Lubricating oil additives

Abstract

 Alkali metal detergents, particularly sodium-containing detergents, for example, a sodium thiophosphonate, may be used to enhance the action of an antiwear agent, especially a zinc dihydrocarbyl dithiophosphate, in a lubricating oil particularly a crankcase lubricating oil. In particular, low temperature wear as measured by the Peugeot TU3 test may be reduced.

Description

[0001] This invention relates to additives for lubricating oils, especially crankcase lubricating oils, and more particularly relates to additives for enhancing the action of antiwear agents, especially additives for promoting a reduction in wear when an engine is operating at low temperatures.

[0002] Crankcase lubricating oils normally contain one or more antiwear agents, that is, agents which reduce the wear of metal parts. Commonly used antiwear agents include dihydrocarbyl dithiophosphate metal salts, the zinc salts being the most widely used. Such zinc salts, known as ZDDPs, may be prepared by, for example, first forming a dithiophosphoric acid, usually by reaction of an alcohol or a phenol with P₂S₅, and then neutralising the dithiophosphoric acid with a zinc compound, for example, zinc oxide, zinc hydroxide or zinc carbonate, optionally in the presence of a promoter. Typical ZDDPs used as antiwear agents in crankcase lubricants have the formula Zn[SP(S)(OR)(OR¹)]₂ where R and R¹ may be the same or different hydrocarbyl radicals containing from 1 to about 18 carbon atoms.

[0003] Although ZDDPs have proved to be very satisfactory antiwear agents for many purposes, there still remains a need to impart adequate low temperature antiwear properties to crankcase lubricants because lubricants containing ZDDPs have been found to fail tests in which the lubricants are evaluated at low temperatures and low speeds. Tests carried out under such conditions simulate those in an engine while it is warming up.

[0004] The applicants have now surprisingly found that certain detergents may be used to enhance the action of antiwear agents in lubricating oils, particularly crankcase lubricating oils, and in particular may be used in the reduction of low temperature wear.

[0005] The term "detergent" as used herein refers to a salt of an acidic organic compound, the salt having a hydrophilic portion and a hydrophobic portion such that it is capable of acting as a surfactant. The detergents with which the invention is concerned are those suitable for use in lubricating oils, and include neutral and overbased metal salts of organic acids, for example, neutral and overbased sulphonates, phenates, phosphonates, thiophosphonates, salicylates and naphthenates.

[0006] The present invention accordingly provides the use of an alkali metal detergent for enhancing the action of an antiwear agent in a lubricating oil, especially a crankcase lubricating oil.

[0007] The invention further provides the use of an alkali metal detergent for improving the low temperature wear properties of a lubricating oil, particularly a crankcase lubricating oil, containing an antiwear agent.

[0008] The invention also provides the use of an alkali metal detergent as a lubricating oil additive, especially a crankcase lubricating oil additive, for reducing wear when operating at low temperatures, the lubricating oil also containing an antiwear agent.

[0009] The invention more particularly provides the use of an alkali metal detergent to enable a crankcase lubricating oil containing an antiwear agent to meet the Peugeot TU3 test requirements. More especially, the invention provides the use of an alkali metal detergent as a crankcase lubricant additive to reduce valve train wear and follower scuffing as measured by the Peugeot TU3 engine test (Test Method CEC L-38-T-87), the lubricant also containing an antiwear agent.

[0010] The alkali metal detergents used in accordance with the invention are particularly useful in connection with the reduction of low temperature wear, more especially in connection with the reduction of valve train wear and follower scuffing when an engine is operating at low temperatures, for example, the temperatures prevailing before the engine has reached its normal operating temperature, and will primarily be described herein in connection with such use. The invention extends, however, to the use of the alkali metal detergents for enhancing the action of antiwear agents at other temperatures and/or for other parts of the engine. The invention also extends to the use of the detergents for enhancing the action of antiwear agents in lubricating oils other than crankcase oils.

