Lubricating oil composition

Abstract

A lubricating oil composition having a kinematic viscosity at 80 °C of 7.0 mm2 / s or less, a product of the kinematic viscosity at 80 °C and the traction coefficient at 80 °C of 0.110 or less, and being 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] Conventionally, in gear mechanisms for power transmission mechanisms and the like, various lubricating oil compositions have 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 for a transmission with a kinematic viscosity at 100°C of 2.5 mm 2 / s to 3.8 mm 2 / s is disclosed. Further, in the examples section of International Publication No. 2013 / 147162 (Patent Document 2), a lubricating oil composition with a kinematic viscosity at 100°C of 6.0 mm 2 / s and a traction coefficient at 40°C of 0.008 or 0.006 is disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2013 / 136582

[0006] Patent Document 2: International Publication No. 2013 / 147162 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a lubricating oil composition that can sufficiently improve the power transmission efficiency during high-speed rotation particularly within a wide temperature range when used in a helical gear mechanism.

[0009] Means for Solving the Problems

[0010] The inventors of the present invention conducted repeated studies and found that: the conventional lubricating oil compositions described in Patent Documents 1 to 2 can sufficiently improve the power transmission efficiency when used in a spur gear mechanism, but when directly used in a helical gear (helical gear: spiral gear) mechanism, they may not necessarily sufficiently improve the power transmission efficiency during high-speed rotation. Further, even considering the known technologies such as Patent Documents 1 to 2, it is not easy for those skilled in the art to conceive that: the effects of improving the power transmission efficiency tend to be different when used in a spur gear mechanism and when used in a helical gear mechanism.

[0011] Based on the above understanding, the inventors of the present invention repeatedly conducted in-depth research and found that: by making the kinematic viscosity of the lubricating oil composition at 80°C 7.0 mm 2 / second or less, and making the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C 0.110 or less for the lubricating oil composition, when the lubricating oil composition satisfying this condition is used in a helical gear mechanism, particularly, the power transmission efficiency during high-speed rotation can be sufficiently improved within a wide temperature range of 20°C to 140°C (more preferably 40 to 120°C), thus completing the present invention.

[0012] That is, the lubricating oil composition of the present invention is as described below.

[0013] 〔1〕A lubricating oil composition having a kinematic viscosity at 80°C of 7.0 mm 2 / second or less, the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C being 0.110 or less, and being a lubricating oil composition for a helical gear mechanism.

[0014] 〔2〕The lubricating oil composition according to the above 〔1〕, wherein the kinematic viscosity at 80°C of the lubricating base oil contained in the lubricating oil composition is 2.0 to 6.0 mm 2 / second.

[0015] 〔3〕The lubricating oil composition according to the above 〔1〕 or 〔2〕, wherein the lubricating base oil contained in the lubricating oil composition contains 60% by mass or more of a mineral oil-based base oil satisfying all of the following conditions (A) to (C) based on the total amount of the lubricating base oil:

[0016] (A) API classification is Group II or Group III,

[0017] (B) The concentration of sulfur component is 200 mass ppm or less,

[0018] (C) The concentration of nitrogen component is 500 mass ppm or less.

[0019] 〔4〕The lubricating oil composition according to any one of the above 〔1〕 to 〔3〕, wherein the density at 15°C of the lubricating base oil contained in the lubricating oil composition is 0.800 to 0.850 g / cm 3 .

[0020] 〔5〕The lubricating oil composition according to any one of the above 〔1〕 to 〔4〕, which contains a viscosity modifier.

[0021] 〔6〕The lubricating oil composition according to the above 〔5〕, wherein the viscosity modifier is a polymer having a weight average molecular weight of 5000 to 20000.

[0022] Advantages of the Invention

[0023] According to the present invention, a lubricating oil composition can be provided which, when used in a helical gear mechanism, can particularly sufficiently improve the power transmission efficiency during high-speed rotation within a wide temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a 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.

[0025] REFERENCE SIGNS

[0026] 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

[0027] 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.

[0028] <Lubricating Oil Composition>

[0029] The kinematic viscosity of the lubricating oil composition of the present invention at 80°C is 7.0 mm 2 / s or less, the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C is 0.110 or less, and it is a lubricating oil composition for a helical gear mechanism.

[0030] The lubricating oil composition of the present invention needs to satisfy the condition that the kinematic viscosity at 80°C is 7.0 mm 2 / s or less (hereinafter, this condition may be sometimes simply referred to as "Condition (I)"). The kinematic viscosity at 80°C of such a lubricating oil composition is more preferably 3.0 to 7.0 mm 2 / s, and further preferably 3.5 to 6.0 mm 2 / s. By having a kinematic viscosity at 80°C of 7.0 mm 2Less than [X] per second, it can sufficiently improve the power transmission efficiency during high-speed rotation within a wide temperature range. In addition, when the kinematic viscosity at 80 °C is above the above lower limit, compared with the case below the above lower limit, the oil film formation property and oil film retention property of the lubricating oil composition at the lubricated part can be further improved, and a better lubrication state can be maintained within a wide temperature range. 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.

