Lubricating oil composition

Abstract

This invention provides a lubricating oil composition, comprising a Fischer-Tropsch-derived base oil with a kinematic viscosity at 100°C of no more than 3.0 cSt; a viscosity modifier comprising a polymethacrylate; and phosphorus containing additives such that the amount of phosphorus in the overall lubricating oil composition is at least 0.18 wt%.

Description

[0001] SP3241

[0002] 1

[0003] LUBRICATING OIL COMPOSITION

[0004] Field of the Invention

[0005] This invention relates to a lubricating oil composition, in particular a lubricating oil composition for use as a manual transmission fluid. Background of the invention

[0006] When a lubricating oil composition is to be used in a manual transmission, it has been very difficult to provide a good balance of energy efficiency properties, hardware protection properties and necessary friction properties.

[0007] An automatic transmission fluid is described in US20170226443. Said fluid comprises a low viscosity GTL based base oil in combination with a higher viscosity Group 1 base oil and is indicated to provide improved fatigue damage prevention. However, the viscosity index of the fluids according to US20170226443 is only of a moderate level, with 128 to 137 being reported in the Examples .

[0008] A higher viscosity index is provided by the lubricating oil compositions for automobile transmissions described in WO2022053427 , which require a base oil, preferably a GTL base oil, and a poly (meth) acrylate and an olefin co-polymer as a viscosity modifier. Such an improvement in viscosity index is balanced with less desirable hardware protection properties.

[0009] It is, therefore, desirable to provide a lubricating oil composition, suitable for use as a transmission fluid with an excellent balance of energy efficiency properties, hardware protection properties and necessary friction properties . Summary of the Invention

[0010] The present invention provides a lubricating oil composition, comprising a Fischer-Tropsch-derived base oil with a kinematic viscosity at 100°C of no more than 3.0 cSt; a viscosity modifier comprising a polymethacrylate; and phosphorus containing additives such that the amount of phosphorus in the overall lubricating oil composition is at least 0.18 wt%.

[0011] The present invention also provides a method for lubricating a manual transmission comprising the steps of applying said lubricating oil composition to the manual transmission and operating the manual transmission. Detailed Description of the Invention

[0012] 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 concise description of these embodiments, not all features of an actual implementation may be described in the specification.

[0013] When introducing elements of various embodiments of 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. 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.

[0014] In the context of the present invention, in a case where a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100 wt% .

[0015] The present inventors have found that a lubricating oil composition comprising a low viscosity Fischer- Tropsch-derived base oil, a polymethacrylate viscosity modifier and phosphorus containing additives, such that the amount of phosphorus in the overall lubricating oil composition is at least 0.18wt%, provides excellent characteristics suitable for use in a transmission fluid, especially a manual transmission fluid.

[0016] 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.

[0017] A Fischer-Tropsch derived base oil typically has a total sulfur content of less than 1 ppm and a total nitrogen content of less than 1 ppm. Also, the aniline point of Fischer-Tropsch derived base oils is typically 90°C or more and 120°C or less, more preferably 95°C or more and 115°C or less, and the refractive index is 1.42 or more and 1.46 or less, more preferably 1.43 or more and 1.45 or less .

[0018] The Fischer-Tropsch-derived base oil has a kinematic viscosity at 100°C of no more than 3.0 cSt. Preferably the Fischer-Tropsch-derived base oil has a kinematic viscosity at 100°C of at least 1.5 cSt, more preferably at least 2.0 cSt. Shell GTL3 is a suitable base oil for the lubricating oil composition.

[0019] Further base oils may be used in combination with the Fischer-Tropsch derived base oil. However, preferably the Fischer-Tropsch derived base oil is present in an amount of at least 65wt%, preferably at least 70wt%, based on the overall weight of the lubricating oil composition. If a further base oil is present in the lubricating oil composition, it is suitably a Group 1 mineral oil, preferably a brightstock Group 1 base oil with a kinematic viscosity at 100°C in the range of from 30 to 34 cSt . Said further base oil is preferably present in an amount in the range of from 5 to 15wt% based on the overall weight of the lubricating oil composition.

[0020] A viscosity modifier is used with the base oil to adjust its viscosity. The viscosity modifier comprises one or more polymethacrylates (PMA) . Optionally, the viscosity modifier may also comprise one or more olefin copolymers (OCP) . The viscosity modifier has a number average molecular weight of 5,000 or more and 30, 000 or less, preferably 5,000 or more and 20,000 or less, and more preferably 5,000 or more and 12,000 or less.

[0021] The viscosity modifier may be blended in a range of about 2%wt to 20%wt, and preferably 5%wt to 15%wt relative to the overall weight of the lubricating oil composition. The polymethacrylates include non-dispersive polymethacrylates and dispersed polymethacrylates, and either type can be used. In some cases, both types may be used together. A polymethacrylate (PMA) and an olefin copolymer (OCP) may essentially be used together as the viscosity modifier . The ratio of poly (meth) acrylate to olefin copolymer (OCP) in the viscosity modifier is in the range of 100:0 to 20:80, preferably in the range of 100:0 to 25:75, and more preferably in the range of 100:0 to 30:70 in terms of mass percentage. When used in this way, a suitable viscosity index can be obtained.

[0022] The lubricating oil composition also contains other additives, including phosphorus containing additives in an amount such that amount of phosphorus in the overall lubricating oil composition is at least 0.18 wt%. Suitably the amount of phosphorus in the overall lubricating oil composition is no more than 2.3wt% . Suitable phosphorus additives are those typically used in lubricating oil compositions and include, but are not limited to, organic derivatives of acids of phosphorus, for example, the organic phosphates and phosphites, including zinc dialkyldithiophosphates .

