Ester-based functional fluids

Abstract

The invention relates to the use of specific esters in functional fluids for electric vehicles.

Description

[0001] The present invention relates to the use of specific esters in functional fluids for electric vehicles.

[0002] The functional fluid is used for lubricating and cooling electrical equipment. More specifically, the functional fluid has good compatibility with the materials constituting the electrical equipment (such as motors and / or batteries in electric vehicles).

[0003] Therefore, preferably, the functional fluid is capable of lubricating and cooling and has good compatibility with elastomers.

[0004] Such a functional fluid is particularly meaningful for applications in electric vehicles.

[0005] In fact, in electric vehicles, motors, transmissions, and power electronics are often integrated together to save volume and weight.

[0006] In addition, in electric vehicles, a battery pack replaces the internal combustion engine to provide power.

[0007] The battery pack consists of a set of batteries and generates a large amount of heat that needs to be cooled. Indirect cooling in internal combustion engine vehicles is not sufficient to ensure uniform cooling.

[0008] In addition, electrical equipment in electric vehicles, especially the battery pack, can be cooled by direct contact, such as immersion cooling.

[0009] Therefore, it is particularly important for the functional fluid to be compatible with the different materials used in the various components of an electric vehicle, as the functional fluid may come into contact with these materials.

[0010] Due to its various properties, the same functional fluid can be used to lubricate gears and cool the motors, transmissions, and power electronics of an electric vehicle without damaging elastomeric seals.

[0011] Preferably, the same functional fluid can be used to lubricate and cool electrical equipment in an electric vehicle without damaging the plastic components of the electrical equipment.

[0012] More preferably, the same functional fluid can be used to lubricate and cool electrical equipment in an electric vehicle without damaging the elastomeric seals and plastic components of the electrical equipment.

[0013] With the increasing interest in electric vehicles, the demand for functional fluids with multiple properties is also growing, such as high-efficiency lubrication, good thermal (heat transfer) performance, good electrical (non-conductive) performance, seal compatibility, and low viscosity. Preferably, the functional fluid should also have good plastic compatibility.

[0014] More specifically, there is a need for a functional fluid that can combine the properties required for electric vehicles, such as the following properties:

[0015] - Good lubricating performance, characterized by the anti-friction ability measured using a ball-disk device, where the frictional force is measured as a function of different contact parameters, for example using a MiniTraction Machine (MTM) device, and the traction curve is lower than the curve obtained using a Group III mineral oil under the same conditions;

[0016] - Low kinematic viscosity measured according to ASTM D445 standard, for example less than 30 mm 2 / s at 40 °C and less than 5 mm 2 / s at 100 °C;

[0017] - Pour point measured according to ASTM D97 standard is at most -40 °C;

[0018] - Flash point measured according to ASTM D92 standard is higher than 200 °C;

[0019] - Oxidation stability is at least 700 minutes measured according to ASTM D2272 standard in the presence of antioxidant additives (less than 2 wt%, preferably less than 1.5 wt% based on the weight of the functional fluid);

[0020] - Thermal conductivity at 20 °C is at least 0.1300 W / (m.°C) measured according to ASTM 7896 standard;

[0021] - Dielectric breakdown voltage at 20 °C is greater than 30 kV measured according to ASTM D877 standard;

[0022] - Good compatibility with elastomers, especially with elastomers selected from acrylonitrile-butadiene rubber (e.g., NBR 1), hydrogenated nitrile rubber (e.g., HNBR 1) and / or fluororubber (e.g., FKM 2).

[0023] Preferably, the functional fluid has the following additional properties:

[0024] - Good compatibility with plastics, especially with plastics selected from polyamide-6 (PA6), epoxy resin, polyimide, polyoxymethylene, polyethylene terephthalate and / or polyurethane resin.

[0025] NBR 1 is an elastomer based on acrylonitrile-butadiene rubber, where the acrylonitrile content is 28 wt% of the total weight of the rubber.

