Gear transmission for electric moving body, lubricating oil composition for gear transmission for electric moving body, and method for lubricating gear transmission for electric moving body using said lubricating oil composition

Abstract

A geared transmission for an electric moving body is provided with: a lubricating oil composition for lubricating a sliding portion; provided is a lubricating oil composition which contains specific components (A) to (F) and all of which satisfy specific conditions (i) to (vi), and a joining part which uses, as a sealing member of the lubricating oil composition, an in-situ molded gasket containing a polysiloxane in at least a portion thereof, and which is characterized in that the lubricating oil composition contains specific components (A) to (F) and all of which satisfy specific conditions (i) to (vi).

Description

Technical Field

[0001] This invention relates to a gear transmission for electric mobile vehicles, a lubricating oil composition for a gear transmission for electric mobile vehicles, and a lubrication method for a gear transmission for electric mobile vehicles using the lubricating oil composition. Background Technology

[0002] In the field of gear transmissions, including gear reducers, speed increasers, and multi-stage transmissions, the use of low-viscosity lubricating oil compositions has long been a requirement for fuel efficiency. In particular, gear transmissions for electric vehicles (such as electric cars) require even lower viscosity lubricating oil compositions to address the need for energy savings. Furthermore, in addition to energy savings, lubricating oil compositions used in gear transmissions for electric vehicles also require improved gear and bearing durability, as well as high electrical insulation to support direct cooling of the motor in the electric vehicle.

[0003] In order to meet such requirements, various lubricant compositions have been studied for use in gear transmissions for electric motors. As an example of such a lubricating oil composition, for instance, International Publication No. 2020 / 189580 (Patent Document 1) discloses a lubricating oil composition for use in the powertrain system of an electric vehicle, comprising: a lubricating oil base oil; an alkaline earth metal detergent at a mass concentration of 10 ppm to 1000 ppm based on the total amount of the lubricating oil composition; a specific triazole compound at a mass concentration of 0.005% to 0.90% based on the total amount of the lubricating oil composition; at least one sulfur-containing compound selected from sulfur-containing heterocyclic ether compounds and thioether compounds at a sulfur content of 10 ppm to 2000 ppm based on the total amount of the lubricating oil composition; and an ashless dispersant at a mass concentration of 0.010% to 4.0% based on the total amount of the lubricating oil composition; furthermore, as a preferred embodiment, a lubricating oil composition further comprising a phosphorus compound at a mass concentration of 100 to 1500 ppm based on the total amount of the lubricating oil composition. It should be noted that in Patent Document 1, the compositions disclosed as examples of lubricating oil compositions (Examples 1 to 31) are all in the form of containing one phosphorus compound.

[0004] Existing technical documents Patent documents Patent Document 1: International Publication No. 2020 / 189580 Summary of the Invention

[0005] The problem that the invention aims to solve However, even with conventional lubricating oil compositions as described in Patent Document 1, there is room for improvement in the use of geared transmissions for electric moving parts (e.g., reducers for electric vehicles) where at least a portion of the lubricating oil composition uses field-molded gaskets containing polysiloxane (also known as "silicone-containing") (hereinafter, for convenience, field-molded gaskets containing polysiloxane are sometimes simply referred to as "FIPGs containing polysiloxane") as sealing members of the lubricating oil composition, in terms of highly suppressing the deterioration of FIPGs containing polysiloxane during the use of the geared transmission, and in terms of keeping foaming during use below a certain level.

[0006] The present invention was made in view of the problems of the prior art described above. The object of the present invention is to: (1) provide a gear transmission for an electric motor that can highly suppress the deterioration of FIPG containing polysiloxane caused by the lubricating oil composition during the use of the gear transmission, and can reduce the foaming of the lubricating oil composition during the use of the gear transmission to a certain level or below, and can simultaneously improve power saving performance and fatigue life; (2) provide a lubricating oil composition for a gear transmission for an electric motor that can highly suppress the deterioration of FIPG containing polysiloxane, and can reduce the foaming during use to a certain level or below, can improve power saving performance due to low viscosity, and can simultaneously improve extreme pressure performance and fatigue life based on anti-wear performance and sintering resistance performance, and can also have the high electrical insulation required for lubricating oil for electric motors; and (3) provide a lubrication method for a gear transmission for an electric motor using the above-described lubricating oil composition.

[0007] Methods for solving problems In order to achieve the above-mentioned objectives, the inventors have repeatedly conducted in-depth research and discovered that in a geared transmission for an electric moving body, which includes a lubricating oil composition for lubricating sliding parts and uses at least a portion of a field-molded gasket (FIPG containing polysiloxane) as a sealing member of the lubricating oil composition at the joint, by including the lubricating oil composition with the following components (A) to (F) and satisfying all of the following conditions (i) to (vi), it is possible to highly suppress the deterioration of the FIPG containing polysiloxane caused by the lubricating oil composition during the use of the geared transmission, and to keep the foaming of the lubricating oil composition during the use of the geared transmission below a certain level, thereby achieving both improved power consumption and improved fatigue life.

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

[0009] [1] A gear-type transmission for an electric mobile body, comprising: a lubricating oil composition for lubricating sliding parts; and a joint wherein at least a portion uses a field-molded gasket containing polysiloxane (also referred to as an "in-situ molded gasket") as a sealing member of the lubricating oil composition, wherein, The lubricating oil composition contains: (A) Lubricating oil base oil, with a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity is below 0.5 m / s and 2.7 mm at 100°C. 2 Hydrocracked mineral oil with a density of over / s; (B) A first phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 8 or less; (C) A second phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 14 or more; (D) Calcium-based detergents; (E) Boron-modified succinimide dispersant; and (F) Poly(meth)acrylate, Furthermore, all of the lubricating oil compositions satisfy the following conditions (i) to (vi): (i) 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 and 0.050% by mass based on the total mass of the lubricating oil composition. (ii) The content of component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content of component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms. (iii) The content of component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms, is 0.009% by mass or more and 0.013% by mass or less; (iv) The content of component (E) based on the total mass of the lubricating oil composition, expressed in boron atoms, is more than 0.9 times and less than 1.2 times the content of component (D) based on the total mass of the lubricating oil composition, expressed in calcium atoms. (v) The content of component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass; (vi) The volume resistivity of the lubricating oil composition at 80°C is ≥ 50 MΩ·m, and the kinematic viscosity at 100°C is 2.7 mm. 2 / s or higher and 3.0mm 2 The viscosity is below 100 / s and the viscosity index is above 100.

[0010] [2] According to the gear transmission for electric moving body as described in [1], wherein the (B) component is a phosphite in which all alkyl groups contained in the structure are alkyl groups with 8 or fewer carbon atoms.

[0011] [3] The geared transmission for an electric moving body according to [1] or [2], wherein the (C) component is an amine salt of a phosphite containing alkyl groups having 14 or more carbon atoms.

[0012] [4] A gear-type transmission for an electric moving body according to any one of [1] to [3], wherein the (D) component is at least one selected from the group consisting of calcium sulfonate with an alkalinity of 200 mg KOH / g or more, calcium phenolate with an alkalinity of 200 mg KOH / g or more, and calcium salicylate with an alkalinity of 200 mg KOH / g or more.

[0013] [5] A geared transmission for an electric moving body 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 for lubricating sliding parts of a geared transmission for an electric mobile body, the geared transmission for the electric mobile body having a joint portion in which at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition, wherein... The lubricating oil composition contains: (A) Lubricating oil base oil, with a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity is below 0.5 m / s and 2.7 mm at 100°C. 2 Hydrocracked mineral oil with a density of over / s; (B) A first phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 8 or less; (C) A second phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 14 or more; (D) Calcium-based detergents; (E) Boron-modified succinimide dispersant; and (F) Poly(meth)acrylate, Furthermore, all of the lubricating oil compositions satisfy the following conditions (i) to (vi): (i) 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 and 0.050% by mass based on the total mass of the lubricating oil composition. (ii) The content of component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content of component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms. (iii) The content of component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms, is 0.009% by mass or more and 0.013% by mass or less; (iv) The content of component (E) based on the total mass of the lubricating oil composition, expressed in boron atoms, is more than 0.9 times and less than 1.2 times the content of component (D) based on the total mass of the lubricating oil composition, expressed in calcium atoms. (v) The content of component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass; (vi) The volume resistivity of the lubricating oil composition at 80°C is ≥ 50 MΩ·m, and the kinematic viscosity at 100°C is 2.7 mm. 2 / s or higher and 3.0mm 2 The viscosity is below 100 / s and the viscosity index is above 100.

[0015] [7] A lubrication method for a geared transmission for an electric mobile body, wherein the sliding parts of the geared transmission for an electric mobile body are lubricated using the lubricating oil composition for a geared transmission for an electric mobile body described in [6], the geared transmission for an electric mobile body having a joint portion, wherein at least a portion of the joint portion uses a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition.

