EP3331972A1

EP3331972A1 - Lubricating compositions for preventing or reducing pre-ignition in an engine

Info

Publication number: EP3331972A1
Application number: EP16750764.9A
Authority: EP
Inventors: Nicolas Obrecht
Original assignee: Total Marketing Services SA
Current assignee: TotalEnergies Marketing Services SA
Priority date: 2015-08-06
Filing date: 2016-08-05
Publication date: 2018-06-13
Also published as: FR3039837A1; CN108026469A; WO2017021522A1; WO2017021523A1; FR3039837B1; FR3039836A1; CN107949628A; US20180223215A1; EP3331973A1; FR3039836B1; US20180230395A1

Abstract

The invention relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound selected from the molybdenum dithiophosphate compounds, for preventing or reducing pre-ignition in an engine, preferably in a vehicle engine.

Description

LUBRICATING COMPOSITIONS FOR PREVENTING OR REDUCING PRE-IGNITION

IN A MOTOR

The invention relates to the use of a lubricating composition to prevent or reduce pre-ignition in an engine. More particularly, the invention relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for preventing or reducing the pre-ignition in an engine, preferably in a vehicle engine, in particular motor vehicle.

The present invention also relates to a method for preventing or reducing the pre-ignition in an engine, preferably in a vehicle engine, especially a motor vehicle, implementing this lubricant composition.

The present invention also relates to the use of an organomolybdenum compound in a lubricant composition for preventing or reducing pre-ignition in an engine, preferably in a motor vehicle, especially motor vehicles.

Technological background

Under ideal conditions, normal combustion in a spark-ignition engine occurs when a mixture of fuel, and in particular fuel and air, is ignited in the combustion chamber inside the cylinder by the production of a fuel. spark from a spark plug. Such normal combustion is generally characterized by expanding the flame front through the combustion chamber in an orderly and controlled manner.

However, in some cases, the air / fuel mixture may be prematurely ignited by a source of ignition prior to ignition by the spark of the spark plug, leading to a phenomenon known as pre-ignition.

However, it is preferable to reduce or even eliminate the pre-ignition, as this generally results in the presence of a sharp increase in temperatures and pressures in the combustion chamber, and thus have a significant negative impact on the efficiency. and the overall performance of an engine. In addition, pre-ignition can cause significant damage to the cylinders, pistons, spark plugs and valves in the engine and in some cases can even lead to engine failure or even engine failure.

Recently, low-speed pre-ignition (LSPI) has been identified, particularly by car manufacturers, as a potential problem for smaller engines (or downsized engines). LSPI generally occurs at low speeds and high loads, and can cause serious damage to the pistons and / or cylinders. Thus it would be desirable to have a lubricant that can prevent or reduce the risk of pre-ignition, including the LSPI.

Solutions for decreasing the calcium content or increasing the zinc dithiophosphate or molybdenum dithiocarbamate content in a lubricant have been described (Takeuchi et al, "Investigation of Engine Oil Effect on Abnormal Combustion in Turbocharged Direct Injection - Spark Ignition Engines, "SAE Int J. Fuels Lubr 5 (3): 1017-1024, 2012; Hirano et al," Investigation of Engine Oil Effect on Abnormal Combustion in Turbocharged Direct Injection - Spark Ignition Engines (Part 2), "SAE Technical Paper 2013-01 -2569, 2013). However, these solutions are still insufficient to significantly reduce pre-ignition and difficult to implement, especially in countries where a high level of basicity is required on fuels. In addition, problems of lubricant stability or compatibility with post-treatment systems are associated with these solutions.

The application WO 2015023559 describes a method for reducing the pre-ignition by adding, in a lubricant composition, an additive for retarding ignition, said additive being chosen from organic compounds comprising at least one aromatic nucleus. However, these light organic compounds could cause an excessive increase in lubricant volatility. An object of the present invention is therefore to provide compounds as well as a lubricating composition comprising these compounds which overcomes all or part of the aforementioned drawbacks.

Another object of the present invention is to provide a lubricant composition for preventing or reducing pre-ignition in an engine and whose formulation is easy to implement.

