Lubricating device

Abstract

Provided is a lubricating device which, by supplying an oil mixed with ultrafine bubbles to a friction engagement element through an oil supply passage, can perform lubrication with a simple configuration. The lubricating device comprises: a bubble generation medium (51) which is formed of a carbon-based porous material and which supplies gas as ultrafine bubbles having a diameter of at most 200 μm to an oil serving as a liquid medium to be supplied to a power transmission device (5) which transmits power to a drive wheel (4) from an engine (3) serving as a traveling drive source of a vehicle; an oil supply passage (34) serving as a fine bubble-mixed medium supply passage for supplying, to a forward / reverse switching clutch (18) and a forward / reverse switching brake (19) serving as friction engagement elements of the power transmission device (5), an oil which contains the ultrafine bubbles of at most 200 μm and which has been supplied from the bubble generation medium (51); and a circulation path (41) for circulating the oil. The bubble generation medium (51) is disposed within the circulation path (41).

Description

Lubricating device

[0001] The present invention relates to a technology for a lubrication device that uses lubricating oil containing ultrafine bubbles.

[0002] As a conventional lubrication device applied to a power transmission device of a vehicle or the like, for example, Patent Document 1 discloses a lubrication device that uses microbubbles, in which air is mixed into lubricating oil using a swirling flow type microbubble generator to generate microbubbles, and the lubricating oil mixed with these microbubbles is supplied to a wet multi-plate clutch to lubricate it, thereby reducing drag torque in the wet multi-plate clutch (see, for example, Patent Document 1).

[0003] Patent No. 6440742

[0004] However, conventional microbubble generation methods have not been able to produce a sufficient amount of ultrafine bubbles, making it impossible to improve the lubricity of lubricating oil. While methods for generating ultrafine bubbles include the swirling flow method and the ejector method, these methods can cause cavitation, resulting in the internal structures of the bubbles mixing into the oil as nanoparticles.

[0005] In view of the above, the present invention provides a lubrication device that can properly lubricate using ultrafine bubbles with a simple configuration by generating ultrafine bubbles in lubricating oil and supplying the oil mixed with the ultrafine bubbles to friction engagement elements through a supply oil passage.

[0006] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0007] That is, the lubrication device of the present invention comprises: a bubble generating medium made of a carbon-based porous material that supplies gas as ultrafine bubbles having a diameter of 200 μm or less to a liquid medium supplied to a power transmission device that transmits power from a drive source for running a vehicle to the drive wheels; and a fine bubble-containing medium supply passage that supplies the liquid medium containing ultrafine bubbles of 200 μm or less supplied from the bubble generating medium to a friction engagement element of the power transmission device.

[0008] In the lubrication device of the present invention, the supplied gas may be air, oxygen, carbon dioxide, ozone, or nitrogen.

[0009] The present invention has the following effects.

[0010] In the present invention, by allowing a sufficient amount of ultrafine bubbles to exist and supplying oil mixed with the ultrafine bubbles to the friction engagement elements through the supply oil passage, it is possible to perform appropriate lubrication using ultrafine bubbles with a simple configuration.

[0011] 1 is a schematic diagram of a vehicle equipped with a lubrication device according to an embodiment of the present invention; 2 is a schematic diagram of a lubrication device according to an embodiment of the present invention; 3 is a partial cross-sectional view showing a bubble generation medium according to an embodiment of the present invention; 4 is a diagram showing a unit and a bubble generation medium according to an embodiment of the present invention, in which (A) is a cross-sectional view of the unit and the bubble generation medium, and (B) is a perspective view of multiple units and the bubble generation medium.

[0012] The lubrication device according to the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially identical.

[0013] First Embodiment FIG. 1 is a schematic diagram of a vehicle equipped with a lubrication device according to a first embodiment, and FIG. 2 is a schematic diagram of the lubrication device according to the first embodiment.

[0014] The lubrication device 1 of this embodiment is configured, for example, as shown in Figure 1, to be incorporated into a hydraulic control circuit of a hydraulic control device 6 that controls the pressure of oil as a liquid medium supplied to a power transmission device 5 of a vehicle 2, and lubricates specified locations of the power transmission device 5.

