JP2009242547A - Automotive transmission oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automotive transmission oil composition which is excellent in seizure prevention performance, and has insulation performance, cooling performance and low temperature lubricity for imparting sufficient coolability even at low temperature. <P>SOLUTION: In the automotive transmission oil composition provided with base oil for lubricant oil, the base oil for lubricant oil comprises ester based synthetic oil by 10 to 100 mass% based on the total quantity of the base oil; wherein, kinematic viscosity at 40°C is <15 mm<SP>2</SP>/s; a viscosity index is ≥120; and density at 15°C is ≥0.85 g/cm<SP>3</SP>, and the heat transfer coefficient of the automotive transmission oil composition is ≥780 W/m<SP>2</SP>×°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transmission oil composition for automobiles, and more particularly to a transmission oil composition for automobiles suitably used for an electric motor-equipped vehicle such as an electric vehicle or a hybrid vehicle.

  In order to improve fuel efficiency in recent years, automobile transmissions are required to improve power transmission efficiency and to be smaller and lighter. As for transmission mechanisms, manual transmissions, automatic transmissions, and recently continuously variable transmissions are more common. Has been installed in some vehicles.

  Meanwhile, electric vehicles equipped with lead livestock batteries, nickel-metal hydride batteries, lithium ion batteries, fuel cells, etc. and equipped with electric motors, or hybrid vehicles using these batteries with an internal combustion engine have been developed. Transmission oil and electric motor oil are used separately in automobiles.

  Recently, in electric vehicles or hybrid vehicles, there is a demand for the common use of these oils and the reduction in size and weight by packaging a transmission and an electric motor. Manual transmission oil, automatic transmission oil or continuously variable transmission oil In addition to the lubrication performance as described above, there has been a demand for a novel oil having both insulating properties and cooling properties as an electric motor oil.

  Transmission oils are required to have heat / oxidation stability, clean dispersibility, wear resistance, seizure resistance, and the like. In order to meet these requirements, transmission oils generally include various additives (antioxidants, detergent dispersants, antiwear agents, rust inhibitors, metal deactivators, friction modifiers) in mineral or synthetic base oils. , Dehumidifying agents, colorants, seal swelling agents, viscosity index improvers, etc.) are used. Such transmission oil has low volume resistivity and insufficient insulation, so when used as an electric motor oil, the electric motor is short-circuited, and the cooling performance is poor due to high kinematic viscosity. And power loss becomes a problem.

  On the other hand, the electric motor oil is required to have insulating properties, cooling properties, etc., and does not require lubricity, and therefore contains almost no additives. Therefore, when electric motor oil is used for a transmission, there is a problem that bearings, gears, and the like are significantly worn. In addition, in electric motors, with the progress of miniaturization and high rotation, there is a strong expectation for the cooling performance of lubricating oil. In other words, in vehicles equipped with an electric motor such as an electric vehicle or a hybrid vehicle, a vehicle gear shift having anti-seizure performance, wear prevention performance, and low-temperature flow performance as transmission oil, and also has insulation and cooling properties that are more than conventional. There is a need for a machine oil composition.

Patent Document 1 discloses a base oil selected from the group consisting of mineral oils, synthetic oils, and mixtures thereof for the purpose of excellent insulating properties, cooling properties, and lubricity, and 0. 1 to 15.0% by mass of (A) a hydrocarbon group-containing zinc dithiophosphate, (B) a triaryl phosphate, (C) a phosphorus compound selected from the group consisting of triaryl thiophosphates and mixtures thereof In addition, an automobile transmission oil composition having a volume resistivity of 1 × 10 ⁷ Ω · m or more at 80 ° C. is disclosed.
International Publication WO2002-097017

  However, the transmission oil composition for automobiles of Patent Document 1 has a problem that not only the cooling property of the electric motor is insufficient, but also a study on the low temperature starting property has not been made.