[0011] An automotive engine will typically operate, when at its normal running temperature, at a lubricant temperature in the range of from 80 to 150°C. At the beginning of the warming-up period, however, the lubricant temperature will be lower and, on a cold day, may be as low as 0°C or below. Tests for evaluating engine wear at low temperatures, therefore, are typically run at least in part at lubricant temperatures in the range of from 20 to 80°C, these temperatures normally being measured in the main oil gallery.

[0012] Engine data and test conditions for the Peugeot TU3 test (Test Method CEC L-38-T-87) referred to above are summarized in Tables I and II respectively. This test evaluates the ability of an oil to protect the valve train of the engine, and measures follower (rocker pad) scuffing (which is given a visual merit rating) and cam wear (measured directly from a notional line extending longitudinally along the surface of the cam at the cam nose). The test specifies maximum figures of 20 µm and 15 µm respectively for maximum cam wear and average cam wear over the test period, and a minimum figure of 7.5 merits for average follower scuffing (assessed visually on a scale of 0 (worst) to 10 (best)).

[0013] Any antiwear agent may be used in accordance with the invention. The antiwear agent is preferably soluble or stably dispersible in oil in the absence of the alkali metal detergent used to enhance its antiwear properties. Further, the antiwear agent is preferably in the form of a finished additive when it is mixed with the detergent additive(s) used in the fully formulated oil; that is, the antiwear agent is preferably not formed in the presence of a or the detergent additive used in the fully formulated oil.

[0014] The preferred antiwear agents are the dihydrocarbyl dithiophosphate metal salts referred to above, particularly ZDDPs. Especially preferred are ZDDPs of the formula Zn[SP(S)(OR)(OR¹)]₂ wherein R and R¹ may be the same or different hydrocarbyl radicals containing from 1 to 18, and preferably 2 to 12, carbon atoms, for example, alkyl, alkenyl, aryl, aralkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R and R¹ radicals are alkyl radicals having 2 to 8 carbon atoms. Examples of radicals which R and R¹ may represent are ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-heptyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl, propenyl and butenyl radicals. In order to obtain oil solubility, the total number of carbon atom in R and R¹ will generally be about 5 or greater.

[0015] The antiwear agent used in accordance with the invention is used in such an amount that, when the detergent additive according to the invention is also present, antiwear properties are imparted to the base fluid. Typically, the antiwear agent may be present in an amount of from 0.001 to 5, preferably 0.001 to 1.5, mass % active ingredient based on the final oil.

[0016] The use of an alkali metal detergent as an additive in accordance with the invention may in some circumstances make it possible to reduce the amount of the antiwear agent, for example the ZDDP, to a level less than that typically used for imparting antiwear properties. Alternatively, or in addition, the use of an additive in accordance with the invention may make it possible to use a less active antiwear agent, for example, a ZDDP containing a lower proportion of hydrocarbyl groups derived from secondary alcohols.

[0017] The alkali metal detergents used in accordance with the invention, which should be oil-soluble or stable in oil dispersion, include, for example, alkali metal sulphonates, phenates, phosphonates, thiophosphonates, salicylates and naphthenates. The salts contain a polar head (the salt-forming group) and one or more groups which together have sufficiently high molecular weight to form a hydrophobic tail to give the salts detergent (surfactant) properties. Mixtures of two or more salts may be used. The preferred alkali metals are lithium, potassium, and, especially, sodium.

[0018] The alkali metal salts may be simple and contain only the stoichiometric amount of metal. Such salts are called normal or neutral salts and typically have a total base number (TBN) of 0 to about 80. Alternatively, a larger than stoichiometric amount of metal may be introduced and, for example, an acidic gas such as carbon dioxide may be blown through the reaction mixture. The resulting overbased salt comprises a dispersion of a metal compound (predominately a carbonate when carbon dioxide is used) stabilized by neutral detergent salt.

