LUBRICATING OIL COMPOSITION FOR AUTOMOBILE TRANSMISSION AND LUBRICATING METHOD USING SAME

Abstract

The present invention relates to an automatic transmission lubricating oil composition, and particularly to an automatic transmission lubricating oil composition comprising an oil of lubricating viscosity, an ashless dispersant, an anti-oxidant, a phosphorus-based anti-wear agent and a friction-modifier, wherein more than 310 ppm of phosphorus is contained, thereby being useful for lubricating or operating an automatic transmission comprising a transmission clutch using a slip lock-up torque converter and a paper based clutch material and a planetary gear system, especially six-speed automatic transmission.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2008-0053833 filed Jun. 9, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a lubricating oil composition for automatic transmissions and a method of lubricating automatic transmission using the lubricating oil.

(b) Background Art

The continuing need for more energy efficient vehicles has driven transmission builders to design ever more sophisticated transmissions that can consume less energy. A recent trend is that transmissions are designed so as to meet the following requirements: (a) higher number of fixed speed ratios; (b) torque converter clutches which are applicable even during aggressive driving (i.e., meaning the torque converter clutch is engaged at least 25% of the time for which the vehicle is in motion); (c) more compact shifting clutches; and (d) more sophisticated planetary gear set designs such as Ravigneaux and overall architecture as in the Lepelletier system, which make it to difficult to lubricate the transmissions while making them more energy efficient.

In order to provide efficient operation and energy efficiency, transmissions must have a specific design that allow a lubricating oil composition to be supplied to the transmissions in a manner so as to operate the transmissions correctly for a long time (mileage accumulation).

For example, the torque converter clutches need to be applied a fluid with exceptionally good friction characteristics and durability. The compact shifting clutches need to be applied with a fluid with excellent high energy friction durability. And, the planetary gear sets need to be applied with a fluid with excellent anti-wear characteristics. This is especially true in case of the torque converter clutches applicable to aggressive driving, more compact shifting clutches; and more sophisticated planetary gear sets.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE DISCLOSURE

In one aspect, the present invention provides lubricating oil compositions for use in an automobile transmission, whose compositions comprise an oil of lubricating viscosity; an ashless dispersant; an anti-oxidant; a phosphorus-based anti-wear agent; and a friction modifier, wherein the lubricating oil composition contains at least 310 parts per million of phosphorus. A non-limiting example of the transmission may be a six speed energy efficient automatic transmission comprising a slipping torque converter, shifting clutches using paper based clutch materials and planetary gear systems.

In another aspect, the present invention provides methods for lubricating an automobile transmission by supplying the above-described compositions to the transmission.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The above and other features of the invention are discussed infra.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the drawings attached hereinafter, wherein like reference numerals refer to like elements throughout. The embodiments are described below so as to explain the present invention by referring to the figures.

Unless described otherwise, all the numerical values used herein regarding an amount of an ingredient, a reaction condition, a dimension, a physical property and a process parameter should be understood as somewhat variable by the term of “about”, and thus can be changed depending on the desired properties. At least, as an intention of ensuring the application of equivalent principle, each of numerical value described herein should be interpreted in view of the number of significant digits and the typical approximation method. Further, all the numerical ranges herein should be understood as comprising any smaller ranges falling within the range described herein. For example, a range “1-10” should be interpreted to comprise any smaller range having a lower limit of 1 or higher and an upper limit of 10 or lower (e.g., 5.5-10). Any patents or academic papers described below are hereby incorporated herein by reference in its entirety.

As used herein, the term of “hydrocarbil substitution group” or “hydrocarbil group” is used in the present invention as typically understood by one skilled in the art. In particular, this refers to a group that shows a dominant hydrocarbon property and includes carbon atoms attached directly to the other part of molecule. Examples of hydrocarbil group include any substitution group that causes no change in dominant hydrocarbon property of hydrocarbon group (such as alkyl and alkenyl group), cycloalkyl group and a main substitution group. The hydrocarbil group can be a hetero atom such as sulfur, oxygen and nitrogen provided the hydrocarbon property is not changed.

