AUTOMATIC TRANSMISSION FLUIDS OF IMPROVED VISCOMETRIC PROPERTIES

Abstract: This invention provides compositions and methods for producing partial synthetic automatic transmission fluids capable of improved viscometric properties and capable of achieving -40 DEG C Brookfield viscosities not greater than 15,000 centipoise.

Description: AUTOMATIC TRANSMISSION FLUIDS OF IMPROVED VISCOMETRIC PROPERTIES RELATED APPLICATION This application is a continuation-in-part of copending patent application, U. S. Serial Number 08/502,954, filed July 17, 1995. BACKGROUND OF THE INVENTION This invention relates to a composition and a method of improving the properties of power transmitting fluids, particularly to obtaining automatic transmission fluids of improved viscosity control. Automatic transmissions continue to become more sophisticated in design as vehicle technology advances. These design changes result from the need to improve vehicle operability, reliability, and fuel economy. Vehicle manufacturers worldwide are increasing vehicle warrantee periods and service intervals on the vehicles. This means that the automatic transmission, and the automatic transmission fluid (ATF), must be designed to operate reliably without maintenance for longer periods of time. In the case of the fluid, this means longer drain intervals. To improve vehicle operability, especially at low temperature, manufacturers have imposed strict requirements for fluid viscosity at -40°C. To cope with longer drain intervals and more severe operating conditions, manufacturers have increased the requirements for oxidation resistance of the ATF, and increased the amount of wear protection that the fluid must provide for the transmission. To improve the fuel economy of the vehicle and reduce energy loss in the torque converter, manufacturers employ sliding torque converter clutches, which require very precise control of fluid frictional properties. One common element in the quest for better reliability, longer service life, and better transmission control is the viscometric properties of the fluid. It is well known that lowering the viscosity of an ATF at low temperatures (e.g., -40°C) will result in improved operability of the transmission at low ambient temperatures, that increasing the amount of antiwear additives in the ATF will result in more wear protection, and that better friction control can be obtained by judicious choice of friction modifiers. However, we have now found that by proper selection of viscosity modifier molecular weight, the low temperature operability, service life, and friction control of the ATF, can be improved simultaneously. Correct choice of the viscosity modifier molecular weight allows the fluid to meet the high temperature viscosity requirements imposed by the manufacturer, while also allowing the fluid to meet rigorous low temperature viscosity limits. High temperature viscosity is also known to control wear in hydrodynamic and elastohydrodynamic wear regimes. High initial viscosity, at high temperatures (e.g., 100°C and 150°C), at both low (i.e., 1 to 200 sec."1) and high shear rates (1 x 10 6 sec. -1 ) helps to control this wear. Equally important is the fluid's ability to maintain this high level of viscosity under both high and low shear rates, even after use. The high initial viscosity at high temperatures and low shear rates is important to transmission operability as well. High viscosity at high temperature and low shear rate controls fluid leakage at high pressures. This is not leakage from the transmission itself, but leakage at high pressures (e.g., 830 kPa (120 psi)) around seals and valves in the transmission control system. No matter how sophisticated the electronic control of the transmission, if the fluid is leaking under pressure in the valve body, the transmission will not function properly. This is particularly important in transmissions using sliding torque converter clutches since control of these devices is accomplished via minute fluctuations in clutch actuating pressure. We have found that by careful selection of the molecular weight of the viscosity modifier, the aforementioned properties of the ATF can be improved simultaneously. If the molecular weight of the viscosity modifier is too low, too much will be needed to produce the required viscosity at high temperatures. This is not only uneconomical, but will eventually cause elevation of the viscosity at low temperature making it difficult or impossible to meet lower -40°C Brookfield viscosities. If the molecular weight of the viscosity modifier is too high, it will degrade by both mechanical shear and oxidation during service such that the high temperature viscosity contributed by the polymer will be lost, making the transmission vulnerable to wear and internal leakage. However, adding sufficient high molecular weight polymer to give the required "used oil viscosity" causes elevation of the low temperature Brookfield viscosity of the fluid, possibly exceeding the specified maximum viscosity. Since fluids exhibiting the characteristics of this invention must have exceedingly good low temperature fluidity (i.e., Brookfield viscosity <15,000 centipoise (cP) at -40°C), it is necessary to use a lubricating oil that contains a synthetic base oil in an amount sufficient to obtain the desired Brookfield viscosity. ATF's provide very precise frictional characteristics to the transmissions that they are used in. To meet this requirement, they must contain friction modifiers. SUMMARY OF THE INVENTION This invention relates to an automatic transmission fluid composition comprising: (a) a major amount of lubricating oil containing 5 to 95 weight % of a synthetic lubricating oil having a kinematic viscosity of 1 to 100 mm2/s (cSt) at 100°C and 5 to 95 weight % of a natural lubricating oil having a kinematic viscosity of 1 to 40 mm2/s (cSt) at 100°C; (b) a viscosity modifier having a molecular weight no greater than about 175,000 atomic mass units; and (c) from 0.01 to 5 weight % of a friction modifier; providing that the composition has a -40°C Brookfield viscosity no greater than 15,000 centipoise and the difference between new and sheared viscosity of the composition is no greater than 0.30 centipoise when measured at a temperature of 150°C and a shear rate of 2x10 2 sec.