Transmission fluid compositions for automobiles

Abstract

A transmission fluid composition for automobiles comprises a lubricating base oil, (A) an oil-soluble metal salt overbased with a specific alkaline earth metal borate, and (B) a sulfur-containing extreme pressure additive. The transmission fluid can enhance a metallic friction coefficient, leading to the achievement of improved transmission torque.

Description

TECHNICAL FIELD

[0001] The present invention relates to transmission fluid compositions for automobiles and more specifically to those which can be used advantageously for automatic transmissions, particularly for metal belt-type continuously variable transmissions.

BACKGROUND ART

[0002] Recently, metal belt-type continuously variable transmissions have been spotlighted as automobile transmission because their energy loss by shifting is small. The transmissions of this type have a mechanism which transmits torque by friction between a metal belt and a pair of metal pulleys looped therearound and conducts gear shift by changing the radius ratio of the pulleys. Therefore, it is extremely important that a lubricating oil used for such metal belt-type continuously variable transmissions has capabilities of increasing the friction coefficient between the metal belt and the pulleys. Furthermore, such a lubricating oil is also required to have capabilities as a lubricating oil for gears taking out torque and bearings supporting the gears and capabilities as a hydraulic pressure control medium for determining gear ratios, i.e., as a hydraulic oil.

[0003] In the case where a continuously variable transmission is equipped with a front/reverse switching wet clutch and a lock-up system for the torque converter, the lubricating oil is required to have capabilities of control the friction characteristics of the wet clutch in addition to the above capabilities.

[0004] Since the lubricating oil for metal belt-type continuously variable transmissions is required to possess various characteristic performances as described above, automatic transmission fluids (ATFs) have generally been used in automobiles equipped with a 1800 CC or less displacement engine with a small engine torque. However, when an ATF is used as a lubricating oil for a metal belt-type continuously variable transmission, it is excellent in capabilities as a hydraulic oil and in functional capabilities of controlling the friction characteristics of the wet clutch but is poor in providing sufficient friction coefficient between the belt and the pulleys. Therefore, so far, it has been found difficult to mount a metal belt-type continuously variable transmission in an automobile equipped with a 2000 cc or more displacement engine. A metal belt-type continuously variable transmission can perform its peculiar silent and fuel efficient characteristics particularly when mounted on an automobile equipped with a 2500 cc or 3000 cc or even higher displacement engine. It is now very important to develop a lubricating oil which can transmit larger torque and provide the higher friction coefficient between the metal parts.

[0005] Therefore, the present invention was made in view of the current circumstances and intends to provide a transmission fluid composition for automobiles which can increase the friction coefficient between the metal parts and thus can obtain a larger torque transmission capacity.

DISCLOSURES OF THE INVENTION

[0006] After an extensive research and development, the present invention was achieved based on the finding that a transmission fluid for automobiles capable of further enhancing the friction coefficient between metals can be obtained using an oil-soluble metal salt overbased with a specific alkaline earth metal borate in combination with a specific extreme pressure additive.

[0007] That is, according to the present invention, there is provided a transmission fluid composition for automobiles which comprises a lubricating base oil, (A) an oil-soluble metal salt overbased with an alkaline earth metal borate, in an amount of 0.001 to 0.3 percent by mass in terms of boron, based on the total mass of the composition and (B) a sulfur-containing extreme pressure additive.

[0008] In the transmission fluid composition for automobiles of the present invention, the oil-soluble metal salt of Component (A) is preferably an alkaline earth metal sulfonate and/or salicylate. The alkaline earth metal borate of Component (A) is preferably calcium borate and/or magnesium borate.

[0009] In the transmission fluid composition for automobiles of the present invention, Component (B) is preferably at least one compound selected from the group consisting of thiophosphites, dithiophosphites, trithiophosphites, thiophosphates, dithiophosphates, trithiophosphates, mono-, di-, and tri-substituted esters thereof, and salts thereof. Component (B) is preferably contained in an amount of 0.005 to 0.3 percent by mass in terms of sulfur and/or 0.005 to 0.1 percent by mass in terms of phosphorus, based on the total mass of the composition.

[0010] The transmission fluid composition for automobiles of the present invention further contains preferably (C) an ashless dispersant.

[0011] The transmission fluid composition for automobiles of the present invention further contains preferably at least one type of additive selected from the group consisting of (D) metal detergents, (E) friction modifiers, (F) anti-oxidants, and (G) viscosity index improvers.

[0012] The transmission fluid composition for automobiles of the present invention is preferably used for automatic transmissions and/or continuously variable transmissions.

[0013] The transmission fluid composition for automobiles of the present invention is preferably used for metal belt-type continuously variable transmissions.

[0014] The present invention will be described below in more details.

[0015] The lubricating base oil of the transmission fluid composition for automobiles of the present invention may be any of mineral oils and/or synthetic oils which have conventionally been used as base oils of lubricating oils.

[0016] Specific examples of mineral oils are paraffinic or naphthenic oils which can be obtained by subjecting a lubricating oil fraction produced by atmospheric- or vacuum-distilling a crude oil, to any one or more refining processes selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, washing with sulfuric acid, and clay treatment; and n-paraffines. Base oils obtained by a high-degree hydrocracking process or those obtained by isomerizing GTL Wax (Gas To Liquid Wax), both of which methods are capable of further decreasing the aromatic content and sulfur content are also preferably used.

[0017] No particular limitation is imposed on synthetic oils. Examples of synthetic oils include poly-&agr; -olefins such as 1-octene oligomer, 1-decene oligomer, and ethylene-propylene oligomer, and hydrides thereof; isobutene oligomer and hydrides thereof; isoparaffines; alkylbenzenes; alkylnaphthalenes; diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl cebacate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethyl hexanoate, and pentaerythritol pelargonate; polyoxyalkylene glycols; dialkyldiphenyl ethers; and polyphenyl ethers.

[0018] No particular limitation is imposed on the kinematic viscosity at 100° C. of the lubricating base oil. However, the kinematic viscosity at 100° C. is 1 to 20 mm2/s and preferably 2 to 10 mm2/s.

[0019] Component (A) of the transmission fluid composition for automobiles of the present invention is an oil-soluble metal salt overbased with an alkaline earth metal borate.

[0020] Component (A), i.e., an oil-soluble metal salt overbased with an alkaline earth metal borate can be obtained by reacting an oil-soluble metal salt such as alkaline earth metal sulfonates, alkaline earth metal salicylates, alkaline earth metal phenates, and alkaline earth metal phosphonates with an alkaline earth metal hydride or oxide and boric acid or boric anhydride.

[0021] Preferred alkaline earth metal sulfonates are alkaline earth metal salts of alkyl aromatic sulfonic acids obtained by sulfonating alkyl aromatic compounds having a molecular weight of 100 to 1,500 and preferably 200 to 700. Specific examples of the alkyl aromatic sulfonic acids include petroleum sulfonic acids and synthetic sulfonic acids.

[0022] Petroleum sulfonic acids may be those obtained by sulfonating alkyl aromatic compounds contained in the lubricant fraction of a mineral oil or mahogany acid by-produced upon production of white oil. The synthetic sulfonic acid may be those obtained by sulfonating an alkyl benzene having a straight-chain or branched alkyl group, by-produced from a plant for producing an alkyl benzene used as the raw materials of detergents or those obtained by sulfonating an alkylnaphthalene such as dinonylnaphthalene. Although not restricted, sulfonating agents used for sulfonating these alkyl aromatic compounds may be fuming sulfuric acids and sulfuric acid.