  An object of the present invention is to provide a transmission or electric motor oil mounted on an electric vehicle, a hybrid vehicle, or the like, or a combination oil thereof, or a transmission and an electric motor packaged, that is, lubrication of the transmission and the electric motor. Useful as an oil for equipment with a shared system, etc. Excellent for seizure prevention performance, insulation performance, cooling performance, and low temperature fluidity to provide sufficient cooling even at low temperatures It is to provide a transmission oil composition.

As a result of intensive studies to solve the above problems, the inventors of the present invention contain an ester-based synthetic oil in an amount of 10% by mass to 100% by mass based on the total amount of the base oil, and a kinematic viscosity at 40 ° C. of less than 15 mm ² / s, By using a lubricating base oil having a viscosity index of 120 or more and a density of 0.85 g / cm ³ or more at 15 ° C., an automotive transmission oil composition having excellent cooling properties and low-temperature fluidity and high insulating properties can be obtained. In other words, the present inventors have found that a transmission oil composition for automobiles having a heat transfer coefficient of 780 W / m ² · ° C. or more can be obtained, thereby completing the present invention.

  The lubricant base oil used in the transmission oil composition for automobiles of the present invention preferably has a dielectric constant of 2.3 or more at 80 ° C.

  The ester-based synthetic oil constituting the lubricating base oil is preferably one or a mixture of two or more selected from the group consisting of monoesters and diesters.

  The transmission oil composition for automobiles of the present invention can be suitably used for hybrid vehicles.

  The transmission oil composition for automobiles of the present invention has excellent anti-seizure performance and is provided with insulating performance, cooling performance, and low-temperature fluidity for imparting sufficient cooling performance even at low temperatures. Therefore, transmission or electric motor oil mounted on an electric vehicle or hybrid vehicle, or a combination oil, or a transmission and an electric motor are packaged, that is, a transmission and electric motor lubrication system is shared. It is useful as a device oil.

Hereinafter, the present invention will be described in detail.
<Ester-based synthetic oil>
The transmission oil composition for automobiles of the present invention (hereinafter sometimes simply referred to as a lubricating oil composition) includes a lubricating base oil having a predetermined property containing a predetermined amount of an ester-based synthetic oil. Hereinafter, the ester synthetic oil will be described.

  The alcohol constituting the ester synthetic oil may be a monohydric alcohol or a polyhydric alcohol, and the acid constituting the ester synthetic oil may be a monobasic acid or a polybasic acid.

  As the monohydric alcohol, those having 1 to 24 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms are usually used. Such alcohols may be linear or branched, It may be saturated or unsaturated. Specific examples of the alcohol having 1 to 24 carbon atoms include methanol, ethanol, linear or branched propanol, linear or branched butanol, and 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 tetradecanol, linear or branched Pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched octadecanol, linear or branched nonade Nord, linear or branched icosanol, linear or branched heicosanol, linear or branched docosanol, linear or branched tricosanol, linear or branched Examples thereof include tetracosanol and a mixture thereof.

  As the polyhydric alcohol, those having 2 to 10 valences, preferably 2 to 6 valences are usually used. Specific examples of the divalent to 10-valent polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, polyethylene glycol (3 to 15 mer of ethylene glycol), propylene glycol, dipropylene glycol, and polypropylene glycol (3 to 3 of propylene glycol). 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 ~ Octamer, eg 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 and the like, and dimers and 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.

