Lubricating oil composition

Abstract

The invention provides lubricating oil composition comprising a base oil composition and a friction modifier, said base oil composition comprising i. a first base oil selected from Fischer-Tropsch derived Group III base oils; and ii. no more than 25wt%, based on the overall weight of the lubricating oil composition, of a further base oil consisting of a monoester base oil, wherein the friction modifier is present in an amount in the range of from 0.25 to 2.5wt% based on the overall weight of the lubricating oil composition and is selected from a glycerol mono ester and a mono ester amine salt of formula (I) wherein R is selected from a saturated or unsaturated C4 to C22 hydrocarbon group, R1 is selected from a saturated or unsaturated C1 to C24 hydrocarbon group and n is an integer in the range of from 1 to 4, and wherein the lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 1.5 to 4.0 mm2 / s, a flash point, measured by the open cup method, of at least 160˚C and an aniline point of at least 80˚C.

Description

[0001] SP3011 - 1 - LUBRICATING OIL COMPOSITION Field of the Invention This invention relates to a lubricating oil composition and the use of said lubricating oil composition as a reduction gear oil in an electric 5 vehicle. Background of the invention E-mobility refers to vehicles powered, at least in part, by batteries, including fully battery powered electric vehicles and the complete range of hybrid 10 vehicles (e.g. plug-in hybrids, series hybrids, etc.). The number of these vehicles on the road has increased rapidly in recent years and it is expected that the rate of take up of vehicles relying on some form of battery power will continue to increase considerably over the coming decades. 15 The growth of, at least partially, electric vehicles has led to increased demands for fluids suitable for use in the powertrain of such vehicles. There is less uniformity between different types of electric vehicle (EV) powertrains than there is in internal combustion 20 engine (ICE) vehicles . In part, this is due to the degree of electrification of any vehicle, but also on the differences in design of the powertrain for vehicles with similar levels of electrification by different manufacturers. The design of fluids suitable for a range 25 of e-mobility options contains many challenges. Transmissions in pure battery-operated vehicles (BEVs) typically have a simple reduction gear set. Such vehicles have higher torques at low speeds and much higher rotational speeds than ICE powertrains. The absence of an 30 internal combustion engine usually means that BEVs operate at lower temperatures than ICE vehicles. Creating fluids to perform effectively in these conditions is a challenge. The provision of a lubricating oil composition for a reduction gear set in an electric or hybrid electric vehicle requires a careful balance in order to provide a 5 low viscosity composition which still provides excellent friction characteristics. Typically, lowering the viscosity of a lubricating oil composition negatively impacts on performance characteristics such as flash point and anti-wear performance. The use of friction modifiers 10 often leads to copper corrosion, potentially damaging key componentry in an electric or hybrid vehicle. JP2019-0137829 describes a lubricating oil composition for electric vehicles comprising, in addition to base oil, a phosphite or an amine salt thereof, a 15 borate, a sulfur-based extreme pressure agent and an organic friction modifier. Further improvements, such as the improvement of efficiency by reducing friction without compromising other performance such as flash point, wear protection and 20 copper corrosion, are still required to provide the necessary characteristics for a lubricating oil composition suitable for use as a reduction gear oil in an electric vehicle. Summary of the Invention 25 The present invention provides a lubricating oil composition comprising a base oil composition and a friction modifier, said base oil composition comprising: i. a first base oil selected from Fischer-Tropsch derived Group III base oils; and 30 ii. no more than 25wt%, based on the overall weight of the lubricating oil composition, of a further base oil consisting of a monoester base oil, wherein the friction modifier is present in an amount in the range of from 0.25 to 2.5wt% based on the overall weight of the lubricating oil composition and is selected from a glycerol mono ester and a mono ester amine salt of formula (I) 5 wherein R is or unsaturated C4 to C22 hydrocarbo grou p is selected from a saturated or unsaturated C1 to C24 hydrocarbon group and n is an integer in the range of from 1 to 4, and wherein the lubricating oil composition has a 10 kinematic viscosity at 100˚C in the range of from 1.5 to 4.0 mm2 / s, a flash point, measured by the open cup method, of at least 160˚C and an aniline point of at least 80˚C. The present invention also provides the use of such a lubricating oil as a reduction gear oil in 15 an electric vehicle. Detailed Description of the Invention One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed 20 techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the specification. When introducing elements of various embodiments of 25 the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 30 Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. In the context of the present invention, in a case where a composition comprises two or more components, 5 these components are to be selected in an overall amount not to exceed 100 wt%. The present inventors have surprisingly found that excellent results with respect to wear, friction, copper corrosion and durability can be achieved by the use of a 10 low viscosity lubricating oil composition comprising a Fischer-Tropsch derived base oil, optionally an ester base oil and a friction modifier selected from a glycerol mono ester and a mono ester amine salt, as well as ensuring the formulation has kinematic viscosity at 100˚C, flash point 15 and aniline point within specific ranges. The present invention provides a lubricating oil composition comprising a base oil composition and a friction modifier. The base oil composition comprises at least a Fischer-Tropsch derived base oil. 20 Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” it is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. Fischer-Tropsch derived base oils are often 25 classified by the starting material in the Fischer-Tropsch process, i.e., ‘X-to-liquids’ or ‘XTL’, with X standing for said starting material. Biomass-to-liquid (BTL, coal to liquids (CTL) and gas-to-liquid (GTL) processes are some examples of Fischer-Tropsch processes producing base 30 fluids. Preferably, the Fischer-Tropsch derived base oil is a GTL (Gas-To-Liquids) base oil. Suitable Fischer- Tropsch derived base oils that may be conveniently used in the present invention are those as for example disclosed in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO0157166. The Fischer-Tropsch derived base oil for use in the invention preferably has a kinematic viscosity at 100°C in the range of from 1.5 to 4.5 mm2 / s, more preferably in the range of from 1.5 to 4.0 mm2 / s. The Fischer-Tropsch derived base oil also preferably has a density at 15˚C of less than 0.83 g / cm3as measured according to JIS K 2249-1. The total amount of Fischer-Tropsch derived base oil present in the lubricating oil composition is preferably at least 50.0wt%, more preferably at least 55.0wt%, even more preferably at least 60.0wt%, most preferably at least 65.0wt% with respect to the total weight of the lubricating oil composition. The total amount of Fischer- Tropsch derived base oil present in the lubricating oil composition is preferably at most 99.0wt%, more preferably at most 95.0wt%, most preferably at most 93.0wt% with respect to the total weight of the lubricating oil composition. Examples of Fischer-Tropsch derived base oils that may be used alone or in combination in the present invention are the Fischer-Tropsch derived base oils available on the market from Shell Plc. as Risella X 415, Risella X411 and Risella X420. These Fischer-Tropsch derived base oils may be used alone or in combinations of two or more. Optionally, the base oil composition may also contain no more than 25wt%, based on the overall weight of the lubricating oil composition, of a further base oil consisting of a monoester base oil. Ester base oils fall within Group V of the API base oil classification. Suitable monoesters include branched or unbranched, saturated or unsaturated monoesters of fatty acids and alcohols. The fatty acid is preferably a C6 to C22 branched or unbranched, and saturated or unsaturated, fatty acid. Such fatty acids include, but are not limited to, stearic acid and oleic acid. The alcohol is preferably a C4 to C20 branched or unbranched, and saturated or unsaturated, 5 alcohol. If used in the lubricating oil composition, the monoester base oils preferably have a kinematic viscosity at 100˚C in the range of from 1.5 to 4.0mm2 / s, more preferably in the range of from 2.0 to 3.5 mm2 / s. 10 If the base oil composition comprises a monoester base oil, preferably said monoester base oil is present in an amount of at least 5wt%, more preferably at least 10wt%, even more preferably at least 15wt% on the basis of the overall weight of the lubricating oil composition. 15 The lubricating oil composition also comprises a friction modifier p resen t in an amount in the range of from 0.25 to 2 .5wt% based on the over all weight of the lubricating oil c omposition. P referably, said friction modifier is present in an amount in the range of at least 20 0.5wt% based on the overall weight of the lubricating oil composition. Also preferably, said friction modifier is present in an amount in the range of at most 2.0wt% based on the overall weight of the lubricating oil composition. The friction modifier is selected from 25 a glycerol mono ester and a mono ester amine salt of formula (I) wherein R is or unsaturated C4 to C22 hydrocarbo R1 is from a saturated or 30 unsaturated C1 to C24 hydrocarbon and n is an integer in the range of from 1 to 4 Preferably, if the friction modifier is a glycerol mono ester the glycerol mono ester comprises glycerol monooleate. If the friction modifier comprises a mono ester amine salt of formula (I), R is selected from a linear or branched, saturated or unsaturated C4 to C22 hydrocarbon group. For example, R may be selected from alkyl groups, alkenyl groups, cycloalkyl groups, aryl groups, and aralkyl groups. Preferably, R is an alkyl group or alkenyl group having 4 to 22 carbons, and more preferably in the range of from 8 to 22 carbon atoms. Suitably, R1represents a branched, unbranched or cyclic hydrocarbon group. Preferably, the total number of carbons in the hydrocarbon groups represented by NR13 is in the range of from 3 to 24, more preferably 9 to 18, and even more preferably 12 to 18. The lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 1.5 to 4.0 mm2 / s. Preferably, the lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 2.0 to 3.7 mm2 / s. The lubricating oil composition has a flash point, measured by the open cup method according to JIS K 2265-4, of at least 160˚C. The lubricating oil composition has an aniline point measured according to JIS K 2256 of at least 80˚C. As well as the base oil composition and the friction modifier, the lubricating oil composition may also contain one or more further additives. Said additives may be incorporated into the lubricating oil composition as individual additives or a part of a combined additive package. As is known, each additive or additive package may optionally be provided in a diluent fluid, such as a base oil. Typical additives in the lubricating oil composition of the present invention include, but are not limited to, extreme pressure additives, antiwear additives, viscosity index improvers, antioxidants, metal deactivators, 5 oiliness improvers, defoaming agents, pour point depressants, detergent dispersants and rust inhibitors. The phosphorous concentration in the lubricating oil composition is preferably at least 0.025 wt% based on the overall weight of the composition. Preferably, the 10 phosphorous concentration in the lubricating oil composition is no more than 0.06 wt%, more preferably no more than 0.04 wt%, based on the overall weight of the composition. The lubricating oil composition may be used in any 15 suitable application. However, it is preferred that the lubricating oil composition is used as a reduction gear oil in an electric vehicle. Said electric vehicle may be a fully battery powered electric vehicle or any form of hybrid electric vehicle wherein at least part of the 20 motive power is provided by an electric motor. The invention will now be further illustrated by reference to the following non-limiting examples. Examples The formulations set out in Tables 4 to 8 were 25 formulated using standard methods. The base oils set out in Table 1 were used.

