LUBRICATING OIL COMPOSITION FOR INTERNAL COMBUSTION ENGINE

Abstract

A lubricating oil composition for an internal combustion engine, having (A) a lubricating base oil including one or more mineral oil-based base oils and having a kinematic viscosity at 100? C. of 2.5 mm.sup.2/s or more and 4.0 mm.sup.2/s or less, and (B) magnesium salicylate in an amount of 0.1 mass % or more and 10 mass % or less based on a total amount of the composition, wherein the composition has an HTHS viscosity at 150? C. of 1.6 mPa.Math.s or more and 2.5 mPa.Math.s or less. The lubricating oil composition for an internal combustion engine has both high fuel-saving performance and LSPI-reducing effect.

Claims

1. A lubricating oil composition for an internal combustion engine, comprising: (A) a lubricating base oil including one or more mineral oil-based base oils and having a kinematic viscosity at 100? C. of 2.5 mm.sup.2/s or more and 4.0 mm.sup.2/s or less, and (B) magnesium salicylate in an amount of 0.1 mass % or more and 10 mass % or less based on a total amount of the lubricating oil composition, wherein the composition has an HTHS viscosity at 150? C. of 1.6 mPa.Math.s or more and 2.5 mPa.Math.s or less.

2. The lubricating oil composition for an internal combustion engine according to claim 1, wherein a content of the magnesium salicylate (B) is 0.1 mass % or more and 3.0 mass % or less based on the total amount of the lubricating oil composition, the lubricating oil composition further comprises (C) a viscosity index improver, and a content of the viscosity index improver (C) is 0.1 mass % or more and 10 mass % or less based on the total amount of the lubricating oil composition.

3. The lubricating oil composition for an internal combustion engine according to claim 1, further comprising (D) a molybdenum-based friction modifier as a friction modifier in an amount of 0.01 mass % or more and 10 mass % or less based on the total amount of the lubricating oil composition.

4. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the magnesium salicylate has a base number of 350 mgKOH/g or less.

5. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the composition has an HTHS viscosity at 150? C. of 1.6 mPa.Math.s or more and 2.0 mPa.Math.s or less.

6. The lubricating oil composition for an internal combustion engine according to claim 1, wherein the composition has an LSPI frequency index calculated by the following equation (6) of 0 or less: $\begin{array}{cc}\mathrm{LSPI}\mathrm{frequency}\mathrm{index}=6.59?\mathrm{Ca}-26.6?P-5.12?\mathrm{Mo}+1.69& \mathrm{Equation}\left(6\right)\end{array}$ wherein Ca represents calcium content (mass %) in the composition, P represents phosphorus content (mass %) in the composition, and Mo represents molybdenum content (mass %) in the composition.

Description

DESCRIPTION OF EMBODIMENT

[A] Lubricating Base Oil

[0018] In a lubricating oil composition of the invention, mineral oil-based base oil may be used as a lubricating base oil.

[0019] Examples of the mineral oil-based base oil used in the lubricating oil composition of the invention include distillate oil obtained by atmospheric distillation of crude oil. Alternatively, it is possible to use a lubricating oil distillate obtained by further vacuum distillation of the distillate oil and by purifying the resulting distillate oil by various refining processes. The refining process can be a combination of, for instance, hydrogenation refining, solvent extraction, solvent dewaxing, hydrogenation dewaxing, sulfuric acid cleaning, and/or white clay treatment, if appropriate. These refining processes may be combined in an appropriate order to produce a lubricating base oil usable in the invention. It is also possible to use a mixture of several refined oils with different properties, as obtained by subjecting different crude oils or distillate oils to different combinations of refining processes.

[0020] The mineral oil-based base oil used in the lubricating oil composition of the invention should preferably be one that belongs to Group III base oils according to the API classification. The API Group III base oils are mineral oil-based base oils with a sulfur content of 0.03 mass % or less, a saturated content of 90 mass % or more, and a viscosity index of 120 or more. Several types of Group III base oils may be used, or only one type may be used.

[0021] The lubricating oil composition of the invention may contain only a mineral oil-based base oil as a lubricating base oil or may optionally contain another lubricating base oil. Specifically, in the lubricating oil composition of the invention, the content of mineral oil-based base oil can 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 base oil.

