JP7618650B2 - Lubricating oil composition and method of using the lubricating oil composition - Google Patents

Description

The present invention relates to a lubricating oil composition and a method for using the lubricating oil composition.

In recent years, for the purpose of effective use of petroleum resources and reduction of carbon dioxide emissions, there is a strong demand for fuel-saving vehicles such as automobiles. There is also a strong demand for fuel-saving lubricating oil compositions used in engines of vehicles such as automobiles. Therefore, in order to obtain lubricating oil compositions with good fuel-saving properties, reduction in the viscosity of lubricating oil compositions has been studied.
For example, Patent Document 1 discloses a lubricating oil composition that contains a magnesium detergent and a zinc dialkylthiophosphate in a lubricating base oil in predetermined amounts and has a boron content limited to less than 100 ppm by mass, for the purpose of providing a lubricating oil composition that can reduce friction even when the viscosity is reduced.

JP 2019-85491 A

Under these circumstances, there is a demand for new lubricating oil compositions that can be suitably applied to engine lubrication.

The present invention provides a lubricating oil composition containing a specified amount of succinimide and polymer together with a mineral oil that meets specific requirements.
Specific aspects of the present invention are as follows [1] to [14].
[1] A lubricating oil composition comprising a mineral oil (A), a succinimide (B), and a polymer (C),
The mineral oil (A) satisfies the following requirements (a1) to (a3):
The following requirement is satisfied: requirement (a1): the kinematic viscosity at 100° C. is less than 3.10 mm ² /s; requirement (a2): the NOACK value is 36.0 mass% or less; and requirement (a3): the % _CP measured in accordance with ASTM D3238 is 75.0 or more.
the content of the succinimide (B) in terms of nitrogen atoms is 0.008 to 0.060 mass% based on the total amount of the lubricating oil composition;
The content of the polymer (C) in terms of resin content is 0.40 to 3.00 mass% based on the total amount of the lubricating oil composition;
Lubricating oil composition.
[2] The lubricating oil composition according to the above item [1], wherein the ratio [(B)/(C)] of the content (unit: mass%) of succinimide (B) calculated as nitrogen atoms to the content (unit: mass%) of polymer (C) calculated as a resin content is 0.001 to 5.00.
[3] The lubricating oil composition according to the above [1] or [2], wherein the polymer (C) comprises a comb polymer (C1).
[4] The lubricating oil composition according to the above [3], wherein the comb polymer (C1) has a weight average molecular weight (Mw) of 200,000 to 1,000,000 and a molecular weight distribution (Mw/Mn) (Mn is the number average molecular weight of the comb polymer (C1)) of 4.0 or less.
[5] The lubricating oil composition according to any one of the above [1] to [4], wherein the mineral oil (A) further satisfies the following requirement (a4):
Requirement (a4): The lubricating oil composition according to any one of the above items [1] to [5], wherein the mineral oil (A) [6] having a % C _N of 3.0 to 25.0 as measured in accordance with ASTM D3238 further satisfies the following requirement (a5):
- Requirement (a5): The temperature at which the distillation amount of the light fraction in a gas chromatography distillation test is 10% by volume is 345°C or higher. [7] The lubricating oil composition according to any one of the above [1] to [6], wherein the kinetic viscosity of the lubricating oil composition at 100°C is less than 5.1 ^mm2 /s.
[8] The lubricating oil composition according to any one of the above [1] to [7], wherein the lubricating oil composition has a HTHS viscosity at 150°C of 1.40 mPa·s or more.
[9] The lubricating oil composition according to any one of the above [1] to [8], wherein the lubricating oil composition has a kinematic viscosity at 140° C. of 2.45 mm ² /s or more.
[10] The lubricating oil composition according to any one of the above [1] to [9], wherein the lubricating oil composition has a HTHS viscosity at 80°C of 4.40 mPa·s or less.
[11] The lubricating oil composition according to any one of [1] to [10] above, which is used for lubricating an engine mounted on a hybrid car or an engine mounted on a generator for an electric vehicle.
[12] The lubricating oil composition according to any one of [1] to [11] above, which is used for lubricating an engine mounted in a range extender for an electric vehicle.
[13] A method for using the lubricating oil composition according to any one of the above [1] to [11] for lubricating an engine mounted on a hybrid car or an engine mounted on a generator for an electric vehicle.
[14] A method for using the lubricating oil composition according to any one of the above [1] to [11] for lubricating an engine mounted in a range extender for an electric vehicle.

A preferred embodiment of the lubricating oil composition of the present invention has excellent properties such as hydraulic characteristics, fuel economy, and oil consumption suppression, and is particularly suitable for use in lubricating engines in hybrid cars and engines installed in generators for electric vehicles.

In this specification, the kinematic viscosity and viscosity index refer to values measured or calculated in accordance with JIS K2283:2000.
In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values calculated as standard polystyrene measured by gel permeation chromatography (GPC), and specifically, they mean values measured by the method described in the Examples.

For the numerical ranges described in this specification, the upper and lower limits can be combined in any combination. For example, when a numerical range is described as "preferably 30 to 100, more preferably 40 to 80," the range "30 to 80" and the range "40 to 100" are also included in the numerical ranges described in this specification.
In addition, as for a numerical range described in this specification, for example, "60 to 100" means a range of "60 or more and 100 or less."
Furthermore, in defining the upper and lower limits described in this specification, a numerical range from the lower limit to the upper limit can be defined by appropriately selecting from each option and combining them in any way.

[Constitution of lubricating oil composition]
The lubricating oil composition of the present invention contains a mineral oil (A), a succinimide (B), and a polymer (C), and preferably further contains a friction modifier (D).
Furthermore, the lubricating oil composition of one embodiment of the present invention may further contain components other than components (A) to (D) as necessary, provided that the effects of the present invention are not impaired.

In one embodiment of the lubricating oil composition of the present invention, the total content of components (A), (B) and (C) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 45 mass% or more, more preferably 55 mass% or more, even more preferably 65 mass% or more, even more preferably 75 mass% or more, particularly preferably 85 mass% or more, and may even be 87 mass% or more, or 90 mass% or more.

Below, we will explain in detail each component contained in the lubricating oil composition of one embodiment of the present invention.

<Component (A): Mineral Oil>
Examples of the mineral oil (A) used in one embodiment of the present invention include atmospheric residual oil obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate base crude oil, naphthenic crude oil, etc.; distillate oil obtained by vacuum distillation of these atmospheric residual oils; refined oil obtained by subjecting the distillate oil to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; mineral oil (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas To Liquids WAX)); and the like.
These mineral oils may be used alone or in combination of two or more kinds.

The mineral oil (A) used in the present invention satisfies the following requirements (a1) to (a3).
Requirement (a1): The kinetic viscosity at 100° C. is less than 3.10 mm ² /s.
Requirement (a2): The NOACK value is 36.0 mass% or less.
Requirement (a3): % _CP measured in accordance with ASTM D3238 is 75.0 or more.
Furthermore, the mineral oil (A) used in one aspect of the present invention preferably satisfies, in addition to the above requirements (a1) to (a3), at least one of the following requirements (a4) and (a5), and more preferably satisfies both of the following requirements (a4) and (a5):
Requirement (a4): % C _N measured in accordance with ASTM D3238 is 3.0 to 25.0.
Requirement (a5): The temperature at which the distillation amount of the light fraction in a gas chromatography distillation test becomes 10% by volume or less is 345° C. or higher.

