Lubricant composition containing traction coefficient additive

Abstract

Provided herein is a lubricant composition suitable for use in electric vehicles that includes a traction coefficient additive. The lubricant composition provides utility as an electric vehicle gear oil, particularly an electric vehicle transmission fluid. The lubricant composition provides improved traction coefficient properties in use compared to a comparable lubricant composition that does not include the traction coefficient additive.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This application was filed on 28 May 2021 and claims priority to U.S. Provisional Patent Application No. 63 / 194,392, entitled “LUBRICANT COMPOSITION COMPRISING TRACTION COEFFICIENT ADDITIVE,” the entire disclosure of which is incorporated herein by reference.

[0002] (Field of Invention) The present invention relates to a lubricant composition suitable for use in electric vehicles, comprising a traction coefficient additive. The lubricant composition described herein offers particular utility in gear oils for electric vehicles, especially in transmission fluids for electric vehicles, and provides improved traction coefficient characteristics during use compared to equivalent lubricant compositions without additives. [Background technology]

[0003] An electric vehicle is a vehicle propelled using one or more electric motors. Electric vehicles can be entirely electric (also known as pure electric or all-electric vehicles) or hybrid (in hybrid electric vehicles, propulsion may sometimes be achieved from alternative means such as hydrocarbon-derived fuels). Electric vehicles also include range-extended electric vehicles, where the vehicle is powered by electric motors and plug-in batteries, but the vehicle may also have an auxiliary combustion engine used only to supplement battery charging and not as the primary propulsion source. The present invention is suitable for use in all of the types of electric vehicles mentioned.

[0004] Gear oil is a subclass of lubricants and typically contains a lubricant base stock (or base oil) as its main component. The selection of the lubricant base stock used in lubricating oils can have a significant impact on properties such as oxidation and thermal stability, volatility, low-temperature fluidity, additives, contaminants, and the solvency of decomposition products, as well as traction. More specifically, the coefficient of traction of a lubricant is an inherent property of the lubricant base stock liquid (i.e., based on the chemical composition of the base oil), and it has been conventionally taught in the industry that the coefficient of traction is not affected by additives. It is widely believed in the industry that the viscosity of the base stock liquid determines the coefficient of traction of the lubricant during use.

[0005] The selection of the lubricant base stock can have a significant impact on properties such as oxidation and thermal stability, volatility, low-temperature fluidity, additives, contaminants, and the solvency of decomposition products, as well as traction. The American Petroleum Institute (API) currently defines five groups of lubricant base stocks (API Publication 1509).

[0006] Groups I, II, and III are mineral oils classified by the amount of saturates and sulfur they contain and their viscosity index. Table 1 below illustrates these API classifications for Groups I, II, and III.

[0007]

Table 1

[0008] Group I base stocks are solvent-refined mineral oils, which are the cheapest base stocks to manufacture and currently account for the majority of base stock sales. They offer satisfactory oxidation stability, volatility, low-temperature performance, and traction properties, and have very good solubility for additives and contaminants. Group II base stocks are mainly hydrotreated mineral oils, which typically offer improved volatility and oxidation stability compared to Group I base stocks. The use of Group II stocks has grown to about 30% of the US market. Group III base stocks are either highly hydrotreated mineral oils or can be produced by wax or paraffin isomerization. They have better oxidation stability and volatility than Group I and II base stocks, but are known to have a limited range of commercially available viscosities.

[0009] Group IV base stocks differ from Groups I-III in that they are synthetic base stocks, such as polyalphaolefins (PAOs). PAOs have good oxidation stability, volatility, and a low pour point. A disadvantage is that they have moderate solubility for polar additives, such as anti-wear additives.

[0010] Group V base stocks are all base stocks not included in Groups I-IV. Examples include alkylnaphthalenes, alkyl aromatic compounds, vegetable oils, esters (including polyol esters, diesters, and monoesters), polycarbonates, silicone oils, and polyalkylene glycols.

[0011] Passenger cars are rapidly shifting towards electrification, which exceeds the current understanding and specifications of original equipment manufacturers (OEMs) and regulatory bodies regarding gear oil specifications. Current generations of hybrid and electric vehicles still use standard automatic transmission fluid (ATF) formulations that were not specifically designed for this application. Current gear oils do not meet OEMs' dynamic requirements due to the rapid advancements in electric vehicle technology, ATF-based fluids, and ADPA. Furthermore, because electric motors in EVs are highly efficient, losses due to gear lubricants in EV powertrain systems can be very significant. Reducing energy losses would result in improved battery life in EVs in use, which means that as battery range increases, EVs will need to be charged less frequently.

[0012] Therefore, despite the ongoing development of lubricant technologies for transmissions and gearboxes in internal combustion engines, hybrid and electric vehicles, there remains a need for lubricant formulations that offer improved energy efficiency over the lifespan of the lubricant. More specifically, there is a need for lubricant technologies optimized and tuned to meet the requirements of electric vehicle gearboxes, which differ from those of conventional combustion engines. Thus, there is still a strong demand for new lubricant compositions that offer high performance (particularly low traction) in electric engines, while being commercially viable for the electric passenger car market.

