LOW-VISCOSITY LUBRICATING OIL COMPOSITION WITH IMPROVED DURABILITY AND NVH PERFORMANCE

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims, under 35 U.S.C. § 119(a), the benefit of and priority to Korean Patent Application No. 10-2024-0121870, filed on Sep. 6, 2024, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates to a low-viscosity lubricating oil composition with improved durability and NVH (noise, vibration, and harshness) performance, in which durability and NVH performance may be improved by appropriately combining mineral oil and/or synthetic oil and a viscosity index improver.

(b) Description of the Related Art

As climate change-related extreme weather events become more frequent around the world, individual countries and national coalitions are making efforts to curb climate change by declaring plans to reduce carbon emissions and achieve carbon neutrality. As part of this plan, the proportion of electric vehicles among new vehicle sales is being raised to reduce carbon emissions in the transportation sector, and electric vehicle sales have been increasing rapidly recently.

The design of the driving unit of electric vehicles is gradually changing from a conventional motor and reducer in separate form to an integrated motor-reducer form, and accordingly, the performance level required for lubricants that have to be commonly used in parts under the integrated system is also increasing compared to the conventional separate form. Since the lubricant for use in a conventional separate reducer is applied only to the reduction gear section, extreme pressure performance and wear resistance for effectively protecting the gear section are regarded as important, but in the integrated form, additional performance such as motor cooling performance, material compatibility with electrical parts, drag loss reduction, and the like is also required along with such performance.

Lowering the viscosity of a lubricant applied to an integrated motor-reducer part is a method capable of improving energy efficiency because internal resistance of a motor is decreased, thus reducing energy consumption due to friction, and heat generated during motor operation is more effectively dissipated, thus improving driving efficiency. However, there are limitations in that, when the viscosity is adjusted downward, the lubricating oil film thickness in proportion to the viscosity becomes lower, which deteriorates durability and NVH performance.

Moreover, since additives that are added to liquid lubricants together with lube base oil to improve various types of performance such as extreme pressure performance and durability, oil oxidation prevention, impurity agglomeration prevention, deposit formation prevention, friction reduction, and the like generally have high viscosity, it is difficult to improve durability and NVH performance by addition of large amounts thereof to low-viscosity oil. Therefore, it is necessary to develop a lubricating oil composition capable of overcoming these limitations and also achieving an improvement in energy efficiency at low viscosity.

The statements in this Background section merely provide background information related to the present disclosure and may not constitute prior art.

SUMMARY

The present disclosure has been made in an effort to solve the problems encountered in the related art. An object of the present disclosure is to provide a lubricating oil composition which improves extreme pressure performance and wear resistance required for conventional lubricating oil compositions, cooling performance, compatibility with electrical parts, and the like in a balanced manner.

Another object of the present disclosure is to provide a lubricating oil composition, which is applied to an integrated motor-reducer part, thereby improving energy efficiency compared to conventional techniques, and preventing durability and NVH performance from deteriorating.

The objects of the present disclosure are not limited to the foregoing. The objects of the present disclosure should be able to be more clearly understood through the following description and to be realized by the means described in the claims and combinations thereof.

An aspect of the present disclosure provides a lubricating oil composition, including lube base oil including mineral oil, a viscosity index improver, and an additive. Also, the lube base oil may include mineral oil and synthetic oil.

In one embodiment, the lubricating oil composition may include 50 to 80 wt % of the mineral oil, 1 to 10 wt % of the viscosity index improver, and 10 to 20 wt % of the additive, based on the total weight thereof.

Also, when the lube base oil of the lubricating oil composition includes mineral oil and synthetic oil, the lubricating oil composition may include 50 to 80 wt % of the mineral oil, 10 to 40 wt % of the synthetic oil, 1 to 10 wt % of the viscosity index improver, and 8 to 20 wt % of the additive, based on the total weight thereof.

In one embodiment, the lubricating oil composition may have kinematic viscosity at 100° C. in a range of 2.8 to 4.0 cSt.

