US20170190996A1

US20170190996A1 - Lubricating oil composition

Info

Publication number: US20170190996A1
Application number: US15/127,107
Authority: US
Inventors: Yoshitaka Manabe
Original assignee: JX Nippon Oil and Energy Corp
Current assignee: Eneos Corp
Priority date: 2014-03-20
Filing date: 2014-09-02
Publication date: 2017-07-06
Also published as: JPWO2015141026A1; CN106103672A; JP6259511B2; WO2015141026A1

Abstract

A lubricating oil composition for a metal belt-type continuously variable transmission with a high metal-to-metal friction coefficient and excellent anti-fatigue and anti-seizure properties is provided. The composition contains a lubricating base oil and (A) a high overbased alkaline earth metal sulfonate having a base number of 300 to 500 mgKOH/g in an amount of 0.01 to 0.03 percent by mass as alkaline earth metal, (B) a low overbased alkaline earth metal sulfonate with a base number of 0 to 40 mgKOH/g in an amount of 0.005 to 0.015 percent by mass as alkaline earth metal, and (C) a sulfur-containing phosphite ester in an amount of 0.02 to 0.06 percent by mass as phosphorus. The ratio ([M]/[P]) of the content of (B) as alkaline earth metal ([M]) to the content of (C) as phosphorus ([P]) is 0.15 or greater.

Description

TECHNICAL FIELD

The present invention relates to lubricating oil compositions, in particular to a lubricating oil composition for a metal belt type continuously variable transmission.

BACKGROUND ART

Recent automatic transmissions or continuously variable transmissions have been demanded to be light and small and sought to be improved in power transmission capability in connection with the increased power output of the engines with which the transmissions are used in combination. The reduction in weight and size is intended to improve the fuel efficiency of the vehicles in which the transmissions are mounted.
In the case of a metal belt type continuously variable transmission in particular, it can be reduced in size if the friction coefficient between the belt and pulleys is enhanced and thus lubricating oil to be used therein is preferably an oil having properties to keep the metal-to-metal friction coefficient at a high level.
Furthermore, a lubricating oil has also been demanded to reduce the fuel consumption of a vehicle in which the composition is used. Specifically, a lubricating oil contributes to an improvement in fuel economy by reducing its viscosity to reduce stir resistance or reduce viscous resistance upon idling of a wet clutch pack or upon fluid film lubrication, resulting in a reduction in power loss.
A transmission fluid has been proposed, in which a friction modifier, a metallic detergent, an ashless dispersant, and an anti-wear agent are optimally added so as to retain the friction characteristics of a lock-up clutch in a good condition, provide long-lasting anti-shudder properties or preventing the generation of scratch noise by making the μ-V characteristics between the belt and pulleys (change in friction coefficient against change in slipping velocity) exhibit positive gradient (see Patent Literatures 1 to 9 below).
For example, Patent Literature 1 discloses a transmission lubricating oil composition comprising a specific calcium salicylate, an SP-based extreme pressure additive, a specific succinimide and a boron-containing ashless dispersant, each in a specific amount, which composition exhibits excellent properties such as excellent anti-shudder properties and long-lasting fatigue life. Patent Literature 2 discloses a continuously variable transmission lubricating oil composition containing an organic acid metal salt with a specific composition, an anti-wear agent, and a boron-containing succinimide, as essential components, to have both higher metal-to-metal friction coefficient and anti-shudder properties for a slip control mechanism. Patent Literature 3 discloses a long-lasting continuously variable transmission lubricating oil composition comprising calcium salicylate, a phosphorous anti-wear agent, a friction modifier, and a dispersant type viscosity index improver, to have both a higher metal-to metal friction coefficient and anti-shudder properties for a slip control mechanism. Patent Literature 4 discloses a lubricating oil composition comprising a dithiocarbamate compound, a condensate of a branched fatty acid having 8 to 30 carbon atoms and amine, and an amine-based antioxidant, to have excellent and long-lasting anti-shudder properties. Patent Literature 5 discloses an automatic transmission fluid composition comprising calcium sulfonate, phosphorous acid esters and further a sarcosine derivative or a reaction product of a carboxylic acid and amine, to have long-lasting anti-shudder properties for a slip lock-up mechanism and long-lasting properties to prevent scratch noise in a belt type continuously variable transmission. Patent Literature 6 discloses an automatic transmission fluid composition comprising a specific alkaline earth metal sulfonate in a specific amount, which composition is excellent in oxidation stability as a fluid used for an automatic transmission with a slip control mechanism and has long-lasting anti-shudder properties. Patent Literature 7 discloses an automatic transmission fluid comprising calcium salicylate, magnesium salicylate, a specific amount of a friction modifier and a specific amount of a boric acid-modified succinimide, with excellent anti-shudder properties and a certain torque capacity. Patent Literature 8 discloses a continuously variable transmission oil with excellent anti-wear properties and a high torque capacity, comprising an overbased calcium sulfonate and orthophosphates each in a specific amount. Patent Literature 9 discloses a lubricating oil composition with a high metal-to-metal friction coefficient on a metal belt and long-lasting anti-shudder properties, comprising one or more types of alkaline earth metal sulfonates or phenates containing both a low base number alkaline earth metal salt and a high base number alkaline earth metal salt, an imide compound, and a phosphorus compound in specific amounts.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2003-113391
Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2001-323292
Patent Literature 3: Japanese Patent Application Laid-Open Publication No. 2000-355695
Patent Literature 4: Japanese Patent Application Laid-Open Publication No. 11-50077
Patent Literature 5: Japanese Patent Application Laid-Open Publication No. 10-306292
Patent Literature 6: Japanese Patent Application Laid-Open Publication No. 10-25487
Patent Literature 7: Japanese Patent Application Publication No. 2000-63869
Patent Literature 8: Japanese Patent Application Laid-Open Publication No. 2008-222904
Patent Literature 9: Japanese Patent Application Laid-Open Publication No. 2001-288488

