Use of a diester in a lubricating composition for vehicle transmissions

Abstract

The present invention relates to the use of a composition comprising at least one diester, as a lubricating composition for transmissions, said diester being formed between: a pentanediol, and two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom, said composition optionally further comprising at least one base oil distinct from the diester and / or at least one additive distinct from the diester, said additive being chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors,copper passivating agents, and their mixtures. Figure for abstract: None,

Description

Title of the invention: Use of a diester in a lubricating composition for vehicle transmissions Technical field

[0001] The present invention relates to the field of lubricating compositions, more particularly the field of lubricating compositions for transmissions in vehicles with thermal engines (gearboxes and / or axles) as well as transmissions, in particular the reducer, in propulsion systems of electric or hybrid vehicles. It relates more particularly to the use of a diester in order to improve the efficiency performance of transmissions in thermal engines as well as the efficiency performance for reducers of electric motors. Prior art

[0002] Lubricating compositions, also called "lubricants", are commonly used in the various components of motor vehicles for the main purpose of reducing the friction forces between the various moving metal parts in these components, in particular the engine, the transmission and the hydraulic circuit. They are also effective in preventing premature wear or even damage to these parts, and in particular to their surface. To do this, a lubricating composition is conventionally composed of a base oil with which several additives are generally associated, designed to stimulate the lubricating performance of the base oil, such as, for example, friction-modifying additives, but also to provide additional performance.

[0003] Lubricating compositions for transmissions (for example, gearboxes or axles) must meet numerous requirements, particularly with regard to the strict specifications imposed by automobile manufacturers. In particular, they must have satisfactory properties in terms of viscosity, viscosity-temperature resistance, cold performance, etc. suitable for their implementation at the level of a transmission component, particularly at the level of the gearbox or axles, in a vehicle.

[0004] The evolution of international standards for the reduction of CO2 emissions, but also for the reduction of energy consumption, pushes car manufacturers to offer alternative solutions to combustion engines.

[0005] One of the solutions identified by car manufacturers is to replace combustion engines with electric motors. Research into reducing CO2 emissions has therefore led to the development of electric vehicles by a number of car companies.

[0006] For the purposes of the present invention, the term “electric vehicle” is understood to mean a vehicle comprising an electric motor as the sole means of propulsion, whereas a hybrid vehicle comprises a combustion engine and an electric motor as combined means of propulsion.

[0007] For the purposes of the present invention, the term "propulsion system" is intended to designate a system comprising the mechanical parts necessary for the propulsion of an electric vehicle. The propulsion system thus more particularly encompasses an electric motor comprising the rotor-stator assembly of the power electronics (dedicated to speed regulation), a transmission (also called a reducer, and when the reducer is attached to the motor, it is then referred to as a geared motor) and a battery. The battery itself is generally made up of a set of electrical accumulators, called cells.

[0008] There is a need to provide lubricating compositions of renewable plant origin having a low impact on the environment.

[0009] Furthermore, current environmental concerns, particularly with a view to reducing carbon dioxide emissions, induce an urgent need to reduce the fuel consumption of motor vehicles. In this respect, it is known that lubricating compositions represent an effective means of acting on fuel consumption via their impact on the friction forces generated between the various components of motor vehicles. Thus, there is a need to develop lubricants making it possible to reduce friction in gearboxes and in axle differentials.

[0010] Improving the “Fuel Eco” properties of transmission lubricants, while also maintaining the required high levels of performance, remains a challenge.

[0011] The invention aims precisely to propose a diester which can be entirely biosourced and capable of improving the efficiency performance of transmissions in thermal engines as well as the efficiency performance for reducers in electric motors. Summary of the invention

[0012] The present invention thus relates to the use of a composition comprising at least one diester, as a lubricating composition for transmissions, said diester being formed between: - a pentanediol, and - two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or several heteroatoms, such as a nitrogen or oxygen atom,

[0013] said composition optionally further comprising at least one base oil distinct from the diester and / or at least one additive distinct from the diester, said additive being chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

[0014] According to a preferred embodiment, the composition has one or more of the following characteristics: - pentanediol is 1,4-pentanediol, and / or - pentanediol is derived from the reduction of a keto acid, preferably levulinic acid, said keto acid preferably being derived from plant raw materials, and / or - said diester has a kinematic viscosity at 100°C ranging from 1 to 6 mm2 / s, preferably ranging from 1 to 4 mm2 / s, and / or - said monocarboxylic acids, identical or different, comprise a linear alkyl chain comprising from 4 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, or even from 5 to 8 carbon atoms, said alkyl chain optionally comprising one or more heteroatoms, for example one or more oxygen atoms, and / or - said diester(s) is(are) chosen from: • a diester formed from 1,4-pentanediol and two hep- acids tanoic, a diester formed from 1,4-pentanediol and two pentanoic acids, a diester formed from 1,4-pentanediol and two isovaleric acids, a diester formed from 1,4-pentanediol and two levulinic acids, a diester formed from 1,4-pentanediol and two non-nanoic acids, a diester formed from 1,4-pentanediol and two octanoic acids, a diester formed from 1,4-pentanediol and two decanoic acids, a diester formed from 1,4-pentanediol and octanoic acid and decanoic acid,

[0015] and mixtures thereof, and / or - the composition includes, in relation to the total mass of the composition: • at least 5% by mass, preferably at least 10% by mass, preferably at least 30% by mass, preferably at least 50% by mass, more preferably at least 70% by mass, or even at least 90% by mass, of one or more diesters; • optionally from 0.01 to 20% by mass, preferably from 0.05 to 15% by mass, more preferably from 0.1 to 10% by mass, even more preferably from 0.5 to 7% by mass, or even from 1 to 5% by mass, of one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof; and • optionally from 5 to 94% by mass, preferably from 10 to 94% by mass, preferably from 15 to 90% by mass of base oil(s) distinct from said diester, and / or - the diester has a carbon content of biological origin of at least 60% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, or even at least 95% by weight, relative to the total weight of the carbon atoms of said ester, and / or - the composition comprises at least 5% by mass, preferably at least 10% by mass, more preferably at least 30% by mass, even more preferably at least 50% by mass, or even at least 70% by mass of said diester(s), relative to the total mass of the composition.

