Automatic transmission lubricant composition with improved anti-wear properties

Abstract

 Automatic transmission fluids are described which contain at least 0.05 weight percent of a dialkyl thiadiazole and sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester, up to about 0.15 weight % of a metal-containing detergent, and/or a mixture thereof. The transmission fluids according to the present invention exhibit improved anti-wear and extreme pressure performance.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] There are no related applications.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This research was not sponsored by any entity of the Federal Government.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0003] This invention relates to oil-based automatic transmission fluid compositions having enhanced performance capabilities, more specifically including improved anti-wear and extreme pressure performance.

2. Description of the Prior Art

[0004] US Patent 5,578,236, to Ethyl Corporation discloses a power transmission fluid with enhanced performance characteristics. The power transmission fluid composition disclosed therein has, inter alia, an oil-soluble boron content of about 0.001 to about 0.1%, an oil soluble phosphorus content of about 0.005 to about 0.2%, and an oil soluble metal additive content of from 0 to about 100 ppm.

[0005] The composition of the '236 patent comprises at least about 50 weight % hydrotreated mineral oils in the range of about 55N to about 125N, about 5 to 40 wt% of hydrogenated poly alpha olefin oligomer having a viscosity of about 2 to about 6 cSt at 100 ° C, about 5 to about 20 wt % of an acrylic viscosity index improver, a seal swell agent, an ashless dispersant, an oil soluble friction modifier, and an inhibitor selected from foam, copper corrosion (including thiadiazoles), rust, and oxidation inhibitors. The finished composition has a Brookfield viscosity of 13,000 cP or less at - 40 ° C, an ASTM D-4683 viscosity of at least 2.6 mPa.s at 150 ° C, and a viscosity of at least 6.8 cSt at 100° C after 40 cycles in the FISST of ASTM D-5275. However, the compositions disclosed are preferably devoid of sulfurized components.

[0006] US Patent 5,441,656, also to Ethyl Corporation, discloses an automatic transmission fluid for overcoming shudder problems in continuous slip torque converter clutches in automatic transmissions. The automatic transmission fluid ("ATF") of the '656 patent includes, among other restrictions, a friction modifier content which contains an N-aliphatic hydrocarbyl substituted diethanolamine in which the N-aliphatic hydrocarbyl substituent is free of acetylenic unsaturation and having in the range of about 14 to about 40 carbon atoms, and an N-aliphatic hydrocarbyl substituted triemethylene diamine in which the N-aliphatic hydrocarby substituent is at least one straight chain aliphatic hydrocarbyl group having in the range of about 14 to about 20 carbon atoms. Conventional copper corrosion inhibitors (including thiadiazoles) and other optional (e.g. lubricity, dye, pour point depressant, etc.) components may be present.

[0007] U.S. Patent Nos. 5,344,579; 5,372,735; and 5,578,236 disclose automatic transmission fluid compositions which exhibit good anti-shudder properties.

[0008] Other U.S. Patents which disclose various automatic transmission fluids include 4,795,583; 4,855,074; 4,857,214; 5,089,156; 5,126,064; 5,164,103; 5,171,466; 5,198,133; 5,256,324; 5,360,562; 5,387,346; 5,387,352; 5,389,273; 5,439,606; 5,505,868; 5,652,201; 5,703,023; 5,817,605; 5,851,962; 5,891,786; and 5,972,851. Each of the above is incorporated by reference.

[0009] These references, however, fail to teach or suggest the combination of components of the present invention, including the combination of at least 0.05% of a ashless dialkyl thiadiazole corrosion inhibitor with with sulfurized fats, sulfurized fatty acids, sulfurized fatty acid esters and/or mixtures thereof.

[0010] Commercially, it is known to add various additive packages to automatic transmission fluid, including, among other things, extreme pressure agents, antiwear agents, antioxidant systems, corrosion inhibitor systems, metal deactivators, anti-rust agents, friction modifiers, dispersants, detergents, anti-foam agents, and viscosity index improvers. However, not all additives interact predictably or well with one another.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention relates to the improvement of anti-wear and extreme pressure performance and stability of an automatic transmission fluid by the inclusion of sulfurized fats, sulfurized fatty acids, sulfurized fatty acid esters and/or mixtures thereof, and an ashless dialkyl thiadiazole. Other optional components, e.g. friction modifiers, antioxidants, dispersants, and viscosity index improvers, allow the fully formulated transmission fluid composition to provide improved antiwear and extreme pressure performance when incorporated into an automatic transmission.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Vehicles meeting the stringent demands of consumers today require durability and performance in all of the vehicular systems. One of the most important systems is the power transmission system ("transmission") which transmits the power generated by the automobile engine to the wheels. It being one of the most complex systems in the vehicle, it is also one of the most costly to diagnose, repair, or replace. The transmission usually includes, inter alia, a clutch with plates, a torque converter, and a plurality of gears to alter the power delivered to the wheels by changing the gear ratio.

[0013] Discriminating consumers primarily desire high performance, low maintenance (high mileage between servicing), and extended life expectancy. However, with the advent of new transmission technologies, old standards of performance which were previously met with approval are now becoming unacceptable.

[0014] For example, there is worldwide activity by the automobile manufacturers to develop automatic transmissions incorporating various electronically controlled converter clutch (ECCC) designs. These developments are being driven by the anticipated increase in Corporate Average Fuel Economy (CAFE) requirements in the U.S.A. The ECCC design allows increases in fuel economy to be gained.

[0015] The advent of ECCC transmissions as well as vehicles equipped with a continuously variable transmission (CVT) and advances in aerodynamic body design result in passenger cars with smaller transmissions which tend to operate with higher energy densities and higher operating temperatures. Such changes have challenged lubricant suppliers to formulate automatic transmission fluids with new and unique performance characteristics including higher torque and friction durability.

[0016] As a result, many original equipment manufacturers (OEMs) are looking for automatic transmission fluids with frictional characteristics capable of meeting the requirements of ECCC, CVT, and other designs while retaining sufficient performance in the anti-wear arena.

[0017] A need exists for an effective way of overcoming the wear problem associated with automatic transmissions, especially to meet the needs of OEM automobile designers and suppliers, for extended transmission fluid life and durability.

[0018] This invention overcomes the durability and anti-wear (extreme pressure) problem by providing an automatic transmission fluid that exhibits good anti-wear performance during its lifetime.

[0019] In accordance with this invention there is provided an ATF which surprisingly gives improved wear performance at lower treat rates. In one of its embodiments, it contains an effective amount of at least one sulfurized fat, e.g. a sulfurized fatty acid ester, an ashless dialkyl thiadiazole, and less than 0.10 wt % of a metal-containing detergent.

