Conductive grease, conductive rolling bearing, and motor drive device

Abstract

To provide a conductive grease that suppresses an occurrence of electrolytic corrosion in a bearing and contributes to prolonging a life of the bearing, and to provide a conductive rolling bearing containing the grease.SOLUTION: A conductive grease contains conductive particles composed of a gallium compound, in which the grease contains 3 mass% to 100 mass% of an amine salt of polyether phosphate or an amide amine salt of polyester acid with respect to the conductive particles, and the gallium compound contains gallium and one or more elements of titanium, zinc, aluminum, thallium, germanium, indium, antimony, selenium, tellurium, tin, phosphorus, arsenic, silicon, fluorine, nitrogen, and oxygen, as a constituent element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a conductive grease, a conductive rolling bearing encapsulated with this conductive grease, and a motor drive device including this conductive rolling bearing.

Background Art

[0002] Conventionally, automotive accessories have been driven by the driving force generated by an engine through belt transmission as a power source. However, in recent years, due to fuel efficiency improvement, electrification has advanced, and they have come to be driven by a motor (the motor is also called an electric motor). In addition, many industrial machines have conventionally been operated by motor drive.

[0003] Motors for automotive accessories and industrial machines are required to be miniaturized, have higher performance, and have higher output year by year, and the usage conditions have become severe. Sealed deep groove ball bearings (rolling bearings) are generally used for these.

[0004] In a rolling bearing incorporated in a motor, current from a circuit may flow into the bearing, and spark through an oil film on the rolling contact surface (hereinafter referred to as the "rolling surface") between the rolling element and the raceway surface. "Electric corrosion" in which the rolling surface is locally melted may occur due to this spark, and the bearing function may deteriorate.

[0005] In order to prevent such problems from occurring, a so-called "conductive bearing" in which the bearing itself has conductivity may be used. Some conductive bearings have conductive grease enclosed inside. For example, in order to lower the volume resistivity of the grease itself (increase conductivity) to prevent electrolytic corrosion, there is a known bearing (see Patent Document 1) in which conductive grease containing carbon black particles or the like as both a conductive substance and a thickener is enclosed. Also known is conductive grease in which graphite particles are blended as a thickener in a fluorine oil as the base oil (see Patent Document 2). Furthermore, a rolling bearing has been proposed in which an ionic liquid is used as the base oil of the grease and carbon black is used as the thickener (see Patent Document 3). In addition, in the enclosed grease, it is also conceivable to blend an additive capable of forming a passive film (oxide film) or the like to prevent electrolytic corrosion.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in Patent Document 1 and Patent Document 2, due to the long-term use of the bearing, the conductive substance gradually separates from or aggregates with the base oil, so that the resistance value of the bearing increases over time even if it is low initially, and electrolytic corrosion is likely to occur. Also, in Patent Document 3, in order to lower the volume resistivity of the enclosed grease, the combination of the base oil and the thickener is limited, and it may be difficult to ensure a long bearing life for a wide variety of bearings.

[0008] The present invention has been made to address such problems, and an object thereof is to provide a conductive grease that suppresses the occurrence of electric corrosion in a bearing and contributes to extending the bearing life, and a conductive rolling bearing in which this grease is enclosed.

Means for Solving the Problems

[0009] The conductive grease of the present invention is a conductive grease containing conductive particles, wherein the conductive particles are particles made of a gallium compound, and the conductive grease contains an amine salt of a polyether phosphate or an amidoamine salt of a polyester acid in an amount of 3% by mass to 100% by mass with respect to the conductive particles.

[0010] The gallium compound contains, as constituent elements, gallium and any one or more elements selected from titanium, zinc, aluminum, thallium, germanium, indium, antimony, selenium, tellurium, tin, phosphorus, arsenic, silicon, fluorine, nitrogen, and oxygen.

[0011] The average primary particle diameter of the conductive particles is 0.01 μm to 10 μm.

[0012] The base oil of the conductive grease is at least one selected from poly-α-olefin oil, fluorine oil, mineral oil, ether oil, glycol oil, and ester oil. Hereinafter, poly-α-olefin oil is referred to as "PAO oil".

[0013] The conductive rolling bearing of the present invention is a rolling bearing that holds a plurality of rolling elements between the raceway surfaces of an inner ring and an outer ring, and is characterized in that the conductive grease is enclosed between the raceway surfaces.

