Aqueous composition for the lubrication and / or cooling of a propulsion system of an electric or hybrid vehicle

Abstract

Aqueous composition for the lubrication and / or cooling of a propulsion system of an electric or hybrid vehicle. This application relates to the use, for cooling and / or lubricating a propulsion system of an electric or hybrid vehicle, of an aqueous lubricating composition comprising at least: water and a polyalkylene glycol; said aqueous lubricating composition comprising a phosphate ester salt content strictly less than 0.1% by mass, relative to the total mass of said composition. It also relates to the use of such an aqueous lubricating composition to reduce pitting due to mechanical fatigue of the mechanical part(s) of an electric or hybrid vehicle propulsion system in contact with said composition.Finally, it concerns an aqueous lubricating composition for the lubrication and / or cooling of an electric or hybrid propulsion system, comprising: at least 45% water by mass, relative to the total mass of the composition, and a polyalkylene glycol; said composition comprising a phosphate ester salt(s) content strictly less than 0.1% by mass, relative to the total mass of said composition. Figure for the abstract: None.

Description

Title of the invention: Aqueous composition for the lubrication and / or cooling of a propulsion system of an electric or hybrid vehicle technical field

[0001] The present invention relates to the field of lubricating compositions intended for a propulsion system of an electric or hybrid vehicle. More particularly, it aims to provide a water-based lubricating composition with both lubricating and cooling properties for the various components of a propulsion system of an electric or hybrid vehicle, such as the transmission, the motor, and the battery. Previous technique

[0002] The evolution of international standards for the reduction of CO2 emissions, but also for the reduction of energy consumption, is pushing 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 or hybrid vehicles by a number of automotive companies.

[0004] For the purposes of this invention, "electric vehicle" means a vehicle comprising an electric motor as the sole means of propulsion, and "hybrid vehicle" means a vehicle comprising a combustion engine and an electric motor as combined means of propulsion.

[0005] For the purposes of this invention, "propulsion system" means a system comprising the mechanical parts necessary for the propulsion of an electric vehicle. The propulsion system thus includes, more specifically, an electric motor, the rotor-stator assembly of the power electronics (dedicated to speed regulation), a transmission, and a battery.

[0006] In general, it is necessary to implement, in electric or hybrid vehicles, compositions to meet the dual constraint of lubrication and cooling of the various parts of the propulsion system mentioned above.

[0007] On the one hand, lubricating compositions, also called "lubricants," are commonly used in engines to reduce friction between the various moving metal parts within the engines, and thus protect the parts against wear. In addition to wear phenomena, friction can oppose the relative movement of the parts in contact and induce energy losses detrimental to optimal operation of the propulsion system.

[0008] To achieve this, a lubricating composition is classically 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 friction modifier additives.

[0009] On the other hand, electric propulsion systems generate heat during operation via the electric motor, power electronics, and batteries. Since the amount of heat generated exceeds the amount of heat normally dissipated to the environment, it is necessary to ensure cooling of the motor, power electronics, and batteries. Generally, cooling is carried out on several parts of the propulsion system that generate heat and / or on heat-sensitive parts of the system, in order to prevent dangerous temperatures from reaching the required levels, particularly for the power electronics and batteries. This cooling is typically provided by a coolant, separate from the hydrocarbon lubricant, such as air, an aqueous fluid like water, or a mixture of water and glycol.

[0010] For obvious reasons of economy and ease of implementation, it would be advantageous to have a composition that simultaneously meets the lubrication and cooling needs of a propulsion system of an electric or hybrid vehicle.

[0011] The most common lubricants are hydrocarbon-based lubricants. However, these hydrocarbon oils generally do not provide sufficient heat dissipation to allow their combined use as coolants.

[0012] More recently, and in response to a growing expectation to move away from the use of toxic solvents and to reduce the impact of products on the environment, studies have focused on the development of water-based lubricants.

[0013] While water is an excellent coolant, it does not possess the tribological properties required for a lubricant, particularly in terms of friction reduction and wear protection. Additive systems have therefore been proposed to provide aqueous fluids with satisfactory lubrication performance.

[0014] For example, an aqueous lubricating composition comprising a polyalkylene glycol, an antifreeze compound and a phosphorus compound was described in application WO 2021 / 259853.

[0015] However, this aqueous lubricant does not provide complete satisfaction, particularly with regard to the phenomenon of pitting due to mechanical fatigue. (Anglo-Saxon) that it is likely to cause. Indeed, it has been observed that this lubricating composition can generate this type of failure in mechanical contacts, particularly depending on the formulation protocol of the composition. Description of the invention

[0016] The present invention aims precisely to propose a new aqueous-based composition, exhibiting tribological and cooling properties, suitable for its implementation for the lubrication and / or cooling of an electric or hybrid vehicle propulsion system, while reducing, or even eliminating, pitting phenomena due to mechanical fatigue.

[0017] More particularly, the present invention relates, according to a first of its aspects, to the use, for cooling and / or lubricating a propulsion system of an electric or hybrid vehicle, in particular an electric vehicle, of an aqueous lubricating composition comprising at least: - water, preferably deionized water; and - at least one polyalkylene glycol; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of said composition.

[0018] Preferably, an aqueous lubricating composition according to the invention comprises less than 0.05% by mass, in particular less than 0.01% by mass, of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, or even is totally free of phosphate ester salts.

[0019] Advantageously, the aqueous lubricating composition according to the invention comprises less than 0.1% by mass of sulfur fatty acid(s), preferably less than 0.01% by mass, in particular is totally free of sulfur fatty acid.

[0020] For the purposes of this invention, "aqueous composition" means a composition comprising water as the base fluid, in other words, as the major solvent. Water, preferably deionized, advantageously represents more than 35% by mass, in particular more than 40% by mass, and especially more than 50% by mass, of the total mass of the lubricating composition.

[0021] In the following text, the term "aqueous lubricating composition" or "aqueous lubricant" will refer to a lubricating composition required according to the invention as defined above and detailed in the following text. Due to its cooling properties, such a composition may also be referred to as an "aqueous cooling composition" or simply an "aqueous cooling composition."

[0022] Advantageously, a lubricating composition implemented according to the invention, consisting mainly of water, presents little toxicological impact, particularly for the people implementing this lubricant.

[0023] Moreover, even though water is the major solvent, a composition according to the invention exhibits good lubrication properties.

[0024] Thus, an aqueous lubricating composition according to the invention advantageously combines good cooling properties due to the presence of water, and good tribological properties, in particular friction reduction and wear resistance. Therefore, an aqueous composition according to the invention can perform the dual function of lubrication and cooling of the powertrain system of an electric or hybrid vehicle, in particular the electric motor, power electronics, transmission, and / or battery of an electric or hybrid vehicle.

