Gear-type transmission for electromotive mobility, lubricating oil composition for gear-type transmission for electromotive mobility, and method for lubricating gear-type transmission for electromotive mobility using same

Abstract

This gear-type transmission for electromotive mobility comprises: a lubricating oil composition for lubricating sliding portions; and a joining part in which a form-in-place gasket containing silicone is used in at least a portion thereof as a sealing member for the lubricating oil composition. The lubricating oil composition contains specific components (A)-(F) and satisfies all specific conditions (i)-(vi).

Description

Geared transmission for electric mobility, lubricating oil composition for geared transmission for electric mobility, and lubricating method for geared transmission for electric mobility using the same

[0001] The present invention relates to a gear transmission for electric mobility, a lubricating oil composition for a gear transmission for electric mobility, and a method for lubricating a gear transmission for electric mobility using the same.

[0002] In the field of gear-type transmissions, such as reducers, step-up gears, and multi-speed transmissions that use gears, there has been a demand for lower viscosity lubricating oil compositions to improve fuel economy. In particular, gear-type transmissions (e.g., reducers for small, ultra-high speed motors) for electric mobility (e.g., electric vehicles such as electric cars) require further lower viscosity lubricating oil compositions to meet the demand for lower electricity costs. Furthermore, lubricating oil compositions used in gear-type transmissions for electric mobility are required to have not only lower electricity costs but also improved gear and bearing durability and high electrical insulation properties that can be used for direct cooling of the motors equipped in electric mobility.

[0003] In order to meet such demands, various lubricating oil compositions have been studied for use in gear-type transmissions for electric mobility.As an example of such a lubricating oil composition, for example, WO 2020 / 189580 (Patent Document 1) describes a lubricating oil composition for use in the powertrain of an electric vehicle, which comprises a lubricating oil base oil; an alkaline earth metal detergent in an amount of 10 mass ppm or more and 1000 mass ppm or less based on the total amount of the lubricating oil composition as an alkaline earth metal amount; a specific triazole compound in an amount of 0.005 mass% or more and 0.90 mass% or less based on the total amount of the lubricating oil composition; and a sulfur-containing heterocyclic ether compound. and sulfide compounds in an amount of 10 ppm by mass or more and 2000 ppm by mass or less in terms of sulfur content, based on the total amount of the lubricating oil composition; and an ashless dispersant in an amount of 0.010% by mass or more and 4.0% by mass or less, based on the total amount of the lubricating oil composition; and as a preferred embodiment, a lubricating oil composition is disclosed that further contains a phosphorus-based compound in an amount of 100 to 1500 ppm by mass in terms of elemental phosphorus, based on the total amount of the lubricating oil composition. Note that all of the compositions (Examples 1 to 31) disclosed as examples of lubricating oil compositions contain one type of phosphorus-based compound.

[0004] International Publication No. 2020 / 189580

[0005] However, even with the conventional lubricating oil composition as described in Patent Document 1, when used in a gear-type transmission for electric mobility (for example, a reducer for an electric vehicle) having a joint at least partly using a silicone-containing foam-in-place gasket (hereinafter, for convenience, the silicone-containing foam-in-place gasket may sometimes be referred to simply as a "silicone-containing FIPG") as a sealing member for the lubricating oil composition, there was room for improvement in terms of highly suppressing the deterioration of the silicone-containing FIPG during use of the gear-type transmission and limiting foaming during use to a specific level or below.

[0006] The present invention has been made in view of the problems associated with the prior art. It is an object of the present invention to (1) provide a geared transmission for electric mobility that can highly inhibit the deterioration of a silicone-containing FIPG caused by the lubricating oil composition when the geared transmission is in use, can keep foaming of the lubricating oil composition at or below a specific level when the geared transmission is in use, and can simultaneously achieve improved power consumption and improved fatigue life; (2) to provide a lubricating oil composition for a geared transmission for electric mobility that can highly inhibit the deterioration of a silicone-containing FIPG, can keep foaming during use at or below a specific level, has a low viscosity and can improve power consumption, while also improving extreme-pressure performance based on anti-wear performance and anti-seizure performance and fatigue life, and has the high level of electrical insulation required of a lubricating oil for electric mobility; and (3) to provide a method for lubricating a geared transmission for electric mobility using the lubricating oil composition.

[0007] As a result of intensive research into achieving the above-mentioned object, the present inventors have discovered that in a gear-type transmission for electric mobility comprising a lubricating oil composition for lubricating sliding parts and a joint at least partly using a silicone-containing foam-in-place gasket (silicone-containing FIPG) as a sealing member for the lubricating oil composition, by making the lubricating oil composition contain the following components (A) to (F) and satisfy all of the following conditions (i) to (vi), it is possible to highly suppress deterioration of the silicone-containing FIPG caused by the lubricating oil composition when the gear-type transmission is in use, and furthermore, it is possible to keep foaming of the lubricating oil composition when the gear-type transmission is in use below a specific level, while also making it possible to achieve both improved power consumption and improved fatigue life, and have completed the present invention.

[0008] That is, the present invention provides the following aspects.

[0009] [1] A gear-type transmission for electric mobility, comprising a lubricating oil composition for lubricating sliding parts, and a joint at least partially using a silicone-containing foam-in-place gasket as a sealing member for the lubricating oil composition, wherein the lubricating oil composition has: (A) a kinematic viscosity at 40°C of 12.0 mm ２ / s or less and the kinematic viscosity at 100°C is 2.7 mm ２ (B) a first phosphorus-based additive containing at least one alkyl group in its structure, each of which has 8 or fewer carbon atoms; (C) a second phosphorus-based additive containing at least one alkyl group in its structure, each of which has 14 or more carbon atoms; (D) a calcium-based detergent; (E) a boron-modified succinimide-based dispersant; and (F) a poly(meth)acrylate, and the lubricating oil composition satisfies the following conditions (i) to (vi): (i) the sum of the content of the (B) component in terms of phosphorus atoms and the content of the (C) component in terms of phosphorus atoms is 0.025% by mass or more and 0.050% by mass or less, based on the total mass of the lubricating oil composition; (ii) the content of component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content of component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition; (iii) the content of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is 0.009 to 0.013 mass%; (iv) the content of component (E) in terms of boron atoms, based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition; (v) the content of component (F) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is less than 0.1 mass%; (vi) the lubricating oil composition has a volume resistivity at 80°C of 50 MΩ m or more and a kinematic viscosity at 100°C of 2.7 mm ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more.

[0010] [2] The gear type transmission for electric mobility according to [1], wherein the component (B) is a phosphite ester in which all of the alkyl groups contained in the structure have 8 or less carbon atoms.

[0011] [3] The gear type transmission for electric mobility according to [1] or [2], wherein the component (C) is an amine salt of a phosphite ester in which all of the alkyl groups contained in the structure have 14 or more carbon atoms.

[0012] [4] The gear type transmission for electric mobility according to any one of [1] to [3], wherein the component (D) is at least one selected from the group consisting of calcium sulfonate having a base number of 200 mgKOH / g or more, calcium phenate having a base number of 200 mgKOH / g or more, and calcium salicylate having a base number of 200 mgKOH / g or more.

[0013] [5] The gear type transmission for electric mobility according to any one of [1] to [4], wherein the weight average molecular weight of the (F) component is 60,000 or less.

[0014] [6] A lubricating oil composition used to lubricate sliding parts of a gear-type transmission for electric mobility, which has a joint at least partially using a silicone-containing foam-in-place gasket as a sealing member for the lubricating oil composition, wherein the lubricating oil composition has: (A) a kinematic viscosity at 40°C of 12.0 mm ２ / s or less and the kinematic viscosity at 100°C is 2.7 mm ２(B) a first phosphorus-based additive containing at least one alkyl group in its structure, each of which has 8 or fewer carbon atoms; (C) a second phosphorus-based additive containing at least one alkyl group in its structure, each of which has 14 or more carbon atoms; (D) a calcium-based detergent; (E) a boron-modified succinimide-based dispersant; and (F) a poly(meth)acrylate, and the lubricating oil composition satisfies the following conditions (i) to (vi): (i) the sum of the content of the (B) component in terms of phosphorus atoms and the content of the (C) component in terms of phosphorus atoms is 0.025% by mass or more and 0.050% by mass or less, based on the total mass of the lubricating oil composition; (ii) the content of component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content of component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition; (iii) the content of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is 0.009 to 0.013 mass%; (iv) the content of component (E) in terms of boron atoms, based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition; (v) the content of component (F) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is less than 0.1 mass%; (vi) the lubricating oil composition has a volume resistivity at 80°C of 50 MΩ m or more and a kinematic viscosity at 100°C of 2.7 mm ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more.

