EP1256619A1

EP1256619A1 - Lubricating oil composition

Info

Publication number: EP1256619A1
Application number: EP01201752A
Authority: EP
Inventors: Christopher Locke; Mark Stevens; Peter Wrench
Original assignee: Infineum International Ltd
Current assignee: Infineum International Ltd
Priority date: 2001-05-11
Filing date: 2001-05-11
Publication date: 2002-11-13

Abstract

A lubricating oil composition comprising:

(A) an oil of lubricating viscosity, in a major amount, and added thereto:

(B) a detergent composition comprising one or more metal detergents which comprises metal salts of organic acids, in a minor amount, wherein the detergent composition comprises more than 50 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition, and

(C) one or more co-additives, in a minor amount;

wherein the total amounts of phosphorus and sulfur derived from (B) or (C) or both (B) and (C) are less than 0.1 mass % of phosphorus and at most 0.5 mass % of sulfur, based on the mass of the oil composition.

Description

The present invention relates to a lubricating oil composition for use in an internal combustion engine, such as a diesel engine, more preferably a heavy duty diesel engine, and a method for the preparation thereof. The invention also concerns the use of a defined detergent composition in a lubricating oil composition for reducing wear in an engine. Further, the present invention provides a method of lubricating an internal combustion engine.
The need for less toxic emissions from exhaust gases is becoming more demanding, mainly because of environmental problems such as the emission of pollutants such as hydrocarbons, carbon monoxide and nitrogen oxides. Catalytic converters in the exhaust systems have been used to reduce the emission of pollutants. Such converters generally use a combination of catalytic metals, such as platinum or variations thereof and metal oxides, and are installed in the exhaust streams, e.g. the exhaust pipes of automobiles to convert the toxic gases to non-toxic gases. Phosphorus components, such as the decomposition products of the zinc dithiophosphate, are believed to poison the catalyst in these converters. Also it is likely that sulfur components poison the catalysts, for example those used in reduction of nitrogen oxides.
Thus, there is governmental and automotive industry pressure towards reducing phosphorus and sulfur contents in lubricating oil compositions.
This can be achieved by reducing the amount of phosphorus and sulfur components in the oil composition, for example, by reducing the amount of zinc dithiophosphate. However, this presents problems, for example, lowering the anti-wear properties of the oil composition.
Generally, the art describes phosphorus-, sulfur- and molybdenum-containing compounds as anti-wear additives.
Applicant has surprisingly found that a defined detergent composition provides wear benefit in lubricating oil compositions having low phosphorus and/or low sulfur content, preferably in lubricating oil compositions which have low phosphorus and low sulfur contents.
Therefore, in a first aspect, the present invention provides a lubricating oil composition comprising:
(A) an oil of lubricating viscosity, in a major amount, and added thereto:
(B) a detergent composition comprising one or more metal detergents which comprises metal salts of organic acid, in a minor amount, wherein the detergent composition comprises more than 50 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition, and
(C) one or more co-additives, in a minor amount;
In a second aspect, the present invention provides a diesel engine, preferably a heavy duty diesel engine, lubricating oil composition comprising (A), (B) and (C) as defined in the first aspect, wherein the amount of phosphorus and sulfur in the oil composition is as defined in the first aspect.
In a third aspect, the present invention provides the use, in a minor amount, of a detergent composition as defined in the first aspect, in a lubricating oil composition, preferably a diesel engine, more preferably a heavy duty diesel engine, lubricating oil composition, for reducing wear in an engine, wherein the amount of phosphorus and sulfur in the oil composition is as defined in the first aspect.
In a fourth aspect, the present invention provides a method of lubricating an internal combustion engine, preferably a diesel engine, more especially a heavy duty diesel engine, comprising supplying to the engine the lubricating oil composition according to either the first or second aspect.
In a fifth aspect, the present invention provides a method of preparing a lubricating oil composition according to either the first or second aspect comprising admixing components (A), (B) and (C) as defined in the first aspect.
Further, the present invention provides the use of an oil composition according to either the first or second aspect for reducing wear in an engine.
The features of the present invention will now be discussed in more detail.

