Lubricant composition with improved eco fuel properties in hybrid vehicles

Abstract

The present invention relates to a lubricant composition comprising at least one diester of formula Ra-C(O)-O-([C(R)2]n-O)s-C(O)-Rb and at least one group II+ base oil having a kinematic viscosity measured at 40°C, according to ASTM D445, of less than 12 cSt, a kinematic viscosity measured at 100°C, according to ASTM D445, of less than 3 cSt and a sulphur content of less than or equal to 5 ppm. The invention also relates to the use of said lubricant composition to lubricate the parts of a motor vehicle engine.

Description

[0001] TITLE: LUBRICANT COMPOSITION WITH IMPROVED FUEL ECO PROPERTIES IN HYBRID VEHICLES

[0002] The present invention relates to a lubricating composition used for light vehicles, in particular hybrid vehicles, and more particularly of the plug-in hybrid vehicle type and hybrid vehicle comprising a range extender. The present invention also relates to improving the low temperature Fuel Eco of the engines of such vehicles.

[0003] Hybrid vehicles consist of two engines: a combustion engine and an electric motor. In most hybrid vehicles, the combustion engine drives the wheels and is assisted by an electric motor. A battery provides the electricity needed to operate the electric motor. In conventional hybrid vehicles, this battery is recharged during braking and deceleration by a kinetic energy recovery system (KERS) integrated into the vehicle.

[0004] There are different hybrid vehicle technologies. These hybrid technologies include:

[0005] - micro-hybrid vehicles (also called mild hybridization), these vehicles, equipped with the “stop&start” system, recover the energy generated by braking to charge a battery which can temporarily assist the thermal engine;

[0006] - mild-hybrid vehicles which include electric assistance during acceleration; and

[0007] - Full hybrid vehicles are vehicles with total hybridization. At low speeds, when the battery is charged, the electric motor takes care of starting and locomotion. At high speeds, or when the battery is discharged, the combustion engine takes over; when increased power is needed (for example, acceleration), the two engines work together. It is thus possible to drive with the combustion engine switched off for a few kilometers.

[0008] Other complementary technologies have recently been developed: plug-in hybrid vehicles and hybrid vehicles with a range extender. Plug-in hybrid vehicles include a combustion engine and an electric motor. The battery can be recharged from the electricity grid. These vehicles can therefore run in 100% electric mode for a distance of several dozen kilometers, for example 50 kilometers. In hybrid vehicles with a range extender, only the electric motor drives the wheels. This electric motor is powered by a battery for a few dozen kilometers.When the battery reaches a certain charge threshold (for example around 30%), the thermal engine starts and drives a current generator to produce the electricity needed to recharge the battery and maintain the operation of the electric motor.

[0009] In both types of hybrid vehicles, the combustion engine is used less frequently and therefore operates at lower temperatures (around, or even below, 40°C) than the engines of other types of hybrid vehicles. However, at low temperatures, conventional lubricant compositions are more viscous and the additives are not as active as in a conventional application at higher temperatures. Current lubricants have been optimized to achieve fuel consumption gains when hot.

[0010] The need for high-performance lubricating compositions is increasing, particularly with regard to energy efficiency and more specifically the improvement of Fuel Economy or Fuel Eco in abbreviated form (FE) of lubricating compositions or the reduction of fuel consumption of engines, particularly hybrid vehicle engines.

[0011] The objective for improving the FE is in particular to have lubricating compositions that are as fluid as possible, and therefore have a low viscosity possibly correlated with a low grade.

[0012] The present invention therefore aims to provide a lubricating composition allowing the lubrication of the engine of a plug-in hybrid vehicle or one comprising a range extender, with improved Fuel Eco properties.