In one embodiment, the mineral oil may include highly-refined mineral oil having an aromatic component content of 0.1 wt % or less.

In one embodiment, the mineral oil may have kinematic viscosity at 100° C. in a range of 2.0 to 4.0 cSt.

In one embodiment, the mineral oil may have a viscosity index (VI) equal to or greater than 100.

In one embodiment, the synthetic oil may include polyalphaolefin (PAO)-based synthetic oil.

In one embodiment, the synthetic oil may have kinematic viscosity at 100° C. in a range of 2.0 to 3.0 cSt.

In one embodiment, the viscosity index improver may include poly(alkyl methacrylate).

In one embodiment, the weight average molecular weight (Mw) of the viscosity index improver may be in a range of 10,000 to 50,000.

In one embodiment, the additive may include at least one of a detergent, an antioxidant, an antiwear agent, a dispersant, a friction modifier, a corrosion inhibitor, or a combination thereof.

As such, the detergent may include at least one of a sulfonate detergent, a phenate detergent, a salicylate detergent, or a combination thereof.

Also, the antioxidant may include at least one of hindered phenols, aromatic amines, or a combination thereof.

In one embodiment, the lubricating oil composition may further include at least one of a pour point depressant, an antifoaming agent, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing results of analyzing lubricating oil compositions according to Example 3 and Comparative Examples 6 to 8 using a mini-traction machine (MTM).

DETAILED DESCRIPTION

The above and other objects, features and advantages of the present disclosure should be more clearly understood from the following embodiments taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed herein, and may be modified into different forms. These embodiments are provided to thoroughly explain the disclosure and to sufficiently transfer the spirit of the present disclosure to those having ordinary skill in the art.

Throughout the drawings, the same reference numerals refer to the same or like elements. For the sake of clarity of the present disclosure, the dimensions of structures are depicted as being larger than the actual sizes thereof. It should be understood that, although terms such as “first”, “second”, and the like may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a “first” element discussed below could be termed a “second” element without departing from the scope of the present disclosure. Similarly, the “second” element could also be termed a “first” element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be further understood that the terms “comprise”, “include”, “have”, and the like, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it should be understood that when an element such as a layer, film, area, or sheet is referred to as being “on” another element, it may be directly on the other element, or intervening elements may be present therebetween. Similarly, when an element such as a layer, film, area, or sheet is referred to as being “under” another element, it may be directly under the other element, or intervening elements may be present therebetween.

Unless otherwise specified, all numbers, values, and/or representations that express the amounts of components, reaction conditions, polymer compositions, and mixtures used herein are to be taken as approximations including various uncertainties affecting measurement that inherently occur in obtaining these values, among others, and thus should be understood to be modified by the term “about” in all cases. Furthermore, when a numerical range is disclosed in this specification, the range is continuous, and includes all values from the minimum value of said range to the maximum value thereof, unless otherwise indicated. Moreover, when such a range pertains to integer values, all integers including the minimum value to the maximum value are included, unless otherwise indicated.

In the present specification, when a range is described for a variable, it should be understood that the variable includes all values including the end points described within the stated range. For example, the range of “5 to 10” should be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values of 5, 6, 7, 8, 9 and 10, and should also be understood to include any value between valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of “10% to 30%” should be understood to include subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, and the like, as well as all integers including values of 10%, 11%, 12%, 13% and the like up to 30%, and should also be understood to include any value between valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

In the present disclosure, each of phrases such as “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, “at least one of A, B or C” and “at least one of A, B, or C, or a combination thereof” may include any one or all possible combinations of the items listed together in the corresponding one of the phrases.

A lubricating oil composition according to an aspect of the present disclosure may include lube base oil including mineral oil and/or synthetic oil, a viscosity index improver, and an additive. More specifically, the lubricating oil composition may include 50 to 80 wt % of the mineral oil, 1 to 10 wt % of the viscosity index improver, and 10 to 20 wt % of the additive, based on the total weight thereof. Also, when the lube base oil of the lubricating oil composition includes mineral oil and synthetic oil, the lubricating oil composition may include 50 to 80 wt % of the mineral oil, 10 to 40 wt % of the synthetic oil, 1 to 10 wt % of the viscosity index improver, and 8 to 20 wt % of the additive, based on the total weight thereof.

