JP2009263439A - Wet clutch lubricating oil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide wet clutch lubricating oil having torque transmission performance and proper friction properties required in common by an electronic control coupling and a multi-disc clutch type LSD having a wet clutch mechanism or a wet brake, and maintaining its performance over a long period, and causing a little increase in viscosity even in cold conditions. <P>SOLUTION: The wet clutch lubricating oil contains a base oil containing an oleate having a 7-9C alkyl group in an ester moiety and exhibiting kinematic viscosity of 2-50 mm<SP>2</SP>/s at 100°C, and based on the total lubricating oil quantity, (A) 0.1-10 mass% of ethers of a higher alcohol having a ≥8C alkyl group and glycerin, and (B) 0.1-5 mass% of a phosphoric acid ester compound. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lubricating oil for wet clutches that has appropriate friction characteristics for preventing vibration and noise caused by stick-slip, can maintain the characteristics for a long period of time, and has a small increase in viscosity under low temperature conditions. More particularly, the present invention relates to a wet clutch mechanism, particularly an electronically controlled coupling having a metal friction clutch, a multi-plate clutch type LSD (Limited Slip Differential), and a wet clutch lubricant suitable for a wet brake.

A wet clutch mechanism, particularly a metal friction clutch, is used for automobile differentials, shaft couplings, agricultural construction machine brakes, and the like, and is a mechanism mainly responsible for controlling power transmission.
Lubricating oil that can be used in such wet clutches requires a certain coefficient of friction (torque transmission performance) and stick-slip prevention to transmit torque.
In addition, when using in cold regions, if the viscosity of the lubricating oil increases greatly as the temperature decreases, the oil does not move even when the clutch is idling in an electronically controlled coupling or a multi-plate clutch type LSD (Limited Slip Differential). Unnecessary power transmission may occur due to the torque generated by the viscous resistance.

Stick-slip is a type of self-excited vibration that occurs intermittently when the clutch rotates at low speed or when it is engaged, and causes abnormal noise and vehicle body vibration.
In order to prevent this stick-slip, the lubricating oil has the characteristic that the friction coefficient increases with the increase of the sliding speed (μ-v characteristic is positive slope) in the relationship between the sliding speed and the friction coefficient (μ-v characteristic). Is required.

Such a μ-v characteristic of the lubricating oil is imparted by adding an additive to the base oil.
Conventionally, fatty acid esters of higher alcohols and polyhydric alcohols, phosphate esters, amine salts thereof, and the like are used as the additive as friction modifiers.
Further, a higher alcohol having an alkyl group with 8 or more carbon atoms, glycerin, and a phosphate ester compound are disclosed (see Patent Document 1).

JP 2004-204002 A

However, in recent years, the equipment has been downsized to reduce the amount of lubricating oil to improve the fuel efficiency of automobiles, while at the same time, it has been required to extend the oil renewal period, and at the same time to maintain performance even at low temperatures. Yes.
Even devices with metal friction clutches with strict lubrication conditions are no exception, and they must maintain better μ-v characteristics over a longer period of time than before and have the ability to transmit power stably even at low temperatures. It has been.

  The present invention has a torque transmission performance and an appropriate friction characteristic commonly required for an electronically controlled coupling having a wet clutch mechanism, a multi-plate clutch type LSD, or a wet brake, and maintains the performance for a long time. Another object of the present invention is to provide a lubricating oil for a wet clutch that has a small increase in viscosity even under low temperature conditions.

  As a result of intensive studies to meet the demands of the mechanism equipped with the above-described wet clutch, the present inventors include a specific ester oil in the base oil, and combine two types of friction modifiers in a specific amount. Thus, it has been found that torque transmission performance as a wet clutch, durability of μ-v characteristics, and an increase in viscosity at low temperatures can be suppressed, and the present invention has been completed.

That is, the present invention includes a base oil containing an oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester portion and having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C., and (A) an alkyl group 0.1 to 10% by mass of higher alcohol having 8 or more carbon atoms and ether of glycerin based on the total amount of the lubricating oil, and (B) 0.1 to 5% by mass of the phosphoric ester compound based on the total amount of the lubricating oil The present invention provides a lubricating oil for a wet clutch.
Further, the present invention provides the wet clutch lubricant, wherein the oleate having an alkyl group having 7 to 9 carbon atoms in the ester portion is 2-ethylhexyl oleate. Is.
The present invention also provides a wet clutch lubricant in which the phosphate ester compound is at least one selected from a phosphate ester, a phosphite ester, and an amine salt thereof. Is.
The present invention also provides a wet clutch lubricant, wherein the wet clutch lubricant is used in any one of an electronically controlled coupling, an LSD gear, and a wet brake. Is.

