JP5350583B2 - Lubricating oil composition and method for improving metal fatigue of automobile transmission using the same - Google Patents

Description

  The present invention relates to a lubricating oil composition. More specifically, the lubricating oil composition has a low viscosity, is excellent in low-temperature fluidity and oxidation stability, has a long metal fatigue life, and is particularly suitable as a lubricating oil for automobile transmissions. It is about.

In recent years, there has been an urgent need to save energy for construction machinery, agricultural machinery, etc., in response to environmental issues, such as automobiles, construction machinery, agricultural machinery, etc., such as engines, transmissions, final reducers, compressors, hydraulic devices, etc. Devices are strongly required to contribute to energy saving. Therefore, the lubricating oil used for these is required to reduce the stirring resistance and frictional resistance as compared with the conventional one.
For example, as one of the fuel saving means for the transmission and the final reduction gear, there is a reduction in the viscosity of the lubricating oil. Among automatic transmissions, automatic transmissions and continuously variable transmissions for automobiles have torque converters, wet clutches, gear bearing mechanisms, oil pumps, hydraulic control mechanisms, etc., and manual transmissions and final reduction gears have gear bearing mechanisms. By lowering the viscosity of the lubricating oil used in these, the stirring resistance and friction resistance of torque converters, wet clutches, gear bearing mechanisms, oil pumps, etc. are reduced, and power transmission efficiency is improved. By improving, it becomes possible to improve the fuel consumption of the automobile.

However, lubricants with reduced viscosity are prone to evaporation loss of lubricants, especially when used in high-humidity atmospheres, and the friction coefficient of the lubricant film increases with decreasing viscosity. Occurs. As a result, the fatigue life is greatly reduced, and seizure or the like may occur, causing problems in the transmission or the like. In particular, when a phosphorus-based extreme pressure agent is blended in order to improve the extreme pressure property of a low-viscosity oil, the fatigue life is remarkably deteriorated, and it is generally difficult to reduce the viscosity.
For example, regarding conventional transmission oils for automobiles, it is possible to maintain various performances such as transmission characteristics for a long period of time. Synthetic oil and / or mineral oil base oil, antiwear agent, extreme pressure agent, metal detergent However, these compositions are disclosed in which ashless dispersants, friction modifiers, viscosity index improvers and the like are optimized (see, for example, Patent Documents 1 and 2). The effect on the fatigue life when viscosity is increased has not been studied at all.

JP 7-268375 A JP 2000-63869 A

  Under such circumstances, the present invention provides a lubricating oil composition that is low in viscosity, excellent in low-temperature fluidity and oxidation stability, has a long metal fatigue life, and is particularly suitable as a lubricating oil for automobile transmissions. It is intended to do.

As a result of intensive studies to develop the lubricating oil composition having the above-described excellent performance, the present inventors have found that an ethylene-α-olefin having a specific range of molecular weight with respect to a base oil having a specific property. It has been found that the purpose can be achieved by blending the copolymer at a predetermined ratio. The present invention has been completed based on such findings.
That is, the present invention
(1) A lubricant base oil and (A) an ethylene-α-olefin copolymer having a number average molecular weight of 2800 to 8000 of 0.5 to 10% by mass, and as the lubricant base oil, A lubricating oil composition having a viscosity of 1.5 to 40 mm ² / s, a viscosity index of 100 or more, a pour point of −25 ° C. or less, and a sulfur content of 0.01% by mass or less. ,
(2) Further, (B) the above-mentioned (B) a phosphorous extreme pressure agent and / or a sulfur extreme pressure agent of 0.01 to 2.0% by mass, and the total sulfur content is 0.15% by mass or less ( The lubricating oil composition according to item 1),
(3) The above (1) or (1) further comprising at least one additive selected from (C) an antioxidant, another extreme pressure agent, an antiwear agent, an oiliness agent, a cleaning dispersant, and a pour point depressant. The lubricating oil composition according to (2), and (4) the lubricating oil composition according to any one of (1) to (3) above, which is used as a lubricating oil for automobile transmissions.
Is to provide.

