WO2025201962A1

WO2025201962A1 - Lubricating oil composition

Info

Publication number: WO2025201962A1
Application number: PCT/EP2025/057340
Authority: WO
Inventors: Mao UEDA
Original assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Current assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2024-03-27
Filing date: 2025-03-18
Publication date: 2025-10-02
Anticipated expiration: 2026-09-27

Abstract

This invention provides a lubricating oil composition having a kinematic viscosity at 100 ° C in the range of from at least 3. 5 mm²/s to less than 7. 0 mm²/s, said lubricating oil composition comprising a Fischer-Tropsch derived base oil and in the range of from 5 to 14wt% of a poly (meth) acrylate viscosity modifier selected from a comb type poly (meth) acrylate and a non-comb type poly (meth) acrylate, wherein the non-comb type poly (meth) acrylate has a weight average molecular weight of less than 100000, contains a nitrogen containing functional group and is sulfur-free, wherein the lubricating oil composition contains at least 0. 1 weight% phosphorus and 2.0wt% sulfur based on the overall weight of the lubricating oil composition. The present invention also provides the use of said lubricating oil composition as a gear oil.

Description

SP3130 - 1 - LUBRICATING OIL COMPOSITION Field of the Invention This invention relates to a lubricating oil composition and to the use of that lubricating oil composition as an automotive gear oil. 5 Background of the invention Different lubricating oil compositions are formulated with different characteristics depending on the use to which the lubricating oil compositions will be put. A lubricating oil composition for gears is used for 10 preventing damage and seizing of gears in use. In recent years, the load-bearing performance required of automotive gear oils has required a level of GL-4 to GL-5 as the American Petroleum Institute (API) gear oil type to support the increased output characteristics of 15 automobiles. The selection of a suitable lubricating oil composition, usually requires the consideration of the “worst case” conditions under which it is operated. For example, automotive gear units that are operated in 20 response to various road conditions should be necessarily assumed to be driven under low-speed conditions in which oil film is not easily formed. Therefore, gear oils are required to have exceptional durability. For gear oils that are required to have such durability, it has been 25 common to employ gear oil with Society of Automotive Engineers (SAE) viscosity number 90, that is a kinematic viscosity at 100˚C in the range of from 13.5 to 18.5 mm²/s, in order to maintain oil film formation on the gear tooth surface. For example, US20180312776 describes gear oil compositions with a kinematic viscosity at 100˚C in the range of from 7.0 mm²/s to 35.0 mm²/s. However, the requirements for improved fuel economy in modern E-axles requires a lower viscosity lubricating 5 oil composition to be used. Such a reduction in viscosity may lead to oil film shortage, causing problems of seizing and wear of gears and bearings. It is, therefore, desirable to produce a lubricating oil composition capable of protecting the gears, especially against scuffing, 10 while allowing operation at increased fuel efficiency. Lubricating compositions for use in automotive transmissions are described in US2017/226443. These compositions require a GTL low viscosity base oil and a Group 1 high viscosity base oil. 15 The gear oil compositions described in US2020/0032160 are focused on lower viscosity lubricating oil compositions with low sulfur content and a combination of a dispersant poly(meth)acrylate compound with a non- dispersant poly(meth)acrylate compound. 20 Comb polymers as antifatigue additives are described in US2011/0306533. The present inventors have sought to provide an improved lubricating oil composition for use as a gear oil composition in which excellent characteristics of scuffing 25 protection are provided while fuel efficiency is maintained. Summary of the Invention The present invention therefore provides a lubricating oil composition having a kinematic viscosity 30 at 100˚C in the range of from at least 3.5 mm²/s to less than 7.0 mm²/s, said lubricating oil composition comprising a Fischer-Tropsch derived base oil and in the range of from 5 to 14wt% of a poly(meth)acrylate viscosity modifier selected from a comb type poly(meth)acrylate and a non- comb type poly(meth)acrylate, wherein the non-comb type poly(meth)acrylate has a weight average molecular weight of less than 100000, contains a nitrogen containing functional group and is sulfur-free, wherein the 5 lubricating oil composition contains at least 0.1 weight% phosphorus and 2.0wt% sulfur based on the overall weight of the lubricating oil composition. The present invention also provides the use of said lubricating oil composition as a gear oil. 10 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 techniques. Additionally, in an effort to provide a 15 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 the present disclosure, the articles “a,” “an,” and “the” 20 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. Additionally, it should be understood that references to 25 “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 30 where a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100 wt%. The present inventors have found that an excellent balance of fuel efficiency and protection against scuffing can be obtained by the use of a lubricating oil composition, having a kinematic viscosity of at least 3.5 and less than 7.0 mm²/s, containing Fischer-Tropsch derived base oil in combination with a selection of poly(meth)acrylate viscosity modifier compositions. Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” 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 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), gas-to-liquid (GTL) and power-to-liquid (PTL) processes are some examples of Fischer-Tropsch processes producing base oils. Preferably, the Fischer-Tropsch derived base oil is a GTL (Gas-To- Liquids) base oil. Suitable Fischer-Tropsch derived base oils are those as for example disclosed in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO 0157166. Preferably, the Fischer-Tropsch derived base oil has kinematic viscosity at 100˚C of at least 2.0 mm²/s, more preferably at least 2.5 mm²/s and preferably 7.5 mm²/s or less, 7.0 mm²/s or less or 6.5 mm²/s or less. The amount of Fischer Tropsch derived base oil in the lubricating oil composition of the invention is preferably not less than 70 wt% in terms of the total amount of the lubricating oil composition, and more preferably not less than 80 wt%. Optionally, other base oils may also be incorporated into the lubricating oil composition. These include base oils in groups 1 to 5 according to the API classification of base oils. In one preferred embodiment of the present invention, an ester base oil is incorporated into the lubricating oil composition. Said ester base oil may be any of monoesters, diesters and partial or total esters of polyhydric alcohols. The alcohols forming the ester base oils may be 5 monohydric alcohols, or any of the polyhydric alcohols, and the acids may be monobasic acids or polybasic acids. The monohydric alcohols may be alcohols of carbon number 1 to 24, but preferably 1 to 12 and more preferably 1 to 8, and may be straight-chain or branched. They may 10 also be saturated or unsaturated. The polyhydric alcohols may be dihydric to decahydric alcohols. There are also polyhydric alcohols such as glycerol, polyglycerol (2~8-mers of glycerol), trimethylolalkanes (trimethylolethane, trimethylolpropane, 15 trimethylolbutane and so on), and 2~8-mers thereof, pentaerythritol and 2~4-mers thereof, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4- butanetetrol, sorbitol, sorbitan, sorbitol-glycerol condensates, adonitol, arabitol, xylitol and mannitol. 20 There are also saccharides such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose and sucrose. Mixtures of the aforementioned polyhydric alcohols may also be mentioned. 