- 1 . This invention also concerns a method for providing a shear-stable automatic transmission fluid. BRIEF DESCRIPTION OF DRAWINGS Figure 1 shows the viscosity loss trapezoid for an ideal, Newtonian fluid. Figure 2 shows a typical viscosity loss trapezoid for a non-Newtonian fluid. DETAILED DESCRIPTION OF THE INVENTION Lubricating Oils Lubricating oils contemplated for use in this invention are derived from mixtures of natural lubricating oils and synthetic lubricating oils. Suitable lubricating oils also include basestocks obtained by isomerization of synthetic wax and slack wax, as well as basestocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude. In general, the natural lubricating oil will have a kinematic viscosity ranging from about 1 to about 40 mm 2 /s (cSt) at 100°C, and the synthetic lubricating oil will have a kinematic viscosity ranging from about 1 to about 100 mm 2 /s (cSt) at 100°C. Typical applications will require each type of oil to have a viscosity ranging preferably from about 1 to about 40 mm 2 /s (cSt), more preferably, from about 2 to about 8 mm 2 /s (cSt) at 100°C. Natural lubricating oils include animal oils, vegetable oils (e.g., castor oil and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale. The preferred natural lubricating oil is mineral oil. The mineral oils useful in this invention include all common mineral oil base stocks. This would include oils that are naphthenic or paraffinic in chemical structure. Oils that are refined by conventional methodology using acid, alkali, and clay or other agents such as aluminum chloride, or they may be extracted oils produced, for example, by solvent extraction with solvents such as phenol, sulfur dioxide, furfural, dichlordiethyl ether, etc. They may be hydrotreated or hydrofined, dewaxed by chilling or catalytic dewaxing processes, or hydrocracked. The mineral oil may be produced from natural crude sources or be composed of isomerized wax materials or residues of other refining processes. Typically the mineral oils will have kinematic viscosities of from 2.0 mm /s (cSt) to 8.0 mm 2 /s (cSt) at 100°C. The preferred mineral oils have kinematic viscosities of from 2 to 6 mm 2 /s (cSt), and most preferred are those mineral oils with viscosities of 3 to 5 mm 2 /s (cSt) at 100°C. Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as oligomerized, polymerized, and interpolymerized olefins [e.g., polybutylenes, polypropylenes, propylene, isobutylene copolymers, chlorinated polylactenes, poly(l-hexenes), poly(l-octenes), poly- (1-decenes), etc., and mixtures thereof]; alkylbenzenes [e.g., dodecyl- benzenes, tetradecylbenzenes, dinonyl-benzenes, di(2-ethylhexyl)benzene, etc.]; polyphenyls [e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.]; and alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, and homologs thereof, and the like. The preferred oils from this class of synthetic oils are oligomers of α-olefins, particularly oligomers of 1 -decene. Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers, and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc. This class of synthetic oils is exemplified by: polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polypropylene glycol having a molecular weight of 1000 - 1500); and mono- and poly-carboxylic esters thereof (e.g., the acetic acid esters, mixed C3-C8 fatty acid esters, and C12 oxo acid diester of tetraethylene glycol). Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoethers, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebasic acid with two moles of tetraethylene glycol and two moles of 2-ethyl- hexanoic acid, and the like. A preferred type of oil from this class of synthetic oils are adipates of C4 to C12 alcohols. Esters useful as synthetic lubricating oils also include those made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane pentaerythritol, dipentaerythritol, tripentaerythritol, and the like. Silicon-based oils (such as the polyalkyi-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) comprise another useful class of synthetic lubricating oils. These oils include tetra-ethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl) silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(p-tert-butylphenyl) silicate, hexa-(4-methyl-2-pentoxy)-disiloxane, poly(methyl)-siloxanes and poly(methylphenyl) siloxanes, and the like. Other synthetic lubricating oils include liquid esters of phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, and diethyl ester of decylphosphonic acid), polymeric tetra-hydrofurans, poly-α-olefins, and the like. The lubricating oils may be derived from refined, rerefined oils, or mixtures thereof. Unrefined oils are obtained directly from a natural source or synthetic source (e.g., coal, shale, or tar sands bitumen) without further purification or treatment. Examples of unrefined oils include a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to the unrefined oils except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, and percolation, ali of which are known to those skilled in the art. Rerefined oils are obtained by treating used oils in processes similar to those used to obtain the refined oils. These rerefined oils are also known as reclaimed or reprocessed oils and are often additionally processed by techniques for removal of spent additives and oil breakdown products. Typically, the lubricating oil mixture of this invention will contain 5 to 95 weight % of a synthetic oil and 95 to 5 weight % of a natural lubricating oil. Preferably the synthetic lubricating oil is a poly-α-olefin, monoester, diester, polyolester, or mixtures thereof. The preferred lubricating oil mixture contains about 5 to 95 weight %, preferably 10 to 75 weight %, and most preferably 10 to 50 weight % synthetic lubricating oil. Viscosity Modifiers Suitable viscosity modifiers for use in this invention are those of a relatively specific molecular weight range. While