LUBRICATING OIL COMPOSITION

The amount of phosphorus and sulfur in the lubricating oil composition is measured according to ASTM D5185.
Preferably the amount of phosphorus in the lubricating oil composition, independent of the amount of sulfur, is less than 0.09, less than 0.08, less than 0.07 or less than 0.06 mass %; more preferably at most 0.05, at most 0.04 or at most 0.03 mass %; such as in the range from 0.001 to 0.03 mass %; for example at most 0.02 or at most 0.01 mass %. In a preferred embodiment, the phosphorus content is zero in the lubricating oil composition.
The amount of sulfur in the lubricating oil composition, independent of the amount of phosphorus, is preferably at most 0.4, at most 0.3 or at most 0.25 mass %; especially at most 0.2 or at most 0.15 mass %; such as in the range from 0.001 to 0.1 mass %. In a preferred embodiment, the sulfur content is zero in the lubricating oil composition
In an embodiment of the invention, the amount of phosphorus and sulfur derived from an anti-wear additive (C), such as a zinc dithiophosphate, is as defined above with respect to the amount in the lubricating oil composition.
Preferably the amount of phosphorus and sulfur in the lubricating oil composition is derived from both (B) and (C); more preferably the amount is derived from (A), (B) and (C).
In a preferred aspect of the present invention, the lubricating oil composition does not comprise a co-additive (C) selected from one or more of a phosphorus-, a sulfur-, or a molybdenum-containing compound. For example, the lubricating oil composition does not comprise a phosphorus- and/or a molybdenum-containing compound, such as a zinc dithiodiphosphate and/or a molybdenum dithiocarbamate.
The lubricating oil compositions have been found to be particularly effective as lubricants for compression ignition engines, i.e. diesel engines, especially heavy duty diesel engines.
The heavy duty trucking market has come to adopt the diesel engine as its preferred power source due to both its excellent longevity and its economy of operation. Specialized lubricants have been developed to meet the more stringent performance requirements of heavy duty diesel engines.
Several engine tests are required to demonstrate satisfactory heavy duty performance, including the Cummins M11 test to evaluate soot-related valve train wear, filter plugging and sludge.
As mentioned earlier, the defined metal detergent composition has been found to exhibit anti-wear properties in lubricating oil compositions having either a low phosphorus content or a low sulfur content. The amount of phosphorus or sulfur in such an oil composition corresponds to the amount of phosphorus and sulfur disclosed above.
In a preferred aspect of the present invention, the oil composition of the present invention has less than 2 % of ash, preferably less than 1.5%, especially less than 1 %; such as in the range from 0 to 0.5 % ash, according to method ASTM D874.

Oil of Lubricating Viscosity (A)

The lubricating oil can be a synthetic or mineral oil of lubricating viscosity selected from the group consisting of Group I, II, III, IV or V basestocks and mixtures of thereof.
Basestocks may be made using a variety of different processes including but not limited to distillation, solvent refining, hydrogen processing, oligomerization, esterification, and rerefining.
API 1509 "Engine Oil Licensing and Certification System" Fourteenth Edition, December 1996 states that all basestocks are divided into five general categories:
Group I basestocks contain less than 90% saturates and/or greater than 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120;
Group II basestocks contain greater than or equal to 90% saturates and less than or equal to 0.03% sulfur and have a viscosity index greater than or equal to 80 and less than 120;
Group III basestocks contain greater than or equal to 90% saturates and less than or equal or 0.03% sulfur and have a viscosity index greater than or equal to 120;
Group IV basestocks contain polyalphaolefins (PAO); and
Group V basestocks contain include all other basestocks not included in Group I, II, III or IV.
Group IV basestocks, i.e. polyalphaolefins (PAO) include hydrogenated oligomers of an alpha-olefin, the most important methods of oligomerization being free radical processes, Ziegler catalysis, cationic, and Friedel-Crafts catalysis.
Preferably the lubricating oil is selected from any one of Group 1 to 5 basestocks, provided the selected basestock contains at most 0.5 % sulfur.
Especially preferred is Groups II , III, IV or V basestock or any two or more mixtures thereof, or mixtures of Group IV basestocks with 5 to 80 mass % of Group I, II, III or V basestocks, provided the sulfur content is at most 0.5 %.
The test methods used in defining the above groups are ASTM D2007 for saturates; ASTM D2270 for viscosity index; and one of ASTM D2622, 4294, 4927 and 3120 for sulfur.