  According to the present invention, it is possible to provide a lubricating oil composition that is low in viscosity, excellent in low-temperature fluidity and oxidation stability, has a long metal fatigue life, and is particularly suitable as a lubricating oil for automobile transmissions. .

In the lubricating oil composition of the present invention, a base oil having the following properties is used.
The said base oil requires that kinematic viscosity in 100 degreeC exists in the range of 1.5-40 mm < ² > / s. When the kinematic viscosity is 1.5 mm ² / s or more, the evaporation loss is small. On the other hand, when the kinematic viscosity is 40 mm ² / s or less, the power loss due to the viscous resistance does not increase so much, and the fuel efficiency improvement effect is obtained. A preferable kinematic viscosity is ^{2 to} 25 mm ² / s, and particularly preferably ^{2 to 10} mm ² / s.
The base oil needs to have a viscosity index of 100 or more and a pour point of −25 ° C. or less. If the viscosity index is 100 or more, the viscosity change due to temperature change is small. This viscosity index is preferably 105 or more, more preferably 110 or more. Moreover, if a pour point is -25 degrees C or less, the lubricating oil composition obtained will have sufficient fluidity | liquidity also in a low-temperature environment. This pour point is preferably −30 ° C. or lower, more preferably −40 ° C. or lower.
The kinematic viscosity and the viscosity index are values measured according to JIS K 2283, and the pour point is a value measured according to JIS K 2265.
Moreover, the said base oil requires that sulfur content is 0.01 mass% or less. If this sulfur content is 0.01 mass% or less, the oxidation stability of the resulting lubricating oil composition will be good. The sulfur content is a value measured according to JIS K2541.

There is no restriction | limiting in particular about the kind as the said base oil, Both mineral oil and synthetic oil can be used. Here, as the mineral oil, various conventionally known oils can be used, for example, paraffin-based mineral oil, intermediate-based mineral oil, naphthenic-based mineral oil, and the like. Specific examples include solvent refining and hydrorefining. And light neutral oil, medium neutral oil, heavy neutral oil or bright stock, and mineral oil obtained by wax isomerization.
As the synthetic oil, various conventionally known oils can be used, for example, poly α-olefin, polybutene, polyol ester, dibasic acid ester, phosphoric acid ester, polyphenyl ether, alkylbenzene, alkylnaphthalene, Polyoxyalkylene glycol, neopentyl glycol, silicone oil, trimethylolpropane, pentaerythritol, hindered ester, and the like can be used. These base oils can be used alone or in combination of two or more kinds, and mineral oil and synthetic oil may be used in combination.

The lubricating oil composition of the present invention comprises a base oil having the above properties and (A) 0.5 to 10% by mass of an ethylene-α-olefin copolymer having a number average molecular weight of 2800 to 8000. To do.
In the lubricating oil composition of the present invention, the ethylene-α-olefin copolymer used as the component (A) has a number average molecular weight in the range of 2800 to 8000, and the number average molecular weight is 2800 or more. And the effect which improves the viscosity index of the obtained lubricating oil composition is exhibited, On the other hand, if it is 8000 or less, the shear stability of the obtained lubricating oil composition will become favorable. From the viewpoint of imparting a viscosity index improving effect and good shear stability, the number average molecular weight is preferably 3000 to 7000.
The number average molecular weight is a value measured by the vapor pressure osmotic pressure method.
As the α-olefin constituting the ethylene-α-olefin copolymer, those having 3 to 20 carbon atoms, more preferably 3 to 10 carbon atoms are used. Examples of such α-olefins include propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene and 1-decene. These α-olefins may be used singly or in combination of two or more, but propylene is particularly preferable from the viewpoint of performance.

Moreover, 15-85 mol% is preferable from the surface of performance, and, as for content of the ethylene unit in the said ethylene-alpha-olefin copolymer, 20-80 mol% is more preferable. There is no restriction | limiting in particular about a copolymerization form, Any of a random and a block may be sufficient.
In the lubricating oil composition of the present invention, as the component (A), one type of the ethylene-α-olefin copolymer may be used, or two or more types may be used in combination. This component (A) is blended in the base oil in order to make the lubricating oil composition of the present invention low viscosity, excellent low-temperature fluidity and oxidation stability, and having a long metal fatigue life. Is a component to be processed.
Therefore, the content of the component (A) is 0.5 to 10% by mass, preferably 0.5 to 6% by mass, more preferably 0.5 to 5% based on the total amount of the composition from the viewpoint of the above performance. 4.5% by mass.

