Use of Wear-Resistant Additives to Improve the Thermal Conductivity of Cooling Fluids for Electric Vehicles

Abstract

The present invention relates to the use of at least one antiwear additive for improving the thermal conductivity of a fluid containing at least one base oil.

Description

Technical Field

[0001] The present invention relates to the field of lubricating compositions for electric vehicles. More particularly, the present invention relates to the field of lubricating and cooling compositions for electric vehicles, and more particularly for cooling the batteries of electric vehicles.

Background Art

[0002] The evolution of international standards for reducing not only CO2 emissions but also energy consumption has encouraged automobile manufacturers to propose alternative solutions to internal combustion engines.

[0003] One of the solutions identified by automobile manufacturers is to replace the internal combustion engine with an electric motor. Thus, due to research for reducing CO2 emissions, several automobile companies have developed electric vehicles.

[0004] Generally, in a vehicle, it is necessary to use a lubricating composition, also known as a "lubricating fluid", mainly for the purpose of reducing the frictional force between different parts of the vehicle propulsion system, particularly between the movable metal parts in the motor. Furthermore, such lubricating compositions are effective in preventing premature wear or damage of such parts, especially their surfaces.

[0005] An electric motor generates heat during operation. If the amount of heat generated is greater than the amount of heat normally dissipated to the environment, the engine requires cooling. Generally, cooling is performed on one or more parts of the engine that generate heat and / or are vulnerable to damage by the heat of the engine to prevent reaching a dangerous temperature.

[0006] Cooling can be carried out either by direct cooling or indirect cooling. Due to the increasing output density of electric motors, it is necessary to develop and improve the direct cooling mode of electric motors, in which the lubricating fluid of the transmission part is further used to cool the high-temperature parts of the electric motor. One example is the Tesla Model S vehicle, where the gearbox lubricant also circulates through the hollow rotor of the electric motor and cools the stator coil head by means of a plurality of oil jets.

[0007] For this purpose, lubricating compositions have conventionally been composed of one or more base oils, which are generally accompanied by a plurality of additives, such as friction modifier additives for example, to stimulate the lubricating performance of the base oil.

[0008] For reasons of economy and ease of implementation, it would be advantageous to have a composition that simultaneously meets the lubrication and cooling requirements of the propulsion system (engine, battery, etc.) of an electric vehicle. Unfortunately, at first glance, these two properties of lubrication and cooling impose opposing constraints.

[0009] One type of performance particularly useful in lubricating compositions for the propulsion system of electric vehicles is to have good properties regarding anti-wear, which is part of the requirements that should be systematically met in the manufacturer's technical specifications.

[0010] Furthermore, such types of lubricating compositions must be able to easily cool the propulsion system of an electric vehicle.

[0011] Therefore, the subject matter of the present invention is to provide a single fluid (a single lubricating composition) that can be used in all components of the propulsion system of an electric vehicle.

Summary of the Invention

[0012] More precisely, the present invention relates to the use of at least one anti-wear additive to improve the thermal conductivity of a fluid containing at least one base oil.

[0013] According to the present invention, the anti-wear additive is selected from a phosphorus-containing anti-wear agent, a phosphorus-sulfur-containing anti-wear agent, a phosphoaminated anti-wear agent, a sulfur-containing anti-wear agent, a boron-containing anti-wear agent, and mixtures thereof.

[0014] According to one embodiment, the anti-wear additive is used to improve the heat transfer properties of the fluid.

[0015] According to one embodiment, the fluid is used to cool the battery of an electric vehicle.

[0016] According to one embodiment, the anti-wear additive is used to prepare a single fluid for lubricating and cooling the propulsion system of an electric vehicle. Thereby, according to such an embodiment, a single fluid (the same fluid) circulates through the entire cooling and lubrication systems of the propulsion system of the electric vehicle.

[0017] Preferably, the anti-wear additive is selected from a phosphorus-containing anti-wear agent, a phosphorus-sulfur-containing anti-wear agent, a phosphoaminated anti-wear agent, and mixtures thereof, preferably from a phosphorus-containing anti-wear agent.

[0018] Preferably, the anti-wear additive is a phosphite polymer, preferably of formula (I):

Chemical formula

[0019] According to one embodiment, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a weight average molecular weight of less than 30,000 g / mol, preferably in the range of 5000-20,000 g / mol.

[0020] According to one embodiment, the antiwear additive accounts for 0.01-10% by weight of the total weight of the fluid.

