CA2680919A1 - Multifunctional driveline fluid - Google Patents

Abstract

A composition including 1 to 20 weight percent of a compound having a tra ction coefficient of at least about 0.045, at least 50 weight percent of an oil of lubricating viscosity, a phosphorus compound and 2,5-dimercapto-1,3,4 -thiadiazole or a derivative thereof, and having a kinematic viscosity at 10 0 °C of up to about 12 mm2/sec, is suitable for lubricating a transmission.

Description

TITLE
Multifunctional Driveline Fluid BACKGROUND OF THE INVENTION
[0001] The present invention relates to a lubricant for transmissions, having ,good lubricating properties and a relatively high traction coefficient.

[0002] There have been continuing efforts in the transmission industry to impi-ove the fuel economy of vehicles in which the transmissions are installed.
This trend first becaa~ne apparent in passen~er cars, as a result of fuel econoiny leaislation, and is increasingly affectine, other types of vehicles, includina heavy trucks.

[0003] One approach to improving fuel economy, while meeting in emission and performance requirements, is to employ a combination of transmission technologies. For example, so-called dual-clutch transmissions incorporate a combination of wet clutches, typical of automatic transmissions, along with manual transmission componentry. Lubricating such a transmission is a chal-lenge since manual transmission fluid technolo(yy is not necessarily compatible with the wet clutches. The present invention provides a fluid which is suitable-for lubricatin~ a wide variety of inechanical powei- transmission devices, includ-ing automatic transmissions, manual transmissions, automatic manual transmis-sions, dual clutch transmissions, traction drives such as toroidal traction drives, continuously variable transmissions such as push-belt transmissions and pull-chain transmissions, infinitely variable transmissions, hybrid transmissions, and transmissions for hybrid-powered vehicIes or for gasoline, diesel, or electric powered vehicles.

[0004] Traction fluids based on a var-iety of base fluids are Itnown. For exaznple, U.S. patent 6,372,696, Tipton, April 1.6, 2002, discioses traction fluid formulations includinff a base fluid of polymers ol.' at least one olel~in.
containing 3 to 5 carbon atoms, hydrocarbon molecules containing non-aromatic cyclic moieties, or mixtures thereof; a low-temperature viscosity control agent (such as polymers or oligomers of linear a-olefins), and an additive package of dispers-ants and deteraents. Examples contain phosphoric acid and dialkyl hydroaen phosphite and alkyl phosphite friction modifier. The same examples also include dialkyl dimercaptothiadiazole.

[0005] U.S. Patent 5,043,497, Muraki et al., August 27, 1991, discloses a lubricatinff oil for a traction drive, inainly composed of a naphthenic hydrocar-bon having 19 carbon atonls comprisinor two substituted cyclohexane rings linked hy a methylene groitn. A(ldit-ives for nrr(ina_rv lubricating oils s rh as antioxidants, agents for increasing the viscosity index, corrosion inhibitors, detergents, defoamers, and so forth are added as necessary. Cal.cium.
sulfonate is disclosed as a detergent.

[0006] U.S. Patent 3,975,278, Wygant, August 17, 1976, discloses hydro-genated dimers of ea-alk.yl styrene, wlaich are useful as tractive fluids.
Additives such as VI improvers, antioxidants, an.tiwear agents, corrosion inhibitors, dispersants, and dyes can be included.

[0007] U.S. Patent 3,966,624, Duling et al., June 29, 1976, discloses a blended traction fluid containing hydrogenated polyolefin and an adamantane ether. The lubricant described can contain other oils and additives, e.g., a sludge dispersant. An especially useful additive, combining detergency, corro-sion inhibition and friction improvement at high speeds, is a Mg, Ca or Ba salt (especially a super-based salt) of certain weak acids.

[0008] A variety of additive formulation for use in ti-ansmission fluids and other functional fluids are generally known. For instance, U.S. Patent 5,858,929, Sumiejski et al., January 12, 1999, equivalent to European Patent publication 747,464, published June 6, 1996, discloses a composition for use in lubricants and functional fluids to provide improved anti-shudder and shudder durability properties to an automatic transmission. The composition comprises alkoxylated fatty amines as well as a mixture of other friction modifiers. Pre-ferred compositions include alkoxylated fatty amines, other friction modifiers, antioxidants, overbased metal organic acid, dispersants, viscosity index im-prover and/or dispersant-viscosity modifier, extreme pressure agent, seal swell agent, and 85% phosphoric acid. The base oils of lubricatina viscosity include liquid petrolcum oils and solvent treated ot- acid treated mine.r-al lubricatina oils of the paraffinic, naphthenic or mixed naphthenic-paraffinic types.

[0009] U.S. patent 6,251,840 , Ward et al., June 26, 2001, discloses lubi-ica-tion fluids for reduced air entrainment and improved gear protection. The improvement results from the use of 2,5-diinercapto-1,3,4-thiadiazole and derivatives thereof together with silicone and/or fluorosilicone antifoam agents.
PlZosphoric acid is also present.

[0010] U.S. patent 6,103,673, Sumiejski et al., August 15, 2000, discloses compositions containing friction niodifiers for continuously variable transmis-sions, including an oil of lubricatincT viscosity, a shear-stable viscosity modifier.
an overbased meta salt, a phosphorus coTnpound, and at least two friction modifiers.