SUMMARY OF INVENTION

Technical Problem

However, when a reduction in the viscosity of a lubricating oil is facilitated, oil film at lubricating sites becomes thinner and thus anti-fatigue properties are deteriorated and also seizure likely occurs particularly when the oil is high in metal-to-metal friction coefficient. Therefore, the present invention has an object to provide a lubricating oil composition which is excellent in anti-fatigue properties and anti-seizure properties even if being reduced in viscosity while keeping the torque capacity by maintaining the metal-to-metal friction coefficient higher, particularly suitable as a metal belt type continuously variable transmission fluid.

Solution to Problem

As the results of extensive studies to achieve the above object carried out by the inventors, the present invention has been accomplished on the basis of the finding that the above object was able to be achieved with a lubricating oil composition comprising alkaline earth metal sulfonates each having a specific base number and a phosphorous additive having a specific structure each in a specific amount.
That is, the present invention provides a lubricating oil composition for a metal belt-type continuously variable transmission comprising a lubricating base oil and (A) an high overbased alkaline earth metal sulfonate having a base number determined by a perchloric acid method of 300 to 500 mgKOH/g in an amount of 0.01 to 0.03 percent by mass as alkaline earth metal, (B) a low overbased alkaline earth metal sulfonate with a base number determined by a perchloric acid method of 0 to 40 mgKOH/g in an amount of 0.005 to 0.015 percent by mass as alkaline earth metal, and (C) a sulfur-containing phosphite ester represented by structural formula (I) below in an amount of 0.02 to 0.06 percent by mass as phosphorus so that the ratio ([M]/[2]) of the content as alkaline earth metal ([M]) of (B) the low overbased alkaline earth metal sulfonate to the content as phosphorus ([P]) of (C) the sulfur-containing phosphite ester is 0.15 or greater:
wherein R is a sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms, R¹is hydrogen, a hydrocarbyl group having 4 to 20 carbon atoms or a sulfur-containing hydrocarbyl group having 4 to 20 carbo atoms.
The present invention also relates to the foregoing continuously variable transmission lubricating oil composition further comprising (D) a phosphite ester and/or an orthophosphate ester in such an amount that the amount of phosphorous in the lubricating oil composition is the range of up to 0.08 percent by mass or less.
The present invention also relates to the foregoing continuously variable transmission lubricating oil composition further comprising at least one type selected from the group consisting of friction modifiers, metallic detergents, viscosity index improvers, pour point depressants, anti-oxidants, corrosion inhibitors, and anti-foamers.

