WO2022053427A1

WO2022053427A1 - Lubricating oil composition for transmission

Info

Publication number: WO2022053427A1
Application number: PCT/EP2021/074477
Authority: WO
Inventors: Kengo Suzuki; Genki KAMEI
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2020-09-08
Filing date: 2021-09-06
Publication date: 2022-03-17
Also published as: CN116096842A; JP2022044925A; EP4211211A1

Abstract

It is an object of the present invention to obtain a lubricating oil composition for a transmission from which excellent performance can be obtained. The invention therefore provides a lubricating oil composition for a transmission comprises a base oil, and a poly(meth)acrylate and an olefin copolymer as a viscosity modifier. The ratio of the poly(meth)acrylate to the olefin copolymer in the viscosity modifier is 100:0 to 20:80 in terms of the mass percentage. The kinematic viscosity at 100°C of the composition is 5.5 mm 2/s or less, the viscosity index is 160 or more, the rate of decrease in the kinematic viscosity at 100°C after a KRL shear stability test (60°C, 20 hr) is 2% or less, and the amount of deposit in a panel coking test is 120 mg or less.

Description

LUBRICATING OIL COMPOSITION FOR TRANSMISSION

Field of the Invention

The present invention relates to a lubricating oil composition that can be suitably used in a transmission, and relates primarily to a lubricating oil composition used in an automobile transmission, specifically a manual transmission.

Background of the Invention

When a lubricating oil composition is adapted for an automobile transmission, it has been very difficult to improve fuel efficiency, which is required of this application, to provide load resistance, and to satisfy all desirable low temperature viscosity characteristics. In response, the present applicant discovered that a gas-to-liquid (GTL) low-viscosity base oil containing a predetermined amount of a Group 1 high-viscosity base oil and preferably containing no viscosity index improver provides the physical properties desired of a transmission oil, and provided such a lubricating oil composition, as disclosed in

JP6284865 .

The viscosity index of such a lubricating oil composition depends largely on the base oil to be blended with the composition, and the viscosity of the lubricating oil composition increases especially in an environment where the oil temperature remains relatively low, such as driving in an urban area where starting and stopping occur repeatedly, as has become more common in recent years, and further improvement in fuel efficiency is desired. When a viscosity index improver is simply added to improve fuel efficiency, oxidation stability may decline relative to heat, viscosity may decline due to shear, and problems may occur such as early deterioration in the lubricating oil and trouble with the transmission.

An object of the present invention is to provide a lubricating oil that makes further improvements compared to the prior art, that has a low viscosity, a high viscosity index , excellent viscosity characteristics at low temperatures, and high stability at high temperatures, that can be suitably used as a lubricating oil composition in a transmission over a wide temperature range, that provides load resistance, shear stability, and oxidation stability, that has excellent high temperature cleanliness, and that can improve fuel efficiency.

Summary of the Invention

The present invention provides a lubricating oil composition for a transmission, comprising: a base oil; and a poly(meth) acrylate and an olefin copolymer as a viscosity modifier, wherein the ratio of the poly (meth)acrylate to the olefin copolymer in the viscosity modifier is 100:0 to 20:80 in terms of the mass percentage, the kinematic viscosity at 100°C is 5.5 mm² /s or less, the viscosity index is 160 or more, the rate of decrease in the kinematic viscosity at 100 °C after a KRL shear stability test (60°C, 20 hr) is 2% or less, and the amount of deposit in a panel coking test is 120 mg or less.

The base oil can be a low viscosity base oil having a kinematic viscosity at 100 °C of 1 to 5 mm² /s, and a gas-to-liquid (GTL) base oil can be used as the low viscosity base oil. The poly (meth)acrylate in the viscosity modifier may be a dispersed poly (meth) acrylate and/or a non- dispersed poly (meth)acrylate .

Detailed Description of the Invention

The lubricating oil composition of the present invention has a low viscosity, a high viscosity index, excellent viscosity characteristics at low temperatures, and good shear stability. In addition, an amount of evaporation at high temperature is low, and a lubricating oil composition with good oxidation stability while maintaining frictional characteristics can be obtained. During high temperature oxidation, the fluctuation in the kinematic viscosity and the viscosity index is low, and the lubricating oil composition provides a good balance of functions such as acting as a power transmission medium, lubricating gears and other components, acting as a heat transfer medium, and keeping friction characteristics constant. As a result, it can be used as a lubricating oil composition for a transmission that provides excellent fuel efficiency and that has durability enabling it to be used in the same state at any time over a long period of time.

