Use of an ester in a cooling composition

Abstract

Use of an ester in a cooling composition The present invention relates to the use, for cooling a propulsion system of an electric or hybrid vehicle, of a composition comprising at least one ester having a kinematic viscosity, measured at -25°C, less than or equal to 200 mm2 / s and an auto-ignition point greater than or equal to 350°C.It also relates to a composition capable of cooling a propulsion system, in particular the battery and / or the power electronics of an electric or hybrid vehicle, said composition comprising (i) at least one ester having a kinematic viscosity, measured at -25°C, less than or equal to 200 mm2 / s and an auto-ignition point greater than or equal to 350°C and (ii) at least one additive chosen from antioxidants, friction modifiers, detergents, anti-wear additives, extreme pressure additives, dispersants, pour point improvers, anti-foams and mixtures thereof. Figure for abstract: None.

Description

Title of the invention: Use of an ester in a cooling composition Technical field

[0001] The present invention relates to the field of compositions for cooling a propulsion system of an electric or hybrid vehicle, and more particularly for cooling the battery and / or the power electronics of an electric or hybrid vehicle. It aims in particular to propose a cooling composition compatible with its implementation at the level of a battery and / or the power electronics, and having improved stability at high temperatures, in particular at the temperatures reached in the event of thermal runaway. Prior art

[0002] 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.

[0003] 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.

[0004] 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.

[0005] For the purposes of the present invention, the term "propulsion system" is understood to mean 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 and a battery. The battery itself is generally made up of a set of electrical accumulators, called cells.

[0006] Generally speaking, it is necessary to implement, in electric or hybrid vehicles, compositions to meet the lubrication and / or cooling constraints of the various parts of the propulsion system mentioned above.

[0007] In particular, electric propulsion systems generate heat during operation via the electric motor, power electronics and batteries. The amount of heat generated being greater than the amount of heat nor poorly dissipated to the environment, it is necessary to ensure cooling of the engine, power electronics and batteries. Generally, cooling is carried out on several parts of the propulsion system generating heat and / or parts of said system sensitive to heat, in order to avoid reaching dangerous temperatures, and in particular the power electronics and batteries.

[0008] Traditionally, it is known to cool electric motors with air or water, possibly combined with glycol. However, with the advent of increasingly smaller and more powerful motors, these cooling methods are no longer sufficient. In addition, the heat that a battery can generate, particularly during rapid charging, cannot be extracted by conventional methods.

[0009] Thus, alternative methods of cooling propulsion systems, in particular batteries, have recently been proposed.

[0010] In this respect, lubricating compositions have been proposed to ensure the dual function of lubrication and cooling. The lubricating compositions are conventionally composed of one or more base oils, to which are generally associated several additives dedicated to stimulating the lubricating performance of the base oils, such as for example friction modifying additives. By way of example, document WO 2018 / 078290 proposes to use, for cooling and / or lubricating a motorization system of an electric vehicle, a composition comprising at least one polyalkylene glycol obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms.

[0011] Despite the implementation of a cooling system, the risk of the battery overheating cannot be completely ruled out, for example in the case of a defective cell, or during an accident during which a cell may be pierced. This can even lead to an explosion and a global fire of the battery, called the "runaway effect". Such overheating is particularly feared in the context of the operation of a Li-ion battery. Safety tests (UN RE100 standard) must therefore be carried out on the batteries before they are marketed.

[0012] Consequently, it is desirable that the properties of the cooling fluid used in the propulsion systems of electric or hybrid vehicles, and in particular in the batteries and / or power electronics, are preserved, even for the high temperatures likely to be reached in the event of overheating of the battery.

[0013] The invention aims precisely to propose a new composition, suitable for its implementation for the cooling of propulsion systems of electric or hybrid vehicles, in particular for the cooling of batteries and / or electronics. of power, while remaining stable at high temperatures, which can be reached when the system overheats, in particular up to a temperature of 350 °C, or even 400°C.

[0014] The present invention thus relates to the use, for cooling a propulsion system, in particular the battery and / or the power electronics, of an electric or hybrid vehicle, of a composition comprising at least one ester having a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 200 mm2 / s and an auto-ignition point, measured according to the ASTM E659 standard, greater than or equal to 350°C.

[0015] An “ester” means a compound comprising at least one ester function. It may in particular be a monoester, diester or triester.

[0016] In the remainder of the text, and unless otherwise indicated, the term "ester according to the invention" will be used to designate an ester satisfying the aforementioned criteria in terms of kinematic viscosity and auto-ignition point.

[0017] The auto-ignition point, called “AIT”, also called auto-ignition point, represents the temperature from which combustion starts itself, without the addition of flames.

[0018] Also, we will speak of “cooling composition” or “cooling composition”, in the remainder of the text, to designate a composition implemented according to the invention, comprising at least one ester according to the invention, as defined above.

[0019] Advantageously, an ester according to the invention has a kinematic viscosity, measured at 25°C according to the ASTM D445 standard, less than or equal to 20 mm2 / s, preferably less than or equal to 15 mm2 / s, in particular less than or equal to 10 mm2 / s.

[0020] Furthermore, an ester according to the invention advantageously has a particularly high auto-ignition point, preferably greater than or equal to 360°C, more preferably greater than or equal to 380°C, in particular greater than or equal to 400°C.

[0021] A composition according to the invention may be formed, in whole or in part, from one or more esters as defined above. Preferably, a cooling composition according to the invention is formed from at least 30% by mass, preferably at least 50% by mass, more preferably at least 70% by mass, even more preferably at least 80% by mass, or even at least 90% by mass, of one or more esters according to the invention, relative to the total weight of the composition.

