Lubricating oil composition

Abstract

A lubricating oil composition contains 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight average molecular weight of 5000 to 20000, and it is a lubricating oil composition for a helical gear mechanism.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition, and more particularly to a lubricating oil composition for a helical gear mechanism. Background Art

[0002] Heretofore, in gear mechanisms for power transmission mechanisms and the like, the use of various lubricating oil compositions has been studied from the viewpoint of improving the power transmission efficiency. For example, in International Publication No. 2013 / 136582 (Patent Document 1), a lubricating oil composition containing a mineral oil-based base oil having a kinematic viscosity at 100 °C of 5 mm 2 / s or less and a polymer having a weight average molecular weight of 15,000 or less is disclosed. In the column of the examples thereof, a copolymer of an α-olefin and an α,β-ethylenically unsaturated dicarboxylic acid diester is disclosed as the polymer having a weight average molecular weight of 15,000 or less.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2013 / 147162 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a lubricating oil composition that can sufficiently improve the power transmission efficiency particularly under severe conditions of high temperature and high load when used in a helical gear mechanism.

[0008] Means for Solving the Problems

[0009] The inventors of the present invention repeatedly conducted studies and found that: the conventional lubricating oil compositions as described in Patent Document 1 above can achieve an improvement in power transmission efficiency when used in a spur gear mechanism, but when directly used in a helical gear (helical gear: spiral gear) mechanism, under severe conditions of high temperature and high load around 100 °C to 140 °C (preferably around 120 °C) (such as high load (preferably around 30 Nm to 70 Nm) and relatively high rotational speed (around 2000 to 4000 rpm) and other load conditions), the power transmission efficiency may not be sufficiently improved. In addition, even referring to known techniques such as Patent Document 1, it is not easy for those skilled in the art to conceive that the improvement effect of the power transmission efficiency will have different tendencies when used in a spur gear mechanism and when used in a helical gear mechanism.

[0010] Based on the above understanding, the inventors of the present invention further conducted in-depth research repeatedly, and as a result, it was found that: by making the lubricating oil composition contain 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight-average molecular weight of 5000 to 20000, when this lubricating oil composition is used in a helical gear mechanism, particularly even under severe conditions of high temperature and high load, the power transmission efficiency can be sufficiently improved, thus completing the present invention.

[0011] That is, the lubricating oil composition of the present invention is as described below.

[0012] 〔1〕A lubricating oil composition containing 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight-average molecular weight of 5000 to 20000, and being a lubricating oil composition for a helical gear mechanism.

[0013] 〔2〕The lubricating oil composition according to the above 〔1〕, wherein the kinematic viscosity of the lubricating oil base oil contained in the lubricating oil composition at 80 °C is 2.0 to 7.0 mm 2 / s.

[0014] 〔3〕The lubricating oil composition according to the above 〔1〕 or 〔2〕, wherein the lubricating oil base oil contained in the lubricating oil composition contains 60% by mass or more of a mineral oil base oil satisfying the condition of API classification as Group II or Group III based on the total amount of the lubricating oil base oil.

[0015] Advantages of the Invention

[0016] According to the present invention, it is possible to provide a lubricating oil composition that can sufficiently improve the power transmission efficiency particularly even under severe conditions of high temperature and high load when used in a helical gear mechanism. Description of the Drawings

[0017] Figure 1 is a cross-sectional view schematically showing a test apparatus of a helical gear mechanism used for evaluating the characteristics of the lubricating oil composition obtained in the evaluation examples and the like.

[0018] Symbol Explanation

[0019] 10 Input Motor, 11 Rotating shaft (input side), 12 Torque meter (input side), 20 Output Motor, 21 Rotating shaft (output side), 22 Torque meter (output side), G1 and G2 Helical gears, 40 Tank 40 for storing the lubricating oil composition, 41 Oil supply pipe, A1 Arrow schematically showing the moving direction of the lubricating oil composition in the oil supply pipe. Detailed Description of the Invention

[0020] Hereinafter, the present invention will be described in detail according to the preferred embodiments of the present invention. In this specification, unless otherwise specified, for numerical values X and Y, the expression "X to Y" means "X or more and Y or less". When a unit is attached only to the numerical value Y in this expression, the unit also applies to the numerical value X.

[0021] The lubricating oil composition of the present invention contains 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight average molecular weight of 5000 to 20000, and it is a lubricating oil composition for a helical gear mechanism.

[0022] <Ethylene-propylene copolymer>

[0023] The weight average molecular weight (Mw) of the ethylene-propylene copolymer used in the present invention is 5000 to 20000. When the weight average molecular weight is below the above upper limit, compared with the case where it exceeds the above upper limit, the shear stability of the obtained lubricating oil composition can be made more excellent, and the performance of maintaining an oil film for a long time (oil film retention) can be further improved. On the other hand, when the weight average molecular weight is above the above lower limit, compared with the case where it is below the above lower limit, the viscosity index of the obtained lubricating oil composition can be increased, and the power transmission efficiency can be sufficiently increased under high temperature conditions. In addition, from the same viewpoint, as the weight average molecular weight of the above ethylene-propylene copolymer, it is more preferably 5000 to 15000, further preferably 6000 to 13000, and particularly preferably 6500 to 12000.