[0019] Sulphonic acids for use in preparing salts according to the invention are well known and are typically obtained by sulphonation of alkyl substituted aromatic hydrocarbons, such as those obtained from the fractionation of petroleum by distillation and/or extraction, or by the alkylation of an aromatic hydrocarbon, for example, benzene, toluene, xylene, naphthalene or diphenyl. The preparation of neutral or overbased salts from such acids is also well known. In the preparation of the overbased salts, the sulphonic acid may be reacted with an excess of a metal base and the excess metal neutralized with an acidic gas, usually carbon dioxide (see, for example, U.S. Patent No. 3 671 430).

[0020] Phenates for use in accordance with the invention include the alkali metal salts of alkyl phenols and sulphurized alkyl phenols. The preparation of such phenates is well known, as is the preparation of the overbased salts, the overbasing process being similar to that used for the sulphonates. One procedure for preparing a sulphurized alkali metal alkyl phenate is to react elemental sulphur with the alkali metal phenate at an elevated temperature. The metal salt can be overbased before or after sulphurizing, or at the same time (see, for example, U.S. Patent No. 3 966 621).

[0021] The phosphonate or thiophosphonate materials which may be used in accordance with the invention include the alkali metal salts of a phosphonic or thiophosphonic acid obtainable by the reaction of a polyolefin, for example, polyisobutylene, with an inorganic phosphorus-containing compound, for example, phosphorus pentasulphide. The preparation of overbased versions of these salts may be carried out in a manner similar to that described above in connection with the sulphonates and phenates.

[0022] Particularly preferred overbased metal detergent salts for use in accordance with the invention include overbased complexes obtainable by the reaction of a phosphosulphurized polymeric hydrocarbon with an alkali metal base in the presence of an alkyl phenol or sulphurized alkyl phenol, the product being treated with carbon dioxide (see, for example, U.S. Patents Nos. 3 182 019 and 3 127 348).

[0023] In the process described in U.S. Patent No. 3 182 019, an acidic sulphur-containing hydrocarbon (preferably a phosphosulphurized derivative obtainable by reacting a hydrocarbon with a phosphorus sulphide, for example P₂S₅ or a mixture of elemental phosphorus and sulphur) and a phenolic compound are dissolved in an inert solvent, an alkali metal base is added in a proportion less than that required to form salts with the total amount of acidic and phenolic compounds present, and the mixture is contacted at an elevated temperature with carbon dioxide while adding additional alkali metal base, the reaction being carried out in the presence of a small amount of water. Preferred phosphosulphurized compounds and phenols for use in this process are described in the U.S. specification. Particularly preferred compounds for use in accordance with the present invention are phosphosulphurized long chain hydrocarbyl compounds and predominantly mono-alkylated phenols having a C₈ to C₁₂ side-chain, for example, nonyl phenol. An especially advantageous overbased material for use in accordance with the present invention is that obtainable by carbonating a mixture of sodium hydroxide, nonyl phenol and phosphosulphurized polyisobutylene. The nonyl phenol may be, for example, o or p nonyl phenol, or a mixture of the two. Some dialkylated material, with nonyl groups in both the o and the p positions, may also be present. This material may be referred to as an overbased sodium thiophosphonate, although a mixture of species will normally be present.

[0024] The sulphonic acids whose overbased metal salts may be used in the present invention will generally have molecular weights in the range of about 300 to about 1200, preferably within the range of about 400 to 800. The alkyl phenols whose overbased metal salts may be used in the present invention will generally have alkyl groups with a total of about 6 to about 24 carbon atoms, preferably from about 8 to about 18 carbon atoms. The polyolefins used in preparing the phosphonate or thiophosphonate materials preferably have a molecular weight of about 500 to about 2000.

[0025] Overbased materials used in accordance with the invention are preferably prepared in the form of oil concentrates having a total base number (TBN) of from about 100 to about 500, preferably from about 200 to about 400, as measured by ASTM-2896, and containing about 30 to 75 mass % active ingredient.

