DE3881411T2 - Lubricant compositions for friction pressure drive. - Google Patents

Description

Field of the invention

The present invention relates to a lubricating oil composition for a traction drive, and more particularly to a lubricating oil composition which has a high traction coefficient, exhibits a limited change in traction coefficient at low temperatures, is excellent in wear resistance, load capacity, thermal stability and oxidation stability and anti-rust properties, and which can be effectively used as a lubricating oil for power transmission systems including a traction drive mechanism.

State of the art

Recently, traction drives (a friction-driven device using rolling contact) have been used as continuously variable transmissions for automobiles and other industrial equipment. The fluids used for such traction drives must have a high traction coefficient and be highly efficient for power transmission.

A number of traction drive fluids have been proposed that meet such requirements (e.g. JP-B-46-338, 46-339, 47-35763 and 58-27838). All of these proposals aim to improve the traction coefficient.

However, a practical test of the performance of such fluids for traction drives showed that at low temperatures have a low power transmission capacity and are therefore inadequate for practical use. In power transmission systems subject to low to high ambient temperatures, the traction coefficient of these fluids changes depending on the temperature and, in particular, drops considerably at low temperatures. This causes problems in practical operation in winter and in cold areas.

EP-A-0 208 541 discloses lubricant compositions for use in traction drives, which contain base oils of a selected type of hydrocarbons combined with certain amounts of selected zinc dialkyldithiophosphates, alkenylsuccinimides or their boron derivatives, carboxylic acid esters of polyalcohols. Although these compositions provide extended durability, high oxidation stability, high shear stability, a high traction coefficient, high wear resistance and rust resistance of a traction drive device, they no longer meet the current, even higher requirements.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a lubricating oil composition for traction drive which has an even higher traction coefficient, shows a limited change in the traction coefficient at low temperatures and is characterized by wear resistance, load capacity, thermal stability and oxidation stability and rust protection properties.

This object is achieved according to the invention by providing a lubricating oil composition for traction drive, comprising:

(A) a base oil having as a major component a saturated hydrocarbon or condensed ring and/or non-condensed ring hydrocarbons,

(B) an ethylene-α-olefin copolymer having an average (number average) molecular weight of 800 to 8,000,

(C) an anti-wear agent, and

(D) a polymethacrylate having a number average molecular weight of 10,000 to 100,000,

wherein the antiwear agent is at least one selected from the group consisting of zinc dithiophosphate, oxymolybdenum organophosphorodithioate sulfide, phosphate, phosphite, amine salt of a phosphate, amine salt of a phosphite, molybdenum dialkyldithiocarbamate, mixtures of sulfurized fats and oils and phosphates, mixtures of sulfurized fats and oils and phosphites, mixtures of sulfurized olefins and phosphates, mixtures of sulfurized olefins and phosphites, and the amine salts of the foregoing mixtures.

Preferred embodiments of the claimed lubricating oil composition are described in the subclaims.

SHORT DESCRIPTION OF THE DRAWING

Fig. 1 shows the traction coefficient u measured in Example 1 and in Comparative Examples 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a base oil containing as the main component a saturated hydrocarbon or Contains condensed ring and/or non-condensed ring hydrocarbons as the component (A).

Various saturated hydrocarbons can be used for this purpose. In particular, it is preferable to use saturated hydrocarbons containing cyclohexyl groups and/or decalyl groups and saturated hydrocarbons having 10 to 40 carbon atoms. For example, the following saturated hydrocarbons containing cyclohexyl groups and/or decalyl groups can be used.

3-Methyl-1,3-dicyclohexylbutane of the following formula:

1-Cyclohexyl-1-decalylethane of the following formula:

2,4-Dicyclohexylpentane of the following formula:

2-Methyl-2,4-dicyclohexylpentane of the following formula:

Alkylcyclohexanes of the following formula

where R¹ is an alkyl group with 10 to 30 carbon atoms. Examples include isododecylcyclohexane and isopentadecylcyclohexane.

In addition, the following saturated hydrocarbons having condensed ring and/or non-condensed ring can be used as component (A) of the present invention.