~

[0(111] The prPsP.nt invention, th0.rpfnra. solves the. nrnh]am of n,-nvirlina a single fluid that can satisfactorily lubricate one or more of a variety of transmis-sions, including automatic transmissions, manual transmissions, continuously variable transmissions, dual clutch transmissions, and other mentioned above.
It is also suitable for use as a hydraulic fluid, final drive oil, hybrid vehicle fluid, and a fluid for other driveline and industrial applications.
SUMMARY OF THE INVENTION
[0012] The present invention pa-ovides a lubricant composition suitable for lubricating a transmission, said composition comprising: (a) I to 20 weight percent of a compound having a traction. coefficient of at least about 0.045 or at least 0.05, selected from the group consistinc, of: (i) hydrocarbons containing non-aromatic cyclic structures, (ii) polybutenes of number average molecular weight 180 to 600, (iii) esters having a branched or non-aromatic cyclic alkyl moiety (for instance, polyol esters having branched or non-aromatic cyclic alkyl rn.oieties in the acid portion or in both the alcohol and acid portions lhercof), and mixtures thereof; (b) at least 50 weight percent of an oil of lubricating viscosity, other than a material of component (a); (c) a phosphorus compound, for exam-ple, a phosphorus acid or phosphorus ester or salt thereof; and (d) 2,5-dimercapto-1,3,4-thiadiazole or a derivative thereof, said lubricant composition having a kinematic viscosity at 100 C of up to 12 mm'/sec.
[0013] The invention also provides a method for lubricating a transmission, comprising supplying thereta the composition as described above. The trans-mission may comprise a traction drive.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Various preferred features and embodiments will be described below by way of non-limiting illustration.
[0015] The first component of the lubricant colnposltion of the present invention is a compotind, that is, a fluid or oil, which may be characteriz-ed as a traction fluid. Such a fluid will exhibit a traction coefficient of at least 0.045 or at least 0.05. Certain such fluids will exhibit a traction coefficient of 0.053 or 0.06 up to 0.12, or 0.08 to 0.10. Traction coefficient is the ratio of force trans-mitted in a sliding/rolling contact, to the normal, or clamping force between ralling elements.
,u (Traction Coefficient) = F (Tangential) / N (Normal) Ti-action coefficient and various traction fluids are described in greater detail in SAE Technical Paper Series 2000-01-2906, October 16-19, 2000. As used herein, the traction coefficient limitation of at least 0.05 and the like refers to measurement at :100 C ~tt a 1.0% slide/roll ratio (SRR), at a speed of 4 rn/s, and at 1.25 GPa.
[0016] Certain types of fluids are particularly suited for use in traction fluids because of their inherently good (high) traction coefficients. The types of fluids which are particularly suitable include (1) hydrocarbon molecules containinu non-aromatic cyclic structures, (2) polybutenes of number average molecular wei~ht 180 to 600; and (3) esters havin- a branched or non-aromatic cyclic alkyl moiety, for instance, polyol esters having branched or non-aromatic cyclic alkyl moiety in the acid portion thereol' or in both the alcohol and acid portions, that is to say, in the poi-tion of the ester correspondin~ to the constituent alcohol or in the portion corresponding to the constituent acid. Mixtures of these types of materials can also be used. For suitable performance, the traction fluid compo-nent (base fluid) may have a viscosity of greater than 2.5 mm'Is (cSt) at 100 C
(ASTM D-445), such as at least 3.0 rnm'/s (cSt) or 3.5 mm'Is (cSt), typically up to 12.0 mm2/s (12.0 cSt) or to 10.0 mm'Is (cSt) or to 8.0 mm'/s (cSt) or 6.0 mm2 Is (cSt) at 100 C. This component may also contain at least 10 carbon atoms, or at least 12 or 15 or I8 carbon atoms and may, if desired contain up to 200 or to 100 or to 50 carbon atoms.
[0017] Suitable fluids of type (1) include a wide variety of cyclic-containing hydrocarbon molecules. Examples of these include di(cyclohexyl)alkanes, cyclohexyl hydrindans and adamantane compounds, as described in U.S. Patent 3,966,624; esters of cyclohexanol and cylohexanecarboxylic acid, as described in U.S. Patent 4,871,476; decahydronaphthalene ("Decalin"'r-M), cycohexyldeca-hydronaphthalene, aCkyl-substituted decahydronaphthaline, alkyl-substituted cyclohexyldecahydronaphthalene, and mixtures thereof, as described in U.S.
Patent 3,803,037; various materials havino- two cyclohexane rings linked by a methylene aroup described in U.S. Patent 5,043,497; various hydrocarbon compounds havin- a bicyclooctane skeleton described in U.S. Patent 5,422,027;
hydrogenated products of dimers, trimers, or tetramers of norbornanes andloi-norbornenes described in U.S. 5,126,065; hydrogenated dimers, trimers, oa-polymers of cyclic monoterpenoid monomers described in U.S. Patent 4,975,215; various ter-cyclohexyl compounds disclosed in U.S. 5,850,745;
perhydrofluoi-ene derivatives disclosed in U.S. 4,774,013; and preferably linear dimers of hydrogenated a-alkyl styrene, as described in U.S. Patent 3,975,278.
Any of the above materials may be used in a hydrogenated form, to assure the removal of carbon unsaturation; indeed, certain hydrogenated styrene deriva-tives (or cyclohexane derivatives) are inherently hydrogenated species. How-ever, aromatic cyrli,r, ,ctructrires sÃ,ich. as those derived fi-oÃn ,5tvrene may also he present in the base fluid, since aromatic cyclic structures are generally consid-ered to be less deleterious than olefinic unsaturation.
[0018] Among the suitable materials for option (1) of the fluid are predomi-nantly hydro~enated linear dimeÃ-s of aa-alkyl styrene. These dimers are said to be predominantly linear, in contrast to the cyclic dimers which represent another possible structure. Sucli materials can be represented by the general structure R R
I I
C6HÃ I -C-CH_I-CH----C6HÃ Ã