[0020] Suitable sulfurized fats include the SUL-PERM™ brand of products. SUL PERM 60-93, a sulfurized fatty ester-polyalkanol amide type product available from Keil Chemical Division of Ferro Corporation; SUL-PERM 10E, a product indicated by the manufacturer thereof, Keil Chemical Division of Ferro Corporation, to contain 9.5% sulfur and to have the following properties: a viscosity at 100° F. of 2000 SUS, a viscosity at 210 °F. of 210 SUS, and a specific gravity at 77°F of 0.9844; EP Oil GE-10, a product supplied by Hornett Brothers and indicated to have a sulfur content of 8.5 to 9.5 wt %, a flash point of 150°C, a viscosity at 100° C. of 30-40 cSt, a density of 0.97 g/mL at 15°C and an acidity in the range of 5 to 9.5 mg KOH per gram. Also suitable are products from Elco, such as Elco 46368.

[0021] The corrosion inhibitors according to the present invention include ashless dialkyl thiadiazoles. Exemplary suitable compounds include bis-tert-dodecylthiothiadiazole; 2,5-bis(hydrocarbylthio)-1,3,4-thiadiazole; and 2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazole. One commercially available dialkyl thiadiazole is HiTEC® 4313, a product of Ethyl Corporation, Richmond, Virginia. The thiadiazole is preferably a dialkyl, in which each alkyl is independently a hydrocarbyl group having from about 9 to about 18 carbon atoms.

[0022] The metal-containing detergents are preferably those containing a metal from Group 2A of the periodic table, e.g. Be, Mg, Ca, Sr, Ba or Ra, more preferably a Mg or Ca containing detergent such as a calcium phenate, calcium sulfonate, magnesium phenate, or magnesium sulfonate. Especially preferred is a low base calcium hydroxide salt of a sulfurized alkylphenate such as OLOA 216 C, manufactured by the Oronite Division of Chevron.

[0023] In one embodiment, the fluids of the present invention are used in formulating automatic transmission fluids which exhibit an 11 stage pass in the FZG test at 150° C, as set forth in ASTM D 5182-97, which is incorporated herein by reference.

[0024] In another embodiment of the present invention, a method of improving wear performance in automatic transmissions and a method of providing good stability is set forth.

[0025] Said methods comprise adding to, and operating in, an automatic transmission an automatic transmission fluid comprising (1) a major amount of a base oil and (2) a minor amount of an additive composition which comprises, as essential components at least Component (A), Component (B), and Component (C) as described below.

[0026] Although the Components above and in the below list are described occasionally with reference to a function, that function may be one of other functions served by the same component and should not be construed as a mandatory limiting function.

Component (A) Ashless Dialkyl Thiadiazole

[0027] Component (A) is an ashless dialkyl thiadiazole. One example of a commercially available ashless dialkyl thiadiazole is HiTEC® 4313 corrosion inhibitor, available from Ethyl Corporation.

[0028] Dialkyl thiadiazoles suitable for the practice of the instant invention are of the general formula (I):

   wherein R¹ is a hydrocarbyl substituent having from 6 to 18 carbon atoms; R² is a hydrocarbyl substituent having from 6 to 18 carbon atoms; and may be the same as or different from R¹. Preferably, R¹ and R² are about 9-12 carbon atoms, and most preferably R¹ and R² are each 9 carbon atoms.

[0029] Mixtures of dialkyl thiadiazoles of formula (I) with monoalkyl thiadiazoles may also be used within the scope of the present invention. Such mono alkyl thiadiazoles occur when either substituent R¹ or R² is H. However, at least 0.05 weight percent of the fully formulated fluid composition should comprise the dialkyl thiadiazole, more preferably at least about 0.10 weight %. A presently preferred range is from about 0.05 weight % to about 1.00 weight %, more preferably about 0.10 to about 0.75 weight %.

Component (B) - Sulfurized fat

[0030] Component (B) comprises a sulfur source selected from sulfurized fats, e.g., sulfurized fatty acid esters. These components may also have functions as lubricity agents and as extreme pressure (EP) agents as well.

[0031] Various products are available as high sulfur donors,, such as BASE 101 Sulfurized Lard oil; BASE 107 Sulfurized Lard oil; BASE 10L Sulfurized fatty compound; BASE 12SE Sulfurized methyl ester; BASE 14L Sulfurized fatty compound; BASE 401 Sulfurized hydrocarbon; BASE 44 Sulfurized Oleic Acid; BASE A92 Sulfurized fatty compound; SUL-PERM® 110 Sulfurized sperm oil replacement; SUL-PERM® 18 Sulfurized sperm oil replacement; and SUL-PERM® 307 Sulfurized sperm oil replacement. Especially preferred is SUL-PERM® 10-E, a sulfurized fatty acid ester containing 10% sulfur. Each of the above products are available from Keil Chemical Division of Ferro Corporation.

[0032] In a presently preferred embodiment, the sulfur-containing component is present in the final fluid in an amount of from 0.10 weight % to about 1.00 weight %, more preferably from about 0.25 weight % to about 0.75 weight %.

Component (C) - Metal Containing Detergent

[0033] Small amounts of certain metal-containing detergents, such as calcium sulfurized phenates, and calcium sulfonates are used in the practice of the invention. However, if an oil-soluble phenate or sulfonate is used it should be proportioned such that the finished fluid contains no more than about 250 ppm of metal, preferably no more than about 100 ppm of metal, and most preferably no more than about 50 ppm of metal. These sulfurized phenates are preferably neutral salts containing a stoichiometric amount of calcium, and in any event should have a total base number (TBN) of not more than about 200 mg KOH/gram.

[0034] An especially preferred detergent is a low-base calcium phenate such as OLOA 216 C, available from the Oronite Division of Chevron. OLOA 216 C is said to be a calcium hydrodroxide salt of a sulfurized alkylphenate having a nominal TBN of 150.

[0035] In the final fluid, the detergent may be present in an amount of from 0.01-0.10% by weight, more preferably from about 0.03% to about 0.07 % by weight, most preferably about 0.05% by weight.

[0036] In addition to the above mandatory components, the present invention may also optionally contain the following additional components:

Component (D) - Dispersant

[0037] Component (D) comprises at least one oil-soluble phosphorus or boron-containing ashless dispersant. The phosphorus or boron-containing ashless dispersants can be formed by phosphorylating or boronating an ashless dispersant having basic nitrogen and/or at least one hydroxyl group in the molecule, such as a succinimide dispersant, succinic ester dispersant, succinic ester-amide dispersant, Mannich base dispersant, hydrocarbyl polyamine dispersant, or polymeric polyamine dispersant.