[0014] The conductive rolling bearing includes a plurality of drive units having a rotating blade and a motor for rotating the rotating blade, is mounted on an electric vertical takeoff and landing aircraft that flies by the rotation of the rotating blade, and is a bearing that supports the rotating shaft in the drive unit.

[0015] The motor drive device of the present invention is a motor drive device including a motor and a speed reducer that reduces the rotation of the motor, and is characterized in that at least one selected from the rotor shaft of the motor and the gears of the speed reducer is supported by the conductive rolling bearing.

[0016] The motor drive device is characterized in that it is used in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

Effects of the Invention

[0017] The conductive grease of the present invention is a conductive grease containing conductive particles. The conductive particles are particles made of a gallium compound. The conductive grease contains a polyether phosphate amine salt or a polyester acid amide amine salt in an amount of 3% to 100% by mass based on the conductive particles. Therefore, aggregation of the conductive particles in the grease hardly occurs, and a uniform dispersion state is maintained. As a result, even when a bearing filled with this conductive grease is used for a long period of time, the conductivity of the grease is likely to be maintained over a long period of time. Thereby, since sparking through the oil film on the rolling surface hardly occurs, the occurrence of electrolytic corrosion can be suppressed, and the bearing life can be extended.

[0018] Since the gallium compound contains, as constituent elements, gallium and any one or more elements selected from titanium, zinc, aluminum, thallium, germanium, indium, antimony, selenium, tellurium, tin, phosphorus, arsenic, silicon, fluorine, nitrogen, and oxygen, the grease containing this gallium compound as conductive particles is more excellent in conductivity and can preferably suppress the occurrence of electrolytic corrosion.

[0019] Since the average primary particle diameter of the conductive particles is 0.01 μm to 10 μm, the conductive particles can also act as a thickener that increases the consistency of the grease. Thereby, the blending amount of a thickener intended only for increasing the consistency of the grease can be reduced, and as a result, the blending ratio of the conductive particles in the grease can be increased, so that the grease is more excellent in conductivity.

[0020] Since the base oil of the conductive grease is at least one selected from PAO oil, fluorine oil, mineral oil, ether oil, glycol oil, and ester oil, the grease is excellent in heat resistance, and even under severe conditions where the bearing becomes hot, the bearing life of the rolling bearing filled with the grease can be extended.

[0021] The conductive rolling bearing of the present invention is a rolling bearing that holds a plurality of rolling elements between the raceway surfaces of the inner ring and the outer ring, and since the conductive grease of the present invention is filled between the raceway surfaces, electric corrosion is less likely to occur on the surface of the rolling surface, and it has a long bearing life.

[0022] In addition, in an electric vertical takeoff and landing aircraft that has been developed in recent years, there is a concern about the occurrence of electric corrosion due to the increase in the capacity of the motor. Since the conductive rolling bearing of the present invention has a conductive grease having the above characteristics, the occurrence of electric corrosion can be suppressed by using it as a bearing that supports the rotating shaft in the drive unit.

[0023] The motor drive device of the present invention supports at least one selected from the rotor shaft of the motor and the gear of the speed reducer with a conductive rolling bearing provided with a conductive grease having the above characteristics, so the occurrence of electric corrosion can be suppressed.

[0024] The motor drive device provided in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle has a larger capacity than the motor for auxiliary equipment provided in a gasoline vehicle, and the voltage (shaft voltage) generated on the rotor shaft of the motor is high. Therefore, although there is a concern about the occurrence of electric corrosion in the motor drive device, by applying the conductive rolling bearing of the present invention, electric corrosion can be preferably prevented.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] The conductive grease of the present invention contains at least a base oil, conductive particles, and a dispersant. As one form, it contains a base oil, a thickener, conductive particles, and a dispersant. When the conductive particles impart a thickening effect to the grease, the conductive particles can be used as both a conductive substance and a thickener, and a configuration that does not contain general thickeners such as soaps and urea compounds can also be adopted. Additives such as extreme pressure agents, antioxidants, rust preventives / metal deactivators, and oiliness agents added to general grease compositions may be further blended in the conductive grease of the present invention.