[0016] According to one embodiment, the composition is used as a lubricating composition for transmissions in thermal engines and / or for reducers in electric motors.

[0017] According to one embodiment, the composition is used: - to improve the efficiency of transmissions, and / or - to reduce the fuel consumption of a vehicle equipped with a transmission member, in particular a gearbox and / or an axle, lubricated by means of said lubricating composition, and / or - to improve the efficiency of reducers in electric motors, and / or - to extend the battery life of an electric or hybrid vehicle.

[0018] The invention also relates to a lubricating composition as such, said lubricating composition comprising: - at least one diester formed between: • a pentanediol, preferably 1,4-pentanediol, and • two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom,

[0019] said diester having a carbon content of biological origin of at least 60% by weight, relative to the total weight of the carbon atoms of said ester,

[0020] and - optionally at least one ingredient chosen from base oils distinct from the diester, additives distinct from the diester, and mixtures thereof.

[0021] Advantageously, the lubricating composition according to the invention has one or more of the characteristics of the composition used according to the invention.

[0022] The diesters defined in the present invention can be used alone or in a composition in admixture with one or more other base oils and / or with one or more functional additives for lubricating transmissions in thermal engines and / or reducers of electric motors.

[0023] More specifically, the diesters defined in the present invention can be used to improve the “fuel eco” properties for thermal engines and to extend the battery life for electric motors.

[0024] Furthermore, the diesters defined in the present invention exhibit excellent cold properties.

[0025] The diesters defined in the present invention make it possible to reduce the coefficient of traction and the coefficient of friction.

[0026] The invention aims precisely to improve the efficiency performance of transmissions in thermal engines as well as the efficiency performance for reducers in electric motors.

[0027] The present invention thus aims to improve the “fuel eco” properties for thermal engines and to extend the battery life for electric motors.

[0028] In the rest of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated.

[0029] Unless otherwise indicated, the expression “comprising a(n)” must be understood as “comprising at least one(n)”. Detailed description

[0030] Firstly, the invention relates to the use as a lubricating composition for transmissions, of a composition comprising one or more diesters, each of said diesters being formed between a pentanediol, preferably 1,4-pentanediol, and two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom.

[0031] The invention also relates to the use, as a lubricant for transmissions, of one or more diesters, each of said diesters being formed between a pentanediol, preferably 1,4-pentanediol, and two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom.

[0032] Thus, the invention relates to a lubricating composition comprising: - at least one diester formed between: • a pentanediol, preferably 1,4-pentanediol, and • two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom,

[0033] said diester preferably having a carbon content of biological origin of at least 60% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, or even at least 95% by weight, relative to the total weight of the carbon atoms of said ester,

[0034] and - optionally at least one ingredient chosen from base oils other than diester, additives other than diester, and mixtures thereof, when present said additive preferably being chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

[0035] The lubricating composition according to the invention may comprise one or more diesters, each of said diesters being formed between: • a pentanediol, preferably 1,4-pentanediol, and • two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain containing 4 to 10 carbon atoms.

[0036] In particular, it is possible to prepare a mixture of diesters by reacting a pentanediol and a mixture of monocarboxylic acids.

[0037] For example, it is possible to react 1,4-pentanediol and three monocarboxylic acids A1, A2 and A3. Thus, according to this example, the mixture of diesters falling within the scope of the present invention is likely to comprise: - a diester formed between 1,4-pentanediol and two acids A1, - a diester formed between 1,4-pentanediol and two A2 acids, - a diester formed between 1,4-pentanediol and two A3 acids, - a diester formed between 1,4-pentanediol and an acid Al and an acid A2, - a diester formed between 1,4-pentanediol and an acid Al and an acid A3, - a diester formed between 1,4-pentanediol and an acid A2 and an acid A3. Diester implemented according to the invention

[0038] As mentioned above, the diester(s) used according to the invention is(are) formed between a pentanediol and two monocarboxylic acids.

[0039] For the purposes of the present invention, the term "diester formed between a pentanediol and two monocarboxylic acids" means a compound obtained by two esterification reactions, each esterification reaction being carried out between one of the two alcohol functions of the pentanediol and the acid function of one of the two monocarboxylic acids.

[0040] According to one embodiment, the diester comprises from 13 to 25 carbon atoms, preferably from 15 to 23 carbon atoms or even from 15 to 21 carbon atoms.

[0041] By “pentanediol” is meant a compound comprising (exactly) two hydroxyl functions (-OH) and five carbon atoms.

[0042] By “1,4-pentanediol” is meant a diol whose alcohol functions are located respectively in position 1 and in position 4 of an alkyl chain comprising 5 carbon atoms.

[0043] For the purposes of the invention, the term "hydrocarbon chain" is intended to denote a linear or branched, saturated or unsaturated alkyl or alkylene chain. The linear or branched hydrocarbon chain may optionally comprise one or more heteroatoms, in particular one or more oxygen or nitrogen atoms. Preferably, the hydrocarbon chain is a linear or branched, saturated or unsaturated alkyl or alkylene chain consisting of carbon and hydrogen atoms.

[0044] The diol used according to the invention may be commercially available or synthesized according to any method known to those skilled in the art.

[0045] According to one embodiment, the diol used in the invention is obtained by reduction of a keto acid, preferably by reduction of levulinic acid.

[0046] A “keto acid” is a compound comprising a carboxylic acid function (-COOH) and a ketone function (>C=O).

[0047] Preferably, the levulinic acid is derived from plant raw materials, such as cellulose or sugar.