[0013] The object of the present invention is to provide a lubricant composition suitable for use in electric vehicle gearboxes that provides improved low traction achieved by including a traction coefficient additive, and thus minimizes energy loss. In addition to providing low traction, the lubricant composition should have sufficient oxidation stability, as well as good low-temperature properties and compatibility with materials such as elastomers and copper. [Overview of the project]

[0014] The inventors have surprisingly discovered a lubricant composition that overcomes or significantly reduces at least one of the aforementioned problems.

[0015] Thus, the present invention provides a lubricant composition comprising a base stock and at least 2% by weight of a traction coefficient additive compound of formula (I) R 1 [(AO) n -R 2 m (I) [wherein R 1 is the residue of a group having at least two active hydrogen atoms, m is at least 2, AO is an alkylene oxide residue, each n is independently from 0 to 100, each R 2 is independently H or R 3 where each R 3 is independently the residue of a polyhydroxyalkyl or polyhydroxyalkenyl carboxylic acid, the residue of a hydroxyalkyl or hydroxyalkenyl carboxylic acid and / or the residue of an oligomer of a hydroxyalkyl or hydroxyalkenyl carboxylic acid, and on average at least 0.5 R 2 groups are R 3 .

[0016] The present invention also provides a method for reducing the traction coefficient in the gearbox of an electric vehicle, which includes using the lubricant composition according to the first embodiment of the present invention.

[0017] The traction coefficient additive described herein can advantageously improve the performance of the gearbox of an electric vehicle to which the lubricant composition is applied by reducing the traction coefficient of the base stock.

[0018] ​The traction coefficient additives described herein can be used in lubricant compositions, more specifically, as traction coefficient reducing additives in gear oil for electric vehicle gearboxes.

[0019] The traction coefficient additive is given by formula (I): R 1 [(AO) n -R 2 ] m (I) [In the formula, R 1 This is a residue of a group having at least two active hydrogen atoms, m is at least 2, AO is an alkylene oxide residue, Each n is independent and ranges from 0 to 100. Each R 2 H or R 3 And here, each R 3 These are independently polyhydroxyalkyl or polyhydroxyalkenylcarboxylic acid residues, hydroxyalkyl or hydroxyalkenylcarboxylic acid residues and / or hydroxyalkyl or hydroxyalkenylcarboxylic acid oligomer residues, On average, at least 0.5 R 2 The base is R 3 It contains the compound [which is].

[0020] This traction coefficient additive can be considered, at least conceptually, as a "core group" of the compound, group R 1 It consists of the following. This core group is preferably a residue of a compound containing at least two active hydrogen atoms, which are present in the hydroxyl group and / or amino group, and more preferably only in the hydroxyl group (after removal of m active hydrogen atoms). Preferably, the core group is a substituted hydrocarbyl group, particularly C3-C3. 30 It is a substituted hydrocarbyl compound residue.

[0021] R 1 Examples of core groups include the following compound residues after removing m active hydrogen atoms: 1. Glycerol and polyglycerol, especially diglycerol and triglycerol, their partial esters, or any triglycerides containing multiple hydroxyl groups, such as castor oil; 2. Polymethylol alkanes of three or more types, such as trimethylolethane, trimethylolpropane, pentaerythritol and dipentaerythritol, and their partial esters; 3. Sugars, especially non-reducing sugars, such as sorbitol, mannitol, and lactitol; etherified derivatives of sugars, such as sorbitan (cyclic dehydro-ether of sorbitol); partially alkyl acetals of sugars, such as methyl glucose and alkyl (poly)saccharides; and other oligomers / polymers of sugars, such as dextrin; partially esterified derivatives of sugars, such as fatty acid esters, such as lauric acid, palmitic acid, oleic acid, stearic acid, and behenic acid; esters of sorbitan, sorbitol, and sucrose; amino sugars, such as N-alkylglucamines and their respective N-alkyl-N-alkenoylglucamides; 4. Polyhydroxycarboxylic acids, especially citrate and tartaric acid; 5. Amines containing bifunctional and polyfunctional amines, in particular alkylamines containing alkyldiamines such as ethylenediamine (1,2-diaminoethane); 6. Amino alcohols, especially ethanolamine, 2-aminoethanol, diethanolamine, and triethanolamine; 7. Carboxylic acid amides such as urea, malonamide, succinamide; and 8. Amidocarboxylic acids, such as succinamide.

[0022] Preferred R 1 The core group is a residue of a group having at least 3, more preferably in the range of 4 to 10, particularly 5 to 8, and especially 6 free hydroxyl and / or amino groups. 1 The group preferably has a linear C4-C7 chain, more preferably a C6 chain. The hydroxyl group or amino group is preferably directly bonded to the carbon atoms of the chain. A hydroxyl group is preferred.

