JP6228104B2 - Lubricating oil composition - Google Patents

Description

The present invention relates to a lubricating oil composition. In particular, the present invention relates to a lubricating oil composition suitably used for a transmission of an electric motor mounted vehicle such as an electric vehicle or a hybrid vehicle.

In recent years, hybrid vehicles and electric vehicles have been developed from the viewpoint of environmental protection, and these are equipped with electric motors. In such an automobile, transmission lubricating oil is also used for cooling the electric motor in order to enhance the cooling effect of the electric motor. That is, the transmission lubricating oil directly contacts the electric motor to perform the cooling function. Therefore, the lubricating oil used for such applications is required to have high electrical insulation.

On the other hand, automatic transmission lubricating oil (ATF) and continuously variable transmission lubricating oil (CVTF) are generally known as lubricating oils used in automobile transmissions. These transmission lubricants have the characteristics required as transmission lubricants, in particular, oxidation stability, extreme pressure performance, and characteristics (friction characteristics) that can impart good friction characteristics to wet clutches. In order to have it, various additives are contained in specific amounts. However, the addition of additives generally reduces the electrical resistance.

Currently, since these transmission lubricating oils that are inferior in electrical insulation are used for cooling the electric motor, there is no choice but to limit the performance of the electric motor. Therefore, there is a demand for a lubricating oil that has characteristics required as a lubricant for transmissions and is excellent in electrical insulation.

As a lubricating oil composition for a transmission, one containing an ashless dispersant, a sulfur extreme pressure agent, and a phosphorus extreme pressure agent together with a base oil is known (for example, Patent Document 1). The composition is excellent in friction characteristics and seizure resistance, and is suitable for a metal belt type continuously variable transmission. This document does not describe that the above composition is used in a vehicle equipped with an electric motor, or is used for cooling the electric motor, and there is no description regarding electrical insulation. Moreover, the said composition does not necessarily have sufficient electrical resistance, and is insufficient in electrical insulation.

As a lubricating oil composition for a transmission that is also used for cooling an electric motor, a base oil, (A) a hydrocarbon group-containing zinc dithiophosphate, (B) a triaryl phosphate, and (C) a triaryl thiophosphate are selected. A composition containing a phosphorous compound to be produced and having a volume resistivity at 80 ° C. of 1 × 10 ⁸ Ωm or more has been proposed (for example, Patent Document 2). Further, a composition containing (a) a base oil, (b) an oil-soluble phosphorus-containing substance, and (c) a corrosion inhibitor has been proposed (for example, Patent Document 3). Dialkyl phosphites, trialkyl phosphites and trialkyl phosphates are described as the oil-soluble phosphorus-containing substances. In addition, a lubricating oil composition is proposed that includes (a) a neutral phosphorus compound, (b) an acidic phosphate amine salt and / or acidic phosphite, and (c) a sulfur compound together with the base oil. (For example, Patent Document 4). None of these compositions is necessarily sufficient in terms of electrical insulation.

Japanese Patent Laid-Open No. 10-8081 International Publication No. 02/097017 Pamphlet JP 2008-195942 A International Publication No. 2011/080970 Pamphlet

An object of the present invention is to provide a lubricating oil composition that is excellent in oxidation stability, extreme pressure performance, frictional properties, and excellent in electrical insulation.

The present inventors have found that the above object can be achieved by including a specific compound as a phosphorus-containing substance and not including a sulfur-based extreme pressure agent.

That is, the present invention
(A) 0.2 mass% to 0.6 mass% of an ashless dispersant based on the total mass of the lubricating base oil and the lubricating oil composition,
(B) 0.7 to 6.0% by mass of at least one compound selected from the group consisting of triaryl phosphates, trialkyl phosphates and triaryl thiophosphates, and (C) 0.01 to 0.08% by mass At least one compound selected from the group consisting of an acidic phosphate represented by the following formula (I) or (II) and an amine salt thereof and a phosphite represented by the following formula (III):
RO-P (= O) (OH) ₂ (I)
(RO) ₂ P (═O) (OH) (II)
(RO) ₂ P (═O) H (III)
[Wherein, each R is independently an aliphatic hydrocarbon group having 6 to 18 carbon atoms]
The lubricating oil composition is characterized in that it contains no sulfur-based extreme pressure agent.