this molecular range may vary according to the particular type of viscosity modifier used, the molecular weight must be no greater than about 175,000 (especially less than 175,000) to acheive the broadest embodiment of this invention, and typically less than 150,000, preferably from about 75,000 to 150,000 atomic mass units to obtain the viscometric and shear stability requirements of a more restrictive embodiment of this invention. Although there is no precise lower limit on the molecular weight of the viscosity modifier with which the benefits of this invention can be obtained, the molecular weight will typically range from 50,000 to no greater than about 175,000 (especially less than 175,000) atomic mass units. The term "atomic mass unit" is a measure of atomic mass defined as equal to 1/12 the mass of a carbon atom of mass 12. The term "molecular weight", for the purposes of this invention, refers to the weight average molecular weight measured for example, by gel permeation chromatography. Also, the term molecular weight, for purposes of this invention, is intended to encompass both "actual" and "effective molecular weights". "Actual" refers to when a single viscosity modifier is used - thus, when only one viscosity modifier is employed, the molecular weight is the actual molecular weight of the viscosity modifier. The term "effective molecular weight" refers to when more than one viscosity modifier is used to achieve this invention's benefits. Effective molecular weight is calculated by summing each individual viscosity modifier's molecular weight contribution, which in turn is determined by multiplying the actual molecular weight of the individual viscosity modifier by its weight fraction in the viscosity modifier mixture. Suitable viscosity modifiers include hydrocarbyl polymers and polyesters. Examples of suitable hydrocarbyl polymers include homopolymers and copolymers of two or more monomers of C2 to C30, e.g., C2 to Cβ olefins, including both α-olefins and internal olefins, which may be straight or branched, aliphatic, aromatic, alkyl-aromatic, cycloaliphatic, etc. Frequently they will be of ethylene with C3 to C30 olefins, particularly preferred being the copolymers of ethylene and propylene. Other polymers can be used such as polyisobutylenes, homopolymers and copolymers of CQ and higher α-olefins, atactic polypropylene, hydrogenated polymers and copolymers and terpolymers of styrene, e.g., with isoprene and/or butadiene. More specifically, other hydrocarbyl polymers suitable as viscosity modifiers in this invention include those which may be described as hydrogenated or partially hydrogenated homopolymers, and random, tapered, star, or block interpolymers (including terpolymers, tetrapolymers, etc.) of conjugated dienes and/or monovinyl aromatic compounds with, optionally, α- olefins or lower alkenes, e.g., C3 to C-|8 α-olefins or lower alkenes. The conjugated dienes include isoprene, butadiene, 2,3-dimethylbutadiene, piperylene and/or mixtures thereof, such as isoprene and butadiene. The monovinyl aromatic compounds include vinyl di- or polyaromatic compounds, e.g., vinyl naphthalene, or mixtures of vinyl mono-, di- and/or polyaromatic compounds, but are preferably monovinyl monoaromatic compounds, such as styrene or alkylated styrenes substituted at the α-carbon atoms of the styrene, such as alpha-methylstyrene, or at ring carbons, such as o-, m-, p- methylstyrene, ethylstyrene, propylstyrene, isopropylstyrene, butylstyrene isobutylstyrene, tert-butylstyrene (e.g., p-tert-butylstyrene). Also included are vinylxylenes, methylethylstyrenes and ethylvinylstyrenes. The α-olefins and lower alkenes optionally included in these random, tapered and block copolymers preferably include ethylene, propylene, butene, ethylene¬ propylene copolymers, isobutylene, and polymers and copolymers thereof. As is also known in the art, these random, tapered and block copolymers may include relatively small amounts, that is less than about 5 mole %, of other copolymerizable monomers such as vinyl pyridines, vinyl lactams, methacrylates, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl stearate, and the like. Specific examples include random polymers of butadiene and/or isoprene and polymers of isoprene and/or butadiene and styrene. Typical block copolymers include polystyrene-polyisoprene, polystyrene- polybutadiene, polystyrene-polyethylene, polystyrene-ethylene propylene copolymer, polyvinyl cyclohexane-hydrogenated polyisoprene, and polyvinyl cyclohexane-hydrogenated polybutadiene. Tapered polymers include those of the foregoing monomers prepared by methods known in the art. Star- shaped polymers typically comprise a nucleus and polymeric arms linked to said nucleus, the arms being comprised of homopolymer or interpolymer of said conjugated diene and/or monovinyl aromatic monomers. Typically, at least about 80% of the aliphatic unsaturation and about 20% of the aromatic unsaturation of the star-shaped polymer is reduced by hydrogenation. Representative examples of patents which disclose such hydrogenated polymers or interpolymers include U.S. Patents 3,312,621 , 3,318,813, 3,630,905, 3,668,125, 3,763,044, 3,795,615, 3,835,053, 3,838,049, 3,965,019, 4,358,565, and 4,557,849. Suitable hydrocarbyl polymers are ethylene copolymers containing from 15 to 90 wt % ethylene, preferably 30 to 80 wt. % of ethylene and 10 to 85 wt. % , preferably 20 to 70 wt. % of one or more C3 to C28. preferably C3 to C<|8. m ore preferably C3 to Cs, α-olefins. While not essential, such copolymers preferably have a degree of crystallinity of less than 25 wt. %, as determined by X-ray and differential scanning calorimetry. Copolymers of ethylene and propylene are most preferred. Other α-olefins suitable in place of propylene to form the copolymer, or to be used in combination with ethylene and propylene, to form a terpolymer, tetrapolymer, etc., include 1- butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -octene, 1-nonene, 1 -decene, etc.; also branched chain α-olefins, such as 4-methyl-1 -pentene, 4-methyl-1- hexene, 5-methyipentene-1 , 