[0016] The reason for achieving the above-mentioned objective using the gear-type transmission for the electric moving body of the present invention may not be clear, but the inventors speculate as follows.

[0017] First, let's examine the case of using a conventional low-viscosity lubricating oil composition, specifically a lubricating oil composition containing phosphorus-based additives, in a gear transmission for an electric motor (e.g., a reducer for an electric vehicle) where the joint has a FIPG containing polysiloxane. Generally, when the lubricating oil composition comes into contact with the FIPG containing polysiloxane, the lower the viscosity of the composition, the easier it is for the lubricating oil composition (especially the base oil) to penetrate into the interior of the FIPG containing polysiloxane, leading to a tendency for the FIPG containing polysiloxane to swell. Furthermore, when a low-viscosity lubricating oil composition penetrates into the FIPG containing polysiloxane, silicon readily dissolves and leaches into the lubricating oil composition, particularly due to the oxides (phosphoric acid) of the phosphorus-based additives generated during use. Therefore, for conventional low-viscosity lubricating oil compositions containing phosphorus-based additives, the composition itself becomes one of the reasons for the reduced strength of the FIPG containing polysiloxane (one of the causes of FIPG deterioration). Furthermore, if the strength of the FIPG decreases, problems such as oil leakage and seepage from the joints can occur, thus requiring improvements to conventional lubricant compositions. Additionally, the inventors have discovered, through research, that as described above, if silicon dissolves into the lubricant composition, it becomes a cause of foaming, and in the case of poly(meth)acrylate as an additive, depending on its amount used, it also contributes to foaming in the lubricant composition.

[0018] Therefore, in the gear transmission for electric vehicles of the present invention, a specific lubricating oil composition containing the components (A) to (F) and satisfying all conditions (i) to (vi) is used to lubricate the sliding parts. While the rationale for using phosphorus-based additives is not necessarily clear, the inventors have found that the aggression of FIPG containing polysiloxanes can be highly suppressed by using such a lubricating oil composition, thereby highly preventing FIPG degradation. Furthermore, combined with the combination of the amounts of other additives used, foaming during use of the lubricating oil composition can be kept below a certain level. It should be noted that by keeping the foaming during use of the lubricating oil composition below a certain level, the possibility of oil spraying from the breather plug of the gear transmission can also be highly suppressed. In addition, since the lubricating oil composition used in the gear transmission for electric vehicles of the present invention has a low kinematic viscosity, it is also possible to improve the energy efficiency of electric vehicles (e.g., electric cars). Furthermore, the geared transmission for electric vehicles of the present invention, by specifying the type of base oil and the formulation of additives in the lubricating oil composition used, achieves high levels of anti-wear performance, anti-sintering performance, and fatigue life suppression during use. Moreover, by specifying the formulation of additives in the lubricating oil composition used in the geared transmission for electric vehicles of the present invention, the volume resistivity at 80°C can be set to a specific level or higher, thereby achieving high electrical insulation. Based on this viewpoint, the inventors speculate that the geared transmission for electric vehicles of the present invention can highly suppress the deterioration of FIPG containing polysiloxanes caused by the lubricating oil composition when using a geared transmission, and can keep the foaming of the lubricating oil composition when using a geared transmission below a specific level, while simultaneously improving power consumption and the durability (fatigue life) of gears, bearings, etc.

[0019] Invention Effects According to the present invention, (1) a gear transmission for an electric motor is provided, which can highly suppress the deterioration of FIPG containing polysiloxane caused by the lubricating oil composition when using the gear transmission, and can reduce the foaming of the lubricating oil composition when using the gear transmission to a certain level or below, and can simultaneously improve power saving performance and fatigue life; (2) a lubricating oil composition for a gear transmission for an electric motor is provided, which can highly suppress the deterioration of FIPG containing polysiloxane, and can reduce the foaming during use to a certain level or below, can improve power saving performance due to low viscosity, and can simultaneously improve extreme pressure performance and fatigue life based on anti-wear performance and sintering resistance performance, and can also have the high electrical insulation required for lubricating oil for an electric motor; and (3) a lubrication method for a gear transmission for an electric motor using the above-described lubricating oil composition is provided. Detailed Implementation

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

[0021] Gear-type transmission for electric mobility devices The gear-type transmission for an electric mobile body of the present invention comprises: a lubricating oil composition for lubricating sliding parts; and a joint wherein at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the aforementioned lubricating oil composition, wherein... The above-mentioned lubricating oil composition contains: (A) Lubricating oil base oil, with a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity is below 0.5 m / s and 2.7 mm at 100°C. 2 Hydrocracked mineral oil with a density of over / s; (B) A first phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 8 or less; (C) A second phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 14 or more; (D) Calcium-based detergents; (E) Boron-modified succinimide dispersant; and (F) Poly(meth)acrylate, Furthermore, all of the above-mentioned lubricating oil compositions satisfy the following conditions (i) to (vi): (i) The sum of the content (mass%) of component (B) above and the content (mass%) of component (C) above, expressed 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) above, based on the total mass of the lubricating oil composition, in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content (mass%) of component (C) above, based on the total mass of the lubricating oil composition, in terms of phosphorus atoms. (iii) The content of the above-mentioned component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms, is 0.009% by mass or more and 0.013% by mass or less; (iv) The content (mass%) of the above-mentioned component (E) based on the total mass of the lubricating oil composition, expressed in terms of boron atoms, is more than 0.9 times and less than 1.2 times the content (mass%) of the above-mentioned component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms. (v) The content of the above-mentioned component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass; (vi) The volume resistivity of the lubricating oil composition at 80°C is ≥ 50 MΩ·m, and the kinematic viscosity at 100°C is 2.7 mm. 2 / s or higher and 3.0mm 2 The viscosity is below 100 / s and the viscosity index is above 100.

[0022] Furthermore, in this specification, "electric mobile body" refers to a moving object that uses an electric motor as a drive source to drive drive wheels, etc., to travel or fly, including so-called electric vehicles (e.g., electric cars) with two wheels or four wheels. Additionally, in this specification, "gear transmission" includes the concept of a reducer, a speed increaser, and a multi-stage transmission. Hereinafter, the lubricating oil composition of the gear transmission for an electric mobile body according to the present invention will be described first.

[0023] <About Lubricating Oil Compositions> As described above, the lubricating oil composition of the present invention contains the components (A) to (F) described above, and all of them satisfy the conditions (i) to (vi) described above. Here, the components used in the lubricating oil composition of the present invention will be explained.

[0024] <Regarding the components in lubricating oil compositions> [(A) Composition: Lubricating oil base oil] The lubricating oil base oil contained as component (A) in the above-mentioned lubricating oil composition has a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity is below 0.5 m / s and 2.7 mm at 100°C. 2Hydrocracked mineral oil with a capacity of over / s.

[0025] Such hydrocracked mineral oils only need to meet the requirement of a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity is below 0.5 m / s and 2.7 mm at 100°C. 2 The condition of / s or above is sufficient. It may contain only one hydrocracking mineral oil that meets such conditions, or it may contain a mixture of two or more hydrocracking mineral oils that meet such conditions.

[0026] Such hydrocracked mineral oil is any oil obtained by hydrocracking a so-called mineral oil, without particular restrictions. Known hydrocracked mineral oils can be used appropriately. Among them, the preferred method is to obtain mineral oil by hydrocracking a vacuum distillation oil (WVGO), a mild hydrocracking (MHC) treated oil of WVGO, a deasphalted oil (DAO), an MHC treated oil of DAO, or a mixture thereof, and then dewaxing the product or the lubricating oil fraction recovered from the product by distillation or the like; or, mineral oil obtained by further distilling the mineral oil (it should be noted that there are no particular restrictions on the various treatment methods such as "hydrocracking" and "dewaxing" mentioned here, and known methods can be used appropriately).

[0027] Furthermore, the hydrocracked mineral oil used as the base oil (component A) of the aforementioned lubricating oil requires a kinematic viscosity of 12.0 mm at 40°C. 2 The kinematic viscosity at 40°C is below 12.0 mm² / s. 2 For values ​​below / s, compared to values ​​exceeding 12.0mm 2 Compared to the case of / s, it can form a low viscosity lubricating oil composition, and in particular, it can achieve a reduction in stirring loss at low temperatures (25°C). Therefore, it can achieve high performance in terms of saving power consumption, and can highly suppress foaming of the composition during use (achieving a high level of defoaming). The kinematic viscosity of such hydrocracked mineral oil at 40°C is preferably 9.0 mm. 2 / s or higher and 12.0mm 2 / s or less, more preferably 10.0mm 2 / s or higher and 11.0mm 2 / s or less. It should be noted that when the kinematic viscosity at 40°C is above the aforementioned lower limit, compared with the case where it is below the aforementioned lower limit, the oil film formation at the lubrication point can be further improved, the lubricity can be further improved, and there is a tendency to further reduce the evaporation loss of the lubricating oil composition.