Detergent Composition (B)

A detergent is an additive that reduces formation of piston deposits, for example high-temperature varnish and lacquer deposits, in engines; it has acid-neutralising properties and is capable of keeping finely divided solids in suspension. It is based on metal "soaps", that is metal salts of organic acids, sometimes referred to as surfactants.
A detergent comprises a polar head, i.e. the metal salt of the organic acid, with a long hydrophobic tail for oil solubility. Therefore, organic acids or surfactants typically have one or more functional groups, such as OH or COOH or SO₃H; and a hydrocarbyl substituent.
Examples of surfactants include sulphonic acids, phenols and sulphurised derivatives thereof, and carboxylic acids.
Applicant has found that a metal detergent composition comprising more than 50 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition, provides wear benefit in lubricating oil compositions having low phosphorus and/or low sulfur content, preferably in lubricating oil compositions having low phosphorus and low sulfur contents.
Preferably the proportion of the metal salt of an aromatic carboxylic acid is at least 60 or at least 70 mole %; more preferably at least 80 or at least 90 mole %, based on the moles of the metal salts of organic acids in the detergent composition.
In a most preferred embodiment, the detergent composition comprises 100 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition; that is the detergent composition comprises only aromatic carboxylic acids as the organic acids.
The aromatic moiety of the aromatic carboxylic acid can contain heteroatoms, such as nitrogen and oxygen. Preferably, the moiety contains only carbon atoms; more preferably the moiety contains six or more carbon atoms; for example benzene is a preferred moiety.
The aromatic carboxylic acid surfactant may contain one or more aromatic moieties, such as one or more benzene rings, either fused or connected via alkylene bridges.
The carboxylic moiety may be attached directly or indirectly to the aromatic moiety. Preferably the carboxylic acid group is attached directly to a carbon atom on the aromatic moiety, such as on the benzene ring.
More preferably, the aromatic moiety also contains a second functional group, such as a hydroxy group or a sulfonate group, which can be attached directly or indirectly to a carbon atom on the aromatic moiety.
Preferred examples of an aromatic carboxylic acids are salicylic acids and sulphurised derivatives thereof, such as hydrocarbyl substituted salicylic acid and derivatives thereof.
Process for sulfurizing, for example a hydrocarbyl-substituted salicylic acid, is similar to those for phenols (see below), and are well known to those skilled in the art.
Salicylic acids are typically prepared by carboxylation, for example, by the Kolbe-Schmitt process, of phenoxides, and in that case, will generally be obtained, normally in a diluent, in admixture with uncarboxylated phenol.
Preferred substituents in oil-soluble salicylic acids are alkyl substituents. In alkyl-substituted salicylic acids, the alkyl groups advantageously contain 5 to 100, preferably 9 to 30, especially 14 to 20, carbon atoms. Where there are more than one alkyl groups, the average number of carbon atoms in all of the alkyl groups is preferably at least 9 to ensure adequate oil-solubility.
The detergent composition can comprise metal salts of surfactant anions other than aromatic carboxylic acids, such as sulphonic acids, phenols and sulphurised derivatives thereof, and carboxylic acids.
Sulphonic acids are typically obtained by sulphonation of hydrocarbyl-substituted, especially alkyl-substituted, aromatic hydrocarbons, for example, those obtained from the fractionation of petroleum by distillation and/or extraction, or by the alkylation of aromatic hydrocarbons. Examples include those obtained by alkylating benzene, toluene, xylene, naphthalene, biphenyl or their halogen derivatives, for example, chlorobenzene, chlorotoluene or chloronaphthalene. Alkylation of aromatic hydrocarbons may be carried out in the presence of a catalyst with alkylating agents having from about 3 to more than 100 carbon atoms, such as, for example, haloparaffins, olefins that may be obtained by dehydrogenation of paraffins, and polyolefins, for example, polymers of ethylene, propylene, and/or butene. The alkylaryl sulphonic acids usually contain from about 22 to about 100 or more carbon atoms. The sulphonic acids may be substituted by more than one alkyl group on the aromatic moiety, for example they may be dialkylaryl sulphonic acids. The alkyl group preferably contains from about 16 to about 80 carbon atoms, with an average number of carbon atoms in the range of from 36-40, or an average carbon number of 24, depending on the source from which the alkyl group is obtained. Preferably the sulphonic acid has a number average molecular weight of 350 or greater, more preferably 400 or greater, especially 500 or greater, such as 600 or greater. Number average molecular weight may be determined by ASTM D3712.
When neutralising these alkylaryl sulphonic acids to provide sulphonates, hydrocarbon solvents and/or diluent oils may also be included in the reaction mixture, as well as promoters.