wherein each R is an alkyl 'aroup of I to 4 carbon atoms and C6HÃ1 represents a cyclohexyl group. Such materials and their preparation are described in detail in U.S. Patent 3,975,278.
[0019] Suitable fluids of type (2) include polymers isobutylene, particularly those havinc, a number average molecular weight of 180 to 600, or 200 to 500.
The polymer may be hydrogenated to remove any residual unsaturation. Such materials and their preparation are well known and are descrihed, for instance, in U.S. patent 3,966,624, as corn.ponent A, described particularly in column line 32 through column 16 line 1.1.
[0020] Suitable fluids of type (3) include esters of one or more polyols having 4 to 8 carbon atoms and 2 to 6 OH ~roups. The acid-derived moiety of the ester may have a branched or cyclic structure, and the polyol-derived poÃ-tion may also have a branched or cyclic structure. Exaniples of suitable polyols include ethylene glycol, 1,2- and 1,3-propylene alycoI, butylene glycol, glycer-ine, neopentyl ~lycol, pentaerythritol 2 methylpropane 1,3 diol, 2 jnethylpropane-I,2-diol, 2-methylglycerol, 1,1.,i-tris(hydroxymcthyl)ethane, cyclohexane diol (1,2 or I,3 or 1,4 isoni.ers, cis or trans}, cyclohexane tÃ-iol, tetrols, pentols, and hexols such as inositol., and various carbohydrates such as fucose, allose, fructose, galactose, glucose, mannose, sorbose, tagatose, and talose. The alcohol functionality of such inolecules may be fully esterified or thei-e may be unreacted hydroxy groups.
[0021] The polyol is condensed with one or moi-e acids, whieh may be cyclic or branched acids, and which are typically monocarboxylic acids. Suitable cyclic acids include cyclopentanecarboxylic acid, cyclopentylacetic acid, cyclo-hexylacetic acid, cyclohexanecarboxylic acid, substituted cyclic acids having alkyl groups with I to 8 carbon atorns, e_g__ methvlcvlohexanecarhoxvlic acid and ethylcyclohexanecarboxylic acid. Also included are polycyclic carboxylic acids such as norbornanecarboxylic acid, norbornaneacetic acid, adamantane-ca1-boxyEic acid, adamantane acetic acid, decahydronaphthalenecarboxylic acid, and substituted versions of such materials. An example of a resultinb ester could be neopentyl glycol cyclohexanecarboxylic acid diester. Suitable branched acids include those having one or multiple quatei-nary carbon atoms within the carbon chain. Examples include 2,2-dimethylbutyric acid and homologues thereof, such as 2,2,4,4-tetramethylpentanoic acid, as well as acids wliich contain both branching and cyclic groups, such as dicyclohexylacetic aci.d.
Suitable linear acids include n-heptanoic acid, n-octanoic acid, n-nonanaoic acid, n-decanoic acid, and other acids of up to 30 or 24 or 1.8 carbon atoms.
Mixtures of such acids may also be used.
[0022] In certain embodiments, the esters are those in which a cyclic group, such as one or more cyclohexyl groups or substituted cyclohexyl gr-oups, is present in the acid-derived portion of the ester, or in both the acid- and the alcohol-derived portion of the ester. These esters and methods of their prepara-tion are described in detail in one or more of U.S. Patents 4,871,476;
4,886,613;
4,886,614; 4,889,650; 5,075,024;and 3,398,165. Suitable esters are commer-cially available as traction fluid materials.
[0023] The amount oi' the compound wi.th. the high traction coefficient will typically be 1 to 20 weight percent of the lubricant composition, alternatively 5 to 18 weight percent or 8 to 12 weight percent.
[0024] The lubricant composition will also contain at least 30 weight percent or at least 50 weight percent of an oil of lubricatina viscosity, other than the traction fluid of component described above. The amount of the oil of l.ubricat-ing viscosity {aI.so referred to as a base oil) may also be 60 to 98 percent by weight or 75 to 95 percent by weight.
[0025] The base oil used in the inventive lubricating oil composition may be selected from any of the base oils in Groups 1-V as specified in the American Peti-oleum Institute (API) Base Oil Interchangeability Guidelines. The five base oi l aroups are as follows:

[00261 Base Oil Viscosity Category Sulfur Io Saturates lo Index Group I >0.03 and/or <90 80 to 120 Group II <0.03 and >90 80 to 120 Group III <0.03 and >90 > 120 Group IV All polyalphaolefins (PAOs) Group V All others not included in Groups 1, Il, 111 oi- IV

Groups 1, II and III are minet-al oil base stocks. The oil of luhÃ-icatina viscosity, then, can include natural or synthetic NubricatincT oils and inixtures thereof.
Mixture of mineral oil and synthetic oils, particularly polyalphaolefin oils and polyester oils, are often used.
[0027] Natural oils include animal oils and vegetable oils (e.g. castor oil, lard oil and other vegetable acid esters) as well as mineral lubricating, oils such as liquid petroleum oils and solvent-treated or acid treated mineral lubricatin.g, oils of the paraffinic, naph.thenic or mixed paraffinic-naphthenic types. Hy-drotreated or hydrocracked oils are included within the scope of useful. oils of lubricating, viscosity.
[002$] Oils of lubricatin~ viscosity derived from coal or shale are also useful. Synthetic lubricatina oils include hydrocarbon oils and halosubstituted hydrocarbon oils such as polymerized and interpolymerized olefins and mixtures thereof, alkylbenzenes, polyphenyl, (e.g., biphenyl.s, terphenyls, and alkylated polyphenyls), alkylated diphenyl ethers and a9.kylated diphenyl sulfides and their derivatives, analogs and homologues thereol'.
[0029] Alkylene oxide polymers and interpolymers and derivatives thereof, and those whei-e terminal hydroxy! groups have been modified by, for example, esterification or etherification, constitute other classes of known synthetic lubricating oils that can be used.
[0030] Another suitable class of synthetic lubricating oils that can be used comprises the esters of dicarboxylic acids and those made from C; to C12 mono-carboxylic acids and polyols or polyol ethers.
[0031] Other synthetic l.ubricatin- oils include liquid esters of phosphorus-containing acids, polymeric tetrahydrofurans, silicon-based oils such as the pol.y-alkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils, and silicate oils.
[0032] Hydrotreated naphthenic oils are also known and can be used, as well as oils prepared by a Fischer-Tropsch -as-tow-liquid synthetic procedure.

