Lubricant Compositions Containing Traction Coefficient Additives - Patent application

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 TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 194,392, filed May 28, 2021, and entitled “LUBRICANT COMPOSITION COMPRISING TRACTION COEFFICIENT ADDITIVE,” the disclosure of which is incorporated herein by reference in its entirety.

[0002] FIELD OF THEINVENTION The present invention relates to lubricant compositions suitable for use in electric vehicles that contain a traction coefficient additive. The lubricant compositions described herein find utility, inter alia, in electric vehicle gear oils, particularly electric vehicle transmission fluids, providing improved traction coefficient properties in use compared to comparable lubricant compositions without the additive. [Background technology]

[0003] An electric vehicle is a vehicle that is propelled using one or more electric motors. Electric vehicles can be fully electric (also known as pure electric or all-electric vehicles) or hybrid in nature (in hybrid electric vehicles, propulsion can sometimes be achieved from alternative means such as hydrocarbon-derived fuels). Electric vehicles also include range-extended electric vehicles in which the vehicle is powered by an electric motor and a plug-in battery, although vehicles also include auxiliary combustion engines that are used only to supplement the battery charge 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 oils are a subclass of lubricants that typically contain a lubricant base stock (or base oil) as its major component. The choice of lubricant base stock utilized in a lubricant can have a significant impact on properties such as oxidation and thermal stability, volatility, low temperature fluidity, ability to dissolve additives, contaminants, and decomposition products, and traction. More specifically, it has been traditionally taught by the industry that the traction coefficient of a lubricant is an inherent property of the lubricant base stock fluid (i.e., based on the chemical composition of the base oil) and that the traction coefficient is not affected by additives. It is widely believed in the industry that the viscosity of the base stock fluid determines the traction coefficient of the lubricant in use.

[0005] The choice of lubricant base stock can have a significant effect on properties such as oxidation and thermal stability, volatility, low temperature fluidity, solvency of additives, contaminants and decomposition products, and 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 produce and currently account for the majority of base stock sales. They provide satisfactory oxidation stability, volatility, low temperature performance, and traction properties, and have very good solvency for additives and contaminants. Group II base stocks are primarily hydrotreated mineral oils, which typically provide improved volatility and oxidation stability compared to Group I base stocks. The use of Group II stocks has grown to about 30% of the U.S. market. Group III base stocks can be highly hydrotreated mineral oils or produced by isomerization of wax or paraffins. They are known to have better oxidation stability and volatility than Group I and II base stocks, but 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, e.g., polyalphaolefins (PAOs). PAOs have good oxidative stability, volatility, and low pour points. Drawbacks include moderate solubility of polar additives, e.g., anti-wear additives.

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

[0011] Passenger vehicles are rapidly changing towards electrification, which exceeds the understanding and specifications of current gear oil specifications of original equipment manufacturers (OEM's) and regulatory agencies. Current generation 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 the dynamic requirements of OEMs due to rapid advancements in electric vehicle technology, ATF base fluids, and adpacks. Furthermore, because electric motors in EVs are so efficient, losses due to gear lubricants in EV powertrain systems can be very large. Reducing energy losses provides improved battery life in EVs during use, which means that EVs require less frequent charging as battery range increases.

[0012] Thus, despite the continued development of lubricant technology for transmissions and gearboxes in internal combustion engines, hybrids and electric vehicles, there remains a need for lubricant formulations with improved energy efficiency over the life of the lubricant. More specifically, there is a need for lubricant technology optimized and tailored to meet the requirements of electric vehicle gearboxes, which differ from those of traditional combustion engines. Thus, there remains an active need for new lubricant compositions that provide high performance (especially low traction) in electric engines, but are commercially viable for the electric vehicle passenger car market.

[0013] It is an object of the present invention to provide a lubricant composition suitable for use in electric vehicle gearboxes that provides improved low traction, achieved by the inclusion of a traction coefficient additive, thus minimizing 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. Summary of the Invention

[0014] We have surprisingly discovered a lubricant composition that overcomes or significantly reduces at least one of the problems set forth above.