[0025] The invention thus relates, according to another of its aspects, to a method of lubrication and / or cooling of a propulsion system of an electric or hybrid vehicle comprising at least one step of bringing at least one mechanical part of said propulsion system into contact with an aqueous lubricating composition as defined above.

[0026] Thus, an aqueous composition according to the invention advantageously makes it possible to avoid the use of two separate fluids, on the one hand a cooling fluid, on the other, a lubricating fluid.

[0027] In particular, an aqueous lubricating composition according to the invention makes it possible to ensure efficient cooling of the motor, power electronics and battery, as well as lubrication of the electric motor, transmission, in particular the reducer, in an electric or hybrid vehicle.

[0028] In particular, an aqueous lubricating composition according to the invention can be used to lubricate and / or cool the reducer and / or the motor and / or the power electronics of an electric vehicle.

[0029] Also, as illustrated in the examples that follow, the inventors have discovered that an aqueous lubricant according to the invention as described above, in particular in which the content of phosphate ester salt(s), if present, remains strictly less than 0.1% by mass, makes it possible to reduce, or even eliminate, the phenomena known as pitting by mechanical fatigue (or “pitting” in Anglo-Saxon terminology).

[0030] An aqueous lubricating composition according to the invention is thus found to be suitable for use in the lubrication and / or cooling of propulsion systems of electric or hybrid vehicles, but also for reducing pitting due to mechanical fatigue in these systems.

[0031] This application therefore relates to the use of an aqueous lubricating composition intended to lubricate and / or cool a propulsion system of an electric or hybrid vehicle, comprising at least: - water, preferably deionized water; and - at least one polyalkylene glycol; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, to reduce pitting by mechanical fatigue of the mechanical part(s) of said propulsion system in contact with said composition.

[0032] The invention further relates, according to another aspect, to an aqueous lubricating composition for the lubrication and / or cooling of an electric or hybrid propulsion system, comprising at least: - at least 45% by mass of water, in particular at least 50% by mass of water, preferably deionized water, relative to the total mass of the composition; and - at least one polyalkylene glycol; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition.

[0033] Furthermore, an aqueous lubricant composition according to the invention advantageously allows for an effective reduction in fuel consumption through its impact on the friction forces generated between the various components of hybrid vehicles. In particular, an aqueous lubricant composition proves especially advantageous for reducing friction in gearboxes, axle differentials, and / or cylinder heads. By thus reducing friction between moving parts in the vehicle's propulsion system, a lubricant composition according to the invention not only reduces wear but also limits energy losses responsible for excessive fuel consumption.

[0034] An aqueous lubricating composition according to the invention thus advantageously presents good properties in terms of reducing the fuel consumption of hybrid vehicles, also known as "Fuel Eco" properties.

[0035] The invention thus relates, according to another aspect, to the use of an aqueous lubricating composition according to the invention to reduce the fuel consumption of an internal combustion engine of a hybrid vehicle lubricated by means of this composition, or of a hybrid vehicle equipped with a transmission, in particular a bridge or gearbox, said transmission being lubricated by means of this composition.

[0036] Other features, variations and advantages of an aqueous lubricating composition according to the invention and of its implementation for lubricating and / or cooling a propulsion system of an electric or hybrid vehicle will become clearer from the following description and examples, given by way of illustration and not limitation of the invention.

[0037] The expressions "between ... and ...", "ranging from ... to ...", "made up of ... to ...", and "varying from ... to ...", must be understood inclusive of limits, unless otherwise stated.

[0038] In the description and examples, unless otherwise stated, percentages are weight percentages. Therefore, percentages are expressed as a percentage of the total mass of the composition. Temperature is expressed in degrees Celsius unless otherwise stated, and pressure is atmospheric pressure unless otherwise stated. Brief description of the drawings

[0039] [Fig-1] schematically represents a vehicle propulsion system electric or hybrid. Detailed description AQUEOUS COMPOSITION

[0040] As mentioned previously, an aqueous lubricating composition implemented according to the invention, also called an aqueous lubricant, is a formulation comprising water as the major solvent.

[0041] For the purposes of the invention, "major solvent" means that water is present in a greater quantity than any other solvent that may be present in the composition. Preferably, an aqueous lubricating composition according to the invention comprises at least 20% by mass of water, in particular deionized water, preferably at least 30% by mass, in particular between 35% and 90% by mass, more preferably between 40% and 75% by mass, in particular between 40% and 60% by mass, relative to the total mass of the composition.

[0042] According to one embodiment, an aqueous lubricating composition according to the invention comprises at least 45% by mass, in particular at least 50% by mass of water, in particular deionized water, preferably between 50% and 90% by mass, more preferably between 50% and 75% by mass of water, in particular between 50% and 60% by mass of water, relative to the total mass of the composition.

[0043] Advantageously, in addition to its role as a solvent, water allows access to a lubricating composition exhibiting good cooling properties, and which can can be implemented as a cooling fluid for the various components in an electric or hybrid vehicle propulsion system.

[0044] For the purposes of this invention, "cooling fluid" means a fluid capable of dissipating the heat generated by the propulsion system of an electric or hybrid vehicle. More specifically, such a fluid is characterized by an increased heat absorption capacity upon contact with a heating part.

[0045] According to a particular embodiment, the water used in an aqueous lubricating composition required according to the invention is demineralized or osmosis water, in particular deionized water.

[0046] For the purposes of this invention, "osmosis water" means water that has undergone purification, particularly by a reverse osmosis process, to reduce the content of organic and / or mineral compounds, for example, to less than 5.0% by weight, preferably less than 1.0% by weight. In the following text, the expressions "demineralized water" or "ultrapure water" will be considered equivalent or synonymous with "osmosis water." In particular, osmosis water may be "deionized water," that is, water that has undergone purification to reduce the content of ions, such as the Ca2+ and HCO3 ions generally present in water. Preferably, deionized water does not contain any ions.

[0047] The implementation of deionized water is therefore particularly advantageous in the context of the use of the aqueous lubricant according to the invention for the components of the propulsion system of an electric or hybrid vehicle requiring a fluid that conducts little, or no, electricity, such as for example the electric motor or the battery.

[0048] An aqueous lubricating composition implemented according to the invention differs from lubricants conventionally used in vehicle propulsion systems, which comprise a majority proportion of one or more base oils not soluble in water.

[0049] The term "water-insoluble oil" includes, in particular, an oil that does not substantially dissolve in water at room temperature (approximately 25°C). In particular, a water-insoluble oil has a solubility in water of less than 0.2 g / L at room temperature.

[0050] This includes lubricating base oils belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) and their mixtures.

[0051] Preferably, an aqueous lubricating composition implemented according to the present invention comprises less than 5% by mass of base oil(s) insoluble in water, preferably less than 2% by mass, more preferably less than 1% by mass, relative to the total mass of the composition.