25 Of the aforementioned polyhydric alcohols, more preferred are ethylene glycol, propylene glycol, neopentyl glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol and sorbitan, and mixtures thereof. As examples of yet more preferred instances, mention may 30 be made of neopentyl glycol, trimethylolethane, trimethylolpropane and pentaerythritol, and mixtures thereof; by means of these even higher thermal and oxidative stability can be achieved. For the acids forming the ester base oils, the monobasic acids include fatty acids of 2 to 24 carbons, and they may be straight-chain or branched, and saturated or unsaturated. 5 For example, the saturated fatty acids include acetic acid and propionic acid, and straight-chain or branched butanoic, pentanoic, hexanoic, heptanoic, octanoic, nonanoic, decanoic, undecanoic, dodecanoic, tridecanoic, tetradecanoic, pentadecanoic, hexadecanoic, 10 octadecanoic, hydroxyoctadecanoic, nonadecanoic, eicosanoic, heneicosanoic, docosanoic, tricosanoic and tetracosanoic acids. The unsaturated fatty acids include acrylic acid and straight-chain or branched butenoic, pentenoic, hexenoic, 15 heptenoic, octenoic, nonenoic, decenoic, undecenoic, dodecenoic, tridecenoic, tetradecenoic, pentadecenoic, hexadecenoic, octadecenoic, hydroxyoctadecenoic, nonadecenoic, eicosenoic, heneicosenoic, docosenoic, tricosenoic and tetracosenoic acids. Mixtures of the 20 aforementioned acids may also be mentioned. Of the aforementioned saturated fatty acids and unsaturated fatty acids, these preferred are saturated fatty acids of carbon number 3 to 20, unsaturated fatty acids of carbon number 3 to 22, and mixtures thereof, but 25 saturated fatty acids of carbon number 4 to 18, unsaturate xtures thereof, are more preferred. Lubricity and handling qualities are enhanced, and if consideration is also given to oxidative stability, saturated fatty acids of carbon number 4 to 18 are most preferred. 30 As examples of the polybasic acids mention may be made of dibasic acids of carbon number 2 to 16 and trimellitic acid. The dibasic acids of carbon number 2 to 16 may be straight-chain or branched and they may also be saturated or unsaturated. They include, for example, ethanedioic acid and propanedioic acid, and straight-chain or branched butanedioic, pentandioic, hexanedioic, heptanedioic, octanedioic, nonanedioic, decanedioic, undecanedioic, dodecanedioic, tridecanedioic, tetradecanedioic, pentadecanedioic and hexadecanedioic acids. Mixtures thereof may also be mentioned. If present, the ester base oil is preferably incorporated into the lubricating oil composition in an amount in the range of from 1 to 20wt%, more preferably an amount in the range of from 5 to 15wt%, based on the overall weight of the lubricating oil composition. The lubricating oil composition also comprises in the range of from 5 to 14wt% of a poly(meth)acrylate viscosity modifier. Said poly(meth)acrylate viscosity modifier is selected from a comb type poly(meth)acrylate and a non- comb type poly(meth)acrylate, wherein the non-comb type poly(meth)acrylate has a weight average molecular weight of less than 100000, contains a nitrogen containing functional group and is sulfur-free. The term “comb type” is well known in the polymer art. A comb type polymer has three-way branch points connecting branching parts (branch polymer chains) to a core part (core polymer chain) and said branched parts themselves also have three-way branch points connecting the side chains to the main chain. In other words, a comb type polymer is a general designation for polymers having a plurality of side chains extended from a main chain in a comb formation. The comb type poly(meth)acrylate viscosity modifier referred to in this invention refers to a polymethacrylate (PMA)-based viscosity modifier which is a comb polymer. Comb type polymethacrylate viscosity modifiers are known in the art, for example as disclosed WO2010532805 and WO2013536293. The comb type polymethacrylate viscosity modifier may contain, for instance, methacrylate-based macromonomers and comb-structure polymers (comb polymers) obtained by copolymerisation of methacrylate-based monomers. Said comb type polymethacrylate based viscosity modifiers may also be comb polymers formed of a polyalkyl(meth)acrylate-based main chain and long hydrocarbon side chains with a carbon number of at least 50. In addition, the comb type polymethacrylate viscosity modifiers may be, for example, polymers which have the monomer constituent formed only of methacrylate-based monomers, or copolymers of methacrylate-based monomers and other monomers, or those incorporating macromolecular compounds other than polymethacrylates in part of the structure. Further, said comb type polymethacrylate viscosity modifiers may be of the dispersive type having polar groups such as amino groups or sulphonic acid groups in their molecular structure, or the non- dispersive type not containing these. In the aforementioned, the amount of methacrylate-based monomers is ideally not less than 70 weight% in terms of the total amount of the above-mentioned comb-like polymethacrylate-based viscosity index improver, but more ideally not less than 80 weight% and still more ideally not less than 90 weight%. The comb type polymethacrylate-based viscosity modifier of the invention should also ideally have a weight average molecular weight of 50,000 to 600,000, but more ideally 70,000 to 500,000 and most ideally 70,000 to 450,000. As regards the weight average molecular weight, the average molecular weights (weight average molecular weight at polystyrene conversion and number average molecular weight) can be analysed (calculated) by using for example a Shodex GPC-101 high-speed liquid chromatograph as made by Showa Denko Ltd, the measuring conditions being a temperature of 40°C, a detector of the differential refractive index (RI) type, a carrier flow rate of THF-1.0 ml/min (ref. 0.3 ml/min), injected sample amount of 100 μl and columns of types KF-G (Shodex x 1) and KF-805L (Shodex x 2) , and by using a range appropriate to the peak molecular weights. If present, the non-comb type poly(meth)acrylate has a weight average molecular weight of less than 100000, contains a nitrogen containing functional group and is sulfur-free. The non-comb type poly(meth)acrylate preferably has a weight average molecular weight of at least 15000. 5 Suitable nitrogen containing functional groups include include those derived from the incorporation of nitrogen-containing monomers during the production of the poly(meth)acrylate. Said nitrogen-containing monomers may be (meth)acrylic monomers such as methacrylamides Said 10 nitrogen-containing monomer may also be other than a (meth)acrylic monomer, such as vinyl-substituted nitrogen heterocyclic monomers and vinyl substituted amines. Nitrogen-containing monomers are well known, examples being disclosed, for instance, in US6331603. Among the 15 suitable monomers are dialkylaminoalkyl acrylates, dialkylaminoalkyl methacrylates, dialkylaminoalkyl acrylamides, dialkylaminoalkyl methacrylamides, N-tertiary alkyl acrylamides, and N-tertiary alkyl methacrylamides, where the alkyl group or aminoalkyl groups may contain,20 independently, 1 to 8 carbon atoms. The nitrogen- containing monomer may be, for instance, t-butyl acrylamide, N-(3-(dimethylamino)propyl)methacrylamide, dimethylaminopropyl methacrylamide, dimethylaminoethyl methacrylamide, N-vinyl pyrrolidone, N-vinylimidazole, or 25 N-vinyl caprolactam. It may also be a (meth)acrylamide based on any of the aromatic amines disclosed in WO2005087821 including 4-phenylazoaniline, 4- aminodiphenylamine, 2-aminobenzimidazole, 3-nitroaniline, 4-(4-nitrophenylazo)aniline, N-(4-amino-5-methoxy-2-30 methyl-phenyl)-benzamide, N-(4-amino-2,5-dimethoxy- phenyl)-benzamide, N-(4-amino-2,5- diethoxy-phenyl)- benzamide, N-(4-amino-phenyl)-benzamide, 4-amino-2- hydroxy-benzoic acid phenyl ester, and N, Ndimethyl- phenylenediamine. Sulfur free preferably requires essentially no sulfur atoms present in the poly(meth)acrylate. The invention will now be further illustrated by reference to the following non-limiting examples. 5 Examples Lubricant oil formulations were blended with the formulations set out in Tables 1 to 4. The following components were used:

Base oils KV100 = kinematic viscosity at 100˚C according to JIS K 2283 Base oil 1 – GTL base oil, KV100 1.8 mm²/s Base oil 2 – GTL base oil, KV100 2.7 mm²/s Base oil 3 – GTL base oil, KV100 4.1 mm²/s Base oil 4 – GTL base oil, KV100 7.8 mm²/s Base oil 5 – Yubase (mineral) base oil, KV100 3.1 mm²/s Ester 1 - trimethylolpropoane ester, KV100 4.4 mm²/s Additive Packages The additive packages used were standard axle oil packages known in the art. Poly(meth) acrylates Molecular weights are weight average molecular weights Sulfur Comb type N- Molecular content functional weight group PMA-1 0 no yes 20000 PMA-2 0 no yes 70000 PMA-3 0 yes no 170000 PMA-4 1000ppm yes yes 330000 PMA-5 3000ppm yes no 80000 PMA-6 2000ppm no yes 70000 PMA-7 0 no no 20000 PMA-8 0 no no 300000 PMA-9 2000ppm no no 20000 Testing Each lubricating oil composition was then subjected to a number of tests as set out below: Kinematic viscosity at 40˚C (KV40) and at 100˚C (KV100) were measured according to JIS K 2283. Viscosity index was measured according to JIS K 2283. Kinematic viscosity at 100˚C was remeasured after the KRL test according to JIS K 2283 and CEC L-45-A-99 and the reduction ratio of KV100 was calculated. Density was measured at 15˚C according to JIS K 2249. 5 Elemental concentrations were measured for phosphorus (P) according to JPI 55 38; sulfur (S) according to JIS K 2541-4; and nitrogen (N) according to JIS K 2609. MTM scuffing was measured with a sliding speed of 2m/s at 100˚C and 45N, with a steel disc-steel ball (surface 10 roughness (Ra) less than 0.01µm) EHL film thickness was measured with an entrainment speed of 10 mm/s, SRR 250%, load 10N, glass disc-steel ball. MTM traction: 40˚C, Pmax 1.0GPa, sliding speed 1.5 m/s, steel disc-steel ball (surface roughness (Ra) less than 15 0.01µm). MTM boundary friction: 40˚C, Pmax 1.0GPa, sliding speed 0.005 m/s, steel disc-steel ball (surface roughness (Ra) less than 0.01µm). The results of these tests are given with the 20 formulations in Tables 1 to 4, below. As can be seen from the Examples, lubricating oil compositions according to the invention provide good traction coefficients and a great anti-scuffing performance. This can be seen in comparison to the 25 comparative Examples in which this balance of traction coefficients and scuffing protection is not generally seen. Comparative Example 2, which includes 20wt% of PMA shows an unacceptably high KV100 reduction ratio. Increased traction coefficients are shown for Comparative 30 Examples 9 and 10, which use base oils outside those suitable for the present invention. Table 1 – Inventive Examples to 5 1 2 3 4 5 Base Oil 1 wt% - - - - - Base oil 2 wt% 82 76 82 82 82 Base oil 3 wt% - - - - - Base oil 4 wt% - - - - - Base oil 5 wt% - - - - - Ester 1 wt% - - - - - Add pack 1 wt% 10 10 10 10 10 Add pack 2 wt% - - - - - PMA-1 wt% 8 14 - - - PMA-2 wt% - - 8 - - PMA-3 wt% - - - 8 - PMA-4 wt% - - - - 8 PMA-5 wt% - - - - - PMA-6 wt% - - - - - PMA-7 wt% - - - - - PMA-8 wt% - - - - - PMA-9 wt% - - - - - Total wt% 2 100 100 100 100 100 KV40 mm 2/s 14.95 21.24 17.21 14.50 14.12 KV100 mm /s 4.007 5.321 4.472 4.364 4.470 VI 2 180 202 187 240 267 KV100 after mm /s 3.887 4.945 4.216 4.061 4.112 KRL test KV100 % 3.0 7.1 5.7 6.9 8.0 Reduction ratio Density g/cm³ 0.828 0.834 0.831 0.827 0.827 (15˚C) P wt% 0.14 0.14 0.14 0.14 0.14 S wt% 2.2 2.2 2.2 2.3 2.3 N wt% 0.09 0.09 0.10 0.08 0.10 MTM scuffing none none none none None EHL film nm 11 10 12 12 12 thickness MTM traction 0.023 0.022 0.022 0.023 0.022 MTM boundary 0.126 0.125 0.115 0.121 0.091 friction