(Requirement (a1))
When the mineral oil (A) satisfies the above requirement (a1), a lubricating oil composition with a low viscosity can be obtained, and the fuel economy of the lubricating oil composition can be improved.
From the above viewpoint, the kinetic viscosity at 100°C of the mineral oil (A) specified in the above requirement (a1) is less than 3.10 ^mm2 /s, preferably less than 3.05 ^mm2 /s, more preferably less than 3.00 ^mm2 /s, even more preferably less than 2.98 ^mm2 /s, and still more preferably less than 2.97 ^mm2 /s.
The kinematic viscosity at 100°C of the mineral oil (A) may be appropriately set within a range that satisfies the other requirements described above, with the lower limit being preferably 2.00 ^mm2 /s or more, more preferably 2.10 ^mm2 /s or more, even more preferably 2.20 ^mm2 /s or more, still more preferably 2.30 ^mm2 /s or more, and particularly preferably 2.40 ^mm2 /s or more.
In other words, the mineral oil (A) used in one embodiment of the present invention has a kinematic viscosity at 100°C of preferably 2.00 ^mm2 /s or more and less than 3.10 ^mm2 /s, more preferably 2.10 ^mm2 /s or more and less than 3.05 ^mm2 /s, even more preferably 2.20 ^mm2 /s or more and less than 3.00 ^mm2 /s, still more preferably 2.30 ^mm2 /s or more and less than 2.98 ^mm2 /s, and particularly preferably 2.40 ^mm2 /s or more and less than 2.97 ^mm2 /s.

(Requirement (a2))
When the mineral oil (A) satisfies the above requirement (a2), the evaporation loss of the mineral oil (A) is reduced, and a lubricating oil composition having excellent oil consumption suppression properties can be obtained.
From the above viewpoint, the NOACK value of the mineral oil (A) specified in the above requirement (a2) is not more than 36.0 mass%, preferably not more than 35.5 mass%, more preferably not more than 35.0 mass%, even more preferably not more than 34.5 mass%, still more preferably not more than 34.0 mass%, and may even be not more than 33.5 mass%, not more than 33.0 mass%, not more than 32.5 mass%, or not more than 32.0 mass%.
The lower limit of the NOACK value of the mineral oil (A) is appropriately set within a range that satisfies the other requirements described above, and is preferably 1.0 mass % or more, more preferably 5.0 mass % or more, even more preferably 10.0 mass % or more, still more preferably 15.0 mass % or more, and particularly preferably 20.0 mass % or more.
That is, the NOACK value of the mineral oil (A) used in one embodiment of the present invention is preferably 1.0 to 36.0 mass%, more preferably 5.0 to 35.5 mass%, even more preferably 10.0 to 35.0 mass%, still more preferably 15.0 to 34.5 mass%, and particularly preferably 20.0 to 34.0 mass%.
In this specification, the NOACK value means a value measured at 250° C. in accordance with JPI-5S-41-2004.

(Requirement (a3), requirement (a4))
By making the mineral oil (A) satisfy the above requirement (a3), the mineral oil (A) has reduced evaporation loss even when it has a low viscosity, and thus provides a lubricating oil having improved fuel economy and reduced oil consumption. It may be a composition.
From the above viewpoints, the % _CP of the mineral oil (A) specified in the above requirement (a3) is 75.0 or more, preferably 77.0 or more, more preferably 78.5 or more, and even more preferably 80. It is preferably 0 or more, more preferably 82.0 or more, and may further be 83.0 or more, 85.0 or more, 87.0 or more, or 90.0 or more.
The upper limit of the % _CP of the mineral oil (A) is appropriately set within a range that satisfies the other requirements described above, but it is preferably 99.0 or less, more preferably 98.0 or less, and even more preferably 97.0 or less, even more preferably 96.0 or less, particularly preferably 95.0 or less, and further preferably 94.0 or less, 93.0 or less, 92.0 or less, 91.0 or less, or 90.0 The following may also be used.
That is, the % _CP of the mineral oil (A) used in one embodiment of the present invention is preferably 75.0 to 99.0, more preferably 77.0 to 98.0, and even more preferably 78.5 to 97.0. , even more preferably 80.0 to 96.0, and particularly preferably 82.0 to 95.0.

The mineral oil (A) used in one embodiment of the present invention satisfies the above requirement (a4), thereby making it possible to provide a lubricating oil composition in which evaporation loss is suppressed even if the composition has a low viscosity.
From the above viewpoints, the % C _N of the mineral oil (A) specified in the above requirement (a4) is preferably 3.0 to 25.0, more preferably 4.0 to 22.0, even more preferably 5.0 to 20.0, still more preferably 6.0 to 19.0, and particularly preferably 6.5 to 18.0.
The % _CN of the mineral oil (A) may further be 6.8 or more, 7.0 or more, 8.0 or more, 9.0 or more, or 10.0 or more, and may be 17.5 or less, 17.0 or less, 16.0 or less, 15.0 or less, or 14.0 or less.

In this specification, % _CP and % _CN refer to values measured in accordance with ASTM D-3238 ring analysis (ndM method).

(Requirement (a5))
When the mineral oil (A) used in one embodiment of the present invention satisfies the above requirement (a5), the evaporation loss of the mineral oil (A) is reduced, and a lubricating oil composition having excellent oil consumption suppression properties can be obtained.
From the above viewpoint, the temperature at which the distillation amount of the light fraction is 10% by volume is preferably 345°C or higher, more preferably 348°C or higher, even more preferably 350°C or higher, still more preferably 352°C or higher, and may further be 353°C or higher, 355°C or higher, 357°C or higher, or 360°C or higher.
In addition, the temperature at which the distillation amount of the light fraction becomes 10% by volume is not particularly limited to an upper limit, but may be 600°C or less, 550°C or less, 500°C or less, 430°C or less, 420°C or less, or 400°C or less.
In this specification, the "temperature at which the distillation amount of the light fraction becomes 10% by volume" means the temperature at which the distillation amount of the light fraction reaches 10% by volume when the distillation amount of the light fraction is measured in the process of increasing the temperature from room temperature by a gas chromatographic distillation test in accordance with ASTM D6352.

(Other requirements for mineral oil (A) other than the above requirements (a1) to (a5))
The viscosity index of the mineral oil (A) used in one embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with little temperature dependency, is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, still more preferably 100 or more, and particularly preferably 110 or more.

The aniline point of the mineral oil (A) used in one embodiment of the present invention is preferably 100 to 140°C, more preferably 108 to 130°C, and even more preferably 110 to 125°C.
In this specification, the aniline point means a value measured in accordance with JIS K2256 (U-tube method).

The mineral oil (A) used in one embodiment of the present invention has a flash point of preferably 180° C. or higher, more preferably 192° C. or higher, even more preferably 194° C. or higher, and preferably 400° C. or lower, more preferably 350° C. or lower, even more preferably 300° C. or lower.
In this specification, the flash point refers to a value measured by the Cleveland open cup (COC) method in accordance with JIS K2265-4.

The pour point of the mineral oil (A) used in one embodiment of the present invention is preferably −20° C. or lower, more preferably −30° C. or lower, even more preferably less than −35° C., and still more preferably −37.5° C. or lower.
In this specification, the pour point means a value measured in accordance with JIS K2269:1987.

When the mineral oil (A) used in one embodiment of the present invention is a mixed mineral oil comprising two or more types of mineral oils, it is sufficient that the mixed mineral oil satisfies the above requirements (a1) to (a5), and the viscosity index, aniline point, flash point, and pour point are within the above preferred ranges. Furthermore, if each of the mineral oils constituting the mixed mineral oil satisfies the above requirements (a1) to (a5), the mixed mineral oil can also be considered to satisfy these requirements. The same applies to the viscosity index, aniline point, flash point, and pour point.

In order to adjust the mineral oil to satisfy the above requirements (a1) to (a5), the mineral oil (A) may be a mixed mineral oil of a low-viscosity mineral oil (α) having a kinetic viscosity at 100°C of less than ^{3.0 mm2} /s and a high-viscosity mineral oil (β) having a kinetic viscosity at 100°C of 3.0 mm2/s or more.
When the above-mentioned mixed mineral oil is used as the mineral oil (A), the blending ratio [(α)/(β)] of the low-viscosity mineral oil (α) and the high-viscosity mineral oil (β) may be appropriately set according to the types and kinematic viscosities of the mineral oils (α) and (β) to be mixed so as to satisfy the above requirements (a1) to (a5).
Specifically, the blending ratio [(α)/(β)] of the low-viscosity mineral oil (α) to the high-viscosity mineral oil (β) is, in mass ratio, preferably 10/90 to 99/1, more preferably 30/70 to 95/5, even more preferably 50/50 to 90/10, still more preferably 55/45 to 85/15, and particularly preferably 60/40 to 80/20.