[0024] In addition, the number average molecular weight (Mn) of the above ethylene-propylene copolymer is preferably 2000 to 10000 (more preferably 3500 to 7000). When the number average molecular weight is below the above upper limit, compared with the case where it exceeds the above upper limit, the shear stability of the obtained lubricating oil composition can be made more excellent, and the oil film retention can be further improved. On the other hand, when the number average molecular weight is above the above lower limit, compared with the case where it is below the above lower limit, the viscosity of the obtained lubricating oil composition can be further increased, and the lubrication state of the contact interface between the gears can be maintained in a better state during use, and the power transmission efficiency can be further increased.

[0025] Furthermore, the molecular weight distribution (Mw / Mn) of the above ethylene-propylene copolymer is preferably 3.0 or less (more preferably 2.5 or less). When the molecular weight distribution is below the above upper limit, compared with the case where it exceeds the above upper limit, the shear viscosity stability of the obtained lubricating oil composition can be further improved, and the lubrication state of the contact interface between the gears can be maintained in a better state during use, and the power transmission efficiency can be further increased.

[0026] In addition, in this specification, Mw, Mn, and Mw / Mn of the above ethylene-propylene copolymer respectively refer to the values obtained by gel permeation chromatography (GPC) (molecular weights converted based on polystyrene). In addition, the measurement conditions for obtaining Mw, Mn, and Mw / Mn by GPC are as described below.

[0027] [GPC Measurement Conditions]

[0028] Apparatus: ACQUITY (registered trademark) APC UV RI system manufactured by Waters Corporation

[0029] Columns: Two ACQUITY (registered trademark) APCXT900A (gel particle size 2.5 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation and one ACQUITY (registered trademark) APC XT200A (gel particle size 2.5 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation are connected in series in this order from the upstream side.

[0030] Column temperature: 40 °C

[0031] Sample solution: A tetrahydrofuran solution with a sample concentration of 1.0 mass%

[0032] Solution injection volume: 20.0 μL

[0033] Detection device: Differential refractive index detector

[0034] Reference substance: Eight-point standard polystyrene (Agilent EasiCal (registered trademark) PS-1 manufactured by Agilent Technologies) (molecular weights: 2698000, 597500, 290300, 133500, 70500, 30230, 9590, 2970)

[0035] When performing GPC measurement according to the above conditions, if the weight-average molecular weight is 10,000 or more, the measurement is directly terminated. On the other hand, if the weight-average molecular weight is less than 10,000, except for the cases where the columns and the reference substance are changed as follows, re-measurement is performed under the same conditions as the above conditions.

[0036] Chromatographic column: One ACQUITY (registered trademark) APC XT 125A (gel particle size 2.5 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation and two ACQUITY (registered trademark) APC XT 45A (gel particle size 1.7 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation are connected in series from the upstream side.

[0037] Reference substance: Ten points of standard polystyrene (Agilent EasiCal (registered trademark) PS-1 manufactured by Agilent Technologies) (molecular weights: 30230, 9590, 2970, 890, 786, 682, 578, 474, 370, 266).

[0038] In addition, in the above ethylene-propylene copolymer, the content of structural units derived from ethylene (ethylene content) is preferably 30 to 80 mol% (more preferably 40 to 60 mol%). When the ethylene content is below the above upper limit, a lubricating oil composition with more excellent low-temperature viscosity characteristics can be obtained compared with the case where it exceeds the above upper limit. On the other hand, when the ethylene content is above the above lower limit, the temperature dependence of the viscosity can be further reduced compared with the case where it is below the above lower limit. In addition, in the present application, the "ethylene content" refers to the value calculated according to the following calculation formulas (I) to (III) using the measurement results obtained under the following measurement conditions. 13 13C-NMR measurement, and using the measurement results, the value calculated according to the following calculation formulas (I) to (III).

[0039] ( 13 13C-NMR measurement conditions

[0040] Device used: AVANCE 400 type NMR manufactured by Bruker

[0041] Solvent: CDCl3

[0042] Sample tube: 10 mm in diameter

[0043] Measurement method: 1H-inverse gated decoupling

[0044] Number of accumulations: 3000 times

[0045] Waiting time: 10 seconds

[0046] Measurement temperature: Room temperature

[0047] Chemical shift standard: CDCl3 (77.1 ppm)

[0048] (Calculation Formulas (I) to (III) of Ethylene Content)

[0049] A P = 3 × A M (I)

[0050] A E = 100 - A P (II)

[0051] X = 100 × (0.5 × A E ) / {(0.5 × A E ) + (1 / 3 × A P )}(III)

[0052] [In Formulas (I) to (III), A M represents 13 the integral value in the 19 - 21 ppm region in 13C - NMR, A P represents 13 the integral value of carbon from propylene in 13C - NMR, A E represents 13 the integral value of carbon from ethylene in 13C - NMR, and X represents the ethylene content (%). In addition, the integral value of all peaks (excluding the solvent) detected by using 13 13C - NMR is set to 100.].

[0053] In addition, the above ethylene - propylene copolymer may be a block copolymer or a random copolymer. Furthermore, the method for manufacturing the above ethylene - propylene copolymer is not particularly limited, and a known method can be suitably adopted. In addition, as the above ethylene - propylene copolymer, commercially available products can also be used.

