CN117836394A

CN117836394A - Lubricant composition comprising traction coefficient additive

Info

Publication number: CN117836394A
Application number: CN202280054061.9A
Authority: CN
Inventors: G·穆迪
Original assignee: Iquis Topco Uk Ltd
Current assignee: Iquis Topco Uk Ltd
Priority date: 2021-06-09
Filing date: 2022-06-08
Publication date: 2024-04-05
Also published as: GB202108216D0; KR20240040722A; EP4352187A1; WO2022258664A1

Abstract

The present invention relates to a lubricant composition suitable for use in an electric vehicle. The lubricant composition comprises a traction coefficient additive, and wherein the traction coefficient additive is an ester that is the reaction product of at least one saturated branched aliphatic monohydric alcohol having from 12 to 32 carbon atoms and at least one aliphatic carboxylic acid having from 6 to 32 carbon atoms. The lubricant compositions as described herein provide electric vehicle gear oils and impart desired traction coefficient characteristics when used.

Description

Lubricant composition comprising traction coefficient additive

Technical Field

The present invention relates to a lubricant composition suitable for use in an electric vehicle comprising a traction coefficient additive. The lubricant composition as described herein is particularly suitable for electric vehicle gear oils, particularly electric vehicle transmission fluids, and provides improved traction coefficient characteristics when in use.

Background

An electric vehicle is a vehicle propelled using one or more electric motors. Electric vehicles may be all-electric (also referred to as electric-only or all-electric vehicles) or hybrid in nature (in hybrid electric vehicles propulsion may be achieved by alternative means, sometimes by hydrocarbon-derived fuels). Electric vehicles also include range-extending electric vehicles in which the vehicle is powered by an electric motor and a plug-in battery, but the vehicle also includes an auxiliary internal combustion engine that is used only to supplement battery charging and not as a primary propulsion source. The present invention is applicable to all of these types of electric vehicles.

Gear oils are a subclass of lubricants and typically contain lubricant base stock (or base oil) as their major component. The choice of lubricant base stock for use in lubricating oils can have a significant impact on properties such as oxidation and thermal stability, volatility, low temperature flow, the solvency of additives, contaminants and degradation products, and traction. More particularly, the industry has traditionally recognized that traction coefficient is an inherent property of the base stock fluid (i.e., based on the chemical composition of the base oil) and that the traction coefficient is not affected by the additive. It is generally accepted in the industry that the viscosity of the base stock fluid determines the traction coefficient of a lubricant in use.

The American Petroleum Institute (API) currently defines five groups of lubricant basestocks (API Publication 1509).

I. Groups II and III are mineral oils, classified according to the amount of saturates and sulfur they contain and their viscosity index. These API classifications of I, II and group III are shown in table 1 below.

TABLE 1

Group of	Saturates	Sulfur (S)	Viscosity Index (VI)
				I	<90％	>0.03％	80-120
II	At least 90%	Not more than 0.03%	80-120
				III	At least 90%	Not more than 0.03%	At least 120

Group I basestocks are solvent refined mineral oils, which are the lowest cost basestocks to produce. They provide satisfactory oxidation stability, volatility, low temperature performance and traction characteristics, and have particularly good solvency for additives and contaminants.

Group II basestocks are primarily hydrotreated mineral oils, which generally provide improved volatility and oxidation stability compared to group I basestocks. The use of group II feedstocks has grown to about 30% of the U.S. market.

Group III (including group III+) basestocks are strictly hydrotreated mineral oils or they can be produced via wax or paraffin isomerization. They are known to have better oxidative stability and volatility than group I and group II base stocks, but have a limited range of commercially available viscosities. Group iii+ basestocks include those derived from GTL (natural gas to liquids) fuel streams.

Group IV basestocks differ from groups I to III in that they are synthetic basestocks, such as Polyalphaolefins (PAOs). PAOs have good oxidative stability, volatility, and low pour points. Disadvantages include moderate solubility of polar additives (e.g., antiwear additives).

Group V basestocks are all basestocks not included in groups I to IV. Examples include alkyl naphthalenes, alkyl aromatics, vegetable oils, esters, polycarbonates, silicone oils, and polyalkylene glycols.

The rapid evolution of passenger cars toward motorization has exceeded the understanding and regulation of current gear oil specifications by OEMs and regulatory authorities. Current generation hybrid and electric vehicles still use standard Automatic Transmission Fluid (ATF) formulations, which are not specifically designed for this application. Due to rapid advances in electric vehicle technology, ATF base fluids, and additive packages, current gear oils do not meet OEM dynamic requirements. Furthermore, because the electric motor in an EV is very efficient, any loss of gear lubricant in the EV driveline may be substantial. Reducing the energy loss will improve the battery life of the EV in use, which means that the charging frequency of the EV will decrease as the battery life increases.