In one embodiment of the lubricating oil composition of the present invention, the content of mineral oil (A) is preferably 40 to 99.5 mass%, more preferably 50 to 99.0 mass%, even more preferably 60 to 98.0 mass%, still more preferably 70 to 96.0 mass%, and particularly preferably 80 to 95.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

<Synthetic oil>
The lubricating oil composition of one embodiment of the present invention may contain a synthetic oil together with the mineral oil (A) as long as the effects of the present invention are not impaired.
Examples of synthetic oils include poly-α-olefins such as α-olefin homopolymers or α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffin; polyalkylene glycol; ester-based oils such as polyol esters, dibasic acid esters, and phosphate esters; ether-based oils such as polyphenyl ether; alkylbenzenes; and alkylnaphthalenes.
These synthetic oils may be used alone or in combination of two or more kinds.

The kinetic viscosity at 100°C of the synthetic oil that can be used in one embodiment of the present invention may be similar to that of the mineral oil (A), and is preferably 2.00 ^mm2 /s or more and less than 3.10 ^mm2 /s, more preferably 2.10 ^mm2 /s or more and less than 3.05 ^mm2 /s, even more preferably 2.20 ^mm2 /s or more and less than 3.00 ^mm2 /s, still more preferably 2.30 ^mm2 /s or more and less than 2.98 ^mm2 /s, and particularly preferably 2.40 ^mm2 /s or more and less than 2.97 ^mm2 /s.

The viscosity index of the synthetic oil that can be used in one embodiment of the present invention is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, still more preferably 100 or more, and particularly preferably 110 or more.
When a mixed synthetic oil obtained by combining two or more synthetic oils is used as the synthetic oil, the kinematic viscosity and viscosity index of the mixed synthetic oil are preferably within the above ranges.

In one embodiment of the lubricating oil composition of the present invention, the content of the synthetic oil is preferably 0 to 50 parts by mass, more preferably 0 to 30 parts by mass, even more preferably 0 to 10 parts by mass, still more preferably 0 to 5 parts by mass, and particularly preferably 0 to 1 part by mass, relative to 100 parts by mass of the total amount of mineral oil (A) contained in the lubricating oil composition.

<Component (B): Succinimide>
The lubricating oil composition of the present invention contains a succinimide (B). By containing the succinimide (B), it is possible to obtain a lubricating oil composition having excellent fuel economy and hydraulic properties.

In addition, in the lubricating oil composition of the present invention, the content of succinimide (B) calculated as nitrogen atoms is adjusted to 0.008 to 0.060 mass% based on the total amount (100 mass%) of the lubricating oil composition. By adjusting the content of component (B) calculated as nitrogen atoms within this range in this manner, it is possible to obtain a lubricating oil composition that has good fuel economy while improving hydraulic properties.

In the lubricating oil composition of one embodiment of the present invention, the content of succinimide (B) in terms of nitrogen atoms is 0.008 mass% or more based on the total amount (100 mass%) of the lubricating oil composition. From the viewpoint of obtaining a lubricating oil composition with further improved hydraulic properties, the content is preferably 0.015 mass% or more, more preferably 0.020 mass% or more, even more preferably 0.025 mass% or more, still more preferably 0.030 mass% or more, particularly preferably 0.035 mass% or more, and may even be 0.037 mass% or more, 0.040 mass% or more, or 0.042 mass% or more.
Furthermore, the content of succinimide (B) calculated as nitrogen atoms is 0.060 mass% or less based on the total amount (100 mass%) of the lubricating oil composition, but from the viewpoint of obtaining a lubricating oil composition with better fuel economy properties, it is preferably 0.057 mass% or less, more preferably 0.055 mass% or less, even more preferably 0.052 mass% or less, still more preferably 0.050 mass% or less, particularly preferably 0.048 mass% or less, and may even be 0.047 mass% or less, 0.046 mass% or less, or 0.045 mass% or less.
In other words, the content of succinimide (B) calculated as nitrogen atoms is preferably 0.015 to 0.057 mass%, more preferably 0.020 to 0.055 mass%, even more preferably 0.025 to 0.052 mass%, still more preferably 0.030 to 0.050 mass%, and particularly preferably 0.035 to 0.048 mass%, based on the total amount (100 mass%) of the lubricating oil composition.
In this specification, the nitrogen atom content refers to a value measured in accordance with JIS K2609.

In addition, in the lubricating oil composition of one embodiment of the present invention, the blending amount (content) of succinimide (B) may be adjusted so that the content in terms of nitrogen atoms falls within the above range, and is preferably 0.01 to 15.0 mass%, more preferably 0.1 to 12.0 mass%, even more preferably 0.5 to 10.0 mass%, and even more preferably 1.0 to 7.0 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

The succinimide (B) used in one embodiment of the present invention may be a succinic acid monoimide, a succinic acid bisimide, or a combination thereof.
As the succinic acid monoimide, an alkenyl succinic acid monoimide represented by the following general formula (b-1) is preferable, and as the succinic acid bisimide, an alkenyl succinic acid bisimide represented by the following general formula (b-2) is preferable.
The succinimides (B) may be used alone or in combination of two or more kinds.

In the above general formulas (b-1) and (b-2), ^R , ^R1 , and ^R2 are each independently an alkenyl group having a weight average molecular weight (Mw) of 500 to 3000 (preferably 1000 to 3000). Examples of the alkenyl group include a polybutenyl group, a polyisobutenyl group, and an ethylene-propylene copolymer, with a polybutenyl group or a polyisobutenyl group being preferred.
R ^B , R ^B1 and R ^B2 each independently represent an alkylene group having 2 to 5 carbon atoms.
R ^C and R ^C1 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a group represented by -(AO) _n -H (wherein each A is independently an alkylene group having 2 to 4 carbon atoms, and n is an integer from 1 to 10).
x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4.
x2 is an integer of 0 to 10, preferably an integer of 1 to 5, and more preferably an integer of 2 to 4.

The succinimide (B) used in one embodiment of the present invention may be a non-modified succinimide or a modified succinimide.
The modified succinimide may be a modified alkenylsuccinimide obtained by reacting a non-modified alkenylsuccinimide represented by the general formula (b-1) or (b-2) with one or more compounds selected from a boron compound, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, an organic acid, and the like.

From the viewpoint of obtaining a lubricating oil composition having improved hydraulic properties and better fuel economy, the succinimide (B) used in one embodiment of the present invention preferably contains an unmodified succinimide, more preferably contains an unmodified succinic acid bisimide (B1), and even more preferably contains an unmodified alkenyl succinic acid bisimide (B11) represented by the general formula (b-2) above.
From the above viewpoints, the content of component (B1) (or component (B11)) in the succinimide (B) used in one embodiment of the present invention is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, still more preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass%, relative to 100 mass% of the total amount of component (B) contained in the lubricating oil composition.

Furthermore, from the viewpoint of adjusting the kinetic viscosity to a low level to obtain a lubricating oil composition with improved fuel economy, the content of boron-modified succinimide in the lubricating oil composition of one embodiment of the present invention is preferably as low as possible.
The specific content of the boron-modified succinimide is preferably 0 to 30 parts by mass, more preferably 0 to 10 parts by mass, even more preferably 0 to 5 parts by mass, still more preferably 0 to 1 part by mass, and particularly preferably 0 to 0.1 parts by mass, relative to 100 parts by mass of the total amount of component (B) contained in the lubricating oil composition.

<Other ashless dispersants>
The lubricating oil composition of one embodiment of the present invention may contain an ashless dispersant other than component (B) to the extent that the effects of the present invention are not impaired.
Examples of such other ashless dispersants include benzylamine, succinic acid esters, and boron or other modified versions of these.