In the lubricating oil composition of the present invention, a phosphorus-based extreme pressure agent and / or a sulfur-based extreme pressure agent can be further contained as the component (B).
Examples of the phosphorous extreme pressure agent include phosphoric acid esters, acidic phosphoric acid esters, acidic phosphoric acid ester amine salts, phosphorous acid esters, acidic phosphorous acid esters, and acidic phosphorous acid ester amine salts. .

  Examples of the phosphate ester include triaryl phosphate, trialkyl phosphate, trialkylaryl phosphate, triarylalkyl phosphate, trialkenyl phosphate, and the like, for example, triphenyl phosphate, tricresyl phosphate, benzyldiphenyl phosphate, ethyl diphenyl phosphate. , Tributyl phosphate, ethyl dibutyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, ethyl phenyl diphenyl phosphate, di (ethylphenyl) phenyl phosphate, propylphenyl diphenyl phosphate, di (propylphenyl) phenyl phosphate, triethylphenyl phosphate, tripropyl Phenyl phosphate, butyl phenol Rudiphenyl phosphate, di (butylphenyl) phenyl phosphate, tributylphenyl phosphate, trihexyl phosphate, tri (2-ethylhexyl) phosphate, tridecyl phosphate, trilauryl phosphate, trimyristyl phosphate, tripalmityl phosphate, tristearyl phosphate, trio Examples include rail phosphate.

  Examples of the acidic phosphate ester include di-2-ethylhexyl acid phosphate, didecyl acid phosphate, didodecyl acid phosphate (dilauryl acid phosphate), tridecyl acid phosphate, dioctadecyl acid phosphate (distearyl acid phosphate), di- 9-octadecenyl acid phosphate (dioleoyl acid phosphate) and the like. Examples of the phosphite ester include triethyl phosphite, tributyl phosphite, triphenyl phosphite, tricresyl phosphite, tri (nonyl). Phenyl) phosphite, tri (2-ethylhexyl) phosphite, tridecyl phosphite, trilauryl phosphite, triisooctyl phosphite, diphe Louis-Soviet decyl phosphite, tristearyl phosphite, and the like can be given trio rail phosphite.

Examples of acidic phosphites include di-2-ethylhexyl hydrogen phosphite, didecyl hydrogen phosphite, didodecyl hydrogen phosphite (dilauryl hydrogen phosphite), and dioctadecyl hydrogen phosphite (distearyl). Hydrogen phosphite), di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite), diphenyl hydrogen phosphite and the like.
Examples of the acid phosphate amine salt and the acid phosphite amine salt include salts of the aforementioned acid phosphate ester and acid phosphite ester with the following amines. As the amines, mono-substituted amines, di-substituted amines or tri-substituted amines are used.

  Examples of mono-substituted amines include butylamine, pentylamine, hexylamine, cyclohexylamine, octylamine, laurylamine, stearylamine, oleylamine, benzylamine, etc. Examples of disubstituted amines include dibutylamine, Dipentylamine, dihexylamine, dicyclohexylamine, dioctylamine, dilaurylamine, distearylamine, dioleylamine, dibenzylamine, stearyl monoethanolamine, decyl monoethanolamine, hexyl propanolamine, benzyl monoethanolamine, Phenyl monoethanolamine, tolyl monopropanolamine and the like. Examples of trisubstituted amines include tributylamine, tripentylamine. , Trihexylamine, tricyclohexylamine, trioctylamine, trilaurylamine, tristearylamine, trioleylamine, tribenzylamine, dioleyl monoethanolamine, dilauryl monopropanolamine, dioctyl monoethanolamine, dihexyl monopropanol Amine, dibutyl propanolamine, oleyl diethanolamine, stearyl dipropanolamine, lauryl diethanolamine, octyl dipropanolamine, butyl diethanolamine, benzyl diethanolamine, phenyl diethanolamine, tolyl dipropanolamine, xylyl diethanolamine, triyl Examples include ethanolamine and tripropanolamine.