Advantageous Effect of Invention

The lubricating oil composition of the present invention is a lubricating oil composition that can maintain the metal-to-metal friction coefficient at a high level, is excellent in anti-fatigue properties, and enhanced in anti-seizure properties, particularly suitable as a metal belt type continuously variable transmission oil.
The lubricating oil composition of the present invention is also excellent in performances required for transmission fluids other than those described above and thus is suitably used for the automatic or manual transmission and the differential gears, of automobiles, construction machines and agricultural machines. Moreover, the lubricating oil composition can be used as gear oils for industrial uses; lubricating oils for the gasoline engines, diesel engines or gas engines of automobiles such as two- and four-wheeled vehicles, power generators, and ships; turbine oils; and compressor oils.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.
No particular limitation is imposed on the lubricating base oil of the lubricating oil composition of the present invention, which may, therefore, be any of mineral base oils and synthetic base oils that are used in ordinary lubricating oils.
Specific examples of the mineral base oil include those which can be produced by subjecting a lubricating oil fraction produced by vacuum-distilling an atmospheric distillation bottom oil resulting from atmospheric distillation of a crude oil, to any one or more treatments selected from solvent deasphalting, solvent extraction, hydrocracking, hydroisomerization, solvent dewaxing, and hydrorefining; wax-isomerized mineral oils; and those produced by isomerizing GTL WAX (Gas to Liquid Wax).
The mineral based oil used in the present invention is preferably a hydrocracked mineral base oil. Alternatively, the mineral base oil is preferably a wax-isomerized isoparaffin base oil, which is produced by isomerizing a raw material oil containing 50 percent by mass or more of wax such as a petroleum-based wax or Fischer-Tropsch synthetic oil. Although these base oils may be used alone or in combination, a sole use of a wax-isomerized base oil is preferable. Although these base oils may be used alone or in combination, a sole use of a wax-isomerized base oil is preferable.
Specific examples of the synthetic base oils include polybutenes and hydrogenated compounds thereof; poly-α-olefins such as 1-octene oligomer, 1-decene oligomer and 1-dodecene oligomer or hydrogenated compounds thereof; diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate and di-2-ethylhexyl sebacate; polyol esters such as neopentylglycol ester, trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate and pentaerythritol pelargonate; aromatic synthetic oils such as alkylnaphthalenes, alkylbenzenes, and aromatic esters; and mixtures of the foregoing.
The lubricating base oil used in the present invention may be any one of the above-described mineral base oils and synthetic base oils or a mixture of two or more types selected therefrom. For example, the base oil may be one or more types of the mineral base oils, one or more types of the synthetic base oils or a mixed oil of one or more types of the mineral base oils and one or more types of the synthetic base oils.
Although no particular limitation is imposed on the kinematic viscosity of the lubricating base oil used in the present invention, the base oil is preferably adjusted to have a 100° C. kinematic viscosity of preferably 2 to 8 mm²/s, more preferably 2 to 6 mm²/s, particularly preferably 2 to 4.5 mm²/s. A base oil with a 100° C. kinematic viscosity of greater than 8 mm²/s is not preferable because the resulting lubricating oil composition would be poor in low temperature viscosity characteristics while a base oil with a 100° C. kinematic viscosity of lower than 2 mm²/s is not also preferable because the resulting lubricating oil composition would be poor in lubricity due to its insufficient oil film formation at lubricating sites and large in evaporation loss of the lubricating base oil.
No particular limitation is imposed on the viscosity index of the lubricating base oil, which is, however, preferably 100 or greater, more preferably 120 or greater, more preferably 130 or greater, particularly preferably 140 or greater and usually 200 or less, preferably 160 or less. The use of a lubricating base oil having a viscosity index of greater than 100 renders it possible to produce a composition exhibiting excellent viscosity characteristics from low temperatures to high temperatures. Whilst, if the viscosity index is too high, the resulting composition tends to be high in viscosity at low temperatures.
In order to improve the low temperature viscosity characteristics and viscosity index of the lubricating oil composition, the base oil is preferably a combination of two or more base oils having a viscosity index of 115 or greater selected from low viscosity base oils having a viscosity index of 115 or greater and a 100° C. kinematic viscosity of 2 mm²/s or higher and lower than 3.5 mm²/s and relatively high viscosity base oils having a viscosity index of 125 or greater and a 100° C. kinematic viscosity of 3.5 mm²/s or higher and 4.5 mm²/s or lower. In particular, mixing these base oils can enhance the viscosity index so that the −40° C. Brookfield viscosity is 10000 mPa·s or lower.
The viscosity index of the above-described low viscosity base oil is preferably 120 or greater, more preferably 125 or greater and the viscosity index of the relatively high viscosity base oil is preferably 130 or greater, more preferably 135 or greater so that the −40° C. Brookfield viscosity can be 8000 mPa·s or lower.
No particular limitation is imposed on the sulfur content of the lubricating base oil used in the present invention, which is, however, preferably 0.1 percent by mass or less, more preferably 0.05 percent by mass or less, more preferably 0.01 percent by mass or less, particularly preferably 0.005 percent by mass or less, most preferably substantially 0. A composition with excellent oxidation stability can be produced by reducing the sulfur content of the lubricating base oil.
No particular limitation is imposed on the evaporation loss of the lubricating base oil. However, the NOACK evaporation loss is preferably from 10 to 50 percent by mass, more preferably from 20 to 40 percent by mass, particularly preferably from 22 to 35 percent by mass. The use of a lubricating base oil with a NOACK evaporation loss adjusted within the above ranges renders it possible to achieve both low temperature characteristics and anti-wear properties. The term “NOACK evaporation loss” used herein denotes an evaporation loss measured in accordance with CEC L-40-T-87.
The lubricating oil composition of the present invention comprises a high overbased alkaline earth metal sulfonate with a base number determined by a perchloric acid method of 300 to 500 mgKOH/g as Component (A).
