US20240240102A1

US20240240102A1 - Lubricating oil composition for internal combustion engine

Info

Publication number: US20240240102A1
Application number: US18/561,773
Authority: US
Inventors: Mari Iino; Hideo TSUNEOKA
Original assignee: Eneos Corp
Current assignee: Eneos Corp
Priority date: 2021-05-25
Filing date: 2022-05-23
Publication date: 2024-07-18
Also published as: CN117321180A; WO2022250017A1; JP2022180775A

Abstract

A lubricating oil composition for an internal combustion engine, having (A) a lubricating base oil, (B) magnesium salicylate, (C) calcium salicylate, and (D) a viscosity index improver, wherein the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.3 mPa·s or less, and an HTHS viscosity at 100° C. of 4.8 mPa·s or less, can provide a lubricating oil composition for an internal combustion engine provided with high fuel-saving performance.

Description

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for an internal combustion engine. The present invention specifically relates to a lubricating oil composition for an internal combustion engine, having excellent fuel-saving performance.

RELATED ART

Internal combustion engines are demanded to be further improved in the fuel-saving performance for environmental measure such as recent CO₂emission regulations.
In improvement of fuel efficiency by a lubricating oil, the viscous resistance has been reduced by decreasing the working viscosity (for example, see Patent Literature 1). However, lubrication of an internal combustion engine has a necessary viscosity, and there is naturally a limit. Internal combustion engine oils are used also as hydraulic power sources such as drive valves, and a certain viscosity is necessary for maintaining the hydraulic pressure. Accordingly, there was also a limit in lowering the viscosity. In order to overcome this, heat management of an internal combustion engine is being introduced. For example, the necessary viscosity can be further reduced by lowering the maximum operating temperature of an internal combustion engine oil according to the purpose and conditions of use of the internal combustion engine or by lowering the hydraulic pressure necessary for a pump through improvement of the internal combustion engine pump. Consequently, further fuel saving can be attempted.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2010-31082
Patent Literature 2: International Publication No. WO 2014/010462

SUMMARY OF INVENTION

Technical Problem

In an internal combustion engine adopting heat management, for the purpose of improving fuel-saving performance, a lubricating oil for an internal combustion engine has been developed (Patent Literature 2). However, further improvement in the fuel-saving property is desired.

Solution to Problem

The present inventors have intensively studied lubricating oil compositions for internal combustion engines, provided with fuel-saving performance. The present inventors have found that the above-mentioned problems can be solved by adopting the following configurations, and the present invention has been accomplished.
The present invention is based on such findings and provided as follows.
<1>
A lubricating oil composition for an internal combustion engine, having:

- (A) a lubricating base oil;
- (B) magnesium salicylate;
- (C) calcium salicylate; and
- (D) a viscosity index improver, wherein
- the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.3 mPa·s or less, and an HTHS viscosity at 100° C. of 4.8 mPa·s or less.
  <2>

The lubricating oil composition for an internal combustion engine according to <1>, wherein the lubricating base oil (A) has a kinematic viscosity at 100° C. of less than 4.2 mm²/s, and the lubricating oil composition has a viscosity index of 140 or more.
<3>
The lubricating oil composition for an internal combustion engine according to <1> or <2>, wherein
a total content of the magnesium salicylate (B) and the calcium salicylate (C) is 1400 mass ppm or more and 2000 mass ppm or less in terms of metal amount, based on a total amount of the composition, and
[the content of (B)/(the content of (B)+the content of (C))] is 0.05 to 0.95 in terms of mass ppm.
<4>
The lubricating oil composition for an internal combustion engine according to any one of <1> to <3>, wherein the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.0 mPa·s or less, and an HTHS viscosity at 100° C. of 4.2 mPa·s or less.

Advantageous Effect of Invention

According to the lubricating oil composition for an internal combustion engine of the present invention, a lubricating oil composition for an internal combustion engine, provided with high fuel-saving performance can be provided.