[0038] The polyamine succinimides in which the succinic group contains a hydrocarbyl substituent containing at least 30 carbon atoms are described for example in U.S. Pat. Nos. 3,172,892; 3,202,678; 3,216,936; 3,219,666; 3,254,025; 3,272,746; and 4,234,435. The alkenyl succinimides may be formed by conventional methods such as by heating an alkenyl succinic anhydride, acid, acid-ester, acid halide, or lower alkyl ester with a polyamine containing at least one primary amino group. The alkenyl succinic anhydride may be made readily by heating a mixture of olefin and maleic anhydride to, for example, about 180-220 °C. The olefin is preferably a polymer or copolymer of a lower monoolefin such as ethylene, propylene, 1-butene, isobutene and the like and mixtures thereof. The more preferred source of alkenyl group is from polyisobutene having a gel permeation chromotography (GPC) number average molecular weight of up to 10,000 or higher, preferably in the range of about 500 to about 2,500, and most preferably in the range of about 800 to about 1,200.

[0039] As used herein the term "succinimide" is meant to encompass the completed reaction product from reaction between one or more polyamine reactants and a hydrocarbon-substituted succinic acid or anhydride (or like succinic acylating agent), and is intended to encompass compounds wherein the product may have amide, amidine, and/or salt linkages in addition to the imide linkage of the type that results from the reaction of a primary amino group and an anhydride moiety.

[0040] Alkenyl succinic acid esters and diesters of polyhydric alcohols containing 2-20 carbon atoms and 2-6 hydroxyl groups can be used in forming the phosphorus-containing ashless dispersants. Representative examples are described in U.S. Pat. Nos. 3,331,776; 3,381,022; and 3,522,179. The alkenyl succinic portion of these esters corresponds to the alkenyl succinic portion of the succinimides described above.

[0041] Suitable alkenyl succinic ester-amides for forming the phosphorylated ashless dispersant are described for example in U.S. Pat. Nos. 3,184,474; 3,576,743; 3,632,511; 3,804,763; 3,836,471; 3,862,981; 3,936,480; 3,948,800; 3,950,341; 3,957,854; 3,957,855; 3,991,098; 4,071,548; and 4,173,540.

[0042] Hydrocarbyl polyamine dispersants that can be phosphorylated are generally produced by reacting an aliphatic or alicyclic halide (or mixture thereof) containing an average of at least about 40 carbon atoms with one or more amines, preferably polyalkylene polyamines. Examples of such hydrocarbyl polyamine dispersants are described in U.S. Pat. Nos. 3,275,554; 3,394,576; 3,438,757; 3,454,555; 3,565,804; 3,671,511; and 3,821,302.

[0043] In general, the hydrocarbyl-substituted polyamines are high molecular weight hydrocarbyl-N-substituted polyamines containing basic nitrogen in the molecule. The hydrocarbyl group typically has a number average molecular weight in the range of about 750-10,000 as determined by GPC, more usually in the range of about 1,000-5,000, and is derived from a suitable polyolefin. Preferred hydrocarbyl-substituted amines or polyamines are prepared from polyisobutenyl chlorides and polyamines having from 2 to about 12 amine nitrogen atoms and from 2 to about 40 carbon atoms.

[0044] Mannich polyamine dispersants which can be utilized in forming the phosphorylated ashless dispersant is a reaction product of an alkyl phenol, typically having a long chain alkyl substituent on the ring, with one or more aliphatic aldehydes containing from 1 to about 7 carbon atoms (especially formaldehyde and derivatives thereof), and polyamines (especially polyalkylene polyamines). Examples of Mannich condensation products, and methods for their production are described in U.S. Pat. Nos. 2,459,112; 2,962,442; 2,984,550; 3,036,003; 3,166,516; 3,236,770; 3,368,972; 3,413,347; 3,442,808; 3,448,047; 3,454,497; 3,459,661; 3,493,520; 3,539,633; 3,558,743; 3,586,629; 3,591,598; 3,600,372; 3,634,515; 3,649,229; 3,697,574; 3,703,536; 3,704,308; 3,725,277; 3,725,480; 3,726,882; 3,736,357; 3,751,365; 3,756,953; 3,793,202; 3,798,165; 3,798,247; 3,803,039; 3,872,019; 3,904,595; 3,957,746; 3,980,569; 3,985,802; 4,006,089; 4,011,380; 4,025,451; 4,058,468; 4,083,699; 4,090,854; 4,354,950; and 4,485,023.

[0045] The preferred hydrocarbon sources for preparation of the Mannich polyamine dispersants are those derived from substantially saturated petroleum fractions and olefin polymers, preferably polymers of mono-olefins having from 2 to about 6 carbon atoms. The hydrocarbon source generally contains at least about 40 and preferably at least about 50 carbon atoms to provide substantial oil solubility to the dispersant. The olefin polymers having a GPC number average molecular weight between about 600 and 5,000 are preferred for reasons of easy reactivity and low cost. However, polymers of higher molecular weight can also be used. Especially suitable hydrocarbon sources are isobutylene polymers.

[0046] The preferred Mannich base dispersants for this use are Mannich base ashless dispersants formed by condensing about one molar proportion of long chain hydrocarbon-substituted phenol with from about 1 to 2.5 moles of formaldehyde and from about 0.5 to 2 moles of polyalkylene polyamine.

[0047] Polymeric polyamine dispersants suitable for preparing phosphorylated ashless dispersants are polymers containing basic amine groups and oil solubilizing groups (for example, pendant alkyl groups having at least about 8 carbon atoms). Such materials are illustrated by interpolymers formed from various monomers such as decyl methacrylate, vinyl decyl ether or relatively high molecular weight olefins, with aminoalkyl acrylates and aminoalkyl acrylamides. Examples of polymeric polyamine dispersants are set forth in U.S. Pat. Nos. 3,329,658; 3,449,250; 3,493,520; 3,519,565; 3,666,730; 3,687,849; and 3,702,300.

[0048] The various types of ashless dispersants described above can be phosphorylated by procedures described in U.S. Pat. Nos. 3,184,411; 3,342,735; 3,403,102; 3,502,607; 3,511,780; 3,513,093; 3,513,093; 4,615,826; 4,648,980; 4,857,214 and 5,198,133.

[0049] In another preferred embodiment, the dispersants or the phosphorus-containing dispersants of the present invention are also boronated.

[0050] Methods that can be used for boronating (borating) the various types of ashless dispersants described above are described in U.S. Pat. Nos. 3,087,936; 3,254,025; 3,281,428; 3,282,955; 2,284,409; 2,284,410; 3,338,832; 3,344,069; 3,533,945; 3,658,836; 3,703,536; 3,718,663; 4,455,243; and 4,652,387.