[0054] In addition, in the lubricating oil composition of the present invention, the content of the above ethylene - propylene copolymer needs to be set to 0.1 - 3.0% by mass. When the content of the ethylene - propylene copolymer is above the above lower limit, compared with the case where it is below the above lower limit, it becomes easier to adjust the viscosity of the lubricating oil composition with the ethylene - propylene copolymer, and under severe conditions such as high temperature and high load, the power transmission efficiency of the helical gear mechanism can be sufficiently improved. On the other hand, when the content of the ethylene - propylene copolymer is below the above upper limit, compared with the case where it exceeds the above upper limit, the increase in the viscosity of the obtained lubricating oil composition can be suppressed and the viscosity index can be improved, and the power transmission efficiency can be sufficiently improved under high - temperature conditions. In addition, the content of the ethylene - propylene copolymer is more preferably 0.15 - 2.5% by mass (further preferably 0.20 - 2.0% by mass) because the power transmission efficiency of the helical gear mechanism can be further improved under severe conditions such as high temperature and high load.

[0055] In addition, the lubricating oil composition of the present invention only needs to contain 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight average molecular weight of 5000 to 20000. The types of other components contained in the lubricating oil composition are not particularly limited, and known lubricating oil base oils and known other components (additives) that can be used in gear mechanisms can be suitably used. Hereinafter, the lubricating oil base oils and other components that can be used in the lubricating oil composition of the present invention will be described.

[0056] <Lubricating oil base oil>

[0057] As the lubricating oil base oil contained in the lubricating oil composition of the present invention, there is no particular limitation, and known lubricating oil base oils (for example, the lubricating oil base oils described in JP-A-2003-155492, WO 2017 / 073748, JP-A-2020-76004, etc.) can be suitably used. It can be a mineral oil-based lubricating oil base oil or a synthetic oil-based lubricating oil base oil. Hereinafter, as such a lubricating oil base oil, the lubricating oil base oils that can be preferably used will be described.

[0058] As the above lubricating oil base oil, the kinematic viscosity at 80°C is preferably 2.0 to 7.0 mm 2 / s (more preferably 3.0 to 6.0 mm 2 / s). When the kinematic viscosity at 80°C is below the above upper limit, compared with the case where it exceeds the above upper limit, the power transmission efficiency can be further improved in a high-temperature region (around 100°C to 140°C). On the other hand, when the kinematic viscosity at 80°C is above the above lower limit, compared with the case where it is below the above lower limit, the oil film forming property and oil film retention property of the lubricating oil composition at the lubricated part can be further improved in a high-temperature region (around 100°C to 140°C), and a better lubrication state can be maintained. In addition, in this specification, the "kinematic viscosity at 80°C" refers to the kinematic viscosity at 80°C measured according to JIS K 2283-2000 using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) as the measuring device.

[0059] In addition, as the above lubricating oil base oil, it is preferably a mineral oil-based base oil that satisfies the condition of being classified as Group II or Group III in the base oil classification conducted by API (American Petroleum Institute) (referred to as "API classification" in this specification) (hereinafter sometimes simply referred to as "Condition (A)"). In addition, a base oil classified as Group II by API is a mineral oil-based base oil with a sulfur content of 0.03% by mass or less, a saturated component (saturated hydrocarbon) of 90% by volume or more, and a viscosity index of 80 or more but less than 120. In addition, a base oil classified as Group III by API is a mineral oil-based base oil with a sulfur content of 0.03% by mass or less, a saturated component (saturated hydrocarbon) of 90% by volume or more, and a viscosity index of 120 or more. In addition, as the above lubricating oil base oil, the content of the mineral oil-based base oil that satisfies Condition (A) is more preferably 60% by mass or more (further preferably 80% by mass or more) based on the total amount of the lubricating oil base oil.

[0060] Furthermore, as the above lubricating oil base oil, it is preferably to satisfy the condition that the concentration of the sulfur component is 200 mass ppm or less (more preferably 100 mass ppm or less, further preferably 1 mass ppm or less). When the concentration of the sulfur component is below the above upper limit, a composition with better thermal and oxidation stability can be obtained. In addition, in this specification, the "concentration of the sulfur component" refers to the value measured according to JIS K 2541-6-2003 (ultraviolet fluorescence method).

[0061] In addition, as the above lubricating oil base oil, it is preferably to satisfy the condition that the concentration of the nitrogen component is 300 mass ppm or less (more preferably 100 mass ppm or less, further preferably 1 mass ppm or less). When the concentration of the nitrogen component is below the above upper limit, a composition with better thermal and oxidation stability can be obtained. In addition, in this specification, the "concentration of the nitrogen component" refers to the value measured according to JIS K 2609-1998 (chemiluminescence method).

[0062] In addition, as the above lubricating oil base oil, the density at 15 °C is preferably 0.800 - 0.850 g / cm 3 (more preferably 0.805 - 0.845 g / cm 3 ). When the density is below the above upper limit, a composition with better thermal and oxidation stability can be obtained compared with the case where it exceeds the above upper limit. On the other hand, when the density is above the above lower limit, the heat transfer characteristics are excellent, and the excessive temperature rise of the sliding surface can be further suppressed. In addition, in this specification, the "density at 15 °C" refers to the density at 15 °C measured according to JIS K 2249-1-1995.