[0023] Preferred alkaline earth metal salicylates are alkaline earth metal salts of alkyl salicylic acids having at least one straight-chain or branched alkyl group having 4 to 30, preferably 6 to 18 carbon atoms.

[0024] Preferred alkaline earth metal phenates are alkaline earth metal salts of alkylphenolsulfides obtained by reacting alkylphenols having at least one straight-chain or branched alkyl group having 4 to 30, preferably 6 to 18 carbon atoms with sulfur, or Mannich reaction products obtained by reacting such alkylphenols with formaldehyde.

[0025] Examples of the alkaline earth metals include magnesium, calcium, and barium, among which calcium and/or magnesium are preferably used.

[0026] In the present invention, alkaline earth metal sulfonates and/or alkaline earth metal salicylates are preferably used for the oil-soluble metal salt from the aspect of friction characteristics.

[0027] No particular limitation is imposed on the method of producing Component (A) . For example, Component (A) may be obtained by reacting any of the above-described oil-soluble metal salts, an alkaline earth metal hydride or oxide, and either boric acid or anhydride borate in the presence of water; an alcohol such as methanol, ethanol, propanol, or butanol; or a diluting solvent such as benzene, toluene, or xylene, at a temperature of 20 to 200° C. for 2 to 8 hours and heating the reaction product at a temperature of 100 to 200° C. so as to remove the water and if necessary the alcohol and the diluting solvent. The conditions for these reactions are arbitrarily selected depending on the amounts of the raw materials and the reaction product.

[0028] The details of the production method are described in for example, Japanese Patent Laid-Open Publication Nos. 60-116688, 61-204298, and 3-68695. Alternatively, Component (A) may be those obtained by conducting the above reaction but conducted in the presence of carbon dioxide gas and those partially containing an alkaline earth metal carbonate, obtained by the above reaction conducted using an oil-soluble metal salt containing an alkaline earth metal carbonate as the reaction raw material. However, in the present invention, preferred are those containing no alkaline earth metal carbonate.

[0029] The average particle size of Component (A) used in the present invention is preferably 0.1 &mgr;m or smaller and particularly preferably from 0.001 to 0.05 &mgr;m.

[0030] The base number of Component (A) is preferably 100 mgKOH/g or more, more preferably from 150 to 300 mgKOH/g, and particularly preferably from 150 to 220 mgKOH/g. The term “base number” used herein denotes a base number measured by the perchloric acid potentiometric titration method in accordance with section 7 of JIS K2501 (1992) “Petroleum products and lubricants-Determination of neutralization number”.

[0031] Preferred for Component (A) are those containing an alkaline earth metal in an amount of 1.0 to 20 percent by mass and preferably 2.0 to 16 percent by mass and boron in an amount of 0.1 to 20 percent by mass and preferably 0.5 to 10 percent by mass.

[0032] The content of Component (A) in the transmission fluid composition for automobiles of the present invention is 0.001 percent by mass or more and preferably 0.003 percent by mass or more in terms of boron, based on the total mass of the composition. The content of Component (A) is 0.3 percent by mass or less, preferably 0.1 percent by mass or less, and particularly preferably 0.05 percent by mass or less. Component (A) of less than 0.001 percent by mass would fail to obtain a large torque transmission capacity, while Component (A) of more than 0.3 percent by mass would fail to achieve advantageous effects as expected with the amount.

[0033] Component (B) of the transmission fluid composition for automobiles of the present invention is a sulfur-containing extreme pressure additive. Specific examples of Component (B) include (B-1) sulfur- and phosphorus-containing compounds such as thiophosphite- and thiophosphate-based compounds and (B-2) sulfur-containing compounds such as thiazole compounds, thiadiazole compounds, dithiocarbamate compounds, dihydrocarbylpolysulfide compounds, and sulfurized ester compounds.

[0034] Examples of (B-1) sulfur- and phosphorus-containing compounds are compounds represented by formulas (1) and (2) and salts thereof: 1

[0035] In formula (1), at least one of X1, X2, and X3 is sulfur, and the others are oxygen. R1, R2, and R3 are each independently hydrogen or a hydrocarbon group having 1 to 30 carbon atoms.

[0036] In formula (2) , X4, X5, and X6 are each independently oxygen or sulfur. R4, R5, and R 6are each independently hydrogen or a hydrocarbon group having 1 to 30 carbon atoms.

[0037] Specific examples of hydrocarbon groups having 1 to 30 carbon atoms of R1 to R6 include alkyl, cycloalkyl, alkyl-substituted cycloalkyl, alkenyl, aryl, alkyl-substituted aryl, and arylalkyl groups.

[0038] Examples of the alkyl group include straight-chain or branched alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl groups.

[0039] Examples of the cycloalkyl group include those having 5 to 7 carbon atoms, such as cyclopentyl, cyclohexyl, and cycloheptyl groups.

[0040] Examples of the alkylcycloalkyl groups include those having 6 to 11 carbon atoms, such as methylcyclopentyl, dimethylcyclopentyl, methylethylcyclopentyl, diethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, methylethylcyclohexyl, diethylcyclohexyl, methylcycloheptyl, dimethylcycloheptyl, methylethylcycloheptyl, and diethylcycloheptyl groups, of which the alkyl groups may bond to any position of the cycloalkyl groups.

[0041] Examples of the alkenyl group include butenyl, pentenyl, hexenyl, heptenyl, octenyl, noneyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, and octadecenyl groups, all of which may be straight-chain or branched and the position of which the double bonds may vary.

[0042] Examples of the aryl group include phenyl and naphtyl groups.

[0043] Examples of the alkylaryl group include those having 7 to 18 carbon atoms, such as tolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, and dodecylphenyl groups, of which the alkyl groups may be straight-chain or branched and may bond to any position of the aryl groups.

[0044] Examples of the arylalkyl groups include those having 7 to 12 carbon atoms, such as benzyl, phenylethyl, phenylpropyl, phenylbutyl, phenylpentyl, and phenylhexyl groups, of which the alkyl groups may be straight-chain or branched.

[0045] Hydrocarbon groups having 1 to 30 carbon atoms of R1 to R6are preferably alkyl groups having 1 to 30 carbon atoms or aryl groups having 6 to 24 carbon atoms, more preferably alkyl groups having 4 to 20 carbon atoms, and further more preferably alkyl groups having 6 to 18 carbon atoms.

