LUBRICATING OILS CONTAINING ASHLESS DISPERSANT AND METAL DETERGENT ADDITIVES

Abstract: This invention relates to the use of lubricating oils containing certain ashless dispersants comprising an oil-soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer having > 30 % of terminal vinylidene unsaturation and an <o>M</o>n of from 500 to 7000, in combination with high molecular weight metal detergent additives giving sludge and varnish control, good engine cleanliness and fuel economy, prepared from an additive package with improved handling and stability properties. It particularly concerns crankcase lubricants in which the detergent additive is an overbased sulfonate having a TBN of from 250 to 450 TBN prepared from an alkaryl sulfonic acid with a number average molecular weight (<o>M</o>n) of at least 550 and having a long chain alkyl group which contains an average of at least 35 carbon atoms.

Description: Lubricating oils containing ashless dispersant and metal detergent additives This invention relates to lubricating oils containing certain ashless dispersants in combination with metal detergent additives. It particularly concerns crankcase lubricants having excellent properties of sludge and varnish control, giving good engine cleanliness and capable of providing improved fuel economy, which l;ubricants are prepared from an additive package with improved handling and stability properties. Lubricating oils used in gasoline and diesel crankcases comprise a natural and/or synthetic basestock containing one or more additives to impart desired characteristics to the lubricant. Such additives typically include ashless dispersant, metal detergent, antioxidant and antiwear components, which may be combined in a package, sometimes referred to as a detergent inhibitor (or Dl) package. The ashless dispersant operates to suspend particulates resulting from combustion or wear within the engine to prevent them depositing to form sludge or varnish in the engine. Detergents which are typically metal containing compounds act to keep the engine surfaces clean, while highly basic or overbased forms of these detergents also operate to neutralise acids formed during combustion which would otherwise cause corrosion within the engine. As engines in modern automobiles operate in an increasing severe environment, with smaller, more powerful engines operating at higher temperatures and with less frequent service intervals, the requirements for lubricants in turn become more severe. This has lead to increasing amounts of dispersants and detergents being introduced into lubricants to achieve the desired performance levels. A new class of ashless dispersants comprising functionalized and/or derivatized olefin polymers based on polymers synthesized using metallocene catalyst systems are described in US-A-5128056, 5151204, 5200103, 5225092, 5266223, 5334775; WO-A- 94/19436, 94/13709; and EP-A-440506, 440508, 513157, 513211. These dispersants are described as providing enhanced lubricating oil dispersancy as exhibited by their enhanced sludge and varnish control. They are described in lubricating oil compositions in combination with conventional additives of the general types described above including detergents such as overbased metal salts which are described in US- A-5266223 as particularly prone to interaction with ashless dispersants. Such salts include highly basic alkaline earth metal sulphonates prepared from sulphonic acids, typically obtained by alkylation of aromatic hydrocarbons. The alkylation is described as being carried out with alkylating agents having from about 3 to more than 30 carbon atoms. EP-A-1318 and US-A-4235810 describe sulphonate with reduced foaming tendency prepared from alkylaryl sulphonic acids containing from 15 to 40 carbon atoms. EP-A-164286 desribes alkaline earth metal alkylaryl sulphonates which have reduced foaming tendency. The sulphonic acid used is also described as containing 15 to 40 carbon atoms, and a molecular weight (as sodium salt) of from 400 to 600. There is a reference to use of such detergents with ashless dispersants, but no indication of the type of dispersant used in the present invention. The Examples describe an apparent molecular weight of the sulphonic acids used which appears to be a value corrected for the diluent present rather than the measured Mn of the active ingredient used. Foaming performance is indicated for the sulphonates as such and not for compositions comprising other additives such as ashless dispersant. EP-A-312313 describes overbased metal sulphonate compositions comprising at least two metal alkyl aryl sulphonates having 1 to 3 alkyl groups, one of the sulphonates having a long chain alkyl group containing an average number of carbon atoms of at least 40 while any remaining alkyl groups contain less than 10 carbon atoms, the other sulphonate having a medium chain alkyl group containing an average number of carbon atoms of 10 to 33 while any remaining alkyl groups contain less than 10 carbon atoms. The long chain alkyl groups are described as being prepared, for example, by polymerisation of propylene or butylenes, specifically n-butene, using known techniques. The overbased sulphonate compositions are described in combination with conventional additives including ashless dispersants and antifoam agents. The ashless dispersants described are various functionalised long chain hydrocarbons and borated polyisobutenyl succinimides are exemplified. Additive packages must be capable of being transported and blended with mineral or synthetic base oils to form the finished lubricating oil, which in turn must be capable of being transported and circulated within the device being lubricated. In particular a tendency of a lubricating oil to foam creates a serious problem for handling the oil, and in an engine foaming of a lubricating oil can lead to oil starvation and severe wear. Lubricants prepared from conventional ashless dispersants and metal detergents display a tendency to foam. It is generally understood that metal detergents and particularly overbased metal detergents are the main source of the foaming tendency. Antifoam additives are conventionally employed to counteract this tendency but they are not a complete answer to the problem. A badly foaming oil may require uneconomic amounts of antifoam additive to suppress the foaming tendency, or may in some instances not respond to the use of antifoams. In addition there is a limit to the amount of antifoam that can be introduced before its presence leads to undesirable visible effects such as haze or "fish-eyes", a term used to describe the formation of immiscible drops on the oil surface. The problem remains to provide lubricating oil compositions capable of providing high levels of dispersancy for combatting sludge and varnish, together with good engine cleanliness, while having reduced tendency to foaming and/or improved response to the action of antifoam additives. Foaming characteristics are measured in the ASTM D 892 IP 146 test, which can be conducted at 24°C in the case of Sequence I conditions and at 93°C in the case of the more severe Sequence II. The foaming requirements for oils are getting more severe still with the development of a Sequence IV test. Crankcase lubricants may be formulated to improve fuel economy and