In addition, in the lubricating oil composition of one embodiment of the present invention, the content of the other ashless dispersant is preferably 0 to 50 parts by mass, more preferably 0 to 30 parts by mass, even more preferably 0 to 10 parts by mass, still more preferably 0 to 5 parts by mass, and particularly preferably 0 to 1 part by mass, relative to 100 parts by mass of the total amount of component (B) contained in the lubricating oil composition.

<Component (C): Polymer>
The lubricating oil composition of the present invention contains a polymer (C). By containing the polymer (C) together with the succinimide (B), it is possible to obtain a lubricating oil composition having improved hydraulic properties and fuel economy in a well-balanced manner.
Furthermore, from the viewpoint of providing a lubricating oil composition that can suppress the formation of deposits while improving hydraulic properties and fuel economy in a well-balanced manner, the content of polymer (C) in the lubricating oil composition of the present invention, calculated as the resin content, is adjusted to 0.40 to 3.00 mass % based on the total amount of the lubricating oil composition.

In the lubricating oil composition of one embodiment of the present invention, the content of polymer (C) in terms of resin content is 0.40 mass% or more based on the total amount (100 mass%) of the lubricating oil composition. From the viewpoint of obtaining a lubricating oil composition having improved hydraulic properties and fuel economy in a well-balanced manner, the content is preferably 0.45 mass% or more, more preferably 0.48 mass% or more, even more preferably 0.50 mass% or more, still more preferably 0.52 mass% or more, particularly preferably 0.55 mass% or more, and may further be 0.57 mass% or more, 0.60 mass% or more, 0.62 mass% or more, 0.65 mass% or more, 0.67 mass% or more, or 0.70 mass% or more.
The content of the polymer (C) in terms of resin content is 3.00 mass% or less based on the total amount (100 mass%) of the lubricating oil composition. From the viewpoint of obtaining a lubricating oil composition that can suppress the formation of deposits while providing a good balance between hydraulic properties and fuel economy, the content is preferably 2.50 mass% or less, more preferably 2.20 mass% or less, even more preferably 2.00 mass% or less, still more preferably 1.70 mass% or less, particularly preferably 1.55 mass% or less, and may further be 1.40 mass% or less, 1.30 mass% or less, 1.20 mass% or less, 1.10 mass% or less, 1.00 mass% or less, or 0.90 mass% or less.
That is, the content of polymer (C) calculated as the resin content is preferably 0.45 to 2.50 mass%, more preferably 0.48 to 2.20 mass%, even more preferably 0.50 to 2.00 mass%, still more preferably 0.52 to 1.70 mass%, and particularly preferably 0.55 to 1.55 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

In consideration of handling properties and solubility in the mineral oil (A), the polymer (C) is often commercially available in the form of a solution in which it is dissolved in a diluent oil.
However, in this specification, the content of polymer (C) is the content converted into the resin component constituting polymer (C) in a solution diluted with diluent oil, excluding the mass of the diluent oil.

In addition, from the viewpoint of obtaining a lubricating oil composition having improved hydraulic properties and fuel economy, in the lubricating oil composition of one embodiment of the present invention, the ratio of the content (unit: mass %) of succinimide (B) calculated as nitrogen atoms to the content (unit: mass %) of polymer (C) calculated as a resin content is preferably 0.001 to 5.00, more preferably 0.005 to 3.00, even more preferably 0.010 to 1.00, still more preferably 0.015 to 0.15, and particularly preferably 0.020 to 0.10.
The ratio of the content (unit: mass%) of succinimide (B) calculated as nitrogen atoms to the content (unit: mass%) of polymer (C) calculated as a resin component, [(B)/(C)], may be 0.025 or more, 0.030 or more, 0.035 or more, 0.040 or more, 0.045 or more, 0.050 or more, or 0.055 or more, or may be 0.095 or less, 0.090 or less, 0.085 or less, 0.080 or less, 0.075 or less, 0.070 or less, or 0.065 or less.

Examples of the polymer (C) used in one embodiment of the present invention include non-dispersed polymethacrylate, dispersed polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymers, etc.), dispersed olefin copolymers, styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers, etc.), etc. In addition, the polymer (C) is not limited to linear polymers, and may be branched polymers, comb polymers, star polymers, etc.
These polymers (C) may be used alone or in combination of two or more kinds.
The polymer (C) used in one embodiment of the present invention includes not only polymers used as so-called viscosity index improvers but also polymers used as pour point depressants.

The weight average molecular weight (Mw) of the polymer (C) used in one embodiment of the present invention is typically 500 to 1,000,000, preferably 1,000 to 1,000,000, and more preferably 3,000 to 1,000,000, but is set appropriately depending on the type of polymer.

From the viewpoint of providing a lubricating oil composition which has improved hydraulic properties, excellent viscosity characteristics independent of temperature range, and can exhibit fuel economy independent of temperature range, it is preferable that the polymer (C) used in one embodiment of the present invention contains a comb polymer (C1).
The comb polymer (C1) functions as a so-called viscosity index improver.
The comb polymer (C1) used in one embodiment of the present invention may be any polymer having a structure in which the main chain has many three-way branching points from which high molecular weight side chains extend.

From the above viewpoints, the content of comb polymer component (C1) in polymer (C) used in one embodiment of the present invention is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, and particularly preferably 95 to 100 mass%, relative to 100 mass% of the total amount of component (C) contained in the lubricating oil composition.

The weight average molecular weight (Mw) of the comb polymer (C1) used in one embodiment of the present invention is preferably 200,000 to 1,000,000, more preferably 300,000 to 900,000, even more preferably 400,000 to 800,000, still more preferably 450,000 to 700,000, and particularly preferably 500,000 to 650,000.

The molecular weight distribution (Mw/Mn) of the comb polymer (C1) used in one embodiment of the present invention (wherein Mn represents the number average molecular weight of the comb polymer (C1)) is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, still more preferably 2.7 or less, particularly preferably 2.5 or less, and is preferably 1.01 or more, more preferably 1.05 or more, even more preferably 1.1 or more, still more preferably 1.2 or more, particularly preferably 1.5 or more.
That is, the molecular weight distribution (Mw/Mn) of the comb polymer (C1) is preferably from 1.01 to 4.0, more preferably from 1.05 to 3.5, even more preferably from 1.1 to 3.0, still more preferably from 1.2 to 2.7, and particularly preferably from 1.5 to 2.5.

The comb polymer (C1) used as component (C) in one embodiment of the present invention is preferably a polymer having at least a structural unit (X1) derived from a macromonomer (x1). This structural unit (X1) corresponds to the above-mentioned "high molecular weight side chain."
In the present invention, the above-mentioned "macromonomer (x1)" means a high molecular weight monomer having a polymerizable functional group, and is preferably a high molecular weight monomer having a polymerizable functional group at its terminal.

In the comb polymer (C1) used in one embodiment of the present invention, the content of the structural unit (X1) is preferably 0.5 to 20 mol %, more preferably 0.7 to 10 mol %, and even more preferably 0.9 to 5 mol %, based on the total amount (100 mol %) of the structural units of the comb polymer (C1).

The number average molecular weight (Mn) of the macromonomer (x1) is preferably 300 or more, more preferably 400 or more, and even more preferably 500 or more, and is preferably 20,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less.
That is, the number average molecular weight (Mn) of the macromonomer (x1) is preferably 300 to 20,000, more preferably 400 to 10,000, and even more preferably 500 to 5,000.

The weight average molecular weight (Mw) of the macromonomer (x1) is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 4,000 or more, and is preferably 50,000 or less, more preferably 25,000 or less, and even more preferably 10,000 or less.
That is, the weight average molecular weight (Mw) of the macromonomer (x1) is preferably from 1,000 to 50,000, more preferably from 2,000 to 25,000, and even more preferably from 4,000 to 10,000.

Examples of the polymerizable functional group possessed by the macromonomer (x1) include an acryloyl group (CH ₂ ═CH-COO-), a methacryloyl group (CH ₂ ═CCH ₃ -COO-), an ethenyl group (CH ₂ ═CH-), a vinyl ether group (CH ₂ ═CH-O-), an allyl group (CH ₂ ═CH-CH ₂ -), an allyl ether group (CH ₂ ═CH-CH ₂ -O-), a group represented by CH ₂ ═CH-CONH-, and a group represented by CH ₂ ═CCH3-CONH-.