Another object of the present invention is to provide a lubricant composition for preventing or reducing pre-ignition in an engine while maintaining satisfactory or improved lubrication properties.

Another object of the present invention is to provide a lubrication method for preventing or reducing pre-ignition in an engine. Summary of the invention The invention thus relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for preventing or reducing preignition in an engine, said organomolybdenum compound being chosen from:

• molybdenum dithiophosphate compounds (Mo-DTP), or

· Molybdenum complexes free from sulfur.

Surprisingly, the Applicant has found that the presence of at least one organomolybdenum compound chosen from Mo-DTP and sulfur-free molybdenum complexes in a lubricating composition allows the lubricating composition, once implemented in an engine, prevent or reduce pre-ignition in the engine.

Thus, the present invention makes it possible to formulate lubricant compositions having both good stability and good pre-ignition prevention or reduction properties when used in an engine. Advantageously, the lubricant compositions according to the invention have good pre-ignition prevention or reduction properties once implemented in an engine without the need to associate them with other technical solutions to prevent or reduce the meadow. ignition, and in particular technical solutions requiring to reduce the calcium or magnesium content or causing an excessive increase in the volatility of the lubricant composition.

Advantageously, the lubricant compositions according to the invention have good prevention or pre-ignition reduction properties once implemented in an engine and whose formulation is easy to implement.

In one embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex selected from organic molybdenum complexes with amide ligands and prepared by reaction of a molybdenum source and a amine, and of fatty acids preferably comprising from 4 to 28 carbon atoms, more preferably from 8 to 18 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound chosen from:

the compounds of formula (A)

(A) in which

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

N represents 1 when X ¹ represents an oxygen atom and m represents 1 when X ² represents an oxygen atom;

N represents 2 when X ¹ represents a nitrogen atom and m represents 2 when X ² represents a nitrogen atom;

R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms;

the compounds of formula (B)

(B)

in which

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

N represents 2 when X ¹ represents a nitrogen atom and m represents 2 when X ² represents a nitrogen atom; R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms;

R ₂ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

a mixture of at least one compound of formula (A) and at least one compound of formula (B). In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound of formula

(A1)

(A1) in which R- _\ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising a compound of formula (A1) in which R 1 represents an alkyl group comprising 11 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a sulfur-free molybdenum complex comprising at least one compound of formula

(A2)

(A2) in which R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

In another embodiment of the invention, the organomolybdenum compound is a Mo-DTP compound comprising

From 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferably from 4 to 15%, advantageously from 5 to 12% by weight of molybdenum, relative to the total mass; Mo-DTP compound;

From 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferentially from 4 to 15% by weight of sulfur, relative to the total weight of the Mo-DTP compound;

From 1 to 10%, preferably from 2 to 8%, more preferably from 3 to 6% by weight of phosphorus, relative to the total mass of the total mass of the Mo-DTP compound.

In another embodiment of the invention, the Mo-DTP compound is chosen from dimeric Mo-DTP compounds or trimeric Mo-DTP compounds.

In another embodiment of the invention, the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C)

(C) in which R3, R4, R9 and R10, which may be identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups,

• R5, R6, R7 and R8, identical or different, independently represent an oxygen atom or a sulfur atom.

In another embodiment of the invention, the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C1)

(C1) in which R3, R4, R9 and R10, which are identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups, preferably an alkyl group comprising from 4 to 12 carbon atoms, advantageously from 6 to 10 carbon atoms.

In another embodiment of the invention, the Mo-DTP compound is a dimeric MoDTP compound of formula (C1) in which R3, R4, R9 and R10, which are identical, represent a C8-alkyl group, preferably an ethylhexyl group. .

In another embodiment of the invention, the content by weight of organomolybdenum compound, relative to the total weight of the lubricating composition, ranges from 0.05 to 3%, preferably from 0.1 to 2%, advantageously from 0.1 to 1%. In another embodiment of the invention, the lubricating composition further comprises an additional additive selected from friction modifiers with the exception of Mo-DTP compounds and sulfur-free molybdenum complexes, detergents, anti-doping additives and - wear, extreme pressure additives, viscosity index improvers, dispersants, antioxidants, pour point improvers, defoamers, thickeners and mixtures thereof.