[0052] Advantageously, an aqueous lubricating composition implemented according to the invention is totally free of water-insoluble oil. POLYALKYLENE GLYCOL

[0053] As previously stated, an aqueous lubricating composition implemented according to the invention comprises at least one polyalkylene glycol.

[0054] Polyalkylene glycols (denoted "PAG") are selected from water-soluble polyalkylene glycols.

[0055] By "water soluble" is meant a polyalkylene glycol having a solubility in water of at least 10 g / L, preferably of at least 500 g / L, in water at room temperature (about 25 °C).

[0056] Polyalkylene glycols can more particularly be formed of alkylene oxide units in C1-C4, preferably in Ci-C3, more particularly in C2-C3.

[0057] Advantageously, a polyalkylene glycol used in an aqueous lubricating composition required according to the invention comprises at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass of propylene oxide and / or ethylene oxide units. It may be a copolymer, possibly random, of ethylene oxide / propylene oxide.

[0058] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a weight average molecular mass (Mw) between 100 and 50,000 g.mol1, preferably between 5,000 and 25,000 g.mol1.

[0059] The average molecular mass by weight can be measured by gel permeation chromatography (GPC).

[0060] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a kinematic viscosity measured at 100 °C (KV100), according to ASTM D445, of between 100 and 25,000 mm2 / s, in particular between 150 and 10,000 mm2 / s.

[0061] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a kinematic viscosity measured at 40 °C (KV40), according to ASTM D445, of between 500 and 100,000 mm2 / s, more particularly between 1,000 and 95,000 mm2 / s.

[0062] The flash point of a polyalkylene glycol used in an aqueous lubricating composition according to the invention is preferably greater than or equal to 160 °C, in particular greater than or equal to 220 °C. The flash point can be measured according to ISO 2592 or ASTM D92.

[0063] Preferably, a polyalkylene glycol used in an aqueous lubricating composition according to the invention has a viscosity index measured according to ASTM D2270, between 100 and 800, preferably between 250 and 550.

[0064] In particular, the polyalkylene glycol compound(s) may be used in an aqueous lubricant composition required according to the invention in a content of at least 5.0% by mass, preferably between 5.0% and 50% by mass, more preferably between 10% and 40% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

[0065] Preferably, an aqueous lubricating composition implemented according to the invention comprises less than 17% of polyalkylene glycol compound(s), more preferably between 10% and 15% by mass of polyalkylene glycol compound(s).

[0066] It is understood that an aqueous lubricating composition implemented according to the invention may comprise a single polyalkylene glycol or a mixture of several different polyalkylene glycols.

[0067] In particular, an aqueous lubricating composition according to the invention may comprise a mixture of at least two distinct polyalkylene glycols, more particularly of at least one polyalkylene glycol of low average molecular weight and at least one polyalkylene glycol of high average molecular weight.

[0068] It is within the general competence of a person skilled in the art to adjust the nature and content of low and high average molecular weight polyalkylene glycols in the polyalkylene glycol mixture, particularly with regard to the viscosity targeted for the final lubricating composition.

[0069] The combination of at least one polyalkylene glycol with a low average molecular weight and at least one polyalkylene glycol with a high average molecular weight is particularly advantageous in order to obtain good solubilization of the different compounds introduced into the aqueous lubricating composition.

[0070] According to one embodiment, it is possible to implement, alternatively to or jointly with polyalkylene glycol(s), one or more vinylpyrrolidone polymer(s).

[0071] By "polymer", we mean, in a broad sense, both homopolymers of vinylpyrrolidone, and copolymers formed from vinylpyrrolidone and one or more other monomers.

[0072] Thus, more generally, an aqueous lubricating composition implemented according to the invention may comprise one or more vinylpyrrolidone polymer(s), in particular chosen from polyvinylpyrrolidones (denoted PVPs).

[0073] Polyvinylpyrrolidones correspond more particularly to the following formula:

[0074] [Chem.l]

[0075] in which n represents the average number of constituent units of the polymer.

[0076] Such compounds can be synthesized by any method known to those skilled in the art, in particular by polymerization of A-vinylpyrrolidone, and may also be commercially available.

[0077] Polyvinylpyrrolidones more particularly suitable for the invention have a weight average molecular mass (Mw) of between 20,000 and 50,000 g.mol1, preferably between 25,000 and 45,000 g.mol1.

[0078] In particular, the vinylpyrrolidone polymer(s), in particular selected from polyvinylpyrrolidones, may be present in an aqueous lubricating composition according to the invention in a content of at least 5.0% by mass, preferably between 5.0% and 50% by mass, more preferably between 10% and 40% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition. ADDITIVES Phosphorus compounds

[0079] As previously stated, the content of phosphorus compound(s) of the type phosphate ester salts, if present, in an aqueous lubricating composition implemented according to the invention, is strictly less than 0.1% by mass, relative to the total mass of the composition.

[0080] Generally speaking, a "phosphorus compound" within the meaning of the present invention is understood to mean a compound comprising at least one phosphorus atom. Preferably, such phosphorus compounds do not contain sulfur.

[0081] The said phosphorus compound(s) can be used in aqueous compositions in a form that is soluble or emulsifiable in water, in particular in the form of ionic salts.

[0082] Examples of phosphate ester salts include alkyl, alkenyl or aryl phosphate ester salts, in particular alkyl or dialkyl phosphate esters in Ci-C8. These salts are found in particular in the form of phosphate ions neutralized by a suitable counter-ion.

[0083] The salts may be salts of alkali or alkaline earth metals, ammonium, alkanolamines, in particular C2-C8, or alkaneamines, in particular C2-C8, of phosphate esters.

[0084] Advantageously, the phosphate ester salt(s) are alkali metal salts of phosphate esters.

[0085] When the aqueous lubricating composition according to the invention comprises one or more phosphate ester salts, for example as described above, these are implemented in a content strictly less than 0.1% by mass, relative to the total mass of said composition.

[0086] Advantageously, an aqueous lubricating composition implemented according to the invention comprises less than 0.05% by mass of phosphate ester salt(s), in other words comprises a phosphate ester salt(s) content ranging from 0.0% to 0.05% by mass, in particular less than 0.01% by mass and more particularly less than 0.001% by mass, relative to the total mass of the composition.

[0087] According to a particularly preferred embodiment, an aqueous lubricating composition implemented according to the invention is totally free of phosphate ester salts.

[0088] An aqueous lubricating composition implemented according to the invention may include one or more other phosphorus compounds distinct from phosphate ester salts, referred to as "additional phosphorus compound(s)".

[0089] Examples of accessory phosphorus compounds may be cited: amine phosphates; polyphosphates; phosphonates such as phosphonate esters, in particular alkyl, alkenyl or aryl phosphonates; polyphosphonates; carbamyl phosphates; phosphinates; and mixtures thereof.