[0031] In addition, the lubricating oil composition of the present invention needs to satisfy the condition that the product of the kinematic viscosity at 80 °C and the traction coefficient at 80 °C is 0.110 or less (hereinafter sometimes abbreviated as "Condition (II)"). For the lubricating oil composition of the present invention, the product of the kinematic viscosity at 80 °C and the traction coefficient at 80 °C is more preferably 0.035 to 0.110. By the product value being 0.110 or less as described above, the power transmission efficiency during high-speed rotation (preferably when the rotational speed (rotating speed) is about 3000 to 10000 rpm) can be sufficiently improved within a wide temperature range (preferably 40 to 120 °C). In addition, when the product value is above the above lower limit, compared with the case below the above lower limit, the oil film formation property and oil film retention property of the lubricating oil composition at the lubricated part can be further improved, and a better lubrication state can be maintained within a wide temperature range. In addition, in this specification, as the "traction coefficient at 80 °C", the value measured under the conditions of using an EHL tester (tester "EHD2" manufactured by PCS Instruments), using a steel disk and a steel ball as components, at a temperature of 80 °C, a load of 40 N, a circumferential speed (average speed) of 1 m / s, and a slip ratio (SRR) of 10% is adopted.

[0032] In addition, the traction coefficient at 80 °C of the lubricating oil composition of the present invention is preferably 0.0300 or less, and more preferably 0.0100 to 0.0250. When the traction coefficient at 80 °C is below the above upper limit, compared with the case exceeding the above upper limit, the power transmission efficiency during high-speed rotation can be further improved within a wide temperature range (preferably 40 to 120 °C). On the other hand, when the traction coefficient at 80 °C is above the above lower limit, compared with the case below the above lower limit, the oil film formation property and oil film retention property of the lubricating oil composition at the lubricated part can be further improved, and a better lubrication state can be maintained within a wide temperature range.

[0033] In addition, the kinematic viscosity at 40 °C of the lubricating oil composition of the present invention is preferably 8.0 to 20.0 mm2 per second, more preferably 9.0 to 18.0 mm 2 per second. When the kinematic viscosity at 40°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, especially in a relatively low temperature range around 40°C (preferably about 20 to 60°C), the power transmission efficiency can be further improved. On the other hand, when the kinematic viscosity at 40°C is above the above lower limit, compared with the case where it is below the above lower limit, especially in a relatively low temperature range around 40°C (preferably about 20 to 60°C), the oil film formability and oil film retention of the lubricating oil composition at the lubricating part can be further improved, and a better lubricating state can be maintained. In addition, in this specification, the "kinematic viscosity at 40°C" refers to the kinematic viscosity at 40°C measured according to JIS K2283-2000 using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) as the measuring device.

[0034] In addition, the kinematic viscosity of the lubricating oil composition of the present invention at 120°C is preferably 1.5 to 3.5 mm 2 per second, more preferably 1.8 to 3.2 mm 2 per second. 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 relatively high temperature range around 120°C (preferably about 100 to 140°C). In addition, 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 relatively high temperature range around 120°C (preferably about 100 to 140°C), the oil film formability and oil film retention of the lubricating oil composition at the lubricating part can be further improved, and a better lubricating state can be maintained. In addition, in this specification, the "kinematic viscosity at 120°C" refers to the kinematic viscosity at 120°C measured according to JIS K2283-2000 using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) as the measuring device.

[0035] 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 above 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 lubricating oil composition can be further reduced, and the power transmission efficiency can be further improved in a wide temperature range. In addition, the "viscosity index" in this specification refers to the viscosity index measured according to JIS K 2283-2000.

[0036] Furthermore, 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 to the case where it exceeds the above upper limit. In addition, in this specification, the "pour point" refers to the pour point measured according to JIS K 2269-1987.

[0037] The lubricating oil composition of the present invention can be designed to satisfy the above conditions (I) and (II). For example, while selecting the type of lubricating oil base oil, other components are appropriately selected and combined according to the type of the lubricating oil base oil to satisfy the above conditions (I) and (II), whereby a lubricating oil composition can be prepared. Hereinafter, the components suitable for use in the lubricating oil composition of the present invention as described above will be described.