The lubricating oil composition of the present invention is excellent in oxidation stability, extreme pressure performance and friction characteristics, and also in electrical insulation. Therefore, in an automobile equipped with an electric motor such as an electric vehicle or a hybrid vehicle, it can be suitably used not only as a lubricating oil for a transmission but also for cooling an electric motor.

The base oil in the lubricating oil composition of the present invention includes mineral oil, synthetic oil and any mixed oil thereof. There is no restriction | limiting in particular about the kind of mineral oil or synthetic oil, Arbitrary things can be suitably selected and used from the conventional mineral oil and synthetic oil currently used as a base oil of lubricating oil.

Examples of mineral oils include paraffinic mineral oils, naphthenic mineral oils, and intermediate base mineral oils obtained by ordinary purification methods such as solvent refining and hydrogenation refining.

Synthetic oils include, for example, polybutenes, polyolefins (α-olefin homopolymers and copolymers (for example, ethylene-α-olefin copolymers)), various esters (for example, polyol esters, dibasic acid esters, Phosphate esters, etc.), various ethers (eg, polyphenyl ethers), polyglycols, polyglycol derivatives (eg, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, etc.), alkylbenzenes, alkylnaphthalenes And silicone oil.

Although there is no restriction | limiting in particular about the viscosity of the said base oil, Although it changes according to the use of a lubricating oil composition, it is preferable that the kinematic viscosity in the temperature of 100 degreeC is 3-15 mm < ² > / s, and is 3-8 mm < ² > / s. More preferably. When the kinematic viscosity at 100 ° C. is 3 mm ² / s or more, the evaporation loss is small. On the other hand, when the kinematic viscosity is 15 mm ² / s or less, the power loss due to the viscous resistance is small and the fuel efficiency improvement effect is obtained.

Moreover, as said base oil,% CA by ring analysis is 3.0 or less, and a sulfur content is 50 mass ppm or less preferably. Here,% CA by ring analysis indicates the ratio (%) of aromatic content calculated by ring analysis (ndM method). The sulfur content is a value measured according to the method described in JIS K2541.

A base oil having a% CA of 3.0 or less and a sulfur content of 50 mass ppm or less has good oxidation stability, can suppress an increase in acid value and generation of sludge, and has little corrosiveness to metals. A lubricating oil composition can be provided. More preferable% CA is 1.0 or less, further 0.5 or less, and a more preferable sulfur content is 30 mass ppm or less.

Furthermore, the viscosity index of the base oil is preferably 70 or more, more preferably 100 or more, and still more preferably 120 or more. The base oil having such a viscosity index has a small viscosity change due to a change in temperature, and a viscosity improving effect can be obtained even at a low temperature.

Specific examples of base oils include Group III and Group IV base oils as classified by API (American Petroleum Institute).

Ingredient (A)
The ashless dispersant is not particularly limited as long as it does not contain a metal such as an alkaline earth metal in the molecule and can be dissolved or uniformly dispersed in a lubricating base oil to mainly exhibit sludge dispersion performance. There is no. Such as, for example, imide compounds such as monoimides, bisimides and their boron-containing compounds (eg, succinimide compounds having an alkyl or alkenyl substituent and their boron-containing compounds), and alkyl or alkenyl substituents Succinic acid amide compounds, benzylamine compounds, succinic acid esters, succinic acid ester amide compounds, and boron-containing compounds thereof, which may be used alone or in combination of two or more.