[0022] As another lubricating base oil, for example, a synthetic oil can be used. Examples of the synthetic oil include polyolefin such as poly-?-olefin, polyester, polyalkylene glycol, alkylbenzene, alkylnaphthalene, and GTL base oil.

[0023] The kinematic viscosity at 100? C. of the lubricating base oil included in the lubricating oil composition of the present invention is 2.5 mm.sup.2/s or more and 4.0 mm.sup.2/s or less. The kinematic viscosity at 100? C. of the lubricating base oil of the present invention is preferably 3.0 mm.sup.2/s or more, more preferably 3.2 mm.sup.2/s or more, and still more preferably 3.4 mm.sup.2/s or more. The upper limit is preferably 3.9 mm.sup.2/s or less, more preferably 3.8 mm.sup.2/s or less, and still more preferably 3.6 mm.sup.2/s or less. The specific range is 2.5 mm.sup.2/s or more and 4.0 mm.sup.2/s or less, preferably 3.0 mm.sup.2/s or more and 3.9 mm.sup.2/s or less, more preferably 3.2 mm.sup.2/s or more and 3.8 mm.sup.2/s or less, and still more preferably 3.4 mm.sup.2/s or more and 3.6 mm.sup.2/s or less. Sufficient fuel-saving performance can be obtained when the kinematic viscosity of the lubricating base oil at 100? C. is 4.0 mm.sup.2/s or less. In addition, the kinematic viscosity of the lubricating base oil at 100? C. may be 2.5 mm.sup.2/s or more. This can ensure oil film formation at lubrication sites and reduce the evaporation loss of the lubricating oil composition.

[0024] The kinematic viscosity at 100? C. means the kinematic viscosity of all lubricating base oils mixed together, i.e., the kinematic viscosity of base oils as a whole. In other words, it does not mean the kinematic viscosity of one specific lubricating base oil when multiple base oils are included.

[0025] Note that as used herein, the wording kinematic viscosity at 100? C. means a kinematic viscosity at 100? C. as measured in accordance with ASTM D-445.

[0026] In the lubricating oil composition of the invention, the content of the lubricating oil base oil based on the total amount of the lubricating oil composition is, for example, from 50 mass % to 95 mass %, preferably from 60 mass % to 95 mass %, more preferably from 70% to 95 mass %, still more preferably from 80 mass % to 95 mass %, and most preferably from 85 mass % to 95 mass %.

[B] Magnesium Salicylate

[0027] In the lubricating oil composition of the present invention, magnesium salicylate is used as a metallic detergent. In addition to magnesium salicylate, another metallic detergent may be included, but it is preferable to include magnesium salicylate only.

[0028] Examples of magnesium salicylate include a compound represented by the following formula (1).

##STR00001##

[0029] wherein R.sup.1 each independently represents a C.sub.14-30 alkyl group or an alkenyl group, and n represents 1 or 2. Mg represents magnesium. Here, n is preferably 1. Note that when n=2, different R.sup.1 groups may be used in combination.

[0030] Magnesium salicylate may be overbased with carbonate or overbased with borate.

[0031] The content of magnesium salicylate included in the lubricating oil composition of the present invention is 0.1 mass % or more, preferably 0.2 mass % or more, more preferably 0.5 mass % or more, and still more preferably 1 mass % or more based on the total amount of the lubricating oil composition. The upper limit is 10 mass % or less, preferably 8 mass % or less, more preferably 5 mass % or less, and still more preferably 4 mass % or less. The specific range is, for example, from 0.1 mass % to 10 mass % or from 0.1 mass % to 3.0 mass % and is preferably from 0.2 mass % to 8 mass %, more preferably from 0.5 mass % to 5 mass %, and still more preferably from 1 mass % to 4 mass %. A content of magnesium salicylate of 0.1 mass % or more provides effective fuel-saving performance and a cleansing effect, and a content of magnesium salicylate of 10 mass % or less can achieve both fuel-saving performance and an LSPI-reducing effect.

[0032] The amount of magnesium derived from magnesium salicylate included in the lubricating oil composition of the present invention is preferably 500 mass ppm or more and more preferably 1000 mass ppm or more based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 mass ppm or less and more preferably 1600 mass ppm or less. The specific range is preferably from 500 mass ppm to 2000 mass ppm, more preferably from 1000 mass ppm to 1600 mass ppm. When the content of magnesium is within the range above, cleanliness inside the engine can be maintained at a high level, while suppressing occurrence of LSPI.