1,2-Di(dimethylcyclohexyl)propane of the following formula:

2,3-Di(methylcyclohexyl)-2-methylbutane of the following formula:

1,2-Di(methylcyclohexyl)-2-methylpropane of the following formula:

2,4-Dicyclohexylpentane of the following formula: Cyclohexylmethyldecalin of the following formula:

1-(Methyldecalyl)-1-cyclohexylethane of the following formulas:

1-(Dimethyldecalyl)-1-cyclohexylethane of the following formulas:

2-Decalyl-2-cyclohexylpropane of the following formula:

Cyclohexylmethylperhydrofluorene of the following formula:

1-Perhydrofluorenyl-1-cyclohexylethane of the following formula:

Cyclohexylmethylperhydroacenaphthene of the following formula:

1,1,2-Tricyclohexylethane of the following formula:

Bisdecalin of the following formula:

1,3,5-Tricyclohexyl-5-methylhexane of the following formula:

2-(2-Decalyl)-2,4,6-trimethylnonane of the following formula:

1,1-Didecalylethane of the following formula:

Tercyclohexyl of the following formula:

1,1,3-Trimethyl-3-cyclohexylhydrindane of the following formula:

2-Methyl-1,2-didecalylpropane of the following formula:

These hydrocarbons can be used alone or in combination with more than two types.

Among other things, 1-cyclohexyl-1-decalylethane of the following formula is preferred:

Preferably, this hydrocarbon should contain the cis compound in a larger amount, including in an amount of 50% or higher.

In the present invention, component (A) is a base oil composed mainly of the aforementioned saturated hydrocarbon or hydrocarbons having a fused ring and/or a non-fused ring, which may further contain mineral oils, in particular naphthenic mineral oils and synthetic oils such as polybutene and alkylbenzene in amounts of up to 50%.

The component (B) used in the present invention is an ethylene-α-olefin copolymer having a number average molecular weight of 800 to 8,000, preferably 1,000 to 5,000, and more preferably 2,000 to 4,000. Copolymers having a number average molecular weight of less than 800 and more than 8,000 are not preferred because the decrease in Traction coefficient is increased at low temperatures. The ethylene-α-olefin copolymers should have a viscosity-density ratio of 20 to 10,000 mm²/s (20 to 10,000 cSt), preferably 40 to 8,000 mm²/s (40 to 8,000 cSt) at 100ºC. The ethylene-α-olefin copolymers are oligomers of ethylene with α-olefins having 3 to 20 carbon atoms, for example propylene, 1-butene and 1-decene, and are synthetic oils from hydrocarbons which are free from any polar group. The ethylene content of the copolymers should preferably be 30 to 80 mol.%, more preferably 50 to 80 mol.%. The component (B) is used in a proportion of 1 to 20% by weight, preferably 2 to 10% by weight, based on the total amount of the compositions. Proportions of the component (B) below 1% by weight and above 20% by weight are not preferred because the decrease in the traction coefficient at low temperatures is increased.

For such ethylene-α-olefin copolymers, commercially available copolymers can be used. For example, Lucant HC10, HC20, HC40, HC100, HC150, HC600 and HC2000 (trade name; manufactured by Mitsui Petrochemical Co., Ltd.) can be used alone or in appropriate combinations.

In the present invention, antiwear agents are further used as component (C).

The anti-wear agents used include zinc dithiophosphate, oxymolybdenum organophosphorodithioate sulphide, phosphorus (V) and phosphorus (III) compounds such as phosphate, phosphite and their amine salts, and molybdenum dialkyldithiocarbamate, as well as mixtures of sulphurised fats and oils and phosphates, mixtures of sulphurised fats and oils and phosphites, mixtures of sulphurised olefin and phosphates, mixtures of sulphurised olefin and phosphites, and the amine salts of the aforementioned mixtures, which are known as High-pressure agents based on sulfur-phosphorus (high-pressure agents based on SP) are known.

The zinc dithiophosphates are represented by the following general formula:

wherein R², R³, R⁴ and R⁵ may be identical or different and represent a primary alkyl group having 3 to 30 carbon atoms, a secondary alkyl group having 3 to 30 carbon atoms or an aryl group having 6 to 30 carbon atoms substituted with alkyl groups.

