Liquid composition for use in electric drives

Abstract

The invention relates to a liquid composition having a dynamic viscosity in the range of 1.5 – 4.0 mm2 / s at 100°C, comprising: - 50-99.93 wt.% of a base oil or base oil blend, selected from polyalphaolefin oils of group IV of the API classification or GTL base oils of group III of the API classification; and the following additives: - a boron-containing, ashless succinic acid amide and / or succinic acid imide, - an alkyl thiadiazole compound according to formula (Ia) and / or (Ib), wherein C9H19 is tert-nonyl.

Description

[0001] Description

[0002] Fluid composition for use in electric drives

[0003] The invention relates to a fluid composition that is particularly suitable as a lubricating fluid in transmissions in a drive system of electrically powered vehicles, in particular exclusively electrically powered vehicles. The fluid composition according to the invention can also come into contact, at least temporarily, with power electronics and a battery cell and serve to cool the power electronics.

[0004] It is known from automotive technology that power-transmitting gears in transmissions, whether straight or helical, need to be lubricated to prevent wear, to dissipate the heat generated during tooth engagement and to reduce the friction generated during tooth engagement in order to ensure their long-term durability and functionality.

[0005] Lubrication is achieved by either splash or forced lubrication. With splash lubrication, the teeth and flanks of the gears are immersed in an oil sump as the gears rotate during operation, absorbing the necessary amount of lubricant. In contrast, with forced lubrication, the lubricant is introduced into the meshing of the gears through active lubrication measures.

[0006] The lubricant composition used for this purpose must possess such physico-chemical properties that the gears to be lubricated (hereinafter referred to as gearing) can perform their power-transmitting function reliably and durably. For this purpose, lubricating or gear oils corresponding to the application described above are formulated in such a way that rheologically suitable base fluids (so-called base oils) are mixed with numerous active ingredients (so-called additives) that improve the properties of the base oil system. The additives belong to various chemical substance classes and act partly physically, partly chemically, or through a combination of both. Engine and gear oils are described using SAE classes (SAE = Society of Automotive Engineers), which specify temperatures for viscosity measurements, viscosity limits, and class assignments.In the hot state, the viscosity of engine and transmission oils is determined uniformly for all SAE classes at 100 °C. The composition according to the invention has such favorable viscosity and shear stability properties that a corresponding classification in the previously valid SAE classification J 306 is not possible.

[0007] Base oils include, in particular, mineral oils, semi-synthetic and synthetic oils and natural oils.

[0008] Mineral oils are generally obtained from petroleum or crude oil through distillation or refining, and possibly further purification and refinement processes. In general, a distinction is made between paraffin-based, naphthenic, and aromatic components in crude oils or mineral oils. The terms "paraffin-based" refer to saturated, unbranched, or branched alkanes, and "naphthenic" refer to cycloalkanes. Depending on their origin and refinement, mineral oils also contain varying proportions of n-alkanes, isoalkanes with a low degree of branching, so-called monomethyl-branched paraffins, and compounds with heteroatoms, particularly O, N, and / or S, which are said to have slightly polar properties.

[0009] The synthetic base oils include, among others, organic esters, for example diesters and polyol esters, polyalkylene glycols, polyethers, synthetic hydrocarbons such as polyalphaolefins (PAO), silicone oils and perfluoroalkyl ethers.

[0010] Natural oils are animal or vegetable oils, such as neatsfoot oil or jojoba oil.

[0011] The base oils can also be used as blends and are often commercially available.

[0012] Lubricating fluids typically contain various substances to specifically improve certain properties. These additives serve, for example, to improve load-bearing capacity and wear protection (extreme pressure and antiwear additives), foaming behavior (foam inhibitors), friction properties (friction modifiers), and oxidation and corrosion stability (oxidation inhibitors, metal passivators, rust inhibitors). Dispersants and detergents are also used as additives. Additionally, flow improvers, known as viscosity index (VI) improvers (higher molecular weight thickeners), can be added in dosages of approximately 5.0 to 15.0 wt.% and / or pour point depressants of approximately 0.2 to 2.0 wt.%.