[0026] At the levels at which the alkali metal detergents are used in accordance with the invention, the decrease in wear is generally proportional to the amount of detergent used. The amount to be used in any particular case may be established by routine experiment. In general a proportion of the alkali metal detergent in the range of from 0.02 to 1.5 mass %, preferably 0.04 to 0.7 mass %, on an active ingredient basis based on the antiwear agent-containing oil before treatment, may be expected to reduce low temperature wear, for example valve train wear and follower scuffing. For example, where the alkali metal detergent was an overbased material as described above derived from sodium hydroxide, nonyl phenol and phosphosulphurized polyisobutylene, the addition to a fully formulated lubricating oil containing 1 mass % ZDDPs, based on the total oil, of at least 0.088 mass % of the detergent, on an active ingredient basis based on the fully formulated oil without the said detergent, improved the performance of the oil sufficiently for it to pass the Peugeot TU3 test.

[0027] The alkali metal detergents used in accordance with the invention are oil-soluble or (in common with certain of the other additives referred to below) are dissolvable in oil with the aid of a suitable solvent, or are stably dispersible materials. Oil-soluble, dissolvable, or stably dispersible as that terminology is used herein does not necessarily indicate that the materials are soluble, dissolvable, miscible, or capable of being suspended in oil in all proportions. It does mean, however, that the detergents and other additives are, for instance, soluble or stably dispersible in oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired.

[0028] The alkali metal detergents used in accordance with the present invention can be incorporated into the oil in any convenient way. Thus, they can be added directly to the oil by dispersing or by dissolving them in the oil at the desired level of concentration. Such blending can occur at room temperature or an elevated temperature.

[0029] Base oils with which the alkali metal detergents may be used include those suitable for use as crankcase lubricating oils for spark-ignited and compression-ignited internal combustion engines, for example, automobile and truck engines, marine and railroad diesel engines.

[0030] Synthetic base oils include alkyl esters of dicarboxylic acids, polyglycols and alcohols; poly-α-olefins, polybutenes, alkyl benzenes, organic esters of phosphoric acids and polysilicone oils.

[0031] Natural base oils include mineral lubricating oils which may vary widely as to their crude source, for example, as to whether they are paraffinic, naphthenic, mixed, or paraffinic-naphthenic, as well as to the method used in their production, for example, distillation range, straight run or cracked, hydrofined, solvent extracted and the like.

[0032] More specifically, natural lubricating oil base stocks which can be used may be straight mineral lubricating oil or distillates derived from paraffinic, naphthenic, asphaltic, or mixed base crude oils. Alternatively, if desired, various blended oils may be employed as well as residual oils, particularly those from which asphaltic constituents have been removed. The oils may be refined by any suitable method, for example, using acid, alkali, and/or clay or other agents such, for example, as aluminium chloride, or they may be extracted oils produced, for example, by solvent extraction with solvents, for example, phenol, sulphur dioxide, furfural, dichlorodiethyl ether, nitrobenzene, or crotonaldehyde.

[0033] The lubricating oil base stock conveniently has a viscosity of typically about 2.5 to about 12 cSt (about 2.5 x 10⁻⁶ to about 12 x 10⁻⁶ m²/s) and preferably about 2.5 to about 9 cSt. (about 2.5 x 10⁻⁶ to about 9 x 10⁻⁶ m²/s) at 100°C.

[0034] An alkali metal detergent used in accordance with the present invention may be employed in a lubricating oil composition which comprises lubricating oil, typically in a major proportion, and the detergent, typically in a minor proportion, for example, in a proportion as indicated above. Additional additives may be incorporated in the composition to enable it to meet particular requirements. Examples of additives which may be included in lubricating oil compositions are viscosity index improvers, corrosion inhibitors, oxidation inhibitors, friction modifiers, dispersants, anti-foaming agents, other anti-wear agents, pour point depressants, other detergents, and rust inhibitors.