In addition, thermal management of components in electric vehicles is becoming increasingly important. In a battery of a vehicle, thermal management is critical to ensure safe operation and use. There is currently a great deal of research being conducted into immersion-cooled battery systems that place the battery in direct contact with a dielectric cooling fluid. Thus, for such applications, fluids with high thermal properties (e.g., heat capacity and thermal conductivity) are needed. It is also desirable to cool power electronics systems, such as electric motors and transmissions, in order to keep them functioning effectively without overheating. Removing excess heat from the electronic system also helps to reduce electrical resistance and thus helps to improve engine efficiency. Thus, the thermal properties of lubricant compositions suitable for use in electric vehicles will be significantly different from those developed for use in automotive internal combustion engines.

Thus, despite the continued development of lubricant technology for transmissions and gearboxes in internal combustion engines, hybrid vehicles, and electric vehicles, there remains a need for lubricating oil formulations having improved energy efficiency over the life of the lubricating oil. More particularly, there is a need for lubricant technology that is optimized and tailored to meet the requirements of electric vehicle gearboxes that differ from the requirements of conventional internal combustion engines in their requirements. Thus, there is still an active search for new base oils that provide high performance (particularly low traction and high thermal conductivity) in electric engines, but are commercially viable for the electric vehicle passenger car market.

It is an object of the present invention to provide a lubricant composition suitable for use in a gearbox of an electric vehicle which provides improved low traction and thus minimizes energy losses. In addition to providing low traction, the lubricant composition should have sufficient oxidation stability as well as good low temperature characteristics and compatibility with materials such as elastomers and copper.

Disclosure of Invention

Accordingly, the present invention provides a lubricant composition suitable for use in an electric vehicle, the lubricant composition comprising a traction coefficient additive, and wherein the traction coefficient additive is an ester, said ester being the reaction product of:

i) At least one saturated branched aliphatic monohydric alcohol having 12 to 24 carbon atoms, and

ii) at least one aliphatic carboxylic acid having from 6 to 24 carbon atoms.

The invention also provides a method of reducing the traction coefficient in a gearbox, the method comprising using a lubricating oil according to the first aspect of the invention.

The traction coefficient additives described herein may advantageously improve the performance of a gearbox to which the lubricant composition is applied by providing a reduced traction coefficient.

The traction coefficient additives described herein may be used as traction coefficient reducing additives in lubricant compositions, and more particularly in gear oils for gearboxes, and particularly in gear oils for gearboxes of electric vehicles.

Detailed Description

It should be understood that any upper or lower limit number or ranges used herein may be independently combined.

It will be understood that when describing the number of carbon atoms in a substituent (e.g., "C1 to C6"), that number refers to the total number of carbon atoms present in the substituent, including the carbon atoms present in any branched groups. In addition, when describing, for example, the number of carbon atoms in a fatty acid, this is meant to include the number of carbon atoms at the carboxylic acid as well as the total number of carbon atoms present in any branched group.

As used in this specification with respect to the described and claimed invention, the term "wt%" as required in the context of this component, refers to the weight percent of the component referred to as the percent of the total weight of the lubricant composition. When the context relates to a particular component, such as a Noack evaporation loss, the term "wt%" refers to the weight percent of the total weight of that component.

According to the present invention there is provided a lubricant composition suitable for use in an electric vehicle, the lubricant composition comprising a traction coefficient additive, and wherein the traction coefficient additive is an ester, said ester being the reaction product of:

iii) At least one saturated branched aliphatic monohydric alcohol having 12 to 32 carbon atoms, and

iv) at least one aliphatic carboxylic acid having from 6 to 32 carbon atoms.

Suitably, the aliphatic carboxylic acid may be saturated or unsaturated, linear or branched. Preferably, the aliphatic carboxylic acid is saturated, as this provides improved oxidation stability.

Desirably, the carboxylic acid may be derived from vegetable fats and/or oils. Thus, preferably, the aliphatic carboxylic acid may be a fatty acid. The fatty acids may be saturated or unsaturated. The fatty acids may be linear or branched. Preferably, the fatty acid is saturated. Naturally, fatty acids having an even number of carbons in their fatty chains are more abundant in nature and thus are more readily and less expensively available, so these forms of fatty acids may be preferred, and in particular those having a chain length of C6, C8, C10, C12, C14, C16, C18 and C20. Fatty acids may be understood to contain medium fatty acid chains, which preferably provide fatty chains containing from 6 to 18 carbons.

