USE OF DIALKYLENE GLYCOLESTER FOR FRICTION REDUCTION IN VEHICLES WITH HYBRID ENGINES

Description

[0001] The present invention relates to the use of dialkylene glycol ester in a lubricating composition for a vehicle equipped with a hybrid engine, to reduce the coefficient of friction when using the engine at low speed and / or when cold.

[0002] Improving lubricant performance is a constant concern. In particular, to meet growing environmental demands, there is a growing demand for improving the performance of lubricants, particularly those used in new-generation vehicles, including hybrid vehicles.

[0003] However, few compositions demonstrate a particular interest for use in hybrid vehicles. Hybrid vehicles have particular constraints, particularly at low speeds and when cold, i.e. over specific periods that can be described as the "start of the cycle", after starting the vehicle. Over these cycles, the temperatures of the oils used in a hybrid vehicle are low, lower than those used in a vehicle comprising a thermal engine, and it is of essential interest to propose a formulation demonstrating gains over these particular periods of use.

[0004] FR 3083244 describes the use, for cooling and lubricating a propulsion system of an electric or hybrid vehicle, of a composition comprising at least one base oil and at least one alkylene glycol diester.

[0005] Against all expectations, the inventors discovered that it is possible to access lubricating compositions, the efficiency of which is increased in terms of Fuel-Eco on operating cycles described as low speed and cold.

[0006] An objective of the present invention is therefore to provide an additive for a lubricating composition for a vehicle equipped with a hybrid engine, to reduce the coefficient of friction when using the engine at low speed.

[0007] Another objective of the present invention is also to provide an additive for a lubricating composition for a vehicle equipped with a hybrid engine, to reduce the coefficient of friction when using the engine when cold.

[0008] Other objectives will appear upon reading the description of the invention which follows.

[0009] These objectives are achieved by the present invention which relates to the use of a diester of formula (I) in a lubricating composition for a vehicle equipped with a hybrid engine, to reduce the coefficient of friction when using the engine at low speed and / or when cold, R a< -C(O)-O-([C(R) 2 ] n -O) s -C(O)-R b< (I) in which: R represent, independently of each other, 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 identical or different; Ra and Rb, 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 n, identical, are 2, at least one of the R groups represents a linear or branched alkyl group 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 bonded to the carbon in the beta position of the oxygen atoms of the ester functions represents a hydrogen atom.

[0010] The present invention also relates to a method for reducing the coefficient of friction when using a hybrid engine at low speed and / or when cold, comprising lubricating said engine with a lubricating composition comprising at least one base oil and a diester of formula (I) R a< -C(O)-O-([C(R) 2 ] n -O) s -C(O)-R b< (I) in which: R represent, independently of each other, 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 identical or different; Ra and Rb, 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 n, identical, are 2, at least one of the R groups represents a linear or branched alkyl group 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 bonded to the carbon in the beta position of the oxygen atoms of the ester functions represents a hydrogen atom.

[0011] In the context of the present invention, "low speed" means a specific engine speed. Engine speed refers to the rotational speed of the engine and is expressed in revolutions per minute. According to the invention, low speed is characterized by a number of revolutions per minute (rpm) of between 600 and 2000 rpm, preferably between 900 and 1500 rpm.

[0012] In the context of the present invention, "cold" means the use of the engines during start-up and during phase 1 of the WLTC cycle, the engine is then at a temperature below 50°C, preferably between 20 and 50°C, preferably between 25 and 40°C.

[0013] The reduction in the coefficient of friction should be understood as a reduction compared to what would be observed with the lubricating composition not comprising the diester of the invention.

[0014] Preferably, in the diester of formula (I) of the invention, when s is different from 1 all the n are identical.

[0015] Preferably, in the diester of formula (I) of the invention n represents 2 or 3, preferably 2.

[0016] Preferably, in the diester of formula (I) of the invention, 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.

[0017] In a particular embodiment, the diester of formula (I) according to the invention is a diester of the following formula (I'): R a< -C(O)-O-([C(R) 2 ] n -O)-([C(R') 2 ] m -O) s-1 -C(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; Ra and Rb, identical or different, represent independently of each other, saturated or unsaturated, linear or branched hydrocarbon groups 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 a linear or branched alkyl group comprising from 1 to 5 carbon atoms.

[0018] Advantageously, at least one of the groups R or R' in the diester of formula (I') represents an alkyl group, linear or branched, comprising from 1 to 5 carbon atoms, preferably from 1 to 4 carbon atoms, preferably methyl, ethyl, or propyl, advantageously methyl.