[0038] <Lubricating oil base oil>

[0039] As the lubricating oil base oil contained in the lubricating oil composition of the present invention, the kinematic viscosity at 80°C is preferably 2.0 to 6.0 mm 2 / s (more preferably 3.0 to 5.9 mm 2 / s, particularly preferably 3.0 to 5.2 mm 2 / s). When the kinematic viscosity of the lubricating oil base oil at 80°C is below the above upper limit, it becomes easier to design a composition that satisfies the above conditions (I) and (II) compared to the case where it exceeds the above upper limit. On the other hand, when the kinematic viscosity at 80°C is above the above lower limit, the oil film formation property and oil film retention property of the lubricating oil composition at the lubricated part can be further improved, and a better lubrication state can be maintained in a wide temperature range.

[0040] In addition, as the above lubricating oil base oil, it is preferably a mineral oil-based base oil that satisfies the condition (A) of being classified as Group II or Group III by API (American Petroleum Institute: American Petroleum Institute) (referred to as "API" classification in this specification). In addition, the base oil classified as Group II by API is a mineral oil-based base oil with a sulfur content of 0.03 mass% or less, a saturated component (saturated hydrocarbon) of 90 volume% or more, and a viscosity index of 80 or more but less than 120. In addition, the base oil classified as Group III by API is a mineral oil-based base oil with a sulfur content of 0.03 mass% or less, a saturated component (saturated hydrocarbon) of 90 volume% or more, and a viscosity index of 120 or more.

[0041] In addition, as the above lubricating oil base oil, it is preferably a base oil (more preferably a mineral oil-based base oil) that satisfies condition (B) where the concentration of sulfur components is 200 mass ppm or less (more preferably 100 mass ppm or less, still more preferably 1 mass ppm or less). When the concentration of sulfur components is below the above upper limit, a composition with more excellent thermal and oxidation stability can be obtained. In addition, in this specification, the "concentration of sulfur components" refers to the value measured according to JIS K 2541-6-2003 (ultraviolet fluorescence method).

[0042] In addition, as the above lubricating oil base oil, it is preferably a base oil (more preferably a mineral oil-based base oil) that satisfies condition (C) where the concentration of nitrogen components is 500 mass ppm or less (more preferably 300 mass ppm or less, still more preferably 100 mass ppm or less, particularly preferably 1 mass ppm or less). When the concentration of nitrogen components is below the above upper limit, a composition with more excellent thermal and oxidation stability can be obtained. In addition, in this specification, the "concentration of nitrogen components" refers to the value measured according to JIS K2609-1998 (chemiluminescence method).

[0043] In addition, as the above lubricating oil base oil, it is more preferably a mineral oil-based base oil that satisfies all of the above conditions (A) to (C). In addition, when the above lubricating oil base oil contains a mineral oil-based base oil that satisfies all of the above conditions (A) to (C), as its content, it is preferably 60 mass% or more (more preferably 80 mass% or more) based on the total amount of the above lubricating oil base oil. By using a lubricating oil base oil containing a mineral oil-based base oil that satisfies all of the above conditions (A) to (C), it is possible to more easily design a lubricating oil composition that satisfies the above condition (I) and the above condition (II).

[0044] In addition, as the above lubricating oil base oil, the density at 15°C is preferably 0.800 to 0.850 g / cm 3 (more preferably 0.805 to 0.845 g / cm 3 ). When the density at 15°C is below the above upper limit, the thermal and oxidation stability is further improved compared to the case where it exceeds the above upper limit. On the other hand, when the density at 15°C is above the above lower limit, the heat transfer characteristics are more excellent compared to the case where it is below the above lower limit, 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.

[0045] 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, compared with the case where it exceeds the above upper limit, since the content of normal paraffins in the base oil is less, a sharp increase in viscosity at low temperatures can be 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 in a wide temperature range (preferably 40 to 120 °C).

[0046] In addition, as the above lubricating oil base oil, the kinematic viscosity at 80 °C is preferably 2.0 to 6.0 mm 2 / s, and the density at 15 °C is 0.800 to 0.850 g / cm 3 , and a mineral oil-based base oil that satisfies all of the above conditions (A) to (C) (hereinafter, this mineral oil-based base oil may sometimes be referred to as "mineral oil-based base oil (I)").

[0047] Furthermore, as the entire lubricating oil base oil, such a lubricating oil base oil as described above may be composed of a single base oil component, or may also contain multiple base oil components. For example, in the lubricating oil composition of the present invention, when using the above mineral oil-based base oil (I) as the above lubricating oil base oil, a product prepared by appropriately combining two or more base oil components selected from the mineral oil-based base oils of Group II and Group III of the API classification in the following manner may also be used: the kinematic viscosity at 80 °C is 2.0 to 6.0 mm 2 / s, and the density at 15 °C is 0.800 to 0.850 g / cm 3 , and all of the above conditions (A) to (C) are satisfied. In this way, the above lubricating oil base oil can also appropriately combine and utilize two or more base oil components so as to satisfy the above various conditions (kinematic viscosity at 80 °C, viscosity index, etc.).

