WO2016152229A1

WO2016152229A1 - Lubricating oil composition for transmission

Info

Publication number: WO2016152229A1
Application number: PCT/JP2016/051858
Authority: WO
Inventors: 中村　俊貴; 剛辰巳; 洋平薄田; 耕平増田
Original assignee: Ｊｘエネルギー株式会社
Priority date: 2015-03-20
Filing date: 2016-01-22
Publication date: 2016-09-29
Also published as: JPWO2016152229A1

Abstract

Provided is a lubricating oil composition having as the base oil a mixed oil containing (A) a hydrocarbon-based base oil having a kinetic viscosity at 40°C of 5-20 mm²/s and (B) one or more types of ester oil of either unsaturated carbon bond-free polybasic acid ester or polyol ester containing two or more ester bonds, with a kinetic viscosity at 40°C of 18 mm²/s or less, and a content ratio of component (B) of 0.5-50 mass% in terms of the total amount of base oil as a lubricating oil composition for a transmission capable of achieving both fuel economy and unit durability that makes it possible to raise the viscosity index even by adding a small amount of viscosity index improver, wherein the lubricating oil composition for a transmission is characterized by having a kinetic viscosity at 40°C of 4-25 mm²/s and a kinetic viscosity at 100°C of 2.0-5.4 mm²/s.

Description

Lubricating oil composition for transmission

The present invention relates to a lubricating oil composition for a transmission that is excellent in load resistance and metal fatigue resistance despite low viscosity.

Conventional lubricating oils used in automatic transmissions, manual transmissions, internal combustion engines, etc., have a viscosity temperature to improve various durability such as thermal oxidation stability, wear resistance and fatigue resistance, and to improve fuel economy. Improvements in low-temperature viscosity properties such as improved properties, reduced low-temperature viscosity, improved low-temperature fluidity are required, and in order to improve such performance, antioxidants, detergent dispersants, and abrasion are appropriately applied to base oils. Lubricating oils containing various additives such as an inhibitor, a friction modifier, a seal swelling agent, a viscosity index improver, an antifoaming agent and a colorant are used.

Recent transmissions and engines are required to be fuel efficient, lighter, smaller, and have higher output. Furthermore, with transmissions that are combined with higher output, improvements in power transmission capability are being pursued. . For this reason, the lubricant used in these products has a reduced product viscosity and base oil viscosity, maintains high lubrication performance, and prevents wear and fatigue on the surface of bearings, gears, etc., and seizure resistance. Is required. In general, in order to improve fuel economy, a technique for improving viscosity temperature characteristics by reducing the base oil viscosity and increasing the viscosity index improver is adopted. Since fatigue resistance deteriorates, development of a lubricating oil that can achieve both fuel saving, wear prevention, seizure resistance, and fatigue prevention at a higher level is eagerly desired.

Under these circumstances, in order to achieve both fuel economy and low-temperature viscosity characteristics and fatigue prevention, use of base oils with good low-temperature performance, use of high-viscosity base oils, phosphorus-based extreme pressure agents and sulfur-based materials It is known to add an appropriate amount of an extreme pressure agent or the like (for example, Patent Documents 1 to 3).
However, the above-mentioned method alone does not sufficiently achieve both viscosity-temperature characteristics and low-temperature performance, anti-fatigue properties, and seizure resistance. There is a need for the development of compositions.

Japanese Patent Application Laid-Open No. 2004-262979 JP-A-11-286696 Special table 2003-514099 gazette

The present invention has been made in view of the above problems, and an object of the present invention is to provide a lubricating oil composition for a transmission that is excellent in load resistance and metal fatigue resistance while reducing viscosity.

As a result of intensive research on the above problems, the present inventors have improved the oxidation stability and copper elution property by using an ester oil having a specific structure as a base oil component, and in addition, further improved metal fatigue resistance. The inventors have found that it can be improved, and have completed the present invention.

That is, the present invention relates to (A) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 5 to 20 mm ² / s and (B) a polybasic acid having two or more ester bonds and having no unsaturated carbon bond. 1 type or 2 or more types of ester oil of ester or polyol ester is contained, dynamic viscosity in 40 degreeC is 18 mm < ² > / s or less, and the content rate of (B) component is 0.5 on the basis of base oil whole quantity. ~ mixed oil is 50% by mass of a lubricating oil composition as a base oil, kinematic viscosity ^{4 ~} 25 mm at 40 ℃ 2 / s, 100 kinematic viscosity at ° C. is 2.0 ~ 5.4 mm ² / s It is the lubricating oil composition for transmissions characterized by these.