[0022] The addition of additives, preferably one or more antioxidant agent(s), is possible, provided that their presence does not affect the properties provided by the ester. implemented according to the invention.

[0023] According to a particular embodiment, the ester used according to the invention is chosen from: - an ester, called “branched ester” in the rest of the text, formed between at least one carboxylic acid comprising at least one branched, saturated or unsaturated, preferably saturated, hydrocarbon chain and at least one alcohol comprising at least one linear or branched, saturated or unsaturated hydrocarbon chain, - an ester comprising at least one heteroatom, preferably an oxygen atom, distinct from the oxygen atoms involved in the said ester function(s) of the said ester; and - their mixtures.

[0024] Preferably, a branched ester according to the invention is formed from at least one carboxylic acid comprising at least one branched, preferably saturated, hydrocarbon chain of 3 to 14 carbon atoms.

[0025] In particular, a branched ester according to the invention can be formed from at least one alcohol comprising at least one branched hydrocarbon chain, preferably saturated, in particular with 3 to 14 carbon atoms.

[0026] An ester according to the invention, comprising at least one heteroatom distinct from the oxygen atoms engaged in said ester function(s), may be formed from at least one alcohol comprising at least one heteroatom distinct from said oxygen atom(s) of said hydroxyl function(s) and / or from at least one carboxylic acid comprising at least one heteroatom distinct from said oxygen atom(s) of said carboxyl function(s), said heteroatom(s) being chosen from oxygen and nitrogen.

[0027] In particular, an ester according to the invention, comprising at least one heteroatom distinct from the oxygen atoms engaged in said ester function(s), is formed from at least one alcohol comprising at least one ether function, preferably from at least one alcohol comprising at least one hydrocarbon chain, linear or branched, preferably linear, saturated or unsaturated, preferably saturated, in particular of 3 to 14 carbon atoms, said hydrocarbon chain being interrupted by at least one oxygen atom.

[0028] An ester according to the invention is advantageously a monoester, diester or triester. Preferably, it is a monoester or a diester, and more preferably a branched monoester as defined above or a diester comprising at least one heteroatom, preferably two heteroatoms, in particular two oxygen atoms, distinct from the oxygen atoms involved in the ester functions of the diester.

[0029] Thus, according to a particularly preferred embodiment variant, a cooling composition according to the invention comprises at least one monoester formed between a monocarboxylic acid comprising a branched, saturated or unsaturated hydrocarbon chain, preferably from 3 to 14 carbon atoms, and a monoalcohol comprising a linear or branched, saturated or unsaturated hydrocarbon chain, preferably from 1 to 14 carbon atoms.

[0030] Advantageously, a monoester according to the invention may be a monoester formed between a branched and saturated C9 monocarboxylic acid and a branched and saturated C9 monoalcohol, such as 3,5,5-trimethyl hexanoate of 3,5,5-trimethyl hexanol.

[0031] In particular, a composition according to the invention may comprise a mixture of monoesters formed between a branched and saturated C9 monocarboxylic acid, for example 3,5,5-trimethylhexanoic acid, and a mixture of branched and saturated C8-Ci0 monoalcohols, preferably a mixture of isomers of branched and saturated C9 monoalcohols.

[0032] According to another variant of the invention, a cooling composition according to the invention comprises at least one diester formed between a dicarboxylic acid comprising a linear, saturated or unsaturated hydrocarbon chain, preferably from 3 to 14 carbon atoms, and a monoalcohol comprising a linear or branched, saturated or unsaturated hydrocarbon chain, preferably from 2 to 14 carbon atoms, interrupted by at least one heteroatom, preferably by an oxygen atom.

[0033] Advantageously, a diester according to the invention can be formed between a linear and saturated C4-C10 dicarboxylic acid and a monoalcohol comprising a linear and saturated C4-C10 hydrocarbon chain interrupted by an oxygen atom. It can be, for example, dibutyl glycol adipate.

[0034] As is apparent from the examples which follow, the inventors have found that the esters according to the invention make it possible to advantageously combine good viscosity properties, suitable for their use for cooling a battery and / or power electronics, and a particularly high auto-ignition point, which thus ensures stability of the cooling composition, in particular resistance to ignition, in the event of overheating of the battery.

[0035] Thus, advantageously, the esters according to the invention have a kinematic viscosity, measured at 25°C according to the ASTM D445 standard, less than or equal to 20 mm2 / s, preferably less than or equal to 15 mm2 / s, in particular less than or equal to 10 mm2 / s.

[0036] Furthermore, the esters according to the invention advantageously have a particularly high auto-ignition point, preferably greater than or equal to 360°C, more preferably greater than or equal to 380°C, in particular greater than or equal to 400°C.

[0037] Advantageously, it is thus possible to access, via the implementation of one or more esters according to the invention, in particular as defined above, a com cooling position, having both a viscosity suitable for its implementation in a propulsion system, in particular a battery and / or power electronics, of an electric or hybrid vehicle, and excellent resistance to ignition.

[0038] A cooling composition according to the invention may be more particularly intended to be placed in direct contact with battery packs of electric vehicles, in particular Li-ion or nickel-cadmium (Ni-Cd) batteries.

[0039] A cooling composition according to the invention advantageously makes it possible to delay or avoid thermal runaway of said battery pack by preventing the cells from reaching a critical temperature and therefore from thermally running away.

[0040] A cooling composition implemented according to the invention further exhibits excellent electrical insulation properties, which makes it particularly well suited for use in hybrid and electric vehicles. The insulating properties can be evaluated by measuring the electrical resistivity of the cooling composition, in particular according to the ASTM DI 169 standard.