[0028] Furthermore, the hydrocracked mineral oil used as the base oil (component A) of the aforementioned lubricating oil requires a kinematic viscosity of 2.7 mm at 100°C. 2 / s or more. The kinematic viscosity of the hydrocracked mineral oil at 100°C was 2.7 mm. 2 / s or higher, compared to less than 2.7mm 2 Compared to the case of / s, the oil film formation performance at the lubrication points is improved, which enhances wear resistance and bearing fatigue life, and also improves resistance to sintering. Furthermore, the kinematic viscosity of this hydrocracked mineral oil at 100°C is preferably 2.7 mm. 2 / s or higher and 3.0mm 2 / s or less, more preferably 2.75mm 2 / s or higher and 2.90mm 2 / s or less. It should be noted that when the kinematic viscosity at 100°C is below the aforementioned upper limit, there is a tendency to achieve a greater effect in improving power consumption savings compared to when it exceeds the aforementioned upper limit. It should also be noted that in this specification, the "kinematic viscosity at 40°C" and "kinematic viscosity at 100°C" for the lubricating oil base oil and lubricating oil composition refer to the kinematic viscosity at each temperature (40°C or 100°C) specified in JIS K2283-2000.

[0029] Furthermore, the sulfur content (sulfur composition) of the aforementioned hydrocracking mineral oil is preferably 30 ppm by mass or less (more preferably 1 to 10 ppm by mass). Setting the sulfur content below the aforementioned upper limit improves oxidation stability compared to conditions exceeding the upper limit. On the other hand, setting the sulfur content above the aforementioned lower limit improves sintering resistance and abrasion resistance, thereby enhancing durability and reliability compared to conditions below the lower limit. It should be noted that this "sulfur content" can be determined by measurement according to ASTM D4951.

[0030] Furthermore, the viscosity index of the aforementioned hydrocracking mineral oil is preferably 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 to the lower limit mentioned above, a greater effect can be achieved in terms of saving power consumption. It should be noted that, in this specification, the "viscosity index" of the lubricating oil base oil and the lubricating oil composition is the value measured according to JIS K 2283-1993.

[0031] The aforementioned hydrocracking mineral oil can preferably use at least one base oil 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 is abbreviated as "API Group"). API Group II base oils are base oils with a sulfur content of 0.03% by mass or less, a saturated component content of 90% by mass or more, and a viscosity index of 80 or more and less than 120. API Group III base oils are base oils with a sulfur content of 0.03% by mass or less, a saturated component content of 90% by mass or more, and a viscosity index of 120 or more. Furthermore, as the aforementioned hydrocracking mineral oil, one base oil selected from API Group II and API Group III base oils can be used alone, or two or more base oils selected from API Group II and API Group III base oils can be used in combination as a blended base oil. Furthermore, from the viewpoint that the viscosity characteristics can be easily adjusted to the desired range, the hydrocracked mineral oil used as the base oil (component A) of the above-mentioned lubricating oil is preferably a blended oil obtained by mixing two or more base oils (two or more mineral oils obtained through the hydrocracking process), wherein, more preferably, it is a blended base oil of two or more API Group II base oils.

[0032] [(B) Ingredient: First phosphorus-based additive] The first phosphorus-based additive as component (B) is a phosphorus-based additive that contains at least one alkyl group in its structure and all alkyl groups in the structure have 8 or fewer carbon atoms. Such a phosphorus-based additive is only required to contain at least one alkyl group in its structure and all alkyl groups in the structure have 8 or fewer carbon atoms. Well-known phosphorus-based additives that meet this condition and contain phosphorus atoms as constituent elements and are used in the field of lubricating oil compositions can be appropriately used.

[0033] The number of carbon atoms in the alkyl groups that can be contained in the structure of the compound used as such a first phosphorus additive (component B) needs to be 8 or less (more preferably 2 to 6). By making the number of carbon atoms in the alkyl groups contained in such a first phosphorus additive 8 or less, and by combining it with component (C), although the reason may not be certain, it is possible to highly suppress the attack on FIPG containing polysiloxane, thereby highly suppressing the deterioration of FIPG.

[0034] Furthermore, compounds used as such a first phosphorus-based additive (B) component can include, for example, phosphites (phosphites), phosphate esters (phosphate esters), their amine salts, their metal salts, and their derivatives, in which all alkyl groups in the structure have 8 or fewer carbon atoms. Among these, phosphites in which all alkyl groups in the structure have 8 or fewer carbon atoms are preferred from the viewpoint of obtaining higher effects in terms of sintering resistance, wear resistance, and fatigue life improvement. Dialkyl phosphites (dialkyl phosphites) in which all alkyl groups have 8 or fewer carbon atoms are more preferred, and dibutyl phosphites are particularly preferred. There are no particular limitations on such a first phosphorus-based additive, and commercially available products can be used.

[0035] [(C) Ingredient: Second phosphorus additive] The second phosphorus-based additive as component (C) is a phosphorus-based additive that contains at least one alkyl group in its structure and all alkyl groups in the structure have 14 or more carbon atoms. Such a phosphorus-based additive is only required to contain at least one alkyl group in its structure and all alkyl groups in the structure have 14 or more carbon atoms. Well-known phosphorus-based additives that meet this condition and contain phosphorus atoms as constituent elements and are used in the field of lubricating oil compositions can be appropriately used.

[0036] The alkyl groups in the structure of the compound used as such a second phosphorus additive (component C) must each have 14 or more carbon atoms (more preferably 16 to 20). By ensuring that the alkyl groups in such a second phosphorus additive have 14 or more carbon atoms, and by combining it with component (B), although the reasons may not be clear, it is possible to highly suppress the attack on FIPGs containing polysiloxanes, thereby highly suppressing the degradation of FIPGs.

[0037] Furthermore, compounds used as such a second phosphorus-based additive (C) component can be exemplified by phosphites (phosphites), phosphate esters (phosphate esters), their amine salts, their metal salts, and their derivatives, in which all alkyl groups in the structure have 14 or more carbon atoms. From the viewpoint of improving sintering resistance, wear resistance, and fatigue life, amine salts of phosphites in which all alkyl groups in the structure have 14 or more carbon atoms are preferred, and amine salts of dialkyl phosphites (dialkyl phosphites) in which all alkyl groups have 14 or more carbon atoms are more preferred. There are no particular limitations on such a second phosphorus-based additive, and commercially available products can be used.

[0038] [(D) Ingredient: Calcium-based detergent] There are no particular limitations on the calcium-based detergent used as component (D), and any known calcium-based detergent used in the field of lubricating oil compositions may be appropriately used. Examples of such calcium-based detergents include calcium sulfonate, calcium phenolate, and calcium salicylate. It should be noted that the calcium-based detergent may, for example, be over-alkalized with a carbonate (calcium carbonate). Examples of such calcium-based detergents include, for example, the calcium-based detergents (sulfonate detergents, phenolate detergents, salicylate detergents) described in paragraphs

[0038] to

[0053] of Japanese Patent Application Publication No. 2020-76004. Furthermore, one type of such calcium-based detergent may be used alone, or two or more may be used in combination. Additionally, commercially available products may be used as such calcium-based detergents.

[0039] Furthermore, the alkalinity of the aforementioned calcium-based detergent (component (D)) is preferably 200 mg KOH / g or higher (more preferably 300 mg KOH / g or higher and 500 mg KOH / g or lower). By setting such an alkalinity above the aforementioned lower limit, a higher effect can be obtained in suppressing the attack on FIPGs compared to cases below the aforementioned lower limit. It should be noted that, in this specification, the alkalinity of the calcium-based detergent is a value determined according to JIS K 2501:2003-9 (a value determined by the perchloric acid method).

[0040] In addition, as the above-mentioned calcium-based detergent ((D) component), it is particularly preferred to be a calcium-based detergent formed from at least one of the following groups: calcium sulfonate with an alkalinity of 200 mg KOH / g or more, calcium phenolate with an alkalinity of 200 mg KOH / g or more, and calcium salicylate with an alkalinity of 200 mg KOH / g or more.

[0041] [(E) Component: Boron-modified succinimide dispersant] As component (E), namely boron-modified succinimide-based dispersants, there are no particular limitations, and those known to be used appropriately in the field of lubricating oil compositions as ashless dispersants formed from boron-modified succinimides are examples of such boron-modified succinimides obtained by modifying polyolefin-derived succinimides having alkenyl or alkyl groups with boron compounds such as boric acid or borates.