[0026] FKM 2 is an elastomer based on fluororubber. More specifically, it consists of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene, and the fluorine content accounts for 68 wt% to 69 wt% of the total weight of the rubber.

[0027] HNBR 1 is an elastomer based on hydrogenated acrylonitrile-butadiene rubber with an acrylonitrile content of 35% by weight of the total weight of the rubber.

[0028] The compatibility of a fluid with an elastomer specifically refers to the ability of the fluid not to cause the elastomer to expand or contract when the elastomer is in contact with the fluid.

[0029] "Having good compatibility with an elastomer" means that the volume change of elastomer NBR 1 after 168 hours at 100 °C does not exceed 15% and / or the volume change of elastomer FKM 2 after 168 hours at 100 °C does not exceed 2.5%; the volume change is measured according to ISO 6072 standard. In addition, the volume change of elastomers AEM and / or ACM after 240 hours at 80 °C is preferably not more than 5%, more preferably not more than 2%.

[0030] This compatibility is very important because elastomers are often used in electric vehicles. For example, the seals of engines and transmissions are made of elastomers.

[0031] The compatibility of a fluid with a plastic specifically refers to the ability of the fluid not to cause the plastic to expand or contract when the plastic is in contact with the fluid.

[0032] "Having good compatibility with a plastic" means that plastics selected from polyamide-6 (PA6), epoxy resin, polyimide, polyoxymethylene, polyethylene terephthalate and / or polyurethane resin have a mass change of not more than 15%, preferably not more than 10%, after 240 hours at 80 °C.

[0033] In fact, battery packs are mainly made of plastics (such as polyamides and polyurethanes), which have been proven to have strong heat resistance and are lighter than metals.

[0034] The applicant has unexpectedly found that specific esters can have all these properties.

[0035] In addition, these esters can be obtained from renewable chemicals.

[0036] Therefore, the present invention relates to the use of esters selected from the group consisting of:

[0037] - esters obtainable by esterifying a saturated branched-chain monohydric alcohol containing 5 to 16 carbon atoms with isostearic acid;

[0038] - esters obtainable by esterifying 2-hexyl-1-decanol with a saturated fatty acid containing 7 to 18 carbon atoms;

[0039] and

[0040] - mixtures thereof;

[0041] for use in functional fluids for electric vehicles.

[0042] Specifically, the functional fluid is used for lubricating and cooling devices in an electric vehicle while having excellent compatibility with elastomers. The devices in the electric vehicle include elastomeric seals.

[0043] More specifically, the esters used in the present invention have various properties, such as lubricity, cooling properties, electrical properties, compatibility with elastomers, and physicochemical properties suitable for electric vehicles. The physicochemical properties required for an electric vehicle are specifically as follows:

[0044] - The kinematic viscosity is less than 30 mm 2 / s at 40 °C and less than 5 mm 2 / s at 100 °C, measured according to ASTM D445 standard;

[0045] - The pour point measured according to ASTM D97 standard is at most -40 °C;

[0046] - The flash point measured according to ASTM D92 standard is higher than 200 °C;

[0047] - The oxidation stability is at least 700 minutes, measured according to ASTM D2272 standard, in the presence of an antioxidant additive (less than 1.5 wt% based on the weight of the ester).

[0048] In the present application, unless otherwise specified, all numerical ranges used should be understood to include the limiting values.

[0049] Preferably, the esters used according to the present invention are used in the absence of additional diesters.

[0050] A branched-chain monohydric alcohol is a branched hydrocarbon chain containing only one hydroxyl functional group.

[0051] Advantageously, in the use according to the present invention, the ester is compatible with elastomers, and the volume change of elastomer NBR 1 after being immersed in the ester at 100 °C for 168 hours does not exceed 15% and / or the volume change of elastomer FKM 2 after being immersed in the ester at 100 °C for 168 hours does not exceed 2.5%; the volume change is measured according to ISO 6072 standard.