[0035] Viscosity index improvers (or viscosity modifiers) impart high and low temperature operability to a lubricating oil and permit it to remain shear stable at elevated temperatures and also exhibit acceptable viscosity or fluidity at low temperatures. Suitable compounds for use as viscosity modifiers are generally high molecular weight hydrocarbon polymers, including polyesters, and viscosity index improver dispersants, which function as dispersants as well as viscosity index improvers. 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, as determined by gel permeation chromatography or light scattering methods.

[0036] Representative examples of suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene, polymethacrylates, methacrylate copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, interpolymers 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.

[0037] Corrosion inhibitors, also known as anti-corrosive agents, reduce the degradation of the metallic parts contacted by the lubricating oil composition.

[0038] Oxidation inhibitors, or antioxidants, reduce the tendency of mineral oils to deteriorate in service, evidence of such deterioration being, for example, the production of sludge and of varnish-like deposits on the metal surfaces, and viscosity growth. Suitable oxidation inhibitors include alkaline earth metal salts of sulphurized alkyl-phenols having preferably C₅ to C₁₂ alkyl side chains, e.g., calcium nonylphenol sulphide, barium octylphenyl sulphide, dioctylphenylamine, phenylalpha-naphthylamine, and phosphosulphurized or sulphurized hydrocarbons.

[0039] Other oxidation inhibitors or antioxidants which may be used in lubricating oil compositions comprise oil-soluble copper compounds. The copper may be blended into the oil as any suitable oil-soluble copper compound. By oil-soluble it is meant that the compound is oil-soluble under normal blending conditions in the oil or additive package. The copper compound may be in the cuprous or cupric form. The copper may, for example, be in the form of a copper dihydrocarbyl thio- or dithio-phosphate. Alternatively, the copper may be added as the copper salt of a synthetic or natural carboxylic acid. Examples of suitable acids include C₈ to C₁₈ fatty acids, such, for example, as stearic or palmitic acid, but unsaturated acids such, for example, as oleic acid or branched carboxylic acids such, for example, as naphthenic acids of molecular weights of from about 200 to 500, or synthetic carboxylic acids, are preferred, because of the improved handling and solubility properties of the resulting copper carboxylates. Also useful are oil-soluble copper dithiocarbamates of the general formula R_aR_b NCSS)_zCu, where z is 1 or 2, and R_a and R_b are the same or different hydrocarbyl radicals containing from 1 to 18, and preferably 2 to 12, carbon atoms, and including radicals such, for example, as alkyl, alkenyl, aryl, aralkyl, alkaryl and cycloaliphatic radicals. Particularly preferred as R_a and R_b groups are alkyl groups of from 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-heptyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl, propenyl, or butenyl radicals. In order to obtain oil solubility, the total number of carbon atoms (i.e. the carbon atom in R_a and R_b) will generally be about five or greater. Copper sulphonates, phenates, and acetylacetonates may also be used.

[0040] Examples of useful copper compounds are copper Cu^I and/or Cu^II salts derived from an alkenyl succinic acid or anhydride. The salts themselves may be basic, neutral or acidic. They may be formed by reacting (a) polyalkylene succinimides (having polymer groups of

_n of 700 to 5,000) derived from polyalkylene-polyamines, which have at least one free carboxylic acid group, with (b) a reactive metal compound. Suitable reactive metal compounds include those such, for example, as cupric or cuprous hydroxides, oxides, acetates, borates, and carbonates or basic copper carbonate.