Specific examples of the high overbased alkaline earth metal sulfonate that is Component (A) in the present invention include: a basic salt produced by at first producing a neutral salt (normal salt) by reacting an alkyl aromatic sulfonic acid produced by sulfonating an alkyl aromatic compound having a molecular weight of 100 to 1,500, preferably 200 to 700 directly with an alkaline earth metal base such as a hydroxide or oxide of an alkaline earth metal such as magnesium and/or calcium or produced by once converting the alkyl aromatic sulfonic acid to an alkali metal salt such as a sodium salt or a potassium salt and then substituting the alkali metal salt with an alkaline earth metal salt and then heating the neutral salt together with an excess amount of an alkaline earth metal salt or an alkaline earth metal base (alkaline earth metal hydroxide or oxide) in the presence of water; and overbased salts (ultrabasic salts) produced by reacting these neutral salts (normal salt) with a base of an alkaline earth metal in the presence of carbonic acid gas and/or a boron compound such as boric acid or a borate. 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).
Specific examples of the alkyl aromatic sulfonic acids referred herein include petroleum sulfonic acids and synthetic sulfonic acids. The petroleum sulfonic acids may be those produced by sulfonating an alkyl aromatic compound contained in the lubricant fraction of a mineral oil or may be mahogany acid by-produced upon production of white oil. The synthetic sulfonic acids may be those produced by sulfonating an alkyl benzene having a straight-chain or branched alkyl group, produced as a by-product from a plant for producing an alkyl benzene used as the raw material of a detergent or produced by alkylating polyolefin to benzene, or those produced by sulfonating dinonylnaphthalene. No particular limitation is imposed on the sulfonating agents used for sulfonating these alkyl aromatic compounds, which may be generally fuming sulfuric acids or sulfuric acid.
Although alkaline earth metal sulfonates as described above are usually commercially available as diluted with a light lubricating base oil, it is preferable to use a metallic detergent whose metal content is from 1.0 to 20 percent by mass, preferably from 2.0 to 16 percent by mass.
In the present invention, Component (A) is blended in an amount of 0.01 to 0.03 percent by mass, preferably 0.02 to 0.03 percent by mass as alkaline earth metal with the objective of improving metal-to-metal friction coefficient and in view of anti-seizure properties. If Component (A) is blended in an amount of less than 0.01 percent by mass, the resulting composition is degraded in oxidation stability. If Component (A) is blended in an amount of more than 0.03 percent by mass, the resulting composition is degraded in anti-seizure properties.
The lubricating oil composition of the present invention comprises a low overbased alkaline earth metal sulfonate having a base number determined by a perchloric acid method of 0 to 40 mgKOH/g as Component (B).
In the present invention, Component (B) is blended in an amount of 0.005 to 0.015 percent by mass, preferably 0.005 to 0.010 percent by mass as alkaline earth metal with the objective of improving metal-to-metal friction coefficient and in view of anti-fatigue properties and anti-seizure properties. If Component (B) is blended in an amount of less than 0.005 percent by mass, the resulting composition is degraded in anti-fatigue properties. If Component (B) is blended in an amount of more than 0.015 percent by mass, the resulting composition is degraded in anti-seizure properties.
Alkaline earth metals of Component (A) and Component (B) are preferably calcium and magnesium, particularly preferably calcium.
The lubricating oil composition of the present invention comprises a sulfur-containing phosphite ester represented by structural formula (I) as Component (C).
The sulfur-containing phosphite ester that is Component (C) in the present invention is a mono- or di-hydrocarbyl phosphite represented by structural formula (I) below:
In formula (I), R is a sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms, R¹is hydrogen, a hydrocarbyl group having 4 to 20 carbon atoms or a sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms.
Examples of the sulfur-containing hydrocarbyl group include hydrocarbyl groups containing a thioether bond (—CH₂—S—CH₂—) in their main chain or branched chain.
Examples of the hydrocarbyl group include alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, alkylaryl, and arylalkyl groups. The hydrocarbyl group may contain halogen or a substituent such as hydroxy, nitro, cyano, and alkoxy groups.
The hydrocarbyl group is preferably an alkyl, cycloalkyl or aryl group having 4 to 20, preferably 6 to 18, most preferably 8 to 16 carbon atoms. Specific examples include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, octadecyl, cyclohexyl and phenyl groups.
The sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms is preferably a hydrocarbyl group which is the above-described hydrocarbyl group having 4 to 20 carbon atoms containing a thioether bond (—CH₂—S—CH₂—) in its main chain or branched chain, for example a group represented by formula (II):
—(CH₂)_m—S—(CH₂)_n—CH₃ (II)
wherein m is an integer of 1 to 18, preferably 2 to 12, more preferably 2 to 6, n is an integer of 2 to 18, preferably 4 to 16, more preferably 6 to 14, and m+n is an integer of 3 to 19, preferably 5 to 17, more preferably 7 to 15.
Specific examples of the sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms include —(CH₂)₂—S—(CH₂)₆—CH₃, —(CH₂)₂—S—(CH₂)₇—CH₃, —(CH₂)₂—S—(CH2)₈—CH₃, —(CH₂)₂—S—(CH₂)₉—CH₃, —(CH₂)₂—S—(CH₂)₁₀—CH₃, —(CH₂)₂—S—(CH₂)₁₁—CH₃, —(CH₂)₂—S—(CH₂)₁₂—CH₃, —(CH₂)₃—S—(CH₂)₆—CH₃, —(CH₂)₃—S—(CH₂)₇—CH₃, —(CH₂)₃—S—(CH₂)₈—CH3, —(CH₂)₃—S—(CH₂)₉—CH₃, —(CH₂)₃—S—(CH₂)₁₀—CH₃, —(CH₂)₃—S—(CH₂)₁₁—CH₃, —(CH₂)₃—S—(CH₂)₁₂—CH₃, —(CH₂)₄—S—(CH₂)₆—CH₃, —(CH₂)₄—S—(CH₂)₇—CH₃, —(CH₂)₄—S—(CH₂)₈—CH₃, —(CH₂)₄—S—(CH₂)₉—CH₃, —(CH₂)₄—S—(CH₂)₁₀—CH₃, —(CH₂)₄—S—(CH₂)₁₁—CH₃, and —(CH₂)₄—S—(CH₂)₁₂—CH₃.
Among these groups, particularly preferred are —(CH₂)₂—S—(CH₂)₈—CH₃(3-thiaundecyl) and —(CH₂)₂—S—(CH₂)₁₂—CH₃(3-thiapentadecyl).
In the present invention, Component (C) is blended in an amount of 0.02 to 0.06 percent by mass, preferably 0.03 to 0.05 percent by mass as phosphorous with the objective of improving metal-to-metal friction coefficient and in view of anti-fatigue properties and anti-seizure properties. If Component (C) is blended in an amount of less than 0.02 percent by mass, the resulting composition is degraded in anti-fatigue properties. If component (C) is blended in an amount of more than 0.06 percent by mass, the resulting composition is decreased in metal-to-metal friction coefficient.
In the lubricating oil composition of the present invention, the ratio ([M]/[P]) of the content ([M]) as metal of (B) the above-described low overbased alkaline earth metal sulfonate to the content ([P]) as phosphorous of (C) the above-described sulfur-containing phosphite ester is necessarily 0.15 or greater, preferably 0.20 or greater, more preferably 0.25 or greater, particularly preferably 0.30 or greater. If [M]/[P] is less than 0.15, belt-pulley μ-V characteristics are degraded, resulting in poor scratch noise preventing properties. Whilst, the upper limit of [M]/[P] is 0.75, preferably 0.70 or less, more preferably 0.65 or less, more preferably 0.60 or less.