The macromonomer (x1) may have, in addition to the above polymerizable functional group, one or more repeating units represented by the following general formulae (i) to (iii).

In the above general formula (i), R ^b1 is a linear or branched alkylene group having 1 to 10 carbon atoms.
In the above general formula (ii), R ^b2 is a linear or branched alkylene group having 2 to 4 carbon atoms.
In the above general formula (iii), R ^b3 is a hydrogen atom or a methyl group, and R ^b4 is a linear or branched alkyl group having 1 to 10 carbon atoms.
When the compound has a plurality of repeating units represented by the above general formulas (i) to (iii), the plurality of R ^b1 , R ^b2 , R ^b3 , and R ^b4 may be the same or different from each other.

In one embodiment of the present invention, the macromonomer (x1) is preferably a polymer having a repeating unit represented by the general formula (i), and more preferably a polymer having a repeating unit (X1-1) in which R ^b1 in the general formula (i) is at least one of a 1,2-butylene group and a 1,4-butylene group.

The content of the repeating unit (X1-1) is preferably 1 to 100 mol%, more preferably 20 to 95 mol%, even more preferably 40 to 90 mol%, and even more preferably 50 to 80 mol%, based on the total amount (100 mol%) of the constituent units of the macromonomer (x1).

In addition, when the macromonomer (x1) is a copolymer having two or more repeating units selected from the general formulas (i) to (iii), the form of the copolymerization may be a block copolymer or a random copolymer.

The comb polymer (C1) used in one embodiment of the present invention may be a homopolymer consisting of only structural units (X1) derived from one type of macromonomer (x1), or may be a copolymer having structural units (X1) derived from two or more types of macromonomers (x1).
Furthermore, the comb polymer (C1) used in one embodiment of the present invention may be a copolymer having, in addition to the structural unit (X1) derived from the macromonomer (x1), a structural unit (X2) derived from a monomer other than the macromonomer (x1).
A specific structure of such a comb polymer is preferably a copolymer having a main chain containing a structural unit (X2) derived from a monomer (x2) and a side chain containing a structural unit (X1) derived from a macromonomer (x1).

Examples of monomer (x2) include alkyl (meth)acrylates, nitrogen atom-containing vinyl monomers, hydroxyl group-containing vinyl monomers, phosphorus atom-containing monomers, aliphatic hydrocarbon vinyl monomers, alicyclic hydrocarbon vinyl monomers, vinyl esters, vinyl ethers, vinyl ketones, epoxy group-containing vinyl monomers, halogen element-containing vinyl monomers, esters of unsaturated polycarboxylic acids, (di)alkyl fumarates, (di)alkyl maleates, aromatic hydrocarbon vinyl monomers, etc.

The monomer (x2) is preferably a monomer other than a phosphorus atom-containing monomer and an aromatic hydrocarbon vinyl monomer, more preferably includes one or more selected from a monomer represented by the following general formula (a1), an alkyl (meth)acrylate, and a hydroxyl group-containing vinyl monomer, and further preferably includes at least a hydroxyl group-containing vinyl monomer (x2-d).

In the above general formula (a1), R ^b11 is a hydrogen atom or a methyl group.
R ^b12 is a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, -O-, or -NH-.
R ^b13 is a linear or branched alkylene group having 2 to 4 carbon atoms. Furthermore, n is an integer of 1 or more (preferably an integer of 1 to 20, more preferably an integer of 1 to 5). When n is an integer of 2 or more, multiple R ^b13 may be the same or different, and further, the (R ^b13 O) _n portion may be a random bond or a block bond.
R ^b14 is a linear or branched alkyl group having 1 to 60 carbon atoms (preferably 10 to 50, more preferably 20 to 40).

The SSI (shear stability index) of the comb polymer (C1) used in one embodiment of the present invention is preferably 100 or less, more preferably 80 or less, even more preferably 70 or less, still more preferably 60 or less, and particularly preferably 50 or less.
The SSI of the comb polymer (C1) is not particularly limited to a lower limit, but is usually 0.1 or more.

In this specification, the term "shear stability index" (SSI) refers to a percentage of the viscosity reduction due to shear caused by a polymer component, and is a value measured in accordance with JPI-5S-29-06, and more specifically, is a value calculated by the following calculation formula (1).
Calculation formula (1): SSI (%) = (Kv ₀ - Kv ₁ )/(Kv ₀ - Kv _oil ) x 100

In the above formula (1), Kv ₀ is the value of the kinetic viscosity at 100°C of the sample oil obtained by diluting the polymer component with mineral oil, Kv ₁ is the value of the kinetic viscosity at 100°C of the sample oil obtained by diluting the polymer component with mineral oil after irradiating the sample oil with ultrasonic waves for 30 minutes in accordance with the output method in accordance with the procedure of JPI-5S-29-06, and Kv _oil is the value of the kinetic viscosity at 100°C of the mineral oil used to dilute the polymer component.

The SSI value of the comb polymer (C1) varies depending on the structure of the comb polymer. Specifically, there are the following tendencies, and the SSI value of the comb polymer (C1) can be easily adjusted by taking these factors into consideration. The following factors are merely examples, and the SSI value can also be adjusted by taking other factors into consideration.
Comb polymers in which the side chains are composed of a macromonomer (x1) and the content of the structural unit (X1) derived from the macromonomer (x1) is 0.5 mol % or more based on the total amount of structural units (100 mol %) tend to have a low SSI value.
The larger the molecular weight of the macromonomer (x1) constituting the side chain of the comb polymer, the lower the SSI value tends to be.

<Component (D): Friction Modifier>
From the viewpoint of further improving fuel economy, the lubricating oil composition of one embodiment of the present invention preferably further contains a friction modifier (D).
Examples of the friction modifier (D) used in one embodiment of the present invention include molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdenum acid; ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers, each having at least one alkyl or alkenyl group having 6 to 30 carbon atoms in the molecule; fats and oils, amines, amides, sulfur esters, phosphate esters, phosphites, and phosphate amine salts.
These friction modifiers (D) may be used alone or in combination of two or more kinds.
Among these, the friction modifier (D) used in one embodiment of the present invention preferably contains one or more selected from molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP), and more preferably contains molybdenum dithiocarbamate (MoDTC).

In the lubricating oil composition of one embodiment of the present invention, the content of the friction modifier (D), calculated as molybdenum atom, based on the total amount (100 mass%) of the lubricating oil composition is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, even more preferably 0.080 mass% or more, still more preferably 0.090 mass% or more, and is preferably 0.200 mass% or less, more preferably 0.180 mass% or less, even more preferably 0.160 mass% or less, and still more preferably 0.140 mass% or less.
In other words, the content of the friction modifier (D) in terms of molybdenum atoms is preferably 0.010 to 0.200 mass%, more preferably 0.050 to 0.180 mass%, even more preferably 0.080 to 0.160 mass%, and still more preferably 0.090 to 0.140 mass%, based on the total amount (100 mass%) of the lubricating oil composition.
In this specification, the molybdenum atom content refers to a value measured in accordance with JPI-5S-38-2003.

<Lubricant Additives>
The lubricating oil composition of one embodiment of the present invention may further contain lubricating oil additives other than components (B) to (D) as necessary, provided that the effects of the present invention are not impaired.
Examples of such lubricating oil additives include anti-wear agents, extreme pressure agents, metal detergents, antioxidants, metal deactivators, rust inhibitors, and anti-foaming agents.
These lubricating oil additives may be used alone or in combination of two or more kinds.

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

In addition, as the lubricating oil additive, a commercially available additive package containing a plurality of additives conforming to API/ILSAC SN/GF-5 standards or the like may be used.
Furthermore, a compound having multiple functions as the above-mentioned additive (for example, a compound having functions as an antiwear agent and an extreme pressure agent) may be used.