The lubricating oil composition according to an embodiment of the present disclosure is capable of improving NVH performance of a vehicle when applied to a vehicle part, particularly an integrated motor-reducer part installed in an electric vehicle, by combining the components in appropriate amounts as described above.

Also, kinematic viscosity of the lubricating oil composition for electric vehicles may be related to energy efficiency of electric vehicles. Kinematic viscosity is a measure of a fluid's resistance to flow over time under temperature conditions in which a fluid flows, particularly at a temperature equal to or higher than room temperature. Accordingly, the lower the kinematic viscosity, the less the friction in the lubricating oil composition, which may improve energy efficiency. For reference, when the lubricating oil composition according to an embodiment of the present disclosure is applied to existing internal combustion engine parts, the “energy efficiency” described above and “energy efficiency” to be used hereinafter may be understood as “fuel efficiency”.

In one embodiment, the lubricating oil composition may have kinematic viscosity at 100° C. of 2.8 to 4.0 cSt. The lubricating oil composition according to an embodiment of the present disclosure has kinematic viscosity at 100° C. of 2.8 to 4.0 cSt, and thus, when the lubricating oil composition is applied to an integrated motor-reducer part, and the like, internal resistance thereof may decrease, thereby reducing energy consumption and heat generation due to friction.

If the kinematic viscosity at 100° C. is less than 2.8 cSt, the oil film may become too thin when the lubricating oil composition is applied to an integrated motor-reducer part, and the like due to excessively low viscosity, deteriorating extreme pressure performance. On the other hand, if the kinematic viscosity at 100° C. exceeds 4.0 cSt, the effect of improving energy efficiency may be insignificant compared to conventional lubricating oil compositions applied to electric vehicles.

Below, individual components included in the lubricating oil composition are described in more detail.

Mineral Oil

Mineral oil is a general term for oils obtained from mineral raw materials such as petroleum, coal, tar, shale oil, and the like, and is commonly used as lubricating oil to reduce friction between machine parts. The mineral oil according to an embodiment of the present disclosure is not particularly limited so long as it is typically used in a lubricating oil composition. However, including highly-refined mineral oil is advantageous. Highly-refined mineral oil may be defined as mineral oil refined to have an aromatic component content of 0.1 wt % or less.

The aromatic component contained in mineral oil is a material that is easily oxidized at high temperatures. Therefore, when highly-refined mineral oil with low aromatic component content is used as in the present disclosure, superior oxidation stability of the lubricating oil composition may be exhibited. Also, since impurities are generally removed during the process of manufacturing highly-refined mineral oil, performance of the mineral oil may be improved and lifespan thereof may be increased.

Also, mineral oil having a viscosity index (VI) of 100 or more may be used. The lubricating oil composition according to an embodiment of the present disclosure may have superior thermal stability because it includes mineral oil having a viscosity index of 100 or more.

The term “viscosity index” represents the relationship between the viscosity of oil (e.g. mineral oil, synthetic oil, and the like) and the temperature. A higher numerical value thereof indicates a smaller change in viscosity due to temperature fluctuations. In general, the higher the viscosity index, the greater the stability of oil to heat, which may increase the lifespan and usability of oil. The viscosity index may be obtained by an equation known in the art or a program reflecting the equation.

In one embodiment, the lubricating oil composition may include mineral oil having kinematic viscosity at 100° C. of 2.0 to 4.0 cSt. The lubricating oil composition according to an embodiment of the present disclosure may satisfy kinematic viscosity at 100° C. of 2.8 to 4.0 cSt when including 50 to 80 wt % of mineral oil having kinematic viscosity at 100° C. of 2.0 to 4.0 cSt.

Synthetic Oil

Synthetic oil is oil composed of artificially modified or synthesized compounds, and may be manufactured from crude oil as well as chemically modified petroleum components or other raw materials.