[0063] In addition, as the above lubricating oil base oil, the viscosity index is preferably 80 or more, more preferably 95 to 160. When the viscosity index is below the above upper limit, the content of n-alkanes in the base oil becomes less than that when it exceeds the above upper limit, so the sharp increase in viscosity at low temperatures is further suppressed. On the other hand, when the viscosity index is above the above lower limit, compared with the case where it is below the above lower limit, the temperature dependence of the viscosity of the obtained lubricating oil composition can be further reduced, and the power transmission efficiency can be further improved under high temperature conditions. In addition, in this specification, the "viscosity index" refers to the viscosity index measured according to JIS K 2283-1993.

[0064] In addition, as the entire lubricating oil base oil, the above lubricating oil base oil may be composed of a single base oil component, or may be composed of a combination of multiple base oil components.

[0065] In addition, in the lubricating oil composition of the present invention, the content of the lubricating oil base oil is preferably 50 to 99% by mass (more preferably 70 to 97% by mass) based on the total amount of the lubricating oil composition. When the content of the lubricating oil base oil is below the above upper limit, compared with the case where it exceeds the above upper limit, it becomes easier to improve the properties such as the formation property of the lubricating coating film using additives. On the other hand, when the content of the lubricating oil base oil is above the above lower limit, compared with the case where it is below the above lower limit, the temperature dependence of the viscosity can be further reduced.

[0066] <Other additives>

[0067] In the lubricating oil composition of the present invention, in order to further improve its performance, other generally used components (other additives) can also be appropriately used in the lubricating oil composition according to the purpose. As such other components, there is no particular limitation, and known components used in the field of lubricating oil compositions (for example, the components described in JP-A-2003-155492, WO 2017 / 073748, WO 2013 / 147162, JP-A-2020-76004, etc.) can be appropriately used. In addition, as such other components, there is no particular limitation, but additives such as antiwear agents, ashless dispersants, pour point depressants, friction modifiers, metal-based detergents, antioxidants, metal deactivators, rubber swelling agents, antifoaming agents, diluent oils, etc. can be preferably used. Hereinafter, the components that can be preferably used as such other components will be described.

[0068] As the above-mentioned antiwear agent, there is no particular limitation, and known compounds used as antiwear agents in the field of lubricating oil compositions can be suitably used (see, for example, Japanese Patent Laid-Open No. 2003-155492, Japanese Patent Laid-Open No. 2020-76004, International Publication No. 2013 / 147162, etc.). In addition, as the antiwear agent, for example, sulfur-based, phosphorus-based or sulfur-phosphorus-based antiwear agents can be used. Among the above-mentioned antiwear agents, from the viewpoint of excellent wear resistance, phosphorus-based or sulfur-phosphorus-based antiwear agents are more preferred, and phosphites and thiophosphates are further preferred. In addition, the antiwear agent can be used alone or in combination of two or more. When using the antiwear agent, its content is not particularly limited, and it is preferably 0.02 to 2.0% by mass (more preferably 0.05 to 1.0% by mass) based on the total amount of the above lubricating oil composition. When the content of the antiwear agent is below the above upper limit, the thermal and oxidation stability can be further improved compared with the case where it exceeds the above upper limit. On the other hand, when the content of the antiwear agent is above the above lower limit, the wear resistance of the lubricating oil composition can be further improved compared with the case where it is below the above lower limit, and the power transmission efficiency can be further improved even under high load conditions.

[0069] In addition, as the above-mentioned ashless dispersant, known compounds used as ashless dispersants in the field of lubricating oil compositions can be suitably used (see, for example, Japanese Patent Laid-Open No. 2003-155492, Japanese Patent Laid-Open No. 2020-76004, International Publication No. 2013 / 147162, etc.). As the ashless dispersant, non-boronated succinimides, boronated succinimides and their mixtures can be preferably used. In addition, the ashless dispersant can be used alone or in combination of two or more. When using the ashless dispersant, its content is not particularly limited, and it is preferably 0.2 to 6.0% by mass (more preferably 0.5 to 5.0% by mass) based on the total amount of the above lubricating oil composition.

[0070] In addition, as the above-mentioned pour point depressant, for example, poly(meth)acrylate, ethylene-vinyl acetate copolymer, etc. can be cited, among which poly(methyl)acrylate is preferred. In addition, as the above-mentioned poly(methyl)acrylate, those having a weight average molecular weight (Mw) of 20,000 to 100,000 are preferred. The pour point depressant can be used alone or in combination of two or more. When using the pour point depressant, its content is preferably 0.01 to 1.0% by mass (more preferably 0.03 to 0.6% by mass) based on the total amount of the above lubricating oil composition.

[0071] In addition, there are no particular limitations on the above-mentioned friction modifiers, and examples thereof include amine-based, amide-based, imide-based, fatty acid ester-based, fatty acid-based, aliphatic alcohol-based, and aliphatic ether-based friction modifiers. Among them, from the viewpoint of obtaining a higher friction reduction effect, amine-based friction modifiers are more preferred. In addition, as such amine-based friction modifiers, alkylamines and alkenylamines are preferred. The friction modifier can be used alone as one kind, or two or more kinds can be used in combination. In addition, when using a friction modifier, its content is preferably 0.005 to 3.0% by mass (more preferably 0.01 to 2.5% by mass) based on the total amount of the above lubricating oil composition.

