FR3034100A1 - LUBRICANT COMPOSITION - Google Patents

Abstract

The invention relates to the field of lubricating compositions, especially lubricating compositions for motor vehicles, in particular the field of lubricating compositions for transmission, gearbox or bridge. The lubricant composition according to the invention comprises at least 30% by weight of the composition of at least one monoester, at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C. ranges from 40 to 3000 mm2.s -1 and at least one polyalphaolefinic oil (PAO) whose kinematic viscosity measured at 100 ° C ranges from 1.5 to 10 mm2.s-1. The invention also relates to the use of this lubricant composition for reducing the fuel consumption of a vehicle equipped with a transmission, in particular a bridge or a gearbox, lubricated with this lubricating composition.

Description

The invention relates to the field of lubricating compositions, especially lubricating compositions for motor vehicles, in particular the field of lubricating compositions for transmission, gearbox or bridge. The lubricant composition according to the invention comprises at least 30% by weight of the composition of at least one monoester, at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C. ranges from 40 to 3000 mm2.s -1 and at least one polyalphaolefinic oil (PAO) whose kinematic viscosity measured at 100 ° C ranges from 1.5 to 10 mm2.s-1. The invention also relates to the use of this lubricant composition for reducing the fuel consumption of a vehicle equipped with a transmission, in particular a bridge or a gearbox, lubricated with this lubricating composition. Oils for gearboxes or for axles, and more generally for gear oils, must satisfy many requirements, notably related to driving comfort (perfect gearshift, quiet running, trouble-free operation, high reliability), at the same time. lifetime of the assembly (reduction of wear during cold passage, no deposits and high thermal stability and oxidation, safety of lubrication at high temperatures, stable viscosity situation and absence of shear loss, long service life) as well as taking into account environmental aspects (lower fuel consumption, reduced oil consumption, low noise, easy evacuation). These are usually the requirements for manual gearbox oils and axle gears. Concerning the requirements imposed on automatic gearbox oils (ATF oils for automatic transmission fluids), because of their use, it appears for ATF oils very specific requirements which are a great constancy of the coefficient of friction throughout the stay for optimal gear change, excellent aging stability for long drain intervals, good viscosity-temperature performance to ensure perfect operation with a hot engine and a cold engine and sufficient sealing compatibility with different elastomers 3034100 2 used in transmission seals so that they do not swell, shrink or embrittle. On the other hand, in the automobile field, the search for the reduction of CO2 emissions makes it necessary to develop lubricant products that make it possible to reduce friction in gearboxes and in bridge differentials. This reduction of friction in the gearboxes and in the bridge differentials must be obtained for different operating conditions. These friction reductions must relate to the internal friction of the lubricant but also the friction of the elements constituting the gearboxes or the bridge differentials, in particular the metallic elements. The nature of automotive engine lubricating compositions has an influence on pollutant emissions and fuel consumption. Vehicle lubricant compositions for energy saving are often referred to as "fuel-eco" (FE) in English terminology. Such "fuel-eco" oils have been developed to meet these new needs. The reduction of energy losses is therefore a constant search in the field of lubricant compositions for vehicles.

The vehicle lubricating compositions must therefore have improved properties and performance. In particular, it is necessary to provide alternative lubricating compositions, in particular lubricant compositions having a high viscosity index (VI) and a low tensile coefficient.

The desired lubricating compositions should have a high viscosity index in order to avoid cold energy losses due to friction but also to keep a sufficient lubricant film on the lubricated elements hot. A high viscosity index thus guarantees a lower drop in viscosity when the temperature increases.

It is also necessary to provide alternative lubricating compositions having good oxidation resistance. There is therefore a need for lubricating compositions for vehicle transmission which can provide a solution to all or part of the problems of the lubricant compositions of the prior art.

Thus, the invention provides a lubricating composition comprising (a) at least 30% by weight of the composition of at least one monoester of formula (I) ## STR1 ## wherein R 1 represents a hydrocarbon group saturated or unsaturated, linear or branched, comprising from 14 to 24 carbon atoms; R 2 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 18 carbon atoms; (b) at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C according to ASTM D445 is from 40 to 3,000 mm 2 s -1; (c) at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C. according to the ASTM D445 standard ranges from 1.5 to 10 mm 2 s -1.