Among them, preferred ashless dispersants are succinimide compounds having an alkyl or alkenyl substituent and boron-containing compounds thereof (hereinafter sometimes simply referred to as “succinimide compounds”), and these may be used alone. It can be used but may be mixed. The alkyl or alkenyl substituent of the succinimide compound is preferably a polybutenyl group. The molecular weight of the polybutenyl group is not particularly limited, but is preferably 500 to 5,000, and more preferably 1,000 to 4,000. Also, the nitrogen content in the succinimide compound and the ratio of the boron and nitrogen content (sometimes expressed as B / N ratio) can be arbitrarily used, and are limited. Although there is no, as nitrogen content in a succinimide compound, 0.3-2.0 mass% is preferred and 0.5-1.5 mass% is more preferred. As boron content in a succinimide compound, 0.0-1.5 mass% is preferable, and 0.0-1.0 mass% is more preferable. Therefore, the succinimide compound may or may not contain boron, but the B / N ratio is preferably 0.1 to 1.0. Furthermore, there are two types of succinimide compounds, bisimide and monoimide, both of which can be used, and both bisimide and monoimide may be used in combination.

In the present invention, the amount of the ashless dispersant is 0.2 to 0.6 mass%, preferably 0.2 to 0.4 mass%, more preferably 0, based on the total mass of the lubricating oil composition. .2 to 0.3% by mass. If the upper limit is exceeded, sufficient electrical insulation cannot be obtained, and if it is less than the lower limit, sufficient friction characteristics and oxidation stability cannot be obtained.

Ingredient (B)
Component (B) is one or more selected from the group consisting of triaryl phosphates, trialkyl phosphates, and triaryl thiophosphates.

The aryl groups of the triaryl phosphate and triaryl thiophosphate include a phenyl group and a phenyl group having one or more alkyl substituents having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms. The three aryl groups in the triaryl phosphate and triaryl thiophosphate may be the same or different. The alkyl group of the trialkyl phosphate is preferably an alkyl group having 1 to 18 carbon atoms, and particularly preferably an alkyl group having 4 to 12 carbon atoms. The three alkyl groups in the trialkyl phosphate may be the same or different. When the number of carbon atoms of the alkyl substituent in the aryl group of the triaryl phosphate and triaryl thiophosphate and the alkyl group of the trialkyl phosphate exceed the above upper limits, solubility may deteriorate and handling may be difficult.

Specific examples of the component (B) include, for example, triphenyl phosphate, tri (methylphenyl) phosphate, tri (ethylphenyl) phosphate, tri (isopropylphenyl) phosphate, trihexyl phosphate, tris (2-ethylhexyl) phosphate, triphenyl. Examples include thiophosphate, tri (methylphenyl) thiophosphate, tri (ethylphenyl) thiophosphate and tri (isopropylphenyl) thiophosphate, and one or more of these can be used. Tri (isopropylphenyl) phosphate, tris (2-ethylhexyl) phosphate and triphenylthiophosphate are particularly preferable.

The amount of component (B) is 0.7 to 6.0 mass%, preferably 0.9 to 3.0 mass%, more preferably 1.0 to 2.0 mass%, based on the total mass of the lubricating oil composition. It is. When the amount is less than the above lower limit, sufficient wear characteristics cannot be obtained, and when the amount exceeds the above upper limit, the electrical insulating property may be inferior or the effect commensurate with the addition amount may not be exhibited.

Ingredient (C)
Component (C) is at least one selected from the group consisting of an acidic phosphate ester represented by the following formula (I) or (II) and an amine salt thereof, and a phosphite ester represented by the following formula (III) A compound.
RO-P (= O) (OH) ₂ (I)
(RO) ₂ P (═O) (OH) (II)
(RO) ₂ P (═O) H (III)
In the above formula, each R is independently an aliphatic hydrocarbon group having 6 to 18 carbon atoms, preferably 7 to 12 carbon atoms, more preferably 8 to 10 carbon atoms. When the number of carbon atoms is less than the lower limit, the electrical insulation is not sufficient, and when the number exceeds the upper limit, the solubility is deteriorated and handling may be difficult.

Examples of the acidic phosphate ester include monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, mono (2-ethylhexyl) acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, mono Lauryl acid phosphate, dihexyl acid phosphate, diheptyl acid phosphate, dioctyl acid phosphate, bis (2-ethylhexyl) acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate and dilauryl acid phosphate.