[0027] The conductive grease of the present invention contains conductive particles composed of a gallium compound. Thereby, the grease has excellent conductivity. From the viewpoint of long-term stability, the gallium compound preferably contains, as constituent elements, gallium and any one or more elements of titanium, zinc, aluminum, thallium, germanium, indium, antimony, selenium, tellurium, tin, phosphorus, arsenic, silicon, fluorine, nitrogen, and oxygen.

[0028] Examples of the conductive particles composed of a gallium compound include gallium-doped zinc oxide (GZO) particles, indium gallium-doped zinc oxide particles, gallium oxide (Ga 2 O 3)Particles such as gallium nitride (GaN) particles, gallium phosphide (GaP) particles, and gallium arsenide (GaAs) particles can be used. GZO and indium gallium-doped zinc oxide are substances with improved conductivity by doping gallium or indium into zinc oxide, which is known as an oxide semiconductor. Depending on the synthesis conditions, they can have various shapes, particle sizes, layer structures, and surface states. As the conductive particles used in the conductive grease of the present invention, GZO particles are particularly preferred from the viewpoints of conductivity, raw material cost, and productivity.

[0029] Compared with carbon-based conductive particles such as graphite, which have been conventionally used as conductive particles in various applications, GZO particles have many hydroxyl groups on the particle surface. The hydroxyl groups on the particle surface interact with or form chemical bonds with dispersants and surface treatment materials used to improve dispersibility in other organic components. Therefore, GZO particles having more hydroxyl groups than carbon-based conductive particles are more likely to exhibit the dispersion effect by the dispersant, have excellent affinity with various components in the grease such as base oil and thickener, and it is considered that a uniform dispersion state in the grease is easily maintained even when the bearing is used for a long time.

[0030] The conductive particles preferably have an average primary particle diameter of 0.01 μm to 10 μm, more preferably 0.02 μm to 1 μm, and even more preferably 0.02 μm to 0.1 μm. When the average primary particle diameter of the conductive particles is 0.01 μm to 10 μm, it is easy to balance the thickening effect of thickening the grease and the ease of spreading of the grease on the running surface. The average primary particle diameter can be measured using, for example, a particle size distribution measuring device using the laser light scattering method, an electron microscope, or the like.

[0031] When the conductive particles are GZO particles, the average primary particle diameter is preferably 0.02 μm to 0.04 μm, and when the conductive particles are Ga 2 O 3In the case of particles, the average primary particle diameter is preferably 0.8 μm to 2.4 μm. Further, when the conductive particles are GaN particles, the average primary particle diameter is preferably 0.1 μm to 2.0 μm.

[0032] When the average primary particle diameter of the conductive particles is 0.02 μm to 0.1 μm, the thickening effect is excellent. Further, due to this thickening effect, the blending amount of a general thickener can be reduced, and accordingly, the blending ratio of the conductive particles in the grease can be increased, resulting in a grease with even better conductivity. Further, when the average primary particle diameter of the conductive particles is ultrafine particles of 0.02 μm to 0.1 μm, the grease containing the conductive particles is less likely to cause absorption and scattering of visible light, and thus has excellent visible light transmittance (transparency). Therefore, when inspecting the roller bearing encapsulated with this grease by visual inspection or the like after use, compared with a bearing encapsulated with a grease containing coarser particles that are more likely to cause light scattering and visible light absorption, the visual inspection is easier. Specifically, it becomes possible to facilitate the inspection by eliminating the need to disassemble the bearing, and the deterioration state of the rolling surface and the like can be grasped more accurately, leading to an extension of the bearing life.

[0033] Depending on the application and usage conditions, the temperature of the roller bearing may rise. However, when the temperature of the bearing rises to a high temperature, the thickener and base oil may deteriorate, and the bearing life may be reduced. Further, when the temperature of one of the inner ring and outer ring of the roller bearing rises excessively and the temperature difference between the inner ring and outer ring becomes large, the preload may fluctuate, the rolling surface may be damaged, and the bearing life may also be reduced. On the other hand, the conductive particles made of a gallium compound also act as a heat-conductive grease because they have heat conductivity. Thereby, heat can be dissipated from the bearing to suppress the temperature rise, or the temperature difference between the inner ring and the outer ring can be reduced, so that the bearing life can be extended.