Preferably, the carboxylic acid is a mono-or dicarboxylic acid, such that the ester is a mono-or diester, and most preferably, the carboxylic acid is a mono-carboxylic acid, such that the ester is a monoester. Suitably, the carboxylic acid may be selected from one or more of the following: caproic acid, enanthic acid, caprylic acid, capric acid, lauric acid, myristic acid, stearic acid, behenic acid, hexenoic acid decenoic acid, linoleic acid, elaidic acid, palmitic acid, oleic acid, elaidic acid, erucic acid, nervonic acid, isocaproic acid, 4-methylpentanoic acid, isocaprylic acid, 2-ethylhexanoic acid, isostearic acid, isobehenic acid, 2-ethyl-1-butyric acid, 2-butyloctanoic acid, 2-hexyldecanoic acid, 2-octyldodecanoic acid, 2-decyltetradecanoic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, behenic acid, cyclohexanedicarboxylic acid, fatty acid, tall oil, reaction products with acrylic acid, and alkenylsuccinic acid.

Suitably, the at least one saturated branched aliphatic monohydric alcohol having from 12 to 32 carbon atoms may be obtained from any suitable source and may generally be selected from guerbet alcohols, oxo alcohols, aldol condensation derived alcohols and mixtures thereof.

Preferably, the at least one saturated branched aliphatic monohydric alcohol has from 12 to 32 carbon atoms, and more preferably from 12 to 24 carbon atoms, and most preferably from 12 to 20 carbon atoms. The preferred shorter chain length has a positive effect on the viscosity of the ester for the intended use. More particularly, the at least one saturated branched aliphatic monohydric alcohol having from 12 to 32 carbon atoms is an alcohol branched at the β -position of the main carbon chain. Preferably, such alcohols may be selected from 2-butyloctanol, isomyristyl alcohol (isomyristyle alcohol), 2-hexyldecanol, isostearyl alcohol, 2-octyldecanol-1, 2-heptylundecanol-1, 2-octyldodecanol-1, 2-nonyltridecanol-1 and 2-decyltetradecanol-1, and mixtures of two or more such alcohols. Such alcohol is conveniently a guerbet alcohol, and preferably the alcohol may be selected from C12 guerbet alcohol, C14 guerbet alcohol, C16 guerbet alcohol, C18 guerbet alcohol, C20 guerbet alcohol and C24 guerbet alcohol or mixtures thereof. The use of the preferred guerbet alcohols is believed to provide very high thermal conductivity for the esters of a given viscosity, that is, the thermal conductivity of the traction coefficient additive is surprising and makes the lubricant composition of the present invention suitable for use in electric vehicles. It has also been found that monoesters according to the invention have in particular a low viscosity, low polarity and low volatility, while providing exceptionally low traction compared to other esters.

Suitably, the traction coefficient additive has a thermal conductivity of greater than 0.131W/mK at 40 ℃, preferably greater than 0.135W/mK at 40 ℃, more preferably greater than 0.141W/mK at 40 ℃, and most preferably greater than 0.151W/mK at 40 ℃. In connection with the examples, thermal conductivity was measured according to the method described below.

Preferably, the traction coefficient additive has a kinematic viscosity at 100 ℃ of no more than 8.0cSt, preferably no more than 6.0cSt, most preferably no more than 4.0cSt, and in some particularly preferred embodiments, the traction coefficient additive has a kinematic viscosity at 100 ℃ of no more than 3.3 cSt. Additionally or alternatively, the traction coefficient additive has a kinematic viscosity at 40 ℃ of no more than 30cSt, preferably no more than 20cSt, and most preferably no more than 10 cSt.

Preferably, the traction coefficient additive has a viscosity index of at least 130, preferably at least 140.

Preferably, the traction coefficient additive has a pour point of no more than-30 ℃, more particularly no more than-35 ℃, and especially no more than-40 ℃.

Preferably, the traction coefficient additive has a Noack evaporation loss of no more than 22 wt%, preferably no more than 20 wt%, more preferably no more than 18 wt%, at 250 ℃. Additionally or alternatively, preferably, the traction coefficient additive has a Noack evaporation loss of no more than 9 wt%, preferably no more than 7 wt%, more preferably no more than 5 wt%, at 200 ℃.

Preferably, the traction coefficient additive has a flash point of at least 200 ℃, more preferably at least 210 ℃, and more particularly at least 220 ℃.

Preferably, the traction coefficient additive has a non-polarity index (NPI) of at least 80, preferably at least 90, as described in EP-B-0792334.

Preferably, the traction coefficient additive is stable when maintained at-20 ℃ for one week. This low temperature stability can be tested by storing about 30ml of the sample in a glass vial and placing the vial in a freezer unit at-20 ℃ for one week, checking the sample at regular intervals and recording any signs of crystal formation or gelation.