[0013] Compared to manual transmissions in conjunction with conventional combustion engines, the torque in electric drives is comparatively constant across the entire speed range, even when starting off. The speed level in electric drives and their gearing is significantly higher. The electrical and electronic components and parts are partially in contact with the lubricating oil, either through direct wetting with the lubricating oil or through penetration of the lubricating oil into design and manufacturing-related gaps, allowing the lubricating oil to reach the electrical and electronic components. As a result, it can be observed that additives in the lubricating oil that contain chemically active sulfur enter into sulfur-corrosive reactions with the metals (particularly copper and silver) of the electrical and electronic components, which can impair the function of the electrical components.

[0014] The antiwear additives commonly used in gear oils are compounds containing sulfur, phosphorus, zinc, and / or halogen. Special high-pressure wear additives (so-called extreme pressure (EP) additives) are particularly used. These additives are chemically composed of long-chain hydrocarbons linked by a sulfur chain. Examples include polysulfides, sulfurized olefins, and sulfurized esters. These sulfur compounds have a strong tendency to decompose into active sulfur upon contact with non-ferrous metals (e.g., copper or silver), which then forms sulfides with the aforementioned metals. Triaryl phosphates, zinc dialkyldithiophosphates, dithiocarbamates, and dimercaptothiadiazoles are also known to be used.

[0015] For example, when thiols come into contact with copper surfaces, copper thiolate complexes are initially formed, accompanied by a redox process in which thiols are oxidized to disulfides and Cu(II) is reduced to Cu(I).

[0016] Document US 4,217,232 discloses reaction products of polysulfides with a Grignard reagent as antioxidants in lubricants. Document US 3,873,454 discloses a similar sulfur-rich additive as an extreme pressure additive for lubricants. Document US 4,194,980 describes a similar extreme pressure lubricant with ingredients formed by the reaction of sulfur-containing olefins with cyclic polydisulfides. Document US 2022 / 0041951 A1 describes a lubricant with a phosphorus-containing dispersant containing 2-3.5 wt.% phosphorus. It may also contain mercaptothiadiazoles and borated succinimides. The claimed viscosity of the lubricating fluid is 3.0 to 6.5 mm. 2 / s, measured at 100°C.

[0017] Document WO 2017 / 079017 A1 discloses a lubricant for use in electric drivetrains containing an antiwear additive with 0.3-2.0% of an amine salt of a phosphorus compound obtained from P2S5, an alcohol, alkylene oxide, and P2O5. The viscosity is 3 to 7.5 mm. 2 / s, measured at 100°C. The lubricant also contains sulfurized olefins in concentrations of 0.5–7 wt.%. The salt has, among other compounds, the structure (RO)2PS-SH, which has been reacted with propylene oxide, where R can be, among other things, an alkyl radical such as 2-methyl-4-pentyl. It may also contain dimercaptothiadiazole and an ashless succinimide.

[0018] The document EP 2 960 321 A1 describes a lubricating fluid with additives resulting in a kinematic viscosity at 100°C of 2.5 - 4.0 mm 2 / s leads.

[0019] Document WO 2020 / 264154 A1 / US 2020 / 039608 describes the production process of methylparaffins from dimers of linear alpha-olefins (l_AO) using a metallocene catalyst system. It claims application as a heat transfer fluid for cooling a battery in an electrically powered vehicle. Advantageous heat transfer properties are mentioned.

[0020] The difficulty in developing an optimal lubricating fluid composition lies in finding one that fully meets the special lubrication requirements in electric drives for gears and rolling bearings at high speeds and consistently high torques with low friction, and at the same time does not cause corrosive changes in and on electrical and electronic components that are in direct contact with the fluid.

[0021] The invention is therefore based on the task of finding an optimized lubricating fluid composition suitable for use in electric motors or electric drives. Metals such as copper and silver should be affected as little as possible, or not at all, by contact. The invention is intended to enable favorable efficiency in a transmission of an electric drive train.