[0023] R 1 Preferably, R is an open-chain tetratol, pentitol, hexitol or heptitol group or an anhydro, such as cycloetheranhydro, or a derivative of such a group. In a particularly preferred embodiment, R 1 R is a residue of a sugar, more preferably a monosaccharide such as glucose, fructose, or sorbitol, a disaccharide such as maltose, palytose, lactitol, or lactose, or a higher-order oligosaccharide, or a residue derived therefrom. 1 This is preferably a monosaccharide residue, more preferably glucose, fructose, or sorbitol, particularly sorbitol.

[0024] R 1 An open-chain form of the group is preferred, but groups containing internal cyclic ether functional groups can be used, and such cyclization may be inadvertently obtained if the synthetic route exposes the group to relatively high temperatures or other conditions that promote such cyclization.

[0025] The subscript m is R 1 The core group's functionality is measured by the alkoxylation reaction, in which the core group replaces some or all of the active hydrogen atoms in the molecule being induced (depending on the molar ratio of the core group to the alkoxylation group). Reactions at specific sites can be limited or prevented by steric hindrance or appropriate protection. The terminal hydroxyl groups of the polyalkylene oxide chain in the resulting compound are then available for reaction with the acyl compound as defined above. The subscript m is preferably in the range of at least 3, more preferably 4-10, particularly 5-8, and especially 5-6. Mixtures may be used, and are commonly used, so m may be an average value or a non-integer.

[0026] The alkylene oxide group AO is typically represented by formula: -(C r H 2rThe group is O)-(wherein r is 2, 3, or 4, preferably 2 or 3), i.e., an ethylene oxy(-C2H4O-) or propylene oxy(-C3H6O-) group, which may represent different groups along the alkylene oxide chain. Generally, it is desirable that this chain be a homopolymer ethylene oxide chain. However, the chain may also be a homopolymer chain of propylene glycol residues, or a block or random copolymer chain containing both ethylene glycol and propylene glycol residues. Typically, when copolymer chains of ethylene oxide units and propylene oxide units are used, the molar ratio of ethylene oxide units used is at least 50%, more commonly at least 70%.

[0027] The number of alkylene oxide residues in the (poly)alkylene oxide chain, i.e., the average value of parameter n, is preferably in the range of 1 to 50, more preferably 2 to 30, more preferably 2 to 20, particularly 2 to 10, and especially 3 to 8.

[0028] base R 2 is the "end group" of the (poly)alkylene oxide chain. The end group is hydrogen or R 3 And here, each R 3 These are independently a polyhydroxyalkyl or polyhydroxyalkenylcarboxylic acid residue, a hydroxyalkyl carboxylic acid or hydroxyalkenyl carboxylic acid residue, and / or a hydroxyalkyl or hydroxyalkenyl carboxylic acid oligomer residue. Preferably, each R 3 These are independently a residue of a polyhydroxyalkylcarboxylic acid, a residue of a hydroxyalkylcarboxylic acid and / or a residue of a hydroxyalkylcarboxylic acid oligomer, more preferably a residue of a polyhydroxyalkylcarboxylic acid.

[0029] Preferably, R 2 At least 1.0 of the bases, preferably at least 1.5, more preferably at least 2.0, especially at least 2.2, and most notably at least 2.4 are R 3 In addition, preferably, R 2A maximum of 6.0 bases, preferably a maximum of 4.0, more preferably a maximum of 3.0, especially a maximum of 2.7, and particularly a maximum of 2.5 are R 3 That is the case.

[0030] Hydroxylalkyl and hydroxyalkenyl carboxylic acids are of the formula HO-X-COOH (wherein X is a divalent saturated or unsaturated, preferably saturated, aliphatic group containing at least 8 and 20 or fewer carbon atoms, typically 11 to 17 carbon atoms), with at least 4 carbon atoms directly between the hydroxyl group and the carboxylic acid group. Preferably, the hydroxyalkyl carboxylic acid is 12-hydroxystearic acid. In practice, such hydroxyalkyl carboxylic acids are commercially available as mixtures of hydroxyl acids and corresponding unsubstituted fatty acids. For example, 12-hydroxystearic acid is typically produced by hydrogenation of castor oil fatty acids containing C18 unsaturated hydroxyl acids and unsubstituted fatty acids (oleic acid and linoleic acid), which, upon hydrogenation, yields a mixture of 12-hydroxystearic acid and stearic acid. Commercially available 12-hydroxystearic acid typically contains about 5% to 8% unsubstituted stearic acid.

[0031] Polyhydroxyalkyl or polyhydroxyalkenylcarboxylic acids can be produced by polymerizing the above-mentioned hydroxyalkyl or hydroxyalkenylcarboxylic acids. The presence of the corresponding unsubstituted fatty acid acts as a termination agent and thus limits the chain length of the polymer. Preferably, the number of hydroxyalkyl or hydroxyalkenyl units is 2 to 12 on average, preferably 3 to 10, more preferably 4 to 9, particularly 5 to 8, and especially 6 to 7. The molecular weight of the polyacid is typically 600 to 3,000, particularly 900 to 2,700, more particularly 1,500 to 2,400, and especially about 2,100.