The synthetic oil according to an embodiment of the present disclosure may be used without particular limitation so long as it is typically used in a lubricating oil composition. For example, synthetic hydrocarbon oil, ester oil, phenyl ether, polyethylene glycol, and the like may be used. For instance, polyalphaolefin (PAO)-based synthetic oil is used.

The polyalphaolefin-based synthetic oil, which is a representative synthetic oil, is manufactured by oligomerization of linear alpha olefin produced during ethylene polymerization, and is widely used in automotive and industrial lubricating oils.

The polyalphaolefin-based synthetic oil according to an embodiment of the present disclosure is composed exclusively of isoparaffin, and thus has a higher viscosity index than the mineral oil, superior low-temperature fluidity, a narrow molecular weight distribution, low evaporation loss, and superior thermal oxidation stability and frictional properties.

The lubricating oil composition according to an embodiment of the present disclosure may exhibit superior frictional properties due to use of lube base oil including highly-refined mineral oil and polyalphaolefin-based synthetic oil, thereby realizing an effect of improving energy efficiency and NVH performance of a vehicle to which the lubricating oil composition is applied.

In one embodiment, the lubricating oil composition may include synthetic oil having kinematic viscosity at 100° C. of 2.0 to 3.0 cSt. The lubricating oil composition according to an embodiment of the present disclosure may satisfy kinematic viscosity at 100° C. of 2.8 to 4.0 cSt when including 10 to 40 wt % of synthetic oil having kinematic viscosity at 100° C. of 2.0 to 3.0 cSt.

Viscosity Index Improver

A viscosity index improver is added to improve the viscosity index of a lubricating oil composition, and serves to increase the viscosity index of the lubricating oil composition, lowering the viscosity at low temperatures and improving energy efficiency.

When a viscosity index improver is added to a lubricating oil composition, the extent to which viscosity index thereof is improved may be proportional to the polarity of the polymer used as the viscosity index improver. However, since the solubility of the polymer in the lubricating oil composition decreases with an increase in the polarity of the polymer, it is important to optimize the viscosity index and solubility by increasing the polarity of the polymer within a range in which the viscosity index improver is dissolved.

Also, the viscosity index increases in proportion to the molecular weight of the viscosity index improver, but the extreme pressure performance tends to be inversely proportional to the molecular weight thereof, so that the viscosity index and extreme pressure performance of the lubricating oil composition may be improved by optimizing the molecular weight.

In one embodiment, the viscosity index improver according to an embodiment of the present disclosure includes an olefin copolymer, a hydrogenated styrene-diene compound, and poly(alkyl methacrylate). For example, the viscosity index improver includes poly(alkyl methacrylate).

The viscosity index improver including poly(alkyl methacrylate) may exhibit superior low-temperature performance and shear stability. Specifically, by virtue of high viscosity index, it is possible to form a certain oil film to prevent wear of integrated motor-reducer parts at high temperatures, and improve energy efficiency of a vehicle by lowering the viscosity of the lubricating oil composition at low temperatures. Moreover, by virtue of superior shear stability, it is possible to prevent the viscosity index improver from breaking during use under harsh conditions for a long period of time, improving durability and lifespan.

Also, the viscosity index improver according to an embodiment of the present disclosure serves to improve extreme pressure performance by optimizing the polarity and molecular weight of the polymer, and the weight average molecular weight (Mw) of the viscosity index improver may fall in the range of 10,000 to 50,000 g/mol. If the weight average molecular weight of the viscosity index improver exceeds 50,000 g/mol, durability of the lubricating oil composition may also decrease due to a decrease in extreme pressure performance.

The lubricating oil composition according to an embodiment of the present disclosure includes 1 to 10 wt % of the viscosity index improver including poly(alkyl methacrylate). If the amount of the viscosity index improver is less than 1 wt %, the viscosity index may be low, reducing friction performance, wear performance, and furthermore, energy efficiency. On the other hand, if the amount of the viscosity index improver exceeds 10 wt %, the viscosity may become excessively high due to the thickening effect, which may reduce energy efficiency and may cause breakage due to shear of the viscosity index improver.