When used as a lubricating oil in a manual transmission, it effectively keeps deposits from being caught in the synchronizer rings of the manual transmission and prevents synchronization failure. In addition, this versatile lubricating oil composition can be used effectively as an automobile gear oil, a transmission oil such as an AT oil, MT oil or CVT oil, or as an industrial lubricating oil such as an industrial gear oil, hydraulic fluid, or compressor oil.

A mineral oil or base oil can be used as the base oil. The type of oil preferably used as the base oil is a gas-to-liquid (GTL) base oil synthesized by the Fischer-Tropsch process common 1y used as a natural gas liquid fuel technology. Compared to a mineral oil base oil refined from crude oil, a GTL base oil has extremely low sulfur content and aromatic content, and has an extremely high paraffin component ratio. As a result, it can be used as a base oil in the present invention having excellent oxidative stability, a high flash point, and very low evaporation loss.

The base oil preferably has a kinematic viscosity at 100 °C of 5 mm² /s or less and 1 mm² /s or more. When the kinematic viscosity is less than 1 mm² /s, significant evaporation occurs and a sufficient oil film may not be secured. When the kinematic viscosity exceeds 5 mm² /s, the viscosity at low temperature may increase and stirring resistance may rise.

A GTL 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 is 90°C or more and 110°C or less, more preferably 95°C or more and 107°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. Shell GTL is one example of a GTL low- viscosity base oil.

The GTL base oil may be used in an amount of 75 to 85% by mass, preferably 80 to 84% by mass. When 75% by mass or less is used, problems may occur due to properties such as low temperature fluidity, and the desired effect may not be obtained.

A viscosity modifier is used with the base oil to adjust its viscosity. Examples of viscosity modifiers include poly (meth)acrylates (PMA) and 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.

The viscosity modifier may be blended in a range of about 2% by mass to 20% by mass, and preferably 5% by mass to 15% by mass, relative to total mass of the composition. When the amount is too low, the high-temperature viscosity of the composition decreases, and there is an increased risk of mechanical component wear when used in a transmission. When the amount is too high, the viscosity of the lubricating oil composition may increase, resulting in an increase in friction loss.

The poly (meth)acrylates mentioned above include non-dispersive poly (meth)acrylates and dispersed poly (meth)acrylates, and either type can be used. In some cases, both types may be used together. A poly (meth)acrylate (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, and high-temperature cleanliness can also be realized.

The lubricating oil composition should have a kinematic viscosity at 100°C of 5.5 mm² /s or less, preferably 5.2 mm² /s or less, and more preferably 5.1 mm² /s or less. If the viscosity is any higher, the stirring resistance increases and fuel efficiency is adversely affected. The kinematic viscosity at 40 °C should be 25 mm² /s or less, preferably 22 mm² /s or less.

The viscosity index has to be 160 or more, preferably 165 or more, and more preferably 170 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.

In a KRL shear stability test conducted at 60 °C for 20 hours (hr), the rate of decrease in kinematic viscosity at 10 0°C after the test is 2.0% or less, preferably 1.5% or less, and more preferably 1.0% or less. When the shear stability is poor, the viscosity of the composition decreases significantly, which adversely affects maintenance of an oil film at high temperatures.

The amount of deposit in the panel coking test described below should be 120 mg or less. A high amount of deposit indicates that the cleanliness at high temperature has deteriorated.

When necessary, any additive common in the art may be added to the lubricating oil composition for a transmission in the present invention . 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. In this case, the use of commercially available additive packages for transmissions alone or in combination is preferred. Ex amp1e s

The lubricating oil composition for a transmission in the present invention will now be described in greater detail with reference to examples and comparative examples. However, the present invention is not limited to these examples. The following materials were prepared in order to create the examples and comparative ex amp1e s .