[0034] The conductive particles can be selected based on the average primary particle diameter, specific surface area, oil absorption amount, etc. As the conductive particles, for example, Pazet GK-40, which is GZO particles manufactured by Hakusuitech Co., Ltd., can be used. This has an average primary particle diameter of 20 to 40 nm and a specific surface area of 30 to 50 m2 / g, and the oil absorption is 30 to 50 ml / 100 g.

[0035] In addition to the conductive particles composed of a gallium compound, the conductive grease of the present invention may be blended with conventionally known heat conductive particles such as titanium oxide particles, alumina particles, boron nitride particles, aluminum nitride particles, diamond particles, gold particles, silver particles, copper particles, nickel particles, indium particles, metal silicon particles, silica particles, and carbon-based particles according to the purpose.

[0036] The blending ratio of the conductive particles is preferably 3% by mass to 50% by mass based on the total amount of the conductive grease. By setting the blending ratio within this range, the conductivity required for suppressing electrolytic corrosion can be obtained. When the conductive particles are used as both a conductive substance and a thickener, the blending ratio is preferably 10% by mass to 50% by mass, more preferably 10% by mass to 40% by mass based on the total amount of the conductive grease. By setting the blending ratio to 10% to 50% by mass, the conductivity required for suppressing electrolytic corrosion, the thickening effect, and excellent fluidity can be obtained. Since the grease has excellent fluidity, when the bearing is used, the grease spreads on the running surface, and an excellent electrolytic corrosion effect is exhibited.

[0037] The conductive grease of the present invention contains at least one of an amine salt of polyether phosphate ester or an amide amine salt of polyester acid as a dispersant.

[0038] Examples of the amine salt of polyether phosphate ester that can be used in the conductive grease of the present invention include amine salts of phosphate esters such as polyoxyethylene alkyl phenyl ether phosphate ester, polyoxyethylene alkyl ether phosphate ester, and higher alcohol phosphate ester.

[0039] The amine salt of polyether phosphate ester can promote the wetting of conductive particles in conductive grease, and can exert effects such as an increase in the blending ratio of conductive particles, suppression of thickening of conductive grease, and shortening of dispersion time. Examples of commercially available amine salts of polyether phosphate ester include Disparon DA-325 (pale yellow to yellowish brown viscous liquid, heating residue: 95% by mass or more, acid value: 14, amine value: 20) manufactured by Kusumoto Chemicals, Ltd.

[0040] The amide amine salt of polyester acid that can be used in the conductive grease of the present invention can be obtained, for example, by reacting a tetracarboxylic dianhydride, an alcoholic diol, and a diamine compound to form a polyamic acid and then imidizing it. The reaction order may be such that the tetracarboxylic dianhydride and the alcoholic diol are reacted first and then reacted with the diamine, or conversely, the tetracarboxylic dianhydride and the diamine are reacted first and then reacted with the alcoholic diol.

[0041] Similar to the amine salt of polyether phosphate ester, the amide amine salt of polyester acid can promote the wetting of conductive particles in conductive grease, and can exert effects such as an increase in the blending ratio of conductive particles, suppression of thickening of conductive grease, and shortening of dispersion time. Examples of commercially available high molecular weight polyester acid amide amine salts include Disparon DA-703-50, Disparon DA-725, Disparon DA-705, etc. manufactured by Kusumoto Chemicals, Ltd.

[0042] The blending ratio of the amine salt of polyether phosphate ester or the amide amine salt of polyester acid blended in the conductive grease of the present invention is 3% by mass to 100% by mass based on the blending amount of the conductive particles. When the blending ratio is 3% by mass to 100% by mass, in a rolling bearing filled with the grease, aggregation of the conductive particles in the grease hardly occurs, and a uniform dispersion state is maintained. As a result, the initial conductivity is maintained, so that electric corrosion hardly occurs and the bearing can be used for a long time.

[0043] Since the conductive particles composed of a gallium compound have hydroxyl groups on the particle surface and a weakly basic surface, the interaction with dispersants such as amine salts and amidoamine salts of the above-mentioned type is particularly likely to occur compared to carbon-based conductive particles such as graphite. Therefore, for the conductive particles composed of a gallium compound, an amine salt of a polyether phosphate ester or an amidoamine salt of a polyester acid is considered to optimize the zeta potential on the surface of the conductive particles even with a small blending amount, making it difficult for the particles to aggregate with each other.