[0021] According to one embodiment, the antiwear additive contains 5-9150 ppm by weight of phosphorus, preferably 5-4500 ppm by weight of phosphorus, based on the total weight of the fluid.

[0022] According to an embodiment, the fluid contains at least 70%, preferably at least 80% by weight, and preferably at least 85% by weight of base oil, based on the total weight of the composition.

[0023] According to one embodiment, the fluid is based on the total weight of said fluid, - one or more base oils in an amount of 70-99.99% by weight, and - an antiwear additive in an amount of 0.01-10% by weight, preferably selected from phosphorus-containing antiwear additives, preferably an antiwear additive selected from phosphite polymers - Optionally, 1 to 30% by weight of one or more functional additives, preferably functional additives selected from viscosity index improvers, antioxidant additives, defoaming additives, dispersants, detergents, viscosity modifiers, and mixtures thereof is included.

[0024] The fluid used according to the present invention has the advantage of being easily used both for lubricating parts of the propulsion system of an electric vehicle and for cooling parts of the propulsion system of an electric vehicle.

[0025] Unless otherwise specified, the amounts in the product are expressed by weight relative to the total weight of the product.

Embodiments for Carrying Out the Invention

[0026] The present invention relates to - improving the thermal conductivity of a fluid containing at least one base oil, and / or - improving the heat transfer characteristics of a fluid containing at least one base oil, and / or - in a fluid containing at least one base oil, regarding the use of at least one antiwear additive for cooling the battery of an electric vehicle.

[0027] "Electric vehicle" as defined by the present invention refers to a vehicle equipped with an electric motor as the sole means of propulsion, and is different from a hybrid vehicle equipped with an internal combustion engine and an electric motor as combined means of propulsion.

[0028] "Propulsion system" as defined by the present invention refers to a system including mechanical parts necessary for vehicle propulsion. Thus, in the context of an electric vehicle, the propulsion system more specifically includes an electric motor, or a rotor-stator assembly of a power electronic system (for speed adjustment only), a transmission also called a speed reducer, and a battery.

[0029] ​The thermal conductivity can be determined in accordance with the standard ASTM D7896-19. Within the framework of the present invention, this is preferably determined at 30°C.

[0030] Antiwear additive The antiwear additives used in lubricating compositions are additives known for their wear-reducing properties when added to base oils.

[0031] According to the present invention, the antiwear additive is selected from phosphorus-containing antiwear agents, phosphorus-sulfur-containing antiwear agents, phosphoaminated antiwear agents, sulfur-containing antiwear agents, boron-containing antiwear agents, and mixtures thereof.

[0032] Preferably, the antiwear additive is selected from phosphorus-containing antiwear agents, phosphorus-sulfur-containing antiwear agents, phosphoaminated antiwear agents, and mixtures thereof.

[0033] The "phosphorus-containing antiwear agent" as defined by the present invention refers to an antiwear agent containing at least one phosphorus atom and no sulfur or nitrogen.

[0034] The "sulfur-containing antiwear agent" as defined by the present invention refers to an antiwear agent containing at least one sulfur atom and no phosphorus or nitrogen.

[0035] The "phosphorus-sulfur antiwear agent" as defined by the present invention refers to an antiwear agent containing at least one phosphorus atom and at least one sulfur atom and no nitrogen atoms.

[0036] The "phosphoaminated antiwear agent" as defined by the present invention refers to an antiwear agent containing at least one phosphorus atom and at least one nitrogen atom and no sulfur atoms.

[0037] The "sulfur-containing antiwear agent" as defined by the present invention refers to an antiwear agent containing at least one sulfur atom and no phosphorus or nitrogen atoms.

[0038] The "boron-containing antiwear agent" defined by the present invention refers to an antiwear agent that contains at least one boron atom and does not contain any phosphorus atoms, nitrogen atoms, or sulfur atoms.

[0039] Antiwear additives such as phosphorus-containing antiwear agents, phosphorus-sulfur antiwear agents, phosphoaminated antiwear agents, sulfur-containing antiwear agents, and boron-containing antiwear agents are commercially available.

[0040] Among the phosphorus-containing antiwear additives, phosphates, phosphites, and phosphonates can be mentioned. Such terms also refer to phosphoric acid, phosphorous acid, and phosphonic acid, their mono-, di-, and triesters, for example, alkyl phosphates, alkyl phosphonates, and their salts.