Another advantage of the traction coefficient additive of the present invention is that it has been found to have minimal swelling effects on FKM and/or HNBR elastomers and therefore can be used at higher inclusion levels than conventional lubricant additives. Thus, in some less preferred embodiments, the lubricant composition may consist of only the traction coefficient additive. Alternatively, the lubricant composition may comprise a majority of the traction coefficient additive such that the lubricant composition comprises more than 50 wt% of the traction coefficient additive. Preferably, however, the lubricant composition comprises at most 50 wt.% of the traction coefficient additive. Preferably, the lubricant composition comprises at least 3 wt.%, more preferably at least 5 wt.% of the traction coefficient additive. The lubricant composition may comprise up to 45 wt.%, more preferably up to 35 wt.%, and more particularly up to 25 wt.% of the traction coefficient additive. In one embodiment of the invention, the lubricant composition comprises 3 to 25 wt.%, preferably 5 to 20 wt.% of the traction coefficient additive.

Preferably, the lubricant composition comprises at least one base oil, and suitably the at least one base oil is selected from group I to group IV base oils, or mixtures of two or more thereof. Preferably, the lubricant composition comprises at least one base oil as a major component of the lubricant composition. One benefit of the present invention is that the traction coefficient additive has good compatibility with group I to group IV base oils, allowing for flexibility in the selection of base oils in the lubricant composition. However, for us, in an electric vehicle, a lubricant composition comprising at least one of a group III base oil or a group IV base oil may be preferred. Examples of suitable group III base oils include mineral oils, as well as examples of group III + GTL base oils that are prepared by converting natural gas (i.e., methane and higher alkanes) to synthesis gas (carbon monoxide and hydrogen) and then converting via oligomerization (e.g., via a fischer-tropsch process) to higher molecular weight molecules that are hydrocracked to produce isoparaffins in the desired lubricant boiling point/viscosity range. Examples of suitable group IV base oils include those derived from C ₈ To C ₁₂ Poly-alpha-olefins (PAOs) that are alpha-olefins and have a kinematic viscosity in the range of 2cSt to 8cSt at 100 ℃. Examples of PAOs include SpectraSyn MaX from Exxon. Examples of group V base oils include polyalkylene glycols (PAGs), alkylbenzenes, and esters (it should be understood that in this case, group V ester base oils are esters other than the traction coefficient additives described above). Examples of esters include Priolube 3970 ^TM TMP nC ₈ /nC ₁₀ Polyol esters.

In one embodiment of the invention, the lubricant composition consists essentially of the traction coefficient additive and at least two base oils comprising at least one group V base oil, particularly an ester.

In one embodiment, the lubricant composition is non-aqueous. However, it should be understood that the components of the lubricant composition may contain a small amount of residual water (moisture), which may thus be present in the lubricant composition. The lubricant composition may comprise less than 5 weight percent 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% of water, based on the total weight of the composition. Preferably, the lubricant composition is substantially anhydrous.

To further tailor the lubricant composition to its intended use, particularly as a gear oil, the composition may comprise one or more of the following additive types.

1. Dispersing agent: such as alkenyl succinimides, alkenyl succinic esters, alkenyl succinimides modified with other organic compounds, alkenyl succinimides modified by post-treatment with ethylene carbonate or boric acid, pentaerythritol, phenolate-salicylates and post-treated analogues thereof, alkali or mixed alkali metal, alkaline earth metal borates, dispersions of hydrated alkali metal borates, dispersions of alkaline earth metal borates, polyamide ashless dispersants, and the like, or mixtures of such dispersants.

2. Antioxidant: antioxidants reduce the tendency of mineral oils to deteriorate in use, as evidenced by oxidation products such as sludge and varnish-like deposits on metal surfaces, as well as by viscosity increases. Examples of antioxidants include phenolic (phenolic) oxidation inhibitors, such as 4,4' -methylene-bis (2, 6-di-t-butylphenol), 4' -bis (2-methyl-6-t-butylphenol), 2' -methylene-bis (4-methyl-6-t-butylphenol), 4' -butylene-bis (3-methyl-6-t-butylphenol), 4' -isopropylidene-bis (2, 6-di-t-butylphenol), 2' -methylene-bis (4-methyl-6-nonylphenol) 2,2' -isobutylidene-bis (4, 6-dimethylphenol), 2' -methylene-bis (4-methyl-6-cyclohexylphenol), 2, 6-di-tert-butyl-4-methylphenol, 2, 6-di-tert-butyl-4-ethylphenol, 2, 6-di-tert-butyl-butylphenol, 2, 4-dimethyl-6-tert-butylphenol, 2, 6-di-tert-butyl-dimethylamino-p-cresol, 2, 6-di-tert-butyl-4- (N), N ' -dimethylaminomethylphenol), 4' -thiobis (2-methyl-6-tert-butylphenol), 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 oxidation inhibitors include alkylated diphenylamines (e.g., irganox L-57, manufactured by BASF), metal dithiocarbamates (e.g., zinc dithiocarbamate), and methylenebis (dibutyl dithiocarbamate).

3. Antiwear agent: as the name suggests, these agents reduce wear of moving metal parts. Examples of such agents include phosphates, phosphites, carbamates, esters, sulfur-containing compounds, and molybdenum complexes.