(Base Number)

[0033] The base number of magnesium salicylate included in the lubricating oil composition of the present invention is preferably 140 mgKOH/g or more, more preferably 180 mgKOH/g or more, and still more preferably 200 mgKOH/g or more, from the viewpoint of further improving the fuel-saving property. The upper limit is preferably 500 mgKOH/g or less, more preferably 400 mgKOH/g or less, and still more preferably 350 mgKOH/g or less. The specific range is preferably from 140 mgKOH/g to 500 mgKOH/g, more preferably from 180 mgKOH/g to 400 mgKOH/g, and still more preferably from 200 mgKOH/g to 350 mgKOH/g. Note that the base number is measured according to JIS K 2501 5.2.3.

[0034] The lower the base number, the less the inhibitory effect by MgCO.sub.3. Accordingly, the fuel-saving property is further improved.

[0035] Within a range that does not impair the effects of the present invention, the lubricating oil composition of the present invention can include a metallic detergent other than magnesium salicylate, for example, a phenate-based detergent, a sulfonate-based detergent, or a salicylate-based detergent other than magnesium salicylate, but it is preferable to include magnesium salicylate only.

[0036] The present inventors found that a lubricating oil composition for an internal combustion engine, provided with an LSPI-reducing effect and fuel-saving performance, can be prepared by using magnesium salicylate as a detergent and further adjusting the HTHS viscosity at 150? C. to a range from 1.6 mPa.Math.s to 2.5 mPa.Math.s. Such a lubricating oil composition for an internal combustion engine was not obtained even if using a metallic detergent including magnesium other than magnesium salicylate. This is remarkable (Examples and Comparative Examples described below).

[C] Viscosity Index Improver

[0037] The lubricating oil composition of the invention preferably contains a viscosity index improver. It is possible to use, as the viscosity index improver, those commonly used in the field of a lubricating oil composition for an internal combustion engine. Specific examples include polymethacrylate, an olefin copolymer, polybutene, polyisobutene, polyisobutylene, polystyrene, an ethylene-propylene copolymer, or a styrene-diene copolymer, or a hydride thereof. Polymethacrylate is preferred.

[0038] The viscosity index improver contained in the lubricating oil composition of the invention has an weight average molecular weight of preferably 10,000 or more, more preferably 50,000 or more, and still more preferably 100,000 or more. The upper limit is preferably 800,000 or less, more preferably 500,000 or less, and still more preferably 400,000 or less. The specific range is preferably from 10,000 to 800,000, more preferably from 50,000 to 500,000, and still more preferably from 100,000 to 400,000.

[0039] The weight average molecular weight of high-molecular-weight polymer means a value determined by gel permeation chromatography (a molecular weight in terms of polystyrene).

[0040] The content of the viscosity index improver included in the lubricating oil composition of the present invention is preferably appropriately adjusted such that the HTHS viscosity of the lubricating oil composition at 150? C. is from 1.6 mPa.Math.s to 2.5 mPa.Math.s. When the lubricating oil composition of the invention contains a viscosity index improver, the content based on the total amount of the lubricating oil composition is 0.1 mass % or more, preferably 0.2 mass % or more, more preferably 0.5 mass % or more, and still more preferably 1 mass % or more. The upper limit is 10 mass % or less, preferably 8 mass % or less, more preferably 5 mass % or less, and still more preferably 3 mass % or less. The specific range is from 0.1 mass % to 10 mass %, preferably from 0.2 mass % to 8 mass %, more preferably from 0.5 mass % to 5 mass %, and still more preferably from 1 mass % to 3 mass %.

[D] Molybdenum-Based Friction Modifier

[0041] The lubricating oil composition of the invention preferably further contains (D) a molybdenum-based friction modifier as a friction modifier. The component (D) is preferably molybdenum dithiocarbamate (hereinafter, may be simply referred to as MoDTC).

[0042] The MoDTC used may be, for example, a compound represented by the following formula (2).