Acid phosphate ester amine salts such as monomethyl hydrogen phosphate, monoethyl hydrogen phosphate, monopropyl hydrogen phosphate, monobutyl hydrogen phosphate, mono-2-ethylhexyl hydrogen phosphate, etc. Salts with amines can also be used.
In this invention, this phosphate ester type compound may be used individually by 1 type, and may be used in combination of 2 or more type.

  On the other hand, any sulfur-based extreme pressure agent may be used as long as it has a sulfur atom in the molecule and can be dissolved or uniformly dispersed in the lubricant base oil to exhibit the extreme pressure agent and excellent friction characteristics. Examples of such compounds include sulfurized fats and oils, sulfurized fatty acids, sulfurized esters, sulfurized olefins, dihydrocarbyl polysulfides, thiadiazole compounds, thiophosphates (thiophosphites, thiophosphates), alkylthiocarbamoyl compounds, thiocarbamate compounds, thioterpene compounds. And dialkylthiodipropionate compounds. Here, sulfurized fats and oils are obtained by reacting sulfur and sulfur-containing compounds with fats and oils (lard oil, whale oil, vegetable oil, fish oil, etc.), and the sulfur content is not particularly limited, but generally 5 to 30 mass. % Is preferred. Specific examples thereof include sulfurized lard, sulfurized rapeseed oil, sulfurized castor oil, sulfurized soybean oil, and sulfurized rice bran oil. Examples of the sulfurized fatty acid include sulfurized oleic acid, and examples of the sulfurized ester include sulfurized methyl oleate and sulfurized rice bran fatty acid octyl.

As the sulfurized olefin, for example, the following general formula (I)
R ¹ -S _q -R ² (I)
(In the formula, R ¹ represents an alkenyl group having 2 to 15 carbon atoms, R ² represents an alkyl group or alkenyl group having 2 to 15 carbon atoms, and q represents an integer of 1 to 8).
The compound etc. which are represented by these can be mentioned. This compound is obtained by reacting an olefin having 2 to 15 carbon atoms or a dimer to tetramer thereof with a sulfurizing agent such as sulfur or sulfur chloride. As the olefin, propylene, isobutene, diisobutene and the like are preferable.
As dihydrocarbyl polysulfide, the following general formula (II)
R ³ -S _r -R ⁴ (II)
(In the formula, R ³ and R ⁴ are each an alkyl group having 1 to 20 carbon atoms or a cyclic alkyl group, an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or 7 to 20 carbon atoms. An arylalkyl group, which may be the same or different from each other, and r represents an integer of 1 to 8.
It is a compound represented by these. Here, when R ³ and R ⁴ are alkyl groups, they are referred to as alkyl sulfides.
Preferred examples of the dihydrocarbyl polysulfide represented by the general formula (II) include dibenzyl polysulfide, various dinonyl polysulfides, various didodecyl polysulfides, various dibutyl polysulfides, various dioctyl polysulfides, diphenyl polysulfide, dicyclohexyl polysulfide, and the like. Can do.

  Examples of thiadiazole compounds include 2,5-bis (n-hexyldithio) -1,3,4-thiadiazole, 2,5-bis (n-octyldithio) -1,3,4-thiadiazole, 2,5 -Bis (n-nonyldithio) -1,3,4-thiadiazole, 2,5-bis (1,1,3,3-tetramethylbutyldithio) -1,3,4-thiadiazole, 3,5-bis ( n-hexyldithio) -1,2,4-thiadiazole, 3,6-bis (n-octyldithio) -1,2,4-thiadiazole, 3,5-bis (n-nonyldithio) -1,2,4 -Thiadiazole, 3,5-bis (1,1,3,3-tetramethylbutyldithio) -1,2,4-thiadiazole, 4,5-bis (n-octyldithio) -1,2,3-thiadiazole 4,5-bis n- nonyldithio) -1,2,3-thiadiazole, 4,5-bis (1,1,3,3-tetramethylbutyl dithio) -1,2,3-thiadiazoles such as can be a preferably exemplified.