  Of the acids constituting the ester used in the present invention, as the monobasic acid, a fatty acid having 2 to 24 carbon atoms is usually used, and the fatty acid may be linear or branched and saturated. Or unsaturated. Specifically, for example, acetic acid, propionic acid, linear or branched butanoic acid, linear or branched pentanoic acid, linear or branched hexanoic acid, linear or branched 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 heptadecanoic acid, linear or branched octadecanoic acid, linear or branched hydroxyoctadecanoic acid, linear or branched nonadecanoic acid, Linear or branched icosanoic acid, linear or branched Saturated fatty acids such as helicosanoic acid, linear or branched docosanoic acid, linear or branched tricosanoic acid, linear or branched tetracosanoic acid, acrylic acid, linear or branched Linear buteneic acid, linear or branched pentenoic acid, linear or branched hexenoic acid, linear or branched heptenoic acid, linear or branched octenoic acid, straight Linear or branched nonenoic acid, linear or branched decenoic acid, linear or branched undecenoic acid, linear or branched dodecenoic acid, linear or branched Tridecenoic acid, linear or branched tetradecenoic acid, linear or branched pentadecenoic acid, linear or branched hexadecenoic acid, linear or branched heptadecenoic acid, linear Linear or branched octadecenoic acid, linear or branched Droxyoctadecenoic acid, linear or branched nonadecenoic acid, linear or branched icosenoic acid, linear or branched heicosenoic acid, linear or branched docosenoic acid, Examples thereof include linear or branched tricosenoic acids, unsaturated fatty acids such as linear or branched tetracosenoic acids, and mixtures thereof. Among these, from the point that lubricity and handleability are further improved, saturated fatty acids having 3 to 20 carbon atoms, unsaturated fatty acids having 3 to 22 carbon atoms and mixtures thereof are particularly preferable, and saturated fatty acids having 4 to 18 carbon atoms. More preferable are unsaturated fatty acids having 4 to 18 carbon atoms and mixtures thereof, and saturated fatty acids having 4 to 18 carbon atoms are most preferable from the viewpoint of oxidative stability.

  Examples of the polybasic acid include dibasic acids having 2 to 16 carbon atoms and trimellitic acid. The dibasic acid having 2 to 16 carbon atoms may be linear or branched, and may be saturated or unsaturated. Specifically, for example, ethanedioic acid, propanedioic acid, linear or branched butanedioic 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 Linear or branched undecanedioic acid, linear or branched dodecanedioic acid, linear or branched tridecanedioic acid, linear or branched tetradecanedioic acid, linear or Branched heptadecanedioic acid, linear or branched hexadecanedioic acid, linear or branched hexenedioic acid, linear or branched heptenedioic acid, linear or branched Octenedioic acid, linear or branched nonene diacid, linear or branched decenedioic acid, linear Or branched undecenedioic acid, linear or branched dodecenedioic acid, linear or branched tridecenedioic acid, linear or branched tetradecenedioic acid, linear or branched Examples thereof include branched heptadecene diacid, linear or branched hexadecene diacid, and mixtures thereof.

The combination of the alcohol and the acid forming the ester synthetic oil is arbitrary and is not particularly limited. As ester which can be used by this invention, the following ester can be mentioned, for example, These ester may be individual, and may combine 2 or more types.
(A) ester of monohydric alcohol and monobasic acid (b) ester of polyhydric alcohol and monobasic acid (c) ester of monohydric alcohol and polybasic acid (d) polyhydric alcohol and polybasic acid Ester (e) Mixture of monohydric alcohol and polyhydric alcohol, mixed ester of polybasic acid (f) Mixed ester of polyhydric alcohol and mixture of monobasic acid and polybasic acid (g) Monohydric alcohol And mixed esters of polyhydric alcohols with monobasic and polybasic acids

  Among these, because of excellent cooling properties, (a) an ester of a monohydric alcohol and a monobasic acid, (b) an ester of a polyhydric alcohol and a monobasic acid, or (c) a monohydric alcohol and a polyhydric acid. It is preferably an ester with a basic acid, and more preferably a monoester of a monohydric alcohol and a monobasic acid, or a diester of a monohydric alcohol and a dibasic acid.

  In the present invention, the ester obtained when a polyhydric alcohol is used as the alcohol component may be a complete ester in which all the hydroxyl groups in the polyhydric alcohol are esterified, or a part of the hydroxyl groups are not esterified and remain as hydroxyl groups. The remaining partial ester may be used. The organic acid ester obtained when a polybasic acid is used as the acid component may be a complete ester obtained by esterifying all carboxyl groups in the polybasic acid, or a part of the carboxyl groups may not be esterified. It may be a partial ester remaining as a carboxyl group.