[0041] The invention also relates to a method for cooling at least one part of a propulsion system of an electric or hybrid vehicle, in particular the battery and / or the power electronics, comprising at least one step of bringing at least said part, in particular said battery, for example a lithium-ion or nickel-cadmium battery, into contact with a composition comprising at least one ester according to the invention, as defined previously.

[0042] The invention also relates, according to another of its aspects, to a composition, capable of cooling a propulsion system, in particular the battery and / or the power electronics, of an electric or hybrid vehicle, said composition comprising: (i) at least one ester according to the invention, as defined above; and (ii) at least one additive selected from antioxidants, antifoams, pour point improvers, anticorrosion agents, antiwear additives, friction modifiers, detergents, extreme pressure additives, dispersants, and mixtures thereof.

[0043] Advantageously, a composition according to the invention can have joint cooling and lubricating properties.

[0044] Thus, according to a particular embodiment, a composition according to the invention, implemented in a propulsion system of an electric or hybrid vehicle, allows, in addition to its cooling function, access to good properties in terms of lubrication of the parts of the propulsion system, for example for the lubrication of the transmission in an electric or hybrid vehicle.

[0045] Other characteristics, variants and advantages of the implementation of an ester according to the invention will emerge more clearly on reading the description and the examples which follow, given for illustrative and non-limiting purposes of the invention.

[0046] 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.

[0047] Unless otherwise indicated, the expression “comprising a(n)” must be understood as “comprising at least one(n)”. Brief description of the drawings

[0048] [Fig.l] schematically represents an electric or hybrid vehicle propulsion system. Detailed description ESTER ACCORDING TO THE INVENTION

[0049] As mentioned above, the ester used according to the invention has a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 200 mnf / s and an auto-ignition point, measured according to the ASTM E659 standard, greater than or equal to 350°C.

[0050] Preferably, an ester according to the invention has a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 150 mm2 / s, in particular less than 120 mm2 / s, preferably less than or equal to 100 mm2 / s, in particular ranging from 20 to 100 mm2 / s and more particularly ranging from 40 to 70 mm2 / s.

[0051] According to a particular embodiment, an ester according to the invention advantageously has a kinematic viscosity, measured at 25°C according to the ASTM D445 standard, less than or equal to 20 mm2 / s, preferably less than or equal to 15 mm2 / s, in particular less than or equal to 10 mm2 / s.

[0052] Also, the ester used according to the invention advantageously has a self-ignition point, measured according to the ASTM E659 standard, greater than or equal to 360°C, in particular greater than or equal to 380°C and more particularly greater than or equal to 400°C.

[0053] An ester according to the invention is preferably a monoester, a diester or a triester, preferably a monoester or diester. It may preferably be a monoester formed between a monocarboxylic acid and a monoalcohol. It may also be a diester formed between a dicarboxylic acid and a monoalcohol, or formed between a monocarboxylic acid and a diol.

[0054] The ester used according to the invention may be saturated or unsaturated, preferably saturated.

[0055] According to a particular embodiment, the ester used according to the invention is chosen from: - a branched ester, formed between at least one carboxylic acid comprising at least a branched, saturated or unsaturated, preferably saturated, hydrocarbon chain and at least one alcohol comprising at least one linear or branched, saturated or unsaturated hydrocarbon chain; - an ester comprising at least one heteroatom, preferably an oxygen atom, distinct from the oxygen atoms involved in the said ester function(s) of the said ester; and - their mixtures.

[0056] For the purposes of the present invention, the term "carboxylic acid" is intended to denote a compound comprising at least one carboxyl function. It may be a monocarboxylic or polycarboxylic acid. It is more preferably a monocarboxylic, dicarboxylic, tricarboxylic or tetracarboxylic acid. Preferably, the carboxylic acid is a monocarboxylic acid.

[0057] For the purposes of the present invention, the term "alcohol" is intended to denote a compound comprising at least one hydroxyl function. It may be a monoalcohol or a polyol. Preferably, it is a monoalcohol, diol or triol. Preferably, the alcohol is a monoalcohol.

[0058] 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 hydrocarbon chain may optionally be interrupted by one or more heteroatoms, in particular by one or more oxygen atoms. Preferably, the hydrocarbon chain is a linear or branched, saturated or unsaturated alkyl or alkylene chain consisting of carbon and hydrogen atoms. It preferably comprises from 1 to 14 carbon atoms, in particular from 3 to 10 carbon atoms, and in particular from 4 to 9 carbon atoms.

[0059] According to a particular embodiment, the ester used according to the invention is an ester, called a “branched ester”, formed between: - at least one carboxylic acid comprising at least one branched hydrocarbon chain, preferably of 3 to 14 carbon atoms, saturated or unsaturated, preferably saturated; and - at least one alcohol comprising at least one hydrocarbon chain, linear or branched, preferably from 1 to 14 carbon atoms, saturated or unsaturated, preferably saturated.

[0060] The branched ester according to the invention is preferably a monoester, a diester or a triester.

[0061] According to a particular embodiment, the branched ester according to the invention may be a monoester formed between a monocarboxylic acid and a monoalcohol.

[0062] According to another particular embodiment, the branched ester according to the invention may be a diester, formed between a diol compound and two monocarboxylic acids, or still formed between a dicarboxylic acid (diacid) and two monoalcohols.

[0063] As mentioned above, a branched ester used according to the invention is obtained from at least one carboxylic acid comprising at least one branched hydrocarbon chain, preferably saturated.