[0046] Examples of compounds represented by formula (1) include the following sulfur- and phosphorus-containing compounds:

[0047] thiophosphites;

[0048] monoalkylthiophosphites of which the alkyl group may be straight-chain or branched, such as monopropylthiophosphite, monobutylthiophosphite, monopentylthiophosphite, monohexylthiophosphite, monoheptylthiophosphite, monooctylthiophosphite, and monolaurylthiophosphite;

[0049] mono((alkyl)aryl)thiophosphites, such as monophenylthiophosphite and monocresylthiophosphite; dialkylthiophosphites of which the alkyl groups may be straight-chain or branched, such as dipropylthiophosphite, dibutylthiophosphite, dipentylthiophosphite, dihexylthiophosphite, diheptylthiophosphite, dioctylthiophosphite, and dilaurylthiophosphite;

[0050] di((alkyl)aryl)thiophosphites such as diphenylthiophosphite and dicresylthiophosphite;

[0051] trialkylthiophosphites of which the alkyl groups may be straight-chain or branched, such as tripropylthiophosphite, tributylthiophosphite, tripentylthiophosphite, trihexylthiophosphite, triheptylthiophosphite, trioctylthiophosphite, and trilaurylthiophosphite;

[0052] tri((alkyl)aryl)thiophosphites such as triphenylthiophosphite and tricresylthiophosphite; dithiophosphite;

[0053] monoalkyldithiophosphites of which the alkyl groups may be straight-chain or branched, such as monopropyldithiophosphite, monobutyldithiophosphite, monopentyldithiophosphite, monohexyldithiophosphite, monoheptyldithiophosphite, monooctyldithiophosphite, and monolauryldithiophosphite;

[0054] mono((alkyl)aryl)dithiophosphites, such as monophenyldithiophosphite and monocresyldithiophosphite;

[0055] dialkyldithiophosphites of which the alkyl groups may be straight-chain or branched, such as dipropyldithiophosphite, dibutyldithiophosphite, dipentyldithiophosphite, dihexyldithiophosphite, diheptyldithiophosphite, dioctyldithiophosphite, and dilauryldithiophosphite;

[0056] di((alkyl)aryl)dithiophosphites such as diphenyldithiophosphite and dicresyldithiophosphite;

[0057] trialkyldithiophosphites of which the alkyl groups may be straight-chain or branched, such as tripropyldithiophosphite, tributyldithiophosphite, tripentyldithiophosphite, trihexyldithiophosphite, triheptyldithiophosphite, trioctyldithiophosphite, and trilauryldithiophosphite;

[0058] tri((alkyl)aryl)dithiophosphites such as triphenyldithiophosphite and tricresyldithiophosphite;

[0059] trithiophosphites;

[0060] monoalkyltrithiophosphites of which the alkyl groups may be straight-chain or branched, such as monopropyltrithiophosphite, monobutyltrithiophosphite, monopentyltrithiophosphite, monohexyltrithiophosphite, monoheptyltrithiophosphite, monooctyltrithiophosphite, and monolauryltrithiophosphite;

[0061] mono((alkyl)aryl)trithiophosphites, such as monophenyltrithiophosphite and monocresyltrithiophosphite;

[0062] dialkyltrithiophosphites of which the alkyl groups may be straight-chain or branched, such as dipropyltrithiophosphite, dibutyltrithiophosphite, dipentyltrithiophosphite, dihexyltrithiophosphite, diheptyltrithiophosphite, dioctyltrithiophosphite, and dilauryltrithiophosphite;

[0063] di((alkyl)aryl)trithiophosphites such as diphenyltrithiophosphite and dicresyltrithiophosphite;

[0064] trialkyltrithiophosphites of which the alkyl groups may be straight-chain or branched, such as tripropyltrithiophosphite, tributyltrithiophosphite, tripentyltrithiophosphite, trihexyltrithiophosphite, triheptyltrithiophosphite, trioctyltrithiophosphite, and trilauryltrithiophosphite;

[0065] tri((alkyl)aryl)trithiophosphites such as triphenyltrithiophosphite and tircresyltrithiophosphite;

[0066] and mixtures thereof.

[0067] In the present invention, preferably two or more of X1 to X3 are sulfur.

[0068] Examples of compounds represented by formula (2) include the following sulfur- and phosphorus-containing compounds:

[0069] thiophosphates;

[0070] monoalkylthiophosphates of which the alkyl groups may be straight-chain or branched, such as monopropylthiophosphate, monobutylthiophosphate, monopentylthiophosphate, monohexylthiophosphate, monoheptylthiophosphate, monooctylthiophosphate, and monolaurylthiophosphate;

[0071] mono((alkyl)aryl)thiophosphates, such as monophenylthiophosphate and monocresylthiophosphate;

[0072] dialkylthiophosphates of which the alkyl groups may be straight-chain or branched, such as dipropylthiophosphate, dibutylthiophosphate, dipentylthiophosphate, dihexylthiophosphate, diheptylthiophosphate, dioctylthiophosphate, and dilaurylthiophosphate;

[0073] di((alkyl)aryl)thiophosphates such as diphenylthiophosphate and dicresylthiophosphate;

[0074] trialkylthiophosphates of which the alkyl groups may be straight-chain or branched, such as tripropylthiophosphate, tributylthiophosphate, tripentylthiophosphate, trihexylthiophosphate, triheptylthiophosphate, trioctylthiophosphate, and trilaurylthiophosphate;

[0075] tri((alkyl)aryl)thiophosphates such as triphenylthiophosphate and tircresylthiophosphate;

[0076] dithiophosphates;

[0077] monoalkyldithiophosphates of which the alkyl group may be straight-chain or branched, such as monopropyldithiophosphate, monobutyldithiophosphate, monopentyldithiophosphate, monohexyldithiophosphate, monoheptyldithiophosphate, monooctyldithiophosphate, and monolauryldithiophosphate;

[0078] mono((alkyl)aryl)dithiophosphates, such as monophenyldithiophosphate and monocresyldithiophosphate;

[0079] dialkyldithiophosphates of which the alkyl groups may be straight-chain or branched, such as dipropyldithiophosphate, dibutyldithiophosphate, dipentyldithiophosphate, dihexyldithiophosphate, diheptyldithiophosphate, dioctyldithiophosphate, and dilauryldithiophosphate;

[0080] di((alkyl)aryl)dithiophosphates such as diphenyldithiophosphate and dicresyldithiophosphate;

[0081] trialkyldithiophosphates of which the alkyl groups may be straight-chain or branched, such as tripropyldithiophosphate, tributyldithiophosphate, tripentyldithiophosphate, trihexyldithiophosphate, triheptyldithiophosphate, trioctyldithiophosphate, and trilauryldithiophosphate;

[0082] tri((alkyl)aryl)dithiophosphates such as triphenyldithiophosphate and tricresyldithiophosphate;

[0083] trithiophosphates;

[0084] monoalkyltrithiophosphates of which the alkyl groups may be straight-chain or branched, such as monopropyltrithiophosphate, monobutyltrithiophosphate, monopentyltrithiophosphate, monohexyltrithiophosphate, monoheptyltrithiophosphate, monooctyltrithiophosphate, and monolauryltrithiophosphate;

[0085] mono((alkyl)aryl)trithiophosphates, such as monophenyltrithiophosphate and monocresyltrithiophosphate;

[0086] dialkyltrithiophosphates of which the alkyl groups may be straight-chain or branched, such as dipropyltrithiophosphate, dibutyltrithiophosphate, dipentyltrithiophosphate, dihexyltrithiophosphate, diheptyltrithiophosphate, dioctyltrithiophosphate, and dilauryltrithiophosphate;

[0087] di((alkyl)aryl)trithiophosphates such as diphenyltrithiophosphate and dicresyltrithiophosphate;

[0088] trialkyltrithiophosphates of which the alkyl groups may be straight-chain or branched, such as tripropyltrithiophosphate, tributyltrithiophosphate, tripentyltrithiophosphate, trihexyltrithiophosphate, triheptyltrithiophosphate, trioctyltrithiophosphate, and trilauryltrithiophosphate;

[0089] tri((alkyl)aryl)trithiophosphates such as triphenyltrithiophosphate and tricresyltrithiophosphate;

[0090] tetrathiophosphates; monoalkyltetrathiophosphates of which the alkyl groups may be straight-chain or branched, such as monopropyltetrathiophosphate, monobutyltetrathiophosphate, monopentyltetrathiophosphate, monohexyltetrathiophosphate, monoheptyltetrathiophosphate, monooctyltetrathiophosphate, and monolauryltetrathiophosphate;