[0015] Accordingly, the present invention relates to a lubricant composition comprising a base stock and at least 2 wt. % of a cyclic ether derivative of formula (I) R 1 [(AO) n -R 2 ] m (I) [In the formula, 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 0 to 100; Each R 2 are independently H or R 3 where each R 3 are 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; At least 0.5 R on average 2 Group is R 3 and a traction coefficient additive compound having a formula:

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

[0017] The traction coefficient additives described herein can advantageously improve the performance of the gearbox of an electric vehicle in 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 as traction coefficient reducing additives in lubricant compositions, and more specifically, in gear oils for electric vehicle gearboxes.

[0019] The traction coefficient additive has the formula (I): R 1 [(AO) n -R 2 ] m (I) [In the formula, 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 0 to 100; Each R 2 are independently H or R 3 where each R 3 are 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; On average, at least 0.5 R 2 Group is R 3 This includes compounds in which:

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

[0021] R 1 Examples of core groups include the residue of the following compounds after removal of m active hydrogen atoms: 1 Glycerol and polyglycerols, in particular diglycerol and triglycerol, their partial esters, or any triglyceride containing multiple hydroxyl groups, such as castor oil; 2 Tri or higher polymethylolalkanes, such as trimethylolethane, trimethylolpropane, pentaerythritol and dipentaerythritol, and their partial esters; 3 sugars, in particular non-reducing sugars such as sorbitol, mannitol, and lactitol, etherified derivatives of sugars such as sorbitan (cyclic dehydro-ether of sorbitol), partial alkyl acetals of sugars such as methylglucose and alkyl(poly)saccharides, and other oligomers / polymers of sugars such as dextrins, partially esterified derivatives of sugars such as fatty acid esters, e.g. 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 citric and tartaric acid; 5. Amines, including difunctional and polyfunctional amines, especially alkylamines, including alkyl diamines 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, etc.; and 8 Amidocarboxylic acids, for example succinamic acid.

[0022] Preferred R 1 The core group is the 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, more preferably a C6 chain. The hydroxyl or amino groups are preferably attached directly to the chain carbon atoms. Hydroxyl groups are preferred.

[0023] R 1 is preferably the residue of an open chain tetratol, pentitol, hexitol or heptitol group or an anhydro, e.g. cycloether anhydro, derivative of such a group. In a particularly preferred embodiment, R 1 R is a residue of, or derived from, a sugar, more preferably a monosaccharide such as glucose, fructose or sorbitol, a disaccharide such as maltose, palytose, lactitol or lactose, or a higher oligosaccharide. 1 is preferably a residue of a monosaccharide, more preferably glucose, fructose or sorbitol, especially sorbitol.

[0024] R 1 Although the open chain form of the group is preferred, groups containing internal cyclic ether functionality may be used and 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 It is a measure of the functionality of the core group, and the alkoxylation reaction replaces some or all (depending on the molar ratio of core group to alkoxylated group) of the active hydrogen atoms in the molecule from which the core group is derived. Reaction at certain sites may be limited or prevented by steric hindrance or appropriate protection. The terminal hydroxyl groups of the polyalkylene oxide chains in the resulting compound are then available for reaction with the acyl compounds as defined above. The subscript m is preferably at least 3, more preferably in the range of 4 to 10, particularly 5 to 8, especially 5 to 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 the formula: -(C r H 2rThe alkylene oxide groups are preferably ethyleneoxy (-C2H4O-) or propyleneoxy (-C3H6O-) groups, where r is 2, 3 or 4, preferably 2 or 3, and may represent different groups along the alkylene oxide chain. Generally, it is desired that the chain is a homopolymeric ethylene oxide chain. However, the chain may also be a homopolymeric chain of propylene glycol residues, or a block or random copolymer chain containing both ethylene glycol and propylene glycol residues. Usually, when a copolymer chain of ethylene oxide and propylene oxide units is used, the molar ratio of ethylene oxide units used is at least 50%, more usually at least 70%.