Table 2 – Inventive Examples 6 to 9 6 7 8 9 Base Oil 1 wt% - - - - Base oil 2 wt% 82 81 72 - Base oil 3 wt% - - - 82 Base oil 4 wt% - - - - Base oil 5 wt% - - - - Ester 1 wt% - - 10 - Add pack 1 wt% 10 - 10 10 Add pack 2 wt% - 11 - - PMA-1 wt% - - - - PMA-2 wt% - 8 8 8 PMA-3 wt% - - - - PMA-4 wt% - - - - PMA-5 wt% 8 - - - PMA-6 wt% - - - - PMA-7 wt% - - - - PMA-8 wt% - - - - PMA-9 wt% - - - - Total wt 2% 100 100 100 100 KV40 mm 2/s 13.23 18.85 20.07 30.43 KV100 mm /s 3.813 5.011 5.217 6.871 VI 2 199 214 212 196 KV100 after KRL mm /s 3.712 4.689 4.912 6.514 test KV100 Reduction % 2.6 6.4 5.8 4.8 ratio Density (15˚C) g/cm³ 0.829 0.830 0.841 0.837 P wt% 0.14 0.207 0.14 0.14 S wt% 2.3 2.3 2.2 2.2 N wt% 0.08 0.09 0.09 0.09 MTM scuffing none none none none EHL film nm 13 12 12 13 thickness MTM traction 0.021 0.023 0.021 0.022 MTM boundary 0.127 0.118 0.126 0.115 friction