[0090] These can be in the form of salts, in particular in the form of phosphonate or phosphinate ions neutralized by a suitable counter-ion.

[0091] The salts may be salts of alkali or alkaline earth metals, ammonium, alkanolamines, in particular C2-C8, or alkaneamines, in particular C2-C8, phosphonate or phosphinate.

[0092] When the aqueous lubricating composition according to the invention comprises one or more accessory phosphorus compound(s), for example as described above, these can be implemented in a content ranging from 0.01% to 5.0% by mass, in particular ranging from 0.1% to 3.0% by mass, relative to the total mass of the composition.

[0093] According to one embodiment, when the aqueous lubricating composition according to the invention comprises one or more accessory phosphorus compound(s), in particular as described above, these are implemented in a content strictly less than 0.1% by mass, relative to the total mass of said composition.

[0094] Advantageously, the overall content of phosphorus compound(s), including phosphate ester salts or any other accessory phosphorus compound, may be strictly less than 0.1% by mass, relative to the total mass of said composition, in particular less than 0.05% by mass.

[0095] In other words, an aqueous lubricating composition implemented according to the invention preferably comprises a content of phosphorus compound(s) strictly less than 0.1% by mass, in particular ranging from 0.0% to 0.05% by mass, in particular less than 0.01% by mass and more particularly less than 0.001% by mass, relative to the total mass of the composition.

[0096] According to a particularly preferred embodiment, an aqueous lubricating composition implemented according to the invention is totally free of phosphorus compound.

[0097] According to a particular embodiment, an aqueous lubricating composition required according to the invention may comprise a phosphorus content less than or equal to 0.05% by mass, in particular less than or equal to 0.02% by mass, and more particularly less than or equal to 0.01% by mass. The phosphorus content may be measured by ICP (Inductively Coupled Plasma). Advantageously, an aqueous lubricating composition required according to the invention is completely free of phosphorus. Antifreeze compound

[0098] An aqueous lubricating composition implemented according to the invention may comprise at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof.

[0099] Thus, according to a preferred embodiment, an aqueous lubricating composition implemented according to the invention comprises at least: - water, preferably deionized water; - at least one polyalkylene glycol; and - at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free of phosphate ester salts.

[0100] These compounds are known for their antifreeze action, in other words for reducing the freezing temperature of the composition.

[0101] Glycols are diols in which the two hydroxyl groups are borne by different carbon atoms, preferably by vicinal carbon atoms.

[0102] Preferably, the glycols are alkylene glycols, in particular having from 2 to 10 carbon atoms, in particular from 2 to 6 carbon atoms. Examples include monoethylene glycol, diethylene glycol and propylene glycol.

[0103] The antifreeze compound can further be selected from glycerol, diglycerol, triglycerol and mixtures thereof.

[0104] Preferably, the antifreeze compound used according to the invention is selected from monoethylene glycol, diethylene glycol, propylene glycol, glycerol, and mixtures thereof. Preferably, the antifreeze compound is diethylene glycol.

[0105] In particular, the said antifreeze compound(s), in particular as defined above, for example diethylene glycol, can be used in an aqueous lubricating composition according to the invention in a content of at least 1.0% by mass, preferably between 5.0% and 50% by mass, more preferably between 10% and 45% by mass, in particular between 20% and 40% by mass, relative to the total mass of the composition.

[0106] Preferably, an aqueous lubricating composition implemented according to the invention comprises a content of antifreeze compound(s), in particular as defined above, for example diethylene glycol, greater than or equal to 33%, in particular between 33.5% and 40% by mass, relative to the total mass of said composition.

[0107] According to a particular embodiment, an aqueous lubricating composition implemented according to the invention comprises at least: - at least 35% by mass of water, in particular deionized water, preferably 40 to 60% by mass of water; in particular 45 to 60% by mass of water; - at least 10% by mass, in particular between 10 and 20% by mass, of at least one polyalkylene glycol, in particular as defined above; - at least 5.0% by mass, in particular between 20 and 40% by mass, of at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof, said antifreeze compound preferably being diethylene glycol.

[0108] According to a particular embodiment, the assembly consisting of water, said polyalkylene glycol(s), and optionally said antifreeze compound(s) represent more than 90% of the total mass of said aqueous lubricating composition, in particular more than 95%, notably more than 96%, or even more than 97%, of the total mass of said aqueous lubricating composition. Other additives

[0109] An aqueous lubricating composition according to the invention may further comprise various additives.

[0110] It is understood that the said additive(s) are compatible with their use in an aqueous medium. Advantageously, the additives are used in a form that is soluble or emulsifiable in water, for example in the form of salts or ionic liquids.

[0111] The said additive(s) are of course chosen with regard to the intended application for the aqueous lubricant.

[0112] Of course, a person skilled in the art will take care to choose any additives and / or their quantity in such a way that the advantageous properties of the aqueous lubricating composition according to the invention, in particular the properties in terms of reducing pitting by mechanical fatigue, and cooling, are not altered by the envisaged addition.

[0113] Such additives may be more particularly selected from antifoaming agents, biocides, pH regulators, corrosion inhibitors, anti-wear and / or extreme-pressure additives, sequestering agents, metal passivating agents, colorants, dispersants, emulsifying agents, and mixtures thereof.

[0114] Advantageously, an aqueous lubricating composition according to the invention may include one or more additives selected from antifoaming agents, extreme-pressure agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, and mixtures thereof.

[0115] An aqueous lubricating composition according to the invention may more particularly comprise from 0.1 to 10% mass of additives, in particular from 1.0 to 8.0% mass of additives, relative to the total mass of the composition. pH regulator

[0116] An aqueous lubricating composition according to the invention may include at least one pH-regulating additive, in particular an alkaline buffer. The pH regulator makes it possible to maintain the desired pH of the lubricating composition, in particular to preserve an alkaline pH, advantageously between 8 and 15.

[0117] The said pH regulator(s), by ensuring that the pH of the aqueous lubricating composition is maintained between 8 and 15, makes it possible in particular to prevent corrosion of the metal surfaces, but also to promote the solubilization of the different compounds in the lubricating composition, in particular of the polyalkylene glycol(s), in particular as defined above.

[0118] The pH regulator can be chosen from the amine family, in particular alkanolamines and amino alcohols.

[0119] This may include, in particular, a pH-regulating additive selected from alkanolamines, such as dimethylethanolamine (DMEA), ethanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), isopropanolamines, such as monoisopropanolamine (MIPA), diisopropanolamine (DIPA) and triisopropanolamine (TIPA); diglycolamine (DGA); ethylene amines, such as ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA) and tetraethylene pentamine (TEPA); cyclamines, such as cyclohexylamine; 2-amino-2-ethyl-1,3-propanediol; 2-amino-2-methyl-1-propanol; and mixtures thereof.