[0064] The branched hydrocarbon chain of said carboxylic acid may more particularly comprise from 3 to 14 carbon atoms, in particular from 5 to 12 carbon atoms, and more particularly from 6 to 10 carbon atoms.

[0065] Preferably, it may be formed from a linear main chain having from 4 to 10 carbon atoms, in particular from 5 to 8 carbon atoms, said main chain having at least one pendant alkyl group, preferably at least two pendant alkyl groups, in particular at least three pendant alkyl groups, said alkyl groups being more particularly C1 to C4, preferably C1 to C3, in particular C1-C2, for example methyl groups.

[0066] According to an alternative embodiment, the branched ester according to the invention is obtained from a monocarboxylic acid having a hydrocarbon chain, in particular as defined previously.

[0067] In a particular embodiment, the branched ester according to the invention is obtained from a branched and saturated C8 to C10 monocarboxylic acid, preferably C9, in particular 3,5,5-trimethylhexanoic acid.

[0068] The alcohol from which a branched ester according to the invention is formed may comprise a hydrocarbon chain, branched or not (linear), preferably saturated.

[0069] The hydrocarbon chain of said alcohol may more particularly comprise from 1 to 14 carbon atoms, in particular from 3 to 12 carbon atoms and more particularly from 6 to 10 carbon atoms.

[0070] According to a particular embodiment, a branched ester according to the invention is formed from at least one alcohol comprising a branched hydrocarbon chain, in particular having from 3 to 14 carbon atoms, in particular from 5 to 12 carbon atoms, and more particularly from 6 to 10 carbon atoms.

[0071] The branched hydrocarbon chain may be formed from a main linear chain having from 4 to 10 carbon atoms, in particular from 5 to 8 carbon atoms, said main chain having at least one pendant alkyl group, preferably at least two pendant alkyl groups, in particular at least three pendant alkyl groups, said alkyl groups being more particularly C1 to C4, preferably C1 to C3, in particular C1-C2, for example methyl groups.

[0072] According to an alternative embodiment, the branched ester according to the invention is obtained from a monoalcohol having a hydrocarbon chain, in particular as defined above, preferably a branched hydrocarbon chain.

[0073] In a particular embodiment, the branched ester according to the invention is obtained from a branched and saturated C8 to C10, preferably C9, monoalcohol, for example from 3,5,5-trimethylhexanol or one of its isomers.

[0074] According to another particular embodiment, the ester used according to the invention is an ester comprising at least one heteroatom, preferably an oxygen atom, distinct from the oxygen atoms involved in the said ester function(s) of the said ester.

[0075] Preferably, the ester used according to the invention is formed between at least one carboxylic acid and at least one alcohol comprising at least one ether function, preferably from at least one alcohol comprising at least one hydrocarbon chain, linear or branched, preferably linear, saturated or unsaturated, preferably saturated, in particular of 2 to 14 carbon atoms, said hydrocarbon chain being interrupted by at least one oxygen atom.

[0076] The hydrocarbon chain of said alcohol may more particularly comprise from 4 to 10 carbon atoms, in particular from 5 to 8 carbon atoms, and be interrupted by one or more oxygen atoms, preferably by an oxygen atom.

[0077] The carboxylic acid from which an ester according to the invention is formed, comprising at least one heteroatom distinct from the oxygen atoms engaged in the said ester function(s) of the said ester, may comprise at least one hydrocarbon chain, linear or branched, preferably linear, saturated or unsaturated, preferably saturated, in particular C3 to C10, in particular C4 to C10, in particular C4 to C8.

[0078] According to a particular embodiment, the ester comprising at least one heteroatom distinct from the oxygen atoms engaged in said ester function(s), is a diester formed between a dicarboxylic acid and at least one monoalcohol comprising a linear or branched, saturated or unsaturated hydrocarbon chain, preferably from 2 to 14 carbon atoms, interrupted by at least one heteroatom, preferably by an oxygen atom.

[0079] Preferably, the dicarboxylic acid comprises a linear or branched, preferably linear, saturated or unsaturated, preferably saturated, hydrocarbon chain, in particular C3-Ci4, preferably C4-Ci0, in particular C6-C8. It may be, for example, adipic acid.

[0080] Preferably, the monoalcohol comprising a hydrocarbon chain interrupted by at least one heteroatom, has a linear and saturated hydrocarbon chain, in particular of 3 to 14 carbon atoms, preferably of 4 to 10 carbon atoms and more particularly of 4 to 8 carbon atoms, said chain being interrupted by one or more oxygen atoms, preferably by an oxygen atom.

[0081] Such a monoalcohol may more particularly comprise a C2 to C4 alkylene chain, carrying at least one C2 to C6 alkoxy group, in particular C4. It may be, for example, butyl glycol.

[0082] In a particular embodiment, the ester used according to the invention is dibutylglycol adipate.

[0083] It is understood that the definitions given above for carboxylic acid and alcohol may be combined, where possible, to define other particular embodiments.

[0084] An ester according to the invention may more particularly correspond to the following formula (I): [Chem 1] G'-C(O)-O-G2 (I) in which: ❖ G1 represents a hydrocarbon chain, preferably branched, saturated or unsaturated, in particular having from 3 to 14 carbon atoms, said hydrocarbon chain possibly carrying one or more R'-OC(O)- groups, preferably one or two R'-OC(O)- groups, with R1 representing a hydrocarbon chain, linear or branched, saturated or unsaturated, preferably from 1 to 13 carbon atoms, optionally interrupted by one or more heteroatoms, such as oxygen atoms; and ❖ G2 represents a hydrocarbon chain, saturated or unsaturated, linear or branched, preferably branched, in particular having from 1 to 14 carbon atoms, said hydrocarbon chain being optionally interrupted by one or more heteroatoms, such as oxygen atoms, and / or optionally carrying one or more -OC(O)-R2 groups, preferably one or two -OC(O)-R2 groups, with R2 representing a hydrocarbon chain, linear or branched, saturated or unsaturated, preferably branched, preferably having 3 to 13 carbon atoms.