The amine salt of the acidic phosphate ester can be obtained by neutralizing part or all of the acidic hydrogen remaining in the acidic phosphate ester with an amine compound. Examples of the amine compound include a mono-substituted amine compound and a di-substituted amine compound represented by the general formula R ′ _p NH _3-p (p is 1 or 2). In the above formula, R ′ is a hydrocarbon group having a linear structure, a branched structure or a cyclic structure and having 4 to 24 carbon atoms, preferably 6 to 20 carbon atoms, and particularly preferably 10 to 18 carbon atoms. As this hydrocarbon group, an alkyl group and an alkenyl group are preferable, and specifically, an alkyl group such as a myristyl group, a palmityl group and a stearyl group, and an alkenyl group such as an oleyl group are preferable. The said amine compound can be used individually by 1 type or in mixture of 2 or more types.

Examples of phosphites include dihexyl hydrogen phosphite, bis (2-ethylhexyl) hydrogen phosphite, dioctyl hydrogen phosphite, dicapryl hydrogen phosphite, dilauryl hydrogen phosphite, dimyristyl hydrogen phosphite, dipalmityl hydrogen phosphite. Phyte, distearyl hydrogen phosphite, dioleyl hydrogen phosphite and the like can be mentioned. Particularly preferred are dihexyl hydrogen phosphite, bis (2-ethylhexyl) hydrogen phosphite and dioctyl hydrogen phosphite.

A component (C) can be added individually by 1 type or in mixture of 2 or more types. The amount of component (C) is from 0.01 to 0.08% by mass, preferably from 0.02 to 0.07% by mass, more preferably from 0.02 to 0.06%, based on the total mass of the lubricating oil composition. % By mass. If it is less than the above lower limit, sufficient frictional properties cannot be obtained, and if it is more than the above upper limit, sufficient electrical insulation may not be obtained.

The lubricating oil composition of the present invention is characterized by not containing a sulfur-based extreme pressure agent from the viewpoint of ensuring electrical insulation, in addition to containing the components (A), (B) and (C). To do. Generally, sulfur-based extreme pressure agents include S-based extreme pressure agents, P-based extreme pressure agents, and SP-based extreme pressure agents. The sulfur-based extreme pressure agent not contained in the present invention means an S-based extreme pressure agent, for example, sulfurized fats and oils, sulfide olefins, dihydrocarbyl polysulfide, sulfide mineral oil, thiocarbamate compounds that are sulfides of animal and vegetable oils or synthetic oil Thioterpene compounds and dialkylthiodipropionate compounds. In addition, even if it uses a sulfur type extreme pressure agent and a phosphorus type extreme pressure agent together, electrical insulation cannot be ensured (comparative example 4 mentioned later).

In the lubricating oil composition of the present invention, other additives such as a viscosity index improver, an antioxidant, a metal deactivator, and a metal-based detergent are added as necessary as long as the object of the present invention is not impaired Further, a pour point depressant, an antifoaming agent and the like can be added as appropriate.

Examples of the viscosity index improver include polymethacrylate, olefin copolymer (polyisobutylene, ethylene-propylene copolymer), polyalkylstyrene, styrene-butadiene hydrogenated copolymer, and styrene-maleic anhydride ester copolymer. . The viscosity index improver may be blended in an amount of 3 to 35% by mass, preferably 4 to 30% by mass, based on the total amount of the lubricating oil composition. Further, either a dispersion type polymer or a non-dispersion type polymer can be used, and the weight average molecular weight is not particularly limited, but is preferably 5,000 to 3,000,000, and 10,000 to 1,000,000. Is more preferable, and 10,000 to 300,000 is even more preferable.