[0120] An aqueous lubricating composition according to the invention may in particular comprise from 0.1% to 10% by mass of pH regulating additive(s), preferably from 0.5% to 5% by mass, relative to the total mass of the composition.

[0121] Advantageously, an aqueous lubricating composition implemented according to the invention comprises at least one pH-regulating additive for maintaining the pH of said lubricating composition between 8 and 15, in particular between 8.5 and 14, more particularly between 9 and 13, said pH-regulating additive being selected in particular from alkanolamines, preferably ethanolamines, and more particularly from dimethylethanolamine (DMEA), triethanolamine (TEA) and mixtures thereof

[0122] Thus, in a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - at least one pH regulating additive to maintain the pH of said lubricating composition between 8 and 15, in particular selected from alkanolamines, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free of phosphate ester salts. Corrosion inhibitor

[0123] An aqueous lubricating composition according to the invention may comprise at least one corrosion inhibitor. Corrosion inhibitors advantageously reduce or even prevent corrosion of metal parts. The nature of said corrosion inhibitor(s) may be chosen according to the metal to be protected against corrosion, such as aluminum, steel, galvanized steel, or yellow metals, for example copper or brass.

[0124] Among the inorganic corrosion inhibitors may be cited nitrites, sulfites, silicates, borates, sodium, potassium, calcium or magnesium phosphates, alkali metal phosphates, hydroxides, molybdates, zinc, magnesium or nickel sulfates.

[0125] Among the organic corrosion inhibitors, alkanolamines such as triethanolamine, monocarboxylic aliphatic acids, in particular those having 4 to 15 carbon atoms, for example octanoic acid, and other acids may be mentioned. Dicarboxylic aliphatic acids having 4 to 15 carbon atoms, for example decanedioic acid, undecanedioic acid, dodecanedioic acid or mixtures thereof; polycarboxylic acids possibly neutralized by triethanolamine, such as 1,3,5-triazine-2,4,6-tri-(6-aminocaproic acid); alkanoylamidocarboxylic acids, in particular isononanoylamidocaproic acid, and mixtures thereof. Borated amides, products of the reaction of amines or amino alcohols with boric acid, may also be used.

[0126] Preferably, the corrosion inhibitor(s) are separate from the pH regulating additive(s), in particular allowing the pH of the lubricating composition to be maintained between 8 and 15, and defined previously.

[0127] An aqueous lubricating composition according to the invention may in particular comprise from 0.1% to 5% by mass of corrosion inhibitor(s), in particular as defined above, preferably from 0.5% to 4% by mass, more preferably from 1% to 2.5% by mass, relative to the total mass of the composition.

[0128] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - at least one corrosion inhibitor, in particular selected from organic corrosion inhibitors, more particularly from monocarboxylic aliphatic acids, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free from phosphate ester salts. Anti-wear / extreme-pressure additive

[0129] An aqueous lubricating composition according to the invention may include at least one anti-wear and / or extreme-pressure additive. Their function is to reduce wear and the coefficient of friction, or to prevent metal-to-metal contact by forming a protective film adsorbed onto these surfaces.

[0130] There is a wide variety of anti-wear additives, among which can be cited those chosen from among the phosphosulfur additives such as metallic alkylthiophosphates or their salts.

[0131] Additives that do not provide phosphorus are preferred, such as, for example, polysulfides, in particular sulfur olefins.

[0132] According to a particular embodiment, an aqueous lubricating composition implemented according to the invention may comprise at least one extreme-pressure additive selected from sulfur fatty acids and dimercaptothiadiazoles, preferably implemented in their neutralized form, in particular by inorganic alkalizing agents or alkanolamines, emulsifiable or soluble in water.

[0133] Advantageously, an aqueous lubricating composition implemented according to the invention comprises less than 0.1% by mass of an extreme-pressure additive of the sulfur fatty acid type, in particular in a neutralized form, preferably less than 0.01% by mass, more particularly less than 0.001% by mass, relative to the total mass of the composition, or is even totally free of extreme-pressure additive of the sulfur fatty acid type.

[0134] Sulphur fatty acids may comprise from 8 to 22 carbon atoms, in particular from 12 to 18 carbon atoms.

[0135] The amount of sulfur according to ASTM D2622 provided by the said sulfur fatty acid(s) may be between 5% and 30% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

[0136] Preferably, the amount of active sulfur at 150°C according to ASTM D 1662 provided by said sulfur fatty acid(s) in the aqueous lubricating composition according to the invention is less than or equal to 2% by mass, in particular less than or equal to 1% by mass, more particularly less than 0.1% by mass, relative to the total mass of the lubricating composition.

[0137] For the purposes of this invention, "active sulfur" means the sulfur that a chemical compound is capable of donating or releasing when that compound is placed under the conditions of ASTM D-1662. ASTM D-1662 defines the active sulfur content of a compound at a given temperature as the difference, expressed as a percentage by weight, in sulfur content before and after reacting a sample of that sulfur compound with a given amount of copper for a fixed time.

[0138] As mentioned previously, the sulfur-containing fatty acid(s) are generally used in an aqueous lubricating composition in their form neutralized by an alkalizing agent, such as sodium hydroxide, potassium hydroxide, or an alkanolamine, such as monoethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine and triisopropanolamine.

[0139] A water-based lubricating composition required according to the invention may comprise between 0.01% and 10% by mass of anti-wear and / or extreme-pressure additive(s), preferably between 0.2% and 5% by mass, relative to the total mass of the composition. Anti-foam

[0140] An aqueous lubricating composition according to the invention may include at least one antifoaming additive. Antifoaming agents prevent foaming of the lubricating fluid.

[0141] This could be, for example, an antifoaming agent based on polysiloxanes or acrylate polymers. Preferably, the antifoaming agent is chosen from among three-dimensional siloxanes.

[0142] Also, antifoaming agents can be polar polymers such as polymethylsiloxanes or polyacrylates.

[0143] In particular, an aqueous lubricating composition according to the invention may comprise from 0.001% to 3.0% by mass of antifoaming additive(s), preferably from 0.005% to 1.5% by mass, more preferably from 0.01% to 1.0% by mass, relative to the total mass of the lubricating composition.

[0144] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - at least one antifoaming additive, in particular selected from three-dimensional siloxanes, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, in relation to the total mass of the composition, preferably being free of phosphate ester salts. Metal passivating agents

[0145] An aqueous lubricating composition according to the invention may include at least one metal passivating agent. Metal passivating agents protect metal parts by promoting the formation of metal oxide on their surface.

