LUBRICANT COMPOSITION HAVING IMPROVED EMULSION STABILITY

Abstract

Disclosed is a lubricant composition comprising: at least one base oil, from 0.1% to 13% by mass of at least one viscosity index improver, at least one organomolybdenum compound, with the content of molybdenum element being at least 400 ppm by mass, at least a first detergent additive chosen from magnesium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, optionally, at least a second detergent additive chosen from calcium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, wherein the combined content of magnesium element and of calcium element, relative to the total mass of the lubricant composition, is at least 1000 ppm by mass.

Claims

1. A lubricant composition comprising: at least one base oil, from 0.1% to 13% by mass, relative to the total mass of the lubricant composition, of at least one viscosity index improver additive, at least one organomolybdenum compound, with the content of molybdenum element being at least 400 ppm by mass, relative to the total mass of the lubricant composition, at least a first detergent additive chosen from magnesium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, optionally, at least a second detergent additive chosen from calcium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, wherein the combined content of magnesium element and of calcium element, relative to the total mass of the lubricant composition, is at least 1000 ppm by mass.

2. A lubricant composition according to claim 1, wherein the content of molybdenum element is less than or equal to 1,500 ppm by mass, relative to the total mass of the lubricant composition.

3. A lubricant composition according to claim 1, wherein the first detergent additive is selected from among magnesium sulfonates.

4. A lubricant composition according to claim 1, comprising at least a second detergent additive selected from among calcium salts of carboxylic acids, sulfonates, salicylates, naphthenates, phenates and any mixture thereof; and wherein the ratio of the calcium element content to the magnesium element content ranges from 10:1 to 1:10.

5. A lubricant composition according to claim 4, wherein the ratio of the calcium element content to the magnesium element content ranges from 5:1 to 1:5.

6. A lubricant composition according to claim 1, wherein the second detergent additive is selected from among calcium carboxylates, preferably from calcium salicylates.

7. A lubricant composition according to claim 1, wherein the organomolybdenum compound is selected from molybdenum dithiocarbamates.

8. A method for the lubrication of a combustion engine, said method comprising bringing at least one part of the engine into contact with the lubricant composition of claim 1.

9. The method according to claim 8 for the lubrication of a combustion engine of a plug-in hybrid vehicle or of a hybrid vehicle with a range extender.

10. The method according to claim 8 in order to: prevent, and/or inhibit, and/or slow down problems associated with cold-starts of the said engine; and/or prevent, and/or inhibit, and/or slow down corrosion phenomena that are likely to occur in the said engine; and/or prevent, and/or inhibit, and/or slow down wear and tear of the said engine; and/or prevent, and/or inhibit, and/or slow down the phenomena of demixing of the lubricant composition.

Description

DETAILED DESCRIPTION

[0015] These objectives are achieved by the present patent application for a lubricant composition comprising: [0016] at least one base oil, [0017] from 0.1% to 13% by mass, relative to the total mass of the lubricant composition, of at least one viscosity index improver additive, [0018] at least one organomolybdenum compound, with the content of molybdenum element being at least 400 ppm by mass, relative to the total mass of the lubricant composition, [0019] at least a first detergent additive chosen from magnesium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, [0020] optionally, at least a second detergent additive chosen from calcium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, [0021] wherein the combined content of magnesium element and of calcium element, relative to the total mass of the lubricant composition, is at least 1000 ppm by mass.

Base Oil

[0022] The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origin, possibly regenerated, belonging to groups I to V according to the categories defined in the American Petroleum Institute (API) classification (or equivalents thereof according to the ATIEL [Technical Association of the European Lubricants Industry] classification) (Table A) or mixtures thereof.

TABLE-US-00001 TABLE 1 Saturates Sulfur Viscosity Index content content (VI) Group I <90% >0.03% 80 VI < 120 Mineral Oils Group II 90% 0.03% 80 VI < 120 Hydrocracked Oils Group III 90% 0.03% 120 Hydrocracked or Hydro- Isomerized Oils Group IV Polyalphaolfines (PAO) Group V Esters and all other base oils not included in Groups I to IV

[0023] The mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerisation and hydrofinishing.

[0024] Mixtures of synthetic and mineral oils, possibly regenerated, may also be used.

[0025] In general, there is no limitation as to the use of different lubricant base oils in order to produce lubricant compositions according to the invention, other than they must have appropriate properties, particularly in terms of viscosity, viscosity index, sulfur content and resistance to oxidation, which are suitable for use in vehicle engines or transmissions.

[0026] The base oils of the lubricant compositions according to the invention may also be selected from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers that contain from 4 to 32 carbon atoms, for example from octene or decene, and that have a viscosity at 100 C. of between 1.5 and 15 mm2.Math.s-1 according to the standard ASTM D445. Their average molecular weight is generally between 250 and 3,000 according to the standard ASTM D5296.

[0027] The lubricant composition according to the invention may comprise at least 50% by weight of base oils relative to the total weight of the composition. In a more advantageous manner, the lubricant composition according to the invention comprises at least 60% by weight, or indeed at least 70% by weight, of base oils relative to the total weight of the composition. In a particularly more advantageous manner, the lubricant composition according to the invention comprises 75% to 95% by weight of base oils relative to the total weight of the composition.