[0019] Preferably, in the compounds of formula (I) and (I'), Ra and Rb have a linear chain of 7 to 14 carbon atoms, preferably of 8 to 12 carbon atoms, more particularly of 8 to 11 carbon atoms, in particular 9 or 11 carbon atoms.

[0020] In a particular embodiment, s, in formulas (I) or (I'), represents 2.

[0021] The diester of the invention is preferably a compound of formula (Ia): R a< -C(O)-O-([C(R) 2 ] n -O)-([C(R') 2 ] m -O)-C(O)-R b< (I'a) 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 methyl, ethyl or propyl, preferably methyl; n represents 2; m represents 2; Ra and Rb, 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.

[0022] 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.

[0023] Even more preferably, in the diester of 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.

[0024] In a particular embodiment, the diester of the invention is a compound of formula (I"a) R a< -C(O)-O-CHR 1< -CHR 2< -O-CHR 3< -CHR 4< -OC(O)-R b< (I"a) in which: one of the groups R 1< and R 2< represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, the other representing a hydrogen atom; one of the groups R 3< and R 4< represents a linear or branched alkyl group comprising from 1 to 5 carbon atoms, the other representing a hydrogen atom; Ra and Rb, identical or different, are as defined previously.

[0025] Preferably, in the compounds of formula (I"a): one of the groups R 1< and R 2< represents a methyl, ethyl or propyl group, preferably methyl, the other representing a hydrogen atom; one of the groups R 3< and R 4< represents a methyl, ethyl or propyl group, preferably methyl, the other representing a hydrogen atom.

[0026] According to another alternative embodiment, in the compounds of formula (I) or (I') s represents 1 and the diesters of the invention are of formula (I'b): R a< -C(O)-O-([C(R) 2 ] n -O)-C(O)-R b< (I'b) in which: 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; n represents 2; Ra and Rb, 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.

[0027] 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.

[0028] 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.

[0029] For the purposes of the present invention, it is to be understood that the expression "comprising from x to y carbon atoms" also covers the limits x and y.

[0030] 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.

[0031] According to a particular embodiment, in formulas (I), (I'), (I'a), (I"a) or (I'b), Ra and Rb, identical or different, are of plant, animal or petroleum origin.

[0032] According to a particular embodiment, in formulas (I), (I'), (I'a), (I"a) or (I'b), Ra and Rb, identical or different, represent saturated groups.

[0033] According to a particular embodiment, in formulas (I), (I'), (I'a), (I"a) or (I'b), Ra and Rb, identical or different, represent linear groups. In particular, Ra and Rb, 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.

[0034] According to another preferred embodiment, in formulas (I), (I'), (I'a), (I"a) or (I'b), Ra and Rb, 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.

[0035] Preferably Ra and Rb are identical.

[0036] 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 WO2019025446.

[0037] Preferably, the diester of formula (I) is added in a proportion of 1 to 40% by mass relative to the total mass of the lubricating composition, preferably 10 to 30%.

[0038] The base oil used in the lubricating compositions of the invention may be 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. Table 1 Saturated substance content Sulfur content 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 ≥ 90 % ≤ 0,03 % ≥ 120 Hydroisomerized Oils Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in groups I to IV

[0039] The mineral base oils of the invention include any type of base oil obtained by atomospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0040] Blends of synthetic and mineral oils can also be used.

[0041] The 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 mm2.s-1 according to the ASTM D445 standard. Their average molar mass is generally between 250 and 3000 according to the ASTM D5296 standard.

[0042] The lubricating composition according to the invention may comprise at least 50% by weight of base oil relative to the total weight 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 weight of the lubricating composition. More preferably, the lubricating composition according to the invention comprises from 75 to 97% by weight of base oils relative to the total weight of the composition.

[0043] The composition of the invention may also comprise at least one additive.

[0044] Many additives can be used in the lubricating compositions according to the invention.

[0045] The preferred additives for the lubricating composition according to the invention are chosen from detergent additives, friction modifying additives different from the molybdenum compounds defined above, extreme pressure additives, dispersants, pour point activators, anti-foaming agents, thickeners and their mixtures.

[0046] Preferably, the lubricating compositions according to the invention comprise at least one extreme pressure additive, or a mixture.

[0047] Anti-wear additives and extreme pressure additives protect surface friction by forming a protective film adsorbed on its surfaces.

[0048] There is a wide variety of anti-wear additives. Preferably, for the lubricating compositions of the invention, the anti-wear additives are chosen from additives comprising phosphorus and sulfur such as alkylthiophosphate metals, in particular zinc alkylthiophosphate, and more precisely zinc dialkyldithiophosphate or ZnDTP. The preferred compounds are 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.