4. Emulsifying agent: for example, linear alcohol ethoxylates.

5. Demulsifier: for example, addition products of alkylphenols and ethylene oxide, polyoxyethylene alkyl ethers and polyoxyethylene sorbitan esters.

6. Extreme pressure agent (EP agent): for example, zinc dialkyldithiophosphates (primary alkyl, secondary alkyl and aryl), sulfurized oils, diphenyl sulfide, methyl trichlorostearate, naphthalene chloride, fluoroalkyl polysiloxanes and lead naphthenate. The preferred EP agent is zinc dialkyldithiophosphate (ZnDTP), for example as one of the co-additive components of an antiwear hydraulic fluid composition.

7. Multifunctional additive: for example, molybdenum dithiocarbamates, organo-dithiophosphates, monoglycerides, diethylamino-molybdenum, amine-molybdenum complexes, and sulfur-containing molybdenum complexes.

8. Viscosity index improver: for example, polymethacrylate polymers, ethylene-propylene copolymers, styrene-isoprene copolymers, hydrogenated styrene-isoprene copolymers, polyisobutylene, and dispersant viscosity index improvers.

9. Pour point depressant: for example, polymethacrylate polymers. While pour points of compounds of formula (I) are suitable for use as gearbox oils are a benefit of the present invention, embodiments utilizing relatively long chain linear molecules may benefit from the addition of pour point depressants. In addition, the presence of some alternative additives may adversely affect the pour point of the formulation, making the addition of pour point depressants attractive.

10. Foam inhibitor: for example, alkyl methacrylate polymers and dimethylsiloxane polymers.

11. Friction modifier: it may include partial fatty acid esters of amides, amines and polyols, and include, for example, glycerol monooleate, oleamides and alternative friction modifiers, which are available under the trade designation "Perfad" from Croda or "Ethomeen" from Nouryon.

Suitably, the lubricant composition may comprise at least 0.5 wt%, preferably at least 1 wt%, more preferably at least 5 wt% of one or more additive types, based on the total weight of the formulation. The lubricant composition may comprise up to 30 wt%, preferably up to 20 wt%, more preferably up to 10 wt% of one or more additive types, based on the total weight of the formulation.

Other additives may also be present in the lubricant composition of known functionality at a level of from 0.01 wt% to 30 wt%, more preferably from 0.01 wt% to 20 wt%, more particularly from 0.01 wt% to 10 wt%, based on the total weight of the lubricant composition. These may include detergents, resists, rust inhibitors, and mixtures thereof. The resist includes sarcosine derivatives such as Crodasinic O available from Croda Europe Ltd. Ashless detergents include carboxylic acid dispersants, amine dispersants, mannich dispersants, and polymeric dispersants. The ash-containing dispersants include neutral and basic alkaline earth metal salts of acidic organic compounds. The additive may have more than one functionality in a single material.

The additives may be available in the form of commercially available additive packages. The composition of such additive packages varies depending on the intended use of the additive package. Those skilled in the art can select a suitable commercial additive package for gear oils. An example of a particularly suitable additive package for gear oil is even 5201 (produced by Lubrizol, USA), which is specifically designed for use in electric vehicles.

The lubricant composition preferably comprises at least 0.05 wt.%, more preferably at least 0.5 wt.%, in particular at least 1 wt.%, and especially at least 1.5 wt.% of other additives (additive packages), based on the total weight of the lubricant composition. The lubricant composition preferably comprises at most 15 wt.%, more preferably at most 10 wt.%, in particular at most 4 wt.%, and especially at most 2.5 wt.% of other additives (additive packages), based on the total weight of the lubricant composition.

In spite of the examples given above, in order for the lubricant composition to be suitable for use in an electric vehicle, any additive should be selected taking into account copper compatibility (due to the requirements of the electric motor) and providing or exhibiting low (but not necessarily zero) electrical conductivity; not all additives commonly used in internal combustion engine automotive engines are suitable for use in electric vehicle powertrain fluids.

The lubricant composition may have a kinematic viscosity according to ISO grade. ISO grade specifies the mid-point kinematic viscosity of the sample at 40℃in cSt (mm ² /s). For example, ISO 100 has a viscosity of 100+ -10 cSt, ISO 1000 has a viscosity of 1000+ -100 cSt. The lubricant composition preferably has a viscosity in the range of ISO 10 to ISO 1500, more preferably ISO 68 to ISO 680.

The invention also provides a gear oil comprising the lubricant composition as described above. Gear oils may be considered lubricant fluids and may be used as lubricants in other fields, even where thermal conductivity and traction are not important. The gear oil formulation may be suitable for use as industrial, automotive and/or marine gear oil in any type of transmission system. However, the gear oil suitably provides a gearbox oil, and more particularly an integrated gearbox oil suitable for use in an electric vehicle; this is because the lubricant composition as described above provides advantageous thermal conductivity characteristics and desirable traction characteristics when used. In addition, providing good thermal characteristics in gear oil may extend engine life.