DESCRIPTION OF EMBODIMENT

[A] Lubricating Base Oil

In the lubricating oil composition of the present invention, a mineral oil-based base oil is preferably used as the lubricating base oil. 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.
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.
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.
In the lubricating oil composition of the present invention, a synthetic oil may be used as the lubricating base oil. Examples of the synthetic oil include poly-α-olefin and its hydride, an isobutene oligomer and its hydride, isoparaffin, alkylbenzene, alkylnaphthalene, diesters (such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate), polyol esters (such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate), polyoxyalkylene glycol, dialkyl diphenyl ether, polyphenyl ether, and mixtures thereof. In particular, poly-α-olefin is preferable. Examples of the poly-α-olefin typically include oligomers or co-oligomers (e.g., 1-octene oligomer, decene oligomer, ethylene-propylene co-oligomer) of C_2-32, preferably C_6-16, α-olefins, and hydrogenation products thereof.
The kinematic viscosity at 100° C. of the lubricating base oil included in the lubricating oil composition of the present invention is preferably less than 4.2 mm²/s. The kinematic viscosity at 100° C. of the lubricating base oil of the present invention is preferably 2.5 mm²/s or more, more preferably 3.0 mm²/s or more, and still more preferably 3.4 mm²/s or more. The upper limit is more preferably 4.1 mm²/s or less and still more preferably 4.0 mm²/s or less. The specific range is preferably from 2.5 mm²/s to 4.1 mm²/s, more preferably from 3.0 mm²/s to 4.0 mm²/s, and still more preferably from 3.4 mm²/s to 4.0 mm²/s. When the kinematic viscosity at 100° C. of the lubricating base oil is less than 4.2 mm²/s, further sufficient fuel-saving performance can be obtained. In addition, the kinematic viscosity of the lubricating base oil at 100° C. may be 2.5 mm²/s or more. This can ensure oil film formation at lubrication sites and reduce the evaporation loss of the lubricating oil composition.
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.
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.
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 %.

Magnesium Salicylate [B] and Calcium Salicylate [C]: Metallic Detergent

In the lubricating oil composition of the present invention, as metallic detergents, magnesium salicylate [B] and calcium salicylate [C] are used. In addition to the magnesium salicylate and calcium salicylate, the composition can include another metallic detergent, but preferably includes only two types: magnesium salicylate and calcium salicylate.
Examples of magnesium salicylate include a compound represented by the following formula (1).
wherein R¹each independently represents a C_14-30alkyl 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 R¹groups may be used in combination. Magnesium salicylate may be overbased with carbonate or overbased with borate.
The content of magnesium salicylate included in the lubricating oil composition of the present invention is 0.01 mass % or more, preferably 0.05 mass % or more, more preferably 0.1 mass % or more, and still more preferably 0.15 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 % and preferably from 0.05 mass % to 8 mass %, more preferably from 0.1 mass % to 5 mass %, and still more preferably from 0.15 mass % to 2 mass %.
The amount of magnesium derived from magnesium salicylate included in the lubricating oil composition of the present invention is preferably 50 mass ppm or more and more preferably 100 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 50 mass ppm to 2000 mass ppm, more preferably from 100 mass ppm to 1000 mass ppm. When the content of magnesium is within the above range, cleanliness inside the engine can be maintained at a high level, while ensuring the fuel-saving performance.