[0013] The present invention also aims to provide a lubricating composition having improved low-temperature Fuel Eco properties for light vehicle engines, in particular hybrid vehicles. Thus, the present invention relates to a lubricating composition comprising:

[0014] - at least one diester of the following formula (I):

[0015] R a -C(O)-O-([C(R)2] n -O)sC(O)-R b (I) in which:

[0016] . the R groups represent, independently of one another, a hydrogen atom or a linear or branched alkyl group comprising from 1 to 5 carbon atoms, in particular a methyl, ethyl or propyl group, preferably methyl;

[0017] . s represents 1 or 2;

[0018] . n represents 1, 2 or 3, it being understood that when s is different from 1, the n may be the same or different;

[0019] . R a and R b, identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, having a linear chain of 6 to 18 carbon atoms; provided that, when s is 2 and the n, identical, are 2, at least one of the R groups represents an alkyl group, linear or branched, comprising

[0020] I to 5 carbon atoms; and provided that, when s is 1 and n is 3, at least one of the R groups bonded to the carbon in the beta position of the oxygen atoms of the ester functions represents a hydrogen atom, and

[0021] - at least one group II+ base oil having a kinematic viscosity measured at 40°C, according to ASTM D445, less than 12 cSt, a kinematic viscosity measured at 100°C, according to ASTM D445, less than 3 cSt and a sulfur content less than or equal to 5 ppm.

[0022] The lubricating composition according to the invention is therefore based on the combination of at least one specific group II+ base oil and at least one diester of formula (I) as defined above.

[0023] It was surprisingly found that this composition exhibits improved Fuel Eco properties, despite the incompatibilities associated with the use of the ester, particularly in the presence of a molybdenum-based friction modifier. Diester of formula (I)

[0024] According to one embodiment, the diester of the invention corresponds to formula (I) as defined above, in which, when s is different from 1, all the n are identical.

[0025] Preferably, in the diester of formula (I) of the invention, n represents 2 or 3, preferably 2.

[0026] Preferably, in formula (I), at least one of the R groups represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably from 1 to 4 carbon atoms, more preferably methyl, ethyl or propyl, advantageously methyl.

[0027] According to a particular embodiment, the diester of formula (I) according to the invention is a diester of the following formula (I'):

[0028] R a -C(O)-O-([C(R)2] n -O)-([C(R')2] m -O)siC(O)-R b (I') in which:

[0029] . R and R' represent, independently of each other, a hydrogen atom or a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably a methyl, ethyl or propyl group, preferably a methyl group;

[0030] . s represents 1 or 2;

[0031] . n represents 2;

[0032] . m represents 2;

[0033] . R a and R b , identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, having a linear chain of 6 to 18 carbon atoms; provided that, when s is 2, at least one of the groups R or R' represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms.

[0034] Advantageously, at least one of the groups R or R' in the diester of formula (I') represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably from 1 to 4 carbon atoms, preferably methyl, ethyl, or propyl, advantageously methyl. Preferably, in the compounds of formula (I) and (I'), R a and R b , have a linear chain of 7 to 14 carbon atoms, preferably 8 to 12 carbon atoms.

[0035] In a particular embodiment, s, in formulas (I) or (I'), represents 2.

[0036] The diester of the invention is preferably a compound of formula (Ia):

[0037] R a -C(O)-O-([C(R)2] n -O)-([C(R')2] m -O)-C(O)-R b (the) in which:

[0038] . R and R' represent, independently of each other, a hydrogen atom or a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl;

[0039] . n represents 2;

[0040] . m represents 2;

[0041] . R a and R b, identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, having a linear chain of 6 to 18 carbon atoms; provided that at least one of the groups R or R' represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl.

[0042] Preferably, at least one of the R groups represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl; and at least one of the R' represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl.

[0043] Even more preferably, in formula (1a), one of the R groups represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl; and one of the R' represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl; the other R and R' groups representing hydrogen atoms. In a particular embodiment, the diester of the invention is a compound of formula (1a):

[0044] R a -C(O)-O-CHR 1 -CHR 2 -O-CHR 3 -CHR 4 -OC(O)-R b (l”a) in which:

[0045] . one of the R groups 1 and R 2 represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, the other representing a hydrogen atom;

[0046] . one of the R groups 3 and R4 represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, the other representing a hydrogen atom;

[0047] . R a and R b , identical or different, are as defined above.