##STR00002##

[0043] wherein R.sup.2 to R.sup.5 may be the same or different and are each a C.sub.2-24 alkyl group or a C.sub.6-24 (alkyl)aryl group, and preferably a C.sub.4-13 alkyl group or a C.sub.10-15 (alkyl) aryl group. The alkyl group may be any of a primary, secondary, or tertiary alkyl group, and may be linear or branched. Note that the (alkyl)aryl group means an aryl group or an alkyl aryl group. In the alkylaryl group, any of the substitution position of the alkyl group in the aromatic ring is allowed. X.sup.1 to X.sup.4 are each independently a sulfur atom or an oxygen atom, and at least one of X.sup.1 to X.sup.4 is a sulfur atom.

[0044] Examples of the molybdenum-based friction modifier other than MoDTC include molybdenum dithiophosphate, molybdenum oxide, molybdic acid, a molybdate (e.g., ammonium molybdate), molybdenum disulfide, sulfides of molybdic acid, or a sulfur-containing organic molybdenum compound.

[0045] When the lubricating oil composition of the present invention includes a molybdenum-based friction modifier, the content thereof is 0.01 mass % or more, preferably 0.1 mass % or more, more preferably 0.2 mass % or more, and still more preferably 0.5 mass % or more based on the total amount of the lubricating oil composition. The upper limit is 10 mass % or less, preferably 8 mass % or less, more preferably 5 mass % or less, and still more preferably 2 mass % or less. The specific range is from 0.01 mass % to 10 mass %, preferably from 0.1 mass % to 8 mass %, more preferably from 0.5 mass % to 5 mass %, and still more preferably from 0.5 mass % to 2 mass %.

[0046] The amount of molybdenum derived from a molybdenum-based friction modifier included in the lubricating oil composition of the present invention is preferably 100 mass ppm or more and more preferably 500 mass ppm or more based on the total amount of the lubricating oil composition. The upper limit is preferably 2000 mass ppm or less and more preferably 1000 mass ppm or less. The specific range is preferably from 100 mass ppm to 2000 mass ppm and more preferably from 500 mass ppm to 1000 mass ppm. When the molybdenum content is the above-mentioned lower limit or more, the fuel-saving performance and LSPI-suppressing ability can be further enhanced. In addition, if the molybdenum content is the upper limit or less, the lubricating oil composition storage stability can be increased.

(Additional Additive)

[0047] The lubricating oil composition of the invention may further contain an anti-wear agent, an antioxidant, or a dispersant.

[0048] Zinc dialkyl dithiophosphate (ZnDTP) is preferably added as the anti-wear agent. Examples of the zinc dialkyl dithiophosphate include a compound represented by the following formula (3).

##STR00003##

[0049] wherein R.sup.6 to R.sup.9 are each independently a hydrogen atom or a linear or branched C.sub.1-24 alkyl group, and at least one of R.sup.6 to R.sup.9 is a linear or branched C.sub.1-24 alkyl group. This alkyl group may be primary, secondary, or tertiary.

[0050] In the lubricating oil composition of the invention, one kind of the zinc dialkyl dithiophosphate may be used singly or two or more kinds thereof may be used in combination. The dialkyl zinc dithiophosphate is preferably zinc dithiophosphate with a primary alkyl group (primary ZnDTP) or zinc dithiophosphate containing a secondary alkyl group (secondary ZnDTP). In particular, those primarily composed of zinc dithiophosphate containing a secondary alkyl group is preferable so as to increase wear resistance.

[0051] When the lubricating oil composition of the present invention includes zinc dialkyl dithiophosphate, the content thereof is 0.01 mass % or more, preferably 0.1 mass % or more, more preferably 0.2 mass % or more, and still more preferably 0.5 mass % or more, based on the total amount of the lubricating oil composition. The upper limit is 10 mass % or less, preferably 8 mass % or less, more preferably 5 mass % or less, and still more preferably 2 mass % or less. The specific range is from 0.01 mass % to 10 mass %, preferably from 0.1 mass % to 8 mass %, more preferably from 0.5 mass % to 5 mass %, and still more preferably from 0.5 mass % to 2 mass %.