In one aspect of the present invention, as discussed, there is provided a lubricating oil composition comprising an oil of lubricating viscosity, an ashless dispersant, an anti-oxidant, a phosphorus-based anti-wear agent and a friction-modifier along with more than 310 ppm of phosphorus. The lubricating oil composition is useful for lubricating and operating various types of transmissions, including an automatic transmission comprising a transmission clutch using a slip lock-up torque converter and a paper based clutch material and a planetary gear system. One of the examples of such transmissions may be a six-speed automatic transmission.

The oil of lubricating viscosity may comprise various oils of lubricating viscosity such as at least one natural oil, at least one synthetic oil or a mixture thereof. In a non-limiting embodiment of the present invention, the oil of lubricating viscosity is contained in a large amount (i.e., more than about 50 wt %). The oil of lubricating viscosity is contained in the amount of preferably 75-95 wt %, and more preferably 80-95 wt % relative to the total weight of the lubricating oil composition.

Examples of the natural oil may include animal oils and vegetable oils as well as mineral lubricating oils such as liquid petroleum oils and solvent treated or acid-treated mineral lubricating oils of paraffinic, naphthenic or mixed paraffinic/naphthenic types which may be further refined by hydro cracking or hydro finishing processes.

Examples of the synthetic lubricating oil may include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins, also known as polyalphaolefin; polyphenyl; alkylated diphenyl ether; and alkylated diphenyl sulfide and derivatives, analogs and homologues of thereof. Other examples of the synthetic lubricating oils may include various esters of alcohols and dicarboxylic acids and esters prepared by using C₄-C₁₅ monocarboxylic acids and polyols or polyol ethers.

The aforementioned natural oils and synthetic oils can be unrefined, refined or re-refined oils. As used herein, the term “unrefined oil” refers to an oil that can be obtained from a natural or a synthetic source without a purification process. As used herein, the term “refined oil” refers to an oil that is treated in a purification process for improving at least one properties. The term “re-refined oil” refers to an oil that is treated in at least two purification processes for improving at least one properties. For example, the oxidative stability of an oil can be improved by hydrogenation.

In a non-limiting embodiment, examples of the oil of lubricating viscosity may include II group oil, III group oil, IV group oil, V group oil, which are defined in API Base Oil Interchangeability Guidelines, and a mixture thereof. Appropriate examples of II group oil and III group oil are Yubase 3 and Yubase 6, respectively (Yubase is a trademark of SK Energy Co., Ltd.). Further, appropriate examples of IV group oil and V group oil are a poly-alpha-olefin and an ester, respectively.

The oil of lubricating viscosity can be a singular-viscosity oil or a mixture of a high-viscosity oil and a low-viscosity oil. In a non-limiting embodiment, the oil of lubricating viscosity may have a kinematic viscosity of about 2-8 mm²/sec(cSt) of 100° C. A total lubricating oil composition can be prepared so that viscosity at 100° C. can be about 5.0-6.0 mm^2/sec, for example about 5.3-5.5 mm²/sec. A total lubricating oil composition can be prepared so that a Brookfield viscosity (ASTM D-2983) at -40° C. can less than 12,000 cP, for example less than 10,000 cp.

In a non-limiting embodiment, the ashless dispersant may be included in the amount of 0.5-5.0 weight parts, such as 1.0-4.0 weight parts or 2.0-3.0 weight parts relative to 100 weight parts of the oil.

Examples of appropriate ashless dispersant include a long-chained (comprising more than 40 carbons) substituted hydrocarbil succinimide or hydrocarbil succinamide, a mixed ester/amide of a long-chained (comprising more than 40 carbons) hydrocarbil-substituted succinic acid, hydroxyester of a long-chain hydrocarbil-substituted succinic acid and a long-chained (comprising more than 40 carbons) hydrocarbil-substituted phenol, Mannich condensation product of formaldehyde and polyamine, and a mixture thereof.