Table 3 – Comparative Examples 1 to 5 1 2 3 4 5 Base Oil 1 wt% - - - - - Base oil 2 wt% 90 70 86 75 75 Base oil 3 wt% - - - - - Base oil 4 wt% - - - - - Base oil 5 wt% - - - - - Ester 1 wt% - - - - - Add pack 1 wt% 10 10 10 10 10 Add pack 2 wt% - - - - - PMA-1 wt% - 20 - - - PMA-2 wt% - - 4 - - PMA-3 wt% - - - - - PMA-4 wt% - - - - - PMA-5 wt% - - - - - PMA-6 wt% - - - 15 - PMA-7 wt% - - - - 15 PMA-8 wt% - - - - - PMA-9 wt% - - - - - Total wt 2% 100 100 100 100 100 KV40 mm 2/s 10.18 26.18 12.33 21.30 19.87 KV100 mm /s 2.750 6.481 3.340 5.408 5.047 VI 2 112 218 151 208 199 KV100 after KRL mm /s 2.737 5.751 3.247 5.107 4.965 test KV100 Reduction % 0.5 11.3 2.8 5.6 1.6 ratio Density (15˚C) g/cm³ 0.821 0.841 0.826 0.837 0.838 P wt% 0.14 0.14 0.143 0.14 0.14 S wt% 2.2 2.2 2.3 2.3 2.2 N wt% 0.08 0.09 0.09 0.11 0.09 MTM scuffing yes none yes yes yes EHL film nm 7 12 7 7 7 thickness MTM traction 0.024 0.022 0.022 0.023 0.023 MTM boundary 0.138 0.121 0.131 0.118 0.128 friction