[0052] The amount of phosphorus derived from the zinc dialkyl dithiophosphate contained in the lubricating oil composition of the invention is preferably 100 mass ppm or more and more preferably 500 mass ppm or more, based on the total amount of the composition. The upper limit is preferably 2000 mass ppm or less and more preferably 1000 mass ppm or less. The specific range is preferably from 100 mass ppm to 2000 mass ppm and more preferably from 500 mass ppm to 1000 mass ppm.

[0053] It is possible to use, as the antioxidant, a known antioxidant such as a phenolic antioxidant or an amine-based antioxidant. Examples include an amine-based antioxidant (e.g., alkylated diphenylamine, phenyl-?-naphthylamine, alkylated-?-naphthylamine) or a phenolic antioxidant (e.g., 2,6-di-t-butyl-4-methylphenol, 4,4-methylenebis(2,6-di-t-butylphenol)).

[0054] The lubricating oil composition may contain an antioxidant. In this case, the content is usually 5.0 mass % or less, preferably 3.0 mass % or less and preferably 0.1 mass % or more, and more preferably 0.5 mass % or more, based on the total amount of the lubricating oil composition.

[0055] Examples of the dispersant include an ashless dispersant such as succinimide or benzylamine.

[0056] The lubricating oil composition may contain a dispersant. In this case, the content is usually 5.0 mass % or less and preferably 0.1 mass % or more, based on the total amount of the lubricating oil composition.

[0057] To further improve the performance, the lubricating oil composition of the invention may contain an additional additive(s) commonly used in lubricating oils depending on the purpose. Examples of such an additive(s) include an additive(s) such as an anti-wear agent, an extreme pressure agent, a pour point depressant, a corrosion inhibitor, an anti-rust agent, a metal deactivator, and/or a defoaming agent.

(Lubricating Oil Composition for an Internal Combustion Engine)

[0058] The HTHS viscosity at 150? C. of the lubricating oil composition of the present invention is from 1.6 mPa.Math.s to 2.5 mPa.Math.s. When the HTHS viscosity at 150? C. is 2.5 mPa.Math.s or less, high fuel-saving performance can be obtained. A HTHS viscosity of less than 1.6 mPa.Math.s has a risk of insufficient lubricity.

[0059] The HTHS viscosity at 150? C. of the lubricating oil composition of the present invention is from 1.6 mPa.Math.s to 2.5 mPa.Math.s, preferably from 1.6 mPa.Math.s to 2.4 mPa.Math.s, more preferably from 1.6 mPa.Math.s to 2.3 mPa.Math.s, more preferably from 1.6 mPa.Math.s to 2.2 mPa.Math.s, still more preferably from 1.6 mPa.Math.s to 2.1 mPa.Math.s, and most preferably from 1.6 mPa.Math.s to 2.0 mPa.Math.s.

[0060] Note that the HTHS viscosity at 150? C. refers to a high-temperature high-shear viscosity at 150? C. as specified in ASTM D 4683.

[0061] The viscosity index of the lubricating oil composition of the present invention is preferably 120 to 220, more preferably 140 to 200. When the viscosity index of the lubricating oil composition is 140 or more, the fuel-saving performance can be further improved while maintaining a low HTHS viscosity at 150? C. In addition, if the viscosity index of the lubricating oil composition exceeds 220, evaporability may deteriorate.

[0062] Note that as used herein, the viscosity index means a viscosity index measured in accordance with JIS K 2283-1993.

[0063] The kinematic viscosity at 40? C. of the lubricating oil composition of the present invention is preferably 10 mm.sup.2/s or more, more preferably 14 mm.sup.2/s or more, still more preferably 16 mm.sup.2/s or more, and most preferably 18 mm.sup.2/s or more. The upper limit is preferably 30 mm.sup.2/s or less, more preferably 28 mm.sup.2/s or less, still more preferably 25 mm.sup.2/s or less, and most preferably 22 mm.sup.2/s or less. The specific range is preferably from 10 mm.sup.2/s to 30 mm.sup.2/s, more preferably from 14 mm.sup.2/s to 28 mm.sup.2/s, still more preferably from 16 mm.sup.2/s to 25 mm.sup.2/s, and most preferably from 18 mm.sup.2/s to 22 mm.sup.2/s. When the kinematic viscosity of the lubricating oil composition at 40? C. is 30 mm.sup.2/s or less, sufficient fuel-saving performance can be obtained. In addition, when the kinematic viscosity of the lubricating oil composition at 40? C. is 10 mm.sup.2/s or more, oil film formation at lubrication sites can be ensured, and the evaporation loss of the lubricating oil composition can also be decreased.