Additive

The lubricating oil composition according to an embodiment of the present disclosure includes an additive to improve performance thereof. The additive may be applied without particular limitation so long as it is typically used in the art to improve performance of the lubricating oil composition, and may include, for example, at least one of a detergent, an antioxidant, an antiwear agent, a dispersant, a friction modifier, a corrosion inhibitor, or a combination thereof (e.g., any one selected from the group consisting of a detergent, an antioxidant, an antiwear agent, a dispersant, a friction modifier, a corrosion inhibitor, and combinations thereof). For example, the additive is used in the form of a package in which two or more selected from among the detergent, antioxidant, antiwear agent, dispersant, friction modifier, and corrosion inhibitor are mixed and combined at a predetermined ratio.

Also, the additive may be added in an amount by wt % corresponding to the remainder after addition of the lube base oil and the viscosity index improver based on the total weight of the lubricating oil composition. For example, the lubricating oil composition may include 8 wt % to 40 wt %, 10 wt % to 40 wt %, 8 wt % to 20 wt %, or 10 wt % to 20 wt % of the additive.

The detergent serves to inhibit the growth of deposits when such deposits are formed due to oxidation of the lubricating oil composition, and may include, for example, at least one of a sulfonate detergent, a phenate detergent, a salicylate detergent, or a combination thereof (e.g., any one selected from the group consisting of a sulfonate detergent, a phenate detergent, a salicylate detergent, and combinations thereof).

Specifically, the sulfonate detergent may include overbased calcium sulfonate, magnesium sulfonate, barium sulfonate, and the like, and the phenate detergent may include calcium phenate, sodium phenate, barium phenate, and the like. Also, the salicylate detergent may include calcium salicylate, and the like.

The antioxidant serves to prevent the lubricating oil composition from reacting with oxygen in the air to produce corrosive acids or sludge, and antioxidants are broadly classified into chain reaction stoppers, peroxide decomposers, and inactivators. Examples of the chain reaction stopper may include hindered phenols such as 2,6-di-tert-butyl-para-cresol, or aromatic amines such as dioctyldiphenylamine and phenylalphanaphthalene. For example, 2,6-di-tert-butyl-para-cresol is used.

The antiwear agent is an additive used to prevent wear by forming a solid lubricating film by adsorption of an organic polar compound onto a metal surface and reaction with the metal surface. The antiwear agent includes, for example, an organophosphorus type and an active sulfur type. For example, an organophosphorus-type antiwear agent is used. Active sulfur-type antiwear agents, when dissolved in the lubricating oil composition, pose a risk of corrosion of non-iron metals such as copper, brass, and bronze due to the dissolved sulfur.

The dispersant may serve to disperse sludge that may occur in the lubricating oil composition, and evenly disperse soot or other small insoluble particles in the lubricating oil composition, suppressing formation of sludge deposits and neutralizing acids. When the dispersant of the present disclosure is used in a mixture of a low-molecular-weight dispersant and a high-molecular-weight dispersant, dispersion of byproducts may be improved.

The friction modifier is an additive that improves lubrication performance by imparting a low coefficient of friction when sliding between metals. The additive according to an embodiment of the present disclosure may include an alcohol-based friction modifier to improve friction reduction performance at low temperatures.

The corrosion inhibitor is an additive that suppresses occurrence of rust caused by oxygen in the air and water, and may be designed such that corrosion prevention performance is optimized when used in a mixture of inactive sulfur-based and non-sulfur-based corrosion inhibitors.

In addition, the lubricating oil composition according to an embodiment of the present disclosure may further include at least one of a pour point depressant, an antifoaming agent, or a combination thereof (e.g., any one selected from the group consisting of a pour point depressant, an antifoaming agent, and combinations thereof).