  The iodine value of the ester-based synthetic oil used in the present invention is preferably 0 to 5, more preferably 0 to 3, further preferably 0 to 2, and most preferably 0 to 1. When the iodine value of the ester-based synthetic oil is within the above range, the obtained lubricating oil has good heat and oxidation stability. In addition, the iodine value here is a value measured by an indicator titration method according to JIS K 0070 “Method for measuring acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponified value of a chemical product”. Say.

The kinematic viscosity of the ester synthetic oil used in the present invention is not particularly limited, but the kinematic viscosity at 40 ° C. is preferably 50 mm ² / s or less, more preferably 30 mm ² / s or less, and still more preferably Is 20 mm ² / s or less, particularly preferably 15 m ² / s or less. The kinematic viscosity of the ester synthetic oil is preferably 1 mm ² / s or more, more preferably 3 mm ² / s or more, and further preferably 5 mm ² / s or more.

  Although there is no restriction | limiting in particular in the pour point and viscosity index of ester type synthetic oil used for this invention, It is preferable that it is -10 degrees C or less, and it is more preferable that it is -20 degrees C or less. The viscosity index is preferably 100 or more and 200 or less.

  The ester synthetic oil 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 base oil of the composition of the present invention may be composed only of ester synthetic oil (that is, the ester content is 100% by mass), but the kinematic viscosity at 40 ° C. is less than 15 mm ² / s. As long as the conditions of viscosity index 120 or higher and density at 15 ° C. of 0.85 g / cm ³ or higher are satisfied, other base oils can be blended as necessary.

<Other base oils>
The base oil other than the ester-based synthetic oil that can be contained in the lubricating oil composition of the present invention may be either mineral oil or synthetic oil, or a mixture of two or more of these.

  Specifically, as a mineral base oil, a lubricating oil fraction obtained by subjecting crude oil to atmospheric distillation obtained under reduced pressure is subjected to solvent removal, solvent extraction, hydrocracking, solvent removal. Lubricant produced by isomerizing GTL WAX (gas-tried wax) produced by wax, hydrorefining, etc., or refined by wax isomerization mineral oil, Fischer-Tropsch process, etc. An oil base oil etc. can be illustrated. In particular, a base oil obtained by hydrocracking / hydroisomerizing a feedstock oil containing normal paraffin so that the urea adduct value is 4% by mass or less and the viscosity index is 100 or more is preferable.

  Specific examples of synthetic base oils include polybutene or hydrides thereof; poly-α-olefins such as 1-octene oligomers and 1-decene oligomers or hydrides thereof; dicarboxylic acids such as dibutyl maleate and 2 carbon atoms. Copolymers with -30 [alpha] -olefins; aromatic synthetic oils such as alkyl naphthalene, alkyl benzene and aromatic esters, or mixtures thereof. In particular, polybutene or hydrides thereof; poly-α-olefins such as 1-octene oligomers and 1-decene oligomers or hydrides thereof can be preferably used.

  When using a base oil other than these ester-based synthetic oils, the content of the ester-based base oil must be 10% by mass or more, preferably 30% by mass or more, based on the total amount of the base oil. 40% by mass or more, more preferably 50% by mass or more, particularly preferably 70% by mass or more, and most preferably 90% by mass or more. If the content of the ester synthetic oil is too small, sufficient cooling performance may not be obtained.

<Lubricant base oil>
The 40 ° C. kinematic viscosity of the lubricating base oil used in the present invention needs to be less than 15 mm ² / s, preferably 14 mm ² / s or less, more preferably 13 mm ² / s or less, and even more preferably 12 mm. ² / s or less. On the other hand, the kinematic viscosity at 40 ° C. is preferably 5 mm ² / s or more, more preferably 6 mm ² / s or more, and further preferably 8 mm ² / s or more. If the 40 ° C. kinematic viscosity is too large, the low-temperature viscosity characteristics may deteriorate, and sufficient cooling performance may not be obtained. On the other hand, if it is too small, the formation of an oil film at the lubrication site is insufficient, so that the lubricity is inferior, and the evaporation loss of the lubricating base oil may increase.