[0146] Metal passivating agents may, for example, be selected from triazole derivatives, such as tetrahydrobenzotriazole (THBTZ), tolyltryazole (TTZ), benzotriazole (BTZ), amines substituted with a triazole group, such as N,N-bis(2-ethylhexyl)-1,2,4-triazol-1-yl methanamine, N'-bis(2-ethylhexyl)-4-methyl-1H-benzotriazol-1-methylamine, N,N-bis(heptyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(nonyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(decyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(undecyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(dodecyl)-ar-methyl-1H-benzotriazole-1-methanamine, N,N-bis(2-ethylhexyl)-ar-methyl-1H-benzotriazole-1-methanamine, 1,2,4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles, 2-alkyldithiobenzothiazoles, 2-(N,N-dialkyldithiocarbamoyl)benzothiazoles, 2,5-bis(alkyldithio)-1,3,4-thiadiazoles, such as 2,5-bis(tert-octyldithio)-1,3,4-thiadiazole, 2,, 2,5-bis(tert-tridecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-tetradecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-pentadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-hexadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-heptadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-octadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-nonadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-eicosyldithio)-l,3,4-thiadiazole, 2,5-bis(N,N-dialkyldithiocarbamoyl)-1,3,4-thiadiazoles, 2-alkyldithio-5-mercaptothiadiazoles, and mixtures thereof.

[0147] Preferably the metal passivating agents are chosen from tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), and their salts, taken alone or in mixtures.

[0148] An aqueous lubricating composition according to the invention may in particular comprise from 0.01% to 2.0% by mass of metal passivating agent(s), preferably from 0.1% to 1.0% by mass, more preferably from 0.2% to 0.8% by mass, relative to the total mass of the composition.

[0149] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - at least one metal passivating agent, in particular chosen from triazole derivatives, more particularly chosen from tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), and their salts, taken alone or in mixtures, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular chosen alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free of phosphate ester salts. Dyes

[0150] An aqueous lubricating composition according to the invention may comprise one or more colorants. The colorants may be natural or synthetic, generally organic.

[0151] The colorants that can be used in an aqueous lubricating composition can be more particularly chosen from natural or synthetic water-soluble colorants, for example the colorants FDC Red 4, DC Red 6, DC Red 22, DC Red 28, DC Red 30, DC Red 33, DC Orange 4, DC Yellow 5, DC Yellow 6, DC Yellow 8, FDC Green 3, DC Green 5, FDC Blue 1, betanin (beetroot), xanthenes, carmine, a chlorophyllin, methylene blue, anthocyanins (enocianin, black carrot and hibiscus), caramel and riboflavin.

[0152] An aqueous lubricating composition according to the invention may comprise between 0.01% and 2.0% by mass of colorant(s), preferably between 0.01% and 1.5% by mass, plus preferably between 0.02% and 1.0% by mass, relative to the total mass of the composition.

[0153] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - at least one colorant, in particular selected from xanthenes, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free from phosphate ester salts. Emulsifying agents

[0154] An aqueous lubricating composition according to the invention may comprise one or more emulsifying agents, also called emulsifiers. Their function is to generate stable emulsions in water.

[0155] Emulsifying agents may be more particularly non-ionic, such as ethoxylated fatty alcohols, ethoxylated fatty acids, ethoxylated fatty amides; anionic, for example KOH soaps, NaOH soaps; sulfonates; cationic, such as quaternary ammonium compounds; or soluble or water-emulsifiable carboxylic acid esters.

[0156] In particular, an aqueous lubricating composition according to the invention may comprise from 0.01% to 10% by mass of emulsifying agent(s), preferably from 0.1% to 5.0% by mass, relative to the total mass of the lubricating composition. Seizuring agents

[0157] An aqueous lubricating composition according to the invention may include at least one sequestering agent. Sequestering agents, also called chelating agents, limit the encrustation of metal ions in the composition.

[0158] Examples of sequestering agents include those derived from phosphonic acids and phosphonates, such as diethylenetriaminepentamethylphosphonic acid (DTPMPA), aminotri(methylenephosphonic) acid (ATMP), hydroxyethanediphosphonic acid (HEDP), 1,1-hydroxyethylidene diphosphonate, 2-hydroxyethylaminedi(methylenephosphonic) acid (HEAMBP), diethylenetriaminopenta(methylenephosphonic) acid (DTMP), multifunctional organic acids and hydroxylated acids, such as ethylenediaminetetraacetic acid (EDTA), pteroyl-L-glutamic acid (PGLU), organic polyacids, such as maleic acid and polyaspartic acid, polysaccharides and carbohydrates, such as inulin, carboxymethylinulin and carboxymethyl ichito sane.

[0159] An aqueous lubricating composition according to the invention may comprise from 0.001% to 2.0% by mass of sequestering agent(s), preferably from 0.01% to 1.0% by mass, relative to the total mass of the composition. Biocides and fungicides

[0160] An aqueous lubricating composition according to the invention may comprise at least one biocidal and / or fungicidal agent. The biocides and fungicides may be used to improve the biological stability of the composition by limiting the proliferation of bacteria, fungi, and yeasts in the lubricating fluid.

[0161] Such biocides may be selected from parabens, aldehydes, reactive acetylacetone compounds, isothiazolinones, phenolic compounds, acid salts, halogenated compounds, quaternary ammonium compounds, certain alcohols and mixtures thereof.

[0162] Preferably, the biocides can be selected from among the benzisothiazolinones (BIT), possibly substituted, such as N-butyl-1,2-benzisothiazolin-3-one, the methylisothiazolinones (MIT), mixtures of methylisothiazolinone and chloromethylisothiazolinone (MIT / CMIT), orthophenylphenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate (IPBC), chlorocresol and N,N-methylenebismorpholine (MBM); sorbic acid; preferably from among orthophenylphenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate, chlorocresol, the benzisothiazolinones and N,N-methyleneisomorpholine.

[0163] An aqueous lubricating composition according to the invention may in particular comprise between 0.01% and 10% by mass of biocide(s) and / or fungicide(s), preferably between 0.5% and 5.0% by mass, relative to the total mass of the composition.

[0164] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; and - one or more additives selected from antifoaming agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, in particular as defined above, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free of phosphate ester salts.

[0165] In a particular embodiment, an aqueous lubricating composition required according to the invention comprises at least: - water, in particular deionized water; - at least one polyalkylene glycol, in particular as defined above; - at least one antifreeze compound selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; and - one or more additives selected from antifoaming agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, in particular as defined above, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of the composition, preferably being free of phosphate ester salts.

[0166] According to a particular embodiment, an aqueous lubricating composition implemented according to the invention comprises: - at least 35% by mass of water, in particular 40 to 60% by mass, especially at least 50% by mass of water, preferably deionized water; - from 5.0% to 50% by mass, in particular from 10% to 20% by mass, of at least one polyalkylene glycol, in particular as defined above; - possibly from 5.0% to 45%, in particular from 20% to 40% by mass, of at least one antifreeze compound, selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol; and - possibly from 0.1% to 10% by mass of one or more additives chosen from antifoaming agents, extreme-pressure agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, emulsifying agents, sequestering agents, and mixtures thereof, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular chosen from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, preferably being free from phosphate ester salts; the contents being expressed relative to the total mass of the lubricating composition.