[0052] Advantageously, in the use according to the present invention, the saturated branched-chain monohydric alcohols are selected from the group consisting of isopentanol, 2-ethylbutanol, 2-butylhexanol, 2-butyl-1-heptanol, 2-butyl-1-octanol, 2-pentyl-1-nonanol, 2-hexyl-1-octanol, and 2-hexyl-1-decanol.

[0053] Preferably, the saturated branched-chain monohydric alcohol contains 5, 12, 14, or 16 carbon atoms.

[0054] More preferably, the saturated branched-chain monohydric alcohol contains 5, 14 or 16 carbon atoms.

[0055] Specifically, the monohydric alcohol is selected from the group consisting of isopentyl alcohol, 2-pentyl-1-nonanol and 2-hexyl-1-decanol.

[0056] Even more preferably, the saturated branched-chain monohydric alcohol contains 14 or 16 carbon atoms.

[0057] Specifically, the monohydric alcohol is selected from the group consisting of 2-pentyl-1-nonanol and 2-hexyl-1-decanol.

[0058] Advantageously, in the use according to the present invention, the saturated fatty acid is selected from the group consisting of enanthic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, isostearic acid and mixtures thereof.

[0059] Preferably, the fatty acid is selected from the group consisting of enanthic acid, caprylic acid, capric acid, lauric acid, isostearic acid and mixtures thereof.

[0060] Advantageously, in the use according to the present invention, the ester is selected from the group consisting of:

[0061] - isopentyl isostearate;

[0062] - 2-pentyl-1-nonyl isostearate;

[0063] - 2-hexyl-1-decyl isostearate;

[0064] - 2-hexyl-1-decyl laurate;

[0065] - 2-hexyl-1-decyl octanoate / caprate; and

[0066] - 2-hexyl-1-decyl enanthate.

[0067] Specifically, in the use according to the present invention, the ester is selected from the group consisting of:

[0068] - 2-pentyl-1-nonyl isostearate;

[0069] - 2-hexyl-1-decyl isostearate;

[0070] - 2-hexyl-1-decyl laurate; and

[0071] - 2-hexyl-1-decyl octanoate / caprate.

[0072] These esters exhibit better lubricating properties, as Figure 1 shown.

[0073] More specifically, in the use according to the present invention, the ester is 2-hexyl-1-decyl isostearate.

[0074] The present invention also relates to a functional fluid for an electric vehicle, comprising:

[0075] - an ester selected from the group consisting of:

[0076] o isopentyl isostearate;

[0077] o 2-pentyl-1-nonyl isostearate;

[0078] o 2-hexyl-1-decyl isostearate;

[0079] o 2-hexyl-1-decyl laurate;

[0080] o 2-hexyl-1-decyl octanoate / caprate;

[0081] o 2-hexyl-1-decyl heptanoate; and

[0082] - an antioxidant additive;

[0083] wherein the functional fluid does not contain any diesters.

[0084] Functional fluids generally include a base oil, usually the main component (the component with the highest content), may include an auxiliary base oil (a second base oil with a content lower than the first base oil), and one or more additives.

[0085] The American Petroleum Institute (API) classifies base oils into five categories:

[0086] - The first three categories are mineral oils refined from petroleum crude oil:

[0087] - Group I base oils have a saturated hydrocarbon content of less than 90 wt%, an aromatic content of more than 1.7 wt%, a sulfur content of more than 0.03 wt%, and a viscosity index between 80 and 120;

[0088] - Group II base oils have a saturated hydrocarbon content greater than 90 wt%, an aromatic content less than 1.7 wt%, a sulfur content less than 0.03 wt%, and a viscosity index between 80 and 120;

[0089] - Group III base oils have a saturated hydrocarbon content greater than 90 wt%, an aromatic content less than 1.7 wt%, a sulfur content less than 0.03 wt%, and a viscosity index greater than 120;

[0090] The weight percentages are based on the weight of the base oil.

[0091] - Group IV base oils are synthetic oils, such as polyalphaolefins.

[0092] - Group V applies to all other base oils not included in Groups I to IV.