In another embodiment of the invention, the lubricant composition is used to prevent or reduce pre-ignition in a vehicle engine, preferably a motor vehicle. In another embodiment of the invention, the lubricant composition is used to prevent or reduce low speed pre-ignition (LSPI) in an engine, preferably a vehicle, preferably a motor vehicle.

The invention also relates to a method for preventing or reducing pre-ignition in an engine, said method comprising at least one step of contacting a mechanical part of the engine with a lubricant composition as defined above.

The invention also relates to the use of an organomolybdenum compound in a lubricating composition comprising at least one base oil for preventing or reducing pre-ignition in an engine, said organomolybdenum compound being chosen from:

• molybdenum dithiophosphate compounds (Mo-DTP), or

• Molybdenum complexes free from sulfur.

Detailed description of the invention

The percentages given below correspond to percentages by mass of active ingredient. The lubricant composition used according to the invention comprises at least one organomolybdenum compound chosen from:

• molybdenum dithiophosphate compounds (Mo-DTP), or

• Molybdenum complexes free from sulfur.

Molybdenum complex free of sulfur

In one embodiment of the invention, the organomolybdenum compound may be chosen from sulfur-free molybdenum complexes such as carboxylates, esters and molybdenum amides, obtainable by reaction of molybdenum oxide or molybdates. ammonium with fatty substances, glycerides, fatty acids or fatty acid derivatives (esters, amines, amides ...).

In a preferred embodiment of the invention, the organomolybdenum compound is chosen from sulfur-free molybdenum complexes with amide ligands, mainly prepared by reaction of a molybdenum source, which may be, for example molybdenum trioxide, and an amine derivative, and fatty acids preferably comprising from 4 to 28 carbon atoms, more preferably from 8 to 18 carbon atoms, such as, for example, the fatty acids contained in the oils vegetable or animal.

The synthesis of such compounds is described, for example, in US Pat. No. 4,889,547, EP 0546357, US Pat. No. 5,412,130 and EP 1770153.

In a preferred embodiment of the invention, the organomolybdenum compound is chosen from sulfur-free molybdenum complexes obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

an amino source of formula (D):

in which :

X ¹ represents an oxygen atom or a nitrogen atom,

X ² represents an oxygen atom or a nitrogen atom,

n and m represent 1 when X ¹ or X ² represent an oxygen atom,

n and m represent 2 when X ¹ or X ² represent a nitrogen atom,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate, in an amount sufficient to provide 0.1 to 30% molybdenum based on the total weight of complex.

In one embodiment of the invention, the sulfur-free molybdenum complex may comprise from 2 to 8.5% by weight of molybdenum based on the weight of complex.

In a preferred embodiment of the invention, the sulfur-free molybdenum complex comprises at least one compound chosen from:

the compounds of formula (A)

(AT)

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

the compounds of formula (B)

(B)

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms; R ₂ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms,

mixture of at least one compound of formula (A) and at least one compound of formula

In one embodiment of the invention, the sulfur-free molybdenum complex is prepared by reacting:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

(ii) diethanolamine or 2- (2-aminoethyl) aminoethanol,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate, in an amount sufficient to provide 0.1 to 20.0% molybdenum based on the weight of complex. In a preferred embodiment of the invention, the sulfur-free molybdenum complex comprises at least one compound of formula (A1) or a compound of formula (A2), taken alone or as a mixture:

in which R- _\ represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms,

in which R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 3 to 30 carbon atoms, preferably from 3 to 20 carbon atoms, advantageously from 7 to 17 carbon atoms.

Advantageously, the organomolybdenum compound is a sulfur-free molybdenum complex comprising a compound of formula (A1) in which R 1 represents an alkyl group comprising 11 carbon atoms. Examples of sulfur-free molybdenum complexes include Molyvan 855 sold by RT Vanderbilt Compagny.

Molybdenum dithiophosphate (Mo-DTP) compound Molybdenum dithiophosphate (Mo-DTP) compounds are complexes formed by a metal ring bonded to one or more ligands, the ligand being an alkyl dithiophosphate group.