In a non-limiting embodiment, examples of the ashless dispersant include a long-chained alkenyl succinimide, and non-cyclic hydrocarbil-substituted succinimide prepared by using various amines or amine derivatives disclosed in patents. Phosphoric acid (or its anhydride) and borated alkenyl succinimide are highly compatible (miscible) with elastomeric seal prepared by using fluoro-elastomer and silicon-containing elastomer, thus being appropriate for the present invention. Polyisobutenyl succinimide (where the polyisobutenyl substitution group comes from polyisobutene having a number average molecular weight of 500-5,000, for example 800-2500), which is prepared by using polyisobutenyl succinic acid anhydride and alkylene polyamine (for example, triethylene tetramine or tetraethylene pentamine), is appropriate for the present invention. The dispersants can, preferably, be post-treated with various known materials as disclosed in, for example, U.S. Pat. Nos. 3,254,025, 3,502,677 and 4,857,214.

According to the present invention, a lubricating composition may comprise at least one anti-oxidant. An anti-oxidant of the present invention is well known to one skilled in the art. In a non-limiting embodiment, anti-oxidants include two types of compounds, i.e., an aromatic amine compound and a hindered phenol compound. Examples of appropriate aromatic amine include aromatic triazole, phenothiazine, diphenyl amine, an alkyl diphenyl amine comprising at least one substitution group with 16 or less carbon atoms, phenyl-alpha-naphthyl amine, phenyl-beta-naphthyl amine and alkyl or aryl-substituted phenyl-alpha-naphthyl amine.

In a non-limiting embodiment, aromatic amine is a diphenyl amine which is alkylated with nonene (C9). This is a mixture of monoalkylated and dialkylated diphenyl amines, where the substitution group is a branched C₉. This compound is commercially available under the trademark of Naugalube 438L (Chemtura Corporation).

Examples of the hindered phenol include ortho-alkylated phenol-based compounds such as 2,6-di-tertiary-butyl phenol, 4-methyl-2,6-di-tertiary-butyl phenol, 2,4,6-tri-tertiary-butyl phenol and analogs or homologues thereof. Other examples of hindered phenol include butylated hydroxyl toluene (BHT), butylated hydroxyl anisole (BHA) and derivatives thereof. Examples of hindered phenol also include methylene bridged alkyl phenol that can be used alone or in combination with other hindered phenol or stereo-hindered non-crosslinked phenol-based compound. Examples of suitable methylene bridged phenol include 4,4′-methylenebis(6-tertiary-butyl-o-cresol), 4,4′-methylenebis (4-methyl-6-tertiary-butylphenol) and 4,4′-methylenebis(2,6-di-tertiary-butylphenol) and derivatives thereof as well as a mixture of two or more such mononuclear phenolic compounds are also suitable.

Suitably, the anti-oxidant may be contained in the amount of about 0.05-5.0 weight parts, for example about 0.1-3.0 weight parts or about 0.25-2.0 weight parts relative to 100 weight parts of the oil.

According to the present invention, a lubricating oil composition may comprise at least one phosphorus-based anti-wear agent. The phosphorus-based anti-wear agent is contained in the amount of 0.03-4.75 weight parts relative to 100 weight parts of the oil. Examples of the phosphorus-based anti-wear agent include the organic ester of a phosphorus acid, such as an amine salt of an organic phosphite or a phosphorus acid.

Appropriate organic phosphite is well known to one skilled in the art. Organic phosphite appropriate in the present invention has the Formula 1:

wherein R₁ and R₂ are independently C₁-C₁₈ alkyl group or hydrogen provided that R₁ and R₂ are not hydrogen at the same time. An alkyl group can be linear or branched, and comprise heteroatoms such as nitrogen, oxygen and sulfur. Appropriate examples of organic phosphite include dibutyl hydrogen phosphite (R₁═R₂═C₄H₉), di-2-ethylhexyl hydrogen phosphite (R₁═R₂═2-ethylhexyl), dioleyl hydrogen phosphite (R₁═R₂=oleyl) and mono-butyl hydrogen phosphite (R₁═C₄H₉, R₂═H).