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

[0028] base R 2 is the "end group" of the (poly)alkylene oxide chain. The end group is hydrogen or R 3 where each R 3 are 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. 3 are independently the residue of a polyhydroxyalkyl carboxylic acid, the residue of a hydroxyalkyl carboxylic acid and / or the residue of an oligomer of a hydroxyalkyl carboxylic acid, more preferably the residue of a polyhydroxyalkyl carboxylic acid.

[0029] Preferably, R 2 At least 1.0, preferably at least 1.5, more preferably at least 2.0, particularly at least 2.2, and especially at least 2.4 of the groups are R 3 In addition, preferably, R 2Up to 6.0, preferably up to 4.0, more preferably up to 3.0, particularly up to 2.7, and especially up to 2.5, of the groups R 3 It is.

[0030] Hydroxyl alkyl and hydroxy alkenyl carboxylic acids are of the formula HO-X-COOH, where X is a divalent saturated or unsaturated, preferably saturated, aliphatic group containing at least 8 carbon atoms and not more than 20 carbon atoms, typically 11-17 carbon atoms, with at least 4 carbon atoms directly between the hydroxyl group and the carboxylic acid group. Desirably, the hydroxy alkyl carboxylic acid is 12-hydroxy stearic acid. In practice, such hydroxy alkyl carboxylic acids are commercially available as a mixture of hydroxy acids and the corresponding unsubstituted fatty acids. For example, 12-hydroxy stearic acid is typically produced by hydrogenation of castor oil fatty acids, which contain C18 unsaturated hydroxy acids and unsubstituted fatty acids (oleic acid and linoleic acid), which upon hydrogenation give a mixture of 12-hydroxy stearic acid and stearic acid. Commercially available 12-hydroxy stearic acid typically contains about 5% to 8% unsubstituted stearic acid.

[0031] Polyhydroxyalkyl or polyhydroxyalkenyl carboxylic acids can be prepared by polymerizing the above hydroxyalkyl or hydroxyalkenyl carboxylic acids. The presence of the corresponding unsubstituted fatty acid acts as a terminator, thus limiting the chain length of the polymer. Desirably, the number of hydroxyalkyl or hydroxyalkenyl units is on average 2 to 12, 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, especially about 2,100.

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

[0033] Oligomers of hydroxyalkyl or hydroxyalkenyl carboxylic acids may differ from polymers in that they are not terminated by the corresponding unsubstituted fatty acid and are desirably dimers of hydroxyalkyl or hydroxyalkenyl carboxylic acids.

[0034] In a preferred embodiment, on average, 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 groups R are polyhydroxyalkyl carboxylic acid residues. 3 In addition, on average, preferably, R 2 Up to 4.0, preferably up to 3.5, more preferably up to 3.0, particularly up to 2.7, and especially up to 2.5, of the groups R are polyhydroxyalkyl carboxylic acid residues. 3 These polyhydroxyalkyl carboxylic acid residues suitably 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 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 all hydroxyalkyl carboxylic acid residues present in a compound of formula (I) as defined herein is suitably in the range an average of 5 to 30, 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, preferably at least 2.5, more preferably at least 3.0, particularly at least 3.3, and especially at least 3.5 of the groups are H. In addition, on average, preferably at least 2.0, preferably at least 2.5, more preferably at least 3.0, particularly at least 3.3, and especially at least 3.5 of the groups are H. 2 At most 5.0, preferably at most 4.5, more preferably at most 4.0, particularly at most 3.7, especially at most 3.6 of the groups are H.