[0048] Thus, preferably, the diol used in the invention is derived from plant raw materials, such as cellulose or sugar.

[0049] Preferably, the diol used according to the invention comprises a carbon content of biological origin of at least 60% by mass, preferably at least 75% by mass, more preferably at least 90% by mass, even more preferably at least 95% by mass, relative to the total mass of carbon atoms of the diol.

[0050] In the context of the present invention, the content of carbon of biological origin can be measured according to the ASTM D6866 standard.

[0051] Advantageously, the diesters according to the invention also have a high flash point, preferably a flash point of at least 120°C. The flash point can be measured according to the ASTM D93Ac standard (open cup Cleaveland method). According to certain embodiments, the flash point of the diesters can be at least 150°C or even at least 160°C. These high flash point values ​​can be obtained in particular when the diester is obtained from a monocarboxylic acid comprising a linear alkyl chain optionally substituted by a heteroatom, such as an oxygen atom.

[0052] The diester used according to the invention is obtained from two identical or different monocarboxylic acids.

[0053] By “monocarboxylic acid” is meant a compound comprising a single carboxyl function (-COOH).

[0054] The carboxylic acids used to form a diester of the invention are chosen from monocarboxylic acids, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, more preferably from 5 to 8 carbon atoms. Preferably, the linear or branched hydrocarbon chain of the monocarboxylic acids is saturated.

[0055] According to one embodiment, the monocarboxylic acids, identical or different, comprise a linear hydrocarbon chain comprising from 5 to 10 carbon atoms, more preferably from 5 to 9 carbon atoms or even from 5 to 8 carbon atoms.

[0056] According to one embodiment, the monocarboxylic acids, identical or different, comprise a linear and saturated alkyl chain comprising from 5 to 10 carbon atoms, more preferably from 5 to 9 carbon atoms or even from 5 to 8 carbon atoms.

[0057] The monocarboxylic acids used according to the invention may be commercially available or synthesized according to any method known to those skilled in the art.

[0058] Preferably, the monocarboxylic acids used according to the invention comprise a carbon content of biological origin of at least 60% by mass, preferably at least 75% by mass, more preferably at least 90% by mass, even more preferably at least 95% by mass, relative to the total mass of carbon atoms of the monocarboxylic acids.

[0059] In the context of the present invention, the content of carbon of biological origin can be measured according to the ASTM D6866 standard.

[0060] Preferably, the diester used according to the invention is saturated.

[0061] For the purposes of the invention, the term “saturated diester” means a diester comprising saturated hydrocarbon chains. Thus, preferably, the monocarboxylic acids used according to the invention each comprise a saturated hydrocarbon chain, preferably, said hydrocarbon chain is made up of carbon and hydrogen atoms.

[0062] According to a particularly preferred embodiment, the diester used in the invention is a branched diester. It should be noted that in the case where the pentanediol is 1,4-pentanediol, the diester thus obtained will be a branched diester.

[0063] For the purposes of the invention, the term “branched diester” means a diester comprising a branched hydrocarbon chain which may be located between the two ester functions and / or at one or both ends of the diester.

[0064] According to a preferred embodiment, the diester used in the invention is saturated and branched.

[0065] According to one embodiment, the diester used according to the invention has a kinematic viscosity, measured at 100°C according to the ASTM D445 standard, ranging from 1 to 6 mm2 / s, preferably from 1 to 4 mm2 / s.

[0066] According to one embodiment, the diester used according to the invention has a kinematic viscosity, measured at 40°C according to the ASTM D445 standard, ranging from 2 to 20 mm2 / s, preferably from 3 to 18 mm2 / s.

[0067] It is understood that the definitions given above for carboxylic acid and alcohol may be combined, where possible, to define other particular embodiments.

[0068] A diester used according to the invention may more particularly correspond to formula (I):

[0069] [Chem.l]

[0070] in which: - R1 represents a hydrocarbon chain, linear or branched, saturated or unsaturated, preferably saturated, having from 3 to 9 carbon atoms, preferably from 4 to 8 carbon atoms, preferably from 5 to 7 carbon atoms, said hydrocarbon chain being optionally interrupted by one or more heteroatoms, such as oxygen atoms, preferably the hydrocarbon chain is made up of carbon and hydrogen atoms; and - R2 represents a hydrocarbon chain, linear or branched, saturated or unsaturated, preferably saturated, having from 3 to 9 carbon atoms, preferably from 4 to 8 carbon atoms, preferably from 5 to 7 carbon atoms, said hydrocarbon chain being optionally interrupted by one or more heteroatoms, such as oxygen atoms, preferably the hydrocarbon chain is made up of carbon and hydrogen atoms.

[0071] In the diester of formula (I), R1 and R2 may be the same or different.

[0072] According to one embodiment, R1 and R2 are chosen from alkyls comprising from 3 with 9 carbon atoms, linear or branched, optionally comprising a ketone functional group (of type >=O). An example of a monocarboxylic acid which can result in a diester of formula (I) in which R1 and / or R2 comprise(s) a carboxyl functional group is levulinic acid.

[0073] According to one embodiment, the diester(s) used according to the invention is (are) chosen from: - a diester formed from 1,4-pentanediol and two heptanoic acids, - a diester formed from 1,4-pentanediol and two pentanoic acids, - a diester formed from 1,4-pentanediol and two isovaleric acids, - a diester formed from 1,4-pentanediol and two levulinic acids, - a diester formed from 1,4-pentanediol and two nonanoic acids, - a diester formed from 1,4-pentanediol and two octanoic acids, - a diester formed from 1,4-pentanediol and two decanoic acids, - a diester formed from 1,4-pentanediol and a mixture of acids comprising an octanoic acid and a decanoic acid,

[0074] and mixtures thereof.

[0075] It is understood that, within the framework of the present invention, a diester according to the invention may be in the form of a mixture of at least two diesters according to the invention, in particular as defined above.