typically this is done by the incorporation of friction modifiers such as partial esters of fatty acids. However the use of such additional additives necessarily increases costs and may in itself introduce further problems of compatability. A further problem is to improve the fuel economy performance of crankcase lubricants, as determined by test procedures such as the Mercedes-Benz M111 engine test, with no or at least reduced levels of friction modifiers. This invention provides a lubricating oil composition prepared by combining in a lubricating oil, a metal detergent comprising: an overbased sulfonate having a TBN of from 250 to 450 TBN prepared from an alkaryl sulfonic acid, which acid has a number average molecular weight (Mn) of at least 550 and contains from 1 to 3 alkyl groups, one of the alkyl groups being a long chain alkyl group which contains an average of at least 35 carbon atoms with any remaining groups containing less than 10 carbon atoms; and an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000. The invention also provides for the use of a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn ) of at least 550, in combination with an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, to reduce the foaming tendency of the lubricating oil composition and/or to improve the response of the lubricating oil composition to antifoam additives. It further provides a process for reducing the foaming tendency of the lubricating oil composition and/or improving the response of the lubricating oil composition to antifoam additives in a crankcase of a crankcase lubricating oil comprising an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, and/or to reduce thickening of the package used to form the lubricating oil caused by interactions in that package, in which the oil is prepared from an additive package which comprises the ashless dispersant and a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn) of at least 550. The invention also provides for the use of a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (M« ) of at least 550, in combination with an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an M of from 500 to 7000, to improve the fuel economy of the lubricating oil composition. It further provides a process for improving the fuel economy of a lubricating oil composition in a crankcase of a crankcase lubricating oil, comprising an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, or to reduce thickening of the package used to form the lubricating oil caused by interactions in that package, in which the oil is prepared from an additive package which comprises the ashless dispersant and a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn ) of at least 550. DETAILED DESCRIPTION A. BASESTOCK The basestock used in the lubricating oil may be selected from any of the synthetic or natural oils used as crankcase lubricating oils for spark-ignited and compression-ignited engines. The lubricating oil base stock conveniently has a viscosity of about 2.5 to about 12 mm 2 /s and preferably about 2.5 to about 9 mm 2 /s at 100°C. Mixtures of synthetic and natural base oils may be used if desired. B. ASHLESS DISPERSANT The ashless dispersant comprises an oil soluble polymeric hydrocarbon backbone having functional groups that are capable of associating with particles to be dispersed. Typically, the dispersants comprise amine, alcohol, amide, or ester polar moieties attached to the polymer backbone often via a bridging group. The ashless dispersant may be, for example, selected from oil soluble salts, esters, amino-esters, amides, imides, and oxazolines of long chain hydrocarbon substituted mono and dicarboxylic acids or their anhydrides; thiocarboxylate derivatives of long chain hydrocarbons; long chain aliphatic hydrocarbons having a polyamine attached directly thereto; and Mannich condensation products formed by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine. The oil soluble polymeric hydrocarbon backbone used in ashless dispersants in the invention is selected from ethylene alpha-olefin (EAO) copolymers and alpha-olefin homo- and copolymers such as may be prepared using the new metallocene catalyst chemistry, having in each case a high degree, >30%, of terminal vinylidene unsaturation. The term alpha-olefin is used herein to refer to an olefin of the formula: R' I H — C =CH2 wherein R' is preferably a C-j - C*|8 alkyl group. The requirement for terminal vinylidene unsaturation refers to the presence in the polymer of the following structure: R I Poly — C =CH 2 wherein Poly is the polymer chain and R is typically a C-j - C-jβ alkyl group, typically methyl or ethyl. Preferably the polymers will have at least 50%, and most preferably at least 60%, of the polymer chains with terminal vinylidene unsaturation. The nature of the unsaturation may be determined by FTIR spectroscopic analysis, titration or C-13 NMR. The oil soluble polymeric hydrocarbon backbone may be a homopolymer (e.g., polypropylene) or a copolymer of two or more of such olefins (e.g., copolymers of ethylene and an alpha-olefin such as propylene or butylene, or copolymers of two different alpha-olefins). Other copolymers include those in which a minor molar amount of the copolymer monomers, e.g., 1 to 10 mole %, is an α,ω-diene, such as a C3 to C22 non-conjugated diolefin (e.g., a copolymer of isobutylene and butadiene, or a copolymer of ethylene, propylene and 1 ,4-hexadiene or 5-ethylidene-2-norbomene). Atactic propylene oligomer typically having Mn of from 700 to 5000 may also be used, as described in EP-A-490454, as well as heteropolymers such as polyepoxides. One preferred class of olefin polymers is polybutenes and specifically poly-n- butenes, such as may be prepared by polymerization of a C4 refinery stream. Other preferred classes of olefin polymers are EAO copolymers that preferably contain 1 to 50 mole% ethylene, and more preferably 5 to 48 mole% ethylene. Such polymers may contain more than one alpha-olefin and may contain one or more C3 to C22 diolefins. Also usable are mixtures of EAO's of varying ethylene content. Different polymer types, e.g., EAO, may also be mixed or blended, as well as polymers differing in M-. ; components derived from these also may be mixed or blended. The olefin polymers and copolymers preferably have an M, of from 700 to 5000, more preferably 2000 to 5000. Polymer molecular weight, specifically M, , can be determined by various known techniques. One convenient method is gel permeation chromatography (GPC), which additionally provides molecular weight distribution information (see W. W. Yau, J. J. Kirkland and D. D. Bly, "Modern Size Exclusion Liquid Chromatography", John Wiley and Sons, New York, 1979). Another useful method, particularly for lower molecular weight polymers, is vapor pressure osmometry (see, e.g., ASTM D3592). Particularly preferred copolymers are ethylene butene copolymers. Suitable olefin polymers and copolymers may be prepared by various catalytic polymerization processes using metallocene catalysts which are, for example, bulky ligand transition metal compounds of the formula: [ ] m M[A] n where L is a bulky ligand; A is a leaving group, M is a transition metal, and m and n are such that the total ligand valency corresponds to the transition metal valency. Preferably