[0041] The phosphorus-sulfur antiwear additive used in the present invention, if present, may be (mono- or di-) thiophosphate and thiophosphite. Such terms include thiophosphoric acid and thiophosphorous acid, esters of said acids, their salts, as well as dithiophosphites and dithiophosphates.

[0042] Examples include phosphorus-sulfur antiwear additives, monobutyl thiophosphate, monooctyl thiophosphate, monolauryl thiophosphate, dibutyl thiophosphate, dilauryl thiophosphate, tributyl thiophosphate, trioctyl thiophosphate, triphenyl thiophosphate, monooctyl thiophosphite, trilauryl thiophosphate, monolauryl thiophosphite, monobutyl thiophosphite, dibutyl thiophosphite, dilauryl thiophosphite, tributyl thiophosphite, trioctyl thiophosphite, triphenyl thiophosphite, trilauryl thiophosphite, and their salts.

[0043] Among the phosphorus-sulfur antiwear agents in salt form, metal dithiocarbamate-type antiwear agents such as zinc dithiophosphate, cobalt dithiophosphate, or nickel dithiophosphate can be mentioned.

[0044] Among sulfur-containing antiwear agents, sulfurized olefins, sulfurized esters, polysulfides, especially disulfides, thiocarbamates and dithiocarbamates, and their salts can be mentioned.

[0045] Among sulfur-containing antiwear agents in the form of salts, metal dithiocarbamate-type antiwear agents such as zinc dithiocarbamate, cobalt dithiocarbamate or nickel dithiocarbamate can be mentioned.

[0046] Among boron-containing antiwear agents, boron-containing esters, calcium borate and potassium borate can be mentioned.

[0047] According to one embodiment, the antiwear additive is selected from phosphite polymers, preferably of formula (I):

Chemical formula

[0048] For the purposes of the present invention, the term "alkyl" refers to a straight or branched chain of a saturated acyclic hydrocarbon system optionally containing one or more heteroatoms such as oxygen, nitrogen or sulfur atoms. Preferably, alkyl consists of carbon atoms and hydrogen atoms.

[0049] "Alkenyl" as defined by the present invention refers to a straight or branched chain of an unsaturated acyclic hydrocarbon system optionally containing one or more heteroatoms such as oxygen, nitrogen or sulfur atoms. Preferably, alkenyl consists of carbon atoms and hydrogen atoms.

[0050] "Cycloalkyl" as defined by the present invention refers to a saturated monocyclic or polycyclic moiety optionally having one or more alkyl or alkenyl substituents, and the one or more rings themselves may be substituted by one or more heteroatoms such as oxygen, nitrogen or sulfur atoms. Preferably, cycloalkyl consists of carbon atoms and hydrogen atoms.

[0051] "Cycloalkenyl" as defined by the present invention refers to an unsaturated monocyclic or polycyclic moiety optionally having one or more alkyl or alkenyl substituents, and the one or more rings themselves may be substituted by one or more heteroatoms such as oxygen, nitrogen or sulfur atoms. Preferably, cycloalkenyl consists of carbon atoms and hydrogen atoms.

[0052] "C i -C j " moiety is a moiety containing i to j carbon atoms.

[0053] According to a preferred embodiment, the moiety Y is selected from alkylene containing 2 to 20 carbon atoms, preferably 2 to 12 carbon atoms, or preferably 2 to 8 carbon atoms if not otherwise stated.

[0054] According to one embodiment, m is in the range of 4 to 100.

[0055] According to one embodiment, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a weight average molecular weight in the range of less than 30,000 g / mol, preferably in the range of 3000 to 20,000 g / mol. The weight average molecular weight can be measured by size exclusion chromatography.

[0056] According to one embodiment, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a number average molecular weight in the range of less than 10,000 g / mol, preferably in the range of 1000 to 5000 g / mol. The number average molecular weight can be measured by size exclusion chromatography.

[0057] According to one embodiment, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a polydispersity index in the range of 1 to 5, preferably in the range of 2 to 4.

[0058] Preferably, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), contains less than 2% by weight, preferably less than 1% by weight, or even less than 0.7% by weight of the (alkyl)phenol moiety relative to the total weight of the phosphite polymer of formula (I).

[0059] Preferably, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), does not contain any aromatic moiety other than the (alkyl)phenol moiety.

[0060] Typically, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), is in liquid form.