[0032] The residual acid value of polyhydroxyalkyl or polyhydroxyalkenylcarboxylic acids is typically less than 50 mgKOH / g, with a preferred range of 30 mgKOH / g to 35 mgKOH / g. Typically, the hydroxyl value of polyhydroxyalkyl or polyhydroxyalkenylcarboxylic acids is at a maximum of 40 mgKOH / g, with a preferred range of 20 mgKOH / g to 30 mgKOH / g.

[0033] Oligomers of hydroxyalkyl or hydroxyalkenylcarboxylic acids may differ from polymers in that their terminals are not composed of the corresponding unsubstituted fatty acids. Preferably, they are dimers of hydroxyalkyl or hydroxyalkenylcarboxylic acids.

[0034] In one preferred embodiment, on average preferably, R 2 At least 1.0, preferably at least 1.5, more preferably at least 2.0, particularly at least 2.3, and especially at least 2.4 of the group are polyhydroxyalkyl carboxylic acid residues. 3 It is the base. In addition, on average preferably, R 2 R has up to 4.0 groups, preferably up to 3.5 groups, more preferably up to 3.0 groups, particularly up to 2.7 groups, and especially up to 2.5 groups, which are polyhydroxyalkyl carboxylic acid residues. 3 These are the groups. These polyhydroxyalkylcarboxylic acid residues preferably contain an average of 3 to 10, preferably 4 to 9, more preferably 5 to 8, particularly 6 to 7, and especially 7 hydroxyalkyl monomer units.

[0035] The polyhydroxyalkyl carboxylic acid residue is preferably terminated with an unsubstituted carboxylic acid, more preferably with stearic acid.

[0036] In another preferred embodiment, R 3When the group comprises a hydroxyalkyl carboxylic acid residue, preferably a polyhydroxyalkyl carboxylic acid residue, the total number of hydroxyalkyl carboxylic acid residues present in the compound of formula (I) as defined herein is preferably in the range of 5 to 30 on average, preferably 8 to 20, more preferably 10 to 17, particularly 12 to 15, and especially 13 to 14 hydroxyalkyl monomer units.

[0037] In a further preferred embodiment, on average, preferably, R 2 At least 2.0 of the groups, preferably at least 2.5, more preferably at least 3.0, particularly at least 3.3, and especially at least 3.5 are H. In addition, on average preferably, R 2 A maximum of 5.0 of the elements, preferably a maximum of 4.5, more preferably a maximum of 4.0, especially a maximum of 3.7, and most notably a maximum of 3.6, are H.

[0038] If the core group is derived from, for example, pentaerythritol, the alkoxylation of the core residue can be uniformly distributed across the four available sites from which active hydrogen can be removed, and the distribution of acyl groups during esterification of the terminal hydroxyl functional group approaches the expected random distribution. However, if the core group is derived from a compound such as sorbitol and not all of the active hydrogen atoms are equivalent, the alkoxylation can result in unequal chain lengths for the polyalkylene oxy chain.

[0039] The traction coefficient additive first contains m active hydrogen atoms R 1 The core group can be produced by alkoxylation, for example, by reacting it with a required amount of alkylene oxide, such as ethylene oxide and / or propylene oxide, using techniques well known in the art. The second step of this process preferably involves reacting the alkoxylated species with polyhydroxyalkyl(alkenyl)carboxylic acid and / or hydroxyalkyl(alkenyl)carboxylic acid under standard catalytic esterification conditions at a temperature up to 250°C. Therefore, the traction coefficient additive of formula (I) is the group R1 It can be produced by reacting with alkylene oxide, and then esterifying the alkoxylated product of this reaction with polyhydroxyalkyl(alkenyl)carboxylic acid, hydroxyalkyl(alkenyl)carboxylic acid, or a mixture thereof.

[0040] In one preferred embodiment, the traction coefficient additive is an alkoxylated core group R 1 It is prepared by reaction with a polyhydroxyalkylcarboxylic acid, where the molar ratio of the alkoxylated core group to the polyacid is preferably in the range of 1:1 to 1:4, more preferably 1:2 to 1:2.8. Preferably, the traction coefficient additive prepared by this route has a molecular weight (Mn) of 3,000 to 10,000, more preferably 4,000 to 7,000, and particularly 5,000 to 6,000.

[0041] The lubricant composition of the present invention includes a base stock. The lubricant composition may contain at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, and even more preferably at least 75% by weight of base stock, based on the total weight of the composition. The lubricant composition may contain up to 98% by weight, preferably up to 95% by weight, and more preferably up to 90% by weight of base stock, based on the total weight of the plastic product.