The composition according to the invention comprises at least one monoester (a), at least one polyalphaolefinic oil (b) and at least one polyalphaolefinic oil (c). It may comprise only one monoester (a), one polyalphaolefinic oil (b) and one polyalphaolefinic oil (c). It may also comprise one, two or three monoesters (a) but also one, two or three polyalphaolefinic oils (b) or alternatively two or three polyalphaolefinic oils (c). The monoester (a) present in the lubricant composition according to the invention is a monoester of formula (I). Preferably, for the monoester (a) of formula (I) according to the invention, R1 represents a linear or branched, saturated or unsaturated hydrocarbon-based group comprising from 14 to 20 carbon atoms, preferably from 14 to 18 carbon atoms. carbon, more preferably from 16 to 18 carbon atoms. Also preferably for the monoester (a) of formula (I) according to the invention, R2 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 3 to 14 carbon atoms, preferably from 4 to 12 atoms. carbon, more preferably from 4 to 10 carbon atoms. Advantageously, the monoester (a) present in the lubricant composition according to the invention is a monoester of formula (I) in which R 'is a linear group and R2 is a branched group; or 3034100 4 R 'is a branched group and R2 is a linear group; or R 'and R2 are linear groups; or R 'and R2 are branched groups. Preferably, the monoester (a) present in the lubricant composition according to the invention is a monoester of formula (I) in which R1 and R2 are linear groups. In a particularly preferred manner, the monoester (a) present in the lubricant composition according to the invention is a monoester of formula (I) in which R 1 and R 2 independently represent a group chosen from a linear saturated group; a branched saturated group comprising from 1 to 5 branching chains; a branched saturated group whose branching chains comprise from 1 to 5 carbon atoms; a branched saturated group comprising from 1 to 5 branching chains and wherein the branching chains comprise from 1 to 5 carbon atoms. Also preferably, the monoester (a) present in the lubricating composition according to the invention is a monoester of formula (I) in which R 1 and R 2 are chosen from a linear saturated group; A branched saturated group comprising from 1 to 5 branching chains; a branched saturated group whose branching chains comprise from 1 to 5 carbon atoms; a branched saturated group comprising from 1 to 5 branching chains and whose branching chains comprise from 1 to 5 carbon atoms.

Also preferably, only R1 or only R2 is selected from one or other of these groups. Preferably, the monoester (a) is of formula (I) in which R 'is a saturated group and R2 is an unsaturated group; or R 'is an unsaturated group and R2 is a saturated group; or R 1 and R 2 are saturated groups; or R 'and R2 are unsaturated groups. A monoester (a) of formula (I) in which R 1 is a saturated group and R 2 is a saturated group is particularly preferred. A monoester (a) of formula (I) wherein R 1 is an unsaturated group and R 2 is a saturated group is more particularly preferred.

The monoester (a) of formula (I) according to the invention may be chosen from numerous monoesters. Preferably, it is chosen from stearates, preferably alkyl stearates and alkenyl stearates, more preferentially C4-C10-alkyl stearates, in particular butyl stearate, pentyl stearate, stearate. hexyl, heptyl stearate, octyl stearate, nonyl stearate, decyl stearate. Also preferably, it is chosen from oleates, preferably alkyl oleates and alkenyl oleates, more preferentially C4-C10 alkyl oleates, in particular butyl oleate, pentyl oleate. , hexyl oleate, heptyl oleate, octyl oleate, nonyl oleate, decyl oleate.