Another type of sulphonic acid which may be used in accordance with the invention comprises alkyl phenol sulphonic acids. Such sulphonic acids can be sulphurized. Preferred substituents in alkyl phenol sulphonic acids are substituents represented by R in the discussion of phenols below.
Sulphonic acids suitably contain 22 to 100 carbon atoms, advantageously 25 to 80 carbon atoms, especially 30 to 60 carbon atoms.
Preferably the sulphonic acid is hydrocarbyl-substituted aromatic sulphonic acid, more preferably alkyl aryl sulphonic acid.
Phenols may be non-sulphurized or, preferably, sulphurized. Further, the term "phenol" as used herein includes phenols containing more than one hydroxyl group (for example, alkyl catechols) or fused aromatic rings (for example, alkyl naphthols) and phenols which have been modified by chemical reaction, for example, alkylene-bridged phenols and Mannich base-condensed phenols; and saligenin-type phenols (produced by the reaction of a phenol and an aldehyde under basic conditions).
Preferred phenols are of the formula
where R represents a hydrocarbyl group and y represents 1 to 4. Where y is greater than 1, the hydrocarbyl groups may be the same or different.
The phenols are frequently used in sulphurized form. Sulphurized hydrocarbyl phenols may typically be represented by the formula:
where x, represents an integer from 1 to 4. In some cases, more than two phenol molecules may be linked by (S)_x bridges, where S represents a sulphur atom.
In the above formulae, hydrocarbyl groups represented by R are advantageously alkyl groups, which advantageously contain 5 to 100 carbon atoms, preferably 5 to 40 carbon atoms, especially 9 to 12 carbon atoms, the average number of carbon atoms in all of the R groups being at least about 9 in order to ensure adequate solubility in oil. Preferred alkyl groups are nonyl (e.g. tripropylene) groups or dodecyl (e.g. tetropropylene) groups.
In the following discussion, hydrocarbyl-substituted phenols will for convenience be referred to as alkyl phenols.
A sulphurizing agent for use in preparing a sulphurized phenol or phenate may be any compound or element which introduces -(S)_X- bridging groups between the alkyl phenol monomer groups, wherein x is generally from 1 to about 4. Thus, the reaction may be conducted with elemental sulphur or a halide thereof, for example, sulphur dichloride or, more preferably, sulphur monochloride. If elemental sulphur is used, the sulphurization reaction may be effected by heating the alkyl phenol compound at from 50 to 250°C, and preferably at least 100°C. The use of elemental sulphur will typically yield a mixture of bridging groups -(S)_X- as described above. If a sulphur halide is used, the sulphurization reaction may be effected by treating the alkyl phenol at from -10°C to 120°C, preferably at least 60°C. The reaction may be conducted in the presence of a suitable diluent. The diluent advantageously comprises a substantially inert organic diluent, for example mineral oil or an alkane. In any event, the reaction is conducted for a period of time sufficient to effect substantial reaction. It is generally preferred to employ from 0.1 to 5 moles of the alkyl phenol material per equivalent of sulphurizing agent.
Where elemental sulphur is used as the sulphurizing agent, it may be desirable to use a basic catalyst, for example, sodium hydroxide or an organic amine, preferably a heterocyclic amine (e.g., morpholine).
Details of sulphurization processes are well known to those skilled in the art, for example US-A-4,228,022 and US-A-4,309,293.
As indicated above, the term "phenol" as used herein includes phenols which have been modified by chemical reaction with, for example, an aldehyde, and Mannich base-condensed phenols.
Aldehydes with which phenols may be modified include, for example, formaldehyde, propionaldehyde and butyraldehyde. The preferred aldehyde is formaldehyde. Aldehyde-modified phenols suitable for use in accordance with the present invention are described in, for example, US-A-5 259 967.
Mannich base-condensed phenols are prepared by the reaction of a phenol, an aldehyde and an amine. Examples of suitable Mannich base-condensed phenols are described in GB-A-2 121 432.
In general, the phenols may include substituents other than those mentioned above. Examples of such substituents are methoxy groups and halogen atoms.
Carboxylic acids include mono- and dicarboxylic acids. Preferred monocarboxylic acids are those containing 8 to 30 carbon atoms, especially 8 to 24 carbon atoms. (Where this specification indicates the number of carbon atoms in a carboxylic acid, the carbon atom(s) in the carboxylic group(s) is/are included in that number). Examples of monocarboxylic acids are iso-octanoic acid, stearic acid, oleic acid, palmitic acid and behenic acid. Iso-octanoic acid may, if desired, be used in the form of the mixture of C8 acid isomers sold by Exxon Chemical under the trade name "Cekanoic". Other suitable acids are those with tertiary substitution at the α-carbon atom and dicarboxylic acids with 2 or more carbon atoms separating the carboxylic groups. Further, dicarboxylic acids with more than 35 carbon atoms, for example, 36 to 100 carbon atoms, are also suitable. Unsaturated carboxylic acids can be sulphurized.