[0015] [7] A lubrication method for a gear-type transmission for electric mobility, comprising lubricating a sliding portion of the gear-type transmission for electric mobility, which has a joint at least partially using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition, with the lubricating oil composition for a gear-type transmission for electric mobility described in [6].

[0016] The reason why the above object is achieved by the gear-type transmission for electric mobility of the present invention is not entirely clear, but the inventors speculate as follows.

[0017] That is, first, let us explain the case where a conventional lubricating oil composition with a low viscosity and containing a phosphorus-based additive is used in a gear-type transmission for electric mobility (e.g., an electric vehicle reducer) having a silicone-containing FIPG at a joint. Generally, when the lubricating oil composition is brought into contact with the silicone-containing FIPG, the lower the viscosity of the composition, the more easily the lubricating oil composition (especially the base oil) penetrates into the silicone-containing FIPG, and the silicone-containing FIPG tends to swell. Furthermore, when a low-viscosity lubricating oil composition penetrates the silicone-containing FIPG, silicon is more likely to dissolve and elute into the lubricating oil composition, especially due to the oxide (phosphate) of the phosphorus-based additive generated in the composition during use. Therefore, conventional lubricating oil compositions with a low viscosity and containing a phosphorus-based additive are themselves one of the causes of a decrease in the strength of the silicone-containing FIPG (one of the causes of FIPG deterioration). Furthermore, when such a decrease in the strength of the FIPG occurs, problems such as oil leakage and oil seepage from the joint occur, and therefore improvements in conventional lubricating oil compositions have been desired. Furthermore, as described above, the inventors have found through their research that when silicon is eluted into a lubricating oil composition, it becomes a substance that causes foaming of the lubricating oil composition, and that when the additive is a poly(meth)acrylate, it can also cause foaming of the lubricating oil composition depending on the amount used, etc.

[0018] Therefore, in the gear-type transmission for electric mobility of the present invention, a specific lubricating oil composition containing the aforementioned components (A) to (F) and satisfying all of the aforementioned conditions (i) to (vi) is used to lubricate the sliding parts. The inventors have discovered that the use of such a lubricating oil composition, even when a phosphorus-based additive is used, can highly suppress aggressiveness toward silicone-containing FIPG, although the reason for this is not entirely clear. This not only highly prevents FIPG deterioration, but also, in combination with the amounts of other additives used, makes it possible to keep foaming during use of the lubricating oil composition below a specific level. Furthermore, by keeping foaming during use of the lubricating oil composition below a specific level, situations such as oil spraying from the breather of the gear-type transmission can also be highly suppressed. Furthermore, the low kinematic viscosity of the lubricating oil composition used in the gear-type transmission for electric mobility of the present invention can also improve the power consumption of electric mobility (e.g., electric vehicles such as electric automobiles). Furthermore, the gear-type transmission for electric mobility of the present invention achieves high levels of wear prevention performance, seizure resistance, and fatigue life suppression during use by specifying the type of base oil and additive blend of the lubricating oil composition used. Furthermore, the gear-type transmission for electric mobility of the present invention achieves high electrical insulation properties by specifying the blend of additives and other components of the lubricating oil composition used, thereby achieving a volume resistivity at 80°C of a specific level or higher. From these perspectives, the inventors believe that the gear-type transmission for electric mobility of the present invention can highly suppress deterioration of the silicone-containing FIPG caused by the lubricating oil composition during use of the gear-type transmission, can keep foaming of the lubricating oil composition below a specific level during use of the gear-type transmission, and can simultaneously achieve improved power consumption and improved durability (improved fatigue life) of gears, bearings, etc.

[0019] According to the present invention, it is possible to (1) provide a geared transmission for electric mobility that can highly inhibit the deterioration of a silicone-containing FIPG caused by the lubricating oil composition when the geared transmission is in use, and can keep foaming of the lubricating oil composition at or below a specific level when the geared transmission is in use, and can simultaneously achieve improved power consumption and improved fatigue life; (2) provide a lubricating oil composition for a geared transmission for electric mobility that can highly inhibit the deterioration of a silicone-containing FIPG, can keep foaming during use at or below a specific level, and can improve power consumption with a low viscosity, while also improving extreme pressure performance based on anti-wear performance and anti-seizure performance and fatigue life, and can have the high level of electrical insulation required of a lubricating oil for electric mobility; and (3) provide a method for lubricating a geared transmission for electric mobility using the lubricating oil composition.

[0020] The present invention will be described in detail below with reference to preferred embodiments. In this specification, unless otherwise specified, the expression "X to Y" for numerical values ​​X and Y means "X or more and Y or less." In such an expression, when a unit is assigned only to numerical value Y, the unit also applies to numerical value X.

[0021] [Gear-type transmission for electric mobility] The gear-type transmission for electric mobility of the present invention is a gear-type transmission for electric mobility comprising a lubricating oil composition for lubricating sliding parts, and a joint at least partly using a silicone-containing foam-in-place gasket as a sealing member for the lubricating oil composition, wherein the lubricating oil composition has: (A) a kinematic viscosity at 40°C of 12.0 mm ２ / s or less and the kinematic viscosity at 100°C is 2.7 mm ２(B) a first phosphorus-based additive containing at least one alkyl group in its structure, each of which has 8 or fewer carbon atoms; (C) a second phosphorus-based additive containing at least one alkyl group in its structure, each of which has 14 or more carbon atoms; (D) a calcium-based detergent; (E) a boron-modified succinimide-based dispersant; and (F) a poly(meth)acrylate, and the lubricating oil composition satisfies the following conditions (i) to (vi): (i) the sum of the content (mass %) of component (B) in terms of phosphorus atoms and the content (mass %) of component (C) in terms of phosphorus atoms is 0.025% by mass or more and 0.050% by mass or less, based on the total mass of the lubricating oil composition; (ii) the content (mass%) of component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content (mass%) of component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition; (iii) the content (mass%) of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is 0.009 to 0.013 mass%; (iv) the content (mass%) of component (E) in terms of boron atoms, based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content (mass%) of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition; (v) the content (mass%) of component (F) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is less than 0.1 mass%; (vi) the lubricating oil composition has a volume resistivity at 80°C of 50 MΩ m or more and a kinematic viscosity at 100°C of 2.7 mm ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more. In this specification, "electric mobility" refers to a moving object that runs or flies by driving drive wheels or the like using an electric motor as a drive source, and includes so-called electric vehicles (e.g., electric automobiles) with two wheels, four wheels, etc. In addition, in this specification, "gear-type transmission" is a concept that includes reducers, speed-up gears, and multi-stage transmissions. First, the lubricating oil composition provided in the gear-type transmission for electric mobility of the present invention will be described below.

[0022] <Lubricating Oil Composition> As described above, the lubricating oil composition of the present invention contains the components (A) to (F) and satisfies all of the conditions (i) to (vi). Here, the components used in the lubricating oil composition of the present invention will be described.

[0023] <Regarding Components in the Lubricating Oil Composition> [Component (A): Lubricating Base Oil] The lubricating base oil contained as component (A) in the lubricating oil composition has a kinematic viscosity of 12.0 mm at 40°C. ２ / s or less and the kinematic viscosity at 100°C is 2.7 mm ２ / s or more.

[0024] Such hydrocracked mineral oil has a kinematic viscosity of 12.0 mm at 40°C. ２ / s or less and the kinematic viscosity at 100°C is 2.7 mm ２ The mineral oil may be any oil as long as it satisfies the condition that the ratio of the hydrocracked mineral oil content to the total hydrocracked mineral oil content is 1 / s or more, and may be made of only one type of hydrocracked mineral oil that satisfies such a condition, or may be made of a mixture of two or more types of hydrocracked mineral oil that are mixed so as to satisfy such a condition.

[0025] Such hydrocracked mineral oils are not particularly limited as long as they are obtained by subjecting so-called mineral oils to a hydrocracking process, and any known hydrocracked mineral oil can be used as appropriate. Among these, preferred are mineral oils obtained by hydrocracking vacuum distillate oil (WVGO), mild hydrocracking (MHC) treated oil of WVGO, deasphalted oil (DAO), MHC treated oil of DAO, or a mixture of these, and then subjecting the resulting product or a lubricating oil fraction recovered from the product by distillation or the like to a dewaxing treatment; or mineral oils obtained by further distilling such mineral oils (note that the methods for the various treatments such as "hydrocracking" and "dewaxing" referred to herein are not particularly limited, and any known method can be used as appropriate).