[0048] Preferably, in formula (l”a):

[0049] . one of the R groups 1 and R 2 represents a methyl, ethyl or propyl group, preferably methyl, the other representing a hydrogen atom;

[0050] . one of the R groups 3 and R 4 represents a methyl, ethyl or propyl group, preferably methyl, the other representing a hydrogen atom.

[0051] According to another embodiment, in formula (I) or (I'), s represents 1 and the diesters of the invention are of formula (I'b):

[0052] R a -C(O)-O-([C(R)2] n -O)-C(O)-R b (l'b) in which:

[0053] . the R groups represent, independently of one another, a hydrogen atom or an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl;

[0054] . n represents 2;

[0055] . R a and R b , identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, presenting a linear chain of 6 to 18 carbon atoms.

[0056] Preferably, in formula (I'b), at least one of the R represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl.

[0057] Preferably, in formula (I'b), one of the R groups represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably methyl, ethyl or propyl, preferably methyl, the others represent hydrogen atoms. In the context of the present invention, it should be understood that the expression "comprising from x to y carbon atoms" also covers the limits x and y.

[0058] In the context of the present invention, the term "linear chain of x to y carbon atoms" should be understood to mean a carbon chain, saturated or unsaturated, preferably saturated, comprising from x to y carbon atoms, one after the other, the carbon atoms possibly present at the level of the branches of the carbon chain not being taken into account in the number of carbon atoms (xy) constituting the linear chain.

[0059] According to a particular embodiment, in formulas (I), (I'), (I'a), (I”a) or (I'b), R a and R b , identical or different, are of plant, animal or petroleum origin.

[0060] According to a particular embodiment, in formulas (I), (I'), (I'a), (I”a) or (I'b), R a and R b , identical or different, represent saturated groups.

[0061] According to a particular embodiment, in formulas (I), (I'), (I'a), (I”a) or (I'b), R a and R b , identical or different, represent linear groupings. In particular, R a and R b , identical or different, represent saturated linear hydrocarbon groups comprising from 6 to 18 carbon atoms, preferably from 7 to 17 carbon atoms, in particular from 7 to 14 carbon atoms, preferably from 8 to 12 carbon atoms, in particular 9 or 12 carbon atoms.

[0062] According to another preferred embodiment, in formulas (I), (I'), (I'a), (I”a) or (I'b), R a and R b , identical or different, represent saturated linear alkyl groups comprising from 6 to 18 carbon atoms, preferably from 7 to 17 carbon atoms, in particular from 7 to 14 carbon atoms, preferably from 8 to 12 carbon atoms, in particular 9 or 12 carbon atoms.

[0063] Preferably, R a and R b are identical.

[0064] The diesters of formula (I) may be commercially available or prepared according to synthetic methods described in the literature and known to those skilled in the art, in particular according to methods described in WO 2019 / 025446.

[0065] According to one embodiment, the lubricating composition according to the invention comprises from 15% to 90%, preferably from 25% to 85%, and in particular from 40% to 80%, by weight of diester of formula (I) relative to the total weight of said lubricating composition. Group 11+ base oil

[0066] According to one embodiment, the aforementioned group 11+ base oil has an aromatic compound content of less than or equal to 2% by weight relative to the total weight of the base oil, this content preferably being zero.

[0067] Preferably, the aforementioned group 11+ base oil has a paraffinic compound content of less than or equal to 85%, preferably less than or equal to 80%, by weight relative to the total weight of the base oil.

[0068] Preferably, the aforementioned group 11+ base oil has a naphthenic compound content of less than or equal to 30%, preferably less than or equal to 25%, by weight relative to the total weight of the base oil.

[0069] The KV40 and KV100 of the above-mentioned base oil are measured according to ASTM D445.

[0070] As stated above, the KV40 (Kinematic Viscosity measured at 40°C) of the above-mentioned base oil is less than or equal to 12 cSt.

[0071] As stated above, the KV100 (Kinematic Viscosity measured at 100°C) of the above-mentioned base oil is less than or equal to 3 cSt.

[0072] Preferably, the sulfur content of the above-mentioned base oil is from 0.00001 ppm to 5 ppm, and preferably from 0.0001 ppm to 1 ppm.