In a non-limiting embodiment, an organic phosphite is reacted with an ashless dispersant, thereby improving its solubility and stability.

In a non-limiting embodiment, the phosphorus-based anti-wear agent can be prepared by producing amine salt of phosphorus acid. Phosphorus acid (H₃PO₃) can be represented as Formula I, where R₁═R₂═H. These compounds are conventionally prepared by reacting phosphorus acid with a polyamine-based ashless dispersant or in the presence of boric acid. U.S. Pat. No. 4,857,214 incorporated herein for the reference discloses such preparation method.

According to the present invention, a lubricating oil composition may comprise at least one friction-modifier. Appropriate friction-modifier is well known to one skilled in the art. U S. Pat. No. 4,792,410 discloses examples of appropriate friction-modifier. Examples of appropriate friction-modifier include without limitation a fatty acid amide, a fatty epoxide, a fatty amine, a borated glycerol ester, an alkoxylated fatty amine, a borated alkoxylated amine, a fatty imidazoline and a condensation product of carboxylic acid or anhydride and polyamine.

Commercially available fatty acid amides can be used in the present invention, and non-limiting examples of such material include stearamide and oleamide. Normally, an acid group include about 10-20 carbon atoms.

Examples of a fatty epoxide appropriate for the present invention include a compound prepared by reacting a per-oxidizing agent (e.g. per-acetic acid) with olefin. A typical olefin appropriate for the preparation of a friction-modifier is a linear olefin including about 10-20 carbon atoms and a double bond at the end of the chain (for example, between the first and the second carbons. Non-limiting examples of an appropriate olefin include 1,2-epoxyhexadecane, 1,2-epoxyoctadecane and a mixture thereof. A borated fatty epoxide can be prepared by reacting a fatty epoxide with a borating agent such as boric acid.

Non-limiting examples of an appropriate borated glycerol ester include an ester of glycerol and a long-chained fatty acid such as stearic acid and oleic acid. A borated glycerol ester can be prepared by reacting one mole of an acid with one mole of glycerol to provide two free hydroxyl groups. Examples of such material include glycerol mono-oleate. Hydroxyl borate ester can be prepared by reacting such diol-containing ester with boric acid.

An alkoxylated fatty amine, a widely known friction-modifier, is bis-(mono ethoxylate) of C10-C20 long-chained amine. This is manufactured by Akzo Nobel (Amsterdam) and on the market as Ethomeen. Examples of such material include bis(2-hydroxyethyl)tallowamine, bis(2-hydroxyethyl)oleylamine and bis(2-hydroxyethyl)octadecylamine. A borated alkoxylated amine can be prepared by reacting bis alkoxylated amine with boric acid. For instance, a product prepared by reacting one moles of alkoxylated amine and diethoxylate with 0.5-2.0 moles of boric acid can be used as a friction-modifier.

A fatty imidazoline is a condensation product of a fatty acid and diamine or polyamine. Examples of appropriate acid include natural acids such as decanoic acid, oleic acid, stearic acid, isostearic acid, palmitic acid, myristic acid, linoleic acid, lauric acid and acids resulting from tallow or palm oil. Examples of appropriate amine include tetraethylene pentamine and polyamine.

The aforementioned imidazoline can be prepared by conducting the condensation between carboxylic acid or anhydride and polyamine. However, this condensation can result in the production of a simple amide when the reaction condition is relatively milder, or the production of succinamide when succinic acid anhydride-based reactants are used.

Other appropriate friction-modifier is produced by the reaction between alkyl-substituted succinic acid anhydride and polyamine. Examples of such friction-modifier include a condensation product of 3-octadecenyl succinic acid anhydride and diethylene triamine or tetraethylene pentamine. The preparation method is disclosed in U.S. Pat. No. 5,840,663.