[0026] The hydrocracked mineral oil used as the lubricating base oil (component (A)) has a kinematic viscosity of 12.0 mm at 40°C. ２It is necessary that the kinematic viscosity at 40°C is 12.0 mm / s or less. ２ / s or less, 12.0 mm ２ The kinematic viscosity of the lubricating oil composition can be lowered compared to when the kinematic viscosity exceeds 9.0 mm / s, and it is possible to reduce stirring loss, particularly at low temperatures (25°C), thereby achieving high performance (effect) in terms of power saving performance and highly suppressing foaming of the composition during use (improving foam removal properties). ２ / s or more 12.0mm ２ / s or less, and 10.0 mm ２ / s or more 11.0mm ２ When the kinematic viscosity at 40°C is equal to or higher than the lower limit, it is possible to further improve the oil film forming ability at lubricated points, thereby making the lubrication even more excellent, and it is also possible to further reduce evaporation loss of the lubricating oil composition, compared to when the kinematic viscosity is below the lower limit.

[0027] The hydrocracked mineral oil, which is the lubricating base oil (component (A)), has a kinematic viscosity of 2.7 mm at 100°C. ２ The kinematic viscosity of hydrocracked mineral oil at 100°C must be 2.7 mm / s or more. ２ / s or more, it is 2.7 mm ２ Compared with a lubricating oil having a kinematic viscosity of less than 2.7 mm / s, the oil film forming performance at the lubrication points is improved, which makes it possible to improve the wear resistance and bearing fatigue life, as well as improve the seizure resistance. ２ / s or more 3.0mm ２ / s or less, and 2.75 mm ２ / s or more 2.90mm ２ / s or less is more preferable. When the kinematic viscosity at 100°C is equal to or less than the above upper limit, there is a tendency for even greater effects to be obtained in terms of improving power saving performance compared to when the kinematic viscosity exceeds the above upper limit. In this specification, the "kinematic viscosity at 40°C" and "kinematic viscosity at 100°C" of the lubricating base oil and lubricating oil composition refer to the kinematic viscosity at each temperature (40°C or 100°C) specified in JIS K 2283-2000.

[0028] Furthermore, the hydrocracked mineral oil preferably has a sulfur content (sulfur content) of 30 ppm by mass or less (more preferably 1 to 10 ppm by mass). By setting the sulfur content at or below the upper limit, it is possible to improve oxidation stability compared to when the sulfur content exceeds the upper limit. On the other hand, by setting the sulfur content at or above the lower limit, it is possible to improve seizure resistance and anti-wear properties, and improve durability and reliability compared to when the sulfur content is below the lower limit. Note that this "sulfur content" can be determined by measurement in accordance with ASTM D4951.

[0029] Furthermore, the hydrocracked mineral oil preferably has a viscosity index of 80 or higher (more preferably 90 or higher, even more preferably 95 or higher, and particularly preferably 100 or higher). By setting the viscosity index at or above the lower limit, even greater effects in terms of power cost saving performance can be obtained. In this specification, the "viscosity index" of the lubricating base oil and lubricating oil composition is a value measured in accordance with JIS K 2283-1993.

[0030] The hydrocracked mineral oil can be at least one selected from the group consisting of Group II and Group III base oils classified by the American Petroleum Institute (API) (hereinafter, the API base oil classification groups will be simply referred to as "API Groups"). API Group II base oils have a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or more, and a viscosity index of 80 to less than 120. API Group III base oils have a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or more, and a viscosity index of 120 or more. Furthermore, the hydrocracked mineral oil can be a single base oil selected from API Group II and API Group III base oils, or a mixed base oil can be a combination of two or more base oils selected from API Group II and API Group III base oils. Furthermore, from the viewpoint of easily adjusting the viscosity characteristics within a desired range, it is preferable to use a mixed oil obtained by mixing two or more types of base oils (two or more types of mineral oils obtained through a hydrocracking process) as the hydrocracked mineral oil that is the lubricating base oil (component (A)), and among these, a mixed base oil of two or more types of API Group II base oils is more preferable.

[0031] [Component (B): First Phosphorus-Based Additive] The first phosphorus-based additive, component (B), is a phosphorus-based additive containing at least one alkyl group in its structure, all of which have a carbon number of 8 or less. Such a phosphorus-based additive may contain at least one alkyl group in its structure, all of which have a carbon number of 8 or less, and any known phosphorus-based additive used in the field of lubricating oil compositions that satisfies these conditions and contains a phosphorus atom as a constituent element may be used as appropriate.

[0032] Any alkyl group that may be contained in the structure of the compound used as such a first phosphorus-based additive (component (B)) must have a carbon number of 8 or less (more preferably 2 to 6). By making the carbon number of the alkyl group contained in such a first phosphorus-based additive 8 or less, and by combining it with component (C), it becomes possible to highly suppress the attack on the silicone-containing FIPG, and thereby to highly suppress the deterioration of the FIPG, although the reason for this is not necessarily clear.

[0033] Compounds used as this first phosphorus-based additive (component (B)) include, for example, phosphites, phosphoric acid esters (phosphates), amine salts thereof, metal salts thereof, and derivatives thereof, all of which have alkyl groups with 8 or less carbon atoms in their structures. Among these, phosphites in which all of the alkyl groups in the structure have 8 or less carbon atoms are preferred, as they provide even greater effects in terms of improving seizure resistance, wear resistance, and fatigue life. Dialkyl phosphites (dialkyl phosphites) in which all of the alkyl groups have 8 or less carbon atoms are more preferred, and dibutyl phosphite is particularly preferred. This first phosphorus-based additive is not particularly limited, and commercially available products may be used.

[0034] [Component (C): Second Phosphorus-Based Additive] The second phosphorus-based additive, component (C), is a phosphorus-based additive containing at least one alkyl group in its structure, all of which have a carbon number of 14 or more. Such a phosphorus-based additive may contain at least one alkyl group in its structure, all of which have a carbon number of 14 or more, and any known phosphorus-based additive used in the field of lubricating oil compositions that satisfies these conditions and contains a phosphorus atom as a constituent element can be used as appropriate.

[0035] Any alkyl group that can be contained in the structure of the compound used as such a second phosphorus-based additive (component (C)) must have a carbon number of 14 or more (more preferably 16 to 20). By making the carbon number of the alkyl group contained in such a second phosphorus-based additive 14 or more, and by combining it with component (B), it becomes possible to highly suppress the attack on the silicone-containing FIPG, and thereby to highly suppress the deterioration of the FIPG, although the reason for this is not necessarily clear.

[0036] Compounds used as this second phosphorus-based additive (component (C)) include, for example, phosphites, phosphoric acid esters (phosphates), amine salts thereof, metal salts thereof, and derivatives thereof, all of which have alkyl groups in their structures having 14 or more carbon atoms. Among these, amine salts of phosphites, all of which have alkyl groups in their structures having 14 or more carbon atoms, are preferred, as they provide even greater effects in terms of improving seizure resistance, wear resistance, and fatigue life, and amine salts of dialkyl phosphites (dialkyl phosphites), all of which have alkyl groups having 14 or more carbon atoms, are more preferred. The second phosphorus-based additive is not particularly limited, and commercially available products may be used.

[0037] [Component (D): Calcium-Based Detergent] The calcium-based detergent of component (D) is not particularly limited, and known calcium-based detergents used in the field of lubricating oil compositions can be used as appropriate. Suitable examples of such calcium-based detergents include calcium sulfonate, calcium phenate, and calcium salicylate. The calcium-based detergent may be overbased with, for example, a carbonate (calcium carbonate). Examples of such calcium-based detergents include the calcium-based detergents (sulfonate detergents, phenate detergents, salicylate detergents) described in paragraphs

[0038] to

[0053] of JP 2020-76004 A. These calcium-based detergents can be used alone or in combination of two or more. Commercially available calcium-based detergents may also be used.

[0038] The base number of the calcium-based detergent (component (D)) is preferably 200 mgKOH / g or more (more preferably 300 mgKOH / g or more and 500 mgKOH / g or less). By setting the base number at or above the lower limit, a higher effect can be obtained in terms of suppressing attack on FIPG compared with a case where the base number is below the lower limit. In this specification, the base number of the calcium-based detergent is the value measured in accordance with JIS K 2501:2003-9 (value measured by the perchloric acid method).

[0039] Furthermore, the calcium-based detergent (component (D)) is particularly preferably at least one calcium-based detergent selected from the group consisting of calcium sulfonate having a base number of 200 mgKOH / g or more, calcium phenate having a base number of 200 mgKOH / g or more, and calcium salicylate having a base number of 200 mgKOH / g or more.

[0040] [Component (E): Boron-modified succinimide-based dispersant] The boron-modified succinimide-based dispersant of component (E) is not particularly limited, and any known dispersant that is used as an ashless dispersant made of boron-modified succinimide in the field of lubricating oil compositions can be used as appropriate. Examples of such boron-modified succinimide-based dispersants include boron-modified succinimides obtained by modifying a succinimide having an alkenyl group or alkyl group derived from a polyolefin with a boron compound such as boric acid or a borate salt.