[0022] The invention relates to a liquid composition having a low dynamic viscosity (measured according to ASTM D 445 at 100°C) in the range of 0.8 to 4.0 mm 2 / s, preferably 2.0 to 2.8 mm 2 / s, particularly preferably 2.2 to 3.1 mm 2 / s, comprehensive

[0023] • 50-99.93 wt.% of a base oil or base oil blend selected from polyalphaolefin oils according to Group IV of the API classification or GTL base oils according to Group III of the API classification; and the following additives:

[0024] • a boron-containing, ash-free succinic acid amide and / or imide,

[0025] • an alkylthiadiazole compound according to formula (Ia) and / or (Ib), where Cg is Higtert-nonyl.

[0026] Comprehensive investigations using both established and specifically newly developed tribological testing procedures and measurement methods revealed surprisingly diverse results for these test oil formulations regarding efficiency in transmission tests with the described drive concepts. The test results demonstrated that predicting efficiency behavior based solely on viscosity data is not possible. Furthermore, an unexpectedly strong, both synergistic and antagonistic influence of lubricant additives on the friction and thus efficiency behavior of the test oils in test procedures and transmissions was observed almost consistently.

[0027] Lubricating fluids based on low-viscosity synthetic oils based on poly-α-olefins (PAO), particularly a combination of dimers of linear alpha-olefins (LAO) with particularly good evaporation loss behavior at high temperatures, and thus combinations with selected ashless borated succinimide dispersants (PIBSA / PAM) and 2,5-alkyl thiadiazole compounds, proved advantageous. Surprisingly, a negative impact was observed when using too high or too low a quantity of the claimed thiadiazoles in combination with the sulfur-phosphorus compounds (such as phosphoric acid esters) added to maintain sufficient wear performance. This revealed unpredictably strong interactions between the various additives in the aforementioned base oil systems.

[0028] To improve material compatibility, especially with copper and seals, a beneficial selection of boron-containing dispersant additives based on PIBSI and PIBSA has proven effective, although surprisingly at a significantly lower dosage than in formulations for applications as lubricating oils for dual-clutch transmissions or so-called ATF oils for stepped automatic transmissions.

[0029] The boron-containing, ash-free succinic acid amides and / or imides used in the liquid composition according to the invention act as dispersants with a comparatively low MW based on PIBSA / PIBSI / PAM. They are industrially preferably produced from maleic anhydrite (MAN) with polyisobutylene (PIB) of various molecular weights. Depending on the manufacturer, a distinction is made between conventional, relatively low-reactivity PIBs and newer, more highly reactive PIBs and mixtures thereof. The production of suitable dispersants based on succinimides is described, for example, in US Pat. No. 897,696 B2, paragraphs 41-47. The preferably used dispersants can optionally be treated with phosphorus and are borated. In the production of the succinimides, DETA or TETA are preferred polyamines, particularly preferably TEPA. Suitable dispersants are further described in EP 0 840 775 B1.

[0030] The selection of PIB influences the properties of the products. Dispersant additives are technical products with resulting properties. PIBSA (polyisobutene succinic anhydride)

[0031] In the inventive combination with the claimed additives and the inventive dosage, the required low viscosity of the liquid composition can be ensured with the selected succinimide dispersants with MW preferably from 600 to 1050. This achieves more favorable results in terms of efficiency and compatibility with polymer materials compared to higher MWs of 2000. Furthermore, these dispersants, at comparatively lower dosages than usual, still lead to sufficient cleanliness (no sludge formation, no undesirable deposits) at high application temperatures without impairing the cold flow properties. Surprisingly, only certain combinations proved advantageous. If the amount of phosphoric acid ester is increased too much, the scuffing load capacity decreases significantly.In particular, good compatibility is ensured both with uncoated copper wire materials and with special wires that are used with special protective coatings for use in windings of electrical machines.