The lubricating oil composition of the present invention comprises preferably a phosphite ester and/or an orthophosphate ester as Component (D).
No particular limitation is imposed on the phosphite ester and/or orthophosphate ester, but examples thereof include phosphate monoesters, phosphate diesters, phosphate triesters, phosphite monoesters, phosphite diesters, and phosphite triesters, all having a hydrocarbon group of 1 to 30 carbon atoms. Alternatively, salts of these esters and amines or alkanol amines or metal salts such as zinc salt of these esters may also be used.
Specific examples of the orthophosphate ester include triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, tris(isopropylphenyl)phosphate, tris(t-butylphenyl)phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecyl phosphate, and trioleyl phosphate.
Specific examples of the phosphite ester include monoalkyl phosphite esters such as monopropyl phosphite, monobutyl phosphite, monopentyl phosphite, monohexyl phosphite, monoheptyl phosphite, and monooctyl phosphite, of which the alkyl groups may be straight-chain or branched; mono(alkyl)aryl phosphite esters such as monophenyl phosphite and monocresyl phosphite; dialkyl phosphites such as dipropyl phosphite, dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, and dioctyl phosphite, of which the alkyl groups may be straight-chain or branched; di(alkyl)aryl phosphite esters such as diphenyl phosphite and dicresyl phosphite; trialkyl phosphite esters such as tripropyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, and trioctyl phosphite, of which the alkyl groups may be straight-chain or branched; tri(alkyl)aryl phosphite esters such as triphenyl phosphite and tricresyl phosphite; and mixtures thereof.
In the present invention, Component (D) is blended in such an amount that the amount of phosphorus in the composition is in the range of up to 0.08 percent by mass or less, preferably up to 0.06 percent by mass or less with the objective of improving metal-to-metal friction coefficient and in view of anti-fatigue properties and anti-seizure properties. If the phosphorus amount is more than 0.08 percent by mass, the resulting composition is degraded in anti-fatigue properties.
The lubricating oil composition of the present invention may be blended with one or more types of friction modifiers and/or metallic detergents. Blending of these additives in the lubricating oil composition of the present invention renders it possible to produce a lubricating oil composition which is more excellent for a belt type continuously variable transmission equipped with a wet friction clutch.
The friction modifier that can be used in combination with the lubricating oil composition of the present invention may be any compound that is usually used as a friction modifier for lubricating oil. Examples of such a compound include amine compounds, fatty acid amides and fatty acid metal salts, each having an alkyl or alkenyl group having 6 to 30 carbon atoms (particularly at least one straight-chain alkyl or alkenyl group having 6 to 30 carbon atoms in their molecules).
The above-exemplified amine compounds include succinimides that are reaction products with polyamines. These include those modified with a boric compound or a phosphorus compound.
Examples of the amine compound include straight-chain or branched, preferably straight-chain aliphatic monoamines and aliphatic polyamines, each having 6 to 30 carbon atoms, alkyleneoxide adducts of these aliphatic amines, salts of these amine compounds and phosphate esters or phosphite esters, and boric acid-modified products of (phosphite)phosphate ester salts of these amine compounds.
Particularly preferred are alkyleneoxide adducts of amine compounds; salts of these amine compounds and phosphate esters (for example, di-2-ethylhexylphosphate), phosphite esters (for example, di-2-ethylhexylphosphate); boric acid-modified products of (phosphite)phosphate ester salts of these amine compounds; and mixtures thereof.
Examples of the fatty acid amide include amides of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms and aliphatic monoaminse or aliphatic polyamines. Specific examples include lauric acid amide, lauric acid diethanol amide, lauric acid monopropanol amide, myristic acid amide, myristic acid diethanol amide, myristic acid monopropanol amide, palmitic acid amide, palmitic acid diethanol amide, palmitic acid monopropanol amide, stearic acid amide, stearic acid diethanol amide, stearic acid monopropanol amide, oleic acid amide, oleic acid diethanol amide, oleic acid monopropanol amide, coconut oil fatty acid amide, coconut oil fatty acid diethanol amide, coconut oil fatty acid monopropanol amide, synthetic mixed fatty acid amide having 12 or 13 carbon atoms, synthetic mixed fatty acid diethanol amide having 12 or 13 carbon atoms, synthetic mixed fatty acid monopropanol amide having 12 or 13 carbon atoms, and mixtures thereof.
Examples of the fatty acid metal salt include alkaline earth metal salts (magnesium salt, calcium salt) and zinc salts of straight-chain or branched, preferably straight-chain fatty acids having 7 to 31 carbon atoms. More specifically, particularly preferred are calcium laurate, calcium myristate, calcium palmitate, calcium stearate, calcium oleate, coconut oil fatty acid calcium, synthetic mixed fatty acid calcium having 12 or 13 carbon atoms, zinc laurate, zinc myristate, zinc palmitate, zinc stearate, zinc oleate, coconut oil fatty zinc, synthetic mixed fatty zinc having 12 or 13 carbon atoms, and mixtures thereof.
In the present invention, any one or more types of compounds selected from these friction modifiers may be blended in any amount but the content thereof is usually preferably from 0.01 to 5 percent by mass, more preferably from 0.03 to 3 percent by mass on the basis of the total mass of the lubricating oil composition.
Examples of the metallic detergent that can be used in combination with the lubricating oil composition of the present invention include alkali metal sulfonates, alkaline earth metal sulfonates other than Component (A) and Component (B), alkali metal phenates or alkaline earth metal phenates, and alkali metal salicylates or alkaline earth metal salicylates. Among these metallic detergents, alkaline earth metal detergents are preferably used.
When the metallic detergents is blended in the present invention, it is blended in an amount of preferably 0.01 percent by mass or more, more preferably 0.1 percent by mass or more, more preferably 0.15 percent by mass or more on the basis of the total mass of the composition in view of rust prevention. It is also blended in an amount of preferably 2 percent by mass or less, more preferably 1.5 percent by mass or less, more preferably 1 percent by mass or less, most preferably 0.8 percent by mass or less on the basis of the total mass of the composition in view of thermal stability and life of anti-oxidation properties.