[0041] As such a boron-modified succinimide-based dispersant, for example, the boron-modified succinimide-based dispersant described in JP 2022-090378 A or the boron-modified succinimide-based ashless dispersant (C) described in JP 2009-108157 A can be appropriately used. Furthermore, such boron-modified succinimide-based dispersants can be used alone or in combination of two or more. Furthermore, commercially available products may be used as such boron-modified succinimide-based dispersants.

[0042] [Component (F): Poly(meth)acrylate] The poly(meth)acrylate used as component (F) is not particularly limited, and any known poly(meth)acrylate used in the field of lubricating oil compositions as a viscosity index improver, pour point depressant, etc. In this specification, "(meth)acrylate" means acrylate and / or methacrylate.

[0043] Furthermore, the poly(meth)acrylate as component (F) is more preferably a poly(meth)acrylate-based pour point depressant (a poly(meth)acrylate used as a pour point depressant). Here, the poly(meth)acrylate as component (F) preferably contains a poly(meth)acrylate-based pour point depressant (a poly(meth)acrylate used as a pour point depressant) and does not contain a poly(meth)acrylate-based viscosity index improver (a poly(meth)acrylate used as a viscosity index improver), since this provides a more effective suppression of foaming of the composition.

[0044] Furthermore, the poly(meth)acrylate used as component (F) preferably has a weight-average molecular weight of 60,000 or less (more preferably 58,000 or less, and even more preferably 50,000 to 57,000). By setting the weight-average molecular weight of the poly(meth)acrylate to the above upper limit or less, a greater effect in terms of suppressing foaming of the composition tends to be obtained. Note that the "weight-average molecular weight" used here refers to the value determined by gel permeation chromatography (GPC) (the molecular weight obtained in terms of standard polystyrene).

[0045] In such component (F), one type of poly(meth)acrylate may be used alone, or two or more types of poly(meth)acrylate may be used in combination.

[0046] [Regarding Components Other Than Components (A) to (F)] The components usable in the lubricating oil composition of the present invention are not limited to the components (A) to (F) described above, and other known components (e.g., antioxidants, metal deactivators, rubber swelling agents, diluent oils, etc.) used in lubricating oil compositions for gear-type transmissions for electric mobility (e.g., reducers for electric vehicles) may be used as appropriate, provided that the effects of the present invention are not impaired. Such other components are not particularly limited, and may include, for example, commercially available performance additives (so-called additive packages: blends of multiple components).

[0047] The components in the lubricating oil composition of the present invention have been explained above. Below, the composition and properties of the lubricating oil composition will be explained.

[0048] <Composition and Properties of Lubricating Oil Composition> First, the above-mentioned conditions (i) to (vi) relating to the lubricating oil composition of the present invention will be explained below, and then other suitable conditions will be explained.

[0049] [Regarding condition (i)] The lubricating oil composition according to the present invention must satisfy the condition (condition (i)) that the sum of the content of component (B) in terms of phosphorus atoms and the content of component (C) in terms of phosphorus atoms is 0.025% by mass or more and 0.050% by mass or less, based on the total mass of the lubricating oil composition. When the sum of the contents of components (B) and (C) in terms of phosphorus atoms is equal to or more than the lower limit, it is possible to improve both the extreme-pressure performance based on anti-wear performance and anti-seizure performance, and fatigue life, compared to when it is below the lower limit. On the other hand, when it is equal to or less than the upper limit, it is possible to suppress the decrease in volume resistivity and maintain a high level of electrical insulation, compared to when it exceeds the upper limit. It is also possible to further prevent deterioration of the silicone-containing FIPG and to maintain foaming of the lubricating oil composition during use at a specific level or less. From the same viewpoint, the total content of the (B) component in terms of phosphorus atoms and the (C) component in terms of phosphorus atoms is more preferably 0.025 mass % or more and 0.050 mass % or less (more preferably 0.030 mass % or more and 0.050 mass % or less) based on the total mass of the lubricating oil composition, since this provides an even greater effect.

[0050] [Regarding condition (ii)] The lubricating oil composition of the present invention must satisfy the condition (condition (ii)) that the content (mass%) of component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content (mass%) of component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition. In other words, when the content (MP1) of component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is defined as "MP1," and the content (MP2) of component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is defined as "MP2," the value ([MP1] / [MP2]) calculated by dividing MP1 by MP2 must be 2.0 to 2.4. By setting MP1 to at least twice MP2 (the value of [MP1] / [MP2] is 2.0 or more), it is possible to improve extreme pressure performance while further preventing deterioration of the silicone-containing FIPG compared to when it is less than twice, and it is also possible to maintain foaming of the lubricating oil composition during use at a specific level or below. On the other hand, by setting MP1 to no more than 2.4 times MP2 (the value of [MP1] / [MP2] is 2.4 or less), it is possible to achieve a significant improvement in fatigue life while further preventing deterioration of the silicone-containing FIPG compared to when it exceeds 2.4 times, and it is also possible to maintain foaming of the lubricating oil composition during use at a specific level or below. Furthermore, from the same perspective, it is more preferable that MP1 be 2.1 to 2.3 times MP2, as this provides even greater effectiveness.

[0051] In the present invention, the first phosphorus-based additive (component (B)) and the second phosphorus-based additive (component (C)) are mixed and used in a specific ratio so as to satisfy the above conditions (i) to (ii). This highly suppresses the distillation of silicon from the silicone-containing FIPG and the resulting deterioration of the silicone-containing FIPG (softening, peeling, and other strength reductions) that occurs when the phosphorus-based additive is used alone. Furthermore, foaming of the composition during use due to silicon distillation from the FIPG can also be suppressed, which highly suppresses problems such as oil spraying from the breather portion of a gear transmission. (Note: Silicon is one of the substances that cause foaming in the composition, and as the amount of silicon leaking increases, it tends to become more difficult to suppress foaming (the ease of foam removal from the composition decreases).) Furthermore, by setting the value of [MP1] / [MP2] within the above range, it is possible to suppress the decrease in volume resistivity and maintain a high level of electrical insulation, making it ideal for gear transmissions for electric mobility (particularly preferably for reducers for electric vehicles).

[0052] [Regarding Condition (iii)] The lubricating oil composition according to the present invention must satisfy the condition (condition (iii)) that the content of the calcium atom equivalent of the (D) component (the content of calcium atoms derived from the (D) component: hereinafter sometimes simply referred to as "MCa"), based on the total mass of the lubricating oil composition, is 0.009 mass% or more and 0.013 mass% or less. By setting the MCa content to 0.009 mass% or more, it is possible to improve fatigue life compared to when the MCa content is less than 0.009 mass%, while highly preventing deterioration of the silicone-containing FIPG and maintaining foaming of the lubricating oil composition during use at a specific level or less. On the other hand, by setting the MCa content to 0.013 mass% or less, it is possible to highly prevent deterioration of the silicone-containing FIPG and maintain foaming of the lubricating oil composition during use at a specific level or less, while improving wear resistance, seizure resistance, and fatigue life compared to when the MCa content exceeds 0.013 mass%. Furthermore, by setting the MCa content to 0.013% by mass or less, it is possible to suppress a decrease in volume resistivity and maintain high electrical insulation properties.Furthermore, from the same viewpoint, since an even higher effect can be obtained, it is preferable that the MCa content be 0.010% by mass or more and 0.012% by mass or less.

[0053] [Regarding condition (iv)] The lubricating oil composition according to the present invention must satisfy the condition (condition (iv)) that the content of component (E) in terms of boron atoms (the content (mass%) of boron atoms derived from component (E): hereinafter sometimes simply referred to as "MB"), based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content (mass%) of component (D) in terms of calcium atoms (MCa (mass%)), based on the total mass of the lubricating oil composition. In other words, the value obtained by dividing MB by MCa ([MB] / [MCa]) must be 0.9 to 1.2. By setting MB to 0.9 times or more the MCa (the value of [MB] / [MCa] is 0.9 or more), it is possible to highly prevent deterioration of the silicone-containing FIPG, and to maintain foaming of the lubricating oil composition during use at or below a specific level, while improving fatigue life, compared to when MB is less than 0.9 times. On the other hand, by setting MB to 1.2 times or less the MCa (the value of [MB] / [MCa] is 1.2 or less), it is possible to maintain the foaming of the lubricating oil composition at a specific level or less, while improving fatigue life and extreme pressure properties, compared to when it exceeds 1.2 times. Furthermore, by setting MB to 1.2 times or less the MCa (the value of [MB] / [MCa] is 1.2 or less), it is possible to suppress a decrease in volume resistivity and maintain high electrical insulation properties. From the same viewpoint, it is more preferable that MB is 1.1 to 1.2 times the MCa.