[0032] In the composition, the 2-tert-nonylthiadiazole compound according to formula (Ia) and / or (Ib), i.e., 2-tert-nonyldithio-5-mercapto-[1,3,4]-thiadiazole according to formula (Ib) and / or 2,5-bis(tert-nonyldithio)-[1,3,4]-thiadiazole according to formula (Ia), acts as a so-called extreme pressure (EP) additive and preferably has a proportion of 0.05 to 1.0 wt.%, in particular 0.2 to 0.8 wt.%. The tert-nonyl group has proven particularly effective compared to other alkyl groups.

[0033] The base oil may in particular be at least one selected from:

[0034] • 80.0-99.5 wt.% of a base oil selected from polyalphaolefin oils with C 20 chain or C24 chain such as Chevron Synlube 2.5 with a dynamic viscosity in the range of 1.0 - 4.2, preferably 2.0 to 2.5 mm 2 / s at 100°C particularly preferably 2.1 to 2.4 mm 2 / s according to Group IV of the API classification

[0035] • A base oil mixture containing 15.0 - 85.0 wt.% of a base oil selected from polyalphaolefin oils with C20 chain and / or C24 chain such as Chevron Synlube 2.5 with a dynamic viscosity in the range of 1.0 - 4.2 mm 2 / s, measured at 100°C preferably 2.0 to 2.5 mm 2 / s particularly preferred 2.0 to 2.6 mm 2 / s according to group IV of the API classification and additionally containing synthetic oils 1-50% GTL 3 produced according to the Fischer-Tropsch process (chain length C18-C50 branched and unbranched, C123H2520) according to the structure (see EC / List no.: 482-220-0, CAS no.: 848301-69-9) • 50.0 -99.95 wt.% of a base oil selected from special polyalphaolefin oils with excellent low evaporation loss behavior at high temperatures produced using metal catalysts with a dynamic viscosity in the range of 0.9

[0036] - 4.2, preferably 1.2 to 2.6 mm 2 / s at 100°C particularly preferably 2.0 to 2.4 mm 2 / s according to Group IV of the API classification

[0037] • 50.0 - 99.95 wt.% of a base oil selected from special polyalphaolefin oils with excellent low evaporation loss behavior at high temperatures, produced using metal catalysts with a dynamic viscosity in the range of 0.9 - 4.2, preferably 0.9 to 1.5 mm2 / s at 100°C particularly preferably 1.2 to 1.4 mm 2 / s according to Group IV of the API classification

[0038] • 10.0 - 88.00 wt.% of a base oil selected from special linear polyolefins with excellent low evaporation loss behavior at high temperatures, produced using metal catalysts with a dynamic viscosity in the range of 0.9

[0039] - 4.2, preferably 2.0 to 4.0 mm 2 / s at 100°C particularly preferably 3.2 to 3.5 mm 2 / s according to Group IV of the API classification

[0040] The additives can in particular be as follows:

[0041] • At least one of the 3 described boron-containing succinimide dispersants in the total concentration of 0.2-4.0 wt-%,

[0042] • 0.1 - 3% of a boron-containing, ash-free dispersant based on polyisobutylene succinimides (PIBSA or PIBSI) with molecular weight MW 500 - 1300, preferably 900 - 1100 molecular weight, particularly preferably 950 - 1050, made from maleic acid amide and / or imide,

[0043] • an alkyl thiadiazole compound according to formula (Ia) and / or (Ib), in particular 1,3,4-thiadiazolidine-2,5-dithione, which are preferably obtained as reaction products of hydrogen peroxide and tert-nonanethiol.

[0044] Dynamic viscosity is determined according to the ASTM D445 test method. At -40°C, the viscosity is below 2000 mPas (measured according to DIN 51398), preferably even <1500 mPas. The API classification of the oils is the classification of the American Petroleum Institute (API).

[0045] Information provided within the scope of the invention regarding contents or concentrations of individual components refers to the entire lubricating fluid composition, unless otherwise stated. The invention also relates to the use of the lubricating fluid composition according to the invention in electronic components, such as battery-powered vehicles, electric drives, and high-speed transmissions in combination with electrical machines. Copper and silver are regularly used in electronic components.

[0046] It is also included that the lubricant composition may contain other additives tailored to the base oil, such as anti-wear additives, antioxidants, metal deactivators, rust inhibitors, dispersants, friction modifiers and foam inhibitors.