[0042] As such boron-modified succinimide dispersants, those similar to the boron-modified succinimide dispersants described in Japanese Patent Application Publication No. 2022-090378 and the boron-modified ashless succinimide dispersant (C) described in Japanese Patent Application Publication No. 2009-108157 can be appropriately used. Furthermore, such boron-modified succinimide dispersants can be used alone or in combination of two or more. Additionally, commercially available products can be used as such boron-modified succinimide dispersants.

[0043] [(F) Ingredient: Poly(meth)acrylate] There are no particular limitations on the poly(meth)acrylate used as component (F), and poly(meth)acrylates known to be used in the field of lubricating oil compositions as so-called viscosity index improvers, pour point depressants, etc., may be appropriately used. It should be noted that in this specification, "(meth)acrylate" refers to acrylates and / or methacrylates.

[0044] Furthermore, the poly(meth)acrylate as such component (F) is more preferably a poly(meth)acrylate-based pour point depressant (poly(meth)acrylate used as a pour point depressant). Here, regarding the poly(meth)acrylate as component (F), from the viewpoint of obtaining a higher effect from the perspective of suppressing foaming of the composition, it is preferable to contain a poly(meth)acrylate-based pour point depressant (poly(meth)acrylate used as a pour point depressant) and not contain a poly(meth)acrylate-based viscosity index improver (poly(meth)acrylate used as a viscosity index improver).

[0045] Furthermore, the poly(meth)acrylate 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 below the above-mentioned upper limit, there is a tendency to obtain a greater effect in terms of suppressing foaming of the composition. It should be noted that the "weight-average molecular weight" referred to here refers to the value obtained by gel permeation chromatography (GPC) (the molecular weight obtained by conversion from standard polystyrene).

[0046] In such (F) components, one type of poly(meth)acrylate may be used alone, or two or more types of poly(meth)acrylate may be used in combination.

[0047] [Regarding components other than (A) to (F) that are available] The components that can be used in the lubricating oil composition of the present invention are not limited to the components (A) to (F) described above. Other known components of lubricating oil compositions for gear transmissions (e.g., reducers for electric vehicles) used in electric motors (e.g., antioxidants, metal passivators, rubber swelling agents, diluents, etc.) may be appropriately used, provided that they do not impair the effects of the present invention. There are no particular limitations on such other components; for example, commercially available performance additives (so-called additive packages: those formulated with multiple components) may be used.

[0048] The components of the lubricating oil composition of the present invention have been described above. The composition, characteristics and other properties of the lubricating oil composition will be described below.

[0049] <Regarding the composition and properties of lubricating oil compositions> Hereinafter, the conditions (i) to (vi) of the lubricating oil composition of the present invention will be described first, and then other preferred conditions will be described.

[0050] [Regarding condition (i)] The lubricating oil composition of the present invention needs to meet the following conditions (condition (i) above): the total amount of phosphorus atoms in the content of component (B) and the total amount of phosphorus atoms in the content of component (C) 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 total amount of phosphorus atoms in the content of component (B) and component (C) is above the lower limit, compared with the case below the lower limit, extreme pressure performance and fatigue life based on anti-wear performance and sintering resistance can be improved simultaneously. On the other hand, when the total amount of phosphorus atoms in the content of component (B) and component (C) is below the upper limit, compared with the case above the upper limit, the decrease in volume resistivity can be suppressed and electrical insulation can be maintained to a high degree. In addition, the degradation of FIPG containing polysiloxane can be further prevented to a high degree, and the foaming height of the lubricating oil composition during use can also be maintained below a certain level. Regarding the total amount of phosphorus atoms in the content of component (B) and component (C) mentioned above, from the perspective of obtaining higher effects from the same point of view, it is more preferable to be 0.025% by mass or more and 0.050% by mass or less (more preferably 0.030% by mass or more and 0.050% by mass or less) based on the total mass of the lubricating oil composition.

[0051] [Regarding condition (ii)] The lubricating oil composition of the present invention needs to satisfy the following condition (condition (ii) above): the content (mass%) of the above-mentioned component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content (mass%) of the above-mentioned component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms. In other words, when the content of the above-mentioned component (B) based on the total mass of the lubricating oil composition is set as "MP1" and the content of the above-mentioned component (C) based on the total mass of the lubricating oil composition is set as "MP2", the value obtained by dividing MP1 by MP2 ([MP1] / [MP2]) needs to be more than 2.0 and less than 2.4. By making MP1 more than twice that of MP2 (the value of [MP1] / [MP2] is 2.0 or more), compared with the case where it is less than twice, extreme pressure performance can be improved, and the degradation of FIPG containing polysiloxane can be further prevented to a high degree. Moreover, the foaming height of the lubricating oil composition during use can be maintained below a certain level. On the other hand, by making MP1 less than 2.4 times that of MP2 (the value of [MP1] / [MP2] is 2.4 or less), compared with the case where it is more than 2.4 times, a high degree of improvement in fatigue life can be obtained, and the degradation of FIPG containing polysiloxane can be highly prevented. Moreover, the foaming height of the lubricating oil composition during use can be maintained below a certain level. Furthermore, from the perspective of obtaining even better effects from the same point of view, it is more preferable that MP1 is more than 2.1 times and less than 2.3 times that of MP2.

[0052] It should be noted that in this invention, the first phosphorus additive (B) component and the second phosphorus additive (C) component are mixed and used in a specific ratio to satisfy the above conditions (i) to (ii). This effectively suppresses the distillation of silicon from the polysiloxane-containing FIPG and the associated deterioration of the polysiloxane-containing FIPG (softening, peeling, and reduced strength), which occurs when phosphorus additives are used alone. It also suppresses foaming of the composition during use caused by silicon distillation from the FIPG. Therefore, it effectively suppresses the problem of oil spraying from the breather plug of the gear transmission. (It should be noted that silicon is one of the causes of foaming in the composition; if the amount of silicon flowing out increases, it tends to make foam suppression more difficult (the ease of foam removal from the composition decreases).) Furthermore, by setting the value of [MP1] / [MP2] to the above range, it is possible to suppress the decrease in volume resistivity and maintain high electrical insulation, making it most suitable for gear transmissions for electric motors (especially preferably reducers for electric vehicles).

[0053] [Regarding condition (iii)] The lubricating oil composition of the present invention needs to satisfy the following condition (condition (iii) above): the content of the above-mentioned component (D) in terms of calcium atoms (the content of calcium atoms from component (D): hereinafter sometimes simply referred to as "MCa") based on the total mass of the lubricating oil composition is 0.009% by mass or more and 0.013% by mass or less. By setting MCa to 0.009% by mass or more, compared with the case of less than 0.009% by mass, fatigue life can be improved, and the deterioration of FIPG containing polysiloxane can be highly prevented, maintaining the foaming height of the lubricating oil composition in use at a specific level or less. On the other hand, by setting MCa to 0.013% by mass or less, compared with the case of more than 0.013% by mass, the deterioration of FIPG containing polysiloxane can be highly prevented, maintaining the foaming height of the lubricating oil composition in use at a specific level or less, and wear resistance, sintering resistance and fatigue life can be improved. In addition, by setting MCa to 0.013% by mass or less, the decrease in volume resistivity can be suppressed, and electrical insulation can be highly maintained. Furthermore, from the perspective of achieving higher results from the same point of view, MCa is preferably 0.010% by mass or more and 0.012% by mass or less.

[0054] [Regarding condition (iv)] The lubricating oil composition of the present invention needs to meet the following conditions (condition (iv) above): the content of boron atoms (mass percentage of boron atoms from component (E) based on the total mass of the lubricating oil composition) and the content of calcium atoms (MCa (mass percentage) of component (D) based on the total mass of the lubricating oil composition) are 0.9 times or more and 1.2 times or less. That is, it needs to meet the condition that the value obtained by dividing MB by MCa ([MB] / [MCa]) is 0.9 times or more and 1.2 times or less. By making MB 0.9 times or more of MCa (the value of [MB] / [MCa] is 0.9 times or more), compared with the case of less than 0.9 times, it is possible to highly prevent the deterioration of FIPG containing polysiloxane, thereby maintaining the foaming height of the lubricating oil composition during use at a specific level and improving fatigue life. On the other hand, by making MB 1.2 times or less of MCa (the value of [MB] / [MCa] is 1.2 or less), compared with the case where it exceeds 1.2 times, the foaming height of the lubricating oil composition can be maintained below a certain level, and fatigue life and extreme pressure properties can be improved. Furthermore, by making MB 1.2 times or less of MCa (the value of [MB] / [MCa] is 1.2 or less), the decrease in volume resistivity can be suppressed, and electrical insulation can be highly maintained. Moreover, from the same viewpoint, MB is more preferably 1.1 times or more and 1.2 times or less of MCa.