[0054] [Regarding condition (v)] The lubricating oil composition according to the present invention must satisfy the condition (condition (v)) that the content of the (F) component is less than 0.1 mass % based on the total mass of the lubricating oil composition. By setting the content of the poly(meth)acrylate, which is the (F) component, to less than 0.1 mass %, it becomes possible to highly suppress foaming, particularly during use of the composition. In other words, if the amount of poly(meth)acrylate added exceeds the upper limit, foaming becomes more likely to occur, making it difficult to suppress foaming during use. Furthermore, the content of such component (F) is more preferably 0.09 mass % or less (more preferably 0.07 mass % or less), since an even greater effect can be obtained from the same perspective.

[0055] [Regarding condition (vi)] The lubricating oil composition of the present invention has a volume resistivity of 50 MΩ·m or more at 80°C and a kinematic viscosity of 2.7 mm at 100°C. ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more (the above-mentioned condition (vi)).

[0056] As described in condition (vi), the lubricating oil composition of the present invention must have a volume resistivity at 80°C of 50 MΩ m or more (more preferably 51 MΩ m or more and 55 MΩ m or less). By achieving a volume resistivity of 50 MΩ m or more, it is possible to obtain a composition with the high level of electrical insulation required in the field of electric mobility (particularly the field of electric vehicles). In this specification, "volume resistivity" means the volume resistivity measured at an oil temperature of 80°C in accordance with the volume resistivity test specified in JIS C2101.

[0057] Furthermore, as described in the condition (vi) above, the lubricating oil composition of the present invention has a kinematic viscosity of 2.7 mm at 100°C. ２ / s or more 3.0mm ２ / s or less (more preferably 2.75 mm ２ / s or more 2.90mm ２ / s or less). By setting the kinematic viscosity of the composition at 100°C to be equal to or greater than the lower limit, it is possible to prevent deterioration of the silicone-containing FIPG to a high degree compared to when the kinematic viscosity is below the lower limit, and it is also possible to maintain the foaming of the lubricating oil composition during use at a specific level or less. Furthermore, by setting the kinematic viscosity of the composition at 100°C to be equal to or less than the upper limit, it is possible to improve power saving performance compared to when the kinematic viscosity exceeds the upper limit.

[0058] Furthermore, as described in the above condition (vi), the lubricating oil composition according to the present invention must have a viscosity index of at least 100 (more preferably at least 103). By making the viscosity index of the composition at or above the lower limit, a higher effect in terms of power saving performance can be obtained compared to when the viscosity index is below the lower limit.

[0059] [Regarding Other Preferred Conditions] The lubricating oil composition according to the present invention is not particularly limited as long as it satisfies all of the above-described conditions (i) to (vi), but it is more preferable that it satisfies the conditions described below.

[0060] In the lubricating oil composition of the present invention, the content of the lubricating base oil (hydrocracked base oil) as component (A) is preferably 90 mass % or more and 98 mass % or less (more preferably 92 mass % or more and 97 mass % or less) based on the total mass of the lubricating oil composition. Furthermore, when the lubricating oil composition of the present invention contains components other than components (A) to (F), the content of such other components is preferably 10 mass % or less (more preferably 3 mass % or more and 8 mass % or less) based on the total mass of the lubricating oil composition.

[0061] In addition, in the lubricating oil composition according to the present invention, the content of the (B) component based on the total mass of the lubricating oil composition is preferably 0.10 mass% or more and 0.30 mass% or less (more preferably 0.12 mass% or more and 0.25 mass% or less) from the viewpoint of improving seizure resistance, anti-wear properties, and fatigue life. Furthermore, in the lubricating oil composition according to the present invention, the content of the (B) component in terms of phosphorus atoms (MP1: the content of phosphorus atoms derived from the (B) component) based on the total mass of the lubricating oil composition is preferably 0.015 mass% or more and 0.040 mass% or less (more preferably 0.020 mass% or more and 0.035 mass% or less). When MP1 is equal to or greater than the lower limit, even greater effects in terms of seizure resistance, wear resistance, and fatigue life improvement tend to be obtained compared to when it is less than the lower limit. On the other hand, when it is equal to or less than the upper limit, even greater effects in terms of seizure resistance, wear resistance, and fatigue life improvement tend to be obtained compared to when it exceeds the upper limit.

[0062] In addition, in the lubricating oil composition according to the present invention, the content of the component (C) based on the total mass of the lubricating oil composition is preferably 0.30 mass% or more and 0.80 mass% or less (more preferably 0.35 mass% or more and 0.70 mass% or less) from the viewpoint of improving seizure resistance, anti-wear properties, and fatigue life. Furthermore, in the lubricating oil composition according to the present invention, the content of the component (C) in terms of phosphorus atoms (MP2: the content of phosphorus atoms derived from the component (C)) based on the total mass of the lubricating oil composition is preferably 0.008 mass% or more and 0.020 mass% or less (more preferably 0.009 mass% or more and 0.018 mass% or less). When MP2 is equal to or greater than the lower limit, even greater effects tend to be obtained in terms of improving seizure resistance, wear resistance, and fatigue life compared to when it is less than the lower limit. On the other hand, when it is equal to or less than the upper limit, even greater effects tend to be obtained in terms of improving seizure resistance, wear resistance, and fatigue life compared to when it exceeds the upper limit.

[0063] Furthermore, in the lubricating oil composition according to the present invention, the content of component (D) based on the total mass of the lubricating oil composition is preferably 0.055 mass % or more and 0.130 mass % or less (more preferably 0.060 mass % or more and 0.120 mass % or less).

[0064] In the lubricating oil composition according to the present invention, the content of component (E) based on the total mass of the lubricating oil composition is preferably 0.40 mass% or more and 0.80 mass% or less (more preferably 0.55 mass% or more and 0.65 mass% or less). Furthermore, in the lubricating oil composition according to the present invention, the content (MB) of component (E) in terms of boron atoms based on the total mass of the lubricating oil composition is preferably 0.010 mass% or more and 0.017 mass% or less (more preferably 0.012 mass% or more and 0.015 mass% or less). When MB is equal to or greater than the lower limit, even greater effects in terms of improving seizure resistance, wear resistance, and fatigue life tend to be obtained compared to when MB is less than the lower limit. On the other hand, when MB is equal to or less than the upper limit, even greater effects in terms of improving seizure resistance, wear resistance, and fatigue life tend to be obtained compared to when MB exceeds the upper limit.

[0065] In addition, when the converted value of the content of each component described in this specification in terms of calcium atoms, boron atoms, or phosphorus atoms can be determined by calculation from the type of raw materials used, the amount added, etc., such a calculated value may be used.

[0066] Furthermore, the lubricating oil composition of the present invention is more effective in terms of power consumption saving performance, and therefore, the kinematic viscosity of the composition at 40°C is 9.0 mm ２ / s or more 12.0mm ２ / s or less (more preferably 10.0 mm ２ / s or more 11.0mm ２ / s or less).

[0067] The lubricating oil composition according to the present invention has been described above. Below, the gear-type transmission for electric mobility according to the present invention, which is equipped with such a lubricating oil composition, will be described.

[0068] <Regarding Gear-Type Transmission for Electric Mobility> The gear-type transmission for electric mobility of the present invention is any transmission that comprises the lubricating oil composition according to the present invention described above as a lubricating oil composition for lubricating sliding parts, and that has joints in at least a portion of which a silicone-containing foam-in-place gasket is used as a sealing member for the lubricating oil composition. The structure of other components is not particularly limited, and any structure that is used in known gear-type transmissions for electric mobility (for example, gear-type transmissions for electric vehicles, preferably reducers for electric automobiles, etc.) can be appropriately adopted.

[0069] Here, "a joint at least partially using a silicone-containing foam-in-place gasket as a sealing member for the lubricating oil composition" refers to a joint between components of a gear-type transmission for electric mobility, in which a silicone-containing FIPG is used in at least a portion of the sealing portion of the joint to seal against leakage of the lubricating oil composition to the outside. Furthermore, such a "joint at least partially using a silicone-containing foam-in-place gasket as a sealing member for the lubricating oil composition" may be present in at least one location in the gear-type transmission for electric mobility. Furthermore, the expression "as a sealing member for the lubricating oil composition" in relation to a silicone-containing FIPG means that the silicone-containing FIPG is present at least in a portion that comes into contact with the lubricating oil composition and is used as a member for sealing the lubricating oil composition, and may also seal the lubricating oil composition as well as the air inside.

[0070] The sliding parts of such a gear-type transmission for electric mobility are not particularly limited, and may be any parts within the gear-type transmission for electric mobility where the components that make up the device slide against each other, such as parts made up of components that move in contact with each other due to rotational sliding or surface sliding, such as gears and bearings within a reducer of an electric vehicle (preferably an electric automobile).