(Base Number)

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. 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.
As used herein, the base number is a value measured according to JIS K 2501 5.2.3.
Examples of calcium salicylate include compounds represented by the following formula (2):
wherein R²each independently represents a C_14-30alkyl group or alkenyl group; n represents 1 or 2; Ca represents calcium; and n is preferably 1. When n is 2, different R²groups may be used in combination. Calcium salicylate may be overbased with carbonate or overbased with borate.
The content of calcium 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 0.3 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 4 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 0.3 mass % to 5 mass %, and still more preferably from 0.5 mass % to 4 mass %.
The amount of calcium derived from calcium salicylate included in the lubricating oil composition of the present invention is preferably 300 mass ppm or more, more preferably 500 mass ppm or more, based on the total amount of the lubricating oil composition. The upper limit is preferably 2500 mass ppm or less and more preferably 2000 mass ppm or less. The specific range is preferably from 300 mass ppm to 2500 mass ppm and more preferably from 500 mass ppm to 2000 mass ppm. When the content of calcium is within the above range, cleanliness inside the engine can be maintained at a high level.

(Base Number)

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. The upper limit is preferably 500 mgKOH/g or less, more preferably 400 mgKOH/g or more, and still more preferably 300 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 300 mgKOH/g.
The lubricating oil composition of the present invention can include a metallic detergent other than calcium salicylate and magnesium salicylate, for example, a phenate-based detergent and a sulfonate-based detergent, within a range that does not impair the effects of the present invention, but it is preferable to include only two types: calcium salicylate and magnesium salicylate.
In the lubricating oil composition of the present invention, the total content of calcium salicylate and magnesium salicylate is preferably 800 mass ppm or more, more preferably 1000 mass ppm or more, still more preferably 1200 mass ppm or more, and most preferably 1400 mass ppm or more in terms of metal amount, based on the total amount of the composition. The upper limit is preferably 3000 mass ppm or less, more preferably 2500 mass ppm or less, still more preferably 2200 mass ppm or less, and most preferably 2000 mass ppm or less. The specific range is preferably from 800 mass ppm to 3000 mass ppm, more preferably from 1000 mass ppm to 2500 mass ppm, still more preferably from 1200 mass ppm to 2200 mass ppm, and most preferably from 1400 mass ppm to 2000 mass ppm. When the content of calcium salicylate and magnesium salicylate is within the above range, cleanliness inside the engine can be maintained at a high level, while ensuring the fuel-saving performance.
In the lubricating oil composition of the present invention, the ratio of the content of the magnesium salicylate (B) to the total content of the magnesium salicylate (B) and the calcium salicylate (C) [the content of (B)/(the content of (B)+the content of (C))] in terms of mass ppm is preferably 0.05 to 0.95, more preferably 0.05 to 0.75, and still more preferably 0.05 to 0.50. When the ratio is within the above range, the fuel-saving performance is further improved.

[D] Viscosity Index Improver

The lubricating oil composition of the invention 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.
The viscosity index improver contained in the lubricating oil composition of the invention has a weight average molecular weight of preferably 10,000 or more, more preferably 100,000 or more, and still more preferably 200,000 or more. The upper limit is preferably 1,000,000 or less, more preferably 800,000 or less, and still more preferably 600,000 or less. The specific range is preferably from 10,000 to 1,000,000, more preferably from 100,000 to 800,000, and still more preferably from 200,000 to 600,000.
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).
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 1.7 mPa·s to 2.3 mPa·s and that the HTHS viscosity at 100° C. is 4.8 mPa·s or less. The content of a viscosity index improver contained the lubricating oil composition of the invention is 0.1 mass % or more, preferably 0.2 mass % or more, more preferably 0.3 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 4 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 0.3 mass % to 5 mass %, and still more preferably from 0.5 mass % to 4 mass %.

[E] Molybdenum-Based Friction Modifier

The lubricating oil composition of the invention preferably further contains (E) a molybdenum-based friction modifier as a friction modifier. The component (E) is preferably molybdenum dithiocarbamate (hereinafter, may be simply referred to as MoDTC).
The MoDTC used may be, for example, a compound represented by the following formula (3).