In addition, the present invention provides an ester oil in which the component (B) is a dibasic acid diester represented by the following formula (1) or a polyol ester represented by the following formulas (2) to (4). The above-mentioned lubricating oil composition for transmissions.

(R ₁ to R ₆ are each independently a saturated hydrocarbon group having 3 to 36 carbon atoms, R ₇ and R ₈ are each independently an alkyl group having 1 to 3 carbon atoms, and n is an integer of 4 to 8)

Further, the present invention is the above-described lubricating oil composition for a transmission, wherein the content of the polymethacrylate viscosity index improver in the composition is 9% by mass or less based on the total amount of the composition.

According to the present invention, it is possible to obtain a lubricating oil composition for a transmission which is excellent in load resistance and metal fatigue resistance while improving fuel economy by reducing viscosity.

Hereinafter, the present invention will be described in detail.

The lubricating base oil according to the present invention comprises (A) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 5 to 20 mm ² / s and (B) a mixed base oil containing a specific ester oil.

The kinematic viscosity at 40 ° C. of the hydrocarbon base oil of component (A) is required to be 5 mm ² / s or more, preferably 7.5 mm ² / s or more, and more preferably 10 mm ² / s or more. By setting the kinematic viscosity at 40 ° C. to 5 mm ² / s or more, sufficient lubricity can be secured and evaporation loss of the lubricating base oil can be suppressed.
Meanwhile, the kinematic viscosity at 40 ° C., is required to be less 20 mm ² / s, preferably not more than 17.5 mm ² / s, more preferably at most 15 mm ² / s. When exceeding 20 mm < ² > / s, since a fuel-saving property and a low-temperature viscosity characteristic deteriorate, it is unpreferable.

The kinematic viscosity at 100 ° C. of the hydrocarbon base oil of component (A) is preferably 1.5 mm ² / s or more, more preferably 1.7 mm ² / s or more, and further preferably 2.0 mm ² / s. That's it. Moreover, Preferably it is 4.4 mm < ² > / s or less, More preferably, it is 4.2 mm < ² > / s or less.
If the kinematic viscosity at 100 ° C. Component (A) is more than 4.4 mm ² / s, worse viscosity temperature characteristics and low temperature viscosity characteristics, in the case of less than 1.5 mm ² / s, oil film formation at lubricating sites Is insufficient because the metal fatigue resistance and heat resistance are inferior, and the evaporation loss of the lubricating base oil increases.

In the present invention, mineral oil base oil and / or hydrocarbon synthetic base oil can be used as the hydrocarbon base oil of component (A). Mineral oil-based base oils and hydrocarbon-based synthetic base oils may be used alone or in combination of two or more. In addition, when (A) component is a mixture, each base oil does not necessarily need to satisfy | fill the said kinematic viscosity characteristic, and should just satisfy | fill the said kinematic viscosity characteristic as a mixture.

There are no particular restrictions on the production method of the mineral base oil, and solvent removal, solvent extraction, hydrocracking, solvent removal can be performed on the lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of crude oil. Mention may be made of paraffinic or naphthenic mineral oils obtained by appropriately combining one or more purification means such as wax, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment.

More specifically, the following base oils (1) to (8) are used as raw materials, and the raw oil and / or the lubricating oil fraction recovered from the raw oils are refined by a predetermined refining method and lubricated. The base oil obtained by collect | recovering an oil fraction can be mentioned.
(1) Distilled oil by atmospheric distillation of paraffinic crude oil and / or mixed base crude oil (2) Distilled oil by vacuum distillation of atmospheric distillation residue of paraffinic crude oil and / or mixed base crude oil ( WVGO)
(3) Wax (such as slack wax) obtained by the lubricant dewaxing process and / or synthetic wax (Fischer-Tropsch wax, GTL wax, etc.) obtained by the gas-liquid (GTL) process, etc.
(4) One or more mixed oils selected from base oils (1) to (3) and / or mild hydrocracked oils of the mixed oils (5) Selected from base oils (1) to (4) (6) base oil (1), (2), (3), (4) or (5) debris oil (7) base oil (6) hydrocracked oil (8 ) Two or more mixed oils selected from base oils (1) to (7)

The above-mentioned predetermined purification methods include hydrorefining such as hydrocracking and hydrofinishing; solvent refining such as furfural solvent extraction; dewaxing such as solvent dewaxing and catalytic dewaxing; acid clay and activated clay White clay purification; chemical (acid or alkali) cleaning such as sulfuric acid cleaning and caustic soda cleaning is preferable. In the present invention, one of these purification methods may be performed alone, or two or more may be combined. Moreover, when combining 2 or more types of purification methods, the order in particular is not restrict | limited, It can select suitably.