Various zinc dithiophosphates represented by the general formula [I] in which the substituents R² to R⁵ may be identical or different may be used alone or in combination. Usually, two or more zinc dithiophosphates in which all the substituents R² to R⁵ are identical are mixed together for use. However, such zinc dithiophosphates may also be used alone. Zinc dithiophosphates in which the substituents R² to R⁵ are different may also be used alone or in a suitable combination with the zinc dithiophosphates in which R² to R⁵ are identical. However, it should be noted that in both cases the amount of zinc dithiophosphate containing a primary alkyl group having 3 to 30 carbon atoms is up to 1/3, in particular 1/2 (on a weight basis) of the total zinc dithiophosphates.

By using zinc dithiophosphates in which the zinc dithiophosphates with a primary alkyl group are at least 1/3 of the total amount of R² to R⁵ of the zinc dithiophosphates, it is possible to further improve the anti-wear property and the load-bearing capacity and to extend the durability, thereby increasing the service life.

For such zinc dithiophosphates, commercially available ones can be used. For example, Lubrizol 1097 (R² to R⁵ are mainly primary octyl groups), Lubrizol 1395 (R² to R⁵ are mainly primary butyl and amyl groups) sold by Nippon Lubrizol Co., OLOA 267 (R² to R⁵ are mainly primary hexyl groups) sold by Kalonite Chemical Co., Hitec E 682 (R² to R⁵ are mainly primary hexyl groups) sold by Nippon Cooper Co., and Amoco 198 (R² to R⁵ are mainly primary butyl and amyl groups) sold by Mnoco Chemical Co. can be used alone or in appropriate combinations. It is then preferred that the proportion of the zinc dithiophosphate in which the substituents R² to R⁵ are primary alkyl groups is set to at least 1/3, preferably at least 1/2.

The oxymolybdenum organophosphorodithioate sulfides are represented by the following formula:

wherein R⁶ and R⁷ may be identical or different and represent an alkyl, cycloalkyl, aryl or alkylaryl group having 1 to 30 carbon atoms and x and y are a positive integer satisfying the equation N + y = 4. The oxymolybdenum organophosphorodithioate sulfides can be prepared by the process described, for example, in JP-B-44-27366. Examples include oxymolybdenum diisopropylphosphorodithioate sulfide, oxymolybdenum diisobutylphosphorodithioate sulfide, oxymolybdenum di-(2-ethylhexyl)phosphorodithioate sulfide, oxymolybdenum di-(p-tert-butylphenyl)phosphorodithioate sulfide and oxymolybdenum di-(nonylphenyl)phosphorodithioate sulfide.

More preferably, the phosphorus(V) and phosphorus(III) compounds are represented by the following formulas [III] or [IV]:

wherein R⁸, R⁹⁰ and R¹⁰ may be identical or different and represent a hydrogen atom or an alkyl, aryl or alkyl-substituted aryl group having 4 to 30 carbon atoms.

For example, the phosphorus(V) and phosphorus(III) compounds may contain phosphates and phosphites such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, tri-(isopropylphenyl) phosphate, butyl acid phosphate, 2-ethylhexylic acid phosphate, lauric acid phosphate, oleic acid phosphate, stearyl acid phosphate, dibutyl hydrogen phosphite, Dioctyl hydrogen phosphite, dilauryl hydrogen phosphite, dioleyl hydrogen phosphite and distearyl hydrogen phosphite and amine salts such as laurylamine, oleylamine, coconut amine and tallow amine salts thereof.

The molybdenum alkyldithiocarbamates are represented by the following general formula [V]:

wherein R¹¹ and R¹² may be identical or different and represent an alkyl group with or without an oxygen atom having 1 to 30 carbon atoms, or a cycloalkyl, aryl or alkylaryl group having 1 to 30 carbon atoms, and wherein x and y are a positive integer satisfying the equation x + y = 4.