the catalyst is four co-ordinate such that the compound is ionizable to a 1 + valency state. The ligands L and A may be bridged to each other, and if two ligands A and/or L are present, they may be bridged. The metallocene compound may be a full sandwich compound having two or more ligands L which may be cyclopentadienyl ligands or cyclopentadienyl derived ligands, or they may be half sandwich compounds having one such ligand L. The ligand may be mono- or polynuclear or any other ligand capable of η-5 bonding to the transition metal. One or more of the ligands may π-bond to the transition metal atom, which may be a Group 4, 5 or 6 transition metal and/or a lanthanide or actinide transition metal, with zirconium, titanium and hafnium being particularly preferred. The ligands may be substituted or unsubstituted, and mono-, di-, tri, tetra- and penta-substitution of the cyclopentadienyl ring is possible. Optionally the substituent(s) may act as one or more bridges between the ligands and/or leaving groups and/or transition metal. Such bridges typically comprise one or more of a carbon, germanium, silicon, phosphorus or nitrogen atom-containing radical, and preferably the bridge places a one atom link between the entities being bridged, although that atom may and often does carry other substituents. The metallocene may also contain a further displaceable ligand, preferably displaced by a cocatalyst - a leaving group - that is usually selected from a wide variety of hydrocarbyl groups and halogens. Such polymerizations, catalysts, and cocatalysts or activators are described, for example, in US-A-4530914, 4665208, 4808561 , 4871705, 4897455, 4937299, 4952716, 5017714, 5055438, 5057475, 5064802, 5096867, 5120867, 5124418, 5153157, 5198401 , 5227440, 5241025; EP-A-129368, 277003, 277004, 420436, 520732; and WO-A-91/04257, 92/00333, 93/08199, 93/08221 , 94/07928 and 94/13715. The oil soluble polymeric hydrocarbon backbone may be functionalized to incorporate a functional group into the backbone of the polymer, or as one or more groups pendant from the polymer backbone. The functional group typically will be polar and contain one or more hetero atoms such as P, O, S, N, halogen, or boron. It can be attached to a saturated hydrocarbon part of the oil soluble polymeric hydrocarbon backbone via substitution reactions or to an olefinic portion via addition or cycloaddition reactions. Alternatively, the functional group can be incorporated into the polymer in conjunction with oxidation or cleavage of the polymer chain end (e.g., as in ozonolysis). Useful functionalization reactions include: halogenation of the polymer at an olefinic bond and subsequent reaction of the halogenated polymer with an ethylenically unsaturated functional compound (e.g., maleation where the polymer is reacted with maleic acid or anhydride); reaction of the polymer with an unsaturated functional compound by the "ene" reaction absent halogenation; reaction of the polymer with at least one phenol group (this permits derivatization in a Mannich base-type condensation); reaction of the polymer at a point of unsaturation with carbon monoxide using a Koch-type reaction to introduce a carbonyl group in an iso or neo position; reaction of the polymer with the functional izing compound by free radical addition using a free radical catalyst; reaction with a thiocarboxylic acid derivative; and reaction of the polymer by air oxidation methods, epoxidation, chloroamination, or ozonolysis. The functionalized oil soluble polymeric hydrocarbon backbone is then further derivatized with a nucleophilic reactant such as an amine, amino-alcohol, alcohol, metal compound or mixture thereof to form a corresponding derivative. Useful amine compounds for derivatizing functionalized polymers comprise at least one amine and can comprise one or more additional amine or other reactive or polar groups. These amines may be hydrocarbyl amines or may be predominantly hydrocarbyl amines in which the hydrocarbyl group includes other groups, e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazoline groups, and the like. Particularly useful amine compounds include mono- and polyamines, e.g. polyalkylene and polyoxyalkylene polyamines of about 2 to 60, conveniently 2 to 40 (e.g., 3 to 20), total carbon atoms and about 1 to 12, conveniently 3 to 12, and preferably 3 to 9 nitrogen atoms in the molecule. Mixtures of amine compounds may advantageously be used such as those prepared by reaction of alkylene dihalide with ammonia. Preferred amines are aliphatic saturated amines, including, e.g., 1,2-diaminoethane; 1 ,3- diaminopropane; 1 ,4-diaminobutane; 1 ,6-diaminohexane; polyethylene amines such as diethylene triamine; t ethylene tetramine; tetraethylene pentamine; and polypropyleneamines such as 1 ,2-propylene diamine; and di-(1 ,2-propylene)triamine. Other useful amine compounds include: alicyclic diamines such as 1 ,4- di(aminomethyl) cyclohexane, and heterocyclic nitrogen compounds such as imidazolines. A particularly useful class of amines are the polyamido and related amido-amines as disclosed in US-A-4857217, 4956107, 4963275 and 5229022. Also usable is tris(hydroxymethyl)amino methane (THAM) as described in US-A-4102798, 4113639, 4116876; and GB-A-989409. Dendrimers, star-like amines, and comb- structure amines may also be used. Similarly, one may use the condensed amines disclosed in US-A-5053152. The functionalized polymer is reacted with the amine compound according to conventional techniques as described in EP-A-208560 and US- A-4234435 and 5229022 . The functionalized oil soluble polymeric hydrocarbon backbones also may be derivatized with hydroxy compounds such as monohydric and polyhydric alcohols or with aromatic compounds such as phenols and naphthols. Polyhydric alcohols are preferred, e.g., alkylene glycols in which the alkylene radical contains from 2 to 8 carbon atoms. Other useful polyhydric alcohols include glycerol, mono-oleate of glycerol, monostearate of glycerol, monomethyl ether of glycerol, pentaerythritol, dipentaerythritol, and mixtures thereof. An ester dispersant may also be derived from unsaturated alcohols such as aliyl alcohol, cinnamyl alcohol, propargyl alcohol, 1- cyclohexane-3-ol, and oleyl alcohol. Still other classes of the alcohols capable of yielding ashless dispersants comprise the ether-alcohols and including, for example, the oxy-alkylene, oxy-arylene. They are exemplified by ether-alcohols having up to 150 oxy-alkylene radicals in which the alkylene radical contains from 1 to 8 carbon atoms. The ester dispersants may be di-esters of succinic acids or acidic esters, i.e., partially esterified succinic acids; as well as partially esterified polyhydric alcohols or phenols, i.e., esters having free alcohols or phenolic hydroxyl radicals. An ester dispersant may be prepared by one of several known methods as illustrated, for example, in US-A- 3381022. A preferred group of ashless dispersants includes those substituted with succinic anhydride groups and reacted with polyethylene amines (e.g., tetraethylene pentamine), aminoalcohols such as trismethylolaminomethane and optionally additional reactants such as alcohols and reactive metals e.g., pentaerythritol, and combinations thereof). Also useful are dispersants wherein a polyamine is attached directly to