(1) Base Oils

(Base Oil A-1): Gas-to-liquid (GTL) base oil (properties: a kinematic viscosity at 40°C of 9.7 mm² /s and a kinematic viscosity at 100°C of 2 .7 mm² /s)

(Base Oil A-2): Gas-to-liquid (GTL) base oil (properties : a kinematic viscosity at 40°C of 5.4 mm² /s and a kinematic viscosity at 100°C of

1 .8 mm²/s)

(2) Additive s

(Additive B-l) : Viscosity modifier, non- dispersive poly (meth) acrylate (number average molecular weight: 8,400)

(Additive B-2) : Viscosity modifier, dispersive poly (meth)acrylate (number average molecular we ight : 12,000)

(Additive B-3) : Viscosity modifier, olefin copolymer (number average molecular weight:

8,700)

(Additive C) : Additive package (commercially available Zn-based GL-4 additive package for manual transmissions)

(Additive D) : Pour point depressant

(Additive E-l) : Defoamer (commercially available silicone defoamer)

(Additive E-2) : Defoamer (commercially available silicone defoamer)

Ex amp1e 1

First, 11.5% by mass of the dispersed poly (meth)acrylate in (Additive B-2), 7.8% by mass of the additive package in (Additive C) , and 0.06% by mass of the defoamer in (Additive E-2) were added to 80.64% by mass of the GTL base oil in (Base Oil A-1 ), and the components were mixed together thoroughly to obtain the lubricating oil composition for a transmission in Example 1. The percentages (mas s%) of Additive B-3 to Additive B in the examples and in comparative examples were determined and shown in Table 1 and Table 2, respectively. In Example 1, it is 0% by mass.

Ex amp1e s 2 to 6

The lubricating oil compositions for transmissions in Examples 2 to 6 were obtained in the same manner as Example 1 using the compositions shown in Table 1.

Comparative Examples 1 to 3

The lubricating oil compositions for transmissions in Comparative Examples 1 to 3 were obtained in the same manner as Example 1 using the compositions shown in Table 2. Testing

The following tests were conducted to determine the properties and performance of the examples and comparative examples.

The kinematic viscosity (mm² /s) at 40°C was measured based on JIS K2283.

The kinematic viscosity (mm² /s) at 100°C was measured based on JIS K2283.

The viscosity index was calculated based on JIS K2283 .Evaluation Criteria:

> 160: Good (o)

< 160: No good (x)

For the KRL Shear Stability Test, processing was performed at 60 °C for 20 hours based on CEC-L- 45-A-99. The kinematic viscosity at 10 0°C was measured after the processing, and the rate of decrease (%) in the viscosity after processing at a kinematic viscosity of 100°C relative to the value before the processing was determined. Evaluation Criteria:

Rate of decrease in kinematic viscosity at 100°C

≤ 2.0%: Good (o )

Rate of decrease in kinematic viscosity at 100°C

> 2.0%: No good (^χ )

For the Panel Coking Test, a rotating splasher splashes test oil at an oil temperature of 90°C on an aluminum panel heated to a temperature of 290°C for 2 hours at intervals of 15 seconds of rotation time followed by 45 seconds of stopping in accordance with US

Federal Test Method Standard 791-3462 to evaluate the suppression of test oil deposits based on the weight increase of the panel before and after the test, which is an indicator of cleanliness . The test results are indicated in terms of the weight increase (mg) in the aluminum panel, and the evaluation criteria indicating high-temperature cleanliness are as follows. Evaluation Criteria:

> 80.0 mg and ≤ 120.0 mg: Good (o)

> 120.0 mg : No good (x)

The results from each test were combined in order to comprehensively evaluate the suitability of each lubricating oil composition as a lubricating oil composition for a transmission according to the following criteria .

Especially suitable as a lubricating oil composition for a transmission: Excellent (© ) Suitable as a lubricating oil composition for a transmission: Good (o)

Unsuitable as a lubricating oil composition for a transmission:

: No good (^χ )

The results of each test are shown in Table

1 and Table 2. When the results of the KRL shear test are left blank in the tables, it means the test was omitted due to the results of other tests .