Further, the mineral base oil according to the present invention is obtained by subjecting a base oil selected from the above base oils (1) to (8) or a lubricating oil fraction recovered from the base oil to a predetermined treatment. The following base oil (9) or (10) is particularly preferred.

(9) Hydrocracking a base oil selected from the base oils (1) to (8) or a lubricating oil fraction recovered from the base oil, and recovering the product or the product by distillation or the like Hydrocracked mineral oil obtained by performing dewaxing treatment such as solvent dewaxing or catalytic dewaxing on the lube oil fraction, or by distillation after the dewaxing treatment (10) The above base oils (1) to (8) ) Or a lubricating oil fraction recovered from the base oil is hydroisomerized, and the product or the lubricating oil fraction recovered from the product by distillation or the like is subjected to solvent dewaxing or catalytic dewaxing. Hydroisomerized mineral oil obtained by performing dewaxing treatment such as or by distillation after the dewaxing treatment

When obtaining the lubricating base oil of (9) or (10) above, as the dewaxing step, the thermal / oxidative stability and low temperature viscosity characteristics can be further enhanced, and the fatigue prevention performance of the lubricating oil composition is further enhanced. It is particularly preferable to include a contact dewaxing step.
Moreover, when obtaining the lubricating base oil of (9) or (10) above, a solvent refining treatment and / or a hydrofinishing treatment step may be further provided as necessary.

In the case of catalytic dewaxing (catalyst dewaxing), the hydrocracking / isomerization product oil is reacted with hydrogen in the presence of an appropriate dewaxing catalyst under conditions effective to lower the pour point. In catalytic dewaxing, some of the high-boiling substances in the cracking / isomerization product are converted to low-boiling substances, the low-boiling substances are separated from the heavier base oil fraction, and the base oil fraction is fractionated. Two or more kinds of lubricating base oils are obtained. The low-boiling substances can be separated before obtaining the target lubricating base oil or during fractional distillation.

In the present invention, a wax isomerized base oil obtained by isomerizing a wax such as petroleum-based or Fischer-Tropsch synthetic oil can be preferably used.

The viscosity index of the mineral base oil is preferably 90 or more, more preferably 100 or more, still more preferably 120 or more, and most preferably 125 or more. Further, it is preferably 160 or less, more preferably 150 or less, further preferably 140 or less, particularly preferably 135 or less, and most preferably 130 or less. When the viscosity index is lower than 90, it is impossible to obtain a viscosity temperature characteristic capable of exhibiting fuel saving performance. On the other hand, if it exceeds 160, normal paraffin increases in the base oil, so that the viscosity at a low temperature increases rapidly and the function as a lubricating oil is lost.

The pour point of the mineral oil base oil is preferably −25 ° C. or lower, more preferably −27.5 ° C. or lower, still more preferably −30 ° C. or lower, particularly preferably −35 ° C. or lower, most preferably Preferably, it is −40 ° C. or lower. The lower limit is not particularly limited, but it is preferably −50 ° C. or higher from the viewpoint of lowering the viscosity index and economical efficiency in the dewaxing process if it is too low. By setting the pour point to −25 ° C. or less, a lubricating oil composition having excellent low-temperature viscosity characteristics can be obtained. On the other hand, if it is lower than −50 ° C., a sufficient viscosity index cannot be obtained.
As the dewaxing step, any of solvent dewaxing and contact dewaxing steps may be applied. However, the contact dewaxing step is particularly preferable because the low temperature viscosity characteristics can be further improved.

It is preferred that the% C _P of the mineral base oil is 85 or more, in that it is possible to further improve the heat and oxidation stability and viscosity temperature characteristics is preferably 90 or more.
% C _A is preferably 3 or less, more preferably 2 or less, and more preferably 1 or less. % C _A thermal-oxidative stability decreases exceeds 3.
Moreover, it is preferable that% _CN is 20 or less, More preferably, it is 15 or less, More preferably, it is 10 or less. Further, it is preferably 2 or more, more preferably 3 or more, further preferably 5 or more, and particularly preferably 7 or more in that the metal fatigue life can be further increased.