the backbone by the methods shown in US-A-3275554 and 3565804 where a halogen group on a halogenated hydrocarbon is displaced with various alkylene polyamines. Another class of ashless dispersants comprises Mannich base condensation products. Generally, these are prepared by condensing about one mole of an alkyl- substituted mono- or polyhydroxy benzene with about 1 to 2.5 moles of carbonyl compounds (e.g., formaldehyde and paraformaldehyde) and about 0.5 to 2 moles polyalkylene polyamine as disclosed, for example, in US-A-3442808. Such Mannich condensation products may include a polymer product of a metallocene cataylsed polymerisation as a substituent on the benzene group or may be reacted with a compound containing such a polymer substituted on a succinic anhydride, in a manner similar to that shown in US-A-3442808. Examples of functionalized and/or derivatized olefin polymers based on polymers synthesized using metallocene catalyst systems are described in publications identified above. The dispersant can be further post-treated by a variety of conventional post treatments such as boration, as generally taught in US-A-3087936 and 3254025. This is readily accomplished by treating an acyl nitrogen-containing dispersant with a boron compound selected from the group consisting of boron oxide, boron halides, " boron acids and esters of boron acids, in an amount to provide from about 0.1 atomic proportion of boron for each mole of the acylated nitrogen composition to about 20 atomic proportions of boron for each atomic proportion of nitrogen of the acylated nitrogen composition. Usefully the dispersants contain from about 0.05 to 2.0 wt. %, e.g. 0.05 to 0.7 wt. % boron based on the total weight of the borated acyl nitrogen compound. The boron, which appears be in the product as dehydrated boric acid polymers (primarily (HB02)3), is believed to attach to the dispersant imides and diimides as amine salts e.g., the metaborate salt of the diimide. Boration is readily carried out by adding from about 0.05 to 4, e.g., 1 to 3 wt. % (based on the weight of acyl nitrogen compound) of a boron compound, preferably boric acid, usually as a slurry, to the acyl nitrogen compound and heating with stirring at from 135° to 190° C, e.g., 140°-170° C, for from 1 to 5 hours followed by nitrogen stripping. Alternatively, the boron treatment can be carried out by adding boric acid to a hot reaction mixture of the dicarboxylic acid material and amine while removing water. C. METAL DETERGENTS Metal detergents or ash-forming detergents function both as detergents to reduce or remove deposits and as acid neutralizers or rust inhibitors, thereby reducing wear and corrosion and extending engine life. Detergents generally comprise a polar head with a long hydrophobic tail, with the polar head comprising a metal salt of an acidic organic compound, sometimes referred to as "soap". The processes and uses of the present invention employ a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn) of at least 550. These may be neutral or overbased metal salts. The acidic organic compound will typically have a number average molecular weight (M n ) of greater than 600, e.g. at least 650, and preferably not more than 3000. Most preferably the M, of the acidic organic compound is from greater than 600 to 1000. The term "number average molecular weight (Mn)" used herein refers to the measured molecular weight of the active ingredient of the acidic organic compound used, and not to an "apparent" molecular weight, corrected for the amount of diluent as the term is used in EP-A-164286. Mn may be measured by the techniques described above. Salts containing a substantially stoichiometric amount of the metal are usually described as normal or neutral salts, and would typically have a metal ratio at or close to 1 (where metal ratio is the total equivalents of metal to equivalents of acidic organic compound). The total base number or TBN (as may be measured by ASTM D2896) of such neutral salts will depend on the specific acidic organic compound but for a sulphonate would typically be close to zero. Neutral phenates and sulphurised phenates can theoretically have TBNs of as high as 200, but typically for such (sulphurised) phenates the TBN would be less than 100. Overbased metal salts include large amounts of a metal base formed by reacting an excess of a metal compound such as an oxide or hydroxide with an acidic material, usually a gas such as carbon dioxide. The resulting overbased detergent comprises neutralised detergent as the outer layer of a metal base (e.g. carbonate) micelle. Such overbased detergents have a metal ratio greater than 1 , and typically from 2 to 50. It is usual to refer to the TBN of such overbased materials and they may have a TBN of 150 or greater, and typically of from 250 to 450 or more. Metal salts which may be used in the invention as detergents include oil-soluble or oil-dispersable neutral or overbased sulfonates, phenates, sulfurized phenates, thiophosphonates, salicylates, and naphthenates and other oil-soluble or oil- dispersable carboxylates of a metal, and it is preferred to use a salt of an alkali metal, e.g., sodium, potassium or lithium, or of an alkaline earth metal, e.g., calcium or magnesium. Mixtures of such salts may also be used. The most preferred salts are one or more alkaline earth metal salts and mixtures of alkaline earth metal salts with sodium salts. Overbased metal salts may be present as the only detergents used in a lubricant, or in mixtures with other detergents such as the neutral metal salts. Particularly convenient metal detergents are overbased sulfonates and/or carboxylates having a TBN of from 250 to 450 TBN, and overbased phenates, sulfurized phenates and salicylates having TBN of from 150 to 500, used alone or in mixtures. Sulfonates may be prepared from sulfonic acids having a number average molecular weight (Mn) of at least 550, typically greater than 600, preferably of not more than 3000, and most preferably of from greater than 600 to 1000. Such sulphonic acids are typically obtained by the sulfonation of alkyl substituted aromatic hydrocarbons such as those obtained from the fractionation of petroleum or by the alkylation of aromatic hydrocarbons. Examples included those obtained by alkylating benzene, toluene, xylene, naphthalene, diphenyl or their halogen derivatives such as chlorobenzene, chlorotoluene and chloronaphthalene. The alkylation may be carried out in the presence of a catalyst with alkylating agents typically having from 3 to more than 70 carbon atoms to form a sulphonic acid having the desired molecular weight. The lubricating compositions of the invention comprise an overbased sulfonate having a TBN of from 250 to 450 TBN prepared from an alkaryl sulfonic acid, which acid has a number average molecular weight (Mn ) of at least 550 and contains from 1 to 3 alkyl groups, one of the alkyl groups being a long chain alkyl group which contains an average of at least 35 carbon atoms with any remaining groups containing less than 10 carbon atoms. These preferred alkaryl sulfonic acids preferably contain a long chain alkyl group having from 35 to 80 carbon atoms, and most preferably from 35 to 60 carbon atoms. The sulphonic acids typically contain a mixture of long chain alkyl groups of different chain