[0042] The lubricant composition contains, based on the total weight of the composition, at least 2% by weight, preferably at least 2.5% by weight, preferably at least 3% by weight, more preferably at least 5% by weight, and even more preferably at least 7% by weight of a traction coefficient additive. The lubricant composition may contain, based on the total weight of the lubricant composition, up to 20% by weight, preferably up to 15% by weight, and most preferably up to 10% by weight of a traction coefficient additive.

[0043] In one embodiment, the lubricant composition is non-aqueous. However, it will be understood that the components of the lubricant composition may contain small amounts of residual water (moisture), and therefore may be present in the lubricant composition. The lubricant composition may contain less than 5% by weight of water based on the total weight of the composition. More preferably, the lubricant composition is substantially water-free, i.e., it contains less than 2% by weight, less than 1% by weight, or preferably less than 0.5% by weight of water based on the total weight of the composition. Preferably, the lubricant composition is substantially anhydrous.

[0044] The lubricant composition provides suitable gearbox oil for use in electric vehicles. To adapt the lubricant composition to its intended application, it may contain one or more of the following additional additive types: 1. Dispersants: For example, alkenyl succinimide, alkenyl succinate esters, alkenyl succinimide modified with other organic compounds, alkenyl succinimide modified by post-treatment with ethylene carbonate or boric acid, pentaerythritol, phenate-salicylate and their post-treated analogs, alkali metals or mixed alkali metals, alkaline earth metal borates, dispersions of hydrated alkali metal borates, dispersions of alkaline earth metal borates, polyamide ashless dispersants, or mixtures of such dispersants. 2. Antioxidants: Antioxidants reduce the tendency of mineral oil to degrade during use, which is manifested by oxidation products such as sludge and varnish-like deposits on metal surfaces, and by an increase in viscosity. Examples of antioxidants include 4,4'-methylene-bis(2,6-di-tert-butylphenol), 4,4'-bis(2,6-di-tert-butylphenol), 4,4'-bis(2-methyl-6-tert-butylphenol), 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), 4,4'-isopropylidene-bis(2,6-di-tert-butylphenol), 2,2'-methylene-bis(4-methyl-6-nonylphenol), 2,2'-isobutylidene-bis(4,6-dimethylphenol), 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 2, Examples of phenolic antioxidants include 6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-l-dimethylamino-p-cresol, 2,6-di-tert-4-(N,N'-dimethylaminomethylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)-sulfide, and bis(3,5-di-tert-butyl-4-hydroxybenzyl). Other types of antioxidants include alkylated diphenylamines (e.g., Irganox L-57, e.g., BASF), metal dithiocarbamates (e.g., zinc dithiocarbamate), and methylenebis(dibutyldithiocarbamate). 3. Anti-wear agents: As the name suggests, these agents reduce wear on moving metal parts. Examples of such agents include phosphates, phosphites, carbamates, esters, sulfur-containing compounds, and molybdenum complexes. 4. Emulsifier: For example, linear alcohol ethoxylate. 5. Deemulsifiers: For example, addition products of alkylphenols and ethylene oxides, polyoxyethylene alkyl ethers, and polyoxyethylene sorbitan esters. 6. Extreme pressure agents (EP agents): For example, zinc dialkyldithiophosphate (primary alkyl, secondary alkyl, and aryl types), sulfurized oil, diphenyl sulfide, methyl trichlorostearate, chlorinated naphthalene, fluoroalkylpolysiloxane, and lead naphthenate. A preferred EP agent is, for example, zinc dialkyldithiophosphate (ZnDTP) as one of the co-additive components for wear-resistant hydraulic fluid compositions. 7. Multifunctional additives: For example, oxymolybdenum dithiocarbamate sulfide, oxymolybdenum organic phosphorodithioate sulfide, oxymolybdenum monoglycehde, oxymolybdenum diethilate amide, amine-molybdenum complex compounds, and sulfur-containing molybdenum complex compounds. 8. Viscosity index improvers: For example, polymethacrylate polymers, ethylene-propylene copolymers, styrene-isoprene copolymers, styrene-hydrogenated copolymers, polyisobutylene, and dispersible viscosity index improvers. 9. Pour point depressants: e.g., polymethacrylate polymers. While the pour point of the compound of formula (I) is suitable for use as gearbox oil, embodiments utilizing relatively long-chain linear molecules can benefit from the addition of pour point depressants. Additionally, the presence of several alternative additives can negatively affect the pour point of the formulation, making the addition of pour point depressants attractive. 10. Foam inhibitors: For example, alkyl methacrylate polymers and dimethyl silicone polymers. 11. Friction modifiers: Examples include amides, amines, and partially aliphatic esters of polyhydric alcohols, such as glycerol monooleate, oleylamide, and alternative friction modifiers available from Croda under the trade name "Perfad" or from Nouryon under the trade name "Ethomeen".