f00331 TTnrefined, i-efined and rerefinecl oils. either natural or synthetic (as well as mixtures of two or more of any of these) of the type disclosed herein-above can used in the compositions of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purifi-cation treatment. Refined oils are similar to the unrefined oils except they have been further treated in one or more ptiirification steps to improve one or more properties. Rerefined oils are obtained by processes similar to those used to obtain refined oils applied to refined oils wE-iich have been already used in service. Such rerefined oils often are additionally pi-ocessed by techniques directed to removal of spent additives and oil breakdown products.
[0034] In certain embodiments of the present invention, the base oil is a synthetic oil such as a poly-alpha olefin (typically hydrogenated) such as a 4 centistoke polyalpha olefin (i.e,, having a nominal viscosity of 4 mrn.2/sec at 100 C). In certain embodiments, mixtures of synthetic and mineral base oil.s are used. In certain embodiments, at least 50, or at least 80, or at least 90 percent by weight of the oil of lubricating viscosity is a synthetic oi1.
[0035] Another optional or typical component of the present lubricant composition is a phosphorus compound, typically a phosphorus acid or phos-phorus ester or salt thereof (that is, a salt of a phosphorus acid or phosphorus ester), which can include a phosphorus acid, a phosphorus acid salt, a phospho-rus ester, or mixtures thereof. The phosphorus acid or ester can be of the for-mula (R'X)(R2X)P(X)õX,,,R3 or a salt thereof, where each X is independently an oxygen atom or a sulfur atom, n is 0 oi- 1, m is 0 or 1, m+n is 1 or 2, and R', R-, and R' are hydrogen or hydrocarbyl aroups, and, in one embodiment, at least one of Rf, R2, or W is hydrogen. This component thus includes organic or inor~anic phosphorous and phosphoric acids, thiophosphorous and thiophos-phoric acids, as well as phosphite esters, phosphate esters, thiophosphite esters, and thiophosphate esters. Suitable salts include metal or amine salts of phospho-rus esters and anline salts of phosphorus acids, such as the salt formed by reaction of a phosphorus acid with an arnine-containing dispersant such as a succininaide dispersant. It is noted that certain of these phosphorus materials can exist in tautomeric forms, and that all such tautomers are intended to be encompassed by the above formula and included within the present invention.
For example, phosphorous acid and cei-tain phosphite esters can be written in at least two ways:

S

n nH

RO-P-H and R~O-P
I I
R'O RZO

dil.'I.'erin.g. merely by th.e placement of the hydrogen. Each of these structures is intended to be encompassed by the present invention.
[0036] The phosphorus-containing acids can be at least one phosphate, phosphonate, phosphinate or phosphine oxide. These pentavalent phosphorus derivatives can be represented by the fort-nula R'O
R'O-P=0 ~I
R'O
wherein R', R2 and R3 are as defined above. The phosphorus-conlainina acid can be at least one phosphite, ph.osphoni.te, phosphinite or phosphine. An example of trivalent phosphorus derivatives can be represented by the formula R'O

R`O-P
R'o wherein. R1, R 2 and R' are defined as above. Generally, the total number of carbon atonls in R~, R' and R' is at least 8, and in one embodiment at least 12, and in one embodiment at least 16. Examples of useful R', R' and R' oi-oups include hydrogen, t-butyl, isobutyl, amyl, isooctyl, decyl, dodecyl, oleyl, C18 allcyl, eicosyl, 2-pentenyl, dodecenyl, phenyl, naphthyl, alkylphenyl, alkylnaphthyl, phenylalkyl, naphthylalkyl, alkylphenylalkyl, and alkylnaphtllylallcyl groups.
[0037] In another embodiment, the phosphorus acid or ester is characterized by at least one direct carbon-to-phosphorus linkage such as those prepared by the treatment of an olefin polymer, such as one or more of the above polyal-kenes (e.Q., polyisobutene havina a molecular weight of 1000) with a phospho-rizinq auent such as phosphoi-us trichloride, phosphorus heptasulfide, phospho-rus pentasulfide, phosphorus trichloride and sulfur, white phosphorus and a sulfur halide, oi- phosphorothioic chloride.