Other monoesters which may be suitable according to the invention include linoleate, preferably alkyl linoleate and alkenyl linoleate, more preferably C4-C10-alkyl linoleate, in particular butyl linoleate, pentyl linoleate, hexyl linoleate, heptyl linoleate, octyl linoleate, nonyl linoleate, decyl linoleate. Mention may also be made of palmitoleates; palmitates; linolenates; eicosenoates; erucic acid esters; the nervonic acid esters. The monoester (a) of formula (I) according to the invention may also be chosen from alkenes monoesters and alkyl monoesters, preferably C2C10-alkyl monoesters, in particular ethyl monoesters, propylene monoesters, butyl monoesters, pentyl monoesters, hexyl monoesters, heptyl monoesters, octyl monoesters, nonyl monoesters, decyl monoesters. Advantageously, the lubricant composition according to the invention comprises from 30 to 70% by weight of the monoester composition of formula (I). Also advantageously, the lubricating composition according to the invention comprises from 30 to 60% by weight of the composition or from 30 to 50% by weight of the monoester composition of formula (I). In addition to the monoester (a), the lubricating composition according to the invention comprises at least two polyalphaolefinic oils (b) and (c). These are hydrogenated PAOs. The polyalphaolefinic oil (b) is a heavy PAO. It has a kinematic viscosity measured at 100 ° C according to ASTM D445 ranging from 40 to 3000 mm2.s-1. The polyalphaolefinic oil (c) is a light PAO. It has a kinematic viscosity measured at 100 ° C according to ASTM D445 ranging from 1.5 to 10 mm2.s-1.

Preferably, the kinematic viscosity of the polyalphaolefinic oil (b), measured at 100 ° C. according to ASTM D445, ranges from 40 to 1500 mm.sup.-2. More preferably, the kinematic viscosity of the polyalphaolefinic oil (b), measured at 100 ° C. according to ASTM D445, ranges from 40 to 300 mm 2 s -1.

Also preferably, the weight average molecular weight of the polyalphaolefinic oil (b) is greater than 2500 Da or ranges from 2500 to 80000 Da. More preferably, the weight average molecular weight of the polyalphaolefinic oil (b) is from 4000 to 50,000 Da. Particularly preferably, the polyalphaolefinic oil (b) has a kinematic viscosity, measured at 100 ° C according to ASTM D445, ranging from 40 to 1,500 mm 2 s -1 and a weight average molecular weight of from 2 500 to 80,000 Da or 4,000 to 50,000 Da. More preferably, the polyalphaolefinic oil (b) has a kinematic viscosity, measured at 100 ° C according to ASTM D445, ranging from 40 to 300 mm 2 s -1 and a weight average molecular weight of 2 500 to 80,000 Da or 4,000 to 50,000 Da. Preferably, the kinematic viscosity of the polyalphaolefinic oil (c), measured at 100 ° C. according to the ASTM D445 standard, ranges from 1.5 to 10 m 2 -2 s -1 or from 2 to 10 mm 2 s -1. More preferably, the kinematic viscosity of the polyalphaolefinic oil (c), measured at 100 ° C according to ASTM D445, is 1.5 to 8 mrd.s-1 or 2 to 8 mm 2. 1. Also preferably, the weight average molecular weight of the polyalphaolefinic oil (c) is less than 500 Da or is from 50 to 500 Da. More preferably, the weight average molecular weight of the polyalphaolefinic oil (c) is 50 to 350 Da or 50 to 300 Da.