[0085] Preferably, G1 represents an alkyl group, preferably branched, in particular C3 to C12, in particular C4 to C18 and more particularly C5 to C9, or a group R1-OC(O)-A1-, with A1 representing an alkylene group, in particular C2 to C12, in particular C3 to C10, and R1 being as defined previously.

[0086] Preferably, G2 represents a linear or branched alkyl chain, in particular C^CU, in particular C3 to C12, and more particularly C6 to C10, optionally interrupted by one or more oxygen atoms, or a group - A2-OC(O)-R2, with A2 representing an alkylene group in particular C1 to C13, and R2 being as defined above, preferably R2 representing an alkyl group, preferably branched, C3 to C13.

[0087] According to a first embodiment variant, an ester according to the invention may be of formula (I) above, in which: ❖ G1 represents an alkyl group, preferably branched, in particular C3 to C13, in particular C4 to Cn and more particularly C5 to C9. G1 is preferably formed from a main linear alkyl chain, in particular C3 to C9, in particular C4 to C7, said main chain having at least one pendant alkyl group, preferably at least two pendant alkyl groups, in particular at least three pendant alkyl groups, said pendant alkyl groups being more particularly C1 to C4, preferably C1 to C3, in particular C1-C2, for example methyl groups. Advantageously, G1 may represent a 2,4,4-trimethylpentyl group. ❖ G2 represents an alkyl group, linear or branched, in particular C1 to C10, in particular C3 to C12, and more particularly C6 to C10.

[0088] According to a particularly advantageous variant, G2 represents a branched alkyl chain, in particular C3 to C10, in particular C6 to C12 and more particularly C8 to C10.

[0089] Such a branched alkyl group may in particular be formed from a main linear alkyl chain, in particular C4 to C10, in particular C5 to C8, said main chain having at least one pendant alkyl group, preferably at least two pendant alkyl groups, in particular at least three pendant alkyl groups, said pendant alkyl groups being more particularly C1 to C4, preferably C1 to C3, in particular C1-C2, for example methyl groups.

[0090] Advantageously, G2 may represent a branched C9 alkyl group, for example 3,5,5-trimethylhexyl or one of its isomers.

[0091] According to another embodiment variant, an ester according to the invention may be of formula (I) above, in which: ❖ G1 represents an alkyl group, preferably branched, in particular C3 to C13, in particular C4 to Cn and more particularly C5 to C9. G1 is preferably formed from a main linear alkyl chain, in particular C 3 to C 9, in particular C 4 to C 7, said main chain having at least one pendant alkyl group, preferably at least two pendant alkyl groups, in particular at least three pendant alkyl groups, said pendant alkyl groups being more particularly C 1 to C 4, preferably C 1 to C 3, in particular C 1 to C 2, for example methyl groups. Advantageously, G1 may represent a 2,4,4-trimethylpentyl group. ❖ G2 represents a group -A2-OC(O)-R2, in which A2 and R2 are as defined previously. Preferably, A2 represents a C1 to C13 alkylene group, in particular C3 to C12, and more particularly C6 to C10.

[0092] According to a particular embodiment, R2 can be as defined previously for the group G1, preferably R2 is identical to G1.

[0093] According to yet another variant embodiment, an ester according to the invention may be of formula (I) above, in which: ❖ G2 represents a saturated or unsaturated, linear or branched hydrocarbon chain, in particular having from 1 to 14 carbon atoms, said hydrocarbon chain being optionally interrupted by one or more heteroatoms, preferably by one or more oxygen atoms. In particular, G2 may represent an alkyl chain, preferably linear, comprising from 1 to 14 carbon atoms, in particular from 3 to 12 carbon atoms, and more particularly from 6 to 10 carbon atoms, and interrupted by at least one oxygen atom, preferably by an oxygen atom; ❖ G1 represents a group R1-OC(O)-A1-, in which A1 and R1 are as defined previously.

[0094] In particular, R1 may be as defined previously for the group G2, preferably R1 is identical to G2.

[0095] Preferably, A1 represents a linear or branched alkylene group, C3 to Cn, in particular C4 to Cn.

[0096] According to a particularly preferred embodiment, an ester according to the invention is chosen from: (i) a branched monoester formed between: - a monocarboxylic acid, having a saturated branched hydrocarbon chain, preferably comprising from 3 to 14 carbon atoms, in particular as defined above; and - a monoalcohol having a saturated hydrocarbon chain, preferably branched, preferably comprising from 3 to 14 carbon atoms, in particular as defined above, or (ii) a diester formed between: - a dicarboxylic acid, having a saturated linear hydrocarbon chain, preferably comprising from 3 to 14 carbon atoms, in particular from 4 to 10 carbon atoms; and - a monoalcohol having a linear saturated hydrocarbon chain, interrupted by an oxygen atom, preferably comprising from 3 to 14 carbon atoms, in particular from 4 to 10 carbon atoms.

[0097] Advantageously, the ester according to the invention may be a monoester formed between 3,5,5-trimethylhexanoic acid and 3,5,5-trimethylhexanol or one of its isomers, or a diester formed between adipic acid and butyl glycol.

[0098] The esters according to the invention may be commercially available or prepared according to synthesis methods known to those skilled in the art. These synthesis methods more particularly implement an esterification reaction between at least one alcohol compound and at least one carboxylic acid compound.