[0064] Note that as used herein, the wording kinematic viscosity at 40? C. means a kinematic viscosity at 40? C. as measured in accordance with ASTM D-445.

[0065] The kinematic viscosity of the lubricating oil composition of the invention at 100? C. is preferably 3 mm.sup.2/s or more and more preferably 4 mm.sup.2/s or more. The upper limit is preferably 7 mm.sup.2/s or less and more preferably 5 mm.sup.2/s or less. The specific range is preferably from 3 mm.sup.2/s to 7 mm.sup.2/s and more preferably from 4 mm.sup.2/s to 5 mm.sup.2/s.

[0066] The density (?15) of the lubricating oil composition of the invention at 15? C. is preferably 0.860 or less and more preferably 0.850 or less. Note that as used herein, the density at 15? C. means a density at 15? C. as measured in accordance with JIS K 2249-1995.

[0067] The LSPI occurrence frequency can be reduced by using the lubricating oil composition of the present invention. As used herein, the wording LSPI occurrence frequency means an occurrence frequency of abnormal combustion at a low engine rotation speed.

[0068] Non Patent Literature 1 reports that the occurrence frequency of LSPI when a lubricating oil composition is used for lubrication of an internal combustion engine has a positive correlation with the Ca content in the lubricating oil composition and has a negative correlation with the P content and Mo content in the lubricating oil composition. More specifically, it has been reported that the index of LSPI frequency can be estimated by the following regressive equation (6) based on the content of each element in a lubricating oil composition.

[00001]$\begin{array}{cc}\mathrm{LSPI}\mathrm{frequency}\mathrm{index}=6.59?\mathrm{Ca}-26.6?P-5.12?\mathrm{Mo}+1.69& \mathrm{Equation}\left(6\right)\end{array}$

(wherein Ca represents the calcium content (mass %) in the composition, P represents the phosphorus content (mass %) in the composition, and Mo represents the molybdenum content (mass %) in the composition).

[0069] The LSPI frequency index (calculated value) of the lubricating oil composition of the present invention by the equation (6) is preferably 0 or less, more preferably 0.1 or less, more preferably 0.2 or less, more preferably 0.3 or less, more preferably 0.4 or less, still more preferably 0.5 or less, and most preferably 0.6 or less.

[0070] Regarding the amount of evaporation loss of the lubricating oil composition of the present invention, the NOACK evaporation amount at 250? C. is preferably 30 mass % or less, further preferably 20 mass % or less, and particularly preferably 15 mass % or less. When the NOACK evaporation amount of the lubricating base oil component exceeds 30 mass %, the evaporation loss of the lubricating oil is high, which disadvantageously causes, for example, an increase in the viscosity. Note that as used herein, the NOACK evaporation loss refers to the amount of evaporation of lubricating oil as measured in accordance with ASTM D 5800. The lower limit of the NOACK evaporation amount of the lubricating oil composition at 250? C. is not particularly limited and is usually 5 mass % or more.

EXAMPLES

[0071] Examples are used to describe the invention below. The invention, however, is not limited to the following disclosure. Unless otherwise indicated, the % indicates mass %.

<Lubricating Oil Formulation>

[0072] In the respective Examples or Comparative Examples, base oils and additives were blended at each formulation ratio designated in Tables 1 to 2 to prepare each test lubricating oil composition. Each test lubricating oil composition obtained was evaluated as shown below. Tables 1 to 2 show the evaluation results.

(A) Base Oil

[0073] Base oil 1: Group III base oil (mineral oil), kinematic viscosity: 3.3 mm.sup.2/s (100? C.), viscosity index: 112 [0074] Base oil 2: Group III base oil (mineral oil), kinematic viscosity: 4.3 mm.sup.2/s (100? C.), viscosity index: 123
Each lubricating base oil was prepared by mixing base oils at each mass ratio designated in Tables 1 to 2. In the tables, the numbers of base oils each represent the mass ratio based on the total amount of base oils.

(2) Additive

[0075] Additives were added as listed in Tables 1 to 2. The details of the additives were as follows. The amount of each additive blended is based on the total amount of the lubricating oil composition.