(Anti-wear agent)
Examples of anti-wear agents used in one embodiment of the present invention include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphates, phosphonates, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, and amine salts or metal salts thereof.
Of these, zinc dialkyldithiophosphate (ZnDTP) is preferred.

(Extreme pressure agent)
Examples of the extreme pressure agent used in one embodiment of the present invention include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, and thiophosphinates, halogen-based extreme pressure agents such as chlorinated hydrocarbons, and organometallic extreme pressure agents. Of the above-mentioned antiwear agents, compounds having a function as an extreme pressure agent can also be used.

(Metal-based detergent)
Examples of the metal-based detergent used in one embodiment of the present invention include organic acid metal salt compounds containing a metal atom selected from alkali metals and alkaline earth metals. Specific examples of the metal detergent include metal salicylates, metal phenates, and metal sulfonates, each of which contains a metal atom selected from alkali metals and alkaline earth metals.
As the metal atom contained in the metal-based detergent, from the viewpoint of improving the detergency at high temperatures, sodium, calcium, magnesium or barium is preferred, and calcium is more preferred.

In addition, the metal sulfonate is preferably a compound represented by the following general formula (1), the metal salicylate is preferably a compound represented by the following general formula (2), and the metal phenate is preferably a compound represented by the following general formula (3).

In the above general formulas (1) and (2), M is a metal atom selected from alkali metals and alkaline earth metals, preferably sodium, calcium, magnesium, or barium, more preferably calcium.
In the above general formula (3), M' is an alkaline earth metal, preferably calcium, magnesium or barium, and more preferably calcium, and y is an integer of 0 or more, preferably an integer of 0 to 3.
In the above general formulas (1) to (3), p is the valence of M and is 1 or 2. R is a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.
Examples of the hydrocarbon group that can be selected as R include an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 ring carbon atoms, an aryl group having 6 to 18 ring carbon atoms, an alkylaryl group having 7 to 18 carbon atoms, and an arylalkyl group having 7 to 18 carbon atoms.

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

(Antioxidants)
The antioxidant used in one embodiment of the present invention can be appropriately selected from known antioxidants that have been conventionally used as antioxidants for lubricating oils, and examples thereof include amine-based antioxidants, phenol-based antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

Examples of the amine-based antioxidants include diphenylamine-based antioxidants such as diphenylamine and alkylated diphenylamines having an alkyl group having 3 to 20 carbon atoms; naphthylamine-based antioxidants such as α-naphthylamine, phenyl-α-naphthylamine, and substituted phenyl-α-naphthylamines having an alkyl group having 3 to 20 carbon atoms; and the like.
Examples of the phenol-based antioxidants include monophenol-based antioxidants such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; diphenol-based antioxidants such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); hindered phenol-based antioxidants; and the like.
Examples of the molybdenum-based antioxidant include molybdenum amine complexes obtained by reacting molybdenum trioxide and/or molybdic acid with an amine compound.
An example of the sulfur-based antioxidant is dilauryl-3,3'-thiodipropionate.
Examples of phosphorus-based antioxidants include phosphites.

(Metal Deactivators)
Examples of the metal deactivator used in one embodiment of the present invention include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds.

(Rust inhibitor)
Examples of the rust inhibitor used in one embodiment of the present invention include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, paraffin oxide, and alkyl polyoxyethylene ethers.

(Antifoaming agent)
Examples of the defoaming agent used in one embodiment of the present invention include silicone oil, fluorosilicone oil, and fluoroalkyl ether.

<Method of producing lubricating oil composition>
The method for producing the lubricating oil composition of one embodiment of the present invention is not particularly limited, but from the viewpoint of productivity, it is preferable that the method comprises a step of blending the succinimide (B) and the polymer (C) with the mineral oil (A), and, as necessary, a synthetic oil, an ashless dispersant other than the succinimide (B), and the other lubricating oil additives described above.
From the viewpoint of compatibility with the mineral oil (A), it is preferable that the resin components such as the polymer (C) are in the form of a solution dissolved in a diluent oil, and the solution is blended with the mineral oil (A).

[Properties of the lubricating oil composition]
The lubricating oil composition of one embodiment of the present invention preferably has a kinematic viscosity at 100°C of less than 5.1 ^mm2 /s, more preferably 3.0 to 5.0 ^mm2 /s, even more preferably 3.2 to 4.8 ^mm2 /s, still more preferably 3.5 to 4.6 ^mm2 /s, and particularly preferably 3.7 to 4.5 ^mm2 /s.

The lubricating oil composition of one embodiment of the present invention has a kinematic viscosity at 40°C of preferably 5.0 to 60.0 mm ² /s, more preferably 6.0 to 50.0 mm ² /s, even more preferably 7.0 to 40.0 mm ² /s, still more preferably 8.0 to 30.0 mm ² /s, and particularly preferably 10.0 to 25.0 mm ² /s.

The viscosity index of the lubricating oil composition of one embodiment of the present invention is preferably 100 or more, more preferably 120 or more, even more preferably 140 or more, even more preferably 160 or more, and particularly preferably 180 or more.

The lubricating oil composition of one embodiment of the present invention can maintain a constant viscosity to such an extent that excellent hydraulic properties can be exhibited over a wide range of high temperature temperatures.
For example, the kinematic viscosity at 140°C of the lubricating oil composition of one embodiment of the present invention is preferably 2.45 mm ² /s or more, more preferably 2.46 to 4.40 m ² /s, even more preferably 2.48 to 4.20 m ² /s, still more preferably 2.50 to 4.00 m ² /s, and particularly preferably 2.55 to 3.80 m ² /s.
When applied to engine lubrication, for example, the kinetic viscosity at 140° C. is an index of hydraulic properties during engine use. In other words, a lubricating oil composition having a kinetic viscosity at 140° C. of 2.45 mm ² /s or more can be said to have excellent hydraulic properties during engine use.

The lubricating oil composition of one embodiment of the present invention has a kinematic viscosity at 110°C of preferably 2.8 to 5.0 ^mm2 /s, more preferably 3.0 to 4.8 ^mm2 /s, even more preferably 3.2 to 4.6 ^mm2 /s, still more preferably 3.3 to 4.5 ^mm2 /s, and particularly preferably 3.5 to 4.4 ^mm2 /s.

The lubricating oil composition of one embodiment of the present invention has a kinematic viscosity at 120°C of preferably 2.7 to 4.8 ^mm2 /s, more preferably 2.9 to 4.6 ^mm2 /s, even more preferably 3.0 to 4.4 ^mm2 /s, still more preferably 3.1 to 4.2 ^mm2 /s, and particularly preferably 3.2 to 4.0 ^mm2 /s.

The lubricating oil composition of one embodiment of the present invention has a kinematic viscosity at 130°C of preferably 2.5 to 4.6 ^mm2 /s, more preferably 2.6 to 4.5 ^mm2 /s, even more preferably 2.7 to 4.3 ^mm2 /s, still more preferably 2.75 to 4.1 ^mm2 /s, and particularly preferably 2.8 to 3.9 ^mm2 /s.

The lubricating oil composition of one embodiment of the present invention has a kinematic viscosity at 150°C of preferably 2.00 to 4.00 ^mm2 /s, more preferably 2.05 to 3.80 ^mm2 /s, even more preferably 2.10 to 3.60 ^mm2 /s, still more preferably 2.15 to 3.40 ^mm2 /s, and particularly preferably 2.20 to 3.20 ^mm2 /s.

The lubricating oil composition of one embodiment of the present invention can exhibit excellent fuel economy over a wide range of high temperature temperatures. For example, the fuel economy in the low temperature range can be evaluated by the HTHS viscosity at 80°C.
Specifically, the lubricating oil composition of one embodiment of the present invention preferably has a HTHS viscosity at 80° C. of 4.40 mPa·s or less, more preferably 2.40 to 4.35 mPa·s, even more preferably 2.50 to 4.32 mPa·s, and still more preferably 2.60 to 4.30 mPa·s.