[0091] mono((alkyl)aryl)tetrathiophosphates, such as monophenyltetrathiophosphate and monocresyltetrathiophosphate;

[0092] dialkyltetrathiophosphates of which the alkyl groups may be straight-chain or branched, such as dipropyltetrathiophosphate, dibutyltetrathiophosphate, dipentyltetrathiophosphate, dihexyltetrathiophosphate, diheptyltetrathiophosphate, dioctyltetrathiophosphate, and dilauryltetrathiophosphate;

[0093] di((alkyl)aryl)tetrathiophosphates such as diphenyltetrathiophosphate and dicresyltetrathiophosphate;

[0094] trialkyltetrathiophosphates of which the alkyl groups may be straight-chain or branched, such as tripropyltetrathiophosphate, tributyltetrathiophosphate, tripentyltetrathiophosphate, trihexyltetrathiophosphate, triheptyltetrathiophosphate, trioctyltetrathiophosphate, and trilauryltetrathiophosphate;

[0095] tri((alkyl)aryl)tetrathiophosphates such as triphenyltetrathiophosphate and tricresyltetrathiophosphate;

[0096] and mixtures thereof.

[0097] In the present invention, preferably one to three of X4 to X6in formula (2) are sulfur, and more preferably one or two of X4 to X6 are sulfur.

[0098] Examples of salts of sulfur- and phosphorus-containing compounds represented by formula (1) or (2) are salts obtained by allowing any of the above-exemplified sulfur- and phosphorus-containing compounds to react with a nitrogen compound such as ammonia or an amine compound having in its molecules only hydrocarbon or hydroxyl-containing hydrocarbon groups having 1 to 8 carbon atoms so as to neutralize the whole or part of the remaining acid hydrogen and salts of the above-exemplified sulfur- and phosphorus-containing compounds and titanium, calcium, magnesium, zinc, sodium, or potassium, such as zinc dialkyldithiophosphates and zinc dialkylthiophosphates.

[0099] Specific examples of the nitrogen compound are ammonia; alkylamines, of which the alkyl groups may be straight-chain or branched, such as monomethylamine, monoethylamine, monopropylamine, monobutylamine, monopentylamine, monohexylamine, monoheptylamine, monooctylamine, dimethylamine, methylethylamine, diethylamine, methylpropylamine, ethylpropylamine, dipropylamine, methylbutylamine, ethylbutylamine, propylbutylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine and dioctylamine; alkanolamines, of which the alkanol groups may be straight-chain or branched, such as monomethanolamine, monoethanolamine, monopropanolamine, monobutanolamine, monopentanolamine, monohexanolamine, monoheptanolamine, monooctanolamine, monononanolamine, dimethanolamine, methanolethanolamine, diethanolamine, methanolpropanolamine, ethanolpropanolamine, dipropanolamine, methanolbutanolamine, ethanolbutanolamine, propanolbutanolamine, dibutanolamine, dipentanolamine, dihexanolamine, diheptanolamine and dioctanolamine; and mixtures thereof.

[0100] Preferred thiazole compounds for (B-2) sulfur-containing compounds are those represented by formulas (3) and (4): 2

[0101] In formulas (3) and (4), R10 and R11 are each independently hydrogen or a hydrocarbon group having 1 to 30 carbon atoms, R is an alkyl group having 1 to 4 carbon atoms, and e, f, and g are each independently an integer of 0 to 3.

[0102] Among these compounds, particularly preferred are benzothiazole compounds represented by formula (4). Examples of the hydrocarbon group having 1 to 30 carbon atoms for R10 and R11 in formulas (3) and (4) are the same as those exemplified with respect to R1 to R6 in formulas (1) and (2) representing (B-1) sulfur- and phosphorus-containing compounds.

[0103] Preferred thiadiazole compounds for (B-2) sulfur-containing compounds are 1,3,4-thiadiazole compounds represented by formula (5), 1,2,4-thiadiazole compounds represented by formula (6) and 1,4,5-thiadiazole compounds represented by formula (7): 3

[0104] In formulas (5), (6), and (7), R13,R14, R15, R16, R17, and R8may be the same or different from each other and are each independently hydrogen or a hydrocarbon group having 1 to 30 carbon atoms, and h, i, j, k, l, and m are each independently an integer of 0 to 8.

[0105] Examples of the hydrocarbon group having 1 to 30 carbon atoms for R13, R14, R15, R16, R17, and R18 in formulas (5), (6), and (7) are the same as those exemplified with respect to R1 to R6 in formulas (1) and (2) representing (B-l) sulfur- and phosphorus-containing compounds.

[0106] Among (B-2) sulfur-containing compounds, dithiocarbamate compounds may be any dithiocarbamates, but preferred are compounds represented by formulas (8) and (9): 4

[0107] In formulas (8) and (9), R19, R20, R21, R22, R23, and R24 are each independently a hydrocarbon group having 1 to 30, preferably 1 to 20 carbon atoms, R25 is hydrogen or a hydrocarbon group having 1 to 30 carbon atoms, preferably hydrogen or a hydrocarbon group having 1 to 20 carbon atoms, n is an integer of 0 to 4, and o is an integer of 0 to 6.

[0108] Examples of the hydrocarbon group having 1 to 30 carbon atoms for R19, R20, R21, R22, R23, R24, and R25 in formulas (8) and (9) are the same as those exemplified with respect to R1 to R6 in formulas (1) and (2) representing (B-1) sulfur- and phosphorus-containing compounds.

[0109] Among (B-2) sulfur-containing compounds, dihydrocarbyl polysulfides are sulfur-based compounds generally so-called polysulfides or olefin sulfides and represented by the formula

R26—Sp—R27   (10)

[0110] In formula (10) , R26 and R27 are each independently a straight-chain or branched alkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms, and p is an integer of 2 to 6, preferably 2 to 5.

[0111] Examples of the alkyl group for R26 and R27 include n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, straight-chain or branched pentyl, straight-chain or branched hexyl, straight-chain or branched heptyl, straight-chain or branched octyl, straight-chain or branched nonyl, straight-chain or branched decyl, straight-chain or branched undecyl, straight-chain or branched dodecyl, straight-chain or branched tridecyl, straight-chain or branched tetradecyl, straight-chain or branched pentadecyl, straight-chain or branched hexadecyl, straight-chain or branched heptadecyl, straight-chain or branched octadecyl, straight-chain or branched nonadecyl, and straight-chain or branched eicosyl groups.

[0112] Examples of the aryl group for R26 and R27 include phenyl and naphthyl groups.