[0015] Although the lubrication device 1 is intended to lubricate the power transmission device 5, it is not limited to this and can also be applied to rotating parts and sliding parts of wind power generation reducers, excavators, machine tools, construction machines, etc.

[0016] The vehicle 2 to which the lubrication device 1 is applied includes an engine 3 as a driving source for traveling, drive wheels 4, a power transmission device 5, a hydraulic control device 6, and an ECU 7 as a control device.

[0017] The engine 3 is a driving source (prime mover) for propelling the vehicle 2, and consumes fuel to generate power that acts on drive wheels 4 of the vehicle 2. The engine 3 generates mechanical power (engine torque) in a crankshaft 8, which is an engine output shaft, as the fuel is burned, and is capable of outputting this mechanical power from the crankshaft 8 to the drive wheels 4.

[0018] The power transmission device 5 transmits power from the engine 3 to the drive wheels 4. The power transmission device 5 is provided in the power transmission path from the engine 3 to the drive wheels 4, and is operated by the pressure (hydraulic pressure) of oil as a liquid medium.

[0019] More specifically, the power transmission device 5 includes a torque converter 9, a forward / reverse switching mechanism 10, a transmission 11, a reduction mechanism 12, a differential gear 13, etc. In the power transmission device 5, the crankshaft 8 of the engine 3 and an input shaft 14 of the transmission 11 are connected via the torque converter 9, the forward / reverse switching mechanism 10, etc., and an output shaft 15 of the transmission 11 is connected to the drive wheels 4 via the reduction mechanism 12, the differential gear 13, a drive shaft 16, etc.

[0020] The torque converter 9 amplifies the torque transmitted to the front cover, which is connected to the crankshaft 8 so as to be rotatable together with the crankshaft 8, via a fluid transmission mechanism including a pump and a turbine, and transmits the torque directly to the forward / reverse switching mechanism 10 via a lock-up clutch. The torque converter 9 switches the lock-up clutch between a released state (lock-up OFF) and an engaged state (lock-up ON) in accordance with the pressure of oil supplied from the hydraulic control device 6, which will be described later.

[0021] The forward / reverse switching mechanism 10 is capable of changing the speed and switching the direction of rotation of power (rotational output) from the engine 3. The forward / reverse switching mechanism 10 is configured to include a planetary gear mechanism 17, and a forward / reverse switching clutch (forward clutch) 18 and a forward / reverse switching brake (reverse brake) 19 as friction engagement elements. The planetary gear mechanism 17 is a differential mechanism including a sun gear, a ring gear, a carrier, etc. as multiple rotating elements that are capable of differential rotation with respect to one another. The forward / reverse switching clutch 18 and the forward / reverse switching brake 19 are engagement elements for switching the operating state of the planetary gear mechanism 17 and can be configured, for example, by a friction engagement mechanism such as a multi-plate clutch. Here, a hydraulic wet multi-plate clutch is used.

[0022] The forward / reverse switching mechanism 10 switches its operating state by actuating a forward / reverse switching clutch 18 and a forward / reverse switching brake 19 due to the pressure of oil supplied from a hydraulic control device 6 (described later). When the forward / reverse switching clutch 18 is engaged (ON state) and the forward / reverse switching brake 19 is disengaged (OFF state), the forward / reverse switching mechanism 10 transmits power from the engine 3 to the input shaft 14 in forward rotation (the direction in which the input shaft 14 rotates when the vehicle 2 moves forward). When the forward / reverse switching clutch 18 is disengaged and the forward / reverse switching brake 19 is engaged, the forward / reverse switching mechanism 10 transmits power from the engine 3 to the input shaft 14 in reverse rotation (the direction in which the input shaft 14 rotates when the vehicle 2 moves backward). When the forward / reverse switching mechanism 10 is in neutral, both the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 are in a disengaged state.

[0023] The transmission 11 is provided between the forward / reverse switching mechanism 10 and the drive wheels 4 in the power transmission path from the engine 3 to the drive wheels 4, and is capable of changing the speed of the power of the engine 3 and outputting it. The transmission 11 is operated by the pressure of oil supplied from the hydraulic control device 6, which will be described later.