It is also contemplated that the base oil may be used as a heat transfer fluid. Such heat transfer fluids may provide a means of removing heat from the system. Such systems requiring or benefiting from the use of a heat transfer fluid may be mechanical or electrical systems. The base oils of the present invention may be well suited for use as heat transfer fluids in electrical systems, and more particularly they may be well suited for use as heat transfer fluids in electric vehicles.

According to an alternative embodiment of the present invention, there is provided a method of improving energy efficiency in an electric vehicle, the method comprising using a lubricant composition according to the first aspect of the present invention in a powertrain of the electric vehicle. The lubricant compositions may be used in various systems within a powertrain, such as axles, differentials, transmissions, battery packs, and power electronics. The lubricant composition has suitable characteristics for use in an electric vehicle powertrain, including traction, thermal conductivity, electrical conductivity, and viscosity characteristics, which have been optimized for use in an electric vehicle. In another alternative, a method of improving heat removal from an electric vehicle powertrain is provided, the method comprising using a base oil according to the first aspect of the invention in the powertrain of an electric vehicle.

Additionally or alternatively, a method of improving energy efficiency in an electric vehicle is provided, the method comprising using a lubricant composition according to an aspect of the invention in a gearbox of an electric vehicle. More particularly, a method of improving energy efficiency of an electric vehicle includes the step of providing a lubricant composition in an integrated gearbox. Thus, there is provided the use of a lubricant composition as described herein in an electric vehicle powertrain, and more particularly in an electric vehicle integrated gearbox. More particularly, the lubricant composition or gear oil may be used in systems within a powertrain, such as axles, differentials, transmissions, battery packs, and power electronics.

Lubricant compositions according to the present invention include those suitable for use in electric vehicle powertrains. More particularly, the lubricant composition is a gear oil suitable for use in both gear systems integrated with and not with electric motors. Such systems include axles, differentials, and transmissions. It should be noted that an electric vehicle may be provided with 2 or more electric motors.

The invention will now be described with reference to the following examples and figures, in which:

FIG. 1 shows the MTM coefficients of traction data for experimental and commercial samples at 40 ℃;

FIG. 2 shows the MTM coefficients of the traction data at 60℃for the experimental and commercial samples;

FIG. 3 shows the MTM coefficients of the traction data for the experimental and commercial samples at 75deg.C;

FIG. 4 shows the MTM coefficients of the traction data at 100deg.C for the experimental and commercial samples;

fig. 5 shows the MTM coefficients of the traction data at 120 ℃ for the experimental and commercial samples.

Material

The following materials were used in this example:

group III base oil-Yubase 4 (produced by SK Lumedicinal)

Group IV base oil-SpectraSyn PAO 4 (produced by Exxon Mobil)

A commercially available low viscosity conventional automobile friction modifier additive, priolube3959 (produced by Croda)

The invention will now be further illustrated with reference to the following examples.

1. Examples

The samples according to the invention are detailed in table 1 below. The process for producing the sample material is carried out by conventional esterification methods known to those skilled in the art. The alcohol of each of the ester examples is provided by guerbet alcohol, available from Sasol under the trade name isool.

TABLE 1.

Sample of	Composition of the composition	Chemical type
			IP-731-89	Isofol 16 isostearate	Monoester esters
IP-731-90	Isofol 16 heptanoate	Monoester esters
			IP-731-84	Isofol 12 stearate	Monoester esters
IP-731-78	Isofol 12 Disebacate	Diester of
			DE11845	Isofol 20 isostearate	Monoester esters
DE10766	Isofol 20 heptanoate	Monoester esters

2. Testing

The following tests were used to evaluate the properties of the exemplary base oils:

2.1 oxidative stability was measured using a Anton Paar RapidOxy machine. A 4 gram sample was placed in a pressure vessel and filled with 700kPa of oxygen before heating to 140 ℃. The time taken for the pressure to drop by 10% was measured as Oxidation Induction Time (OIT). This provides a relative measure of the resistance of the test sample to oxidative degradation, the longer the OIT, the higher the oxidative stability of the sample.

2.2 Kinematic Viscosity (KV) was measured at 100℃and 40℃using an Anton Paar SVM viscometer. Viscosity Index (VI) of the tested materials is also provided. The higher the VI value, the more stable the material is over a temperature range.

2.3 thermal conductivity was measured using a thermal THW-L2 based on hot wire transient method. Ten data points were collected at temperatures of 40 ℃ and 80 ℃ to produce a reliable average, with 5 minutes between each data point to allow fluid to settle. The test power was set such that the measured output power was 70 to 90mW and gave a temperature rise of about 3 ℃, and the test time was set to 1 second.

2.4 pour point testing was performed at ISL Mini Pour Point 5Gs to determine the lowest temperature at which the material would still flow, which correlates with ASTM D97 and D2500.