The kinematic viscosity at 100 ° C. of the lubricating base oil used in the present invention is not particularly limited, but is preferably 6.5 mm ² / s or less, more preferably 5.0 mm ² / s or less, and even more preferably 4.5 mm. ² / s or less, particularly preferably 4.0 mm ² / s or less, and most preferably 3.5 mm ² / s or less. The kinematic viscosity at 100 ° C. of the lubricating base oil used in the present invention is preferably 1 mm ² / s or more, more preferably 1.5 mm ² / s or more, and 2.0 mm ² / s or more. More preferably. When the kinematic viscosity at 100 ° C. of the lubricating base oil is too large, the low-temperature viscosity characteristics may be deteriorated and sufficient cooling performance may not be obtained. Conversely, when the kinematic viscosity at 100 ° C. of the lubricating base oil is too small, the formation of an oil film at the lubricating location becomes insufficient, resulting in poor lubricity, and the evaporation loss of the lubricating base oil may increase. is there.

  The viscosity index of the lubricating base oil used in the present invention is 120 or more in order to obtain excellent viscosity characteristics from low temperature to high temperature, and to prevent evaporation even at low viscosity. Is preferably 130 or more, more preferably 140 or more, still more preferably 150 or more, and particularly preferably 160 or more. There is no particular limitation on the upper limit of the viscosity index.

Specifically, the density (ρ ₁₅ ) at 15 ° C. of the lubricating base oil used in the present invention is 0.850 or more, preferably 0.860 or more, more preferably 0.870 or more, and still more preferably. 0.880 or more.

  In addition, the density in 15 degreeC said by this invention means the density measured in 15 degreeC based on JISK2249-1995.

  The iodine value of the lubricating base oil used in the present invention is preferably 1 or less, more preferably 0.5 or less, still more preferably 0.3 or less, and particularly preferably 0.15 or less. Further, the iodine value may be less than 0.01, but is preferably 0.01 or more, more preferably 0.05 or more, from the viewpoint of small effects that are commensurate with the iodine value and economy. By setting the iodine value of the lubricating base oil to 1 or less, the heat and oxidation stability can be dramatically improved, and further, the cooling performance and the insulation performance can be improved.

  Further, the pour point of the lubricating base oil used in the present invention depends on the viscosity grade of the lubricating base oil, but is preferably −15 ° C. or lower, more preferably −20 ° C. or lower, and further preferably −25 ° C. or lower. Most preferably, it is −30 ° C. or lower. If the pour point is too large, the low temperature fluidity of the entire composition using the lubricating base oil may be reduced. In addition, the pour point as used in the field of this invention means the pour point measured based on JISK2269-1987.

  The dielectric constant at 80 ° C. of the lubricating base oil used in the present invention is preferably 2.3 or more, more preferably 2.5 or more, and further preferably 3.0 or more. The dielectric constant of the lubricating base oil is preferably 30 or less, more preferably 15 or less, and even more preferably 10 or less. If the dielectric constant at 80 ° C. is too large, the insulation performance may be degraded. Conversely, if the dielectric constant at 80 ° C. is too small, the cooling performance may be reduced. The dielectric constant was measured according to JIS C 2101 23.

The volume resistivity at 80 ° C. of the lubricating base oil used in the present invention is preferably 0.01 × 10 ¹² Ω · cm or more, more preferably 0.02 × 10 ¹² Ω · cm or more, and still more preferably. It is 0.05 × 10 ¹² Ω · cm or more. When the volume resistivity at 80 ° C. is too small, there is a risk of causing a decrease in insulation. The volume resistivity was measured according to JIS C 2101 24.

<Additives>
In addition, the lubricating oil composition of the present invention can contain various additives as necessary as long as the cooling property, the low temperature fluidity and the insulating property 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 additives include metal detergents, ashless dispersants, antioxidants, extreme pressure agents, antiwear agents, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, Examples include rust preventives, demulsifiers, metal deactivators, and antifoaming agents. These additives may be used individually by 1 type, and may be used in combination of 2 or more type.