In order to further enhance the properties of the lubricating oil composition of the present invention, it may be blended with any one or more of conventional lubricating oil additives, such as ashless dispersants, viscosity index improvers, anti-oxidants, corrosion inhibitors, anti-foamers and colorants.
The ashless dispersants that can be used in combination with the lubricating oil composition of the present invention may be any compounds that are used as ashless dispersants for lubricating oil. Examples of such compounds include nitrogen-containing compounds having per molecules at least one alkyl or alkenyl group having 40 to 400, preferably 60 to 350 carbon atoms, bis-type or mono-type succinimides having an alkenyl group having 40 to 400 carbon atoms, preferably 60 to 350 carbon atoms, and modified products produced by allowing these compounds to react with boric acid, phosphoric acid, carboxylic acid or derivatives thereof, or a sulfur compound. Any one or more of these compounds may be used in combination.
The alkyl or alkenyl group referred herein may be straight-chain or branched but is preferably a branched alkyl or alkenyl group derived from oligomers of olefins such as propylene, 1-butene or isobutylene or a cooligomer of ethylene and propylene. The alkyl or alkenyl group is preferably polybutenyl group derived from polymers produced by polymerizing a butene mixture or a high purity isobutylene with an aluminum chloride-based catalyst or a boron fluoride-based catalyst, particularly preferably those from which a halogen compound is removed.
If the carbon number of the alkyl or alkenyl group is fewer than 40, the ashless dispersant would be poor in detergent dispersibility. Whilst, if the carbon number of the alkyl or alkenyl group exceeds 400, the resulting lubricating oil composition would be degraded in low temperature fluidity. Although the content of these compounds are arbitrarily selected, it is preferably from 0.1 to 10 percent by mass, more preferably 1 to 8 percent by mass on the basis of the total mass of the lubricating oil composition. The ashless dispersants that may be used in combination in the present invention are particularly preferably succinimides having a polybutenyl group and a weight-average molecular weight of 700 to 3,500, preferably 900 to 2,000 and/or boric acid-modified compounds thereof with the objective of further improving shifting properties. With the objective of enhancing the ability to avoid the peel-off of a wet clutch, the ashless dispersants are blended with preferably a boric acid-modified succinimide, more preferably a boric acid-modified succinimide as one type of component.
Specific examples of viscosity index improvers that can be used in combination with the lubricating oil composition of the present invention include non-dispersant type viscosity index improvers such as copolymers of one or more monomers selected from various methacrylate esters or hydrogenated compounds thereof; and dispersant type viscosity index improvers such as copolymers of various methacrylate esters further containing nitrogen compounds. Specific examples of other viscosity index improvers include non-dispersant- or dispersant-type ethylene-α-olefin copolymers of which α-olefin may be propylene, 1-butene, or 1-pentene, or a hydrogenated compound thereof; polyisobutylenes or hydrogenated compounds thereof; styrene-diene hydrogenated copolymers; styrene-maleic anhydride ester copolymers; and polyalkylstyrenes.
The molecular weight of these viscosity index improvers is necessarily selected, taking account of the shear stability thereof. Specifically, the number-average molecular weight of the non-dispersant or dispersant type polymethacrylate is from 5,000 to 150,000, preferably from 5,000 to 35,000. The number-average molecular weight of polyisobutylenes or hydrogenated compounds thereof is from 800 to 5,000, preferably from 1,000 to 4,000. The number-average molecular weight of ethylene-α-olefin copolymers or hydrogenated compounds thereof is from 800 to 15,000, preferably from 3,000 to 12,000. Among these viscosity index improvers, the use of ethylene-α-olefin copolymers or hydrogenated compounds thereof renders it possible to produce a lubricating oil composition which is particularly excellent in shear stability. One or more compounds selected from these viscosity index improvers may be blended in any amount in the lubricating oil composition of the present invention. However, the content of the viscosity index improver is usually from 0.1 to 40 percent by mass, on the basis of the total mass of the composition.
The anti-oxidant may be any anti-oxidant that has been usually used in lubricating oil, such as phenol- or amine-based compounds. Specific examples of the anti-oxidant include alkylphenols such as 2-6-di-tert-butyl-4-methylphenol; bisphenols such as methylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol); naphthylamines such as phenyl-α-naphthylamine; dialkyldiphenylamines; zinc dialkyldithiophosphoric acids such as di-2-ethylhexyldithiophosphoric acid; and esters of (3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) with a monohydric or polyhydric alcohol such as methanol, octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene glycol, triethylene glycol and pentaerythritol. Any one or more compounds selected from these compounds may be contained in any amount, which is, however, usually from 0.01 to 5.0 percent by mass on the basis of the total mass of the composition.
The corrosion inhibitors that can be used in combination with the lubricating oil composition of the present invention may be any compounds that have been usually used as corrosion inhibitors for lubricating oil. Examples of such compounds include triazole-type compounds such as benzotriazole and tolyltriazole, thiadiazole-, and imidazole-types compounds. Anyone or more of compounds selected from these compounds may be contained in any amount, which is, however, usually from 0.01 to 3.0 percent by mass on the basis of the total mass of the composition.
The anti-foamer that can be used in combination with the lubricating oil composition of the present invention may be any compounds that have been usually used as anti-foaming agents for lubricating oil. Examples of such compounds include silicones such as dimethylsilicone and fluorosilicone. Any one or more of compounds selected from these compounds may be contained in any amount, which is, however, usually from 0.001 to 0.05 percent by mass on the basis of the total mass of the composition.
The colorants that may be used in combination with the transmission lubricating oil composition of the present invention may be any colorants and contained in any amount, which is, however, desirously from 0.001 to 1.0 percent by mass on the basis of the total mass of the lubricating oil composition.