[0044] The blending ratio of the amine salt of the polyether phosphate ester or the amidoamine salt of the polyester acid blended in the conductive grease is more preferably 3% by mass to 50% by mass, and even more preferably 3% by mass to 30% by mass with respect to the blending amount of the conductive particles. Generally, in a certain weight of particles, as the particle diameter becomes smaller, the total particle surface area increases, so the amount of dispersant required for suppressing particle aggregation tends to increase. On the other hand, if the amount of the dispersant in the grease increases too much, the amount of other components will relatively decrease, which may lead to a decrease in bearing characteristics and is not preferable. In the conductive grease of the present invention, by combining the conductive particles composed of a gallium compound with an amine salt of a polyether phosphate ester or an amidoamine salt of a polyester acid, more conductive particles can be dispersed with a small amount of dispersant.

[0045] As described above, the conductive particles composed of a gallium compound have conductivity and thermal conductivity, and can reduce the blending amounts of thickeners and dispersants other than the conductive particles. Therefore, they are excellent in the conductivity and thermal conductivity of the grease and contribute to the extension of the bearing life using the grease.

[0046] The base oil that can be used in the present invention is not particularly limited, and common ones used in the field of ordinary greases can be used. For example, mineral oils such as spindle oil, refrigeration oil, turbine oil, machine oil, and dynamo oil, highly refined mineral oils, liquid paraffin oils, polybutene oils, GTL oils synthesized by the Fischer-Tropsch method, PAO oils, alkylnaphthalene oils, hydrocarbon-based synthetic oils such as alicyclic compounds, alkylbenzene oils, or natural fats and oils, polyol ester oils, phosphate ester oils, polymer ester oils, aromatic ester oils, carbonate ester oils, diester oils, etc. ester oils, glycol oils such as polyalkylene glycol oils, ether oils such as polyphenyl ether oils and alkyldiphenyl ether oils, non-hydrocarbon-based synthetic oils such as silicone oils and fluorine oils, etc. These can be used alone or in combination of two or more.

[0047] Among these, due to excellent heat resistance and lubricity, it is preferable to use at least one oil selected from PAO oil, fluorine oil, mineral oil, ether oil, glycol oil, and ester oil.

[0048] The kinematic viscosity of the base oil (in the case of a mixed oil, the kinematic viscosity of the mixed oil) is preferably 10 to 200 mm 2 / s at 40°C. More preferably, it is 10 to 120 mm 2 / s. By using a base oil with a kinematic viscosity of 10 mm 2 / s or more, the evaporation amount can be reduced and the bearing life can be extended. Also, a base oil with a kinematic viscosity of 200 mm 2 / s or less has excellent lubricity and is suitable for use as a bearing.

[0049] The thickeners that can be used in the conductive grease of the present invention can be used without particular limitation. For example, soaps such as lithium soap, lithium complex soap, calcium soap, calcium complex soap, aluminum soap, aluminum complex soap, etc., urea compounds such as diurea compounds, polyurea compounds, fluororesins such as PTFE resin, etc. can be mentioned. Further, in order to sufficiently increase the conductivity of the grease, the above-mentioned conductive particles composed of a gallium compound may be used as the thickener.

[0050] An embodiment of the conductive rolling bearing encapsulated with the conductive grease of the present invention will be described with reference to FIG. 1. An example of the conductive rolling bearing that supports the rotor of the motor is shown in FIG. 1. FIG. 1(a) is a schematic cross-sectional view of the motor using the bearing as a bearing for the output motor, and FIG. 1(b) is an enlarged view of part A in FIG. 1(a). As shown in FIGS. 1(a) and 1(b), the motor 10 rotates a load object by mounting a belt 18 on a pulley 17 interlocked with the main shaft 11. A rotor 13 is attached to the main shaft 11, a pulley 17 is attached to one end thereof, and a belt 18 for rotating an air-conditioning fan or the like is mounted. Further, the main shaft 11 is rotatably supported by a flange 14 by first radial ball bearings 15 and second radial ball bearings 16 attached to both ends of the rotor 13. A stator 12 is fixed to the flange 14 so as to face the rotor 13. Further, a wave washer 19 is positioned between the flange 14 and the second radial ball bearing 16 to apply a preload. The first radial ball bearing 15 and the second radial ball bearing 16 are the conductive rolling bearings of the present invention, and support the rotor 13 which is a rotor via the main shaft 11.