[0049] Amine phosphates are also anti-wear additives that can be used in the lubricating compositions of the invention. However, the phosphorus atoms provided by these additives can act as a poison for automobile catalytic systems since they generate ash. It is possible to minimize these effects by substituting a portion of the amine phosphates with additives that do not provide phosphorus, such as, for example, polysulfides, in particular sulfur-containing olefins.

[0050] Advantageously, the lubricating compositions 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 total weight of lubricating composition, of anti-wear and extreme pressure additives.

[0051] Advantageously, the lubricating compositions according to the invention 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 total weight of lubricating composition, of anti-wear additives (or anti-wear compound).

[0052] Advantageously, the compositions according to the invention may comprise at least one friction modifying additive different from the molybdenum compounds of the invention. The friction modifying additives may in particular be chosen from compounds providing metallic elements and ashless compounds. Among the compounds providing metallic elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu, Zn for which the ligands may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. The ashless friction modifying additives are generally of organic origin or may be chosen from fatty acid monoesters and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, fatty epoxide borates, fatty amines or glycerol acid esters.According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

[0053] 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 from 0.1 to 2% by weight relative to the total weight of the lubricating composition, of friction modifying additive other than the molybdenum compounds according to the invention.

[0054] Advantageously, the lubricating composition according to the invention may comprise at least one antioxidant additive.

[0055] Antioxidant additives generally delay the degradation of the lubricating composition. This degradation is most often expressed by the formation of deposits, by the presence of sludge or by an increase in the viscosity of the lubricating composition.

[0056] Antioxidant additives generally act as free radical inhibitors or hydroperoxide destructive inhibitors. Commonly used antioxidants include phenolic antioxidants, amine antioxidants, sulfur- and phosphorus-containing antioxidants. Some of these antioxidants, for example those comprising sulfur and phosphorus, may generate ash. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. Antioxidant additives may include, but are not limited to, sterically hindered phenols, sterically hindered phenol esters, sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C1-C12 alkyl group, N,N'-dialkylaryldiamines, and mixtures thereof.

[0057] Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group for which at least one of the carbon atoms in the vicinity of the carbon atom carrying the alcohol function is substituted by at least one C1 to C10 alkyl group, preferably a C1 to C6 alkyl group, preferably a C4 alkyl group, preferably a tert-butyl group.

[0058] Amine 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 the formula NRaRbRc in which Ra represents an aliphatic group or an aromatic group, optionally substituted, Rb represents an aromatic group, optionally substituted, Rc represents a hydrogen atom, an alkyl group, an aryl group or a group of the formula RdS(O)zRe in which Rd represents an alkylene or alkenylene group, Re represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

[0059] Sulfur-containing alkylphenols or their alkali or alkaline earth metal salts can also be used as antioxidant additives.

[0060] Other classes of antioxidant additives are compounds containing copper, e.g. copper thio- or dithio-phosphate, copper salts of carboxylic acids, dithiocarbamates, sulfonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts may also be used.

[0061] The lubricating compositions according to the invention may also comprise any type of antioxidant known to those skilled in the art.

[0062] Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

[0063] Also advantageously, the lubricating composition according to the invention comprises from 0.1 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

[0064] The lubricating composition according to the invention may also comprise at least one detergent additive.

[0065] Detergent additives generally reduce the formation of deposits on the surface of metal parts by dissolving secondary oxidation and combustion products.

[0066] The detergent additives that can be used in the lubricating compositions 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 hydrophobic head. The associated cation may be a metal cation of an alkali or alkaline earth metal.

[0067] The detergent additives are preferably selected from alkali or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, and phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium, or barium.

[0068] These metal salts generally comprise the metal in stoichiometric or excess quantity, i.e. in a content greater than the stoichiometric content. These are then overbased detergents; the excess metal implying the overbased nature of the detergent additive is generally in the form of an oil-insoluble metal salt, e.g. carbonate, hydroxide, oxalate, acetate, glutamate, preferably carbonate.

[0069] Advantageously, the lubricating composition according to the invention may comprise from 0.5 to 8% or from 2 to 4% by weight of overbased detergent additives relative to the total weight of the lubricating composition.

[0070] Also advantageously, the lubricating composition according to the invention may also comprise a pour point lowering additive.

[0071] By slowing the formation of paraffin crystals, the pour point lowering additive generally improves the cold behavior of the lubricating composition according to the invention.

[0072] Examples of pour point depressant additives include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, and alkyl polystyrenes.

[0073] Advantageously, the lubricating composition according to the invention may also comprise a dispersing agent.