EXAMPLES

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

Examples 1 to 10 and Comparative Examples 1 to 11

Lubricating oil compositions of the examples and comparative examples set forth in Table 1 were prepared and subjected to the following tests, the results of which are also set forth in Table 1. Each additive in Table 1 is added in an amount on the basis of the total mass of the composition.
(1) Last non-seizure load (LNSL) evaluated by Four-Ball Extreme Pressure Test Method in accordance with ASTM D2783
(2) Wear scar diameter evaluated by Four-Ball Extreme Pressure Test Method in accordance with ASTM D4172
(3) Seizure load evaluated by Falex Seizure test in accordance with ASTM D 3233
(4) Metal-to-metal friction coefficient evaluated by LFW-1 Test in accordance with JASO Method M358:2005

	TABLE 1

	Examples

		1	2	3	4	5	6	7	8

Mineral oil 1)	mass %	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance
High overbased Ca sulfonate 2)	ppm/Ca	250		250	250	100	250	250	250
High overbased Ca sulfonate 3)	ppm/Ca		250
Low overbased Ca sulfonate 4)	ppm/Ca
Low overbased Ca sulfonate 5)	ppm/Ca	100	100	100	100	100	100	100	60
High overbased Ca salicylate 6)	ppm/Ca
High overbased Ca phenate 7)	ppm/Ca
Total	ppm/Ca	350	350	350	350	200	350	350	310
Sulfur-containing	ppm/P	300	300	300	300	300	600	200	300
phosphite ester 8)
Phosphite ester 9)	ppm/P			300
Phosphate ester 10)	ppm/P				300
Acid phosphate ester 11)	ppm/P
Total	ppm/P	300	300	600	600	300	600	200	300
Other performance additives 12)	mass %	13.0	13.0	13.0	13.0	13.0	13.0	13.0	13.0
[M]/[P]	—	0.33	0.33	0.33	0.33	0.33	0.17	0.50	0.20
(Low basic Ca/sulfur-containing P)
Fatigue life (L50) 13)	h	110	105	105	110	105	120	80	95
Metal-to-metal friction	—	0.131	0.132	0.137	0.138	0.130	0.132	0.132	0.13
coefficient 14)
Seizure Load 15)	N	1050	1050	1050	1050	1050	1150	1000	1050
ISOT remaining base	mgKOH/g	0.5	0.5	0.5	0.5	0.3	0.5	0.5	0.5
number 16)

Metal-to-metal friction	0.93	0.92	0.93	0.93	0.92	0.98	0.89	0.98
characteristics
(uV characterisitcs) 17)

Examples

Comparative Examples

		9	10	1	2	3	4	5

Mineral oil 1)	mass %	Balance	Balance	Balance	Balance	Balance	Balance	Balance

High overbased Ca sulfonate 2)	ppm/Ca	250	250	250	250	250		250
High overbased Ca sulfonate 3)	ppm/Ca
Low overbased Ca sulfonate 4)	ppm/Ca							100
Low overbased Ca sulfonate 5)	ppm/Ca	150	50	100	100		100
High overbased Ca salicylate 6)	ppm/Ca
High overbased Ca phenate 7)	ppm/Ca
Total	ppm/Ca	400	300	350	350	250	100	350
Sulfur-containing	ppm/P	600	200	800		300	300	300
phosphite ester 8)
Phosphite ester 9)	ppm/P
Phosphate ester 10)	ppm/P				600
Acid phosphate ester 11)	ppm/P
Total	ppm/P	600	200	800	600	300	300	300
Other performance additives 12)	mass %	13.0	13.0	13.0	13.0	13.0	13.0	13.0
[M]/[P]	—	0.25	0.25	0.13	—	0.00	0.33	0.00
(Low basic Ca/sulfur-containing P)
Fatigue life (L50) 13)	h	120	80	140	55	70	110	85
Metal-to-metal friction	—	0.131	0.13	0.119	0.132	0.130	0.132	0.131
coefficient 14)
Seizure Load 15)	N	1150	1000	1150	1000	1050	1050	1050
ISOT remaining base	mgKOH/g	0.4	0.5	0.5	0.5	0.5	0	0.5
number 16)

Metal-to-metal friction	0.95	0.93	1.08	0.85	1.15	0.93	1.12
characteristics
(uV characterisitcs) 17)

Comparative Examples

		6	7	8	9	10	11

Mineral oil 1)	mass %	Balance	Balance	Balance	Balance	Balance	Balance

High overbased Ca sulfonate 2)	ppm/Ca	250			500	250	250
High overbased Ca sulfonate 3)	ppm/Ca
Low overbased Ca sulfonate 4)	ppm/Ca
Low overbased Ca sulfonate 5)	ppm/Ca	250	100	100	100	60	150
High overbased Ca salicylate 6)	ppm/Ca		250
High overbased Ca phenate 7)	ppm/Ca			250
Total	ppm/Ca	500	350	350	600	310	400
Sulfur-containing	ppm/P	300	300	300	300	550	800
phosphite ester 8)
Phosphite ester 9)	ppm/P
Phosphate ester 10)	ppm/P				300
Acid phosphate ester 11)	ppm/P
Total	ppm/P	300	300	300	600	550	800
Other performance additives 12)	mass %	13.0	13.0	13.0	13.0	13.0	13.0
[M]/[P]	—	0.83	0.33	0.33	0.33	0.11	0.19
(Low basic Ca/sulfur-containing P)
Fatigue life (L50) 13)	h	110	70	65	105	110	140
Metal-to-metal friction	—	0.130	0.131	0.132	0.137	0.13	0.117
coefficient 14)
Seizure Load 15)	N	750	1050	1050	750	1100	1200
ISOT remaining base	mgKOH/g	0.4	0.9	0.4	0.7	0.5	0.4
number 16)