[0041] Examples of these metal salts are Cu salts derived from polyisobutenyl succinic anhydride, and Cu salts of polyisobutenyl succinic acid. Preferably, the copper is in its divalent form, Cu^II. The preferred substrates are polyalkenyl succinic acids in which the alkenyl group has a molecular weight greater than about 700. The alkenyl group desirably has a

_n from about 900 to 1,400, and up to 2,500, with a

_n of about 950 being most preferred. Especially preferred is polyisobutylene succinic anhydride or acid. These materials may desirably be dissolved in a solvent, such as a mineral oil, and heated in the presence of a water solution (or slurry) of the metal bearing material to a temperature of about 70°C to about 200°C. Temperatures of 100°C to 140°C are normally adequate. It may be necessary, depending upon the salt produced, not to allow the reaction mixture to remain at a temperature above about 140°C for an extended period of time, e.g., longer than 5 hours, or decomposition of the salt may occur.

[0042] The copper antioxidants (e.g., Cu-polyisobutenyl succinate, Cu-oleate, or mixtures thereof) will generally be employed in an amount of from about 5 to 500 ppm by weight of the metal, in the final lubricating or fuel composition.

[0043] Friction modifiers and fuel economy agents which are compatible with the other ingredients of the final oil may also be included. Examples of such materials are glyceryl monoesters of higher fatty acids, for example, glyceryl mono-oleate, esters of long chain polycarboxylic acids with diols, for example, the butane diol ester of a dimerized unsaturated fatty acid, and oxazoline compounds.

[0044] Dispersants maintain oil-insoluble substances, resulting from oxidation during use, in suspension in the fluid, thus preventing sludge flocculation and precipitation or deposition on metal parts. So called ashless dispersants are organic materials which form substantially no ash on combustion, in contrast to the metal-containing (and thus ash-forming) detergents described above. Suitable dispersants include, for example, derivatives of long chain hydrocarbon - substituted carboxylic acids in which the hydrocarbon groups contain 50 to 400 carbon atoms, examples of such derivatives being derivatives of high molecular weight hydrocarbyl-substituted succinic acid. Such hydrocarbon-substituted carboxylic acids may be reacted with, for example, a nitrogen-containing compound, advantageously a polyalkylene polyamine, or with an ester. Such nitrogen-containing and ester dispersants are well known in the art, and require no further description here. Particularly preferred dispersants are the reaction products of polyalkylene amines with alkenyl succinic anhydrides.

[0045] In general, suitable dispersants include oil soluble salts, amides, imides, oxazolines and esters, or mixtures thereof, of long chain hydrocarbon-substituted mono and dicarboxylic acids or their anhydrides; long chain aliphatic hydrocarbons having a polyamine attached directly thereto; and Mannich condensation products formed by condensing about 1 molar proportion of a long chain substituted phenol with about 1 to 2.5 moles of formaldehyde and about 0.5 to 2 moles of a polyalkylene polyamine. In these dispersants long chain hydrocarbon groups are suitably derived from polymers of a C₂ to C₅ monoolefin, the polymers having a molecular weight of about 700 to about 5000.

[0046] As indicated above, a viscosity index improver dispersant functions both as a viscosity index improver and as a dispersant. Examples of viscosity index improver dispersants suitable for use in accordance with the invention include reaction products of amines, for example polyamines, with a hydrocarbyl-substituted mono - or dicarboxylic acid in which the hydrocarbyl substituent comprises a chain of sufficient length to impart viscosity index improving properties to the compounds. In general, the viscosity index improver dispersant may be, for example, a polymer of a C₄ to C₂₄ unsaturated ester of vinyl alcohol or a C₃ to C₁₀ unsaturated mono - or dicarboxylic acid with an unsaturated nitrogen-containing monomer having 4 to 20 carbon atoms; a polymer of a C₂ to C₂₀ olefin with an unsaturated C₃ to C₁₀ mono-or dicarboxylic acid neutralised with an amine, hydroxyamine or an alcohol; or a polymer of ethylene with a C₃ to C₂₀ olefin further reacted either by grafting a C₄ to C₂₀ unsaturated nitrogen - containing monomer thereon or by grafting an unsaturated acid onto the polymer backbone and then reacting carboxylic acid groups of the grafted acid with an amine, hydroxy amine or alcohol.