[0055] [Regarding condition (v)] The lubricating oil composition of the present invention needs to meet the following condition (condition (v) above): the content of the above-mentioned component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass. By setting the content of poly(meth)acrylate as component (F) to less than 0.1% by mass, foaming during use of the composition can be highly suppressed. That is, when the amount of poly(meth)acrylate added exceeds the above-mentioned upper limit, foaming is easily caused, and it is difficult to suppress foaming during use. In addition, regarding the content of such component (F), from the viewpoint that a higher effect can be obtained, it is more preferable to be 0.09% by mass or less (more preferably 0.07% by mass or less).

[0056] [Regarding condition (vi)] The lubricating oil composition of the present invention needs to meet the following conditions (condition (vi) above): 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 higher and 3.0mm 2 Products with a viscosity index of less than 100 and a viscosity index of 100 or higher.

[0057] As described in condition (vi), the lubricating oil composition of the present invention requires a volume resistivity of 50 MΩ·m or more (more preferably 51 MΩ·m or more and 55 MΩ·m or less) at 80°C. By setting such a volume resistivity of 50 MΩ·m or more, it is possible to achieve the high level of electrical insulation required in the field of electric mobility (particularly electric vehicles). In this specification, "volume resistivity" refers to the volume resistivity measured at an oil temperature of 80°C according to the volume resistivity test specified in JIS C2101.

[0058] Furthermore, for the lubricating oil composition of the present invention, as described in condition (vi) above, the kinematic viscosity of the composition at 100°C needs to be 2.7 mm. 2 / s or higher and 3.0mm 2 / s or less (more preferably 2.75mm) 2 / s or higher and 2.90mm 2 (below / s). By setting the kinematic viscosity of the composition at 100°C to or above the aforementioned lower limit, compared to cases below the aforementioned lower limit, it is possible to highly prevent the deterioration of FIPG containing polysiloxanes, and to maintain the foaming height of the lubricating oil composition during use at a specific level or below. In addition, by setting the kinematic viscosity of the composition at 100°C to or below the aforementioned upper limit, compared to cases exceeding the aforementioned upper limit, it is possible to improve power saving performance.

[0059] Furthermore, for the lubricating oil composition of the present invention, as described in condition (vi) above, the viscosity index of the composition needs to be 100 or more (more preferably 103 or more). By setting the viscosity index of the composition to the lower limit above, a higher effect can be obtained in terms of saving power consumption compared to the case where it is less than the lower limit.

[0060] [Regarding other preferred conditions] The lubricating oil composition of the present invention only needs to satisfy all the conditions (i) to (vi) described above. Other conditions are not particularly limited, but it is more preferable to satisfy the conditions described below.

[0061] In the lubricating oil composition of the present invention, the content of the lubricating oil base oil (hydrocracked base oil) as component (A) is preferably 90% by mass or more and 98% by mass or less (more preferably 92% by mass or more and 97% by mass or less) based on the total mass of the lubricating oil composition. Furthermore, when the lubricating oil composition of the present invention contains other components besides components (A) to (F), the content of such other components is preferably 10% by mass or less (more preferably 3% by mass or more and 8% by mass or less) based on the total mass of the lubricating oil composition.

[0062] Furthermore, in the lubricating oil composition of the present invention, from the viewpoint of improving sintering resistance, wear resistance, and fatigue life, the content of the aforementioned component (B), based on the total mass of the lubricating oil composition, is preferably 0.10% by mass or more and 0.30% by mass or less (more preferably 0.12% by mass or more and 0.25% by mass or less). Furthermore, in the lubricating oil composition of the present invention, the content of the aforementioned component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms (MP1: the content of phosphorus atoms from component (B)), is preferably 0.015% by mass or more and 0.040% by mass or less (more preferably 0.020% by mass or more and 0.035% by mass or less). When MP1 is at or above the aforementioned lower limit, compared to cases below the lower limit, there is a tendency to obtain greater effects in terms of improving sintering resistance, wear resistance, and fatigue life. On the other hand, when MP1 is at or below the aforementioned upper limit, compared to cases exceeding the aforementioned upper limit, there is a tendency to obtain greater effects in terms of improving sintering resistance, wear resistance, and fatigue life.

[0063] Furthermore, in the lubricating oil composition of the present invention, from the viewpoint of improving sintering resistance, wear resistance, and fatigue life, the content of the aforementioned component (C), based on the total mass of the lubricating oil composition, is preferably 0.30% by mass or more and 0.80% by mass or less (more preferably 0.35% by mass or more and 0.70% by mass or less). Furthermore, in the lubricating oil composition of the present invention, the content of the aforementioned component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms (MP2: the content of phosphorus atoms from component (C)), is preferably 0.008% by mass or more and 0.020% by mass or less (more preferably 0.009% by mass or more and 0.018% by mass or less). When MP2 is at or above the aforementioned lower limit, compared to cases below the lower limit, there is a tendency to obtain greater effects in terms of improving sintering resistance, wear resistance, and fatigue life. On the other hand, when MP2 is at or below the aforementioned upper limit, compared to cases exceeding the aforementioned upper limit, there is a tendency to obtain greater effects in terms of improving sintering resistance, wear resistance, and fatigue life.

[0064] Furthermore, in the lubricating oil composition of the present invention, the content of the above-mentioned (D) component based on the total mass of the lubricating oil composition is preferably 0.055% by mass or more and 0.130% by mass or less (more preferably 0.060% by mass or more and 0.120% by mass or less).

[0065] Furthermore, in the lubricating oil composition of the present invention, the content of the aforementioned (E) component, based on the total mass of the lubricating oil composition, is preferably 0.40% by mass or more and 0.80% by mass or less (more preferably 0.55% by mass or more and 0.65% by mass or less). Moreover, in the lubricating oil composition of the present invention, the content (MB) of the aforementioned (E) component, based on the total mass of the lubricating oil composition, in terms of boron atoms, is preferably 0.010% by mass or more and 0.017% by mass or less (more preferably 0.012% by mass or more and 0.015% by mass or less). When MB is at or above the aforementioned lower limit, compared to cases below the lower limit, there is a tendency to obtain greater effects in terms of improved sintering resistance, wear resistance, and fatigue life. On the other hand, when MB is at or below the aforementioned upper limit, compared to cases exceeding the aforementioned upper limit, there is a tendency to obtain greater effects in terms of improved sintering resistance, wear resistance, and fatigue life.

[0066] It should be noted that the conversion values ​​based on calcium, boron, or phosphorus atoms related to the content of each component described in this specification can be used if they can be calculated based on the type of raw material used and its amount added.

[0067] Furthermore, regarding the lubricating oil composition of the present invention, from the viewpoint of achieving a higher effect in saving power consumption, the kinematic viscosity of the composition at 40°C is preferably 9.0 mm. 2 / s or higher and 12.0mm 2 / s or less (more preferably 10.0mm) 2 / s or higher and 11.0mm 2 / s or less).

[0068] The lubricating oil composition of the present invention has been described above. Hereinafter, a gear transmission for an electric moving body of the present invention having such a lubricating oil composition will be described.

[0069] <Regarding gear transmissions for electric mobility devices> The gear transmission for electric mobile bodies of the present invention only needs to have the above-described lubricating oil composition of the present invention as a lubricating oil composition for lubricating sliding parts, and to have a joint where at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the above-described lubricating oil composition. The structure of the device itself is not particularly limited, and the structure used in known gear transmissions for electric mobile bodies (e.g., gear transmissions for electric vehicles, preferably reducers for electric vehicles, etc.) can be appropriately adopted.

[0070] Here, the phrase "using a field-molded gasket containing polysiloxane as a sealing member joint of the aforementioned lubricating oil composition in at least a portion" simply means that at least a portion of the sealing part of the joint of the constituent components of the gear transmission for electric motors uses a FIPG containing polysiloxane. This is used to seal the lubricating oil composition from leakage to the outside. Furthermore, such "using a field-molded gasket containing polysiloxane as a sealing member joint of the aforementioned lubricating oil composition in at least a portion" only needs to be present at least once in the gear transmission device for electric motors. Additionally, the statement regarding the FIPG containing polysiloxane "as a sealing member of the aforementioned lubricating oil composition" means that the FIPG containing polysiloxane is present at least in the portion in contact with the lubricating oil composition and is used as a member for sealing the lubricating oil composition; it can also seal internal air together with the lubricating oil composition.

[0071] There are no particular limitations on the sliding part of such a gear transmission for an electric mobile body. Any part that is a component of the gear transmission for an electric mobile body that slides against each other is acceptable. Examples include components such as gears and bearings in the reducer of an electric vehicle (preferably an electric vehicle) that move by contacting each other through rotational sliding or surface sliding.