Metal-to-metal friction	0.85	0.93	0.92	0.93	1.10	0.98
characteristics
(uV characterisitcs) 17)

The footnotes of Table 1 are as follows:
1) 100° C. kinematic viscosity: 3.0 mm²/s, viscosity index 109, S content 0.1 percent by mass or less
2) base number 300 mgKOH/g, Ca content 11.6 percent by mass
3) base number 500 mgKOH/g, Ca content 18.0 percent by mass
4) base number 80 mgKOH/g, Ca content 4.5 percent by mass
5) base number 20 mgKOH/g, Ca content 2.4 percent by mass
6) base number 170 mgKOH/g, Ca content 6.3 percent by mass
7) base number 250 mgKOH/g, Ca content 9.3 percent by mass
8) 3-thiopentylhydrogen phosphite
9) dibutylhydrogen phosphite
10) tricresyl phosphate
11) butyl acid phosphate
12) ashless dispersant, anti-oxidant, viscosity index improver, friction modifier, sealing agent, metal deactivators
13) Four-ball fatigue life test (IP 300): rotation speed 3000 rpm, temperature 120° C., contact pressure 3.9 GPa
14) Block on ring test (LFW-1): load 400N, sliding velocity 0.05 m/s, temperature 80° C.
15) Pin/V-block seizure test: rotation speed 290 rpm, temperature 80° C.
16) Base number determined by a hydrochloric acid method at 165.5° C., after 72 hours
17) Block on ring test (LFW-1): load 90N, slipping velocity 0 to 0.2 m/s, temperature 60° C. When the ratio (μ2/μ20) of the friction coefficient at a slipping velocity of 0.2 m/s to that at a slipping velocity of 0.02 m/s is 1 or less, in particular less than 1, the μ-V slope is a positive gradient and thus the composition is evaluated as being excellent in scratch noise preventing properties.

As apparent from the results set forth in Table 1, Comparative Example 4 wherein (A) the high overbased alkaline earth metal sulfonate is blended in an amount of less than 0.01 percent by mass as calcium is lower in ISOT remaining base number than the examples and likely to be poor in oxidation stability while Comparative Example 9 wherein the same is blended in an amount of more than 0.03 percent by mass is lower in seizure load than the examples and likely to be poor in anti-seizure properties. Comparative Examples 7 and 8 containing an high overbased alkaline earth metal salicylate and an high overbased alkaline earth metal phenate, respectively are shorter in anti-fatigue life than the examples and thus likely to be poor in anti-fatigue properties.
Comparative Examples 3 and 5 wherein (B) the low overbased alkaline earth metal sulfonate is blended in an amount of less than 0.005 percent by mass as calcium are shorter in anti-fatigue life than the examples and likely to be poor in anti-fatigue properties while Comparative Example 6 wherein the same is blended in an amount of more than 0.015 percent by mass is lower in seizure load than the examples and likely to be poor in anti-seizure properties.
Comparative Example 2 wherein (C) the sulfur-containing phosphite ester is blended in an amount of less than 0.02 percent by mass as phosphorous is shorter in anti-fatigue life than the examples and likely to be poor in anti-fatigue properties while Comparative Examples 1 and 11 wherein the same is blended in an amount of more than 0.06 percent by mass are lower in metal-to-metal friction coefficient than the examples and give an adverse effect on torque capacity.
Comparative Example 10 wherein the content ([P]) of (B) the low overbased alkaline earth metal sulfonate as phosphorous and the content ([M]) of (C) the sulfur-containing phosphite ester as metal are within the ranges as defined by the present invention but the ratio ([M]/[P]) is less than 0.15 is negative in μ-V gradient evaluated by the block on ring test when compared with the examples and likely to be poor in belt-pulley scratch noise preventing properties.

Claims

1. A lubricating oil composition for a metal belt-type continuously variable transmission comprising a lubricating base oil and (A) an high overbased alkaline earth metal sulfonate having a base number determined by a perchloric acid method of 300 to 500 mgKOH/g in an amount of 0.01 to 0.03 percent by mass as alkaline earth metal, (B) a low overbased alkaline earth metal sulfonate with a base number determined by a perchloric acid method of 0 to 40 mgKOH/g in an amount of 0.005 to 0.015 percent by mass as alkaline earth metal, and (C) a sulfur-containing phosphite ester represented by structural formula (I) below in an amount of 0.02 to 0.06 percent by mass as phosphorus so that the ratio ([M]/[P]) of the content as alkaline earth metal ([M]) of (B) the low overbased alkaline earth metal sulfonate to the content as phosphorus ([P]) of (C) the sulfur-containing phosphite ester is 0.15 or greater:

wherein R is a sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms, R¹is hydrogen, a hydrocarbyl group having 4 to 20 carbon atoms or a sulfur-containing hydrocarbyl group having 4 to 20 carbo atoms.

2. The lubricating oil composition for a metal belt-type continuously variable transmission according to claim 1 further comprising (D) a phosphite ester and/or an orthophosphate ester in such an amount that the amount of phosphorous in the lubricating oil composition is the range of up to 0.08 percent by mass or less.

3. The lubricating oil composition for a metal belt-type continuously variable transmission according to claim 1 further comprising at least one type selected from the group consisting of friction modifiers, metallic detergents, viscosity index improvers, pour point depressants, anti-oxidants, corrosion inhibitors, and anti-foamers.

4. The lubricating oil composition for a metal belt-type continuously variable transmission according to claim 2 further comprising at least one type selected from the group consisting of friction modifiers, metallic detergents, viscosity index improvers, pour point depressants, anti-oxidants, corrosion inhibitors, and anti-foamers.