[0047] The composition according to the invention advantageously allows the use of conventional flow improvers in comparatively low concentrations of only < 0.5 wt.%. In the prior art, so-called flow improvers (viscosity index (VI) improvers and pour point depressants), for example, higher molecular weight thickeners, are normally added in amounts of 5 to 15 wt.% to modify the flow properties of the base oil.

[0048] The invention advantageously makes it possible to use polysulfides only in small quantities, or without them, while still achieving good lubricating properties. This prevents or slows down chemical attack on copper, which is found in electric motors, batteries, etc.

[0049] The fluid composition according to the invention is characterized by excellent thermal conductivity properties when used as a coolant and in transmissions.

[0050] Furthermore, no or very little corrosion is observed with electrical and electronic components and coated copper wires used in the windings of electric motors and drive units. At the same time, the lubricant composition ensures excellent lubrication of gears with very low drag losses due to very low friction coefficients in tribological contacts.

[0051] Advantageously, the fluid composition according to the invention also exhibits good compatibility with the elastomer materials and polyamides used in transmissions and drive trains (such as special radial shaft seals (RWDR) made of ACM), even at comparatively high speeds or high application temperatures. Good compatibility also exists with uncoated copper wire materials.

[0052] In addition, there is sufficient chemical compatibility with comparatively sensitive sealants, such as silicone-containing liquid sealants, which can be achieved, among other things, by the targeted use of the claimed borated succinimides in combination with the P / S compounds.

[0053] In addition to the low viscosity of 1.5 to 3.1 mm 2 / s at 100°C (measured using test method ASTM D445) or below 2000 mPas at -40°C (measured according to DIN 51398), the composition according to the invention advantageously also exhibits a shear loss (viscosity after shear) according to ASTM D445 of less than 5%. This advantageously prevents classification in the internationally valid SAE classification J 306 (as of 2019) for gear oils, since only significantly higher viscosity ranges (> 3.8 mm) have been available there. 2 / s at 100°C).

[0054] In a preferred embodiment of the invention, the liquid composition additionally comprises a phosphorus compound or

[0055] Phosphorus sulfur compound according to formula (II): In this embodiment, it is particularly preferably an ammonium salt of the phosphorus compound according to formula (II), wherein at least one of the radicals on the ammonium cation is a C12-C14 tert-alkyl radical.

[0056] In one embodiment, the liquid composition comprises the reaction product of 4-methyl-2-pentanol and diphosphorus pentasulfide, propoxylated and esterified with diphosphorus pentaoxide and salted with amines with a C12-14 tert-alkyl radical

[0057] Furthermore, the liquid composition may contain up to 6 wt.%, in particular 3 to 6 wt.%, of a dispersing polymethacrylate. Polymethacrylates are esters of polymethacrylic acid, esterified with, for example, alkyl alcohols, such as C1-C4 alkyl, in particular with methanol (leading to polymethyl methacrylate, PMMA).

[0058] In a similarly preferred embodiment of the invention, the base oil also comprises a GTL base oil according to Group III of the API classification. This advantageously improves the applicability of this base oil to electronic components. The grouping of base oils is shown in the table in the exemplary embodiment.

[0059] The composition according to the invention preferably comprises a flow improver (PPD) in an amount of <0.5 wt. %, wherein the flow improver is selected from hydrogenated polystyrene-co-isoprene (HSI), ethylene-propylene copolymers (OCP), polyisobutylene (PIB), polyalkyl acrylates and methacrylates and their copolymers (PAMA), vinylpyrrolidone / methacrylate copolymers, polyvinylpyrrolidone, polybutenes, olefin copolymers, styrene / acrylate copolymers, polyethers, alkylated naphthalene derivatives, and mixtures thereof. Polyalkyl acrylates and methacrylates are particularly preferred.

[0060] In a preferred embodiment of the invention, the composition has a boron content of 20 to 300 mg / kg.

[0061] Preferably, the composition contains no or only small amounts of sulfur compounds of the sulfurized olefin type, ranging from 0 to <0.4%. These compounds have unfavorable corrosion behavior with copper materials.