[0072] Furthermore, the joint of the gear-type transmission for electric mobile bodies must be a joint that is sealed by using a FIPG containing polysiloxane in at least a portion of the joint that requires sealing with a gasket. It should be noted that the components constituting the joint that requires sealing with a FIPG containing polysiloxane in at least a portion can be components made of the same metal, or components made of different metals. Furthermore, there are no particular limitations on the FIPG containing polysiloxane; those known (such as those formed from known liquid gaskets containing polysiloxane (silicone resin)) or those formed from commercially available products (such as Henkel's product name: 5460) can be used appropriately. It should be noted that in this specification, "field-molded gasket (FIPG)" refers to a liquid-curing gasket formed by applying a liquid gasket (using the liquid gasket to bond the sealing surface) to the area to be sealed and then curing it.

[0073] In this invention, the aforementioned lubricating oil composition is a low-viscosity composition, and during use, it can suppress the distillation of silicon from FIPG containing polysiloxane, and can highly suppress the deterioration of FIPG, thus effectively preventing oil leakage (seepage) from the joints coated with FIPG containing polysiloxane. Furthermore, in this invention, the aforementioned lubricating oil composition, as described above, can highly suppress the distillation (dissolution / leaching) of silicon from FIPG containing polysiloxane during use, and the addition of poly(meth)acrylate (a high-viscosity polymer) is kept below a specific amount, thus highly suppressing foaming of the lubricating oil composition during use, and highly suppressing problems such as oil spraying from the breather plug. In addition, the gear transmission for electric vehicles of this invention, due to the low-viscosity lubricating oil composition, also excels in power saving. Moreover, since the aforementioned lubricating oil composition is used in a manner that satisfies the above-mentioned conditions in terms of the content and mixing ratio of each component, the gear transmission for electric vehicles of this invention achieves improved sintering resistance and wear resistance, and also improves the fatigue life of gears and bearings. Therefore, according to the present invention, in electric mobile devices, the degradation of FIPG containing polysiloxane caused by the lubricating oil composition when using a geared transmission can be highly suppressed, and the foaming of the lubricating oil composition when using a geared transmission can be kept below a certain level, while simultaneously improving energy efficiency and fatigue life.

[0074] The gear transmission for an electric mobile body of the present invention has been described above. Hereinafter, the lubricating oil composition for the gear transmission for an electric mobile body of the present invention and the lubrication method for the gear transmission for an electric mobile body of the present invention will be described.

[0075] [Lubricating oil composition for gear transmissions in electric motor vehicles and lubrication method for gear transmissions in electric motor vehicles] The lubricating oil composition for a geared transmission for an electric mobile body of the present invention is a lubricating oil composition for lubricating the sliding parts of a geared transmission for an electric mobile body. The geared transmission for an electric mobile body has a joint in which at least a portion of a field-molded gasket containing polysiloxane is used as a sealing member of the lubricating oil composition. The lubricating oil composition contains the above-mentioned components (A) to (F) and satisfies all of the above-mentioned conditions (i) to (vi).

[0076] Furthermore, the lubrication method for the geared transmission for an electric mobile body according to the present invention is a method for lubricating the sliding parts of the geared transmission for an electric mobile body using the above-described lubricating oil composition for the geared transmission for an electric mobile body according to the present invention. The geared transmission for an electric mobile body has a joint portion in which at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition.

[0077] The lubricating oil composition for a geared transmission for an electric vehicle according to the present invention is the same as the lubricating oil composition described above for the geared transmission for an electric vehicle according to the present invention (and its preferred conditions are also the same). Therefore, by using the lubricating oil composition for a geared transmission for an electric vehicle according to the present invention to lubricate the sliding parts of a geared transmission for an electric vehicle (e.g., a reducer for an electric vehicle) having joints where at least a portion uses field-molded gaskets containing polysiloxane as sealing members, even if the lubricating oil composition comes into contact with FIPG containing polysiloxane, the deterioration of FIPG containing polysiloxane and the dissolution of silicon can be highly suppressed. Therefore, leakage of the lubricating oil composition from the joints can be highly suppressed, and the sliding parts of the geared transmission for an electric vehicle can be lubricated.

[0078] Example The present invention will now be described in more detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0079] (Regarding the ingredients used in the various embodiments, etc.) First, the base oils and additives used in the various embodiments are shown below.

[0080] [Regarding the base oil (hydrocracked mineral oil) used in the preparation of lubricating oil base oil (component (A))] <(A-1)Component> Hydrocracked mineral oil [API Group II, kinematic viscosity at 40°C: 8.169 mm] 2Kinematic viscosity at 100℃ / s: 2.355 mm³ / s 2 / s, viscosity index: 104, sulfur content in base oil (sulfur composition in base oil): less than 10 ppm by mass] <(A-2)Component> Hydrocracked mineral oil [API Group II, kinematic viscosity at 40°C: 12.43 mm] 2 Kinematic viscosity at 100℃ / s: 3.12mm 2 / s, viscosity index: 112, sulfur content in base oil (sulfur composition in base oil): less than 10 ppm by mass (<10 ppm by mass) <(A-3) Ingredients> Hydrocracked mineral oil [API Group III, kinematic viscosity at 40°C: 19.57 mm] 2 Kinematic viscosity at 100℃ / s: 4.23 mm 2 / s, viscosity index: 122, sulfur content in base oil (sulfur composition in base oil): less than 10 ppm by mass (<10 ppm by mass).

[0081] [Regarding phosphorus-based additives (B) and (C) components, etc.] <(B-1) Ingredients> Di(n-butyl) phosphite [phosphorus (P) content: 15.5% by mass, all alkyl groups in the compound contain 4 carbon atoms] <(C-1) component> Amino salts of phosphite (distearate phosphite) [phosphorus (P) content: 24.3% by mass, nitrogen (N) content: 0.30% by mass, and the alkyl groups in the compound structure all contain 18 carbon atoms] [(Z-1) Ingredients: Phosphorus-based additives used for comparison] Dilauryl phosphite [phosphorus (P) content: 6.5% by mass, all alkyl groups in the compound contain 12 carbon atoms].

[0082] [Regarding calcium-based detergents (component (D))] <(D-1) Ingredients> Calcium sulfonate [Alkali value (perchloric acid method): 400 mg KOH / g, Calcium (Ca) content: 15.5% by mass] <(D-2) Ingredients> Calcium phenolate [base value (perchloric acid method): 255 mg KOH / g, calcium (Ca) content: 9.3% by mass, sulfur (S) content: 3.5% by mass] <(D-3) Ingredients> Calcium salicylate [base value (perchloric acid method): 280 mg KOH / g, calcium (Ca) content: 8.1% by mass].

[0083] [Regarding the composition of boron-modified succinimide dispersant (E)] <(E-1) Ingredients> Boron-modified succinimide [boron (B) content: 2.0% by mass, nitrogen (N) content: 2.3% by mass].

[0084] [Regarding the poly(meth)acrylate (F) component] <(F-1) Ingredient> Poly(meth)acrylate pour point depressant [poly(meth)acrylate) with a weight-average molecular weight (Mw) of 55,800] <(F-2) Ingredient> Poly(meth)acrylate viscosity modifier [poly(meth)acrylate with a weight-average molecular weight (Mw) of 50,000].

[0085] <Other Additives (G) Ingredients> <(G-1) component> A mixture of antioxidant (1.35 wt%), metal passivator (0.05 wt%), rubber swelling agent (0.6 wt%), and diluent oil (0.6 wt%) (total: 2.6 wt%).

[0086] (Examples 1-9 and Comparative Examples 1-16) Lubricating oil compositions of Examples 1-9 and Comparative Examples 1-16 were prepared using the components described above, in the manner shown in Tables 1-3. Furthermore, regarding the "Composition" items in Tables 1-3, "-" indicates that the component was not used. Additionally, in the "Composition" items in Tables 1-3, "mass%" represents the content (mass%) of component (A-1) to (A-3) (the constituent base oils of the lubricating oil) relative to the total amount of the lubricating oil composition, and "inmass%" represents the content (mass%) of component (A-1) to (A-3) relative to the total amount of the lubricating oil base oil, based on mass. Furthermore, in Tables 1-3, MP1 represents the content of component (B) ((B-1)) in terms of phosphorus atoms, based on a mass ratio, relative to the total amount of the lubricating oil composition; MP2 represents the content of component (C) ((C-1)) in terms of phosphorus atoms, based on a mass ratio, relative to the total amount of the lubricating oil composition; MCa represents the content of component (D) in terms of calcium atoms, based on a mass ratio, relative to the total amount of the lubricating oil composition; MB represents the content of component (E) in terms of boron atoms; and "MP1+MP2" represents the sum of the content of component (B) ((B-1)) in terms of phosphorus atoms and the content of component (C) ((C-1)) in terms of phosphorus atoms, based on a mass ratio, relative to the total amount of the lubricating oil composition. In addition, the values ​​of MP1, MP2, MCa, and MB are all calculated based on the proportions of each component. Furthermore, for the lubricating oil compositions obtained in the various embodiments, the kinematic viscosity at 40°C, the kinematic viscosity at 100°C, and the viscosity index are values ​​measured according to JIS K2283-2000. Additionally, for the lubricating oil compositions obtained in the various embodiments, the volume resistivity is a value measured at an oil temperature of 80°C according to the volume resistivity test specified in JIS C2101.