lengths, having the preferred average chain length discussed above and preferably a mixture of alkyl groups of from 16 to 60 carbon atoms or greater, and thus including longer chain moieties than discussed in the prior art such as EP-A-1318, US-A-4235810 and EP-A-164286 which disclose groups of only 15 to 40 carbon atoms. Preferably the long chain alkyl group is a branched alkyl group derived from a polyalkene such as a homo- or copolymer of an olefin having from 2 to 18 carbon atoms - e.g., propene, a butene or another alpha-olefin as defined hereinbefore. Poly-n-butenes are particularly preferred. The polyalkenes may also be prepared using a metallocene catalyst as described above in relation to the ashless dispersant. The oil soluble sulfonates or alkaryl sulfonic acids may be neutralized with oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides, hydrosulfides, nitrates, borates and ethers of the desired metal. The amount of metal compound is chosen having regard to the desired TBN of the final product. Calcium and magnesium sulfonates are highly preferred. Metal carboxylates may be prepared in a number of ways: for example, by adding a basic metal compound to a reaction mixture comprising a carboxylic acid having a number average molecular weight (Mn ) of at least 550 (typically of not more than 3000, and preferably of from greater than 600 to 1000, which may be part of a mixture with another organic acid such as a sulfonic acid) or its metal salt and promoter, and removing free water from the reaction mixture to form an metal salt, then adding more basic metal compound to the reaction mixture and removing free water from the reaction mixture. The carboxylate is then overbased by introducing the acidic material such as carbon dioxide to the reaction mixture while removing water. This can be repeated until a product of the desired TBN is obtained. The carboxylic acids from which metal overbased salts may be prepared include aliphatic, cycloaliphatic and aromatic mono- and polybasic carboxylic acids. Aliphatic carboxylic acids may be saturated or unsaturated, and include fatty acids such as, for example, polyalkene-substituted carboxylic acids prepared by reacting a pσlyalkene with an α, β-unsaturated acid or its anhydride such as maleic anhydride. The number average molecular weight of the polyalkenes may be from 400, those having Mn of from 500 to 3000 are most preferred. The polyalkenes is preferably branched as described above in relation to the preferred alkylating group for the alkaryl sulphonic acids. Hydrocarbyl-substituted succinic acids, and particularly poly-n-butenyl succinic acids and anhydrides, are a preferred class of carboxylates which may be used to prepared the alkali metal overbased salts. Aromatic carboxylic acids which may be employed are aliphatic subtituted aromatic groups having one or more carboxy substituents and optionally one or more hydroxy or thiol subtituents. Specific examples of aromatic carboxylic acids include substituted benzoic, phthalic and salicylic acids. Preferred aliphatic substituents on the aromatic nucleus are those described above in relation to sulphonic acids. Combinations of sulphonic acids and carboxylic acids may be employed and the preferred sulphonic acids are those described hereinbefore in connection with overbased sulfonates. Metal salts of phenols and sulfurised phenols are prepared by reaction with an appropriate metal compound such as an oxide, hydroxide or alkoxide and overbased products may be obtained by methods well known in the art. Sulfurised phenols may be prepared by reacting a phenol with sulfur or a sufur containing compound such as hydrogen sulfide, sulfur monohalide or sulfur dihalide, to form products which are generally mixtures of compounds in which 2 or more phenols are bridged by sulfur containing bridges. The phenol used for preparing the metal detergents for the invention have a number average molecular weight (Mn ) of at least 550, typically of not more than 3000, and preferably of from greater than 600 to 1000, and these are preferably aliphatic-substituted phenols wherein the aliphatic substituents are preferably as defined above in relation to the preferred sulphonic acids. The overbasing process is well known in the art and typically comprises reacting acidic material with a reaction mixture comprising the organic acid or its metal salt and a metal compound. That acidic material may be a gas such as carbon dioxide or sulphur dioxide, or as discussed below may be boric acid. The overbased alkali metal detergents can be borated. The boron may be introduced by using boric acid as the acidic material used in the overbasing step. However a preferred alternative is to borate the overbased product after formation by reacting a boron compound with the overbased alkali metal salt. Boron compounds include boron oxide, boron oxide hydrate, boron trioxide, boron trifluoride, boron tribromide, boron trichloride, boron acid such as boronic acid, boric acid, tetraboric acid and metaboric acid, boron hydrides, boron amides and various esters of boron acids. Boric acid is preferred. Generally, the overbased metal salt may be reacted with a boron compound at from 50°C to 250°C, in the presence of a solvent such as mineral oil or xylene. A borated overbased metal salt preferably comprises at least 0.5%, preferably from 1 % to 5%, by weight boron. D. OTHER COMPONENTS Additional additives are typically incorporated into the compositions of the present invention. Examples of such additives are viscosity modifiers, antioxidants, anti-wear agents, friction modifiers, rust inhibitors, anti-foaming agents, demulsifiers, and pour point depressants. The viscosity modifier (VM) functions to impart high and low temperature operability to a lubricating oil. The VM used may have that sole function, or may be multifunctional (MFVM). Multifunctional viscosity modifiers that also function as dispersants are also known and may be prepared as described above for ashless dispersants. The oil soluble polymeric hydrocarbon backbone will usually have a M, of from 20,000, more typically from 20,000 up to 500,000 or greater. In general, these dispersant viscosity modifiers are functionalized polymers (e.g. inter polymers of ethylene-propylene post grafted with an active monomer such as maleic anhydride) which are then derivatized with, for example, an alcohol or amine. Suitable compounds for use as monofunctional viscosity modifiers are generally high molecular weight hydrocarbon polymers, including polyesters. Oil soluble viscosity modifying polymers generally have weight average molecular weights of from about 10,000 to 1 ,000,000, preferably 20,000 to 500,000, which may be determined by gel permeation chromatography (as described above) or by light scattering. Representative examples of suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene and higher alpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, inter polymers of styrene and acrylic esters, and partially hydrogenated copolymers of styrene/ isoprene, styrene/butadiene, and isoprene/butadiene, as well as the partially hydrogenated homopolymers of butadiene and isoprene and isoprene/divinylbenzene. The viscosity modifier used in the invention will be used in an amount to give the required viscosity