[0051] Preferred procedures for phosphorylating and boronating ashless dispersants such as those referred to above are set forth in U.S. Pat. Nos. 4,857,214 and 5,198,133.

[0052] The amount of phosphorylated ashless dispersant on an "active ingredient basis" (i.e., excluding the weight of impurities, diluents and solvents typically associated therewith) is generally within the range of about 0.5 to about 7.5 weight percent (wt%), typically within the range of about 0.5 to 5.0 wt%, preferably within the range of about 0.5 to about 4.0 wt%, and most preferably within the range of about 1.0 to about 3.0 wt%.

[0053] In a preferred embodiment of the present invention, an ashless dispersant with an N/P ratio as set forth in US Patent 5,972,851, which is incorporated herein by reference. In this preferred embodiment, an optional component of the present invention is a dispersant having a nitrogen to phosphorus mass ratio between about 3:1 and about 10:1. The dispersant of the preferred embodiment can be prepared in at least two ways. In one method, an ashless dispersant is phosphorylated to such a degree that the nitrogen to phosphorus mass ratio between about 3:1 and about 10:1. In another embodiment, a phosphorylated dispersant and a non-phosphorylated dispersant are blended together such that the total nitrogen to phosphorus mass ratio of the dispersant is between about 3:1 and about 10:1.

[0054] Overall, the dispersant is preferably present in the final fluid in an amount of about 1.00% to about 15.00 % by weight, more preferably from about 1.00 weight % to about 8.00 weight %.

Component (E) - Antioxidants

[0055] The compositions of the present invention may include one or more antioxidants, for example, one or more phenolic antioxidants, hindered phenolic antioxidants, additional sulfurized olefins, aromatic amine antioxidants, secondary aromatic amine antioxidants, sulfurized phenolic antioxidants, oil-soluble copper compounds, phosphorus-containing antioxidants (e.g. organic phosphites), and mixtures thereof.

[0056] Suitable exemplary compounds include include 2,6-di-tert-butylphenol, liquid mixtures of tertiary butylated phenols, 2,6-di-tert-butyl-4-methylphenol, 4,4'-methylenebis(2,6-di-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), mixed methylene-bridged polyalkyl phenols, 4,4'-thiobis(2-methyl-6-tert-butylphenol), N,N'-di-sec-butyl-p-phenylenediamine, 4-isopropylaminodiphenyl amine, phenyl- α-naphthyl amine, and phenyl-β-naphthyl amine.

[0057] Especially preferred antioxidants include diphenyl amine derived antioxidants; such as Naugalube® 438-L.

[0058] In the class of amine antioxidants, oil-soluble aromatic secondary amines; aromatic secondary monoamines; and others are suitable. Suitable aromatic secondary monoamines include diphenylamine, alkyl diphenylamines containing 1 to 2 alkyl substituents each having up to about 16 carbon atoms, phenyl-α-naphthylamine, phenyl-γ-naphthylamine, alkyl- or aralkylsubstituted phenyl-α-naphthylamine containing one or two alkyl or aralkyl groups each having up to about 16 carbon atoms, alkyl- or aralkyl-substituted phenyl-β-naphthylamine containing one or two alkyl or aralkyl groups each having up to about 16 carbon atoms, alkylated p-phenylene diamines available from Goodyear under the tradename "Wingstay 100" and from Uniroyal, and similar compounds.

[0059] The preferred type of aromatic amine antioxidant is that embodied in the commercial product Naugalube 483L is an alkylated diphenylamine of the general formula :

        R₁ --C6H4--NH--C6H4 --R₂

wherein R₁ is an alkyl group (preferably a branched alkyl group) having 8 to 12 carbon atoms, (more preferably 8 or 9 carbon atoms) and R₂ is a hydrogen atom or an alkyl group (preferably a branched alkyl group) having 8 to 12 carbon atoms, (more preferably 8 or 9 carbon atoms). Most preferably, R₁ and R₂ are the same. Particularly preferred is a nonylated diphenyl amine containing 4,4'-dinonylated diphenyl amine; a bis(4-nonylphenyl)(amine) wherein the nonyl groups are branched.

[0060] In the class of phenolic antioxidants, suitable compounds include ortho-alkylated phenolic compounds, e.g. 2-tert-butylphenol, 2,6-di-tertbutylphenol, 4-methyl-2,6-di-tertbutylphenol, 2,4,6-tri-tertbutylphenol, and various analogs and homologs or mixtures thereof; one or more partially sulfurized phenolic compounds as described in US Patent 6,096,695, the disclosure of which is incorporated herein by reference; methylene-bridged alkylphenols as described in U.S. Pat. No. 3,211,652, the disclosure of which is incorporated herein by reference.

[0061] Antioxidants may be optionally included in the fully formulated final inventive lubricating composition at from about 0.00 to about 5.00 weight percent, more preferably from about 0.01 weight % to about 1.00 weight %.

Component (F) - Friction Modifiers

[0062] The compositions of the present invention may optionally contain one or more friction modifiers. These typically include such compounds as fatty amines or ethoxylated fatty amines, aliphatic fatty acid amides, ethoxylated aliphatic ether amines, aliphatic carboxylic acids, glycerol esters, aliphatic carboxylic ester-amides, aliphatic phosphonates, aliphatic phosphates, aliphatic thiophosphonates, aliphatic thiophosphates, fatty imidazolines, fatty tertiary amines etc., wherein the aliphatic group usually contains above about eight carbon atoms so as to render the compound suitably oil soluble. Also suitable are aliphatic substituted succinimides formed by reacting one or more aliphatic succinic acids or anhydrides with ammonia or other primary amines.

[0063] One preferred group of friction modifiers is comprised of the N-aliphatic hydrocarbyl-substituted diethanol amines in which the N-aliphatic hydrocarbyl-substituent is at least one straight chain aliphatic hydrocarbyl group free of acetylenic unsaturation and having in the range of about 14 to about 20 carbon atoms.

[0064] Some commercially available friction modifiers which are especially suitable in the practice of the invention are Ethomeen T-12 an ethoxylated tallow diamine, and Ethomeen C-12, an ethoxylated cocoalkylamine, both available from Akzo Nobel Chemical Company.

[0065] A particularly preferred friction modifier system is composed of a combination of at least one N-aliphatic hydrocarbyl-substituted diethanol amine and at least one N-aliphatic hydrocarbyl-substituted trimethylene diamine in which the N-aliphatic hydrocarbyl-substituent is at least one straight chain aliphatic hydrocarbyl group free of acetylenic unsaturation and having in the range of about 14 to about 20 carbon atoms. Further details concerning this friction modifier system are set forth in U.S. Pat. Nos. 5,372,735 and 5,441,656, incorporated herein by reference.