[0038] If the core group is derived from, for example, pentaerythritol, the alkoxylation of the core residue may be uniformly distributed over the four available sites where active hydrogens can be removed, and upon esterification of the terminal hydroxyl functional groups, the distribution of acyl groups will be close to the expected random distribution. However, if the core group is derived from a compound such as sorbitol, where all of the active hydrogen atoms are not equivalent, the alkoxylation may give unequal chain lengths for the polyalkyleneoxy chains.

[0039] The traction coefficient additive is first prepared by mixing R 1 The core group can be prepared by alkoxylation by techniques well known in the art, for example by reaction with the required amount of alkylene oxide, e.g., ethylene oxide and / or propylene oxide. The second stage of the process preferably involves reacting the alkoxylated species with polyhydroxyalkyl(alkenyl)carboxylic acid and / or hydroxyalkyl(alkenyl)carboxylic acid under standard catalytic esterification conditions at temperatures up to 250° C. Thus, the traction coefficient additive of formula (I) comprises a group R1 with an alkylene oxide and then esterifying the alkoxylated product of this reaction with a polyhydroxyalkyl(alkenyl)carboxylic acid, a hydroxyalkyl(alkenyl)carboxylic acid, or a mixture thereof.

[0040] In one preferred embodiment, the traction coefficient additive comprises an alkoxylated core group R 1 with a polyhydroxyalkyl carboxylic acid, where the molar ratio of alkoxylated core groups to polyacid is preferably in the range of 1:1 to 1:4, more preferably 1:2 to 1:2.8. Preferably, the traction coefficient additives prepared by this route have a molecular weight (Mn) of 3,000 to 10,000, more preferably 4,000 to 7000, especially 5,000 to 6,000.

[0041] The lubricant composition of the present invention comprises a base stock. The lubricant composition may comprise at least 50 wt.%, preferably at least 60 wt.%, more preferably at least 70 wt.%, even more preferably at least 75 wt.% of the base stock, based on the total weight of the composition. The lubricant composition may comprise up to 98 wt.%, preferably up to 95 wt.%, more preferably up to 90 wt.% of the base stock, based on the total weight of the composition.

[0042] The lubricant composition comprises at least 2 wt%, suitably at least 2.5 wt%, preferably at least 3 wt%, more preferably at least 5 wt%, even more preferably at least 7 wt% of the traction coefficient additive based on the total weight of the composition. The lubricant composition may comprise up to 20 wt%, preferably up to 15 wt%, most preferably up to 10 wt% of the traction coefficient additive based on the total weight of the lubricant composition.

[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 thus may be present in the lubricant composition. The lubricant composition may contain less than 5 wt.% water based on the total weight of the composition. More preferably, the lubricant composition is substantially free of water, i.e., contains less than 2 wt.%, less than 1 wt.%, or preferably less than 0.5 wt.% water based on the total weight of the composition. Preferably, the lubricant composition is substantially anhydrous.