The flash point of the mineral base oil is preferably 150 ° C. or higher, more preferably 160 ° C. or higher, still more preferably 175 ° C. or higher, and particularly preferably 190 ° C. or higher. When the flash point is lower than 150 ° C., there is a risk of causing a problem in safety at high temperature use.
In addition, the flash point as used in the field of this invention means the flash point measured based on JISK2265 (open type flash point).

The aniline point of the mineral oil base oil is not particularly limited, but it is preferably 90 ° C or higher, more preferably 95 ° C or higher in that a lubricating oil composition having excellent low temperature viscosity characteristics and fatigue life can be obtained. More preferably, it is 100 ° C. or higher. Further, the upper limit is not particularly limited, and may exceed 130 ° C. as one aspect of the present invention, but is preferably 130 because it is more excellent in solubility of additives and sludge and more excellent in compatibility with a sealing material. ° C or lower, more preferably 120 ° C or lower.

The sulfur content of the mineral oil base oil is not particularly limited, but is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, still more preferably 0.01% by mass or less, and most preferably It is desirable that it is not substantially contained.
The nitrogen content of the component (A) is not particularly limited, but is preferably 5 ppm by mass or less, more preferably 3 ppm by mass or less, in that a composition excellent in thermal and oxidation stability can be obtained. Most preferably, it should be substantially free.
In addition, content of sulfur content and nitrogen content as used in the field of this invention means the value measured based on ASTM D4951.

Specific examples of hydrocarbon-based synthetic base oils include polybutene or hydrides thereof; poly-α-olefins such as 1-octene oligomers, 1-decene oligomers and 1-dodecene oligomers or hydrides thereof; alkylnaphthalenes And an aromatic synthetic oil of alkylbenzene or a mixture thereof.
Of these, poly-α-olefins such as 1-octene oligomers, 1-decene oligomers and 1-dodecene oligomers, or hydrides thereof are preferred.

The component (B) according to the present invention is a polybasic acid ester or a polyol ester or a mixture thereof, and the polybasic acid ester and the polyol ester contain two or more ester bonds and have an unsaturated carbon bond. There is no ester oil.

Polybasic acid ester is an ester of polybasic acid and monohydric alcohol or polyhydric alcohol, and polyol ester is an ester of polyhydric alcohol and monobasic acid or polybasic acid.

As the monohydric alcohol, a saturated alcohol having usually 1 to 36 carbon atoms, preferably 1 to 24, more preferably 1 to 12, and further preferably 1 to 8 carbon atoms is used. Such alcohols may be linear or branched, and specifically include, for example, methanol, ethanol, linear or branched propanol, linear or branched butanol, Linear or branched pentanol, linear or branched hexanol, linear or branched heptanol, linear or branched octanol, linear or branched nonanol , Linear or branched decanol, linear or branched undecanol, linear or branched dodecanol, linear or branched tridecanol, linear or branched tetra Decanol, linear or branched pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched octadecano , Linear or branched nonadecanol, linear or branched icosanol, linear or branched heicosanol, linear or branched tricosanol, linear or branched tetra Examples include cosanol, gel alcohol and mixtures thereof.

As the polyhydric alcohol, usually a saturated alcohol having 2 to 10 valences, preferably 2 to 6 valences, is used. Specific examples of the divalent to 10-valent polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, polyethylene glycol (ethylene glycol tri- to 15-mer), propylene glycol, dipropylene glycol, polypropylene glycol (propylene glycol 3- 15-mer), 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 2-methyl-1, Dihydric alcohols such as 3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, neopentylglycol; glycerin, polyglycerin (glycerin 2 ~ 8 mer, such as diglycerin, trig Serine, tetraglycerin, etc.), trimethylol alkanes (trimethylol ethane, trimethylol propane, trimethylol butane, etc.) and their 2- to 8-mer, pentaerythritol and their 2- to 4-mer, 1,2,4- Butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol, sorbitol, sorbitan, sorbitol glycerin condensate, adonitol, arabitol, xylitol, mannitol, etc. Polyhydric alcohols; sugars such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, and mixtures thereof And the like.