[0071] Furthermore, the joints of the gear-type transmission for electric mobility must be sealed by a gasket, and at least a portion of the joint must be sealed by using a silicone-containing FIPG. The components constituting the joints that require at least a portion of the sealing with the silicone-containing FIPG may be made of the same metal or different metals. The silicone-containing FIPG is not particularly limited, and known products (such as those made of known liquid gaskets containing silicone (silicone resin)) can be used as appropriate, or products formed from commercially available products (e.g., 5460, manufactured by Henkel) can also be used as appropriate. In this specification, a "formed-in-place gasket (FIPG)" refers to a liquid-curing gasket formed by applying a liquid gasket to the area to be sealed (adhering the sealing surface with the liquid gasket) and then curing the gasket.

[0072] In the present invention, the lubricating oil composition has a low viscosity, yet is capable of suppressing the distillation of silicon from the silicone-containing FIPG during use, and is able to highly suppress FIPG degradation, etc., thereby highly preventing oil leakage (bleeding) from joints coated with the silicone-containing FIPG. Furthermore, in the present invention, the lubricating oil composition can highly suppress the distillation of silicon from the silicone-containing FIPG during use (dissolution / elution into the composition), as described above, and since the addition of poly(meth)acrylate (high-viscosity polymer) is less than a specific amount, it is possible to highly suppress foaming of the lubricating oil composition during use, making it possible to highly suppress problems such as oil spraying from the breather. Furthermore, because the lubricating oil composition has a low viscosity, the gear-type transmission for electric mobility of the present invention is also excellent in terms of power saving. Furthermore, the gear transmission for electric mobility of the present invention utilizes the lubricating oil composition such that the contents and blending ratios of each component satisfy the above-mentioned conditions, thereby improving seizure resistance and wear prevention, as well as improving the fatigue life of gears and bearings. Therefore, according to the present invention, in electric mobility, it is possible to highly suppress deterioration of the silicone-containing FIPG caused by the lubricating oil composition when the gear transmission is in use, and it is possible to keep foaming of the lubricating oil composition below a specific level when the gear transmission is in use, and it is also possible to achieve both improved power consumption and improved fatigue life.

[0073] The gear type transmission for electric mobility of the present invention has been described above. Below, the lubricating oil composition for the gear type transmission for electric mobility of the present invention and the lubrication method for the gear type transmission for electric mobility of the present invention will be described.

[0074] [Lubricating oil composition for gear-type transmissions for electric mobility and lubrication method for gear-type transmissions for electric mobility] The lubricating oil composition for gear-type transmissions for electric mobility of the present invention is a lubricating oil composition used to lubricate sliding parts of a gear-type transmission for electric mobility that has joints at least partly using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition, and the lubricating oil composition contains the components (A) to (F) above and satisfies all of the conditions (i) to (vi) above.

[0075] The lubrication method for a gear-type transmission for electric mobility of the present invention is a method of lubricating, with the lubricating oil composition for gear-type transmission for electric mobility of the present invention, sliding parts of the gear-type transmission for electric mobility that has a joint at least partly using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition.

[0076] The lubricating oil composition for a gear-type transmission for electric mobility of the present invention is the same as the lubricating oil composition provided in the gear-type transmission for electric mobility of the present invention (the preferred conditions are also the same). Therefore, by using the lubricating oil composition for a gear-type transmission for electric mobility of the present invention to lubricate the sliding parts of a gear-type transmission for electric mobility (for example, a reducer for an electric vehicle) having joints at least partly using a foam-in-place gasket containing silicone as a sealing member, even if the lubricating oil composition comes into contact with the silicone-containing FIPG, deterioration of the silicone-containing FIPG and elution of silicon can be highly suppressed, and therefore the sliding parts of the gear-type transmission for electric mobility can be lubricated while highly suppressing leakage of the lubricating oil composition from the joints.

[0077] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0078] (Components Used in Each Example) First, the base oils and additives used in each example are shown below.

[0079] [Regarding the base oil (hydrocracked mineral oil) used to prepare the lubricating base oil (component (A))] <Component (A-1)> Hydrocracked mineral oil [API Group II, kinematic viscosity at 40°C: 8.169 mm ２ / s, kinematic viscosity at 100 ° C: 2.355 mm ２ / s, viscosity index: 104, sulfur content in base oil (sulfur content in base oil): less than 10 ppm by mass] <Component (A-2)> Hydrocracked mineral oil [API Group II, kinematic viscosity at 40°C: 12.43 mm ２ / s, kinematic viscosity at 100 ° C: 3.12 mm ２ / s, viscosity index: 112, sulfur content in base oil (sulfur content in base oil): less than 10 ppm by mass (<10 ppm by mass)] <Component (A-3)> Hydrocracked mineral oil [API Group III, kinematic viscosity at 40°C: 19.57 mm ２ / s, kinematic viscosity at 100 ° C: 4.23 mm ２ / s, viscosity index: 122, sulfur content in base oil (sulfur content in base oil): less than 10 ppm by mass (<10 ppm by mass)].

[0080] Regarding phosphorus-based additives (component (B) and component (C), etc.), component (B-1) is di(n-butyl)phosphite (phosphorus (P) content: 15.5% by mass, the number of carbon atoms in each alkyl group contained in the compound structure is 4). component (C-1) is an amine salt of a phosphite ester (distearyl phosphite) (phosphorus (P) content: 24.3% by mass, nitrogen (N) content: 0.30% by mass, the number of carbon atoms in each alkyl group contained in the compound structure is 18). component (Z-1): a phosphorus-based additive for comparison is dilauryl hydrogen phosphite (phosphorus (P) content: 6.5% by mass, the number of carbon atoms in each alkyl group contained in the compound structure is 12).

[0081] Regarding calcium-based detergents (component (D)), component (D-1) is calcium sulfonate, having a base number (perchloric acid method) of 400 mg KOH / g and a calcium (Ca) content of 15.5% by mass. Component (D-2) is calcium phenate, having a base number (perchloric acid method) of 255 mg KOH / g and a calcium (Ca) content of 9.3% by mass, and a sulfur (S) content of 3.5% by mass. Component (D-3) is calcium salicylate, having a base number (perchloric acid method) of 280 mg KOH / g and a calcium (Ca) content of 8.1% by mass.

[0082] [Boron-modified succinimide-based dispersant (component (E))] <Component (E-1)> Boron-modified succinimide [boron (B) content: 2.0 mass%, nitrogen (N) content: 2.3 mass%].

[0083] Regarding the poly(meth)acrylate (component (F)): <component (F-1)>: Poly(meth)acrylate-based pour point depressant [polymethacrylate having a weight-average molecular weight (Mw) of 55,800]. <component (F-2)>: Poly(meth)acrylate-based viscosity modifier [polymethacrylate having a weight-average molecular weight (Mw) of 50,000].

[0084] <Regarding Other Additives (Component (G))> <Component (G-1)> A mixture of an antioxidant (1.35% by mass), a metal deactivator (0.05% by mass), a rubber swelling agent (0.6% by mass), and a diluent oil (0.6% by mass) (total amount: 2.6% by mass).

[0085] (Examples 1 to 9 and Comparative Examples 1 to 16) The lubricating oil compositions of Examples 1 to 9 and Comparative Examples 1 to 16 were prepared using the components described above so as to obtain the compositions shown in Tables 1 to 3. Note that in the "Composition" section of Tables 1 to 3, "-" indicates that the component was not used. Furthermore, in the "Composition" section of Tables 1 to 3, "mass%" represents the content (mass%) based on mass relative to the total amount of the lubricating oil composition, and "in mass%" represents the content (mass%) of components (A-1) to (A-3) (constituent base oils of the lubricating base oil) based on mass relative to the total amount of the lubricating base oil. Furthermore, MP1 shown in Tables 1 to 3 indicates the content of component (B) (component (B-1)) in terms of phosphorus atoms based on the mass of the total amount of the lubricating oil composition, MP2 indicates the content of component (C) (component (C-1)) in terms of phosphorus atoms based on the mass of the total amount of the lubricating oil composition, MCa indicates the content of component (D) in terms of calcium atoms based on the mass of the total amount of the lubricating oil composition, MB indicates the content of component (E) in terms of boron atoms, and "MP1 + MP2" indicates the sum of the content of component (B) (component (B-1)) in terms of phosphorus atoms based on the mass of the total amount of the lubricating oil composition and the content of component (C) (component (C-1)) in terms of phosphorus atoms based on the mass of the total amount of the lubricating oil composition. The values ​​of MP1, MP2, MCa, and MB are all values ​​calculated from the blending amounts of each component. For the lubricating oil compositions obtained in each example, the kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index were measured in accordance with JIS K2283-2000. For the lubricating oil compositions obtained in each example, the volume resistivity was measured at an oil temperature of 80°C in accordance with the volume resistivity test specified in JIS C2101.