Viscosity Index Improver Additive

[0028] The lubricant composition according to the invention comprises at least one viscosity index improver for improving the viscosity index of the lubricant composition.

[0029] For the purposes of the invention, the term viscosity index improver is understood to refer to a chemical compound that serves to ensure that the lubricant composition has good cold flow properties and minimum viscosity at high temperatures.

[0030] Examples of viscosity index improver polymers that may be mentioned include polymer esters; hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene; homopolymers or copolymers of olefins such as ethylene or propylene; and polyacrylates and polymethacrylates (PMA).

[0031] The lubricant composition according to the invention typically comprises from 0.1% to 13% by weight of viscosity index improver(s), relative to the total weight of the lubricant composition.

[0032] Preferably, the lubricant composition according to the invention comprises from 0.5% to 12% by weight of viscosity index improver(s), relative to the total weight of the lubricant composition, more preferentially from 1% to 10% by weight, still more preferentially from 5% to 10% by weight.

Organomolybdenum Compound

[0033] The lubricant composition according to the invention comprises at least one organomolybdenum compound.

[0034] The term organomolybdenum compound according to the invention is understood to refer to any liposoluble (fat-soluble) organomolybdenum compound.

[0035] The organomolybdenum compound according to the present invention may be selected from organic molybdenum complexes comprising at least one chemical element molybdenum (Mo), preferably at least two chemical elements molybdenum (Mo), and at least one ligand such as a carboxylate ligand, an ester ligand, an amide ligand, a dithiophosphate ligand, or a dithiocarbamate ligand.

[0036] For example, organic complexes of molybdenum with carboxylates, esters and amides can be obtained by reacting molybdenum oxide or ammonium molybdates with fatty substances, glycerides, fatty acids or fatty acid derivatives (esters, amines, amides, etc.).

[0037] For the purposes of the invention, the carboxylate ligands, ester ligands and amide ligands are free from sulfur and phosphorus.

[0038] In one embodiment, the organomolybdenum compound of the invention is selected from complexes of molybdenum with amide ligands, mainly prepared by reacting a molybdenum source, which may for example be molybdenum trioxide, and an amine derivative, and fatty acids containing for example from 4 to 36 carbon atoms such as for example the fatty acids contained in plant or animal oils.

[0039] The synthesis of such compounds is described, for example, in the patents U.S. Pat. No. 4,889,647, EP0546357, U.S. Pat. No. 5,412,130 or EP1770153.

[0040] According to one preferred embodiment, the organomolybdenum compound is selected from among dinuclear organomolydbene compounds.

[0041] For the purposes of the invention the term dinuclear organomolybdenum compound is understood to refer to organomolybdenum compounds in which the nucleus contains two molybdenum atoms. They are also referred to as dimeric organomolybdenum compounds.

[0042] In one preferred embodiment of the invention, the organomolybdenum compound is selected from organic complexes of molybdenum with amide ligands obtained by reaction of: [0043] (i) a fatty substance of the type: mono-, di- or triglyceride, or fatty acid; [0044] (ii) an amino source having the formula (A):

##STR00001## [0045] in which: [0046] X.sup.1 represents an oxygen atom or a nitrogen atom; [0047] X.sup.2 represents an oxygen atom or a nitrogen atom; [0048] n or m represents 1 when respectively X.sup.1 or X.sup.2 represents an oxygen atom; [0049] n or m represents 2 when respectively X.sup.1 or X.sup.2 represents a nitrogen atom; [0050] (iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferentially ammonium molybdate.

[0051] In one embodiment of the invention, the organomolybdenum compound may comprise from 0.1 to 30% by weight, preferably from 0.1 to 20%, more preferentially from 2 to 8.5% by weight of molybdenum relative to the total weight of the organomolybdenum complex.

[0052] Preferably, the organomolybdenum compound comprises at least one organic molybdenum complex having the formula (I) or (II), alone or in a mixture:

##STR00002## [0053] in which: [0054] X.sup.1 represents an oxygen atom or a nitrogen atom; [0055] X.sup.2 represents an oxygen atom or a nitrogen atom; [0056] n represents 1 when X.sup.1 represents an oxygen atom, and m represents 1 when X.sup.2 represents an oxygen atom; [0057] n represents 2 when X.sup.1 represents a nitrogen atom, and m represents 2 when X.sup.2 represents a nitrogen atom; [0058] R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group, containing from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms;

##STR00003## [0059] in which: [0060] X.sup.1 represents an oxygen atom or a nitrogen atom; [0061] X.sup.2 represents an oxygen atom or a nitrogen atom; [0062] n represents 1 when X.sup.1 represents an oxygen atom, and m represents 1 when X.sup.2 represents an oxygen atom; [0063] n represents 2 when X.sup.1 represents a nitrogen atom, and m represents 2 when X.sup.2 represents a nitrogen atom; [0064] R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group, containing from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms; [0065] R.sub.2 represents a linear or branched, saturated or unsaturated alkyl group, containing from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms.

[0066] Advantageously, the organic complex of molybdenum having the formula (I) or (II) is prepared by reaction of: [0067] (i) a fatty substance of the type: mono-, di- or triglyceride, or fatty acid; [0068] (ii) diethanolamine or 2-(2-aminoethyl) aminoethanol; [0069] (iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferentially ammonium molybdate.