In one embodiment, the Mo-DTP compound used in the lubricant compositions according to the invention may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferably from 4 to 15%, advantageously 5 to 12% by weight of molybdenum, relative to the total mass of Mo-DTP compound.

In one embodiment, the Mo-DTP compound used in the lubricant compositions according to the invention may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, even more preferably from 4 to 15% by weight of sulfur, based on the total mass of Mo-DTP compound.

In one embodiment, the Mo-DTP compound used in the lubricant compositions according to the invention may comprise from 1 to 10%, preferably from 2 to 8%, more preferably from 3 to 6% by weight of phosphorus, relative to to the total mass total mass of Mo-DTP compound. The Mo-DTP compound used in the lubricant compositions according to the invention can be chosen from compounds whose structure comprises two molybdenum atoms (also called dimeric Mo-DTP) and those whose structure comprises three molybdenum atoms (also called Mo Trimeric DTP).

The trimeric Mo-DTP compound corresponds to the following formula Mo ₃ S _k L _n in which: k represents an integer at least equal to 4, preferably from 4 to 10, advantageously from 4 to 7,

n represents an integer ranging from 1 to 4, and

L represents an alkyl dithiophosphate group comprising from 1 to 100 carbon atoms, preferably from 1 to 40 carbon atoms, advantageously from 3 to 20 carbon atoms. Examples of trimeric Mo-DTP compounds according to the invention include the compounds and methods for their preparation as described in WO 98/26030 and US 2003/022954.

Advantageously, the Mo-DTP compound used in the context of the invention is a dimeric Mo-DTP compound.

As examples of dimeric Mo-DTP compounds, mention may be made of the compounds as described in documents EP 0757093 or EP 0743354.

The dimeric Mo-DTPs generally correspond to the compounds of formula (C):

(C) wherein:

R3, R4, R9 and R10, which may be identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups,

In one embodiment, R3, R4, R9 and R10, which are identical or different, independently represent an alkyl group comprising from 4 to 18 carbon atoms or an alkenyl group comprising from 2 to 24 carbon atoms.

In one embodiment, R5, R6, R7 and R8 may be the same and may be a sulfur atom.

In another embodiment, R5, R6, R7 and R8 may be the same and may be an oxygen atom.

In another embodiment, R5 and R6 may represent a sulfur atom and R7 and R8 may represent an oxygen atom. In another embodiment, R5 and R6 may represent an oxygen atom and R7 and R8 may represent a sulfur atom.

In a preferred embodiment of the invention, the compound Mo-DTP is chosen from compounds of formula (C) in which: R5 and R6 represent an oxygen atom,

R7 and R8 represent a sulfur atom,

R3 represents an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms,

R 4 represents an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms,

R 9 represents an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms,

- R10 represents an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms. Advantageously, the compound Mo-DTP is chosen from compounds of formula (C) in which:

R5 and R6 represent an oxygen atom,

R7 and R8 represent a sulfur atom,

- R3 represents an ethylhexyl group, - R4 represents an ethylhexyl group,

R 9 represents an ethylhexyl group,

- R10 represents an ethylhexyl group.

Advantageously, the compound Mo-DTP is chosen from compounds of formula

(C1)

(C1) wherein R3, R4, R9 and R10 are as defined for formula (C).

Advantageously, the compound Mo-DTP is chosen from the compounds of formula (C1) in which R3, R4, R9 and R10, which are identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl, preferably an alkyl group comprising from 4 to 12 carbon atoms, preferably from 6 to 10 carbon atoms.

Even more advantageously, the compound Mo-DTP is chosen from the compounds of formula (C1) in which R3, R4, R9 and R10 represent a C8-alkyl group, preferably an ethylhexyl group.

As examples of Mo-DTP compounds, mention may be made of the Molyvan L product sold by the company R.T Vanderbilt Compagny or the Sakuralube 300 or Sakuralube 31 OG products marketed by the company Adeka.

In one embodiment of the invention, the content by weight of organomolybdenum compound, relative to the total weight of the lubricating composition, ranges from 0.05 to 3%, preferably from 0.1 to 2%, advantageously from 0 to , 1 to 1%.