[0048] 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 99% by mass, particularly preferably 80 to 99% 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 is easier to use additives to improve characteristics such as the formation of a lubricating coating film. 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, and it is easier for the lubricating oil composition to satisfy condition (I).

[0049] <Viscosity modifier>

[0050] As the lubricating oil composition of the present invention, under the condition of a relatively high temperature near 120 °C (preferably about 100 - 140 °C), the power transmission efficiency of the helical gear mechanism can be further improved. Therefore, it is preferably to contain a viscosity modifier while containing the above-mentioned lubricating oil base oil. Such a viscosity modifier is not particularly limited, and known compounds used as viscosity modifiers in the field of lubricating oil compositions can be appropriately used. For example, low molecular weight polymers with a weight average molecular weight (Mw) of 100,000 or less can be appropriately used. In addition, among the above-mentioned viscosity modifiers, from the viewpoint of shear stability, polymers with a weight average molecular weight of 5000 - 20,000 (more preferably 6000 - 15,000) are preferred. In addition, as the polymer with a weight average molecular weight of 5000 - 20,000 used for the viscosity modifier, an ethylene-propylene copolymer is more preferred. In addition, the ethylene-propylene copolymer can be a block copolymer or a random copolymer. In addition, as the viscosity modifier, commercially available products can also be used. In addition, the viscosity modifier can be used alone in one kind, or two or more kinds can be used in combination. Furthermore, the weight average molecular weight of the polymer refers to the value measured by gel permeation chromatography (GPC) (weight average molecular weight obtained by conversion with standard polystyrene). The measurement conditions of this GPC are as described below.

[0051] [GPC Measurement Conditions]

[0052] Apparatus: ACQUITY (registered trademark) APC UV RI system manufactured by Waters Corporation

[0053] Columns: Two ACQUITY (registered trademark) APC XT900A (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 order from the upstream side.

[0054] Column temperature: 40 °C

[0055] Sample solution: Tetrahydrofuran solution with a sample concentration of 1.0 mass%

[0056] Solution injection volume: 20.0 μL

[0057] Detection device: Differential refractive index detector

[0058] Reference substance: Standard polystyrene (gilent EasiCal® PS-1 manufactured by Agilent Technologies), 8 points (molecular weights: 2,698,000, 597,500, 290,300, 133,500, 70,500, 30,230, 9,590, 2,970)

[0059] Under the above conditions, GPC measurement is performed. When the weight-average molecular weight is 10,000 or more, the measurement is directly terminated. On the other hand, when the weight-average molecular weight is less than 10,000, except for changing the chromatographic column and the reference substance to the following substances, re-measurement is performed under the same conditions as the above conditions.

[0060] Chromatographic column: One ACQUITY® APC XT125A (gel particle size 2.5 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation and two ACQUITY® APC XT45A (gel particle size 1.7 μm, column size (inner diameter × length) 4.6 mm × 150 mm) manufactured by Waters Corporation are connected in series in order from the upstream side.

[0061] Reference substance: Standard polystyrene (Agilent EasiCal® PS-1 manufactured by Agilent Technologies), 10 points (molecular weights: 30,230, 9,590, 2,970, 890, 786, 682, 578, 474, 370, 266).

[0062] In addition, when a viscosity modifier is used, its content is not particularly limited, but it is preferably 0.1 to 10.0% by mass (more preferably 0.15 to 5.0% by mass) based on the total amount of the above lubricating oil composition. When the content of the viscosity modifier is below the above upper limit, the shear stability becomes better than when it exceeds the above upper limit; on the other hand, when the content of the viscosity modifier is above the above lower limit, the power transmission efficiency of the helical gear mechanism can be further improved under conditions of a relatively high temperature near 120 °C (preferably about 100 to 140 °C) compared to when it is below the above lower limit.

[0063] <Wear-resistant agent>

[0064] As the lubricating oil composition of the present invention, from the viewpoint of further improving the performance of preventing metal contact at the friction surfaces of gears with each other, an antiwear agent is preferably contained. As such an antiwear agent, there is no particular limitation, and known compounds used as antiwear agents in the field of lubricating oil compositions can be appropriately used (see, for example, Japanese Patent Application Laid-Open No. 2003-155492, Japanese Patent Application Laid-Open No. 2020-76004, International Publication No. 2013 / 147162, etc.).