The pour point depressant is an additive that lowers the pour point, and when wax is formed in lubricating oil at low temperatures, the pour point depressant is adsorbed to the wax and prevents the wax from clumping together, thereby lowering the pour point of the lubricating oil composition. Any pour point depressant typically used in the art may be used.

Also, the antifoaming agent may serve to suppress foaming by changing surface tension of the lubricating oil composition. Any antifoaming agent typically used in the art may be used.

Therefore, the lubricating oil composition according to an embodiment of the present disclosure is low-viscosity lubricating oil having kinematic viscosity at 100° C. of 2.8 to 4.0 cSt but is capable of preventing durability and NVH performance from deteriorating in low-viscosity lubricating oil by appropriately combining highly-refined mineral oil and polyalphaolefin-based synthetic oil and adding poly(alkyl methacrylate) having an appropriate molecular weight as a viscosity index improver.

Also, in the lubricating oil composition according to an embodiment of the present disclosure, not only extreme pressure performance and wear resistance required for conventional lubricating oil compositions, but also cooling performance, compatibility with electrical parts, and the like may be improved in a balanced manner.

A better understanding of the present disclosure may be obtained through the following examples and comparative examples. However, these examples are not to be construed as limiting the technical spirit of the present disclosure.

Examples 1 to 3 and Comparative Examples 1 to 8

In order to prepare a low-viscosity lubricating oil composition according to an embodiment of the present disclosure, individual lubricating oil compositions were obtained by mixing components in the amounts shown in Tables 1 and 2 below. Examples 1 to 3 are shown in Table 1 below, and Comparative Examples 1 to 8 are shown in Table 2 below. The individual components used herein are as follows. For reference, the additive in the lubricating oil composition was added such that the sum of the proportions of the components was 100 wt %.

[Components]

The mineral oil used was highly-refined mineral oil commercially available from S-OIL.

• • aramcoULTRA 2: Highly-refined mineral oil with kinematic viscosity at 100° C. of about 2 cSt
  • aramcoULTRA 3: Highly-refined mineral oil with kinematic viscosity at 100° C. of about 3 cSt
  • aramcoULTRA 4: Highly-refined mineral oil with kinematic viscosity at 100° C. of about 4 cSt

The synthetic oil used was polyalphaolefin-based synthetic oil commercially available from ExxonMobil and INEOS.

• • PAO 2: Polyalphaolefin-based synthetic oil with kinematic viscosity at 100° C. of about 2 cSt
  • PAO 3.5: Polyalphaolefin-based synthetic oil with kinematic viscosity at 100° C. of about 3.5 cSt
  • PAO 4: Polyalphaolefin-based synthetic oil with kinematic viscosity at 100° C. of about 4 cSt

3) The viscosity index improver used was a modified poly(alkyl methacrylate)-based viscosity index improver (VISCOPLEX series) commercially available from Evonik.

• • Low-molecular-weight: polymethacrylate with weight average molecular weight (Mw) of 10,000 to 50,000 g/mol, SSI (shear stability index) 9 (KRL shear stability tester, 20 hours (test standard: CEC L-45-A-99))
  • High-molecular-weight: polymethacrylate with weight average molecular weight (Mw) greater than 50,000 g/mol, SSI (shear stability index) 26 (KRL shear stability tester, 20 hours (test standard: CEC L-45-A-99))

4) The additive used was an additive package for lubricating oil for an integrated motor-reducer from INFINIUM (including a detergent, a friction modifier, an antiwear agent, an antioxidant, and the like).

5) The pour point depressant used was a PAMA (poly(alkyl methacrylate))-type pour

5 point depressant commercially available from Evonik.

6) The antifoaming agent used was a silicone-type antifoaming agent commercially available from Evonik.