[0061] According to one embodiment, the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a phosphorus concentration of 0.5 to 20% by weight, preferably 1 to 10% by weight, based on the total weight of the phosphite polymer.

[0062] The phosphite polymer that can be used in the present invention can be obtained by the method described in WO2011102861. More specifically, the polymer can be obtained by the method described in paragraphs 27 to 32 of the said document.

[0063] The synthesis of the polymer of formula (I) generally involves transesterification, and triphenyl phosphite (or any other suitable alkyl or aryl phosphite) is reacted with a saturated or unsaturated alcohol, or a polyethylene or polypropylene glycol ether, and a diol or diol polymer diol H(OY) m OH (wherein Y and m are as defined above herein) at a temperature included in 20°C to 250°C, preferably at a temperature included in 50°C to 185°C. Examples of saturated or unsaturated alcohols include, but are not limited to, decyl, isodecyl, lauryl, tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, stearyl, isostearyl, oleic acid, and monohydroxylated glycol ethers.

[0064] Preferably, the fluid used according to the present invention contains 0.01 to 10% by weight, preferably 0.01 to 5% by weight, of an antiwear additive based on the total weight of the fluid.

[0065] The amount of the antiwear additive can be adjusted to obtain a phosphorus content in the range of 5 to 9150 ppm by weight in the fluid. Preferably, the concentration of phosphorus in the fluid used according to the present invention is in the range of 5 to 4500 ppm by weight based on the total weight of the fluid.

[0066] Base oil The fluid used according to the present invention contains one or more base oils at a concentration preferably in the range of at least 70% by weight, preferably 70 - 99% by weight, alternatively preferably 80 - 98% by weight, and preferentially 85 - 95% by weight, with respect to the fluid.

[0067] Such base oils can be selected from base oils conventionally used in the field of lubricating oils, such as synthetic or natural mineral oils, animal or vegetable oils, or mixtures thereof.

[0068] Mixtures of multiple base oils, such as mixtures of 2, 3, or 4 base oils, may be present.

[0069] The base oils of the fluid contemplated by the present invention can in particular be mineral oils or synthetic oils belonging to Groups I - V, or mixtures thereof, defined by the API classification (or its equivalent according to the ATIEL classification) and by the classes shown in Table 1 below.

Table 1

[0070] Examples of mineral base oils include any type of base oil obtained by purification operations such as atmospheric and vacuum distillation of crude oil, subsequent solvent extraction, dewaxing, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization, and hydrofinishing.

[0071] Mixtures of synthetic oils and mineral oils, which may be biosourced, can also be further used.

[0072] Regarding the use of various base oils for manufacturing the composition used according to the present invention, there are generally no restrictions, except that the composition must have properties suitable for use in the propulsion system of an electric vehicle or a hybrid vehicle, particularly properties related to viscosity, viscosity index, or oxidation resistance.

[0073] The base oil of the fluid used according to the present invention can further be selected from synthetic oils, such as certain carboxylic acid esters and alcohol esters, polyalphaolefins (PAO), and polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides containing 2 to 8 carbon atoms, particularly 2 to 4 carbon atoms.

[0074] The PAO used as the base oil is obtained, for example, from monomers containing 4 to 32 carbon atoms, such as octene or decene. The weight average molecular weight of PAO can vary quite significantly. Preferentially, the weight average molecular weight of PAO is less than 600 Da. The weight average molecular weight of PAO can further be in the range of 100 to 600 Da, 150 to 600 Da, or further 200 to 600 Da.

[0075] Advantageously, one or more base oils of the fluid used according to the present invention can be selected from Group II or III base oils.

[0076] According to an alternative embodiment, one or more base oils of the oil used according to the present invention are selected from polyalphaolefins (PAO), polyalkylene glycols (PAG), and carboxylic acid esters and alcohol ethers.

[0077] Additional additives The fluid used according to the present invention may also further contain all kinds of functional additives suitable for use in lubricants for electric vehicles, which are different from the anti-wear additives defined in the context of the present invention.

[0078] Such additives known to those skilled in the art in the field of lubrication of electric vehicles can be selected from detergents, dispersants, antioxidants, pour point depressants, anti-foaming additives, viscosity index improvers, and mixtures thereof.

[0079] Advantageously, the fluid used according to the present invention comprises at least one functional additive selected from detergents, dispersants, antioxidants, pour point depressants, defoaming additives, viscosity index improvers, and mixtures thereof.