[0072] In addition, there are no particular limitations on the above-mentioned metal detergents, and examples thereof include alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, etc. The metal detergent can be used alone as one kind, or two or more kinds can be used in combination. In addition, when using a metal detergent, its content is preferably 0.01 to 1.0% by mass (more preferably 0.05 to 0.6% by mass) based on the total amount of the above lubricating oil composition.

[0073] In addition, there are no particular limitations on the above-mentioned antioxidants, and examples thereof include phenolic antioxidants and amine-based antioxidants. The antioxidant can be used alone as one kind, or two or more kinds can be used in combination. When using an antioxidant, its content is preferably 0.1 to 2.0% by mass (more preferably 0.2 to 1.0% by mass) based on the total amount of the above lubricating oil composition.

[0074] In addition, there are no particular limitations on the above-mentioned metal deactivators, and examples thereof include imidazoline, pyrimidine derivatives, alkylthiadiazole, mercaptobenzothiazole, benzotriazole or its derivatives, tolyltriazole or its derivatives, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazole-2,5-bis(dialkyldithiocarbamate), 2-(alkyldithio)benzimidazole, β-(o-carboxybenzylthio)propionitrile, etc. The metal deactivator can be used alone as one kind, or two or more kinds can be used in combination. In addition, when using a metal deactivator, its content is preferably 0.01 to 0.5% by mass (more preferably 0.02 to 0.3% by mass) based on the total amount of the above lubricating oil composition.

[0075] In addition, there is no particular limitation on the above-mentioned rubber swelling agent, and known compounds that can be used as a sealing swelling agent for lubricating oil can be suitably used. Examples include sealing swelling agents such as ester-based, sulfur-based, and aromatic-based (e.g., sulfolane compounds, etc.). The rubber swelling agent can be used alone as one kind, or two or more kinds can be used in combination. In addition, when using a rubber swelling agent, its content is not particularly limited, and it is preferably 0.01 to 1.0% by mass (more preferably 0.05 to 0.8% by mass) based on the total amount of the above lubricating oil composition.

[0076] In addition, examples of the above defoaming agent include silicone oil having a kinematic viscosity of 1000 to 100000 mm 2 / s at 25°C, alkenyl succinic acid derivatives, esters of polyhydroxy aliphatic alcohols and long-chain fatty acids, methyl salicylate, o-hydroxybenzyl alcohol, etc. The defoaming agent can be used alone as one kind, or two or more kinds can be used in combination. In addition, when using a defoaming agent, its content is not particularly limited, and it is preferably 0.0001 to 0.005% by mass (more preferably 0.0003 to 0.003% by mass) based on the total amount of the above lubricating oil composition.

[0077] <Regarding the characteristics of the lubricating oil composition, etc.>

[0078] Above, the preferred conditions of the composition of the lubricating oil composition of the present invention have been described. Hereinafter, the preferred conditions of the characteristics of the lubricating oil composition of the present invention will be described.

[0079] The kinematic viscosity of the lubricating oil composition of the present invention at 120°C is preferably 1.5 to 4.0 mm 2 / s, more preferably 1.8 to 3.5 mm 2 / s. When the kinematic viscosity at 120°C is below the above upper limit, compared with the case where it exceeds the above upper limit, when used in a helical gear mechanism, the power transmission efficiency can be further improved in a high-temperature region of about 100 to 140°C. On the other hand, when the kinematic viscosity at 120°C is above the above lower limit, compared with the case where it is below the above lower limit, especially in a high-temperature region of about 100 to 140°C, the oil film formation property and oil film retention property of the lubricating oil composition at the lubricating part can be further improved, and a better lubricating state can be maintained even under high-temperature conditions. In addition, in this specification, the "kinematic viscosity at 120°C" refers to the kinematic viscosity at 120°C measured using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) in accordance with JIS K 2283-2000.

[0080] In addition, the kinematic viscosity of the lubricating oil composition of the present invention at 80°C is preferably 3.0 to 9.0 mm 2 / s, more preferably 3.5 to 7.0 mm 2 / s. When the kinematic viscosity at 80°C is below the above upper limit, the power transmission efficiency can be further improved under severe conditions such as high temperature and high load compared with the case where it exceeds the above upper limit. In addition, when the kinematic viscosity at 80°C is above the above lower limit, the oil film forming property and oil film retention property of the lubricating oil composition at the lubricated part during use can be further improved, and a better lubrication state can be maintained even under high temperature conditions.

[0081] The kinematic viscosity of the lubricating oil composition of the present invention at 40°C is preferably 8.0 to 30.0 mm 2 / s, more preferably 9.0 to 20.0 mm 2 / s. When the kinematic viscosity at 40°C is below the above upper limit, the power transmission efficiency can be further improved under severe conditions such as high temperature and high load compared with the case where it exceeds the above upper limit. In addition, when the kinematic viscosity at 40°C is above the above lower limit, the oil film forming property and oil film retention property of the lubricating oil composition at the lubricated part during use can be further improved, and a better lubrication state can be maintained even under high temperature conditions. In addition, in this specification, the "kinematic viscosity at 40°C" refers to the kinematic viscosity at 40°C measured using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) in accordance with JIS K 2283-2000.

[0082] In addition, the viscosity index of the lubricating oil composition of the present invention is preferably 90 or more, more preferably 100 or more. When the viscosity index is above the above lower limit, the temperature dependence of the viscosity of the lubricating oil composition can be further reduced, and the power transmission efficiency can be further improved compared with the case where it is below the above lower limit.