[0070] More advantageously, the organic complex of molybdenum having the formula (I) is constituted of at least one compound having the formula (I-a) or (I-b), alone or in a mixture:

##STR00004## [0071] in which R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group, containing from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms,

##STR00005## [0072] in which R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group, containing from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms.

[0073] By way of an example of sulfur-free molybdenum complexes according to the invention mention may be made of Molyvan 855@ marketed by the company Vanderbilt.

[0074] In one other embodiment of the invention, the organomolybdenum compound is selected from among organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

[0075] Within the meaning of the invention, organic complexes of molybdenum with dithiophosphate ligands are also referred to as molybdenum dithiophosphates or Mo-DTP compounds, and organic complexes of molybdenum with dithiocarbamate ligands are also referred to as molybdenum dithiocarbamates or Mo-DTC compounds.

[0076] In a more preferred embodiment of the invention, the organomolybdenum compound is selected from molybdenum dithiocarbamates.

[0077] Mo-DTC compounds are complexes formed from a molybdenum metal core bound to one or more ligands, the ligand being an alkyl dithiocarbamate group. These compounds are well known to the person skilled in the art.

[0078] In one embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferentially from 3 to 28%, advantageously from 4 to 15% by weight of molybdenum, relative to the total weight of the Mo-DTC compound.

[0079] In one other embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferentially from 3 to 28%, advantageously from 4 to 15% by weight of sulfur, relative to the total weight of the Mo-DTC compound.

[0080] In a preferred embodiment of the invention, the Mo-DTC compound is a dimeric Mo-DTC compound.

[0081] Examples of dimeric Mo-DTC compounds that may be mentioned include the compounds and related preparation methods thereof as described in the documents EP 0757093, EP 0719851, EP 0743354 or EP 1013749.

[0082] Dimeric Mo-DTC compounds generally correspond to compounds having the formula (III):

##STR00006## [0083] in which: [0084] R.sub.3, R.sub.4, R.sub.5, R.sub.6, which may be identical or different, independently represent a hydrocarbon group selected from the alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups; [0085] X.sub.3, X.sub.4, X.sub.5 and X.sub.6, which may be identical or different, independently represent an oxygen atom or a sulfur atom.

[0086] The term alkyl group within the meaning of the invention, is understood to refer to a linear or branched, saturated or unsaturated hydrocarbon group, containing from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms.

[0087] In one embodiment of the invention, the alkyl group is selected from the group formed by methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-ethylhexyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldodecyl, 2-octyldodecyl, 2-decyltetradecyl, 2-dodecylhexadecyl, 2-hexadecyloctadecyl, 2-tetradecyloctadecyl, myristyle, palmityl and stearyl.

[0088] The term alkenyl group within the meaning of the present invention is understood to refer to a linear or branched hydrocarbon group comprising at least one double bond and containing from 2 to 24 carbon atoms. The alkenyl group may be selected from vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl and oleic.

[0089] The term aryl group within the meaning of the present invention is understood to refer to a polycyclic aromatic hydrocarbon or an aromatic group, whether or not substituted by an alkyl group. The aryl group may contain from 6 to 24 carbon atoms.

[0090] In one embodiment, the aryl group may be selected from the group formed by phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, phenyl-styrene, p-cumylphenyl and naphthyl.

[0091] The term cycloalkyl group within the meaning of the present invention is understood to refer to a cyclic or polycyclic hydrocarbon, whether or not substituted by an alkyl group.

[0092] The term cycloalkenyl group within the meaning of the present invention is understood to refer to a cyclic or polycyclic hydrocarbon, whether or not substituted by an alkyl group, and comprising at least one unsaturation.

[0093] The cycloalkyl groups and cycloalkenyl groups may contain from 3 to 24 carbon atoms.

[0094] For the purposes of the present invention, the cycloalkyl groups and the cycloalkenyl groups may be selected, without limitation, from the group consisting of cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl, methylcyclohexenyl.

[0095] In one preferred embodiment of the invention, R.sub.3, R.sub.4, R.sub.5, and R.sub.6, which may be identical or different, independently represent an alkyl group containing from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms, or an alkenyl group containing from 2 to 24 carbon atoms.

[0096] In one embodiment of the invention, X.sub.3, X.sub.4, X.sub.5 and X.sub.6 may be identical and may represent a sulfur atom.

[0097] In one other embodiment of the invention, X.sub.3, X.sub.4, X.sub.5 and X.sub.6 may be identical and may be an oxygen atom.

[0098] In one other embodiment of the invention, X.sub.3 and X.sub.4 may represent a sulfur atom, and X.sub.5 and X.sub.6 may represent an oxygen atom.

[0099] In one other embodiment of the invention, X.sub.3 and X.sub.4 may represent an oxygen atom, and X.sub.5 and X.sub.6 may represent a sulfur atom.

[0100] In one other embodiment of the invention, the ratio of the number of sulfur atoms to the number of oxygen atoms (S/O) of the Mo-DTC compound may vary from (1/3) to (3/1).

[0101] In one other embodiment of the invention, the Mo-DTC compound having the formula (III) may be selected from a symmetric Mo-DTC compound, an asymmetric Mo-DTC compound and a combination thereof.

[0102] The term symmetric Mo-DTC compound according to the invention is understood to refer to a Mo-DTC compound having the formula (V) in which the groups R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are identical.