Advantageously, hydrocarbyl groups in surfactants for use in accordance with the invention are aliphatic groups, preferably alkyl or alkylene groups, especially alkyl groups, which may be linear or branched. The total number of carbon atoms in the surfactants should be at least sufficient to impact the desired oil-solubility. The hydrocarbyl group may contain contain 5 to 100, preferably 9 to 30, especially 14 to 20, carbon atoms.
The metal detergent may be neutral or overbased.
The term 'neutral' as used herein refers to metal salts that are predominantly neutral in character, that is most of the metal is associated with the surfactant anion. For a detergent to be completely neutral, the total number of moles of the metal cation to the total number of moles of surfactant anion associated with the metal will be stoichiometric. For example, for every one mole of calcium cations there should be two moles of sulfonate anions.
Neutral detergents may comprise minor amounts of non-surfactant anions, such as carbonate and/or hydroxide, provided their presence does not alter the predominantly neutral character of the detergent. Thus, neutral detergents preferably have a metal ratio of less than 2, more preferably less than 1.95, especially 1.9, such as 1.8. The metal ratio, as used herein, is the ratio of total metal to the metal associated with the surfactant. So detergents having a metal ratio of less than 2 have greater than 50% of the metal associated with the surfactant anion.
Overbased detergents comprise a major amount of metal salts of non-surfactant anions and a minor amount of metal salts of surfactant anions; accordingly overbased detergents have a metal ratio of at least 2, preferably greater than 2.
The metal ratio can be calculated by
a) measuring the total amount of metal in the neutral metal salt; and then
b) determining the amount of metal associated with the surfactant.
Suitable methods for measuring the total metal content are well known in the art and include X-ray fluorescence and atomic absorption spectrometry.
Suitable methods for determining the amount of metal associated with the surfactant include potentiometric acid titration of the metal salt to determine the relative proportions of the different basic constituents (for example, metal carbonate and metal surfactant); hydrolysis of a known amount of metal salt and then the potentiometric base titration of the organic surfactant to determine the equivalent moles of surfactant; and determination of the non-surfactant anions, such as carbonate, by measuring the CO₂ content.
In the case of a metal sulphonate, ASTM D3712 may be used to determine the metal associated with the sulphonate.
In the instance where a composition comprises a detergent and one or more co-additives, then the detergent may be separated from the co-additives, for example, by using dialysis techniques and then the detergent may be analysed as described above to determine the metal ratio. Background information on suitable dialysis techniques is given by Amos, R. and Albaugh, E. W. in "Chromatography in Petroleum Analysis" Altgelt, K. H. and Gouw, T. H., Eds., pages 417 to 421, Marcel Dekker Inc., New York and Basel, 1979.
Preferably the detergent composition comprises at least one overbased metal detergent additive.
A preferred overbased metal detergent comprises one or more metal salts of aromatic carboxylic acids, preferably one or more metal salts of salicylic acids.
Group 1 and Group 2 metals are preferred as metals in the detergents; more preferably calcium and magnesium, especially calcium is preferred.
The detergents can have a Total Base Number (TBN) in the range of 15 or 60 to 600, preferably 100 to 450, more preferably 160 to 400. TBN is measured according to ASTM D-2896.
The detergents of the present invention may be salts of one type of surfactant or salts of more than one type of surfactant, for example hybrid detergents. Preferably, they are salts of one type of surfactant.
In the instance where more than one type of surfactant is present in a single detergent, the proportion of any one type of surfactant to another is not critical.
It will be appreciated by one skilled in the art that a single type of surfactant may contain a mixture of surfactants of the same type. For example, a sulphonic acid surfactant may contain a mixture of sulphonic acids of varying molecular weights. Such a surfactant composition is considered as one type of surfactant.
For the avoidance of doubt, the detergent composition may also comprise ashless detergents, i.e. non-metal containing detergents.
Detergent compositions comprising at least one calcium salicylate detergent, preferably at least one overbased calcium salicylate detergent, have been found to particularly effective in the present invention, provided the proportion, as defined in the first aspect, of the metal salt of an aromatic carboxylic acid, in this instance the metal salt of the salicylic acid, is satisfied.
Applicant, therefore, considers that detergent compositions comprising only calcium salicylate detergents, whether neutral or overbased, would be advantageous.