[0045] The lubricant composition may contain at least 0.5% by weight, preferably at least 1% by weight, and more preferably at least 5% by weight of further additives or a mixture of further additives, based on the total weight of the composition. The lubricant composition may also contain up to 30% by weight, preferably up to 20% by weight, and more preferably up to 10% by weight of further additives or a mixture of further additives, based on the total weight of the composition.

[0046] Additives may be available in the form of commercially available additive packs. The composition of such additive packs varies depending on the required use of the additive pack. Those skilled in the art can select a suitable commercially available additive pack for gear oil. An example of an additive pack particularly suitable for the gear oil of the present invention is Evogen 5201, e.g., Lubrizol, USA, which is specifically designed for use in electric vehicles.

[0047] Despite the examples above, in order to make a lubricant composition suitable for use in electric vehicles, the selection of any additive(s) should take into consideration copper compatibility (due to the requirements of electric motors) and providing or exhibiting low (but not necessarily zero) conductivity, and not all additives commonly used in conventional combustion engine automobile engines are suitable for use in electric vehicle powertrain fluids.

[0048] This specification uses the base stock group nomenclature defined by the American Petroleum Institute (API). Base stocks can be selected based on the intended use of the lubricant composition.

[0049] Preferably, the base stock is selected from the group consisting of API Group I, II, III, IV, V base stocks or mixtures thereof. More preferably, the base stock is selected from API Group II, III, IV, V, or mixtures thereof. If the base stock contains polyalphaolefin (PAO) from Group IV, the base stock may also preferably contain mineral oil from Group I, II, or III or ester from Group V to improve the solubility of the traction coefficient additive in the base stock. In the latter case, the ester from Group V may be present in 5% to 20% by weight of the lubricant composition to improve the solubility of the traction coefficient additive in the base stock. Therefore, the base stock may be a mixture of Group IV and Group V base stocks or Group IV and Group I, II, or III base stocks.

[0050] The lubricant composition of the present invention is suitably used as gearbox oil for electric vehicles. When the lubricant composition is gearbox oil, the traction coefficient additive is preferably present at a concentration in the range of 2% to 10% by weight based on the total weight of the gearbox oil.

[0051] The lubricant composition may have a kinematic viscosity according to the ISO grade. The ISO grade is defined as the midpoint kinematic viscosity of the sample at 40°C, expressed as cSt(mm²). 2 Specify in seconds. For example, ISO 100 has a viscosity of 100 ± 10 cSt, and ISO 1000 has a viscosity of 1000 ± 100 cSt. The lubricant composition preferably has a viscosity in the range of ISO 10 to ISO 680, more preferably ISO 15 to ISO 320.

[0052] The lubricant composition of the present invention enables a reduction in the traction coefficient over a temperature range of 0°C to 200°C, preferably over a temperature range of 20°C to 100°C, and more preferably over a temperature range of 40°C to 60°C, compared with equivalent lubricant compositions that do not contain additives.

[0053] The lubricant compositions of the present invention may be used in other arts where improving the traction coefficient of the lubricant composition may be advantageous; that is, the present invention may have broader utility than merely its use in electric vehicles. Accordingly, the gear oils described herein may be industrial, automotive, and / or marine gear oils. When the lubricant composition is a gear oil, the traction coefficient additive is preferably present in an amount ranging from 2% to 10% by weight based on the total weight of the gear oil, such that an improvement in the traction coefficient of the lubricant base stock (or base oil) is achieved.

[0054] Industrial gear oils are suitable for use in gearboxes containing spur gears, helical gears, bevel gears, hypoid gears, planetary gears, and worm gears. Suitable applications include factories such as mining, paper mills, textile mills, and sugar mills, as well as steel production and wind turbines. One preferred application is a wind turbine, where the gearbox typically has planetary gears. In a wind turbine, the gearbox is typically located between the rotor of the wind turbine blade assembly and the rotor of the generator. The gearbox can connect a low-speed shaft, rotated by the wind turbine blade rotor at approximately 10 to 30 revolutions per minute (rpm), to one or more high-speed shafts that drive the generator at approximately 1000 to 2000 rpm, which is the rotational speed required by most generators to produce electricity. The high torque applied to the gearbox can generate enormous stresses on the gears and bearings within the wind turbine. The gear oils of the present invention can improve the fatigue life of the wind turbine gearbox by reducing traction between the gears. Lubricants for use in wind turbine gearboxes are often subjected to long periods of use between maintenance, i.e., long service intervals. Therefore, a long-lasting lubricant composition with high stability may be required to provide appropriate performance over long periods. The gear oil according to the present invention may be suitable for such use.

[0055] Conventional automotive gear oils (i.e., for combustion engines) are suitable for use in manual transmissions, transfer cases, and differentials (all of which typically use hypoid gears). A transfer case refers to a part of a four-wheel drive system found in four-wheel drive and all-wheel drive systems. It is connected to the transmission and also to the front and rear axles by drive shafts. In the literature, this is also called a transfer gear case, transfer gearbox, transfer box, or jockey box. Although the present invention is specifically designed for use in electric vehicles (which have different physical property requirements than conventional automotive gear oils), the gear oil of the present invention can provide an improvement in the traction coefficient characteristics of the base stock for use with conventional automotive gear oils.