[0074] The dispersing agents can be chosen from Mannich bases, succinimides and their derivatives.

[0075] 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 weight of lubricating composition.

[0076] Advantageously, the lubricating composition according to the invention may also further comprise at least one other additional polymer improving the viscosity index. As an example of an additional polymer improving the viscosity index, mention may be made of polymeric esters, homopolymers or copolymers, hydrogenated or not, of styrene, butadiene, and isoprene, polymethacrylates (PMA). Also advantageously, the lubricating composition according to the invention may comprise from 1 to 15% by weight relative to the total weight of lubricating composition, of additive improving the viscosity index.

[0077] The lubricating composition according to the invention may also comprise at least one thickening agent.

[0078] The lubricating composition according to the invention may also comprise an antifoaming agent and a demulsifying agent.

[0079] Preferably, the lubricating composition of the invention further comprises at least one anti-wear agent, in particular based on Zinc, in particular ZnDTP.

[0080] In the context of the present invention, hybrid-powered vehicles or vehicles equipped with a hybrid engine are understood to mean vehicles using two separate energy sources for their operation. In particular, hybrid vehicles combine a thermal internal combustion engine and an electric motor, said electric motor participating in the traction of the vehicle.

[0081] The invention also relates to a method for reducing friction when using a hybrid engine at low speed and / or when cold, comprising the addition to the lubricating composition of said engine of a diester according to the invention.

[0082] The invention also relates to a method for reducing friction when using a hybrid engine at low speed and / or when cold, comprising lubricating said engine with a lubricating composition comprising a diester according to the invention.

[0083] The present application will now be described using non-limiting examples. Example 1: Preparation of lubricating compositions

[0084] 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. Table 2 CC1 (% by weight) CC2 (% by weight) CL1 (% by weight) CC3 (% by weight) CL2 (% by weight) Additive package 12,7 12,7 12,7 12,7 12,7 MoDTC 0,5 0,5 0,5 0,5 0,5 PPD 0,2 0,2 0,2 0,2 0,2 Antioxidant 0,5 0,5 0,5 0,5 0,5 Viscosity modifier 0,4 0,8 0,8 1,3 1,5 DTP 0 30 0 0 0 Ester of formula (I) 0 0 30 0 20 Base oil 85,7 55,3 55,3 84,8 64,6 Grade 0W12 0W12 0W12 0W12 0W12 Table 3 CC4 (% by weight) CL3 (% by weight) CC5 (% by weight) CL4 (% by weight) CC6 (% by weight) Additive package 13 13 12,6 12,6 12,6 MoDTC 0,5 0,5 0,5 0,5 0,5 PPD 0,2 0,2 0,2 0,2 0,2 Viscosity modifier 1,3 4 4 4 4 DTP 0 0 0 0 20 Ester of formula (I) 0 10 0 20 0 Base oil 85 72,3 82,7 62,7 62,7 Grade 0W12 0W12 0W12 0W12 0W12 Table 4 CC7 (% by weight) CL5(% by weight) CC8 (% by weight) Additive package 10,1 10,1 10,1 MoDTC 0,4 0,4 0,4 Viscosity modifier 6,7 6,7 5,8 Ester of formula (I) 0 20 0 Base oil 82,8 62,8 83,7 Grade 0W20 0W20 0W20 Example 2 : PMF test results

[0085] A PMF (Mean Friction Pressure) bench is used to measure the friction of an engine. The engine is driven by a generator and the torque that this generator must provide is measured (this torque is therefore the image of the engine friction).

[0086] In this type of test, the engine does not burn any fuel, it is just driven exactly as if it were in the engine braking situation of a vehicle.

[0087] The bench properties in terms of regime and temperature are as follows: Engine speed: 900* - 6000 rpm Oil temperature: 35 - 110°C** Water temperature: 37 - 90°C**

[0088] 4 thermal conditions were tested: Engine oil temperature = 37°C / Coolant temperature = 37°C Engine oil temperature = 50°C / Coolant temperature = 50°C Engine oil temperature = 80°C / Coolant temperature = 80°C Engine oil temperature = 110°C / Coolant temperature = 90°C

[0089] The engine speed sequences tested are: 900, 1450, 2000, 2500, 3000, 3500, 4000, 4500

[0090] The test consists of drawing up a complete map of engine friction according to the different rotation speeds and the different water and oil temperatures.

[0091] The friction map created at the end of the test will be made up of 8 engine speeds and 4 temperatures.

[0092] The time taken to complete this mapping is approximately 11 hours.

[0093] The results are expressed as an average friction coefficient gain.