characteristics. Since they are typically used in the form of oil solutions the amount of additive employed will depend on the concentration of polymer in the oil solution comprising the additive. However by way of illustration, typical oil solutions of polymer used as VMs are used in amount of from 1 to 30% of the blended oil. The amount of VM as active ingredient of the oil is generally from 0.01 to 6 wt%, and more preferably from 0.1 to 2 wt%. Dihydrocarbyl dithiophosphate metal salts are frequently used as anti-wear and antioxidant agents. The metal may be an alkali or alkaline earth metal, or aluminum, lead, tin, molybdenum, manganese, nickel or copper. The zinc salts are most commonly used in lubricating oil in amounts of 0.1 to 10, preferably 0.2 to 2 wt. %, based upon the total weight of the lubricating oil composition. They may be prepared in accordance with known techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually by reaction of one or more alcohol or a phenol with P2S5 and then neutralizing the formed DDPA with a zinc compound. For example, a dithiophosphoric acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely primary in character. To make the zinc salt any basic or neutral zinc compound could be used but the oxides, hydroxides and carbonates are most generally employed. Commercial additives frequently contain an excess of zinc due to use of an excess of the basic zinc compound in the neutralization reaction. The preferred zinc dihydrocarbyl dithiophosphates are oil soluble salts of dihydrocarbyl dithiophosphoric acids and may be represented by the following formula: wherein R and R" may be the same or different hydrocarbyl radicals containing from 1 to 18, preferably 2 to 12, carbon atoms and including radicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R and R' groups are alkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, for example, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl, propenyl, butenyl. In order to obtain oil solubility, the total number of carbon atoms (i.e. R and R') in the dithiophosphoric acid will generally be about 5 or greater. The zinc dihydrocarbyl dithiophosphate can therefore comprise zinc dialkyl dithiophosphates. Conveniently at least 50 (mole) % of the alcohols used to introduce hydrocarbyl groups into the dithiophosphoric acids are secondary alcohols. Oxidation inhibitors or antioxidants reduce the tendency of mineral oils to deteriorate in service which deterioration can be evidenced by the products of oxidation such as sludge and varnish-like deposits on the metal surfaces and by viscosity growth. Such oxidation inhibitors include hindered phenols, alkaline earth metal salts of alkylphenolthioesters having preferably C5 to C12 alkyl side chains, calcium nonylphenol sulfide, ashless oil soluble phenates and sulfurized phenates, phosphosulfurized or sulfurized hydrocarbons, phosphorous esters, metal thiocarbamates, oil soluble copper compounds as described in US-A-4867890, and molybdenum containing compounds. Typical oil soluble aromatic amines having at least two aromatic groups attached directly to one amine nitrogen contain from 6 to 16 carbon atoms. The amines may contain more than two aromatic groups. Compounds having a total of at least three aromatic groups in which two aromatic groups are linked by a covalent bond or by an atom or group (e.g., an oxygen or sulfur atom, or a -CO-, -SO2- or alkylene group) and two are directly attached to one amine nitrogen are also considered aromatic amines. The aromatic rings are typically substituted by one or more substituents selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl, acylamino, hydroxy, and nitro groups. The invention may provide improved fuel economy without the use of additional additives, but to achieve further improvement it may be desirable to include friction modifiers, though generally at a reduced level as compared to conventional treatments. Oil-soluble alkoxylated mono- and diamines are well known to improve boundary layer lubrication. The amines may be used as such or in the form of an adduct or reaction product with a boron compound such as a boric oxide, boron halide, metaborate, boric acid or a mono-, di- or trialkyl borate. Other friction modifiers include esters formed by reacting carboxylic acids and anhydrides with alkanols, and other conventional friction modifiers generally consisting of a polar terminal group (e.g. carboxyl or hydroxyl) covalently bonded to an oleophillic hydrocarbon chain. Esters of carboxylic acids and anhydrides with alkanols are described in US-A-4702850. Examples of other conventional friction modifiers are described by 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. Rust inhibitors selected from the group consisting of nόnionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids may be used. Copper and lead bearing corrosion inhibitors may be used. Typically such compounds are the thiadiazole polysulfides containing from 5 to 50 carbon atoms, their derivatives and polymers thereof. Derivatives of 1 ,3,4 thiadiazoies such as those described in US-A-2719125, 2719126 and 3087932 are typical. Other similar materials are described in US-A-3821236, 3904537, 4097387, 4107059, 4136043, 4188299 and 4193882. Other additives are the thio and polythio sulfenamides of thiadiazoies such as those described in GB-A-1560830. Benzotriazoles derivatives also fall within this class of additives. A small amount of a demulsifying component may be used. A preferred demulsifying component is described in EP-A-330522. It is obtained by reacting an alkylene oxide with an adduct obtained by reacting a bis-epoxide with a polyhydric alcohol. The demulsifier should be used at a level not exceeding 0.1 mass % active ingredient. A treat rate of 0.001 to 0.05 mass % active ingredient is convenient. Pour point depressants, otherwise known as lube oil flow improvers, lower the minimum temperature at which the fluid will flow or can be poured. Such additives are well known. Typical of those additives which improve the low temperature fluidity of the fluid are CQ to C-js dialkyl fumarate/vinyl acetate copolymers and polyalkylmethacrylates. To improve the compatabiiity of the ashless dispersants described herein with elastomer seals used in engines, and particularly with fluorocarbon seals such as Viton seals, it may be desirable to employ a seal compatabiiity aid with those ashless dispersants, and such aids may be used in the compositions of the invention. A number of materials have been described for use generally as seal compatabiiity aids and may be used with the ashless dispersants described herein. Particularly suitable are acylating agents such as carboxylic acids and anhydrides or derivatives thereof. Typical aids include dicarboxylic acids and anhydrides including fumaric acid, maleic anhydride and hydrocarbyl substituted succinic anhydrides wherein the hydrocarbyl group is, for example, an alkyl or alkenyl group having from 8 to 200 carbon atoms. Polybutenyl succinic anhydrides and dodecyl or tetrapropenyl succinic anhydride are particularly preferred. The compositions of the invention are intended to address the problem of foam control of lubricants, particularly in an engine. In some instances the compositions of the invention have inherently better foam performance, but