[0051] In FIGS. 1(a) and (b), a method of applying preload using a spring is adopted, and a flat spring, a wave washer 19, etc. are located between the flange 14 and the second radial ball bearing 16 to show a state of applying preload. As shown in FIG. 1(b), the second radial ball bearing 16 includes an inner ring 2 as an inner member, an outer ring 3 as an outer member, a plurality of balls 4 as rolling elements, and a cage 5 for holding the plurality of balls 4. Further, seal members (not shown) are provided at both axial ends of the inner ring 2 and the outer ring 3, and conductive grease is enclosed around the balls 4. Also, the first radial ball bearing 15 has the same structure as the second radial ball bearing 16. In this embodiment, deep groove ball bearings are used as the first radial ball bearing 15 and the second radial ball bearing 16. In addition to deep groove ball bearings, for example, angular contact ball bearings, cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, etc. can also be adopted as required.

[0052] The details of the above conductive rolling bearing (deep groove ball bearing) will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view of the bearing. The conductive rolling bearing 1 is a deep groove ball bearing, in which an inner ring 2 having an inner ring raceway surface 2a on its outer peripheral surface and an outer ring 3 having an outer ring raceway surface 3a on its inner peripheral surface are concentrically arranged, and a plurality of balls 4, which are rolling elements, are arranged between the inner ring raceway surface 2a and the outer ring raceway surface 3a. Also, a cage 5 for holding the plurality of balls 4, which are rolling elements, is provided. Further, a seal member 6 fixed to the outer ring 3, etc. is provided at both axial ends 8a, 8b of the inner ring 2 and the outer ring 3. At least conductive grease 7 is enclosed around the balls 4.

[0053] Bearing members such as inner rings, outer rings, rolling elements, and cages can be formed of ferrous metal materials. In the present invention, due to the action of the conductive grease described above to prevent electrical erosion, it is not necessary to use ceramic materials for these bearing members. The ferrous metal material is any material commonly used in the bearing field, for example, high-carbon chromium bearing steel (such as SUJ1, SUJ2, SUJ3, SUJ4, SUJ5; JIS G 4805), carburized steel (such as SCr420, SCM420; JIS G 4053), stainless steel (such as SUS440C; JIS G 4303), high-speed steel (such as M50), cold-rolled steel, and the like.

[0054] In the conductive rolling bearing of the present invention, since the conductive grease is enclosed between the raceway surfaces of the bearing, electrical erosion is less likely to occur on the running surface, and it has a long bearing life.

[0055] In recent years, flying cars, so-called airborne cars, which are flyable means of transportation replacing automobiles, have attracted attention. Airborne cars are expected to solve the above social problems and are expected to be used in various scenarios such as intra-regional movement, inter-regional movement, tourism and leisure, emergency medical treatment, and disaster relief.

[0056] As an airborne car, vertical take-off and landing aircraft (VTOL) have attracted attention. Since vertical take-off and landing aircraft can vertically take off and land from and to the air, they do not require a runway and are excellent in convenience. In particular, in recent years, due to social demands for CO2 reduction and the like, electric vertical take-off and landing aircraft (eVTOL) that fly with batteries and motors have become the mainstream of development.

[0057] The electric vertical takeoff and landing aircraft equipped with the rolling bearing of the present invention will be described with reference to FIG. 3. The electric vertical takeoff and landing aircraft 21 shown in FIG. 3 is a multicopter having a main body 22 located at the center of the aircraft and four drive units 23 arranged on the front, rear, left, and right. The drive unit 23 is a device that generates lift and propulsion force for the electric vertical takeoff and landing aircraft 21, and the electric vertical takeoff and landing aircraft 21 flies by driving the drive unit 23. In the electric vertical takeoff and landing aircraft 21, there may be a plurality of drive units 23, and it is not limited to four.

