and 2.5 or less, on a mass ppm basis.

The ratio of the magnesium content derived from (C) magnesium salicylate to the calcium content derived from calcium borate salicylate (Mg content/Ca content) is preferably 0.1 or more and 2.5 or less, more preferably 0.15 or more and 2.0 or less, and even more preferably 0.18 or more and 1.5 or less, based on ppm by mass.
The ratio of the magnesium content derived from (C) magnesium salicylate to the boron content derived from (B) calcium borate salicylate (Mg content/B content), expressed in ppm by mass, is preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 4.0 or less, and even more preferably 0.4 or more and 3.5 or less.

The lubricating oil composition of the present invention may contain metal-based detergents other than magnesium salicylate and calcium borate salicylate, such as phenate-based detergents or sulfonate-based detergents, within the range that does not impair the effects of the present invention, but it is preferable that the composition contains only magnesium salicylate and calcium borate salicylate.

[D] Molybdenum-Based Friction Modifier The lubricating oil composition of the present invention preferably further contains a molybdenum-based friction modifier, preferably molybdenum dithiocarbamate (hereinafter sometimes simply referred to as MoDTC).

As MoDTC, for example, a compound represented by the following formula (3) can be used.

In the formula (3), R ³ to R ⁶ may be the same or different and are 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 may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group, and may be linear or branched. The "(alkyl)aryl group" means an "aryl group or an alkylaryl group." In the alkylaryl group, the alkyl group may be substituted at any position on the aromatic ring. X ¹ to X ⁴ are each independently a sulfur atom or an oxygen atom, and at least one of X ¹ to X ⁴ is a sulfur atom.

Examples of molybdenum-based friction modifiers other than MoDTC include molybdenum dithiophosphate, molybdenum oxide, molybdic acid, molybdates such as ammonium salts, molybdenum disulfide, molybdenum sulfide, molybdic sulfide acid, and sulfur-containing organic molybdenum compounds.

When the lubricating oil composition of the present invention contains a molybdenum-based friction modifier, the amount of molybdenum derived from the molybdenum-based friction modifier is preferably 100 ppm by mass or more, more preferably 300 ppm by mass or more, even more preferably 500 ppm by mass or more, and most preferably 700 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 ppm by mass or less, more preferably 1000 ppm by mass or less, and even more preferably 800 ppm by mass or less. The specific range is preferably 100 ppm by mass or more and 2000 ppm by mass or less, more preferably 300 ppm by mass or more and 1000 ppm by mass or less, even more preferably 500 ppm by mass or more and 800 ppm by mass or less, and most preferably 700 ppm by mass or more and 800 ppm by mass or less. By having the molybdenum content be equal to or more than the lower limit, fuel saving performance can be further improved. Furthermore, by having the molybdenum content be equal to or less than the upper limit, the storage stability of the lubricating oil composition can be improved.

(Other additives)
The lubricating oil compositions of the present invention may further contain viscosity index improvers, antiwear agents, antioxidants, and dispersants.

Viscosity index improvers that are commonly used in the field of lubricating oil compositions for internal combustion engines can be used. Specifically, polymethacrylate, olefin copolymer, polybutene, polyisobutene, polyisobutylene, polystyrene, ethylene-propylene copolymer, styrene-diene copolymer, and hydrogenated products thereof can be used.

The weight average molecular weight of the viscosity index improver is, for example, 10,000 or more and 1,000,000 or less, 100,000 or more and 800,000 or less, or 200,000 or more and 600,000 or less.
The weight average molecular weight of the viscosity index improver means a value determined by gel permeation chromatography (GPC) (molecular weight obtained in terms of polystyrene).

When the lubricating oil composition of the present invention contains a viscosity index improver, the content thereof can be appropriately adjusted so that the viscosity index of the lubricating oil composition is preferably 120 or more and 350 or less, more preferably 120 or more and 310 or less, even more preferably 130 or more and 270 or less, and most preferably 130 or more and 230 or less.