[0099] Of course, it is up to the person skilled in the art to adjust the synthesis conditions to obtain an ester according to the invention.

[0100] Advantageously, a branched ester according to the invention has a kinematic viscosity, measured at 25°C according to the ASTM D445 standard, of less than or equal to 20 mm2 / s, preferably less than or equal to 15 mm2 / s, in particular less than or equal to 10 mm2 / s.

[0101] Advantageously, a branched ester according to the invention has a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 150 mm 2 / s, in particular less than or equal to 120 mm2 / s, in particular ranging from 20 to 100 mm2 / s and more particularly ranging from 40 to 70 mm2 / s.

[0102] Advantageously, a branched ester according to the invention advantageously has an auto-ignition point greater than or equal to 360°C, in particular greater than or equal to 380°C and more particularly greater than or equal to 400°C.

[0103] It is understood that, within the framework of the present invention, an ester according to the invention, in particular a branched ester according to the invention, may be in the form of a mixture of at least two esters according to the invention, in particular as defined above.

[0104] The ester or mixture of esters according to the invention may represent more than 30% by mass, preferably more than 50% by mass, more preferably more than 70% by mass, even more preferably more than 80% by mass, in particular more than 90% by mass, more particularly more than 95% by mass, or even more than 98% by mass, of the total mass of the cooling composition according to the invention.

[0105] In particular, a cooling composition used according to the invention may comprise between 30% and 100% by mass of an ester or mixture of esters 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.

[0106] According to a particular embodiment, a cooling 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 esters according to the invention, in particular one or more branched esters according to the invention. Annex base oil(s)

[0107] A cooling composition used according to the invention may comprise, in addition to one or more esters according to the invention, one or more base oils distinct from the esters according to the invention.

[0108] Said base oil(s), optionally present in a cooling composition according to the invention, are chosen appropriately, with regard to their compatibility with said ester(s) used according to the invention.

[0109] It may be a mixture of several base oils, for example a mixture of two, three or four base oils.

[0110] Preferably, the base oil or mixture of additional base oils, used in a cooling 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.

[0111] 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.

[0112] [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

[0113] 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.

[0114] Mixtures of synthetic and mineral oils, which can be bio-sourced, can also be used.

[0115] There are generally no limitations on the use of additional different base oils to make cooling compositions, except that they must have properties, in particular viscosity index, sulfur content or oxidation resistance, suitable for use in propulsion systems of an electric or hybrid vehicle.

[0116] The base oils can also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, distinct from the ester defined according to the invention, among the polyalphaolefins (PAO), and among the 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] Advantageously, the additional base oil or oils are chosen from polyalphaolefins (PAO).

[0121] It is up to a person skilled in the art to adjust the content of additional base oil(s) present in a cooling composition according to the invention.

[0122] In particular, a cooling composition according to the invention may comprise less than 70% by mass of additional base oil(s), in particular less than 50% by mass, in particular less than 30% by mass, or even less than 20% by mass or less than 10% by mass and more particularly less than 5% by mass, relative to the total mass of said composition. ADDITIVES

[0123] A cooling composition according to the invention may further comprise one or more additives known to those skilled in the art in the field of lubrication and / or cooling of propulsion systems of electric or hybrid vehicles.

[0124] 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.

[0125] Preferably, a cooling composition according to the invention may further comprise one or more additives chosen from antioxidants, antifoams, pour point improvers and anti-corrosion agents.

[0126] The addition of one or more additives chosen from anti-wear additives, modi friction reducers, detergents, extreme pressure additives and dispersants, may also prove advantageous in the context of the implementation of the cooling 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.

[0127] It is understood that the nature and quantity of additives used are chosen so as not to affect the properties of the cooling composition conferred by the ester according to the invention.

[0128] 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.

[0129] Said additive(s) may be present in the cooling composition according to the invention in a content of less than or equal to 10% by mass, in particular less than or equal to 5% by mass, and more particularly ranging from 0.01 to 3% by mass, relative to the total mass of said composition.

[0130] A cooling composition implemented according to the invention can thus comprise at least one antioxidant additive.

[0131] The invention thus relates, according to another of its aspects, to a cooling composition, in particular capable of cooling a propulsion system, in particular the battery and / or the power electronics of an electric or hybrid vehicle, said composition comprising (i) at least one branched ester as defined previously, and (ii) at least one antioxidant additive.

[0132] 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.

[0133] 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 ash-generating. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C1-C12 alkyl group, N,N'-dialkyl-aryl-diamines and mixtures thereof.

[0134] 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.

[0135] 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.

[0136] Sulphurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

[0137] 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.

[0138] Advantageously, a cooling composition comprises at least one ash-free antioxidant additive.

[0139] Said additive(s) may be used, in a cooling composition according to the invention, at a rate of 0.1 to 2% by mass, relative to the total mass of the composition.

[0140] A cooling composition according to the invention may comprise at least one anti-wear and / or extreme pressure additive.

[0141] Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces.

[0142] There is a wide variety of anti-wear additives. Preferably, the anti-wear additives 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)(OR2)(OR3))2, in which R2 and R3, identical or different, re independently have an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

[0143] 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.

[0144] A cooling 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.

[0145] A cooling composition according to the invention may further comprise an antifoaming agent.

[0146] The antifoaming agent may be chosen from silicones.

[0147] A cooling 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 weight of the composition.

[0148] A cooling composition according to the invention may comprise at least one friction modifying additive.

[0149] 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.

[0150] A cooling 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 weight of the composition.