[0093] In the functional fluid according to the present invention, the base oil and the auxiliary base oil can independently be base oils selected from any group of Group I to Group V.

[0094] The esters used according to the present invention are classified as Group V.

[0095] In the functional fluid, the esters used according to the present invention can be used as base oils or auxiliary base oils.

[0096] Therefore, the base oil and the auxiliary base oil (if present) need to have both lubricating, thermal, electrical, and elastomer compatibility characteristics.

[0097] Additives are used to enhance one or more inherent properties of the base oil and / or provide one or more additional properties thereto.

[0098] In the functional fluid, the esters used according to the present invention can also be used as additives.

[0099] The amount of the esters used according to the present invention is preferably at least 5% by weight, more preferably at least 7% by weight, based on the weight of the functional fluid.

[0100] The amount of the esters used according to the present invention is preferably at most 95% by weight, more preferably at most 90% by weight, based on the weight of the functional fluid.

[0101] If the base oil and the antioxidant additive are compatible, i.e., there is no competition between them, the antioxidant additive can improve the oxidation stability of the base oil.

[0102] As shown in Example 1.3, the presence of the antioxidant additive can increase the oxidation stability of the ester to at least 700 minutes in the RPVOT test according to ASTM D2272.

[0103] Preferably, the amount of the antioxidant additive is at least 0.05% by weight, more preferably at least 0.1% by weight, based on the weight of the functional fluid.

[0104] Preferably, the amount of the antioxidant additive is at most 1.5% by weight, more preferably at most 1% by weight, based on the weight of the functional fluid.

[0105] Preferably, the antioxidant additive is selected from the group consisting of phenols, amines, thiadiazoles, dialkyldithiophosphates, and amine phosphates.

[0106] In addition to the antioxidant additive, the functional fluid can further contain one or more additives used in the lubricant field.

[0107] Those skilled in the art can easily select the additives used in the lubricant field, and they know how to select the most suitable additives and their dosages according to the application. For example, the following manuals can be referred to: "Fuels and Lubricants Handbook: technology, properties performance and testing" published by George E. Totten in 2003 and "Handbook of lubrification and tribology, vol II: Theory and Design" published by Robert W. Bruce in 2012.

[0108] The additives used in the lubricant field are preferably selected from the group consisting of metal deactivators, corrosion inhibitors, extreme pressure additives, defoamers, demulsifiers, solubility improvers, and mixtures thereof.

[0109] The total amount of the additives is preferably at least 5% by weight, more preferably at least 7% by weight, based on the total weight of the functional fluid.

[0110] The total amount of the additives is preferably at most 30% by weight, more preferably at most 25% by weight, even more preferably at most 20% by weight, based on the total weight of the functional fluid.

[0111] "The total amount of the additives" refers to the amount of all additives present in the functional fluid, including antioxidants and additives other than antioxidants used in the lubricant field.

[0112] Preferably, in the functional fluid, the esters used according to the present invention are selected from the group consisting of 2-pentyl-1-nonyl isostearate, 2-hexyl-1-decyl isostearate, 2-hexyl-1-decyl laurate, and 2-hexyl-1-decyl octanoate / caprate.

[0113] The present invention also relates to a method for lubricating and cooling one or more devices in an electric vehicle by bringing the devices into contact with an ester selected from the group consisting of:

[0114] - esters obtainable by esterifying a saturated branched-chain monohydric alcohol containing 5 to 16 carbon atoms with isostearic acid;

[0115] - esters obtainable by esterifying 2-hexyl-1-decanol with a fatty acid containing 7 to 18 carbon atoms; and

[0116] - mixtures thereof.

[0117] The esters, in particular saturated branched-chain monohydric alcohols and fatty acids, as described above, include the preferred and advantageous features.

[0118] The device in an electric vehicle comprises an elastomeric seal.

[0119] Preferably, the device is a gear, an electric motor, a transmission, a battery and / or power electronics.