[0167] In particular, an aqueous lubricating composition implemented according to the invention may consist of: - from 5.0% to 50% by mass, in particular from 10% to 20% by mass, of at least one polyalkylene glycol, in particular as defined above; - possibly from 5.0% to 45%, in particular from 20% to 40% by mass, of at least one antifreeze compound, selected from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol; and - possibly from 0.1% to 10% by mass of one or more additives chosen from antifoaming agents, extreme-pressure agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, emulsifying agents, sequestering agents, and mixtures thereof, said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular chosen from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, in particular being free from phosphate ester salts; the contents being expressed in relation to the total mass of the lubricating composition, the remainder being made up of water, preferably deionized water.

[0168] It is understood that the various particular embodiments described above can be combined, as far as possible, to define other particular embodiments.

[0169] In particular, each of the additives specifically described above can be introduced alone, or in combination with at least one other of the additives specifically described, which defines different variants of realization of an aqueous lubricating composition according to the invention.

[0170] In other words, particular embodiments of the invention are defined by an aqueous lubricating composition according to the invention, comprising at least water; and one or more polyalkylene glycol(s), in particular as defined above, preferably in the proportions indicated above, and further comprising one or more of the additives detailed specifically in the text.

[0171] According to a particular embodiment, an aqueous lubricating composition implemented according to the invention comprises:

[0172] - 40 to 55% by mass of water, in particular deionized water, especially more than 45 mass percentage of water;

[0173] - 10 to 15% by mass of one or more polyalkylene glycols; - possibly 30 to 40% by mass of an antifreeze compound chosen from glycols, preferably alkylene glycols; glycerol; diglycerol; triglycerol, and mixtures thereof; preferably diethylene glycol; - possibly from 0.1% to 10% by mass of one or more additives chosen from among antifoaming agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, emulsifying agents, sequestering agents, and mixtures thereof, said composition being free from phosphate ester salts and, more preferably, free from phosphorus compounds, said composition being free from extreme pressure additives of the sulfur fatty acid type.

[0174] According to a particular embodiment, an aqueous lubricating composition implemented according to the invention comprises hypericin in a content strictly less than 0.1% by mass, preferably less than or equal to 0.01% by mass, more preferably less than or equal to 0.01% by mass, relative to the total weight of the composition. In particular, an aqueous lubricating composition implemented according to the invention is completely free of hypericin.

[0175] More generally, an aqueous lubricating composition implemented according to the invention comprises one or more polycyclic dianthraquinone-type compounds in a content strictly less than 0.1% by mass, preferably less than or equal to 0.01% by mass, more preferably less than or equal to 0.01% by mass, relative to the total weight of the composition. In particular, an aqueous lubricating composition implemented according to the invention is completely free of polycyclic dianthraquinone-type compounds. APPLICATION

[0176] As previously stated, an aqueous lubricating composition can be implemented, by virtue of its combined lubrication and cooling properties, both as a cooling fluid and as a lubricating fluid for a propulsion system of an electric or hybrid vehicle, in particular of the motor, power electronics, transmission and / or battery, in an electric or hybrid vehicle, preferably in an electric vehicle.

[0177] As schematically represented in [Fig. 1], the propulsion system of an electric or hybrid vehicle includes, in particular, the electric motor (1), an electric battery (2), and a transmission, specifically a speed reducer (3). Suitable batteries for the propulsion systems of an electric or hybrid vehicle include, in particular, Li-ion batteries and nickel-cadmium batteries.

[0178] The electric motor typically comprises power electronics (11) connected to a stator (13) and a rotor (14). The stator includes coils, in particular copper coils, which are alternately energized by an electric current. This generates a rotating magnetic field. The rotor itself comprises coils, permanent magnets, or other magnetic materials, and is set in rotation by the rotating magnetic field.

[0179] The power electronics (11), the stator (13) and the rotor (14) of a propulsion system (1) are complex components that generate a significant amount of heat during motor operation. Therefore, it is essential to ensure cooling of the electric motor and the power electronics.

[0180] 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.

[0181] Advantageously, an aqueous lubricating composition according to the invention can be used to cool the battery in an electric or hybrid vehicle, particularly in an electric vehicle. In particular, it is intended to be in direct contact with the battery.

[0182] Cooling can be achieved by any method known to those skilled in the art. The battery can be immersed or semi-immersed, static or circulating, in said composition.

[0183] Examples of direct contact include cooling by injection, jet, spraying or by forming a mist from the composition required according to the invention under pressure and by gravity on the battery.

[0184] A composition according to the invention can further be implemented 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, preferably in an electric vehicle.

[0185] An aqueous lubricating 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 the motor, the power electrics, the transmission and / or the battery, more particularly the bearings located between the rotor and the stator of an electric motor, or the transmission, in particular the reducer, in an electric or hybrid vehicle.

[0186] More specifically, an aqueous lubricating composition according to the invention allows for the cooling and lubrication of an electric motor in an electric or hybrid vehicle. It is particularly effective for cooling the power electronics and / or the rotor and / or the stator of an electric motor. It also provides lubrication for the bearings located between the rotor and the stator of an electric motor in an electric or hybrid vehicle.

[0187] Advantageously, an aqueous lubricating composition according to the invention makes it possible to ensure the lubrication of the transmission, when present, in particular the reducer, of an electric or hybrid vehicle.

[0188] Thus, advantageously, it is possible, for example, by implementing a single composition according to the invention, to ensure both the cooling of the battery and the lubrication of the transmission, in particular the reducer, in an electric or hybrid vehicle.

[0189] Advantageously, the present invention relates to the use of an aqueous lubricating composition as defined according to the invention, for lubricating and / or cooling the reducer and / or the motor and / or the power electronics of an electric vehicle.

[0190] The particular, advantageous or preferred characteristics relating to the uses and methods of implementation of an aqueous lubricating composition according to the invention, make it possible to define particular, advantageous or preferred modes of an aqueous lubricating composition according to the invention. Examples

[0191] 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. Measurement of pitting by mechanical fatigue

[0192] Mechanical fatigue pitting (or “pitting” in English) is evaluated by a test on an MPR tribometer (for “Micro Pitting Rig” in English).

[0193] The MPR tribometer is a machine that brings a central roller (12 mm diameter) into contact with three rings (54 mm diameter) arranged around the roller. This geometric configuration allows the test roller to be subjected to a large number of rolling contact cycles over a short test period, which promotes pitting due to mechanical fatigue.

[0194] The test is carried out over a period of 20 hours. The detection of pitting due to fatigue is performed by an accelerometer connected to a vibration monitor. When the vibration setpoint is exceeded due to the occurrence of pitting, the test is stopped.