Table 4 – Comparative Examples 6 to 10 6 7 8 9 10 Base Oil 1 wt% - - 82 - - Base oil 2 wt% 75 75 - - - Base oil 3 wt% - - - - - Base oil 4 wt% - - - 82 - Base oil 5 wt% - - - - 82 Ester 1 wt% - - - - - Add pack 1 wt% 10 10 10 10 10 Add pack 2 wt% - - - - - PMA-1 wt% - - - - - PMA-2 wt% - - 8 8 8 PMA-3 wt% - - - - - PMA-4 wt% - - - - - PMA-5 wt% - - - - - PMA-6 wt% - - - - - PMA-7 wt% - - - - - PMA-8 wt% 15 - - - - PMA-9 wt% - 15 - - - Total wt 2% 100 100 100 100 100 KV40 mm 2/s 44.00 19.98 10.81 63.62 23.95 KV100 mm /s 12.78 5.127 3.460 11.37 5.779 VI 2 303 205 229 174 199 KV100 after KRL mm /s 5.023 5.025 3.215 10.65 5.368 test KV100 Reduction % 60.7 2.0 7.1 6.3 7.1 ratio Density (15˚C) g/cm³ 0.839 0.841 0.820 0.851 0.852 P wt% 0.14 0.14 0.14 0.14 0.14 S wt% 2.2 2.2 2.3 2.2 2.2 N wt% 0.09 0.09 0.09 0.09 0.09 MTM scuffing yes yes yes none none EHL film nm 7 7 8 15 12 thickness MTM traction 0.023 0.023 0.020 0.026 0.028 MTM boundary 0.135 0.121 0.138 0.083 0.121 friction

Claims

SP3130 - 17 - C L A I M S 1. A lubricating oil composition having a kinematic viscosity at 100˚C in the range of from at least 3.5 mm²/s to less than 7.0 mm²/s, said lubricating oil composition comprising a Fischer-Tropsch derived base oil and in the range of from 5 to 14wt% of a poly(meth)acrylate viscosity modifier selected from a comb type poly(meth)acrylate and a non- comb type poly(meth)acrylate, wherein the non-comb type poly(meth)acrylate has a weight average molecular weight of less than 100000, contains a nitrogen containing functional group and is sulfur-free, wherein the lubricating oil composition contains at least 0.1 weight% phosphorus and 2.0wt% sulfur based on the overall weight of the lubricating oil composition. 2. A lubricating oil composition as claimed in Claim 1, wherein the Fischer-Tropsch derived base oil has a kinematic viscosity at 100˚C in the range of from 2.0 mm²/s to 6.5 mm²/s. 3. A lubricating oil composition as claimed in Claim 1 or Claim 2, wherein the lubricating oil composition also comprises an ester base oil in an amount in the range of from 2 to 20wt% based on the overall weight of the lubricating oil composition. 4. Use of the lubricating oil composition as claimed in any of claims 1 to 3 as a gear oil composition.