[0058] The main body 22 has a living space where passengers (for example, about 1 to 2 people) can board. This living space is provided with an operating system for determining the traveling direction, altitude, etc., and instruments for indicating altitude, speed, flight position, etc. Four arms 22a extend from the main body 22, and drive units 23 are provided at the tips of the respective arms 22a. In FIG. 3, an annular portion that covers the rotation circumference of the rotary wing 24 is integrally provided on the arm 22a to protect the rotary wing 24. Further, a skid 22b for supporting the aircraft during landing is provided at the lower part of the main body 22.

[0059] The drive unit 23 has a rotary wing 24 and a motor 25 that rotates the rotary wing 24. In the drive unit 23, a pair of rotary wings 24 are provided on both axial sides with the motor 25 interposed therebetween. Each rotary wing 24 has two blades extending radially outward.

[0060] A battery (not shown) and a control device (not shown) are provided in the main body 22. The control device is also called a flight controller. The control of the electric vertical takeoff and landing aircraft 21 is carried out by the control device as follows, for example. The control device outputs a command to change the rotation speed to the motor 25 for which the lift should be adjusted from the difference between the current attitude and the target attitude. Based on the command, an amplifier provided in the motor 25 adjusts the amount of electric power sent from the battery to the motor 25, and the rotation speed of the motor 25 (and the rotary wing 24) is changed. Further, the rotation speed of the motor 25 is adjusted simultaneously for a plurality of motors 25, and thereby the attitude of the aircraft is determined.

[0061] Figure 4 shows a schematic cross-sectional view of the motor in the drive unit. In Figure 4, the above-described rotating blades are attached to one end side (upper side in the figure) of the rotating shaft 27 of the motor 25, and a rotor is attached to the other end side (lower side in the figure). The rotor is disposed opposite to the stator fixed to the housing 26 and is rotatable with respect to the stator. Note that the motor 25 can adopt the configuration of an outer rotor type brushless motor or an inner rotor type brushless motor.

[0062] In Figure 4, the motor 25 includes a housing (device housing) 26, a rotor (not shown), a stator (not shown), an amplifier (not shown), and two rolling bearings 31, 31. The housing 26 has an outer cylinder 26a and an inner cylinder 26b, and a cooling medium flow path 26c is provided therebetween. By flowing a cooling medium through this flow path 26c, an excessive temperature rise can be prevented. The material of the housing 26 is not particularly limited, and for example, an iron-based material or CFRP (carbon fiber reinforced plastic) can be used.

[0063] Also, the rolling bearings 31 rotatably support the rotating shaft 27 within the housing 26. In Figure 4, the outer diameter shape of the outer ring 33 of the rolling bearing 31 is the same as the shape of the fitting portion on the inner periphery of the housing, and it is directly fitted to the housing 26 without using a bearing housing or the like. An inner ring spacer 28 and an outer ring spacer 29 are inserted between the rolling bearings 31 and 31, and a preload is applied.

[0064] In an electric vertical takeoff and landing aircraft, compared with a drone, since the motor has a higher capacity, the drive current increases, and it is considered that the voltage (shaft voltage) generated on the rotating shaft of the motor increases. Along with this, there is a concern about the occurrence of electrical erosion, but by applying the conductive rolling bearing of the present invention, electrical erosion can be preferably prevented.

[0065] Note that the bearing configuration in the drive unit is not limited to the configuration shown in FIG. 4. In FIG. 4, the rotation axes of the motor and the rotary blade are the same rotation axis, but a configuration in which the rotation axis of the motor and the rotation axis of the rotary blade are connected via a transmission mechanism may also be used. In this case, the rolling bearing that supports the rotation axis in the drive unit may be the rolling bearing that supports the rotation axis of the motor or the rolling bearing that supports the rotation axis of the rotary blade.

[0066] Also, from the perspective of reducing carbon dioxide emissions, the shift from internal combustion engine vehicles such as gasoline vehicles and diesel vehicles (hereinafter referred to as gasoline vehicles) to electric vehicles is progressing. As electric vehicles, electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), fuel cell vehicles (FCEVs), etc. have been developed, and electric vehicles, including hybrid vehicles, have been rapidly spreading in recent years.