The lubricating oil for wet clutches of the present invention maintains a good frictional adjustment function over a long period of time by the synergistic effect of (poly) glyceryl ether as component (A) and phosphorus compound as component (B). By using an oleic acid ester having an alkyl group having 7 to 9 carbon atoms, particularly oleic acid-2-ethyl-hexyl, an increase in viscosity at a low temperature can be suppressed.
For this reason, the lubricating oil of the present invention is used for LSD, coupling, wet brake, AT, CVT, etc. with a built-in wet clutch. It is possible to prevent unnecessary transmission of the driving force due to an increase in the viscosity.

The base oil used in the present invention has a kinematic viscosity at 100 ° C. of ² to 50 mm ² / s, preferably ² to 40 mm ² / s, more preferably ² to 30 mm ² / s, still more preferably ^{2 to 20} mm ² / s. is there. If the base oil has a kinematic viscosity outside this range, the function as a lubricating oil cannot be obtained.
The base oil used in the present invention includes an oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester part.
Examples of the oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester part include heptyl oleate, octyl oleate, and nonyl oleate. Octyl oleate is preferable, and -2-ethyl-hexyl oleate is preferable. Is particularly preferred.
The content of the oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester part is preferably 30 to 100% by mass, more preferably 40 to 100% by mass, and still more preferably in the whole base oil. Is 50 to 100% by mass. When the content of the oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester part in the entire base oil is less than 20% by mass, the increase in low temperature viscosity may not be sufficiently suppressed.

Moreover, as a base oil, 1 or more types chosen from other ester base oil, mineral oil, and synthetic oil can also be used in the range which does not reduce performance, A C7-C9 alkyl group is used for an ester part. It is also possible to use a mixed oil in combination with an oleic acid ester having as the base oil.
The mineral oil and synthetic oil in this case desirably have as little sulfur as possible, and the allowable sulfur content is up to 0.1% by mass, preferably 0.05% by mass or less, more preferably 0.02%. It is below mass%. If the sulfur content exceeds 0.1% by mass, sludge formation may be promoted when used at high temperatures.
The base oil used in the present invention has a viscosity index of 100 or more, preferably 110 or more, more preferably 120 or more.

  As the mineral oil having the above properties, for example, highly refined paraffinic mineral oils such as hydrorefined oils and catalytic isomerized oils are preferably used. As synthetic oils, poly-alpha olefins (PAO) and Esters are preferably used.

  The component (A) used in the present invention is (poly) glyceryl ether represented by the general formula (1).

In the general formula (2), R ¹ represents a hydrocarbon group, and examples thereof include an alkyl group, an alkenyl group, an aryl group, a cycloalkyl group, and a cycloalkenyl group.
Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, pentyl, isopentyl, secondary pentyl, neopentyl, tertiary pentyl, hexyl, secondary hexyl, heptyl, 2 Secondary heptyl, octyl, 2-ethylhexyl, secondary octyl, nonyl, secondary nonyl, decyl, secondary decyl, undecyl, secondary undecyl, dodecyl, secondary dodecyl, tridecyl, isotridecyl, secondary tridecyl, tetradecyl, secondary tetradecyl , Hexadecyl, secondary hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldecyl, - octyldodecyl, 2-decyltetradecyl, 2-dodecyl-hexadecyl, 2-hexadecyl octadecyl, 2-tetradecyl-octadecyl, monomethyl branched - include isostearyl and the like.

Examples of the alkenyl group include vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl, oleyl and the like.
As an aryl group, for example, phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, Nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, styrenated phenyl, p-cumylphenyl, α-naphthyl, β-naphthyl group and the like can be mentioned.

  Examples of the cycloalkyl group and the cycloalkenyl group include a cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl, methylcyclohexenyl, methylcycloheptenyl group Etc.

R ¹ is preferably an alkyl group or an alkenyl group, and more preferably an alkyl group or alkenyl group having 4 to 30 carbon atoms.
When the number of carbon atoms is less than 4, sufficient effects cannot be obtained, and when the number of carbon atoms is more than 30, the viscosity becomes high and solidifies.
Moreover, in General formula (1), n is a coefficient showing the polymerization degree of glycerol, is a number of 1 or more, preferably a number of 1 to 5.
In addition, when n is 1 or more, n is an average value.

  The blending amount of the component (A) is 0.1 to 10% by mass, preferably 1 to 5% by mass, based on the total amount of the lubricating oil. If it is less than 0.1% by mass, the μ-v characteristic does not have a positive gradient and stick-slip prevention may not be imparted. If it exceeds 10% by mass, the absolute value of the friction coefficient becomes too low, or low-temperature fluidity. The performance as a lubricating oil is reduced.

  The phosphoric acid ester compound as the component (B) is a phosphoric acid ester, a phosphite ester, or an amine salt thereof represented by the general formula (2) of Chemical Formula 2. An acidic phosphate ester and its amine salt are preferred.