[0113] Examples of the alkylaryl group for R26 and R27 include tolyl (inclusive all structural isomers), ethylphenyl (inclusive all structural isomers), straight-chain or branched propylphenyl (inclusive all structural isomers), straight-chain or branched butylphenyl (inclusive all structural isomers), straight-chain or branched pentylphenyl (inclusive all structural isomers), straight-chain or branched hexylphenyl (inclusive all structural isomers), straight-chain or branched heptylphenyl (inclusive all structural isomers), straight-chain or branched octylphenyl (inclusive all structural isomers), straight-chain or branched nonylphenyl (inclusive all structural isomers), straight-chain or branched decylphenyl (inclusive all structural isomers), straight-chain or branched undecylphenyl (inclusive all structural isomers), straight-chain or branched dodecylphenyl (inclusive all structural isomers), xylyl (inclusive all structural isomers), ethylmethylphenyl group (inclusive all structural isomers), diethylphenyl (inclusive all structural isomers), di(straight-chain or branched)propylphenyl (inclusive all structural isomers), di (straight-chain or branched)butylphenyl (inclusive all structural isomers), methylnaphtyl (inclusive all structural isomers), ethylnaphtyl (inclusive all structural isomers), straight-chain or branched propylnaphtyl (inclusive all structural isomers) , straight-chain or branched butylnaphtyl (inclusive all structural isomers), dimethylnaphtyl (inclusive all structural isomers), ethylmethylnaphtyl (inclusive all structural isomers), diethylnaphtyl (inclusive all structural isomers), di(straight-chain or branched)propylnaphtyl (inclusive all structural isomers), and di(straight-chain or branched)butylnaphtyl groups (inclusive all structural isomers).

[0114] Examples of the arylalkyl groups for R26 and R27 include benzyl, phenylethyl(inclusive all isomers), and phenylpropyl (inclusive all isomers).

[0115] R26 and R27 each are preferably an alkyl group having 3 to 18 carbon atoms derived from propylene, 1-butene, or isobutylene, an aryl group having 6 to 8 carbon atoms, an alkylaryl group having 7 or 8 carbon atoms, or an arylalkyl group having 7 or 8 carbon atoms.

[0116] Specific examples of the alkyl group include isopropyl, branched hexyl derived from a propylene dimmer (inclusive all branched isomers), branched nonyl derived from a propylene trimer (inclusive all branched isomers), branched dodecyl derived from a propylene tetramer (inclusive all branched isomers), branched pentadecyl derived from a propylene pentamer (inclusive all branched isomers), branched octadecyl derived from a propylene hexamer (inclusive all branched isomers), sec-butyl, tert-butyl, branched octyl derived from a 1-butene dimmer (inclusive all branched isomers), branched octyl derived from an isobutylene dimmer (inclusive all branched isomers), branched dodecyl derived from a 1-butene trimer (inclusive all branched isomers), branched dodecyl derived from an isobutylene trimer (inclusive all branched isomers), branched hexadecyl derived from a 1-butene tetramer (inclusive all branched isomers), and branched hexadecyl derived from an isobutylene tetramer (inclusive all branched isomers). Specific examples of the aryl groups include phenyl group. Specific examples of the alkylaryl groups are tolyl (inclusive all structural isomers), ethylphenyl (inclusive all structural isomers), and xylyl (inclusive all structural isomers). Specific examples of the arylalkyl group are benzyl and phenetyl (inclusive all structural isomers).

[0117] R26 and R27 are each independently preferably a branched alkyl group having 3 to 18 carbon atoms, derived from propylene, 1-butene, or isobutylene, particularly preferably a branched alkyl group having 6 to 15 carbon atoms, derived from ethylene or propylene because the resulting transmission fluid is capable of obtaining a higher torque transmission capacity.

[0118] Eligible dihydrocarbylpolysulfide compounds may be those containing sulfur in an arbitrary amount. However, preferred are those containing sulfur in an amount of generally 10 to 55 percent by mass and preferably 20 to 50 percent by mass because the resulting transmission fluid is capable of obtaining a higher torque transmission capacity.

[0119] Specific examples of sulfurized ester compounds among (B-2) sulfur-containing compounds include animal or vegetable fatty oils such as beef tallow, lard, fish oil, rape oil, or soybean oil; unsaturated fatty acid esters obtained by reacting an unsaturated fatty acid such as oleic acid, linoleic acid, or fatty acids extracted from the aforesaid animal or vegetable fatty oils with various alcohols; and those obtained by sulfurizing the mixtures thereof in a suitable manner.

[0120] No particular limitation is imposed on the sulfur content of the sulfurized ester compounds. However, preferred are those containing sulfur in an amount of generally 2 to 40 percent by mass, preferably 5 to 35 percent by mass because the resulting transmission fluid is capable of obtaining a higher torque transmission capacity.

[0121] Any one or more compounds selected from the above-described Components (B) may be blended in the transmission fluid composition for automobiles of the present invention. When Component (B) is blended in a lubricating oil for automatic transmissions, the lubricating oil can not only obtain a large torque transmission capacity but also provide a wet clutch with the optimized friction characteristics.

[0122] In the case of using Component (B-1), i.e., sulfur- and phosphorus-containing compound as Component (B), the content of Component (B-1) is 0.005 percent by mass or more and preferably 0.008 percent by mass or more in terms of phosphorus, based on the total mass of the transmission fluid composition, while the content is 0.1 percent by mass or less and preferably 0.08 percent by mass or less in terms of phosphorus, based on the total mass of the transmission fluid composition. Component (B-1) of less than 0.005 percent by mass in terms of phosphorus would fail to obtain a large torque transmission capacity, while Component (B-1) of more than 0.1 percent by mass would also fail to obtain a large torque transmission capacity as corresponding to the content.

[0123] In the case of using Component (B-2), i.e., sulfur-containing compound as Component (B), the content of Component (B-2) is 0.005 percent by mass or more and preferably 0.008 percent by mass or more in terms of sulfur, based on the total mass of the transmission fluid composition, while the content is 0.3 percent by mass or less and preferably 0.2 percent by mass or less in terms of sulfur, based on the total mass of the transmission fluid composition. Component (B-2) of less than 0.005 percent by mass would fail to obtain a large torque transmission capacity, while Component (B-2) of more than 0.3 percent would also fail to obtain a large torque transmission capacity.

[0124] The transmission fluid composition for automobiles of the present invention containing Components (A) and (B) in combination can obtain a sufficient torque transmission capacity. However, in order to obtain a larger torque transmission capacity, the transmission fluid composition contains preferably (C) an ashless dispersant.

[0125] Component (C), i.e., ashless dispersant, may be any of compounds which are generally used as ashless dispersants for lubricating oils. Specific examples of Component (C) include nitrogen-containing compounds having at least one alkyl or alkenyl group having 40 to 400 carbon atoms in the molecules, derivatives thereof, and modified products of alkenyl succinimides.

[0126] The alkyl or alkenyl group may be straight-chain or branched but is preferably a branched alkyl or alkenyl group derived from an oligomer of an olefin such as propylene, 1-butene, and isobutylene or from a cooligomer of ethylene and propylene. The carbon number of the alkyl or alkenyl group is preferably 40 to 400 and preferably 60 to 350. An alkyl or alkenyl group having fewer than 40 carbon atoms would deteriorate the solubility of the compound in a lubricating base oil, while an alkyl or alkenyl group having more than 400 carbon atoms would deteriorate the low-temperature fluidity of the resulting transmission fluid composition.

[0127] Specific examples of the nitrogen-containing compounds include polybutenylsuccinimides, polybutenylamines, and polybutenylbenzylamines. Specific examples of the derivatives of the nitrogen-containing compounds include acid-modified compounds obtained by allowing the above-described nitrogen-containing compounds to react with a monocarboxylic acid having 2 to 30 carbon atoms, such as fatty acid or a polycarboxylic acid having 2 to 30 carbon atoms, such as oxalic acid, phthalic acid, trimellitic acid, and pyromellitic acid so as to neutralize or amidize the part or whole of the remaining amino and/or imino groups; boron-modified compounds obtained by allowing the above-described nitrogen-containing compounds to react with boric acid so as to neutralize or amidize the part or whole of the remaining amino and/or imino groups; sulfur-modified compounds obtained by allowing the above-described nitrogen-containing compounds to react with a sulfuric compound; and modified products obtained by a combination of 2 or more selected from the oxygen modification, boron modification, and sulfur modifications, of the above-described nitrogen-containing compounds.