[0056] Marine thruster gearboxes have specific gear oils that contain higher proportions of additives, such as dispersants and corrosion inhibitors, compared to industrial and automotive gear oils, to address corrosion and water entrainment. There are also outboard gear oils used in propeller units, which may be more suitable for smaller vessels. The gear oils of the present invention may also provide improved traction coefficient characteristics of the base stock for use in marine thruster gearboxes.

[0057] Compounds of formula (I) as defined herein can reduce the traction coefficient of a traction coefficient lubricant composition, preferably a gear oil for electric vehicles, by at least 5%, preferably at least 10%, more preferably at least 15%, particularly at least 20%, and especially at least 25%, compared to an equivalent lubricant composition without traction coefficient additives, measured using a mini-traction machine (MTM) according to the tests described herein, at temperatures of 40°C and 60°C, a load of 1.0 GPa, and a sliding-to-rolling ratio (SRR) of 30%. The traction coefficient can be reduced over a temperature range of 0°C to 200°C, preferably over a range of 20°C to 100°C, and more preferably over a range of 40°C to 60°C, compared to an equivalent lubricant composition without traction coefficient additives, as described herein. [Examples]

[0058] The present invention will now be described by the following non-limiting embodiments, using the following materials and test procedures.

[0059] Test materials API Group IV synthetic polyalphaolefin-based stocks produced by the reaction of linear alphaolefins available from PAO 4-Spectra Syn(trademark) 4-ExxonMobil. API Group III VHVI base stock available from YUBASE 4-SK Lubricants. Priolube (trademark) 3970 - API Group V synthetic ester base stock available from Croda Inc. API GRII base stock available from EHC-45-ExxonMobil. Perfad® 3050 - A commercially available polymer friction modifier from Croda Inc.

[0060] Test Procedure Mini Traction Machine (MTM) The MTM was supplied by PCS Instruments (London, UK). The MTM provides a method for measuring the traction and friction coefficients of a given test sample using a ball-on-disk configuration while varying several characteristics, including speed, load, and temperature. The MTM is a computer-controlled precision traction measurement system, and its test specimens and configurations are designed to achieve realistic pressures, temperatures, and speeds without requiring large loads, motors, or structures. Details of the test parameters used in the data provided herein are as follows:

[0061] The disc was made of AISI 52100 hardened bearing steel with a mirror finish (Ra < 0.01 mm), and the balls were also made of AISI 52100 hardened bearing steel. The contact pressure was 0.43 GPa at a rolling speed of 0.2 m / s and 1 GPa at a rolling speed of 0.1 m / s. Approximately 50 mL of the test sample was then added. The balls were loaded against the surface of the disc, and the balls and disc were driven independently to create a rolling / sliding mixed contact with a sliding-to-rolling ratio (SRR) of 30%. The frictional force between the balls and disc was measured by a force transducer. Additional sensors measured the applied load and the temperature of the test sample.

[0062] The traction coefficient of the lubricant control composition (i.e., base stock without traction-reducing additives) test samples was determined at 40°C and 60°C using a MTM with a 3 / 4-inch ball on a smooth disc (as defined above). The MTM test was then repeated using test samples (either Sample 1 or Sample 2 shown below) containing the lubricant control composition with 2.5% by weight, 5% by weight, 7.5% by weight, or 10% by weight of the traction-reducing additive to be evaluated. Further tests were performed using test samples containing commercially available lubricant additives. The test samples are described in more detail below.

[0063] Example 1: Preparation of traction coefficient additive (Sample 1) Traction additive sample 1 was prepared according to the following method: 12-hydroxystearic acid (68.7 wt%), PEG-12 sorbitol (31.3 wt%), and tin oxalate catalyst (Tegokat 160 from Goldschmidt) were placed in a glass reactor and heated to 190°C under nitrogen. The reaction was continued for 12 to 24 hours, then cooled to below 100°C, and the product was discharged. This yielded a product (sample 1) with the generalized composition shown below. R 1 [(AO) n -R 2 ] m During the ceremony, R 1 These are the residues of sorbitol that have been excreted. m is 6, AO is an ethylene oxide residue, The average of n is 2. Each R 2 H or R 3 And here, each R 3 It is poly(12-hydroxystearic acid), R 2 The average of 0.58 units is R 3 That is the case.

[0064] Example 2: Preparation of traction coefficient additive (Sample 2) Traction additive sample 2 was prepared according to the following method: 12-hydroxystearic acid (68.7 wt%), PEG-50 sorbitol (31.3 wt%), and tin oxalate catalyst (Tegokat 160 from Goldschmidt) were placed in a glass reactor and heated to 190°C under nitrogen. The reaction was continued for 12 to 24 hours, then cooled to below 100°C, and the product was discharged. This yielded a product (sample 2) with the generalized composition shown below. R 1 [(AO) n -R 2 ] m During the ceremony, R 1This is a residue of sorbitol, m is 6, AO is an ethylene oxide residue, The average of n is 9. Each R 2 H or R 3 And here, each R 3 It is poly(12-hydroxystearic acid), R 2 The average of 0.58 units is R 3 That is the case.