[0002] Table 1 Kinematic Base oil viscosit erence Base oi y ref l type at 1 200˚C (mm / s) Base oil-1GTL base oil1.8Base oil-2GTL base oil2.7Base oil-3GTL base oil4.1Base oil 4mono ester base oil2.7Base oil 5 mono ester base oil 2.9 Base oil 6 Group II mineral oil 3.1 Two standard reduction gear oil additive package were used (addpack 1 and 2 in Tables 4 to 9). The 5 following friction modifiers were tested. Table 2 FM1glycerol monooleateFM2Dibasic acid monoester amine salt of Formula (I) FM3Oleylamine FM4Bis(2-ethylhexyl) phosphonateFM5MoDTC(450ppm Mo) (R= mixture of C8 and C13) The following tests were completed for the compositions. Table 3 10 Kinematic viscosity at 40 and 100˚C were measured according to JIS K 2283. Viscosity index was calculated according to JIS K 2293. Elemental analysis was carried out according to JPI 5S 38, JIS K 2541-4 and JIS K 2609. 15 Aniline point was measured according to JIS K 2256. Flash Point COC (open cup method) was measured according to JIS K 2265-4 MTM (PCS Instruments) EHD friction was measured at: oil temperature 40˚C; Pmax 1.0GPa; and sliding speed 1.5 m / . 20 AISI52100 ball and disc specimens with Ra <0.01 µm surface roughness were used. MTM (PCS Instruments) Boundary friction was measured at: oil temperature 40˚C; Pmax 1.0GPa; and sliding speed 0.005 m / s. AISI52100 ball and disc specimens with Ra <0.01 µm surface roughness were used. Copper corrosion was measured at 150˚C, with a test duration of 48 h according to JIS K 2513. 4 ball wear was measured at an oil temperature of 100 ˚C, Load 40kgf, Rotation speed 1500rpm and Test duration 1h according to ASTM D 417. The results of the Examples are shown in Tables 4 to 8. Table 4 – Examples 1 to 5 (inventive) Ex.1 2 3 4 5 Base Oil 2 wt%90.5 90 89 67.5 67.5Base Oil 4 wt%- --22.5 -Base Oil 5 wt%- - - - 22.5Addpack 1 wt% 9 9 9 9 9 Addpack 2 wt% - - - - - FM1 wt% 0.5 1 2 1 1 To100 100 100 100 100 KVt4a0l wmtm%2 / s11.73 11.92 12.26 11.61 11.79 KV100 mm2 / s3.049 3.074 3.122 3.072 3.129 VI119 118 117 126 131 %P wt%0.030 0.030 0.030 0.030 0.030 %Ca wt%0.063 0.063 0.063 0.063 0.063 %Mo wt%<0.001 <0.001 <0.001 <0.001 <0.001 %S wt%0.025 0.025 0.025 0.025 0.025 %N wt%0.14 0.14 0.14 0.14 0.14 Aniline point ˚C112 111 112 97 89Flash point ˚C192 192 192 200 200MTM traction0.032 0.032 0.032 0.030 0.029MTM boundary 0.084 0.082 0.078 0.089 0.088 friction Cu corrosion1a 1a 1b 1a 1a4ball wear mm0.45 0.58 0.60 0.51 0.53 Table 5- Examples 6 to 10 (inventive)Ex.6 7 8 9 10Base Oil 1 wt%90 - - - -Base Oil 2 wt%90.5 90 89 91Addpack 1 wt%9 9 9 9 -Addpack 2 wt% - - - -8FM1 wt%1 - - - 1FM2 wt%0.5 1 2Total (wt%) wt%100 100 100 100 100KV40 mm2 / s7.032 11.61 11.65 11.75 12.60KV100 mm2 / s2.201 3.043 3.047 3.049 3.223 VI 123 121 121 119 124% P wt%0.030 0.030 0.030 0.030 0.036 % Ca wt% 0.063 0.063 0.063 0.063 0.041 % Mo wt% <0.001 <0.001 <0.001 <0.001 <0.001 % S wt% 0.025 0.025 0.025 0.025 0.14 % N wt% 0.14 0.14 0.14 0.14 0.13Aniline point ˚C105 110 110 109 111Flash point ˚C168 190 190 192 190MTM traction0.029 0.032 0.032 0.032 0.037MTM boundary 0.088 0.086 0.086 0.086 0.089 frictionCu corrosion1a 1a 1b 1b 1a4 ball wear wt%0.51 0.52 0.41 0.51 0.55