In Example 1, the GTL low-viscosity base oil in Base Oil A-1 was used as the base oil, and Additive B-2 was used as Additive B (the ratio of Additive B-3 was 0% by mass) . Appropriate values were obtained for the 40 °C kinematic viscosity and the 100°C kinematic viscosity, and the viscosity index at 165 met the appropriate criteria. In the panel coking test, the amount of deposit was low at 31.1 mg, and an overall assessment of excellent (© ) was obtained. In Example 2, the amount of Additive B-2 used was greater than the amount in Example 1. The viscosity index improved to 174, and the rate of decrease in the 100°C kinematic viscosity after the KRL shear stability test was very low 0.9%. However, the amount of deposit in the panel coking test was a slightly higher 109.2 mg, so the overall assessment was somewhat lower than that of Example 1 at good (o).

In Example 3, the amount of Additive B used was nearly the same as Example 1, but Additives B-2 and B-3 were used in combination, and the ratio of B-3 was 21% by mass. Because the viscosity index and KRL shear stability were good, and the amount of deposit in the panel coking test was low at 72.2 mg, an overall assessment of excellent (© ) was obtained, which is the same as that of Example 1. In Example 4, Additives B-2 and B-3 were used in combination as Additive B, and the ratio of B-3 was 51% by mass. Because the viscosity index and KRL shear stability were good, and the amount of deposit in the panel coking test was somewhat higher at 103.2 mg, the overall assessment was good (o).

In Example 5, Additive B-l was used instead of Additive B-2 as in Example 4, and Additive B- 3 was used in combination to reach the same percentage of 51% by mass. The viscosity index and results of the KRL shear stability test were about the same, so the overall assessment was good (o). As indicated here, nearly the same result can be obtained by replacing the dispersed poly (meth) acrylate in Additive B-2 used in combination with Additive B-3 with the non-dispersed poly (meth)acrylate in Additive B-

1 . In Examp 1e 6, the amount of Additive B-2 was reduced and the amount of Additive B-3 was increased to reach a percentage of 65% by mass for Additive B-3. The viscosity index and results of the KRL shear stability test were about the same as Example 4, so the overall assessment was good (o).

In Comparative Example 1, Additive B-2 and Additive B-3 were used in combination but the percentage of Additive B-3 was higher at 81% by mass. Values similar to those in Example 6 were obtained for the 40° C kinematic viscosity, the 10 0°C kinematic viscosity, and the viscosity index. However, the result from the panel coking test was high at 141.1 mg, so the overall assessment was no good (^χ).

In Comparative Example 2, the ratio of Additive B-3 was 100% by mass for Additive B, and the defoamer was changed from Additive E-2 to Additive E-l. The viscosity index was nearly similar to those of the examples of the present invention, and the KRL shear stability was better than those of the examples of the present invention . However, the result from the panel coking test was as high as Comparative Example 1 at 143 mg, so the overall assessment was no good (x). In Comparative Example 3, Additive A-2 was used as the base oil, the amount of Additive B-3 was increased compared to Comparative Example 2 to a percentage of 100% by mass. Small amounts of the pour point lowering agent in Additive D and the defoaming agent in Additive E-l were also used. Although the viscosity index improved significantly at 207, the result in the panel coking test rose to 171.8 mg, which indicates deterioration, so the overall assessment was no good (x).

Claims

C L A I M S

1. A lubricating oil composition for a transmission, comprising: a base oil; and a poly (meth)acrylate and an olefin copolymer as a viscosity modifier, wherein the ratio of the poly (meth)acrylate to the olefin copolymer in the viscosity modifier is 100:0 to 20:80 in terms of the mass percentage, the kinematic viscosity at 100 °C is 5.5 mm² /s or less, the viscosity index is 160 or more, the rate of decrease in the kinematic viscosity at 100°C after a KRL shear stability test (60°C, 20 hr) is 2% or less, and the amount of deposit in a panel coking test is 120 mg or less.

2. A lubricating oil composition for a transmission according to claim 1, wherein the base oil is a low viscosity base oil having a kinematic viscosity at 10 0°C of 1 to 5 mm² /s .

3. A lubricating oil composition for a transmission according to claim 2, wherein the base oil is a gas-to-liquid (GTL) base oil.

4. A lubricating oil composition for a transmission according to any one of claims 1 to 3, wherein the poly (meth)acrylate in the viscosity modifier is a dispersed poly (meth)acrylate and/or a non-dispersed poly (meth)acrylate .