Examples of the thiophosphate include alkyl trithiophosphate, aryl or alkylaryl thiophosphate, zinc dilauryl dithiophosphate, and lauryl trithiophosphate and triphenyl thiophosphate are particularly preferable.
Examples of alkylthiocarbamoyl compounds include bis (dimethylthiocarbamoyl) monosulfide, bis (dibutylthiocarbamoyl) monosulfide, bis (dimethylthiocarbamoyl) disulfide, bis (dibutylthiocarbamoyl) disulfide, and bis (diamilthiocarbamoyl) disulfide. Bis (dioctylthiocarbamoyl) disulfide and the like can be preferably mentioned.

Further, as the thiocarbamate compound, for example, zinc dialkyldithiocarbamate, as the thioterpene compound, for example, a reaction product of phosphorus pentasulfide and pinene, and as the dialkylthiodipropionate compound, for example, dilaurylthiodipropionate. And distearyl thiodipropionate. Of these, thiadiazole compounds and benzyl sulfide are preferable from the viewpoints of extreme pressure, friction characteristics, thermal oxidation stability, and the like.
These sulfur type extreme pressure agents may be used individually by 1 type, and may be used in combination of 2 or more type.

In the lubricating oil composition of the present invention, as the component (B), only the phosphorus extreme pressure agent may be used, or only the sulfur extreme pressure agent may be used, or the phosphorus extreme pressure agent and A sulfur-based extreme pressure agent may be used in combination.
The content of the component (B) is usually about 0.01 to 2.0% by mass, preferably about 0.00% by mass, based on the total amount of the lubricating oil composition, from the viewpoint of the balance as an extreme pressure agent and the economy. It is 05-1.5 mass%.
When using a sulfur-based extreme pressure agent, from the viewpoint of corrosion prevention, the total sulfur content in the composition is preferably 0.15% by mass or less, more preferably 0.10% by mass or less. It is preferable to adjust the amount.
In the lubricating oil composition of the present invention, as component (C), at least one selected from antioxidants, other extreme pressure agents, antiwear agents, oiliness agents, detergent dispersants, and pour point depressants. Additives can be included.

Examples of the antioxidant include amine-based antioxidants, phenol-based antioxidants, and sulfur-based antioxidants.
Examples of amine-based antioxidants include monoalkyl diphenylamines such as monooctyldiphenylamine and monononyldiphenylamine, 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, 4, Polyalkyldiphenylamines such as 4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, dialkyldiphenylamines such as 4,4'-dinonyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine , Α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexyl Butylphenyl -α- naphthylamine, heptylphenyl -α- naphthylamine, octylphenyl -α- naphthylamine, there may be mentioned naphthylamine such as nonylphenyl -α- naphthylamine, among others those of the dialkyl diphenylamine is preferred.

Examples of the phenolic antioxidant include monophenols such as 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butyl-4-ethylphenol, 4,4′- Examples include diphenols such as methylene bis (2,6-di-tert-butylphenol) and 2,2′-methylene bis (4-ethyl-6-tert-butylphenol).
Examples of the sulfur-based antioxidant include phenothiazine, pentaerythritol-tetrakis- (3-laurylthiopropionate), bis (3,5-tert-butyl-4-hydroxybenzyl) sulfide, thiodiethylenebis (3- ( 3,5-di-tert-butyl-4-hydroxyphenyl)) propionate, 2,6-di-tert-butyl-4- (4,6-bis (octylthio) -1,3,5-triazine-2- And methylamino) phenol.
These antioxidants may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, the compounding quantity is 0.01-10 mass% normally on the basis of lubricating oil composition whole quantity, Preferably it selects in the range of 0.03-5 mass%.