[0103] The term asymmetric Mo-DTC compound according to the invention, is understood to refer to a Mo-DTC compound having the formula (V) in which the R.sub.3 and R.sub.4 groups are identical, the R.sub.5 and R.sub.6 groups are identical, and the R.sub.3 and R.sub.4 groups are different from the R.sub.5 and R.sub.6 groups.

[0104] In one preferred embodiment of the invention, the Mo-DTC compound is a mixture of at least one symmetric Mo-DTC compound and at least one asymmetric Mo-DTC compound.

[0105] In one embodiment of the invention, R.sub.3 and R.sub.4, which are identical, represent an alkyl group containing from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms; and R.sub.5 and R.sub.6, which are identical, represent an alkyl group containing from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms; and the R.sub.3 and R.sub.4 groups are identical to or different from the R.sub.5 and R.sub.6 groups.

[0106] In one other preferred embodiment of the invention, R.sub.3 and R.sub.4, which are identical, represent an alkyl group containing from 6 to 10 carbon atoms; and R.sub.5 and R.sub.6, which are identical, represent an alkyl group containing from 10 to 15 carbon atoms; and the R.sub.3 and R.sub.4 groups are different from the R.sub.5, and R.sub.6 groups.

[0107] In one other preferred embodiment of the invention, R.sub.3 and R.sub.4, which are identical, represent an alkyl group containing from 10 to 15 carbon atoms; and R.sub.5, and R.sub.6, which are identical, represent an alkyl group containing from 6 to 10 carbon atoms; and the R.sub.3 and R.sub.4 groups are different from the R.sub.5, and R.sup.6 groups.

[0108] In one other preferred embodiment of the invention, R.sub.3, R.sub.4, R.sub.5, and R.sub.6, which are identical, represent an alkyl group containing from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms.

[0109] In an advantageous manner, the Mo-DTC compound is selected from compounds having the formula (III) in which: [0110] X.sup.3 and X.sup.4 represent an oxygen atom; [0111] X.sup.5 and X.sup.6 represent a sulfur atom; [0112] R.sub.3 represents an alkyl group containing 8 carbon atoms or an alkyl group containing 13 carbon atoms; [0113] R.sub.4 represents an alkyl group containing 8 carbon atoms or an alkyl group containing 13 carbon atoms; [0114] R.sub.5 represents an alkyl group containing 8 carbon atoms or an alkyl group containing 13 carbon atoms; [0115] R.sub.6 represents an alkyl group containing 8 carbon atoms or an alkyl group containing 13 carbon atoms.

[0116] Thus, in an advantageous manner, the Mo-DTC compound is selected from among the compounds having the formula (III-a)

##STR00007##

[0117] in which the groups R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are as defined for formula (III).

[0118] In a more advantageous manner, the Mo-DTC compound is a mixture of: [0119] a Mo-DTC compound having the formula (III-a) wherein R.sub.3, R.sub.4, R.sub.5, and R.sub.6 represent an alkyl group containing 8 carbon atoms; [0120] a Mo-DTC compound having the formula (III-a) wherein R.sub.3, R.sub.4, R.sub.5, and R.sub.6 represent an alkyl group containing 13 carbon atoms; and/or [0121] a Mo-DTC compound having the formula (III-a) wherein R.sub.3, R.sub.4 represent an alkyl group containing 8 carbon atoms; and R.sub.5 and R.sub.6 represent an alkyl group containing 13 carbon atoms.

[0122] Examples of Mo-DTC compounds that may be mentioned include the products Molyvan L, Molyvan 807@, or Molyvan 822@ marketed by the R.T Vanderbilt Company, or the products Sakura-lube 200@, Sakura-lube 165@, Sakura-lube 525, or Sakura-lube 600@ marketed by the company Adeka.

[0123] The lubricant composition according to the invention typically comprises at least 400 ppm by weight of the element molybdenum, relative to the total weight of the lubricant composition.

[0124] Preferably, the lubricant composition according to the invention is such that the content of molybdenum element therein is less than or equal to 1,500 ppm by weight, relative to the total weight of the lubricant composition, more preferentially from 500 ppm to 1200 ppm, even more preferentially from 750 ppm to 1000 ppm.

First Detergent Additive (Magnesium-Based)

[0125] The lubricant composition according to the invention also comprises at least one first detergent additive.

[0126] Detergent additives generally serve to reduce the formation of deposits on the surface of metal parts by dissolving the secondary products of oxidation and combustion.

[0127] The detergent additives that may be used in lubricant compositions according to the invention are generally known to the person skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophobic head. The associated cation may be a metal cation of an alkali or alkaline earth metal.

[0128] The first detergent additive is typically selected from magnesium salts of carboxylic acids, sulphonates, salicylates, naphthenates, phenates and any mixture thereof.

[0129] According to one preferred embodiment, the first detergent additive is selected from among magnesium sulfonates.