[0151] Advantageously, a cooling composition is free of friction modifying additive, in particular for use aimed at cooling the battery part.

[0152] A cooling composition according to the invention may comprise at least one detergent additive.

[0153] 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.

[0154] Detergent additives usable in a cooling composition are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon group and a hydrophilic head. The associated cation may be a metal cation of an alkali or alkaline earth metal.

[0155] 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.

[0156] 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.

[0157] A cooling composition may for example comprise from 2 to 4% by mass of detergent additive, relative to the total mass of the composition.

[0158] A cooling composition may also comprise at least one pour point depressant additive.

[0159] 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.

[0160] Also, a cooling composition may comprise at least one dispersing agent.

[0161] The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives. A cooling composition may, for example, comprise from 0.2 to 10% by mass of dispersing agent, relative to the total mass of the composition.

[0162] According to a particular embodiment, a cooling composition used according to the invention comprises, or is even formed (i) from at least one ester according to the invention, in particular from at least one branched ester as defined previously 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 and anticorrosion agents.

[0163] Advantageously, a cooling composition used according to the invention is formed (i) from at least one ester according to the invention, in particular from at least one branched ester as defined above and (ii) from at least one antioxidant additive.

[0164] According to a particular embodiment, a cooling composition implemented according to the invention comprises, or even consists of: - at least 30% by mass, preferably at least 50% by mass, preferably at least 70% by mass, preferably at least 80% by mass, more preferably at least 90% by mass, or even at least 95% by mass, of one or more esters according to the invention, in particular of one or more branched esters according to the invention; - from 0.01 to 10% by mass, preferably from 0.05 to 5% by mass, of one or more additives chosen from antioxidants, antifoams, antiwear and extreme pressure additives, friction modifiers, detergents, pour point lowering additives, dispersing agents and mixtures thereof, preferably chosen from antioxidants, antifoams, pour point lowering additives, anticorrosion agents and mixtures thereof; and - optionally from 5 to 70% by mass, preferably from 10 to 50% by mass, preferably from 15 to 30% by mass of base oil(s) distinct from the ester according to the invention, the contents being expressed in relation to the total mass of said composition.

[0165] A cooling composition used according to the invention advantageously has a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 200 mm2 / s, in particular less than or equal to 120 mm2 / s, in particular ranging from 20 to 100 mm2 / s and more particularly from 40 to 70 mm2 / s.

[0166] Also, advantageously, a cooling composition used according to the invention has a kinematic viscosity, measured at 25°C according to the ASTM D445 standard, less than or equal to 20 mm2 / s, in particular less than or equal to 15 mm2 / s, in particular ranging from 2 to 12 mm2 / s and more particularly ranging from 5 to 10 mm2 / s.

[0167] Furthermore, a cooling composition used according to the invention has a particularly high auto-ignition point. In particular, a cooling composition according to the invention advantageously has an auto-ignition point greater than or equal to 360°C, in particular greater than or equal to 380°C and more particularly greater than or equal to 400°C. APPLICATION

[0168] As indicated previously, a composition according to the invention can be used as a cooling fluid for a propulsion system of an electric or hybrid vehicle.

[0169] 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).

[0170] 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.

[0171] 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 motor. It is therefore imperative to ensure cooling of the electric motor, and the power electronics.

[0172] 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 rotational speed at the output of the electric motor and to adapt the speed transmitted to the wheels, making it possible at the same time to control the speed of the vehicle.

[0173] Advantageously, a composition according to the invention can be used to cool the battery of an electric or hybrid vehicle. In particular, it is intended to be placed in direct contact with the battery.

[0174] As batteries suitable for the propulsion systems of an electric or hybrid vehicle, mention may be made in particular of Li-ion batteries or nickel-cadmium batteries.

[0175] The invention also relates, according to another of its aspects, to a method for cooling at least one part of a propulsion system of an electric or hybrid vehicle, in particular the battery, comprising at least one step of bringing at least said part, in particular said battery, for example a lithium-ion or nickel-cadmium battery, into contact with a composition comprising at least one branched ester according to the invention, as defined previously.

[0176] Bringing the cooling composition according to the invention into contact with the battery may consist of immersion or semi-immersion of the battery in said composition or even of injection of said composition onto the surface of the battery.

[0177] By "immersion" is meant that the entire battery is surrounded by the cooling composition according to the invention. By "semi-immersion" is meant that only a portion of the battery is in contact with said composition.

[0178] Cooling can be implemented by any method known to those skilled in the art. The battery can be immersed or semi-immersed, static or circulating, in said composition.

[0179] Examples of direct contact include cooling by injection, jet, spraying or even by forming a mist from the composition according to the invention under pressure and by gravity on the battery.

[0180] Advantageously, the composition is injected by jet under fairly high pressure into the zones to be cooled of the propulsion system. Advantageously, the shear resulting from this injection makes it possible to reduce the viscosity of the fluid at the injection zone, compared to the kinematic viscosity at rest, and thus, to further increase the cooling potential of the composition.

[0181] In addition, oil circulation systems commonly used in electric motors may be employed, as for example described in WO 2015 / 116496.

[0182] A composition according to the invention can also be used to cool the electric motor of an electric or hybrid vehicle, in particular to cool the power electronics and / or the rotor and / or the stator of the electric motor.

[0183] The cooling composition according to the invention has in particular electrical insulation properties which are particularly satisfactory for use in electric or hybrid vehicles.

[0184] It is possible to take advantage, in addition to the cooling properties of a composition according to the invention, of its lubricating properties.