[0076] Preferably, the diester used according to the invention comprises a carbon content of biological origin of at least 60% by mass, preferably at least 75% by mass, more preferably at least 90% by mass, even more preferably at least 95% by mass, relative to the total mass of carbon atoms of the diester.

[0077] In the context of the present invention, the content of carbon of biological origin can be measured according to the ASTM D6866 standard.

[0078] By way of example, the diesters according to the invention may be formed from a pentanediol, preferably 1,4-pentanediol and a biosourced cut comprising several monocarboxylic acids comprising from 4 to 10 carbon atoms, for example a biosourced cut comprising monocarboxylic acids comprising an alkyl chain having from 8 to 10 carbon atoms. According to this example, a mixture of diesters according to the invention is obtained and used in the composition of the invention.

[0079] The diester or the mixture of diesters according to the invention may represent at least 5% by mass of the composition according to the invention, preferably at least 10% by mass, preferably at least 30% by mass, more preferably at least 50% by mass, even more preferably at least 70% by mass, in particular at least 80% by mass, more particularly at least 90% by mass, or even at least 95% by mass, or even 100% by mass, of the total mass of the composition according to the invention.

[0080] The diester(s) according to the invention may be used with one or more additional base oils (also called co-bases). According to this embodiment, preferably, the composition will comprise: - from 5 to 95% by mass, preferably from 5 to 50% by mass, more preferably 10 to 40% by mass, of the diester(s) according to the invention, and - from 5 to 95% by mass, preferably from 50 to 95% by mass, preferably from 60 to 90% by mass, of one or more base oils different from the diesters according to the invention,

[0081] relative to the total mass of the diester(s) and the base oils other than the diesters.

[0082] According to one embodiment, a lubricating composition according to the invention may comprise at least 30% by mass of a diester or mixture of diesters according to the invention, more particularly between 50% and 99.5% by mass, preferably between 70% and 99% by mass, more preferably between 80% and 99% by mass, or even between 80% and 95% by mass, relative to the total mass of said composition.

[0083] According to a particular embodiment, a lubricating composition according to the invention may be formed at more than 95% by mass, in particular at more than 98% by mass, of one or more diesters according to the invention. Annex base oil(s) (co-base(s))

[0084] The lubricating composition according to the invention may comprise, in addition to one or more diesters according to the invention, one or more base oils distinct from the diesters according to the invention, called “additional base oil”.

[0085] Said base oil(s), optionally present in the lubricating composition according to the invention, are chosen appropriately, with regard to their compatibility with said diester(s) used according to the invention.

[0086] It may be a mixture of several base oils, for example a mixture of two, three or four base oils.

[0087] Preferably, the base oil or mixture of additional base oils, used in the lubricating composition according to the invention, may have a kinematic viscosity, measured at 100°C according to the ASTM D445 standard, ranging from 1.5 to 8 mm2 / s, in particular from 1.5 to 6.1 mm2 / s, more particularly from 1.5 to 4.1 mm2 / s, even more particularly from 1.5 to 2.1 mm2 / s.

[0088] The base oils can be chosen from oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) and presented in table 1 below or their mixtures.

[0089] [Tables 1] Saturates content Sulphur content Viscosity index (VI) Group I (Mineral oils) <90% > 0.03% 80 <VI < 120 Groupement II (Huiles hydrocraquées) >90% <0.03% 80 <VI < 120 Groupement III (Huiles hydrocraquées ou hydro-isomérisées) >90% <0.03% >120 Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in groups I to IV

[0090] Mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, de-alphatting, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

[0091] Mixtures of synthetic and mineral oils, which can be bio-sourced, can also be used.

[0092] The base oils may also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, distinct from the ester defined according to the invention, from polyalphaolefins (PAO), and from polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbon atoms.

[0093] The PAOs used as base oils are for example obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene.

[0094] The mass average molecular mass of PAO can vary quite widely. Preferably, the mass average molecular mass of PAO is less than 600 Da. The mass average molecular mass of PAO can also range from 100 to 600 Da, from 150 to 600 Da, or from 200 to 600 Da.

[0095] For example, the PAOs used in the context of the invention, having a kinematic viscosity, measured at 100°C according to the ASTM D445 standard, ranging from 1.5 to 8 mm2 / s are sold commercially by Ineos under the brands Durasyn® 162, Durasyn® 164, Durasyn® 166 and Durasyn® 168.

[0096] Advantageously, the additional base oil or oils are chosen from polyalphaolefins (PAO).

[0097] It is up to the person skilled in the art to adjust the content of additional base oil(s) present in the composition according to the invention.

[0098] In particular, a composition according to the invention may comprise from 5 to 95% by mass, preferably from 50 to 95% by mass, more preferably from 60 to 90% by mass, of one or more base oils different from the diesters according to the invention, relative to the total mass of said composition. Additives

[0099] A lubricating composition according to the invention may further comprise one or more additives known to those skilled in the art in the field of transmission lubrication, in particular for thermal engines and for propulsion systems of electric or hybrid vehicles.

[0100] The additives that can be incorporated into a composition according to the invention can be chosen from antioxidants, pour point lowering additives, anti-foaming agents, anti-corrosion agents, anti-wear and / or extreme pressure additives, friction modifiers, detergents, dispersing agents and mixtures thereof, in particular from antioxidants, pour point lowering additives, anti-foaming agents and anti-corrosion agents.

[0101] Preferably, a lubricating composition according to the invention may comprise further one or more additives selected from antioxidants, antifoams, pour point improvers, viscosity index improvers, and anticorrosion agents.

[0102] The addition of one or more additives chosen from anti-wear additives, friction modifiers, detergents, extreme pressure additives and dispersants, may also prove advantageous in the context of the implementation of the lubricating composition according to the invention as a multifunctional fluid, for example for cooling the battery and / or the power electronics, and for lubricating parts of the propulsion system, for example the transmission, in an electric or hybrid vehicle.