[0130] The detergents used will be non-overbased (or neutral) or overbased. The term non-overbased or neutral detergent is used when the metal salts contain the metal in an approximately stoichiometric quantity. The term overbased detergents refers to detergents where the metal is in excess (in a quantity greater than the stoichiometric quantity). The excess metal that gives the detergent its overbased nature is in the form of metal salts that are insoluble in oil. The overbased detergents thus take the form of micelles made up of insoluble metal salts kept in suspension in the lubricant composition by the detergents in the form of oil-soluble metal salts. These micelles may contain one or more types of insoluble metal salts, stabilized by one or more types of detergent. The overbased detergents are referred to as of mixed type if the micelles comprise several types of detergent, which differ from each other in respect of the nature of their hydrophobic chain.

[0131] Advantageously, the one or more first detergent additive(s) represent(s) from 0.5 to 8% by weight, preferably from 2% to 4% by weight, relative to the total weight of the lubricant composition.

Second Detergent Additive (Calcium-Based)

[0132] According to one preferred embodiment, the composition according to the invention further comprises at least one second detergent additive.

[0133] The second detergent additive is typically selected from among calcium salts.

[0134] Preferably, the second detergent additive is selected from among calcium salts of carboxylic acids, sulfonates, salicylates, naphthenates, phenates and any mixture thereof.

[0135] Advantageously, the second detergent additive is selected from among calcium carboxylates, preferably from calcium salicylates.

[0136] The detergents used will be non-overbased (or neutral) or overbased. The term non-overbased or neutral detergent is used when the metal salts contain the metal in an approximately stoichiometric quantity. The term overbased detergents refers to detergents where the metal is in excess (in a quantity greater than the stoichiometric quantity). The excess metal that gives the detergent its overbased nature is in the form of metal salts that are insoluble in oil. The overbased detergents thus take the form of micelles made up of insoluble metal salts kept in suspension in the lubricant composition by the detergents in the form of oil-soluble metal salts. These micelles may contain one or more types of insoluble metal salts, stabilized by one or more types of detergent. The overbased detergents are referred to as of mixed type if the micelles comprise several types of detergent, which differ from each other in respect of the nature of their hydrophobic chain.

[0137] Advantageously, when present, the second detergent additive represents from 0.5 to 8% by weight, preferably from 2% to 4% by weight, relative to the total weight of the lubricant composition.

[0138] According to one embodiment, the composition according to the invention is free of a second detergent additive.

[0139] Preferably, according to this embodiment, the content of magnesium element is at least 1000 ppm by weight, relative to the total weight of the lubricant composition, more preferentially from 1100 ppm to 3000 ppm, even more preferentially from 1400 ppm to 2800 ppm, typically from 1600 ppm to 2650 ppm.

[0140] According to one preferred embodiment, the composition according to the invention comprises at least one first detergent additive and at least one second detergent additive.

[0141] Preferably, according to this preferred embodiment, the combined content of magnesium element and of calcium element, relative to the total weight of the lubricant composition, is at least 1000 ppm by weight, more preferentially from 1100 ppm to 3000 ppm, even more preferentially from 1400 ppm to 2800 ppm, typically from 1600 ppm to 2650 ppm.

[0142] For the purposes of the invention, the term combined content of magnesium element and of calcium element is understood to refer to the sum of the content of magnesium element present in the lubricant composition and the content of calcium element present in the lubricant composition.

[0143] Preferably, the ratio of the calcium element content (from the first detergent additive) to the magnesium element content (from the second detergent additive) ranges from 10:1 to 1:10.

[0144] Advantageously, the ratio of the calcium element content to the magnesium element content ranges from 5:1 to 1:5, preferably from 5:2 to 5:2, and more preferentially from 5:2 to 1:1.

[0145] The contribution to the BN (Base Number measured in accordance with ASTM D-2896) of the lubricant compositions according to the present invention is totally or partially attributable to the neutral or overbased detergents based on alkali metals or alkaline earth metals, in particular to the first and second detergent additives.

[0146] The BN value of the lubricant compositions according to the present invention, measured according to ASTM D-2896, may vary from 1 to 140 mg KOH/g, preferably from 3 to 80 mg KOH/g, more preferentially from 5 to 50 mg KOH/g, typically from 5 to 20 mg KOH/g. The BN value should be selected based on the conditions of use of the lubricant compositions and in particular the sulfur content of the fuel used.

Other Additives

[0147] Numerous optional additives may also be present in the lubricant compositions according to the invention.

[0148] The preferred additives for the lubricant composition according to the invention are selected from among detergent additives other than the first and second detergent additives defined above, friction modifier additives other than the molybdenum compounds defined above, extreme pressure additives, dispersants, pour point activators, anti-foaming agents, thickeners and mixtures thereof.

[0149] Preferably, the lubricant compositions according to the invention comprise one or more extreme pressure additive(s) or a mixture thereof.

[0150] Anti-wear additives and extreme pressure additives provide friction protection for surfaces by forming a protective film adsorbed onto these surfaces.

[0151] There exists a wide variety of anti-wear additives. Preferably, for the lubricant compositions of the invention, the anti-wear additives are selected from additives comprising phosphorus and sulfur such as alkylthiophosphate metals, in particular zinc alkylthiophosphate, and more precisely zinc dialkyldithiophosphate or ZnDTP. The preferred compounds are those having the formula Zn((SP(S)(OR)(OR))2, in which R and R, which may be identical or different, independently represent an alkyl group, preferably an alkyl group containing from 1 to 18 carbon atoms.