[0065] Example 3. MTM test data The MTM data shown in Tables 1, 2, 3, 4, and 5 below demonstrate that both Sample 1 and Sample 2 (above) are effective in reducing the traction coefficient of conventional lubricant base stocks, with the reduction in traction coefficient observed after the introduction of the additives compared to the base stock alone control sample. The MTM test data are provided for the selection of lubricant base stocks (i.e., control samples) chosen to demonstrate the usefulness of this additive technology across a range of API base stocks. The base stock selection for testing includes the following base stocks: Group III (YUBASE 4), as well as blends of conventional Group II, Group V (PAO 4), and ester (Priolube 3970).

[0066] The effectiveness of Samples 1 and 2 as additives to improve the traction coefficient of base stocks is also compared to the effect on the traction coefficient of base stocks containing PAO 100. PAO 100 is a very commonly used thickener in conventional automotive gear oil formulations, and the inclusion of PAO 100 is known to increase the viscosity of base stocks, which can have a positive effect on the traction coefficient because a more viscous base stock can maintain a film at the test boundary.

[0067] The data provided in the table below shows that the use of Samples 1 and 2 resulted in a reduction of 2 to 10 times (in percentage) the traction coefficient of the base stock, particularly in the treatment rate range of 2.5% to 7.5% by weight. For Samples 1 and 2, there appears to be an optimal treatment rate of 5% to 7.5% by weight based on the total weight of the composition, and further increases in concentration do not result in any benefit to the traction coefficient, or even result in a more detrimental increase. This improvement in the traction coefficient is distinct from the viscosity-increasing effect achieved by the inclusion of PAO 100.

[0068] [Table 2]

[0069] [Table 3]

[0070] [Table 4]

[0071] [Table 5]

[0072] Referring to Table 5 below, the traction data for the commercially available polymer friction modifier Perfad 3050 clearly shows that it is not effective in reducing the traction coefficient at 40°C. Under less severe, more hydrodynamic lubrication type test conditions, the inclusion of Perfad 3050 results in an undesirable increase in the traction coefficient. Under more severe test conditions at 60°C and slower speeds, Perfad 3050 exhibits a traction reduction effect similar to that of PAO 100, but this is inferior to the reduction in traction coefficient improvement observed for the samples according to the present invention.

[0073] Table 6

Claims

1. The use of a lubricant composition as gearbox oil in electric vehicles, The lubricant composition comprises, based on the total weight of the lubricant composition, at least 75% by weight of base stock and 2% to 10% by weight of formula (I): R １ [(AO) ｎ -R ２ ] ｍ (I) [In the formula, -R １ This is a residue of sorbitol, -m is in the range of 5 to 6. -AO is an ethylene oxide residue, -n is in the range of 2 to 10. -Each R ２ H or R ３ And here, each R ３ is a residue of (poly)12-hydroxystearic acid, - on average at least 0.5 R ２ groups are R ３ in the traction coefficient additive compound of ] and use of a lubricant composition containing the same.

2. The use according to claim 1, wherein the lubricant composition comprises at least 2.5% by weight of the traction coefficient additive based on the total weight of the lubricant composition.

3. The use according to claim 2, wherein the lubricant composition further comprises one or more of the following additional additive types: dispersants, antioxidants, anti-wear agents, emulsifiers, deemulsifiers, extreme pressure agents, multifunctional additives, viscosity index improvers, pour point depressants, anti-foaming agents, and friction modifiers.

4. The use according to claim 3, wherein the lubricant composition comprises at least 0.5% by weight of further additives or a mixture of further additives based on the total weight of the lubricant composition.

5. The use according to claim 3, wherein the lubricant composition comprises up to 10% by weight of further additives or a mixture of further additives based on the total weight of the lubricant composition.

6. The use according to any one of claims 1 to 5, wherein the base stock is selected from the group consisting of API group I, II, III, IV, V base stocks or mixtures thereof.

7. A method for reducing the traction coefficient in the gearbox of an electric vehicle, comprising using a lubricant composition, The lubricant composition comprises, based on the total weight of the lubricant composition, at least 75% by weight of base stock and 2% to 10% by weight of formula (I): R 1 [(AO) n −R 2 ] m (I) [In the formula, -R 1 is a residue of sorbitol, -m is in the range of 5 to 6. -AO is an ethylene oxide residue, -n is in the range of 2 to 10. - Each R2 is independently H or R3, where each R3 is a residue of (poly)12-hydroxystearic acid. A method comprising a traction coefficient additive compound having at least 0.5 R2 groups on average being R3.

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