[Formula 3]

wherein R³to R⁶may be the same or different and are each a C_2-24alkyl group or a C_6-24(alkyl) aryl group, and preferably a C_4-13alkyl group or a C_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. X¹to X⁴are each independently a sulfur atom or an oxygen atom, and at least one of X¹to X⁴is a sulfur atom.
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.
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 %.
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 can be enhanced. In addition, if the molybdenum content is the upper limit or less, the lubricating oil composition storage stability can be increased.

(Additional Additive)

The lubricating oil composition of the invention may further contain an anti-wear agent, an antioxidant, or a dispersant.
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 (4).
wherein R⁷to R¹⁰are each independently a hydrogen atom or a linear or branched C_1-24alkyl group, and at least one of R⁷to R¹⁰is a linear or branched C_1-24alkyl group. This alkyl group may be primary, secondary, or tertiary.
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.
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 %.
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.
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-a-naphthylamine, alkylated-a-naphthylamine) or a phenolic antioxidant (e.g., 2,6-di-t-butyl-4-methylphenol, 4,4′-methylenebis (2,6-di-t-butylphenol)).
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.
Examples of the dispersant include an ashless dispersant such as succinimide or benzylamine.
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.
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)

The HTHS viscosity at 150° C. of the lubricating oil composition of the present invention is from 1.7 mPa·s to 2.3 mPa·s. When the HTHS viscosity at 150° C. is 2.3 mPa·s or less, high fuel-saving performance can be obtained. A HTHS viscosity of less than 1.7 mPa·s has a risk of insufficient lubricity.
The HTHS viscosity at 150° C. of the lubricating oil composition of the present invention is more preferably from 1.7 mPa·s to 2.2 mPa·s, more preferably from 1.7 mPa·s to 2.1 mPa·s, and still more preferably from 1.7 mPa·s to 2.0 mPa·s.
As used herein, the HTHS viscosity at 150° C. refers to a high-temperature high-shear viscosity at 150° C. as specified in ASTM D 4683.
The HTHS viscosity at 100° C. of the lubricating oil composition of the present invention is 4.8 mPa·s or less. When the HTHS viscosity at 100° C. exceeds 4.8 mPa·s, there is a risk that sufficient fuel-saving performance is not obtained.
The HTHS viscosity at 100° C. of the lubricating oil composition of the present invention is preferably from 3.0 mPa·s to 4.5 mPa·s, more preferably from 3.2 mPa·s to 4.2 mPa·s, and still more preferably from 3.4 mPa·s to 4.0 mPa·s.
As used herein, the HTHS viscosity at 100° C. indicates the high temperature high shear viscosity at 100° C. according to the provisions of ASTM D4683.
The ratio of HTHS viscosity (100° C.)/HTHS viscosity (150° C.) is preferably 1.95 or more and less than 2.20 and more preferably 2.00 or more and less than 2.20.
The viscosity index of the lubricating oil composition of the present invention is preferably 140 to 240, more preferably 140 to 220. When the viscosity index of the lubricating oil composition is 140 or more, the fuel-saving performance can be improved while maintaining a low HTHS viscosity at 150° C. In addition, if the viscosity index of the lubricating oil composition exceeds 240, evaporability may deteriorate.
Note that as used herein, the viscosity index means a viscosity index measured in accordance with JIS K 2283-1993.
The kinematic viscosity at 40° C. of the lubricating oil composition of the present invention is preferably 10 mm²/s or more, more preferably 14 mm²/s or more, still more preferably 16 mm²/s or more, and most preferably 18 mm²/s or more. The upper limit is preferably 30 mm²/s or less, more preferably 28 mm²/s or less, still more preferably 26 mm²/s or less, and most preferably 25 mm²/s or less. The specific range is preferably from 10 mm²/s to 30 mm²/s, more preferably from 14 mm²/s to 28 mm²/s, still more preferably from 16 mm²/s to 26 mm²/s, and most preferably from 18 mm²/s to 25 mm²/s. When the kinematic viscosity at 40° C. of the lubricating oil composition is 30 mm²/s or less, sufficient fuel-saving performance can be obtained. When the kinematic viscosity at 40° C. of the lubricating oil composition is 10 mm²/s or more, oil film formation at lubrication sites can be ensured, and the evaporation loss of the lubricating oil composition can also be reduced.
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.
The kinematic viscosity of the lubricating oil composition of the invention at 100° C. is preferably 3 mm²/s or more and more preferably 4 mm²/s or more. The upper limit is preferably 7 mm²/s or less and more preferably 6 mm²/s or less. The specific range is preferably from 3 mm²/s to 7 mm²/s and more preferably from 4 mm²/s to 6 mm²/s.
The density (p15) 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.
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. 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