[0087] [Evaluation Tests Regarding the Properties of the Lubricating Oil Compositions Obtained in the Various Examples, etc.] <Confirmation Tests on the Anti-Deterioration Performance of FIPG Containing Polysiloxane in Lubricating Oil Compositions> The anti-deterioration performance of FIPG containing polysiloxane was evaluated using the lubricating oil compositions obtained in each example, etc., as follows.

[0088] <Confirmation Test of Shape Changes in FIPG Containing Polysiloxane (FIPG Degradation Confirmation Test 1)> First, an iron plate (iron material: ISOT test catalyst) was prepared as the test piece for the JIS K 2514-1 oxidation stability test (ISOT). 5g of FIPG containing polysiloxane (manufactured by Henkel, trade name: 5460) was coated onto this iron plate, resulting in a test piece with a FIPG coating containing polysiloxane. Next, the test piece with the aforementioned FIPG coating containing polysiloxane was introduced into a 1000mL beaker containing 500mL of a lubricating oil composition, and immersed in the lubricating oil composition at 150°C for 288 hours. After immersing the test piece in the lubricating oil composition at 150°C for 288 hours, the test piece was removed, and the change in the shape of the FIPG coating containing polysiloxane formed on the test piece was visually inspected. A case where the shape of the coating remained unchanged was visually assessed as "E", and a case where the shape of the coating changed or deteriorated due to peeling or other defects was visually assessed as "F". The measurement results are shown in Tables 1-3.

[0089] <Test for determining the amount of silicone dissolved from the polysiloxane-containing FIPG into the lubricating oil composition after the above-mentioned FIPG degradation confirmation test 1 (FIPG degradation confirmation test 2)> In the aforementioned "Confirmation Test of Shape Change of FIPG Containing Polysiloxane (FIPG Deterioration Confirmation Test 1)," the amount of dissolved silicon (Si) in the lubricating oil composition was determined according to JIS K0116 (by ICP luminescence analysis) after the test piece was immersed in the lubricating oil composition at 150°C for 288 hours. It should be noted that since the silicon measured in this way is clearly silicon dissolved from the polysiloxane-containing FIPG, the measured amount of silicon is shown as the amount of silicon dissolved in Tables 1-3.

[0090] It should be noted that, among the results of the above-mentioned degradation confirmation tests 1 to 2, the lubricating oil composition whose evaluation result of degradation confirmation test 1 is "E" and whose silicon dissolution amount measured in degradation confirmation test 2 is "less than 200 ppm by mass" can be evaluated as having a high level of anti-degradation performance of FIPG containing polysiloxane.

[0091] <Evaluation Test of Foaming Properties of Lubricating Oil Compositions After Contact with FIPG Containing Polysiloxanes> In the above-mentioned FIPG degradation confirmation test 1 (confirmation test of shape change of FIPG containing polysiloxane), the foaming test (sequence I to sequence III) was performed using a lubricating oil composition after the test piece was impregnated at 150°C for 288 hours. The results of foaming degree and foam stability (foaming degree / foam stability) after the test of each sequence are shown in Tables 1 to 3.

[0092] It should be noted that in this test, when the test results of Sequence I are "[values below 200] / 0", the test results of Sequence II are "[values below 50] / 0", and the test results of Sequence III are "[values below 200] / 0", it can be evaluated that the foaming property is low and the performance of suppressing the foaming of the composition is at a high level. On the other hand, a lubricating oil composition that does not meet at least one of the conditions that the test results of Sequence I are "[values below 200] / 0", the test results of Sequence II are "[values below 50] / 0", and the test results of Sequence III are "[values below 200] / 0" is judged to have a low performance of suppressing the foaming of the composition.

[0093] <Confirmation Test of Extreme Pressure Performance of Lubricating Oil Composition> <High-Speed Four-Ball Test> The lubricating oil compositions obtained in each of the embodiments, etc., were respectively used to measure the maximum non-seizure load (LNSL [unit: N]) at a rotational speed of 1800 rpm through the high-speed four-ball test according to ASTM D2783. The measurement results are shown in Tables 1 to 3. It should be noted that 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.

[0094] <Shell Four-Ball Test> The lubricating oil compositions obtained in each of the embodiments, etc., were respectively used to conduct the Shell four-ball test according to ASTM D4172 under the conditions of load: 392 N, rotational speed: 1500 rpm, temperature: 100 °C, and test time: 1 hour, and the wear scar diameter (mm) was measured. The measurement results are shown in Tables 1 to 3. In addition, 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.

[0095] Based on the results of the confirmation test of wear resistance based on the high-speed four-ball test and the Shell four-ball test, a lubricating oil composition that meets the conditions of LSNL being 619 N or more and wear scar diameter being 0.60 or less can be evaluated as having a high level of wear resistance (anti-wear performance).

[0096] <Falex Sintering Resistance Test> The lubricating oil compositions obtained in each of the embodiments, etc., were respectively used to measure the sintering load (unit: N) under the test conditions of temperature: 110 °C and rotational speed: 290 rpm using the Falex testing machine (pin-V block testing machine) described in ASTM D3233. The obtained results are shown in Tables 1 to 3. When the sintering load is 4000 N or more in this way, it can be evaluated that the sintering resistance (extreme pressure property between steels) is excellent.

[0097] <Unisteel Test (Thrust Needle Roller Bearing (BRG))> Using the lubricating oil compositions obtained in each of the embodiments and the like, the rolling fatigue life of the thrust bearing was measured by the Unisteel test (Institute of Petroleum method: IP305 / 79) using a Unisteel rolling fatigue testing machine (manufactured by Tokyo Testing Machine Co., Ltd., triple-type high-temperature rolling fatigue testing machine (TRF-1000 / 3-01H)). For a test bearing in which one raceway ring of the thrust needle roller bearing (FNTA-2542C manufactured by NSK) was replaced with a flat test piece (material: SUJ2), the time until fatigue damage occurred in either the roller or the test piece was measured under the 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. It should be noted that when the vibration acceleration of the test section measured by the vibration accelerometer equipped with the Unisteel rolling fatigue testing machine reaches 1.5 m / s 2 , it is judged that fatigue damage has occurred. Based on the time until fatigue damage in 10 repeated tests, the fatigue life was calculated as the 50% life (L50: the time when the cumulative probability reaches 50%) through a Weibull plot. 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 judged that there is an effect of improving the fatigue life (pitting life) (an effect of extending the fatigue life).

[0098] <Confirmation Test of Power Consumption Saving Property of Lubricating Oil Composition> <Evaluation of Power Consumption Saving Property (Fuel Consumption Saving Property)> Using the lubricating oil compositions obtained in each of the embodiments and the like, the kinematic viscosity at the test start temperature of 25°C in the fuel consumption test in the WLTC mode was measured in accordance with JIS K 2283-2000, and the power consumption saving property was evaluated based on the value of the kinematic viscosity at 25°C. The obtained results are shown in Tables 1 to 3. When the kinematic viscosity at 25°C (kinematic viscosity at low temperature) is 20 mm 2 / s or less, it is possible to reduce the resistance (agitation loss) caused by the lubricating oil agitation by rotating bodies such as gears at the start of the fuel consumption test, and thus it can be evaluated that the power consumption saving property is excellent.

[0099] As shown in Tables 1-3, the lubricating oil compositions obtained in Examples 1-9 (equivalent to the lubricating oil compositions for gear transmissions of electric motors of the present invention) can highly suppress the degradation of FIPG containing polysiloxanes, and can keep foaming during use below a certain level, thereby improving energy-saving performance due to their low viscosity. Furthermore, the lubricating oil compositions obtained in Examples 1-9 (equivalent to the lubricating oil compositions for gear transmissions of electric motors of the present invention) can simultaneously improve extreme pressure performance and fatigue life based on anti-wear performance and sintering resistance. Moreover, the volume resistivity results show that the lubricating oil compositions obtained in Examples 1-9 (equivalent to the lubricating oil compositions for gear transmissions of electric motors of the present invention) possess the high level of electrical insulation required for lubricating oils of electric motors (e.g., electric vehicles).

[0100] In contrast, the kinematic viscosity of the lubricating base oil used in the composition is less than 2.7 mm at 100°C. 2 In the case of / s (Comparative Example 1), the anti-deterioration performance of the FIPG containing polysiloxane could not reach a high level, and the foaming suppression performance of the composition was also low. Furthermore, it was found that the kinematic viscosity of the lubricating oil base oil used in the composition at 40°C exceeded 12.0 mm. 2 In the case of / s (Comparative Examples 2-3), the foaming suppression performance of the composition is low, and the power saving performance is low. Furthermore, when the content of poly(meth)acrylate is 0.1% by mass or more (Comparative Examples 4-5), the foaming suppression performance of the composition is low, and the power saving performance is low. In addition, in Comparative Examples 3-5, it is not possible to set the wear resistance (abrasion resistance) to a high level.