Any combination of the aforementioned friction-modifiers can also be used in the present invention.

Preferably, about 0.05-5.0 weight parts, more preferably, about 0.1-4.0 weight parts of the friction-modifier may be contained relative to 100 weight parts of oil.

In the present invention, a lubricating oil composition comprises 310 ppm or more of phosphorus. The typical lubricating oil composition comprises less than 1500 ppm of phosphorus. Phosphorus may come from at least one of the components of the composition as long as the amount of phosphorus is at least 310 ppm relative to the total amount of the composition.

A lubricating oil composition of the present invention may further comprise various additional components. Examples of such additional components include the followings without limitation: a viscosity modifier, an anticorrosive, an antifoaming agent, a seal swell agent, a pour-point depressant, a detergent, a fluidizer and a dye.

Viscosity modifiers and dispersants are well known to one skilled in the art. Their examples include polymethacrylate, polyacrylate, polyolefin, styrene-maleic acid anhydride copolymer and analogous homopolymer, copolymer and graft copolymer. In a non-limiting embodiment of the present invention, examples of Viscosity modifier include polymethacrylate, which are manufactured by RohMax and on the market as Acryloid and Viscoplex series polymer manufactured.

A lubricating oil composition shows a kinematic viscosity of 5.2 cSt or higher (preferably 5.2-6.0 cSt) at 100° C. and Brookfield viscosity of 12,000 cP or lower (preferably 3,000-12,000 cP) at −40° C.

In another aspect, as discussed above, the present invention provides a method for lubricating automobile transmissions using the above-described lubrication oil compositions. As discussed above, the kind and size of the transmissions are not limited. The above-described lubricating oil compositions may be supplied to the transmissions in a way known to those skill in the art.

EXAMPLES

The following examples illustrate the invention and are not intended to limit the same. As used herein, “parts” and “%” are based on the weight unless described otherwise.

Examples 1-5

In Example 1, a lubricating oil composition according to the present invention was prepared by a conventional method with the following components.

(1) An oil of lubricating viscosity: 100 weight parts of API III group oil;

(2) An ashless dispersant: 1.50 weight parts of a dispersant prepared by reacting polyisobutenyl(MW: about 1000)-substituted succinic acid anhydride with alkylene polyamine;

(3) A friction-modifier comprising: (a) 3.60 weight parts of a friction-modifier prepared by reacting 3-octadecenyl succinic acid anhydride with a polyamine; (b) 0.10 weight parts of carboxylic acid friction-modifier; (c) 0.10 weight parts of an alkyl thio ether ester friction-modifier; and (d) 0.09 weight parts of a fatty acid amide friction-modifier;

(4) An anti-oxidant comprising: (a) 0.25 weight parts of a hindered phenol an anti-oxidant; and (b) 0.75 weight parts of an alkyl diphenylamine anti-oxidant; and

(5) A phosphorus-based anti-wear agent: 4.00 weight parts of succinic acid anhydride substituted with polyisobutenyl(MW: about 2000) reacted with a mixture of monoalkyl and dialkyl phosphite such that the final product after the additional reaction with polyamine may comprise about 0.8 wt % of phosphorus and a total lubricating oil composition may comprise more than 330 ppm of phosphorus.

The following additional components were added to the composition: (1) 0.10 weight parts of an anticorrosive; (2) 0.20 weight parts of calcium dispersant; (3) 1.50 weight parts of a heterocyclic seal swelling agent; (4) 2.00 weight parts of a polymethacrylate Viscosity modifier; and (5) 200 ppm of an antifoaming agent.

In Examples 2-5, lubricating oil compositions according to the present invention were prepared by the method used in Example 1 except that the components shown in Table 1 were used with the following respective oils of lubricating viscosity: (a) 4cSt III group (Example 2); (b) 4cSt III group (Example 3); (c) 3cSt III group (Example 4); and (d) 3cSt III group (Example 5).