[0103] It is understood that the nature and quantity of additives used are chosen so as not to affect the properties of the lubricating composition conferred by the diester according to the invention.

[0104] These additives can be introduced in isolation and / or in the form of a mixture like those already available for sale for formulations of commercial lubricants for vehicle engines, with performance levels as defined by the ACEA (Association of European Automobile Manufacturers) and / or the API (American Petroleum Institute), well known to those skilled in the art.

[0105] Said additive(s) may be present in the lubricating composition according to the invention in a content of less than or equal to 20% by mass, in particular ranging from 0.01 to 20% by mass, preferably from 0.1 to 15% by mass, more preferably from 0.5 to 10% by mass, relative to the total mass of said composition.

[0106] A lubricating composition used according to the invention can thus comprise at least one antioxidant additive.

[0107] The invention thus relates, according to another of its aspects, to a lubricating composition, in particular capable of lubricating a transmission, in particular of a thermal engine or of a propulsion system of an electric or hybrid vehicle, said composition comprising (i) at least one diester according to the invention, and (ii) at least one antioxidant additive.

[0108] The antioxidant additive generally makes it possible to delay the degradation of the 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 composition.

[0109] Antioxidant additives act in particular as radical inhibitors or hydroperoxide destroyers. Among the commonly used antioxidant additives, mention may be made of phenolic type antioxidant additives, amine type antioxidant additives, phosphosulfur antioxidant additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, may be generators of ash. 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.

[0110] 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 Cr-Cio alkyl group, preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group.

[0111] 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 NR4R5R6 in which R4 represents an aliphatic group or an aromatic group, optionally substituted, R5 represents an aromatic group, optionally substituted, R6 represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R7S(O)ZR8 in which R7 represents an alkylene group or an alkenylene group, R8 represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

[0112] Sulphurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0113] Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

[0114] Advantageously, a lubricating composition comprises at least one ash-free antioxidant additive.

[0115] Said additive(s) may be used, in a lubricating composition according to the invention, at a rate of 0.1 to 2% by mass, relative to the total mass of the composition.

[0116] A lubricating composition according to the invention may comprise at least one anti-wear and / or extreme pressure additive.

[0117] Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces.

[0118] There are a wide variety of anti-wear additives. Preferably, the additives anti-wear are chosen from phosphosulfur 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)(OQ2)(OQ3))2, in which Q2 and Q3, identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

[0119] Amine phosphates are also anti-wear additives that can be used in a 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.

[0120] A lubricating composition 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 of anti-wear additives and extreme pressure additives, by mass relative to the total mass of composition.

[0121] A lubricating composition according to the invention may further comprise an antifoaming agent.

[0122] The antifoaming agent may be chosen from silicones.

[0123] A lubricating composition may comprise from 0.01 to 2% by mass or from 0.01 to 5% by mass, preferably from 0.1 to 1.5% by mass or from 0.1 to 2% by mass of antifoaming agent, relative to the total mass of the composition.

[0124] A lubricating composition according to the invention may comprise at least one friction modifying additive.

[0125] The friction modifying additive may be chosen from a compound providing metallic elements and an ash-free compound. 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 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.

[0126] A lubricating composition may comprise from 0.01 to 2% by mass or from 0.01 to 5% by mass, preferably from 0.1 to 1.5% by mass or from 0.1 to 2% by mass of friction modifying additive, relative to the total mass of the composition.

[0127] A lubricating composition according to the invention may comprise at least one additive making it possible to improve the viscosity index of the lubricating composition (in English “viscosity index improver”).

[0128] By "additive for improving the viscosity index" is meant, within the meaning of the invention, a chemical compound for guaranteeing good cold resistance and minimal viscosity at high temperature of the lubricating composition.

[0129] Examples of viscosity index improving polymers include polymeric esters; hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene; homopolymers or copolymers of olefins, such as ethylene or propylene; polyacrylates and polymethacrylates (PMA).

[0130] The lubricating composition according to the invention typically comprises from 0.1% to 15% by mass of additive(s) improving the viscosity index, relative to the total mass of the lubricating composition.

[0131] A lubricating composition according to the invention may comprise at least one detergent additive.

[0132] 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.

[0133] The detergent additives usable in a lubricating composition are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a lipophilic hydrocarbon group and a hydrophilic head. The associated cation may be a metal cation of an alkali or alkaline-earth metal.

[0134] 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.

[0135] These metal salts generally comprise the metal in a stoichiometric quantity or in excess, therefore 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 a metal salt insoluble in oil, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

[0136] A lubricating composition used according to the invention may, for example, comprise from 2 to 4% by mass of detergent additive, relative to the total mass of the composition.

[0137] A lubricating composition used according to the invention can also include at least one pour point depressant additive.

[0138] By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the composition. Examples of pour point depressant additives include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

[0139] A lubricating composition used according to the invention may, for example, comprise from 0.05 to 2% by mass of pour point lowering additive, relative to the total mass of the composition.

[0140] Also, a lubricating composition implemented according to the invention may comprise at least one dispersing agent.

[0141] The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives. A lubricating composition used according to the invention may, for example, comprise from 0.2 to 10% by mass of dispersing agent, relative to the total mass of the composition.

[0142] According to a particular embodiment, a lubricating composition used according to the invention comprises, or is formed from (i) the diester according to the invention and (ii) at least one additive chosen from antioxidants, antifoaming agents, pour point depressant additives, anticorrosion agents, antiwear and / or extreme pressure additives, friction modifiers, detergents, dispersing agents and mixtures thereof, preferably from antioxidants, pour point depressant additives, antifoaming agents, anticorrosion agents, and mixtures thereof.

[0143] Advantageously, a lubricating composition used according to the invention comprises (i) the diester according to the invention and (ii) at least one antioxidant additive.