[0083] In addition, the pour point of the lubricating oil composition of the present invention is preferably -30°C or lower (more preferably -40°C or lower). When the pour point is below the above upper limit, a lubricating oil composition with excellent low-temperature viscosity characteristics can be obtained compared with the case where it exceeds the above upper limit. In addition, in this specification, the "pour point" refers to the pour point measured in accordance with JIS K 2269-1987.

[0084] In addition, the method for producing the lubricating oil composition of the present invention is not particularly limited as long as it can contain the ethylene-propylene copolymer having a weight-average molecular weight of 5000 to 20000 in the lubricating oil composition in the above-mentioned content. It can be appropriately selected according to the target use and design, and the lubricating oil base oil and other components as described above (such as the above viscosity modifier, the above ashless dispersant, etc.) can be prepared by adding the above ethylene-propylene copolymer and other components to the lubricating oil base oil.

[0085] In addition, when adding other components as described above to the lubricating oil composition of the present invention, the other components can be separately prepared and added for each component, or a mixture of the other components can be prepared and then added. As a mixture of the other components as described above, a commercially available package (for example, an additive package containing an ashless dispersant, a metal-based detergent, an antioxidant, a friction modifier, an antiwear agent, a rubber swelling agent, a metal deactivator, a diluent component (diluent oil), etc.) can also be appropriately used.

[0086] Examples

[0087] Hereinafter, the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to the following examples.

[0088] [Components used in each example, etc.]

[0089] The lubricating oil base oil, low molecular weight polymer component, and other additives used in each example, etc. are as follows. In addition, the density of the lubricating oil base oil shown below is the density at 15°C. In addition, regarding the following low molecular weight polymer components, the weight-average molecular weight is a value analyzed by gel permeation chromatography (GPC) according to the above GPC measurement conditions.

[0090] (1) Lubricating oil base oil

[0091] [Mineral oil (I)] Kinematic viscosity at 80°C: 3.61 mm 2 / s, sulfur component: less than 1 mass ppm, nitrogen component: less than 1 mass ppm, API classification: Group II (mineral oil), density: 0.837 g / cm 3

[0092] (2) Polymer component having a molecular weight of 20000 or less

[0093] [Polymer (A)] Ethylene-propylene copolymer (weight-average molecular weight: 11500, ethylene content: 60%)

[0094] [Polymer (B)] Ethylene-propylene copolymer (weight-average molecular weight: 7080, ethylene content: 58%)

[0095] [Polymer (C)] Copolymer of an α-olefin and a diester of an α,β-ethylenically unsaturated dicarboxylic acid (weight-average molecular weight: 4,730)

[0096] [Polymer (D)] Copolymer of an α-olefin and a diester of an α,β-ethylenically unsaturated dicarboxylic acid (weight-average molecular weight: 6,000)

[0097] [Polymer (E)] Non-dispersed polymethacrylate (weight-average molecular weight: 7,950)

[0098] [Polymer (F)] Non-dispersed polymethacrylate (weight-average molecular weight: 20,000)

[0099] (3) Other additives

[0100] [Additive package] An additive package containing the following components: ashless dispersant (a mixture of non-boronated succinimide and boronated succinimide); metallic detergent (calcium sulfonate, total base number: 300 (TBN 300)); antioxidant (a mixture of amine-based antioxidant and phenol-based antioxidant); friction modifier (amine-based); antiwear agent (phosphite); rubber swelling agent (sulfolane compound); metal deactivator (thiadiazole); and diluent oil

[0101] [Pour point depressant] Polymethacrylate (non-dispersed, weight-average molecular weight: 50,000).

[0102] (Examples 1 to 4 and Comparative Examples 1 to 5)

[0103] Each component was used in accordance with the composition shown in Table 1 below to prepare a lubricating oil composition. In addition, "-" in Table 1 indicates that the component was not used. In Table 1, the unit of "mass % occupied" for the content of the lubricating oil base oil represents the content (mass %) of mineral oil (I) relative to the total amount of the lubricating oil base oil contained in the composition, and the unit of "mass %" for the content of the polymer component and other additives represents the content (mass %) of each component relative to the total amount of the lubricating oil composition. In Table 1, the kinematic viscosities of each lubricating oil composition of Examples 1 to 4 and Comparative Examples 1 to 5 at 40 °C, 80 °C, and 120 °C are also shown (values measured using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) as the measuring device in accordance with JIS K 2283-2000).

[0104]

[0105] [Regarding the characteristics of the lubricating oil compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 5]

[0106] Using the lubricating oil compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 5 respectively, the properties were evaluated as described below.