[0066] Another particularly preferred friction modifier system is based on the combination of (i) at least one di(hydroxyalkyl) aliphatic tertiary amine in which the hydroxyalkyl groups, being the same or different, each contain from 2 to about 4 carbon atoms, and in which the aliphatic group is an acyclic hydrocarbyl group containing from about 10 to about 25 carbon atoms, and (ii) at least one hydroxyalkyl aliphatic imidazoline in which the hydroxyalkyl group contains from 2 to about 4 carbon atoms, and in which the aliphatic group is an acyclic hydrocarbyl group containing from about 10 to about 25 carbon atoms. Further details concerning this friction modifier system are set forth in U.S. Pat. No. 5,344,579, incorporated herein by reference.

[0067] Component (i), the di(hydroxyalkyl) aliphatic tertiary amine, has a nitrogen atom to which are bonded two hydroxyalkyl groups and one non-cyclic aliphatic hydrocarbyl group having 10 to 25 carbon atoms, and preferably 13 to 19 carbon atoms. The hydroxyalkyl groups of these tertiary amines can be the same or different, but each contains from 2 to 4 carbon atoms. The hydroxyl groups can be in any position in the hydroxyalkyl groups, but preferably are in the β-position. Preferably the two hydroxyalkyl groups in component (i) are the same, and most preferably are 2-hydroxyethyl groups. The aliphatic group of these tertiary amines can be straight or branched chain and it can be saturated or olefinically unsaturated and if unsaturated, it typically contains from one to three olefinic double bonds. Component (i) can have a single type of aliphatic group or it can comprise a mixture of compounds having different aliphatic groups in which the average number of carbon atoms falls within the foregoing range of from 10 to 25 carbon atoms.

[0068] From the foregoing it will be clear that component (i) can be a single compound or a mixture of compounds meeting the structural criteria described above.

[0069] The hydroxyalkyl aliphatic imidazolines, component (ii), suitable for use in the practice of this invention are characterized by having in the 1-position on the imidazoline ring a hydroxyalkyl group that contains from 2 to 4 carbon atoms, and by having in the adjacent 2-position on the ring a non-cyclic hydrocarbyl group containing 10 to 25 carbon atoms. While the hydroxyl group of the hydroxyalkyl group can be in any position thereof, it preferably is on the β-carbon atom, such as 2-hydroxyethyl, 2-hydroxypropyl or 2-hydroxybutyl. Typically the aliphatic group is a saturated or olefinically unsaturated hydrocarbyl group, and when olefinically unsaturated, the aliphatic group may contain one, two or three such double bonds. Component (ii) may be a single substantially pure compound or it may be a mixture of compounds in which the aliphatic group has an average of from 10 to 25 carbon atoms. Preferably the aliphatic group has 15 to 19 carbon atoms, or an average of 15 to 19 carbon atoms. Most preferably the aliphatic group has, or averages, 17 carbon atoms. The aliphatic group(s) may be straight or branched chain groups, with substantially straight chain groups being preferred. A particularly preferred compound is 1-hydroxyethyl-2-heptadecenyl imidazoline. One commercially available imidazoline based friction modifier suitable for use in the present invention is Unamine O, available from Lonza Chemical.

[0070] It will thus be clear that component (ii) can be a single compound or a mixture of compounds meeting the structural criteria described above.

[0071] Also suitable for use in the present invention are various alkanol amides. One especailly suitable commercial alkanol amide is Schercomid SLML, a lauramide diethanolamine, available from Scher Chemicals, Inc.

[0072] Generally speaking, the fully formulated final compositions of this invention will optionally contain up to about 1.25 wt% on an active ingredient basis, and preferably from about 0.05 to about 1 wt% on an active ingredient basis of one or more friction modifiers.

Component (G) - Anti-Rust

[0073] Various known anti-rust agents or additives are known for use in transmission fluids, and are suitable for use in the fluids according to the present invention. Especially preferred are alkyl polyoxyalkylene ethers, such as Mazawet® 77, C-8 acids such as Neofat® 8, oxyalkyl amines such as Tomah PA-14, 3-decyloxypropylamine, and polyoxypropylene-polyoxyethylene block copolymers such as Pluronic® L-81.

[0074] Mixtures of the above anti-rust agents are especially preferred. Anti-rust agents are preferably used in low quantities, e.g from about 0.01 to about 0.10 weight %, preferably from about 0.03 to about 0.07 weight %.

Component (H) - Anti-Foam

[0075] Anti-foam agents may also be included in a fluid according to the present invention. Various agents are known for such use. Especially preferred are copolymers of ethyl acrylate and hexyl ethyl acrylate, such as PC-1244, available from Solutia. Also preferred are silicone fluids such as 4% DCF. Mixtures of anti-foam agents are especially preferred.

[0076] Given their high activity levels, anti foam agents are generally present in small amounts, from about 0.00 - 0.05 weight %, more preferably about 0.01 weight %.

Component (I) - Diluent

[0077] If the additives are provided in an additive package concentrate, a suitable carrier diluent is added to ease blending, solubilizing, and transporting the additive package. The diluent oil needs to be compatible with the base oil and the additive package. Generally, the diluent is present in the concentrate in an amount of between 5-20%, although it can vary widely with application. Generally speaking, less diluent is preferable as it lowers transportation costs and treat rates.

Component (J) - Base Oil

[0078] If the inventive composition is to be prepared as a concentrate, then base oil may be omitted and an appropriate adjustment made in the weight % of each of the above optional and mandatory ingredients to prepare a suitable concentrate, taking care that solubility and compatibility is maintained. However, if a fully formulated fluid is to be prepared, then base oil is a mandatory component.

[0079] The base oils used in forming the automatic transmission fluids of this invention can be any suitable natural or synthetic oil having the necessary viscosity properties for this usage. Natural oils include animal oils and vegetable oils (e.g., castor oil, lard oil etc.), liquid petroleum oils and hydrorefined, severely hydrotreated, iso-dewaxed, solvent-treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale are also useful base oils.

[0080] The synthetic lubricating oils suitable for use in this invention include one of any number of commonly used synthetic hydrocarbon oils, which include, but are not limited to, poly-alpha-olefins, synthetic esters, alkylated aromatics, alkylene oxide polymers, interpolymers, copolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification etc., esters of dicarboxylic acids and silicon-based oils. Thus, the base oil may be composed entirely of a natural oil such as mineral oil of suitable viscosity or it may be composed entirely of a synthetic oil such as a poly-alpha-olefin oligomer of suitable viscosity.