Among these polyhydric alcohols, ethylene glycol, diethylene glycol, polyethylene glycol (ethylene glycol 3-10 mer), propylene glycol, dipropylene glycol, polypropylene glycol (propylene glycol 3-10 mer), 1,3- Propanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, glycerin, diglycerin, triglycerin, trimethylolalkane (trimethylolethane, trimethylolpropane, trimethylol Methylol butane, etc.) and dimers to tetramers thereof, pentaerythritol, dipentaerythritol, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetrio Le, 1,2,3,4 butane tetrol, sorbitol, sorbitan, sorbitol glycerin condensate, adonitol, arabitol, xylitol, divalent to hexavalent polyhydric alcohols, and mixtures thereof, such as mannitol and the like are preferable. Furthermore, ethylene glycol, propylene glycol, neopentyl glycol, glycerin, trimethylol ethane, trimethylol propane, pentaerythritol, sorbitan, and a mixture thereof are more preferable.
Among these, neopentyl glycol, trimethylol ethane, trimethylol propane, pentaerythritol, and a mixture thereof are most preferable because higher thermal / oxidative stability can be obtained.

As the monobasic acid, a saturated fatty acid having 2 to 24 carbon atoms is usually used, and the fatty acid may be linear or branched. Specifically, for example, acetic acid, propionic acid, linear Linear or branched butanoic acid, linear or branched pentanoic acid, linear or branched hexanoic acid, linear or branched heptanoic acid, linear or branched Octanoic acid, linear or branched nonanoic acid, linear or branched decanoic acid, linear or branched undecanoic acid, linear or branched dodecanoic acid, linear Or branched tridecanoic acid, linear or branched tetradecanoic acid, linear or branched pentadecanoic acid, linear or branched hexadecanoic acid, linear or branched heptadecane Acid, linear or branched octadecanoic acid, linear or branched Nonadecanoic acid, linear or branched icosanoic acid, linear or branched heicosanoic acid, linear or branched docosanoic acid, linear or branched tricosanoic acid, linear And tetracosanoic acid in the form of a branch or a mixture thereof, and the like. Among these, saturated fatty acids having 3 to 20 carbon atoms are particularly preferable, and saturated fatty acids having 4 to 18 carbon atoms are more preferable from the viewpoint that lubricity and handleability are further improved.

Examples of polybasic acids include dibasic acids having 2 to 36 carbon atoms and trimellitic acid. The dibasic acid having 2 to 36 carbon atoms may be linear or branched, and specific examples thereof include ethanedioic acid, propanedioic acid, linear or branched butane diacid. Acid, linear or branched pentanedioic acid, linear or branched hexanedioic acid, linear or branched heptanedioic acid, linear or branched octanedioic acid, Linear or branched nonanedioic acid, linear or branched decanedioic acid, linear or branched undecanedioic acid, linear or branched dodecanedioic acid, linear Linear or branched tridecanedioic acid, linear or branched tetradecanedioic acid, linear or branched heptadecanedioic acid, linear or branched hexadecanedioic acid, dimer of oleic acid Polymers of unsaturated fatty acids such as those having no unsaturated carbon bond and mixtures thereof Etc. The.

The polybasic acid ester of the component (B) may be a complete ester in which all carboxyl groups in the polybasic acid are esterified, or a partial ester in which a part of the carboxyl group is not esterified and remains as a carboxyl group. However, it is preferably a complete ester. The polyol ester may be a complete ester in which all the hydroxyl groups in the polyhydric alcohol are esterified, or a partial ester in which a part of the hydroxyl groups are not esterified and remain as hydroxyl groups, but is preferably a complete ester.

The ester oil which is the component (B) used in the present invention may be composed of only one kind of the above-described ester compound, or may be composed of a mixture of two or more kinds.

The ester oil according to the present invention is any one selected from the group consisting of a dibasic acid diester represented by the following formula (1) and a polyol ester represented by any of the following formulas (2) to (4): Or it is preferable that it is ester oil which consists of 2 or more types of mixtures.

In the general formulas (1) to (4), R ₁ to R ₆ are each independently a saturated hydrocarbon group having 3 to 36 carbon atoms, R ₇ and R ₈ are each independently an alkyl group having 1 to 3 carbon atoms, and n is An integer of 4 to 8 is shown.

Examples of the saturated hydrocarbon group having 3 to 36 carbon atoms include an alkyl group having 3 to 36 carbon atoms, a cycloalkyl group, and an alkylcycloalkyl group. The alkyl group may be linear or branched.
Specific examples of the alkyl group having 3 to 36 carbon atoms include n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, linear or branched pentyl group. Linear or branched hexyl group, linear or branched heptyl group, linear or branched octyl group, linear or branched nonyl group, linear or branched decyl group, linear or branched Branched undecyl group, linear or branched dodecyl group, linear or branched tridecyl group, linear or branched tetradecyl group, linear or branched pentadecyl group, linear or branched hexadecyl group, Linear or branched heptadecyl group, linear or branched octadecyl group, linear or branched nonadecyl group, linear or branched icosyl group, linear or branched triacontyl group, linear or branched And the hexatriacontyl group of Examples of the cycloalkyl group include a cyclohexyl group.