[0107] <Measurement test of power transmission efficiency in a spur gear mechanism: FZG spur gear test>

[0108] Except for adopting different conditions at the points described below, the same method as the method described in the document "FVA Information Sheet No. 345, March 2002 (hereinafter sometimes abbreviated as 'Reference Document 1')" was used to measure the power transmission efficiency when the FZG spur gear test device was operated under the following test conditions. That is, as the test device, a power circulation type FZG spur gear test device was used, and the gearbox equipped with the test gear C-PT(C) (gear material: 16MnCr5) was set to a horizontal state where the shaft center part was impregnated with the lubricating oil composition. At the load stage: 7 (ST7 [surface pressure: about 1300 N / mm 2 ), the test temperature (the temperature of the lubricating oil composition during the test) was 90 °C, and the engine speed was 1440 rpm. The above test device was operated under these test conditions, and the input torque [unit: Nm] and the loss torque [[unit: Nm]] were measured, and the following formula (1) was calculated to obtain the power transmission efficiency (gear efficiency). In addition, when performing this measurement, the product name "Super oil M100" manufactured by ENEOS Corporation was used instead of the reference oil "mineral oil FVA3A" described in Reference Document 1, and the step described in the "Vc) Steady-state-tempeature" column in Chapter 7 of Reference Document 1 was omitted. Furthermore, as the value of the loss torque, the measured value under the above test conditions was directly adopted, rather than the value obtained by subtracting the "no load loss torque" value as described in Chapter 8.2 of Reference Document 1. Although different conditions from Reference Document 1 were adopted at these points, the same method as the method described in Reference Document 1 was adopted except for these. The results obtained through the above FZG spur gear test are shown in Table 3. In addition, in Table 3, the increase amount of the power transmission efficiency of each example, etc. (the increase amount relative to the reference value: the difference from the power transmission efficiency of Comparative Example 1: the efficiency increase value) when the power transmission efficiency of Comparative Example 1 was used as the reference value is also shown.

[0109] [Power transmission efficiency (%)] = {(T in - T out ) / T in} × 100 (1)

[0110] (In formula (1), T inIndicates the input torque, T out Indicates the loss torque.)

[0111] <Measurement Test of Power Transmission Efficiency in Helical Gear Mechanism: Helical Gear Test>

[0112] Use Figure 1 The test device of the helical gear mechanism schematically shown in, a lubricating oil composition is supplied to a pair of helical gears, and the power transmission efficiency (gear efficiency) is obtained as described below. Hereinafter, the test device and test conditions will be described separately.

[0113] (Regarding the test device)

[0114] First, the test device will be described. Figure 1 Among them, the test device is a test device that utilizes a gearbox 30 having a pair of helical gears composed of a helical gear G1 and a helical gear G2. More specifically, Figure 1 The test device shown includes: an input engine (Input Motor: drive engine) 10 for inputting driving force, a rotating shaft 11 for the input engine 10, a helical gear G1 on the input side (drive side) provided at the front end of the rotating shaft 11, a torque meter 12 connected to the rotating shaft 11 for measuring the input torque (drive torque), an output engine (Output Motor: absorption engine) 20, a rotating shaft 21 for the output engine 20, a helical gear G2 on the output side (absorption side) installed at the front end of the rotating shaft 21, a torque meter 22 connected to the rotating shaft 21 for measuring the output torque (absorption torque), a gearbox 30 in which a pair of helical gears G1 and G2 are internally arranged, a tank 40 for storing the lubricating oil composition supplied to the gears, and an oil supply pipe 41 for supplying the lubricating oil composition from the tank 40 to the contact portion (the portion where the gears mesh) of the pair of helical gears G1 and G2. In addition, Figure 1 An oil introduction pipe (not shown) for introducing the lubricating oil composition into the tank is connected to the tank 40 shown, and it is designed to be able to introduce a necessary amount of the lubricating oil composition into the tank. In addition, Figure 1 The arrow A1 in indicates schematically the moving direction of the lubricating oil composition when it moves in the supply pipe 41. The specifications of the gears for such a test device are shown in Table 2.

[0115] Table 2

[0116]

[0117] (Regarding the test conditions)

[0118] Next, the test conditions and the like will be described. That is, it operates under the conditions shown below Figure 1The test device of the helical gear mechanism shown measures the input torque [unit: Nm] and the output torque [unit: Nm] respectively, and calculates the following formula (1’) based on the measured values and the rotational speeds of the respective rotating shafts on the input side (driving side) and the output side (absorbing side) to obtain the power transmission efficiency (gear efficiency).

[0119] [Power transmission efficiency (%)] = {(T2 × n2) / (T1 × n1)} × 100 (1’)

[0120] [In formula (1’), T1 represents the input torque (driving torque), n1 represents the rotational speed of the helical gear G1 on the input side (driving speed), T2 represents the output torque (absorbing torque), and n2 represents the rotational speed of the helical gear G2 on the output side (absorbing speed).]

[0121] The measurement of the power transmission efficiency as described above is carried out 2 times after changing the test conditions (operating conditions of the above test device) regarding the test temperature (temperature at the time of supplying the lubricating oil composition: supply oil temperature), rotational speed (rotational speed of the rotating shaft 11 (input side: driving side)), and load (load applied to the tooth surface of the helical gear G2 (output side)). In addition, in each test, the supply speed of the lubricating oil composition to the contact part (meshing part of the gears) of the pair of helical gears G1 and G2 in the above test device is set to 1.0 L / minute (the same). The following are the test conditions adopted in each test.

[0122] [Test conditions adopted in test (A)]

[0123] Test temperature (supply oil temperature): 120 °C, rotational speed (input side): 3000 rpm, load (output side): 30 Nm, supply speed of lubricating oil composition: 1.0 L / minute

[0124] [Test conditions adopted in test (B)]

[0125] Test temperature (supply oil temperature): 120 °C, rotational speed (input side): 2000 rpm, load (output side): 50 Nm, supply speed of lubricating oil composition: 1.0 L / minute.