4,4-dimethyl-l -pentene, and 6-methyl-heptene- 1, etc., and mixtures thereof. Terpolymers, tetrapolymers, etc., of ethylene, said C3 to C28 α-olefin, and non-conjugated diolefin or mixtures of such diolefins may also be used. The amount of the non-conjugated diolefin generally ranges from about 0.5 to 20 mole percent, preferably from about 1 to about 7 mole percent, based on the total amount of ethylene and α-olefin present. The preferred viscosity modifiers are polyesters, most preferably polyesters of ethylenically unsaturated C3 to Cs mono- and dicarboxylic acids such as methacrylic and acrylic acids, maleic acid, maleic anhydride, fumaric acid, etc. Examples of unsaturated esters that may be used include those of aliphatic saturated mono alcohols of at least 1 carbon atom and preferably of from 12 to 20 carbon atoms, such as decyl acrylate, lauryl methacrylate, cetyl methacrylate, stearyl methacrylate, and the like and mixtures thereof. Other esters include the vinyl alcohol esters of C2 to C22 fatty or monocarboxylic acids, preferably saturated such as vinyl acetate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and the like and mixtures thereof. Copolymers of vinyl alcohol esters with unsaturated acid esters such as the copolymer of vinyl acetate with dialkyl fumarates, can also be used. The esters may be copolymerized with still other unsaturated monomers such as olefins, e.g., 0.2 to 5 moles of C2-C20 aliphatic or aromatic olefin per mole of unsaturated ester, or per mole of unsaturated acid or anhydride followed by esterification. For example, copolymers of styrene with maleic anhydride esterified with alcohols and amines are known, e.g., see U.S. Patent 3,702,300. Such ester polymers may be grafted with, or the ester copolymerized with, polymerizable unsaturated nitrogen-containing monomers to impart dispersancy to the viscosity modifiers. Examples of suitable unsaturated nitrogen-containing monomers to impart dispersancy include those containing 4 to 20 carbon atoms such as amino substituted olefins as p-(beta- diethylaminoethyl)styrene; basic nitrogen-containing heterocycles carrying a polymerizable ethylenically unsaturated substituent, e.g. the vinyl pyridines and the vinyl alkyl pyridines such as 2-vinyl-5-ethyl pyridine, 2-methyl-5-vinyl pyridine, 2-vinyl-pyridine, 3-vinyl-pyridine, 4-vinyl-pyridine, 3-methyl-5-vinyl- pyridine, 4-methyl-2-vinyl-pyridine, 4-ethyl-2-vinyl-pyridine and 2-butyl-5-vinyl- pyridine and the like. N-vinyl lactams are also suitable, e.g. N-vinyl pyrrolidones or N-vinyl piperidones. The vinyl pyrrolidones are preferred and are exemplified by N-vinyl pyrrolidone, N-(1 -methyl-vinyl) pyrrolidone, N-vinyl-5-methyl pyrrolidone, N- vinyl-3,3-dimethylpyrrolidone, N-vinyl-5-ethyl pyrrolidone, etc. Typically, the selected viscosity modifier will be present in a finished ATF composition in an amount between 3 and 15 wt.%, preferably between 4 and 10 wt.%, especially when the viscosity modifier is a polymethacrylate, the preferred viscosity modifier. Friction Modifier? A wide variety of friction modifiers may be employed in the present invention including the following: (i) Alkoxylated Amines Alkoxylated amines are a particulariy suitable type of friction modifier for use in this invention. These types of friction modifiers may be selected from the group consisting of (I), (II), and mixtures thereof, where (I) and (II) are: and R 6 R (R3θ) n H I / Rl - (X) m - R2 " N - R 9 - N ( II ) | \ (R 5 0) n H (R 0) n H R 8 R 7 where: R is H or CH3; R-l is a C8-C28 saturated or unsaturated, substituted or unsubstituted, aliphatic hydrocarbyl radical, preferably C10-C20. most preferably C 1 -C 18 ; R2 is a straight or branched chain C-i-Cβ alkylene radical, preferably C2-C3; R3, R4, and R5 are independently the same or different, straight or branched chain C2-C5 alkylene radical, preferably C2-C4; Rβ, R7, and Rs are independently H or CH3; Rg is a straight or branched chain C1-C5 alkylene radical, preferably C2-C3; X is oxygen or sulfur, preferably oxygen; m is 0 or 1 , preferably 1 ; and n is an integer, independently 1-4, preferably 1. In a particularly preferred embodiment, this type of friction modifier is characterized by formula (I) where X represents oxygen, R and R-i contain a combined total of 18 carbon atoms, R2 represents a C3 alkylene radical, R3 and R4 represent C2 alkylene radicals, RQ and R7 are hydrogens, m is 1 , and each n is 1. Preferred amine compounds contain a combined total of from about 18 to about 30 carbon atoms. Preparation of the amine compounds, when X is oxygen and m is 1 , is, for example, by a multi-step process where an alkanol is first reacted, in the presence of a catalyst, with an unsaturated nitrile such as acrylonitrile to form an ether nitrile intermediate. The intermediate is then hydrogenated, preferably in the presence of a conventional hydrogenation catalyst, such as platinum black or Raney nickel, to form an ether amine. The ether amine is then reacted with an alkylene oxide, such as ethylene oxide, in the presence of an alkaline catalyst by a conventional method at a temperature in the range of about 90-150°C. Another method of preparing the amine compounds, when X is oxygen and m is 1 , is to react a fatty acid with ammonia or an alkanol amine, such as ethanolamine, to form an intermediate which can be further oxyalkylated by reaction with an alkylene oxide, such as ethylene oxide or propylene oxide. A process of this type is discussed in, for example, U.S. Patent No. 4,201,684. When X is sulfur and m is 1 , the amine friction modifying compounds can be formed, for example, by effecting a conventional free radical reaction between a long chain alpha-olefin with a hydroxyalkyl mercaptan, such as beta-hydroxyethyl mercaptan, to produce a long chain alkyl hydroxyalkyl sulfide. The long chain alkyl hydroxyalkyl sulfide is then mixed with thionyl chloride at a low temperature and then heated to about 40°C to form a long chain alkyl chloroalkyl sulfide. The long chain alkyl chloroalkyl sulfide is then caused to react with a dialkanolamine, such as diethanolamine, and, if