where even better foam control is desired it may be achieved by the addition of conventional antifoamants, such as those of the polysiloxane type - for example, silicone oil or polydimethyl siloxane. Compositions of the invention have shown improved response to such antifoamants so that foam control may in some instances be achieved with a smaller treat rate of antifoamant, or a better overall foam performance may be achieved with a given antifoamant treat rate. Some of the above-mentioned additives can provide a multiplicity of effects; thus for example, a single additive may act as a dispersant-oxidation inhibitor. This approach is well known and does not require further elaboration. When lubricating compositions contain one or more of the above-mentioned additives, each additive is typically blended into the base oil in an amount which enables the additive to provide its desired function. Representative effective amounts of such additives, when used in crankcase lubricants, are listed below. All the values listed are stated as mass percent active ingredient. ADDITIVE MASS % MASS % (Broad) (Preferred) Ashless Dispersant 0.1 - 20 1 - 8 Metal detergents 0.1 - 15 0.2 - 9 Corrosion Inhibitor 0 - 5 0 - 1.5 Metal dihydrocarbyl dithiophosphate 0.1 - 6 0.1 - 4 Supplemental anti-oxidant 0 -5 0.01 - 1.5 Pour Point Depressant 0.01 - 5 0.01- 1.5 Anti-Foaming Agent 0 - 5 0.001-0.15 Supplemental Anti-wear Agents 0 - 0.5 0 - 0.2 Friction Modifier 0 - 3 0 - 1 Viscosity Modifier- 0.01- 6 0 - 4 Mineral or Synthetic Base Oil Balance Balance Note: 1 In a multigrade oil The components may be incorporated into a base oil in any convenient way. Thus, each of the components can be added directly to the oil by dispersing or dissolving it in the oil at the desired level of concentration. Such blending may occur at ambient temperature or at an elevated temperature. Preferably all the additives except for the viscosity modifier and the pour point depressant are blended into a concentrate or additive package described herein as the detergent inhibitor package, that is subsequently blended into basestock to make finished lubricant. Use of such concentrates is conventional. The concentrate will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration in the final formulation when the concentrate is combined with a predetermined amount of base lubricant. Preferably the concentrate is made in accordance with the method described in US 4,938,880. That patent describes making a premix of ashless dispersant and metal detergents that is pre-blended at a temperature of at least about 100°C. Thereafter the pre-mix is cooled to at least 85°C and the additional components are added. The final formulations may employ from 2 to 15 mass % and preferably 5 to 10 mass %, typically about 7 to 8 mass % of the concentrate or additive package with the remainder being base oil. The compositions of the invention suprisingly enable the enhanced dispersancy of the ashless dispersants to be realised in an oil having excellent detergent properties which may provide a higher resistance to foaming, than a formulation containing the ashless dispersant in combination with lower molecular weight metal salts as detergents. The invention will now be described by way of illustration only with reference to the following examples. In the examples, unless otherwise noted, all treat rates of all additives are reported as mass percent active ingredient, and amounts expressed inparts are parts by weight. EXAMPLES The foaming tendency of compositions of the invention is demonstrated in the following tests where compositions of the invention are tested in foaming tests against comparative formulations in which conventional polyisobutenyl succinimides are used as ashless dispersants and/or conventional metal salts are used as detergents. Foaming tests The foaming tests employed are the Sequence I and Sequence II procedures for determining foaming characteristics of lubricating oils under ASTM D 892 IP 146, in which a sample is blown with air under specified conditions for 5 minutes and the volume of foam is recorded. The sample is left to settle for 10 minutes and the volume of foam is again recorded. The difference between Sequence I and II is in the temperature at which the test is conducted: 24°C in the case of Seq. I and 93°C in the case of Seq. II. The results are quoted in the Table below as: foam volume (ml) after blowing (foaming tendency) / foam volume (ml) after settling (foam stability) Examples 1-4 and Comparative Examples A to L The samples tested comprised 2 mass % of metal detergent additive (comprising a stable oil dispersion of an overbased calcium or magnesium sulphonate) and 6 mass % ashless dispersant additive (comprising an oil solution of the active material) in SIS 3453 base oil, with and without the addition of 400ppm of a conventional silicone antifoam, Dow Corning DC200, 12500 cSt antifoam. The ashless dispersant was preblended with the base oil for 1 hour at 60°C and then the metal detergent was added. In samples containing antifoam this was preblended with the metal detergent for 1 hour at 60°C. The results are set out in Table 1 below. Table 1 | Foam stability | Ashless Metal Example Antifoam dispersant deterqent Sec| 1 (23C) Seq II (93C) 1 EBCO/PAM 0 Ca-1 190/15 240/0 2 EBCO/PAM 400ppm Ca-1 0/0 0/0 A PIBSA PAM 0 Ca-1 45/20 170/0 B PIBSA/PAM 400ppm Ca-1 0/0 0/0 C EBCO/PAM 0 Ca-2 450/160 650/130 D EBCO/PAM 400ppm Ca-2 0/0 0/0 E PIBSA/PAM 0 Ca-2 250/40 400/0 F PIBSA PAM 400ppm Ca-2 0/0 0/0 3 EBCO/PAM 0 Mg-1 320/200 160/0 4 EBCO PAM 400ppm Mg-1 20/10 100/0 G PIBSA PAM 0 Mg-1 300/120 140/0 H PIBSA/PAM 400ppm Mg-1 20/0 30/0 I EBCO/PAM 0 Mg-2 450/410 700/520 J EBCO/PAM 400ppm Mg-2 10/0 230/0 K PIBSA/PAM 0 Mg-2 350/280 600/380 L PIBSA/PAM 400ppm Mg-2 10/0 240/0 The ashless dispersants used are: PIBSA/PAM = a conventional borated polyisobutenyl succinimide prepared from a polyisobutene having an Mn of 2225; and EBCO/PAM = an ashless dispersant as required by the present invention prepared from an ethylene-butene copolymer having an Mn of 3250, an ethylene content of 46% and a terminal vinylidene content of 66%, functionalised by a carbonyl group introduced by the Koch reaction, and subsequently aminated and then borated, as described in WO-A-94/13709. The metal detergents used are: Mg-1 = 400TBN overbased magnesium sulfonate containing 26% soap, prepared from a poly-n-butene-substituted benzene sulphonic acid having an M of 682, by a process as taught by WO-A-92/20694; Mg-2 = 400TBN overbased magnesium sulfonate containing 26% soap, prepared by a similar process to Mg-1 but from mixed sulphonic acids comprising C*|8 straight chain alkyl substituted benzene sulphonic acid and 0*15.33 branched chain alkyl substituted benzene sulphonic acid, the mixed acids having an Mn of 480; Ca-1 = 300TBN overbased calcium sulfonate containing 29% soap, prepared from the same poly-n-butene-substituted benzene sulphonic acid as Mg-1 , but by a process as taught by EP-A-264; and Ca-2 = 300TBN calcium sulphonate comprising 29% soap prepared from the same sulphonic acid as used in the preparation of Mg-2, but by a process as taught by EP-A-264. These results show that the compositions of the invention show a reduced foaming tendency and/or improved response to antifoamant, as compared to the