f00381 Tn certain Pmhnrlimnnt.c at le.sact twn nf tE-in X satnrnc in thP.
ahnrrP.
structure are oxyg' en, so that the structure will be (R'O)(R'O)P(X)nX,,,R' or (RtO)(R'`O)P(X).X.,H. This structure can correspond, for example, to phospho-ric acid when Rt, R'`, and R' are hydrogen. Phosphoric acid exists as the acid itself, H;f 04 and other forms equivalent thereto such as pyrophosphoric acid and anhydrides of phosphoric acid, includinb 85% phosphoric acid (aqueous), which. is the commonly available commercial grade material. The formula can also correspond to a mono- or dialkyl hydrogen phosphite such. as dibutyl hydrogen phosphite (a pl-tosphite ester) when one or both of R' and R 2 are alkyl, respectively and R 3 is hydrogen, or a tr-ialkyl phosphite ester when each of R
R2, and R is alkyl; in each case where n is zero, m is 1 and the remaininb X
is 0. The structure will correspond to phosphoric acid or a related material when n and m are each 1; for example, it can be a phosphate ester such as a mono-, di-or trialkyl monothiophosphate when one of the X atoms is sulfur and one, two, or three of the R groups are alkyl, respectively.
[0039] Phosphoric acid and phosphorous acid are well-known items of commerce. Thiophosphoric acids and thiophosphorous acids are likewise well known and are prepared by reaction of phosphorus coznpounds with elemental sulfur or other sulfur sources. Processes for preparing thiophosphorus acids are reported in detail in Organic Phosphorus Compounds, Vol. 5, pa-es 110-111, G.
M. Kosolapoff et al., 1973.
[0040] Salts of the above phosphorus acids are well known. Salts include animonium and amine salts as well as metal salts. Zinc sal.ts, such as zinc dialkyldithiophosphates and zinc dialkylphosphates, are well known and are useful in certain applications. In certain embodinlents, the salts may be metal or amine dihydrocarbyidithiophosphate salts or metal or amine mono- and dihy-drocarbylphosphate salts.
[0041] Thus, the phosphorus compound can be any of the phosphorus acids, dialkyl hydrogen phosphites, rnetal dihydrocarbyCdithiophosphates, metal dihydrocarbylphosphates, and mixtures thereol'. The amount of the phosphorus compound may be a suitable amount to provide 0.03 to 0.1 weight percent phosphorus to the composition, or in other embodiments to provide 0.04 to 0.09 or 0.05 to 0.08 or to 0.06 weiaht percent phosphorus. The requisite amounts of the particular phosphorus compound of interest can be readily calculated by those skilled in the art.
[0042] The lubricant composition of the present invention will further coml3rise a 2,5-dirnercapto-1,3,4-thiadiazole or a derivative thereof, whicli may ffiinr,tinn in nnrt sac a r.ni-rncinn inhihitnr Fxsimnl-.c nf crriÃah1P
rt;mp.rrintnthisirli_ r .__ __u _. -______ -- ------ ----- -.--=---r---. -. -._._- .- -----.__r_ _..._--azoles inciude 2,5-di.m.ercapto-1,3-4-thiadiazole, hydi-ocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole, and hydrocarbylthio substituted 2,5-dimercapto-1,3,4-thiadiazole. In several embodiments the number of carbon atoms on the hydrocarbyl-substituent group may be I to 30, 2 to 25, 4 to 20, or 6 to 16.
Additional specific examples include 2,5-bis(tert-octyldithi.o)-I.,3,4-thiadiazole, 2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-decyldithio)-1,3,4-thiadi-azole, 2,5-bis(tert-undecyldithio)-1,3,4-thiadiazo[e, 2,5-bis(tert-dodecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-tridecyldithio)-1,3,4-thiadiazole, 2,5--bis(tert-tetra-decyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-pentadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-hexadecyldithio)-1,3,4-th.iadiazolc, 2,5-bis(tert-heptadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-octadecyidithio)-1,3,4-thiadiazole, 2,5-bis(tert-nonadecyldithio)-1,3,4-thiadi.azole, and 2,5-bis(tert-eicosyldithio)-1,3,4-thiadi-azole. Moreovei- the dimercaptothiadiazole or its derivatives may be provided by a combination or reaction product an of oil soluble dispersant, as described below, with dimercaptothiadiazole. Such treated dispersants (e.g., treated succinimide dispersants) and their preparation are known and are described in U.S. Patent 4,136,043, see col.. 9 lines 18-36, col. 10 line 47 throulgh col.

11 line 25, and examples 26-35.
[0043] In one embodiment, the diniercaptothiadiazole of the present inven-tion can be present in an ai:n.ount of 0.05 to 4.0 or to 2.0 percent by weight, or 0.1 to 1.5 percent by weight, or about 0.15 to 1.0 percent by weight of the lubricant composition. In certain embodiments, the 2,5-dimercapto-1,3,4-thiadiazole or derivative thereof niay be present in an amount to provide 0.005 to 1%, or 0.01% to 0.5%, by weight sulfur to the composition.
[0044] Each of the components or additives listed herein naay be mixed as such into the final lubricant composition. AlternativeEy, any one or more of them may be supplied as a concentrate in oil. For example, the phosphorus compound and the thiadiazole compound, as well as any of the additional optional ingredients described below, may be prepared in a relatively small amount of a diluent, typically, oi.l. If desired, some or all of the component havinig the specified traction coefficient may be also incItided within the concen-trate, and any such. concentrates may be blended with the larger amounts of oil or oil plus traction component, as the case may be, to provide the final lubricant composition. The traction component itself may serve as the diluent for a concentrate. If an oil of lubricating viscosity is used as the diluent, the amount n-f .,nil in ccirh ~ .. nnr~antrata macr hr~ fnr inctinrP '1f1 nr '3fl tn 5[1 txnial-it np.a-rrr.nt . .. ... .,u.,.. ..~...,.,......... .._.. ~ ~. ....,.~.... . ...., .,.. ~õ .v M~ ..- ~ and the amounts of the other components will be correspondingly increased.