desired, with an alkylene oxide, such as ethylene oxide, in the presence of an alkaline catalyst and at a temperature near 100°C to form the desired amine compounds. Processes of this type are known in the art and are discussed in, for example, U.S. Patent No. 3,705,139. In cases when X is oxygen and m is 1 , the present amine friction modifiers are well known in the art and are described in, for example, U.S. Patent Nos. 3,186,946, 4,170,560, 4,231 ,883, 4,409,000 and 3,711 ,406. Examples of suitable amine compounds include, but are not limited to, the following: N,N-bis(2-hydroxyethyl)-n-dodecylamine; N,N-bis(2-hydroxyethyl)-1-methyl-tridecenylamine; N,N-bis(2-hydroxyethyl)-hexadecylamine; N,N-bis(2-hydroxyethyl)-octadecylamine; N,N-bis(2-hydroxyethyl)-octadecenylamine; N,N-bis(2-hydroxyethyl)-oleylamine; N,N-bis(2-hydroxyethyl)-stearylamine; N,N-bis(2-hydroxyethyl)-undecylamine; N-(2-hydroxyethyl)-N-(hydroxyethoxyethyl)-n-dodecylamine; N,N-bis(2-hydroxyethyl)-1-methyl-undecylamine; N,N-bis(2-hydroxyethoxyethoxyethyl)-1-ethyl-octadecylamine; N,N-bis(2-hydroxyethyl)-cocoamine; N , N-bis(2-hydroxyethyl)-tallowamine; N,N-bis(2-hydroxyethyl)-n-dodecyloxyethylamine; N,N-bis(2-hydroxyethyl)-lauryloxyethylamine; N,N-bis(2-hydroxyethyl)-stearyloxyethylamine; N, N-bis(2-hydroxyethyl)-dodecylthioethylamine; N,N-bis(2-hydroxyethyl)-dodecylthiopropylamine; N , N-bis(2-hydroxyethyl)-hexadecyloxypropylamine; N,N-bis(2-hydroxyethyl)-hexadecylthiopropylamine; N-2-hydroxyethyl,N-[N',N'-bis(2-hydroxyethyl) ethylamine] -octadecylamine; and N-2-hydroxyethyl,N-[N , ,N'-bis(2-hydroxyethyI) ethylamine] -stearylamine. The most preferred additive is N,N-bis(2-hydroxyethyl)- hexadecyloxypropylamine. This additive is available from Tomah Company under the designation Tomah E-22-S-2. The amine's hydrocarbyl chain length, the saturation ofthe hydrocarbyl chain, and the length and position of the polyoxyalkylene chains can be varied to suit specific requirements. For example, increasing the number of carbon atoms in the hydrocarbyl radical tends to increase the amine's melting temperature and oil solubility, however, if the hydrocarbyl radical is too long, the amine will crystallize from solution. Decreasing the degree of saturation in the hydrocarbyl radical, at the same carbon content of the hydrocarbyl chain, tends to reduce the melting point of the amine. Increasing the amount of alkylene oxide, to lengthen the polyoxyalkylene chains, tends to increase the amine's water solubility and decrease its oil solubility. The amine compounds may be used as such. However, they may also be used in the form of an adduct or reaction product with a boron compound, such as a boric oxide, a boron halide, a metaborate, boric acid, or a mono-, di-, and trialkyl borate. Such adducts or derivatives may be illustrated, for example, by the following structural formula: R ( R3θ ) n | / \ R_ - (X) m - R 2 -N B-O-R 10 (R 0) n where R, R « j, R2, R3, R4, X, , and n are the same as previously defined and where R-io is either hydrogen or an alkyl radical. (ii) Carboxylic Acids/Anhydrides with Polyamines A second type of friction modifier useful with this invention is the reaction product of a polyamine and a carboxylic acid or anhydride. Briefly, the polyamine reactant contains from 2 to 60 total carbon atoms and from 3 to 15 nitrogen atoms with at least one of the nitrogen atoms present in the form of a primary amine group and at least two of the remaining nitrogen atoms present in the form of primary or secondary amine groups. Non-limiting examples of suitable amine compounds include: polyethylene amines such as diethylene triamine (DETA); triethylene tetramine (TETA); tetraethylene pentamine (TEPA); polypropylene amines such as di-(1,2-propylene)triamine, di(1,3-propylene) triamine, and mixtures thereof. Additional suitable amines include polyoxyalkylene polyamines such as polyoxypropylene triamines and polyoxyethylene triamines. Preferred amines include DETA, TETA, TEPA, and mixtures thereof (PAM). The most preferred amines are TETA, TEPA, and PAM. The carboxylic acid or anhydride reactant of the above reaction product is characterized by formula (III), (IV), (V), (VI), and mixtures thereof: o o R" - c OH ( III ) ; R" C - R" ( IV) ; where R" is a straight or branched chain, saturated or unsaturated, aliphatic hydrocarbyl radical containing from 9 to 29 carbon atoms, preferably from 11 to 23. When R" is a branched chain group, no more than 25% of the carbon atoms are in side chain or pendent groups. R" is preferably straight chained. The R" hydrocarbyl group includes predominantly hydrocarbyl groups as well as purely hydrocarbyl groups. The description of these groups as predominantly hydrocarbyl means that they contain no non-hydrocarbyl substituents or non-carbon atoms that significantly affect the hydrocarbyl characteristics or properties of such groups relevant to their uses as described here. For example, a purely hydrocarbyl C20 alkyl group and a C20 alkyl group substituted with a methoxy substituent are substantially similar in their properties and would be considered hydrocarbyl within the context of this disclosure. Non-limiting examples of substituents that do not significantly alter the hydrocarbyl characteristics or properties of the general nature of the hydrocarbyl groups of the carboxylic acid or anhydride are: Ether groups (especially hydrocarbyioxy such as phenoxy, benzyloxy, methoxy, n-isotoxy, etc., particularly alkoxy groups of up to ten carbon atoms); Oxo groups (e.g., -O- linkages in the main carbon chain); O ll Ester groups (e.g., -C-O-hydrocarbyl); O II Sulfonyl groups (e.g., - S - hydrocarbyl); and II o Sulfinyl groups (e.g., - S - hydrocarbyl). II O These types of friction modifiers can be formed by reacting, at a temperature from about 120 to 250°C, at least one polyamine and one carboxylic acid or anhydride in proportions of about 2 to 10 molar equivalents of carboxylic acid or anhydride per mole of amine reactant. (iii) Other Friction Modifiers Optionally, other friction modifiers may be used either alone or in combination with the foregoing described friction