[0120] Advantageously, in the method according to the invention, the ester is contacted by the functional fluid according to the invention.

[0121] In the method according to the invention, the ester is compatible with the elastomer, and when immersed in the ester at 100 °C for 168 hours, the volume change of elastomer NBR 1 does not exceed 15% and / or the volume change of elastomer FKM 2 does not exceed 2.5%; the volume change is measured according to the ISO 6072 standard.

[0122] The present invention will be further described in the following examples, which are given by way of illustration and with reference to Figure 1 , which shows a graph of the variation of the traction coefficient of different esters and Group III mineral oils according to the applied slip-roll ratio.

[0123] Example 1: Characteristics of the esters used in the present invention

[0124] 1.1. Chemicals used

[0125] - Isoamyl isostearate: Prepared by esterifying isoamyl alcohol (from Tradebe Chemicals) with isostearic acid (Radia 0905 from Oleon);

[0126] - 2-Pentyl-1-nonyl isostearate: Prepared by esterifying 2-pentyl-1-nonanol with isostearic acid (Radia 0905 from Oleon);

[0127] 2-Pentyl-1-nonanol is prepared by the Guerbet reaction using n-heptanol as the primary alcohol. The reaction is as described, for example, in US Patent US 4,518,810, with KOH as the base and palladium as the catalyst, and the reaction medium is heated to the boiling point. The crude reaction mixture is washed several times with deionized water to remove all soap bases. The washed product is then filtered and dried under vacuum. The remaining primary alcohol is separated by distillation. Then, 2-pentyl-1-nonanol is separated by distillation.

[0128] - 2-Hexyl-1-decyl isostearate: Prepared by esterifying 2-hexyl-1-decanol (Isofol 16 from Sasol) with isostearic acid (Radia 0905 from Oleon);

[0129] - 2 - hexyl - 1 - decyl laurate: Prepared by esterifying 2 - hexyl - 1 - decanol (Isofol 16 from Sasol) with lauric acid (Radia 0653 from Oleon);

[0130] - 2 - hexyl - 1 - decyl caprate / caprylate: Prepared by esterifying 2 - hexyl - 1 - decanol (Isofol 16 from Sasol) with capric / caprylic acid (Radia 0640 from Oleon);

[0131] - 2 - hexyl - 1 - decyl heptanoate: Prepared by esterifying 2 - hexyl - 1 - decanol (Isofol 16 from Sasol) with heptanoic acid (Oleris n - heptanoic acid from Arkema).

[0132] 1.2. Lubricity

[0133] The lubricity of a fluid refers to its ability to reduce friction (friction or deformation between moving parts) and / or reduce component wear.

[0134] Therefore, the lubrication performance of the esters was evaluated by measuring the friction reduction under the following conditions using a Mini Traction Machine (MTM) device and compared with Group III mineral oil (Nexbase 3043 containing isoparaffins from Neste), which is widely used in industrial and automotive lubricants:

[0135] Materials: Steel ball against steel disc

[0136] Load: 75 N

[0137] Temperature: 80 °C

[0138] Rolling speed: 1000 mm / s

[0139] Slide - roll ratio: From 0 to 100%.

[0140] The resulting curves are as Figure 1 shown.

[0141] From Figure 1 it can be seen that the traction coefficient curves of each ester (isopentyl isostearate, 2 - pentyl - 1 - nonyl isostearate, 2 - hexyl - 1 - decyl isostearate, 2 - hexyl - 1 - decyl laurate, and 2 - hexyl - 1 - decyl caprate / caprylate) are lower than those of the Group III mineral oil.

[0142] The esters used in the present invention have better lubricating properties than traditional mineral oils. In particular, the traction coefficients of 2-pentyl-1-nonyl isostearate, 2-hexyl-1-decyl isostearate, 2-hexyl-1-decyl laurate, and 2-hexyl-1-decyl caprate / caprylate are the lowest, all below 0.033.

[0143] 1.3. Physicochemical properties

[0144] The kinematic viscosity, pour point, and flash point of each specific ester used according to the present invention were measured.