[0128] The transmission fluid composition for automobiles of the present invention may contain one or more types of compounds arbitrarily selected from the above-described ashless dispersants, i.e., Component (C) in an arbitrary amount. However, the content of Component (C) is from 0.1 to 10 percent by mass and preferably from 0.5 to 8 percent by mass, based on the total mass of the composition. Component (C) of less than 0.1 percent by mass would fail to achieve synergistic effects with Components (A) and (B) , while Component (C) of more than 10 percent by mass would fail to achieve further synergistic effects with Components (A) and (B).

[0129] A larger torque transmission capacity can be obtained with the transmission fluid composition for automobiles of the present invention comprising (A) an oil-soluble metal salt overbased with an alkaline earth metal borate and (B) an extreme pressure additive and additionally (C) an ashless dispersant. However, if necessary, the transmission fluid composition contains preferably at least one additive selected from the group consisting of (D) metal detergents, (E) friction modifiers, (F) anti-oxidants, and (G) viscosity index improvers.

[0130] Component (D) , i.e., metal detergents may be one or more types of any compounds other than Components (A) , which are generally used as metal detergents for lubricating oils, such as sulfonate, phenate, salicylate, and naphthenate of an alkali metal such as sodium or potassium or an alkaline earth metal such as calcium or magnesium. However, in order to achieve a larger torque transmission capacity, sulfonate, phenate, or salicylate of calcium or magnesium is preferably used alone or in combination, as Component (D).

[0131] The details of the alkaline earth metal sulfonates, salicylates, and phenates are as described with respect to the oil-soluble metal salt of Component (A). However, Component (D) also includes neutral salts(normal salts) obtained by reacting alkyl aromatic sulfonic acids, alkylsalicylic acids, alkylphenols, alkylphenolsuflides, Mannich reaction products of alkylphenols directly with an alkaline earth metal base of the oxide or hydroxide of an alkaline earth metal such as magnesium and/or calcium or obtained by converting alkyl aromatic sulfonic acids, alkylphenols, alkylsalicylic acids, alkylphenolsuflides, Mannich reaction products of alkylphenols to alkali metal salts such as sodium salt and potassium salt, followed by substitution with an alkaline earth metal salt; basic salts obtained by heating these neutral salts with an excess amount of an alkaline earth metal salt or alkaline earth metal base (hydroxides or oxides of alkaline earth metals) in the presence of water; and overbased salts (superbasic salts) obtained by reacting these neutral salts with an alkaline earth metal base in the presence of carbonic acid gas.

[0132] These reactions are generally carried out in a solvent (aliphatic hydrocarbon solvents such as hexane, aromatic hydrocarbon solvents such as xylene, and light lubricating base oil).

[0133] No particular limitation is imposed on the base number of Component (D) . Therefore, Component (D) may be those with a base number of 0 to 500 mgKOH/g and thus is arbitrarily selected from those with a suitable base number depending on the required capabilities as a lubricating oil. However, in order to secure a large torque transmission capacity, the base number is preferably 100 mgKOH/g or higher, more preferably 150 mgKOH/g or higher and particularly preferably 200 mgKOH/g or higher, while the base number is preferably 400 mgKOH/g or lower, more preferably 350 mgKOH/g or lower, and particularly preferably 300 mgKOH/g or lower. The term “base number” used herein denotes a base number measured by the perchloric acid potentiometric titration method in accordance with section 7 of JIS K2501 (1992) “Petroleum products and lubricants-Determination of neutralization number”.

[0134] Although Components (D), i.e., the metal detergents are usually commercially available in the form of diluted with a light lubricating base oil, it is preferable to use metal detergents of which metal content is within the range of 1.0 to 20 percent by mass and preferably 2.0 to 16 percent by mass.

[0135] The transmission fluid composition for automobiles of the present invention may contain one or more types of compounds arbitrarily selected from (D) the above-described metal detergents in an arbitrary amount. However, the content of Component (D) is from 0.01 to 10 percent by mass, preferably from 0.05 to 5 percent by mass, and more preferably from 0.1 to 1.5 percent by mass based on the total mass of the transmission fluid composition.

[0136] Component (E), i.e., friction modifiers maybe any compounds which are generally used as friction modifiers for lubricating oils, such as imide compounds, amine compounds, fatty acid esters, fatty acid amides, and fatty acid metal salts, all having in the molecules at least one alkyl or alkenyl group having 6 to 30 carbon atoms.

[0137] Examples of imide compounds include succinimides having a straight-chain or branched alkyl or alkenyl group having 6 to 30, preferably 8 to 24, and particularly preferably 10 to 20 carbon atoms and acid-modified products thereof with boric acid, phosphorus acid, carboxylic acid, or sulfuric acid.

[0138] Examples of amine compounds include straight-chain or branched, preferably straight-chain aliphatic monoamines having 6 to 30 carbon atoms; straight-chain or branched, preferably straight-chain aliphatic polyamines having 6 to 30 carbon atoms; and alkyleneoxide adducts of these aliphatic amines.

[0139] Examples of fatty acid esters include esters of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms and either aliphatic monohydric alcohols or aliphatic polyhydric alcohols.

[0140] Examples of fatty acid amides include amides of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms and either aliphatic monoamines or aliphatic polyamines.

[0141] Examples of fatty acid metal salts include alkaline earth metal salts (magnesium salts and calcium salts) or zinc salts of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms.

[0142] The transmission fluid composition for automobiles of the present invention may contain one or more types of compounds arbitrarily selected from (E) the above-described friction modifiers in an arbitrary amount. However, the content of Component (E) is from 0.01 to 5.0 percent by mass and preferably from 0.03 to 3.0 percent by mass, based on the total mass of the transmission fluid composition.

[0143] Component (F) , i.e., anti-oxidants may be phenol- or amine-based compounds which are usually used as anti-oxidants for lubricating oils.

[0144] Specific examples of anti-oxidants include alkylphenols such as

[0145] 2-6-di-tert-butyl-4-methylphenol; bisphenols such as 4,4-methylenebis(2,6-di-tert-butylphenol);

[0146] naphtylamines such as phenyl-&agr;-naphtylamine; dialkyldiphenylamines; zinc dialkyldithiophosphates such as zinc di-2-ethylhexyldithiophosphate; and

[0147] esters of (3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid such as propionic acid and either monohydric or polyhydric alcohols such as methanol, octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene glycol, triethylene glycol, and pentaerythritol.

[0148] The transmission fluid composition for automobiles of the present invention may contain one or more types of compounds arbitrarily selected from (F) the above-described anti-oxidants in an arbitrary amount. However, the content of Component (F) is from 0.01 to 5.0 percent by mass, based on the total mass of the transmission fluid composition.

[0149] Component (G), i.e., viscosity index improvers may be non-dispersion type viscosity index improvers such as copolymers of one or more monomers selected from various methacrylates or hydrides thereof and dispersion type viscosity index improvers such as copolymers of various methacrylates further containing nitrogen compounds. Examples of other viscosity index improvers include non-dispersion- or dispersion-type ethylene-&agr;-olefin copolymers of which the &agr;-olefin may be propylene, 1-butene, or 1-pentene, or the hydrides thereof; polyisobutylenes or hydrides thereof; styrene-diene copolymers or hydrides thereof; styrene-maleic anhydride ester copolymers; and polyalkylstyrenes.