[0045] The lubricant composition of the present invention may thus also include additional additives such as at Ieast one dispersant, or at least one detergent, or mixtures thereof. Dispersants and detergents ai-e extremely well-known and coriimonly used materials in the field of lubrication.
[0046] Detergents are typically overbased materials, otherwise referred to as overbased or superbased salts, are generally single phase, homo-eneous Newto-nian systems characterized by a metal content in excess of that which would be presea it for neutralization accordinb to the stoichiometry of the metal and the particular acidic or~anic compound reacted with the metal. The overbased materials are pi-epared by reacting an acidic material (typically an inorgai:lic acid or lower carboxylic acid, preferably carbon dioxide) with a mixture comprising an acidic organic compound, a reaction medium comprisin~ at least one inert, organic solvent (mineral oil, naphtha, toluene, xylene, etc.) for said acidic organic material, a stoichiometric excess of a metal base, and a promoter such as a phenol or alcohol. The acidic organic mater-ial will normally have a sufficient number of carbon atoms to provide a degree of solubility in oil. The amount of excess metal is commonly expressed in terms of metal ratio. The term "metal ratio" is the ratio of the total equivalents of the metal to the equivalents of the acidic or~anic compound. A neutral metal saEt has a metal ratio of one. A salt having 4.5 times as much metal as pl-esent in a normal salt wi.ll have metal excess of 3.5 equivalents, or a ratio of 4.5.
[0047] Such overbased materials are well known to those skilled in the art.
Patents describing techniques for making basic salts ol' sulfonic acids, carbox-yii.c acids, phenols, phosphonic acids, and mixtures of any two or more of these include U.S. Patents 2,501,731; 2,616,905; 2,616,911; 2,616,925; 2,777,874;
3,256,186; 3,384,585; 3,365,396; 3,320,162; 3,318,809; 3,488,284; and 3,629,109.
[00481 Other overbased materials include salixarate detergents. These include overbased materials prepared from salicylic acid (which may be unsubstituted) with a hydrocarbyl-substituted phenol, such entities being linked through --or other alky].ene bridges. It is believed that the salixarate derivatives have a predominantly linear, rather than macrocyclic, structure, although both structures are intended to be encompassed by the term "salixarate." Salixarate-derivatives and methods of their prepai-ation are described in greater detail in U.S.
patent number 6,200,936 and PCT Publication WO 0I/5696&.

[0049] The amount of the detergent in the luhricant cornpo.sii:ion of ihe present invention, if it is present, may be 1 to 10 weight percent, or 1.5 to weight percent, or 2 to 3 weight percent.
[0050] Dispersants are well known in the field of lubricants and include primarily what is known as ashless-type dispersants and polymeric dispersants.
Ashless type dispersants are charactert-ized by a polar group attached to a rela-tively high molecular weight hydrocarbon chain. Typical ashless dispersants include N-substituted long chain alkenyl succinimides, having a variety of chemical structures including typically R'-CH-C ~-CH-R~
/ N-[R--NH]a-R'-N
CH~-C C- H~
~
where each R' is independently an alkyl group, fi-equently a pol.yisobutylene group with a molecular weight of 500-5000, and R' are alkylene groups, com.-monly ethylene (C2H4) groups. Such molecules are commonly derived from reaction of an alkenyl acylating ajent with a polyamine, and a wide variety of linkages between the two moieties is possible beside the simple imide structure shown above, including a variety of amides and quatei-nary ammonium salts.
Also, a variety of modes of linkage of the R' gi-oups onto the im.ide structure are possible, including various cyclic linkajes. Succinimide dispersants are more fully described in U.S. Patents 4,234,435 and 3,172,892 and in EP 0355895.
[0051] Another class of ashless dispersant is high molecular weight esters.
These materials are similar to the above-described succinimides except that they may be seen as having been prepared by reaction of a hydrocarbyl acylating agent and a polyhydric aliphatic alcohol such as glycerol, pentaerythritol, or sorbitol. Such materials are described in more detail in U.S. Patent 3,381,022.
[0052] Another class of ashless dispersant is Mannich bases. These are materials which are formd by the condensation of a hiaher molecular weight, alkyl substituted phenol, an alkylene polyamine, and an aIdehyde such as formaldehyde. Such materials may have the general structure OH OH
CH2-NH-(RR2NH)x-R2NHCH2 R' R' (including, a variety of isomers and the like) and are described in more detail in U.S. Patent 3,634,515.
[0053] Other dispersants inclr_ide polymeric disper,s.tnt additives, which are uenerally hydrocarbon-based polymers which contain polar functionality to i~mpart dispersa.ncy characteristics to the polyrner.
[0054] Dispersants can also be post-treated by rcaction with any of a variety of agents. Among these are urea, thiourea, dimercaptothiadiazoles, carbon disulfide, aldehydes, ketones, carboxylic acids, hydrocarbon-substituted suc-cinic anhydrides, nitriles, epoxides, boron compounds, and phosphorus com-pounds. References detailing such treatment are listed in U.S. Patent 4,654,403.
[0055) The amount of the dispersant in the lubricant composition of the present invention, if it is present, may be I to 10 weight percent, or 1.5 to we] aht percent, or 2 to 3 weight percent.
[0056] The compositions of the present invention may also contain a viscos-ity index modifier, for example, in limited amoLints, that is, up to 10 percent by weight of the composition. In certain embodiments the amount of this compo-nent is 0 to 1 percent by weight, and in one embodiment the traction fluids are substantially free from (that is, less than 1 percent or less than 0.1 percent) polymeric viscosity index modifiers.
[0057] Polyrneric viscosity index modifiers (VMs) are extremely well known in the art and most are commercially available. Hydrocarbon VMs include polybutenes, poly(ethylenelpropylene) copolymers, and hydrogenated polymers of styrene with butadiene or isoprene. Ester VMs include esters of sty-rene/maleic anhydride polymers, esters of styrene/maleic anhydride/acrylate terpolymers, and polymethacrylates. The acrylates are available from RohMax and from The Lubrizol Corporation; polybutenes from Afton Corporation and Lubrizol; ethylene/propylene copolymers from ExxonMobil and Afton; hydro-Lyenated polystyrenelisoprene polymers fi-om Shell; styrene/maleic esters from Lubrizol, and hydro~enated styrenelbutadiene polymei-s from BASF.
[0058] Suitable VMs include acrylate- or methacrylate-containing copoly-mers or copolymers of styrene tind an ester of an unsaturated carboxylic acid 1.4 mir.h ac ctvrPnP/malPjr, eSt_P.r (tvnirallv nrPnarPr{ hv Pgt~ri_fir~~tinn nf a ctv-~ r ~ r r rene/rnal.eic anhydride copolymer). Preferably the viscosity modifier is a polymethacrylate viscosity modifier. Polymethacrylate viscosity modifiers are prepared from mixtures of methacrylate monomers having different alkyl groups. The alkyl groups may be either straight chain or branched chain groups containing from 1 to IS carbon atoms. When a small amount of a nitrogen-containing monomei- is copolymerized with alkyl methacrylates, dispersancy propei-ties are also incorporated into the product. Thus, such a product has the multiple function of viscosity modification, pour point depressancy and disper-sancy. Such products have been referred to in the art as dispersant-type viscos-ity modifiers or simply dispersant-viscosity modifiers. Vinyl pyridine, N-vinyl pyrrolidone and N,N'-dimethylaminoethyl methacrylate are examples of nitro-gen-containing monomers. Polyacrylates obtained from the polymerization or copolymerization of one or more alkyl aci-ylates also are useful as viscosity modifiers. It is preferred that the viscosity modifier of the present invention is a dispersant viscosity modifier.
[0059] When the viscosity modifier component includes a polyisobutene, this component is distinauished from the material indicated as having a traction coefficient of at least 0.045 or 0.05, on the basis of its higher molecular weight.
The traction fluid component has a relatively low molecular wei~ht, e.g., 180 to 600, while the polybutene viscosity modifier component, if present, will have a higher molecular weight, as desci-ibed below, or alternatively ainoleeular weight sucli as 800 to 6000 or 1000 to 3600 or 1200 to 2400. The polybutene viscosity modifier component may, nonetheless, impart some improved traction properties to the composition.
[0060] The polymers described above may commonly have a weight averaae moleccilar weight (M,,) of 1,000 or 2,000 or 10,000 up to 500,000, such as 30,000 to 250,000, or alter-natively 20,000 to 100,000, and polydispersity values (M, /Mõ) of 1.2 to 5.
[0061] Another optional material that i-nay be present are present invention is one or more friction modifiers. Friction modifiers include alkoxylated fatty amines, borated fatty epoxidcs, fatty phosphites, fatty epoxides, fatty amines, borated alkoxylated fatty amines, metal salts of fatty acids, fatty acid amides, glycerol esters, borate.d glycerol esters, and fatty imidazolines. The amount of friction modifier or modifiers, if present, may be 0.01 to 2 percent by weight of the fluid composition, or 0.05 to 1.2 pei-cent, oi- 0.1 to 1 percent by weight.