[0044] The lubricant composition suitably provides a gearbox oil suitable for use in electric vehicles. To adapt the lubricant composition for its intended use, the lubricant composition may include one or more of the following additional additive types: 1. Dispersants: for example, alkenyl succinimides, alkenyl succinic acid esters, alkenyl succinimides modified with other organic compounds, alkenyl succinimides modified by post-treatment with ethylene carbonate or boric acid, pentaerythritol, phenate-salicylates and their post-treated analogues, alkali metal or mixed alkali metal, alkaline earth metal borates, dispersions of hydrated alkali metal borates, dispersions of alkaline earth metal borates, polyamide ashless dispersants, etc., or mixtures of such dispersants. 2. Antioxidants: Antioxidants reduce the tendency of mineral oils to deteriorate in service, the deterioration being evidenced by oxidation products such as sludge and varnish-like deposits on metal surfaces and by an increase in viscosity. Examples of the antioxidant 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, phenolic antioxidants such as 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 methylene bis(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. Emulsifiers: For example, linear alcohol ethoxylates. 5. Demulsifiers: For example, addition products of alkylphenols and ethylene oxide, polyoxyethylene alkyl ethers, and polyoxyethylene sorbitan esters. 6. Extreme pressure agents (EP agents): for example, zinc dialkyl dithiophosphates (primary alkyl, secondary alkyl, and aryl types), sulfurized oils, diphenyl sulfide, methyl trichlorostearate, chlorinated naphthalenes, fluoroalkyl polysiloxanes, and lead naphthenate. A preferred EP agent is zinc dialkyl dithiophosphate (ZnDTP), for example, as one of the co-additive components for antiwear hydraulic oil compositions. 7. Multifunctional additives: for example, sulfurized oxymolybdenum dithiocarbamate, sulfurized oxymolybdenum organic phosphorodithioate, oxymolybdenum monoglycehde, oxymolybdenum diethylate 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, hydrogenated styrene-isoprene copolymers, polyisobutylene, and dispersant type viscosity index improvers. 9. Pour point depressants: for example, polymethacrylate polymers. It is an advantage of the present invention that the pour points of the compounds of formula (I) are suitable for use as gearbox oils, however, embodiments utilizing relatively long chain linear molecules may benefit from the addition of a pour point depressant. Additionally, the presence of some alternative additives may adversely affect the pour point of the formulation, making the addition of a pour point depressant attractive. 10. Foam suppressors: for example, alkyl methacrylate polymers and dimethyl silicone polymers. 11. Friction Modifiers: include amides, amines, and partial aliphatic esters of polyhydric alcohols, and may include, for example, glycerol monooleate, oleylamide, and alternative friction modifiers available from Croda under the tradename "Perfad" or available from Nouryon under the tradename "Ethomeen."

[0045] The lubricant composition may comprise at least 0.5 wt.-%, preferably at least 1 wt.-%, more preferably at least 5 wt.-%, of the further additive or mixture of further additives, based on the total weight of the composition. The lubricant composition may comprise up to 30 wt.-%, preferably up to 20 wt.-%, more preferably up to 10 wt.-%, of the further additive or mixture of further additives, based on the total weight of the composition.

[0046] The additive(s) may be available in the form of a commercially available additive pack. Such additive packs vary in composition depending on the required use of the additive pack. Those skilled in the art may select a suitable commercially available additive pack for gear oil. An example of an additive pack that is 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] Notwithstanding the above examples, in order for a lubricant composition to be suitable for use in an electric vehicle, the selection of any additive(s) should take into consideration copper compatibility (due to the requirements of electric motors), as well as providing or exhibiting low (but not necessarily zero) electrical conductivity; not all additives commonly utilized in conventional combustion engine automotive engines are suitable for use in electric vehicle powertrain fluids.

[0048] The base stock group nomenclature defined by the American Petroleum Institute (API) is used herein. The base stocks may 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. When the base stock comprises a polyalphaolefin (PAO) from Group IV, the base stock may also desirably comprise a mineral oil from Group I, II or III or an 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 at 5% to 20% by weight of the lubricant composition to improve the solubility of the traction coefficient additive in the base stock. Thus, 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 suitable for use as a gearbox oil in an electric vehicle. When the lubricant composition is a gearbox oil, the traction coefficient additive is preferably present in 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 an ISO grade, which is defined as the midpoint kinematic viscosity of a sample at 40° C. in cSt (mm 2 The viscosity is specified in units of 1 / sec. 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 provides a reduced 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 to an equivalent lubricant composition not containing the additive.

[0053] The lubricant composition of the present invention may be used in other technical fields where an improvement in the traction coefficient of the lubricant composition may be advantageous, i.e., the present invention may have broader utility than just use in electric vehicles. Thus, the gear oil described herein may be an industrial, automotive and / or marine gear oil. When the lubricant composition is a gear oil, the traction coefficient additive is preferably present in the range of 2 wt. % to 10 wt. %, 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 realized.