[0073] This content is measured according to ASTM D2622.

[0074] According to one embodiment, the lubricating composition according to the invention comprises from 5% to 60%, preferably from 8% to 40%, and in particular from 10% to 30%, by weight of group II+ base oil as defined above relative to the total weight of said lubricating composition.

[0075] Preferably, the lubricating composition according to the invention has a grade according to the SAEJ300 classification of type XW-(Y) with X representing 0, 5 or 10 and Y representing an integer between 6 and 50, preferably 8 or 40, preferably X=0 and Y=8.

[0076] The Noack volatility at 250°C is measured according to the CEC L-40-A-93 method. Preferably, the Noack volatility at 250°C of the lubricating composition of the invention is between 10 and 20%, and preferably between 12 and 15%. The lubricating composition according to the invention may further comprise compounds or additives other than the group 11+ base oil and the diester of formula (I) mentioned above.

[0077] According to a particular embodiment, the lubricating composition of the invention comprises an additional base oil, different from the group 11+ base oil as defined above.

[0078] The additional base oil used in the lubricating compositions of the invention may be chosen from oils of mineral or synthetic origin belonging to groups I to V according to the classes defined by the API classification (or their equivalents according to the ATIEL classification (Table 1) or their mixtures.

[0079] [Table 1]

[0080] Mineral base oils include any type of base oil obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization, and hydrofinishing.

[0081] Blends of synthetic and mineral oils can also be used.

[0082] The additional base oils of the lubricating compositions according to the invention may also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, and 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 for which the viscosity at 100°C is between 1.5 and 15 mm 2 .s-1 according to ASTM D445. Their average molar mass is generally between 250 and 3000 according to ASTM D5296.

[0083] The composition of the invention may also comprise at least one additive.

[0084] Many additives can be used in the lubricating compositions according to the invention.

[0085] According to one embodiment, the lubricating composition according to the invention further comprises a friction modifying additive, preferably based on molybdenum.

[0086] Preferably, the lubricating composition according to the invention comprises at least one friction-modifying additive. The friction-modifying additives make it possible to limit friction by forming adsorbed monolayers on the surfaces of the metals in contact with them. They may be chosen from compounds providing metallic elements and ash-free compounds. Among the compounds providing metallic elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu, Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms.The ash-free friction modifying additives are generally of organic origin and may be chosen from fatty acid esters and polyols, distinct from the monoester required according to the invention, 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. In particular, the molybdenum-based compounds may be chosen from molybdenum dithiocarbamates (Mo-DTC), molybdenum dithiophosphates (Mo-DTP), and mixtures thereof.Advantageously, the lubricating composition according to the invention may comprise from 0.01 to 10% by mass or from 0.01 to 5% by mass, preferably from 0.01 to 2% by mass, preferably from 0.1 to 1.5% by mass or from 0.1 to 2% by mass relative to the total mass of the lubricating composition, of friction modifying additive.

[0087] The Molybdenum (Mo) in the lubricating composition of the invention is provided by an organomolybdenum compound, in particular a compound chosen from a molybdenum dithiocarbamate derivative (MoDTC), a molybdenum dithiophosphate derivative (MoDTP) or a sulfur-free molybdenum complex, preferably a molybdenum dithiocarbamate derivative (MoDTC).

[0088] Molybdenum dithiocarbamate compounds (MoDTC compound) are complexes formed of a metal core bound to one or more ligands independently selected from alkyl dithiocarbamate groups. The MoDTC compound of the compositions used according to the invention may comprise from 0.01 to 5%, preferably from 0.1 to 1.5% by mass of molybdenum, relative to the total mass of the MoDTC compound.

[0089] Preferably, the composition according to the invention comprises a molybdenum-based friction modifying additive and preferably comprises (in active content) from 1 to 1,000 ppm of Mo, preferably from 400 to 600 ppm relative to the weight of lubricating composition.