[0047] Examples of dispersants and viscosity index improver dispersants which may be used in accordance with the invention may be found in European Patent Specification No. 24146 B, the disclosure of which is incorporated herein by reference.

[0048] Pour point depressants, otherwise known as lube oil flow improvers, lower the 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 C₈ to C₁₈ dialkyl fumarate/vinyl acetate copolymers, polymethacrylates, and wax naphthalene. Foam control can be provided by an antifoamant of the polysiloxane type, for example, silicone oil or polydimethyl siloxane.

[0049] Detergents and metal rust inhibitors include the metal salts of sulphonic acids, alkyl phenols, sulphurized alkyl phenols, alkyl salicylates, naphthenates and oil soluble mono- and di-carboxylic acids. Alkali metals salts, for example, those discussed above, or alkaline earth metal salts, for example, calcium, magnesium or barium salts, may be used in addition to the salts used in accordance with the invention as antiwear agents. Particularly suitable additional detergents are the overbased sulphonates and phenates of calcium or magnesium.

[0050] 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 need not be further elaborated herein.

[0051] When lubricating compositions contain one or more of the above-mentioned additives, each additive is typically blended into the base oil in amount which enables the additive to provide its normal function. Representative effective amounts of such additives, when used in crankcase lubricants, are illustrated as follows:

[0052] When a plurality of additives are employed it may be desirable, although not essential, to prepare additive concentrates comprising the additives (the concentrate being referred to herein as an additive package) whereby several additives can be added simultaneously to the base oil to form the lubricating oil composition. Dissolution of the additive concentrate into the lubricating oil may be facilitated, for example, by mixing accompanied by heating, but this is not essential. The concentrate or additive package will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration in the final formulation when the additive package is combined with a predetermined amount of base lubricant. Thus, one or more alkali metal detergents used in accordance with the present invention can be added to small amounts of base oil or other compatible solvents along with other desirable additives to form additive packages containing active ingredients in an amount, based on the additive package, of, for example, from about 2.5 to about 90 mass %, and preferably from about 5 to about 75 mass %, and most preferably from about 8 to about 50 mass % by weight, additives in the appropriate proportions with the remainder being base oil.

[0053] The final formulations may employ typically about 10 mass % of the additive-package with the remainder being base oil.

[0054] The following Examples illustrate the invention.

Example 1

[0055] 518 g of an oil solution containing 50 mass % of phosphosulphurized polyisobutene (molecular weight 950; phosphorus content 2.1 mass %), 167 g nonyl phenol (mixture of o and p isomers, with some o, p di-nonyl phenol) and 336 gm of diluent oil (conventionally refined neutral basestock having a kinematic viscosity at 100°C of 5.2 x 10⁻⁶ m²/s) were introduced into a 2 litre glass reaction vessel fitted with a stirrer, heater, temperature controller, gas injection tube, and a distillation condenser. The mixture was heated to 145°C and maintained at that temperature while 3 g of a 50 mass % aqueous solution of sodium hydroxide were slowly added. The mixture so obtained was maintained at 145°C for 30 minutes, following which a further 114 g of the sodium hydroxide solution was slowly added over a 8.5 hour period while injecting carbon dioxide into the mixture at a rate of 40 cm³/min.

[0056] At the end of the 8.5 hour period the product was blown with nitrogen at 100 cm³/min for 3 hours and the resulting product was filtered in a pressure filter using a filter aid. The filtrate contained 19.5 mass % sodium and had a Total Base Number (TBN), measured by ASTM D2896, of 480 mg KOH/g. This concentrate was diluted with the diluent oil referred above to give a 44 mass % detergent solution, based on the solution, the solution containing about 16.6 mass % sodium and about 0.5 mass % phosphorus, based on the solution, and having a TBN of 410 mg KOH/g.