[0024] The transmission 11 changes the speed of rotational power (rotational output) from the engine 3, which is transmitted (input) to the input shaft 14, at a predetermined gear ratio and transmits it to the output shaft 15, which is the transmission output shaft, and outputs the speed-changed power from this output shaft 15 toward the drive wheels 4. Here, as an example, the transmission 11 is illustrated as a belt-type continuously variable automatic transmission (CVT) that includes a primary pulley 20 connected to the input shaft (primary shaft) 14, a secondary pulley 21 connected to the output shaft (secondary shaft) 15, a belt 22 stretched between the primary pulley 20 and the secondary pulley 21, and the like. The transmission 11 performs gear shifting operations in accordance with the pressure (primary pressure, secondary pressure) of oil supplied from the hydraulic control device 6 described below to the primary sheave hydraulic chamber 23 of the primary pulley 20 and the secondary sheave hydraulic chamber 24 of the secondary pulley 21, and continuously changes the gear ratio, which is the ratio between the input rotational speed (primary rotational speed) corresponding to the input rotational speed of the primary pulley 20 and the output shaft rotational speed (secondary rotational speed) corresponding to the output rotational speed of the secondary pulley 21.In addition, the force with which the secondary pulley 21 etc. clamps the belt 22 (belt clamping pressure) is adjusted, and power is transmitted with a torque capacity corresponding to this.

[0025] The reduction mechanism 12 reduces the rotational speed of the power from the transmission 11 and transmits it to the differential gear 13. The differential gear 13 transmits the power from the reduction mechanism 12 to each drive wheel 4 via each drive shaft 16. The differential gear 13 absorbs the difference in rotational speed between the drive wheel 4 on the center side of the turn, i.e., the inner side, and the outer side, which occurs when the vehicle 2 turns.

[0026] The power transmission device 5 configured as described above can transmit the power generated by the engine 3 to the drive wheels 4 via the torque converter 9, forward / reverse switching mechanism 10, transmission 11, reduction mechanism 12, differential gear 13, etc. As a result, a driving force [N] is generated at the contact surface of the drive wheels 4 with the road surface, allowing the vehicle 2 to travel.

[0027] The hydraulic control device 6 operates the power transmission device 5, which includes engagement elements such as the lock-up clutch of the torque converter 9, the forward / reverse switching clutch 18 of the forward / reverse switching mechanism 10, and the forward / reverse switching brake 19, using the hydraulic pressure of oil as a fluid. The hydraulic control device 6 is configured to include, for example, various hydraulic control circuits controlled by the ECU 7. The hydraulic control device 6 is configured to include a plurality of oil passages, an oil reservoir, an oil pump, a plurality of electromagnetic valves, etc., and controls the flow rate or hydraulic pressure of oil supplied to each part of the power transmission device 5 in response to signals from the ECU 7, which will be described later. The hydraulic control device 6 also functions as a lubricating oil supply device that lubricates predetermined parts of the power transmission device 5, as will be described later.

[0028] The ECU 7 controls the operation of each part of the vehicle 2. The ECU 7 is an electronic circuit mainly composed of a well-known microcomputer including a CPU, ROM, RAM, and an interface. The ECU 7 is electrically connected to, for example, various sensors and detection devices provided in each part of the vehicle 2. The ECU 7 is electrically connected to the fuel injection device, ignition device, throttle device, hydraulic control device 6, etc. of the engine 3. The ECU 7 receives electrical signals corresponding to the detection results detected by the various sensors and outputs drive signals to each part in accordance with the input detection results to control the operation of these parts. For example, the ECU 7 adjusts the throttle opening based on the accelerator opening, vehicle speed, etc. to adjust the amount of intake air to the engine 3, controls the fuel injection amount in response to changes in the throttle opening, and adjusts the amount of mixture filled into the combustion chamber to control the output of the engine 3. The ECU 7 also controls the gear ratio, typically the input rotation speed to the transmission 11, based on the accelerator opening, vehicle speed, etc., to control the shifting of the transmission 11.

[0029] [Lubrication Device] As shown in FIG. 2 , the lubrication device 1 configured to be incorporated into the hydraulic control circuit of the hydraulic control device 6 of this embodiment includes a drain 33 as an outlet for generating ultrafine bubbles in oil as a liquid medium, and an oil supply passage 34 as a fine-bubble-containing medium supply passage that connects the drain 33 with the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 as friction engagement elements of the power transmission device 5.