Co-additives (C)

Co-additives suitable in the present invention include viscosity index improvers, corrosion inhibitors, other oxidation inhibitors or antioxidants, friction modifiers, dispersants, rust inhibitors or rust prevention agents, anti-wear agents, pour point depressants, demulsifiers, and anti-foaming agents.
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.
Corrosion inhibitors reduce the degradation of metallic parts contacted by the lubricating oil composition. Thiadiazoles, for example those disclosed in US-A-2 719 125, 2 719 126 and 3 087 932, are examples of corrosion inhibitors for lubricating oils.
Oxidation inhibitors, or antioxidants, reduce the tendency of mineral oils to deteriorate in service, evidence of such deterioration being, for example, the production of varnish-like deposits on metal surfaces and of sludge, and viscosity increase. Suitable oxidation inhibitors include sulphurized alkyl phenols and alkali or alkaline earth metal salts thereof; diphenylamines; phenyl-naphthylamines; and phosphosulphurized or sulphurized hydrocarbons.
Other oxidation inhibitors or antioxidants which may be used in lubricating oil compositions include 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 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, for example, a C₈ to C₁₈ fatty acid, an unsaturated acid, or a branched carboxylic acid. Also useful are oil-soluble copper dithiocarbamates, sulphonates, phenates, and acetylacetonates. Examples of particularly useful copper compounds are basic, neutral or acidic copper Cu^I and/or Cu^II salts derived from alkenyl succinic acids or anhydrides.
Copper antioxidants will generally be employed in an amount of from about 5 to 500 ppm by weight of the copper, in the final lubricating composition.
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, esters of long chain polycarboxylic acids with diols, and oxazoline compounds, and oil-soluble molybdenum compounds. Molybdenum compounds can also provide anti-wear and anti-oxidant benefits.
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 metal-containing (and thus ash-forming) detergents. Borated metal-free dispersants are also regarded herein as ashless dispersants. 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 hydrocarbyl-substituted carboxylic acids may be reacted with, for example, a nitrogen-containing compound, advantageously a polyalkylene polyamine, or with an ester. Particularly preferred dispersants are the reaction products of polyalkylene amines with alkenyl succinic anhydrides. Examples of specifications disclosing dispersants of the last-mentioned type are US-A-3 202 678, 3 154 560, 3 172 892, 3 024 195, 3 024 237, 3 219 666, 3 216 936 and BE-A-662 875.
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 lubricating compositions 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.
Examples of dispersants and viscosity index improver dispersants may be found in EP-A-24146.
Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids may be used.
Antiwear agents, as their name implies, reduce wear of metal parts. Zinc dihydrocarbyl dithiophosphates (ZDDPs) are very widely used as antiwear agents. Examples of ZDDPs for use in oil-based compositions are those of the formula Zn[SP(S)(OR¹)(OR²)]₂ wherein R¹ and R² contain from 1 to 18, and preferably 2 to 12, carbon atoms.
Sulfur- and molybdenum-containing compounds are also examples of anti-wear additives. Also suitable are ashless phosphorus- and sulfur-containing compounds.
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. Foam control may be provided by an antifoamant of the polysiloxane type, for example, silicone oil or polydimethyl siloxane.
A small amount of a demulsifying component may be used. A preferred demulsifying component is described in EP-A-0 330 522. It is obtained by reacting an alkylene oxide with an adduct obtained by reacting a bis-epoxide with polyhydric alcohol.
Some of the above-mentioned additives may 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.
Preferably at least one co-additive is an anti-wear additive, such a metal dihydrocarbyldithiophosphate, for example zinc dihydrocarbyldithiophosphate.