  The lubricating oil composition of the present invention may contain one or more selected from sulfonate detergents, salicylate detergents, and phenate detergents as metal detergents. As these metallic detergents, any of normal salts, basic salts and overbased salts with alkali metals or alkaline earth metals can be blended.

  In the lubricating oil composition of the present invention, any ashless dispersant used in lubricating oils can be used as the ashless dispersant. For example, a linear or branched alkyl group or alkenyl group having 40 to 400 carbon atoms can be used. Mono- or bissuccinimide having at least one in the molecule, benzylamine having at least one alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, or an alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule And polyamines having at least one of them, or modified products of these boron compounds, carboxylic acids, phosphoric acids and the like. In use, one kind or two or more kinds arbitrarily selected from these can be blended.

  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.

  As the extreme pressure agent and antiwear agent that can be used in the lubricating oil composition of the present invention, any extreme pressure agent and antiwear agent used in lubricating oil can be used. For example, sulfur-based, phosphorus-based, sulfur-phosphorus extreme pressure agents and the like can be used. Specifically, phosphites, thiophosphites, dithiophosphites, trithiophosphites Esters, phosphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts thereof, metal salts thereof, derivatives thereof, dithiocarbamate, zinc dithiocarbamate, molybdenum dithiocarbamate, disulfide , Polysulfides, sulfurized olefins, sulfurized fats and oils, and the like.

  As the viscosity index improver, polymethacrylate viscosity index improver, olefin copolymer viscosity index improver, styrene-diene copolymer viscosity index improver, styrene-maleic anhydride copolymer viscosity index improver or poly Examples thereof include alkylstyrene viscosity index improvers. The weight average molecular weight of these viscosity index improvers is usually 800 to 1,000,000, preferably 100,000 to 900,000.

  As the pour point depressant, for example, a polymethacrylate polymer compatible with the lubricating base oil to be used can be used.

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

  Examples of the rust inhibitor 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, and polyoxyethylene alkyl naphthyl ether.

  Examples of metal deactivators include imidazoline, pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazoles or derivatives thereof, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazolyl-2,5-bis. Examples thereof include dialkyldithiocarbamate, 2- (alkyldithio) benzimidazole, and 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, or o -Hydroxybenzyl alcohol etc. are mentioned.

  When these additives are contained in the lubricating oil composition of the present invention, the content thereof is 1 to 20% by mass based on the total amount of the composition.

<Lubricating oil composition>
The kinematic viscosity at 40 ° C. of the lubricating oil composition of the present invention is not particularly limited, but the upper limit is preferably 30 mm ² / s or less, more preferably 25 mm ² / s or less, and still more preferably 20 mm ² / s. Hereinafter, it is particularly preferably 15 mm ² / s or less. The lower limit is preferably 5 mm ² / s or more, more preferably 8 mm ² / s or more, and particularly preferably 10 mm ² / s or more. If the kinematic viscosity at 40 ° C. is too small, there is a risk of problems in oil film retention and evaporation at the lubrication site, and if the kinematic viscosity at 40 ° C. is too large, the cooling property may be insufficient.

The kinematic viscosity at 100 ° C. of the lubricating oil composition of the present invention is not particularly limited, but the upper limit is preferably 7.0 mm ² / s or less, more preferably 6.0 mm ² / s or less, more preferably 5 mm ² / s or less, particularly preferably 4.0 mm ² / s or less. Moreover, as a lower limit, Preferably it is 1.5 mm < ² > / s or more, More preferably, it is 2.0 mm < ² > / s or more, Most preferably, it is 2.5 mm < ² > / s or more. If the kinematic viscosity at 100 ° C. is too small, there may be a problem in oil film retention and evaporability at the lubrication site. If the kinematic viscosity at 100 ° C. is too large, the cooling property may be insufficient.