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

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) Lubricating Base Oil

- Base oil 1: Group III base oil (mineral oil), kinematic viscosity: 3.3 mm²/s)(100° C., viscosity index: 112
- Base oil 2: Group III base oil (mineral oil), kinematic viscosity: 4.3 mm²/s (100° C.), viscosity index:

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

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 1: calcium salicylate (calcium content: 8.0 mass %, base number: 225 mgKOH/g)
(C) Metallic detergent 2: magnesium salicylate (magnesium content: 7.4 mass %, base number: 342 mgKOH/g)
(D) Viscosity index improver

- Viscosity index improver 1: polymethacrylate (weight average molecular weight: 520,000)

(E) Friction modifier

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

(1) Fuel-Saving Performance

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: 1.2 L) lubricated with the lubricating oil composition (oil temperature: 80° C.) by an electric motor at a constant rate was measured. The measurement was performed at 1000 rpm, 2000 rpm and 3000 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.
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 8 or Comparative Example 1 is all 0.850 or less.

TABLE 1

Example	Example	Example	Example	Example
1	2	3	4	5

Base oil	Base oil 1	mass %	58	30	10	4	0
	Base oil 2	mass %	42	70	90	96	100
Metallic	Metallic detergent 1	mass %	1.25	1.25	1.25	1.25	1.25
detergent	Metallic detergent 2	mass %	0.81	0.81	0.81	0.81	0.81
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 %	3.50	1.67	0.72	0.37	0.14
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	t.00
	Antioxidant 2	mass %	0.50	0.50	0.50	0.50	0.50
Base oil	Kinematic viscosity	mm²/s	3.50	3.83	4.12	4.19	4.20
properties	(100° C.)
Composition	HTHS viscosity	mPa · s	1.80	1.85	1.83	1.85	1.83
characteristics	(150° C.)
	HTHS viscosity	mPa · s	3.65	3.84	3.92	4.03	4.02
	(100° C.)
	HTHS viscosity		2.03	2.08	2.14	2.18	2.20
	(100° C.)/HTHS
	viscosity (150° C.)
	Kinematic viscosity	mm²/s	20.34	22.68	24.15	24.76	25.07
	(40° C.)
	Kinematic viscosity	mm²/s	5.028	5.064	5.099	5.126	5.135
	(100° C.)
	Viscosity index		189	160	145	142	139
	Ca content	massppm	970	970	1000	970	1000
	Mg content	massppm	590	590	600	590	600
	Mg/(Ca + Mg)		0.38	0.38	0.38	0.38	0.38
	Mo content	massppm	690	690	670	690	680
	P content	massppm	800	800	780	800	780
K12C	Improvement rate	%	3.2	3.0	2.8	2.4	2.2
MOTORING	(80° C., 1000 rpm)
	Improvement rate	%	4.7	4.3	4.1	3.5	3.2
	(80° C., 2000 rpm)
	Improvement rate	%	4.7	4.0	3.6	3.1	2.8
	(80° C., 3000 rpm)