[0090] According to one embodiment, the lubricating composition may also comprise at least one viscosity index (VI) improving additive. Viscosity index improvers, in particular viscosity index improving polymers, ensure good cold resistance and minimal viscosity at high temperatures. Examples of viscosity index improving polymers include hydrogenated or non-hydrogenated polymer esters, homopolymers or copolymers of styrene, butadiene and isoprene, homopolymers or copolymers of olefin, such as ethylene or propylene, polyacrylates and polymethacrylates (PMA), preferably homopolymers, polymethacrylates, or copolymers of olefin, such as ethylene or propylene.

[0091] In particular, a lubricating composition according to the invention may comprise from 1% to 15% by mass of additive(s) improving the viscosity index, preferably from 5% to 10% by mass, relative to the total weight of the lubricating composition.

[0092] As preferred additives for the lubricating composition according to the invention, mention may be made, for example, of detergent additives, anti-wear additives, extreme pressure additives, pour point improvers, anti-foaming agents, thickeners and mixtures thereof.

[0093] Preferably, the lubricating composition according to the invention comprises at least one anti-wear additive, at least one extreme pressure additive or their mixtures.

[0094] 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. Preferably for the lubricating composition according to the invention, the anti-wear additives are chosen from phospho-sulfur additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTP. The preferred compounds are of formula Zn((SP(S)(OR)(OR'))2, in which R and R', identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

[0095] Amine phosphates are also anti-wear additives that can be used in the lubricating composition according to the invention. However, the phosphorus provided by these additives can act as a poison for automobile catalytic systems because these additives generate ash. These effects can be minimized by partially substituting the amine phosphates with additives that do not provide phosphorus, such as, for example, polysulfides, in particular sulfur-containing olefins.

[0096] Advantageously, the lubricating composition according to the invention may comprise from 0.01% to 6% by mass, preferably from 0.05% to 4% by mass, more preferably from 0.1% to 2% by mass relative to the total mass of lubricating composition, of anti-wear additives and extreme pressure additives.

[0097] Advantageously, the lubricating composition according to the invention may comprise at least one antioxidant additive.

[0098] The antioxidant additive generally helps to delay 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 lubricating composition.

[0099] Antioxidant additives act in particular as radical inhibitors or hydroperoxide destroyers. Among the commonly used antioxidant additives, mention may be made of phenolic antioxidant additives, amine antioxidant additives, and phosphosulfur antioxidant additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, may be ash-generating. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular 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 C1-C12 alkyl group, N,N'-dialkyl-aryl-diamines and mixtures thereof.

[0100] Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group of which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one C1-C10 alkyl group, preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

[0101] Amino compounds are another class of antioxidant additives that can be used, possibly in combination with phenolic antioxidant additives. Examples of amino compounds are aromatic amines, for example aromatic amines of the formula NR a R b R c in which R a represents an aliphatic group or an aromatic group, optionally substituted, R b represents an aromatic group, optionally substituted, R crepresents a hydrogen atom, an alkyl group, an aryl group or a group of formula R d S(O) z R e in which R d represents an alkylene group or an alkenylene group, R e represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

[0102] Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0103] Another class of antioxidant additives is copper compounds, e.g. copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulfonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

[0104] The lubricating composition according to the invention may contain any type of antioxidant additives known to those skilled in the art.

[0105] Advantageously, the lubricating composition according to the invention comprises at least one ash-free antioxidant additive.

[0106] Also advantageously, the lubricating composition according to the invention comprises from 0.1% to 2% by weight relative to the total mass of the lubricating composition, of at least one antioxidant additive.

[0107] The lubricating composition according to the invention may also comprise at least one detergent additive. Detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving secondary oxidation and combustion products.

[0108] The detergent additives that can be used in the lubricating 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 or alkaline earth metal.

[0109] The detergent additives are preferably chosen from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, as well as phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

[0110] These metal salts generally comprise the metal in a stoichiometric quantity or in excess, i.e. in a quantity greater than the stoichiometric quantity. These are then overbased detergent additives; the excess metal providing 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.

[0111] Advantageously, the lubricating composition according to the invention may comprise from 0.5% to 8% or from 2% to 4% by weight of detergent additive relative to the total mass of the lubricating composition.