[0080] Typically, when present, the additional functional additives (in total) account for from 1 to 30% by weight, preferably from 1.5 to 25% by weight, and preferentially from 2 to 20% by weight of the total weight of the fluid.

[0081] Such additives can be introduced separately and / or as mixtures similar to those of additives already commercially available for commercial lubricant formulations for vehicle engines having performance levels defined by ACEA (European Automobile Manufacturers' Association) and / or API (American Petroleum Institute) well known to those skilled in the art.

[0082] The fluid used according to the present invention may contain at least one antioxidant additive.

[0083] Antioxidant additives generally make it possible to retard the decomposition of the composition during use. Such decomposition can significantly result in the formation of deposits, the presence of sludge, or an increase in the viscosity of the composition.

[0084] Antioxidant additives act particularly as radical inhibitors or hydroperoxide decomposers. Commonly used antioxidant additives include phenolic antioxidants, amine-based antioxidant additives, and phosphorus-sulfur-containing antioxidant additives. Some such antioxidant additives, such as phosphorus-sulfur-containing antioxidant additives, may generate ash. Phenolic antioxidant additives may be ashless or in the form of neutral or basic metal salts. Antioxidant additives can be selected in particular from sterically hindered phenols, esters of sterically hindered phenols, and sterically hindered phenols containing thioether bridges, diphenylamine, diphenylamine substituted with at least one C1-C12 alkyl moiety, N,N'-dialkylaryldiamines, and mixtures thereof.

[0085] Preferably, according to the present invention, at least one of the carbons adjacent to the carbon atom having an alcohol functional group in the sterically hindered phenol has at least one C1-C 10 alkyl moiety, preferably a C1-C6 alkyl moiety, preferably a C4 alkyl moiety, preferably a tert-butyl moiety, and is selected from compounds containing a phenol moiety substituted thereby.

[0086] The amine compound is another class of antioxidant additives that can optionally be used in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines such as the formula NR 10 R 11 R 12 (wherein R 10 represents an aliphatic moiety, or an optionally substituted aromatic moiety, R 11 represents an optionally substituted aromatic moiety, R 12 represents a hydrogen atom, an alkyl moiety, an aryl moiety or a moiety having the formula R 13 S(O) z R 14 wherein R 13 represents an alkylene or alkenylene moiety, R 14 represents an alkyl moiety, an alkenyl moiety or an aryl moiety, and z is 0, 1 or 2) and is an aromatic amine.

[0087] Sulfur alkylphenol, or its alkali or alkaline earth metal salt, can also be further used as an antioxidant additive.

[0088] Another class of antioxidant additives is the class of copper compounds, such as copper thio- or dithio-phosphates, copper salts and carboxylates, copper dithiocarbamates, copper sulfonates, copper phenates, copper acetylacetonates. Copper salts I and II, succinates or succinic anhydrides can likewise be used.

[0089] The fluid used according to the present invention can further contain any type of antioxidant known to those skilled in the art.

[0090] Advantageously, the fluid used according to the present invention contains at least one ashless antioxidant additive.

[0091] The fluid used according to the present invention can contain from 0.5 to 2% by weight, based on the total weight of the fluid, of at least one antioxidant additive.

[0092] The fluid used according to the present invention can further contain at least one detergent additive.

[0093] Detergent additives generally reduce the formation of deposits on the surface of metal parts by dissolving oxidation and combustion by-products.

[0094] Detergent additives that can be used in the fluids used according to the present invention are generally known to those skilled in the art. The detergent additive can be an anionic compound containing a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation can be a metal cation of an alkali metal or an alkaline earth metal.

[0095] Detergent additives are preferably selected from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, and phenates. The alkali metals and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

[0096] Such metal salts generally contain the metal in stoichiometric or excess amounts, i.e., amounts greater than stoichiometric. At this time, these are overbased detergents, and the excess metal that gives the detergent additive overbased properties is generally in the form of an oil-insoluble metal salt, such as a carbonate, hydroxide, oxalate, acetate, glutamate, preferably a carbonate.

[0097] The fluid used according to the present invention can contain from 0.5 to 4% by weight of detergent additive, based on the total weight of the composition.

[0098] The fluid used according to the present invention can also contain at least one dispersant. Typically, the dispersant serves to maintain suspension and discharge insoluble solid contaminants consisting of oxidation by-products formed during the use of the fluid.