As an anti-wear agent, it is preferable to add zinc dialkyldithiophosphate (ZnDTP). For example, an example of zinc dialkyldithiophosphate is the compound shown in the following general formula (4):

In the general formula (4), R ⁷ to R ¹⁰ are each independently a linear or branched alkyl group having 1 to 24 carbon atoms. This alkyl group may be primary, secondary, or tertiary. As the zinc dialkyldithiophosphate, zinc dithiophosphate having a primary alkyl group (primary ZnDTP) or zinc dithiophosphate containing a secondary alkyl group (secondary ZnDTP) is preferred, and in particular, those containing zinc dithiophosphate having a secondary alkyl group as the main component are preferred because they enhance wear resistance.
In the lubricating oil composition of the present invention, these zinc dialkyldithiophosphates may be used alone or in combination of two or more.

The amount of phosphorus derived from zinc dialkyldithiophosphate contained in the lubricating oil composition of the present invention is preferably 100 ppm by mass or more, more preferably 500 ppm by mass or more, and even more preferably 600 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 ppm by mass or less, more preferably 1000 ppm by mass or less, and even more preferably 800 ppm by mass or less. The specific range is preferably 100 ppm by mass or more and 2000 ppm by mass or less, more preferably 500 ppm by mass or more and 1000 ppm by mass or less, and even more preferably 600 ppm by mass or more and 800 ppm by mass or less.

The amount of zinc derived from zinc dialkyldithiophosphate contained in the lubricating oil composition of the present invention is preferably 100 ppm by mass or more, more preferably 500 ppm by mass or more, and even more preferably 700 ppm by mass or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 ppm by mass or less, more preferably 1500 ppm by mass or less, and even more preferably 1000 ppm by mass or less. The specific range is preferably 100 ppm by mass or more and 2000 ppm by mass or less, more preferably 500 ppm by mass or more and 1500 ppm by mass or less, and even more preferably 700 ppm by mass or more and 1000 ppm by mass or less.

As the antioxidant, known antioxidants such as phenol-based antioxidants and amine-based antioxidants can be used. Examples include amine-based antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine, and alkylated-α-naphthylamine, and phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4′-methylenebis(2,6-di-t-butylphenol).
When the lubricating oil composition contains an antioxidant, the content thereof is usually 5.0 mass % or less, preferably 3.0 mass % or less, and also preferably 0.1 mass % or more, more preferably 0.5 mass % or more, based on the total amount of the lubricating oil composition.

Dispersants include ashless dispersants such as succinimides or benzylamines.
When the lubricating oil composition contains a dispersant, the content thereof is usually 5.0 mass % or less, and preferably 0.1 mass % or more, based on the total amount of the lubricating oil composition.

The lubricating oil composition of the present invention may further contain other additives commonly used in lubricating oils depending on the purpose in order to improve its performance. Such additives may include antiwear or extreme pressure agents, pour point depressants, corrosion inhibitors, rust inhibitors, metal deactivators, antifoaming agents, and the like.

(Lubricating oil composition for internal combustion engines)
The HTHS viscosity of the lubricating oil composition of the present invention at 150 ° C. is 1.7 mPa · s or more and 2.3 mPa · s or less, preferably 1.7 mPa · s or more and 2.2 mPa · s or less, more preferably 1.7 mPa · s or more and 2.1 mPa · s or less, and even more preferably 1.7 mPa · s or more and 2.0 mPa · s or less. By having an HTHS viscosity of 2.3 mPa · s or less at 150 ° C., even better fuel saving performance can be obtained. If it is less than 1.7 mPa · s, there is a possibility that lubricity is insufficient.
The HTHS viscosity at 150° C. refers to the high temperature, high shear viscosity at 150° C. as specified in ASTM D 4683.

The viscosity index of the lubricating oil composition of the present invention is preferably 120 or more and 350 or less, more preferably 120 or more and 310 or less, even more preferably 130 or more and 270 or less, and most preferably 130 or more and 230 or less. By having a viscosity index of 120 or more of the lubricating oil composition, it is possible to further improve the fuel saving performance while maintaining a low HTHS viscosity at 150°C. In addition, if the viscosity index of the lubricating oil composition exceeds 350, there is a risk of the volatility being deteriorated.