[0126] The results (power transmission efficiency of each example, etc.) obtained through the above helical gear test are shown in Table 3. The types and contents of the low molecular weight polymer components used are also shown. In addition, in Table 3, the increase in the power transmission efficiency of each example, etc. (increase relative to the reference value: difference from the power transmission efficiency of Comparative Example 1: efficiency increase value) and its average value are shown when the power transmission efficiency of Comparative Example 1 is used as the reference value.

[0127]

[0128] It is clearly understood from the results of the FZG spur gear tests shown in Table 3 that, from the viewpoint of the power transmission efficiency of spur gears, there is no difference between the lubricating oil compositions obtained in Examples 1 to 4 and the lubricating oil compositions obtained in Comparative Examples 1 and 4 to 5, and the power transmission efficiencies are equal values. Thus, it can be known that, from the viewpoint of the power transmission efficiency of spur gears, the lubricating oil compositions obtained in Examples 1 to 4 and the lubricating oil composition obtained in Comparative Example 1 serving as a reference have achieved the same effects.

[0129] In contrast, it is also clearly understood from the results of the helical gear tests shown in Table 3 that, with respect to the lubricating oil compositions obtained in Examples 1 to 4, regardless of the test conditions of Test (A) and Test (B), the increase amount (efficiency increase value) of the power transmission efficiency with respect to the lubricating oil composition obtained in Comparative Example 1 serving as a reference is 0.1 or more. In addition, it is also known from the results of the helical gear tests shown in Table 3 that, regarding the average value of the increase amount (efficiency increase value) of the power transmission efficiency of both Test (A) and Test (B), the lubricating oil compositions obtained in Examples 1 to 4 are all 0.2, while the maximum of the lubricating oil compositions obtained in Comparative Examples 1 to 5 is 0.1. Furthermore, it is also known that since the power transmission efficiency of the lubricating oil composition obtained in Comparative Example 1 is at a high level of 99.4% in both Test (A) and Test (B), by setting the increase amount of the power transmission efficiency compared with this power transmission efficiency to be 0.1 or more, that is, by increasing the power transmission efficiency by 0.1% or more compared with Comparative Example 1, the degree of reducing the loss torque in the gear mechanism becomes large enough. If the increase amount of the power transmission efficiency based on Comparative Example 1 reaches 0.1 or more in each test, it can be determined that the power transmission efficiency of the helical gear mechanism can be sufficiently improved. From the confirmation from the above viewpoints, it can be known that the lubricating oil compositions (Examples 1 to 4) of the present invention have an increase amount (efficiency increase value) of the power transmission efficiency with respect to the lubricating oil composition obtained in Comparative Example 1 serving as a reference of 0.1 or more in both Test (A) and Test (B), and the average value of the increase amount (efficiency increase value) of the power transmission efficiency of both Test (A) and Test (B) is a value exceeding 0.1 (0.2). Therefore, under the severe use conditions of the conditions of a temperature of 120°C, a load of 30 Nm, and a rotational speed of 3000 rpm (Test (A)) and the conditions of a temperature of 120°C, a load of 50 Nm, and a rotational speed of 2000 rpm (Test (B)), the power transmission efficiency of the helical gear mechanism can be sufficiently improved.

[0130] Furthermore, it is also clearly understood from the results shown in Table 3 that, particularly in Test (B) under the high load condition where the load (output side) is 50 Nm, the increase in the power transmission efficiency (efficiency increase value) of the lubricating oil compositions obtained in Examples 1 to 4 all reached 0.2 or more, while the increase in the power transmission efficiency (efficiency increase value) of the lubricating oil compositions obtained in Comparative Examples 1 to 5 were all 0. Therefore, when the lubricating oil composition of the present invention (Examples 1 to 4) is used in a helical gear mechanism, under high temperature and high load conditions, particularly under conditions where the load on the output side gear becomes higher, the power transmission efficiency of the helical gear mechanism can be increased to a higher level.

[0131] Industrial applicability

[0132] As described above, according to the present invention, a lubricating oil composition can be provided which, when used in a helical gear mechanism, can sufficiently increase the power transmission efficiency particularly under severe conditions of high temperature and high load. Therefore, the lubricating oil composition of the present invention can be suitably used for various devices using a helical gear mechanism, and is particularly useful for various automotive transmissions (automatic transmissions, manual transmissions, etc.), speed reducers, etc. including electric vehicles and hybrid vehicles.

Claims

1. A lubricating oil composition containing 0.1 to 3.0% by mass of an ethylene-propylene copolymer having a weight average molecular weight of 6,000 to 13,000, and being a lubricating oil composition for a helical gear mechanism, The content of the structural unit derived from ethylene in the ethylene-propylene copolymer is 30 to 80 mol%, The kinematic viscosity at 80 °C of the lubricating oil base oil contained in the lubricating oil composition is 2.0 to 7.0 mm 2 / s. The lubricating oil base oil contains 80% by mass or more of a mineral oil base oil satisfying the condition of API classification as Group II or Group III based on the total amount of the lubricating oil base oil, The density of the lubricating base oil at 15 °C is 0.800 to 0.850 g / cm 3 , The kinematic viscosity of the lubricating oil composition at 40 °C is 9.0 to 20.0 mm 2 / s.

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