[0067] An example of the motor drive device provided with the rolling bearing of the present invention will be described with reference to FIG. 5. FIG. 5 is a schematic cross-sectional view of an embodiment of the motor drive device of the present invention. The motor drive device 40 shown in FIG. 5 includes a motor 41 and a speed reducer 42 that decelerates the rotation of the motor 41. The motor 41 has a rolling bearing 43, and the speed reducer 42 has a rolling bearing 44. The rolling bearing 43 supports the rotor shaft 45 of the motor 41, and the rolling bearing 44 supports the gears 46 and 47 of the speed reducer 42. In the motor drive device, the number of gears provided in the speed reducer may be plural and is not limited to two. Also, the number, position, size, etc. of the rolling bearings provided in the motor drive device are not limited to the mode shown in FIG. 5.

[0068] The motor drive device provided in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle has a larger capacity than the motor for auxiliary equipment provided in a gasoline vehicle in order to generate a large driving force, and the voltage (shaft voltage) generated on the rotor shaft of the motor is high. Along with this, there is a concern about the occurrence of electric corrosion in the bearings provided in the motor drive device, but by applying the conductive rolling bearing of the present invention, electric corrosion can be suitably prevented. Therefore, the motor drive device of the present invention is suitably used in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

Industrial Applicability

[0069] Since the conductive grease of the present invention is excellent in conductivity and can suppress the occurrence of electric corrosion in the bearing, it contributes to extending the bearing life. As a result, the conductive rolling bearing filled with this conductive grease can be suitably used for rolling bearings in various applications that require a long bearing life. In particular, it is suitable for rolling bearings used in automotive auxiliary equipment and motors for industrial machines, rolling bearings in the drive unit of an electric vertical takeoff and landing aircraft, and further, rolling bearings used in the motor drive device provided in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

Explanation of Symbols

[0070] 1 Conductive rolling bearing 2 Inner ring 3 Outer ring 4 Ball (rolling element) 5 Cage 6 Seal member 7 Conductive grease 8a Opening 8b Opening 10 Motor 11 Main shaft 12 Stator 13 Rotor 14 Flange 15 First radial ball bearing 16 Second radial ball bearing 17 Pulley 18 Belt 19 Wave washer 21 Electric vertical takeoff and landing aircraft 22 Body part 23 Driving part 24 Rotor blade 25 Motor 26 Housing 27 Rotating shaft 28 Inner ring spacer 29 Outer ring spacer 30 Nozzle member 31 Rolling bearing 32 Inner ring 33 Outer ring 34 Ball 35 Retainer 40 Motor drive device 41 Motor 42 Reducer 43, 44 Rolling bearings 45 Rotor shaft 46, 47 Gears

Claims

1. A conductive grease containing conductive particles, wherein the conductive particles are particles composed of a gallium compound, the conductive grease is characterized by containing 3% to 100% by mass of an amine salt of a polyether phosphate or an amidoamine salt of a polyester acid with respect to the conductive particles.

2. The conductive grease according to claim 1, wherein the gallium compound contains, as constituent elements, gallium and any one or more elements selected from titanium, zinc, aluminum, thallium, germanium, indium, antimony, selenium, tellurium, tin, phosphorus, arsenic, silicon, fluorine, nitrogen, and oxygen.

3. The conductive grease according to claim 1 or claim 2, wherein the average primary particle diameter of the conductive particles is 0.01 μm to 10 μm.

4. The conductive grease according to any one of claims 1 to 3, wherein the base oil of the conductive grease is at least one selected from poly-α-olefin oil, fluorine oil, mineral oil, ether oil, glycol oil, and ester oil.

5. A rolling bearing that holds a plurality of rolling elements between the raceway surfaces of an inner ring and an outer ring, wherein the conductive grease according to any one of claims 1 to 4 is enclosed between the raceway surfaces.

6. The conductive rolling bearing is provided with a plurality of drive units having a rotating blade and a motor for rotating the rotating blade, and is mounted on an electric vertical takeoff and landing aircraft that flies by the rotation of the rotating blade. The conductive rolling bearing according to claim 5, wherein it is a bearing that supports the rotating shaft in the drive unit.

7. A motor drive device including a motor and a speed reducer for reducing the rotation of the motor, The motor drive device is characterized in that at least one selected from the rotor shaft of the motor and the gears of the speed reducer is supported by the conductive rolling bearing according to claim 5.

8. The motor drive device according to claim 7, wherein the motor drive device is used in an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle.

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