Examples of other extreme pressure agents, antiwear agents, and oil-based agents include zinc dithiophosphate (ZnDTP), zinc dithiocarbamate (ZnDTC), sulfurized oxymolybdenum organophosphorodithioate (MoDTP), and sulfurized oxymolybdenum dithiocarbamate (MoDTC). And organometallic compounds such as These compounding quantities are 0.05-5 mass% normally on the basis of lubricating oil composition whole quantity, Preferably it is 0.1-3 mass%.
In addition, aliphatic saturated and unsaturated monocarboxylic acids such as stearic acid and oleic acid, polymerized fatty acids such as dimer acid and hydrogenated dimer acid, hydroxy fatty acids such as ricinoleic acid and 12-hydroxystearic acid, lauryl alcohol, oleyl alcohol, etc. Oily agents such as aliphatic saturated and unsaturated monoalcohols, aliphatic saturated and unsaturated monoamines such as stearylamine and oleylamine, aliphatic saturated and unsaturated monocarboxylic amides such as lauric acid amide and oleic acid amide .
The preferable compounding amount of these oil-based agents is in the range of 0.01 to 10% by mass, particularly preferably in the range of 0.1 to 5% by mass, based on the total amount of the lubricating oil composition.

Examples of the detergent / dispersant include succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinic acid esters, monovalent or divalent carboxylic acid amides represented by fatty acids or succinic acid. Ashless dispersants, neutral metal sulfonates, neutral metal phenates, neutral metal salicylates, neutral metal phosphonates, basic sulfonates, basic phenates, basic salicylates, overbased sulfonates, overbased salicylates And metal detergents such as overbased phosphonates. These compounding quantities are 0.1-20 mass% normally on the basis of lubricating oil composition whole quantity, Preferably it is 0.5-10 mass%.
As the pour point depressant, polymethacrylate having a weight average molecular weight of about 50,000 to 150,000 can be used.

If desired, the lubricating oil composition of the present invention may contain additives other than those described above, such as a rust inhibitor, a metal deactivator, an antifoaming agent, and a surfactant.
Examples of rust inhibitors include alkenyl succinic acid and partial esters thereof, and examples of metal corrosion inhibitors include benzotriazole, benzimidazole, benzothiazole, thiadiazole, and the like as metal deactivators. For example, benzotriazole, benzotriazole derivative, benzothiazole, benzothiazole derivative, triazole, triazole derivative, dithiocarbamate, dithiocarbamate derivative, imidazole, imidazole derivative and the like are used. Examples of the antifoaming agent include dimethylpolysiloxane and polyacrylate, and examples of the surfactant include polyoxyethylene alkylphenyl ether.

  The lubricating oil composition of the present invention has features such as low viscosity, excellent low-temperature fluidity and oxidation stability, and has a long metal fatigue life. For example, oil for vehicle transmission and power steering oil , Shock absorber oil, engine oil and automobile / industrial gear oil, hydraulic oil, bearing oil, etc., but especially as transmission oil for automobile automatic transmission, manual transmission, continuously variable transmission, etc. Is preferred.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
The physical properties of the base oil and the lubricating oil composition were determined according to the following method.
<Base oil and lubricating oil composition>
(1) Kinematic viscosity (40 ° C, 100 ° C)
The measurement was performed according to JIS K 2283.
(2) Viscosity index (VI)
The measurement was performed according to JIS K 2283.
(3) Sulfur content Measured according to JIS K2541.
<Base oil>
(4) Pour point Measured according to JIS K 2265.
<Lubricating oil composition>
(5) Low temperature viscosity (-40 ° C)
The Brookfield viscosity at −40 ° C. was measured according to ASTM D 2983.
(6) Fatigue life Fatigue life was measured using a four-ball rolling fatigue tester in the following manner.
(bearing)
Material: Bearing steel Test piece: φ60 x 5mm thickness
Test steel ball dimensions: φ3 / 8 inch (3/8 × 2.54 cm)
(Test conditions)
Load: 147N
Rotational speed: 2200 rpm
Oil temperature: 120 ° C
L50 (average value) was calculated from the results of six tests, using the time until flaking occurred on the test piece as the fatigue life.
(7) Oxidation stability In accordance with JIS K 2514, the test oil was forcibly deteriorated by the ISOT test (150 ° C.), the viscosity change rate after 144 hours (40 ° C., 100 ° C.), the total acid value increase, the base Value, n-heptane insoluble content, and copper element increase were measured.

The kind of each component used for preparation of a lubricating oil composition is as follows.
・ Base oil A to F
The properties are shown in Table 1.