[0081] Likewise, the base oil may be a blend of natural and/or synthetic base oils provided that the blend has the requisite properties for use in the formation of an automatic transmission fluid. Ordinarily, the base oil should have a kinematic viscosity in the range of 3 to 8 centistokes (cSt) at 100 °C. Preferred automatic transmission fluids used in the practice of this invention can be formulated without a viscosity index improver so as to possess a kinematic viscosity of at least 3.0 cSt at 100°C and a Brookfield viscosity of no more than 20,000 cP at -40 °C, or formulated using a viscosity index improver so as to possess a kinematic viscosity of at least 6.8 cSt at 100 °C and a Brookfield viscosity of no more than 20,000 cP at -40 °C.

[0082] Suitable base stock oil includes, preferably, Group I, II, and III base oils, as are known to those of skill in the art. In certain instances, usually depending on the final use of the lubricant composition according to the present invention, Group I is preferred, and in other instances, Group II and III are preferred.

[0083] Group I base stocks contain less than 90% saturates (as determined by ASTM D 2007) and/or greater than 0.03 percent sulfur (as determined by ASTM D 2622, D 4294, D 4927, or D 3120) and have a viscosity index greater than or equal to 80 and less than 120 (as determined by ASTM D 2270).

[0084] Group II base stocks contain greater than or equal to 90 % saturates and less than or equal to 0.03 % sulfur and have a viscosity index greater than 80 and less than 120 using the above noted test methods. Group II + oils may also be used. These are oils which have a VI at the high end of the VI spectrum, e.g. about 120.

[0085] Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 % sulfur and have a viscosity index greater than or equal to 120 using the tests noted above.

[0086] In another embodiment, the transmission fluid contains less than 5% poly-alpha-olefins (PAO) and is more preferably PAO free.

[0087] Base oil usually comprises the balance to 100 weight % of the fully formulated oil after all other additives are considered.

Component (K) - Viscosity Index Improver

[0088] The compositions of the present invention optionally, but preferably, contain a viscosity index improver (VII). Preferred VIIs include, but are not limited to, olefin copolymer VIIs, polyalkylmethacrylate VIIs and styrene-maleic ester VIIs. Of these, polyalkylmethacrylate VIIs are particularly preferred. The viscosity index improver is supplied in the form of a solution in an inert solvent, typically a mineral oil solvent, which usually is a severely refined mineral oil. The viscosity index improver solution as received often will have a boiling point above 200 °C, and a specific gravity of less than 1 at 25 °C. Preferably, the viscosity index improver will have sufficient shear stability such that the finished composition possesses a kinematic viscosity of at least 5, and more preferably at least 6.8, cSt at 100 °C after 40 cycles in the FISST (Fuel Injector Shear Stability Test) of ASTM D-5275.

[0089] On an active ingredient basis (i.e., excluding the weight of inert diluent or solvent associated with the viscosity index improver as supplied), the finished fluid compositions of this invention will normally contain in the range of about 0 to about 15 wt% of the polymeric viscosity index improver. Small departures from this range may be resorted to as necessary or desirable in any given situation.

[0090] Suitable materials for use as component (K) include styrene-maleic ester VIIs such as LUBRIZOL® 3702, LUBRIZOL®3706 and LUBRIZOL®3715 available from The Lubrizol Corporation; polyalkylmethacrylate VIIs such as those available from RÖHM GmbH (Darmstadt, Germany) under the trade designations: VISCOPLEX® 5543, VISCOPLEX® 5548, VISCOPLEX® 5549, VISCOPLEX® 5550, VISCOPLEX® 5551 and VISCOPLEX® 5151, from Rohm & Haas Company (Philadelphia, Pennsylvania) under the trade designations ACRYLOID® 1277, ACRYLOID® 1265 and ACRYLOID® 1269, and from Ethyl Corporation (Richmond, Virginia) under the trade designation HiTEC® 5710 viscosity index improver; and olefin copolymer VIIs such as HiTEC® 5747 VII, HiTEC® 5751 VII, HiTEC® 5770 VII and HiTEC® 5772 VII available from Ethyl Corporation and SHELLVIS® 200 available from Shell Chemical Company. Mixtures of the foregoing products can also be used as well as dispersant and dispersant/antioxidant VIIs.

[0091] Preferably, the viscosity index improver will be provided as a hydrocarbon solution having a polymer content in the range of from about 25 to about 80 wt% and a nitrogen content in the range of about 0 to about 0.5 wt%. Such products preferably exhibit a permanent shear stability index (a PSSI value) using ASTM test method D-3945A of no higher than about 75, preferably 50 or less, and most preferably 35 or less.

[0092] Especially preferred is a dispersant polymethacrylate viscosity index improver such as HiTEC® 5738, or a non dispersant polymethacrylate viscosity index improver such as HiTEC®5739, both products of Ethyl Corporation, Richmond Virginia. Especially preferred is a mixture of dispersant and non-dispersant viscosity index improvers.

[0093] Quantitatively, the viscosity index improver may be present in an amount of from 0-25% by weight, preferably from 5-20% by weight.

Component (L) - Dye

[0094] It is preferred to add a colorant to the fluid to give it a unique character which is detectable. Generally, azo class dyes are used, such as C.I. Solvent Red 24 or C.I. Solvent Red 164, as set forth in the "Colour Index" of the American Association of Textile Chemists and Colorists and the Society of Dyers and Colourists (U.K.) which is incorporated herein by reference. For automatic transmission fluids, Automate Red Dye is especially preferred. Dye is present in a very minimal amount, of 200-300 ppm in the finished oil.

Component (M) - Seal Swell Agents

[0095] The automatic transmission fluids of the present invention may further include seal swell agents. Seal swell agents such as ester, sulfones, alcohols, alkylbenzenes, substituted sulfolanes, aromatics, or mineral oils cause swelling of elastomeric materials used as seals in engines and automatic transmissions.

[0096] Alcohol-type seal swell agents are generally low volatility linear alkyl alcohols, such as decyl alcohol, tridecyl alcohol and tetradecyl alcohol.

[0097] Alkylbenzenes useful as seal swell agents include dodecylbenzenes, tetradecylbenzenes, dinonyl-benzenes, di(2-ethylhexyl)benzene, and the like.

[0098] Substituted sulfolanes (e.g. those described in U.S. Pat. No. 4,029,588, incorporated herein by reference) are likewise useful as seal swell agents in compositions according to the present invention.

[0099] Mineral oils useful as seal swell agents in the present invention include low viscosity mineral oils with high naphthenic or aromatic content.

[0100] Aromatic seal swell agents include the commercially available Exxon Aromatic 200 ND seal swell agent.

[0101] Commercially available examples of mineral oil seal swell agents include Exxon® Necton®-37 (FN 1380) and Exxon® Mineral Seal Oil (FN 3200).