The lubricating composition used according to the invention also comprises at least one base oil.

In general, the lubricant composition used according to the invention may comprise any type of mineral, synthetic or natural lubricating base oil, animal or vegetable, known to those skilled in the art. The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A) or their mixtures.

Content Content in Saturated Sulfur Viscosity Index (VI)

Group I

<90%> 0.03% 80 <VI <120 Mineral oils Group II

≥90% <0.03% 80 <VI <120 Hydrocracked oils

Group III

Hydrocracked oils ≥90% <0.03% ≥120

or hydro-isomerized

Group IV Polyalphaolefines (PAO)

Esters and other bases not included in groups 1

Group V

at IV

Table A

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, desalphating, solvent dewaxing, hydrotreatment, hydrocracking. , hydroisomerization and hydrofinition.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases for producing the lubricating compositions used according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur, oxidation resistance, adapted for use for engines or for vehicle transmissions.

The base oils of the lubricant compositions used according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100 ° C. is between 1, 5 and 15 mm ² . s ^"1 according to the ASTM D445 standard, their average molecular weight is generally between 250 and 3000 according to the ASTM D5296 standard.

Preferably, the base oils of the present invention are chosen from the above base oils whose aromatic content is between 0 and 45%, preferably between 0 and 30%. The aromatic content of the oils is measured according to UV Burdett method. Advantageously, the lubricant composition used according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition.

More advantageously, the lubricant composition used according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total mass of the composition.

More particularly advantageously, the lubricant composition used according to the invention comprises from 60 to 99.5% by weight of base oils, preferably from 70 to 99.5% by weight of base oils, relative to the total mass of the composition. Many additives can be used for this lubricant composition used according to the invention.

The preferred additives for the lubricating composition used according to the invention are chosen from the friction modifiers with the exception of the Mo-DTP compounds and sulfur-free molybdenum complexes, the detergents, the anti-wear additives and the extreme additives. pressure, viscosity index improvers, dispersants, antioxidants, pour point depressants, defoamers, thickeners, and mixtures thereof.

Preferably, the lubricant composition used according to the invention comprises at least one antiwear additive, at least one extreme pressure additive or their mixtures. Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces.

There is a wide variety of anti-wear additives. In a preferred manner for the lubricating composition according to the invention, the anti-wear additives are chosen from phosphosulfur additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds are of formula Zn ((SP (S) (OR ¹¹ ) (OR ¹² )) ₂ , in which R ¹¹ and R ¹² , which may be identical or different, independently represent an alkyl group, preferably an alkyl group containing from 1 to 18 carbon atoms.

Amine phosphates are also anti-wear additives which can be used in the lubricating composition according to the invention. However, the phosphorus provided by these additives can act as a poison of the catalytic systems of automobiles because these additives are ash generators. These effects can be minimized by partially substituting phosphates of amines by additives not providing phosphorus, such as, for example, polysulfides, especially sulfur-containing olefins.

Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight relative to the mass. total lubricating composition, antiwear additives and extreme pressure additives.

Advantageously, the lubricant composition according to the invention may comprise at least one additional friction modifying additive with the exception of Mo-DTP compounds and sulfur-free molybdenum complexes. The additional friction modifier additive may be selected from a compound providing metal elements and an ash free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus. The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides; fatty amines or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms. 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 0.1 at 2% by weight relative to the total mass of the lubricant composition, additional friction modifier additive.

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

The antioxidant additive generally serves to retard the degradation of the lubricating composition in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition. Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, can be ash generators. Additives Phenolic antioxidants may be ash-free or may be in the form of neutral or basic metal salts. The antioxidant additives may especially be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C ₁ -C ₁₂ alkyl group, N , N'-dialkyl-aryl diamines and mixtures thereof.

Preferably, according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one alkyl group in the form of d-C ₁₀ , preferably a grouping. C ₁ -C ₆ alkyl, preferably a C ₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ¹³ R ¹⁴ R ¹⁵ in which R ¹³ represents an optionally substituted aliphatic or aromatic group, R ¹⁴ represents an optionally substituted aromatic group, R ¹⁵ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ¹⁶ S (O) _z R ¹⁷ in which R ¹⁶ represents an alkylene group or an alkenylene group, R ¹⁷ represents an alkyl group, a alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts can also be used.