[0030] The hydraulic control device 6 in which the lubrication device 1 is incorporated is configured to include various control valves such as an oil pan 25, an oil pump 26, a primary regulator valve 27, a secondary regulator valve 28, a line pressure control valve 29, and a sheave pressure control valve 30, as well as various oil passages that interconnect these various control valves and each part of the power transmission device 5 such as the primary sheave hydraulic chamber 23, the secondary sheave hydraulic chamber 24, the lock-up clutch of the torque converter 9, the forward / reverse switching clutch 18, and the forward / reverse switching brake 19, allowing oil to flow between them.

[0031] The oil pan 25 is a storage means for storing oil as a liquid medium. The oil pump 26 is driven in synchronization with the rotation of the crankshaft 8 (see FIG. 1 ) of the engine 3, and sucks in, pressurizes, and discharges the oil stored in the oil pan 25. Here, the oil pump 26 will be described as using the engine 3 as a drive source, but this is not limiting, and an electric motor or the like may also be used as a drive source.

[0032] The primary regulator valve 27 and the secondary regulator valve 28 regulate the first line pressure and adjust the first line pressure to a predetermined level, for example, in response to a solenoid pressure input from a solenoid valve (not shown). The first line pressure is the source oil pressure for the entire hydraulic control circuit of the hydraulic control device 6, which controls the oil supplied to the power transmission device 5. The primary regulator valve 27 has a spool valve element and multiple ports (input port, output port, drain port, etc.; the same applies hereinafter). For example, the input port of the primary regulator valve 27 is connected to the discharge port of the oil pump 26, and the output port is connected to the input port of the secondary regulator valve 28 and various lubrication holes. Furthermore, the output port of the primary regulator valve 27 is connected to the lock-up clutch of the torque converter 9 via a lock-up control valve (not shown) for controlling the lock-up pressure. The secondary regulator valve 28 also has a spool valve element and multiple ports. For example, the input port of the secondary regulator valve 28 is connected to the output port of the primary regulator valve 27, and the output port is connected to the suction port of the oil pump 26.

[0033] The line pressure control valve 29 adjusts the second line pressure, for example, to a constant pressure equal to or higher than a predetermined value. The second line pressure is the source pressure of oil introduced into a clutch control valve (not shown) or the like for controlling the clutch pressure introduced into each clutch hydraulic chamber 31, 32. The line pressure control valve 29 has a spool valve and multiple ports, and for example, an input port is connected to the discharge port of the oil pump 26, and an output port is connected to each clutch hydraulic chamber 31, 32, etc. via a clutch control valve (not shown) or the like.

[0034] The sheave pressure control valve 30 controls the sheave pressure. The sheave pressure is the pressure (primary pressure, secondary pressure) of oil supplied to the primary sheave hydraulic chamber 23 or the secondary sheave hydraulic chamber 24. The sheave pressure control valve 30 has a spool valve element and multiple ports, and, for example, an input port is connected to the discharge port of the oil pump 26, and an output port is connected to the primary sheave hydraulic chamber 23, the secondary sheave hydraulic chamber 24, etc. via a control valve (not shown) or the like.

[0035] The hydraulic control device 6 configured as described above supplies oil at a predetermined pressure as hydraulic oil to each of the clutch hydraulic chambers 31, 32 via the line pressure control valve 29 and a clutch pressure control valve (not shown), to the primary sheave hydraulic chamber 23 and the secondary sheave hydraulic chamber 24 via the sheave pressure control valve 30, and to the lock-up clutch of the torque converter 9 via the primary regulator valve 27 and a lock-up control valve (not shown).

[0036] A circulation path 41 is provided below the oil pan 25 to circulate the oil in the oil pan 25. A check valve 41a for rectifying the flow of oil in the circulation path 41 and a circulation pump 42 are provided midway through the circulation path 41.

[0037] The circulation pump 42 is a pump for returning the oil A inside the oil pan 25 back into the oil pan 25 via the circulation path 41. When the circulation pump 42 is driven to return the oil from the bottom of the oil pan 25 through the circulation path 41, the check valve 41a regulates the flow of the oil in one direction, preventing backflow.

[0038] An air bubble generation medium 51 is provided inside the circulation path 41. As shown in Fig. 2, the air bubble generation medium 51 is arranged so as to be parallel to the flow of oil inside the circulation path 41. An internal space 51a is provided inside the air bubble generation medium 51.