The kinematic viscosity of the lubricating oil composition of the present invention at 40°C is preferably 10 ^mm2 /s or more, more preferably 14 ^mm2 /s or more, even more preferably 18 ^mm2 /s or more, and most preferably 20 ^mm2 /s or more. The upper limit is preferably 40 ^mm2 /s or less, more preferably 35 ^mm2 /s or less, even more preferably 30 ^mm2 /s or less, and most preferably 28 ^mm2 /s or less. The specific range is preferably 10 ^mm2 /s or more and 40 ^mm2 /s or less, more preferably 14 ^mm2 /s or more and 35 ^mm2 /s or less, even more preferably 18 ^mm2 /s or more and 30 ^mm2 /s or less, and most preferably 20 ^mm2 /s or more and 28 ^mm2 /s or less. By having the kinematic viscosity of the lubricating oil composition at 40°C of 40 ^mm2 /s or less, it is possible to obtain more sufficient fuel saving performance. Furthermore, by ensuring that the kinetic viscosity of the lubricating oil composition at 40° C. is 10 mm ² /s or more, the formation of an oil film at lubricated points can be ensured and evaporation loss of the lubricating oil composition can be reduced.
In this specification, the term "kinematic viscosity at 40° C." means the kinematic viscosity at 40° C. measured in accordance with ASTM D-445.

The kinetic viscosity of the lubricating oil composition of the present invention at 100°C is preferably 3.0 ^mm2 /s or more, more preferably 4.0 ^mm2 /s or more. The upper limit is preferably 7.0 ^mm2 /s or less, more preferably 6.0 ^mm2 /s or less. The specific range is preferably 3.0 ^mm2 /s or more and 7.0 ^mm2 /s or less, more preferably 4.0 ^mm2 /s or more and 6.0 ^mm2 /s or less. By having the kinetic viscosity of the lubricating oil composition at 100°C of 7.0 ^mm2 /s or less, more sufficient fuel saving performance can be obtained. In addition, by having the kinetic viscosity of the lubricating oil composition at 100°C of 3.0 ^mm2 /s or more, the formation of an oil film at the lubricating part can be ensured, and the evaporation loss of the lubricating oil composition can also be reduced.
In this specification, the term "kinematic viscosity at 100° C." means the kinematic viscosity at 100° C. measured in accordance with ASTM D-445.

The lubricating oil composition of the present invention preferably has a density (ρ ₁₅ ) at 15° C. of not more than 0.860 g/cm ³ , more preferably not more than 0.850 g/cm ³ . In this specification, the density at 15° C. means the density measured at 15° C. in accordance with ASTM D4052.

The present invention will be described below using examples. The present invention is not limited to the following embodiments. Note that, unless otherwise specified, % indicates % by mass.

<Lubricant blend>
Lubricating oil compositions for testing were prepared by blending the base oil and additives in the blending ratios shown in Tables 1 and 2 for each Example and Comparative Example. The obtained lubricating oil compositions for testing were evaluated as follows. The evaluation results are shown in Tables 1 and 2.

(A) Base oils Base oil 1: Group III base oil (mineral oil) kinematic viscosity 4.2 mm ² /s (100°C), viscosity index 125

Additives were added as shown in Tables 1 and 2. Details of the additives are as follows: The blending amount of the additives is based on the total amount of the lubricating oil composition.
(B) Metal-Based Detergents Metal-Based Detergent 1: Calcium borate salicylate (calcium content: 6.8% by mass, boron content: 2.7% by mass, base number: 190 mg KOH/g)
Metallic detergent 2: calcium salicylate (calcium content: 8.0% by mass, base number: 225 mg KOH/g)
Metallic detergent 3: Magnesium salicylate (magnesium content: 7.4% by mass, base number: 340 mg KOH/g)
Metallic detergent 4: Magnesium sulfonate (magnesium content: 9.1% by mass, base number: 405 mg KOH/g)
(C) Antiwear Agents Antiwear agent 1: Zinc dialkyldithiophosphate (zinc content 9.3% by mass, phosphorus content 8.5% by mass, sulfur content 17.6% by mass, secondary ZnDTP)
(D) Friction modifiers Friction modifier 1: Molybdenum dithiocarbamate (molybdenum content: 10.1% by mass, sulfur content: 10.8% by mass)
(E) Dispersants Dispersant 1: alkenylsuccinic acid polyalkylene polyimide (nitrogen content 1.75% by mass)
(F) Antioxidants Antioxidant 1: Alkylated diphenylamine Antioxidant 2: Benzenepropanoic acid, 3,4-bis(1,1 dimethyl ethyl)-4 hydroxy-C7, C9 side chain alkyl ester