The lubricant composition according to the invention may contain all types of antioxidant additives known to those skilled in the art. Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive. Also advantageously, the lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

The lubricant composition according to the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products.

The detergent additives that can be used in the lubricant composition according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably chosen from the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It is then overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate .

Advantageously, the lubricant composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total mass of the lubricating composition.

Also advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive.

By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricant composition according to the invention. As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

Advantageously, the lubricant composition according to the invention may also comprise at least one dispersing agent.

The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives.

Also advantageously, the lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total mass of the lubricating composition.

The lubricating composition of the present invention may also comprise at least one viscosity index improving additive. Examples of additives improving the viscosity index include polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, in particular polyacrylates, polymethacrylates ( PMA) or olefin copolymers, especially ethylene / propylene copolymers.

The lubricating composition according to the invention can be in various forms. The lubricant composition according to the invention may in particular be an anhydrous composition. Preferably, this lubricating composition is not an emulsion.

The lubricant composition defined above is used to prevent or reduce preignition in an engine. Motor according to the invention more particularly means the vehicle engines, such as:

- motor vehicle engines, including petrol and diesel engines, but also gas and petrol engines (dual fuel gas / gasoline engines) and gas and diesel engines (dual fuel gas engines) / diesel);

- the engines of heavy goods vehicles, and more specifically the engines of heavy goods vehicles running on gas. By engine according to the invention is also meant 4-stroke engines, and more specifically 4-stroke marine engines, preferably 4-stroke marine engines operating on gas. In a preferred embodiment of the invention, the lubricant composition is used to prevent or reduce pre-ignition in a vehicle engine, preferably a motor vehicle.

Pre-ignition according to the invention includes the phenomenon of low frequency vibration producing a sound effect of humming (or "Rumble" in English).

By pre-ignition according to the invention is more particularly meant the low speed pre-ignition (LSPI).

In a preferred embodiment of the invention, the lubricant composition is used to prevent or reduce low speed pre-ignition (LSPI) in an engine, preferably in a vehicle engine, preferably a motor vehicle.

All of the features and preferences described for the above use also apply to this method.

The invention also has the use of an organomolybdenum compound in a lubricating composition comprising at least one base oil for preventing or reducing preignition in an engine, said organomolybdenum compound being chosen from:

• molybdenum dithiophosphate compounds (Mo-DTP), or

• Molybdenum complexes free from sulfur.

The set of characteristics and preferences relating to the organomolybdenum compound and the lubricating composition described above also apply to this use.

The different aspects of the invention can be illustrated by the following examples Example 1 Preparation of Lubricating Compositions According to the Invention

The various components of the lubricating compositions according to the invention CM and CI2 are mixed according to the nature and the amounts presented in Table 1

Table 1

Example 2: Preparation of Comparative Lubricating Compositions

The various components of the comparative lubricating composition CC1 are mixed according to the nature and amounts shown in Table 2

CC1

Gr III base oil 84,90

Improving the viscosity index 5.00

(Polyisobutene hydrogenated styrene or

Pish)

Anti-wear (DTPZn) 0.80

Antioxidant amine (Diphenylamine) 0.80

Detergent (calcium sulphonate) 2.00

Dispersant (Bis-succinimide) 6.00

Mo-DTC (Sakuralube 525) 0.50

KV 100 (measured in mm ² / s according to 8.3

ASTM D445 standard)

Table 2

EXAMPLE 3 Evaluation of the Pre-ignition Reduction Properties of the Lubricating Compositions According to the Invention CM and CI2 and the Comparative Lubricating Composition CC1 This evaluation is carried out by evaluating the impact of each lubricant composition on the low pre-ignition. speed (LSPI).

For this, the LSPI phenomenon is quantified by means of a GM Ecotech controlled-ignition turbocharged engine composed of 4 cylinders in line for a total displacement of 2.0L. After a heating period of 20 minutes at an engine speed of 2000 rpm and an engine load of 4.10 ⁵ Pascal effective average pressure (PME), the test procedure consists of 2 sequences under heavy load (23.10 ⁵ Pascal of PME at a speed of 2,000 rpm), 2 sequences under low load (13.10 ⁵ Pascal of PME at a speed of 1 .250 rpm) and 2 sequences under heavy load identical to the first 2. Each sequence comprises 25,000 motor cycles to ensure a good statistical representativeness of the phenomenon studied.