[0144] According to a particular embodiment, a lubricating composition implemented according to the invention comprises, or even consists of: - at least 5% by mass, preferably at least 10% by mass, preferably at least 30% by mass, preferably at least 50% by mass, more preferably at least 70% by mass, or even at least 90% by mass, of diester(s) corresponding to formula (I); - optionally from 0.01 to 20% by mass, preferably from 0.05 to 15% by mass, more preferably from 0.1 to 10% by mass, even more preferably from 0.5 to 7% by mass, or even from 1 to 5% by mass, of one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof; And - optionally from 5 to 94% by mass, preferably from 10 to 94% by mass, preferably from 15 to 90% by mass of base oil(s) distinct from the diester according to the invention,

[0145] the contents being expressed relative to the total mass of said composition.

[0146] According to a particular embodiment, a lubricating composition implemented according to the invention comprises, or even consists of: - from 5 to 95% by mass, preferably from 5 to 50% by mass, more preferably 10 to 40% by mass, of said diester(s) corresponding to formula (i); - from 5 to 95% by mass, preferably from 50 to 95% by mass, preferably from 60 to 90% by mass, of one or more base oils different from said diesters; - optionally from 0.01 to 20% by mass, preferably from 0.05 to 15% by mass, more preferably from 0.1 to 10% by mass, even more preferably from 0.5 to 7% by mass, or even from 1 to 5% by mass, of one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof,

[0147] the contents being expressed relative to the total mass of said composition.

[0148] According to a particular embodiment, a lubricating composition used according to the invention comprises, or even consists of: - from 5 to 95% by mass, preferably from 10 to 90% by mass, more preferably from 20 to 80% by mass, even more preferably from 30 to 70% by mass, or even from 40 to 60% by mass, of diester(s) corresponding to formula (i); - optionally from 5 to 95% by mass, preferably from 10 to 90% by mass, more preferably from 20 to 80% by mass, even more preferably from 30 to 70% by mass, or even from 40 to 60% by mass of one or more base oils different from said diesters; - optionally from 0.01 to 20% by mass, preferably from 0.05 to 15% by mass, more preferably from 0.1 to 10% by mass, even more preferably from 0.5 to 7% by mass, or even from 1 to 5% by mass of one or more additives distinct from the diester and distinct from the base oil(s), among friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, index improvers viscosity (VI), pour point depressants (PPD), dispersants, antifoaming agents, thickeners, corrosion inhibitors, copper passivators, and mixtures thereof,

[0149] the contents being expressed relative to the total mass of said composition.

[0150] A lubricating composition used according to the invention advantageously has a kinematic viscosity, measured at 100°C according to standard ASTM D445, ranging from 1 to 6 mm2 / s, preferably from 1 to 4 mm2 / s.

[0151] A lubricating composition used according to the invention advantageously has a kinematic viscosity, measured at 40°C according to standard ASTM D445, ranging from 2 to 20 mm2 / s, preferably from 3 to 18 mm2 / s. Preparation process

[0152] The diesters according to the invention can be prepared according to synthesis methods known to those skilled in the art. These synthesis methods more particularly implement two esterification reactions, each esterification reaction being implemented between an alcohol function of the diol and the acid function of the monocarboxylic acid.

[0153] Of course, it is up to the person skilled in the art to adjust the synthesis conditions to obtain a diester according to the invention.

[0154] The invention also relates to a process for preparing the lubricating composition according to the invention, said process comprising:

[0155] a) a step of esterification of each hydroxyl function of the pentanediol using one or more monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom, in order to obtain one or more diesters,

[0156] b) optionally mixing the diester(s) from step a) with at least one base oil distinct from the diester and / or at least one additive distinct from the diester, said additive being chosen from friction modifying additives, antiwear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, antifoaming agents, thickeners, corrosion inhibitors, copper passivating agents, and mixtures thereof.

[0157] According to one embodiment, the preparation method further comprises a preliminary step of preparing pentanediol, said preliminary step preferably being a step of reducing a keto-acid, preferably levulinic acid, said keto-acid preferably being derived from plant raw materials.

[0158] Thus, pentanediol, monocarboxylic acids, base oils and additives used in the preparation process according to the invention can each presenting one or more of the characteristics defined within the framework of the composition according to the invention. Application

[0159] As indicated previously, the lubricating composition according to the invention can be used as a lubricating fluid for transmission.

[0160] In particular, the lubricating composition defined in the present invention makes it possible to improve the efficiency of transmissions.

[0161] The diester defined in the invention makes it possible to improve the efficiency of transmissions when it is incorporated into a lubricating composition used to lubricate transmissions.

[0162] The diester defined in the invention also makes it possible to improve the fuel economy properties, so-called “Fuel-Eco” properties of the lubricating composition comprising said diester defined in the invention. Indeed, the diester defined in the invention makes it possible to reduce the traction coefficient of the lubricating composition comprising said diester.

[0163] The transmissions may be transmissions for thermal vehicle engines and / or transmissions for electric or hybrid vehicle propulsion systems.

[0164] The transmission of a propulsion system of an electric or hybrid vehicle more specifically comprises a speed reducer. Thus, the diester according to the invention makes it possible in particular to improve the efficiency of the reducers in the propulsion systems of electric or hybrid vehicles.

[0165] As shown schematically in [Fig.l], the propulsion system of an electric or hybrid vehicle comprises in particular the electric motor part (1), an electric battery (2) and a transmission, and in particular a speed reducer (3).

[0166] The electric motor typically comprises power electronics (11) connected to a stator (13) and a rotor (14). The stator comprises coils, in particular copper coils, which are alternately supplied with an electric current. This makes it possible to generate a rotating magnetic field. The rotor itself comprises coils, permanent magnets or other magnetic materials, and is rotated by the rotating magnetic field.