Antioxidants include amine-based antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine and 4,4′-tetramethyl-diaminodiphenylmethane, 2,6-di-tert- Butyl-p-cresol, 2,6-di-tert-butylphenol, 4,4′-methylenebis- (2,6-di-tert-butylphenol) and 4,4′-thiobis (6-di-tert-butyl- o-cresol) and the like, sulfur antioxidants such as dilauryl-3,3′-thiodipropionate, phosphorus antioxidants such as phosphite, and zinc dithiophosphate. In particular, amine-based antioxidants and phenol-based antioxidants are preferably used. The antioxidant is added in an amount of 0.05 to 5% by mass, preferably 0.1 to 3% by mass, based on the total amount of the lubricating oil composition.

Examples of the metal deactivator include benzotriazole, triazole derivatives, benzotriazole derivatives and thiadiazole derivatives. The metal deactivator is blended in an amount of 0.01 to 3% by mass, preferably 0.01 to 2% by mass, based on the total amount of the lubricating oil composition.

Examples of metal detergents include sulfonates, phenates, salicylates and phosphonates of metals such as Ca, Mg, Ba and Na. The metal detergent may be blended in an amount of 5% by mass or less, preferably 3% by mass or less, based on the total amount of the lubricating oil composition.

Examples of the pour point depressant include ethylene-vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polymethacrylate and polyalkylstyrene. In particular, polymethacrylate is preferably used. The pour point depressant is 0 to 10% by mass, preferably 0 to 8% by mass, based on the total amount of the lubricating oil composition.

Examples of the antifoaming agent include dimethylpolysiloxane such as dimethylsilicone dilution. The antifoaming agent is blended in an amount of 0.0001 to 1% by mass, preferably 0.001 to 0.7% by mass, based on the total amount of the lubricating oil composition.

Furthermore, corrosion inhibitors can be used as desired.

Other antiwear agents include zinc dithiophosphate, metal dithiophosphate (Pb, Sb, Mo, etc.), metal dithiocarbamate (Zn, Pb, Sb, Mo, etc.), metal naphthenate (Pb, etc.), fatty acid, etc. Metal salts (such as Pb) and boron compounds may be blended as desired.

The lubricating oil composition of the present invention conforms to JIS C2101 (electrical insulation oil test) and has a volume resistivity of 1.2 × 10 ¹⁰ Ωcm or more measured at a voltage of 10 V and a temperature of 160 ° C. Excellent in properties. Therefore, the lubricating oil composition of the present invention can be suitably used not only as a lubricating oil for a transmission but also for cooling an electric motor in an automobile equipped with an electric motor such as an electric vehicle or a hybrid vehicle. .

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

Examples 1-12 and Comparative Examples 1-9
The following ingredients were blended in the amounts (mass%) shown in Table 1 to prepare a lubricating oil composition.
Base oil: Mineral oil (API, group III) (kinematic viscosity at 100 ° C. 3.4 mm ² / s, viscosity index 111)
Viscosity index improver: methacrylate polymer, (non-dispersed, weight average molecular weight 30,000)
Antioxidant: combined use of phenol and diphenylamine metal deactivator: combined use of benzotriazole and thiazole TAP: triaryl phosphate (aryl: isopropylphenyl)
TEHP: Tris (2-ethylhexyl) phosphate TATP: Triarylthiophosphate (aryl: phenyl)
C8-AP: Mixture of monooctyl acid phosphate and dioctyl acid phosphate C18-AP: Mixture of monostearyl acid phosphate and distearyl acid phosphate C8-APOAS: Oleylamine salt of C8-AP C8-P: Bis (2-Ethylhexyl) hydrogen phosphite (phosphite)
C4-AP: Mixture of monobutyl acid phosphate and dibutyl acid phosphate ARP: Aryl acid phosphate (monophenyl phosphate)
PIBSI: polyisobutenyl succinimide (number average molecular weight of polyisobutenyl group 3000, nitrogen content 1% by mass, boron content 0.2% by mass, bisimide type)
SO: Sulfurized olefin

The following tests (1) to (4) were performed on the obtained lubricating oil composition. The results are shown in Tables 1 and 2.
(1) Volume resistivity Based on JIS C2101 (electrical insulation oil test), the volume resistivity at a voltage of 10 V and a temperature of 160 ° C. was measured. Since the volume resistivity generally decreases with increasing temperature, the above temperature is determined assuming the highest temperature that can actually be reached in the transmission. If the volume resistivity at 160 ° C. is 1.2 × 10 ¹⁰ Ωcm or more, it is judged that the object of the present invention is satisfied.