[0099] The dispersant can be selected from Mannich bases or succinimide compounds such as polyisobutylene succinimide (PIBSI).

[0100] The fluid used according to the present invention can contain, for example, 0.2 to 10% by weight of a dispersant based on the total weight of the fluid.

[0101] The fluid used according to the present invention can further contain at least one defoaming additive.

[0102] The defoaming additive can be selected from silicones.

[0103] The fluid used according to the present invention can contain 0.01 to 2% by weight or 0.01 to 5% by weight, preferably 0.1 to 1.5% by weight or 0.1 to 2% by weight of a defoaming additive based on the total weight of the fluid.

[0104] The fluid used according to the present invention can further contain at least one pour point depressant (PPD) additive.

[0105] By slowing the formation of paraffin crystals, pour point depressant additives generally improve the behavior of fluids under low temperature conditions. Examples of pour point depressant additives include alkyl polymethacrylates, polyacrylates, polyaryl amides, polyalkyl phenols, polyalkyl naphthalenes, and alkyl polystyrenes.

[0106] The fluid used according to the present invention can contain at least one additive (VI improver) for improving the viscosity index. Examples of VI improvers include polymethacrylate, polyisobutene or fatty acid esters. When present, such additives can account for 1 to 25% by weight of the total weight of the fluid.

[0107] Regarding the formulation of such fluids, anti-wear additives can be added to the oil or mixture of base oils, followed by the addition of other possible auxiliary additives.

[0108] Alternatively, anti-wear additives can be added to existing conventional lubricant formulations, especially those containing one or more base oils and one or more auxiliary additives.

[0109] Alternatively, the anti-wear additive can, if present, be combined with one or more additives, and the resulting additive "package" is added to the base oil or mixture of base oils.

[0110] Advantageously, the fluid according to the present invention has a kinematic viscosity in the range of 5 to 300 mm 2 / s, more particularly 10 to 25 mm 2 / s, when measured at 40 °C according to standard ASTM D445.

[0111] Advantageously, the fluid used according to the present invention has a kinematic viscosity in the range of 1 to 20 mm 2 / s, more particularly 2 to 15 mm 2 / s, when measured at 100 °C according to standard ASTM D445.

[0112] According to a particular embodiment, the fluid used according to the present invention is - a base oil or mixture of base oils, - one or more anti-wear agents, - optionally, one or more additional additives selected from viscosity index modifiers, detergents, dispersants, antioxidants, pour point depressants, anti-foam additives and mixtures thereof comprising or even consisting of these.

[0113] According to certain embodiments, the fluid according to the invention relative to the total weight of said fluid - one or more base oils in an amount of 70 to 99.99% by weight, - an antiwear additive in an amount of 0.01 to 10% by weight, preferably selected from phosphorus-containing antiwear additives, preferably an antiwear additive selected from phosphite polymers, - optionally, one or more functional additives in an amount of 1 to 30% by weight, preferably selected from viscosity index improvers, antioxidant additives, antifoaming additives, dispersants, detergents, viscosity modifiers, and mixtures thereof comprising or even consisting of these.

[0114] According to certain embodiments, the fluid according to the invention relative to the total weight of said fluid - one or more base oils in an amount of 70 to 99% by weight, - an antiwear additive in an amount of 0.01 to 10% by weight, preferably selected from phosphorus-containing antiwear additives, preferably an antiwear additive selected from phosphite polymers, - optionally, one or more functional additives in an amount of 1 to 30% by weight, preferably selected from viscosity index improvers, antioxidant additives, antifoaming additives, dispersants, detergents, viscosity modifiers, and mixtures thereof comprising or even consisting of these.

[0115] According to certain embodiments, the fluid used according to the invention relative to the total weight of said fluid - at least 70% by weight, preferably 70 to 99% by weight of base oil, - a phosphite polymer corresponding to formula (I) in an amount of 0.05% to 10% by weight, in particular 0.1% to 7% by weight, more particularly 1% to 5% by weight, - Optionally, 1% to 20% by weight, preferably 1.5% to 10% by weight, more particularly 2% to 5% by weight, preferably one or more functional additives selected from viscosity index improvers, detergents, anti - settling agents, antioxidants, pour point depressants, defoaming additives and mixtures thereof comprising, or even consisting of, these.