	TABLE 1
	Example

Component (wt %)	1	2	3

Highly-refined mineral oil	aramcoULTRA 2	70	40	30
	aramcoULTRA 3		40	30
	aramcoULTRA 4	10
Synthetic oil	PAO 2			20
	PAO 3.5
	PAO 4
Viscosity index improver	Low-molecular-weight	2	3	2
	High-molecular-weight

Liquid lubricant additive package	10-20	10-20	10-20
Pour point depressant	0.1	0.1	0.1
Antifoaming agent	0.2	0.2	0.2
Total	100	100	100

	TABLE 2
	Comparative Example

Component (wt %)	1	2	3	4	5	6	7	8

Highly-refined	aramcoULTRA 2			60	85	40	65	65	70
mineral oil	aramcoULTRA 3	65	75			40	20
	aramcoULTRA 4	15		20
Synthetic oil	PAO 2
	PAO 3.5							20
	PAO 4		10						15
Viscosity	Low-molecular-weight			4			2	2	2
index improver	High-molecular-weight	7	2			3

Liquid lubricant additive package	10-20	10-20	10-20	10-20	10-20	10-20	10-20	10-20
Pour point depressant	0.2	0.1	0.1	0.1	0.1	0.1	0.1	0.1
Antifoaming agent	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Total	100	100	100	100	100	100	100	100

Test Example

In order to evaluate the required extreme pressure performance, wear resistance, cooling performance, compatibility with electrical parts, and the like, various property measurement tests were performed on Examples 1 to 3 and Comparative Examples 1 to 8. The property test methods 5 are as follows, and the test results thereof are shown in Tables 3 to 7 below and FIG. 1. For reference, Table 7 shows the results of Comparative Examples described in Tables 4 to 6 in one table.

Test Methods

The kinematic viscosity at 40° C. and kinematic viscosity at 100° C. of the lubricating oil composition were measured according to ASTM D445.

The low-temperature viscosity at −40° C. of the lubricating oil composition was measured according to ASTM D2983 (Brookfield low-temperature viscosity).

The wear resistance of the lubricating oil composition was measured according to ASTM D5182 (scuffing load measurement method, FZG (Forschungstelle für Zahnräder und Getriebebau) visual method).

The extreme pressure performance of the lubricating oil composition was measured according to ASTM D2783 (4-ball).

The frictional properties of the lubricating oil composition were measured using MTM (mini-traction machine) at 40° C. and SRR (slide-to-roll ratio) 30%.

The transfer efficiency of the lubricating oil composition was measured using an electrical dynamometer.

	TABLE 3
	Example

Evaluation items	1	2	3

Kinematic	@ 40° C.	12.17	14.27	12.25
viscosity	@ 100° C.	3.254	3.634	3.263

Viscosity index	141	145	140
FZG	10	12	—

4-ball	LNSL (last non-seizure	63	—	—
	load), kgf
	LWI (load wear index), kgf	20.47	—	—
	Weld point, kgf	200	—	—

MTM	—	—	0.0487
Transfer efficiency-FTP75 (Federal	97.71	—	—
Test Procedure) conditions
Transfer efficiency-representative	97.52	—	—
efficiency

	TABLE 4
	Example	Comparative Example

Evaluation items	1	1	2	3	4

Kinematic viscosity	@ 40° C.	12.17	22.23	17.95	14.71	10.19
	@ 100° C.	3.254	5.399	4.287	3.792	2.781

Viscosity index

141

193

152

157

118

4-ball	LNSL, kgf	63	50	80	63	50
	LWI, kgf	20.47	25	27.63	20.47	16.27
	Weld point, kgf	200	200	200	200	160

Transfer efficiency-FTP75 conditions	97.71	97.62	97.67	97.65	—
Transfer efficiency-representative	97.52	97.43	97.43	97.43	—
efficiency

	TABLE 5
				Comparative
	Evaluation items		Example 2	Example 5

	Kinematic	@ 40° C.	14.27	14.43
	viscosity	@ 100° C.	3.634	3.816

Viscosity index	145	167
FZG	12	11

TABLE 6
	Example	Comparative	Comparative	Comparative
Evaluation items	3	Example 6	Example 7	Example 8

Kinematic	@ 40° C.	12.25	12.28	12.25	12.39
viscosity	@ 100° C.	3.263	3.264	3.268	3.278