Particularly preferably, the polyalphaolefinic oil (c) has a kinematic viscosity, measured at 100 ° C according to ASTM D445, ranging from 1.5 to 8 mm 2 s -1 and a weight average molecular weight ranging from 50 to 500 Da or 50 to 350 Da or 50 to 300 Da or a kinematic viscosity, measured at 100 ° C according to ASTM D445, ranging from 2 to 8 mm2.s-1 and a weight average molecular weight Ranging from 50 to 500 Da or 50 to 350 Da or 50 to 300 Da. More preferably, the polyalphaolefinic oil (c) has a kinematic viscosity, measured at 100 ° C according to ASTM D445, ranging from 1.5 to 6 mm 2 s -1 and a weight average molecular weight ranging from 50 to 500 Da or 50 to 350 Da or 50 to 300 Da or a kinematic viscosity, measured at 100 ° C according to the ASTM D445 standard, ranging from 2 to 6 mm2.s-1 and an average molecular weight in weight ranging from 50 to 500 Da or 50 to 350 Da or 50 to 300 Da. As the particular polyalphaolefinic oil (c) according to the invention, mention may also be made of an oil with a kinematic viscosity at 100 ° C., measured according to the ASTM D445 standard, ranging from 3 to 4 mm 2 s -1, comprising more than 50% by weight of 9-methyl-11-octyl-henicosane, trimer of 1-decene. The respective proportions of polyalphaolefinic oils (b) and (c) within the lubricating composition according to the invention may vary. Preferably, the lubricating composition according to the invention comprises from 5 to 30% by weight, preferably from 5 to 25%, by weight of the polyalphaolefinic oil composition (b). Also preferably, the lubricating composition according to the invention comprises from 5 to 70%, preferably from 30 to 70%, by weight of the polyalphaolefinic oil composition (c). The respective proportions of polyalphaolefinic oils (b) and (c) in the lubricating composition 15 according to the invention may also vary according to the intended application for the lubricant composition according to the invention. Thus, for use as a gearbox lubricant, the lubricant composition according to the invention may comprise from 1 to 40% by weight of the polyalphaolefinic oil composition (b) and from 30 to 69% by weight of the composition of polyalphaolefinic oil (c).

In general, besides the monoester (a) and polyalphaolefinic oils (b) and (c), the lubricating composition according to the invention may comprise other oils as well as additives. The lubricating composition according to the invention may comprise any type of mineral lubricating base oil, synthetic or natural, animal or vegetable adapted to its use.

The base oils used in the lubricating 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 in saturated sulfur content viscosity (VI) Group I Mineral oils <90%> 0.03% 80 VI <120 Group II 90% 0.03% 80 VI <120 Hydrocracked oils 3034100 8 Group III Hydrocracked oils 90% 0.03% 120 or hydro-isomerized Group IV polyalphaolefin (PAO) Group V esters and other bases not included in groups I to IV Table A The mineral base oils useful according to the invention include all types of bases obtained by atmospheric distillation and vacuum of crude oil, followed by refining operations such as solvent extraction, desalphating, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing. 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 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 lubricating compositions according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, as well as from polyalphaolefins. The other 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 mes-1 according to ASTM D445. Their weight average molecular weight is generally between 250 and 3000 Da according to ASTM D5296. Advantageously, the lubricant composition according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition. More advantageously, the lubricating composition 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. Also advantageously, the lubricating composition according to the invention comprises from 75 to 99.9% by weight of base oils relative to the total mass of the composition.

Many additives can be used for the lubricant composition according to the invention.

The preferred additives for the lubricating composition according to the invention are chosen from detergent additives, anti-wear additives, friction modifying additives, extreme pressure additives, dispersants, pour point improvers, agents and the like. antifoams, thickeners and mixtures thereof.

Preferably, the lubricating composition according to the invention comprises at least one pour point or PPD agent additive (for depressant point or pour point reducing agent). By slowing the formation of paraffin crystals, the pour point reducing agents generally improve the cold behavior of the lubricating composition of the invention. Examples of pour point reducing agents include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

The lubricating composition according to the invention may also comprise at least one antiwear additive, at least one extreme pressure additive or mixtures thereof. 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 have the formula Zn ((SP (S) (OR 3) (OR 4)) 2, in which R 3 and R 4, which may be identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms. The 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 for the catalytic systems of automobiles because these additives are generators. These effects can be minimized by partially substituting the amine phosphates with additives which do not add phosphorus, such as, for example, polysulfides, especially sulfur-containing olefins, and advantageously the lubricating composition according to the invention. 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 mass relative to the total mass of lubricating composition, antiwear additives and extreme pressure additives. Advantageously, the lubricant composition according to the invention may comprise at least one friction modifying additive. The friction modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds supplying metal 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, oxygen, nitrogen, or carbon atoms. 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 lubricating 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, friction modifier additive.