[0086] [Evaluation Tests of the Properties of the Lubricating Oil Compositions Obtained in Each Example, etc.] <Confirmation Test of the Anti-Deterioration Performance of the Lubricating Oil Composition for Silicone-Containing FIPG> The lubricating oil compositions obtained in each Example, etc. were used to evaluate the anti-deterioration performance of the silicone-containing FIPG, etc., as follows.

[0087] <Confirmation Test for Shape Change of Silicone-Containing FIPG (FIPG Deterioration Confirmation Test 1)> First, an iron plate (iron material: ISOT test catalyst) was prepared as a test specimen used in the JIS K 2514-1 oxidation stability test (ISOT). 5 g of silicone-containing FIPG (manufactured by Henkel, product name: 5460) was applied to the iron plate to obtain a test specimen with a silicone-containing FIPG coating film formed thereon. Next, the test specimen with the silicone-containing FIPG coating film formed thereon was placed in a 1000 mL beaker containing 500 mL of lubricating oil composition, and the test specimen was immersed in the lubricating oil composition at 150°C for 288 hours. After immersing the test specimen in the lubricating oil composition at 150°C for 288 hours, the test specimen was removed, and the change in shape of the silicone-containing FIPG coating film formed on the test specimen was visually confirmed. If it could be judged by visual inspection that there was no change in the shape of the coating film, it was rated as "E", and if peeling or the like had occurred and the shape of the coating film had changed, it could be judged that the coating film had deteriorated, it was rated as "F". The measurement results are shown in Tables 1 to 3.

[0088] <Test for measuring the amount of silicon eluted from a silicone-containing FIPG into a lubricating oil composition after use in the FIPG deterioration confirmation test 1 (FIPG deterioration confirmation test 2)> In the "test for confirming change in shape of a silicone-containing FIPG (FIPG deterioration confirmation test 1)," a test piece was immersed in the lubricating oil composition at 150°C for 288 hours, and the amount of silicon (Si) dissolved in the lubricating oil composition was measured in accordance with JIS K0116 (measured by ICP atomic emission spectrometry). Note that, since it is clear that the silicon measured in this manner is silicon eluted from the silicone-containing FIPG, the amount of silicon measured is shown in Tables 1 to 3 as the amount of silicon eluted.

[0089] In addition, in the results of the Deterioration Confirmation Tests 1 and 2, a lubricating oil composition that receives an evaluation result of "E" in Deterioration Confirmation Test 1 and has an amount of silicon elution measured in Deterioration Confirmation Test 2 of "200 mass ppm or less" can be evaluated as having a high level of performance in preventing deterioration of the silicone-containing FIPG.

[0090] <Test to evaluate the foamability of lubricating oil compositions after contact with silicone-containing FIPG> In the FIPG deterioration confirmation test 1 (test to confirm shape change of silicone-containing FIPG), a test piece was immersed in the lubricating oil composition at 150°C for 288 hours, and the foamability tests (sequence I to sequence III) specified in JIS K2518 were carried out using the lubricating oil compositions. The results of the foamability and foam stability (foamability / foam stability) after each sequence test are shown in Tables 1 to 3.

[0091] In this test, if the test result for Sequence I is "[numerical value of 200 or less] / 0," the test result for Sequence II is "[numerical value of 50 or less] / 0," and the test result for Sequence III is "[numerical value of 200 or less] / 0," the composition can be evaluated as having low foaming properties and a high level of foam-suppressing performance. On the other hand, a lubricating oil composition that does not satisfy at least one of the conditions of the test result for Sequence I being "[numerical value of 200 or less] / 0," the test result for Sequence II being "[numerical value of 50 or less] / 0," and the test result for Sequence III being "[numerical value of 200 or less] / 0" is determined to have low foam-suppressing performance.

[0092] <Test to confirm extreme pressure performance of lubricating oil composition> <High speed four-ball test> Using each of the lubricating oil compositions obtained in the examples, the maximum non-seizure load (LNSL [unit: N]) was measured at a rotation speed of 1800 rpm in a high speed four-ball test in accordance with ASTM D2783. The measurement results are shown in Tables 1 to 3. In this test, it can be seen that the larger the maximum non-seizure load (for example, 619 N or more), the more excellent the wear resistance.

[0093] <Shell Four-Ball Test> Using each of the lubricating oil compositions obtained in the examples, a Shell four-ball test in accordance with ASTM D4172 was performed under the conditions of a load of 392 N, a rotation speed of 1500 rpm, a temperature of 100°C, and a test time of 1 hour, and the wear scar diameter (mm) was measured. The measurement results are shown in Tables 1 to 3. In this test, it can be seen that the smaller the wear scar diameter (for example, 0.60 mm or less), the more excellent the wear resistance.

[0094] Based on the results of wear resistance confirmation tests using a high-speed four-ball test and a Shell four-ball test, lubricating oil compositions that satisfy both the conditions of an LSNL of 619 N or more and a wear scar diameter of 0.60 or less can be evaluated as having a high level of wear resistance (wear prevention performance).

[0095] <Falex Anti-Seizure Test> Using each of the lubricating oil compositions obtained in the examples, the seizure load (unit: N) was measured using a Falex testing machine (pin-V block testing machine) described in ASTM D3233 under test conditions of a temperature of 110°C and a rotation speed of 290 rpm. The results are shown in Tables 1 to 3. When such a seizure load is 4000 N or more, it can be evaluated as having excellent seizure resistance (extreme pressure resistance between steels).

[0096] <Unisteel Test (Thrust Needle BRG)> Using each of the lubricating oil compositions obtained in the examples, the rolling fatigue life of thrust bearings was measured by the Unisteel test (British Institute of Petroleum method: IP305 / 79) using a Unisteel rolling fatigue tester (Tokyo Testing Machines Co., Ltd., triple-barrel high-temperature rolling fatigue tester (TRF-1000 / 3-01H)). Test bearings were prepared by replacing one raceway of a thrust needle bearing (NSK FNTA-2542C) with a flat test piece (material: SUJ2). The time until fatigue damage occurred to either the rollers or the test piece was measured under conditions of a load of 7000 N, a surface pressure of 1 GPa, a rotational speed of 1450 rpm, and an oil temperature of 120°C. The vibration acceleration of the test section measured by a vibration accelerometer attached to the Unisteel rolling fatigue tester was 1.5 m / s. ２ It was determined that fatigue damage had occurred when the fatigue life reached 50%. The fatigue life was calculated as the 50% life (L50: the time when the cumulative probability reaches 50%) using a Weibull plot from the time until fatigue damage in 10 repeated tests. The results are shown in Tables 1 to 3. If the 50% life measured in this test is 2000 minutes or more, it can be determined that there is an effect of improving the fatigue life (pitting life) (effect of extending the fatigue life).

[0097] <Confirmation test of the power consumption saving property of lubricating oil composition> <Evaluation of power consumption saving property (fuel consumption saving property)> Using each of the lubricating oil compositions obtained in the examples, the kinematic viscosity at 25°C, which is the test start temperature in the WLTC mode fuel consumption test, was measured in accordance with JIS K 2283-2000, and the power consumption saving property was evaluated from the kinematic viscosity value at 25°C. The results obtained are shown in Tables 1 to 3. ２ If the fuel consumption rate is less than 1 / s, the resistance (agitation loss) caused by stirring of the lubricating oil by rotating bodies such as gears at the start of the fuel consumption test can be reduced, and the fuel consumption rate can be evaluated as being excellent in terms of power saving.

[0098]

[0099]

[0100]

[0101] As is clear from the results shown in Tables 1 to 3, the lubricating oil compositions obtained in Examples 1 to 9 (corresponding to the lubricating oil compositions for electric mobility gear transmissions of the present invention) were able to highly inhibit the deterioration of silicone-containing FIPG, and were able to keep foaming during use below a specific level, thereby improving power consumption at low viscosity. It was also found that the lubricating oil compositions obtained in Examples 1 to 9 (corresponding to the lubricating oil compositions for electric mobility gear transmissions of the present invention) were able to improve both extreme pressure performance based on anti-wear performance and anti-seizure performance, and fatigue life. Furthermore, the volume resistivity results also revealed that the lubricating oil compositions obtained in Examples 1 to 9 (corresponding to the lubricating oil compositions for electric mobility gear transmissions of the present invention) had the high level of electrical insulation required for lubricants for electric mobility (e.g., electric vehicles such as electric cars).