[0062] The sulfur content in the lubricating fluid composition according to the invention is preferably 0.05 to 0.25 wt. %, particularly preferably 0.07 to 0.13 wt. %. This sulfur content refers in the present case to the total content of bound and unbound sulfur in the composition, comprising sulfur contained in the sulfur compounds according to the alkylthiadiazole compound according to formula (I) and optionally, in a preferred embodiment, with the ammonium salt of a phosphorus compound according to formula (II). Any sulfur present in base oils and adjusting oils from additives must be taken into account at 0.01 to 0.05 wt. % (PAO / GtL only residual sulfur). The sulfur content describes a standard analytical parameter in the context of quality assurance of gear oils.

[0063] In a preferred embodiment of the invention, the phosphorus content of the composition is 0.02 to 0.1 wt. %, particularly in the form of phosphorus bound in various additives. Phosphorus content, as used herein, refers to the total content of bound and unbound phosphorus in the composition, including any phosphorus present in the base oil as well as phosphorus bound in corresponding additives. Phosphorus-containing additives are known to improve the lubricity of the composition against abrasive wear.

[0064] In a preferred embodiment of the composition according to the invention, the kinematic viscosity measured at 100 °C is 1.5 to 3.3 mm 2 / s (centistokes), preferably 2.0 to 2.9 mm 2 / s particularly preferred 2.5 to 2.9 mm 2 / s. Viscosities in the above-mentioned ranges are particularly suitable for lubricating gears in electric drives.

[0065] To modify the flow properties of the base oil, so-called flow improvers (viscosity index (VI) improvers and pour point depressants), for example, high-molecular-weight thickeners of 5 to 15 wt.%, are normally added. The composition according to the invention preferably contains these classic flow improvers only in comparatively low concentrations of <0.5 wt.%.

[0066] For a target viscosity of the final formulated lubricant of KV100 = 3cSt or lower, a GTL 3 and possibly also a GTL 4 are particularly preferred (see Table 1).

[0067] Table 1 :

[0068] Table 2: Typical data of GTL according to the technical data sheets compared with PAO

[0069] Synthetic base oils of Groups III and IV, as specified in the American Petroleum Institute (API) "Base Oil Interchangeability Guidelines," can be used as the base oil for the lubricant composition according to the invention. The API base oil groups I to V are shown in Table 3.

[0070] Table 3: 2 ASTM D1552, ASTM D2622, ASTM D3120, ASTM D4294 or ASTM D4927.

[0071] 3 ASTM D2007

[0072] 4 ASTM D2270

[0073] Further preferred embodiments of the invention emerge from the remaining features mentioned in the subclaims.

[0074] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0075] Examples

[0076] Materials

[0077] Base oil: Syn 2.5: Chevron Synfluid 2.5

[0078] PAO 4: Polyalphaolefin 4 HC 3 / 4

[0079] Viscosity improver: D-PMA: Dispersing polyalkyl methacrylate

[0080] Dispersant: B-PP: borated PIBSA / PAM succinimide

[0081] PP: boron-free PIBSA / PAM succinimide

[0082] Extreme Pressure Additive: EP 1: AT: Alkyl thiadiazole with CgHi9 (tert-nonyl); according to (la) / (lb) EP 2: olefinic polysulfide

[0083] Wear protection additive: AW 1: Phosphoric acid compound (reaction product of 4-methyl-

[0084] 2-pentanol and diphosphorus pentasulfide, which is propoxylated, esterified with diphosphorus pentaoxide and salted with amines and has a C12-14 tert-alkyl radical; according to (II) AW 2: Alkylphosphatamine salt AW 3: lrgalube®353 (BASF) AW4: Alkyl phosphite AW5: Dibutylphosphonate AW6: Amine-neutralized phosphoric acid ester Friction improver: FM 1 : Molybdenum dicarbamate

[0085] FM 2: ethoxylated amine

[0086] Corrosion protection additive: KS 1: Triazolealkylamine

[0087] KS 2: Irgamet® TTZ (BASF)

[0088] KS 3: alkyl benzotriazole alkylamine

[0089] Antioxidant: AO 1: Bisnonylphenylamine

[0090] AO 2 : Diphenylamine

[0091] Adjusting oil

[0092] Examples 1 to 10

[0093] Compositions according to Table 4 were prepared by mixing, with all values ​​being in % by weight.