Example 2

[0057] A crankcase lubricating oil was tested in the Peugeot TU3 test without an additive in accordance with the invention and with varying amounts of the 44 mass % solution obtained in accordance with Example 1. The results are shown in Table III. Figures in brackets in Table III are the results of repeated tests at the same concentration of additive.

[0058] It will be seen from the table that the addition of 0.2 mass % of the detergent solution according to Example 1, based on the oil without the detergent solution, is sufficient to allow the oil to pass the TU3 test. This corresponds to 0.088 mass % of the alkali metal detergent, on an active ingredient basis, based on the oil without the said detergent.

[0059] The oil used in Example 2 had the formulation given below. The antiwear agent was in the form of a finished additive when it was mixed with the detergent addtives; that is, the antiwear agent was not formed in the presence of any of the detergent additives used in this Example.

[0060] The antiwear agent was a mixture of 0.46 mass % of a ZDDP derived from a mixture of alcohols containing 65 mass % isobutanol and 35 mass % isopentanol and 0.46 mass % of a ZDDP derived from a mixture of alcohols containing 85 mass % sec. butanol and 15 mass % isooctanol, the proportions of the ZDDPs being based on the final oil and those of each alcohol mixture being based on the respective mixture. The detergent in the said oil was a mixture of 0.5 mass % of a 400 TBN magnesium sulphonate and 0.48 mass % of a 300 TBN calcium sulphonate, the proportions being based on the oil without the detergent according to the invention.

Claims

1. The use of an alkali metal detergent for enhancing the action of an antiwear agent in a lubricating oil.

2. The use of an alkali metal detergent for improving the low temperature wear properties of a lubricating oil containing an antiwear agent.

3. The use of an alkali metal detergent as a lubricating oil additive for reducing wear when operating at low temperatures, the lubricating oil also containing an antiwear agent.

4. An invention as claimed in any one of claims 1 to 3, wherein the lubricating oil is a crankcase lubricating oil.

5. The use of an alkali metal detergent to enable a crankcase lubricating oil containing an antiwear agent to meet the Peugeot TU3 test requirements.

6. The use of an alkali metal detergent as a crankcase lubricant additive to reduce valve train wear and follower scuffing as measured by the Peugeot TU3 engine test, the lubricant also containing an antiwear agent.

7. An invention as claimed in any one of claims 1 to 6, wherein the antiwear agent is a zinc dihydrocarbyl dithiophosphate.

8. An invention as claimed in any one of claims 1 to 7, wherein the antiwear agent is present in an amount of 0.001 to 5 mass %, based on the final oil.

9. An invention as claimed in any one of claims 1 to 8, wherein the alkali metal is sodium.

10. An invention as claimed in any one of claims 1 to 9, wherein the detergent is a thiophosphonate.

11. An invention as claimed in any one of claims 1 to 9, wherein the detergent is obtainable from a basic sodium compound, preferably sodium hydroxide, an alkyl phenol, preferably a C₈ to C₁₂ alkyl phenol, and a phosphosulphurized hydrocarbyl compound.

12. An invention as claimed in any one of claims 1 to 9, wherein the detergent is obtainable from sodium hydroxide, nonyl phenol and phosphosulphurized polyisobutene.

13. An invention as claimed in any one of claims 1 to 12, wherein the detergent is overbased.

14. An invention as claimed in any one of claims 1 to 13, wherein the detergent is used in an amount of 0.02 to 1.5 mass %, preferably 0.04 to 0.7 mass %, based on the mass of the antiwear agent-containing lubricating oil without the said detergent.

15. An invention as claimed in claim 13 or claim 14, wherein the detergent is obtained by carbonating a mixture of the substances specified in claim 12, and is preferably used in an amount of at least 0.088 mass %, based on the mass of the antiwear-containing lubricating oil without the said detergent.