2.5 traction was measured using a micro-tractor (MTM), and testing was performed on PCS MTM 1. All pieces required to set MTM and standard samples provided by PCS (detailed in table 2 below) were sonicated 3 times in heptane for 15 minutes using a Camsonix C940 ultrasonic bath, with heptane drained and refilled after each sonication. All pieces were dried using nitrogen prior to assembly in MTM. The test curve was varied from 0% to 100% slip ratio (SRR) at 16N, taking 41 data points at a given temperature to generate a traction curve. This was repeated at 40 ℃, 60 ℃, 75 ℃, 100 ℃ and 120 ℃ to show performance over a wide temperature range. The test parameters are detailed in table 3 below.

2.6 NOACK volatility at 250℃was measured according to standard test method ASTM D5800. Since electric vehicles do not operate at such high temperatures, a modified test based on ASTM D5800 but at a temperature of 200 ℃ is also performed to provide a NOACK volatility measurement at 200 ℃.

2.7 Hydrolytic stability measured over 15 days (RR 1006).

250g of oil and 25g of water were mixed in a conical flask and fitted with a water trap (sluice). It was placed in an oven at 90℃for 15 days, and the acid value was measured every few days.

2.8 seal swell test seals of different materials were immersed in the sample to be tested at 100 ℃ for 2 weeks.

Table 2 mtm sample parameters。

	Disk	Ball with ball body
			Diameter (mm)	46	3/4 inch
Roughness of	<0.01μmRa	-
			Steel and method for producing same	AISI 52100	AISI 52100
Hardness of	720-780Hv

TABLE 3 MTM test parameters。

Parameters (parameters)	Friction step
		Temperature (. Degree. C.)	40、60、75、100、120
Ball load (N)	16
		Rolling speed (mms) ^-1 )	2200
SRR％	0-100

3. Test data

The sample materials detailed in table 1 and commercially available base oils from groups III and IV as detailed above were subjected to the test outlined in section 2 above.

TABLE 4 physical Properties of example samples compared to group III and IV base oils。

The physical properties of the example samples of the present invention make them useful as additives for use in lubricant compositions for electric vehicles. In particular, the balance between Kinematic Viscosity (KV) and thermal conductivity is particularly applicable to the powertrain of an electric vehicle. More particularly, the sample denoted DE10766 provides a material particularly suitable for electric vehicles, since the sample has a low kinematic viscosity material of only 2.9cSt at 100 ℃, an excellent Viscosity Index (VI) and a very low NOACK for the viscosity of the sample (NOACK data is provided in table 5 below). The pour point of DE10766 is also acceptable for use in electric vehicle lubricant applications.

Table 5.De10766 NOACK data

NOACK at 250 DEG C	Loss%	17.5
			NOACK at 200 DEG C	Loss%	2

Sample DE10766 was further tested to consider its electrical breakdown voltage, which is an important consideration for fluids suitable for electric vehicles. The electrical breakdown voltage value is lower than expected.

TABLE 6 DE10766

The hydrolytic stability of sample DE10766 was excellent and varied by only 0.38 AV units within 15 days; this is surprising for monoesters and it is believed that the use of guerbet alcohols provides some resistance to hydrolysis, although the reasons for this are not clear.

Compatibility with engine seals is another important feature of any additive used in electric vehicle powertrains. Sample DE10766 was also tested for seal swell within a two week period. Typically, low viscosity materials are highly polar and will swell the elastomer significantly. Priolube3959 (a commercially available lubricant additive diester with a KV of 2.5cSt at 100 ℃) was also tested as a comparative additive. A small amount of seal swelling is desirable, so the result of DE10766 is desirable, where prioube 3959 swells the elastomer to a greater, undesirable extent. The result of 1% swelling in FKM means that DE10766 can be used at high processing rates despite its low viscosity.

TABLE 7 seal swell data for DE10766 compared to Priolube3959 (alternative ester)。

	HNBR	FKM
			DE10766	7％	1％
Priolube 3959	37％	16％

At 40 ℃, all test samples had significantly lower traction than both group III and group IV base oils, this trend continued at 60 ℃ and 75 ℃, whereas at 100 ℃, the samples denoted 731-90 began to exhibit high traction coefficients at low slip ratios. It is believed that the very low viscosity of the 731-90 samples is responsible for this (KV at 100 ℃ c. Of 2.2 cSt) and that the samples are not able to maintain lubricant films at low slip ratio conditions. Samples, denoted 731-84, also showed an increase in traction coefficient at 120 ℃; the reason for this is unknown because samples 731-84 have a higher viscosity than DE10766, which can maintain low traction levels even at high temperatures, and it is expected that higher viscosity materials will perform better. However, in any event, since operating temperatures in electric vehicles are typically below 100 ℃, all example samples prepared therefrom are believed to have utility in electric vehicle powertrains. More particularly, DE10766 appears to be an excellent choice for reducing electric vehicle traction. It is low viscosity, low polarity and has excellent thermal properties, low traction properties and elastomer compatibility. In addition, other example samples tested herein showed that samples containing isosol 12 and isosol 16 provided the very low traction desired.