Viscosity index	140	140	141	139
MTM	0.0487	0.0534	0.0503	0.0522

	TABLE 7
	Comparative Example

Evaluation items	1	2	3	4	5	6	7	8

Kinematic	@ 40° C.	22.23	17.95	14.71	10.19	14.43	12.28	12.25	12.39
viscosity	@ 100° C.	5.399	4.287	3.792	2.781	3.816	3.264	3.268	3.278

Viscosity index	193	152	157	118	167	140	141	139
FZG					11

4-ball	LNSL, kgf	50	80	63	50
	LWI, kgf	25	27.63	20.47	16.27
	Weld point,	200	200	200	160
	kgf

MTM						0.0534	0.0503	0.0522
Transfer efficiency-	97.62	97.67	97.65
FTP75 conditions
Transfer efficiency-	97.43	97.43	97.43
representative efficiency

When comparing the results of Example 1 with the results of Comparative Examples 1 to 3 as shown in Table 4, it can be confirmed that the lower the kinematic viscosity at 100° C., the better the transfer efficiency.

Also, in Comparative Example 2 containing some PAO, the transfer efficiency was slightly better than that of Comparative Example 3 not containing PAO and having lower kinematic viscosity, suggesting that the addition of PAO is effective at improving energy efficiency due to superior frictional properties.

The lower the viscosity, the lower the extreme pressure performance measured by the 4-ball BP test, and Comparative Example 4 having kinematic viscosity at 100° C. of 2.781 cSt is expected to have improved energy efficiency due to low kinematic viscosity, but the extreme pressure performance level thereof was lower than that of Comparative Example 1. Accordingly, the viscosity of about 2.8 to 4.0 cSt was confirmed to be suitable for improving energy efficiency and maintaining durability.

When comparing the kinematic viscosity, viscosity index, and wear resistance of Example 2 and Comparative Example 5 through Table 5, the use of poly(alkyl methacrylate) having a molecular weight of 10,000 to 50,000 (low-molecular-weight polymethacrylate) as a viscosity index improver was confirmed to exhibit superior durability.

In addition, referring to the results of Table 6 and FIG. 1 showing the frictional properties of the lubricating oil compositions according to Example 3 and Comparative Examples 6 to 8, which were mixed under the condition of maintaining the same kinematic viscosity at 100° C., frictional properties were the best in Example 3 using PAO 2 as the polyalphaolefin-based synthetic oil.

In Comparative Example 6 using only highly-refined mineral oil, frictional properties were inferior, which was disadvantageous for NVH performance, so the use of polyalphaolefin-based synthetic oil with superior frictional properties was required. Also, referring to the results of Example 3 and Comparative Examples 7 and 8, when the product with kinematic viscosity at 100° C. of 2 cSt was used as the polyalphaolefin-based synthetic oil, frictional properties were superior compared to when using 3.5 and 4 cSt products.

As is apparent from the foregoing, a lubricating oil composition according to an embodiment of the present disclosure is a low-viscosity lubricating oil having kinematic viscosity at 100° C. of 2.8 to 4.0 cSt, but is capable of preventing durability and NVH performance from deteriorating in low-viscosity lubricating oil by appropriately combining highly-refined mineral oil and polyalphaolefin-based synthetic oil and adding poly(alkyl methacrylate) having an appropriate molecular weight as a viscosity index improver.

The low-viscosity lubricating oil composition according to an embodiment of the present disclosure is capable of reducing energy consumption due to friction by lowering internal resistance of a motor, and improving driving efficiency by more effectively dissipating heat generated during motor operation, ultimately improving energy efficiency.

The effects of the present disclosure are not limited to the foregoing. It should be understood that the effects of the present disclosure include all effects that can be inferred from the description of the present disclosure.

As the embodiments of the present disclosure have been described above, those having ordinary skill in the art should appreciate that various modifications and alterations are possible through change, deletion or addition of components without departing from the scope and spirit of the present disclosure as described in the accompanying claims, which should also be considered as being included within the scope of rights of the present disclosure.