[0094] This mapping is then compared to that of a so-called reference oil which will be measured before and after testing the candidate oil in order to qualify any drift in the test method and integrate it into the interpretation of the results.

[0095] The so-called reference oil has the following composition: Table 5 DTP 10,00 DTP 10,00 MoDTC 0,50 Pour point depressant 0,20 Base oil 61,70 Additive package 12,70 Amino antioxidant 0,50 Viscosity index improving polymer 4,40 It is in relation to the latter that the friction gain percentages are calculated.

[0096] The results in terms of friction gain compared to the reference oil are given in tables 6 to 8 below. Table 6 CC1 (%) CC2 (%) CL1 (%) CC3 (%) CL2 (%) 30°C 1,42 1,06 3,38 1,20 3,35 50°C 1,7 1,71 2,48 1,85 2,72 Table 7 CC4 (%) CL3 (%) CC5 (%) CL4 (%) CC6 (%) 30°C 1,44 3,55 3,01 4,19 2,66 50°C 1,27 2,93 2,67 2,88 2,25 Table 8 CC7 (%) CL5 (%) CC8 (%) 30°C 3,89 6,25 0,2 50°C 2,78 3,98 0,54

[0097] The results show the ability of the ester according to the invention to improve friction gains at temperatures between 30°C and 50°C.

Claims

1. Use of a diester of formula (I) in a lubricant composition for vehicle equipped with a hybrid engine, to reduce friction when the engine is used at low speed <b>characterized by a number of revolutions per minute (rpm) of between 600 and 2000 rpm and / or when cold,         Ra-C(O)-O-([C(R)2]n-O)s-C(O)-Rb     (I) where: R, each independently, are a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; s is 1 or 2; n is 1, 2 or 3, on the understanding that when s differs from 1, the n values can be the same or different; Ra and Rb, the same or different, are each independently linear or branched, saturated or unsaturated hydrocarbon groups having a linear sequence of 6 to 18 carbon atoms; provided that when s is 2 and n all the same are 2, at least one of the R groups is a linear or branched alkyl group having 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 at beta position of the oxygen atoms of the ester functions is a hydrogen atom.

2. The use according to claim 1, wherein when s differs from 1, all the n values are the same.

3. The use according to any of claims 1 or 2, wherein n is 2 or 3.

4. The use according to any of claims 1 to 3, wherein at least one of the R groups is a linear or branched alkyl group having 1 to 5 carbon atoms.

5. The use according to any of claims 1 to 4, wherein the diester of formula (I) of the invention is a diester of following formula (I'):         Ra-C(O)-O-([C(R)2]n-O)-([C(R')2]m-O)s-1-C(O)-Rb     (I') where: R and R', each independently, are a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; s is 1 or 2; n is 2; m is 2; Ra and Rb, the same or different, are each independently linear or branched, saturated or unsaturated hydrocarbon groups having a linear sequence of 6 to 18 carbon atoms; provided that when s is 2, at least one of the groups R or R' is a linear or branched alkyl group having 1 to 5 carbon atoms.

6. The use according to any of claims 1 to 5, wherein the diester is a compound of formula (I"a)         Ra-C(O)-O-CHR1-CHR2-O-CHR3-CHR4-O-C(O)-Rb     (I"a) where: one of the groups R1 and R2 is a linear or branched alkyl group having 1 to 5 carbon atoms, the other being a hydrogen atom; one of the groups R3 and R4 is a linear or branched alkyl group having 1 to 5 carbon atoms, the other being a hydrogen atom. Ra and Rb, the same or different, are such as defined in claim 1.

7. The use according to any of claims 1 to 6, wherein the diester of formula (I) is added in a proportion of 1 to 40 % by weight relative to the total weight of the lubricant composition.

8. A method for reducing friction when using a hybrid engine at low speed characterized by a number of revolutions per minute (rpm) of between 600 and 2000 rpm and / or when cold comprising the addition, to the lubricant composition of said engine, of a diester of formula (I)         Ra-C(O)-O-([C(R)2]n-O)s-C(O)-Rb     (I) where: R, each independently, are a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; s is 1 or 2; n is 1, 2 or 3, on the understanding that when s differs from 1, the n values can be the same or different; Ra and Rb, the same or different, are each independently linear or branched, saturated or unsaturated hydrocarbon groups, having a linear sequence of 6 to 18 carbon atoms; provided that when s is 2 and n all the same are 2, at least one of the R groups is a linear or branched alkyl group having 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 at beta position of the oxygen atoms of the ester functions, is a hydrogen atom.

9. The method according to claim 8, wherein the diester is such as defined in claims 2 to 7.