[0167] The power electronics (11), the stator (13) and the rotor (14) of a propulsion system (1) are parts whose structure is complex and generates a large quantity of heat during operation of the engine.

[0168] A bearing (12) is generally integrated between the stator (13) and the rotor (14). A transmission, and in particular a speed reducer (3), makes it possible to reduce the rotation speed at the output of the electric motor and to adapt the speed transmitted to the wheels, allowing at the same time to control the speed of the vehicle.

[0169] Advantageously, a lubricating composition defined in the present invention can be used to improve the efficiency of transmissions, in particular for thermal vehicle engines and for the propulsion system of an electric or hybrid vehicle. In particular, a lubricating composition defined in the present invention can be used to improve the efficiency of the reducers of the propulsion system of an electric or hybrid vehicle.

[0170] The invention also relates, according to another of its aspects, to a method for lubricating at least one mechanical part of a transmission member of motor vehicles, in particular light or heavy vehicles, for example gearbox, axles, preferably manual gearbox and heavy goods vehicle axles, or even reducer of electric or hybrid vehicles, said method comprising at least one step in which said mechanical part is brought into contact with at least one lubricating composition according to the invention.

[0171] The invention also relates to the use of the diester according to the invention, as defined above, for reducing the traction coefficient of a lubricating composition for transmission in a motor vehicle, in particular a gearbox lubricant and / or an axle lubricant, in particular heavy goods vehicle axles, or even reducers for electric or hybrid vehicles.

[0172] Also, as mentioned previously, a lubricating composition according to the invention has excellent properties in terms of reducing fuel consumption (“Fuel Eco” properties).

[0173] Advantageously, a lubricating composition according to the invention thus has low traction coefficients.

[0174] The invention will now be described by means of the following examples, given of course by way of illustration and not limitation of the invention. Examples Example 1: Preparation of the tested compounds

[0175] The following compounds were prepared: - Diester A: diester formed from 1,4-pentanediol and two hep-tanoic acids, - Diester B: diester formed from 1,4-pentanediol and two isovaleric acids, - Diester C: diester formed from 1,4-pentanediol and two levulinic acids, - Diester D: diester formed from 1,4-pentanediol and a biosourced cut of C8-C10 acids (octanoic acids and decanoic acids), - monoester comprising 20 carbon atoms, formed from a monocarboxylic acid comprising a saturated hydrocarbon chain of 3 to 14 carbon atoms; and a monoalcohol comprising a saturated hydrocarbon chain of 3 to 14 carbon atoms.

[0176] The diesters and the monoester were prepared according to known methods for preparing esters.

[0177] The compositions tested in the following examples comprise 100% of each ester (diester or monoester) defined in this example 1. Example 2: Viscosity measurement

[0178] The kinematic viscosity at 100°C (KV100) and the kinematic viscosity at 40°C (KV40) were determined according to ASTM D445.

[0179] The viscosities are presented in Table 2.

[0180] [Tables2] KV100 (mm2 / s) KV40 (mm2 / s) Diester A 1.96 5.81 Diester B 1.50 4.32 Diester C 3.43 16.95 Diester D 2.55 8.24 Monoester 1.8 5.2

[0181] The diesters used according to the invention have a viscosity of less than 4 mm2 / s at 100°C.

[0182] The diesters according to the invention also have good cold properties. Indeed, diester A according to the invention has a Brookfield viscosity at -40°C of 3010 mPa.s. The Brookfield viscosity was measured according to ASTM D 2983, 2022. Example 3: Measurement of friction coefficients

[0183] Tribological properties can be evaluated by a test on a rotating ball-disc tribometer (also called ball-plate) of the Linear Reciprocating Tribometer type. This test makes it possible in particular to evaluate the performance of lubricants in terms of friction in mixed / limit regime according to the load, pressure or speed conditions applied.

[0184] The coefficient of friction of the lubricating compositions tested is determined at 140°C by using a hardened steel ball of approximately 2 cm in diameter, for example 1.905 cm in diameter, on a hardened steel plane.

[0185] The tribometer may be a device for setting a steel ball and a steel plane into relative motion in order to determine the friction coefficients for a given lubricating composition, while varying various properties. such as speed, load, and temperature. The hardened steel plane is AISI 52100 with a mirror finish and the ball is also AISI 52100 made of hardened steel.

[0186] The applied load is 25 N respectively and the drive speed varies from 10 mm / s to 2500 mm / s. The coefficient of friction is in particular determined at a rotation speed of 10 mm / s. The coefficient is determined at a sliding speed / drive speed ratio ("Slide-to-Roll Ratio" or %SRR) of 20% to 100%.

[0187] Approximately 50 ml of the tested lubricating composition was introduced into the device. The ball is engaged face against plane, said ball and said plane being actuated independently so as to create a mixed rolling / sliding contact.

[0188] The coefficient of friction is measured and recorded via a force sensor.

[0189] The results with a drive speed of 225 mm2 / s are shown in Table 3.

[0190] The lubricating compositions tested comprise 100% ester as defined in Example 1.

[0191] [Tables3] 20% 40% 60% 80% 100% Diester A 0.0414 0.0634 0.0612 0.0548 0.548 Diester C 0.0472 0.0482 0.0482 0.0487 0.0488 Diester D 0.0591 0.0669 0.0662 0.0658 0.0666 Monoester 0.0681 0.0702 0.0699 0.0693 0.705

[0192] These results show that the diesters used according to the invention have very low coefficients of friction, in particular a coefficient of friction lower than the monoester.

[0193] The diesters according to the invention thus have excellent lubricating properties, thus making it possible in particular to reduce fuel consumption or to extend the battery life. Example 4: Measuring the mini pour point

[0194] The mini pour point is measured according to ASTM D7346.

[0195] The values ​​are shown in Table 4.

[0196] [Tables4] Mini pour point (°C) Diester A -95 Diester B -81 Diester C -45 Monoester -34

[0197] The results in Table 5 show that the diesters used in the lubricating composition according to the invention have a low pour point, in particular lower than the monoester.