Advantageously, the lubricating 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 may notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricating 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. Phenolic antioxidant additives 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 with at least one C 1 -C 12 alkyl group, and 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 C 1 -C 10 alkyl group, preferably a group 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 5 R 6 R 7 in which R 5 represents an optionally substituted aliphatic or aromatic group, R 6 represents an optionally substituted aromatic group, R 7 represents a hydrogen atom an alkyl group, an aryl group or a group of the formula R8S (O), R9 in which R8 represents an alkylene group or an alkenylene group, R9 represents an alkyl group, an 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, sulfonates, 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 and the naphthenates, as well as the salts of phenates. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium. These metal salts generally comprise the metal in a 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 lubricating composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total mass of the lubricant composition. 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. Advantageously, the lubricating composition may also comprise at least one viscosity index improver polymer. Examples of viscosity index improver polymers include polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, polymethacrylates (PMA). Also advantageously, the lubricant composition according to the invention may comprise from 1 to 15% by weight based on the total weight of the viscosity index improving lubricant composition. The invention also relates to the use as a lubricant of the lubricating composition according to the invention. Preferably, the lubricant composition according to the invention is useful for lubricating a gear system, in particular a vehicle transmission, in particular a bridge or a gearbox. The composition according to the invention is also advantageously used to reduce the fuel consumption of an engine, in particular a vehicle engine. Preferably, the composition according to the invention is used to reduce the fuel consumption of a vehicle equipped with a transmission, in particular a deck or a gearbox, lubricated with this composition.

The invention also relates to the use of at least one lubricating composition according to the invention for reducing the traction coefficient of a transmission oil, preferably for reducing the tensile coefficient of a box oil. speeds, in particular of a gearbox of a vehicle. The invention also relates to the use for decreasing the tensile coefficient of a lubricating composition comprising at least one heavy PAO (b) and at least one light PAO (c) and at least 30% by weight of composition of a monoester (a) of formula (I) 10 defined according to the invention. The uses of the lubricant composition according to the invention comprise contacting at least one element of the transmission, in particular the gearbox or the bridge, with a lubricant composition according to the invention.

By analogy, the particular, advantageous or preferred characteristics of the lubricating composition according to the invention, as well as the monoester (a) and polyalphaolefinic oils (b) and (c), define particular, advantageous or preferred uses according to the invention. 'invention.

The various aspects of the invention will be the subject of the following examples. They are provided for illustration. EXAMPLE 1 Preparation of Lubricating Compositions According to the Invention Decyl oleate (Stéarinerie Dubois) is mixed with a heavy PAO (product Spectrasyn mPA0150 from the company Exxon - KV100 of about 150 mm 2 s -1). first light PAO (Spectrasyn 6 product from Exxon - KV100 of about 6 mm2.s-1) and a second light PAO (Spectrasyn 8 product from Exxon - KV100 of about 8 mm2.s-). In a similar manner, a second composition according to the invention is prepared in which the decyl oleate is replaced by butyl stearate (Stéarinerie Dubois). The respective amounts of the various constituents are presented in Table 1 and are expressed in weight% relative to the weight of the final composition. The viscosity index (Viscosity Index in English or VI) is measured according to the ASTM D2270 standard.

Composition (1) according to the invention (%) Composition (2) according to the invention (%) Decyl oleate 30 Butyl stearate 0 30 Heavy PAO (b) 8 10 Light PAO (cl) (Spectrasyn 6) 4 Light PAO (c2) (Spectrasyn 8) 32 56 Viscosity Index (VI) 174 176 Table 1 Comparative Example 1: Preparation of Comparative Lubricating Compositions Analogous to Example 1, 3 comparative lubricating compositions were prepared by replacing decyl oleate respectively with methyl oleate (Stéarinerie Dubois), methyl stearate (Stéarinerie Dubois) and isononyl isononanoate (Stéarinerie Dubois). The respective amounts of the various constituents are presented in Table 2 and are expressed in weight% relative to the weight of the final composition. Composition Composition Comparative composition (1) (0/0) comparative (2) (0/0) comparative (3) (0/0) methyl oleate 30 0 methyl stearate 0 30 isononyl isononanoate 0 0 30 PAO heavy (b) 13 12.3 13 light PAO (cl) (Spectrasyn 6) 0 0 57 light PAO (c2) (Spectrasyn 8) 57 57.7 0 viscosity index (VI) 182 180 173 10 Table 2 Example 2: comparison of the tensile coefficient of the compositions according to the invention and comparative lubricating compositions The tensile coefficient of the lubricating compositions prepared is evaluated and the results obtained are shown in Table 3.