[0152] Amine phosphates are also anti-wear additives that may be used in the lubricant compositions of the invention. However, the phosphorus atoms provided by these additives can act as a poison for the catalytic systems of automobiles since they generate ash. It is possible to minimize these effects by substituting part of the amine phosphates with additives that do not contribute phosphorus, such as polysulphides, in particular sulfur-containing olefins.

[0153] Advantageously, the lubricant compositions according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferentially from 0.1 to 2% by weight, relative to the total weight of lubricant composition, of anti-wear and extreme pressure additives.

[0154] Advantageously, the lubricant compositions according to the invention comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferentially from 0.1 to 2% by weight, relative to the total weight of lubricant composition, of anti-wear additives (or anti-wear compounds).

[0155] Advantageously, the compositions according to the invention may comprise at least one friction-modifier additive other than the molybdenum compounds of the invention. The friction-modifier additives may in particular be selected from among compounds that provide metallic elements, and ashless compounds. Among the compounds providing metallic elements mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, for which the ligands may be hydrocarbon compounds that contain oxygen, nitrogen, sulfur or phosphorus atoms. Ashless friction modifier additives are generally of organic origin or may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, fatty epoxide borates, fatty amines or glycerol acid esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

[0156] Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0.1 to 2% by weight relative to the total weight of the lubricant composition, of friction-modifier additive other than the molybdenum compounds according to the invention.

[0157] Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive.

[0158] Antioxidant additives generally delay the degradation of the lubricant composition. This degradation is most often manifested by the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

[0159] Antioxidant additives generally act as inhibitors of free radicals or inhibitors that decompose hydroperoxide. Commonly used antioxidants that may be mentioned include phenolic-type antioxidants, amine-type antioxidants, sulfur- and phosphorus-containing antioxidants. Some of these antioxidants, for example those containing sulfur and phosphorus, can generate ash. The phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be selected from sterically hindered phenols, esters of sterically hindered phenols, sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C1 to C12 alkyl group, N,N-dialkyl-aryl-diamines and mixtures thereof.

[0160] Preferably according to the invention, the sterically hindered phenols are selected from among compounds comprising a phenol group for which at least one of the carbon atoms in the vicinity of the carbon atom carrying the alcohol functional group is substituted with at least one C1 to C10 alkyl group, preferably a C1 to C6 alkyl group, preferably a C4 alkyl group, preferably a ter-butyl group.

[0161] Amine compounds are another class of antioxidant additives that may be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds include aromatic amines, for example aromatic amines having the formula NRaRbRc wherein Ra represents an aliphatic group or an aromatic group, which may be optionally substituted; Rb represents an aromatic group, which may be optionally substituted; Rc represents a hydrogen atom, an alkyl group, an aryl group or a group having the formula RdS(O)zRe wherein Rd represents an alkylene or alkenylene group; Re represents an alkyl group, an alkenyl group or an aryl group; and z represents 0, 1 or 2.

[0162] Sulphur-containing alkyl phenols or the alkali metal or alkaline earth metal salts thereof may also be used as antioxidant additives.

[0163] Other classes of antioxidant additives include copper containing compounds, for example copper thio- or dithio-phosphate; salts of copper and of carboxylic acids; dithiocarbamates; sulphonates; phenates; copper acetylacetonates. Copper I and II salts and salts of succinic acid or succinic anhydride may also be used.

[0164] The lubricant compositions according to the invention may also include any type of antioxidant known to the person skilled in the art.

[0165] Advantageously, the lubricant composition comprises at least one ash-free antioxidant additive.

[0166] Also advantageously the lubricant composition according to the invention comprises from 0.1 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

[0167] The lubricant composition according to the invention may also comprise at least one detergent additive that is distinct from the first and second detergent additives defined above.

[0168] The said detergent additives are preferably selected from among alkali metal or alkaline-earth metal salts of carboxylic acid, sulphonates, salicylates, naphthenates, as well as phenate salts. The alkali and alkaline-earth metals are preferably sodium or barium.

[0169] These metal salts generally comprise the metal either in a stoichiometric quantity or in excess, that is to say at a content level greater than the stoichiometric content. These latter are thus then overbased detergents; the excess metal relating to the overbased nature of the detergent additive is generally in the form of an oil-insoluble metal salt, for example carbonate, hydroxide, oxalate, acetate, glutamate, and preferably carbonate.

[0170] Advantageously, the lubricant composition according to the invention may comprise from 0.2% to 8% or from 0.5% to 3% by weight of additional detergent additives (distinct from the first and second detergent additives defined above), relative to the total weight of the lubricant composition.

[0171] As well, in an advantageous manner, the lubricant composition according to the invention may also comprise a pour point depressant additive.

[0172] By slowing down the formation of paraffin crystals, the pour point depressant additive generally ameliorates the cold temperature behavior of the lubricant composition according to the invention.

[0173] Examples of pour point depressant additives that may be mentioned include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalene and alkyl polystyrenes.

[0174] Advantageously, the lubricant composition according to the invention may also comprise a dispersing agent.

[0175] The dispersing agents may be selected from Mannich bases, succinimides and derivatives thereof.

[0176] As well, in an advantageous manner, the lubricant composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total weight of lubricant composition.

[0177] The lubricant composition according to the invention may also comprise at least one thickening agent.

[0178] The lubricant composition according to the invention may also comprise an antifoaming agent and a demulsifying agent.