In the general formula (2), R ² is a monovalent hydrocarbon group, X is an oxygen atom or a sulfur atom, a is 1, 2 or 3, and b is 0 or 1.
The monovalent hydrocarbon group represented by R ² is a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 5 to 20 carbon atoms (for example, an alkyl group or an alkenyl group), an aromatic having 6 to 26 carbon atoms. Group hydrocarbon group or cycloalkyl group. When the carbon number is smaller than the above, a sufficient effect cannot be obtained, and when the carbon number is larger than the above, the viscosity becomes high and solidifies.

Specific examples of the amine salt include compounds obtained by neutralizing an acidic phosphate ester, acidic phosphite ester, acidic thiophosphate ester, or acidic dithiophosphate ester with an alkylamine.
Examples of the acidic phosphate ester include butyl acid phosphate, 2-ethylhexyl acid phosphate, octyl acid phosphate, isodecyl acid phosphate, lauryl acid phosphate, tridecyl acid phosphate, oleyl acid phosphate, trial acid phosphate, di-2-ethyl hexyl phosphate Etc.

  Acid phosphites include triphenyl phosphite, tri (P-cresyl) phosphite, tri (octylphenyl) phosphite, tri (nonylphenyl) phosphite, triisooctyl phosphite, tridodecyl phosphite, diphenyl Isodecyl phosphite, triisodecyl phosphite, tritearyl phosphite, trioleyl phosphite, di-2-ethylhexyl hydrogen phosphite, didodecyl hydrogen phosphite, dilauryl hydrogen phosphite, dioleyl hydrogen phosphite For example, fights.

Examples of acidic thiophosphates include dioctyl thioacid phosphate, trioctyl thioacid phosphate, tridodecyl thioacid phosphate, trihexadecyl thioacid phosphate, trioctadecenyl thioacid phosphate, tri (octylphenyl) thioacid phosphate, etc. It is done.
Examples of the acidic dithiophosphate include tridecyl dithioacid phosphate and di (2-ethylhexyl) dithioacid phosphate.
The amine salt of phosphate ester is an alkylamine salt obtained by neutralizing the above phosphate ester with an alkylamine represented by the following general formula (3).

（式中、Ｒ^３、Ｒ^４およびＲ^５は、１価の炭化水素基または水素原子であり、少なくとも１つは炭化水素基である）

(Wherein R ³ , R ⁴ and R ⁵ are a monovalent hydrocarbon group or a hydrogen atom, and at least one is a hydrocarbon group)

Specific examples of the general formula (3) include dibutylamine, octylamine, dioctylamine, laurylamine, dilaurylamine, oleylamine, coconutamine, and beef tallow amine.
The phosphoric acid ester represented by the general formula (3) and its amine salt are used alone as a friction modifier (FM) or an extreme pressure agent, but in the present invention, due to a synergistic action with the component (A), (A) The effect | action which prevents exhaustion of a component is expressed.

(B) The compounding quantity of a component is 0.1-5 mass% with respect to lubricating oil whole quantity, Preferably it is 0.5-2 mass%. When the blending amount of the component (B) is too small, the consumption of the component (A) cannot be prevented and the durability is insufficient. When the blending amount is too large, the absolute value of the friction coefficient becomes too low, the transmission torque is reduced, and the heat resistance Also decreases.
In addition, when only (B) component is mix | blended without mix | blending (A) component, an appropriate friction characteristic cannot be acquired in a specific temperature range and sliding speed.

In addition to the base oil and the component (A) and the component (B), the lubricating oil of the present invention may contain known additives such as ashless dispersants, antiwear agents, extreme pressure agents, if necessary. Friction modifiers, antioxidants, corrosion inhibitors, viscosity index improvers, pour point depressants, antifoaming agents and the like can be added.
Examples of the ashless dispersant include alkenyl succinimides, alkenyl succinates, amides of long-chain fatty acids and polyamines (aminoamide type), antiwear agents such as ZnDTP, and extreme pressure agents. , Hydrocarbon sulfides, sulfurized fats and oils, friction modifiers such as organic molybdenum compounds, antioxidants such as amines and phenolic antioxidants, corrosion inhibitors such as benzotriazole, Alkenyl succinic acid esters, etc., viscosity index improvers such as polymethacrylates and olefin copolymers, pour point depressants such as polymethacrylates, and antifoaming agents such as silicon compounds and ester antifoaming agents. Each is listed.
The lubricating oil for wet clutches of the present invention has a BF viscosity at −40 ° C. of less than 2000 MPa · s, and more preferably 1800 MPa · s or less, at low temperature viscosity.