[0198] The diesters according to the invention thus have excellent cold properties. Example 5: Measurements of traction coefficients

[0199] The coefficient of traction (COT) was measured using the PCS instrument MTM tribometer. It allows the performance of lubricants to be evaluated in terms of friction in mixed / hydrodynamic conditions. This test consists of putting a steel ball and a steel plane into relative motion, at different speeds, making it possible to define the %SSR (Slide-to-Roll Ratio) which corresponds to the sliding speed / drive speed. This test aims to reproduce limit lubrication conditions.

[0200] The measurement conditions were 25 N load, a disc speed of 1.4 m / s for an evaluated temperature of 140 °C and an SRR of 60%, 80% and 100%.

[0201] The lower the traction coefficient for a lubricating composition, the more the friction between the metal parts is reduced, thus resulting in a greater gain in terms of fuel economy.

[0202] The results obtained are shown in Table 5.

[0203] [Tables5] 60%SRR 80%SRR 100%SRR Diester A 0.0136 0.0144 0.0153 Diester C 0.0107 0.0124 0.014 Monoester 0.016 0.0182 0.0198

[0204] These results show that the diesters defined in the invention have a good traction coefficient and in particular a better traction coefficient than the monoester. Example 6

[0205] The mini flash point is measured according to ASTM D93Ac (method of Cleaveland open vessel).

[0206] The values ​​are shown in Table 6.

[0207] [Tableauxô] Mini flash point (°C) Diester A 169.3 Diester C 207.5 Diester D 206

[0208] The diesters according to the invention have a very good flash point.

Claims

Claims

1. Use of a composition comprising at least one diester as a lubricating composition for improving transmission performance, said diester being formed between: • a pentanediol, and • two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom, said composition optionally further comprising at least one base oil distinct from the diester and / or at least one additive distinct from the diester, said additive being chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners,corrosion inhibitors, copper passivating agents, and mixtures thereof.,

2. Use according to claim 1, wherein the pentanediol is 1,4-pentanediol.

3. Use according to claim 1 or 2, wherein the pentanediol is derived from the reduction of a keto acid, preferably levulinic acid, said keto acid preferably being derived from plant raw materials.

4. Use according to any one of claims 1 to 3, wherein said diester has a kinematic viscosity at 100°C ranging from 1 to 6 mm2 / s, preferably ranging from 1 to 4 mm2 / s.

5. Use according to any one of claims 1 to 4, in which said monocarboxylic acids, identical or different, comprise a linear alkyl chain comprising from 4 to 10 carbon atoms, preferably from 5 to 9 carbon atoms, or even from 5 to 8 carbon atoms, said alkyl chain optionally comprising one or more heteroatoms, for example one or more oxygen atoms.

6. Use according to any one of claims 1 to 5, in

7. in which said diester(s) is(are) chosen from: - a diester formed from 1,4-pentanediol and two heptanoic acids, - a diester formed from 1,4-pentanediol and two pentanoic acids, - a diester formed from 1,4-pentanediol and two isovaleric acids, - a diester formed from 1,4-pentanediol and two levulinic acids, - a diester formed from 1,4-pentanediol and two nonanoic acids, - a diester formed from 1,4-pentanediol and two octanoic acids, - a diester formed from 1,4-pentanediol and two decanoic acids, - a diester formed from 1,4-pentanediol and an octanoic acid and a decanoic acid, and their mixtures. Use according to any one of claims 1 to 6, wherein the composition comprises: - at least 5% by mass, preferably at least 10% by mass, preferably at least 30% by mass, preferably at least 50% by mass, more preferably at least 70% by mass, or even at least 90% by mass, of one or more diesters; - optionally from 0.01 to 20% by mass, preferably from 0.05 to 15% by mass, more preferably from 0.1 to 10% by mass, even more preferably from 0.5 to 7% by mass, or even from 1 to 5% by mass, of one or more additives chosen from friction modifying additives, anti-wear additives, extreme pressure additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersants, anti-foaming agents, thickeners, inhibitors of corrosion, copper passivating agents, and mixtures thereof; and - optionally from 5 to 94% by mass, preferably from 10 to 94% by mass, preferably from 15 to 90% by mass of base oil(s) distinct from said diester, relative to the total mass of the composition.

8. Use according to any one of claims 1 to 7, in which the diester has a carbon content of biological origin of at least 60% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, or even at least 95% by weight, relative to the total weight of the carbon atoms of said ester.

9. Use according to any one of claims 1 to 6 or 8, in which the composition comprises at least 5% by mass, preferably at least 10% by mass, more preferably at least 30% by mass, even more preferably at least 50% by mass, or even at least 70% by mass of said diester(s), relative to the total mass of the composition.

10. Use according to any one of claims 1 to 9, for transmissions in thermal engines and / or for reducers in electric motors.

11. Use according to any one of claims 1 to 10, for reducing the fuel consumption of a vehicle equipped with a transmission member, in particular a gearbox and / or an axle, lubricated by means of said lubricating composition.

12. Use according to any one of claims 1 to 10, for improving the efficiency of reducers in electric motors.

13. Use according to any one of claims 1 to 10 or 12, for extending the battery life of an electric or hybrid vehicle.

14. Lubricating composition comprising: - at least one diester formed between: • a pentanediol, preferably 1,4-pentanediol, and • two monocarboxylic acids, identical or different, comprising a linear or branched hydrocarbon chain comprising from 4 to 10 carbon atoms, said hydrocarbon chain optionally comprising one or more heteroatoms, such as a nitrogen or oxygen atom, said diester having a carbon content of biological origin of at least 60% by weight, relative to the total weight of the carbon atoms of said ester, And - optionally at least one ingredient chosen from base oils distinct from the diester, additives distinct from the diester, and mixtures thereof.

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