(2) Extreme pressure performance test (Abrasion resistance test)
In accordance with ASTM D2783 (shell four-ball test), the rotation speed was 1760 rpm, and the load (initial baking load: ISL) when the diameter of wear marks generated on the hard sphere exceeded a certain value was evaluated as extreme pressure performance. If the initial baking load is 80 kg or more, it is determined that the object of the present invention is satisfied.

(3) Oxidation stability test According to JASO M315-04 (Indiana Stirring Oxidation Test: ISOT), the lubricating oil composition was stirred with a stir bar at 150 ° C for 96 hours, and applied to a varnish bar. The presence or absence of lacquer-like substance or sludge was visually evaluated. If there is no deposit, it is judged that the object of the present invention is satisfied.

(4) Friction property test In accordance with JASO M348, SAE No. Using two testing machines (friction characteristics testing machine), the friction characteristics at the time of shifting were evaluated as follows. While rotating the wet clutch plate of the automatic transmission is engaged in a steel plate, the friction coefficient was measured mu _d in the course of stopping 1800 rpm. If the friction coefficient mu _d is 0.13 or more when it was repeated 3000 cycles, it is determined to satisfy the object of the present invention.

As is clear from Table 1, the composition of the present invention is excellent in extreme pressure performance, oxidation stability and frictional properties, and has a volume resistivity of 1.2 × 10 ¹⁰ Ωcm or more, and therefore has an electrical insulation property. Also excellent.

On the other hand, as is clear from Table 2, the composition of Comparative Example 1 in which the amount of component (A) is less than the range of the present invention is inferior in friction properties, and the amount of component (A) is greater than the range of the present invention. The composition of Example 2 is inferior in electrical insulation. The composition of Comparative Example 8 in which the amount of component (B) is less than the range of the present invention is inferior in friction characteristics. As a comparative component (C), the composition of Comparative Example 6 using an acidic phosphate ester having an aromatic hydrocarbon group is inferior in electrical insulation, and the amount of component (B) is larger than the range of the present invention. The composition of 5 is inferior in electrical insulation. The composition of Comparative Example 7 containing no component (C) is inferior in friction properties, and the composition of Comparative Example 3 in which the amount of component (C) is larger than the range of the present invention is inferior in electrical insulation. As a comparative component (C), the composition of Comparative Example 9 using an acidic phosphate ester having a carbon number smaller than the range of the present invention is inferior in electrical insulation. The composition of Comparative Example 4 in which the sulfur-based extreme pressure agent is used in combination with components (B) and (C) is inferior in electrical insulation.

Claims (3)

(A) 0.2 mass% to 0.6 mass% of an ashless dispersant based on the total mass of the lubricating base oil and the lubricating oil composition,
(B) 0.7 to 6.0% by mass of at least one compound selected from the group consisting of triaryl phosphates, trialkyl phosphates and triaryl thiophosphates, and (C) 0.01 to 0.08% by mass At least one compound selected from the group consisting of an acidic phosphate represented by the following formula (I) or (II) and an amine salt thereof and a phosphite represented by the following formula (III):
RO-P (= O) (OH) ₂ (I)
(RO) ₂ P (═O) (OH) (II)
(RO) ₂ P (═O) H (III)
[Wherein, each R is independently an aliphatic hydrocarbon group having 6 to 18 carbon atoms]
And a sulfur-based extreme pressure agent is not contained. The lubricating oil composition according to claim 1, wherein the volume resistivity at 160 ° C. is 1.2 × 10 ¹⁰ Ωcm or more. The lubricating oil composition according to claim 1 or 2, which is used for a transmission of an automobile equipped with an electric motor.