As an ashless dispersant, 950 MW PIBSA/PAM was used in Examples 2 and 3 and 2000 MW PIBSA/PAM was used in Examples 4 and 5.

As an anti-oxidant, (i) alkyl diphenyl amine and (ii) hindered phenol were used in Examples 2-5.

As a phosphorus-based anti-wear agent, a dibutyl hydrogen phosphate was used in Example 2, a diphenyl hydrogen phosphate was used in Example 3, and 950 MW PIBSA/PAM dispersant reacted with H₃PO₃ and H₃PO₃ was used in Examples 4 and 5.

As a friction-modifier, a product prepared by reacting isostearic acid and tetraethylene pentamine was used in Example 2, (i) a product prepared by reacting 3-octadecenyl succinic acid anhydride and diethylene triamine and (ii) a diethoxylated tallow amine were used in Example 3, (i) a product prepared by reacting isostearic acid and tetraethylene pentamine and (ii) 1-hydroxyethyl-2-heptadecyl imidazoline were used in Example 4 and (i) a product prepared by reacting 3-octadecenyl succinic acid anhydride and diethylene triamine and (ii) diethoxylated tallow amine were used in Example 5.

TABLE 1
	Example 2*	Example 3*	Example 4*	Example 5*
	(parts by	(parts by	(parts by	(parts by
	weight % on an	weight % on an	weight % on an	weight % on an
Components	oil-free basis)	oil-free basis)	oil-free basis)	oil-free basis)
Ashless dispersant	2.50	2.50	2.0	2.0
Anti-oxidant	(i) 0.75	(i) 0.75	(i) 0.75	(i) 0.75 (ii)
	(ii) 0.25	(ii) 0.25	(ii) 0.25	0.25
Phosphorus-based	0.25	0.18	4.75	4.05
anti-wear agent
Friction Modifier	2.0	(i) 2.0	(i) 2.0	(i) 2.0
		(ii) 0.2	(ii) 0.5	(ii) 0.2
*relative to 100 weight parts of oil

Performance tests were conducted for the lubricating oil composition prepared in Example 1. As a Comparative Example, the same tests were conducted by using commercially available 4-speed automatic transmission oil used in a car manufacturing plant and DiaQueen SP-III ATF of Mitsubishi Motor Company. The results are presented in Table 2.

TABLE 2
Performance test
	Tests	Example 1	Comp. Ex. 1
	Phosphorus content [ppm]	330	240
	Wear
	FZG A/3.3/90a	13	11
	Failure load stage
	Friction
	Anti-shudder durabilityb	384	168
	hours to failure
	SAE NO. 2
	MERCON method	0.125	0.120
	static friction coefficientc
	JASO methodd	0.118	0.110
	static friction coefficient [μt]
	Ratio of friction coefficients	0.95	1.00
	[μ0/μd]
	Oxidation
	DKA methode [TAN increase]	0.65	0.97
	Viscosity
	Kinematic viscosity at 100° C.	5.41	7.53
	ASTM D-445[mm2/s(cSt)]
	Brookfield viscosity at −40° C.	8,850	15,600
	ASTM D-2983[cP]
	aAs per method DIN 51354-2.
	bAs per JASO method M-349-2001 using Dynax D512 friction discs.
	cAs per Ford MERCON Specification, “MERCON ® Automatic Transmission Fluid for Service”, January 1997, Appendix 4. using Borg Warner BW 6100 friction discs.
	dAs per method JASO M-348-2002 using NissekiWarner NW461E friction discs.
	eAs per CEC-L-48, 170° C. for 192 hours.

Table 2 shows that lubricating oil composition of Example 1 is superior to that of Comparative Example 1 in all the tests.