As the molybdenum alkyldithiocarbamates represented by the general formula [V], those described in JP-B-49-6362 and 53-31646 and JP-A-56-61397 and 56-62894 can be used. Examples are molybdenum diethyldithiocarbamate sulfide, molybdenum dibutyldithiocarbamate sulfide, molybdenum diamyldithiocarbamate sulfide, molybdenum di(2-ethylhexyl)dithiocarbamate sulfide, molybdenum dilauryldithiocarbamate sulfide, molybdenum di(oleyl-linoleyl)dithiocarbamate sulfide, molybdenum dicyclohexyldithiocarbamate sulfide, molybdenum dinonylphenyldithiocarbamate sulfide, molybdenum 2-ethylhexyl(2-ethylhexyl-o-propoxy)dithiocarbamate sulfide, molybdenum 2-ethylhexyl(butyl-o-propoxy)dithiocarbamate sulfide and Molybdenum 2-ethylhexyl-(stearyl-o-propoxy)dithiocarbamate sulfide.

According to the invention, the aforementioned component (C) should be used in proportions of 0.1 to 10 wt.%, preferably 0.5 to 10 wt.%, based on the total amount of the compositions. A proportion of component (C) below 0.1 wt.% is not preferred due to increased wear losses, whereas a proportion of component (C) above 10 wt.% is undesirable due to increased corrosion and impaired stability.

The traction drive lubricating oil compositions of the present invention comprise the above-mentioned components (A) to (C) and the following-mentioned component (D) and may, if necessary, contain various additives such as antifoaming agents, lubricity improvers, friction modifiers, corrosion inhibitors and durability improvers including rust inhibitors, antioxidants, pour point depressants and viscosity index improvers.

Various rust inhibitors can be used. Examples include calcium sulfonate, barium sulfonate and sodium sulfonate as well as alkyl or alkenyl succinates or their derivatives, alkylamines such as tri-n-butylami-, n-octylamine, tri-n-octylamine and cyclohexylamine, alkylamines or ammonium salts of carboxylic acids such as fatty acids or aromatic carboxylic acids with 6 to 20 carbon atoms and dibasic acids with 2 to 20 carbon atoms or other condensed products of these carboxylic acids with amines. Calcium sulfonate and barium sulfonate are preferred, among others.

Phenolic antioxidants such as 2-6-di-t-butyl-p-cresol and 4-4'-methylene-bis-(2,6-di-t- butylphenol) and amine-based antioxidants such as dioctyldiphenylamine.

Polymethacrylates with an average (number average) molecular weight of 10,000 to 100,000 are particularly mentioned as agents for reducing the pour point or improving the viscosity index. In addition, olefin copolymers such as ethylene/propylene copolymers and styrene/propylene copolymers can be used for this purpose.

The lubricating oil compositions of the present invention have been effectively used in winter and cold regions because they have a high traction coefficient and show a limited change in traction coefficient at low temperatures.

Examples

The present invention will now be explained in more detail by the examples and comparative examples.

Production of base oil

1000 g of tetralin (tetrahydronaphthalene) and 300 g of concentrated sulfuric acid were placed in a 3 l glass flask, the contents of which were then cooled to 0 ºC in an ice bath. With stirring, 400 g of styrene was then slowly added dropwise to the flask over 3 hours. Stirring was continued for another hour to complete the reaction. Stirring was stopped and the reaction product was allowed to stand to separate an oily phase. The oily phase was washed with three portions of 500 ml each of a 1 N aqueous sodium hydroxide solution and 500 ml of a saturated sodium chloride solution and was then dried over anhydrous sodium sulfate. After removing The unreacted tetralin was distilled under reduced pressure to obtain 750 g of a fraction having a boiling point of 135 to 148 ºC/22.66 Pa (0.17 mmHg). Analysis revealed that this fraction was a mixture of 1-(1-tetralyl)-1-phenylethane and 1-(2-tetralyl)-1-phenylethane.

500 ml of the fraction was then placed in a 1 liter autoclave, to which 50 g of a 5% ruthenium/carbon catalyst was further added and hydrogenation was carried out under a hydrogen pressure of 2.0 MPa (20 kg/cm2) at a reaction temperature of 120 ºC for 4 hours. After cooling, the reaction liquid was filtered to separate the catalyst. After subsequent removal of the light material from the filtrate, the product was analyzed. It was found that a hydrogenation degree of more than 99.9% was achieved and that the product was a mixture of 1-(1-decalyl)-1-cyclohexylethane with 1-(2-decalyl)-1-cyclohexylethane. The mixture thus obtained was found to have a specific gravity of 0.94 (15/4 ºC), a viscosity-density ratio of 4.9 mm²/s (4.9 cSt) (100 ºC), a refractive index nD²⁰ of 1.5048 and a cis ratio of 88%.