The dibasic acid diester represented by the general formula (1) and the polyol ester represented by the general formulas (2) to (4) may be used alone or in combination of two or more. When two or more are combined, a mixture of dibasic acid diesters represented by general formula (1) may be used, or a mixture of general formula (1) and polyol esters represented by general formulas (2) to (4) may be used. . Similarly, it may be a mixture of polyol esters represented by general formulas (2) to (4), or a mixture of all of general formulas (1) to (4).

The content of the ester oil of the component (B) in the mixed base oil according to the present invention is at least 0.5% by mass, preferably 1% by mass or more, more preferably 2% by mass or more, based on the total amount of the base oil composition. More preferably, it is 3% by mass or more, and particularly preferably 5% by mass or more. On the other hand, the upper limit is 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 25% by mass or less, and particularly preferably 20% by mass or less, based on the total amount of the base oil composition. 10 mass% or less is the most preferable. If the content of ester oil is too large, the oxidation stability of the composition tends to deteriorate, such being undesirable. The fatigue life is significantly improved by setting the content of the component (B) ester oil in the above range.

The viscosity index of the mixed base oil according to the present invention is not particularly limited, but is preferably 110 or more, and more preferably 120 or more. By setting the viscosity index to 110 or more, it is possible to obtain a composition exhibiting favorable viscosity characteristics from a low temperature to a high temperature.
On the other hand, the upper limit is not particularly limited, but is usually 200 or less, and preferably 160 or less. If the viscosity index is too high, the viscosity at low temperatures tends to increase, which is not preferable.

Kinematic viscosity at 40 ° C. in the mixed base oil of the invention must be less than or equal 18 mm ² / s, preferably not more than 16 mm ² / s, more preferably at most 14 mm ² / s. By making it 18 mm ² / s or less, the minimum fuel efficiency can be secured. On the other hand, the lower limit of the kinematic viscosity at 40 ° C. of the mixed base oil is not particularly limited, but is preferably 5.0 mm ² / s or more, more preferably 7.5 mm ² / s or more.

The mixed base oil according to the present invention may contain a mineral oil base oil and / or a synthetic base oil used for ordinary lubricating oil other than the components (A) and (B). In this case, the content of the component (A) and the component (B) is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 85% by mass or more, based on the total amount of the lubricating base oil. Yes, particularly preferably 90% by mass or more, and most preferably 95% by mass or more.

The transmission lubricating oil composition of the present invention (hereinafter also referred to as the lubricating oil composition of the present invention) has a polymethacrylate viscosity index improver content of 9% by mass or less based on the total amount of the composition. Is preferably 6% by mass or less, more preferably 3% by mass or less, and most preferably substantially not contained. If the content of the polymethacrylate viscosity index improver exceeds 9% by mass, it is not preferable because sufficient shear stability cannot be secured.

The lubricating oil composition of the present invention can contain various additives as required as long as the excellent viscosity temperature characteristics and low temperature performance, fatigue resistance and seizure resistance are not impaired. Such an additive is not particularly limited, and any additive conventionally used in the field of lubricating oils can be blended. Specific examples of such lubricating oil additives include ashless dispersants, antioxidants, extreme pressure agents, antiwear agents, friction modifiers, corrosion inhibitors, rust inhibitors, demulsifiers, metal deactivators, Examples include antifoaming agents. These additives may be used individually by 1 type, and may be used in combination of 2 or more type.

As an ashless dispersant, for example, a nitrogen compound having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms or a derivative thereof, or a boron compound, acylating agent or sulfur compound of alkenyl succinimide is used. Examples include modified products.

Examples of the antioxidant include ashless antioxidants such as phenols and amines, and metal antioxidants such as copper and molybdenum.

Examples of the friction modifier include ashless friction modifiers such as fatty acid esters, aliphatic amines, and fatty acid amides, and metal friction modifiers such as molybdenum dithiocarbamate and molybdenum dithiophosphate.

Examples of the corrosion inhibitor include benzotriazole, tolyltriazole, and imidazole compounds.

Examples of the rust preventive include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, and polyhydric alcohol ester.

Examples of the demulsifier include polyalkylene glycol nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, or polyoxyethylene alkyl naphthyl ether.

Examples of the metal deactivator include imidazoline, pyrimidine derivatives, benzotriazole or derivatives thereof, 2- (alkyldithio) benzimidazole, β- (o-carboxybenzylthio) propiononitrile.