Wear: FZG test was preformed for evaluating the capability of the oils of preventing gear scuffing. The lubricating oil of Example 1 was superior to the oil of Comparative Example 1 in this test. The oil of Comparative Example 1 failed at the 11^th level while that of Example 1 failed at 13^th level.

Friction: According to JASO M-349-2001 test, the lubricating oil of Example 1 showed a remarkable increase in anti-shudder durability (384 hours) as compared to the oil of Comparative Example 1 (168 hours). This means the lifespan of torque converter clutch can be increased when the lubricant of Example 1 is used. Further, according to SAE #2 test, static friction coefficients were increased in Example 1. This means that higher torque capacity can be achieved under higher load conditions (e.g., towing) by using the lubricant of Example 1.

Oxidation resistance: The lubricating oil of Example 1 was superior to the oil of Comparative Example 1 in the resistance to oxidation. Lower degree of TAN (total acid number) increase means better oxidative stability and improved durability.

Viscosity: The 100° C. viscosity and −40° C. Brookfield viscosity of the lubricating oil of Example 1 were lower than those of Comparative Example 1. As a result, the lubricating oil of Example 1 maintained an appropriate thickness on hydrodynamic lubricating parts of transmissions such as a bearing, and increases total energy efficiency of transmissions.

As described above, the lubricating oil compositions according to the present invention are useful for lubricating and operating various types of automobile transmissions including one which comprises a transmission clutch using a slip lock-up torque converter and a paper based clutch material and an planetary gear system, especially a six-speed automatic transmission.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A lubricating oil composition for a six-speed transmission having a slipping torque converter clutch and Ravigneaux gear set, the composition comprising:

100 weight parts of an oil of lubricating viscosity;

0.5-5 weight parts of an ashless dispersant;

0.05-5 weight parts of an anti-oxidant;

0.03-4.75 weight parts of a phosphorus-based anti-wear agent; and

0.05-5 weight parts of a friction modifier,

wherein phosphorus is contained at least 310 parts per million.

2. The lubricating oil composition of claim 1, wherein the oil of lubricating viscosity is selected from the group consisting of a Group II oil, a Group III oil, a Group IV oil, a Group V oil and a mixture thereof.

3. The lubricating oil composition of claim 1, wherein the ashless dispersant is selected from the group consisting of (a) a long-chain substituted hydrocarbil succinimide or hydrocarbil succinamide, (b) a mixed ester/amide of a long-chain hydrocarbil-substituted succinic acid, (c) a hydroxyester of a long-chain hydrocarbil-substituted succinic acid, and (d) a Mannich condensation product of a long-chain hydrocarbil-substituted phenol, formaldehyde and polyamine.

4. The lubricating oil composition of claim 1, wherein the ashless dispersant is a long-chained alkenyl succinimide.

5. The lubricating oil composition of claim 1, wherein the anti-oxidant is an aromatic amine or a hindered phenol.

6. The lubricating oil composition of claim 1, wherein the phosphorus-based anti-wear agent is an organic phosphite or an amine salt of phosphorus acid.

7. The lubricating oil composition of claim 1, wherein the phosphorus-based anti-wear agent is prepared by reacting phosphorus acid with a polyamine-based ashless dispersant.

8. The lubricating oil composition of claim 1, wherein the friction modifier is selected from the group consisting of fatty acid amides, fatty epoxides, fatty amines, borated glycerol esters, alkoxylated fatty amines, borated alkoxylated amines, fatty imidazolines, condensation products of carboxylic acids and anhydrides with polyamines.

9. The lubricating oil composition of claim 1, wherein the friction modifier is a reaction product of 3-octadecenyl succinic acid anhydride and a polyamine.

10. The lubricating oil composition of claim 1, which has a kinematic viscosity at 100° C. of 5.2 cSt or higher and a −40° C. Brookfield viscosity of 12,000 cP or lower.

11. A method for lubricating a six speed automatic transmission having a slipping torque converter clutch and Ravigneaux gear set comprising supplying to said transmission the lubricating oil composition of claim 1.