[0112] Also advantageously, the lubricating composition according to the invention also comprises at least one pour point lowering additive.

[0113] By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricating composition according to the invention.

[0114] Examples of pour point depressant additives include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

[0115] According to one embodiment, the lubricating composition according to the invention further comprises at least one dispersing agent. Such dispersing agents ensure the maintenance in suspension and the evacuation of insoluble solid contaminants constituted by the secondary oxidation products which are formed when the lubricating composition is in service. They can be chosen from Mannich bases, succinimides and their derivatives, such as derivatives of polyisobutylene succinic anhydride, polyolefin amide alkene amine polyol.

[0116] Preferably, the lubricating composition according to the invention comprises between 0.5% and 4.5% by weight of dispersant, preferably between 1% and 2.5% by weight of dispersant relative to the total weight of the lubricating composition.

[0117] The present invention also relates to the use of the lubricating composition according to the invention for lubricating the parts of an engine such as a motor vehicle engine, more particularly a plug-in hybrid vehicle engine or a hybrid vehicle engine comprising a range extender.

[0118] The present invention also relates to the use as defined above of the lubricating composition according to the invention for reducing friction between engine parts.

[0119] The present invention also relates to the use as defined above of the lubricating composition according to the invention for reducing the fuel consumption of the engine.

[0120] The present invention also relates to a method for lubricating a plug-in hybrid vehicle engine or a hybrid vehicle engine comprising a range extender, comprising bringing at least one part of the engine into contact with a lubricating composition according to the invention.

[0121] The present invention also relates to a method for reducing the fuel consumption of a plug-in hybrid vehicle or a hybrid vehicle comprising a range extender, comprising bringing at least one mechanical part of the engine into contact with a lubricating composition as defined above.

[0122] The invention also relates to a method for reducing friction occurring inside an engine, said method comprising the use of a lubricating composition according to the invention.

[0123] The composition is preferably as described above.

[0124] The invention also relates to a method for improving the fuel economy (FE or fuel eco) properties of a lubricating composition, said method comprising the use of at least one diester of formula (I) and at least one group II+ base oil as defined above.

[0125] The various aspects of the invention can be illustrated by the following examples.

[0126] EXAMPLES

[0127] Example 1: Preparation of lubricating compositions

[0128] The following lubricating compositions (CL compositions according to the invention and CC comparative compositions) are prepared according to methods known to those skilled in the art.

[0129] The compositions are shown in Table 2 below: [Table 2]

[0130] The parameters of the lubricating compositions in Table 2 above are shown in Table 3 below:

[0131] [Table 3] HTHS (High Temperature, High Shear) viscosity is a measure of the viscosity of the residual oil film under high stress (shearing under mechanical pressure) at elevated temperatures. Here, the HTHS viscosity value 100 is measured at 100°C.

[0132] These values ​​are measured according to CEC L-036-90 or ASTM D4683 standards.

[0133] The BOV is a calculation of the viscosity at 100°C of the mixture of base oils in the formula (in mm 2 / s).

[0134] Example 2: Results for Fuel Eco properties

[0135] A test was carried out on a Suzuki K12C engine (1.2L 4 cylinders) which is driven (no combustion). The friction (resistive torque in Nm) of the engine is measured, which varies depending on the lubricant used. The friction gains are then converted into fuel consumption (Fuel Eco).

[0136] The K12C is an engine from the manufacturer Maruti-Suzuki. It is a 4-cylinder, naturally aspirated 1.2L petrol engine made of aluminium alloy. It is equipped with chain-driven distribution, double overhead camshafts, 16 valves with variable valve timing control system for the intake and exhaust.

[0137] The friction (resistive torque in Nm) of the engine is measured, which varies depending on the lubricant used. The friction gains are then converted into fuel consumption (Fuel Eco).

[0138] The results are given in Table 4 below and present the friction gain expressed in % (compared to the reference oil) as a function of temperature for the compositions in the example.

[0139] The reference oil is a "standard" OW-8 oil with the same additives as the 0W-20 GF-6 oil. Its BOV is 4.1 and its viscosity at 100°C is 5.2, and its HTHS 150°C is 1.80.