[0185] Thus, a composition according to the invention can simultaneously be used to lubricate the various parts of a propulsion system of an electric or hybrid vehicle, in particular bearings located between the rotor and the stator of an electric motor, or even the transmission, in particular the reducer, in an electric or hybrid vehicle.

[0186] In the case of such an application, a cooling composition according to the invention advantageously further comprises one or more additives chosen from anti-wear additives, friction modifiers, detergents, dispersants, extreme pressure additives, and mixtures thereof.

[0187] 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

[0188] Different compositions, formed from the following compounds, were evaluated:

[0189] - a branched ester A, in accordance with the invention: 3,5,5-trimethylhexanoate of 3,5,5-trimethylhexanol;

[0190] - an ester B, in accordance with the invention: dibutyl glycol adipate which is a diester formed between a dicarboxylic acid having an unbranched alkylene chain of 6 carbon atoms and a butyl glycol monoalcohol;

[0191] - a polyalphaolefin C of the hydrogenated decene dimer type, conventionally used for these battery cooling applications; and

[0192] - an ester D, not in accordance with the invention: diisodecyl adipate which is a diester formed between a dicarboxylic acid having a linear, unbranched alkylene chain of 6 carbon atoms and a monoalcohol having a branched alkyl chain having 10 carbon atoms.

[0193] The stability of the compositions at high temperatures, in other words their resistance to flammability, is evaluated by determining their auto-ignition point according to the ASTM E659 standard.

[0194] The viscosities of the compositions at 25°C and at -25°C are determined according to the ASTM D 445 standard.

[0195] The results of the auto-ignition point and cold viscosities measurements are compiled in Table 2 below.

[0196] [Tables2] Compositions ABCD Autoignition point (°C) 401.5 356.0 216.0 357.0 Viscosity at -25°C (mm2 / s) 55.8 146.2 81.6 525.6 Viscosity at 25°C (mm2 / s) 6.7 10.9 8.0 23.5

[0197] The branched ester A and the ester B, in accordance with the invention, have a low cold viscosity, while having a high auto-ignition point, which makes each of these esters compatible with its implementation at the level of a battery and / or the power electronics of an electric or hybrid vehicle.

[0198] The stability and resistance to flammability of esters A and B are thus ensured, even in the event of overheating of the battery.

[0199] It will be noted more particularly that an ester as defined in the present invention has viscosity and auto-ignition properties which are particularly advantageous for its use in a cooling composition for a propulsion system, in particular a battery and power electronics, of electric or hybrid vehicles.

Claims

Claims

1. Use, for cooling a propulsion system of an electric or hybrid vehicle, of a composition comprising at least one ester having a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 200 mm2 / s and an auto-ignition point, measured according to the ASTM E659 standard, greater than or equal to 350°C; said ester being a monoester formed between a monocarboxylic acid, having a saturated branched hydrocarbon chain of 3 to 14 carbon atoms and a monoalcohol having a saturated hydrocarbon chain, preferably branched, preferably comprising 3 to 14 carbon atoms.

2. Use according to claim 1, in which the composition comprises at least 30% by mass, preferably at least 50% by mass, more preferably at least 70% by mass, even more preferably at least 80% by mass, or even at least 90% by mass of said monoester, relative to the total weight of the composition.

3. Use according to claim 1 or 2, for cooling the battery and / or the power electronics of an electric or hybrid vehicle, in particular a lithium-ion or nickel-cadmium battery.

4. Use according to any one of the preceding claims, wherein said monoester has a kinematic viscosity, measured at -25°C according to the ASTM D445 standard, less than or equal to 150 mm2 / s, in particular less than or equal to 120 mm2 / s, preferably less than or equal to 100 mm2 / s, in particular ranging from 20 to 100 mm2 / s, and more particularly ranging from 40 to 70 mm2 / s, and / or an auto-ignition point, measured according to the ASTM E659 standard, greater than or equal to 360°C, in particular greater than or equal to 380°C, more preferably greater than or equal to 400°C.

5. Use according to any one of the preceding claims, characterized in that said monoester corresponds to the following formula (I): [Chem 1] G'-C(O)-O-G2 (I) in which: ❖ G1 represents an alkyl group, preferably branched, in particular C3 to Cu, in particular C4 to Cn and more particularly C5 to C9; and ❖ G2 represents an alkyl group, linear or branched, in particular C1 to C14, in particular C3 to C12, and more particularly C6 to C

6. 10- Use according to any one of claims 1 to 5, characterized in that said monoester is formed between a branched and saturated C8 to C10, preferably C9, monocarboxylic acid, in particular 3,5,5-trimethylhexanoic acid and a branched and saturated C8 to C10, preferably C9, monoalcohol such as 3,5,5-trimethylhexanol or one of its isomers.

7. Use according to any one of the preceding claims, characterized in that said composition comprises, in addition to said monoester(s), at least one additive chosen from antioxidants, pour point depressant additives, antifoaming agents, anticorrosion agents, antiwear and / or extreme pressure additives, friction modifiers, detergents, dispersing agents and mixtures thereof, in particular from antioxidants, pour point depressant additives, antifoaming agents and anticorrosion agents.

8. Composition capable of cooling a propulsion system, in particular the battery and / or the power electronics of an electric or hybrid vehicle, said composition comprising: (i) at least one monoester as defined in claim 1; and (ii) at least one additive 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; said composition being formed at more than 95% by mass of said monoester(s).

9. Composition according to claim 8 characterized in that said monoester is as defined according to any one of claims 4 to 6.

10. Composition according to claim 8 or 9, characterized in that it comprises at least one antioxidant additive, said composition being more particularly formed from said monoester(s) and one or more antioxidant additives.

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