[0039] The bubble generation medium 51 is made of a carbon-based porous material and has a large number of fine pores 51A with diameters of several micrometers to several tens of micrometers, as shown in FIG. 3 . The bubble generation medium 51 is also a conductor, and the bubbles generated from the bubble generation medium 51 are negatively charged. In other words, free electrons are added to ultrafine bubbles as they pass through the conductive bubble generation medium 51, causing them to become negatively charged. This negative charge prevents the bubbles from repelling each other and merging to form larger bubbles. This allows ultrafine bubbles to be efficiently present in the liquid. When ultrafine bubbles are contained using the bubble generation medium 51, the concentration of ultrafine bubbles is 10⁻⁹ / mL or more.

[0040] Carbon-based porous materials are inorganic materials that are composed of only carbon or a composite material containing carbon and ceramic. A film several nanometers thick is formed on the surface of the carbon-based porous material. This film is made of an inorganic film containing silicon. Carbon-based porous materials are oxidation-resistant, and do not deteriorate due to oxidation even when placed in oil for a long period of time. Furthermore, the surface is made of an inorganic film containing silicon, making them resistant to the adhesion of dirt.

[0041] A gas supply unit 55 is connected to the bubble generation medium 51. The gas supply unit 55 is a device that supplies gas to the bubble generation medium 51 arranged in the circulation path 41. The gas supplied by the gas supply unit 55 is, for example, oxygen, hydrogen, carbon dioxide, air, nitrogen, ozone, or the like.

[0042] 3, in this embodiment, the gas supply unit 55 includes a compressor that compresses atmospheric air and supplies the compressed air. The gas supplied from the gas supply unit 55 is pressurized air, and the pressure can be adjusted by a supply valve 58. The air is compressed and sent to a gas supply passage 59 by opening and closing the supply valve 58.

[0043] The gas supply passage 59 is a passage for pressure-feeding gas from the gas supply unit 55 to the bubble generation medium 51 provided in the oil pan 25. The upstream end of the gas supply passage 59 is connected to the supply valve 58, and the downstream end is connected to the internal space 51 a of the bubble generation medium 51.

[0044] The lubrication device 1 configured as described above can supply oil mixed with ultrafine bubbles stored in the oil pan 25 to the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 through the oil supply passage 34. As a result, the lubrication device 1 can properly lubricate and cool the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 with the oil mixed with ultrafine bubbles, thereby reducing the drag torque generated in the forward / reverse switching clutch 18 and the forward / reverse switching brake 19, thereby reducing power loss and improving fuel efficiency, for example.

[0045] Furthermore, the lubrication device 1 can supply oil containing ultrafine bubbles to the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 via the oil supply passage 34 without passing through the oil pump 26 or a filter (not shown), thereby preventing the amount of air bubbles mixed in the oil from decreasing before the oil is supplied to the forward / reverse switching clutch 18 and the forward / reverse switching brake 19, and can supply a sufficient amount of ultrafine bubbles to the forward / reverse switching clutch 18 and the forward / reverse switching brake 19. Furthermore, the lubrication device 1 can prevent air entrapment in the oil pump 26, and can prevent an increase in pump load and a decrease in pump efficiency, which also reduces power loss and improves fuel efficiency.

[0046] The lubrication device 1 according to the embodiment described above comprises a bubble-generating medium 51 made of a carbon-based porous material that supplies gas as ultrafine bubbles having a diameter of 200 μm or less to oil as a liquid medium supplied to a power transmission device 5 that transmits power from an engine 3, which serves as a drive source for running the vehicle, to the drive wheels 4, and a supply oil path 34 as a fine bubble-containing medium supply passage that supplies oil containing ultrafine bubbles of 200 μm or less supplied from the bubble-generating medium 51 to a forward / reverse switching clutch 18 and a forward / reverse switching brake 19, which serve as friction engagement elements of the power transmission device 5, and a circulation path 41 for circulating the oil, in which the bubble-generating medium 51 is disposed within the circulation path 41.

[0047] Therefore, ultrafine bubbles of the supplied gas can be present in the oil in the circulation path 41 at a concentration of 10 to the power of 9 bubbles / mL or more, and by supplying the oil mixed with ultrafine bubbles to the friction engagement elements through the supply oil path, it is possible to perform appropriate lubrication using ultrafine bubbles with a simple configuration.