[0054] Industrial gear oils include those suitable for use in gearboxes having spur gears, helical gears, bevel gears, hypoid gears, planetary gears and worm gears. Suitable applications include use in mining, factories such as paper mills, textile mills and sugar mills, steel production and wind turbines. One preferred application is in wind turbines 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 may connect a low-speed shaft rotated by the wind turbine blade rotor at about 10 to 30 revolutions per minute (rpm) to one or more high-speed shafts that drive the generator at about 1000 rpm to 2000 rpm, which is the rotational speed required by most generators to generate electricity. The high torque applied to the gearbox can generate enormous stresses on the gears and bearings in the wind turbine. The gear oil of the present invention can improve the fatigue life of the gearbox of the wind turbine by reducing the 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. Long-lasting lubricant compositions with high stability may therefore be required to provide adequate performance over long periods. Gear oils according to the present invention may be suitable for such use.

[0055] Conventional automotive gear oils (i.e., for combustion engines) include those suitable for use in manual transmissions, transfer cases, and differentials, all of which typically use hypoid gears. By transfer case is meant the 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. It is also referred to in the literature as a transfer gear case, transfer gear box, transfer box, or jockey box. Although the present invention is specifically designed to be suitable for use in electric vehicles (which have different physical property requirements than conventional automotive gear oils), the gear oils of the present invention can provide improved traction coefficient properties of base stocks for use with conventional automotive gear oils.

[0056] Marine thruster gearboxes have certain gear oils with higher additives, such as dispersants, anticorrosives, to combat corrosion and water entrainment, compared to industrial and automotive gear oils. There are also outboard gear oils used for propeller units, which may be more suitable for smaller vessels. The gear oils of the present invention may also provide improved traction coefficient properties of base stocks for use in marine thruster gearboxes.

[0057] The compounds of formula (I) as defined herein may reduce the traction coefficient of a traction coefficient lubricant composition, preferably an electric vehicle gear oil, by at least 5%, preferably at least 10%, more preferably at least 15%, particularly at least 20%, and especially at least 25%, as measured using a Mini Traction Machine (MTM) according to the test described herein at temperatures of 40° C. and 60° C., a load of 1.0 GPa, and a slide-to-roll ratio (SRR) of 30%, when compared to an equivalent lubricant composition not containing the traction coefficient additive. The traction coefficient may be reduced over a temperature range of 0° C. to 200° C., preferably over a range of 20 to 100° C., more preferably over a range of 40 to 60° C., as described herein, when compared to an equivalent lubricant composition not containing the traction coefficient additive. EXAMPLES

[0058] The invention will now be illustrated by the following non-limiting examples, using the following materials and testing procedures.

[0059] Test materials PAO 4 - Spectra Syn™ 4 - An API Group IV synthetic polyalphaolefin base stock produced by the reaction of linear alpha olefins available from ExxonMobil. API Group III VHVI base stock available from YUBASE 4-SK Lubricants. Priolube™ 3970 - API Group V synthetic ester base stock available from Croda Inc. EHC-45 - API GRII base stock available from ExxonMobil. Perfad™ 3050 - a commercial polymeric friction modifier available from Croda Inc.

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

[0061] The disks were AISI 52100 hardened bearing steel with a mirror finish (Ra<0.01 mm) and the balls were 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 test sample was then added. The ball was loaded against the face of the disk and the ball and disk were driven independently to create a mixed rolling / sliding contact with a sliding-to-rolling ratio (SRR) of 30%. The friction force between the ball and disk was measured by a force transducer. Additional sensors measured the applied load and the test sample temperature.