The HTHS viscosity at 100°C of the lubricating oil composition of one embodiment of the present invention is preferably 2.00 to 4.00 mPa·s, more preferably 2.10 to 3.90 mPa·s, even more preferably 2.20 to 3.80 mPa·s, and even more preferably 2.40 to 3.60 mPa·s.

The lubricating oil composition of one embodiment of the present invention preferably has an HTHS viscosity at 150° C. of 1.40 mPa·s or more, more preferably 1.45 to 3.80 mPa·s, even more preferably 1.50 to 3.60 mPa·s, and still more preferably 1.55 to 3.40 mPa·s.
In this specification, the HTHS viscosity at each temperature refers to a value measured in accordance with ASTM D 4741, after shearing at a shear rate of 10 ⁶ /s at each measurement temperature.

The SAE viscosity grade of the lubricating oil composition of one embodiment of the present invention is preferably 0W-4 or 0W-8, and more preferably 0W-4. With these SAE viscosity grades, various performance properties can be fully exhibited when used, for example, to lubricate engines mounted on hybrid cars or generators.

The NOACK value of the lubricating oil composition of one embodiment of the present invention is preferably 32 mass % or less, more preferably 31 mass % or less, and even more preferably 30.5 mass % or less.
If the NOACK value is 32 mass % or less, oil consumption due to evaporation is suppressed, and the lubricating oil composition can be said to be excellent in oil consumption suppression properties.

In the lubricating oil composition of one embodiment of the present invention, the content of molybdenum atoms, based on the total amount (100 mass%) of the lubricating oil composition, is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, even more preferably 0.080 mass% or more, still more preferably 0.090 mass% or more, and is preferably 0.200 mass% or less, more preferably 0.180 mass% or less, even more preferably 0.160 mass% or less, and still more preferably 0.140 mass% or less.
That is, the content of molybdenum atoms is preferably 0.010 to 0.200 mass%, more preferably 0.050 to 0.180 mass%, even more preferably 0.080 to 0.160 mass%, and still more preferably 0.090 to 0.140 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[Uses of the lubricating oil composition]
As described above, the lubricating oil composition of one embodiment of the present invention is excellent in properties such as hydraulic properties, fuel economy, and oil consumption suppression. Therefore, the lubricating oil composition of one embodiment of the present invention can be suitably used for lubricating engines, and in particular, can be suitably used for lubricating engines mounted on hybrid cars or engines mounted on generators for electric vehicles, and can be even more suitably used for lubricating engines mounted on range extenders for electric vehicles.
In other words, taking into consideration the above-mentioned properties of the lubricating oil composition of one embodiment of the present invention, the present invention can also provide engines described in the following [1] and [2], and methods of using the lubricating oil compositions described in the following [3] and [4].
[1] An engine of a hybrid car or an engine mounted on a generator for an electric vehicle, to which the lubricating oil composition according to one embodiment of the present invention is applied.
[2] An engine mounted on a range extender for an electric vehicle, to which the lubricating oil composition according to one embodiment of the present invention is applied.
[3] A method for using the lubricating oil composition according to one embodiment of the present invention described above, which comprises applying the lubricating oil composition to the engine of a hybrid car or an engine mounted on a generator for an electric vehicle.
[4] A method for using the lubricating oil composition according to one embodiment of the present invention described above, comprising applying the lubricating oil composition to the lubrication of an engine mounted in a range extender for an electric vehicle.

The fuel for the engines [1] to [4] above is not particularly limited, and examples thereof include gas, gasoline, and bio-methanol.
In the above [1] and [3], the engine of the hybrid car may be a parallel type engine using both an internal combustion engine and an electric motor as the driving source of the vehicle, a split type engine, etc. In addition, the hybrid car may be an electric vehicle equipped with an internal combustion engine capable of running on an electric motor alone (for example, a full hybrid vehicle such as a plug-in hybrid vehicle), or a mild hybrid vehicle using an electric motor (such as an alternator) as a driving assistance for the internal combustion engine.

In addition, in the above [1] and [3], the engine mounted on the generator for the electric vehicle includes an engine that uses an electric motor as the only driving source for the vehicle and is used to generate electricity for the electric motor, specifically, an engine mounted on a range extender for an electric vehicle that supplements the power generation of the electric motor of the electric vehicle.

The range extender in the above [2] and [4] refers to a mechanism that generates electricity using the engine when power supply is required, such as when the remaining capacity of the battery is low or when a relatively large amount of power is required during acceleration or heating operation, and stops the engine when power generation is not required. The lubricating oil composition of the present invention can be suitably applied to the lubrication of engines mounted on hybrid car engines and generators for electric vehicles, and is particularly preferably used for engines mounted on range extenders for electric vehicles.
The engine mounted on the range extender does not require as much power as a conventional gasoline engine, and is repeatedly started and stopped in a short period of time. On the other hand, there is a demand for improving fuel efficiency by reducing the viscosity of the lubricating oil composition, but reducing the viscosity causes an increase in oil consumption and a shortage of oil pressure. However, as described above, the lubricating oil composition of one embodiment of the present invention has excellent properties such as hydraulic characteristics, fuel efficiency, and oil consumption suppression even with a low viscosity. Therefore, it can be suitably applied to the above embodiments [2] and [4].

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The methods for measuring or evaluating various physical properties are as follows.

(1) Kinematic Viscosity and Viscosity Index Measured and calculated in accordance with JIS K2283:2000.
(2)%C _P ,%C _N
The measurement was performed in accordance with ASTM D-3238 ring analysis (ndM method).
(3) NOACK Value: Measured at 250° C. in accordance with JPI-5S-41-2004.
(4) Aniline point: Measured in accordance with JIS K2256 (U-tube method).
(5) Flash point: Measured by the Cleveland open cup (COC) method in accordance with JIS K2265-4.
(6) Pour point: Measured in accordance with JIS K2269:1987.
(7) Temperature at which the amount of distilled light fraction reaches 10% by volume According to ASTM D6352, the amount of distilled light fraction during the process of increasing the temperature from room temperature was measured by a gas chromatography distillation test, and the temperature at which the amount of distilled light fraction reached 10% by volume was measured.
(8) Nitrogen Atom Content: Measured in accordance with JIS K2609.
(9) Molybdenum Atom Content: Measured in accordance with JPI-5S-38-2003.
(10) Weight average molecular weight (Mw), number average molecular weight (Mn),
Measurements were carried out using a gel permeation chromatograph (Agilent Technologies, "1260 Model HPLC") under the following conditions, and values measured in terms of standard polystyrene were used.
(Measurement conditions)
- Column: Two "Shodex LF404" columns connected in series.
Column temperature: 35°C
Developing solvent: chloroform Flow rate: 0.3 mL/min
The ratio [Mw/Mn] of the measured weight average molecular weight (Mw) to the number average molecular weight (Mn) was calculated as the molecular weight distribution.
(11) SSI (shear stability index)
A sample oil was prepared by adding mineral oil as a diluent to the polymer to be measured, and the sample oil and the mineral oil were used to carry out the measurement in accordance with JPI-5S-29-06.
Specifically, the values of Kv ₀ , Kv ₁ and Kv _oil in the above formula (1) were measured for the target polymer, and calculation was performed from the formula (1).
(12) HTHS Viscosity According to ASTM D 4741, the viscosity after shearing at a shear rate of 10 ⁶ /s was measured at each measurement temperature.

Examples 1 to 2, Comparative Examples 1 to 4
Lubricating oil compositions were prepared by blending mineral oil, succinimide, polymer, and various additives in the amounts shown in Table 2. The blending amount of polymer shown in Table 2 is the blending amount converted into active ingredient (solid content equivalent) excluding the mass of diluent oil. When a mixed mineral oil made by combining two or more types of mineral oils is used as the mineral oil, the "Properties of mineral oil" in Table 2 indicates the properties of the mixed mineral oil.
Details of the mineral oil, succinimide, polymer and various additives used in the preparation of each lubricating oil composition are as follows:

<Mineral oil>
Mineral oils (A-1) to (A-4): Paraffinic mineral oils classified into Group 2 or 3 of the API base oil category described in Table 1 below.