[0048] As shown in FIG. 4 , a unit 41A can be provided that can be placed midway through the circulation path 41. The unit 41A includes one pipe 41B and one bubble-generating medium 51. The bubble-generating medium 51 is disposed within the pipe 41B and configured to be connectable in series in a direction parallel to the direction of oil flow through the pipe 41B (the direction indicated by the black arrow in FIG. 4 ). That is, cylindrical connecting portions 52 are provided at the upstream and downstream ends of the pipe 41B, and the units 41A are connected in series via the connecting portions 52. This configuration allows the bubble-generating medium 51 to further supply ultrafine bubbles to oil already containing ultrafine bubbles. For example, in a method of generating ultrafine bubbles using shear force, continuous application of shear force causes the ultrafine bubbles to recombine, thereby reducing the amount of coexisting ultrafine bubbles.

[0049] Furthermore, in systems that generate ultrafine bubbles using a swirling flow, the resistance caused by the viscosity of the oil reduces the amount of ultrafine bubbles generated. In contrast, by arranging the bubble generation medium 51 in series in the oil flow direction, the time the oil is in contact with the bubble generation medium 51 is extended, allowing the oil flow to be effectively utilized to produce a high concentration of ultrafine bubbles. Furthermore, in systems that generate ultrafine bubbles using already dissolved gas components, such as the pressurized dissolution system and static mixer system, erosion is likely to occur due to the generation of thin, flat gas phases called micropancakes when cavitation occurs. In contrast, the bubble generation medium 51 makes it difficult to generate jet streams that generate micropancakes, making erosion less likely.

[0050] Furthermore, by incorporating ultrafine bubbles into the oil, the oil's wettability is improved, making it easier to maintain an oil film on solid surfaces. This reduces the oil's viscosity and improves wettability, allowing for proper lubrication and improving heat conduction efficiency, allowing for more efficient cooling of equipment and preventing deterioration.

[0051] Furthermore, since the bubble generation media 51 are arranged in series, ultrafine bubbles can coexist without recombining, which increases the amount of ultrafine bubbles that coexist in the liquid.

[0052] In addition, by increasing or decreasing the number of units 41A, it is possible to arrange the bubble generation medium 51 in the existing circulation path 41 according to the amount of oil stored in the oil pan 25.

[0053] In the above description, the oil supply passage 34 has been described as connecting the drain 33 of the sheave pressure control valve 30 with the forward / reverse switching clutch 18 and the forward / reverse switching brake 19, but this is not limited to this. The outlet to which the oil supply passage 34 is connected may be any outlet that generates ultrafine bubbles due to the pressure reduction when oil is discharged from the control valve, and may be, for example, the drain of the line pressure control valve 29, as long as ultrafine bubbles are generated when oil is discharged. Furthermore, the friction engagement element connected to the oil supply passage 34 is not limited to the forward / reverse switching clutch 18 and the forward / reverse switching brake 19 of the forward / reverse switching mechanism 10, but may be any other friction engagement element included in the power transmission device 5.

[0054] The present invention can be used in a lubrication system that uses lubricating oil containing ultrafine bubbles.

[0055] REFERENCE SIGNS LIST 1 Lubrication device 3 Engine 4 Drive wheels 5 Power transmission device 18 Forward / reverse switching clutch (friction engagement element) 19 Forward / reverse switching brake (friction engagement element) 34 Supply oil passage (fine bubble mixed medium supply passage) 41 Circulation passage 51 Bubble generating medium

Claims

1. A lubrication system comprising: a bubble-generating medium made of a carbon-based porous material that supplies gas as ultrafine bubbles with a diameter of 200 μm or less to a liquid medium supplied to a power transmission device that transmits power from a vehicle's driving source to the drive wheels; and a fine bubble-containing medium supply passage that supplies the liquid medium containing ultrafine bubbles of 200 μm or less supplied from the bubble-generating medium to a friction engagement element of the power transmission device; and a circulation path that circulates the liquid medium, wherein the bubble-generating medium is disposed within the circulation path.

2. The lubricating device according to claim 1, wherein the gas supplied is air, oxygen, carbon dioxide, ozone, or nitrogen.