[0062] The traction coefficients of the lubricant control composition (i.e., base stock with no traction reducing additive present) test samples were determined at 40°C and 60°C utilizing an 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) that included the lubricant control composition with 2.5%, 5%, 7.5%, or 10% by weight of the traction reducing additive being evaluated. Further testing was performed utilizing test samples that included the addition of a commercial lubricant additive. 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 charged to a glass reactor and heated to 190°C under nitrogen. The reaction was allowed to continue for 12-24 hours, then cooled to below 100°C and the product discharged. This resulted in a product (Sample 1) with the generalized composition shown below: R 1 [(AO) n -R 2 ] m During the ceremony, R 1 is the residue of excreted sorbitol. m is 6, AO is an ethylene oxide residue; The average of n is 2, Each R 2 are independently H or R 3 where each R 3 is poly(12-hydroxystearic acid), R 2 The average of 0.58 groups is R 3 It is.

[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 charged to a glass reactor and heated to 190° C. under nitrogen. The reaction was allowed to continue for 12-24 hours, then cooled to below 100° C. and the product discharged. This resulted in a product (Sample 2) having the generalized composition shown below: R 1 [(AO) n -R 2 ] m During the ceremony, R 1is the residue of sorbitol, m is 6, AO is an ethylene oxide residue; The average of n is 9, Each R 2 are independently H or R 3 where each R 3 is poly(12-hydroxystearic acid), R 2 The average of 0.58 groups is R 3 It is.

[0065] Example 3. MTM Test Data The MTM data shown in Tables 1, 2, 3, 4 and 5 below indicate that both Sample 1 and Sample 2 (above) are effective in reducing the traction coefficient of conventional lubricant base stocks, with a reduction in traction coefficient observed after the introduction of the additive compared to the base stock alone control sample. MTM test data is provided for a selection of lubricant base stocks (i.e., control samples) selected to demonstrate the utility of the additive technology across a range of API base stocks. The base stock selection for testing includes the following base stocks: Group III (YUBASE 4), and a blend 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 their effect on the traction coefficient of a base stock containing PAO 100. PAO 100 is a very commonly utilized thickener in conventional automotive gear oil formulations, and the inclusion of PAO 100 is known to increase the viscosity of the base stock, which can have a positive effect on the traction coefficient since the more viscous base stock is able to maintain a film at the test boundary.

[0067] From the data provided in the table below, it can be seen that the use of Samples 1 and 2 resulted in a 2 to 10 times greater (in percentage terms) reduction in the traction coefficient of the base stock, especially for the 2.5 wt% to 7.5 wt% treat rate range. For Samples 1 and 2, there appears to be an optimum treat rate of 5 wt% to 7.5 wt% content based on the total weight of the composition, with further increases in concentration resulting in no benefit or even a detrimental increase in traction coefficient, and this traction coefficient improvement is distinct from the viscosity increasing effect achieved by the PAO 100 inclusion.

[0068] [Table 2]

[0069] [Table 3]

[0070] [Table 4]

[0071] [Table 5]

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

[0073]

Table 6

Claims

1. Use of a lubricant composition as a gearbox oil in an electric vehicle, wherein the lubricant composition comprises, based on the total weight of the lubricant composition, at least 75% by weight of a base stock and 2% to 10% by weight of a compound of formula (I): R １ [[(AO)]] ｎ -R ２ ｍ (I)​ [wherein, -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 R ２ is, independently, H or R ３ wherein each R ３ is a residue of (poly)12-hydroxystearic acid - on average at least 0.5 R ２ groups are R ３ a traction coefficient additive compound of ] and 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 said 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: dispersant, antioxidant, antiwear agent, emulsifier, demulsifier, extreme pressure agent, multifunctional additive, viscosity index improver, pour point depressant, antifoaming agent, and friction modifier.

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

5. The use according to claim 3, wherein the lubricant composition comprises at most 10% by weight of an additional additive or a mixture of additional 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 a gearbox of an electric vehicle, comprising using a lubricant composition, wherein the lubricant composition comprises, based on the total weight of the lubricant composition, at least 75% by weight of a base stock and 2% to 10% by weight of a compound of formula (I): R1[(AO)n - R2]m (I) [wherein, - R1 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, - on average at least 0.5 of the R2 groups are R3] and a traction coefficient additive compound.