[0023] The phosphorus containing additives may be provided to the lubricating oil composition alone or as part of an additive package.

[0024] Other additives that may be used as part of said additive package or may be added to the lubricating oil composition separately include any additive common in the art for a lubricating oil composition for a transmission. Examples include extreme pressure agents, dispersants, metal cleaners, friction modifiers, antioxidants, corrosion inhibitors, rust inhibitors, anti-emulsifiers, metal deactivators, flow point depressants, seal swelling agents, defoamers, and colorants. These types of additives can be used alone or in combination.

[0025] The lubricating oil composition preferably has a kinematic viscosity at 100°C of 5.5 cSt or less, preferably 5.2 cSt or less. Also preferably, the lubricating oil composition has a kinematic viscosity at 100°C of 4.8 cSt or more.

[0026] The viscosity index of the lubricating oil composition is preferably 150 or more, more preferably 155 or more. If the viscosity index is any lower, the viscosity at low temperature increases, stirring resistance rises, and it becomes difficult to maintain an oil film and prevent increased wear at high temperatures.

[0027] Preferably, the lubricating oil composition provides a film thickness of at least 5nm at lOmm / s under 20N and 100°C when measured by EHD

[0028] The invention will now be further illustrated by reference to the following non-limiting examples.

[0029] Examples

[0030] A number of formulations were blended as set out in Table 1 using the following components:

[0031] • Base oil 1: Fischer-Tropsch derived base oil with a kinematic viscosity of 4.1cSt.

[0032] • Base oil 2 : Fischer-Tropsch derived base oil with a kinematic viscosity of 2.7cSt.

[0033] • Base oil 3: a Group I paraffinic base oil with a kinematic viscosity at 100°C of 32cSt.

[0034] • PPD: Viscoplex 1-254 pour point depressant (ex. Evonik)

[0035] • VM 1: Dispersant type PMA with nitrogen sites (ex. Evonik)

[0036] • VM2 : Olefin co-polymer viscosity modifier with a molecular weight of 4700 (ex. Lucant)

[0037] • Addpack 1: Commercially available manual transmission fluid containing ZnDTP.

[0038] • Addpack 2: Commercially available manual transmission fluid containing ZnDTP.

[0039] • Antifoam agent: silicon based antifoam

[0040] The formulated compositions were tested according to the following procedures and the results are also set out in Table 1.

[0041] • Kinematic viscosity was measured according to ASTM • Viscosity index was measured according to ASTM D2270.

[0042] • %P was measured according to ASTM D4951.

[0043] • Unit efficiency test was measured using an MIDC cycle, using a diesel vehicle with a 5-speed manual transmission, run with an AVL simulation system.

[0044] • Film thickness at 100°C (10 mm / s) was measured using an EHD2 tester by PCS instruments Co. under 20N, 100°C and O.Olm / s sliding speed condition. Table 1 In the unit efficiency test , comparative example 1 was taken as a baseline measurement and the remaining samples were te sted to see if they met this baseline (baseline ) or exceeded it (better ) . Film thicknes s i s an indicator of hardware protection and friction propertie s , with a thicker film providing better properties .

[0045] It can be seen f rom the examples above that the lubricating oil composition of the invention provide s an excellent balance of efficiency and hardware protection properties compared to the comparative examples .

Claims

SP32419C L A I M S1. A lubricating oil composition, comprising a Fischer- Tropsch-derived base oil with a kinematic viscosity at 100°C of no more than 3.0 cSt; a viscosity modifier comprising a polymethacrylate; and phosphorus containing additives such that the amount of phosphorus in the overall lubricating oil composition is at least 0.18 wt%.

2. The lubricating oil composition as claimed in Claim 1, wherein the lubricating oil composition has a viscosity index of at least 150.

3. The lubricating oil composition as claimed in Claim 1 or Claim 2, wherein the viscosity modifier also comprises one or more olefin copolymers.

4. The lubricating oil composition as claimed in any one of Claims 1 to 3, wherein the lubricating oil composition has a kinematic viscosity at 100°C of 5.5 cSt or less, preferably 5.2 cSt or less, and 4.8 cSt or more.

5. The lubricating oil composition as claimed in any one of Claims 1 to 4, wherein a further base oil is present in the lubricating oil composition, and said further base oil is a brightstock Group 1 base oil with a kinematic viscosity at 100°C in the range of from 30 to 34 cSt, and is present in an amount in the range of from 5 to 15wt% based on the overall weight of the lubricating oil composition .

6. The lubricating oil composition as claimed in any one of claims 1 to 5, wherein the phosphorus containing additives are selected from organic derivatives of acids of phosphorus including zinc dialkyldithiophosphates .

7. The lubricating oil composition as claimed in any one of Claims 1 to 6, wherein said lubricating oil compositionprovides a film thickness of at least 5nm at lOmm / s under 20N and 100°C when measured by EHD.

8. A method for lubricating a manual transmission comprising the steps of applying the lubricating oil composition as claimed in any one of Claims 1 to 7 to the manual transmission and operating the manual transmission.

9. Use of a phosphorus containing additive in a lubricating oil composition, said lubricating oil composition comprising a Fischer-Tropsch-derived base oil with a kinematic viscosity at 100°C of no more than 3.0 cSt; a viscosity modifier comprising a polymethacrylate, wherein the amount of phosphorus in the overall lubricating oil composition is at least 0.18 wt%, to provide improved efficiency and / or hardware protection properties when said lubricating oil composition is used as a manual transmission fluid.

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