ff1f1F,7.7 ()thPr rnnvPntinnril rmmnnnPntc crir.h sic sintinxir~antc cPal cwP11 ,~___, ~----- ----- ----------- -----r~-------- __.__ agents, corrosion inhibitors, anti-foam agejits, and dyes may be present in conventional amounts.
[0063] In certain embodiments, molybdenum-containing additives such as molybdenum dithiocarbamates and titanium-containing additives may also be present to impart desirable properties such as antiwear performance, anti-oxidancy, and friction modification.
[0064] The lubricant composition thus prepared should have a kinematic viscosity at 100 C of tip to about 12 mlrt'`/sec, for example, 2 to 10 or 6 to 8 mxr.3.2/sec. Obtaining a lubricant with such viscosity will be within the skills of the person skilled in the art, by means of selection of a base stock and other components with suitable viscosity.
[0065] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation inay be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules.
The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevei-theless, all such modifications and reaction products are included within the scope of the present invention; the present invention encom-passes the composition. prepared by admixing the components described above.
[0066] As used herein, the term "hydrocarbyl substituent" or "hydrocar-byl group" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the t-noiecule and having predominantly hydrocarbon character.
Examples of hydrocarbyl groups include:
hydrocai-bon substituents, that is, aliphatic (e.g., alkyl or al~kenyl), ali-cyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-, aliphatie-.
and alicyclic-substituted aromatic substituents, as well as cyclic substituents wherein the ring is completed through anoth.er portion of the molecule (e.g., two substituents together form a ring);
substituted hydrocarbon substituents, that is, substituents containing non-hydrocarbon aroups which, in the context of this invention, do not alter the predoniinantly liydrocarbon nature of the substituent (e.g., halo (especially chloro and fluoro), liydroxy, alkoxy, nlercapto, alkylmea-capto, nitro, nitroso, and sulfoxy);

