CN108431186A - Lubricating oil composition for internal combustion engine - Google Patents

Abstract

A kind of lubricant composition for internal combustion engine is provided, equipped with DLC internal combustion engine and be not equipped in the internal combustion engine of DLC can be achieved low friction.A kind of [solution] lubricant composition for internal combustion engine, it is characterized in that, the lubricant composition for internal combustion engine is the composition by the way that molybdenum dithiocarbamate (MoDTC) and polyalkylene glycol (PAG) to be obtained by mixing in base oil, the weight average molecular weight of the polyalkylene glycol is 2,750 4500, and the content of the polyalkylene glycol not less than 0.05 mass % and is less than 10 mass % relative to the gross mass of the composition.

Description

Lubricating oil composition for internal combustion engine

technical field

The present invention relates to a lubricating oil composition for an internal combustion engine containing specified components.

Background technique

Numerous lubricating oil compositions have been proposed in the past. For example, WO2005014763 proposes a lubricating oil comprising a lubricant base oil and a sulfur-containing molybdenum complex. Meanwhile, "Wear Analysis of DLC Coating in Oil Containing Mo-DTC (WearAnalysis of DLC Coating in Oil Containing Mo-DTC)", Takatoshi Shinyoshi, YoshioFuwa, Yoshinori Ozaki, JSAE 20077103 SAE 2007-01-1969 proposes that The case of MoDTC: When MoDTC is combined with hydrogen-containing DLC film (a-C:H), it will promote the wear of the film.

However, in the case of lubricating oil compositions according to WO2005014763, real engines were used for the evaluation. Friction reduction performance was evaluated on a system where DLC contact surfaces and non-DLC contact surfaces without a DLC film (such as ordinary steel for engines) were lubricated at the same time, but it is not clear if the steel lubrication effect is greater than the DLC contact surface lubrication effect Suitable for DLC film. Furthermore, no method has been given to solve the problems in "Wear Analysis of DLC Coatings in Mo-DTC-Containing Oil", Takatoshi Shinyoshi, Yoshio Fuwa, Yoshinori Ozaki, JSAE 20077103 SAE 2007-01-1969.

In view of these circumstances, an object of the present invention is to provide a lubricating oil composition for an internal combustion engine capable of achieving low friction in both a DLC-equipped internal combustion engine and a DLC-non-equipped internal combustion engine.

Contents of the invention

The present inventors conducted intensive studies to achieve this object, and as a result found that by mixing polyalkylene glycol (PAG) and a specific organic molybdenum compound as additional components in a lubricating oil composition for internal combustion engines, the molecular weight of PAG can be specified. And by specifying the mixing amount of PAG, regardless of the presence or absence of DLC, low friction can be realized in the internal combustion engine, thereby completing the present invention.

That is, the present invention is a lubricating oil composition for an internal combustion engine, characterized in that the lubricating oil composition for an internal combustion engine is obtained by mixing molybdenum dithiocarbamate (MoDTC) and polyalkylene glycol (PAG) in a base oil In the composition obtained by mixing, the polyalkylene glycol has a weight average molecular weight of 2750-4500, and the content of the polyalkylene glycol is not less than 0.005% by mass and less than 10% by mass relative to the total mass of the composition.

Furthermore, the lubricating oil composition for an internal combustion engine of the present invention may be a lubricating oil composition for an internal combustion engine that can be used for an internal combustion engine equipped with DLC and an internal combustion engine not equipped with DLC (conventional internal combustion engine).

Detailed ways

According to the present invention, there can be provided a lubricating oil composition for an internal combustion engine, which can be used for an internal combustion engine equipped with DLC and an internal combustion engine not equipped with DLC.

The configuration, properties and intended use of the lubricating oil composition for an internal combustion engine according to the present aspect will now be described.

In the lubricating oil composition for an internal combustion engine according to the present aspect, molybdenum dithiocarbamate (MoDTC) and polyalkylene glycol (PAG) are mixed into the base oil, and other additives may also be mixed into the base oil if necessary. in oil. Now, the lubricating oil composition for an internal combustion engine according to the present invention will be described in detail, but the present invention is by no means limited to these compositions.

The base oil used in this aspect is not particularly limited, and mineral oils, synthetic oils, vegetable oils, and animal oils used in conventional lubricating oil and grease compositions, and mixtures thereof can be suitably used. Specific examples thereof include base oils of Groups 1 to 5 in the American Petroleum Institute (API) base oil category. Here, an API base oil category is a broad classification of base oil materials defined by the American Petroleum Institute in order to develop guidelines for lubricating oil base stocks. In order to achieve excellent oxidation stability, base oils belonging to Group 3 are preferred.