Each cylinder is equipped with a sensor to measure the pressure in the combustion chamber during engine operation. A high frequency recorder records the pressure signal allowing a fine analysis of the combustion. A combustion is considered an LSPI event if one of the following 2 criteria is fulfilled: the maximum pressure of one cycle is greater than the average of the maximum pressures on the entire sequence considered + 4.7 times the standard deviation of maximum pressure measured on the sequence;

The crankshaft angle at which 2% of the mass of fuel mixture burned on a given cycle is less than the average of the crankshaft angles at which 2% of the fuel mixture mass burned over the entire sequence considered plus 4.7 times the standard deviation on the crankshaft angle at which 2% of the fuel mixture mass burned throughout the sequence.

The sum of the LSPI events is counted on all 6 sequences of the procedure for a given lubricant composition. This test is repeated 4 times for each lubricating composition tested.

The impact of the lubricant composition on the LSPI is compared by comparing the average number of LSPI events on the 4 engine tests and taking into account the standard deviation calculated on the 4 engine tests.

The results concerning the lubricant compositions according to the invention CM and CI2 and the comparative lubricating composition CC1 are given in Table 3; the lower the number of LSPI events, the better the lubricating composition's performance in preventing or reducing pre-ignition.

Table 3 The results show that the lubricant compositions according to the invention comprising respectively a Mo-DTP (composition CM) and a sulfur-free molybdenum complex (composition CI2) exhibit improved LSPI reduction properties with respect to a lubricating composition comprising an organomolybdenum compound of the molybdenum dithiocarbamate type (Mo-DTC).

Claims

1. Use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for preventing or reducing pre-ignition in a vehicle engine, said organomolybdenum compound being selected from molybdenum dithiophosphate compounds (Mo-DTP).

The use according to claim 1 wherein the organomolybdenum compound is a Mo-DTP compound comprising

From 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, still more preferably from 4 to 15%, advantageously from 5 to 12% by weight of molybdenum, relative to the total weight of the Mo-DTP compound;

Use according to claim 1 or 2 wherein the Mo-DTP compound is selected from dimeric Mo-DTP compounds or trimeric Mo-DTP compounds.

Use according to any one of claims 1 to 3 wherein the Mo-DTP compound is a dimer Mo-DTP compound of formula (C)

(VS)

in which

R3, R4, R9 and R10, which may be identical or different, independently represent a hydrocarbon group chosen from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl groups, • R5, R6, R7 and R8, identical or different, independently represent an oxygen atom or a sulfur atom.

5. Use according to any one of claims 1 to 4 wherein the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C1)

6. Use according to the preceding claim wherein the Mo-DTP compound is a dimeric Mo-DTP compound of formula (C1) in which R3, R4, R9 and R10, identical, represent a C8-alkyl group, preferably an ethylhexyl group. .

7. Use according to any one of the preceding claims wherein the content by weight of organomolybdenum compound, relative to the total weight of the lubricating composition, ranges from 0.05 to 3%, preferably from 0.1 to 2%, advantageously from 0.1 to 1%.

8. Use according to any preceding claim wherein the lubricating composition further comprises an additional additive selected from friction modifiers except Mo-DTP compounds, detergents, anti-wear additives, extreme additives pressure improvers, viscosity index improvers, dispersants, antioxidants, pour point depressants, defoamers, thickeners, and mixtures thereof.

9. Use according to any one of the preceding claims for preventing or reducing pre-ignition in a vehicle engine, preferably a motor vehicle.

10. Use according to any one of the preceding claims for preventing or reducing the low speed pre-ignition (LSPI) in an engine, preferably a vehicle, preferably a motor vehicle.

1 1. Use of an organomolybdenum compound selected from Mo-DTP compounds in a lubricant composition comprising at least one base oil to prevent or reduce pre-ignition in an engine.