When lubricating compositions contain one or more of the above-mentioned additives, including the detergents, 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 lubricants, are as follows:

Additive	Mass % a.i. (Broad)	Mass % a.i. (Preferred)
Viscosity Modifier	0.01-6	0.01-4
Corrosion Inhibitor	0.01-5	0.01-1.5
Oxidation Inhibitor	0.01-5	0.01-1.5
Friction Modifier	0.01-5	0.01-1.5
Dispersant	0.1-20	0.1-8
Detergent	0.01-6	0.01-3
Anti-wear Agent	0.01-6	0.01-4
Pour Point Depressant	0.01-5	0.01-1.5
Rust Inhibitor	0.001-0.5	0.01-0.2
Anti-Foaming Agent	0.001-0.3	0.001-0.15
Demulsifier	0.001-0.5	0.01-0.2
Mineral or Synthetic Base Oil	Balance	Balance

The additives may be incorporated into a base oil in any convenient way. Thus, each of the additive 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.
When a plurality of additives are employed it may be desirable, although not essential, to prepare one or more additive packages comprising the additives, whereby several additives can be added simultaneously to the base oil to form the lubricating oil composition. Dissolution of the additive package(s) into the lubricating oil may be facilitated by solvents and by mixing accompanied with mild heating, but this is not essential. The additive package(s) 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(s) is/are combined with a predetermined amount of base lubricant. Thus, one or more detergents may be added to small amounts of base oil or other compatible solvents together 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 60 mass % by weight, additives in the appropriate proportions with the remainder being base oil.
Thus, the method of preparing the oil composition according to the fifth aspect can involve admixing component (A) and an additive package that comprises components (B) and (C).
The final formulations may typically contain about 5 to 40 mass % of the additive package(s) with the remainder being base oil.
The term "hydrocarbyl" as used herein means that the group concerned is primarily composed of hydrogen and carbon atoms and is bonded to the remainder of the molecule via a carbon atom, but does not exclude the presence of other atoms or groups in a proportion insufficient to detract from the substantially hydrocarbon characteristics of the group.
It should be appreciated that interaction may take place between any two or more of the additives, including any two or more detergents, after they have been incorporated into the oil. The interaction may take place in either the process of mixing or any subsequent condition to which the composition is exposed, including the use of the composition in its working environment. Interactions may also take place when further auxiliary additives are added to the compositions of the invention or with components of oil. Such interaction may include interaction which alters the chemical constitution of the additives. Thus for example the compositions of the invention include compositions in which interaction, for example, between any of the additives, has occurred, as well as compositions in which no interaction has occurred, for example, between the components mixed in the oil.
The terms "comprising" or "comprises" when used herein is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
The terms "oil-soluble" or "oil-dispersible", as used herein, does not mean that the additives are soluble, dissolvable, miscible or capable of being suspended in the oil in all proportions. They do mean, however, that the additives are, for instance, soluble or stable dispersible in the oil to an extent sufficient to exert their intended effect in the environment in which the oil composition is employed. Moreover, the additional incorporation of other additives such as those described above may affect the solubility or dispersibility of the additives.
The invention is illustrated by, but in no way limited to, the following examples.