Example 1 and comparative example 1

The components shown in Table 1 were added to the base oil (the component A) obtained in the preparation example in the given proportions to obtain lubricating oil compositions, on which various tests were carried out by the following methods.

Test procedure Traction coefficient

The tests were carried out using a two-cylinder rolling friction test apparatus. Specifically, while a cylinder A with a curve (which had a diameter of 52 mm and a radius of curvature of 10 mm) was brought into contact with a cylinder B with a plane (which had a diameter of 52 mm) with 68,670 N (7,000 kgf), the cylinder A was rotated at a constant speed (1,500 rpm) and the rotation speed of the cylinder B was increased from 1,500 rpm. The traction coefficient was then determined by measuring a traction force occurring between both cylinders at a slip rate of 5%.

The two cylinders were formed of bearing steel SUJ-2 and the surfaces were adjusted to a surface roughness Rmax of 0.1 micrometer or less with aluminum oxide (0.03 micrometer) and allowed to contact each other at a Hertz contact pressure of 1 098.7 N (112 kgf)/mm2. The results are shown in Table 1.

Wear test

The four-ball test according to ASTM D-4172 was carried out under the following conditions to determine the wear losses (mm). The results are shown in Table 1.

Conditions: revolutions per minute - 1 800 rpm.

Load - 294.3 N (30 kgf).

Time - 2 hours.

Oil temperature - 120 ºC.

Comparison example 2

Example 1 was repeated except that 4 wt.% of polybutene (having a number average molecular weight of 2,300) was used instead of component (B). Various tests were carried out on the lubricating oil composition thus prepared. The results are shown in Table 1 and Fig. 1. Table 1 Composition (wt%) Component Polybutene Wear loss (mm) Example Comparative Example *1: Base oil obtained in Preparation Example. *2: Ethylene-α-olefin copolymer having a number average molecular weight of 2,600. *3: I ... zinc dialkylthiophosphate in which R² to R⁵ are primary hexyl groups. II ... tricresyl phosphate. *4: Polymethacrylate having a number average molecular weight of 40,000.

Claims (7)

1. A traction drive lubricating oil composition comprising: (A) a base oil containing as a major component a saturated hydrocarbon or condensed ring and/or non-condensed ring hydrocarbons, (B) an ethylene-α-olefin copolymer having an average (number average) molecular weight of 800 to 8,000, (C) an anti-wear agent, and (D) a polymethacrylate having an average (number average) molecular weight of 10,000 to 100,000, wherein the antiwear agent is at least one selected from the group consisting of zinc dithiophosphate, oxymolybdenum organophosphorodithioate sulfide, phosphate, phosphite, amine salt of phosphate, amine salt of phosphite, molybdenum dialkyldithiocarbamate, mixtures of sulfurized fats and oils and phosphates, mixtures of sulfurized fats and oils and phosphites, mixtures of sulfurized olefins and phosphates, mixtures of sulfurized olefins and phosphites, and the amine salts of the foregoing mixtures. 2. A composition according to claim 1, which contains 1 to 20 wt.% of the ethylene-α-olefin copolymer and 0.1 to 10 wt.% of the antiwear agent. 3. The composition of claim 1, wherein the saturated fused ring hydrocarbon comprises a decalyl group. 4. The composition of claim 1, wherein the saturated non-condensed ring hydrocarbon comprises a cyclohexyl group. 5. The composition of claim 1, wherein the ethylene-α-olefin copolymer has a number average molecular weight of 1,000 to 5,000. 6. The composition of claim 1, wherein the ethylene-α-olefin copolymer has a number average molecular weight of 2,000 to 4,000. 7. The composition of claim 1, wherein the ethylene content of the ethylene-α-olefin copolymer is 30 to 80 mol%.