Examples of antifoaming agents include silicone oils having a kinematic viscosity at 25 ° C. of less than 0.1 to 100 mm ² / s, alkenyl succinic acid derivatives, esters of polyhydroxy aliphatic alcohols and long chain fatty acids, methyl salicylates and o -Hydroxybenzyl alcohol and the like.

When these additives are contained in the lubricating oil composition of the present invention, the content is preferably 0.001 to 20% by mass based on the total amount of the composition.

The kinematic viscosity at 40 ° C. of the lubricating oil composition of the present invention needs to be 4 mm ² / s or more, preferably 7.5 mm ² / s or more, and more preferably 10 mm ² / s or more. By setting the kinematic viscosity at 40 ° C. of the lubricating oil composition to 4 mm ² / s or more, sufficient lubricity can be secured and evaporation loss of the lubricating base oil can be suppressed.
Meanwhile, the kinematic viscosity at 40 ° C., is required to be less 25 mm ² / s, preferably not more than ^{^{20mm 2 / s, 16mm 2 /}} s or less is more preferable. By setting the kinematic viscosity at 40 ° C. of the lubricating oil composition to 25 mm ² / s or less, a lubricating oil composition having excellent low-temperature viscosity characteristics can be obtained.

Kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention is required to be 2.0 mm ² / s or more, preferably at least 2.5 mm ² / s, more preferably not less than 3.0 mm ² / s . By setting the kinematic viscosity at 100 ° C. of the lubricating oil composition to 2.0 mm ² / s or more, sufficient lubricity can be secured, and evaporation loss of the lubricating base oil can be suppressed.
Meanwhile, the kinematic viscosity at 100 ° C., is required to be less 5.4 mm ² / s, preferably not more than 5.0 mm ² / s, more preferably at most 4.5 mm ² / s. By setting the kinematic viscosity at 100 ° C. of the lubricating oil composition to 5.4 mm ² / s or less, a lubricating oil composition having excellent low-temperature viscosity characteristics can be obtained.

The low-temperature viscosity characteristics are determined by measuring the Brookfield viscosity (BF viscosity) at −40 ° C. of the lubricating oil composition according to ASTM D 2983. It means that the smaller the value of the BF viscosity, the better the low temperature fluidity.
The BF viscosity at −40 ° C. of the lubricating oil composition of the present invention is preferably 23,000 mPa · s or less, more preferably 14,000 mPa · s or less, and even more preferably 10,000 mPa · s or less. Moreover, it is preferably 1,000 mPa · s or more, more preferably 1,500 mPa · s or more, and even more preferably 2,000 mPa · s or more. If it is less than 1,000 mPa · s, seal leakage at low temperatures increases, and there is a fear that hydraulic pressure cannot be secured.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples. *

(Examples 1 to 11, Comparative Examples 1 to 9)
Lubricating oil compositions having the compositions shown in Table 1 were prepared. The proportion (mass%) of the base oil is based on the total amount of the base oil, and the added amount (mass%) of each additive is based on the total amount of the composition. The properties of each lubricating oil composition were evaluated by the following test and listed in Table 1.

[Oxidation stability test]
In accordance with JIS K 2514, each lubricating oil composition was forcibly deteriorated at 150 ° C. for 480 hours under ISOT, and the acid value (mgKOH / g) was measured. From the measured acid value before and after the test, the acid value was measured. The amount of increase in value was determined. A smaller acid value increase means better oxidation stability.

[Fatigue life test]
Using a high-temperature unisteel testing machine, the pitting occurrence life was evaluated under the following test conditions. Further, the fatigue life ratio was calculated based on the test result of Comparative Example 1.
Thrust needle bearing (surface pressure: 1.9 GPa, rotation speed: 1410 rpm, oil temperature: 120 ° C.)

[Shear stability test]
In accordance with JASO M347-95, an ultrasonic shear test was performed, and the kinematic viscosity at 100 ° C. of each lubricating oil composition after 1 hour was measured. In this test, the viscosity drop after shearing is small, and the higher the kinematic viscosity at 100 ° C., the better the shear stability.
The lubricating stability of the lubricating oil composition of the present invention is preferably 1.5% or less, more preferably 1.2% or less, and particularly preferably 0.9%. It is as follows.

In addition, the content of the component of each lubricating oil composition in Table 1 is as follows.