[0065] In addition, as the above antiwear agent, for example, sulfur-based, phosphorus-based or sulfur-phosphorus-based antiwear agents can be used. In addition, as such sulfur-based, phosphorus-based or sulfur-phosphorus-based antiwear agents, phosphites, thiophosphites, dithiophosphites, trithiophosphites, phosphates, thiophosphates, dithiophosphates, trithiophosphates, their amine salts, their metal salts, their derivatives, dithiocarbamates, zinc dithiocarbamates, disulfides, polysulfides, sulfurized olefins, sulfurized oils and fats, etc. can be cited. Among the above 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 more preferred. As such phosphorus-based or sulfur-phosphorus-based antiwear agents, an antiwear agent with a phosphorus atom (P) content of 2.0 to 35.0% by mass is preferred. In addition, the antiwear agent can be used alone as one kind, or two or more kinds can be used in combination.

[0066] When using an 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, compared with the case where it exceeds the above upper limit, the thermal and oxidation stability can be further improved. On the other hand, when the content of the antiwear agent is above the above lower limit, compared with the case where it is below the above lower limit, the wear resistance of the lubricating oil composition can be further improved, and the power transmission efficiency can be further improved even under high load conditions.

[0067] <Dispersant>

[0068] As the lubricating oil composition of the present invention, from the viewpoint of enabling the metal powder generated by wear during use to be more highly dispersed and maintaining the lubricating performance sufficiently for a longer period, a lubricating oil composition containing an ashless dispersant is preferred. As such an ashless dispersant, known compounds used as ashless dispersants in the field of lubricating oil compositions can be appropriately used (see, for example, Japanese Patent Application Laid-Open No. 2003-155492, Japanese Patent Application Laid-Open No. 2020-76004, International Publication No. 2013 / 147162, etc.). As such an ashless dispersant, for example, mono- or bis-succinimides having at least 1 linear or branched alkyl or alkenyl group in the molecule, benzylamines having at least 1 alkyl or alkenyl group in the molecule, or polyamines having at least 1 alkyl or alkenyl group in the molecule, or modified products thereof with boron compounds, carboxylic acids, phosphoric acids, etc. can be cited. In addition, in such an ashless dispersant, the above-mentioned linear or branched alkyl or alkenyl group is preferably a linear or branched alkyl or alkenyl group having 40 to 400 carbon atoms (more preferably 60 to 350 carbon atoms). Further, as such an ashless dispersant, from the viewpoint of imparting better dispersibility to metal powder, etc., non-boronated succinimides (such as the above-mentioned mono- or bis-succinimides), boronated succinimides (boron-modified compounds of the above-mentioned mono- or bis-succinimides), and mixtures thereof can be preferably used. In addition, as the non-boronated succinimide, boronated succinimide, or a mixture thereof, the content of nitrogen atoms is preferably 0.5 to 3.0% by mass. In addition, the ashless dispersant can be used alone or in combination of two or more kinds.

[0069] When using an 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-mentioned lubricating oil composition. When the content of the ashless dispersant is below the above upper limit, compared with the case where it exceeds the above upper limit, since the viscosity increase of the lubricating oil composition can be more sufficiently suppressed, it becomes easier to obtain a lubricating oil composition that satisfies condition (I). On the other hand, when the content of the ashless dispersant is above the above lower limit, compared with the case where it is below the above lower limit, the effect of further improving the lubricating performance maintained sufficiently for a long time can be achieved.

[0070] <Other additives>

[0071] In the lubricating oil composition of the present invention, in addition to containing the above components (the above lubricating oil base oil, the above viscosity modifier, the above antiwear agent, and the above ashless dispersant), in order to further improve its performance, other commonly used additives may be appropriately contained in the lubricating oil composition according to the purpose. As such other additives, there is no particular limitation, and known additives used in the field of lubricating oil compositions (for example, additives described in Japanese Patent Application Laid-Open No. 2003-155492, International Publication No. 2017 / 073748, Japanese Patent Application Laid-Open No. 2020-76004, etc.) can be appropriately used. In addition, as such other additives, additives such as pour point depressants, friction modifiers, metal detergents, antioxidants, metal deactivators, rubber swelling agents, defoamers, diluent oils, etc. can be cited.

[0072] As the above pour point depressant, for example, poly(meth)acrylate, ethylene-vinyl acetate copolymer, etc. can be cited, and among them, poly(methyl)acrylate is preferred. In addition, as the above poly(methyl)acrylate, from the viewpoints of pour point depressing action and shear stability, those having a weight average molecular weight of 20,000 to 100,000 are preferred. The pour point depressant can be used alone in one kind, or two or more kinds can be used in combination. When using a 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.

[0073] As the above friction modifier, there is no particular limitation, and for example, amine-based, amide-based, imide-based, fatty acid ester-based, fatty acid-based, aliphatic alcohol-based, aliphatic ether-based friction modifiers can be cited. As such a friction modifier, from the viewpoint of obtaining a higher friction reducing effect, amine-based friction modifiers are more preferred, and alkylamines and alkenylamines are further preferred. The friction modifier can be used alone in 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.