[0145] The oxidation stability of the esters was determined using the Rotating Pressure Vessel Oxidation Test (RPVOT) according to standard ASTM D2272, in which 1.5% of an additive (RC 9321 from Lanxess) mainly composed of phenolic, amine, thiadiazole, and amine phosphate antioxidant additives was added. The results are summarized in Table 1 below.

[0146] The results are summarized in Table 1 below.

[0147]

[0148] Table 1 : Physicochemical properties

[0149] The kinematic viscosity of the esters used according to the present invention is below 30 mm 2 / s at 40 °C and below 5 mm 2 / s at 100 °C, the pour point is below -40 °C, and the flash point is above 200 °C. They also have good oxidation stability because their values in the RPVOT test are greater than 700 minutes. In addition, it can be concluded that these specific esters are compatible with the antioxidants commonly used in the field of lubricants containing mineral base oils.

[0150] 1.4. Thermal properties

[0151] The thermal conductivity was measured according to ASTM 7896 standard.

[0152] The results are summarized in Table 2 below.

[0153] Thermal conductivity at 20 °C (W / m.°C) Isoamyl isostearate 0.137 2-Pentyl-1-nonyl isostearate 0.152 2-Hexyl-1-decyl isostearate 0.148 2-Hexyl-1-decyl laurate 0.153 2-Hexyl-1-decyl caprylate / caprate 0.148

[0154] Table 2 : Thermal properties

[0155] The esters used in the present invention have good thermal conductivity. Since thermal conductivity refers to the ability to conduct heat, these esters can be used as coolants.

[0156] 1.5. Electrical properties

[0157] The dielectric breakdown voltage was measured according to ASTM D877 standard.

[0158] The results are summarized in Table 3 below.

[0159] Dielectric breakdown voltage at 20 °C (kV) Isoamyl isostearate 40.8 2-Hexyl-1-decyl isostearate 38 2-Hexyl-1-decyl laurate 32 2-Hexyl-1-decyl heptanoate 56,3 2-Hexyl-1-decyl caprylate / caprate 55,4

[0160] Table 3 : Electrical properties

[0161] The dielectric breakdown voltage is higher than 30 kV, which means that the esters used according to the present invention can all be used as dielectric fluids.

[0162] 1.6. Elastomer compatibility

[0163] The compatibility of the ester with elastomers was measured according to ISO 6072 standard by immersing each elastomer in the ester at 100 °C for 168 hours.

[0164] The results are summarized in Table 4 below.

[0165]

[0166] Table 4 : Compatibility of elastomers NBR 1, HNBR and FKM 2

[0167] The esters used in the present invention have good compatibility with elastomers. Specifically, when elastomer NBR 1 is immersed in the ester used in the present invention, its volume change is less than 15%, and when elastomer FKM 2 is immersed in the ester used in the present invention, its volume change is less than 2.5%. The volume change rate was measured according to ISO6072 standard after soaking at 100 °C for 168 hours.

[0168] The compatibility of the ester with the following elastomers was also measured:

[0169] - Ethylene acrylic acid (AEM): Vamac 7900 from Jeantet Elastomères;

[0170] - Acrylic ester (ACM): HyTemp ACM AR12 from Zeon Chemicals;

[0171] It was measured by soaking each elastomer in the ester at 80 °C for 240 hours.

[0172] The volume change is expressed as a percentage and is summarized in Table 5 below.

[0173]

[0174] Table 5 : Compatibility of elastomers AEM and ACM

[0175] It can be seen that 2-hexyldecyl isostearate has a slight effect on the volume of elastomers AEM and ACM. Therefore, it can be concluded that 2-hexyldecyl isostearate has good compatibility with AEM and ACM.

[0176] 1.7. Plastic compatibility

[0177] The method for measuring the compatibility of the ester with plastics was carried out by immersing each plastic in the ester at 80 °C for 242 hours and comparing the mass of each plastic before and after immersion.