<Hydrocarbon base oil>
(1) Base oil A-1: Mineral oil base oil (40 ° C. kinematic viscosity 7.5 mm ² / s, 100 ° C. kinematic viscosity 2.3 mm ² / s)
(2) Base oil A-2: Mineral oil base oil (40 ° C. kinematic viscosity 19.9 mm ² / s, 100 ° C. kinematic viscosity 4.3 mm ² / s)
(3) Base Oil A-3: mineral base oil (40 ° C. kinematic viscosity 35.3mm ² / s, 100 ℃ kinematic viscosity 6.3 mm ² / s, viscosity index 131)
(4) Base oil A-4: poly-α-orphine oil (40 ° C. kinematic viscosity 5.0 mm ² / s, 100 ° C. kinematic viscosity 1.7 mm ² / s)

<Ester oil>
(1) Base oil B-1: dibasic acid diester having the structure represented by the general formula (1); diester of azelaic acid and saturated alcohol having 8 carbon atoms in total, 40 ° C. kinematic viscosity 11.0 mm ² / s, 100 ℃ kinematic viscosity 3.1 mm ² / s, viscosity index 146)
(2) Base oil B-2: polyol ester having a structure represented by the general formula (2); diester of neopentyl glycol and a saturated fatty acid having a total carbon number of 8 (40 ° C. kinematic viscosity 7.5 mm ² / s, 100 ° C. Kinematic viscosity 2.1mm ² / s)
(3) Base oil B-3: polyol ester having a structure represented by the general formula (3); triester of trimethylolpropane and saturated fatty acid having a total carbon number of 8 to 10 (kinematic viscosity at 40 ° C. 19.7 mm ² / s) , 100 ° C. kinematic viscosity 4.4 mm ² / s)
(4) Base oil B-4: Monoester containing an unsaturated hydrocarbon group; Monoester of oleic acid and saturated alcohol having a total carbon number of 8 (40 ° C. kinematic viscosity 8.5 mm ² / s, 100 ° C. kinematic viscosity 2 .7 mm ² / s, viscosity index 177)
(5) Base oil B-5: polyol ester in which R ₃ and R ₄ are unsaturated hydrocarbon groups in the structure represented by the general formula (2); diester of neopentyl glycol and oleic acid (kinematic viscosity at 40 ° C. (24.2 mm ² / s, 100 ° C. kinematic viscosity 5.9 mm ² / s)

<Viscosity index improver>
C-1: Non-dispersed polymethacrylate viscosity index improver (weight average molecular weight 20,000)
<Performance additive>
D-1: Phosphite ester antiwear agent (phosphorous addition amount (composition basis) 300 mass ppm), overbased Ca sulfonate (Ca addition amount (composition basis) 100 mass ppm), non-borated succinic acid Imide (bis type, addition amount (composition basis) 2.0 mass%), boronated succinimide (bis type, addition amount (composition basis) 2.0 mass%, B addition amount (composition basis) 50 Mass ppm), phenolic antioxidant (addition amount (composition basis) 1.0 mass%), amine antioxidant (addition amount (composition basis) 1.0 mass%), amide friction modifier ( Transmission oil containing an addition amount (composition basis) 2 mass%), a triazole derivative (addition amount (composition basis) 0.05 mass%), dimethyl silicone (Si addition amount (composition basis) 10 mass ppm), etc. Additive package

Claims

(A) a hydrocarbon base oil having a kinematic viscosity at 40 ° C. of 5 to 20 mm 2 / s and (B) a polybasic acid ester or polyol ester containing two or more ester bonds and having no unsaturated carbon bond Or one or more ester oils, the kinematic viscosity at 40 ° C. is 18 mm 2 / s or less, and the content of component (B) is 0.5 to 50% by mass based on the total amount of the base oil. mixed oil a lubricating oil composition as a base oil, and wherein the kinematic viscosity at 40 ° C. is 4 ~ 25mm 2 / s, kinematic viscosity at 100 ° C. is 2.0 ~ 5.4mm 2 / s A lubricating oil composition for a transmission.
The component (B) is a dibasic acid diester represented by the following formula (1) or a polyol ester represented by the following formulas (2) to (4), or two or more ester oils. The lubricating oil composition for a transmission according to claim 1.

(R 1 to R 6 are each independently a saturated hydrocarbon group having 3 to 36 carbon atoms, R 7 and R 8 are each independently an alkyl group having 1 to 3 carbon atoms, and n is an integer of 4 to 8)
The lubricating oil composition for a transmission according to claim 1 or 2, wherein the content of the polymethacrylate viscosity index improver in the composition is 9% by mass or less based on the total amount of the composition.