hete;t-n stihstitttentc, th,tt ic ctthstittientc whirh, while 1-i_avina a nrP.rlnmi-=-c nantly llydrocarbon character, in the context of this invention, contain other than carbon in ai-ing or chain otherwise composed of carbon atoms and encompass substituents as pyridyl, furyl, thienyl and imidazolyl. Heteroatoms include sul.fur, oxygen, and nitrogen. In general, no more than two, preferably no n~ore than one, non-hydrocarbon substituent wi]l be present for every ten carbon atoms in the hydrocarbyl group; typically, there will be no non-hydrocarbon substituents in the hydrocarbyl group.
EXAMPLES
[0067] Examples 1-3. Lubricant coinpositions are prepared as shown in Table I, and have the 100 C kinematic viscosities as shown.
Table I
Example 1 Z 3 PAO 4 mm2/s (cSt) 70.5 70.5 70.5 Hydroggenated dirner (see below) 10.0 Isobutene oligomer 10.0 Synthetic ester 10.0 PMA VM 7.0 7.0 7.0 Polybutene 2000 M,, 6.0 6.0 6.0 Additive package 6.5 6.5 6.5 Kinematic viscosity, mm2/s 7.6 7.1. 7.3 [0068] The materials desibnated PAOs are commei-cial poly-alpha olefin based fluids (oils of lubricating viscosity) havina nominal kinematic viscosity at 100 C of 4 mm_/s. The synthetic ester is a pentaerythritol (tech. grade) ester prepared with 3,5,5-trimethylhexanoic acid (70%), n-heptanoic acid (15%) and n-C8-10 acids (15%), available undet- the trade names Solest 68 NATNs or Hatcol 3368'1'1". The hydrogenated dimer is a hydi-ogenated linear a-methyl styrene dinner, available under the trade name Santotr-ac 20"". The isobutene oligomer is a hydrogenated olijomer of isobutene, Mõ 300-350, available under the trade name Panalane"'M. The PMA VM is a commercially available polymethacrylate viscosity modifier, and the polybutene i.s an additional viscosity modifying additive havinff approximately the indicated molecular weiaht (significantly (yreater than that of the isobutene o1.igomer). The additive package comprises a dialkyl hydrogen phosphite antiwear agent/friction modifier and 2,5-bis(t-nonyldithio)-1,3,4-thiadiazole (a dimercaptothiadiazole), as well as a small amottnt (0.5%, includin~ 49% diluent oil) of a succinimide dispersant that is treatecl witl) ahntit 6 In rlimi-,rr.antnthinriisa7nle ThP ;arEciitivF.
narlraCrP. silcn rnn-_ __ ._ _ - -----------r-_ ___ ._..___. ..._ w~___._ . _ r------~- -=--- -~--tains a borated succinimide dispersant, an aromatic amine antioxidant, over-based calcium detergents, a seaI swell agent, corrosion inhibitor, antifoam agent, and additional diluent oil.
[0069] Materials of cei-tain of the above examples are tested for traction coefficient (results reported at 100 C, 10% SRR) and wear testing. The wear test is the FZG step load test A10/16.6R/120, which uses a 10 mm wide "A"
profile test gear operated in a reverse direction (wheel driving) at 16.6 m/s pitchline velocity and a starting temperature of 120 C. The test measures the scuffing load capacity of lubricants. The lubricant is tested at inei-easing torque levels (load stages) until the failure criteria is met. This is !<nown as the fail load stage; the irnmediately preceding passing stage is reported as the pass stage. A higher number represents better performance. (Reproducibility is typically 1 stage.) The results of these tests are shown in Table II. Each of the fluids exhibits good performance.
Table II
Example 1 2 3 Traction Coefficient 0.018 0.021 0Ø19 FZG Reverse (stages) 8 8 10 [0070] Each of the documents referred to above is incorporated herein by z-eference. Except in the Examples, or where otllerwise explicitly indicated, all numerical cluantities in this description specifying amounts of materials, reac-tion conditions, nlolecular weights, number of earbon atoms, and the like, are to be understood as m.odified by the word "about." Unless otherwise indicated, each chemical or composition referrecl to herein should be interpreted as beincT a commercial arade matet-ial which may contain the isomers, by-products, deriva-tives, and other such materials which are normally understood to be present in the commercial grade. However, the amount of each chemical component is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, unless otherwise indicated. It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Sirnilarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements. As used herein, the expression "consisting essentially of" permits the inclusion of substances that do not materially affect the basic and novel characteristics of the composition under consideration.

Claims (15)

1. A lubricant composition suitable for lubricating a transmission, said composition comprising:
(a) about 1 to about 20 weight percent of a compound having a traction coefficient of at least about 0.045, selected from the group consisting of:
(i) hydrocarbons containing non-aromatic cyclic structures, (ii) polybutenes of number average molecular weight about 180 to about 600, (iii) esters having a branched or non-aromatic cyclic alkyl moiety, and mixtures thereof;
(b) at least about 50 weight percent of an oil of lubricating viscosity, other than a material of component (a);
(c) a phosphorus acid or phosphorus ester or salt thereof; and (d) 2,5-dimercapto-1,3,4-thiadiazole or a derivative thereof.
said lubricant composition having a kinematic viscosity at 100 °C of up to about 12 mm2/sec.

2. The composition of claim 1 wherein the compound having a traction coefficient of at least about 0.045 is a material having a traction coefficient of about 0.05 to about 0.12.

3. The composition of claim 1 or claim 2 wherein the ester molecule (a)(iii) comprises a polyol ester having a branched or non-aromatic cyclic alkyl moiety in the acid portion thereof, or in both the alcohol and acid portions.

4. The composition of any of claims 1 through 3 wherein the compound having a traction coefficient of at least about 0.045 comprises a pentaerythritol ester.

5. The composition of any of claims 1 through 4 wherein the amount of the compound having a traction coefficient of at least about 0.045 is about 5 to about 18 percent by weight

6. The composition of any of claims 1 through 5 wherein the oil of lubricating viscosity comprises a synthetic oil.

7. The composition of any of claims claim 1 through 6 wherein at least about 50 percent by weight of the oil of lubricating viscosity is a synthetic oil.

8. The composition of claim 6 or claim 7 wherein the synthetic oil is a poly-.alpha.-olefin.

9. The composition of any of claims 1 through 8 wherein the phosphorus acid or phosphorus ester or salt of a phosphorus ester is selected from the group consisting of phosphorus acids, dialkyl hydrogen phosphites, metal or amine dihydrocarbyldithiophosphate salts, metal or amine mono- and dihydrocarbyl-phosphate salts, and mixtures thereof.

10. The composition of any of claims 1 through 9 wherein the phospho-rus acid or phosphorus ester or salt of a phosphorus ester is present in an amount to provide about 0.03 to about 0.1% by weight phosphorus to the composition.

11. The composition of any of claims 1 through 10 wherein the 2,5-dimercapto-1,3,4-thiadiazole or derivative thereof is present in an amount of about 0.05 to about 4 percent by weight.

12. The composition of any of claims 1 through 11 wherein the 2,5-dimercapto-1,3,4-thiadiazole or derivative thereof is present in an amount to provide about 0.005 to about 1% by weight sulfur to the composition.

13. The composition of any of claims 1 through 12 further comprising a viscosity index modifier.

14. A composition prepared by admixing the components of any of claims 1 through 13.

15. A method for lubricating a transmission, comprising supplying thereto the composition of any of claims 1 through 14.