modifiers to achieve the desired fluid performance. Among these are esters of carboxylic acids and anhydrides with alkanols. Other conventional friction modifiers generally consist of a polar terminal group (carboxyl, hydroxyl, amino, etc.) covalently bonded to an oleophilic hydrocarbon chain. Particularly preferred esters of carboxylic acids and anhydrides with alkanols are described in, for example, U.S. Patent 4,702,850. This reference teaches the usefulness of these esters as friction modifiers, particularly the esters of succinic acids or anhydrides with thio-bis-alkanols, most particularly with esters of 2-octadecenyl succinic anhydride and thiodiglycol. Examples of other conventional friction modifiers (i.e., polar terminal group + oleophilic hydrocarbon chain) are described by, for example, M. Belzer in the "Journal of Tribology" (1992), Vol. 114, pp. 675-682 and M. Belzer and S. Jahanmir in "Lubrication Science" (1988), Vol. 1 , pp. 3-26. Typically the friction modifiers will be present in finished ATF composition in an amount between 0.01 to 5, preferably 0.1 to 3 wt.%. Other additives known in the art may be added to the ATF. These additives include dispersants, antiwear agents, antioxidants, corrosion inhibitors, detergents, extreme pressure additives, and the like. They are generally disclosed in, for example, "Lubricant Additives" by C. V. Smalheer and R. Kennedy Smith, 1967, pp. 1-11 and U.S. Patents 5,389,273; 5,326,487; 5,314,633; 5,256,324; 5,242,612; 5,198,133; 5,185,090; 5,164,103; 4,855,074; and 4,105,571. Representative amounts of these additives are summarized as follows: (Broad) (Preferred) Additive wt,% Wt.% Corrosion Inhibitor 0.01 - 3 0.02 - 1 Antioxidants 0.01 - 5 0.2 - 3 Dispersants 0.10 - 10 2 - 5 Antifoaming Agents 0.001- 5 0.001 - 0.5 Detergents 0.01 - 6 0.01 - 3 Antiwear Agents 0.001- 5 0.2 - 3 Seal Swellants 0.1 - 8 0.5 - 5 Suitable dispersants include hydrocarbyl succinimides, hydrocarbyl succinamides, mixed ester/amides of hydrocarbyl-substituted succinic acid, hydroxyesters of hydrocarbyl-substituted succinic acid, and Mannich condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines. Mixtures of such dispersants can also be used. The preferred dispersants are the alkenyl succinimides. These include acyclic hydrocarbyl substituted succinimides formed with various amines or amine derivatives such as are widely disclosed in the patent literature. Use of alkenyl succinimides which have been treated with an inorganic acid of phosphorus (or an anhydride thereof) and a boronating agent are also suitable for use in the compositions of this invention as they are much more compatible with elastomeric seals made from such substances as fluoro- elastomers and silicon-containing elastomers. Polyisobutenyl succinimides formed from polyisobutenyl succinic anhydride and an alkylene polyamine such as triethylene tetramine or tetraethylene pentamine wherein the polyisobutenyl substituent is derived from polyisobutene having a number average molecular weight in the range of 500 to 5000 (preferably 800 to 2500) are particulariy suitable. Dispersants may be post-treated with many reagents known to those skilled in the art. (see, e.g., U.S. Pat. Nos. 3,254,025, 3,502,677 and 4,857,214). Suitable antioxidants are amine-type and phenolic antioxidants. Examples of the amine-type antioxidants include phenyl alpha naphthylamine, phenyl beta naphthylamine, diphenylamine, bis- alkylated diphenyl amines (e.g., p,p'-bis(alkylphenyl)amines wherein the alkyl groups contain from 8 to 12 carbon atoms each). Phenolic antioxidants include sterically hindered phenols (e.g., 2,6-di-tert-butylphenol, 4-methyl-2,6-di-tert- butylphenol, etc.) and bis-phenols (e.g., 4,4'- methylenebis(2,6-di-tert- butylphenol), etc.) and the like. Additive concentrates of this invention will contain the viscosity modifier, friction modifier, and other desired additives in a natural and/or synthetic lubricating oil, in relative proportions such that by adding the concentrate to a larger amount of a suitable natural and/or synthetic oil the resulting fluid will contain each of the ingredients in the desired concentration. Thus, the concentrate may contain a synthetic oil as the lubricating oil if the desired final composition contains a lesser amount of synthetic oil relative to the mineral oil. The concentrate typically will contain between 25 to 100, preferably from 65 to 95, most preferably from 75 to 90 weight percent of the viscosity modifier, friction modifier, other desired additives, and synthetic and/or natural oil. Viscometric Properties A common method of characterizing the viscometric behavior of lubricants relative to high temperature viscosity at both high and low shear rates, and the ability of the fluid to retain these viscometrics after use, is called the 'Viscosity Loss Trapezoid'. The viscosity loss trapezoid is developed by measuring the viscosity of the fluid under a variety of conditions both "new" (i.e., fresh or unused) and "sheared" (i.e., used). The "sheared" fluid is produced by passing it through a fuel injector shear tester forty times. The measurements required to construct a 'Viscosity Loss Trapezoid' and some of the presently desired minimum values for the more restrictive embodiment of this invention are shown below: Table 1 VISCOSITY LOSS TRAPEZOID SHEAR RATE (Type) NEW SHEARED Fluid Viscosity (150°C), cP 2 x 10 2 sec."1 (Low) >2.60 >2.60 Fluid Viscosity (150°C), cP 1 x 1θ6 sec.