Composition (1) according to the invention Composition (2) according to the invention Comparative composition (3) Traction coefficient (MTM: T = 40 ° C, Ve = 1 m-1, SRR = 20% charge = 75 N) 0.034 0.033 0.048 Table 3 Lubricating compositions according to the invention have a better coefficient of traction than comparative lubricating compositions.

Example 3: Comparison of the oxidation resistance properties of the lubricant composition (1) according to the invention and the comparative lubricating composition (1) The oxidation resistance properties of the lubricating compositions prepared are evaluated according to the standard CEC-L48-A-00 method A and the results obtained are shown in Table 4. The greater the variation of KV 100 (R KV 100), the lower the oxidation resistance. The greater the variation of KV 40 (R KV 40), the lower the resistance to oxidation. The greater the variation of TAN (Total Acid Number in English, R TAN), the lower the resistance to oxidation. The higher the PAI (Peak Area Increase in English), the lower the resistance to oxidation. Lubricating composition (1) Comparative lubricating composition according to the invention (1) Duration (h) 192 192 KV 100 initial (mm2.s-1) 6.68 6.79 KV 100 final (mm2.s-1) 7.88 11.08 R KV 100 (%) 18.01 63.18 KV 40 initial (mm2.s-1) 31.13 30.44 KV 40 initial (mm2.s-1) 37.79 60.15 R KV 40 (%) 21.39 97.60 Insoluble Compounds 0 4 cm Bottom TAN Initial 1.87 1.46 3034100 16 Final TAN 3.48 4.12 R TAN (%) 1.6 2.7 PAI <20 34 Table The lubricating composition according to the invention has an oxidation resistance which is greater than that of the comparative lubricating composition. No deposit of insoluble compounds occurs with the lubricating composition according to the invention.

These results also show that the lubricant compositions according to the invention retain a high viscosity index and are therefore compatible with applications as transmission lubricants or motor lubricants. 10

Claims (14)