・ Ethylene-α-olefin copolymer I
Made by Mitsui Chemicals, trade name “Lucanto HC600”, number average molecular weight 2600, 100 ° C. kinematic viscosity 600 mm ² / s, viscosity index 240, S content less than 0.1% by mass ・ Ethylene-α-olefin copolymer II
Made by Mitsui Chemicals, Inc., trade name “Lucant HC2000”, number average molecular weight 3700, kinematic viscosity at 100 ° C. 2000 mm ² / s, viscosity index 300, S content less than 0.1% by mass. Ethylene-α-olefin copolymer III 50% by weight diluted oil included)
Made by Mitsui Chemicals, trade name “Lucanto HS4010M”, number average molecular weight 6600, kinematic viscosity at 100 ° C. 2000 mm ² / s, viscosity index 335, S content less than 0.1% by mass ・ Viscosity index improver I
Product name “VISCOPLEX 0-050”, manufactured by Romax, polymethacrylate number average molecular weight 18000, kinematic viscosity at 100 ° C. 450 mm ² / s
・ Viscosity index improver II
Sanyo Kasei Co., Ltd., trade name “Aclude C728”, polymethacrylate number average molecular weight 45000, 100 ° C. kinematic viscosity 852 mm ² / s
・ Pour point depressant, Sanyo Kasei Co., Ltd., trade name “Acrub C728”, polymethacrylate type ・ Extreme pressure agent: thiadiazole ・ ATF additive package, Infinium, trade name “Infineum T4261,” Phosphorus extreme pressure agent, sulfur Contains extreme pressure agent, cleaning dispersant, friction modifier, antioxidant

Reference Examples 1 to 3, Example 1 and Comparative Examples 1 to 6
Lubricating oil compositions having the compositions shown in Table 2 were prepared and evaluated for physical properties other than oxidation stability. The results are shown in Table 2.
The oxidation stability was evaluated for Reference Example 1 and Comparative Example 1. The results are shown in Table 3.

As can be seen from Table 2, the lubricating oil compositions of Reference Examples 1 to 3 and Example 1 all have a low-temperature viscosity (−40 ° C.) of less than 10,000 and a fatigue life [L50] of more than 150 minutes. It has good low temperature fluidity and long metal fatigue life. On the other hand, Comparative Examples 1 to 4 and Comparative Example 6 each have a fatigue life [L50] of less than 150 and a short metal fatigue life, and Comparative Examples 1, 4 and 6 have a low temperature viscosity (−40 ° C. ) Exceeds 10,000 and is inferior in low-temperature fluidity.
On the other hand, in Comparative Example 5, the fatigue life [L50] exceeds 150 and the metal fatigue life is long, but the low-temperature fluidity is extremely poor, and as can be seen from Table 3, compared with Reference Example 1, Poor oxidation stability.

  The lubricating oil composition of the present invention has low viscosity, excellent low-temperature fluidity and oxidation stability, and has a long metal fatigue life, such as automobile transmission oil, power steering oil, shock absorber oil, engine oil and It is suitably used for automobile / industrial gear oil, hydraulic oil, bearing oil and the like.

Claims (4)

A lubricant base oil, (A) 0.5 to 10% by mass of an ethylene-α-olefin copolymer having a number average molecular weight of 2800 to 8000, and (B) a thiadiazole compound 0.01 to 2.0 as an extreme pressure agent. As the lubricating base oil, the kinematic viscosity at 100 ° C. is 1.5 to 40 mm ² / s, the viscosity index is 100 or more, the pour point is −25 ° C. or less, and the sulfur content is 0.00. A lubricating oil composition characterized by using one having a mass of 01% by mass or less. Furthermore, (C) an antioxidant selected from amine-based antioxidants, phenol-based antioxidants, and sulfur-based antioxidants , other extreme pressure agents, antiwear agents, oil-based agents, cleaning dispersants, and pour point depressants. The lubricating oil composition according to claim 1, comprising at least one additive selected from the group consisting of:   The lubricating oil composition according to claim 1 or 2, which is used as a lubricating oil for automobile transmissions.   A method for improving metal fatigue of an automobile transmission, wherein the lubricating oil composition according to claim 1 or 2 is added to an automobile transmission.