Below, this invention is demonstrated in detail based on an Example and a comparative example. In addition, this invention is not restrict | limited at all by these examples.
(Examples 1-6)
Each component shown in Table 1 is blended at a ratio (mass%) shown in Table 1 into oleic acid-2-ethyl-hexyl alone or a base oil obtained by mixing oleic acid-2-ethyl-hexyl and polyalphaolefin. Thus, a lubricating oil for wet clutches was prepared.
In Table 1, regarding the base oil, it is represented by mass% in the total amount of the base oil.
(Comparative Examples 1-5)
Each component listed in Table 2 was blended with the base oil listed in Table 2 at the blending ratios listed in Table 2 to prepare a wet clutch lubricating oil.
As in Table 1, in Table 2, the base oil is represented by mass% in the total amount of the base oil, and each component other than the base oil is represented by mass% in the total amount of the lubricating oil.

[Durability of friction characteristics]
Using a low speed friction tester, the friction plate and the friction disk were continuously rubbed at an oil temperature of 80 ° C., a surface pressure of 3 MPa, and a rotation speed of 100 rpm, and the stick-slip prevention property was evaluated approximately every 24 hours. The method detects torque when the friction plate surface is slid by rotating the friction disk at 1, 2, 5, 10, 25, 50, 100, and 200 rpm while applying a surface pressure of 0.59 MPa by hydraulic pressure. The coefficient of friction was determined. Here, μ1 is a friction coefficient at a rotation speed of 1 rpm, and μ10 is a friction coefficient at a rotation speed of 10 rpm.
Those having a ratio of both friction coefficients (μ1 / μ10) smaller than 1 were judged to be excellent in stick-slip prevention, and the point when this value was 1 or more was regarded as the endurance life.

(Measurement of low temperature viscosity)
The -40 ° C and -30 ° C BF viscosities were measured by the ASTM D 2983 method.

In addition, * 1-11 in Table 1 has the following meaning.
1: Polyalphaolefin (100 ° C. kinematic viscosity 2 mm ² / s)
2: Polyalphaolefin (100 ° C. kinematic viscosity 4 mm ² / s)
3: oleic acid-2-ethyl-hexyl 4: obtained by esterifying isodecyl alcohol, diester base oil obtained by esterifying adipic acid 5: 3,5,5-trimethyl-1-hexanol and adipic acid Diester base oil 6: Diester base oil obtained by esterifying 2-ethyl-1-hexanol and dodecanedioic acid 7: Diester base oil obtained by esterifying 2-ethyl-1-hexanol and sebacic acid

8: Polymethacrylate (molecular weight 60,000)
9: ATF package type additive for DEXRON III (antiwear agent, antioxidant, antifoaming agent, dispersant, etc.)
10: oleyl (poly) glyceryl ether (a mixture of oleyl alcohol: monoether: polyether of about 40: 30: 30% by mass)
11: Dioleyl hydrogen phosphate 12: Amine salt of 2-ethylhexyl acid phosphate 13: Amine salt of oleyl acid phosphate 14: Dilauryl hydrogen phosphate phosphite

As is apparent from Tables 1 and 2, the wet clutch lubricating oil (Example 1) of the present invention containing, for example, oleic acid-2-ethyl-hexyl, additive 2, and additive 3 has an anti-stick-slip property. Excellent persistence of the coefficient of friction, and even at a low temperature of −40 ° C., the BF viscosity at −40 ° C. is less than 2000 MPa · s, and the increase in viscosity is small compared to the others. Moreover, sufficient time is shown also in durability of a friction characteristic.
On the other hand, even when oleic acid-2-ethyl-hexyl is used, the wet clutch lubricant (Comparative Example 2) which does not contain the component (A) and contains only the * 11 component of the component (B) has sufficient durability. And low temperature performance is not obtained.
In addition, when other ester oil is used as the base oil, the BF viscosity at −40 ° C. exceeds 2000 MPa · s, and the increase in viscosity is larger than that in Examples.

Claims (4)

To the base oil containing an oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester part and having a kinematic viscosity of ² to 50 mm ² / s at 100 ° C.,
(A) 0.1 to 10% by mass of a higher alcohol having 8 or more carbon atoms in the alkyl group and an ether of glycerine with respect to the total amount of the lubricating oil, and (B) a phosphoric ester compound with respect to the total amount of the lubricating oil 1-5 mass% of lubricating oil for wet clutches characterized by the above-mentioned. The wet clutch lubricating oil according to claim 1, wherein the oleic acid ester having an alkyl group having 7 to 9 carbon atoms in the ester portion is oleic acid-2-ethyl-hexyl. The lubricating oil for wet clutches according to claim 1 or 2, wherein the phosphoric acid ester compound is at least one selected from phosphoric acid esters, phosphorous acid esters, and amine salts thereof. The lubricating oil for wet clutches according to any one of claims 1 to 3, wherein the lubricating oil for wet clutches is used for any one of an electronically controlled coupling, an LSD gear, and a wet brake.