[0102] When used in the ATF of the present invention, a seal swell agent will typically comprise from about 1 to about 30 wt. %, preferably from about 1 to about 20 wt. %, most preferably from about 1 to about 10 wt. %, based on the total weight of ATF.

Component (N) - Additional Corrosion Inhibitors

[0103] The automatic transmission fluids of the present invention may further include additional corrosion inhibitors. Other suitable additional inhibitors of copper corrosion include ether amines; polyethoxylated compounds such as ethoxylated amines, ethoxylated phenols, and ethoxylated alcohols; imidazolines; and the like.

[0104] Thiazoles, triazoles and thiadiazoles may also be used in the present invention. Examples include benzotriazole; tolyltriazole; octyltriazole; decyltriazole; dodecyltriazole; 2-mercaptobenzothiazole; 2,5-dimercapto-1,3,4-thiadiazole; 2-mercapto-5-hydrocarbylthio-1,3,4-thiadiazoles; and 2-mercapto-5-hydrocarbyldithio-1,3,4-thiadiazoles. The preferred compounds are the 1,3,4-thiadiazoles, especially the 2-hydrocarbyldithio-5-mercapto-1,3,4-dithiadiazoles, a number of which are available as articles of commerce. These may be present in an amount of from 0.00 to 0.50 weight percent, more preferably from about 0.01 to about 0.10 weight percent, based on the final formulation.

Component (O) - Anti Wear/ Extreme Pressure Additive

[0105] The automatic transmission fluids of the present invention may further include anti-wear/extreme pressure additives.

[0106] When the desired phosphorus content of the finished fluid is not completely supplied by use of a phosphorus-containing ashless dispersant (or a boron- and phosphorus-containing ashless dispersant), the remainder of the phosphorus content is preferably supplied by inclusion in the composition of one or more phosphorus-containing esters or acid-esters such as oil-soluble organic phosphites, oil-soluble organic acid phosphites, oil-soluble organic phosphates, oil-soluble organic acid phosphates, oil-soluble phosphoramidates. Examples include trihydrocarbyl phosphates, trihydrocarbyl phosphites, dihydrocarbyl phosphates, dihydrocarbyl phosphonates or dihydrocarbyl phosphites or mixtures thereof, monohydrocarbyl phosphates, monohydrocarbyl phosphites, and mixtures of any two or more of the foregoing. Oil-soluble amine salts of organic acid phosphates are a preferred category of auxiliary phosphorus-containing additives for use in the fluids of this invention. Sulfur-containing analogs of any of the foregoing compounds can also be used, but are less preferred. Most preferred as a commercially-available auxiliary phosphorus additive is an amine phosphate antiwear/extreme pressure agent available from Ciba-Geigy Corporation as Irgalube® 349.

[0107] The extreme pressure/anti wear additive is preferably present in the final fully-formulated fluid in an amount of from 0.00 to about 1.00 weight %, more preferably from about 0.25 to about 1.00 weight %.

[0108] In selecting any of the foregoing optional additives, it is important to ensure that the selected component(s) is/are soluble or stably dispersible in the additive package and finished ATF composition, are compatible with the other components of the composition, and do not interfere significantly with the performance properties of the composition, such as the friction, viscosity and/or shear stability properties, needed or at least desired in the overall finished composition.

[0109] In general, the ancillary additive components are employed in the oils in minor amounts sufficient to improve the performance characteristics and properties of the base fluid. The amounts will thus vary in accordance with such factors as the viscosity characteristics of the base fluid employed, the viscosity characteristics desired in the finished fluid, the service conditions for which the finished fluid is intended, and the performance characteristics desired in the finished fluid. However, generally speaking, the following concentrations (weight percent unless otherwise indicated) of the additional components (active ingredients) in the base fluids are illustrative:

Component	Typical Range	Preferred Range
D	1.00 - 15.00	1.00 - 8.00
E	0.1 - 5.00	0.25 - 3.00
F	≤ 1.25	0.05 - 1.00
G	≤ 0.02	0.01 - 0.10
H	≤ 0.05	0.005-0.02
I	≤ 25 (in the concentrate)	5.00 - 20.00 (in the concentrate)
J	Balance	Balance
K	0.00 - 25.00	5.00 - 20.00
L	0 - 400 ppm	200-300 ppm
M	1.00 - 30.00	5.00 - 15.00
N	0.00 - 0.50	0.01 - 0.10
O	0.00 -1.00	0.25 - 1.00

[0110] It will be appreciated that the individual components employed can be separately blended into the base fluid or can be blended therein in various subcombinations, if desired. Ordinarily, the particular sequence of such blending steps is not critical. Moreover, such components can be blended in the form of separate solutions in a diluent. It is preferable, however, to blend the additive components used in the form of a concentrate, as this simplifies the blending operations, reduces the likelihood of blending errors, and takes advantage of the compatibility and solubility characteristics afforded by the overall concentrate.

[0111] Additive concentrates can thus be formulated to contain all of the additive components and if desired, some of the base oil component, in amounts proportioned to yield finished fluid blends consistent with the concentrations described above. In most cases, the additive concentrate will contain one or more diluents such as light mineral oils, to facilitate handling and blending of the concentrate. Thus concentrates containing up to about 50% by weight of one or more diluents or solvents can be used, provided the solvents are not present in amounts that interfere with the low and high temperature and flash point characteristics and the performance of the finished power transmission fluid composition. In this connection, the additive components utilized pursuant to this invention should be selected and proportioned such that an additive concentrate or package formulated from such components will have a flash point of 170 °C or above, and preferably a flash point of at least 180 °C, using the ASTM D-92 test procedure.

EXAMPLES

[0112] Illustrative compositions suitable for use in the practice of this invention are presented in the following Examples, wherein all parts and percentages are by weight unless specified otherwise.

[0113] The fluids prepared in the Examples were then subjected to testing under the commonly known FZG test. The test is conducted in the FZG gear rig test machine. This test, IP (Institute of Petroleum) 334/79, which is incorporated herein by reference, measures lubricity, and in the test, two steel spin gears are rotated together for a series of 75 minute stages. The relative torque between the gears is increased by a fixed amount after each stage and the gears are run together for a given period after which they are examined for wear or damage. The result of the test is quoted in terms of the final pass stage and the first fail stage. The test is technically equal to ASTM D 5182-97. This test can be conducted at selected temperatures, nominally 90 degrees C and 150 degrees C.

[0114] Thus, one embodiment of the present invention comprises an automatic transmission fluid, containing (1) a major amount of a base oil and (2) a minor amount of an additive comprising (A) at least .025 wt%, preferably .05 wt %, based on the fluid, of an ashless dialkyl thiadiazole, and (B) a sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester or a mixture thereof.