The kinematic viscosity of the base oil is not particularly limited, but the kinematic viscosity at 100°C is preferably 2-32 mm ² /s, and more preferably 3-8 mm ² /s from practical viewpoints such as preventing wear and achieving fuel efficiency.

The viscosity index of the base oil is not particularly limited, but from practical viewpoints such as preventing wear and achieving fuel efficiency, the viscosity index is preferably 10-200, and more preferably 100-200.

Molybdenum dithiocarbamate (MoDTC) used in the present aspect may be, for example, molybdenum dialkyldithiocarbamate represented by the following formula (1).

In Formula 1, R ¹ to R ⁴ each represent an alkyl group, and X ¹ to X ⁴ each represent an oxygen atom or a sulfur atom.

The alkyl groups R ¹ , R ² , R ³ and R ⁴ contained in the molybdenum dialkyldithiocarbamate represented by formula (1) are each independently a lipophilic group having 2 to 30 carbon atoms, and Preferably at least one of the four lipophilic groups is a second lipophilic group.

Here, molybdenum dithiocarbamate (MoDTC) used in this aspect is preferably molybdenum dithiocarbamate represented by the following formula (2).

In formula (2), R ¹ to R ⁴ each represent an alkyl group.

The content of molybdenum dithiocarbamate used in this aspect is not particularly limited, but is preferably 50 to 1500 ppm in terms of molybdenum content relative to the total mass of the lubricating oil composition.

Polyalkylene glycols (PAGs) are compounds in which multiple alkylene glycols are polymerized and are formed by the general formula HO-(C _n H _m O) _s -H or the general formula HO-(C _n H _m O) _s -OH represents, but not particularly limited. In order to use a material having low oil solubility, it is preferable to use one or more compounds selected from polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. From the viewpoint of compatibility with the base oil, polypropylene glycol and polytetramethylene glycol are more preferable.

In addition, the polyalkylene glycol according to the present aspect has a weight average molecular weight of 2750-4500, and preferably 3000-4000. By setting the weight-average molecular weight of the polyalkylene glycol within this range, the compatibility with the base oil can be improved, and the friction coefficient can be reduced.

Furthermore, the content of the polyalkylene glycol according to the present aspect is not less than 0.05% by mass and less than 10% by mass, preferably 0.5-8.0% by mass, and more preferably 1.0-5.0% by mass relative to the total mass of the lubricating oil composition %. By setting the content of the polyalkylene glycol within this range, the compatibility with the base oil can be improved, and the lubricating performance of the polyalkylene glycol can be exhibited.

One or more of various additives, such as ashless dispersants, antiwear agents, extreme pressure additives, metal cleaners, antioxidants, viscosity index improvers, friction modifiers, rust inhibitors, nonionic surfactants, anti-corrosion Emulsifiers, metal deactivators and defoamers may be mixed as optional components in the lubricating oil composition according to the present aspect.

The HTHS viscosity of the lubricating oil composition of the present invention at 150°C and 10 ⁶ s ^-1 is preferably 3.5 mPa·s or less, more preferably 3.0 mPa·s or less, further preferably 2.8 mPa·s or more low, and particularly preferably 2.7 mPa·s or lower. In addition, this HTHS viscosity is preferably 1.4 mPa·s or higher, more preferably 2.0 mPa·s or higher, further preferably 2.3 mPa·s or higher, particularly preferably 2.5 mPa·s or higher, and most preferably It is preferably 2.6 mPa·s or higher. In addition, this high temperature high shear viscosity is a value measured using the test method disclosed in ASTM D5481.

The range of use of the lubricating oil composition according to the present invention is not particularly limited as long as the composition is used for an internal combustion engine.

Specifically, according to the lubricating oil composition of the present aspect, by setting the weight-average molecular weight and the content of the polyalkylene glycol in the composition within the specified range, regardless of the presence or absence of DLC, the non-equipment can be reduced. Friction on surfaces with DLC and significantly reduced friction on surfaces equipped with DLC, and thus low friction can be achieved, said composition is obtained by mixing molybdenum dithiocarbamate and polyalkylene glycol in base oil and obtained. As a result, the lubricating oil composition according to the present invention can be used in internal combustion engines equipped with DLC and internal combustion engines not equipped with DLC (i.e., can be used as a lubricating oil composition in internal combustion engines equipped with DLC and internal combustion engines not equipped with DLC ).