[0074] In addition, as the above metal detergent, there is no particular limitation, and for example, alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, etc. can be cited. The metal detergent can be used alone in 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.

[0075] In addition, there are no particular restrictions on the above-mentioned antioxidants, and examples thereof include phenolic antioxidants and amine 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.

[0076] In addition, there are no particular restrictions on the above-mentioned metal deactivators, and examples thereof include imidazoline, pyrimidine derivatives, alkyl thiadiazole, mercaptobenzothiazole, benzotriazole or its derivatives, tolyltriazole or its derivatives, 1,3,4-thiadiazole polysulfides, 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.

[0077] In addition, there are no particular restrictions on the above-mentioned rubber swelling agents, and known compounds that can be used as seal swelling agents for lubricating oils can be appropriately used. Examples thereof include ester-based, sulfur-based, aromatic-based seal swelling agents (such as 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 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.

[0078] In addition, examples of the above-mentioned defoaming agents include silicone oils 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 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.

[0079] In addition, the lubricating oil composition of the present invention can be prepared by the following steps: First, considering the characteristics of the lubricating oil base oil used, in a manner that satisfies the above conditions (I) and (II), for the lubricating oil base oil, components to be used (and their dosages are also appropriately designed) are appropriately selected from among the other components as described above (such as the above viscosity modifier, the above ashless dispersant, etc.) and added. In addition, when adding the other components as described above to the lubricating oil base oil, the other components can be added separately after being separately prepared for each component, or can be added after preparing a mixture of the other components. As a mixture of the other components as described above, commercially available packages (for example, additive packages containing ashless dispersants, metal detergents, antioxidants, friction modifiers, antiwear agents, rubber swelling agents, metal deactivators, diluting components (diluting oils), etc.) can also be appropriately utilized.

[0080] Examples

[0081] 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.

[0082] [Components used in each example, etc.]

[0083] The lubricating oil base oils and additives used in each example, etc. are as follows. In addition, the density of the lubricating oil base oils shown below is the density at 15°C. Sometimes, the "kinematic viscosity at 80°C" is expressed as "kinematic viscosity (80°C)" or "80°C kinematic viscosity", and in addition, "ppm" regarding the concentrations of sulfur components and nitrogen components is parts per million by mass (mg / kg).

[0084] (1) Lubricating oil base oil

[0085] (Lubricating oil base oil used in the examples)

[0086] [Mineral oil (A)] Kinematic viscosity at 80°C: 3.61 mm 2 / s, sulfur component: less than 1 ppm, nitrogen component: less than 1 ppm, API classification: Group II (mineral oil), density: 0.837 g / cm 3

[0087] [Mineral oil (B)] Kinematic viscosity at 80°C: 4.96 mm 2 / s, sulfur component: less than 1 ppm, nitrogen component: less than 1 ppm, API classification: Group III (mineral oil), density: 0.815 g / cm 3

[0088] [Mineral oil (C)] Kinematic viscosity at 80°C: 3.79 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group III (mineral oil), density: 0.809 g / cm 3

[0089] [Mineral oil (D)] Kinematic viscosity at 80°C: 3.13 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group II (mineral oil), density: 0.830 g / cm 3

[0090] [Lubricating oil base oil used in the comparative example]

[0091] [Mineral oil (E)] Kinematic viscosity at 80°C: 6.70 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group III (mineral oil), density: 0.836 g / cm 3

[0092] [Mineral oil (F)] Kinematic viscosity at 80°C: 4.86 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group II (mineral oil), density: 0.836 g / cm 3

[0093] [Mineral oil (G)] Kinematic viscosity at 80°C: 6.31 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group III (mineral oil), density: 0.834 g / cm 3

[0094] [Mineral oil (H)] Kinematic viscosity at 80°C: 5.75 mm 2 / sec, sulfur content: less than 1 ppm, nitrogen content: less than 1 ppm, API classification: Group III (mineral oil), density: 0.826 g / cm 3 .

[0095] (2) Additives

[0096] [Viscosity modifier]

[0097] Ethylene-propylene copolymer (weight-average molecular weight: 11,500)

[0098] [Anti-wear agent]

[0099] Phosphite (phosphorus atom content: 7.3 mass%)

[0100] [Ashless dispersant]

[0101] Non-boronated succinimide (nitrogen atom content: 1.3% by mass)

[0102] [Pour point depressant]

[0103] Polymethacrylate (non-dispersive, weight average molecular weight: 50,000)

[0104] [Additive package]

[0105] A package containing the following components: ashless dispersant (a mixture of non-boronated succinimide and boronated succinimide); metal 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.