<Evaluation method>
(1) Friction characteristics The friction characteristics of each test lubricating oil composition were tested. Using an MTM (Mini Traction Machine) tester (manufactured by PCS Instruments), the friction characteristics of each lubricating oil composition at a certain load and sliding ratio were calculated as a friction coefficient (μ). The test conditions are shown below. In this test, the smaller the friction coefficient, the more excellent the friction characteristics. The friction coefficient is a value after sliding for 3 hours at a peripheral speed of 100 mm/s.
Rolling speed: 200 mm/s
Load: 30N
Slip rate: 50%
Oil temperature: 40℃ and 100℃
At 100° C., those having a value of 0.05 or less were evaluated as having excellent friction characteristics.
At 40° C., those having a value of 0.06 or less were evaluated as having excellent friction characteristics.

The evaluation results of each test lubricating oil composition are shown in the following Tables 1 and 2. The density at 15°C of each of the test lubricating oil compositions of Examples 1 to 5 and Comparative Examples 1 to 6 was 0.850 g/ ^cm3 or less.

Examples 1 to 5, which contain calcium borate salicylate and magnesium salicylate as metal detergents and have a calcium content of 300 ppm by mass or more and 1,200 ppm by mass or less based on the lubricating oil composition, showed good friction coefficient values when measured at both 40°C and 100°C.

In Comparative Example 1, in which the amount of calcium derived from calcium borate salicylate was 1,300 ppm by mass based on the lubricating oil composition, the friction coefficient increased in measurements at both 40°C and 100°C.
In Comparative Example 2, in which the amount of calcium derived from calcium borate salicylate was 0 ppm by mass based on the lubricating oil composition, the friction coefficient increased when measured at 40°C.
Comparative Examples 3 to 6, which did not contain magnesium salicylate, showed increased friction coefficients in measurements at both 40°C and 100°C.

The lubricating oil composition for internal combustion engines of the present invention can provide a lubricating oil for internal combustion engines that has excellent fuel economy not only at high oil temperatures but also at low oil temperatures.

Claims (3)

A lubricating oil composition for an internal combustion engine comprising: (A) a lubricating base oil; and (B) calcium salicylate borate and (C) magnesium salicylate as metal-based detergents ,
the amount of calcium derived from the calcium borate salicylate (B) is 300 ppm by mass or more and 1,200 ppm by mass or less based on the total amount of the lubricating oil composition for internal combustion engines ,
the content of boron derived from the calcium borate salicylate (B) is 100 ppm by mass or more and 600 ppm by mass or less based on the total amount of the lubricating oil composition for internal combustion engines ,
The HTHS viscosity at 150°C is 1.7 mPa·s or more and less than 2.0 mPa·s,
The lubricating oil composition for internal combustion engines, wherein the content of magnesium derived from the magnesium salicylate (C) is 100 ppm by mass or more and 1000 ppm by mass or less based on the total amount of the lubricating oil composition for internal combustion engines. The lubricating oil composition for internal combustion engines according to claim 1 , wherein the lubricating base oil (A) has a kinematic viscosity at 100° C. of 3.0 mm ² /s or more and 5.0 mm ² /s or less. 3. The lubricating oil composition for internal combustion engines according to claim 1 or 2 , further comprising (D) a molybdenum-based friction modifier in an amount of 100 ppm by mass or more and 1,000 ppm by mass or less in terms of molybdenum, based on the total amount of the composition.