Furthermore, a DLC-equipped internal combustion engine is an internal combustion engine in which all or at least some surfaces as frictional surfaces are coated with DLC. In addition, diamond-like carbon (DLC) generally refers to an amorphous substance mainly composed of elemental carbon, and in which bonds between carbon atoms include diamond structures (SP3 bonds) and graphite bonds (SP2 bonds). kind. Specifically, these include α-C (amorphous carbon) containing only elemental carbon, hydrogen-containing α-C:H (hydrogenated amorphous carbon), and α-C:H containing some metallic elements such as titanium (Ti) or molybdenum (Mo). MeC. Also, as the hydrogen content in the DLC increases, the coefficient of friction tends to increase, but any hydrogen content can be selected, such as 10 atomic % or less, 5 atomic % or less, or 0.5 atomic % or less.

example

The present invention will now be explained in more detail by using working examples and comparative examples, but the present invention is not limited to these examples.

Preparation of lubricating oil composition

The starting materials used in the working examples are as follows.

base oil

The gas-to-liquid (GTL) base oils synthesized by the Fischer-Tropsch process belonging to Group 3 have a kinematic viscosity of 7.58 mm ² /s at 100° C. and a viscosity index of 141.

additive

PAG

PEG#400 (manufactured by NOF Corporation, PEG, weight average molecular weight 100)

D-250 (manufactured by NOF Corporation, PPG, OH groups at both ends, weight average molecular weight 250)

D-1000 (manufactured by NOF Corporation, PPG, OH groups at both ends, weight average molecular weight 1000)

D-2000 (manufactured by NOF Corporation, PPG, OH groups at both ends, weight average molecular weight 2000)

D-4000 (manufactured by NOF Corporation, PPG, OH groups at both ends, weight average molecular weight 4000)

MB7 (manufactured by NOF Corporation, PPG, one terminal OH group, weight average molecular weight 700)

MB700 (manufactured by NOF Corporation, PPG, one terminal OH group, weight average molecular weight 3000)

50MB-2 (manufactured by NOF Corporation, PPG·PEG, weight average molecular weight 200)

MoDTC

Sakuralube-165 (manufactured by ADEKA, molybdenum content 4.5% by mass, sulfur content 5.0% by mass)

1. Viscosity index improver

Polymethacrylate based viscosity index improvers

Packaging Additives

GF-5DI (composition details: metal cleaner, ashless dispersant, zinc dithiophosphate, rust inhibitor, preservative, antioxidant, ashless friction modifier, etc.).

Lubricating oil compositions were obtained by mixing and formulating the above raw materials in the ratios (mass percentages) shown in the table.

test

friction test

The lubricating oil compositions of Working Examples and Comparative Examples were applied to sliding surfaces composed of DLC-coated sliding members coated with diamond-like carbon having a hydrogen content of 0.5 atomic % and made of SUJ2 Sliding members composed of materials were obtained and subjected to friction tests. The coefficient of friction was measured using a cylinder-on-disk SRV friction tester (ASTM D6425). The conditions are as follows: temperature: 80° C., frequency: 50 Hz, load: 100 N. Similar friction tests were conducted by applying the lubricating oil compositions of the working examples and comparative examples to sliding surfaces composed of DLC-uncoated SUJ2 sliding members and sliding members composed of SUJ2 materials. The results are shown in the table.

As shown in the table, the present invention achieves a friction reduction effect on both metal contact surfaces if the DLC film is present. Since the low coefficient of friction reduces the heat generated by friction, it can suppress the softening of the surface caused by carbonization (the amount of SP2 bonded amount increases) caused by friction in the case of DLC surface and improve Abrasion resistance of DLC, and the reduction in abrasion resistance leads to a reduction in stress within the DLC film and between the DLC film and the underlying member, and reduces the problem of detachment of the DLC-coated coating film.

In this way, the present invention contributes to fuel efficiency and maintenance of good condition in DLC lubrication systems.

According to the present invention, also in the case of metal surfaces, organomolybdenum compounds exhibit functionality, friction reduction occurs and fuel efficiency is achieved even in non-DLC lubrication systems.

Table 1 - Comparative Examples 1-8 and Working Examples 1-2

Table 2 - Comparative Examples 9-16 and Working Example 3

Claims (3)

1. A lubricating oil composition for an internal combustion engine, characterized in that, the lubricating oil composition for an internal combustion engine is by mixing molybdenum dithiocarbamate (MoDTC) and polyalkylene glycol (PAG) in base oil In the obtained composition, the weight average molecular weight of the polyalkylene glycol is 2750-4500, and the content of the polyalkylene glycol is not less than 0.05% by mass and less than 0.05% by mass relative to the total mass of the composition. 10% by mass. 2. The lubricating oil composition for an internal combustion engine according to claim 1, which can be used for a DLC-equipped internal combustion engine and a DLC-non-equipped internal combustion engine. 3. The lubricating oil composition for an internal combustion engine according to claim 1 or claim 2, wherein the polyalkylene glycol is polypropylene glycol (PPG).