The Lubricant Composition

[0179] Preferably, the lubricant composition comprises, relative to the total weight of the lubricant composition: [0180] from 50% to 95% by weight of at least one base oil, [0181] from 0.1% to 13% by weight of at least one viscosity index improver additive, [0182] at least one organomolybdenum compound, with the content of molybdenum element ranging from 400 ppm to 1500 ppm by weight, [0183] at least a first detergent additive chosen from magnesium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, [0184] optionally, at least a second detergent additive chosen from calcium salts of carboxylic acids, of sulfonates, of salicylates, of naphthenates, of phenates and any mixture thereof, [0185] wherein the combined content of magnesium element and of calcium element, relative to the total weight of the lubricant composition, ranges from 1000 ppm to 3000 ppm by weight.

[0186] Advantageously, the lubricant composition comprises, relative to the total weight of the lubricant composition: [0187] from 60% to 95% by weight of at least one base oil, [0188] from 0.5% to 12% by weight of at least one viscosity index improver additive, [0189] at least one organomolybdenum compound, with the content of molybdenum element ranging from 500 ppm to 1500 ppm by weight, [0190] at least a first detergent additive chosen from magnesium sulfonates, [0191] optionally, at least a second detergent additive chosen from calcium salicylates, [0192] wherein the combined content of magnesium element and of calcium element, relative to the total weight of the lubricant composition, ranges from 1400 ppm to 2800 ppm by weight.

[0193] In a more advantageous manner, the lubricant composition comprises, relative to the total weight of the lubricant composition: [0194] from 75% to 95% by weight of at least one base oil, [0195] from 5% to 10% by weight of at least one viscosity index improver additive, [0196] at least one organomolybdenum compound, with the content of molybdenum element ranging from 750 ppm to 100 ppm by weight, [0197] at least a first detergent additive chosen from magnesium sulfonates, [0198] optionally, at least a second detergent additive chosen from calcium salicylates, [0199] wherein the combined content of magnesium element and of calcium element, relative to the total weight of the lubricant composition, ranges from 1600 ppm to 2650 ppm by weight.

Uses and Methods

[0200] The invention also relates to the use of a lubricant composition as defined above for the lubrication of a combustion engine.

[0201] Preferably, the engine is selected from gasoline engines and diesel engines, preferably the combustion engine is a gasoline engine.

[0202] In one preferred embodiment, the engine is an engine of a plug-in hybrid vehicle or of a hybrid vehicle with a range extender.

[0203] In the context of the present invention, the term plug-in hybrid vehicle is understood to refer to a vehicle that comprises an internal combustion engine and an electric motor, wherein the battery can be recharged over the electrical grid; as a result, it is possible for such vehicles to be driven in 100% electric mode over a distance of several tens of kilometers, such as 50 kilometers, for example.

[0204] In the context of the present invention, the term hybrid vehicle with range extender is understood to refer to a hybrid vehicle in which only the electric motor drives the wheels. This electric motor is powered by a battery over a distance of several tens of kilometers. When the battery reaches a certain threshold level of charge (e.g. of the order of 30%), the internal combustion engine starts up and drives a current generator thereby enabling production of the electricity needed to recharge the battery and keep the electric motor running.

[0205] According to a first embodiment, the invention relates to the use of the lubricant composition according to the invention in order to: prevent, and/or inhibit, and/or slow down problems associated with cold-starts of the engine.

[0206] According to a second embodiment, the invention relates to the use of the lubricant composition according to the invention in order to: prevent, and/or inhibit, and/or slow down corrosion phenomena that are likely to occur in the said engine.

[0207] According to a third embodiment, the invention relates to the use of the lubricant composition according to the invention in order to: prevent, and/or inhibit, and/or slow down wear and tear of the said engine.

[0208] According to a fourth embodiment, the invention relates to the use of the lubricant composition according to the invention in order to: prevent, and/or inhibit, and/or slow down the phenomena of demixing of the lubricant composition.

[0209] Within the meaning of the present invention the term demixing is understood to refer to the phenomenon whereby the water present in the lubricant composition, initially in the form of emulsions, spontaneously separates from the mixture so as to form a continuous aqueous phase.

[0210] The ability of a lubricant composition to prevent the demixing phenomena may, for example, be assessed according to the following protocol: [0211] 1) prepare a 100 mL mixture comprising: 60 mL of the lubricant composition to be tested; 20 mL of water; and 20 mL of fuel, for example E10 type petrol; [0212] 2) agitate the mixture in order to make it homogeneous; [0213] 3) place the mixture in a closed frustoconical flask and then place in an oven at 60 C. for a period of 18 hours.

[0214] After 18 h stored in the oven, the ability of the lubricant composition to prevent demixing is visually assessed by an operator.

[0215] If the mixture is found to be in the form of a single phase, this signifies that the emulsion is stable. The lubricant composition is then assigned the rating PASS, indicating that the lubricant composition has very low susceptibility to demixing phenomena.

[0216] Conversely, in the event that the mixture is not homogeneous, in particular due to the formation of an oily supernatant phase, the lubricant composition is then assigned the rating FAIL. The emulsion is not sufficiently stable and the lubricant composition does not serve to sufficiently prevent demixing phenomena.