<Succinimide>
Unmodified succinic acid bisimide: unmodified succinic acid bisimide, nitrogen atom (N) content=1.2% by mass.
<Polymer>
Comb polymer: A comb polymer having Mw=600,000, Mw/Mn=2.4, and SSI=49.
<Various additives>
Additive mixture: a mixture of additives including an anti-wear agent (ZnDTP), a friction modifier (MoDTC, formulated so that the content in terms of molybdenum is 0.10 mass% based on the total amount of the lubricating oil composition), a metal-based detergent, an antioxidant, and an antifoaming agent.

The lubricating oil compositions thus prepared were measured for kinematic viscosity at each temperature, viscosity index, HTHS viscosity at 80° C., 100° C., and 150° C., and NOACK value according to the methods described above. The results are shown in Table 2.
In addition, regarding fuel economy, the following motoring torque test was further carried out, and the driving torque improvement rate was calculated and used as one of the indices for evaluating fuel economy.

[Calculation of driving torque improvement rate by motoring torque test]
The lubricating oil compositions of the Examples and Comparative Examples were filled into an engine having the specifications shown below, and a motoring torque test was carried out under the test conditions shown below, measuring the torque (dB) at an oil temperature of 80° C. and rotation speeds of 1500 rpm, 2000 rpm, and 2500 rpm.
(Test conditions)
・Equipment used: Engine motoring device ・Engine: Water-cooled 1,500cc in-line 4-cylinder engine for four-wheel vehicles ・Valve type: DOHC (roller)
Engine speed: 1,500 rpm, 2,000 rpm, and 2,500 rpm
・Oil pan temperature: 80℃
Then, using the torque value measured at each rotation speed for the lubricating oil composition of Comparative Example 1 as a reference, the driving torque improvement rate at each rotation speed was calculated according to the following formula.
Driving torque improvement rate (%) = ([torque measurement value measured using the lubricating oil composition of Comparative Example 1] - [torque measurement value measured using the target lubricating oil composition]) / [torque measurement value measured using the lubricating oil composition of Comparative Example 1] x 100
It should be noted that the driving torque improvement rate calculated from the above formula is positive when the torque measurement value of the target lubricating oil composition is smaller than the torque measurement value measured using the lubricating oil composition of Comparative Example 1. Conversely, when the torque measurement value of the target lubricating oil composition is larger, the driving torque improvement rate calculated from the above formula is negative.
The larger the value of the driving torque improvement rate, the more the driving torque is improved, and therefore the lubricating oil composition being measured can be said to have high fuel economy. In this embodiment, a lubricating oil composition having a driving torque improvement rate of "0.50% or more" is judged to have high fuel economy, more preferably 0.55% or more, even more preferably 0.60% or more, and even more preferably 0.70% or more.

Based on the measured physical property values and the drive torque improvement rate calculated as described above, the hydraulic properties, fuel economy, and oil consumption suppression properties of each lubricating oil composition were evaluated according to the following criteria. The evaluation results are shown in Table 2.

<Evaluation criteria for hydraulic characteristics>
A: The lubricating oil composition has a 140° C. kinetic viscosity of 2.45 mm ² /s or more, and has a viscosity sufficient to maintain oil pressure in the temperature environment during engine use.
F: The lubricating oil composition has a kinetic viscosity at 140° C. of less than 2.45 mm ² /s, and since the viscosity is low in the temperature environment during engine use, there is a risk that oil pressure may not be sufficiently maintained.

<Fuel economy evaluation criteria>
A: The driving torque improvement rate at rotation speeds of 1500 rpm, 2000 rpm, and 2500 rpm at an oil temperature of 80°C is 0.5% or more at all rotation speeds, and the HTHS viscosity at 80°C is 4.40 mPa·s or less.
F: The driving torque improvement rate at at least one of the rotational speeds of 1500 rpm, 2000 rpm, and 2500 rpm at an oil temperature of 80°C is less than 0.5% at the rotational speed, and/or the HTHS viscosity at 80°C is more than 4.40 mPa·s.

<Evaluation criteria for oil consumption suppression>
A: The NOACK value is 32 mass% or less, and it can be said that the lubricating oil composition has reduced oil consumption due to evaporation.
F: The NOACK value is greater than 32% by mass, the loss due to evaporation is large, and oil consumption is not sufficiently suppressed.

As can be seen from Table 2, the lubricating oil compositions prepared in Examples 1 and 2 were excellent in hydraulic properties, fuel economy, and oil consumption suppression, resulting in a good balance of these properties. On the other hand, the lubricating oil compositions prepared in Comparative Examples 1 to 4 were inferior in at least one of hydraulic properties, fuel economy, and oil consumption suppression, resulting in room for improvement in the balance of these properties.

Claims (13)

A lubricating oil composition comprising a mineral oil (A), a succinimide (B), and a polymer (C),
The mineral oil (A) satisfies the following requirements (a1) to (a3):
The following requirement is satisfied: requirement (a1): the kinematic viscosity at 100° C. is less than 3.10 mm ² /s; requirement (a2): the NOACK value is 36.0 mass% or less; and requirement (a3): the % _CP measured in accordance with ASTM D3238 is 75.0 or more.
the content of the succinimide (B) in terms of nitrogen atoms is 0.008 to 0.060 mass% based on the total amount of the lubricating oil composition;
the content of the polymer (C) in terms of the resin content is 0.40 to 3.00 mass% based on the total amount of the lubricating oil composition;
The polymer (C) is any one of a non-dispersed polymethacrylate, a dispersed polymethacrylate, an olefin-based copolymer, a dispersed olefin-based copolymer, and a styrene-based copolymer;
The polymer (C) comprises a comb polymer (C1),
Lubricating oil composition. The lubricating oil composition according to claim 1, wherein the ratio [(B)/(C)] of the content (unit: mass%) of succinimide (B) calculated as nitrogen atoms to the content (unit: mass%) of polymer (C) calculated as resin content is 0.001 to 5.00. The lubricating oil composition according to claim 1 or 2, wherein the comb polymer (C1) has a weight average molecular weight (Mw) of 200,000 to 1,000,000 and a molecular weight distribution (Mw/Mn) (Mn is the number average molecular weight of the comb polymer (C1)) of 4.0 or less. The lubricating oil composition according to any one of claims 1 to 3 , wherein the mineral oil (A) further satisfies the following requirement (a4):
Requirement (a4): % C _N measured in accordance with ASTM D3238 is 3.0 to 25.0 The lubricating oil composition according to any one of claims 1 to 4 , wherein the mineral oil (A) further satisfies the following requirement (a5):
Requirement (a5): The temperature at which the distillation amount of the light fraction becomes 10% by volume in a gas chromatography distillation test is 345° C. or higher. The lubricating oil composition according to any one of claims 1 to 5 , wherein the lubricating oil composition has a kinematic viscosity at 100°C of less than 5.1 mm ² /s. The lubricating oil composition according to any one of claims 1 to 6 , wherein the lubricating oil composition has a HTHS viscosity at 150°C of 1.40 mPa·s or more. The lubricating oil composition according to any one of claims 1 to 7 , wherein the lubricating oil composition has a kinematic viscosity at 140°C of 2.45 mm ² /s or more. The lubricating oil composition according to any one of claims 1 to 8 , wherein the lubricating oil composition has a HTHS viscosity at 80°C of 4.40 mPa·s or less. The lubricating oil composition according to any one of claims 1 to 9 , which is used to lubricate an engine mounted on a hybrid car or an engine mounted on a generator for an electric vehicle. The lubricating oil composition according to any one of claims 1 to 10 , which is used to lubricate an engine mounted in a range extender for an electric vehicle. A method for using the lubricating oil composition according to any one of claims 1 to 11 for lubricating an engine mounted on a hybrid car or an engine mounted on a generator for an electric vehicle. A method for using the lubricating oil composition according to any one of claims 1 to 11 for lubricating an engine mounted in a range extender for an electric vehicle.