comparative formulations so enabling the dispersant benefits of the EBCO/PAM ashless dispersants to be more readily deployed in lubricating particularly crankcases of gasoline and diesel engines. It is particularly suprising that the compositions of the invention containing overbased magnesium sulphonates perform so well under the Seq. II conditions, as the conventional compositions show that the high temperature conditions are more severe and that in general magnesium containing formulations are more prone to foam. Example 5 and Comparative Examples M and N Fuel economy testing was carried out in a Mercedes-Benz M1 1 1 engine using a procedure designed to mimic industry cycles ECE15 and EUDC. The same procedure was adopted in each test. The tests were carried out on a series of SAE 10W/40 lubricating oils containing ashless dispersant, a metal detergent system comprising calcium and magnesium overbased sulphonates and neutral calcium sulphonate and phenate, zinc dialkyldithiophosphates, antioxidants, and antifoam demulsifier and seal compatabiiity additives in identical amounts by weight. The fuel consumption of the engine was measured when being lubricated by each of the oils, and the results are expressed in terms of percentage fuel economy credit versus an SAE 15W/40 industry reference oil RL191. In Example 5 of the invention the ashless dispersant was: EBCO/PAM-2 = an ashless dispersant as required by the present invention prepared from an ethylene-butene copolymer having an Mn of 1560 and an ethylene content of 42% and a terminal vinylidene content of about 63%, functionalised by a carbonyl group introduced by the Koch reaction, and subsequently aminated and then borated, as described in WO-A-94/13709. The overbased sulphonates were Mg-1 and Ca-1. The neutral calcium sulphonate was: nCa-1 = a neutral calcium sulphonate prepared from the same sulphonic acid as used in preparing Ca-1 and Mg-1. In Comparative Examples M and N either the ashless dispersant was replaced by PIBSA/PAM or the overbased sulphonates and neural sulphonate were replaced by Mg-2 and Ca-2, and nCa-2, respectively as indicated in Table 2 below. Table 2 Example M N 5 Ashless dispersant EBCO/PAM-2 PIBSA/PAM EBCO/PAM-2 Overbased Mg sulphonate Mg-2 Mg-1 Mg-1 Overbased Ca sulphonate Ca-2 Ca-1 Ca-1 Neutral Ca sulphonate nCa-2 nCa-1 nCa-1 Result (% credit vs. RL191) 1.32 1.46 1.75 The results show that the composition of the invention gave a significant fuel economy improvement in the M111 test relative to the reference oil, better than was achieved by the comparative examples using either the EBCO/PAM-2 dispersant with lower molecular weight sulphonates, or the conventional PIBSA/PAM dispersant.

Claims: CLAIMS 1. A lubricating oil composition prepared by combining in a lubricating oil, a metal detergent comprising: an overbased sulfonate having a TBN of from 250 to 450 TBN prepared from an alkaryl sulfonic acid, which acid has a number average molecular weight (Mn ) of at least 550 and contains from 1 to 3 alkyl groups, one of the alkyl groups being a long chain alkyl group which contains an average of at least 35 carbon atoms with any remaining groups containing less than 10 carbon atoms; and an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000. 2. A composition as claimed in claim 1 , in which the hydrocarbon backbone is derived from an EAO copolymer containing 1 to 50 wt.% ethylene. 3. A composition as claimed in claim 2, in which the hydrocarbon backbone is derived from an EAO copolymer containing 5 to 48 wt.% ethylene. 4. A composition as claimed in any of claims 1 to 3, in which the olefin polymer has an 5. A composition as claimed in claim 4, in which the olefin polymer has an Mn of from 2000 to 5000. 6. A composition as claimed in any of the preceding claims, in which the olefin polymer is an ethylene butene copolymer containing from 5 to 48% ethylene. 7. A composition as claimed in any of the preceding claims, in which the olefin polymer is prepared by a catalytic polymerization process using a metallocene catalyst which is a bulky ligand transition metal compound of the formula: [L]mM[A] n where L is a bulky ligand; A is a leaving group, M is a transition metal, and m and n are such that the total ligand valency corresponds to the transition metal valency. 8. A composition as claimed in any of the preceding claims, in which the sulphonic acid has a number average molecular weight (Mn ) of from greater than 600 to 1000. 9. A composition as claimed in any of the preceding claims, in which the long chain alkyl group has an average of from 35 to 80 carbon atoms, and preferably from 35 to 60 carbon atoms. 10. A composition as claimed in claim 9, in which the long chain alkyl group is a branched alkyl group derived from a homo- or copolymer of an olefin having from 2 to 18 carbon atoms. 11. A composition as claimed in claim 10, in which the long chain alkyl group is a poly- n-butene. 12. The use of a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn ) of at least 550, in combination with an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, to reduce the foaming tendency of the lubricating oil composition or to improve the response of the lubricating oil composition to antifoam additives. 13. A process for reducing the foaming tendency of the lubricating oil composition or improving the response of the lubricating oil composition to antifoam additives in a crankcase of a crankcase lubricating oil comprising an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, or to reduce thickening of the package used to form the lubricating oil caused by interactions in that package, in which the oil is prepared from an additive package which comprises the ashless dispersant and a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight ( > ) of at least 550. 14. The use of a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn) of at least 550, in combination with an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, to improve the fuel economy of the lubricating oil composition. 15. A process for improving the fuel economy of a lubricating oil composition in a crankcase of a crankcase lubricating oil, comprising an ashless dispersant comprising an oil soluble polymeric hydrocarbon backbone having functional groups in which the hydrocarbon backbone is derived from an ethylene alpha-olefin (EAO) copolymer or alpha-olefin homo- or copolymer and the hydrocarbon backbone has >30% of terminal vinylidene unsaturation and an Mn of from 500 to 7000, or to reduce thickening of the package used to form the lubricating oil caused by interactions in that package, in which the oil is prepared from an additive package which comprises the ashless dispersant and a metal detergent comprising a metal salt of an acidic organic compound, which compound has a number average molecular weight (Mn ) of at least 550.

Inventors: ADAMS DAVID ROBERT, CLEVERLEY JOHN ARTHUR, MACDONALD ISABEL PETRINA, ADAMS, DAVID, ROBERT, CLEVERLEY, JOHN, ARTHUR, MACDONALD, ISABEL, PETRINA
Applicants: ADAMS DAVID ROBERT, CLEVERLEY JOHN ARTHUR, EXXON CHEMICAL PATENTS INC, MACDONALD ISABEL PETRINA, ADAMS, DAVID, ROBERT, CLEVERLEY, JOHN, ARTHUR, EXXON CHEMICAL PATENTS INC., MACDONALD, ISABEL, PETRINA
Application year: 1995
Main classification: C10M163
IPC codes: C10M163, C10N30, C10N40, F02B77