[0150] It is necessary to select the molecular weight of these viscosity index improvers considering the shear stability thereof. Specifically, the number-average molecular weight of non-dispersion or dispersion type polymethacrylates is from 5,000 to 150,000 and preferably from 5,000 to 35,000. The number-average molecular weight of polyisobutylenes or hydrides thereof is from 800 to 5,000 and preferably from 1,000 to 4,000. The number-average molecular weight of ethylene-&agr;-olefin copolymers and hydrides thereof is from 800 to 150,000 and preferably from 3,000 to 12,000.

[0151] Among (G) the above-described viscosity index improvers, the use of ethylene-&agr;-olefin copolymers or hydrides thereof is contributive to production of a transmission fluid composition for automobiles which is excellent particularly in shear stability.

[0152] The transmission fluid composition for automobiles of the present invention may contain one or more types of compounds arbitrarily selected from (G) the above-described viscosity index improvers in an arbitrary amount. However, the content of Component (G) is from 0.1 to 40 percent by mass, based on the total mass of the transmission fluid composition.

[0153] In order to enhance the capabilities, the transmission fluid composition for automobiles of the present invention may be blended with (H) compounds capable of increasing the friction coefficient between metals, such as titanium compounds, silicone compounds, or boron compounds and further known lubricating oil additives. Examples of such known additives include (I) anti-wear agents, (J) rust inhibitors, (K) corrosion inhibitors, (L) pour-point depressants, (M) rubber swelling agents, (N) anti-foamers, and (O) dyes.

[0154] Components (H), i.e., compounds capable of increasing the friction coefficient between metals, such as titanium compounds, silicone compounds, or boron compounds are as follow.

[0155] Examples of titanium compounds include organic orthotitanates, condensates of organic orthotitanates and polyamines, condensates of organic orthotitanates and polyols, having a hydrocarbon group having 1 to 30 carbon atoms, and titanium phosphate.

[0156] Examples of silicone compounds include organic orthosilicates, condensates of organic orthosilicates and polyamines, and condensates of the organic orthosilicates and polyols, having a hydrocarbon group having 1 to 30 carbon atoms.

[0157] Examples of boron compounds include organic borates, condensates of organic borates and polyamines, condensates of organic borates and polyols, adducts of organic borates and phosphites, and organic mercaptoalkylborates, having a hydrocarbon group having 1 to 30 carbon atoms.

[0158] Each of the above-described titanium, silicone, or boron compounds may be used alone or in combination. Alternatively, the above-described titanium, silicone, and boron compounds may be used in combination. In the case where these compounds are added, the content thereof (total content if two or more types of the compounds are added) is preferably from 0.01 to 10 percent by mass, more preferably from 0.02 to 5 percent by mass, and particularly preferably from 0.05 to 3 percent by mass, based on the total mass of the transmission fluid composition. Lubricating oil compositions containing these compounds are disclosed in Japanese Patent Laid-Open Publication Nos. 2001-27533, 2001-27534, and 2001-27535.

[0159] Examples of (I) anti-wear agents include phosphoric acid; monophosphates; diphosphates; triphosphates; phosphorus acid; monophosphites; diphosphites; triphosphites; metal salts or amine salts of phosphoric acid, phosphorus acid, monophosphates, monophosphites, diphosphates, and diphosphites; and mixtures thereof. Among these anti-wear agents, those other than phosphoric acid and phosphorus acid are generally compounds containing a hydrocarbon group having 2 to 30, preferably 3 to 20 carbon atoms.

[0160] In the case of adding the anti-wear agents, the content thereof is from 0.005 to 0.2 percent by mass in terms of phosphorus, based on the total mass of the transmission fluid composition. The anti-wear agents of less than 0.005 percent by mass in terms of phosphorus would be ineffective in anti-wear properties, while the anti-wear agents of more than 0.2 percent by mass would deteriorate the oxidation stability of the resulting composition.

[0161] Examples of Component (J), i.e., rust inhibitors include alkenyl succinic acids, alkenyl succinic acid esters, polyhydric alcohol esters, petroleum sulfonates, and dinonylnaphthalenesulfonate.

[0162] Component (K), i.e., corrosion inhibitors may be any compounds which are used as corrosion inhibitors for lubricating oils. Examples of corrosion inhibitors include benzotriazole-, tolyltriazole-, thiadiazole-, and imidazole-based compounds.

[0163] Examples of Component (L), i.e., pour-point depressants include polymethacrylate-based polymers, which are adaptable to a lubricating base oil to be used.

[0164] Examples of Component (M) , i.e., rubber swelling agents include aromatic compounds and sulfuric compounds.

[0165] Examples of Component (N), i.e., anti-foamers include silicones such as dimethylsilicone and fluorosilicone.

[0166] In the present invention, the contents of these additives may be arbitrarily selected. However, the content of the rust inhibitors, corrosion inhibitors, pour-point depressants, and rubber swelling agents is from 0.005 to 3 percent by mass and the content of the anti-foamers is from 0.0005 to 0.01 percent by mass, based on the total mass of the transmission fluid composition.

[0167] The kinematic viscosity at 100° C. of the transmission fluid composition for automobiles of the present invention is preferably from 4 to 30 mm2/s and more preferably from 5 to 25 mm2/s.

[0168] The transmission fluid composition for automobiles of the present invention is suitably used for automatic transmissions and/or continuously variable transmissions and particularly suitably for metal belt-type continuously variable transmissions. Furthermore, the transmission fluid composition is also suitably used for automatic- or manual transmissions with a wet clutch.

BEST MODE FOR CARRYING OUT THE INVENTION

[0169] Hereinafter, the present invention will be described in more details by way of the following examples and comparative examples, which should not be construed as limiting the scope of the invention.

EXAMPLES 1 TO 7 AND COMPARATIVE EXAMPLES 1 TO 10

[0170] Transmission fluid compositions for automobiles of the present invention (Examples 1 to 7) and those for comparison (Comparative Examples 1 to 10) were prepared using a hydrogenated refined mineral oil as a base oil in accordance with the formulations shown in Tables 1 and 2, respectively.

[0171] LFW-1 friction test was conducted for each of the compositions in accordance with the test conditions prescribed in ASTM D2714 to measure the frictional force at each slipping velocities thereby determining the friction coefficient.

[0172] (Test Conditions)

[0173] Ring: Falex S-10 Test Ring

[0174] (SAE 4620 Steel)

[0175] Block: Falex H-60 Test Block

[0176] (SAE 01 Steel)

[0177] Test oil temperature: 110° C.