REVENDICATIONS1. A lubricating composition comprising (a) at least 30% by weight of the composition of at least one monoester of formula (I) wherein R1 represents a linear or branched, saturated or unsaturated hydrocarbon group, comprising from 14 to 24 carbon atoms; R2 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 2 to 18 carbon atoms; (b) at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C according to ASTM D445 is from 40 to 3,000 mm 2 s -1; (c) at least one polyalphaolefinic (PAO) oil whose kinematic viscosity measured at 100 ° C. according to the ASTM D445 standard ranges from 1.5 to 10 mm 2 s -1. 2. Lubricating composition according to claim 1 comprising from 30 to 70% by weight of the composition or from 30 to 60% by weight or else from 30 to 50% by weight of the monoester composition of formula (I). 3. Lubricating composition according to one of claims 1 and 2 wherein R 'isa saturated group and R2 is an unsaturated group; or R 'is an unsaturated group and R2 is a saturated group; or R 'and R2 are saturated groups; or R 'and R2 are unsaturated groups. 4. Lubricating composition according to one of claims 1 to 3 wherein ^ R1 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 14 to 20 carbon atoms, preferably from 14 to 18 carbon atoms, more preferably from 16 to 18 carbon atoms; or R2 represents a hydrocarbon group, saturated or unsaturated, linear or branched, comprising from 3 to 14 carbon atoms, preferably from 4 to 3034100 18 12 carbon atoms, more preferably from 4 to 10 carbon atoms; or R1 is a linear group and R2 is a branched group; or R1 is a branched group and R2 is a linear group; or R1 and R2 are linear groups; or R1 and R2 are branched groups. 5. Lubricating composition according to one of claims 1 to 4 wherein only R1, only R2 orR1 and R2 are selected from 10 a linear saturated group; a branched saturated group comprising from 1 to 5 branching chains; a branched saturated group whose branching chains comprise from 1 to 5 carbon atoms; a branched saturated group comprising from 1 to 5 branching chains and wherein the branching chains comprise from 1 to 5 carbon atoms. 6. Lubricating composition according to one of claims 1 to 5 wherein the monoester is selected from stearates, preferably alkyl stearates and alkenyl stearates, more preferably C4-C10-alkyl stearates, in particular butyl stearate, pentyl stearate, hexyl stearate, heptyl stearate, octyl stearate, nonyl stearate, decyl stearate; the oleates, preferably the alkyl oleates and the alkenyl oleates, more preferably the C 4 -C 10 alkyl oleates, in particular the butyl oleate, the pentyl oleate, the hexyl oleate, , heptyl oleate, octyl oleate, nonyl oleate, decyl oleate. 7. Lubricating composition according to one of claims 1 to 6 wherein the monoester is selected from alkenes monoesters and alkyl monoesters, preferably C2-C10-alkyl monoesters. 8. Lubricating composition according to one of claims 1 to 7 wherein ^ the kinematic viscosity of the polyalphaolefinic oil (b), measured at 100 ° C according to ASTM D445, ranges from 40 to 1500 mm2.s- 1; or 3034100 the kinematic viscosity of the polyalphaolefinic oil (b), measured at 100 ° C according to ASTM D445, ranges from 40 to 300 mm 2 s -1; or the weight average molecular weight of the polyalphaolefinic oil (b) is greater than 2500 Da or ranges from 2500 to 80 000 Da; or the weight average molecular weight of the polyalphaolefinic oil (b) is from 4000 to 50,000 Da. 9. Lubricating composition according to one of claims 1 to 8 wherein ^ the kinematic viscosity of the polyalphaolefinic oil (c), measured at 100 ° C according to ASTM D445, ranges from 1.5 to 10 mm2.s -1; or the kinematic viscosity of the polyalphaolefinic oil (c) measured at 100 ° C according to ASTM D445 is 1.5 to 6 mm 2 s -1; or the kinematic viscosity of the polyalphaolefinic oil (c), measured at 100 ° C according to ASTM D445, is from 2 to 8 mm 2 s -1; or the weight average molecular weight of the polyalphaolefinic oil (c) is less than 500 Da or is from 50 to 500 Da; or the weight average molecular weight of the polyalphaolefinic oil (c) is 50 to 350 Da; or the weight average molecular weight of the polyalphaolefinic oil (c) is from 50 to 300 Da. Lubricating composition according to one of claims 1 to 9, comprising 5 to 30% by weight, preferably 5 to 25% by weight, of the polyalphaolefinic oil composition (b); or 25 to 5 to 70% by weight, preferably 30 to 70% by weight, of the polyalphaolefinic oil composition (c); or 5 to 30% by weight, preferably 5 to 25% by weight, of the polyalphaolefinic oil composition (b) and 5 to 70% by weight, preferably 30 to 70% by weight, of the polyalphaolefinic oil composition (c). 30 11. Lubricating composition according to one of claims 1 to 10 comprising one, two or three monoesters (a); or one, two or three polyalphaolefinic oils (b); or one, two or three polyalphaolefinic oils (c); or 3034100 comprising a single monoester (a), a single polyalphaolefinic oil (b) and a single polyalphaolefinic oil (c). Lubricating composition according to one of Claims 1 to 11, also comprising at least one additive, preferably a PPD agent (for depressant point or pour point reducing agent). 13. Use of at least one lubricant composition according to one of claims 1 to 12 for lubricating a gear system, in particular a vehicle transmission, in particular a bridge or a gearbox, or for reducing the fuel consumption. fuel of a vehicle equipped with a transmission, in particular a deck or a gearbox, lubricated with that compound. 14. Use for decreasing the tensile coefficient of a lubricating composition comprising at least one heavy PAO (b) and at least one light PAO (c) and at least 30% by weight of composition of a monoester (a) of Formula (I) defined according to one of Claims 1 to 7.