[0140] [Table 4]

[0141] CC1

[0142] CC2

[0143] CC3

[0144] CL The CL lubricating composition significantly reduces friction on the K12C engine due to better lubrication, especially at colder temperatures, which is more favorable on a plug-in hybrid vehicle or a hybrid vehicle engine including a range extender. The fuel saving calculated on the NEDC cycle is also greater on the CL lubricating composition than other oils (CC1 -CC3).

Claims

CLAIMS 1. Lubricating composition comprising: - at least one diester of the following formula (I): R a -C(O)-O-([C(R)2] n -O)sC(O)-R b (I) in which: . the R groups represent, independently of one another, a hydrogen atom or a linear or branched alkyl group comprising from 1 to 5 carbon atoms, in particular a methyl, ethyl or propyl group, preferably methyl; . s represents 1 or 2; . n represents 1, 2 or 3, it being understood that when s is different from 1, the n may be the same or different; . R a and R b, identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, having a linear chain of 6 to 18 carbon atoms; provided that, when s is 2 and the n, identical, are 2, at least one of the R groups represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms; and provided that, when s is 1 and n is 3, at least one of the R groups linked to the carbon in the beta position of the oxygen atoms of the ester functions represents a hydrogen atom, and - at least one group II+ base oil having a kinematic viscosity measured at 40°C, according to ASTM D445, less than 12 cSt, a kinematic viscosity measured at 100°C, according to ASTM D445, less than 3 cSt and a sulfur content less than or equal to 5 ppm.

2. Lubricating composition according to claim 1, comprising from 15% to 90%, preferably from 25% to 85%, and in particular from 40% to 80%, by weight of diester of formula (I) relative to the total weight of said lubricating composition.

3. Lubricating composition according to claim 1 or 2, in which the diester of formula (I) is a diester of the following formula (I'): R a -C(O)-O-([C(R)2] n -O)([C(R')2] m -O)siC(O)-R b (I') in which: . R and R' represent, independently of each other, a hydrogen atom or a linear or branched alkyl group comprising from 1 to 5 carbon atoms, preferably a methyl, ethyl or propyl group, preferably a methyl group; . s represents 1 or 2; . n represents 2; . m represents 2; . R a and R b, identical or different, represent independently of each other, hydrocarbon groups, saturated or unsaturated, linear or branched, having a linear chain of 6 to 18 carbon atoms; provided that, when s is 2, at least one of the groups R or R' represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms.

4. Lubricating composition according to any one of claims 1 to 3, comprising from 5% to 60%, preferably from 8% to 40%, and in particular from 10% to 30%, by weight of base oil relative to the total weight of said lubricating composition.

5. Lubricating composition according to any one of claims 1 to 4, in which the base oil has an aromatic compound content of less than or equal to 2% by weight relative to the total weight of the base oil, this content preferably being zero.

6. Lubricating composition according to any one of claims 1 to 5, in which the base oil has a content of paraffinic compounds less than or equal to 85%, preferably less than 80%, by weight relative to the total weight of the base oil.

7. A lubricating composition according to any one of claims 1 to 6, wherein the base oil has a content of naphthenic compounds less than or equal to 30%, preferably less than 25%, by weight relative to the total weight of the base oil.

8. Lubricating composition according to any one of claims 1 to 7, further comprising a friction modifying additive, preferably based on molybdenum.

9. Use of a lubricating composition according to any one of claims 1 to 8, for lubricating the parts of a motor vehicle engine.

10. Use according to claim 9, for reducing friction between engine parts and / or for reducing engine fuel consumption.

11. A method of lubricating a plug-in hybrid vehicle engine or a hybrid vehicle engine comprising a range extender, comprising bringing at least one mechanical part of the engine into contact with a lubricating composition according to any one of claims 1 to 8.

12. Method for reducing the fuel consumption of a plug-in hybrid vehicle or a hybrid vehicle comprising a range extender comprising bringing at least one mechanical part of the engine into contact with a lubricating composition according to any one of claims 1 to 8.

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