Examples

Lubricating oil compositions containing 0.10, 0.07, 0.04 and 0.00 mass % of phosphorus were prepared by blending methods known in the art. The oil compositions contain a dispersant, an anti-oxidant, a zinc dithiophosphate in varying amounts due to the different phosphorus levels and a detergent composition. Comparative Examples 1 to 4 contain only a phenate and sulfonate detergent, while Examples 1 to 4 contain only a salicylate detergent. Table 1 shows the properties of the compositions.
The film thickness and wear performance of the compositions were measured on the Elastohydrodynamic Film Thickness Rig, the Traction rig adapted to the pin on disc option, and the Four Ball Extreme Pressure Test.
Briefly, the Elastohydrodynamic rig measures film thickness between a steel ball and a coated glass disc that are in rolling contact. The test conditions are a varying rolling speed; a temperature of 100 °C; 100 % rolling contact (0 % slide/roll ratio) and a load of 20 N. Full details of the apparatus and test procedure are described in Tribology International, 33 (2000), 241-247; SAE 962037; SAE 961142; and SAE 962640.
Oil compositions that exhibit larger film thickness are more likely to provide better wear performance; this is because thicker films are more likely to a) separate contacting surfaces and b) shear at lower stress than the underlying metal, thereby mitigating adhesive wear.
For the pin on disc wear option, the Traction rig is as described in SAE 962037; SAE 961142; and SAE 962640; however, the steel ball is replaced by a steel pin of 0.5 mm diameter which contacts the steel disc at a constant load and temperature as described in SAE 981406. The disc is driven at a constant speed and the wear is measured by a Linear Voltage Displacement Transducer. The test conditions are a time of 1 hour; a temperature of 100 °C, a load of 30 N; and a sliding speed of 1 m/s¹.
The apparatus used in the Four Ball Extreme Pressure Test is that used in the industry test IP239. The conditions are specified in the Peugeot D55-1136 method, and briefly these are a rotating speed of 1500 rpm; a time of 60 seconds; and a load of either 100kg or 85 kg.
Both the pin on disc wear test and four ball extreme pressure test measure wear under high pressure sliding contact conditions. Therefore, oil compositions, which exhibit less wear in these tests are more likely to provide better wear performance.
Table 2 shows that the films formed in Examples 1 to 4 (salicylate-containing oil compositions) are thicker than those formed in the corresponding comparative examples in respect of lubricating oil compositions containing less than 0.1 mass % phosphorus.
Further, the salicylate-containing oil compositions (Examples 1 to 4) show a surprising and significant advantage at lower phosphorus levels. In particular the salicylate-containing oil compositions substantially maintain the film thickness as the phosphorus level is reduced. This effect is demonstrated in the elastohydrodynamic rig in least three different rolling speeds.
Similarly, the data in Table 3 support the superior and unexpected performance of salicylate-containing oil compositions at low phosphorus levels. The salicylate-containing oil compositions exhibit less wear in compositions containing 0.04 mass % or less of phosphorus in the traction rig adapted to the pin on disc option.
The data from the four ball extreme pressure test also confirm that salicylate-containing oil compositions provide improved wear performance, in particular in oils containing no phosphorus in at least two different loads (100 and 85 kg) (see Table 4).

Claims

A lubricating oil composition comprising:

(A) an oil of lubricating viscosity, in a major amount, and added thereto:

(B) a detergent composition comprising one or more metal detergents which comprises metal salts of organic acids, in a minor amount,
wherein the detergent composition comprises more than 50 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition, and

(C) one or more co-additives, in a minor amount;

wherein the total amounts of phosphorus and of sulfur derived from (B) or (C) or both (B) and (C) are less than 0.1 mass % of phosphorus and at most 0.5 mass % of sulfur, based on the mass of the oil composition.
The composition claimed in any one of the preceding claims wherein the detergent composition comprises at least one overbased metal detergent additive.
The composition claimed in claim 5 wherein the overbased metal detergent additive comprises a metal salt of an aromatic carboxylic acid.
The composition claimed in any one of the preceding claims wherein the aromatic carboxylic acid is a hydrocarbyl substituted salicylic acid.
The composition claimed in any one of the preceding claims wherein at least one of the detergents has a TBN in the range of 15 to 600, such as 100 to 450, preferably 160 to 400.
The composition claimed in any one of the preceding claims wherein at least one of the detergents is either magnesium or calcium salicylate.
The composition claimed in any one of the preceding claims wherein the lubricating oil composition is in the form of a diesel engine lubricating oil composition.
The use, in a minor amount, of a detergent composition comprising one or more metal detergents, which comprises metal salts of organic acids, wherein the detergent composition comprises more than 50 mole % of a metal salt of an aromatic carboxylic acid, based on the moles of the metal salts of organic acids in the detergent composition, in a lubricating oil composition for reducing wear in an engine, wherein the amount of phosphorus and sulfur in the oil composition is as defined in any one of claims 1, 2, 12 and 13.
A method of lubricating an internal combustion engine, preferably a diesel engine, more especially a heavy duty diesel engine, comprising supplying to the engine the lubricating oil composition claimed in any one of claims 1 to 14.
A method of preparing a lubricating oil composition claimed in any one of claims 1 to 14 comprising admixing components (A), (B) and (C) as defined in any one of claims 1 to 14.