The lower limit value of the heat transfer coefficient of the lubricating oil composition of the present invention is 780 W / m ² · ° C or more, more preferably 785 W / m ² · ° C or more, more preferably 790 W / m ² · ° C or more, Particularly preferably, it is 795 W / m ² · ° C. or more. Although there is no restriction | limiting in particular in an upper limit, Preferably it is 1100 W / m < ² > * C or less, More preferably, it is 1000 W / m < ² > * C or less, Most preferably, it is 900 W / m < ² > * C or less. When the heat transfer coefficient is too small, the cooling property of the transmission lubricating oil composition is insufficient, and when the heat transfer coefficient is too large, there is a risk of problems in oil film retention and lubricity at the lubrication site.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these.

(Examples 1-3, Comparative Examples 1-4)
As shown in Table 1, lubricating oil compositions of the present invention (Examples 1 to 3) and comparative lubricating oil compositions (Comparative Examples 1 to 3) were prepared. About the obtained composition, the heat transfer coefficient was measured and the result was also written together in Table 1. As the additive, 3% by mass of an additive package for transmission oil containing an antiwear agent, a friction modifier, an antioxidant and the like was uniformly added. In Comparative Example 4, a commercially available ATF (manufactured by Nippon Oil Corporation) was used.

The contents of the base oil shown in Table 1 are as follows.
Ester base oil 1: monoester (ester of i-C ₈ alcohol and oleic acid)
Ester base oil 2: Diester (ester of i-C ₈ alcohol and C ₉ dicarboxylic acid)
Ester base oil 3: Neopentyl glycol ester (ester of neopentyl glycol and i-C ₈ carboxylic acid)
Mineral oil base oil 1: hydrocracked mineral oil (40 ° C. kinematic viscosity: 9.3 mm ² / s, viscosity index: 111)
Mineral oil base oil 2: Solvent refined mineral oil (40 ° C. kinematic viscosity: 95.0 mm ² / s, viscosity index: 97)
Mineral oil base oil 3: Solvent refined mineral oil (40 ° C. kinematic viscosity: 480.9 mm ² / s, viscosity index: 97)

(Measurement of heat transfer coefficient)
Using the apparatus of FIG. 1, the heat between the lubricating oil and the cooling water when the heater heat amount (250 W), the cooling water flow rate (1000 ml / min) and the stirring speed (300 rpm) are constant and the sample oil temperature reaches equilibrium. The transfer coefficient was obtained by the following equation.
_{h = q / A (T h} -T c)
Here, h: heat transfer coefficient, q: the heat movement amount, _{T h:} lubricating oil temperature, _{T c:} the coolant temperature, A: a heat exchange area.

  Since the transmission oil composition for automobiles of the present invention (Examples 1 to 3) is superior in insulation and cooling properties to the composition of the comparative example, it is mounted on an electric automobile or a hybrid car. It may be useful as a transmission or electric motor oil, or a combination oil thereof, or an oil for a device in which the transmission and the electric motor are packaged, that is, the lubrication system of the transmission and the electric motor is shared. I understood.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the invention is limited to the embodiments disclosed herein. However, the invention can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification, and an automotive transmission oil composition that includes such a change is also included in the technical scope of the present invention. Must be understood as being.

It is a conceptual diagram of the apparatus used for the measurement of a heat transfer coefficient.

Claims (3)

The ester-based synthetic oil is contained in an amount of 10% by mass to 100% by mass based on the total amount of base oil, the kinematic viscosity at 40 ° C. is less than 15 mm ² / s, the viscosity index is 120 or more, and the density at 15 ° C. is 0.85 g / cm ³ or more. An automotive transmission oil composition comprising a lubricating base oil and having a heat transfer coefficient of 780 W / m ² · ° C. or higher. The transmission oil composition for automobiles according to claim 1, wherein the lubricating base oil has a dielectric constant at 80 ° C of 2.3 or more. The transmission oil composition for automobiles according to claim 1 or 2, which is used for a hybrid vehicle.

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