[0106] (Examples 1 to 11 and Comparative Examples 1 to 4)

[0107] Use each component according to the composition shown in Table 1 below to prepare a lubricating oil composition. In addition, "-" in Table 1 indicates that the component is 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 oils (A) to (H) relative to the total amount of the lubricating oil base oil, and the unit of "mass %" for the content of the additives represents the content (mass %) of each additive relative to the total amount of the lubricating oil composition. In Table 1, the kinematic viscosities at various temperatures (40°C, 80°C, 120°C), the traction coefficient at 80°C, and the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C, which were measured for each of the lubricating oil compositions of Examples 1 to 11 and Comparative Examples 1 to 4 as described below, are also shown.

[0108] The "kinematic viscosity" is measured at each temperature (40°C, 80°C, 120°C) using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Company) as the measuring device in accordance with JIS K 2283-2000.

[0109] The "traction coefficient at 80°C" is measured using an EHL test machine (test machine "EHD2" manufactured by PCS Instruments) as the measuring device, with steel disks and steel balls as components, under the conditions of a temperature of 80°C, a load of 40 N, a circumferential speed (average speed) of 1 m / s, and a slip ratio (SRR) of 10%.

[0110]

[0111] [Regarding the characteristics of the lubricating oil compositions obtained in Examples 1 to 11 and Comparative Examples 1 to 4]

[0112] The lubricating oil compositions obtained in Examples 1 to 11 and Comparative Examples 1 to 4 were used to evaluate the properties as described below.

[0113] <Measurement test of power transmission efficiency in a spur gear mechanism: FZG spur gear test>

[0114] Except for adopting different conditions at the points described below, the same method as that 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, a power circulation type FZG spur gear test device was used as the test device, 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. Under these test conditions, the above test device was operated, 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 column "Vc) Steady-state-temperature" in Chapter 7.4 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 torque loss" 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 that described in Reference Document 1 was adopted otherwise. The results obtained through the above measurements 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 taking the power transmission efficiency of Comparative Example 1 as the reference value is also shown.

[0115] [Power transmission efficiency (%)] = {(T in - T out ) / T in} × 100 (1)

[0116] 〔In formula (1), T inIndicates the input torque, T out Indicates the loss torque.

[0117] <Measurement Test of Power Transmission Efficiency in Helical Gear Mechanism: Helical Gear Test>

[0118] Use Figure 1 The test device of the helical gear mechanism schematically shown in, a lubricating oil composition at each temperature of 40 °C, 80 °C, and 120 °C is supplied to a pair of helical gears, and the power transmission efficiency (gear efficiency) is obtained respectively. Hereinafter, the test device and test conditions will be described respectively.

[0119] (Regarding the test device)

[0120] 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 arranged inside, 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.

[0121] Table 2

[0122]

[0123] (Regarding the test conditions)

[0124] 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. According to the measured values and the rotational speeds of the respective rotating shafts on the input side (driving side) and the output side (absorbing side), the following formula (1’) is calculated to obtain the power transmission efficiency (gear efficiency).

[0125] [Power transmission efficiency (%)] = {(T2 × n2) / (T1 × n1)} × 100 (1’)

[0126] 〔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).〕

[0127] The measurement of the power transmission efficiency as described above was carried out 3 times while changing the test temperature (for convenience, the above 3 measurement tests are hereinafter referred to as test (A), test (B), or test (C)). In addition, at each measurement of the above tests (A) to (C), the temperature at the time of supplying the lubricating oil composition (supply oil temperature: test temperature) was set to 40 °C for test (A), 80 °C for test (B), and 120 °C for test (C). Furthermore, at each measurement of tests (A) to (C), the lubricating oil composition was supplied to the contact part (meshing part of the gears) of a pair of helical gears G1 and G2 at 1.0 L / min. At the same time, the test device ( Figure 1 ) was operated under the following conditions: the rotational speed of the rotating shaft 11 (input side: driving side) became 6000 rpm (the rotational speed common to each test), and the load applied to the tooth surface of the helical gear G2 (output side) became 10 Nm (the load common to each test). The results obtained through the above measurements (the power transmission efficiency of each example, etc.) are shown in Table 3. In addition, in Table 3, the increase in the power transmission efficiency of each example, etc. (the increase relative to the reference value: the difference from the power transmission efficiency of Comparative Example 1: efficiency increase value) when the power transmission efficiency of Comparative Example 1 is used as the reference value is also shown.

[0128]

[0129] It is clearly known from the results of the FZG spur gear test shown in Table 3 that from the viewpoint of the power transmission efficiency of spur gears, there is no significant difference between the lubricating oil compositions obtained in Examples 1 to 11 and the lubricating oil compositions obtained in Comparative Examples 1 and 4, and the power transmission efficiencies are approximately the same values.