[0217] The invention also relates to a lubrication method for lubricating a combustion engine, in particular an engine of a plug-in hybrid vehicle or of a hybrid vehicle with a range extender, the said method comprising of bringing at least one part of the engine into contact with the lubricant composition according to the invention.

[0218] The variants and embodiments detailed below for the viscosity index improver additive, the orgnomolybdenum compound, the first detergent additive, and the second detergent additive are also applicable to the various uses defined above.

[0219] The particular, advantageous or preferred characteristic features of the combined use according to the invention define the particular, advantageous or preferred combinations that may be used according to the invention.

[0220] The various different aspects of the invention may be better illustrated by the examples that follow.

EXAMPLE

Example 1: Preparation of Lubricant Compositions

[0221] The lubricant compositions C1, C2, C3* and C4* are prepared from the following components: [0222] Base Oil 1: Group Ill base oil with kinematic viscosity at 40 C., measured according to the standard ASTM D445, equal to 19.57 mm.sup.2/s; kinematic viscosity at 100 C., measured according to the standard ASTM D445, equal to 4.23 mm.sup.2/s; viscosity index, measured according to the standard ASTM D2270, equal to 122; NOACK volatility, measured according to the standard DIN 51581, equal to 15% by weight; [0223] Additive VII: a viscosity index improver, which is a conventional olefin polymer; [0224] MoDTC Compound: molybdenum dialkyldithiocarbamate compound, commercially available under the reference Sakuralube 525@ from the company Adeka; [0225] PPD: Pour Point Depressant; [0226] Additive Package 1: conventional additive package comprising 5% by weight of a first detergent additive of the type: magnesium sulphonate; and 15% by weight of a second detergent additive of the type: calcium salicylate. Additive package 1 does not include any other detergent additives. [0227] Additive Package 2: conventional additive package. Additive Package 2 differs from Additive Package 1 in that it does not comprise a magnesium-based detergent additive. In particular, Additive Package 2 comprises only, by way of the sole detergent additive, 15% by weight of a detergent additive of the type: calcium salicylate. Additive Package 2 does not include any other detergent additives, in particular no magnesium-based detergent additives. [0228] Additional Detergent Additive: conventional detergent additive such as magnesium sulfonate.

[0229] More particularly, the compositions C1, C2, C3* and C4* are prepared by mixing the compounds described in Table 2, at a temperature of the order of 60 C. The percentages indicated correspond to percentages by weight relative to the total weight of the composition.

TABLE-US-00002 TABLE 2 C1 C2 C3* C4* Base Oils 1 (% by weight) 82.5 81.5 83.8 83 Additif VII (% by weight) 6.5 6.5 6.5 6.5 MoDTC Compound 0.8 0.8 0.8 (% by weight) With Molybdenum Content 800 800 800 (ppm by weight) PPD (% by weight) 0.2 0.2 0.2 0.2 Additive Package 1 10 (% by weight) With Magnesium-Based 0.5 First Detergent Additive (% by weight) With Magnesium Content 480 (ppm by weight) With Calcium-Based 1.5 Second Detergent Additive (% by weight) With Calcium Content (ppm 1290 by weight) Additive Package 2 9.5 9.5 9.5 (% by weight) With Calcium-Based 1.5 1.5 1.5 Detergent Additive (% by weight) Mg-Based Additional 1.5 0.55 Detergent Additive (% by weight) With Magnesium Content 1290 480 (ppm by weight) Total Calcium Element 1290 1290 1290 1290 Content ( ppm by weight) Total Magnesium Element 480 1290 480 Content (ppm by weight)

[0230] The compositions C1 and C2 are according to the invention.

[0231] The composition C3* is a comparative composition in that it comprises no organomolybdenum compound.

[0232] The composition C4* is a comparative composition in that it comprises no magnesium-based detergent additives.

Example 2: Ability to Prevent Demixing Phenomena

[0233] The ability of the lubricant compositions prepared as above to prevent demixing phenomena was assessed according to the following protocol:

[0234] A 100 mL composition is prepared by mixing: 60 mL of the lubricant composition to be tested; 20 ml of water; and 20 mL of E10 type petrol fuel. The composition is then mixed using ultraturax (10,000 rpm) for a period of 1 minute. The composition is poured into a closed frustoconical flask, and then placed in an oven at 60 C. for a period of 18 hours.

[0235] After 18 h stored in the oven, the flasks are recovered and the ability of the lubricant composition to prevent demixing is visually assessed by an operator.

[0236] If the mixture is found to be in the form of a single phase, this signifies that the emulsion is stable. The lubricant composition is then assigned the rating PASS, indicating that the lubricant composition has very low susceptibility to demixing phenomena.

[0237] Conversely, in the event that the mixture is not homogeneous, in particular due to the formation of an oily supernatant phase, the lubricant composition is then assigned the rating FAIL. The emulsion is not sufficiently stable and the aqueous phase separates from the oil phase. The lubricant composition does not serve to sufficiently prevent demixing phenomena.

[0238] The results obtained are presented in Table 3.

TABLE-US-00003 TABLE 3 C1 C2 C3* C4* Results PASS PASS FAIL FAIL

[0239] The compositions C1 and C2 according to the invention serve to effectively prevent demixing phenomena.

[0240] Conversely, the emulsions obtained from the lubricant compositions C3* and C4* are not stable. These latter lubricant compositions therefore do not serve to prevent demixing phenomena.