[0116] According to one embodiment, the fluid used according to the present invention contains 5 to 9150 weight ppm of phosphorus, preferably 5 to 4500 weight ppm of phosphorus, based on the total weight of the fluid.

[0117] According to one embodiment, the fluid used according to the present invention contains 5 to 4000 weight ppm of sulfur, preferably 7 to 1000 weight ppm of sulfur, or preferably 10 to 800 weight ppm of sulfur, based on the total weight of the fluid.

[0118] The present invention further relates to the use of at least one anti - wear additive for improving the heat transfer properties of a fluid containing at least one base oil.

[0119] Preferably, one or more anti - wear additives have one or more features defined in the present invention.

[0120] Preferably, the fluid has one or more properties defined in the present invention.

[0121] The present invention further relates to the use of at least one anti - wear additive in a fluid containing at least one base oil, said fluid being used for cooling the battery of an electric vehicle.

[0122] Preferably, one or more anti - wear additives have one or more features defined in the present invention.

[0123] Preferably, the fluid has one or more properties defined in the present invention.

[0124] The present invention further relates to the use of a fluid comprising at least one base oil and at least one antiwear additive for improving the thermal conductivity of the fluid, and / or for improving the heat transfer properties of the fluid, and / or for cooling the battery of an electric vehicle.

[0125] Preferably, the one or more antiwear additives have one or more features defined in the present invention.

[0126] Preferably, the fluid has one or more properties defined in the present invention.

[0127] According to another aspect of the present invention, there is further provided a method for lubricating and cooling a propulsion system of an electric vehicle, the method comprising circulating a single fluid within a lubricating and cooling system for the entire propulsion system of the electric vehicle, the fluid comprising a base oil and at least one antiwear additive.

[0128] Preferably, the one or more antiwear additives have one or more features defined in the present invention.

[0129] Preferably, the fluid has one or more properties defined in the present invention.

[0130] Typically, the propulsion system of an electric vehicle includes an electric motor, or a rotor-stator assembly of a power electronic system (for speed regulation only), a transmission (also called a reduction gear), and a battery.

[0131] According to another aspect of the present invention, there is further provided a method for improving the thermal conductivity of a fluid comprising at least one base oil, the method comprising mixing at least one antiwear additive defined in the present invention with at least one base oil, preferably the antiwear additive is selected from phosphorus-containing antiwear additives, preferably a phosphite polymer, preferably a phosphite polymer corresponding to formula (I).

[0132] Preferably, the one or more antiwear additives have one or more features defined in the present invention.

[0133] Preferably, the fluid has one or more properties defined in the present invention.

[0134] Here, the present invention will be described by the following examples, which are given by way of illustration of the present invention but are not limited thereto.

[0135] Example Example 1 In this example, an antiwear agent such as a phosphite polymer was used. It is a phosphite polymer corresponding to formula (I) described in the present invention. It contains 4.50% by weight of phosphorus, sulfur is zero, has a weight average molecular weight of about 10,000 g / mol and a number average molecular weight of about 3000 g / mol, and can be obtained, for example, by the method described in Example 2 of document WO2011 / 102861.

[0136] In this example, a Group III base oil was used. The base oil has a viscosity of 7.62 cSt at 40 °C as measured according to standard ASTM D445.

[0137] In this example, Fluid 1 contains 99% by weight of the base oil and 1% by weight of the antiwear agent, and Fluid 2 contains 95% by weight of the base oil and 5% by weight of the antiwear agent.

[0138] Table 2 summarizes the thermal conductivities of the tested compositions at 30 °C, 60 °C and 90 °C. The thermal conductivity was measured according to standard ASTM D7896-19. [Table 2]

[0139] The results in Table 2 show that the antiwear additive improves the thermal conductivity of the lubricating composition at 30 °C, 60 °C and 90 °C.

[0140] Example 2 The lubricating composition was prepared by mixing the components at a temperature of about 40 °C by a method well known to those skilled in the art. The details of the prepared and tested lubricating compositions are shown in Table 3 below.

[0141] The phosphorus and sulfur element concentrations were calculated as a function of the element concentrations in the components and are also shown in Table 3 in weight ppm.

[0142] Finally, the kinematic viscosities at 40 °C and 100 °C were determined by method ASTM D445 and are shown in Table 3.