TABLE 2

Example	Example	Example	Comparative
6	7	8	Example 1

Base oil	Base oil 1	mass %	58	58	58	0
	Base oil 2	mass %	42	42	42	100
Metallic	Metallic detergent 1	mass %	2.20	1.80	0.60	2.50
detergent	Metallic detergent 2	mass %	0.17	0.43	1.22	0.00
Anti-wear	Anti-wear agent 1	mass %	0.94	0.94	0.94	0.94
agent
Friction	Friction modifier 1	mass %	0.70	0.70	0.70	0.70
modifier
Viscosity	Viscosity index	mass %	3.50	3.50	3.50	10.9
index	improver 1
improver
Dispersant	Dispersant 1	mass %	3.52	3.52	3.52	3.52
Antioxidant	Antioxidant 1	mass %	1.00	1.00	1.00	1.00
	Antioxidant 2	mass %	0.50	0.50	0.50	0.50
Base oil	Kinematic viscosity	mm²/s	3.50	3.50	3.50	4.20
properties	(100° C.)
Composition	HTHS viscosity	mPa · s	1.79	1.78	1.77	2.70
characteristics	(150° C.)
	HTHS viscosity	mPa · s	3.66	3.64	3.63	5.22
	(100° C.)
	HTHS viscosity		2.04	2.04	2.05	1.93
	(100° C.)/HTHS
	viscosity (150° C.)
	Kinematic viscosity	mm²/s	20.49	20.42	20.21	30.52
	(40° C.)
	Kinematic viscosity	mm²/s	5.071	5.045	5.012	8.421
	(100° C.)
	Viscosity index		191	190	190	274
	Ca content	massppm	1800	1500	500	1900
	Mg content	massppm	140	330	910	11
	Mg/(Ca + Mg)		0.07	0.18	0.65	0.01
	Mo content	massppm	690	690	700	710
	P content	massppm	780	790	790	790
K12C	Improvement rate	%	3.6	3.8	3.1	—
MOTORING	(80° C., 1000 rpm)
	Improvement rate	%	4.8	5.4	4.3	—
	(80° C., 2000 rpm)
	Improvement rate	%	4.6	5.2	4.2	—
	(80° C., 3000 rpm)

In Examples 1 to 8, the torque was reduced in all conditions of 1000 rpm, 2000 rpm, and 3000 rpm, compared to Comparative Example 1. Accordingly, the compositions of Examples 1 to 8 are superior in the fuel-saving performance compared to that of Comparative Example 1.

INDUSTRIAL APPLICABILITY

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 high fuel-saving performance can be provided.

Claims

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

(A) a lubricating base oil;

(B) magnesium salicylate;

(C) calcium salicylate; and

(D) a viscosity index improver, wherein

the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.3 mPa·s or less, and an HTHS viscosity at 100° C. of 4.8 mPa·s or less.

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

the lubricating base oil (A) has a kinematic viscosity at 100° C. of less than 4.2 mm²/s, and

the lubricating oil composition has a viscosity index of 140 or more.

3. The lubricating oil composition for an internal combustion engine according to claim 1, wherein

a total content of the magnesium salicylate (B) and the calcium salicylate (C) is 1400 mass ppm or more and 2000 mass ppm or less in terms of metal amount, based on a total amount of the lubricating oil composition, and

[the content of (B)/(the content of (B)+the content of (C))] is 0.05 to 0.95 in terms of mass ppm.

4. The lubricating oil composition for an internal combustion engine according to claim 1, wherein

the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.0 mPa-s or less, and an HTHS viscosity at 100° C. of 4.2 mPa-s or less.

5. The lubricating oil composition for an internal combustion engine according to claim 2, wherein

6. The lubricating oil composition for an internal combustion engine according to claim 2, wherein

the lubricating oil composition has an HTHS viscosity at 150° C. of 1.7 mPa·s or more and 2.0 mPa·s or less, and an HTHS viscosity at 100° C. of 4.2 mPa·s or less.

7. The lubricating oil composition for an internal combustion engine according to claim 3, wherein

8. The lubricating oil composition for an internal combustion engine according to claim 5, wherein