[0101] Furthermore, when only one phosphorus-based additive is used (Comparative Examples 6-8), it is mainly impossible to achieve a high level of anti-deterioration performance in the FIPG containing polysiloxane, and excellent performance in terms of sintering resistance and fatigue life is also not achieved. Moreover, even when using two phosphorus-based additives, if the total amount of these phosphorus-based additives (MP1+MP2) based on the total mass of the lubricating oil composition is less than 0.025% by mass (Comparative Example 9), it is also impossible to achieve a high level of anti-deterioration performance in the FIPG containing polysiloxane, and excellent improvement in wear resistance (anti-wear performance), sintering resistance, and fatigue life cannot be achieved. Furthermore, even when using two phosphorus-based additives, if the total amount of phosphorus-based additives (MP1+MP2) based on the total mass of the lubricating oil composition exceeds 0.050% by mass (Comparative Example 10), it is also impossible to achieve a high level of anti-deterioration performance in the FIPG containing polysiloxane, and the foaming suppression performance of the composition is also low. Furthermore, even when using two phosphorus-based additives, when the size of MP1 is not more than 2.0 times and less than 2.4 times the size of MP2 (Comparative Examples 11-12), it is impossible to achieve a high level of anti-deterioration performance for the FIPG containing polysiloxane, the foaming suppression performance of the composition is also low, and excellent wear resistance cannot be achieved (it should be noted that in Comparative Example 11, the sintering resistance also cannot be excellent, and in Comparative Example 12, the fatigue life also cannot be excellent). Additionally, when the calcium atom content (MCa) of component (D) based on the total mass of the lubricating oil composition is not more than 0.009% by mass and less than 0.013% by mass (Comparative Examples 13-14), it is impossible to achieve a high level of anti-deterioration performance for the FIPG containing polysiloxane, the foaming suppression performance of the composition is also low, and excellent fatigue life cannot be achieved (it should be noted that in Comparative Example 14, neither excellent wear resistance nor excellent sintering resistance can be achieved). Furthermore, when the content of boron atoms (MB) of component (E) is not more than 0.9 times and less than 1.2 times the content of calcium atoms (MCa) of component (D) (Comparative Examples 15-16), the foaming suppression performance of the composition is low, and the fatigue life cannot be excellent (it should be noted that in Comparative Example 15, the anti-deterioration performance of FIPG containing polysiloxane could not reach a high level, and in Comparative Example 16, the wear resistance and sintering resistance could not reach an excellent level).

[0102] As can be seen from these results, the lubricating oil composition containing components (A) to (F) and satisfying all of the above conditions (i) to (vi) can prevent the deterioration of the polysiloxane-containing FIPG in the gear transmission of electric moving parts (e.g., the reducer for electric vehicles) during use, prevent oil leakage from the joints for a long time, and have high foaming suppression ability during use. Therefore, it can effectively prevent oil from spraying out of the breather plug of the gear transmission. Furthermore, the lubricating oil composition used in electric moving parts can also achieve the required characteristics (extreme pressure performance, performance to improve the fatigue life of gears, etc., and fuel-saving performance).

[0103] [Industrial Applicability] As explained above, according to the present invention, (1) it is possible to provide a gear transmission for an electric motor that can highly suppress the deterioration of FIPG containing polysiloxane caused by the lubricating oil composition during the use of the gear transmission, and can reduce the foaming of the lubricating oil composition during the use of the gear transmission to a certain level or below, and can simultaneously improve power consumption and fatigue life; (2) it is possible to provide a lubricating oil composition for a gear transmission for an electric motor that can highly suppress the deterioration of FIPG containing polysiloxane, and can reduce the foaming during use to a certain level or below, can improve power consumption due to low viscosity, and can simultaneously improve extreme pressure performance and fatigue life based on anti-wear performance and sintering resistance, and can also have the high electrical insulation required for lubricating oils for electric motors; and (3) it is possible to provide a lubrication method for a gear transmission for an electric motor using the above-described lubricating oil composition.

[0104] The lubricating oil composition for gear transmissions of electric moving parts according to the present invention is very useful in gear transmissions (e.g., reducers) of electric moving parts that use FIPG containing polysiloxane as a sealant for joints, and is very useful in improving the energy-saving performance and fatigue life of electric moving parts.

Claims

1. A gear-type transmission for an electric mobile body, comprising: a lubricating oil composition for lubricating sliding parts; and a joint wherein at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition, wherein, The lubricating oil composition contains: (A) a lubricating oil base oil which is a hydrocracked mineral oil having a kinematic viscosity at 40°C of 12.0 mm 2 / s or less and a kinematic viscosity at 100°C of 2.7 mm 2 / s or more; (B) A first phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 8 or less; (C) A second phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 14 or more; (D) Calcium-based detergents; (E) Boron-modified succinimide dispersant; and (F) Poly(meth)acrylate, Furthermore, all of the lubricating oil compositions satisfy the following conditions (i) to (vi): (i) 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 and 0.050% by mass based on the total mass of the lubricating oil composition. (ii) The content of component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content of component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms. (iii) The content of component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms, is 0.009% by mass or more and 0.013% by mass or less; (iv) The content of component (E) based on the total mass of the lubricating oil composition, expressed in boron atoms, is more than 0.9 times and less than 1.2 times the content of component (D) based on the total mass of the lubricating oil composition, expressed in calcium atoms. (v) The content of component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass; (vi) the volume resistivity at 80°C of the lubricating oil composition is 50 MΩ-m or more, the kinematic viscosity at 100°C is 2.7 mm 2 / s or less, and the viscosity index is 100 or more. 2 / s or less, and the viscosity index is 100 or more.

2. The gear-type transmission for an electric mobile body according to claim 1, wherein, The component (B) is a phosphite in which all alkyl groups in the structure have 8 or fewer carbon atoms.

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

4. The gear-type transmission for an electric mobile body according to claim 1, wherein, The (D) component is selected from at least one of the following groups: calcium sulfonate with an alkalinity of 200 mg KOH / g or higher, calcium phenolate with an alkalinity of 200 mg KOH / g or higher, and calcium salicylate with an alkalinity of 200 mg KOH / g or higher.

5. The gear-type transmission for an electric mobile body according to claim 1, wherein, The weight-average molecular weight of component (F) is below 60,000.

6. A lubricating oil composition for lubricating sliding portions of a geared transmission for an electric mobile body, the geared transmission for the electric mobile body having a joint portion in which at least a portion utilizes a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition, wherein, The lubricating oil composition contains: (A) a lubricating oil base oil which is a hydrocracked mineral oil having a kinematic viscosity at 40°C of 12.0 mm 2 / s or less and a kinematic viscosity at 100°C of 2.7 mm 2 / s or more; (B) A first phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 8 or less; (C) A second phosphorus-based additive, which contains at least one alkyl group in its structure and the number of carbon atoms of each alkyl group in the structure is 14 or more; (D) Calcium-based detergents; (E) Boron-modified succinimide dispersant; and (F) Poly(meth)acrylate, Furthermore, all of the lubricating oil compositions satisfy the following conditions (i) to (vi): (i) 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 and 0.050% by mass based on the total mass of the lubricating oil composition. (ii) The content of component (B) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms, is more than 2.0 times and less than 2.4 times the content of component (C) based on the total mass of the lubricating oil composition, expressed in terms of phosphorus atoms. (iii) The content of component (D) based on the total mass of the lubricating oil composition, expressed in terms of calcium atoms, is 0.009% by mass or more and 0.013% by mass or less; (iv) The content of component (E) based on the total mass of the lubricating oil composition, expressed in boron atoms, is more than 0.9 times and less than 1.2 times the content of component (D) based on the total mass of the lubricating oil composition, expressed in calcium atoms. (v) The content of component (F) based on the total mass of the lubricating oil composition is less than 0.1% by mass; (vi) the volume resistivity at 80°C of the lubricating oil composition is 50 MΩ-m or more, the kinematic viscosity at 100°C is 2.7 mm 2 / s or less, and the viscosity index is 100 or more. 2 / s or less, and the viscosity index is 100 or more.

7. A lubrication method for a geared transmission for an electric mobile body, comprising lubricating a sliding portion of the geared transmission for an electric mobile body using the lubricating oil composition for a geared transmission for an electric mobile body as described in claim 6, wherein the geared transmission for an electric mobile body has a joint portion in which at least a portion uses a field-molded gasket containing polysiloxane as a sealing member of the lubricating oil composition.

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