[0003] Table 6 - (comparative Examples 1 to 4) Comp. Ex.1 2 3 4Base Oil 2 wt%91 90 90 90Addpack 1 wt%9 9 9 9FM3 wt%- 1 - -FM4 wt%- - 1 -FM5 wt% - - - 1Total wt%100 100 100 100KV40 mm2 / s11.55 11.46 11.43 11.62KV100 mm2 / s3.026 3.013 3.009 3.038VI 120 121 121 120% P wt%0.030 0.03 0.133 0.029% Ca wt% 0.063 0.063 0.063 0.063 % Mo wt% <0.001 <0.001 <0.001 0.044 % S wt% 0.025 0.025 0.025 0.025 % N wt% 0.13 0.18 0.14 0.14Aniline point ˚C112 111 110 111Flash point ˚C192 192 192 192MTM traction0.032 0.032 0.032 0.032MTM boundary 0.095 0.883 0.109 0.093 frictionCu corrosion1a 2b 1a 2c4 ball wear mm1.91 0.49 0.51 1.04

[0004] Table 7 – Comparative Examples 5 to 8 Comp. Ex. 56 7 8Base Oil 1 wt% -- - 91Base Oil 2 wt% 8888 - -Base Oil 3 wt% -- 90 -Addpack 1 wt% 99 9 9FM1 wt% 3- 1 -FM2 wt% -3 - -Total wt% 100100 100 100KV40 mm2 / s12.45 11.61 20.71 7.000KV100 mm2 / s3.142 3.0454.48 2.195VI 115 122132 124% P wt%0.03 0.03 0.03 0.03% Ca wt% 0.063 0.063 0.063 0.063 % Mo wt% <0.001 <0.001 <0.001 <0.001 % S wt% 0.025 0.025 0.025 0.025 % N wt% 0.14 0.14 0.14 0.14Aniline point ˚C110 109 120 105Flash point ˚C192 192 224 168MTM traction0.032 0.0320.034 0.029MTM boundary0.077 0.0840.093 0.105 frictionCu corrosion2b 2b 1a 1a4 ball wear mm0.58 0.49 0.61 1.12