Claims

1. A lubricant composition suitable for use in an electric vehicle, the lubricant composition comprising a traction coefficient additive, and wherein the traction coefficient additive is an ester that is the reaction product of:

i) At least one saturated branched aliphatic monohydric alcohol having 12 to 32 carbon atoms, and

ii) at least one aliphatic carboxylic acid having from 6 to 32 carbon atoms.

2. The lubricant composition of claim 1, wherein the at least one aliphatic carboxylic acid is saturated.

3. The lubricant composition of claim 1 or 2, wherein the at least one aliphatic carboxylic acid is a monocarboxylic acid or a dicarboxylic acid such that the ester is a monoester or a diester.

4. The lubricant composition of any preceding claim, wherein the at least one saturated branched aliphatic monohydric alcohol has 12 to 24 carbon atoms.

5. The lubricant composition of claim 4, wherein the at least one saturated branched aliphatic monohydric alcohol has 12 to 20 carbon atoms.

6. The lubricant composition of any preceding claim, wherein the at least one saturated branched aliphatic monohydric alcohol is selected from the group consisting of 2-butyloctanol, isomyristyl alcohol, 2-hexyldecanol, isostearyl alcohol, 2-octyldecanol-1, 2-heptylundecyl-1, 2-octyldodecanol-1, 2-nonyltridecanol-1, and 2-decyltetradecanol-1, and mixtures of two or more such alcohols.

7. The lubricant composition of any preceding claim, wherein the at least one saturated branched aliphatic monohydric alcohol is selected from C12 guerbet alcohol, C14 guerbet alcohol, C16 guerbet alcohol, C18 guerbet alcohol, C20 guerbet alcohol, and C24 guerbet alcohol, or mixtures thereof.

8. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a thermal conductivity of greater than 0.131W/mK at 40 ℃.

9. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a kinematic viscosity at 100 ℃ of no more than 8.0 cSt.

10. The lubricant composition of claim 9, wherein the traction coefficient additive has a kinematic viscosity at 100 ℃ of no more than 3.3 cSt.

11. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a kinematic viscosity of no more than 30cSt at 40 ℃.

12. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a viscosity index of at least 130.

13. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a Noack evaporation loss of no more than 22 wt% at 250 ℃.

14. The lubricant composition of any preceding claim, wherein the traction coefficient additive has a Noack evaporation loss of no more than 9 wt% at 200 ℃.

15. The lubricant composition of any preceding claim, wherein the lubricant composition comprises up to 50 weight percent of the traction coefficient additive.

16. The lubricant composition of any preceding claim, wherein the lubricant composition comprises at least 3 wt% of the traction coefficient additive.

17. The lubricant composition of claim 15 or 16, wherein the lubricant composition comprises up to 25 weight percent of the traction coefficient additive.

18. The lubricant composition of any preceding claim, wherein the lubricant composition comprises at least one base oil selected from group I to group IV base oils, or a mixture of two or more thereof.

19. The lubricant composition of claim 18, comprising at least one of a group III base oil or a group IV base oil.

20. The lubricant composition of any preceding claim, further comprising one or more of the following additive types: dispersants, antioxidants, antiwear agents, emulsifiers, demulsifiers, extreme pressure agents, multi-functional additives, viscosity index improvers, pour point depressants, foam inhibitors, and friction improvers.

21. The lubricant composition according to claim 20, comprising at least 0.5 wt%, preferably at least 1 wt% of the one or more additive types, based on the total weight of the formulation.

22. The lubricant composition of claim 20 or 21, comprising up to 30 wt% of the one or more additive types, based on the total weight of the formulation.

23. The lubricant composition of any preceding claim, further comprising a level of other additives of from 0.01 to 30 wt%, based on the total weight of the lubricant composition.

24. A gear oil comprising the lubricant composition according to any one of claims 1 to 23.

25. A method of improving energy efficiency in an electric vehicle, the method comprising using the lubricant composition of any one of claims 1 to 23 or the gear oil of claim 24 in a powertrain of the electric vehicle.

26. The method of claim 25, wherein the lubricant composition or the gear oil is used in at least one system within the electric vehicle powertrain selected from the group consisting of axles, differentials, transmissions, battery packs, and power electronics.

27. The method of claim 25 or 26, wherein the lubricant composition or the gear oil is used in a gearbox of an electric vehicle.

28. Use of the lubricant composition according to any one of claims 1 to 23 or the gear oil according to claim 24 in an electric vehicle powertrain.

29. Use according to claim 28 in an electric vehicle integrated gearbox.