-1 ( Hi 9 n ) >2.60 >2.60 The viscosity loss trapezoid is then constructed graphically by plotting the four measurements shown above against shear rate. Figures 1 and 2 show the types of phenomena that are observed in this testing. Figure 1 shows a fluid which meets the requirements shown above, it is Newtonian in nature, that is, its viscosity is not dependent on shear stress and is not reduced by mechanical shearing. Figure 2 shows a fluid that is non- Newtonian, i.e., its viscosity is dependent on shear rate (known as temporary shear) as is indicated by the decreasing viscosity when going from 200 sec." ' ' to 1θ6 sec." ' ' shear rates. This fluid also loses viscosity when subjected to mechanical stress (known as permanent shear which is evidenced by the overall loss in viscosity between the fresh and used oil Iines). Additionally, the kinematic viscosity of the more restrictive embodiment measured at 100°C, before and after shearing is desired to be at least 6.8 mm2/s (cSt). That is, the "new" and "sheared" fluid must have a minimum viscosity at 100°C of at least 6.8 mm 2 /s (cSt). Also, since improved operation of vehicles at low ambient temperatures is an objective, it is desirable that the Brookfield viscosity at -40°C not be greater than 15,000 cP for all embodiments of this invention. Furthermore, since seal leakage is more of a concern when dealing with less viscous materials (due to the low -40°C Brookfield requirement), it is necessary for all embodiments of this invention to have a difference between the "new" and "sheared" viscosities measured at 150°C and the low shear rate of 2x10 2 sec." ' ' of no greater than 0.30 centipoise. This invention may be further understood by the following examples which are illustrative and not restrictive for this invention. EXAMPLES Sixteen finished ATF's were blended using a standard ATF additive package and a mixture of solvent extracted neutral oils and synthetic hydrocarbon (poly-α-olefin, PAO). The formulation for these fluids is shown below: Test Formulations Component Mass Percent Fluid Additive Package 8.00 4 mm 2/s (cSt) PAO 30.00 Viscosity Modifier as shown Solvent Extracted 100 Neutral \ 50/50 ratio to 100% Solvent Extracted 75 Neutral J The additive package contained conventional amounts of a succinimide dispersant, antioxidants, antiwear agents, friction modifiers, a corrosion inhibitor, an antifoamant, and a diluent oil. The controlled variable in this series of blends was the molecular weight (as previously defined) of the polymethacrylate viscosity modifier used. The test blends are shown in Table 2 as Examples 1-16. Table 2 also contains the measured fluid properties of -40°C Brookfield viscosity, and the more restrictive embodiments of this invention: i.e., "new" and "sheared" viscosity at 100°C, 150°C "new" and "sheared" viscosity at the low shear rate of 2 x 10 2 sec."1 (150°C - LS), and 150°C "new" and "sheared" viscosity at the high shear rate of 1 x 10^ sec." ' ' (150°C - HS). Examples 1 through 11 in Table 2 utilize single viscosity modifiers — namely, polymethacrylate viscosity modifiers varying in molecular weight from 75,000 to 420,000. The data in Table 2 define the acceptable molecular weight range for meeting the viscosity requirements for these fluids. Examples 1, 2, 3 and 4 show that high molecular weight viscosity modifiers are unsuitable for producing the fluids of this invention. Example 1 is blended to a conventional ATF kinematic viscosity of 7.34 mm2/s (cSt) at 100°C, and satisfies the -40°C Brookfield viscosity requirement (<15,000 cP). However, the broad aspects of this invention are not met since the difference between the "new" and "sheared" measurement at the low shear rate of 2 x 10 2 sec."1 and 150°C of 0.61 cP is greater than 0.30 cP. Furthermore, in the more restrictive embodiment of the invention, Example 1 fails to meet the "sheared" viscosity requirement of at least 6.8 mm2/s (cSt) at 100°C, the 150°C low shear "sheared" requirement of at least 2.6 cP, and both the "new" and "sheared" high shear viscosities of at least 2.6 cP at 150°C and the high shear rate (10 6 sec." 1 ). Example 2 uses the same viscosity modifier as Example 1 , but in an amount sufficient to pass the more restrictive 150°C low shear "sheared" requirement of at least 2.6 mm2/s (cSt). However, increasing the amount of viscosity modifier to this level, increased the kinematic viscosity of the fluid at 100°C to over 11 mm 2 /s (cSt) and increased the -40°C Brookfield to over 45,000 cP. Also, the 150°C low shear viscosity difference between the "new" and "sheared" fluid is 1.46 cP which is significantly greater than the 0.30 cP limit. Finally, even with this high viscosity modifier treat rate, and resultant very high 11 mm 2 /s (cSt) viscosity at 100°C, the blend still fails to meet the more restrictive 150°C high shear requirement on the "sheared" fluid, i.e., 2.44 cP measured versus >2.6 cP. Example 3 uses a viscosity modifier of lower molecular weight which is, therefore, more shear resistant. Example 3 is blended to a kinematic viscosity at 100°C similar to Example 1, i.e., 7.38 mm 2 /s (cSt). Example 3 also meets the -40°C Brookfield requirement. Comparing Example 3 with Example 1 shows that VP 5011H is more shear stable than the VP 5011B (i.e., in general, the viscometric values obtained for Example 3 are higher than those obtained for Example 1). However, Example 3 still fails all the same parameters as Example 1. Example 4 uses the same viscosity modifier as Example 3, but in an amount sufficient to pass all the "sheared" fluid requirements of the more restrictive embodiment of this invention. However, the fluid of Example 4 yielded a kinematic viscosity of 11.2 mm 2 /s (cSt) at 100°C and a failing -40°C Brookfield of 19,500 cP. Example 4 still did not meet the 150°C high shear "sheared" fluid requirement of at least 2.6 cP. Adding more viscosity modifier to pass this requirement would only increase the -40°C Brookfield viscosity further. Thus, adding more viscosity modifier to meet the 150°C high shear "sheared" requirement is not a viable option as the -40°C Brookfield would increase further above the 15,000 cP requirement. Examples 5 and 6 show that at a molecular weight of 175,000, the 150°C low shear and high shear "sheared" values of at least 2.6 cP for the more restrictive embodiment of the invention are not met. However, these examples satisfy the broader aspects of this invention because the viscosity modifier's molecular weight is not greater than 175,000 and the difference between the 150°C "new" and "sheared" low shear viscosity is no greater than 0.30 cP and the -40°C Brookfield viscosity is no greater than 15,000 cP. Examples 7 and 8, and 10 and 11, demonstrate that there is a lower