[0195] The performance of the compositions in terms of pitting by mechanical fatigue is described as insufficient if the pitting time is less than 10 hours, average if the pitting time is between 10 and 20 hours and good in the absence of pitting after 20 hours of testing. EXAMPLE 1 Preparation of lubricating compositions

[0196] Two aqueous lubricating compositions (II and I2) according to the invention, and a comparative lubricating composition (C1) comprising a phosphorus compound content exceeding 0.1% by weight, were formulated by simply mixing, at room temperature, the following components in the mass percentages indicated in Table 1 below. The percentages are therefore expressed as a percentage of the total mass of the composition.

[0197] [Tables] Composition Composition II according to the invention Composition 12 according to the invention Comparative composition Cl Deionized water [%] 42.65 51.94 43.41 Polyalkylene glycol [%] 14.25 11.94 19.49 Diethylene glycol [%] 40 33.52 32.83 Neutralized alcohol phosphate [%] - - 1.0 Alkanolamine pH regulator [%] L1 0.92 0.9 Neutralized sulfur fatty acid [%] - - 0.7 Additives^ [%] 2 1.68 1.67 Mixture of additives comprising one or more anti-corrosion additives, one or more metal passivating agents, one or more anti-foaming additives and / or one or more colorants. EXAMPLE 2

[0198] Characterization of the compositions according to the invention and comparative in terms of pitting by mechanical fatigue

[0199] The performance in terms of mechanical fatigue pitting of composition 12, according to the invention, and of the comparative composition Cl, was evaluated according to the detailed protocol above.

[0200] The results are presented in Table 2 below:

[0201] [Tables2] Composition 12 cl Performance "pitting" Good Insufficient

[0202] As can be seen from these results, composition 12, according to the invention, exhibits resistance to pitting by mechanical fatigue which is much superior to that obtained for the comparative composition Cl, characterized in particular by the presence of a phosphorus compound in a content greater than 0.1% by weight, relative to the total weight of the composition.

[0203] Furthermore, compositions II and 12 according to the invention exhibit excellent performance in terms of cooling in an electric or hybrid vehicle propulsion system, in particular for cooling the electric motor.

[0204] Consequently, an aqueous lubricating composition according to the invention can be implemented for the lubrication and / or cooling of an electric or hybrid vehicle propulsion system, without presenting an adverse effect on pitting by mechanical fatigue of the parts lubricated and / or cooled using said composition.

Claims

Demands

1. Use, for cooling and / or lubricating a propulsion system of an electric or hybrid vehicle, of an aqueous lubricating composition comprising at least: - water; - at least one polyalkylene glycol; and - at least one antifreeze compound selected from alkylene glycols, glycerol, diglycerol, triglycerol, and mixtures thereof, more preferably from monoethylene glycol, diethylene glycol, propylene glycol, glycerol and mixtures thereof in a content greater than or equal to 33% by mass, relative to the total mass of the composition; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of said composition.

2. Use according to claim 1, wherein the antifreeze compound is selected from monoethylene glycol, diethylene glycol, propylene glycol, glycerol and mixtures thereof.

3. Use according to the preceding claim, wherein the aqueous lubricating composition comprises between 33.5% and 40% of antifreeze compound(s), relative to the total mass of said composition.

4. Use according to any one of the preceding claims, wherein the water is reverse osmosis water, in particular deionized water.

5. Use according to any one of the preceding claims, wherein the aqueous lubricating composition comprises at least 20% by mass of water, in particular deionized water, preferably between 35% and 90% by mass, more preferably between 40% and 75% by mass, in particular between 40% and 60% by mass, relative to the total mass of said composition.

6. Use according to any one of the preceding claims, characterized in that said polyalkylene glycol(s) comprises at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass of propylene oxide and / or ethylene oxide units, in particular said polyalkylene glycol(s) is an ethylene oxide / propylene oxide copolymer.

7. Use according to any one of the preceding claims, characterized in that said polyalkylene glycol(s) has a kinematic viscosity measured at 100 °C (KV100), according to ASTM D445, of between 100 and 25,000 mm2 / s, in particular between 150 and 10,000 mm2 / s.

8. Use according to any one of the preceding claims, wherein the aqueous lubricating composition comprises at least 5.0% by mass of polyalkylene glycol(s), preferably between 5.0% and 50% by mass, more preferably between 10% and 40% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

9. Use according to any one of the preceding claims, wherein the aqueous lubricating composition comprises less than 0.05% by mass of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, preferably less than 0.01% by mass, more particularly less than 0.001% by mass, relative to the total mass of the composition, the aqueous lubricating composition being more preferably totally free of phosphate ester salts, in particular alkali metal salts of phosphate esters.

10. Use according to any one of the preceding claims, wherein the aqueous lubricating composition further comprises at least one additive selected from antifoaming agents, biocides, pH regulators, corrosion inhibitors, anti-wear and / or extreme-pressure additives, sequestering agents, metal passivating agents, colorants, dispersants, emulsifying agents, and mixtures thereof, preferably selected from antifoaming agents, extreme-pressure agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, and mixtures thereof.

11. Use according to any one of the preceding claims, wherein the aqueous lubricating composition further comprises at least one pH regulating additive for maintaining the pH of the lubricating composition between 8 and 15, in particular selected from alkanolamines.

12. Use according to any one of the preceding claims, wherein the aqueous lubricating composition comprises less than 0.1% by mass of an extreme-pressure additive of the sulfur fatty acid type, preferably less than 0.01% by mass, more particularly less than 0.001% by mass, relative to the total mass of the composition, more preferably is totally free of extreme-pressure additive of the sulfur fatty acid type.

13. Use of an aqueous lubricating composition as defined according to any one of the preceding claims, for lubricating and / or cooling the gearbox and / or motor and / or power electronics of an electric vehicle.

14. Use of an aqueous lubricating composition intended for lubricating and / or cooling a propulsion system of an electric or hybrid vehicle, comprising at least: - water; and - at least one polyalkylene glycol; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of said composition, to reduce pitting by mechanical fatigue of the mechanical part(s) of said propulsion system, brought into contact with said composition.

15. Aqueous lubricating composition for the lubrication and / or cooling of an electric or hybrid propulsion system, comprising at least: - at least 45% water by mass, relative to the total mass of the composition; - at least one polyalkylene glycol; and - at least one antifreeze compound selected from glycols in a content greater than or equal to 33% by mass, relative to the total mass of the composition; said aqueous lubricating composition comprising a content of phosphate ester salt(s), in particular selected from alkali metal salts of phosphate esters, strictly less than 0.1% by mass, relative to the total mass of said composition.

16. Aqueous lubricating composition according to the preceding claim, said composition being as defined according to any one of claims 2 to 4 or 6 to 12.

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