[0005] Table 8 – Comparative Examples 9 to 11 Comp. Ex.9 10 1112 Base Oil 2 wt%68.25 - 92-Base Oil 4 wt%22.75 90 --Base oil 6 Wt%- - -91Addpack 1 wt%9 9 -9 Addpack 2 wt%- - 8- FM1 wt% - 1 - - Total wt%100 100 100-KV40 mm2 / s11.50 11.67 12.35 14.69KV100 mm2 / s3.051 3.187 3.204 3.470VI126 145128 114% P wt%0.03 0.03 0.036 0.03 % Ca wt% 0.063 0.063 0.041 0.063 % Mo wt% <0.001 <0.001 0.14 <0.001 % S wt% 0.025 0.025 0.14 0.025 % N wt% 0.13 0.13 113 0.14 Aniline point ˚C98 29 3a 106Flash point ˚C200 222 0.52 206MTM traction0.030 0.030 12.35 0.040MTM boundary 0.092 0.080 3.204 0.096 friction Cu corrosion1a 1b 128 1a4ball wear mm0.82 0.60 0.036 1.02The inventive examples may easily be compared to the comparative examples to demonstrate the technical effect of the combination of base oil and friction modifier as well as the required kinematic viscosity, flash point and aniline point. Inventive examples 1 to 10 demonstrate excellent friction properties without compromising other performance such as wear protection and copper corrosion. Comparative Examples 1, 8, 9 and 11 contain no friction modifiers and a range of base oils. Each of these examples demonstrate worse properties for at least one of friction, anti-wear and copper corrosion. Comparative Examples 2, 3 and 4 also demonstrate worse properties for at least one of friction, anti-wear and copper corrosion when different friction moderators are used in the lubricating oil composition. The importance of the amount 5 of friction modifier is shown by comparative Examples 5 and 6. Comparative Example 7 highlights the importance of the limit for kinematic viscosity at 100˚C. A base oil composition outside that required by Claim 1 also provides worse properties for at least one of friction, anti-wear 10 and copper corrosion, as evidenced by comparative example 10.

Claims

SP3011 - 16 - C L A I M S 1. A lubricating oil composition comprising a base oil composition and a friction modifier, said base oil composition comprisingi. a first base oil selected from Fischer-Tropsch 5 derived Group III baseoils; and ii. no more than 25wt%, based on the overall weight of the lubricating oil composition, of a further base oil consisting of a monoester base oil, wherein the friction modifier is present in an amount in 10 the range of from 0.25 to 2.5wt% based on the overall weight of the lubricating oil composition and is selected from a glycerol mono ester and a mono ester amine salt of formula (I) 15 wherein R isor unsaturated C4 to C22 hydrocarbo group, is selected from a saturated or unsaturated C1 to C24 hydrocarbon group and n is an integer in the range of from 1 to 4, and wherein the lubricating oil composition has a 20 kinematic viscosity at 100˚C in the range of from 1.5 to 4.0 mm2 / s, a flash point, measured by the open cup method, of at least 160˚C and an aniline point of at least 80˚C.

2. A lubricating oil as claimed in Claim 1, wherein the lubricating oil composition contains at least 25 0.025 wt% of phosphorus based on the overall weight of the composition.

3. A lubricating oil composition as claimed in Claim 1 or Claim 2, wherein the Fischer-Tropsch derived Group III base oil has a kinematic viscosity at 100°C in the rangeof from 1.5 to 4.5 mm2 / s, preferably in the range of from 1.5 to 4.0 mm2 / s.

4. A lubricating oil composition as claimed in any one of Claims 1 to 3, wherein the monoester base oil is present 5 in an amount of at least 5wt%, preferably at least 10wt%, more preferably at least 15wt%.

5. A lubricating oil composition as claimed in any one of Claims 1 to 4, wherein the friction modifier is present in an amount in the range of from 0.5 to 2.0wt% based on the 10 overall weight of the lubricating oil composition.

6. Use of a lubricating oil composition as claimed in any one of Claims 1 to 5 as a reduction gear oil in an electric vehicle. 15

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