(B) Metallic Detergent

[0076] Metallic detergent 1: calcium salicylate (calcium content: 8.0 mass %, base number: 225 mgKOH/g) [0077] Metallic detergent 2: calcium sulfonate (calcium content: 12.5 mass %, base number: 320 mgKOH/g) [0078] Metallic detergent 3: magnesium salicylate (magnesium content: 7.4 mass %, base number: 342 mgKOH/g) [0079] Metallic detergent 4: magnesium salicylate (magnesium content: 6.1 mass %, base number: 292 mgKOH/g) [0080] Metallic detergent 5: magnesium salicylate (magnesium content: 4.3 mass %, base number: 218 mgKOH/g) [0081] Metallic detergent 6: magnesium salicylate (magnesium content: 8.3 mass %, base number: 390 mgKOH/g) [0082] Metallic detergent 7: magnesium sulfonate (magnesium content: 9.1 mass %, base number: 405 mgKOH/g)

(C) Viscosity Index Improver

[0083] Viscosity index improver 1: polymethacrylate (weight average molecular weight: 380,000)

(D) Friction Modifier

[0084] Friction modifier 1: molybdenum dithiocarbamate (molybdenum content: 9.1 mass %, sulfur content: 10.8 mass %) [0085] Anti-wear agent 1: zinc dialkyl dithiophosphate (zinc content: 9.3 mass %, phosphorus content: 9.3 mass %, sulfur content: 17.6 mass %; secondary ZnDTP) [0086] Dispersant 1: polyimide succinate (nitrogen content: 1.75 mass %) [0087] Antioxidant 1: amine-based antioxidant [0088] Antioxidant 2: phenol-based antioxidant

<Evaluation Procedure>

(1) Fuel-Saving Performance

[0089] Each test lubricating oil composition was subjected to a motoring engine torque test. For each test lubricating oil composition, the torque necessary for rotating the output shaft of a DOHC engine (displacement: 2.0 L) lubricated with the lubricating oil composition (oil temperature: 95? C.) by an electric motor at a constant rate was measured. The measurement was performed at 1000 rpm, and the torque reduction proportion with respect to the measured value in Comparative Example 1 was calculated. It means that the higher the torque reduction proportion, the better the fuel-saving performance.

(2) LSPI Frequency Calculated Value

[0090] The LSPI frequency index of each test lubricating oil composition was calculated using the above-mentioned equation (6). The results demonstrate that the lower the LSPI frequency index, the better the LSPI-suppressing ability.

[0091] Tables 1 to 2 below show the results of evaluating each test lubricating oil composition. Note that the density of each test lubricating oil composition at 15? C. in Examples 1 to 4 or Comparative Examples 1 to 7 is all 0.850 or less.

TABLE-US-00001 TABLE 1 Example Example Example Example Comparative 1 2 3 4 Example 1 Base oil Base oil 1 mass % 58 58 58 58 58 Base oil 2 mass % 42 42 42 42 42 Metallic Metallic detergent 1 mass % 2.50 detergent Metallic detergent 2 mass % Metallic detergent 3 mass % 1.62 Metallic detergent 4 mass % 2.10 Metallic detergent 5 mass % 3.00 Metallic detergent 6 mass % 1.56 Metallic detergent 7 mass % Anti-wear Anti-wear agent 1 mass % 0.94 0.94 0.94 0.94 0.94 agent Friction Friction modifier 1 mass % 0.70 0.70 0.70 0.70 0.70 modifier Viscosity Viscosity index mass % 1.70 1.70 1.70 1.70 1.70 index improver 1 improver Dispersant Dispersant 1 mass % 3.52 3.52 3.52 3.52 3.52 Antioxidant Antioxidant 1 mass % 1.00 1.00 1.00 1.00 1.00 Antioxidant 2 mass % 0.50 0.50 0.50 0.50 0.50 Base oil Kinematic viscosity mm.sup.2/s 3.5 3.5 3.5 3.5 4.2 properties (100? C.) Composition HTHS viscosity mPa .Math. s 1.7 1.7 1.7 1.7 1.7 characteristics (150? C.) Viscosity index 145 145 147 145 147 Kinematic viscosity mm.sup.2/s 20.02 19.82 20.00 19.88 20.40 (40? C.) Kinematic viscosity mm.sup.2/s 4.53 4.50 4.54 4.51 4.60 (100? C.) Mg content massppm 1300 1300 1300 1300 12 Mo content massppm 670 670 670 670 660 P content massppm 780 780 780 780 770 Evaluation Fuel-saving % 2.3 2.0 1.7 1.6 Reference results performance LSPI frequency ?0.7 ?0.7 ?0.7 ?0.7 0.6 calculated value

TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Comparative Example Example Example Example Example 2 3 4 5 6 Base oil Base oil 1 mass % 58 58 58 Base oil 2 mass % 100 100 42 42 42 Metallic Metallic detergent 1 mass % 2.50 2.50 detergent Metallic detergent 2 mass % 1.60 Metallic detergent 3 mass % 1.62 Metallic detergent 4 mass % Metallic detergent 5 mass % Metallic detergent 6 mass % Metallic detergent 7 mass % 1.30 Anti-wear Anti-wear agent 1 mass % 0.94 0.94 0.94 0.94 0.94 agent Friction Friction modifier 1 mass % 0.70 0.70 0.70 0.20 0.70 modifier Viscosity Viscosity index mass % 12.7 12.2 2.00 1.70 1.70 index improver 1 improver Dispersant Dispersant 1 mass % 3.52 3.52 3.52 3.52 3.52 Antioxidant Amine-based mass % 1.00 1.00 1.00 1.00 1.00 Phenol-based mass % 0.50 0.50 0.50 0.50 0.50 Base oil Kinematic viscosity mm.sup.2/s 4.2 4.2 3.5 3.5 3.5 properties (100? C.) Composition HTHS viscosity mPa .Math. s 2.6 2.6 1.7 1.7 1.6 characteristics (150? C.) Viscosity index 224 220 145 147 142 Kinematic viscosity mm.sup.2/s 33.88 34.38 20.01 20.56 19.38 (40? C.) Kinematic viscosity mm.sup.2/s 8.05 8.05 4.52 4.62 4.40 (100? C.) Mg content massppm 1200 14 1300 12 12 Mo content massppm 710 700 670 200 670 P content massppm 800 810 780 770 780 Evaluation Fuel-saving % ?4.5 ?4.2 ?0.2 ?2.7 ?2.5 results performance LSPI frequency ?0.8 0.4 ?0.7 0.9 0.6 calculated value

[0092] In Examples 1 to 4 in which the HTHS viscosity at 150? C. was adjusted to 1.7 using magnesium salicylate as a metallic detergent, the fuel-saving performance was improved and the LSPI frequency calculated value was decreased, compared to Comparative Example 1.

[0093] In Comparative Example 1 where calcium salicylate was used as the metallic detergent, the LSPI frequency calculated value was increased.

[0094] In Comparative Example 2 where the HTHS viscosity at 150? C. was adjusted to 2.6, the fuel-saving performance was deteriorated compared to Comparative Example 1.

[0095] In Comparative Example 3 where calcium salicylate was used as the metallic detergent and the HTHS viscosity at 150? C. was adjusted to 2.6, the fuel-saving performance was deteriorated and the LSPI frequency calculated value was increased, compared to Comparative Example 1.

[0096] In Comparative Example 4 where magnesium sulfonate was used as the metallic detergent, the fuel-saving performance was deteriorated.

[0097] In Comparative Example 5 where calcium salicylate was used as the metallic detergent and the amount of the molybdenum-based friction modifier was decreased, the LSPI frequency calculated value was increased.

[0098] In Comparative Example 5 where calcium sulfonate was used as the metallic detergent, the fuel-saving performance was deteriorated, and the LSPI frequency calculated value was increased.

[0099] In Comparative Example 6 where calcium sulfonate was used as the metallic detergent and the HTHS viscosity at 150? C. was adjusted to 1.6, the fuel-saving performance was deteriorated, and the LSPI frequency calculated value was increased.

INDUSTRIAL APPLICABILITY

[0100] According to the lubricating oil composition for an internal combustion engine according to the present invention, a lubricating oil composition for an internal combustion engine, provided with both high fuel-saving performance and LSPI-reducing effect, can be provided.