[0178] Plastics tested:

[0179] - Polyamide: Ertalon 6SA PA6 (PA6) of Mitsubishi Chemical Group;

[0180] - Epoxy resin: Vetronit EGS 619 of Von Roll;

[0181] - Polyimide (PI): Kapton HN of DuPont;

[0182] - Polyoxymethylene (POM): Tecaform AH black of Ensinger;

[0183] - Polyethylene terephthalate (PET): Mylar A of Dr. Dietrich;

[0184] - Polyurethane resin (PU): Scotchcast 40 of 3M.

[0185] The mass changes are expressed as percentages and summarized in Table 6 below.

[0186]

[0187] Table 6 : Plastic Compatibility

[0188] It can be observed that 2-hexyldecyl isostearate has little or no effect on the mass of plastics. Therefore, it can be concluded that 2-hexyldecyl isostearate has good compatibility with different plastics, especially those that may be used in electric vehicles and may come into direct contact with it.

Claims

1. Use of an ester selected from the group consisting of: - an ester obtained by esterifying a saturated branched-chain monohydric alcohol containing 5 to 16 carbon atoms with isostearic acid; - an ester obtained by esterifying 2-hexyl-1-decanol with a saturated fatty acid containing 7 to 18 carbon atoms; and - a mixture thereof; The ester is used in a functional fluid for an electric vehicle.

2. The use according to claim 1, wherein the ester is compatible with an elastomer, and the volume change of elastomer NBR 1 after being immersed in the ester at 100 °C for 168 hours does not exceed 15% and / or the volume change of elastomer FKM 2 after being immersed in the ester at 100 °C for 168 hours does not exceed 2.5%; the volume change is measured according to the ISO 6072 standard.

3. The use according to claim 1 or 2, wherein the saturated branched-chain monohydric alcohol is selected from the group consisting of isopentanol, 2-ethylbutanol, 2-butylhexanol, 2-butyl-1-heptanol, 2-butyl-1-octanol, 2-pentyl-1-nonanol, 2-hexyl-1-octanol, and 2-hexyl-1-decanol.

4. The use according to any one of claims 1 to 3, wherein the saturated fatty acid is selected from the group consisting of heptanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, isostearic acid, and mixtures thereof.

5. The use according to any one of claims 1 to 4, wherein the ester is selected from the group consisting of: - isopentyl isostearate; - 2-pentyl-1-nonyl isostearate; - 2-hexyl-1-decyl isostearate; - 2-hexyl-1-decyl laurate; - 2-hexyl-1-decyl octanoate / decanoate; and - 2-hexyl-1-decyl heptanoate.

6. The use according to any one of claims 1 to 4, wherein the ester is selected from the group consisting of: - 2-pentyl-1-nonyl isostearate; - 2-hexyl-1-decyl isostearate; - 2-hexyl-1-decyl laurate; and - 2-hexyl-1-decyl octanoate / decanoate.

7. The use according to any one of claims 1 to 4, wherein the ester is 2-hexyl-1-decyl isostearate.

8. A functional fluid for an electric vehicle, comprising: - an ester selected from the group consisting of: o isopentyl isostearate; o 2-pentyl-1-nonyl isostearate; o 2-hexyl-1-decyl isostearate; o 2-hexyl-1-decyl laurate; o 2-hexyl-1-decyl octanoate / decanoate; o 2-hexyl-1-decyl heptanoate; and - an antioxidant additive; Among them, The functional fluid does not contain any diesters.

9. A method of lubricating and cooling one or more devices in an electric vehicle by bringing the devices into contact with an ester selected from the group consisting of: - an ester obtained by esterifying a saturated branched-chain monohydric alcohol containing 5 to 16 carbon atoms with isostearic acid; - an ester obtained by esterifying 2-hexyl-1-decanol with a fatty acid containing 7 to 18 carbon atoms; and - a mixture thereof.

10. The method according to claim 9, wherein the ester is contacted by the functional fluid according to claim 8.

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