[0094] The compositions of Examples 1 to 10 were investigated for various physical and thermodynamic properties. The results are summarized in Tables 5 to 8.

[0095] The elemental composition of the compositions of Examples 1 to 10 is shown in Table 9, with all values ​​given in mg / kg of the total composition. Example 10 is a typical modern manual transmission oil with excellent lubrication properties. However, both its thermal stability and compatibility with copper are inadequate for applications in the electric drivetrain of an electric machine. The efficiency was also significantly lower.

[0096] Table 4:

[0097] Table 5:

[0098] Table 6:

[0099] Table 7:

[0100] Table 8:

[0101] Table 9:

Claims

Patent claims Liquid composition with a dynamic viscosity in the range of 0.8 to 4.0 mm 2 / s at 100°C, comprising • 50-99.93 wt.% of a base oil or base oil blend selected from polyalphaolefin oils according to Group IV of the API classification or GTL base oils according to Group III of the API classification; and the following additives: • a boron-containing, ash-free succinic acid amide and / or imide, • an alkylthiadiazole compound according to formula (Ia) and / or (Ib), where C9H19 is terf-nonyl. A liquid composition according to claim 1, further comprising at least one of the following phosphorus compounds (II): preferably the reaction product of 4-methyl-2-pentanol and Diphosphorus pentasulfide, which is propoxylated, esterified with diphosphorus pentaoxide and Amines and has a C12-14 tert-alkyl radical. The liquid composition according to claim 1 or 2, wherein the boron-containing, ashless succinic acid amide and / or imide is a dispersant based on poly(isobutylene) succinamide or imide (PIBSA or PIBSI) prepared from maleic acid amide or imide. The liquid composition according to claim 1 to 3, wherein the boron-containing, ashless succinic acid amide and / or imide has a proportion of 0.2 to 4.0 wt. %. A liquid composition according to any one of claims 1 to 4, wherein the boron-containing, ash-free succinic acid amide and / or imide has a molecular weight, MW, of 500 to 1300, preferably 900 to 1100, particularly preferably 950 to 1050. A liquid composition according to any one of claims 1 to 5, wherein the alkylthiadiazole compound according to formula (Ia) and / or (Ib) has a proportion of 0.05 to 1.0 wt. %. A liquid composition according to any one of claims 1 to 6, further comprising the thiophosphite EG 424-820-7. A liquid composition according to any one of claims 1 to 7, further comprising a flow improver in an amount of < 0.5 wt.-%, wherein the flow improver is selected from hydrogenated polystyrene-co-isoprene (HSI), ethylene-propylene copolymer (OCP), polyisobutylene (PIB), polyalkyl acrylates and methacrylates and their copolymers (PAMA), vinylpyrrolidone / methacrylate copolymers, polyvinylpyrrolidone, polybutenes, olefin copolymers, styrene / acrylate copolymers, polyethers, alkylated naphthalene derivatives, and mixtures thereof. The fluid composition according to any one of claims 1 to 8, wherein it has a boron content of 20 to 300 mg / kg. The fluid composition according to any one of claims 1 to 9, wherein the sulfur content is 0.05 to 0.25 wt.%, in particular 0.07 to 0.13 wt.%. A fluid composition according to any one of claims 1 to 10, wherein the phosphorus content is 0.02 to 0.1 wt.%. A fluid composition according to any one of claims 1 to 11, wherein the kinematic viscosity at 100°C is 2.0 to 2.8 mm. 2 / s, especially 2.2 to 3.1 mm 2 / s. Use of the liquid composition according to any one of claims 1 to 12 in battery-powered vehicles, electric drives, and high-speed transmissions in combination with electric machines.

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