[0178] Test load: 250 lb

[0179] Slipping velocity: 25 cm/s 1 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Lubricating base oil1) mass % 99.00  89.40  89.40  89.40  89.40  88.90  89.19  (A) Oil-soluble metal salt A2) mass % 0.50 0.50 — 0.50 — 0.50 0.50 (A) Oil-soluble metal salt B3) mass % — — 0.50 — 0.50 — — (B concentration) mass %  0.016  0.016  0.015  0.016  0.015  0.016  0.016 (Ca concentration) mass %  0.038  0.038  0.034  0.038  0.034  0.038  0.038 (B) Sulfur-containing extreme pressure additivd A4) mass % 0.50 0.50 0.50 — — 0.50 0.50 (B) Sulfur-containing extreme pressure additive B5) mass % — — — 0.50 0.50 — — (P concentration) mass %  0.043  0.043  0.043  0.045  0.045  0.043  0.043 (S concentration) mass %  0.091  0.091  0.091  0.048  0.048  0.091  0.091 (C) Ashless-dispersant A6) mass % — 3.00 3.00 3.00 3.00 3.00 3.00 (C) Ashless-dispersant B7) mass % — — — — — 0.5  — (D) Metal detergent A8) mass % — — — — — — 0.21 (Ca concentration) mass % — — — — — —  0.025 (F) Phenol-based anti-oxidant9) mass % 0.30 0.30 0.30 0.30 0.30 0.30 0.30 (F) Amine-based anti-oxidant10) mass % 0.30 0.30 0.30 0.30 0.30 0.30 0.30 (G) Viscosity index improver11) mass % 6.00 6.00 6.00 6.00 6.00 6.00 6.00 Friction coefficient (25 m/s)  0.156  0.161  0.160  0.155  0.153  0.163  0.158 1)Hydrogenated refined mineral oil (kinematic viscosity: 4 mm2/s @ 100° C., viscosity index: 120) 2)Calcium borate-containing overbased calcium sulfonate (base number: 180, calcium content: 7.6 mass %, boron content: 3.3 mass %) 3)Calcium borate-containing overbased calcium salicylate (base number: 200, calcium content: 6.8 mass %, boron content: 3.1 mass %) 4)Di-2-ethylhexyldithiophosphate 5)Di-2-ethylhexylthiophosphate 6)Bispolybutenylsuccinimide (bis type, number average molecular weight of polybutenyl group: 1,300, nitrogen content: 1.6 mass %) 7)Borated polybutenylsuccinimide (bis type, number average molecular weight of polybutenyl group: 1,300, nitrogen content: 2.2 mass %, boron content: 2.0 mass %) 8)Overbased calcium sulfonate (base number: 300, calcium content: 12.0 mass %, boron content: 0.0 mass %) 9)Octyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate 10)Octyldiphenylamine 11)Polymethacrylate (weight average molecular weight: 60,000)

[0180] 2 TABLE 2 Compara- Compara- Compara- Compara- Compara- Compara- Compara- Compara- Compara- Compara- tive tive tive tive tive tive tive tive tive tive Ex- Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 ample 10 Lubricating mass % 89.90  89.90  89.90  89.90  89.88  79.90  89.48  89.07  89.36  89.70  base oil1) (A) Oil-soluble mass % 0.50 — — — 0.02 10.00  — — — 0.50 metal salt A2) (A) Oil-soluble mass % — 0.50 — — — — — — — — metal salt B3) (B concentration) mass %  0.016  0.015 — —  0.0007  0.330 — — —  0.016 (Ca concentration) mass %  0.038  0.034 — —  0.0015  0.760 — — —  0.038 (B) Sulfur- mass % — — 0.50 — 0.50 0.50 0.50 0.50 0.50 — containing extreme pressure additive A4) (B) Sulfur- mass % — — — 0.50 — — — — — — containing extreme pressure additive B5) Sulfur-free etreme mass % — — — — — — — — — 0.50 pressure additive12) (P concentration) mass % — —  0.043  0.045  0.043  0.043  0.043  0.043  0.043  0.050 (S concentration) mass % — —  0.091  0.048  0.091  0.091  0.091  0.091  0.091 — (C) Ashless- mass % 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 dispersant A6) (C) Ashless- mass % — — — — — — — — — — dispersant B7) (D) Metal mass % — — — — — — 0.42 — — — detergent A8) (D) Metal mass % — — — — — — — 0.83 — — detergent B13) (D) Metal mass % — — — — — — — — 0.54 — detergent C14) (Ca concentration) mass % — — — — — —  0.050  0.050 — — (Mg concentration) mass % — — — — — — — —  0.050 — (F) Phenol-based mass % 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 anti-oxidant9) (F) Amine-based mass % 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 anti-oxidant10) (G) Viscosity index mass % 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 improver11) Friction coefficient  0.140  0.135  0.110  0.145  0.130  0.145  0.147  0.144  0.134  0.147 (25 m/s) 1) to 11) the same as those in Table 1 12)Di-2-ethylhexylphosphate 13)Overbased calcium salicylate (base number: 170, calcium content: 6.0 mass %, boron content: 0.0 mass %) 14)Overbased magnesium sulfonate (base number: 300, calcium content: 9.3 mass %, boron content: 0.0 mass %)

[0181] As apparent from the results shown in Tables 1 and 2, the transmission fluid compositions for automobiles of the present invention containing (A) an oil-soluble metal salt overbased with an alkaline earth metal borate and (B) a sulfur-containing extreme pressure additive can enhance the friction coefficient between metals which is an index of torque transmission capacity, more than the compositions of Comparative Examples 1 to 4 which did not contain either one of Component (A) or (B) ; the compositions of Comparative Examples 5 and 6 the content of which Component (A) deviated the range defined by the present invention; the compositions of Comparative Examples 7 to 9 which contained an oil-soluble metal salt overbased only with an alkaline earth metal carbonate instead of Component (A); and the composition of Comparative Example 10 which contained a sulfur-free phosphorus compound instead of Component (B).

[0182] [Applicability in the Industry]

[0183] The use of the transmission fluid composition for automobiles of the present invention can enhance the friction coefficient between metals. Therefore, the transmission fluid composition can secure a sufficient torque transmission capacity and thus is applicable to a higher displacement engines, particularly 2500 cc or higher engines than ever before. As a result, the transmission fluid composition can improve the silentness and fuel efficiency of automobiles equipped with a metal belt-type continuously variable transmission.

Claims

1. A transmission fluid composition for automobiles which comprises a lubricating base oil, (A) an oil-soluble metal salt overbased with an alkaline earth metal borate, in an amount of 0.001 to 0.3 persent by mass in terms of boron, based on the total mass of the composition and (B) a sulfur-containing extreme pressure additive.

2. The transmission fluid composition for automobiles according to claim 1 wherein said oil-soluble metal salt of Component (A) is an alkaline earth metal sulfonate and/or salicylate.

3. The transmission fluid composition for automobiles according to claim 1 wherein said alkaline earth metal borate of Component (A) is calcium borate and/or magnesium borate.

4. The transmission fluid composition for automobiles according to claim 1 wherein Component (B) is at least on compound selected from the group consisting of thiophosphites, dithiophosphites, trithiophosphites, thiophosphates, dithiophosphates, trithiophosphates, mono-, di-, and tri-substituted esters thereof, and salts thereof.

5. The transmission fluid composition for automobiles according to claim 1 wherein Component (B) is contained in an amount of 0.005 to 0.3 percent by mass in terms of sulfur and/or 0.005 to 0.1 percent by mass in terms of phosphorus, based on the total mass of the composition.

6. The transmission fluid composition for automobiles according to claim 1 which further comprises (C) an ashless dispersant.

7. The transmission fluid composition for automobiles according to claim 6 which further contains at least one type of additive selected from the group consisting of (D) metal detergents, (E) friction modifiers, (F) anti-oxidants, and (G) viscosity index improvers.

8. The transmission fluid composition for automobiles according to claim 1 which is used for automatic transmissions and/or continuously variable transmissions.

9. The transmission fluid composition for automobiles according to claim 8 which is used for metal belt-type continuously variable transmissions.