limit to the amount of viscosity modifier required (treat rate) at a particular molecular weight to obtain this invention's more restrictive embodiment. For instance, Example 7 having 8.0 weight % VP 5089 fails the minimum 2.6 cP 150°C high shear "sheared" viscosity requirement, while Example 8 having 8.5 weight % VP 5089 meets all the requirements of the invention's more restrictive embodiment. Also, Example 10 fails the "new" and "sheared" high shear requirements at 150°C, while Example 11 satisfies the 2.6 cP requirements. However, the broader aspects of the invention are met in each of Examples 7-11 because the molecular weight of the viscosity modifiers are no greater than 175,000, the -40°C Brookfield viscosities are no greater than 15,000 cP, and the difference between the 150°C "new" and "sheared" low shear viscosity is no greater than 0.30 cP. Examples 12 through 16 are blends of two viscosity modifiers which have molecular weights of the blends from 100,000 to 250,000. The blends with molecular weights no greater than 175,000 fully meet both the broad aspects and the more restrictive embodiment of this invention. Accordingly, Example 12 with the higher molecular weight (252,000) fails to meet this invention's more restrictive embodiment's 150°C low shear "sheared" viscosity of 2.6 cP and this invention's broader aspect of having the "new" and "sheared" low shear viscosity difference at 150°C of no greater than 0.30 cP. It can be seen from Table 2 that only those blends in which the molecular weight of the viscosity modifier is no greater than 175,000, can this invention's broad aspects be met (i.e., a -40°C Brookfield viscosity of no greater than 15,000 cP and a 150°C "new" and "sheared" low shear viscosity difference of no greater than 0.30 cP). Although it is possible to make blends using viscosity modifiers of the preferred molecular weights that fail one or more of the viscometric criteria of this invention's more restrictive embodiment by raising or lowering the treat rate (see, Example 7 versus Example 8 and Example 10 versus Example 11), the converse cannot be said about viscosity modifiers with molecular weights greater than 175,000. That is, that merely manipulating the treat rate of viscosity modifiers of higher molecular weight, fluids containing them cannot be made to meet all of the necessary viscometric criteria, as has been previously shown. The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected herein is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Claims: Claims: 1. An automatic transmission fluid composition comprising: (a) a major amount of lubricating oil containing 5 to 95 weight % of a synthetic lubricating oil having a kinematic viscosity of 1 to 100 mm 2 /s at 100°C and 5 to 95 weight % of a natural lubricating oil having a kinematic viscosity of 1 to 40 mm 2 /s at 100°C; (b) a viscosity modifier having a molecular weight no greater than about 175,000 atomic mass units; and (c) from 0.01 to 5 weight % of a friction modifier; providing that the composition has a -40°C Brookfield viscosity no greater than 15,000 centipoise and the difference between the composition's new and sheared viscosity of the composition is no greater than 0.30 centipoise when measured at a temperature of 150°C and shear rate of 2x10 2 sec. -1 . 2. The composition of claim 1, where the synthetic oil is poly-α-olefin, monoester, diester, polyolester, or mixtures thereof. 3. The composition of claim 2, where the lubricating oil is a mixture of mineral oil and poly-α-olefin. 4. The composition of claim 3, where the viscosity modifier is a polymethacrylate. 5. The composition of claim 4, where the friction modifier is selected from the group consisting of (I); (II); reaction products of polyamines with (III), (IV), (V), (VI); and mixtures thereof, where (I), (II), (III), (IV), (V), (VI) are: ( I D O R" = C OH ( III ) R" - I CI O - C R" ( IV) where: R is H or CH3; R-j is a C8-C28 saturated or unsaturated, substituted or unsubstituted, aliphatic hydrocarbyl radical; R2 is a straight or branched chain Ci-Cβ alkylene radical; R3, R4, and R5 are independently the same or different, straight or branched chain C2-C5 alkylene radical; Rs, R7, and Rs are independently H or CH3; Rg is a straight or branched chain C-1-C5 alkylene radical; X is oxygen or sulfur; m is 0 or 1 ; n is an integer, independently 1-4; and R" is a straight or branched chain, saturated or unsaturated, aliphatic hydrocarbyl radical containing from 9 to 29 carbon atoms with the proviso that when R" is a branched chain group, no more than 25% of the carbon atoms are in side chain or pendent groups. 6. The composition of claim 5, where the friction modifier is an ethoxylated amine, alkyl amide, or mixtures thereof. 7. The composition of claim 6, where the composition further comprises a borated or non-borated succinimide dispersant, a phenolic or amine antioxidant, such that the sum of the dispersant, antioxidant, and friction modifier is between 2.0 to 11 weight percent of the composition. 8. The composition of claim 1 , where the composition has new and sheared viscosities of at least 6.8 mm /s at 100°C. 9. The composition of claim 1 , where the composition has new and sheared viscosities of at least 6.8 mm 2 /s at 100°C and at least 2.6 cP at 150° C for shearing rates up to 1x10^ sec.-1. 10. A method for producing the composition of claim 1 comprising the steps of: (a) providing a major amount of the lubricating oil; and (b) adding to the lubricating oil the viscosity modifier and 0.01 to 5.0 weight % of the friction modifier. 11. The composition of any of the claims 1-9, where the viscosity modifier has a molecular weight less than about 175,000 atomic mass units and the synthetic lubricating oil has a kinematic viscosity of 1 to 40 mm 2 /s at 100°C.

Inventors: BLOCH RICARDO ALFREDO, CORNISH CHRISTOPHER WILLIAM, WATTS RAYMOND FREDERICK, BLOCH, RICARDO, ALFREDO, CORNISH, CHRISTOPHER, WILLIAM, WATTS, RAYMOND, FREDERICK
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1996
Main classification: C10M169
IPC codes: C10M161, C10M169, C10N20, C10N30, C10N40