Table 1 -

Composition and Testing of Examples
Component	Ex. 1	Comp. Ex. 1*	Comp. Ex. 2*	Comp. Ex. 3*	Comp. Ex. 4*	Comp. Ex. 5*	Description
A	0.10***	0.00	0.00	0.10	0.00	0.00	Ashless Dialkyl Thiadiazole ****
X	0.00	0.10	0.00	0.00	0.00	0.00	Ashless Monoalkyl Thiadiazole*****
B	0.50	0.50	0.50	0.00	0.00	0.00	Sulfurized fatty acid ester
C	0.05	0.05	0.05	0.05	0.05	0.05	Low base Calcium Phenate
D,E,F, G,H,I	7.65	7.65	7.65	7.65	7.65	7.65	Dispersant/Inhibitor concentrate
J	78.88	78.88	78.98	79.38	79.48	79.48	Base oil
K	12.80	12.80	12.80	12.80	12.80	12.80	Viscosity index improver
L	0.02	0.02	0.02	0.02	0.02	0.02	Red dye
Total	100.00	100.00	100.00	100.00	100.00	100.00
FZG Pass* *	11.33	10.83	7.5	8	6	9
Kinematic Viscosity 100C (cSt)	7.56	7.52	7.46	7.34	7.31	7.29
Brookfield Viscosity -40C (cPs)	13280	11900	11600	10440	10180	9540

* Comparative Example, Not within Scope of Invention

** Cumulative Average of Tests.

***All in weight % based on finished fluid

****HiTEC® 4313, Ethyl Corporation, Richmond, Virginia

*****HiTEC® 4312, Ethyl Corporation, Richmond, Virginia

[0115] It is clear, upon examination of the data presented, that the compositions of the present invention exhibit superior performance in the FZG test, passing on average above stage 11.

[0116] Thus it is now possible, as evidenced by the data presented, to formulate power transmission fluids which exhibit excellent FZG wear characteristics sufficient to consistently pass the FZG wear test beyond stage 11.

[0117] This invention is susceptible to considerable variation in its practice. Accordingly, this invention is not limited to the specific exemplifications set forth hereinabove. Rather, this invention is within the spirit and scope of the appended claims, including the equivalents thereof available as a matter of law.

[0118] The patentee does not intend to dedicate any disclosed embodiments to the public, and to the extent any disclosed modifications or alterations may not literally fall within the scope of the claims, they are considered to be part of the invention under the doctrine of equivalents.

Claims

1. An automatic transmission fluid, comprising:

(1) a major amount of a base oil and

(2) a minor amount of an additive comprising

(A) at least 0.05 wt %, based on the fluid, of a dihydrocarbyl thiadiazole, a bis(hydrocarbylthio)thiadiazole or a bis(hydrocarbyldithio)thiadiazole,

(B) a sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester or a mixture thereof, and

(C) up to about 0.15 wt %, based on the fluid, of a metal-containing detergent.

2. An automatic transmission fluid, comprising:

(1) a major amount of a base oil and

(2) a minor amount of an additive comprising:

(A) at least 0.05 wt %, based on the fluid, of a dihydrocarbyl thiadiazole, a bis(hydrocarbylthio)thiadiazole or a bis(hydrocarbyldithio)thiadiazole.

(B) a sulfurized fatty acid ester,

(C) up to about 0.15%, based on the fluid, of a metal containing detergent,

(D) a dispersant having a total nitrogen to phosphorus mass ratio between 3:1 and 10:1,

(E) a diphenylamine antioxidant, and

(F) a mixed viscosity index improver system containing

(i) a nondispersant polymethacrylate, and

(ii) a dispersant polymethacrylate.

3. An automatic transmission fluid comprising:

(1) a major amount of base oil and

(2) a minor amount of an additive comprising:

(A) at least 0.10%, based on the fluid, of a dihydrocarbyl thiadiazole, a bis(hydrocarbylthio)thiadiazole or a bis(hydrocarbyldithio)thiadiazole

(B) at least 0.10%, based on the fluid, of at least one sulfurized fatty acid ester, and

(C) up to 0.15%, based on the fluid, of a metal-containing detergent.

4. An automatic transmission fluid as claimed in any preceding claim, wherein component (A) is a compound of the formula:

wherein:
R¹ and R², which may be the same or different, represent a hydrocarbyl substituent having from 6 to 18 carbon atoms; and
n and n', which may be the same or different, represents 0, 1 or 2.

5. An automatic transmission fluid as claimed in any preceding claim, wherein component (A) is a dialkyl thiadiazole, a bis(alkylthio)thiadiazole, or a bis(alkyldithio)thiadiazole.

6. An automatic transmission fluid as claimed in any preceding claim, wherein component (A) is an ashless thiadiazole.

7. An automatic transmission fluid as claimed in any preceding claim, wherein component (B) comprises at least one sulfurized fatty acid ester.

8. An automatic transmission fluid as claimed in any preceding claim, wherein component (C) comprises at least one calcium-containing detergent.

9. An automatic transmission fluid as claimed in any preceding claim, wherein component (A) is present in an amount from 0.05 to 0.75 weight percent, based on the transmission fluid.

10. An automatic transmission fluid as claimed in Claim 9, wherein component (A) is present in an amount from 0.075 to 0.25 weight percent, based on the transmission fluid.

11. An automatic transmission fluid as claimed in any preceding claim, wherein component (B) is present in an amount of about 0.50 weight %, based on the transmission fluid.

12. An automatic transmission fluid as claimed in any preceding claim, further comprising at least one inhibitor selected from the group consisting of foam inhibitors, corrosion inhibitors, rust inhibitors, and oxidation inhibitors.

13. An automatic transmission fluid as claimed in any preceding claim, further comprising at least one viscosity index improver, dispersant, or friction modifier.

14. An automatic transmission fluid as claimed in claim 13, wherein there is a mixture of viscosity index improvers present.

15. An automatic transmission fluid as claimed in Claim 13, where there is at least one dispersant present, and the at least one dispersant has a total nitrogen to phosphorus mass ratio between 3:1 and 10:1.

16. An automatic transmission fluid as claimed in any preceding claim, further comprising at least one additive selected from the group consisting of seal swell agents, foam inhibitors, lubricity agents, and dyes.

17. A method of improving automatic transmission antiwear and extreme pressure performance, said method comprising adding to said automatic transmission an automatic transmission fluid according to any preceding claim; and operating said automatic transmission.

18. Use in a transmission fluid comprising a major amount of a base oil and a minor amount of an additive comprising (A) at least 0.025 wt%, based on the fluid, of an ashless dialkyl thiadiazole and (B) a sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester or a mixture thereof to improve the antiwear and/or extreme pressure performance of the transmission.