[0130] In contrast, it is also clearly known from the results of the helical gear tests shown in Table 3 that the average value of the increase in power transmission efficiency (efficiency increase value) in Tests (A) to (C) in the temperature range of 40°C to 120°C is 0.5 or more in the lubricating oil compositions obtained in Examples 1 to 11, while it is 0.3 or less in the lubricating oil compositions obtained in Comparative Examples 1 to 4. Additionally, considering that the power transmission efficiency of the lubricating oil composition obtained in Comparative Example 1 is 96.8% in Test (A), 97.5% in Test (B), and 98.0% in Test (C), it can be seen that when the average value of the increase in power transmission efficiency in Tests (A) to (C) based on Comparative Example 1 reaches 0.40 or more (more preferably 0.50 or more), by using this lubricating oil composition, compared with Comparative Example 1, in the wide temperature range of 40°C to 120°C, the loss torque of the helical gear mechanism during high-speed rotation is reduced to a greater extent, and the power transmission efficiency during high-speed rotation reaches a higher level. From this perspective, in the results of the above helical gear tests, when the average value of the increase in power transmission efficiency in Tests (A) to (C) based on Comparative Example 1 reaches 0.40 or more (more preferably 0.50 or more), it can be determined that this lubricating oil composition can sufficiently improve the power transmission efficiency of the helical gear mechanism during high-speed rotation in the wide temperature range of 40°C to 120°C. Therefore, from the results of the above helical gear tests, it can be seen that the kinematic viscosity at 80°C of the lubricating oil composition of the present invention (Examples 1 to 11) which is 7.0 mm 2 / s or less and the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C is 0.110 or less can sufficiently improve the power transmission efficiency of the helical gear mechanism during high-speed rotation in the wide temperature range of 40°C to 120°C.

[0131] In addition, since the lubricating oil compositions of Example 1 and Examples 4 and 10 have the same composition in aspects other than the viscosity modifier, by comparing them, it can be seen that when the viscosity modifier is used (Examples 4 and 10), a higher value of the increase in power transmission efficiency is obtained in Test (C) under the temperature condition of 120°C. Similarly, since Examples 3 and Example 5 have the same composition in aspects other than the viscosity modifier, by comparing them, it can be seen that when the viscosity modifier is used (Example 5), a higher value of the increase in power transmission efficiency is still obtained in Test (C) under the temperature condition of 120°C. From the above results, it can be seen that when the viscosity modifier is used (Examples 4 to 5, 10), compared with the case where the viscosity modifier is not used (Examples 1, 3), the power transmission efficiency can be further improved under the high temperature condition of 120°C. In addition, from the results shown in Table 1 and Table 3, when the viscosity modifier is used at a ratio of 2.0% by mass (Example 11), the increase in power transmission efficiency in Test (C) under the temperature condition of 120°C is 0.60.

[0132] From the above results, it can be seen that according to the lubricating oil composition of the present invention (Examples 1 to 11) having a kinematic viscosity at 80°C of 7.0 mm 2 / s or less and the product of the kinematic viscosity at 80°C and the traction coefficient at 80°C of 0.110 or less, when used in a helical gear mechanism, especially in a wide temperature range, the power transmission efficiency during high-speed rotation can be further improved.

[0133] Industrial Applicability

[0134] 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 improve the power transmission efficiency during high-speed rotation, especially in a wide temperature range. 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 for a helical gear mechanism, having a kinematic viscosity at 80 °C of 3.0 to 7.0 mm 2 / s, a traction coefficient at 80 °C of 0.0134 to 0.0300, and the product of the kinematic viscosity at 80 °C and the traction coefficient at 80 °C is 0.035 to 0.

110.

2. The lubricating oil composition according to claim 1, wherein the kinematic viscosity of the lubricating oil base oil contained in the lubricating oil composition at 80 °C is 2.0 to 6.0 mm 2 / s.

3. The lubricating oil composition according to claim 1 or 2, wherein the lubricating oil base oil contained in the lubricating oil composition contains 60% by mass or more, based on the total amount of the lubricating oil base oil, of a mineral oil base oil satisfying all of the following (A) to (C) conditions: (A) API classification is Group II or Group III, (B) the concentration of sulfur component is 200 mass ppm or less, (C) the concentration of nitrogen component is 500 mass ppm or less.

4. The lubricating oil composition according to claim 1 or 2, wherein the density of the lubricating oil base oil contained in the lubricating oil composition at 15 °C is 0.800 to 0.850 g / cm 3 .

5. The lubricating oil composition according to claim 1 or 2, which contains a viscosity modifier.

6. The lubricating oil composition according to claim 5, wherein, The viscosity modifier is a polymer having a weight average molecular weight of 5,000 to 20,000.

Images