[0102] In contrast, the kinematic viscosity at 100°C of the lubricating base oil used in the composition is 2.7 mm ２When the kinematic viscosity at 40°C of the lubricating base oil used in the composition was less than 12.0 mm / s (Comparative Example 1), the deterioration prevention performance of the silicone-containing FIPG could not be made to a high level, and the foam suppression performance of the composition was also low. ２ / s (Comparative Examples 2 and 3), the foaming suppression performance of the composition was poor and the power consumption was also poor. Furthermore, when the poly(meth)acrylate content was 0.1% by mass or more (Comparative Examples 4 and 5), the foaming suppression performance of the composition was poor and the power consumption was also poor. Furthermore, in Comparative Examples 3 to 5, it was not possible to achieve a high level of abrasion resistance (abrasion prevention performance).

[0103] Furthermore, when only one type of phosphorus-based additive was used as the phosphorus-based additive (Comparative Examples 6 to 8), the deterioration prevention performance of the silicone-containing FIPG could not be made to a high level, and the anti-seizure properties and fatigue life could not be made to be excellent. Even when two types of phosphorus-based additives were used, when the total content of those phosphorus-based additives (MP1 + MP2) in terms of phosphorus atoms was less than 0.025 mass% based on the total mass of the lubricating oil composition (Comparative Example 9), the deterioration prevention performance of the silicone-containing FIPG could not be made to a high level, and the wear resistance (anti-wear performance), anti-seizure properties, and fatigue life improvement effects could not be made to be excellent. Furthermore, even when two types of phosphorus-based additives were used, when the total content of the phosphorus-based additives (MP1 + MP2) in terms of phosphorus atoms exceeded 0.050 mass% based on the total mass of the lubricating oil composition (Comparative Example 10), the deterioration prevention performance of the silicone-containing FIPG could not be made to a high level, and the foam suppression performance of the composition was also poor. Furthermore, even when two phosphorus-based additives were used, if the size of MP1 was not within the range of 2.0 to 2.4 times the size of MP2 (Comparative Examples 11 and 12), the silicone-containing FIPG could not be provided with a high level of anti-degradation performance, the composition's ability to suppress foaming was poor, and it was not possible to provide excellent wear resistance (note that Comparative Example 11 did not provide excellent anti-seizure performance, and Comparative Example 12 did not provide excellent fatigue life). Furthermore, if the content MCa of component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, was not within the range of 0.009 to 0.013 mass% (Comparative Examples 13 and 14), it was not possible to provide a high level of anti-degradation performance of the silicone-containing FIPG, the composition's ability to suppress foaming was poor, and it was not possible to provide excellent fatigue life (note that Comparative Example 14 did not provide excellent wear resistance or anti-seizure performance).Furthermore, when the content MB of component (E) in terms of boron atoms was not within the range of 0.9 to 1.2 times the content MCa of component (D) in terms of calcium atoms (Comparative Examples 15 to 16), the foaming suppression performance of the composition was poor, and the fatigue life was not excellent either (note that in Comparative Example 15, the deterioration prevention performance of the silicone-containing FIPG could not be made to a high level, and in Comparative Example 16, the wear resistance and seizure resistance could not be made to be excellent).

[0104] These results show that a lubricating oil composition containing the components (A) to (F) and satisfying all of the conditions (i) to (vi) described above can prevent deterioration of the silicone-containing FIPG during use in a gear-type transmission for electric mobility (for example, a reducer for an electric vehicle) in which joints are sealed with a silicone-containing FIPG, can prevent oil leakage from the joints over a long period of time, and has a high ability to suppress foaming during use, so can effectively prevent situations such as oil spraying out from the breather of the gear-type transmission.It was also found that the properties required of a lubricating oil composition for use in electric mobility (extreme pressure performance, performance to improve the fatigue life of gears, etc., and fuel-saving performance) can be enhanced.

[0105] As explained above, according to the present invention, it is possible to (1) provide a geared transmission for electric mobility that can highly inhibit deterioration of a silicone-containing FIPG caused by the lubricating oil composition when the geared transmission is in use, can keep foaming of the lubricating oil composition at or below a specific level when the geared transmission is in use, and can simultaneously achieve improved power consumption and improved fatigue life; (2) provide a lubricating oil composition for a geared transmission for electric mobility that can highly inhibit deterioration of a silicone-containing FIPG, can keep foaming during use at or below a specific level, and can improve power consumption with a low viscosity, while also improving extreme pressure performance based on anti-wear performance and anti-seizure performance and fatigue life, and can have the high level of electrical insulation required of a lubricating oil for electric mobility; and (3) provide a method for lubricating a geared transmission for electric mobility using the lubricating oil composition.

[0106] The lubricating oil composition for gear-type transmissions for electric mobility of the present invention is extremely useful for improving the power saving performance and fatigue life of electric mobility by using it in gear-type transmissions (e.g., reducers) of electric mobility that use a silicone-containing FIPG as a sealant for joints.

Claims

1. A gear-type transmission for electric mobility, comprising a lubricating oil composition for lubricating sliding parts, and a joint part at least partially using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition, wherein the lubricating oil composition has: (A) a kinetic viscosity at 40°C of 12.0 mm ２ / s or less and the kinetic viscosity at 100°C is 2.7 mm ２ (B) a first phosphorus-based additive having at least one alkyl group in its structure, each of which has 8 or less carbon atoms; (C) a second phosphorus-based additive having at least one alkyl group in its structure, each of which has 14 or more carbon atoms; (D) a calcium-based detergent; (E) a boron-modified succinimide-based dispersant; and (F) a poly(meth)acrylate, and the lubricating oil composition comprises the following conditions (i) to (vi): (i) the sum of the content of the (B) component in terms of phosphorus atoms and the content of the (C) component in terms of phosphorus atoms is 0.025 mass % or more and 0.050 mass % or less, based on the total mass of the lubricating oil composition; (ii) the content of the component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content of the component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition; (iii) the content of the component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is 0.009 to 0.013 mass%; (iv) the content of the component (E) in terms of boron atoms, based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content of the component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition; (v) the content of the component (F) is less than 0.1 mass% based on the total mass of the lubricating oil composition; (vi) the lubricating oil composition has a volume resistivity at 80°C of 50 MΩ·m or more and a kinetic viscosity at 100°C of 2.7 mm ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more.

2. The gear-type transmission for electric mobility according to claim 1, wherein the component (B) is a phosphite ester in which all of the alkyl groups contained in the structure have 8 or less carbon atoms.

3. The gear-type transmission for electric mobility according to claim 1, wherein the component (C) is an amine salt of a phosphite ester in which all of the alkyl groups contained in the structure have 14 or more carbon atoms.

4. The gear-type transmission for electric mobility according to claim 1, wherein the component (D) is at least one selected from the group consisting of calcium sulfonate having a base number of 200 mg KOH / g or more, calcium phenate having a base number of 200 mg KOH / g or more, and calcium salicylate having a base number of 200 mg KOH / g or more.

5. A gear-type transmission for electric mobility according to claim 1, wherein the weight average molecular weight of component (F) is 60,000 or less.

6. A lubricating oil composition used to lubricate sliding parts of a gear-type transmission for electric mobility, which has a joint at least partially using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition, wherein the lubricating oil composition has: (A) a kinetic viscosity at 40°C of 12.0 mm ２ / s or less and the kinetic viscosity at 100°C is 2.7 mm ２ (B) a first phosphorus-based additive having at least one alkyl group in its structure, each of which has 8 or less carbon atoms; (C) a second phosphorus-based additive having at least one alkyl group in its structure, each of which has 14 or more carbon atoms; (D) a calcium-based detergent; (E) a boron-modified succinimide-based dispersant; and (F) a poly(meth)acrylate, and the lubricating oil composition comprises the following conditions (i) to (vi): (i) the sum of the content of the (B) component in terms of phosphorus atoms and the content of the (C) component in terms of phosphorus atoms is 0.025 mass % or more and 0.050 mass % or less, based on the total mass of the lubricating oil composition; (ii) the content of the component (B) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition, is 2.0 to 2.4 times the content of the component (C) in terms of phosphorus atoms, based on the total mass of the lubricating oil composition; (iii) the content of the component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition, is 0.009 to 0.013 mass%; (iv) the content of the component (E) in terms of boron atoms, based on the total mass of the lubricating oil composition, is 0.9 to 1.2 times the content of the component (D) in terms of calcium atoms, based on the total mass of the lubricating oil composition; (v) the content of the component (F) is less than 0.1 mass% based on the total mass of the lubricating oil composition; (vi) the lubricating oil composition has a volume resistivity at 80°C of 50 MΩ·m or more and a kinetic viscosity at 100°C of 2.7 mm ２ / s or more 3.0mm ２ / s or less and a viscosity index of 100 or more.

7. A method for lubricating a gear-type transmission for electric mobility, comprising lubricating a sliding portion of the gear-type transmission for electric mobility, the sliding portion having a joint at least partially using a foam-in-place gasket containing silicone as a sealing member for the lubricating oil composition, with the lubricating oil composition for gear-type transmission for electric mobility described in claim 6.