Table 3

[0143] In the compositions of Table 3: - The base oil is a Group III base oil, - The phosphite polymer is the same as the phosphite polymer used in Example 1, - The phosphorus-containing antiwear agent is tert-butylphenyl phosphate (not corresponding to formula (I)), a commercially available antiwear additive containing 8.10 wt% phosphorus and zero sulfur, - The antioxidant is an alkylated diphenylamine antioxidant, - The corrosion inhibitor is triazine, - The detergent is a calcium overbased sulfonate detergent, - The additive package contains a pour point depressant and an antifoaming agent.

[0144] The antiwear properties of the additive having formula (I) were determined by the FZG A / 8.3 / 90 method at low load.

[0145] The lubricating compositions described in Table 3 were subjected to the FZG A / 8.3 / 90 method (in accordance with standard ISO 14635-1). The results are shown in Table 3 below.

[0146] At equal concentrations of phosphorus, the composition CI1 according to the invention has better antiwear properties than the composition CC1.

Claims

**Claim 1** Use of at least one antiwear additive for improving the thermal conductivity of a fluid comprising at least one base oil, wherein the antiwear additive is selected from a phosphorus-containing antiwear agent, a phosphorus-sulfur-containing antiwear agent, a phosphoaminated antiwear agent, a sulfur-containing antiwear agent, a boron-containing antiwear agent, and mixtures thereof. **Claim 2** Use of at least one antiwear additive according to claim 1 for improving the heat transfer properties of the fluid. **Claim 3** Use of at least one antiwear additive according to claim 1 or 2, wherein the fluid is used for cooling a battery of an electric vehicle. **Claim 4** Use of at least one antiwear additive according to any one of claims 1 to 3 for preparing a single fluid for lubricating and cooling a propulsion system of an electric vehicle. **Claim 5** Use of at least one antiwear additive according to any one of claims 1 to 4, wherein the antiwear additive is selected from a phosphorus-containing antiwear agent, a phosphorus-sulfur-containing antiwear agent, a phosphoaminated antiwear agent, and mixtures thereof, preferably a phosphorus-containing antiwear agent. **Claim 6** The antiwear additive is a phosphite polymer, preferably of formula (I): 【Chemical 1】 (wherein, -R １ , R ２ , R ３ and R ４ Each of them may be independently selected from C1-C20 alkyl, C3-C22 alkenyl, C6-C40 cycloalkyl, C7-C40 cycloalkenyl, C1-20 methoxyalkyl glycol ether and the moiety Y-OH, -Y is selected from the group consisting of C2-C40 alkylene, C2-C40 alkyl lactone, -R ７ -N(R ８ )-R ９ , where R ７ , R ８ and R ９ are, independently of one another, selected from hydrogen, C1-C20 alkyl, C3-C22 alkenyl, C6-C40 cycloalkyl, C7-C40 cycloalkenyl, C1-20 methoxyalkyl glycol ether -m is an integer from 2 to 100, -n is an integer from 1 to 1000) Use of at least one antiwear additive according to any one of claims 1 to 5, which is a phosphite polymer corresponding to the formula. **Claim 7** Use of at least one antiwear additive according to claim 6, wherein the phosphite polymer, preferably the phosphite polymer corresponding to formula (I), has a weight average molecular weight of less than 30,000 g / mol, preferably in the range of 5000 to 20,000 g / mol. **Claim 8** Use of at least one antiwear additive according to any one of claims 1 to 7, wherein the antiwear additive accounts for 0.01 to 10% by weight of the total weight of the fluid. **Claim 9** Use of at least one antiwear additive according to any one of claims 1 to 8, wherein the antiwear additive contains 5 to 9150 ppm by weight of phosphorus, preferably 5 to 4500 ppm by weight of phosphorus, based on the total weight of the fluid. **Claim 10** Use of at least one antiwear additive according to any one of claims 1 to 9, wherein the fluid contains at least 70% by weight, preferably at least 80% by weight, more preferably at least 85% by weight of base oil(s) based on the total weight of the fluid.

11. wherein the fluid comprises, based on the total weight of the fluid - 70 to 99.99% by weight of one or more base oils, and - 0.01 to 10% by weight of an antiwear additive(s), preferably selected from phosphorus-containing antiwear additives, more preferably an antiwear additive(s) selected from phosphite polymers, and - optionally, 1 to 30% by weight of one or more functional additives, preferably selected from viscosity index improvers, antioxidant additives, antifoaming additives, dispersants, detergents, viscosity modifying additives, and mixtures thereof Use of at least one antiwear additive according to any one of claims 1 to 10.

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